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HYDROMECHANICS NEW RESEARCH RESOURCES ATTHE DAVID TAYLOR MODEL BASIN

AERODYNAMICS

Captain E.A. Wright, USN

STRUCTURAL

MECHAN ICS

RESEARCH AND DEVELOPMENT REPORT APPLIED MATHEMATICS January 1959 Report 1292 NEW RESEARCH RESOURCES AT THE DAVID TAYLOR MODEL BASIN

Captain E.A. Wright, USN

Reprint of paper presented at Spring Meeting of The Society of Naval Architects and Marine Engineers Old Point Comfort, Virginia, June 2-3 1958

January 1959 Report 1292 New Research Resources at the David Taylor Model Basin

By Capt. E. A. Wright, USN,'Member

This paper describes briefly many of the new laboratory facilities and instruments in the field of ship model research.A planar-motion mechanism now provides hydrodynamic coefficients for the differential equations of motion, a heaving towpoint simulates ship pitching for bodies towed over the stern, a boundary-layer research tunnel reveals the effects of pressure gradients, differential transformers permit miniaturized transducers and remote digital recording, a pneumatic wavemaker generates a programmed frequency spectrum, a large transonic tunnel provides high Reynolds numbers in air, a submarine test tank extends the scope of structural research, a flutter dynamometer explores the phenomenon on control surfaces in water, a large variable-pressure water tunnel provides for testing contra-rotating propellers, and seakeeping and rotating-arm basins add new dimensions to research in naval architecture at the David Taylor Model Basin.The gamut in size runs from a 6-knot towing carriage for a 57-ft model basin to a 60-knot towing carriage for a 2968-ft basin, and from a transient-thrust dynamometer that serves as the strut barrel of a ship model to a 40,000-lb vibration generator that excites full-scale ship structures.Developments like these suggest to the author several trends in ship research.

Nw frontiers of research in naval architecturethat higher speeds and higher performance control are often inaccessible without inspired develop-surfaces are already touching the fringes of this ments in laboratory instruments and facilities.phenomenon, for long well known and explored in Because technical knowledge is exploding radially,aeronautics. laboratories are in contact with these frontiers on The considerable body of research in air is not a rapidly increasing perimeter.The purposes offully applicable to naval design because of differ- of this paper are (a) to describe briefly recent andences in the Strouhal number, Mach number, forthcoming resources for research at the Davidviscosity effects, cavitation, virtual mass, and Taylor Model Basin, and (b) to indicate therebystructuraldamping.Hence a comprehensive some of the current pressure points on the un-study is being made theoretically and experi- known. mentally [1].2 Apparatus has been developed for exploratory Rudder Flutter rudder flutter investigations under the 60-knot Except for singing propellers, hydrodynam- towing carriage.A spade rudder supported by a ically-excited flutter has fortunately been rare instiff shaft, Fig. 1, is free to rotateina cage, in naval architecture.Indicationsare,however,which torsion springs determine the natural frequency in rotation.The cage is supported by I Commanding Officer and Director, David Taylor Model Basin, Washington, D. C. horizontal flexures from a frame bolted directly For presentation at the Spring Meeting, Old Point Com- fort, Va., June 2-3, 1958, of THE SOCIETY OF NAVAL I Numbers in brackets designate the References at the ARCHITECTS AND MARINE ENGINEERS. end of the paper. Positioning is accomplished through a range of ± 45 deg at preselected rates from 8 to 16 deg per sec.The rudder may be positioned either as a direct continuous control by the operator, by steps in increments of 5 deg, or by homing to a preselected fixed position. Lift, drag, and torque on each rudder are measured through strain-gaged flexures in the rudder stock, constituting a 3-component balance. Present capacities are 60 lb lift, 10 lb drag, and 40 in-lb torque. This equipment has direct wire connections, via a fish-pole to avoid forces on the model, to a control console on the towing carriage.Signals for rudder position and forces, as well as heading, heel, and trim from gyros mounted in the model, are brought up to strip-chart recorders on the carriage.

Radio-Controlled Models In the new 240-ft by 360-ft maneuvering basin, it is planned to self-propel battery-operated ship models up to 30 ft or more in length.A system is being provided for complete remote control of shaft speeds and rudder angles.This control will be of the continuous-function type rather than in steps, and will be exercised from a console ashore, Fig. 3. Fig. IControl-surface flutter apparatus.3 Command signals from the console are trans- mitted to the model as subcarriers modulating a very high-frequency(vhf)radio carrier.Cir- cuitry in the model demodulates the vhf carrier, to the structure of the towing carriage.Notseparates the various command signals, and dis- shown in the figure is a large surface plate whichtributes them to the proper propulsion and rud- simulates the ship hull over the rudder. der channels.Simultaneously,atelemetering As an essential condition for flutter is that thetransmitter in the model is sending back data energy dissipated by the system must be equal towhich are displayed at the console as dial readings. or less than the energy extracted from the flow,Thus the operator has continuous direct indica- the former has been kept low in the design of thistions before him of the actual values of the quan- apparatus.The mass balance of the rotatabletities he is controlling by the radio link, and the system can be shifted relative to the rudder axis.feel of the over-all system is the same as though he A controllable eddy-current damper is providedwere controlling through direct wire connections. for both translational and rotational motion. The propulsion system in the model will con- Metalectric strain gages transmit amplitude sig-sist of 1 to 4 series d-c propulsion motors, powered nals to recorders on the carriage.This equipmentby I or 2 variable-voltage d-c generators in motor- was designed by Reed Research, Incorporatedgenerator sets, the m-g sets in turn being driven [2], to DTMB basic specifications and built in theby high-capacity nickel-cadmium batteries.Such Model Basin shops. a system, though seemingly elaborate, is necessary to obtain the required fineness of speed control Rudder-Measuring System and constancy of speed during a run, both to A twin-rudder positioning control and force-better than i per cent. measuring system is now in use for maneuvering The rudder control and force-measuring dy- tests of surface ship models, Fig. 2. namometer will be used in the model.Addi- tional radio control and data-handling channels from model to shore are provided for tailoring to All photographs are Official, U.S. Navy, unless other- wise credited. the particular experiment.

