EPA-600/2-76-115
May 1976
Environmental Protection Technology Series
      A  PASSIVE  FLOW MEASUREMENT SYSTEM  FOR
                       STORM  AND  COMBINED  SEWERS
                                   Municipal Environmental Research Laboratory
                                        Office of Research and Development
                                       U.S. Environmental Protection Agency
                                               Cincinnati, Ohio 45268

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                                          EPA-600/2-76-115
                                          May 1976
            A PASSIVE FLOW MEASUREMENT SYSTEM

              FOR STORM AND COMBINED SEWERS
                           by
                      K. M. Foreman
                   Research Department
              Grumman Aerospace Corporation
                Bethpage, New York  11714
                 Contract No. 68-03-2121
                     Project Officer

                      Hugh Masters
            Storm and Combined Sewer Section
              Wastewater Research Division
Municipal Environmental Research Laboratory (Cincinnati)
                Edison, New Jersey  08817
          U.S. ENVIRONMENTAL PROTECTION AGENCY
           OFFICE OF RESEARCH AND DEVELOPMENT
       MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
                 CINCINNATI, OHIO  45268

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                                 DISCLAIMER

This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion.  Approval does not signify that the contents necessarily reflect the
views and policies of the U. S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
                                     11

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                                 FOREWORD

The Environmental Protection Agency was created because of increasing public
and government concern about the dangers of pollution to the health and
welfare of the American people.  Noxious air, foul  water, and spoiled land
are tragic testimony to the deterioration of our natural environment.  The
complexity of the environment and the interplay between its components require
a concentrated and integrated attack on the problem.

Research and development is that necessary first step in problem solution
and it involves defining the problem, measuring its impact, and searching  for
solutions.  The Municipal Environmental Research Laboratory develops new
and improved technology and systems for the prevention, treatment,  and
management of wastewater and solid and hazardous waste pollutant discharges
from municipal and community sources, for the preservation and treatment
of public drinking water supplies, and to minimize  the adverse economic,
social, health, and aesthetic effects of pollution.  This publication is one
of the products of that research; a most vital communications link  between
the researcher and the user community.

The need exists to develop innovative, passive, nonintrusive, and low cost
solutions to the problems of continuous measurement and recording of flows
in storm and combined sewers.  This experimental investigation is of one
such technique that monitors the pseudosound produced by flow past  a channel
discontinuity.  The results of laboratory and field tests demonstrate the
feasibility of this method of flow measurement using an accelerometer trans-
ducer attached to the outside surface of a flow channel.
                                     Francis  T. Mayo,  Director
                                     Municipal Environmental Research
                                     Laboratory
                                      111

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                          ABSTRACT
This investigation concerns a new, nonintrusive, low cost,
passive flow measurement method to meet the urgent needs for
good management of storm and combined sewer systems.  Opera-
tion of the system is based on sensing the near field sound
emitted by the disturbed flow at a channel discontinuity.
These local pressure pulses are called pseudosound and radi-
ate as dipole sound sources orthogonal to the flow direction.
The output signal of passive transducers, such as accelerome-
ters, attached to the outer wall of  the channel indicates
flow rate after processing by a Fourier Analyzer.  Feasibility
has been demonstrated by laboratory  tests using full scale
sewer pipe elements, and by a brief  series of field tests mea-
suring sanitary sewage  flow.  Recommendations are made for
further field site testing using an  instrumented sewer line.
This report was submitted in fulfillment of EPA Contract
68-03-2121 by Grumman Aerospace Corporation under the sponsor-
ship of the Environmental Protection Agency.  Work was com-
pleted as of August 22, 1975.
                              IV

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                                  CONTENTS

                                                                      Page
 Foreword                                                              iii
Abstract                                                               iv
Figures                                                                 vi
Acknowledgments                                                       xiii
1    Conclusions                                                         1
II   Recommendations                                                     5
III  Technical Study                                                     7
IV   References                                                        119
V    Glossary
                                                                       120

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                           FIGURES
No.                                                     Page

  1   Ringing Frequency, fr, for Various Diameter
     Pipes and Pipe Materials  „.„....„ ................    14

  2   Limiting Transmission Loss of Sound Across
     Cylindrical Steel Pipe Walls at Less than
     the Ringing Frequency , f r . „ .....................    15

  3   Theoretical Sound Transmission Loss, R, for
     Mass Controlled Panels ..........................    17
 4   Grumman Research Water Supply Facility  ..........    19

 5   240 Gallon FaciH ty Water Storage Tank  ..........    20

 6   Air Pressurization and Water Supply Pipes
     to Storage Tank  .................................    20

 7   20 Foot Length of 3-in. Diameter Pipe of
     Facility Water Supply System ....................    21

 8   View of Facility Test Section Showing Diversion
     Trough, Water Collection Drums, and Weighing
     Scale.  8 -in. Diameter Aluminum Pipe on Test
     in Concentric Configuration .....................    21

 9   View of Water Flowing from 8-in. Diameter
     Test Pipe into Diversion Trough ........... „ .....    23

10   Overall Side View of Facility Test Section
     Showing Diversion Trough, Water Collection
     Drums, and Weighing Scale.  4-in.  Diameter
     Transite Pipe on Test „ „ „ „ „ . . . . ...................    23

11   Sensor Locations and Channel Discontinuities
     Tested in Research Laboratory ...................    24

12   Schematic of Testing Instrumentation ......... „..    27

13   Side View of Box for Containing Sand Used  to
     Simulate Buried Pipe Installation  ...............    29

                             vi

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No.                                                     page
14   Top View of Box Used to Simulate Buried Pipes.
     6-in. Diameter Transite Pipe is Shown on Test
     with Sand Removed.  Flow Direction is from
     Left to Right 	   29

15   End View of 8-in. Diameter Pipe Showing Initial
     Condition of Heavy (1-in.) Bed Load of Stone
     Chips 	   30

16   Heavy Bed Load After Being Disturbed by Water
     Flow at Rates up to 3 Pounds Per Second 	   30

17   Equipment Used to Feed Sand Grit into Upstream
     Water Supply 	   31

18   Closeup of Speed Controlled Motor and Supply
     Hopper Used to Feed Sand Grit into Water Supply ..   31

19   Screen Tray Added to Water Collection System to
     Separate Grit from Collected Water.  6-in. Di-
     ameter Transite Pipe is Shown on Test.  Tray is
     Just Below Pipe Exit 	   34

20   Exterior View of Valve Vault (Foreground at
     Grumman Waste Treatment Plant "A".  This is
     First Site of Field Test Preview Experiments 	   34

21   Interior View of Valve Vault Showing 8-in.
     Plug Valve and 8 x 10-in. Reducer Section with
     Accelerometer Attached to Outer Wall for
     Acoustic Emission Monitoring of Flow 	   35

22   Exterior View of Aeration Tank at Grumman Waste
     Treatment Plant "A".  10-in. Diameter Pipe
     Emerges from Underground Installation at
     Left Center of Photo.  This is Site of Second
     Series of Field Test Preview Experiments 	   35

23   Closeup of 10-in. Diameter Pipe Where Second
     Field Test Preview Series Was Conducted.
     Sensor is Shown Attached to Top Center of
     Horizontal Pipe.  Tape Recorder and Amplifier
     Used is Shown in Foreground 	   37
                             Vll

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No._

24   Data Processing Equipment Used to Obtain Spectral
     Distribution from Flow Acoustic Emission Re-
     cordings.  HP-5465A Fourier Analyzer Computer
     is in Center of Picture 	   37

25   Schematic of Acoustic Emission Data Processing
     System  	   38

26   Closeup of Data Processing Equipment Showing
     (L to R) HP-5465A Fourier Analyzer Computer,
     Penco Continuous Loop Recorder and Playback,
     and Nagra Tape Recorder Used for Laboratory
     and Field 	   38

27   Typical Fourier Processed Spectral Distributions
     of Laboratory Sound Recordings (10 Hz Bandwidth)  .   40

28   Acoustic Signal Variation with Flow Rate in a
     3-in. (7.62 cm) Diameter Steel Pipe 	   46

29   Typical Spectral Distributions of Laboratory
     Sound Recordings.  Distributions Obtained by
     Fourier Analyzer (10 Hz Bandwidth) 	   47

30   Hydraulic Radius of Test Channel For Different
     Water Level Heights 	   49

31   Calibration of Research Facility Water Supply
     (A = Flow Area, Q = Volumetric Flow Rate) 	   51

32   Variation of Normalized Acoustic Signal with
     Flow (Cylindrical Pipe Exiting to a Trapezoidal
     Open Channel) 	   53

33   Acoustic Signal Variation with Flow Rate
     (Cylindrical Pipe Discharging to Trapezoidal
     Open Channel) 	   54

34   Variation of Normalized Acoustic Signal with
     Flow Rate - Different Sensor Locations (Cylin-
     drical to Trapezoidal Channal Transition) 	   55
                             Vlll

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No.

35   Variation of Normalized Acoustic Signal with
     Flow Rate - Effect of Sensor Location
     (Eccentric Cylindrical Pipe Elements and
     Extended Inlet) .................................     57

36   Effect of Sensor on Variation of Normalized
     Acoustic Signal with Flow Rate (Eccentric
     (Cylindrical Pipe Elements and Extended Inlet)  ..     58

37   Effect of Extended Inlet on Acoustic Signal
     Variation with Flow Rate (Eccentric Cylin-
     drical Pipe Elements) ...........................     60

38   Effect of Sensor Position and Sound Frequency
     on Acoustic Emission of Water Flow (Eccentric
     Cylindrical Pipe Elements and Flush Inlet) ......     61
39   Effect of Exit Weir Height on Normalized
     Acoustic Signal of Water Flow (Eccentric
     Cylindrical Pipe Elements and Flush Inlet) ......     62

40   Effect of Exit Weir Height on Normalized
     Acoustic Signal of Water Flow Eccentric
     Cylindrical Pipe Elements and Flush Inlet) ......     63

41   Variation of Signal with Flow at Different
     Sensor Locations; (Eccentric Cylindrical
     Pipe Elements and Flush Inlet) (with 4.24-in.
     Weir at Exit Unless Noted Otherwise) ............     65

42   Variation of Normalized Acoustic Signal with
     Flow Rate for Different Frequencies and Test
     Conditions (Eccentric Cylindrical Pipe
     Elements and Flush Inlet) .......................     67

43   Variation of Normalized Acoustic Signal with
     Flow Rate for Different Test Conditions (Flush
     Inlet, Eccentric Cylindrical Pipe Step) .........     68

44   Variation of Acous tic Signal with Flow for 3
     Sensor Locations and Various Test Conditions  ....     70

45   Closeup of Concentric Discontinuity Plane
     Assembly of 3-in. Steel Water Supply Pipe
     to 8-in. Diameter Aluminum Test Pipe ............     70
                               x

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No.

46   Internal Relation of 3-in. Supply Pipe to
     8-in. Test Pipe with Heavy Bed Load of Stone
     Chips„  View Taken Before Flow Established 	    72

47   View of Upset Bed Load After Water Flow Rate
     of 5 Pounds Per Second 	    72

48   Variation of Normalized Acoustic Signal wtih
     Flow Rate at Various Sensor Locations and
     Characteristic Frequency (Concentric Cylin-
     drical Pipe Array with Extended Inlet) 	    74

49   Variation of Normalized Acoustic Signal with
     Flow Rate for Different Frequencies (Concentric
     Cylindrical Pipe Array with Extended Inlet) 	    75

50   Effect of Sensor Circumferential and Axial
     Location on Useful Signal (Concentric Cylin-
     drical Pipe Array with Flush Inlet) 	    77

51   Varation of Acoustic Signal with Flow at Two
     Sensor Locations for Different Test Conditions
     (Flush Inlet, Concentric Cylindrical Pipes) 	    78

52   Variation of Acoustic Signal with Flow at Three
     Sensor Locations and for Two Frequencies - with
     4.24" Weir at Pipe Exit Plane - (Concentric
     Cylindrical Pipe Elements) 	    79

53   Variation of Acoustic Signal with Flow at Three
     Sensor Locations and Three Frequency Bands - with
     4.24-in. Weir at Pipe Exit Plane - (Concentric
     Cylindrical Pipe Elements)„  See Fig, 52 for
     Sensor Position Location on Pipe 	    80

54   Variation of Acoustic Signal with Flow at Two
     Sensor Locations and Two Frequency Bands (Con-
     centric Cylindrical Pipe Elements) - with 4024"
     Weir at Pipe Exit and 8" Deep Sand Overburden,
     Except Where Noted	    82

55   Varation of Acoustic Signal  with Flow at Five
     Frequency Bands and One Sensor Location (Con-
     centric Cylindrical Pipe Elements)  - with 4024"
     Weir at Pipe Exit and 8" Deep Sand Overburden,
     Except Where Noted 	    83
                              x

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No.

56   Effect of Heavy Bed Load of Stones (1M Deep)
     in 8" Diameter Pipe on Acoustic Signal Varia-
     tion with Flow - Sand Covered Array 	    84

57   Effect of Two Bed Loads of Sternes in 8-in.
     Diameter Pipe on Acoustic Signal Variation with
     Flow - Sand Covered Array with 4.24-in. Weir 	    85

58   Sketches of Heavy Bed Load Movement at Different
     Stages of Water Flow Test Conditions 	    86

59   Variation of Acoustic Signal with Flow at Four
     Frequencies and Two Sensor Positions (8" Sand
     Cover and Monolayer of Stone Chips Within 8"
     Diameter Pipe.  4.24" Weir at Exit of Pipe) 	    88

60   Closeup of Eccentric Connection of 3-in. Water
     Supply Pipe to 4-in. Diameter Transite Test Pipe .    91

61   Closeup of Special Assembly Collar Used for
     Eccentric Connection of 3-in. Pipe to 6-in.
     Diameter Transite Test Pipe.  Flow is from Right
     to Left.  Two Sensor Mounting Studs are Shown
     Cemented at Top Centerline Surface of Transite
     Pipe 	    91

62   Variation of Acoustic Signal with Flow (Eccentric
     Cylindrical Pipe Array) - Transite and Steel
     Pipe Elements without Sand Overburden Except
     Where Noted 	    93

63   Variation of Acoustic Signal with Flow (Eccentric
     Cylindrical Pipe Array) - Transite and Steel
     Pipe Elements Buried Under 8-in. (20.3 cm) of
     Sand, Except Where Noted 	    95

64   Variation of Acoustic Signal with Flow (Eccentric
     Cylindrical Pipe Array) - Transite and Steel
     Pipe Elements Without Sand Overburden, Except
     Where Noted 	     95

65   Effect of Grit Addition to Water Flow on the
     Acoustic Signal Variation with Flow - Transite
     and Steel Pipe Elements, Without Sand Over-
     burden, in Eccentric Assembly 	     96
                              XI

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No.

66   Variation of Acoustic Signal with Flow at
     Grumman Waste Treatment Plant "A" Valve Vault
     for Different Sensor Positions - First Test
     Series 	   98

67   Variation of Signal with Flow at Grumman Waste
     Treatment Plant "A" Aeroation Pond for Different
     Frequencies and Sensor Positions - Second Test
     Series 	  i00

68   Typical Variation of Acoustic Signal with Flow
     for Two Conduit Configurations (Cylindrical to
     Trapezoidal Cross-Sectional Discontinuity) 	  l03

69   Effect of Extended Inlet on Acoustic Signal
     Variation with Flow Rate (Concentric Cylin-
     drical Pipe Elements) 	  106

70   Effect of Pipe Configuration on Normalized
     Acoustic Signal Variation with Flow Rate
     (Cylindrical Pipe Elements) with 4.24-in.
     Weir, 8-in. Sand Overburden, and Flush Inlet 	  11U

71   Effect of Pipe Material on Normalized Acoustic
     Signal Variation with Flow Rate (Eccentric
     Cylindrical Pipe Elements and Flush Inlet) -
     8-in. Sand Overburden 	  113
                             Xll

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                       ACKNOWLEDGMENTS

This work was performed for Grumman Ecosystems Corporation,
Bethpage, New York, who are the prime contractors to the U.S.
Environmental Protection Agency (EPA) under Contract 68-03-
2121.
We acknowledge the assistance of Mr. James Rogers of Grumman
Aerospace Corporation (GAC) for programming and otherwise
assisting in the computer processing of our recorded sound
data.  Thanks are also directed to Mr. Chris Clamser and
Mr. Norman Peele of GAC for making possible the many facility
and testing changes, on a timely basis, during the course of
this program.
Finally we are indebted to Mr. Hugh Masters and Mr. Richard
Field of EPA who provided helpful guidance during the pro-
gram, and enlightenment regarding simulation of sewage solids.
                              Xlll

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                          SECTION I
                         CONCLUSIONS

The  results  of  this  program demonstrate  the  feasibility  of
                                              *
Grumman  s  acoustic emission flowmeter  concept  for  channels
where  a  discontinuity exists because  of  a  conduit cross-
sectional  increase.   Since  these  geometric cross section
changes  are  common in sewer systems,  this  passive,  nonintru-
sive,  flow measurement technique  is directly applicable  to
storm  and  combined sewers.
On a scale that is without  precedent  regarding  physical  size
and  variety  of  laboratory  test conditions, the  acoustic  emis-
sion monitored  by an accelerometer has been  found to  produce
unambiguous  signals  that increase in  magnitude  as the fluid
flow rate  increases.  The  source  of the  acoustic emission is
the  pseudosound created by  the interaction of fluid with a
solid  surface in the near  field of a  conduit discontinuity.
Pseudosound  does not propagate with the  flow, but radiates as
a  dipole,  orthogonal to the flow  direction.   Data has been
obtained for open channel,  full flow,  and  pressurized flow
conditions involving full  scale metallic and Transite pipe
sections used to conduct fluid waste.
During these laboratory tests, steady, unsteady, uniform, and
nonuniform flows were established.  In addition to  tests of
freely suspended pipes flowing clean  water,  corroborative
data has been obtained from tests with simulated buried  in-
stallations  of  the pipes and with water  containing  suspended
and  settleable  solids characteristic  of  sewage.  Tests with
Patent pending.

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 cylindrical as  well  as  trapezoidal conduits cross sections
 have confirmed  general  similarity of results  for these geome-
 tries.
 A field test preview,  in which the  acoustic  emission flowmeter
 technique was used to  monitor sanitary sewage from  large indus-
 trial buildings, demonstrated good  correlations  with test trends
 obtained in the laboratory,  and with  theoretical predictions.
 Data of value to future engineering design of prototype  sys-
 tems have been  obtained.   This experience indicates  that low
 cost accelerometers  having a  wide range  of voltage  sensitivi-
 ties, between  10 and   100 mv/g,  are well  suited  to the
 acoustic monitoring  function.  These  sensors  are easily  em-
 placed or removed by screwing on to inexpensive, dedicated
 mounting plates which may be  cemented  or magnetically at-
 tached  to the outer  surface of the flow  channel.  Epoxy  ce-
 ment with high  metallic content has proven very  satisfactory
 for  this purpose.  For  discontinuities  involving sudden  en-
 largements  of conduit cross section,  the sensor  location
 yielding the  strongest  signal for the  greatest range of  flows
 is at the bottom-most circumferential  position and  two to
 three (upstream)  pipe diameters downstream of the discontinu-
 ity  plane.  Transmission  of flow acoustic emission  through
 most  sewer  conduit walls  is of a sufficiently high  percentage
 so that  adequate  signal quality is available  to the  sensors.
 Sound transmission circumferentially  in  solid conduit walls
 is of such  high magnitude  that useful  sensor  signals can be
 obtained at nearly any  circumferential position,  at a given
 axial position.  These  results  hold for metallic  as  well  as
 inhomogeneous material  (e.g.,  cement and Transite) used in.
 pipe  constructions and  for conventional wall  thickness to
pipe  diameter ratios of sewers.

