WATER POLLUTION CONTROL RESEARCH SERIES
15080FWO 02/71
I '
Floating Oil Recovery Device
1NVIRONMENTAL PROTECTION AGENCY WATER QUALITY OFFICE
-------
WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Series describes
the results and progress in the control and abatement
of pollution in our Nation's waters. They provide a
central source of information on the research, develop-
ment, and demonstration activities in the Water Quality
Office, Environmental Protection Agency, through inhouse
research and grants and contracts with Federal, State,
and local agencies, research institutions, and industrial
organizations.
Inquiries pertaining to Water Pollution Control Research
Reports should be directed to the Head, Project Reports
System,- Office of Research and Development, Water Quality
Office, Environmental Protection Agency, Room 1108,
Washington, D. C. 20242.
-------
FLOATING OIL RECOVERY DEVICE
by
Physical Science Laboratory
New Mexico State University
Las Graces, New Mexico 88001
for the
ENVIRONMENTAL PROTECTION AGENCY
WATER QUALITY OFFICE
Program No. 15080 FWO
Contract No. 14-12-903
February, 1971
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1
Stock Number 5501-0116
-------
EPA Review Notice
This report has been reviewed by the Environmental
Protection Agency and approved for publication.
Approval does not signify that the contents neces-
sarily reflect the views and policies of the
Environmental Protection Agency, nor does mention
of trade names or commercial products constitute
endorsement or recommendation for use.
EBVIBONMENTAL PROTECTION AGEFCt
ii
-------
ABSTRACT
Flow bench tests of a model rotating belt-Couette flow oil recovery device were conducted
in a calm water environment primarily, although a few tests were conducted in the presence
of waves. These tests revealed clearly that the device is capable of harvesting oils over a broad
range of viscosities at the rates and purities specified by the EPA, if the inlet can be made to
"track" the water surface.
Analyses were conducted to design a catamaran vessel suitable for mounting the Oil Pickup
Unit (OPU) and also providing the requisite surface following performance. Vessel response
analyses showed that the required surface following behavior cannot be provided by the cat-
amaran itself, but can be achieved by floating the OPU and decoupling this assembly from the
vessel in heave and surge. A servo control for the foil device used at the OPU inlet will further
enhance the surface tracking behavior.
"This report was submitted in fulfillment of project 15080 FWO, Contract No. 14-12-903
under the sponsorship of the Federal Water Pollution Control Administration."
iii
-------
-------
TABLE OF CONTENTS
Section Page No.
I Conclusions 1
II Recommendations 3
in Introduction 5
IV OPU Model Tests 7
V OPU System Design 13
VI Hull Design Analysis and Layout 15
VII Vessel Response Characteristics ^7
VIII Acknowledgment ^g
IX Symbols 21
X Appendix A (Figures 1-42) 23
XI Appendix B (Dr. Breslin's Report) ^
-------
FIGURES
Page No.
1 OPU Test Model 23
2 OPU Test Model 24
3 OPU Test Model Belt 25
4 OPU Test Model With Boom _,
zo
5 OPU Test Channel
6 Test Channel Wave Paddle 00
20
7 OPU Test Model Carriage
8 OPU Test Model and Symbols
9 Oil Test Sample Box
10 OPU Test Model Carriage & Sample Box Frame
J*»
11 Oil Thickness Measurement
12 Test Data Form
34
13 Oil Test Samples
14 Oil Recovery Rate
' 36
15 Oil Recovery Rate
37
16 Oil Recovery Rate
*3O
17 Oil Recovery Rate
3 39
18 Oil Recovery Rate
40
19 Dimensionless Oil Recovery Rate Parameter
41
20 Dimensionless Oil Recovery Rate Parameter
3 42
21 Dimensionless Oil Recovery Rate Parameter
7 43
22 Dimensionless Oil Recovery Rate Parameter
44
23 Oil Recovery Efficiency
24 Oil Recovery Efficiency
46
vi
-------
FIGURES
Page No.
25 Oil Recovery Efficiency 47
26 Oil Recovery Efficiency , g
27 OPU Test Model (top view) 49
28 Oil Recovery Performance CQ
29 Oil Recovery Performance _.
30 Oil Recovery Performance _2
31 Oil Recovery Performance _.
32 Oil Recovery Performance for Various Test _.
Configurations and In Waves
33 Wave In Test Channel 55
34 OPU Prototype Configuration 56
35 Hull Lines Configuration A
36 Hull Body Plan - Configuration B 58
59
37 Horsepower Required Catamaran
38 Catamaran Oil Recovery Vessel 60
39 Catamaran Bridge and Hull Structure 61
40 Catamaran Bridge Structural Beam
41 Catamaran Heave & Pitch Amplitude Response "*
42 Catamaran Heave & Pitch Phase Response °^
43 Wave Lengths for Various Encounter Frequencies '*
at Selected Speeds
vii
-------
-------
SECTION I
CONCLUSIONS
The following conclusions are appropriate upon completion of Phase I of this program.,.-,
Model Tests
The OPU model tests have demonstrated that the proposed technique wiH achieve the re-
quired harvesting rates in calm water. It has further been demonstrated that the water ,-<: o
content in the harvested oil can be constrained within the specified limit of 10 percent. > .
The percentage of oil left on the water appears to be at or near the specified limit of 1 >,
percent, although uncertainties in the measurements preclude a clear conclusion. The per*
formance is largely insensitive to the broad range of viscosities of the oils employed in the
tests, except as noted in Test Results Summary on page 7. The test results obtained were!',
under conditions of full scale for the significant parameters involved, such as oil film thick-
ness, vessel speed, belt speed, and belt-plate gap. The only scaling was of the belt width,-
the roller diameter, and the distance travelled along the plate. The latter parameter is con-
ceded to have a small deteriorating effect in a full scale system, since the friction losses will
be greater.
It is quite evident that the model tests in waves produced inferior test results. This was
expected, however, since the model was constrained on the carriage so that if could not
follow the wave surface. In the PSL letter of 26 March 1970 containing final Proposal Rev,
visions, the following was stated: "It should be pointed out that the OPU test bench model
will not respond to wave action in the way that the catamaran-mounted unit would because
the model is restrained against all degrees of motion. This constitutes the major limitation
to rough-water testing with the flow bench, but an initial indication can be obtained as to
the prospects of good rough-water performance."
The testing with waves served to emphasize the importance of achieving excellent surface,
following performance with the OPU.
The testing with the boom was conducted primarily as an attempt to sweep the entire chan-
nel of oil, so that after a test run a sample of the swept water behind the model could be.
checked for oil content. This approach was unsuccessful because the particular bpom con-
figurations employed were not of proper design. Since PSL was directed to avoid any effort
in the area of boom design, it was deemed advisable to abandon this test technique in favor
of another method. The point here is that the unfavorable test results obtained with booms
should not be interpreted to mean the OPU is incompatible with booming techniques.
Although the construction features of the model prevented setting gaps larger than 0.87",
the data suggests that even greater recovery rates can be achieved with larger gaps, assuming
the oil film thickness at the entrance can be brought to about the same dimension. The data
further suggests that the peak oil recovery efficiencies will be reached at gaps greater than
0.87", except for kerosene.
Catamaran
Analyses were conducted to design a catamaran vessel suitable for mounting the Oil Pickup
Unit (OPU) and also providing the requisite surface following performance. Vessel response
analyses showed that the required surface following behavior cannot be provided by the
catamaran itself, but can be achieved by floating the OPU and decoupling this assembly from
the vessel in heave and surge. A servo control for the foil device used at the OPU inlet will
further enhance the surface-tracking behavior.
-------
-------
SECTION II
RECOMMENDATIONS
The following recommendations are offered for the consideration of the Water Quality
Office in regard to this program.
The program should be continued to accomplish the scale model testing of the vessel and
OPU as an assembly in a scaled rough-water environment, in a manner which will create no
unrealistic motion constraints as was the case with flow bench testing. Two options have
been considered as to the means of accomplishing these tests.