2 Fig. 2Rudder dynamometer for positioning and force measurements

Free-Running Submarine Models tion will be 12 ft diam, more than 30 ft long, and Turning and maneuvering tests employing free-capable of applying pressures of over 1500 psi [3]. running dynamically-scaled models have becomeThe new facility will be the largest tank in the an essential part of the procedure for predictingUnited States for liquid pressure tests of this the handling qualities of new submarines duringmagnitude. the early design stages.This is especially true Submarine structural models weighing up to for submerged maneuvers in the horizontal plane25 tons are secured vertically in the tank to avoid where, because of coupled motions and other corn-gravity bending forces, and hydrostatic pressure plex effects, it may be difficult or cumbersome tois applied to the exterior of the model, Fig. 5. evaluate performance by analytical methods. Actually, oil is used as the pressure medium to The model isequipped for remote controleliminate the need for waterproofing the 250 to through drop cords extending from the carriage300 wire resistance strain gages used in each test. boom down through a tube into the model, Fig. 4.The deflections of the model as the pressure is The cable tube also carries lights which are pho- increased are scanned by a probe, amplified me- tographed to record the model path.The modelchanically, and plotted automatically on a turn- is run in a flooded condition and carries a pro-table.The deflector neter is removed prior to pulsion motor, rudder-actuator mechanism, stern-collapse of the cylinder. plane control mechanism, vertical gyro, horizontal The 12-ft pressure tank was fabricated by the and rate gyros, and ballast and trim tanks.AllNorfolk Naval Shipyard of steel with a yield recording is done on the towing carriage. strength of 100,000 psi.The main tank body and The helmsman and stern-plane operators findlower ellipsoidal head weigh 56 tons and there- they must be highly alert and practiced, becausemovable head 16 tons.The site for the Sub- the time scale is compressed by the square root ofmarine Structures Facilityis adjacent to the the linear ratio of ship to model.Good correla-Underwater Explosions Test Pond and Air Blast tions have been obtained between predictions byPits for dynamic investigations of hull structures, this technique and full-scale behavior. Fig. 6.

12-Ft Submarine Pressure Tank 40,000-Pound Vibration Generator The increase in size, structural complexity, and Through yearsof development and appli- versatility of modern submarines has led to stillcation, the David Taylor Model Basin has ac- another submarine pressure tank in the series ofquired probably the most complete set of vi- these facilities at Carderock.The latest addi-bration generators in existence, Table 1.These

3 Table iVibration Generators at the David Taylor Modal Basin

440-LB MACMINE TUB MIDGET LAZAN BERNHARD TUB 5000-LB 1MO 3-MASS TUB 3-MASS LOSONHAUSEN 5000-LB 40,000-LO

Allerrrating Force, lb

Normal Rating 50 440 1000 1000 5.000 5000 40000

Overload Rating 100 4000 1600 4000 20,000 5000 40000

Torsional Moment, lb It

Normal Rating 8 235 320 9,400 8500 120,000 Not Applicable Overload Rating 16 2140 320 37,500 8500 120,000

Frequency 200-9400 300-3000 0-3400 75-3000 60-1500 50-2000 40-1200 Range, cpm

Weight, lb 14 140 160 308 5,000 2000 12,500

Dirirensions, 9i,9l4,584 19i4x 15ko 10'îsv1294,,11la6lb 2014o16 5349o25 63i 12 16 I086044 L i W,< H, in.

Voltage TUB Diesel Gen. 220 oC TUB Diesel Gen. Re ured OID AC 120 or 240 DC 110 AC 110 AC or DC or or ai 22O-440-60-3. 22O-44D-60».3 22O-44D-6O 3.

Power Regd, 150 1000 DO 8000 30,000 25,000 75,000 watts

The newest addition to the family is a 3-mass 10,000 lb vibration generator designed and built at Carderock, Fig. 7.Although the weight of the machine is only 12,000 lb, it can generate sinusoidal forces of 40,000 Ib in any direction normal to the longitudinal axis of a ship, and torques of 120,000 ft-lb about the longitudinal axis.The speed range of 40 to 1200 rpm provides a wide range of exciting frequencies.The midget is a 50-lb force generator used to excite small structures.A 3-mass 5000-Ib generator has been built for submarine vibration studies; the machine and its controls are designed to pass through submarine openings. A hydraulic machine is being developed for use both as a vibration generator and as a calibrator for vibration transducers.As a generator, it will produce reaction forces of 400 lb at I cps and 1000 lb at 5 cps; as a calibrator, it will provide sinusoidal displacements up to 12 in. single amplitude and accelerations of i g at frequencies as low as i cps.Several types of electrodynamic vibration generators are available for measurements above the upper frequency limits of the mechanical machines. Ship-Vibration Electrical Analog Fig. 3Console for radio control of maneuvering ship models The ship-vibration electrical analog models the flexural modes ofvibration and criticalfre- quencies of complex mechanical systems like ship machines are used to generate sinusoidal forceshulls and shipboard machinery assemblies15]. and couples for the purpose of exciting flexural andRecently, this facility has been redesigned and re- torsional vibration of ship hulls, machinery, andbuilt, Fig. 8. equipment [4]. An extensive array of passive electrical elements