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In the early phases of this project, no special measures were
taken to simulate real sewer installation features in our
laboratory experiments.  This initial oversimplification of
the test setups was intended to expedite acquisition of test
data and to avoid special equipment costs if unneeded.  As a
result, however, some of the acoustic emission data appeared
to conflict with the expected trends of pseudosound produc-
tion.  To overcome this equipment inadequacy, we developed in-
expensive but effective techniques to simulate properly sewer
installations.  The acoustic emission signals obtained under
these changed test conditions were completely unambiguous, and
in general agreement with dipole theory predictions.
The most reliable unambiguous signal for flow rate measure-
ment is the acoustic emission component at a characteristic
frequency,  f ,  which is inversely proportional to the maxi-
mum geometric step at the discontinuity,  6,  and directly
proportional to the bulk sound speed,  c,  of the fluid, or
f  ^ c/5.  Because of secondary flow interaction processes,
minor transient changes in  c,  instrumentation sensitivity,
and acoustic energy conversion process, the useful signal
actually exists in a frequency band of up to  200 Hz  width,
centered about  f .  For most practical sewer applications the
characteristic frequency will be in the midaudible range of
the sound spectrum.  Random background noise is of the order
       Q         /
of  10    to  10    (i.e.,  -30  to  -40 dB)   the intensity
of flow acoustic emission.  Response of sewer pipes to this
noise follows a general mass distribution law where amplitude
varies inversely with frequency.  In contrast, the spectra of
flow acoustic emission have high amplitude content at fre-
quency bands associated with flow-related sources„  In this
regard, a bed load that does not adhere to the conduit wall

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 in the near field of the discontinuity will not alter the
 basic character of the flow acoustic emission.   However,  some
 conversion of the acoustic emission energy to sound propa-
 gating downstream with the flow can take place  if the bed load
 consists of sharp edged material that induces much turbulence.
 In the laboratory, at low flows, the acoustic signal at char-
 acteristic frequency increases with flow at a rapid rate, ap-
 proximating the ideal  (~ w )   dipole theoretical prediction
 of  12 dB  per doubling of flow rate.  However, while this
 trend is moderated at higher flow rates, it increases without
                                                            . T
 ambiguity and assumes a direct proportionality  to flow  (~ w)
 at the highest rates tested in the laboratory.   In the limited
 field test preview,  the trend  of high flow rate data taken at
 an underground pipe  installation follows dipole theoretical
 predictions reasonably well.
 In addition to its flow measurement capability, acoustic emis-
 sion  monitoring can  be an operational tool for  determining
 maintenance needs of the sewer.  To the experienced human
 monitor  at  a central location, qualitative evaluation of total
 sound content  from various and diverse remote sites can pro-
 vide  a mental  image  of local sewer conditions that almost
 rivals  in  situ  observations  by a mobile crew, but with
 greater  convenience  and lower  cost0
The contractual  limitations  of this project did not permit  an
exhaustive  investigation to  reveal the  full potential  of Grum-
man *s  passive measurement technique for  all pipe geometries.
However, there  are sufficient  reasons, by  virtue of the data
obtained, to justify  extreme optimism on the future prospects
for this new,  low cost  approach  to  flow measurement.
 w = rate of change of weight flow = Aw/At

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                         SECTION II

                       RECOMMENDATIONS

Feasibility of the passive acoustic emission flowmeter has
been demonstrated in the laboratory with a breadboard, re-
search type, instrumentation system.  The features of this
technique should be appealing to management of municipal and
regional sewer districts.  Therefore, to expedite the imple-
mentation of this method we recommend the following action:
     1.   Extend field testing conditions to a well in-
          strumented sewer site, using the laboratory
          breadboard system.  Testing should be conducted
          for a long enough duration (i.e., months) to
          experience at least a realistic variation of
          runoff and flushing conditions.
     2.   Based on the laboratory and extended field test-
          ing results, design and build a prototype flow
          measurement system, and test it at the well in-
          strumented sewer site previously used.  Labora-
          tory calibration of the system should precede
          the field testing.  After initial shakedown and
          possible system design modifications at the
          field site, continue evaluation over a twelve
          to twenty four month period for system relia-
          bility, maintainability, and operational per-
          formance data.  These data should be compared
          to ultimate system objectives defined by EPA.

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      3.    Depending  on  the  experience of step 2 above, either
           design  and construct an advanced prototype or build
           several initial production systems for more wide-
           spread  field  tests  throughout the nation.
 Although it may be premature  to  be  unduly  concerned about
 operational aspects  of  this passive measurement technique,  it
 is clear that its utility would  be  enhanced  if field site cal-
 ibration could be eliminated. One  expeditious and economical
 way of doing this is to calibrate the transducer  in a  flow
 facility where small scale  models simulate the relevant  local
 features of the actual  sewer  installatio n<,   To use these  cali-
 brations with confidence requires that  scaling laws be devel-
 oped so  that model data can be correctly applied  directly to
 the field site geometry.  Accordingly,  we  recommend that  theo-
 retical  studies be conducted  to  determine  appropriate  scaling
 laws for the acoustic emission process.  These similarity laws
 then should be verified using data  from field tests (such as
 recommended above) and  laboratory work  reported here as well as
 from future supplementary laboratory tests.
 In  order to explore  more fully the  growth  potential of this mea-
 surement technique,  we  recommend further laboratory research
 with  several pipe discontinuity  configurations other than sud-
 den  enlargements.  Among these are  contractions,  turns, tees,
 Y-sections,  valve bodies, and sumps.  Investigations should in-
 clude  independent internal  flow  diagnostic instrumentation as
well as  passive acoustic sensing.   At least  one study should
 concern  identifying  and quantifying flow infiltration into
 sewer  lines;  simulation methods  should be established  for the
 infiltration.   Other  studies  should investigate  reverse flow
 identification  and correlations  of  field measurement perform-
ance with laboratory calibrations under  simulated  field condi-
tions .

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                         SECTION III
                       TECHNICAL STUDY
A.   INTRODUCTION
The project investigations reported here are the first phase
of a program to develop a passive flow measurement system for
storm and combined sewers.  It was performed by Grumman Aero-
space Corporation under subcontract to Grumman Ecosystems
Corporation in conformance with U.S. Environmental Protection
Agency  (EPA) Contract 68-03-2121, dated June 28, 1974.
The purpose of this project is to determine, by experiment
and analysis, the feasibility of Grumman1s innovative acous-
                               *
tic emission flowmeter concept.   Tests have been conducted
in the  controlled environment of Grumman Research's water
flow laboratory under a variety of flow and simulated sewer
pipe installations.  A brief field test also was conducted
to preview the type of data that-could be expected from a
full field test program.  Secondary objectives are to obtain
engineering data to guide future flowmeter designs and in-
stallations, and to explore the growth potential of the con-
cept to meet ultimate design goals for a sewer flowmeter.
The acoustic emission flowmeter concept uses passive sensors
to monitor the sound emitted by fluid flow, and in this way
determines flow rate.  This sound signal results from the
pressure disturbances when flow passes a channel discontinu-
ity.  The discontinuity can be any change in conduit cross
section or shape, or where flow direction is significantly
altered.  In the vicinity of the discontinuity, the pressure
_
 Patent pending.

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 disturbances  depend  on  the mean velocity of the flow and can
 be monitored  by appropriate  sensors  at  the boundary of  the
 flow.  However, because this near  field sound  does not  pro-
 pagate throughout the flow with the  sound speed of the  fluid
                          •I r\
 it is termed  pseudosound.  '    This differentiates it from  the
 more conventional acoustic processes that become coupled to
 the fluid's far field radiation.   Pseudosound  has radiation
                                      1  3
 characteristics like a  dipole source,  ' so it emits acoustic
 energy orthogonal to the fluid flow  direction.  For usual
 sewer pipe construction, a passive sensor, such as an accel-
 erometer,  mounted to the outer surface  of the  sewer wall can
 listen to  pseudosound.   The  sensor's output signal can  be
 transmitted to  nearby or remote devices that use the rela-
 tionship of pseudosound to local mean velocity to determine
 flow rate.  The features of  this simple, passive, nonintru-
 sive flow  measurement system are ideally suited to the  oper-
 ational conditions and  environment found in storm and com-
 bined sewers.
 Background
 The  EPA need  to characterize and assess storm-generated water
 pollution,  and  to develop, demonstrate, and evaluate water
 treatment and control systems, establishes a requirement for
 real-time data  from  fast response  and remote sensors.   Severe
 flow  conditions  in combined  sewers obviate use of convention-
 al flowmeters.   Problems of  cost,  accuracy, reliability, op-
 erational simplicity, and maintenance have limited the appli-
cation of other  advanced active measurement techniques  de-
veloped in recent years.

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A reliable flowmeter that is nonintrusive and passive has at-
tractive prospects for sewer applications because it can be
used on new as well as old sewer lines, does not have to be
physically subjected to the variable quality of sewer flow,
and can have low power requirements.
Pursuing its own independent studies for advanced flow mea-
surement techniques, Grumman Research invented a way by which
the relatively little known theory of pseudosound could be
used to determine fluid flow rate.  This method is inherently
passive because it is activated by the sound energy emitted
by the flow.
About two years prior to the inception of this contract,
Grumman had demonstrated that the variation of pseudosound
intensity with flow rate could be measured and that it fol-
lowed theoretical predictions.  The test configuration in-
volved a  0.875-in.   (2.22 cm)  diameter aluminum pipe dis-
charging to an open rectangular aluminum channel  1.0-in.
(2.54 cm)  wide by  1.5-in.   (3.81 cm)  high.  Measurements
were made at water flow rates to  0.66 Ib/sec   (0.3 Kg/sec)
and used a single transducer type (B&K model 4332) attached
to the underside of the open channel by double adhesive faced
tape.
However, because of the very limited conduit size and con-
figuration, water flow rate range, and transducer type and
installation in these earlier demonstration tests, reserva-
tions remained about the applicability of the concept for
more representative conditions of storm and combined sewers.
To demonstrate feasibility, tests were necessary for greatly
extended conditions of:

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      a)   Flow rate
           1)   partial flow
           2)   full flow
           3)   pressurized flow
      b)   Conduit configurations
           1)   size
           2)   construction materials
           3)   geometry
      c)   Transducer
           1)   type
           2)   sensitivity
           3)   method  of attachment
           4)   location relative  to  discontinuity  plane
 In addition, examination of such  operational factors  as
 buried pipe  installations and the addition of solids  to
 water flow were required.
 Te s_it_Pha s ing
 The test program discussed in this report  was designed to
 examine these  questions in a phased  sequence, giving  system-
 atically increased  knowledge and  preparation for progres-
 sively  more  complex situations.   First, we scaled  up  the sup-
 ply conduit  flow area  by a factor of  10,   and roughly dupli-
 cated  the  circular  to  open rectangular conduit transition
 cross section  geometry used in the original  demonstration.
Next, we examined the  characteristics of various candidate
 transducers  and  selected  the  best for our  purposes.  Methods
 of sensor  attachment were  considered and tested for acoustic
coupling,  ease of installation, and operational reliability.
                              10

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Supply flow rates were established in the water flow research
laboratory that were ten times the maximum previously used in
concept demonstration; later, flow rates twenty times greater
than initial demonstrations were used.
Following demonstration of reproducibility of results of the
prior demonstration tests, with cylindrical-to-rectangular
elements, we proceeded to test conduit arrays embodying only
cylindrical metal elements.  After validating the acoustic
emission concept in completely cylindrical conduit geometry,
we returned to more detailed studies of the original conduit
test sections.  The next test series was a detailed examina-
tion of metallic cylindrical pipe configurations, and in-
cluded extending the flow rates to the maximum capable of
being accurately measured.  We then proceeded to test non-
metallic (Transite) cylindrical pipe elements.  After con-
firming the similarity of flow acoustic emission measurements
for Transite and metallic pipes, we examined simulated buried
installations of cylindrical pipe discontinuities.  The simu-
lated overburden was found to be helpful in reducing airborne
noise and did not adversely affect the flow acoustic emission
signal.  Several succeeding tests with simulated buried con-
duits involved metallic and Transite cylindrical pipe ele-
ments.  These data revealed detailed flow characteristics for
different sensors and sensor locations relative to the pipe
discontinuity.  Toward the end of this series, exploratory
tests were made of the effect of solids in the water.  Screened
grit was added to the upstream water supply in one set of
runs, and coarse stone chips were pre-placed as a pipe bed
in other tests.  Finally a preview of field test acoustic
                               11

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 emission measurements was made at various locations of the
 sanitary sewer line to Grumman's main sewage treatment plant.
 The test apparatus used in this program is described in Sec-
 tion IIIB.  The results of tests for each phase of this pro-
 ject are described in Section IIIC, and discussed in Sec-
 tion HID.
 Theoretical Approach
 Fluid flow in pipes or conduits produces sound that may be
 caused by over-all or locally induced unsteadiness of em-
 bedded turbulence.  The local pressure disturbances induced
 by channel discontinuities and not propagated downstream is
 pseudosound.   The sound pressure of pseudosound,   p ,   is of
                 2                                  P
 the order of   pu   where  p  is the average fluid density
 and  u  is the fluid velocity.   The radiation field of pseu-
 dosound is like a dipole source so the total sound power,
 P  ,   in a free field is
                                  2
                                     2
where
                                    TJu
                                 pc
          p  =  pressure  disturbance
          I  =  characteristic  dimension of  the  local  flow
                conduit
          pc = characteristic  acoustic  impedance of fluid
               fluid  ;
               water)
c  = fluid sonic speed  (~15 x 10  cm/sec  for
                       2
However, since  p  ^ pu  ,  the theoretical sound power is
                                  2 4
                              - Pi
                            T     c
                             12

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This equation is the theoretical basis for the fourth power
relation of flow rate and sound emission.  Note that the
                        •
volumetric flow rate,  Q,  is proportional to velocity,  U,
in a given conduit geometry, so  P  ^ Q  .
The characteristic frequency,  f ,  of the dipole sound pro-
                                t_^
duced at the conduit discontinuity is inversely proportional
to the characterizing dimension of the discontinuity,  6.
From the fundamental relation  f= c/A,  where  A  is sound
wavelength in the fluid,  f  ^ c/6  or  6 ^ A. (Empirically,
                           v_
we have determined that the proportionality factor for  A/8
is  4,  or  46 = A.)
When the sound is "shadowed" by the shape of the discontinuity,
from being radiated  locally downstream, the net radiated power
within the conduit is   (eP. ).  There is a sound power loss
through the walls of the conduit by the transmission coeffici-
ent,  T,  so that at the outer surface of the pipe the radiated
sound power is
                           Pr - PT eT
For bends and branch points in a conduit,  e  tends to unity;
valves and metering  sections have values of  e  less than one.
The ratio of transmitted to incident acoustic power equals  T.
It is approximately  proportional to the pipe diameter to wall
thickness ratio,  D/t,  for excitation wavelengths larger than
                                             2
the circumference of the cylindrical conduit,   TfD = A .  The
ringing frequency,   f  ,  equals  c/A^  (see Fig. 1).
The "limiting transmission loss"  in  dB,  for steel cylindri-
cal pipe is given by Fig. 2.  The minor correction for actual
frequency relative to   f   is shown.
                               13

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                                      ALUMINUM
                                      STEEL
                                      CONCRETE
                            10     12

                        D, PIPE DIAMETER, in.
                                         14
                                                16
18
      20
Fig.  1    Ringing frequency, fr,  for  various diameter
          pipes  and pipe  materials
                            14

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PQ
CO
o
   60
   50
                          -2

                dB         _o
                CORRECTION
                FOR
                FREQ      -4
                          -5
                           .05
                                     0.1
                                                           \
                                               I      I    I   I   I  I
                                         0.2    0.3   0.4  0.5   0.7 |   1.0
                                                        0.6  0.8
                                   f/fr = 6.23x10"4f D

                                   fr = C/TTD = 5050 m/sec (FQR SJEEL)
CO
CO
CO
   40
   30
   20
    10
-2
                      5  6 7 8 9 10'
                                 -1
5 6  7  8 9 10U
                                   t/D
    Fig.  2    Limiting transmission  loss  of sound across
               cylindrical  steel  pipe walls  at  less than the
               ringing frequency,  fr
                                   15

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 For smaller wavelengths than  A^  the loss corresponds to
 that of a flat panel of equal material and thickness to the
 conduit.   Here, the controlling factor is the product of
 the surface mass (equal to the mass density divided by the
 thickness) and the frequency.  Figure 3 shows the theoreti-
 cal transmission loss, in  dB,  for mass-controlled flat
 panels.  The three loss curves apply to different criteria,
 discussed in Ref. 4fused for the directionality of the inci-
 dent sound.   The transmission losses for steel, aluminum, and
 concrete panels are shown for several frequencies between
 1000  and  20,000 Hz.  At the ringing frequency,  f ,   the
                   4                                r
 loss is a minimum.    Therefore,  the maximum signal through
 the pipe wall will be obtained at this frequency,  f ,   if
 the sound sources within the pipe contain  f .
 The transmission of sound from one medium to another depends
 on the  acoustic coupling of the  media.  Using the transmis-
 sion relation involving acoustic impedances,   r = pc/S,   in
           3
 two media,   where  S = surface area at the interface:
                                 4r,r
                         P   =     L /	
                         *12
                               /    ^   s
                               
The sound  transmission  from water to iron or concrete is
about   157,  and   53%,   respectively.  The poor acoustic
coupling to  air  is  indicated by  values of  P,0,   of about
  -3.    -4r          -5
10  7,,  10  7,,  and   10  70  for water to  air,  concrete to
air and iron to  air interfaces,  respectively.
B.   EXPERIMENTAL FACILITIES
Most of the  investigations made  under  this contract were con-
ducted in  the Grumman Research water flow facility.  AS shown
                             16

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CO
•o
   70
   60
   50
   40
   30
   20
   10 —
              f =
      Ro (NORMAL INCIDENCE) - IN WATER


             R = lOlog — ,dB
                   T


      3 4 5 7 10 15 20KHz
      I  I I  I  I  II
                     5 7 10 1520KHz
                     I  I   I  I  I
                        10 1520KHz
                         I  I  I
                           CONCRETE PANEL
     10a
10C
10'
10ฐ
10s
                        FREQ x SURFACE MASS, Hz-Kg/rn
     Fig. 3   Theoretical sound  transmission  loss,
               for  mass  controlled  panels
                                  17