Utilize a private or government-owned model basin facility, employing either a 1/8 or 1/4
scale model of the vessel and OPU. Conduct tests in the presence of regular and irregular
waves, the latter being representative of the spectrum encountered on the open sea. Con-
duct tests in two series, the first with water only and the OPU belt not operating, for ad-
justments and verification of required surface following characteristics. The second series
would involve operations with an oil film on the water, the OPU operating, and some type
of simple boom arrangement. This approach offers the advantage of precise control of
vessel speed arid wave enrironment plus the availability of force measurements for more
accurate characterization of the vessel response than was possible during the analyses re-
ported herein. The disadvantages are high cost and the inability to simulate quartering
waves to assess roll response.
Conduct 1/4 scale model tests of the catamaran and OPU in a trench tank as originally pro-
posed by PSL, with and without oil as described in Option 1, and with regular and irregular
waves. Follow these tests with open-water trials (no oil) on Lake Caballo, approximately
75 miles north of the University campus. The advantage of this approach is lower cost and
the possibility of a more realistic wave environment during the lake tests, especially quarter-
ing waves. The disadvantages are less precision in the control of test parameters such as
vessel speed and wave amplitude and frequency, and no force measurement capability.
The Physical Science Laboratory recommends that Option 1 be followed if government-
owned model basin test time can be secured at little or no cost to the EPA. Otherwise PSL
recommends adoption of Option 2.
Complete the detail design of the OPU with particular attention to the decoupling linkages
and the foilssecvo control. This should be accomplished first so these features can be incor-
porated into the scale model.
In addition to the decoupling linkage and the foil servo control, incorporate instrumentation
into the model which will permit assessment of the surface following characteristics, such as
a resistance probe which senses the position of the oil-water interface with respect to the
upper surface of the foil!
Provide a scaled working recovery belt and oil removal provision, plus the necessary gear for
harvested oil sample collection aboard the model. This is in accordance with PSL's original
proposal.
-------
-------
SECTION III
INTRODUCTION
It is the intent of the EPA (Environmental Protection Agency) -WQO (Water Quality Office)
to develop a floating oil recovery system with performance superior to existing devices and
techniques for removing spilled oils from both protected and unprotected waters. Some
major requirements of the system, as outlined by the EPA are as follows.
Harvest capacities for light to heavy oils of at least 3000 gal./hr of oil with 10% or less water
content while operating in protected waters with up to 2 foot waves in combination with 20
mph winds and 6 knot currents.
Harvest capacities for light to heavy oils of 50,000 gal./hr of oil with 10% or less water con-
tent while operating in unprotected waters with up to 5 foot seas in combination with 20
mph winds and 2 knot currents.
Vessel with oil harvesting equipment must be capable (while not recovering oil) of speeds of
at least 12 knots under the sea conditions listed above.
System must be reliable, economical to operate and maintain, and readily transportable to
the affected area and quickly put into operation.
An oil recovery system which will accomplish these objectives has been proposed to the EPA
by the Physical Science Laboratory of New Mexico State University. The basic part of the
proposed system utilizes a rotating drumbelt device operating on Couette flow theory in com-
bination with a catamaran vessel. Additional components required in the open sea are two
(2) ocean going tug boats and flexible floating booms, between the tugs and the catamaran,
for thickening the oil.
Several tasks related to the proposed system were assigned to PSL under contract with the
EPA. They include conducting a performance analysis on the OPU, designing, building, and
testing a working model of the OPU and performing hull design analysis and layout work.
This document describes the work accomplished under this contract.
-------
-------
SECTION IV
OPU MODEL TESTS
Description of Test Components and Procedure
Model
The primary parts of the model are the belt, drive and idler rollers, belt tension adjustment
roller, lower plate, upper plate, hydrofoil, wiper blade, drive motor, drive belt, pulleys, and
plexiglas sides, see figures 1 and 2 (drive components not shown); The rollers, hydrofoil,
and upper and lower plates are all made from Ponderosa pine and coated with white epoxy
finish. The belt, see figure 3, a product of Arthur S. Brown Manufacturing Co. of Tilton,
New Hampshire, is a 4 ply 5/64 in. thick endless woven belt treated topside with 5-56B
teflon white and treated pulley side with HT-50 black. The width of the belt is 4 in. and
the circumference is 12-25/32 in. When the belts were received from the Brown Co. they
appeared to be unsatisfactory because the outer surface was both water and oil permeable.
This condition was corrected by turning the belt inside out and applying five (5) coats of
teflon spray. The inside was already impermeable to both oil and water due to the HT-50
black treatment. After spraying with teflon it also became both hydrophobic and oleophilic,
the desired characteristics. The wiper blade for removing oil from the belt surface is a
strip of neoprene mounted in an aluminum block. The belt-plate gap is varied by loosening
the wing nuts and moving the plate up or down. The maximum gap obtainable is 0.87 in.
The plate mounting holes in the plexiglas are oversize to allow for this adjustment. The
upper plate and hydrofoil can also be moved up or down (or fore or aft) accommodated by
oversize mounting holes.
The belt drive motor is a 3/8 in. drill motor mounted on a hinge on the forward slope of the
plexiglas sides. The hinge provides a means for adjusting the drive belt tension. The drive
motor speed is varied by utilizing an adjustable autotransformer mounted on the carriage
frame.
On several test runs a boom was attached to the model for thickening the oil ahead of the in-
let, see figure 4. In checking out the operation of the model, prior to the recorded test series,
a simple boom model with a throat section 6 in. long and a straight sided vee section 17 in.
long was tried. It was unsatisfactory due to severe turbulence in the throat area which caused
a drastic reduction in oil recovery rate. The present boom with its long gently curved sides
is a considerable improvement over the earlier one although still not entirely satisfactory as
explained on page 6, Other Configurations and Wave Tests.
Test Channel
The test channel is 96 ft long having inside dimensions of 10 x 22-l/4in. See figure 5.
Plexiglas panels between the supports allow viewing of the water and oil surfaces. A plywood
panel with a crank was installed near one end for making waves. See figure 6. A motor
driven continuous cable moves the carriage with the OPU model on steel angle tracks the full
length of the channel. The cable drive motor is a reversible gear head type rated 12 to 24
volts dc, torque rated 75 ft-lbs @ 24 volts dc. The power supply for the drive motor has a
variable dc voltage output and is rated at 1000 amps.
-------
Test Fluids
The fluids used in the tests are shown in the following table:
NAME NO. VISCOSITY @ 60° F SPECIFIC GRAVITY
lb-sec/ft2
Enco Gear Oil GX90 1.94 x 10'2 0.8607
Enco Lube Motor Oil SAE30 4.81 x 10'3 0.8877
Enco Lube Motor Oil SAE10W 2.36 x 10'3 0.8708
Kerosene 4.50 x 10'5 0.8184
All products were purchased from the Humble Oil and Refining Co. The viscosities and spe-
cific gravities were converted from SUS and API units supplied by the oil company for tem-
peratures of 100° and 210° Fahrenheit.
Instrumentation
The primary instrumentation consisted of cameras, manometers, a tachometer for measuring
belt speeds, a timer for use in computing model speeds, and oil sample box and timer cir-
cuitry, see figure 7. A 16 mm movie camera was used to record flow characteristics at the
belt inlet and gap area. (In water only). A 35 mm still camera was used to record manom-
eter and tachometer readings. Four (4) pressure orifices were located in the plate as shown
in figure 8. The forward orifices were directly under the axis of the forward roller and the
rear orifices were under the axis of the aft roller. The differential pressure across the side
orifices is sensed by the forward mounted "U" tube and the differential pressure across the
center orifices is sensed by the aft mounted "U" tube. The tachometer cable is connected
to the idler roller and the instrument dial indicates linear belt speeds in feet/second.