4 Fig. 4Free-running submarine model making a turn in the J-basin at Carderock of resistance, capacitance, and inductance repre- another is to cut the stern of the model free and sentsthemechanical equivalents ofsprings, then to cancel the propeller excitation by small masses, and damping.Points of resonance andvibration generators.The newest system at the various modes of vibration in different parts of theTaylor Model Basin for measuring transient axial network are easily determined by varying thepropeller forces depends upon a thrust transient frequency of the alternating-current input.Thedynamorneter, Fig. 9. electrical analog has broad ability to solve coni- The differential-reluctance type of transducer plex problems involving coupled bending, shear,operates by flexing under load to increase one air sectional rotation, and torsion. gap and decrease another [6].Thereby one mag- Vibration generators can be used to excite shipnetic circuit is weakened and the other strength- components during construction and so provideened, resulting in a net output from the secondary observedvibratorycharacteristicsforinput. coilsproportional to the applied force.The Typical problems are the critical frequencies ofthrust transient dynamotneter embodies this prin- lateral vibration or whipping of a propeller-shaftciple in a thrust transducer called a magnithrust. system, a prediction of hull vibration includingAnnular slots are cut in an enlarged section of the effects of entrained water, rotary inertia, bending, propeller shaft to form a compression spring.To torsion, shear, and sprung niasses, and the longi-keep the frequency response high, the flexure was tudinal and torsional vibration of ship-propulsionmade very stiff; the natural frequency is 240 cps systems. with a 5-lb mass attached.Flexing axially then moves a sleeve pinned to the shaft which alters two adjacent air gaps.Recording is by carrier Thrust-Transient-Vibration Dynamometer amplifier in conjunction with a vibration analyzer. As companion techniques to the use of vibration The dynamometer is quite small, 1.12 in. diam generators and vibration analogs, several methodsby 4.5 in. long.It has served as the shaft strut are available for measuring propeller excitingbarrel of a large model, representing the nuclear- forces on model scale.One such method is topowered carrier Enterprise, to measure the thrust measure the transient-pressure fields on the modeltransients excited by the rudders (luring turning hull and appendages in way of the propellers;maneuvers.

5 The propeller shaft is necked-down and rings attached to produce a differential movement of air gaps in a circumferential direction. Bleed Line The revolution counter is simply a copper disk with 10 radial Aper slots which pulse the induced voltage. For contra-rotating propeller tests in models,

Rnq a dynamometer has been designed to measure thrust up to 50 lb, torque up to 50 lb-in., and revolutions per minute up to 8500 on each of the two propeller shafts, Fig. Il.From a common motor coupling, the outer shaft is driven through two gear boxes and a hollow-shaft transmission dynamometer. The 3g-in. inner shaft rides in nylon sleeve bearings and incorporates a solid shaft transmission dynamometer.The dynamometer is completely submersible, with corrosion-resist- ant parts and encapsulated coils. Self-Propulsion Recorders To Developmentsindynamometer transducers and circuitry have made possible a large degree Oil Line of automation inself-propulsionexperiments. Heart of the control center on the towing carriage is a revolution-speed-time recorder, Fig. 12. The RST recorder [6] is basically a counting Fig. 5Diagram of submarine pressure tank showing instrument for pulses originating from (a) the slot- defiectometer in model ted-disk shaft-revolution pickups in each of four propeller dynamometers for a 4-shaft ship model, (b) an electromagnetic pulse generator on the Transmission Dynamometers idler wheel of the towing carriage, and (c) a precision tuning-fork-controlled oscillator which pro- Culminating a periodofsignificant break- duces timing pulses at the rate of 1000 per sec. throughs in the design of ship model propulsionFor the preselected time interval of the test, pulse instruments, the DTMB transmission dynamorn- totals are accumulated in six 4-decade decimal eter is the latest addition to the family whichcounting units, and translated if need be into pro- began with the pendulum reaction-type dyna-peller revolutions per second and carriage speed mometer having a self-contained propulsion motorin feet per second. [6].Model propeller-shaft torque, thrust, and During this same interval, thrust and torque revolutions are the basic variables measured. values from each of the four propeller shafts are Transmission dynamometers are so-called be-recorded graphically or displayed on digital indi- cause they are fitted into the shafts between thecators.At the end of the test interval the average drive motors and the propellers.Sorne advan- rps for each shaft, average carriage speed, time tages of this type are that their natural fre-duration of the run, and a sequential test number quency in thrust and torque is relatively high,are all automatically tabulated on an adding- response is insensitive to model motions comparedmachine-type printer. to the pendulum type, propeller shafts may be synchronized mechanically, slip rings are elimi-General-Purpose Digital Computers nated, small size and freedom from drive motor The automatic handling and digitizing of model permit flexibility in location, and motors can betest observations lead directly to reduction of different types to simulate full-scale power-plantthese data in general-purpose digital computers, characteristics. Fig. 13.The Ship Powering Division in collab- Basic elements are a torque transducer or mag-oration with the Applied Mathematics Laboratory nitorque, thrust transducer or magnithrust, andat the Model Basin has now programmed all rou- revolution counter,Fig.10.The differential-tine calculations of effective horsepower, shaft reluctance type of transducer for torque operateshorsepower,andpropellercharacterizations, by the same principle as the magnithrust de-markedly reducing the time and man-hours for scribed under the thrust transient dynamometer.data reduction.

6 Fig. 612-ft submarine pressure tank arrives at facility site

Fig. 7Three-mass 40,000-lb vibration generator for sinusoidal forces and torques

Naval mathematics is, in fact, pervading navalcomputers are being used to calculate the buck- architecture on a wide front, particularly as aling strength of submarine models subjected to partner to the developments described in thisexternal pressure, the equations of motion for paper [7].For example, general-purpose digitalemergency control of a damaged submarine,

7 Fig. 8Ship-vibration electrical analog

critical frequencies of a planetary-gear propulsion system, power spectrum analysis of ocean- wave records and of ship model motions in irregular seas, equilibrium configuration of a flexible cable in a uniform stream, boundary-layer development, inception of cavitation on bodies of revolution, stress distributions in propeller blades, pressure distribution on propeller-shaftstruts, neutron-flux distributions in reactors, and re- Fig.9Thrust-vibration dynamometer for measuring sponse of ship hulls to harmonic driving forces. transient axial loads in model propeller shafts The Sperry Rand Corporation is developing