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 in Fig. 4, this facility uses a  240 gallon (908 liter) cyl-
 indrical tank (see Fig. 5) as the primary water supply to
 feed a  3-in.  (7.6 cm)  diameter steel pipe.  Water is fed
 into the tank by means of a hose connection from the plant
 water supply, and stored under pressure until needed for
 test.  Pressure is supplied by a regulated air supply intro-
 duced above the water level in the vertically oriented tank
 (see Fig. 6).  A plastic sight tube provides indications of
 the water level.   Flow rate is controlled by a  3-in.  (7.6
 cm)  globe valve  inserted in the  6 ft (1.8 m)  high verti-
 cal riser between the tank outlet and the  3-in.  (7.6 cm)
 horizontal pipe.   With initial tank pressures up to  30 psi
           2
 (2.1 kg/cm )   maximum water flow rates of over  15 Ib/sec
 (6.82 kg/sec)  are manageable with the flow measurement tech-
 nique used;  this  technique will be described later.  Constant
 flow rates  during tests of up to about  2.5 Ib/sec  (1.10 kg/
 sec)   are possible by having the plant water supply feeding
 directly  through  the  tank to the  3-in.  (7.6 cm)   pipe.
 The   20 ft   (6.1  m)   length of  3-in.  (7.6 cm)   pipe (see
 Fig.  7) effectively eliminates the flow profile  irregulari-
 ties  induced  by the flexible line and three 90 degree bands
 between the tank  and  the  pipe.  At the downstream end of  the
 3-in.   (7.6 cm)   pipe the conduit discontinuity  is introduced
 by means  of a test pipe section.  Duration of tests usually
 are between   30 seconds and one minute,  and for  flows  above
 about  3.5  Ib/sec   (1.4 kg/sec)   the  flow rate slowly  de-
 creases during the latter part of the run.  The  outflow drops
 into a wooden trough  (Figs.  8  and 9)  where  it can be diverted
by a flapper  valve into a drain,  or into  a collection drum.
The  55 gallon  (208  liter)  drum  is  connected by hose (see
                              18

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OP
 0
 ft)
05

05

l-i
o
 P3
 rt
 05
 r-i

 en

ฃ
VI
 Hi
 n
 H-
                               U   SIGHT TUBE                 GRIT
                                         240 GAL. TANK      INJECTOR

                                                    	/_
      AIR PRESSURE
      REGULATOR     WATER
                        SUPPLY
                        VALVE
                                                 V
                                                  FLOW
                                                  CONTROL
                                                  VALVE
                                                                         20
                                                                            FT
                                                                       V
                                                                 3 IN. DIA. STEEL PIPE
                                                                  WOODEN SUPPORTS
SENSOR
MOUNTING
STUD
(TYP.)
                                                                                                                  /////////////
                                        FLOW DIVERSION
                                        TROUGH
                                   ?%#^J^%#S-^%^%%S^^
                                                                                                  TOLEDO          55 GAL. DRUMS
                                                                                                  SCALE            FOR COLLECTING AND
                                                                                                  (2500 LB CAP)     MEASURING TEST FLOW
                                                  PLANT
                                                  DRAIN
 I-1-
 rt

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   Fig. 5   240 gallon facility water storage tank
Fig. 6   Air pressurization and water supply pipes to
         storage tank
                         20

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                   •     .ปER  HA _  naii
Fig.  7  20 foot length of 3-in.  diameter pipe of facility
        water supply system
 Fig.  8   View  of  facility test section showing diversion
         trough,  water collection drums, and weighing
         scale.   8-in. diameter aluminum pipe on test in
         concentric configuration
                           21

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 Figs. 10 and 8)  to another one to double the total collec-
 tion capacity and both drums rest on the weighing platform
 of a Toledo scale.  This scale has a  2500 Ib  (1136 kg)
 weighing capacity and has been calibrated to  l/8th Ib
 (0.06 gm)  accuracy.  Prior to each test run, a tare weight
 reading is taken.  When flow conditions  are  stabilized,  the
 flapper valve is opened allowing water to be diverted into
 the drums, and a stop watch is activated. At the conclu-
 sion of the test period,  the watch is  stopped as  the flapper
 valve is closed  and a final weight is  read off the scale
 dial.  The average rate of flow during this  time  is deter-
 mined from these data.  By reducing the collection time to,
 for example,   10 seconds,  a fairly constant  flow  rate is ob-
 tained for all but the highest rates.   After each run, a new
 tare reading  is  taken or  the drums are drained, depending on
 the anticipated  magnitude  of flow rate for the next run.
 For this program,  the test  sections  of conduit were:
      •     ~ 2-in.  (5.1 cm)  high  by ^ 5-in. (12.7  cm)
           wide open aluminum channel
      •     8-in.  (20.3 cm)  diameter aluminum  pipe
      •     4-in.  (10.2  cm)  diameter transite  sewer pipe
      •     6-in.  (15.3  cm)  diameter transite  sewer pipe
and  they were attached  either  concentrically or eccentrical-
ly.  The resulting  discontinuity geometries  and distances
are depicted by Fig.  11.
The transducer types used  to monitor the  pseudosound at  the
discontinuity are accelerometers.  We  selected accelerometers
in preference to several other  transducer  types that appeared
                              22

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      9-  flew sf Water flowing from 8-'inch, diameijea:
          pipe Into
Fig. 10  Overall side view  of  facility test section
         showing diversion  trough, water collection drums,
         and weighing scale.   4-inch diameter transite
         pipe on test
                             23

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             1. CLOSED CYLINDRICAL TO OPEN TRAPEZOIDAL
              FLOW-
              SENSOR
              POSITION

Jr


)N \D

A^ 	


(T)Q
J U 1
~

I
1-
f 2.53"
IW^> i f
i U U V
k*-*4 	 1-3" A /i art"
~ H \ 4.SJ —

K>
1
\ 	 ,
I
+< — w
3" DIAM
STEEL
PIPE
1 	 1

1.62"
t

                                                                           SECTION A-A
                                                     h* = 4.15,4.625,4.8 IN.
             2. 3-IN. DIAM STEEL PIPE TO 3-IN. DIAM STEEL PIPE
                                                 • COUPLING
                FLOW-
                                       I_
                               .28"
-h* = 0.25"    J 3" DIAM |

               3.5" DIAM
                                                  SENSOR POSITION
             3. 3-IN. DIAM STEEL PIPE TO 8-IN. DIAM ALUMINUM PIPE
             a) CLOSED ECCENTRIC CYLINDRICAL CONFIGURATION
               1) WITH EXTENDED INLET

              3" DIAM PIPE
              FLOW.
                             NOTE: 1 IN. = 2.54 cm
A •
fi

0_
-*•'
2.5" —
1
-^
ฉ ฉ ฉ
•A fcl^ — aJ — 7" 1
~>
y
!„ A
i I
\
                                                                8" DIAM PIPE
              2) WITH FLUSH INLET
             FLOW
t
                                 i* = 4.45 IN.
                                 1 ฉ
                                                                  (NUMBER IN CIRCLE
                                                                  DENOTES SENSOR
                                                                  POSITION REFERENCE)
                                      -9"-
                Fig.  11    Sensor  locations  and channel  discontinuities
                            tested  in  research  laboratory,  sheet  1 of 2
                                                24

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                             -H
                                I
                                •8" DIAM PIPE
3" DIAM
ฉ —
'"%
o .
'LI
^^_ (T " ^^^^
^^— iJ — ^^p
^ฉ-3

0 ]
J
^
A /
ฉ ฉ ฉ Ih* = 2.2"( /
LJ U U U

                3. b) CLOSED CONCENTRIC CYLINDRICAL CONFIGURATION
                           1) WITH EXTENDED INLET
  3" DIAM PIPE

FLOW
                                       -8" DIAM PIPE
r
/f,_7.5.._ป,
0_
-'


i
\

h* -
2
k /^N /^
U 1
i * ป


J
)'
,'e rt V
	 	 i_i ^
r
j
8ฐ40' —
ALTERNATE
                                                  AT SECTION A-A
   3" DIAM PIPE
    FLOW
ฉ
           3.0"
                             2) WITH FLUSH INLET
                                        • 6" DIAM PIPE
                2.3"-
                    ฉ
                          TJ^  U
                        — 6"-
                      +	9--
                 4. 3-IN. DIAM STEEL PIPE TO 6-IN. DIAM TRANSITE PIPE
           CLOSED ECCENTRIC CYLINDRICAL CONFIGURATION WITH FLUSH INLET

   Fig.  11   Sensor  locations  and channel  discontinuities
               tested  in research  laboratory, sheet  2 of 2
                                   25

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 potentially useful because these  devices  are  inexpensive
 (~ $250),  have the best frequency and sensitivity character-
 istics, and are capable of being  environmentally sealed with-
 out difficulty.  Condenser microphones  require  an opening to
 equalize static pressure and  cannot  be  effectively sealed.
 Piezoelectric microphones also  require  pressure equalization
 and usually are limited to 10,000 Hz  frequency.   Hydrophone
 type microphones are  very expensive,  and  piezoresistive
 microphones have low  output sensitivity.  Magnetic variable
 reluctance transducers  are affected  by  ambient  magnetic
 fields and do not have  high frequency sensitivity.
 The accelerometer is  screwed  onto mounting studs  that are
 cemented to the outer surface of  the  test conduit.  We  have
 found Devcon "F" epoxy  cement with  8070  aluminum content to
 provide good acoustic coupling  between  the mounting stud and
 the various test conduit materials.   However, this cement
 takes about four hours  to cure  properly.  The many sensor
 locations  needed to be  examined for  signal optimization can
 be  accommodated best  by attaching many  mounting studs at
 judiciously selected  locations  prior  to test.   Several  ac-
 celerometer models were used  during  the program.   They  vary
 in  sensitivity,  size, weight, and one model has an integral
 preamplifier to match impedance with  external recording
 circuits.   All  acoustic data  have been  recorded on ฃ-in.
 by   600  ft   (6.3  mm   by  180 m)   Scotch brand magnetic  in-
                           ป
 strumentation  tape using a  Nagra  III  model tape recorder.  The
 typical  instrumentation equipment used  is shown schematically
 in Fig.  12.
About midway in  the program, a wooden container,  22.4-in
 (57 cm)  wide by  48-in.   (122 cm)  long was  constructed to
                              26

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TEST CONDUIT (CROSS-SECTION)

            MOUNTING STUD FOR SENSOR
  ACCELEROMETER     PREAMPLIFIER      AMPLIFIER
  (TYPICAL)
NAGRA MODEL III MAGNETIC
TAPE RECORDER
         Fig.  12   Schematic  of testing instrumentation
                                    27

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 hold sand or soil (see  Fig.  13).   This  equipment simulates
 buried installations of the  pipeline  especially in the vi-
 cinity of the conduit discontinuity (see  Fig.  14).  A maxi-
 mum buried depth of  8-in.   (20.3  cm)   can be  accommodated
 with a uniform layer of sand circumferentially around the
 largest test pipes  used.   It is possible  to test with either
 completely uncovered, partially buried, or fully buried in-
 stallations of the  pipes.  This simulation closely meets
 ASTM C-361 specifications  for two  pipe  bedding techniques in
 field installations.
 In one of the tests conducted to simulate  a heavy bed load
 of coarse grit relatively  large stone chips were placed at
 the bottom of the test  pipe  and retained  by a  metal dam at
 the exit plane of the pipe.   Figure 15  shows an extra heavy
 bed loading before  water flow.  Figure  16  shows the partial
 washout of the uniform  bed after being  subjected to flow
 rates  above  2-3  Ib/sec (0.9-1.4  kg/sec).
 In another study, medium-to-coarse  sand grit (sieve sizes  be-
 tween   8   and  20  and  a specific  gravity  of  2.62)   was in-
 jected into the  flow.   This  required an additional piece of
 equipment at  the  upstream end of the  3-in.  (7.6 cm)   pipe.
 This grit feed device uses a   dc   servo motor-generator
 (Motomatic  Model E6500  Series  125)  and  a motor speed con-
 troller  (see  Figs.  17 and 18).  The motor  shaft is  attached
 to a   5/8-in.   (1.6 cm)  diameter  feed  screw that traverses
 the bottom  of  a grit storage  hopper.  The  flow  rate  of  the
grit depends  on the rotational speed of the motor which  is
set by a   1000 division vernier rheostat on  the controller
box.  For a given rheostat setting, the motor speed  is main-
tained constant by  the  servo  circuit.
                              28

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 Fig. 13  Side view of box for containing sand used to
          simulate buried pipe installation
Fig. 14  Top view of box used to simulate buried pipes.
         6-inch diameter transite pipe is shown on test
         with sand removed.  Flow direction is from
         left to right
                          29

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Fig-  15  End view of 8-inch diameter  pipe  showing initial
         condition of heavy (1-inch)  bed load of stone chips
  Fig. 16  Heavy bed load after being disturbed by water
           flow at rates up to 3 pounds per second
                            30

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 Fig.  17  Equipment used to  feed sand grit  into upstream
          water supply
Fig. 18  Closeup of speed controlled motor and supply
         hopper used to feed sand grit into water supply
                           31

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 Dry loose  sand  is  dropped  into  the water  flow  through a
 ฃ-in.   (0.64  cm)   wide  slit near  the upstream  end of the
 3-in.   (7.6 cm)  pipe.  As seen by the  photos,  the upper por-
 tion of this  pipe  was partially removed and  replaced by a
 curved plastic  shield.  In this way the movement  of the sand
 particles  downstream of the slit  can be tracked visually.
 However, because of the opening in the  pipe  it  is not possi-
 ble to introduce sand and exceed  a water  flow  rate of some-
 what more  than  6  Ib/sec   (2.73 kg/sec).  This  flow rate cor-
 responds to a completely filled pipe.   To eliminate clogging
 of  the drains and  prevent serious error in measuring water
 flow with  the collection barrels, the grit is  separated from
 the water  at  the outflow of the test pipe.   This  is done by
 a screening tray,  mounted on rails, just  under  the test pipe
 exit (see  Fig.  19); the separated sand  is removed for drying
 and reused.   Baffle plates prevent the  outflow  from splashing
 out of the tray.   The concentration of  grit  in  the test water
 flow is determined from a grab  sample taken  about midway
 through a  test run.  The sample is contained in a  250 ml
 glass  beaker  that  has been manually inserted into the out-
 flow.  The grit is filtered from  the water sample and mea-
 surements  are made of the captured water  volume and the grit
weight in  order to determine  mg/liter  concentration value.
 It  is assumed that the  grab sample is representative  of the
entire flow composition while the acoustic recordings are
made.  For the test made,  the sand concentrations  were  be-
tween  86  and  1682 mg/liter.  These values simulate  very
closely the recommended sewage  characteristics  for  grit
(20-360 mg/liter)  and settleable solids   (200-1150
                              32

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In order to provide a preview of the type of results that
could be obtained in a field test phase, a limited amount of
field testing was made during this project.  Several flow
measurements were made using pipelines feeding Grumman's
main sanitary sewage treatment plant.  Figure 20 shows where
some of these data were obtained.  This location is an under-
ground concrete vault, at the SE corner of the treatment
plant, where valves are installed to control the diversion of
sewage to two aerating tanks on either side of the building
at the rear of the picture.  Figure 21 shows the  8-in.
(20.3 cm)  plug valve and the  8 by 10-in.  (20.3 x 25.4 cm)
expansion section which adapts the valve to the  10-in.
(25.4 cm)  diameter cast iron sewer pipe.  The accelerometer
sensor is seen about  two-thirds of the section length down-
stream from the valve flange.  To expedite versatility in
field measurements, a magnetic mounting stud was used to
couple acoustically the sensor to the pipe.  A more intimate
coupling would have resulted if we used the epoxy-based ad-
hesive for the mounting stud, but the time necessary to cure
the epoxy would have delayed the test program.  With the
magnetic attachment, we are able to shift rapidly sensor
locations upstream and downstream of the valve body.  Another
field location used to make acoustic measurements is shown
in Fig. 22.  This is at the north aeration tank of the treat-
ment plant.  The  10-in.  diameter sewer pipe rises from its
buried installation to enter a comninuter as shown in
Fig. 23.  The sewer pipe changes from a cylindrical steel
channel to an open concrete conduit before entering the corn-
minuter.  A smaller, 4-in.  diameter  (10.2 cm)  pipe can be
seen in Fig. 23 as also rising from underneath the surface
                              33

-------
  Fig.  19  Screen tray added to  water collection system to
           separate grit  from collected water.   6-inch
           diameter transite pipe  is  shown on test.   Tray
           is just below  pipe exit
Fig. 20  Exterior view of valve vault (foreground) at
         Grumman waste treatment plant "A".  This is first
         site of field test preview experiments
                            34

-------
Fig. 21  Interior view of valve vault showing 8-inch plug
         valve and 8 x 10-inch reducer section with
         accelerometer attached to outer wall for acoustic
         emission monitoring of flow
                               -••-••_ •  • •  • .  --.T-. ^- r
Fig. 22  Exterior view of aeration  tank  at  Grumman waste
         treatment plant "A".   10-inch diameter  pipe
         emerges from underground installation at left
         center of photo.  This  is  site  of  second series
         of field test preview  experiments
                            35

-------
and conducting its flow over the concrete wall.  This pipe
brings sewage from another Grumman plant and discharges it
into  the comminuter channel vertically above the exit plane
of the  10-in.  (25.4 cm)  pipe.  Several pipe locations
were  acoustically examined at this site for flow of just the
10-in.  (25.4 cm)  pipe as well as combined flow with the
4-in.  (10.2 cm)  pipe.
Processing of the tape recorded data is made with Grumman's
Fourier analyzer computer facilities shown in Fig. 24.  The
block schematic of electronic and display equipment is shown
in Fig. 25.  A closeup of the Nagra data recorder, Pemco con-
tinuous loop transfer recorder and HP-5465A, HP-5460A, and
HP-2114B Fourier Analyzer system is shown from right to left
in Fig. 26.
Total sound data, in the  40  to  22,000 Hz  frequency band,
is transferred from the Nagra recorder to the Pemco continu-
ous loop recorder.  The amount of original data transferred
depends on the length of the loop on the Pemco recorder;
usually at least  10 seconds  of continuous recording was
used  in our program for each test point.  Sixty random sam-
plings of the loop, representing about one-fifth to  one-
tenth of the total original recorded information, are pro-
cessed by the HP-5465A computer.  Each sampling is broken
down by this digital computer into  1028 frequency components
and associated amplitudes using Fourier transforms of the
time-varying sensor signals, and then the spectra are co-
added (this process is called ensemble averaging).  This tech-
nique extracts the useful signal from the recordings and prac-
tically cancels extraneous random noise.  The rms average data
                              36

-------
 Fig. 23  Closeup of 10-inch diameter pipe where second
          field test preview series was conducted.  Sensor
          is shown attached to top center of horizontal
          pipe.  Tape recorder and amplifier used is shown
          in foreground
Fig. 24  Data processing equipment used to obtain spectral
         distribution from flow acoustic emission recordings
         HP-5465A Fourier analyzer computer is in center of
         picture
                             37