The oil sample box, see figure 9, is towed behind the model in a low slung frame with wheels
which roll on the steel angle tracks. See figure 10. It is made of plexiglas and has a spring
hinged door in front for admitting oil from the model during the test run. The sample box
and timer circuitry includes the following items: solenoid, two (2) single pole double throw
switches, and two (2) switch trippers. The solenoid is a pull type with 1 inch stroke and
7-Vz Ibs pull and is activated by 110 ac voltage to open the sample box door at the proper
time. The two switches are mounted side by side on the carriage directly above the channel
edge with their actuating arms down for contact with the switch trippers. The switch
trippers are thin strips of spring steel mounted vertically eight (8) feet apart on top of the
channel wall. The following describes the operation of the sample box and timer circuitry:
With the carriage at rest several feet from the 8-foot sampling section the power is applied
to the belt drive motor first and then to the carriage drive motor. The carriage is accelerated
to a constant speed prior to reaching the first switch tripper. When one of the two switch
arms contacts the first tripper, power is applied to the timer and solenoid starting the timer
and opening the sample box door to admit the oil sample. At the completion of the 8-foot
run the other switch arm contacts the second tripper and the circuit is again opened stop-
ping the timer and deenergizing the solenoid, allowing the sample box door to be closed by
its spring type hinge. Before and after the 8-foot travel period oil from the model is ejected
onto the top of the sample box and back into the test channel. After the test run the car-
riage motor is reversed and as the carriage passes back over the switch trippers the switches
are reset in preparation for the next run.
-------
The oil thickness in the sampling section was measured with a scale scribed in l/100ths of an
inch. The scale was held vertically against one of the plexiglas side panels adjacent to the oil
layer and the reading taken with the aid of a magnifying glass, see figure 11. Measurements
were made at three (3) locations along the test section prior to each run and the average re-
corded. Because of meniscus effects the error in the readings is estimated to be as much as
±2%.
Test Procedure
Testing began with several runs in water alone to check out the test bench and model opera-
tion. A 16 mm movie camera was used on these runs to record flow characteristics. A
total of 241 test runs with oil on the water surface were made varying the primary param-
eters of fluid type, belt and model speeds, and gap dimension. Also several runs were made
with each of the following changes: with boom, without hydrofoil, hydrofoil chord plane
parallel to oil-water interface plane except submerged 1/8" in water, tilt angle 65°, and
with waves. The majority of the runs were made in calm water, without the boom, with
the hydrofoil chord plane in the oil-water interface, and with a tilt angle of 74.2°. All data
were recorded on forms similar to the one shown in figure 12, and later transferred to the
form shown. Symbol definitions appear on page 14.
At the conclusion of each run the fluid in the sample box was poured into a graduated
cylinder, see figure 13. The fluid remained in the cylinder for l-Vz to 2-Mj hours before water
content was measured. It was found that this time period was sufficient for virtually all
water to separate from the oil. For kerosene, however, the settling period required was much
less. In order to conserve the volume of oil required for testing, a 50 foot section of the chan-
nel was blocked off from the channel ends by means of wood gates. The gates effectively
contained the oil, but not water. When adding oil to this section the weight of the oil would
force water through the gates into the ends of the channel, thus lowering slightly the water
level in the test section. When removing oil from this section the converse was true. As a
result of the small variation in water level occasional adjustments in model height were nec-
essary. Incidently, when changing oils the OPU was used most effectively in removing the
oil for which the tests had been completed.
Discussion of Test Results
Oil Recovery Rate
The oil recovery rates are represented in figures 14 through 17 as a function of belt-speed to
model-speed ratio and belt-plate gap. The oil recovery rate value of 0.87 gal./sec indicated
by a dashed line in these figures is equivalent to a full scale recovery rate of 50,000 gal./hr
(5-Vz ft wide belt) neglecting Froude number scaling effects. While the data shows consid-
erable scatter it is readily apparent for all of the oils tested that the wider the gap the
greater the oil flow rate for the range of gaps considered. The oil recovery rate for the
widest gap (0.87") is shown in figure 18 for all of the oils. These data show quite clearly
that the flow rates are inversely proportional to the belt-speed to model speed ratios. It
would appear that the more closely the belt speed is matched to the model speed the more
effective the recovery of oil, at least as long as the oil layer thickness ahead of the OPU
inlet is not greater than the belt-plate gap.
-------
A dimensionless oil recovery rate parameter was computed and plotted as a function of
belt-speed to model-speed ratio in figures 19 through 22. These plots show that the oil
recovery rate is essentially independent of the oil type for those oils tested.
Oil Recovery Efficiency
Oil recovery efficiency (the percent oil removed) is determined by comparing the amount
of oil removed from the water surface with the amount of oil available for removal. The
volume available is computed by knowing the model inlet width (4-V& inches), the oil
thickness, and the distance traveled during sampling (8 feet).
The percent of oil removed from the water surface is shown in figures 23 through 26.
From these figures it would appear that belt-plate gap has little if any effect on the per-
cent of oil recovered for gear oil GX 90 and motor oil SAE 30, but not so for motor oil
SAE 10 and kerosene. A gap of 0.87 inches produces the highest efficiency for SAE 10
and a gap of 0.75 inches results in the highest efficiency for kerosene. Also indicated in
the plots for the higher viscosity oils is a reduction in efficiency at the lower belt-speed to
model-speed ratios. This is the opposite effect to that indicated for oil recovery rate where
the flow increases with decreasing speed ratios. It is noted that several data points indicate
efficiencies greater than 100 percent. It is believed that there are two sources for these
apparent discrepancies. One, the estimated ± 2% error in oil thickness measurements, and
two, additional oil drawn into the model from the sides of the inlet due to sink action as
depicted in figure 27.
It was observed in several test runs that oil piled up at the belt inlet indicating that the belt
speed was too low for that particular model speed, gap, and oil type. In these cases recov-
ery efficiencies were generally low because the model was not able to remove all of the oil
available for recovery, consequently, the excess oil flowed out and around the leading edges
of the model sides (the opposite effect to the sink action). When, of course, the speeds and
other variables were correct for removing all of the oil available there was usually room for
a little more to enter the model due to the fact that the oil thickness was always several
hundreths of an inch less than the gap dimension, thus resulting in efficiency values exceed-
ing 100 percent.
Oil Recovery Performance
A summary of the results of the oil recovery rate, the percent oil recovered, and in addition,
the percent water in the recovered fluid appears in figures 28 through 31 plotted as a func-
tion of belt-plate gap. These curves were constructed by using the computed averages for
all data points for each gap dimension. These data show the widest belt-plate gaps of 0.75
and 0.87 inches to be most favorable to all three qualities of performance for all oils tested.
For SAE 30 and GX 90 oils the value of the percent water in the oil peaks at a gap setting
of 0.62 inches. The reason for this was that the model was set too low (hydrofoil chord
plane was below the oil-water interface) for the nine (9) runs on SAE 30 and the following
three (3) runs on GX 90. How much too low is unknown, however, for subsequent tests
the model was raised so that the hydrofoil chord plane was at the oil-water interface re-
sulting in a significant decrease in water content. The very low water content for SAE 30
at a 0.75 inch gap resulted from a small adjustment required in the model height. Due to
the small variation in water level mentioned on page 4, Test Procedure, the model height
had to be adjusted occasionally. Because the model height was not adjusted after each run
10
-------
or even as often as every 4 or 5 runs, the hydrofoil chord plane was not always exactly at
the oil-water interface plane. This was reflected in small changes in both the percent water
content in the oil and the percent of oil removed.
The rise in water content for SAE 30 between gaps of 0.75 inches and 0.87 inches is due to
slight oil pile-up at the belt inlet on several runs.