Fig. 10Exploded view of model transmission dynamometer for self-propelled models

8 New Research Resources at DTMB Fig. 11Contra-rotating propeller dynamometer

Fig. 12Recorders on the towing carriage for self-propulsion tests for the Atomic Energy Commission and theruption.Many hitherto untouchable problems Bureau of Ships a general-purpose digital com-in naval architecture will become possible when puter considerably faster and more versatile thanLARC is added to the DTMB Applied Mathe- the two UNIVAC which have been the work-matics Laboratory. horses at Carderock.The large automatic research calculator (LARC) will operate at a speed Propeller Boat of 100,000 multiplications per sec, and will have The purpose of the double-ended aluminum an internal memory of 30,000 words in the ma- propeller boat is to characterize single or contra- chine planned for the Taylor Model Basin.It isrotating propellers in open water, Fig. 14. a solid-state design with transistors and magnetic- The boat is supported from the floating girder core memory. LARC will be a two-headed sys- of either of the deep-water-basin towing carriages, tem; one computer does the staff work such asand the shaft centerline submerged to the desired automatic programming while the other computerdepth between 8 and 14 in. depending on the pro- proceeds with the main calculation without inter-peller diameter.Maximum test speed is 8 knots

New Research Resources at DTMB 9 Fig. 13General purpose digital computers complement developments in ship-model facilities and runs can be made in either or both directions.writing oscillograph when dynamic conditions are One end of the boat is equipped with contra-present. rotating shafts, the inner 3/in. in diam and the Some principal characteristics are thrust 700 outer shaft l-in. diam. A single propeller can belb ahead to 200 lb astern, speed 2500 rpm maxi- tested on either outer or inner shaft.The othermum, power 35 hp maximum from 1000 to 2500 end of the boat is iltted with a single 3'-in. solidrpm, weight 3000 lb complete, and depth of sub- shaft.Any DTMB propulsion dynamometer,mergence 48 in. to centerline of propeller. either pendulum or transmission type, can be used. 36-Inch Variable-Pressure Water Tunnel Theversatilityofvariable-pressurewater 35-Horsepower Propeller Dynamometer tunnels has been well established by the variety Supplementing the propeller boat, equipmentof investigations over the past 15 years in the is now available for open-water characterizationDTMB 24-in, tunnel [0], but likewise the limi- of propellers up to about 20 in. diam and 35 hp.tations in many directions have become apparent. It was designed by the DTMB staff and built byIt is anticipated that most of the limitations will the Norfolk Naval Shipyard. be overcome in the 36-in, tunnel currently under The 35-hp propeller dynamometer consists ofconstruction, Fig. 16. an underwater body housing a transmission-type The new tunnel, Fig. 17, will have two remov- dynamometer which measures torque, thrust andable dynamometer shafts, one from each direction, rpm of a test propeller [8].The test propeller isso that either the upstream or downstream shaft supported on a sting, well forward of the maincan be used, or both in the case of contra-rotating body to avoid interference, Fig. 15.This under-propellers [10].Pressure in the test section will water assemblage is supported by struts from thebe variable from 2 to 60 psi absolute, and the water towing carriage over either the high-speed or deep-velocity up to a maximum of 50 knots.Both water basins.The dynamometer drive motor isclosed-jet and open-jet test sections will be pro- located above water and drives through a ver-vided, and it is anticipated that propellers up to tical shaft and right-angle gear box located in the24 in. diam can be tested in the latter, Fig. 18. underwater body. The transmission dynamom-Test-section conditions were explored on a 6-in. eter employs differential transformers combinedpilot model by the St. Anthony Falls Hydraulic with elastic elements.Signals from the trans-LabQratory [Il]. ducer elements are handled through slip rings. Every effort is being made to achieve a low am- Readings are obtained by a manual null balancingbient noise level for experiments involving the system which may be supplemented by a direct-measurement of sound pressures.

10 New Research Resources atDTMB Fig. 14Double-ended propeller boat for characterizing propellers in open water

The main drive motor will be 3500 hp, 2300 volt, synchronous at 300 rpm, operating through a water-cooled eddy-current coupling to a 78-in. adjustable 4-bladed propeller pump. Thence the water will flow to a resorber to redissolve entrained air bubbles before they return to the test section.To provide pressure as well as time for this process, the resorber extends 70 ft vertically underground into bed rock, Fig.19.The resorber shell and all structural parts of the tunnel exposed to flow are either stainless-clad or stainless steel. 60-Knot Towing Carriage In the original design of the towing carriages and basin rail system at the David Taylor Model Basin [12], these basic facilities were not only built with a precision well beyond that considered possible by engineers at the time, but also they Fig.15 35-hp open-water propeller dynamorneter were made extremely rugged with exceptional stiffness to minimize deflections.This all-too- novel approach of designing for deformation rather than stress has proved invaluable to the nationalcarriage was designed and the high-speed basin defense by providing a large precision instrumentwas extended from 1168 to 2968 ft on the water, able to tow full-scale weapon, minesweeping andFig. 20. A further requirement was that the anti-submarine devices that developed loads onfacility have a low noise level for acoustic experi- the carriages and rails of thousands of pounds. ments.The carriage is driven by 12 d-c niotors, To extend full-scale testing of these defenseweighing 1300 lb apiece and rated at 400 hp each developments to higher speeds, a 60-knot towingfor short duration, with their armatures connected

New Research Resources at DTMB 11 Fig. 16Building to house 36-in, variable-pressure water tunnel

682" Honey Oynarnorneter arid Screens Oynarnometer Contraction e'-oLO. Shaft Shaft Diffuser 1000 SHP 000 SHP

3-d'lo. l6"I.D. 9,-0,, Open - Jet Test Section ID.