-------
    SPECTRAL DYNAMICS SD104A-5
    SWEEP OSCILLATOR
                                          HP5460A
                                          DISPLAY
                                          UNIT
                                         HP5465A
                                         FOURIER
                                         ANALYZER
                                         & A/D
                                         CONVERTER

                                         HP2114B
                                         COMPUTER

                                          HP2748A
                                          TAPE
                                          READER
          HP6823A POWER SUPPLY
          AND AMPLIFIER
 THIS EQUIPMENT USED FOR FREQUENCY
' CALIBRATION ONLY.
           HP5233L ELECTRONIC COUNTER
   Fig.  25  Schematic of acoustic emission data  processing
             system
Fig.  26  Closeup  of data processing  equipment  showing  (L to
          R) HP-5465A Fourier analyzer computer,  Pemco
          continuous loop recorder and playback,  and Nagra
          tape recorder used  for laboratory and  field,
                                38

-------
value of the signal is displayed digitally on the HP-5460A
unit and a spectral distribution of amplitude is plotted on
semilog paper  (dB versus frequency) by the Moseley 2FRA
plotter.  Typical spectral distributions for the April 28
test series (see Section IIIC-7) are shown in Fig. 27 (a)
and (b).  The upper curve  (a) for the no flow condition
shows the mass distribution law fall-off of amplitude with
                                      3
frequency for random, broadband noise.   By contrast, the
spectra at a relatively high flow  (^ 13 Ib/sec = 5.9 kg/sec)
given by curve  (b)  shows specifically strong content in
various frequency bands that are produced by the flow across
the conduit discontinuity as well as from other nonrandom
sources (e.g., bubbles, turbulence, valve noises, etc.).  In
addition, the rms signal (i.e., integrated over-all frequen-
cies between  40  and  22,000 Hz)  is  32 db  greater for
the flow case [curve (b)] than the ambient noise level
[curve  (a)].
A few select studies during the course of this program in-
dicated that biasing the transferred acoustic data to a par-
ticular portion of the original recording can result in a
ฑ 2 db  change in the rms signal value, for given test flow
conditions.  This bias can be minimized but at considerable
inconvenience by transferring  and connecting small pieces
of the original recording taken over its entire duration for
a test point.  The limited magnitude of this bias effect,
and the extent of reproducibility of results, considering
the number of components integrated into all laboratory sys-
tems, did not warrant the delay that would be incurred in
processing with greater care the thousands of data points.
 Referenced to  1 volt.
                              39

-------
FULL SCALE
 = 94 dB r-
  -10dB
  -20 dB
  -30 dB
           RMS DATA - 26 dB
                              NAGRA SETTING:  120db
                              AMPLIFIER:        0 db
  -40 dB
                                                               POS.3
                                                               SENSOR TYPE:
                                                               1020
                                                               (98 mv/g)
       a) AMBIENT- NO FLOW
FULL SCALE
= 126dB i—
  -10 dB -
  -20 dB -
 -30 dB -
            RMS DATA - 34 dB
                              NAGRA SETTING:  140 db
                              AMPLIFIER:       20 db
 -40 dB
                                                               POS. 3
                                                               SENSOR TYPE:
                                                               1020
                                                               (98 mv/g)
      b) FLOW RATE = 13 Ib/sec       FREQUENCY/4, Hz
                                                                       10
 Fig.  27   Typical  Fourier  processed spectral  distributions
            of  laboratory sound  recordings (10  Hz  bandwidth)
                                   40

-------
Another study to improve processing accuracy involved doub-
ling the quantity of samples randomly selected by the Fourier
analyzer.  The processing time is doubled, but the results
obtained for several exploratory cases are not sufficiently
better than with  60 samples to justify the extra processing
time.  Apparently, our standard sampling number produces
statistically good results.
Co   EXPERIMENTAL PHASE
The experimental investigations of this program were mainly
concerned with clean water flow in Grumman1s hydraulics re-
search laboratory.  However, a brief field test preview was
conducted after the laboratory tests were concluded.  De-
scriptions of these facilities have been presented in the
previous section.
The test program was conducted from August 14, 1974 to July
1, 1975 and used various size pipes as well as an open chan-
nel.  Salient features of the conduits, transducers, flow
parameters, and experimental setup conditions of each test
series are summarized in chronological order in the table.
In reviewing these tests here, each group of closely related
experiments is described separately with minimal comment.
Full discussion of the results is covered in Section HID.
It is to be noted that approximately the initial half of the
test program has been run with no special attempt to simulate
real underground installations of sewers (see item number 8
of Table T-l).  This measure simplified the test setups and
                              41

-------
                                                TABLE T-1. SUMMARY OF TESTING FEATURES (SHEET 1 OF 2)


No.
1





2



3
4
5


6
7

8


9
10

11


12



13


Date of Test
Feature
Channel size
a. 3" diam steel (stl)
b. 3" diam steel to 2" x 5" trapezoidal
c 3" diam steel to 8" diam aluminum
d. 3" diam steel to 4" diam transite
e. 3" diam steel to 6" diam transite
Channel type
a. Concentric cylindrical, closed
b. Eccentric cylind., closed
c. Closed cylind. to open trapezoidal
M ci's t" "tv Hi I" \
Characteristic frequency (kHz)
Sensor type
a. B&K model (no.)
b. Vibrametncs model (no.)
Sensor sensitivity, (mv/g)
Sensor installations
a. No. of axial positions
b. No. of circumferential posit.
Pipe installation features
a. Freely suspended in air
b. Simulated underground
c. In sim. box but not buried'
Max. flow rate (Ib/sec)
Pipe exit condition
a. Open exit
b. Exit weir installed
Supply pipe inlet condition
a. Extended inlet (overlap dist., in.)
b. Flush inlet
Solids in flow?
a. None (except rust)
b. Heavy bed load of stone chips
c. Light bed load of stone chips
d. Upstream dispersed grit
Remarks


1974
8/14


•





ซ


0 25
-60.

4332

62

1
1


8.4




•




Prelim
data

8/22



•






ซ
3 8
3.91

4332

62.

1



NA



• (3)





8/23



•






•
3 8
3.91

4333

19.5

1



NA



• (3)





Exploratory
acoustical
data
9/9




•




•

4 25
3.50

4333
4332

19.5
62

2



7.6



• (3)








9/12



•






•
4 625
3.21

4332
4333

19.5
62

2



5.5



• (3)








10/28




•




•

4 2
3.54

4332

62

3



7.0



• (2.5)








10/29




•




•

4 2
3.54

4333

19.5

3



7.0



• (2.5)








10/29




•



•


2 2
6.76







3



8.0



• (2.5)








10/30




•



•


2 2
6.76











7,0



•(2.5)








11/8



ซ






ซ
A 1 C
H. I D
3.58







3



7.0



• 116








1/11



•






•
4 8
3.10











7.5



• (16)








11/11



•






•
415
3.58







3



7.25



• (16)








11/11




•



•


0 0
6 76







-i
i



7.5



• (2.5)









1/16




•



•






4333
(2)

19.5
21.5





8




*







1/17




•



•






4333
4339

19.5
10.





8




•







112




•



•






4333
(2)

19.5
21.5

1



10

•


•







123




•



•



•^.
^•^











15

•


•







/29




•




•

t 45
3.32

333
(2) *

9.5.
1.5'





11

•


•







to

-------
                                                 TABLE T-1.  SUMMARY OF TESTING FEATURES (SHEET 2 OF 2)


No.

1





2


3
4
5





7

8



9
10


11

12


13





Date of Test
Feature

Channel size

a. 3" diam steel (stl)
b. 3" diam steel to 2" x 5" trapezoidal
d. 3" diam steel to 4" diam transite
e. 3" diam steel to 6" diam transite
Channel type
a. uo ce t ic cyii orica , c oseo.
c. Closed cylind. to open trapezoidal


Sensor type


. .
bensor sensitivity, imv/g)

Sensor installations

Pipe installation features
a. Freely suspended in air
b. Simulated underground
c. In sim. box but not buried
Max. flow rate (Ib/sec)
Pipe exit condition
a. Open exit
b. Exit weir installed
Supply pipe inlet condition
a. Extended mlet (overlap dist., in.)
Solids in flow?
b. Heavy bed load of stone chips
c. Light bed load of stone chips
d. Upstream dispersed grit
Remarks





2/26






•




0 69


4333
(2)
19.5
21.5


3

.


10

•












2/27






.













2



•
10

•












2/28






.
















•

8

•












3/6














4333
(2)
1020
19.5,
21.5,
98





•
12.5


•











3/12











4 25











•

13.25


•











3/21











2 2












•
12


•











3/27























•

12


•










1975
3/31














4333
(2)
19.5
21.5





•

11.5

•












3/31























•

8.25


•



.







4/9














4333
(2)
19.5,
21.5
98




•

11.0


•




*






4/23







•
















•
11.0

•












4/24







•








19.5,
21.5






•
14.2

•












4/24







•






^








•

11.6

•












4/28







•







1020
19.5
98





•

14.0

•












5/8







•






4333
(2)
19.5
21.5





•

2

•












5/8







•
















•
15.4

•












6/26







•







1020
19.5
98






•
5

•





•
8-20
Sieve
Size
S.G.=
2.62

7/1






















a) In buried vault,
3) Emerging from1
underground
125.0

•





Sanitary
Sewage •
Field
Test
3 review •


CO

-------
was designed originally to expedite test schedules as well
as to avoid constructing test equipment that might prove
superfluous.  Some of the data obtained with this initial
simple test setup, particularly for cylindrical pipe ele-
ments, appear in conflict with dipole theory trend pre-
dictions.  In the interest of completeness several plots
of these discrepant data are included in the material of
this section.  The reader is cautioned not to interpret
these data as evidence of a basic defect in our flow mea-
surement concept.  As will be explained later in Section
HID, Discussion,  these discrepant test data are solely
the result of shortcomings in our initial laboratory simu-
lation technique.  This situation was rectified in the
latter half of the experimental program with relatively
simple, yet effective, measures developed to simulate
underground sewer installations.
1.   Steel Supply Pipe (Tests of August 14, 1974)
Measurements were made for a   5 ft   (1.52 m)    length of
3-in.   (7.6 cm)  diameter steel pipe coupled to the  20 ft
(6.1 m)   long,  3-in.  (7.6 cm)   steel water supply pipe of
the test facility.  Because of the threaded coupling geome-
try   [3.25-in.    (8.3 cm)  long]  and pipe wall thickness
[0.216-in.   (0.55 cm)]   a  0.25-in.  (0.64 cm)  annular step
existed for a distance of  1.28-in.  (3.25 cm)   between the
two pipe sections (see Fig. 11).
                             44

-------
The objective of this test was to record the inherent noise
of the facility supply line for a case where just a minor
perturbation discontinuity was introduced into the pipeline.
A B&K 4332 accelerometer was attached to a steel mounting
stud  that had been cemented to the outer surface of the pipe
at a position abutting the downstream end of the coupling and
on the bottom centerline.  Devcon "F" epoxy cement with  80%
aluminum content, was the adhesive.  Initial supply pressure
                            2             2
for the water was  15 Ib/in.   (1.05 kg/cm )  and  20 seconds
collection time was employed to obtain average flow rates for
several control value settings.  Between flows of  0  to
8.4 Ib/sec   (0  to  3.8 kg/sec),  the overall signal between
frequencies  40 and  22,000 Hz  varied as shown by Fig. 28.
These data are duplicated by data obtained during the October
28-30 test series  (see Section IIIC-3) in which the sensor
was located  2.5 pipe diameters upstream of a significant
conduit discontinuity (see Fig. 28).  Both sets of acoustic
data appear  to follow a lower rate of change with flow than
predicted by dipole theory.  Data for two frequencies ex-
hibiting repeated  peak amplitudes in the spectral distribu-
tion also are plotted on Fig. 28.  The ambient sound (zero
flow) recorded in  the laboratory displays two major peak
amplitudes in its  spectral distribution, at  80 and 2160 Hz,
and a general trend of decreasing signal with increasing
frequency (see Fig. 29); this is characteristic of a mass-
                                              3
law distribution of broadband acoustic energy.   Spectral
distributions for  several flow rates exhibit less of the
                             45

-------
                           LEGEND:

                           DATA OF 8/14/74

                           0 - ALL FREQUENCIES
                               (40-22,000 Hz)
                           A - -2160 Hz

                           4. - -880 Hz

                           DATA OF 10/28-30/74

                           " - ALL FREQUENCIES
                               (40-22,000 Hz)
                               (2.5D UPSTRM OF DISCONT'Y)
O
>
LU
cc
CO
•a
tn
O


-------
FULL SCALE = 108 dB     RMS DATA: -22 dB
                                       NAGRASETTING:  110dB
                                       AMPLIFIER:       20 dB
      -10 -
   dB  -20 -
      -40
      -30 —
         a) AMBIENT-NO FLOW
                                       NAGRASETTING:  130 dB
                                       AMPLIFIER:       20 dB
FULL SCALE = 130 dB    RMS DATA:  -20  dB

        0
      -10 -
   dB -20 -
      -30 -
         b) FLOW RATE = 5 (b/sec
                             102                   103
                                  FREQUENCY/4, Hz
                                                                      10
      Fig.  29  Typical  spectral distributions of  laboratory
                sound recordings.   Distributions obtained  by
                Fourier  analyzer (10  Hz bandwidth)
                                   47

-------
mass-law fall off that characterizes ambient noise and more
of a profile distinguished by several minor peaks, with a
major band at about  880 Hz.  Figure 29b for a flow rate of
5 Ib/sec  (2.27 kg/sec)  typifies these latter type spectra.
The epoxy-based adhesive for accelerometer mounting studs was
judged satisfactory on the basis of adhesion and sound trans-
mission, and used in all subsequent tests.
2.   Open Channel Conduit (Tests of August 22-23, September
     12, and November 8-11. 1974)
In this test series, the supply pipe discharged into an open
channel having a trapezoidal flow cross section with a (see
Fig. 11)  4.82-in.  (12.2 cm)  minimum width and  1.66-in.
(4.2 cm)  height.  The maximum cross-sectional width of this
6 ft  (1.8 m)  long aluminum channel is  5.78-in.  (14.7 cm).
The hydraulic radius of this open channel for different water
levels varies according to Fig. 30.  The cylindrical supply
pipe was supported at a minus  40 minute slope above and in-
dependent of the trapezoidal channel so as to permit various
waterfall heights equal to or greater than  4.15-in.  (10.5
cm).  The supply pipe exit also overlapped by   16-in.
(40.6 cm)  the upstream end of the open channel.  The chan-
nel was mounted with a downward slope of   25 minutes of
arc.  Two types of transducers were installed at four dif-
ferent axial locations along the outside bottom centerline
of the aluminum channel (see Fig. 11).  In outward physical
appearance this test setup was an approximately ten times
scale version of the original exploratory tests conducted by
Grumman Research in August 1972.
                             48

-------
   1.7
   1.6
   1.4
   1.2
   1.0
 I
 o
 I 0.8
 tr
 in
 H
   0.6
   0.4
   0.2
               0.2
r
                          5.78".
                                   .4775"
                                i_ 212'
                                 t
                                .465"
                      TRAPEZOIDAL

                      TEST CHANNEL
                          I
                         0.4        0.6         0.8

                            HYDRAULIC RADIUS, in.
                                                        1.0
                                                                  1.2
Fig.  30   Hydraulic radius  of test  channel for different

           water  level  heights
                                 49

-------
The open channel downstream of the discontinuity made it con-
venient to determine the relation of flow rate to water level
in the  3-in.  (7.6 cm)  diameter supply pipe, as well as  the
outfall trajectory parameters.  These results are shown in
Fig. 31.  The data for water level and flow rate are experi-
mental in the upper half of this figure; the area and volume
flow ratios are from tables in Ref. 5,  and full flow area is
        2           2
7.07-in.    (45.6 cm ).    Using the measured flow rate and
the flow ratios from this figure the supply pipe will run
full for flow rates above about  7.0 Ib/sec  (3.18 kg/sec)
and have a velocity at the pipe exit of at least  2.3 ft/sec
(0.70 m. /sec).  Higher exit velocities corresponding to
higher flow rates can be obtained by pressurization of the
water supply.  For example, the highest flow rate measured
during the entire laboratory test phase was  15.4 Ib/sec
(7.0 kg/sec)  for which the exit velocity is  5 ft/sec
(1.52 m/sec).  The measured variation with flow rate of the
normalized axial offset distance for the waterfall's center
of contact upon the receiver channel,  Xc/h,  is shown in the
bottom half of Fig.  31,  Extrapolated to the maximum flow
rate experienced in our tests, the normalized axial offset
would be a maximum of  2.2.
The acoustic measurements taken concurrent with the flow mea-
surements employed two accelerometers with sensitivities of
62.7 mv/g  and  19.5 mv/g  and with corresponding working
frequency ranges of  26,000  and  35,000 Hz,  respectively
                          2
(1 g  equals  980.6 cm/sec ).   The  3:1  ratio for the trans-
ducer sensitivities is equivalent to a  10 dB  signal dif-
ference.  Flow rates up to  7.6 Ib/sec  (3.45 kg/sec)  were
                              50

-------
   1.0 I—
Y/D
                                 "FULL'Q/QFULL

      a) HEIGHT OF PARTIALLY FILLED PIPE FLOW VS WATER FLOW RATE
    1.8 i—
    1.6 —
                                                      3"D
 Xc
 h
                                   w, Ib/sec
      b) NORMALIZED DISTANCE TO WATERFALL CENTER OF CONTACT VS FLOW RATE
   Fig. 31   Calibration  of research  facility water supply
              (A =  flow  area,   Q = volumetric  flow  rate)
                                  51

-------
established at initial supply pressures between about  8  and
                              2
18 psi  (0.56  and  1.27 kg/cm ).
Typical results of processed signal level to flow rate are
presented in Figs. 32 to 34 for two waterfall heights, two
accelerometer sensitivities, and four sensor locations.  In
Fig. 32 the signals at two frequency bands are shown nor-
malized to the zero flow (ambient)  condition.  This has been
done to compensate for the difference in accelerometer sensi-
tivity that would produce a  10 dB  level difference, if
shown on an absolute scale.  In Fig. 33 the signal components
at  3600 Hz  (i.e., f/4 - 900)  are considered characteristic
for the waterfall height,  h,  of  4.15-in. (10.5 cm) accord-
ing to our empirical rule that  h =A/4  where  A=c/f.  The
other frequencies  (f/4= 800 and 710 Hz),  shown in Fig. 32,
correspond to  h = A/4.5 and A/5,  respectively, and have been
presented because peak signal amplitudes are observed in the
computer processed spectral distributions at these frequencies.
Figure 34 shows typical results for a waterfall height,  h,
of  4.8-in.  (12.2 cm).  This configuration has a character-
istic frequency of  3125 Hz.  Processed data are presented
for other frequencies,  2040  and  2460 Hz,  which exhibit
peaking amplitudes in the spectral distribution.  These other
frequencies correspond to approximately  A/6  and  A/5,  re-
spectively.
3.   Eccentric Steel and Aluminum Pipes  (Tests of September 9,
     October 28-29, 1974, and January 29, March 6 and 12, 1975)
The conduit arrangement for these tests consisted of the 3-in.
(7.6 cm)  diameter steel pipe discharging into a nominal
8-in.  (20.3 cm)  diameter, 4 ft  (1.22 m)  long, aluminum
                               52