Other Configurations and Wave Tests
The three (3) primary quantities; oil recovery rate, percent of oil removed, and the percent
of water in the oil are compared in the form of a bar chart, figure 32, when changes in the
model configuration were made and waves induced. Again, the values are averages of several
test runs. The standard configuration, also included on the chart, is that for which the test
results have just been discussed. Test runs were made only with SAE 30 and kerosene. The
chart shows that adding the boom to the model, decreasing the tilt angle to 65°, or inducing
waves, significantly reduces the oil recovery rates. With the hydrofoil off of the model oil
recovery rates are somewhat reduced. During the tests with the boom on, a mound of oil
was observed in the throat region just ahead of the belt inlet indicating turbulence which
likely forced oil underneath the boom. This mound of oil was also noticed to occur with the
earlier boom though larger in size. Decreasing the tilt angle, i.e., increasing the angle between
the plate and the horizontal, increased the gravity effects which reduced recovery rate. Also,
it is assumed that by decreasing the angle between the hydrofoil chord plane and the plate,
oil would have a greater tendency to flow down between the hydrofoil and the plate, reducing
the recovery rate. The adverse effect of waves on the oil recovery rate is obvious when con-
sidering that the OPU model is fixed vertically relative to the undisturbed water surface. The
waves generally had a height of about 2 inches, a speed of 4 ft/sec, and a length of between
42 and 48 inches.
The oil recovery efficiency (not measured with boom on) was quite high, 95% or greater for
all tests except for those where the model tilt angle was 65° and in waves. In waves the re-
covery efficiency reduction was much greater for kerosene than for motor oil SAE 30, a
result of the lower wave dampening effect of kerosene. Otherwise the explanations per-
taining to recovery rates apply.
The percent of water in the recovered oil was increased significantly by removing the hydro-
foil, lowering the model so that the hydrofoil chord plane was 1/8 in. below the oil-water
interface, and inducing waves. With the hydrofoil on the model, some water passes down
through the gap between the hydrofoil trailing edge and the plate leading edge. With the
hydrofoil removed this gap no longer exists and the water which otherwise would pass down
and under the model is picked up by the belt, thus increasing the water content in the oil.
It was noted throughout rough water testing that motor oil SAE 30 had a significant effect
in dampening the waves. The dampening action of kerosene was very low.
Note: Cursory examination of the test data and attempts to correlate flow rate measure-
ments with analytical computations had indicated a need for modification of the analytical
equations, but further effort will be required which was not completed in time to include
in this Report.
11
-------
Test Results Summary
The following statements apply only to the ranges of variables considered in the tests.
Oil recovery rate for all oils increases with gap dimension.
The recovery rates are inversely proportional to belt speed to model speed ratios.
The recovery rates are essentially independent of oil type.
The oil recovery efficiency is affected little if any by the belt-plate gap dimension for gear
oil GX 90 and motor oil SAE 30 (high viscosity).
The oil recovery efficiency for motor oil SAE 10 and kerosene (low viscosity) increases
with the belt-plate gap dimension, the former rising to a maximum at 0.87 in. gap and the
latter peaking at 0.75 in. gap.
The oil recovery efficiency for gear oil GX 90 and motor oil SAE 30 falls off at the lower
belt speed to model speed ratios.
Belt speed, model speed, and gap dimension must be of appropriate magnitudes for the type
oil to be recovered if pile-up of oil at the belt inlet is to be eliminated and recovery efficien-
cies are to remain high.
Adding the boom to the model, decreasing the tilt angle to 65°, or inducing waves, signifi-
cantly reduces the oil recovery rates.
Removing the hydrofoil from the model somewhat reduces the oil recovery rate.
The water content in the recovered oil was considerably increased by removing the hydro-
foil, lowering the model so that the hydrofoil chord plane was 1/8 in. below the oil-water
interface, and inducing waves.
12
-------
SECTION V
OPU SYSTEM DESIGN
The Oil Pick-Up Unit (OPU) has not been subjected to detail design in view of the
dependence on the flow bench test results.
Several definitive statements can be made concerning general design features. The results
of the hull response analysis described in detail in Vessel Response Characteristics, page 11,
definitely indicate that it will be essential that the OPU be decoupled from the catamaran
hull in heave and surge, in order to provide the required capability to "track" the water
surface. The Appendix provides an analysis of the response characteristics of the OPU
when decoupled from the catamaran. Although hampered by a lack of knowledge of the
applicable wave exciting force coefficients which are required for detailed assessment of
the response over the frequency range of interest, the analysis of natural frequencies
points out the importance of minimizing OPU weight. The analysis also suggests the sizing
and proportions of the OPU flotation "pontoons". From figure 34, the overall shape of
the OPU can be observed to consist of the two flotation "pontoons" spaced at the full
width permissible (66") between the catamaran hulls, with the oil-plate supported by the
pontoons, at an inclination angle of 15 degrees to the calm water surface. Note that the
OPU itself does not have an integral oil receiving tank as originally proposed, in order to
reduce weight. The two end rollers for the belt are planned to be 24 in. dia. max. fabri-
cated of thin-wall fiberglass tubing with aluminum bulkheads at each end and a stiffener
ring in the middle. The aft, driven roller will incorporate a hydraulic drive motor mounted
inside. A woven cotton belt treated with teflon, similar to that used in the flow bench
tests, will be utilized. The intermediate belt roller used on the flow bench model proved to
be unnecessary, and is not included in the prototype design. The oil plate will incorporate
integral side plates to contain the oil flow, and also will constitute the bearing supports for
the rollers and a gap adjustment mechanism. The side plates will also provide the structural
tie-in points for the OPU suspension linkage. An oil collection hopper will be mounted
rigidly to the oil plate surface and side plates at the aft end of the OPU. A spring-loaded
belt wiper will be mounted to the upper edge of the hopper, with the springs permitting
sufficient wiper pressure, plus displacement required for gap adjustment. Two flexible
hoses will serve to transfer the oil from the hopper to the hull tanks.
The total OPU suspended weight is targeted at 300 Ib max., and this must be achieved by the
use of lightweight fiberglass and aluminum materials and possibly composites, for example
the OPU plate will be fabricated of a foam-filled aluminum honeycomb core with a fiber-
glass skin.
The OPU unitized structure, attached to the catamaran at the decoupling linkage, is quite
compatible with the concept of breakdown for air transportation. The major elements of
the decoupling linkage, i.e. the surge guide rails and constant-tension surge cables, plus the
heave guides and heave shock absorbers, will be attached to the catamaran hulls. The OPU
incorporates the heave slide and shock absorber end attachment provisions. The heave
motion guide rails will incorporate provisions for raising and locking the OPU in an elevated,
stowed position during high-speed operation in traveling to and from the spill area.
13
-------
The model employed in the flow bench tests utilized a foil just ahead of the plate en-
trance as a flow splitter. This foil was effective in separating the flow at the oil-water inter-
face, causing the water flow to deflect down and the oil to deflect upward onto the plate.
The efficacy of this device was indicated by the lower water content in the harvested oil
when the foil was employed. The foil does not significantly affect total harvesting rates,
nor the percentage of oil removed from the water. The employment of the foil in the full-
scale prototype is desirable in the interest of overall harvest efficiency. Referring again to
the Appendix, the prognosis that the OPU can be made to follow the water surface to within
12% of the wave amplitude, or within approximately ± 3.5 in. in 5 ft waves, means that to
assure that oil does not flow under the OPU it would be necessary to set the ramp inlet at
a depth which would assure harvesting a substantial percentage of water. This can be
avoided by using the foil with a servo control to further compensate for the residual heave
motion of the OPU. As shown in the inset of figure 34, this can be accomplished by a
straight forward linear actuator servo which extends or retracts the foil relative to the plate
surface. The sensing of the proper foil depth can be accomplished by several means, of
which a reflected light measurement is one. Here the significant differences in optical
transmissibility and reflectance properties between oil and water can serve to sense the
location of the water interface in the heave direction.
It should be noted that the Appendix recommendations (b) and (c) refer to oil recovery
techniques which are fundamentally different from the recovery belt-Couette flow system
tested on the flow bench. Both represent independent ideas of Dr. Breslin, the author of
the Appendix and the program marine engineering consultant. Recommendation (b) in-
volves a scheme whereby a planing plate is installed between the catamaran hulls near the
bow, inclined leading edge-up with the vessel operated at high speeds, 10 knots or more.