Propeller Pump 2887 SHP

Resorber

25' 01.0. o

Bed Rack

Fig. 17Vertical elevation through 36-in, water-tunnel circuit

in series to equalize loads.Speed is controlled byrail head are used in this arrangement.Presently an automatic feedback system toplus or minusthe 16 drive wheels are fitted with rubber tires 0.03-knot over the range. having steel cords and inflated with water to 280 Acceleration with steel tires requires more trac- psi; their greater coefficient of friction is sufficient tive effort than could be obtained by gravityfor acceleration without side drivers.Normal loading alone, and so side drivers squeezing thebraking is by regenerative action of the drive

12 Fig. 18Open-jet test section under construction for the 36-in, variable-pressure water tunnel

motors.Emergency braking is by track brakes mounted on the carriage which grip the sides of the drive-rail heads, and by tapered-nose runners on the underside of the main frame which enter spring-loaded shoes attached to the basin walls at the extreme end.The total mass to be ac- celerated and braked is about 100,000 lb. The carriage construction is a welded tubular steel trusswork, 70 ft long by 26 ft wide [13]. An open rectangular bay is provided for a variety of towing girders to suit particular test require- ments.The girders can be disconnected and removed readily from the carriage for model fitting without tying up the carriage for other tests. Drag loads up to 8000 lb and side loads to 2000 lb can be accommodated. Two independent sources, one up to 2500 amp and the other up to 1000 amp, are available for supplying variable voltage up to 400 volts to powered models. The 60-knot towing carriage is used for a wide variety of testing, such as full-scale torpedoes towed and self-propelled, characterization of large propellers, sonar domes and hydrophones, hydrofoils, and parachutes. Courtesy Washington Evening Sta, Auxiliary Towing Carriage Fig. 19View from research pit looking skyward When ships are maneuvering in close proximity, such as in replenishment-at-sea operations, complex interaction forces are created.To studydistances apart, yaw angles and rudder positions, such effects systematically, it was necessary toand to measure the forces between them [14]. design an auxiliary carriage to tow two models The box-shaped auxiliary towing carriage is alongside each other at various relative speeds,mounted on rollers which ride along two machined

13 Fig. 20 60-knot towing carriage wich rubber-tired wheels aluminum I-beams attached to the underside of a For the Panama Canal tests, a special plat- main towing carriage.The line of motion of theform was suspended below the towing carriage, two models can be adjusted up to 10 ft trans-and the floor of the high-speed basin used as the versely.A motor-powered cable provides up tochannel bottom, Fig. 22.The box girder carry- 2 knots relative speed of the auxiliary carriage.ing the model could be positioned transversely Provision is made to yaw the model.Variousor angularly, and the outputs from the three rudder angles can be used to determine equilib-variable-reluctance gages carried to recorders on ritmiconditions at different positions, speedsthe platform.Rudder-angle settings and pro- over-the-ground, and relative speeds of the twopeller rpm were controlled remotely from the re- models, Fig. 21. cording area.Trim and sinkage were measured Interaction forces are measured by modularby multiplying pulleys to indicating scales. block gages of the variable reluctance type with capacities of 50, 100 and 300 pounds.ThreeMiniature Model Basin gages are attached to the dynamometer beam, A model basin only 57 ft long overall and with two at the forward towpoint and one at the aftera 2-ft square cross section has been built for fun- towpoint, to measure drag and side forces.A damental hydromechanics research, particularly sum-and-difference network is used to convert thethe dynamics of geometrical forms.It has been side forces into moments about the center ofused, for example, to study the forces on bodies gravity of the model. of revolution in waves, to observe the action of hydrofoils with and without wave action, and to Restricted-Channel Instrumentation measure the fluctuating lift and drag forces acting An interaction dynamometer of the type usedon a cylinder moving in a stream [16]. in measuring forces between two ship models is The tank has a pneumatic wavemaker at the employed also in measuring drag and yawingfar end, and a beach at the near end, Fig. 23.At forces on models in restricted channels. mid-length, 10-ft glass panels in the bottom and On tests of supertankers in a channel simulatingsides permit lighting and viewing the flow con- the narrow portion of Gaillard cut in the Panamaditions. Canal, the yaw angles and rudder angles necessary The miniature towing carriage is driven by an to obtain equilibrium have been measured as aendless cable in continuous speed variations from function of distance from the channel wall [15].0.5 to 9.0 fps.The drive system is equipped with Tugboat forces necessary to check the swing of thean electromagnetic brake actuated by a track model when it sheers across the channel are alsotrip; in event of failure, the carriage is arrested measured. by a pneumatic bumper.Carriage speedis

14 Fig. 21A small model under an auxiliary towing carriage maneuvers alongsidea large model

measured by a 30-ft brass speed bar fitted with The tank is steel and is lined with a wax com- insulated plugs.Interruptions of current throughpound to inside dimensions of 28 by 46 in. on the a point contactor travelling along the bar permitbottom;it may be filled to a depth of 15 in. speed measurements to an accuracy of ± 0.001Heavy copper electrodes are available for the tank fps.Guide wheels limit the side movement ofsides.The probe for exploring the electric field the carriage to 0.003 in. is carried either on the arm of a pantograph or on Carriage equipment includes a mechanical oscil-a small carriage, Fig. 24.Double probes are use- lator for driving a model in a vertical plane, tow-ful in obtaining the pressure and velocity field points on both the forward and after sides of theaway from a body.Precise alignment of the con- carriage, and a dynamometer for loads up to 60ducting surfaces,tank boundaries and probe lb drag and 250 lb lift.Power to the carriagemovement is essential.Model tolerances must equipment and readings from the carriage in-be held to a few thousandths of an inch, and strunients are brought in and out by overheaddielectric models machined out of plastic material. cables. Low-Turbulence Wind Tunnel Electrolytic Tank For the investigation of turbulent boundary The David Taylor Model Basin, like a numberlayer and wake phenomena related to problems of other hydrodynamic laboratories, found needof hydrodynamic noise and frictional resistance, for an electrolytic tank to study the potentiala wind tunnel has been constructed with low flow patterns about two and three-dimensionalinitialintensityofturbulence[18]. A tur- bodies [17].Either a dielectric model represent-bulence level of about 0.1 per cent is achieved ing the hydrodynamic body is placed in a semicon-primarily by making the tunnel an open-return ducting medium so that streamlines correspond totype, by the use of 6 turbulence damping screens lines of constant electric flux and equipotentialin the settling chamber, and by a contraction lines correspond to lines of constant electric po-ratio of 12.5:1. tential, or a conducting model is placed in a di- The closed test section is rectangular in cross electric medium and the correspondence is reversed.section, 4 ft high and nominally 2 ft wide.Both