-------
                            3" DIAM PIPE
                             ^
                         -5"x 1.6"
                         TRAPEZOIDAL CHANNEL
	1	4.15"

 QU     ฎ   ฎ   L
                   16"	ซ
 CD
 T>
 UJ

 CQ
 O
 ffl
 CD

 1/3

 O
 O
 O
 <
 Q
 LU
 N
 CC
 O
   50
   40
   30
   20
   10
                                f/4 = 800, POS 4


                        f/4 = 710, POS5


                f/4 = 800, POS 5
                            f/4 = 800, POS 1
                                        I	I
0 1
2
3
4
w, Ib/sec
5
6
7 ฃ
Fig.  32  Variation  of normalized acoustic  signal with
          flow  (cylindrical pipe exiting  to a trapezoidal
          open  channel)
                              53

-------
   3" DIAMPIPE
           s
J  .      ฉ
T)b-N	D-

                   4—*
                                          \
                                         -5"x 1.6"
                                         TRAPEZOIDAL CHANNEL
                     DATA OF f/4 = 900 Hz
  150
  140 —
                                                    DIPOLE THEORY
                                                       SENSOR
                                                       4332, POS. 4
Fig.  33   Acoustic  signal variation with flow  rate
          (cylindrical pipe  discharging to trapezoidal
          open channel)
                              54

-------
                          .3" DIAM PIPE
                                                5" x 1.6" TRAPEZOIDAL
                                                     CHANNEL
                                                SENSOR POSITIONS
                                                        POS 1
                                                           POS 2 & 5
                                                            POS 1
                                                         POS 1
                                                        POS 2
0 1
2
3
4
w, Ib/sec
5
6
7
8
Fig.  34  Variation  of  normalized  acoustic signal  with flow
          rate - different sensor  locations  (cylindrical
          to trapezoidal channel transition)
                               55

-------
pipe.  This setup was the first one involving completely
cylindrical elements and was designed to demonstrate  the
production of acoustic emission in channels that were not
always completely open  (see Fig. 11).  The pipes were at-
tached in an eccentric manner so that the waterfall height
was  4.2-in.  (10.67 cm) or  4.45-in.  (11.3 cm).  The height
depends on whether the smaller pipe has an extended inlet
within the larger one, or is assembled as a sudden enlarge-
ment so that the roof line for the joined pipes is tangent.
The upstream end of the  8-in.  (20.3 cm)  pipe was closed
by an aluminum plate having an eccentric hole large enough
to fit the  3-in.  (7.6 cm)  pipe (see Fig. 8).  All joints
were sealed watertight with  1-in.  (2.54 cm)  wide adhesive
faced lead tape.  The slope of both pipes was minus  0.3%.
Flow rates up to more than  13 Ib/sec  (5.9 kg/sec)  were
established at water supply pressures between  8  and  27 psi
                      2
(0.56  and  1.90 kg/cm ).   Three different accelerometer
models were attached to mounting studs at four axial loca-
tions on the  8-in.  (20.3 cm)  diameter pipe and one loca-
tion on the  3-in.  (7.6 cm)  pipe.  In addition, during
several tests two circumferential locations were monitored,
at  45  and  180 degrees  counterclockwise from the bottom
centerline viewed looking upstream, at an axial position
6-in.  (15.2 cm)  from the upstream end of the larger pipe.
After a series of tests in which the smaller pipe extended
2.5-in.  (6.4 cm)  into the  8-in.  (20.3 cm)  pipe, tape re-
corded acoustic  data were  processed and typical results are
shown in Figs. 35 and 36.   The sensor acoustic signals at
different positions are shown varying with flow rate in
Fig.  35;  these trends are  for the characteristic frequency
                             56

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      3" DIAM PIPE
          \
                                   8" DIAM PIPE
fc
(D
"••-P


-ปu
U-2.5"-^
ฉ ฉ /
U i
*-3"->J
<ซ 	 6.4" 	 ป
j
                                                 POS.
                                                 POS. 6
35  Variation  of normalized acoustic signal with
    flow rate  -  effect of sensor location
    (eccentric cylindrical pipe elements and
    extended inlet)
                       57

-------
                        NUMBERS IN CIRCLES DENOTE
                        SENSOR POSITIONS
                       3" DIAM PIPE
                                               8" DIAM PIPE
                          SENSOR       SENSITIVITY,
                    SYMBOL  TYPE  POSITION    mv/g
z
UJ
CO
LU

O
m
y
l-
t/i

O
O
<
Q
LU
N
Lt
O
    40 r-
\>od
o
•
+
A X
a
•
ys
4332
4333
4333
4332
4333
4333
4333
4332
3
6
4
4
3
1
5
5
62.7
19.5
19.5
62.7
19.5
19.5
19.5
62.7
                              w, Ib/sec
  Fig.  36  Effect of  sensor  on variation of normalized
            acoustic signal with flow rate  (eccentric
            cylindrical pipe  elements and extended  inlet)
                                58

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of  3540 Hz.  Figure 36 shows similar data to Fig. 35 but for
an additional sensor and at another sensor location.  Data
points allow results of different test setups to be distin-
guished from one another.
In another test, the smaller diameter pipe was mounted so
that its exit plane and the entrance plane of the larger pipe
were flush.  The purpose of this geometric array is to exam-
ine the influence of the air space behind the waterfall, as
a resonance chamber driven by waterfall instabilities, to
modulate the flow acoustic emission signal strength.  Test
data given in Fig. 37 show that for comparable sensor loca-
tions  (relative to the discontinuity plane) the setup with
the maximum air volume behind the waterfall produces the
largest signal amplitude.  These data are for the signal com-
ponent at the characteristic frequency and for flow rates up
to  11 Ib/sec   (5.0 kg/sec).
Visual observation of nonuniform or high flow rates reveal
various types of mild hydraulic jump conditions in the down-
stream channel.  To investigate the effect that such rapid
changes in water level might have on flow sound emission, we
made three weirs to be attached to the exit plane of the
8-in.  (20.3 cm)  diameter pipe.  The weirs have heights of
2.24,  3.24,  and  4.24-in.  (5.7, 8.2,  and  10.8 cm).  Be-
cause  of the slope and length of the test pipe section, the
shortest weir retains just a film of water directly below
the discontinuity, and the highest weir retains a  2-in.
(5.1 cm)  deep water pool there, which almost halves the free
fall of water from the  3-in.   (7.6 cm)  pipe.
Typical trends  of the processed acoustic data to a flow rate
of  11 Ib/sec   (5.0 kg/sec)  are shown in Figs. 38-40.  In
                               59

-------
                   • DATA AT CHARACTERISTIC FREQUENCIES
                   • (SENSOR TYPE - 4333, SENSITIVITY - 19.5 mv/g)
             3" DIAM PIPE
m
•o
z
o
co
O

CO
O
O
  140 I—
  120  —
100
   80
   60
                EXTENDED
                INLET
D
t4,5" f
i #3 #4 L

2.5"
3"

* ป
	 fi
                                                  8" DIAM PIPE
                         FLUSH
                         INLET
                               I
                                    4.45"
                                                  — POS3, f/4 = 900Hz
                                           POS4, f/4 =900 Hz
"•  — —  ___ POS 2, f/4 = 830 Hz

             POS 1, f/4 = 830 Hz
                                        #2
                                      *J	6"
                                      	L
                                6         8
                                   w, Ib/sec
                                                 10
                                                          12
                                                                    14
 Fig.  37   Effect of  extended  inlet on acoustic signal
            variation  with flow rate (eccentric  cylindrical
            pipe  elements)
                                   60

-------
3" DIAM 8" DIAfl.
\ /
I t
4.45"
ฉ ฉ tf
           ALL FREQUENCIES (40-22,000 Hz)
                                                  POS 1
  LU 20
IT
O
   10
                                  fc/4 = 830Hz               POS 1,f/4 = 2010Hz


                               fc  = CHARACTERISTIC FREQUENCY = 3320 Hz
                                    6

                                  w, Ib/sec
                                                         10
                                                                   12
    Fig.  38  Effect of  sensor position  and sound  frequency
              on acoustic emission of water flow  (eccentric
              cylindrical pipe elements  and flush  inlet)
                                  61

-------
            3" DIAM-
                                           ' DIAM
                      .  SENSOR POS. 2
                      •  DATA AT f = 3320 Hz
                                                  NO WEIR
0
246
w, Ib/sec
8
10
12
Fig. 39  Effect of  exit weir height on normalized
         acoustic signal of water flow (eccentric
         cylindrical  pipe elements and flush  inlet)
                         62

-------
                        3" DIAM
                                      .8" DIAM
z
UJ
                                                . SENSOR POS. 2
                                                • DATA AT f = 6640 Hz
                                    W/3.24"WEIR
                                              W/OWEIR
                               w, Ib/sec
     Fig.  40  Effect  of exit weir  height on normalized
              acoustic signal of water flow  (eccentric
              cylindrical pipe  elements and  flush inlet)
                               63

-------
the first of these figures the data for two sensor positions
and no weir displays the signal for the entire acoustic spec-
trum and the minimum characteristic frequency  (3320 Hz),
computed on the basis of maximum waterfall height
(4.45-in. = 11.3 cm).  The rapid increase in signal above
ambient up to about  2 Ib/sec  (0.91 kg/sec)  flow agrees
with dipole theory predictions.  At greater flows, the in-
crease in useful signal is not as large as theoretically
predicted.
Figure 39 shows that when a greater depth of water pool
exists (highest weir) the acoustic signal is reduced, at the
low flow rates, compared to shallower or nonexistent water
pools.  At flow rates greater than about  12 Ib/sec  (5.45
kg/sec),  however, the acoustic emission signals for all
four pool conditions appear to converge into a single trend.
If the water backed up by the weir were to behave exactly
like the solid wall of the conduit in producing pseudosound,
then the data at a characteristic frequency based on the free
fall distance to the water pool should yield improved acous-
tic signal data.  This is not indicated by the data compari-
son of Fig. 40 with Fig. 39, where the characteristic fre-
quency of Fig. 40 is computed to correspond to the shortened
drop to the  2-in.  (5.1 cm)  deep water pool.  The trends of
these two figures are very similar and probably differ only
by the differences in background (ambient) noise level at the
two frequencies compared.
Figure 41 depicts the variation of normalized acoustic signal
with flow at four locations of accelerometer installation.
At position 1, closest to the discontinuity plane, the
                             64

-------
                  3" DIAM PIPE
                                     8"DIAM PIPE
  70 I—
                                                  WEIR
                         3"
                                             •  DATA AT CHARACTERISTIC
                                               FREQUENCY = fc = 3320 Hz
                  DIPOLE THEORY
                      POS 1, W/O WEIR
                   V
                   POS 1
               POS2
                        SENSOR   SENSOR SENSITIVITY
                        POSITION  TYPE     mv/g
2,4
3
1
                                4333     19.5
                                1020     98.0
                                4333     21.5
                              6        8

                                w, Ib/sec
                                                10
                                                         12
                                                                 14
Fig.  41  Variation of  signal with flow at  different
          sensor  locations;  (eccentric  cylindrical
          pipe elements  and flush inlet) (with 4.24-
          inch weir at  exit unless noted otherwise)
                                 65

-------
normalized acoustic signals for the weir equipped pipe are
similar to the open-ended conduit, up to a flow of  3 Ib/sec
(1.36 kg/sec).  At higher flows the latter pipe configura-
tion gives  3  to  4 dB  greater signal.
At positions 2 and 4, which are at the same axial position
but circumferentially separated by  45 degrees,  the signal
trends for both locations are almost identical and follow
dipole theory to flow rates of  1.5 Ib/sec  (0.68 kg/sec).
For greater flows up to about  10 Ib/sec  (45.5 kg/sec),
the signal at position 4 is greater than at the bottom cen-
terline (position 2).  At still greater flows there is neg-
ligible difference between the signal levels at each sensor
location.
Most practical sewers are in buried installations where the
overburden depth is at least equal to one pipe diameter.  We
have simulated such installations in our laboratory by en-
closing the section of test pipe, in the vicinity of the dis-
continuity plane, within a special wooden box (see Section
IIIB) and Figs. 13 and 14).  The four feet  (1.2 m)  long
box contains coarse sand that we have used to simulate typi-
cal backfill.  A maximum overburden depth of  8-in.  (20.3
cm)  is possible as well as partial burials and freely sus-
pended pipe installations.  The sand is tamped down before a
test series to eliminate air pockets.  Typical data obtained
for these conditions are presented in Figs. 42-44.   In the
first figure of this series, the normalized acoustic signal
trends are shown for flows up to  13.25 Ib/sec  (6.02 kg/
sec).  These curves are at a characteristic frequency,  f
of  3320 Hz,  and at twice  f .  They indicate a signal
                             66

-------
                3" DIAM
                   V
                                   8" DIAM
)

I- d

r
                                                  WEIR
                          Upos 1   U POS 3
               • COVERED BY 8" OVER BURDEN OF COARSE SAND;
               • WITH 4.24" WEIR UNLESS OTHERWISE NOTED
              f/4 = 1660 Hz, POS 3, W/O WEIR
                                              f/4 = 1660-1500 Hz, POS 3
                              fc/4 = 830 Hz, POS 3, W/O WEIR

                 fc/4 = 830 Hz, POS 3                    f/4 = 1660 to 1500 Hz, POS 1
                                 SENSOR  SENSITIVITY
                          POSITION   TYPE     mv/g
Fig.  42   Variation of normalized acoustic signal with
           flow  rate for different frequencies  and test
           conditions  (eccentric  cylindrical  pipe
           elements and flush inlet)
                              67

-------
                    3" DIAM
                                   8" DIAM
                                    /
                                   #2
                                                 #4
                                               45ฐ
                     •  COVERED BY 8" SAND EXCEPT WHERE NOTED.
                     •  DATA AT fc/4 = 830 Hz
                     •  POS.4
100 |—
                        LINEARIZED SCALE, W/WEIR
                                           W/WEIR, W/O SAND OVERBURDEN
 Fig. 43   Variation  of normalized acoustic signal with
           flow rate  for different test conditions (flush
           inlet, eccentric  cylindrical pipe  step)

-------
level reduction of about  5 dB  when the highest weir is
placed at the pipe exit.  This is measured at a sensor loca-
tion slightly greater than one diameter downstream from the
discontinuity plane.
The effect, at one sensor location, of the  8-in.  (20.3 cm)
deep overburden of sand on the normalized signal trend, at
the characteristic frequency, is given by Fig. 43.  At flows
above  1.5 Ib/sec  (0.68 kg/sec)  and no weir at the pipe
exit, the sand covered installation has a greater signal for
a flow rate than the unburied conduit.  This trend also
exists for the buried pipe with a weir.  The acoustic signal
trend assumes a large change in slope, for  dB  versus  w
axes, above  w ~ 1.5 Ib/sec  (0.68 kg/sec).  This curve shape
change does not mean greatly reduced resolution, however.  If
we convert the  dB  scale to a linear ratio scale, as depicted
on Fig. 43, it is possible to resolve  0.025 Ib/sec  (0.011
kg/sec)  in flow rate with working scale curves.  In most prac-
tical system applications, a linear scale would be used for
readout devices such as gauges and strip charts.  The data of
Fig. 44 presents absolute signal  levels in  dB,  for three
accelerometer  locations.
4.   Concentric Steel and Aluminum Pipes  (Tests of October 29^
     30, November 11, 1974. and January 16-17, 22-23, March
     21, 27, 31, and April 9, 1975)
The arrangements of flow conduits for these tests are similar
to those described in the preceding Series 3 except  that the
3-in.  (7.6 cm)  diameter steel pipe is attached concentric
to the  8-in.  (20.3 cm)  aluminum pipe.  Because of the ac-
tual physical  dimensions of the pipes the waterfall  height
is  2.2-in.   (5.6 cm)  which corresponds  to a characteristic
                               69

-------
       DATA AT
       CHARACTERISTIC
       FREQ = fc/4 = 830Hz
                            '_)#4
     3-K-J   I
     •*-6"-ซH
     -—9"—H
                                 #3
                   NOTE:
                   * = POS 4, W/SAND, W/O WEIR
    120i—
                           POS 3, W/SAND, W/O WEIR
                                                    POS 3, W/O SAND, W/WEIR
                                                     POS 4, W/SAND, W/WEIR
                                                    POS 1, W/O SAND, W/WEIR

                                                     POS 1 W/SAND, W/WEIR

                                          POS 1, W/SAND, W/O WEIR
   POS 4, W/O SAND, W/WEIR

POS 3, W/SAND, W/WEIR
     60
                                  w, Ib/sec
   Fig.  44   Variation of acoustic  signal  with  flow for  3
              sensor  locations  and various  test  conditions
•ig.  45   Closeup  of concentric  discontinuity plane  assembly
          of 3-inch steel  water  supply pipe  to 8-inch
          diameter aluminum test pipe
                                 70

-------
frequency of  6700 Hz  in water.  The upstream end of the
8-in.  (20.3 cm)  pipe was closed by an aluminum plate and
sealed with adhesive faced lead tape (see Fig. 45).  The
slope of the pipe assembly was minus   0.3%  initially;
this was altered in later tests to minus   370   to improve
drainage.  Flow rates to   15 Ib/sec   (6.8 kg/sec)   were
established at water supply pressures between  8  and  27 psi
                      2
(0.56  and  1.90 kg/cm ).  Four different accelerometer
models were used at four axial locations relative to the dis-
continuity plane, and at five circumferential positions at
one axial position.  As with the eccentric arrangement pre-
viously described, three weirs of differing heights were
used at the exit plane of the conduit to force retention of
water, of different depths, beneath the discontinuity plane.
Also, tests were conducted with the pipes buried under one
pipe diameter depth of coarse sand.
One additional test was made with this concentric array in
which the bottom of the  8-in.  (20.3 cm)  diameter was
filled with stone chips to a maximum depth of  1-in.  (2.54
cm)  along its entire  4 foot  (1.22 m)  length.  This ex-
treme pipe bed load condition was prevented from being washed
away by the  4.24-in.  (10.8 cm)  weir plate at the exit
plane.  Views of this bed load, with the weir removed, are
shown in Figs. 15 and 46 taken before water flows, and
Figs. 16 and 47 taken after a series of tests with flow rates
above  2-3 Ib/sec  (0.9  to  1.4 kg/sec),  and  5 Ib/sec
(2.3 kg/sec),  respectively.  The purpose of these stone
chips is threefold.  First, it is used to indicate whether a
diffuse solid material, which is not cemented to the con-
duit construction, could change the amplitude of acoustic
                              71

-------
Fig.  46  Internal relation  of  3-inch  supply  pipe  to  8-inch
         test pipe with heavy  bed  load  of  stone chips.
         View taken before  flow established
Fig. 47  View of upset bed load after water flow rate of
         5 pounds per second
                           72