This approach relies on the proper plate trim angle setting which will produce a flow stag-
nation stream line coincident with the water-oil interface. The oil would be turned forward
and up into a vacuum nozzle which would draw the oil flow into hull tanks. The water flow
would be deflected down and aft past the plate trailing edge.
In the judgement of PSL this approach suffers from several liabilities, one of which is the
loss of the assistance from booms to thicken the oil, since booming at 10 knots or more is
a doubtful proposition. Thus the system would be required to operate on extremely thin
oil films which would preclude achieving the specified recovery rates. Maintaining the
proper plate trim angle in rough water is viewed as another serious problem.
Recommendation (c) suggests a technique similar to the PSL approach except for elimi-
nation of the belt system. Here the dynamic head produced by the vessel motion would
be relied upon to produce oil flow up the plate, where the flow could be augmented by
a vacuum system. This does not appear feasible since early test runs with the PSL system
made with the belt not operating clearly showed the head to be insufficient to produce
flow up the plate to the output end. A gross calculation shows that the dynamic head
developed at a vessel speed of 3 knots is approximately 25 Ib/ft . A speed of at least 10
knots would be required to make this approach practical, and here again the inability to
use booms at this speed mitigates against such an approach.
14
-------
SECTION VI
HULL DESIGN ANALYSIS AND LAYOUT
This phase of the program has been accomplished largely by Dr. Breslin, except for prelim-
inary vessel equipment arrangement and weight estimates for these items.
The first step in this effort was the selection of the hull configuration. Two sets of hull
lines were developed and submitted. Configuration A, shown in figure 35, and Configura-
tion B, shown in figure 36. Both designs are similar, with the same inboard profile, the
same length (40 ft), draft (2.5 ft), beam (5 ft per hull), and keel-to-deck height (6 ft). Both
utilize parallel, flat inner sides, except that Configuration A does employ shaping of the
inner walls at the bow, stern and bottom areas. The pure flat side of Configuration B sug-
gests that it will be more economical to build. The use of "wall sides" in each configuration
was dictated by the early expectation that decoupling of the OPU would be necessary, the
"wall" sides being necessary to accommodate the relative motions between the OPU and
the vessel. Figure 36 shows an early concept for the OPU decoupling guide rails.
The sizing of the hulls was determined by early gross estimates of the "all-up" vessel weight.
The weight estimates included allowances for short-term oil storage within the hulls. The
vessel displacement at 2.5 ft draft is 28,000 Ib, while the latest estimates of "all-up" vessel
weight total approximately 26,000 Ib. On this basis, for protected waters operations such
as rivers and harbors where the 3 ft depth limit is applicable, approximately 2,000 gallons
of oil can be accommodated in the hulls for short-term storage. On the open seas where
greater draft can be permitted, more oil can be stored, approximately 5,000 gallons per addi-
tional one foot of draft.
After establishing the hull lines, propulsion power requirements were computed as a function
of vessel speed. These are shown in figure 37, and it can be seen that the effective horse-
power required at 12 knots (the required non-harvesting speed capability) is 170 hp. This
led to the selection of two 115 hp outboard engines to provide the required power.
After selection of the engines, refined estimates of other equipment weights and their loca-
tions aboard the vessel were determined by preparation of the general arrangement drawing
shown in figure 38. It was deemed necessary to conduct some preliminary structural design
and analysis of the hull and bridge structure in order to verify the weight estimates for these
major items. The results of these structural-design steps are shown in figures 39 and 40.
Two points should be noted here - the bridge beams were designed on the basis of handling
loads incurred while lifting the assembled vessel during launch or recovery. It was assumed
that the "worst case" structurally would be inadvertent lifting from two points, at the bow
end of one hull and the aft end of the other. It was deemed that this mode would be far
more severe than any waterborne loadings, since even in rough waters, some distribution of
loading would occur. The other point to note is that by integrally molding aluminum angle
longitudinal stringers into the inside surface of the fiberglas hull skin, the hull is sufficiently
strengthened to act as an oil storage tank itself. The bridge beams as shown are only repre-
sentative of the.overall weight and stiffness required. The final design will utilize a different
arrangement to also provide support for the deck panels.
15
-------
-------
SECTION VII
VESSEL RESPONSE CHARACTERISTICS i ^'
With the catamaran size, configuration, weight, and weight distribution established it was
possible to proceed with essential preliminary analysis of the vessel response to wav^e action.
Figures 40 and 41 show the heave and pitch amplitude and phase response as a function of
water wave length at a vessel speed of 3 knots. These data were computed using a digital
computer program available at the Davidson Laboratory of Stevens Institute. The'program
is one normally used for mono-hull analysis, and its accuracy has been rigorously demon-
strated for this type of hull. The program's accuracy when applied to catamarans is -kiss
certain, because of possible interference effects due to the proximity of the two hulls. Un-
fortunately, empirical data is not available to check the results of these computed responses.
It is unlikely that the data are sufficiently in error to change the main conclusion tofce
drawn, however. Since normalized values of heave and pitch amplitude are plotted,'the
ideal situation for the oil recovery catamaran is to achieve values of 1.0, indicating that the
vessel follows the water surface precisely. The data show that this situation is not ap-
proached in pitch or heave except for wave lengths of 60 ft or greater. These long wave
lengths can be expected in unprotected waters in the open ocean, but not in protected
waters. Even for the long wave lengths the amplitude ratios are not sufficiently close to
unity to state that the vessel will follow the water within the few inches required.
This led to the conclusion that the OPU must be decoupled from the vessel in heave and
surge. Decoupling in pitch is not considered necessary at this time sincerthe OPU.entriaiice
will be located at the same longitudinal station as the vessel center of gravity.
One undesirable characteristic which is a by-product of a vessel design which has good sur-
face tracking characteristics is high accelerations. These have been computed to fall in the
range of 1.5 g upward and 0.6 g downward in heave for sea states of four to five at a vessel
speed of 3.4 knots. In a sea state three situation, closer to the specified r6ugh sea environ-
ment, the accelerations are 1.12 g up and 0.7 g down. This certainly implies considerable
personnel discomfort at times, and the decoupling of the OPU also serves to apply remedies
for this problem. By storing more oil to appropriately increase the vessel draft, these accel-
erations can be reduced. Although this deteriorates water surface following properties, the
decoupling of the OPU makes this less important.
Due to limitations in time and budget, no analysis was conducted to assess roll and yaw
response. The catamaran configuration possesses excellent inherent response characteristics
for these motions, and these were deemed to be of lesser priority fdr' dynamic analysis at
this stage. The same can be said of coupled vessel motions although these must be given
proper attention in the following phases of the program.
Catamaran Vessel Design
The catamaran configuration and sizing have been reasonably well defined, along with the
most important response characteristics, heave and pitch. The coilcept of decoupling the
OPU in heave and surge has served to relieve somewhat the stringent catamaran hull response
requirements, although roll, yaw and coupled responses need further examination.
17
-------
OPU Design
Sufficient data has been obtained to allow more detailed full-scale design of the oil
recovery, flotation, and motion decoupling elements of the OPU. The response analysis
of the decoupled OPU as presented in the Appendix has shown a favorable water surface
following characteristic for water wave lengths of 40 ft or greater. For shorter wave
lengths it will be necessary to rely on the oil film to provide damping of the wave motions
ahead of the OPU. The rough water experiments with the model have certainly served to
point out the powerful damping of the oil film, and Mollo-Christensen of M.I.T. has re-
ported similar behavior in that he shows significant reductions in the power density spectra
produced by an oleyl alcohol film on water for wave lengths shorter than-35:ft((*). The
debris screens to be installed between the catamaran hulls near the bow can also contribute
significantly to high-frequency wave damping by judicious design.
The use of a servo control to maintain the foil in position ahead of the OPU entrance will
assure achievement of the "fine-grained" control required.
* "Physics of Turbulent Flow", by Dr. Erik Mollo-Christensen, Massachusetts Institute of Technology.
Presented at the American Institute of Aeronautics and Astronautics 7th annual meeting, Houston, Texas,
October 1970.