15 Fig. 22 Panama Canal tests of a supertanker model test-section side walls are constructed of flexible The newest addition to the DTMB aerody- sheet steel and can be adjusted so that the sectionnamics facilities is a transonic wind tunnel with width can be continuously varied from 1 to 3 ft.a test section 10 ft wide and 7 ft high.Reynolds In this way a large variety of axial pressurenumbers up to 1.2 x 108 can be obtained on a 20- gradients can be obtained.The position of eachft submarine model. side wall is individually controlled by 28 adjust- The transonic tunnel is a closed-circuit, single- ing screws, Fig. 25. return type with a contraction ratio of 14.4 to 1 A maximum velocity of approximately 140 fpsand a diffuser angle of about 3 deg, Fig. 26.It is obtained in the test section.The air flow isis constructed of reinforced concrete, except for created by an 8-bladed wooden fan, 6 ft diam,the high-velocity portions which are made of located downstream of an 18-ft-long diffuser.machined steel.The tunnel is designed to oper- The fan is driven by a direct-coupled 60-hp motorate over a Mach-number range of approximately whose speediscontinuously variable up to0.3 to 1.2, and at test section pressures between 1800 rpm. 0.25 and 1.75 atm.There are two contra-rotating propellers, each driven by a 12,000-hp con- Transonic Wind Tunnel stant-speed electric motor through a variable- Flexible use of aerodynamics facilities for hy-speed coupling. A continuously operating desic- dromechanics research and vice versa has beencant-type air dryer is capable of maintaining a a tradition since Rear Admiral Taylor marrieddewpoint of - 15° F. A finned-tube radiator in the wind tunnels and towing tanks in 1914.Forthird corner of the tunnel, combined with a cool- example, submarine models and underwater cableing tower, is used to control the air temperature. fairings are tested in wind tunnels, parachutes inAt a flow of 14,000 gal of cooling water per mm, a model basin, and stack smoke flow in a circulat-the stagnation temperature can be maintained ing water channel. below 135° F. even with maximum power input.

16 Fig. 23Minature model basin and towing carriage

In the test section, Fig. 27, longitudinal slots in the floor and overhead are proportioned to eliminate choking and toreduce tunnel-wall boundary interference.The vertical side walls diverge slightly to control the static pressure gradient.Through side windows, visual indica- tion of the density gradientsintheflowfield is provided by an 18-in. Schlieren system. A sting type of support permits changing both pitch and yaw attitudes of the model at the same time.Force measurements are made by internal strain-gage balances.Balance outputs are recorded by self-balancing potentiometers equipped with digital converters and printing counters. Data from 12 channels are fed through an ALWAC II digital computer which corrects and converts to coefficient form.The aerodynamic coefficients are then plotted conventionally by an automatic plotter. Smoke Tests Under Water Wind tunnels have been the natural and tra- ditional facility for conducting flow studies of flue Fig. 24Electrolytic tank, fitted with cross beams and gases from the stacks of passenger and naval ships. carriage

17 Fig. 25Low-turbulence wind tunnel, looking toward adjustable side wall of test section

First as an expedient because the DTMB wind tunnels were occupied at the time, but now as a routine procedure, smoke- flow experiments are run in the circulating water channel [19]. In this new technique[20], the water flow relative to the model simulates the wind, while a dye solution pumped through the stacks simulates the smoke. A waterline model complete with superstructure is secured to a large flat plate, and is held submerged in an inverted position in the test section of the circulating water channel. Water is pumped through the stack, at the desired ratio of smoke discharge velocity to relative wind velocity, until the flow pattern is fully developed.Then dye is injected into the stack water connection, and the flow observed visually or photographed, Fig. 28. Compared to wind-tunnel testvelocities,a much lower water speed can be used, facilitating the visual observation of smoke-flow patterns. At the sanie time, Reynolds numbers above those considered critical for good model-ship correlation can be maintained easily. Wax and Plastic Models For 50 years, wood was used exclusively for Fig. 26 View looking downstream in the transonic windmaking towing models at the U.S. Experimental tunnel Model Basin and the David Taylor Model Basin, because the low-temperature soft paraffin wax used in European tanks was unsuitable for summer

18 Fig. 27Test section of 7 by 10 ft transonic wind tunnel

Fig. 28 Smoke flow study of a landing ship in the circulating water channel

months in the Washington area.With the gen-Entirely satisfactory models up to 30 ft in length eral development of synthetic products, it hashave been constructed, Fig. 29.Hogging wires now been possible to develop a suitable high-are usually fitted for models 20 ft and longer. temperature hard-wax composition.While theAbout 95 per cent of the wax can be salvaged and blending and casting techniques are more com- reused; savings in construction compared to a plicated than foreign methods, considerable sav-standard 20-ft wood model are in the order of ings in time and cost have been effected (21].20 man-days productive effort and 2 weeks' time. The wax blend developed consists of 30 perWood models continue to be used widely for such cent refined paraffin, 32.5 per cent hydrogenatedapplicationsas maneuvering, seakeeping, and castor oil, and 37.5 per cent n-butyl methacrylate.submerged models, as well as for final designs.