-------
emission at the original characteristic frequency.  Then,
would the characteristic frequency be changed if the stones
change the free fall height  of  the waterfall?  Finally would
the movement  of the stones,  under  the influence of water
flow, alter the amplitude  of acoustic emission of the flow,
or otherwise  interfere with  interpretation  of the acoustic
data?  It was  realized at  the time that a bed load of stones
(average specific  gravity  of 2.75)   that  reduced the flow
cross section by almost  7.5 percent  was likely to be an un-
common event.  The test, however, was considered as poten-
tially informative for more  carefully designed future experi-
ments.  However, in recognition of the fact that the extremely
heavy bed  load conditions  imposed by this test setup were un-
realistic, a  follow-up test  was made in which the stone chips
were uniformly distributed in as near a single layer of
stones as  possible, along  the bottom inner  surface of the en-
tire length of 8-in.   (20.3 cm)  pipe.
Typical data  for the concentric  mounting with an extended in-
let are presented  in Figs. 48 and 49.  The  first gives the
sensor signal  component at a characteristic  frequency of
6700 Hz  for  four  sensor mounting locations.  This signal has
been normalized to the ambient  noise level  (zero flow) to
compensate for the differences  in sensitivity and installa-
tion for the  two accelerometers.  At a good  sensor location,
3-in.  (7.6 cm)  downstream  from the discontinuity plane, the
normalized signals  for several  frequencies  are shown by
Fig. 49.  It  is evident from this figure that the trend at
the characteristic frequency is  uniquely unambiguous and use-
ful for relating signal amplitude to flow rate.  The other
frequencies shown  correspond to  other peak  amplitudes in
                              73

-------
              3" DIAM
                      (
                               ฉ
                         ซ-ป
                                               8" DIAM
                                             NUMBERS IN CIRCLES DENOTE
                                             SENSOR POSITIONS
                                             SENSOR TYPE 4333 AT ALL
                                             LOCATIONS (SENSITIVITY =
                                             19.5 mv/g)
                                             DATA ATfc/4= 1675 Hz
                                                          	POS 4
                                                           POS 1
                                                             POS 3
                              w,Ib/sec
Fig. 48   Variation of normalized  acoustic  signal with
          flow rate at various sensor locations and
          characteristic  frequency (concentric cylindrical
          pipe array with extended inlet)
                               74

-------
            3" DIAM
                                               8" DIAM
                                              TRANSDUCER 4332
                                              SENSITIVITY = 62.7 mv/g
GO
TD
                                                        fc/4= 1675 Hz

                                                    f/4 = 775 Hz

                                                         f/4 = 1350 Hz
                                                         f/4 = 510 Hz
 Fig. 49   Variation  of normalized acoustic signal  with
           flow rate  for different frequencies  (concentric
           cylindrical pipe array with  extended  inlet)
                               75

-------
the spectral distribution resulting from Fourier processing
of the recorded data.
The normalized data shown in Fig. 50 are results of the in-
vestigation into signal improvement by varying the circum-
ferential location of the sensor attachment.  The concentric
cylindrical pipe array has a flush inlet in these tests.
While all locations yield a generally similar result at low
flows, the trends indicate that a position of  45 degrees to
the bottom centerline appears to yield greater signals, at
the intermediate to high flow rates, than at other circum-
ferential positions.
The effect of different weir heights on the acoustic signal
monitored at two positions, along the bottom centerline of
the larger pipe, is shown by Fig. 51 for the characteristic
frequency.  Data obtained at position 2 are somewhat better
than for position 1 at flow rates greater than about  8 lb/
sec  (3.6 kg/sec).
Comparative data for component frequencies of the sound other
than the characteristic frequency, are given in Figs. 52 and
53 for the highest weir-equipped conduit.  The overall signal
strength for the entire recorded frequency range of  40  to
22,000 Hz  is also given in Fig. 53.  Data at position 3 al-
ways is of the highest amplitude because the sensitivity of
the transducer used at this mounting location is about five
times greater than for the other accelerometers.  If the
sources of acoustic signals were equally strong at each mount-
ing stud location  the accelerometer with enhanced sensitivity
would produce a  14 dB  greater signal than the less sensitive
transducers.
                              76

-------
               3" DIAM
                             8" DIAM
               SENSOR
               POSITION
                         DATA ATfc/4= 1675 Hz
CD
T3
LLJ

CD
O
CO
CO

O

I-
cn


O
O
<

O
HI
N
tr
o
2
                                                       45ฐ POS 1
0 1
2 3 4 5 6 7 ฃ
w, pps
3 9
10
 Fig. 50   Effect of sensor circumferential and  axial
           location on  useful signal  (concentric cylindrical
           pipe array with flush inlet)
                               77

-------
              3" DIAWI-
                                            8" DIAM
                           ,u
                           -6"-*-l
                       • DATA AT ^-=1680 Hz
                      2.24" WEIR    3.24" WEIR
                                              NO WEIR
  m
  T3
  en
  o
  in
  O
  U
                                   L,...     \
                                                      POS2
                                                       NO WEIR
                                                      POS 1
Fig. 51  Variation of acoustic  signal with flow at two sensor
         locations for different  test conditions (flush inlet,
         concentric cylindrical pipes)
                               78

-------
          3" diam
          STEEL
          8" diam	
          ALUMINUM
                             #1 #2 #3
  150 i—
  130
  110
   90
<  70
2
2
CO
o
H
co

O
O
                                                             POS3
                                                              POS2
                                                              POS 1
                                                  DIPOLE THEORY
                                                  TREND
                                                  re: w=1 Ib/s
024

 a) DATA AT f/4 ~ 200 HZ
6        8
  W, Ib/sec
10
         12
                  14
    DIPOLE THEORY TREND
    (re: w=1 Ib/s)
  110 r—
   90
   70
   50
                                                    POS 2
                                                          POS 3
                                                             POS 1
                                      DIPOLE THEORY TREND
                                      (re: w=2 Ib/s)
              2        4

     b) DATA AT fc/4 = 1680 Hz
                                                 10
                                                           12
                                                                   14
                             w, Ib/sec
  Fig.  52  Variation of acoustic signal with flow  at three
            sensor  locations and  for two frequencies - with
            4.24" weir at pipe exit plane -  (concentric
            cylindrical pipe elements)
                                 79

-------
              130
              110
              90
              70
              50
                                              POS3
                                                     POS 1
                      _L
                            DIPOLE THEORY TREND
                            (re: w=2 Ib/s)
                                 _L
                                             _L
                                                   _L
                                                        J
                0     2     4      6     8     10     12    14

                                  w, Ib/sec

                a) DATA ATf/4= 1400 Hz
           CO
           •a
           O

           C/3
           D
           O
           O
              140 r
              120 -
                                             POS 3
DIPOLE THEORY TREND
(re: w=2 Ib/sec)
              100 -
                 b) (ALL FREQUENCIES
                   BETWEEN 40 AND
                   22,000 Hz)
              120
              100
              80
              60
              50
                                                  POS 3
                                                     POS 1
                            DIPOLE THEORY TREND
                           ' (re: w=2 Ib/s)
                                 _L
                                       _L
                                  6     8
                                  w, Ib/sec
                                             10
                       12
                             14
                c) DATA AT f/4 = 2700 Hz
Fig.  53  Variation of acoustic  signal with  flow  at three
          sensor  locations  and  three  frequency bands - with
          4.24 inch weir  at pipe exit plane  - (concentric
          cylindrical pipe  elements).  See Fig. 52  for  sensor
          position  location on  pipe.
                                 80

-------
Typical acoustic signal data where the section of joined
pipes near the discontinuity plane is buried into a minimum
of  8-in.  (20.3 cm)  of sand is given in Figs. 54 and 55.
These curves are for three accelerometer locations and pre-
sent the normalized acoustic signal component at four fre-
quencies as well as the absolute overall signal.  The nor-
malized dipole theory trend is close to the signal trend at
sensor positions 2 and 3 for the characteristic frequency
(6720 + 80 Hz).
The effect of the very heavy bed of stones, placed at the
bottom of the  8-in.  (20.3 cm)  pipe, is indicated from the
data plots of Fig. 56.  At the characteristic frequency, the
signals at both sensor positions are within  2 dB  of each
other, whereas for the overall range of frequencies about a
7 dB  difference exists.  It appears from the data shown
in Fig. 56 that the weir's use results in a more gradual
and resolvable signal trend, especially at the low flow
rates up to about  8 Ib/sec  (3.6 kg/sec).
The acoustic signal obtainable for a bare conduit is com-
pared to that with both heavy and light bed loads of stones,
in Fig. 57.  These data are for the characteristic frequency
component as well as the integrated value over the entire
frequency spectrum.
An appreciation of the physical action of the waterfall in
displacing even a heavy bed of stones can be obtained from
the sketches of Fig. 58, and Figs. 15, 16, 46, and 47.  The
drawings are interpretations of the experimenter's observa-
                              81

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                             COVERED BY SAND TO 8" DEPTH
                    POSITION ( 1
              FOR ALL FREQUENCIES (WITHOUT WEIR)
              (DATA NOT SMOOTHED)
                                    FOR ALL FREQUENCIES
                                    IN 40- 22000 Hz BAND
                                    (DATA NOT SMOOTHED FOR CURVE)
                                               280 Hz = f/4


                                           420 Hz = f/4


                               DIPOLE THEORY  (NORMALIZED TO 1 pps)
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          B) SENSOR POSITION 1
                           6       8

                            w,Ib/sec
                                        10
                                                12
                                                            14
Fig.  54  Variation of  acoustic  signal  with  flow  at two
          sensor  locations  and two frequency bands
           (concentric cylindrical  pipe  elements)  - with 4.24"
          weir at pipe  exit and  8" deep sand overburden,
          except  where  noted
                                  82

-------
                                   FOR ALL FREQUENCIES IN
                                   40- 22,000 Hz BAND
                                   (DATA NOT SMOOTHED FOR CURVE)
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FOR ALL FREQUENCIES IN
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         (SEE FIG. 54 FOR SENSOR LOCATIONDATA)
                          280 Hz = f/4
                                          DIPOLE THEORY (NORMALIZED TO 1 pps)
                                                         672 Hz = f/4
                                     8

                                   w, Ib/sec
                                             10
                                                    12
                                                            14
                                                                    16
Fig.  55  Variation oฑ. acoustic  signal  with  flow at  five
          frequency bands  and one sensor location
          (concentric cylindrical pipe  elements) - with 4.24"
          weir at  pipe exit and  8" deep sand over burden,
          except where noted

-------
                 3" diam •
                 8" diam •
                  POS. 1 (W/O WEIR AND STONES)
  120 |—
  100
  80
ง 60
                                                 POS. 2 (W/O WEIR AND STONES)
                   POS 2 W/WEIR
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     a) DATA AT ALL FREQUENCIES (40-22,000 Hz)
                                       POS 1
                                       W/WEIR
                                       AND STONES
                                                 POS 1 (W/O WEIR AND STONES)
                            POS 2 W/O WEIR & STONES
               POS 2 W/WEIR & STONES
                                   6

                                w,Ib/sec
                                                       10
                                                                 12
     b) DATA AT fc = 6720 Hz
  Fig.  56  Effect  of heavy bed load of  stones (1"  deep)  in
            8"  diam.  pipe  on  acoustic signal  variation  with
            flow -  sand  covered array
                                  84

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     60
     50
                          W/THIN
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                                      POS. 1 & 2 (W/1" STONE LAYER)
                         I
                                                               j
                                                                14
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       b) DATA AT fc/4 = 1680 Hz
                           6        8

                              w,Ib/sec
                                                    10
                                                              12
Fig.  57   Effect of  two bed loads of  stones in  8 inch diameter
           pipe  on acoustic  signal variation with flow - sand
           covered array with 4.24 inch weir
                                   85

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  3" diam STEEL PIPE
                                       8" diam ALUMINUM PIPE

                                                 A-

   STONE.
   CHIPS
                a) PIPE CONFIGURATION BEFORE TEST
                                   SECTION
                                     A-A
                b) PIPE CONFIGURATION AFTER 3.08 Ib/sec FLOW RATE
                                        AVJ&
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-------
tion after various stages of the tests.  The observed local
washout of the stone bed as the flow increases practically
assures that the full discontinuity geometry will be main-
tained, and the characteristic frequency will be unaltered.
Further tests where a bed load can be securely attached
(e.g., by cement) to withstand such washout, could provide
valuable extrapolation of the data already obtained.  Fig-
ure 59 shows that absolute signal components at frequencies
much above as well as much below the characteristic fre-
quency  (f )  are of larger amplitude than  f   for the sen-
          c                                  c
sor location closest to the discontinuity plane (i.e., posi-
tion 1).  Note that since the zero flow (ambient) signal
level is greatest for the lowest frequencies because of the
mass distribution law, the signal-above-ambient at, for ex-
ample,  800 Hz,  actually is less than at the characteristic
frequency for all flow rates.  Position 3 is well downstream
of the  base of the waterfall but the acoustic data obtained
there (see Fig. 59) are generally similar to that obtained
at position 1.
5.   Four Inch (10 cm) Diameter Transite Pipe (Tests of
     February 26-28, 1975)
A  4-in.  (10 cm)  ID Transite pipe,  44-in.  (1.12 m)  long,
was installed at the end of the  3-in.  (7.6 cm)  ID facility
water supply pipe (see Fig. 60).  The main purpose of this
test setup is to assess the transmission of flow acoustic
emission through a nonhomogeneous, nonmetallic sewer pipe
wall.  Another objective is to examine a low sound loss tech-
nique for attaching transducers to the outer surface of the
nonmetallic conduit.  From physical properties data supplied
                              87

-------
                3" diam
                PIPE
   130 i—
   110  -
    90  -
    70
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                                                     f/4 =
                                                     200 Hz

                                                     1400
                                                     1680 = fc/4

                                                     1850

                                                     2700
      a) POSITION 3
    110 i—
Fig. 59   Variation of  acoustic signal with flow at four
          frequencies and two sensor positions  (8" sand
          cover and monolayer of  stone chips within 8" diam
          pipe.  4.24"  weir at exit  of pipe)
                               88

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by the manufacturer  (Johns Manville  ), it has been determined
that  the acoustic properties  of Transite are comparable to
concrete used  in sewer pipe construction.
The discontinuity plane between the  steel and Transite pipes
is of the eccentric  sudden enlargement type (flush entry)
in which the roof line of the joined pipe sections is
continuous.  The eccentric, crescent-shaped gap between
the pipes is filled  by an aluminum plate and sealed by a
Velmix (quick-setting) cement.  The  step discontinuity is
0.69-in.  (1.75 cm)  which corresponds to a characteristic
frequency of   21,500 Hz.  While the  processed recorded data
show  acoustic  spectral distributions generally similar to
spectra obtained with metallic pipes, the characteristic
frequency is found to be at or just  above the upper thresh-
hold  of frequency response of the magnetic tape recorder
used.  Therefore, the reduced data could not be correlated
reliably with  mass flow and no graphic data presentations
are to be made here.  This temporary inconvenience was over-
come  by purchase of  a  6-in.  (15 cm)  ID Transite pipe sec-
tion  as a replacement.
No difficulty  was experienced in attaching the accelerome-
ter mounting studs by Devcon  "F"    (8070. aluminum) epoxy
cement.  However, it was noticed that the mounting studs were
somewhat more  easily sheared  off the Transite pipe than the
metallic pipe  because of the  tearing of a thin veneer  of
epoxy impregnated Transite from the  parent material.   If a
sensor installed in  this way were to remain undisturbed in  a
  Private communication from R.  C.  Elliott,  Johns  Manville
  Sales Corporation,  Manville, New  Jersey (January 1975).
                               89

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buried installation, we would not expect this kind of shear
failure.
6.   Six Inch (15.2 cm) Diameter Transite Pipe (Tests of
     April 23, 24, 28, May 5, and June 26, 1975)
The second series of tests involving a nonmetallic nonhomo-
geneous conduit material used a  6-in.  (15.2 cm)  diameter
Transite,  5 foot  (1.52 m)  long, sewer pipe section.  The
3-in.  (7.6 cm)  diameter steel pipe of the facility water
supply was attached to the Transite pipe by a machined plas-
tic mounting collar and blanking plate (see Fig. 61) so that
the roof line was continuous, and a sudden  3-in.  (7.6 cm)
step resulted at the discontinuity plane (see Fig. 11).  This
step size corresponds to a characteristic frequency of about
5570 Hz.  The joint was sealed at the external surface by
silicone-based caulking.  Data were obtained with three ac-
celerometer transducers at .six mounting locations including
one on the bottom centerline of the  3-in.   (7.6 cm)  steel
pipe and  3-in.  (7.6 cm)  upstream of the  discontinuity
(position 7).  Other sensor locations, not  monitored during
previous test series, were at the bottom centerline of the
Transite pipe,  7-in.  (17.8 cm)  upstream of the exit plane
(position 9)  and  2.3-in.  (5.9 cm)  downstream of the dis-
continuity plane (position 1).  The Transite pipe was set at
a  3 degree  downward slope and the bottom lip of the pipe
was  19.25-in.  (49.0 cm)  above the floor of the diversion
trough.  Test conditions included simulated buried and un-
buried pipe installations, flow rates up to  15 Ib/sec
(6.8 kg/sec),  and initial pressurization levels of  12  to
29 psi  (0.84  to  2.04 kg/cm2).
                             90

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Fig. 60  Closeup of eccentric connection of 3-inch water
         supply pipe to 4-inch diameter transite te&t pipe
Fig.  61   Closeup  of  special assembly  collar used  for
          eccentric connection of  3-inch pipe  to 6-inch
          diameter transite test pipe.  Flow is from right
          to  left.  Two  sensor mounting studs  are  shown
          cemented at top  centerline surface of transite
          pipe
                             91

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For a special set of runs using this pipe configuration,
laboratory equipment was developed to introduce solid parti-
cles (screened sand) into the water supply at a point  18
feet  (5.5 m)  upstream from the test section; this equipment
and technique has been described in detail in Section IIIB.
Because of the slot in the  3-in.  (7.6 cm)  pipe line for
feeding sand, flow rates above  6 Ib/sec  (2.7 kg/sec)  could
not be run without water spillage from the opening.  Typical
results of this test series are presented by Figs. 62 to 65.
7.   Field Test Preview (Test of July 1, 1975)
The field test preview was conducted at the Grumman sewage
treatment plant "A" adjacent to the corporation's building
12 in Bethpage, New York.  The flow conduits monitored con-
sist of  10-in.  (25.4 cm)  diameter steel pipes.  Because
of the preliminary nature of the tests and the need for
flexibility, we decided to attach the accelerometer sensor
to the outer surface of the pipe by a special magnetic
mounting stud marketed by the transducer supplier.  Unfor-
tunately, this mounting technique had not been used in the
previous laboratory tests so no rigorous basis of compara-
tive sound transmission ability was possible.  Testing took
place between approximately  10 am and 1 pm.  Acoustic mea-
surements were recorded on instrumentation tape over a  30
second  time period.  The first test location was in an
underground control valve vault shown by Figs. 20 and 21.
Sanitary sewage from several Grumman buildings feed into a
distant wet-well where collection continues until a pump-
activation level is reached.  The pump supplies an approxi-
mately constant average flow of  650 gpm  (2460 1/m) through
                              92

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i STEEL	ป_K~
                                       I
                                        7"
                                    	POS. 7