18
-------
SECTION VIII
ACKNOWLEDGMENT
The Physical Science Laboratory wishes to acknowledge the contributions of
Dr. John P. Breslin, Director, Davidson Laboratory, Stevens Institute of Technology,
especially his participation in the catamaran preliminary design and dynamic response
analysis.
19
-------
-------
SECTION IX
SYMBOLS
Vb Linear belt speed *v ft/sec
Vm Model speed ^ ft/sec
|3 Angle between model plate wetted surface and vertical plane *\/ degrees
a Angle between hydrofoil chord plane and model plate wetted surface -
positive when leading edge below wetted surface plane *\/ degrees
z Oil thickness ahead of model ^ inches
h Belt-plate gap ^ inches
t Duration of test run 'v seconds
AP Differential pressure-side or center orifices *v m m H2O
T Oil temperature ~ degrees centigrade
Vfl Volume of oil available for recovery during test run 'V in.3
Vr Volume of oil recovered during test run "* in.3
E Percent of oil removed = Vr/Vfl x 100
H Wave height "* inches
L Wave length ^ inches
C Wave celerity or propagations! speed ^ ft/sec
Of Quantity of fluid recovered during test run ^ gallons
q^ Quantity of water in recovered fluid during test run 'v gallons
e Percent water in recovered fluid = qvv/Pf x 100
Q Oil recovery rate, gal./sec
Q' Oil recovery rate, ft3/sec
W Belt width, ft
21
-------
-------
Q
O
H
P
a.
O
I
O
II
En
23
-------
Q
O
O
I
(N
55
I
24
-------
CO
Q
O
s
c/i
Ed
o
I
ro
O
25
-------
; }
FIGURE 4 - OPU TEST MODEL WITH BOOM
26
-------
I-J
w
iz;
CO
IS
I
m
O
E
27
-------
t-J
Q
Q
W
H
C/2
28
-------
I
o
<
&
Pi
ttl
Q
O
C/3
o
I
o
29
-------
OPU TEST MODEL PRESSURE
ORIFICES AND SYMBOLS
Plate
Plate
FIGURE 8 - OPU TEST MODEL AND SYMBOLS
30
-------
X
§
c/)
EH
hj
tI
o
I
ON
O
31
-------
FIGURE 10 - OPU TEST MODEL CARRIAGE & SAMPLE BOX FRAME
32
-------
I
cd
P
C/3
C/3
C/3
O
H
i-J
o
I
o
E
33
-------
cc
o
o
Q
Z
I
I
s
IE
Q
i
li
E*
O)
W
H
I
s
tf
p
34
-------
FIGURE 13 - OIL TEST SAMPLES
35
-------
33S/"IVO -v (0) 3XVH AH3AOD3H1IO
-------
~-t
O O
o o
VO
II
eo
"4-
O
eo
»
O
eo
o N in t--
B X
-s
1
5
oo
VERY RATE
L R
.£
T3
s
«
a
8
VO
CT5
H
-O
O
4-rf
O
§
w
ca
CQ
o
in
o
(O)
AH3AOD3H 110
37
-------
v* ve ^ '*
gn\ gfc CO F1*"
^5 C> CO \O
II II II II
O\ O\ 9\ O\
"S "S -g -S
O O CO O
O
in o t^ cq
o o o o
IO t-
t
i
"r
i
:::;:::;:::::::::::!::;::::;:!:!;:!:!::=
8
2
§
O
U
w
co y
I '
o ~
t^ tt]
a 03
W LJ
CO
5
a
O
E
i::::::::::::::::::::::::::::::::::::::::::::::
Das/'ivo ~ (6) aiv«
no
38
-------
il^H^K
x CO
O O O O
111
I
>H
o
.s
f 3
CO
d
0.3
O EzJ
P >
^ S
^ o
3 I
i s
Is
w ^^
s ^
fc E
S
BQ
oasnvo (6) aivH
no
39
-------
3 -H -°
3
S
Q
i
8
Q
I §
CO
(0) aiv«
no
-------
a*«*!
&»!
B PS
Ed
<
OS
OS
u
3
o
%
Ed
S 1
c«
I
-t-r- >~l
5 Q
I
£
u v-'
« sa
i
0> £
T3 O
S >
>
O
co
Q
Ed
CO
Ed
Q
i
5
Ed
n
CO
w
S
H I
Q
I
1
1C
o
CO
d
O
.>
>°
41
-------
CO
CO
o
(N
Ed
05
P
42
-------
-------
cd
w
i
*»* 11 r.«
*»** **<» I I <
|
.s
11
S fe
^
O
ffi
H
o otf
oo
i o
O 03
H W
W 2
IM
P
O
in
o
-------
^5 C1! LO Is*
dodo
oo
a::::::::::::::::
O
-E «
> HH
^- O
Q
O
s
Q
W
I
ft
w
>
o
O
I
CO
O
»««*»»
§!)!**»**»BIBB«
!«*»«««!
!!>*»*
(a) aaAOwan no
45
-------
2;
H
o
o
o
fa1
p
g
(a) aaAowan no
46
-------
: ^ ::: : ::::: ::: --] '-] -'
-: ta 3 W - :: - ::::: :::| ::::::::::
g § ^ '° 1 I |||l|lll|||||| 1 Ililffllj || | 1
:: 0 « "g : ::: ::::::::: :::::::::::: ::!
:: U -3 g " :::::::::::::::::::::: ji::: ::i ::::
= g § " :: :::= =" :=:::::-: " = : :
;: ri s ;;;:;;!::;i;;!ii;;i ;;!ii;;; jiii:;:;
m o ^5 1 1 mm
:;;; ;±:; ±:: :; ± ;::: :;:: c;::; :±; :::;;::; w
4- - - - ^H
|;;:;::;i;;;i ;=:;:;=;; ;;;;;;ii;;ii;;:;; J g
:::: 1:1 ::: : :::: :: :::: :::: OS ^
:::;;:::;!:;;:: i::;;;;;;:;::;::;;;:;;:; _, Q 0(5
iiijiiiijij:;;;! ;!;!;;;;;;!!:!;;::;;;;; g S
... I ..! ,1 . . E ± PH ?*
!! l|iii!|: ; iiiii;;; iiii iiiiiiiiiiiii; S 8
;li;;:;i iiiijbii:; ;;; 1; ii;;;;;;; § §
I II |^ s §
::: ::;ji!::: :: j :: " ::= :":::::: ^ ,
:::: :;l :::: :: | ::::::::: :::: ::: ::::::::: p 1
II; !^ i I ll ii i'l i!' ^1 !^l S p
|;;;;;li;; i; ; ;;;;;;;; i;:;: ! ;;!;;;;;; " « £
W9^^^^^
(a) aaAowan no AO
47
-------
i
en
nJ
W
Q
i
Q
W
g
P-i
CO
H
o
I
-------
Q
O
I
>
O-
O
O
OS
Q
OH
Q
O
H
OH
O
I
i>
-------
12
10
-H £«
o
Jt
X
I
O
O
Pn
O
g
w
td
OH
td OH
ii
> W
o u
ri
o
4
OIL RECOVERY PERFORMANCE
1/16 scale model in calm water
gear oil G X 90
% water in oil
% oil removed
0.50
0.60 0.70 0.80
BELT-PLATE GAP ^ INCHES
0.90
FIGURE 28 - OIL RECOVERY PERFORMANCE
50
-------
^
O i-Q
-H <(
X O
^^. x
a " S
III
OIL RECOVERY PERFORMANCE
1/16 scale model in calm water
motor oil SAE 30
12
% water in oil
oil recovery rate
% oil removed
0.87gal./aec req'd. 3
iii > iiii iiiii iii«
mjniiiiiiiiiiiiiikii iiiiiiiii
N9I !* «
»»«» *! t '*
*(!»» >* «*
!«« !