19 Fig. 29 A 30-ft model of a Great Lakes ore carrier

Fig. 30 Mold and plastic model of an air-sea rescue boat

Substantial progress is being made in the use ofPlanar-Motion-Mechanism System fiberglass reinforced plastics for model construc- The hvdrodynamic-stability derivatives in all tion, Fig. 30.The higher strengths and thinnersix degrees of freedom of deeply submergedmodels skin of fiberglass provides additional weight andcan be determined by the planarmotion niecha- space for propulsion equipment andinstrumenta-nism system 122].Models varying in length from tion, a particular advantage in subsurface models.9 to 23 ft are supported by two struts intandem, Fiberglass laminates are being used also for air-Fig. 31.Force components are measured at each craft models because of the favorable strength-strut by internal force balances.These balances to-weight ratio compared to wood.This mate-are individual flexure boxesemploying variable- rial is bridging the wide gap that existed betweenreluctance displacement gages as transducers. wood and metal in model construction, both in Static forces and moments associated withhull regard to cost and physical properties. angles are measured by remotely rotating the tilt

20 Fig. 31Planar motion mechanism with subsurface model attached

Fig. 32Analog computer array for simulating motions and trajectories

21 heaving orpitchingoscillations.Amplitudes, forces, amI phase relations are measured.

Simulator Facilities Studies are made in the simulator facilities of the stability, control aoci stabilization of submarines, surface ships, torpedoes and missiles. Designvariations which normally require tra- jectory studies for satisfactory evaluation are sim- ulated and corrective action recommended early in the design process.Captive model data are extended by this means to provide design infor- niation in the sanie form as from full-scale ship trials 12.51. The Facility consists of electronic analog computers used to solve linear and nonlinear differential equations of motion, a submarine diving station to simulate the control area and pitching motion of a submarine, arid nunerous auxiliary equipment such as instrument displays, automatic plotting boards, and strip-chart recorders.A total of 138 operational amplifiers are now available for computation, Fig. 32. As an example, the designers and prospective commanding officers of new submarines can fly their boats here before they are built.Movement of the joy stick in the submarine control cab pro- duces inputs to the computer which then calculates the resultant motions and path of the submarine. The submarine attitude angles and depth are Fig. 33Heaving towpoint facility attached co side ofshown on the instruments in front of the operator, towing carriage and the cab rotates to the computed pitch angle. The joy stick is moved again to perform the desired maneuver and the cycle repeats.Mean- while a graphical record of the submarine path is table carrying the entire model-strut system.Theobtained automatically on a plotting board. force-balance signals from such tests are recorded by servo-null-balance type of digital indicators. Heaving Towpoint The data are tabulated automatically by an Laboratory experiments to predict full-scale electric typewriter. behavior nearly always involve decisions whether Dynamic forces and moments are obtained bycertain variables can be neglected. When a sub- oscillating the model in heave with the strutsmerged body is towed from a ship, it was suspected moving up and down in unison, and then bythat the ship motions had an appreciable effect oscillating in pitch with the struts moving out ofon the behavior of the body, particularly when the phase.The sinusoidal signals measured by thetowpoint passed over the ship's stern.To in- force balances during the oscillation runs arevestigate such effects, a facility was designed electronically resolved, rectified, integrated andto vary methodically the vertical position of a recorded, saving many man-months of data re- towpoint [26]. duction [23].Linear acceleration coefficients are The heaving towpoint facility is attached to an determined by accelerating the towing carriage.18-knot towing carriage near the centerline of the A related apparatus is the pitch and heavedeep-water basin, Fig. 33.The towpoint oscil- oscillator,designed primarily fordetermininglates vertically either in a sinusoidal motion with experimentally the coefficients for the equationsdouble-amplitude variable from O to 10 ft and of mction of a ship in a seaway [24].Surfaceperiod from 3 sec to infinity, or in a single-step ship models up to 12 ft in length are towed atfunction.The maximum loading on the towpoint constant speed and forced to perform sinusoidalis 1000 lb drag, 1000 lb vertical force, and 500 lb

22 Fig. 34Pneumatic wavemaker for the deep.water basin

side force.The track is readily demountable tois under construction to provide complex seas avoid interference with other tests. from any relative direction [28]. In the 3'0-scale model of this facility, Fig. 35, Pneumatic Wavemaker pneumatic wavemakers of the type developed for Waves in the open ocean have been found tothe deep-water basin are arranged in banks of 8 have a frequency spectrum which varies dependingalong one end and 13 along an adjacent side. upon the sea state.For modern studies of sea-Short crested seas will be generated not only by keeping in the laboratory, it is necessary to haveintersecting wave trains from the two banks, but wavemakers that can be programmed to producealso by intersecting circular trains generated by model seas of this character.The pneumaticindividual wavemakers acting as a point source principle of wave generation, first applied at the [29].Highly absorbent beaches, developed in California Institute of Technology and Lausannecollaboration with the St. Anthony Falls Hydrau- University in France, is highly suitable for fre-lic Laboratory [30], line the opposite tank sides. quency shifting because of the low inertia of theOne beach is masked when it is desired to produce moving parts. regular or irregular waves in only one direction. Development at Carderock began in the 2-ft- The full-scaleseakeeping and maneuvering wide towing tank, continued in the 10-ft-widebasin [31] will be 360 ft long by 240 ft wide, Fig. tank, and culminated in the 51-ft-wide deep-36.Spanning the basin will be a 376-foot steel water basin, Fig. 34.Waves are produced bybridge weighing about 230 tons, Fig. 37.Run- oscillating the air pressure from positive to nega-ning on the underside of the bridge will bea car- tive in a plenum chamber which embraces a stripriage for test personnel and instruments, and to of the water surface [27].Wave length is con-tow or guide captive models with limited degrees trolled by the frequency of shifting valves fromof freedom. The carriage will be a welded-alumi- pressure to suction, and wave height is varied bynum, tubular truss structure, supported and adjusting blower speed.Regular waves 5 to 40guided by steel wheels, and driven through rubber- ft long and 4 to 24 iti. high can be generated, andtired wheels preloaded against the vertical faces are fully stabilized within a travel down the basinof a traction rail.Acceleration rates up to 0.4 g of less than 75 ft. can be obtained thereby and maximum speeds of As conventional model basins with wavemakers15 knots.The bridge will be positionable from permit tests only in long-crested head and follow-o to 45 deg to the long axis of the basin which, ing seas, a seakeeping basin has been designed andcoupled with a 90-deg choice of wavemakers,