                       — — — — ~                         \  DOO Q J
                                                           •POS. 9
                                        \"
                                                       POS. 9 (UNDER SAND)
                                                   POS. 7
                                                   (UNDER SAND)
                           _L
                      _L
      a) DATA AT ALL FREQUENCIES (40 to 22,000 Hz)
   110 ,-
                                                           -POS.9
                                                          \
                       	POS. 7
                                            •POS. 7
                                             (UNDER SAND)
                                            POS. 9
                                            (UNDER SAND)
                                                       J	I
      b) DATA AT fc/4 = 1400' Hz
                                  DIPOLE THEORY TREND

                                                            POS. 9
                                                          POS. 9
                                                          (UNDER SAND)
      024


      c) DATA ATf/4= 180 Hz
               6      8

                  w, Ib/sec
                             10
                                    12
                                                   POS. 7 (UNDER SAND)
                                           14   15
Fig.  62   Variation of  acoustic signal with flow (eccentric
           cylindrical pipe array)  -  transite and steel pipe
           elements without sand overburden except where noted
                                  93

-------
        3" diam STEEL	Wj~
         REGION BURIED UNDER
         SAND
                       ^
                                              -6" diam TRANSITE
         130 r-
         110 -
              DIPOLE THEORY TREND

                      \
                                               POS. 3 W/O SAND

                                               	POS. 3
                                             -- POS. 4 W/O SAND


                                            	POS. 9
<
2
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      in
      D
      O
      O
              a) DATA AT fc/4 = 1400 Hz
                             	—-^-_2.-^IL	POS.7
         130 i-
   110 -
                                                J



                                           POS. 4 W/O SAND


                                              POS. 3

                                                   POS. 9
              b) DATA AT ALL FREQUENCIES (40 to 22,000 Hz)


         140 r                   	- POS. 3 W/O SAND
         120 -
         100
                                            — POS. 4 W/O SAND

                                                    POS. 3
                                   DIPOLE THEORY TREND

                           	POS. 7
                              W, Ib/sec
              c) DATA ATf/4 =180 Hz
Fig.  63   Variation  of acoustic  signal with flow  (eccentric
           cylindrical  pipe  array) -  transite and  steel pipe
           elements buried under  8 in.  (20.3 cm)  of  sand,
           except  where noted
                                 94

-------
    140
    120 —
    100
  <  60
       a) DATA ATf/4 = 1400 Hz
      -0        2


       b) DATA ATf/4 = 180 Hz
                                               10
W, Ib/sec
                                                       POS. 3
                                                         POS. 4
                                                          POS. 1
                                                       POS. 3
                                                           POS. 1
                                                        12
                                                                14
Fig.  64   Variation  of acoustic signal with flow (eccentric
          cylindrical  pipe array)  -  transite and steel pipe
          elements without sand overburden, except where noted
                                95

-------
                rdiam STEEL
                                           6" diam TRANSITE
                                               DIPOLE THEORY TREND
                                      > I \J\J. *J
               a) DATA ATf/4 = 1400 Hz
                                               DIPOLE THEORY TREND

                                                 POS.3
             60
                      2       4

               b) DATA ATf/4= 180 Hz
Fig. 65   Effect of  grit addition to water  flow on  the acoustic
          signal variation with  flow - transite and steel
          pipe elements, without sand overburden, in eccentric
          assembly
                                 96

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the  10-in.  (25.4 cm)  pipe until the level in the wet-well
drops to a cutoff point.  The pipe discontinuity accessible
for our measurements was an  8-in.  (20.3 cm)  plug valve
connected by an  8 by 10 by 6-in.  tee fitting to the  10-in0
(25.4 cm)  upstream supply pipe, and by an  8 by 10-in.  re-
ducer section to the downstream pipe.  Several positions on
the reducer, exit pipe, and upstream tee section were examined
(see Fig. 66).  Ambient noise measurements were recorded when
no flow was evident; this  fact was established by correlation
of the observed level indicated by the tape recorder's moni-
toring meter and visual verification at the exit of the pipe,
about  500 feet  (152 m)   away, at the aeration tank.  The
sources of ambient noises  at the value include moderate road
traffic about  500 feet   (152 m)  to the south and a railroad
about  750 feet  (228 m)   to the east.  One of the two am-
bient noise measurements  coincided with passage of an eight-
car passenger train.
The second field site where acoustic emission measurements
were taken was at the point where the  10-in0  (25.4 cm)
pipe emerges from beneath  the surface and discharges hori-
zontally into an open,  tortuous concrete channel feeding a
comminuter (see Figs.  22  and  23).  Close by, a  4-in.
(10.2 cm)  diameter steel  pipe also discharges into  the com-
minuter feed channel except the direction of flow  is verti-
cally downward.  This smaller pipe conducts an additional
250 gpm   (746  1/m),  from a pump-equipped wet-well located
in the Grumman factory  building just north  of  the  treatment
plant.
                               97

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                                                       CONCRETE WALL
                      ,10" diam

                          ,8x10 reducer
8" plug valve
          ,8x10x6 tee
                       SENSOR POSITIONS IDENTIFIED
                       BY NUMBER IN CIRCLE
   120 r—
   100 —
                                                   DIPOLE THEORY TREND
                        VOLUMETRIC FLOW RATE, q, gpm x 10
                                               ,-2
Fig.  66  Variation of  acoustic signal with  flow  at Grumman
          waste  treatment plant "A"  valve vault for
          different sensor positions - first test  series
                                 98

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Four locations on the horizontal leg of the  10-in.  (25.4
cm)  diameter steel pipe were monitored as shown by Fig. 67.
D.   DISCUSSION
The results of this program can be summarized by the state-
ment that no fundamental questions remain concerning the
feasibility of Grumman1s acoustic emission flow measurement
technique applied to discontinuities at enlargements of
conduit cross sections.

The test data have removed each of our initial reservations
about the technique discussed in Section IIIA.  The numerous
tests established to demonstrate feasibility were, perhaps,
influenced by the failures of so many more complex tech-
niques when applied to sewer flow, and the contrasting rela-
tive simplicity of our passive nonintrusive method.  But
now, after extending the range of flow rate by a factor of
20,  using four different pipe geometries or constructions,
employing accelerometer sensors with four different sensi-
tivities, and conducting a field test preview, the acoustic
emission technique remains viable and appropriate for more
exhaustive field testing leading to prototype systems.
To date, only laboratory equipment has been used to monitor
flow acoustic emission and to process the raw data.  This
approach has had the advantages of minimizing equipment costs
to the program, and of presenting greater measurement capa-
bility than the basic needs of tests to allow flexibility  in
conducting the exploratory research.
The assemblage of many high quality but multipurpose  labora-
tory components to obtain acoustic recordings and  to  feed
                              99

-------
                                        SENSOR POSITIONS
                                        IDENTIFIED BY NUMBER
                                        IN CIRCLE
                           SIDE VIEW
 140 i—
                                                 f = 2200 Hz
                                                 f = 3400
 80 -
  60
DIPOLE
THEORY
TREND
I
3 2

I I
4 6

I I
8 10

I
12

I
14
                     VOLUMETRIC FLOW RATE, q, gpm x 10'
                                           -2
Fig. 67   Variation  of signal with flow at  Grumman waste
          treatment  plant "A" aeration pond for different
          frequencies  and sensor  positions  - second  test
          series
                             100

-------
these recordings through the Fourier analysis computer, in-
troduces and compounds the inaccuracies and mismatches of
each component in the system.  The result of these unwanted
signal distortions, or noise, is that the reproducibility of
the processed signal components in narrow  10 Hz  frequency
bands is no better than  + 2 dB  over the frequency response
of the tape recorders.  A  2 dB  change is equivalent to a
ratio of sensor signal levels of  1.26;  while this seems
small, at high flow rates this change can represent large
absolute quantities of flow.  The prospects for improving
this situation are extremely good if less versatile, well-
integrated electronic circuits and special purpose data
processors are used.  Now that most of  the feasibility
questions have been answered, prototype hardware need only
consist of a  simple accelerometer, for  attachment to the
sewer pipe, and a  communications  link  to a simple, cheap,
dedicated minicomputer.
While we have not  determined the  accuracy  limits  for  the  acous-
tic data because of the equipment involved, we have estimated
the accuracy  of the test  facility's flow rate measurement equip-
ment as from  + 7% for  low  flow, short sampling  time  (e.g.,
10  seconds) conditions  to  + 4%   for high  flow,  long  sampling
time  (e.g.,   30 seconds  or more)  situations.  These values  com-
pare  favorably to  commercial flow meters for  sewage that
often have accuracies worse  than  + 10%.
The research  facility has demonstrated sufficient versatil-
ity for the  program, and  accommodated  various changes  of  pipe
test  configurations with  relative ease. The  only limitation
we  have experienced is  an inability to sustain  steady flow
at  high flow rates because  of  the  limited  plant  water supply
                               101

-------
to the pressurization tank.  Uniform as well as nonuniform
flow conditions were established during the program although
the latter profile was limited to flow rates less than
6 Ib/sec  (2.7 kg/sec).   The maximum flow rate of about
15 Ib/sec  (6.8 kg/sec)   is imposed by the present flow col-
lection and measurement  method.  This capability could be
doubled by facility modifications if justified by the scope
of future test programs.
The superior acoustic data resulting from use of a high weir
at the pipe exit and with simulated buried installations
demonstrate that special precautions against acoustic reflec-
tions should be taken in laboratory investigations involving
passive acoustic monitoring.  Anechoic chambers typify such
special measures.  However, our simple inexpensive measures
proved effective in accomplishing almost complete sound isola-
tion.  In most field measurements for sewer pipes, this prob-
lem does not exist.  At  outfalls, except if there are reflect-
ing surfaces surrounding the exit, there should not be signi-
ficant reflected sound to distort the acoustic emission char-
acteristics of the flow.
The test results summarized in Fig. 68 indicate that the
characteristic frequency component of acoustic emission of
flow into an open trapedzoidal channel increases with flow.
No undue precautions have been taken against sound reflec-
tions, but the open channel apparently produces diffuse
radiation that does not  reflect back efficiently to the chan-
nel.  Although the dipole theory trend is approximated only
at low flows, the signal component is unambiguous and there-
fore useful for flow measurement.  For flows above  2.2 lb/
sec  (1.0 kg/sec)  the  3 dB  higher acoustic signature for
                             102

-------
                           4.8"
   150 i—
                                            DIPOLE THEORY TREND
   70
   50
                                        fr = 3600 Hz
                                                         10
                             w, Ib/sec
Fig. 68   Typical variation of  acoustic signal with  flow
          for  two conduit configurations (cylindrical  to
          trapezoidal cross-sectional discontinuity)
                            103

-------
 the higher waterfall is not considered trend-setting at  this
 time, and is more likely peculiar to the test equipment  set-"
 ups at the two different test periods.  Since these results
 confirmed and extended Grumman's 1972 exploratory data,  fur-
 ther investigations with this conduit configuration were  sus-
 pended in favor of completely closed cylindrical pipe ele-
 ments .
The data for the   3-in.   (7.6  cm)   diameter steel water  sup-
ply pipe (see Fig. 28)  has   20  to   30  dB   lower overall (all
recorded frequencies)  sound emission at intermediate to  high
 flow rates than for the test conduits downstream of a discon-
 tinuity.  This difference cannot be the result merely of trans-
mission loss through the pipe  walls because all pipes used
 (i.e.,  steel, aluminum,  and Transite) have theoretical wall
 transmission losses within  +3 dB.   It  is  concluded, then, that
 the greater output of the sensors  on the various downstream
 test pipes are the result of strong acoustic radiation by pseu-
dosound, dipole type,  sources  caused by the discontinuity.  At
 zero flow, peak signal component amplitudes on the  3-in.  (7.6
cm)  pipe are observed at  80  and   2160 Hz,  excited by pre-
sently unidentified sources in the  laboratory (see Fig.  29b).
Clearly,  the latter frequency  duplicates a major excitation
source  of the laboratory environment and although the signal
amplitude increases with flow  to about   5  Ib/sec  (2.27  kg/
sec),   it decreases for  higher flows.  Therefore, this  signal
component is ambiguous  for  flow  measurement purposes because
the same signal strength can represent  more than one flow
rate value at this frequency.  The  other  peak in th^ spectral
distribution, at  the lower   (880 Hz)  frequency, increases in
amplitude with flow rate at a  somewhat  slower rate than  would
                              104

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                                         • A 1 2
be predicted by dipole theory  (i.e.,  ^ w )  '   at low to in-
termediate flow rates, but becomes more compatible toward the
higher flow rates tested.  On  the other hand, this frequency
component exhibits poor adherence to the theoretical near-
                                    ~  r
field boundary layer variation   (~ w ).   The  880 Hz  fre-
quency is close to that which would be calculated as charac-
teristic on the basis of the   17-in.  (43.2 cm)  drop from
the pipe to the wooden diversion trough, so it is tempting
to hypothesize the source of this peak signal component as
the flow interaction with the  solid surface of the trough.
The monitored signal would be  the sound reflected back
through the open end of the  3-in.  (7.6 cm)  pipe.  In any
event, the slight  0.25-in.  (0.64 cm)  discontinuity caused
by the pipe coupling produces no dipole sound signal within
the  22,000 Hz  frequency response limit of our recording
equipment and no useful signal for flow measurement.
Figures 37 and 69 summarize the effect of an extended inlet
on acoustic emission signal at characteristic frequency, for
eccentric and concentric cylindrical pipe element assemblies.
While Fig. 37 data show higher  dB  levels for the extended
inlet, the useful signal above ambient is almost equal for
both inlets because the zero flow (ambient) signal level is
lower for the flush inlet.  On the other hand, this does not
hold true for concentric installations as shown by Fig. 69,
where all signals are normalized to the zero flow level.  For
the extended inlet shown in Fig. 69, the sensor position atop
the downstream pipe (5), measures  5  to  7.5 dB  greater
levels than at the bottom centerline, (3), but at the same
axial distance from the pipe discontinuity.  We interpret
                              105

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                                              FLUSH INLET
                                     A) WITHOUT WEIR
        B) WITH WEIR
CO

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(D
in
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Q
LU
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O
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           DIPOLE THEORY TREND
       EXTENDED
       INLET
NO. 3
0
2
4
6
w, Ib/sec
8
10
12
 Fig. 69   Effect of  extended  inlet on acoustic signal
           variation  with flow rate (concentric cylindrical
           pipe elements)
                               106

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this as showing greater susceptibility of position 5 to re-
flected sound.  As flow increases, the trend is for signals
at both positions to converge.  The flush inlet with a
4.24-in.  (10.8 cm)  weir produces lower signals than the
open pipe exit at the same sensor position but its trend
follows more closely that of dipole theory, to about  6 lb/
sec  (2.7 kg/sec)  flow.  At higher flow rates, the open and
weir-equipped pipes display signal components approaching
equality.  Figures 43 and 44 effectively summarize the in-
fluence of laboratory sound reflections on signals obtained
with the eccentric cylindrical pipe array.
With an end-positioned weir and sand burial, a constant
7.5 dB  lower signal is monitored at position 4 (see Figo 43)
6-in.  (15.2 cm)  from the discontinuity.  At position 1
(see  Fig. 44) the nearly constant difference of  5 dB  for
weir-equipped pipes with and without sand overburden is
equivalent to the exposed installation having a sound source
that is  1.8  times greater than the buried pipes, for flows
greater than  1.5 Ib/sec  (0.68 kg/sec).  At position 4 this
signal difference because of sand overburden also is about
5 dB  but only at flows between  2  and  9 Ib/sec  (0.9  and
4.09 kg/sec).  When the only difference between test condi-
tions is the presence or absence of the end weir, the signal
level with the open ended pipe is  9 db  greater than with
the weir, for sensors at both positions 1 and 4.  This dif-
ference is equivalent to an apparent ratio of sound source
strengths of about  2.8.  Similarly, at position 3 reductions
in signal are caused by overburden or weir attachment (see
Fig. 44) but of somewhat smaller magnitude than the previous
two positions analyzed.  Presumably, sensor position 3 has
                              107

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different exposure susceptibility to reflected sound because
of its downstream-most location.  The curves for positions 3
and 4 show that the effectiveness of the sand overburden in
preventing sound reflection from affecting the sensor at each
location^ becomes unimportant above  9 Ib/sec  (4.09 kg/sec)
flows.  This can be explained on the basis that the magnitude
of externally reflected sound becomes  10 dB  less than the
internally produced flow interaction signal at flows of about
9.0 Ib/sec  (4.09 kg/sec)  (e.g., two separate  100 dB
acoustic signal sources produce  106 dB  of combined acoustic
signal, but if only one signal increases to  110 dB  the
combined signal is only  112 dB).  Thus, we conclude that the
exit plane weir and  8-in.  (20.3 cm)  deep sand cover screen
the accelerometer pickups from being overpowered by flow
sound and other external noises reflected back from the
laboratory walls.  When compensation is made for these re-
flected sounds, under laboratory conditions, completely un-
ambiguous signals are obtained for the acoustic emission flow
measurement technique in eccentric cylindrical pipe installa-
tions.
The results of Fig. 50 signify that acoustic signals are
transmitted circumferentially with negligible loss at any
particular axial pipe station.  For unburied installations,
the upper sector of the pipe surface probably is more vul-
nerable to externally produced noises.  However, for typical
buried pipe installations, acoustic pickups can be attached
at any convenient circumferential position, which simplifies
field instrumentation of existing sewer pipes.
Figures 51 through 55 indicate that the effect of an end weir
plate and simulated buried installation is similar for the
                            108

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concentric arrangement of cylindrical pipe elements as it was
for the eccentric pipe assembly.  The highest weir prevents
reflected sound, off the laboratory walls, from reentering
the pipe and augmenting the acoustic signal of flow at the
discontinuity.  Because of the downward slope of the  8-in.
(20.3 cm)  conduit, the shorter weirs have no practical
shadowing effect and result in data almost identical to the
open ended pipe.  When the acoustic reflection is minimized
by pipeline burial and weirs, the data appear to follow
closely the dipole theory prediction curve and are unambigu-
ous with respect to flow rate.
Summary Fig. 70 shows how the pipe configuration changes the
normalized acoustic emission signal at a fixed axial position
downstream from the discontinuity plane.  Both curves shown
are for signal components at the characteristic frequency cor-
responding to the disturbance distance of the configuration.
The influence of acoustic reflections is minimized here by
burial under sand and attachment of an end weir.  The moni-
toring position selected for data presentation always is
downstream of the base of the waterfall but more so for the
concentric pipes than the eccentric array because of the dif-
ferent discontinuity distances.  Both data trends are unam-
biguous and useful for flow measurement although the concen-
tric configuration data follows the dipole theory trend bet-
ter than the eccentric configuration over a larger range of
flows.
Figures 56 and 57 effectively show that stone bed loads do
not thwart the acoustic emission technique.  Further analy-
sis of the spectral distributions resulting from the compu-
ter processed recorded sound reveals that a major part of
                              109