*>
«* <
»«»»> !«
KKlDBMa « ^
»*f*# >
*«»«*iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
*«»« )
M«*«B*^i«« >
0
0 0.50
0.60
0.70
0.80
0.90
FIGURE 29 - OIL RECOVERY PERFORMANCE
51
-------
OIL RECOVERY PERFORMANCE
1/16 scale model in calm water
Motor oil SAE 10
% water in oil
oil recovery rate
% oil removed
0.87 gal./sec req'd
0.50
0.60 0.70 0.80
BELT-PLATE GAP ~ INCHES
FIGURE 30 - OIL RECOVERY PERFORMANCE
0.90
52
-------
OIL RECOVERY PERFORMANCE
1/16 scale model in calm water
Kerosene
-I
OS
.J
o
'0 0.50
0.60 0.70 0.80
BELT-PLATE GAP ~ INCHES
0.90
FIGURE 31 - OIL RECOVERY PERFORMANCE
53
-------
OIL RECOVERY RATE (Q) XI02 gaU«
PERCENT OF OIL REMOVED (E)
I I
S § .8
3 § S
I I
\ I
l I
Standard'
h = 0.75
SAE30
Boom on
h = 0.75
SAE30
Boom on Hydrofoil off
h = 0.75
SAE30
Hydrofoil off
h = 0.75
SAE30
Standard1
h = 0.50
SAE30
t
J.
Tilt Angle 65'
h = 0.50
SAE30
Hydrofoil chord plane 1/8 inch
below oil-water interface
h=0.?5
SAE30
Waves
h=0.75
SAE30
Waves
h=0.75
Kerosene
o.
fl
HKNWM
Standard*
h=0.75
Kerosene
I
g g
PERCENT WATER IN OIL (e)
O
PJ
54
-------
as
u
E-
c«
W
co
co
Pi
£3
o
55
-------
o
o
I
I
w
OJ
p
56
-------
OU>U>C
2
»££
Sg?J °
w t8 rpsis
PV Q z ui h-srawiS-j
II §8 £ 3£isl?y £
:St-3 ly
TT
s
iz;
O
C/3
ffi
I
in
eo
g
57
-------
o
o
I BNI1 H31N33
S -Nvavwvivo
CQ
Q
O
oa
p
I
58
-------
200
ESTIMATES OF EFFECTIVE AND SHAFT HORSEPOWER
FOR 40-FT. CATAMARAN-DESIGN B
180
PROBABLE UPPER BOUNDS
160
140
120
100
§
80
60
40
20
0
SHAFT HORSEPOWER
@ PROPULSIVE EFFICIENCY
OF 60 PERCENT
68 10 12
SPEED, Knots
FIGURE 37 - HORSEPOWER REQUIRED-CATARMARAN
14
59
-------
-------
PRELIMINARY DESIGN & MODIFICATION
OF CONFIGURATION (B) TYPE HULL FOR
CATAMARAN OIL RECOVERY RIG
FOR
PHYSICAL SCIENCE LABORATORY OF
NEW MEXICO STATE UNIVERSITY
DESIGN BY J.P.B.
NOV. 10, 1970 SCALE AS NOTED
FOR WATER-LINE FAIRING
SEE PRELIMINARY DRAWING
OF CONFIGURATION (A)
6061-T6 STRUCTURAL
ALUMINUM-I BEAM
6" X 3.443 X .343
BRIDGE STRUCTUAL BEAM FOR CATAMARAN
CROSS SECTION 2 REQD ONE ON STATION 2
THE OTHER ON STATION 8 SCALE HALF SIZE
1/2" THICK ALUMINUM PLATE
RIVETED AS SHOWN
SCALE A =
1-1/2 = V - 0"
LENGTH BETWEEN PERPENDICULAR 40' - 0'
FIGURE 38 - CATAMARAN OIL RECOVERY VESSEL
60
\ I
-------
p
PS
Q
iz:
O
Q
hH
tf
pa
u
I
ON
CO
p
O
E
61
-------
62
-------
1.0
oi
w
a
o-
::::::::::::::: CA
|E;E|;;;i; :::-;
::i:H:H±:::± :::
;;;;:!!-|lN
;EE;;;:E;;;::;;~;;|
TAMARAN HEAVE & PITCH AMPLITUDE RESP
VESSEL SPEED 3 KNOTS
:E|;£;;;;;;E; ;;;::;;|:;;; ;;;;;; PITCH SLOPE/WAV
I;;;;!;;;;;;;;: fE±;i:i :g::E:l:::E:i:EI;;:;;iJi;i:iiiiii;ii:i
::::: ::::::::: ::::::::: :| ::: + :: ;!:::::::::::::::::::::::: ,.,
:;;;;:;;;;:;;;:i;;!:;;;: E;;;!;E;:;;;;:;E;;;;>:!; HEAVE DI
:::+TJ:::::::: : |: ::::::, i! ::::::: ::: . : : : | : BTTrrrrm-i . ,-rrr
:--.:. t ::::| :::: ::::: ::1:::| :::: |::: .:::: 1:: :::: :::::
ONSE ;;;;;-;;;:;;; ;-;;;;;;
ESLOPE E:::::::::::: ;|::;;::;
!!ii!!!!!!!!;;!ii!!iiiiiiiiji;ii|
SPAVAVE HEIGHT '. ::: :i;|
-- 1 -T
:::::::I:::::::::::::::::|: ff:::p:
0.5
20 40 60
WAVE LENGTH (X) -v FEET
80
100
120
FIGURE 41 - CATAMARAN HEAVE & PITCH AMPLITUDE RESPONSE
63
-------
100
C/3
Ed
Ed
Pi
O
Ed
Q
Ed
J
o
Ed
C/3
-40
CATAMARAN HEAVE AND PITCH PHASE RESPONSE
(NODE OF FORWARD FACE OF WAVE AT VESSEL C. G.) I
1 VESSEL SPEED 3 KNOTS -M
TI t-rH-
20 40
WAVE LENGTH-FT.
80
FIGURE 42 - CATAMARAN HEAVE & PITCH PHASE RESPONSE
64
-------
APPENDIX B
ESTIMATION OF THE WAVE LENGTHS
FOR SUITABLE OPERATION OF THE OIL PICKUP UNIT AND
RECOMMENDATIONS FOR AN EXTENSION OF THE DEVELOPMENT PROGRAM
by
J. P. Breslin
Consultant
Prepared for
Physical Science Laboratory
New Mexico State University
10 November 1970
65
-------
-------
INTRODUCTION
It is necessary to ascertain the range of encounter frequencies over which the dynamic
responses of the OPU will be larger than that of the wave. The actual motions are difficult,
if not impossible, to calculate with acceptable accuracy because of the fact that the draft of
the flotation device is generally not sufficiently large with respect to the wave amplitudes
to permit confident application of existing methods. Furthermore, the geometry of the
scoop inlet falls beyond available experience for the estimation of the various hydrodynamic
coefficients required by the linear analysis of floating bodies in waves. Within the framework
of linear analysis, estimates of the wave lengths for which the relative motions will be likely
to be unacceptable can be made.
EQUATIONS OF MOTION
It is assumed that the OPU is connected by freely pivoting or translating links to a
carriage which is free to surge fore and aft on virtually frictionless guides attached to the
catamaran. The linkage and carriage will provide inertia forces and moments to the OPU.
At the outset, these constraints will be considered to be small. It is also assumed that the
OPU is towed by a cable which provides a spring-type restoring force to keep the mean posi-
tion near to the mid-length of the catamaran.
If the unit is beset with regular waves of frequency cj (radians/sec) while moving for-
ward with speed U, then the forced response will be at the wave encounter frequency J2
which, for head seas, is given by
(c+U)
n = 2ir (1)
where c is the wave celerity which depends upon wave length
X is the wave length
In terms of wave length, this is
(2,
Values of encounter frequency fi for selected forward speed are graphed in Figure 43 as a
function of wave length X.
67
-------
When the excitation is at frequency J2, the motion response under assumption of
linearity of the system will be at this single frequency. If x and z are the instantaneous
coordinates of the excursions of the center of mass of the OPU with respect to a frame
of reference moving at constant speed, and 8 the angle of pitch from the horizontal, then
it is convenient to split off the time dependence by writing
x =
z =
e =
(3)
where x, z and 6 are complex amplitudes in surge, heave and pitch. The real parts of
these expressions are ultimately retained.