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                       CONCENTRIC CONFIG
       60 I—
    m
    T3
    UJ
    m
    5
    o
    CD
       50
       40
dd
                                            DIPOLE THEORY TREND
LJ_
4.25"
T
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VNO.
-ซ— 9"-^|
Iฃ - ซ-5n u.
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3 SENSOR POSITION
                                           ECCENTRIC CONFIG
                                   1
                                   6

                                 w,Ib/sec
                                                    10
                                         12
Fig. 70  Effect  of pipe configuration on normalized  acoustic
         signal  variation with  flow rate (cylindrical  pipe
         elements)  with 4.24 in. weir,  8 in. sand overburden,
         and  flush inlet
                              110

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the  7 dB  difference in overall signal value between the  tv?o
sensor positions, displayed  in Fig.  56, is  in the  low fre-
quency range, below  1200 Hz,  rather  than  in the  high range
near the characteristic frequency  of  6720  Hz.  From Fig.  57
we see that when  the tumbling stones of the heavy  bed load
are continuously being moved by the  force of the water flow
there results a greater sound level, integrated overall fre-
quencies, than for the clean pipe, and a greater variation
of the overall signal at different sensor positions.  How-
ever, the spectral discrimination exercised to extract a
signal relatable to flow (i.e., by obtaining signal compo-
nents at characteristic frequencies) makes  our technique ef-
fectively insensitive to the consequences of extreme salta-
tion of the bed load; the bulk of the additional sound pro-
duced by rolling stones is in an unused part of the spectral
distribution.  While Fig. 57 indicates comparable trends for
the thick layer of stones and the bare conduit,  at the char-
acteristic frequency, for a nearly monolayer bed load of
stones the acoustic component is much larger than either of
the other two test conditions at low flow rates.  As the
flows increase to intermediate and high rates the thin layer
of stones is displaced just  like the thicker, more mobile,
bed load so that the persistent slightly higher acoustic sig-
nal measured must represent additional sound sources near the
discontinuity.  One explanation is that the turbulence pro-
duced by the sharp-edged stones scatters pseudosound and con-
verts part of it into intense sound  fields which are in a
propagating mode.
One of the pleasant features of passive acoustic monitoring
of flow is that the overall sound quality is good enough to
                              111

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be  listened  to by humans.  Further,  the  sound  of processes  as
rolling  stones are  fully  interpretable as  such by  experienced
personnel  listening to  the sensor  output.  This type  of in-
formation  can be extremely helpful in remote operational
monitoring of the condition of sewers to determine where
maintenance is  necessary.
If the thickness  of the monolayer bed of stones were to be
considered as reducing the discontinuity distance and acting
like the solid wall of the conduit, the characteristic fre-
quency would change to  7400  Hz  from the  6720 Hz  for the
clean pipe.  But  the data  of  Fig. 59 at  7400 Hz  coincides
with that at the  frequency for the bare conduit at all but
the lowest flow ranges below   2.2 Ib/sec  (1.0 kg/sec).
Where the very low flows do not move the stones, the signal
at  7400 Hz  is within  2  dB   of the level at the original
6720 Hz.  The data trend of Fig. 59 does not exactly match
the  12 dB  per doubling of flow rate predicted by dipole
theory.  However, the acoustic signals obtained are unambigu-
ous for the range of flows tested,  and are therefore useful
for flow measurement in a  geometrical setup similar to the
laboratory arrangement.
Summary Fig. 71 shows that the acoustic emission flow mea-
surement method can be used with metallic as well as inhomo-
geneous nonmetallic conduit materials of construction.  Al-
though the discontinuity distances of the Transite and alumi-
num pipes are different, we interpret the results of Fig. 71
at two sensor positions  as indicating basically similar
trends that are useful for flow measurement in both instances.
The quality of sound transmission through the inhomogeneous
                              112

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                  3" DIAM STEEL
                                 8" DIAM ALUMINUM
     60,—
                                 fc = 6400 Hz
0
2
4
6
w, Ib/sec
8
10
12
Fig. 71  Effect  of pipe material on normalized acoustic
         signal  variation with flow rate  (eccentric
         cylindrical pipe elements and  flush inlet) - 8 in
         sand  overburden
                             113

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Transite material is very good and because concrete has simi-
lar acoustic properties to Transite, the prognosis for as yet
untested concrete pipe sections is excellent.
In the data display of Fig. 62, the trends for the acoustic
signal components at the characteristic frequency  (~ 5600 Hz)
and  720 Hz  are shown for the Transite pipe exit monitoring
location (position 9) and the  3-in.  (7.6 cm)  steel pipe
monitoring location.  Also shown is the overall signal for
frequencies between  40  and  22,000 Hz.  Since a  4 foot
(1.2 m)  long section of the pipe configuration, equally dis-
tributed on either side of the discontinuity plane, was sup-
ported within the wooden box made for simulation of buried
installation, tests were made with and without sand overbur-
den.  However, of the two sensor locations plotted, only po-
sition 7 is physically affected by the overburden because
the other position 9 is well downstream of the confines of
the box.  From Fig. 62 we see that the sound signal at posi-
tion 9 is greater than on the steel pine.   This position on
the Transite pipe has greater exposure to the sound produced
by the interaction of falling water with the diversion trough.
If the  19.25-in.  (49 cm)  drop to the trough is considered
the exit discontinuity distance, the exit characteristic fre-
quency would be  720 Hz.  The difference in signal amplitude
between positions 9 and 7, at intermediate flow rates, is
11 dB  at the assumed exit characteristic frequency,  whereas
it is  6 dB  different for all recorded frequencies,  and
18 dB  different at the discontinuity characteristic  fre<-
quency of  5600 Hz.  A flow interaction mechanism to  explain
the higher acoustic signal at position 9 seems unsupported
                              114

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by the data.  In addition, when the sound produced by the
upstream pipe discontinuity is prevented from radiating nor-
mal to the pipeline axis into the laboratory (and reflecting
back to the sensors) by an  8-in.  (20.3 cm)  layer of
surrounding sand, the reduced signal amplitude is within
2 dB  of being the same at both positions and all frequencies
presented in Fig. 62.
Position 9 is in the far field of the pseudosound source near
                                     1 2
the discontinuity plane„  It is known '  that at these large
distances from their source, pseudosound energy is converted
into real sound which propagates throughout the flow.  This
is especially true where turbulence is added to the flow by
sharp edges such as at the exit plane of the pipe or by a bed
load of newly crushed stones (not weathered smooth) as noted
earlier.  From these considerations we then attribute the
higher signal near the Transite pipe exit to sound reflected
longitudinally back into the pipe by the nearby laboratory
walls and diversion trough surfaces.
The higher magnitude of near field component signal levels,
at positions closer to the pipe discontinuity plane (e.g.,
positions 3 and 4 compared to positions 7 and 9), is evident
from Fig. 63.  About  14 dB  of the higher signal at posi-
tion 3 is produced by the higher sensitivity of the acceler-
ometer mounted there.  The remaining  3-8 dB  enhanced sig-
nal, depending on frequency, at positions 3 and 4 compared
to position 9, undoubtedly is evidence of pseudosound pro-
duction in the near field of the discontinuity plane.  Fur-
thermore, since position 4 is further downstream from the
discontinuity, the signal obtained is about  4 dB  less than
                             115

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that at position 3, for the characteristic frequency.  Other
data in Fig. 64 show that except in the low flow range, the
acoustic signal obtained at position 3 is superior to signals
at the other sensor locations examined, for the characteristic
frequency component.  This signal also is better or equal to
that of the other positions at other frequencies.  The sound
insulation obtained with simulated buried installations is
evident in both Figs. 62 and 63 at all sensor positions.  The
signal variation with flow at position 3 increases faster
than the dipole trend at low flows, and varies slower than
the dipole trend at intermediate to high flows.  However,
within the range of flows tested, an unambiguous signal is
produced at the characteristic frequency and is usable for
flow measurement.
Figure 65 shows the effect of adding solids to the flow.
These sand particles, passing through mesh sizes between
0.85  and  2.36 mm,  simulate sewage grit and were metered
into the water supply well upstream so as to be well inte-
grated into the flow passing the abrupt cross-sectional
change in the pipe.  However, although one can safely presume
that each particle impacts the pipe wall many times, the ag-
gregate effect of such collisions appears inconsequential
relative to the near field acoustic emission of the flow.
The acoustic signal at the characteristic frequency, as well
as at a much lower frequency, is almost exactly the same for
the flow containing grit as for the clean water flow.  Also,
despite a wide variation in grit concentration (between  86
and  1682 mg/liter of water) which was introduced for vari-
ous test points,  there is no discernible change in the result.
                              116

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In the field test documented by Fig. 66, overall (all fre-
quencies) sound levels of  80  to  84 dB  were recorded for
ambient noise, with the higher level occurring during the
train movement„  Overall sound levels of  96-104 dB  were
recorded with flow passing through the pipes.  The lowest
sound level was recorded at the top of the  10-in.  (25.4
cm)  pipe, some  27-in.  (68.6 cm)  downstream of the valve
centerline.  The highest overall sound level was measured
at the bottom of the tee section,  18-in.  (45.7 cm)  up-
stream of the valve centerline.  All four locations in the
vicinity of the plug valve have peak amplitude components
at a frequency of  2800 + 80 Hz,  as well as at several other
frequencies which are not so universally present.  This is an
example of a situation where acoustic properties of the fluid
and dimensional details are not accessible for direct mea-
surement, and a characteristic frequency has to be determined
by inspection of the spectral distribution.  Compared to the
ambient sound level at  2800 Hz  (see Fig. 66) the sound
level at three of the four locations in the vault are between
17  and  20 dB  louder when flow is present.  At the fourth
location near the top centerline of the upstream tee section,
the sound level at  2800 Hz  is  14 dB  louder when the flow
is present than the ambient recorded near the top of the
10-in.  (25.4 cm)  downstream pipe  [45-in.  (1.14 m)  awayj.
Comparison with a dipole theory trend drawn through the
650 gpm  (2460 liter/min)  data point shows reasonably good
agreement with a linearized extrapolation of the trend
through the ambient data point.
At the second field test site, the largest acoustic signal
change with increasing flow (see Fig. 67) is for the com-
                              117

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ponent at a frequency of  2000 to  2200 Hz.  Unfortunately,
since the wet-well pumps produce constant volumetric flow
rate, the acoustic data are at only two rates and full trends
can only be estimated.  It should be further noted that the
signal at  900 gpm  (3406 liter/min)  is produced by flow
discharged into the open channel from two pipe source sizes
and with different flow orientations.  At the characteris-
tic frequency of  2200 Hz,  selected by inspection of the
spectral distribution, the increase in sound level is
11.5 dB  between flows of  650  to  900 gpm  (2460  to  3406
liter/min).  The exponential law that follows these data for
                                        Q
sound power,  P ,  appears to be  PT ~ Q   rather than the
      /
PT ~ Q   relation of dipole theory.  At  2200 Hz,  the ver-
tical discharge of the  4-in.  (10.2 cm)  pipe and the re-
verberations by the walls of the open channel appear to be
much greater sources of acoustic emission than the flow dis-
turbance caused by the  90 degree  bend in the  10-in.
(25.4 cm)  pipe.  However, at another empirically selected
frequency,  500 Hz,  the increase in sound component ampli-
tude agrees almost exactly with the  5 dB  increment pre-
dicted by dipole theory for the ratio of flows for which data
are available.
Perhaps the best explanation for these few data points is
that dipole theory applies strictly to flow changes where
the discontinuity geometry is of a singular nature and the
conduit is extremely long in both directions.  When two dis-
similar discontinuities and sound reflections contribute to
the overall sound being monitored, as is the case in the
second of our field tests, the complex sound field is not
properly described by simple dipole theory; further empiri-
cal investigation is needed for these situations.
                              118

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                           SECTION IV
                           REFERENCES

1.   Ffowes-Williams, J., "Hydrodynamic Noise," in Annua1
     Reviews of Fluid Mechanics, Vol. 1, Annual Reviews,
     Inc., Palo Alto, California, 1969.
2.   Blokhintsev, D. I., "Acoustics of a Non-Homogeneous
     Moving Medium," NACA TM 1399, February 1956.
3.   Olson, H., Acoustic Engineering, D. Van Nostrand Co.,
     Princeton, 1957.
4.   Beranek, L. L., ed., Interaction of Sound Waves with
     Solid Structures, Chapter 11, "Noise and Vibration
     Control," McGraw-Hill Book Co., New York, 1971.
5.   Fair, G. M. and Geyer, J. C., Water Supply and Waste-
     Water Disposaj., John Wiley and Sons, New York, 1954.
6.   Haddle, G. and Skudrzyk, E., "The Physics of Flow Noise,"
     Journal of the Acoustical Society of America, Vol. 46,
     No. 1 (Part 2), pp. 130-157, 1969.
                              119

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                           SECTION V
                           GLOSSARY

 Accelerometer -  an electromechanical  transducer  that  gener-
      ates an electrical  output when subjected  to accelera-
      tion.  Piezoelectric  discs  clamped  between  a mass  and
      base develop a potential field when the acceleration
      of the mass exerts  a  force  on the discs.  The ratio of
      electrical  output to  mechanical  input  is  called  sensi-
      tivity.
 Acoustic Emission - the  radiation of  sound  generated  by the
      interaction of fluid  flow with a solid surface.
 Acoustic Reflection -  the  change of direction  of sound  pres-
      sure waves  impinging  on a less than perfect sound  ab-
      sorbing surface.
 Conduit Discontinuity  -  any change in a  flow channel  because
      of channel  cross  section or shape,  or  where flow direc-
      tion is significantly changed.
 Decibels (dB)  -  a measure  of the ratio of two  amounts of
      sound power.   The range of  sound pressure or intensity
      is  so large  that it is more convenient to use the  loga-
      rithm to  the  base ten to express this  ratio (bel).
      Decibel  equals  one  tenth of a bel.  When  other quanti-
      ties  (e.g.,  voltage)  are related to the square root of
      power,  the number,  n,  of  dB are: n  = 20  log,0(v/vo),
     where  v   is  the referenced quantity.
Dipole - the type  of sound source created when a fluid  in-
      teracts with  a  solid  surface to  produce unsteady forces.
                             120

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     Because of its oscillating nature, this source is
     analogous to two point-sources equal in strength but
     opposite in phase and separated by a very small dis-
     tance.  The radiated power is proportional to the
     fourth power of flow speed.  Because of the pressure
     cancellation in the plane normal to the dipole axis,
     the directionality of radiation is strongest along
     the dipole axis which is normal to the flow direction.
Hertz (Hz) - an international unit of frequency equal to
     the number of cycles per second.
Nonintrusive - not penetrating the fluid flow boundary.
Normalized Acoustic Signal - when transducers of different
     sensitivities measure the same sound source, their dB
     sound signals are different by the ratio of sensitivi-
     ties.  Similarly, when a constant sound source signal
     is measured against different background noise levels,
     the total signals are different by the relative dif-
     ference in backgrounds.  When using decibel units for
     sound level, the irrelevant variables of measurement
     such as background noise or sensor sensitivity can be
     eliminated by subtracting their  dB  contribution from
     the total signal.  The resulting  dB  level then is the
     normalized signal, and is a more valid measure of the
     sound source alone.
Overburden - the soil or backfill covering a buried sewer
     pipe or flow conduit.
Passive Flow Measurement - a method of determining the mass
     or volumetric rate of flow by using energy normally
                             121

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     radiated by the fluid flow as opposed to imposing ex-
     ternal energy sources or flow energy dissipating de-
     vices .
Pseudosound - the pressure pulses produced in locally dis-
     turbed fluid flow that have characteristics of sound
     in the Rear field but do not propagate into the far
     field of the fluid.  The radiation pattern of pseudo-
     sound is like a dipole sound source.
Sound Power (PT) - the total amount of energy radiated by a
     sound source throughout a spherical envelope in a
     period of time (watts).  In practice, the sound power
     level,  L ,  is used to relate the ratio of sound power
     to a reference power.  By international agreement, this
                          -12
     reference power is 10    watts, and  L  = 10
     log10(PT/10'12),  dB.
Unambiguous Signal - a sensor output signal that can be in-
     terpreted as relating to only one flow quantity.  Over
     a continuous range of signal output there are no in-
     termediate minima or maxima with regard to the depen-
     dent parameter.
                             122

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
 1. REPORT NO.
     EPA-600/2-76-115
                                                           3. RECIPIENT'S ACCESSI Of* NO.
4. TITLE AND SUBTITLE
     A Passive Flow Measurement System for Storm and
     Combined Sewers
                                                       5. REPORT DATE
                                                         May  1976 (Issuing Date)
                                                       6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
                                                           8. PERFORMING ORGANIZATION REPORT NO.
          K. M. Foreman*
9. PERFORMING ORG \NIZATION NAME AND ADDRESS
     Grumman Ecosystems  Corporation, Bethpage,  N.Y.  11714
     Through subcontract with:
    ^Research Dept., Grumman Aerospace Corporation
     Bethpage, N.Y.  11714
                                                       10. PROORAM ELEMENT NO.
                                                          1BC611
                                                       11. CONTRACT/GRANT NO.

                                                          EPA Contract  68-03-2121
 12. SPONSORING AGENCY NAME AND ADDRESS
     Municipal Environmental  Research Laboratory
     Office of Research  and Development
     U.S.  Environmental  Protection Agency
     Cincinnati, Ohio  45268
                                                       13. TYPE OF REPORT AND PERIOD COVERED
                                                          Final Report  6/'74 to 8/'75
                                                       14. SPONSORING AGENCY CODE
                                                          EPA-ORD
 15. SUPPLEMENTARY NOTES
     PO:   Hugh Masters
 16. ABSTRACT.
  is investigation concerns a new, nonintrusive, low cost, passive  flow measure-
ment method  to meet the urgent needs  for good management of storm and  combined
sewer systems.   Operation of the  system is based on sensing the near  field sound
emitted by the disturbed flow at  a channel discontinuity.  These  local pressure
pulses are called pseudosound and radiate as dipole sound sources orthogonal to
the flow direction.  The output signal  of passive transducers, such as accelero-
meters, attached to the outer wall of the channel indicates flow  rate  after
processing by  a Fourier Analyzer.  Feasibility has been demonstrated  by labora-
tory tests using full scale sewer pipe  elements, and by a brief series of field
tests measuring sanitary sewage flow.   Recommendations   are made for  further
field site testing using an instrumented sewer line.
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b.IDENTIFIERS/OPEN ENDED TERMS
                                                                       COSATI Field/Group
     Flow,  Acoustics, Sewers,  Flowmeters,
     Experimental Design, Acoustic Signatures
     Sound  Level Meters, Electronic Computer
     Electroacoustic transducers
                                            Acoustic Emission
                                            Flowmeter
  20C, 20A
  13B
  14B
  17A
   9A, 9B
13. DISTRIBUTION STATEMENT

     Release Unlimited
                                          19. SECURITY CLASS (This Report)
                                              unclassified
21. NO. OF PAGES
     137
                                              20. SECURITY CLASS (This page)
                                                  unclassified
                                                                         22. PRICE
EPA Form 2220-1 (9-73)
                                            123
                                                     U. S. GOVERtflHNT PRHffWG BffKE: \376-6S7-k^/^22 Region No. 5-11

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