The equations of motion are, in general, given in the form:
AH
A21
A31
A12
A22
A32
A13
A23
A33
x
z
10
For example, the equation for heave is
A21x + A22z + A230 = Fz
M
(4)
(5)
The quantities A- are complex force or moments per unit amplitude of response. For exam-
ple, the term A2^x is the heave force due to surge and, therefore, represents a cross-coupling
of surge into heave. Aj2 is the surge force due to heave. The quantities on the right side of
(4) are the wave-exciting forces and moments. Each of the quantities Aj- are of the form
(-coV
+
To be specific
n
an + cn + iojbn)
(6)
(7)
/
Here the first term -co aj j is the force associated with surge acceleration of the body in
calm water, aj j being the force per unit acceleration, being the sum of the mass of the body
68
-------
plus the entrained fluid mass in surge. The quantity Cj j is the restoring or spring force in
surge per unit amplitude of surge. This is usually zero for ships and may be zero for the
OPU if a constant tension winch-cable system is employed to balance the mean drag force
acting on the unit at constant forward speed. The term bj j is the damping force in surge
per unit amplitude due to motion induced by surge.
The wave-exciting forces are of the form
Fx = (-<*>2Al +Cj + icoBj)^ (8)
where Aj is the force per unit wave acceleration -co T?, i? being the complex wave
amplitude
Cj is the hydrostatic force per unit 1 17 | in surge
Bj is the surge force arising from wave velocity
It may be seen from these expressions that there are, in general, 27 body coefficients
and 9 wave-generated coefficients which must be known in order to solve the equation
system (4). Fortunately, not all are distinct and many of the cross-coupling coefficients
are either zero or negligible because of symmetries or near symmetries in the hull form.
The body coefficients ay and by are generally obtained by oscillating a model in calm
water to obtain that part of ay which is due to the added mass of the fluid and the damping
force coefficient by. The restoring forces cy are calculated from hydrostatic principles.
The added mass and damping can be calculated for certain simplified forms generally apply-
ing two-dimensional theory. More general methods for arbitrary forms also exist which
employ computer programs.
The wave-exciting force coefficients A;, B^ are frequently obtained from tests in which
a model is held fixed in waves of discrete frequencies. Calculational procedures are also
available.
It must be appreciated that, because of its unusual form, the OPU does not belong to
a class of shapes for which a body of knowledge exists. In the absence of specific measure-
ments of the body coefficients (ay, by) and the wave-exciting coefficients (A:, Bj), it is
indeed impossible to make specific motion predictions over the entire frequency or wave
length regime of interest. This is particularly true for the OPU where the error in the
prediction of the motion of the leading edge must be less than a fraction of the oil film
thickness at that location.
69
-------
However, the equations do provide an opportunity to assess the natural frequencies
in the separate modes which ought to be strived.for in order to assure that the OPU will
respond closely to the wave over a large range of encounter frequencies.
For example, consider heave under the assumption that the cross-couplings from surge
and pitch are negligible. Then, from Equations (4) and (6), we have
2 2
(-co 322 + C22 + I
-------
A = (13)
Cv * h
Hence
4
-------
Using the values w = 1601bs.; A = 6.95; g = 32 ft/sec2; 7 = 64 lbs/ft3 gives
z 1 - 0.0113ft2
T? 1 -
For an encounter frequency ft = 3 (corresponding to meeting waves of 40, 58 and 77
ft. at speeds of 3, 6 and 10 knots)
= 1.12 (18)
n i - 0.20
In view of the fact that response in irregular waves is generally smaller than in regular
waves, the excursions due to heave alone will be generally acceptable for waves in excess
of 40, 58 and 77 ft. in length at 3, 6 and 10 knots. The mitigating effects of the oil on
wave amplitude will also help.
The response in pitch and the relative phase of heave and pitch depends upon a knowl-
edge of the mass moment of inertia of the OPU which is not available at this time.
To achieve close following of the waves, it is essential to reduce the inertia of the OPU.
If the "belt-pump" concept is retained, it may be necessary to transmit the drive by means
of a flexible shaft to remove the weight of the driving motor or to use an hydraulic pump
with flexible hoses to the hydraulic motor located on the catamaran. Otherwise, if the
number of short waves is great (as the writer expects in coastal waters) it will be necessary
to activate the inlet scoop lip with a pitching control servoed to the oil layer thickness.
To design this system effectively, it would appear necessary to characterize the coupled
motions of the catamaran OPU system by means of a carefully scaled model test since
the tolerance required for the inlet scoop submergence appears so severe as to preclude
dependence on existing methods of calculations, even if all the body and exciting force
(and moment) coefficients were known from oscillator and restrained model measurements
in waves.
72
-------
RECOMMENDATIONS
It is recommended that a program seeking extension of support be sought which
includes development of a configuration
a) of very low inertia
b) exploiting a phenomenon which would accommodate relative motion of the
inlet relative to the water surface, i.e., the planing concept which will skim a
layer proportional to the square of the trim angle of a planing plate;
c) employing a vacuum system to assist the upward flow of the oil and thereby
eliminate the need for weight on the OPU, placing machinery and oil storage
directly on and into the catamaran hulls;
d) characterized by means of a model test program to secure the motions of the
OPU-catamaran system in a sequence of regular waves.
Adoption of these concepts should result in an OPU which is extremely light and should,
at the same time, eliminate the need for booms to funnel the oil. The rate of recovery
could be achieved by operating at higher speeds than contemplated with the presently
conceived system.
73
-------
350
300
250
200
150
100
50
= 6 KNOTS
= 10 KNOTS
o li I i I i I i I i I i I . I TT~1 i ! i °i r
0
6 8 10
Encounter Frequency ft
12
14
16
FIGURE 43 - WAVE LENGTHS FOR VARIOUS
ENCOUNTER FREQUENCIES AT
SELECTED SPEEDS
74
-------
1
5
,4 cce.s.s/on Number
2
Subject Field &, Croup
05G
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organization
New Mexico State University
Physical Science Laboratory
Las Cruces, New Mexico
Title
FLOATING OIL RECOVERY DEVICE
10
Author(s)
I ,t Project Designation
15080 FWO
21
Note
22 Citation
Floating Oil Recovery Device Final Report, 66 pages,
February 1971 43 Figures, 1 Reference.
no Descriptors (Starred First)
jescriptors (Starred rirsij
*Floating oil recovery, *oil removal, *water channel, *oil spill, *model, *tests, device, vessel,
test channel, oil recovery rate, oil recovery efficiency, oil recovery performance.
25
Identifiers (Starred First)
*Oil pickup unit (OPU), *belt/plate, *rotating belt, *Couette flow, *catamaran.
27
A bstract
Flow bench tests of a model rotating belt-Couette flow oil recovery device were conducted in a
calm water environment primarily, although a few tests were conducted in the presence of waves.
These tests revealed clearly that the device is capable of harvesting oils over a broad range of
viscosities at the rates and purities specified by the EPA, if the inlet can be made to "track" the
water surface.
Analyses were conducted to design a catamaran vessel suitable for mounting the Oil Pickup
Unit (OPU) and also providing the requisite surface following performance. Vessel response
analyses showed that the required surface following behavior cannot be provided by the cat-
amaran itself, but can be achieved by floating the OPU and decoupling this assembly from the
vessel in heave and surge. A servo control for the foil device used at the OPU inlet will further
enhance the surface tracking behavior.
Abstractor
H. R. Glevrp
WR:102 (REV. JULY 1969)
WRSI C
1 Institute n
Physical Science Laboratory, New Mexico State University. Las Cruces, N.M
SN TO: WATER RESOURES SINF A
SEND TO: WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASH I NGTON, D. C. 20240
U.S. GOVERNMENT PRINTING OFFICE : 1971 0440-869
-------
------- |