23 Fig. 35One-tenth scale model of the seakeeping basin with pneumatic wavemakers produc- ing a waflle pattern

will permit the carriage to run under the bridgenationally by the construction of 7 rotating-arm at any angle relative to a wave system. basins in different countries [32]. Basin depth will be 20 ft generally, except for a The DTMB rotating arm basin will be 260 ft trench 50 ft wide and 35 ft deep adjacent to thediam and 21 ft deep.The arm will pivot iii the beach on the long side.In this deep portion, it iscenter of the basin on tapered roller bearings de- planned to operate free-running submarine modelssigned for a centrifugal force of 145,000 lb, and and to observe their behavior through a series ofwill be supported by and driven from a peripheral underwater windows in the basin wall.Looptrack.The rotating arm is a tubular aluminum filling and draining connections have been madestructure, Fig. 39, weighing about 37,500 lb and to the existing 3,000,000-gal per day filtrationhaving natural frequencies in the vertical, hori- plant to provide suitable conditions for under-zontal and torsional modes exceeding 3 cps.The water photography. drive system is designed to accelerate the arm to 30 knots at the 120-ft radius in half a revolution. Rotating-Arm Basin Thereby surface ships models can be brought up Housed under the same 695-ft by 373-ft column-to speed and readings taken before meeting their free roof as the seakeeping and maneuveringown wake.Traction is through two 30-in, steel basin will be a rotating-arm basin, Fig. 38.Thewheels preloaded against the track surface to a two facilities will be functionally independent ofnormal force of over 60,000 lb per wheel, and di- each other except for certain supporting servicesrect connected to 400-hp motors capable of 230 A con- [31 J. per cent overload during acceleration. Rotary coefficients for the differential equationstrol console will be located on the inner bay of the of motion of surface ships and submarines are bestrotating arm near the island pivot. obtained in a rotating-arm basin designed for the The models will be attached to a towing car- purpose.Here constrained models are towed inriage which can be positioned remotely on the circular paths of different radii and the resultantunderside of the rotating arm at any radius from forces and moments measured at different driftabout 12 to 120 ft.Surface-ship models will be angles.The need for experimental observationsattached to a beam, and submerged models to of this nature to analyze and predict directionalstruts supported by a yaw table. A balance will stability and control has been recognized in ter-measure concurrently the forces and moments

24 Ç_Bridge Ç_Top Chord

Fin. Grade Carriage Ç_ Bottom Chord

Approximate Surface Elevation Top of Rock Stop

D E Bridge in Extreme"\ il Ç_Track D Rotational Position Stop

Control Ali. II Platform - 376-O" Drive Arresting Engine \ Electrical Equip. (Ç_Pivots) - Truck Platform Platform

Submarine Trench Water Depth 35-O"\

Bridge in Extreme Transverse Ç_ Bridge PsThon Ill

to -I#= =1 Stop Plan Fig. 36Plan and elevation of the seakeeping and maneuvering basin

about 3 axes. A drydock 26 ft long by 16 ftship design has become highly imfettered and wide and 18 ft deep, supported by rails on theattack is from many different directions. basin floor, will be movable to carry subsurface The wisdom of building functional test models out under the rotating arm, to attachfacilities for seen and unseen future demands has them at any desired radius, and to make modelbeen reaffirmed strongly. changes and adjustments between tests. Theories are more often reflected in ex- Both the rotating-arm basin and maneuveringperiments, which are planned either to make spot basin are still in the heavy construction stage,checks or to provide coefficients. Fig. 40, proceeding toward a tentative completion date of late calendar 1959.It is hoped that these Motions and maneuvers of free bodies are important facilities for ship research will be instudied widely in six deg of freedom. operation by the time of the 1960 Spring Meeting Dynamic experiments have become the of this Society, presently planned for the Wash-rule, markedly increasing the scope and versa- ington area. tility of model testing. Model size varies throughout the range Conclusions from very small to full scale. These developments in facilities and instrumen- Analog computers permit modeling elec- tation at the David Taylor Model Basin are in-trically a broad diversity of problems in ship de- dicative of several trends in ship research: sign. (a)The laboratory approach to problems of Automation of routine model experiments,

25 Fig. 37Maneuvering basin bridge being erected, viewing ports for submarine models in lower background

Fig. 38Arrangement model of rotating-arm and maneuvering basin

26 Fig. 39 Aluminum truss rotating arm under construction

both the data taking and data reduction, is in-Together they create a sound and productive creasing rapidly. pattern for research in naval architecture. Digital computers are opening hitherto untouchable fields of analysis and mathematicalAcknowledgment modeling. Many individuals in all laboratories and depart- Continued miniaturization of instrumen-ments of the David Taylor Model Basin con- tation will lead to further applications in modeltributed to the developments described in this experiments. paper. Versatile and accurate differential reluctance transducers and strain-gage flexures arc References revolutionizing the design of dynamometers, both iR. T. McGoldrick and D. A. Jewell, "A transient and steady state. Control Surface Flutter Study in the Field of (i)Research in underwater acoustics exertsNaval Architecture,' DTMB Report 1222 in a broad and rapidly growing influence on facilitiespreparation. and instrumentation. 2Reed Research, Inc., "Design Calculations Seakeeping theory and experiment arefor Rudder Vibration Test Gear,' Project RR- bringing into the laboratory all the complex hut 1097, February 1957. orderly environment of surface mariners. 3 M. E. Lunchick, "A New Facility for the No longer isthe aeronautical industryStructural Testing Of Submarine Models," Society more forward looking or acting in research than ofExperimental Stress Analysis, Washington our own profession. Area Section, May 1958. Substantial savings incost,time, and 4Q. R. Robinson, "Vibration Machines at the engineering manpower have been effected byDavid W. Taylor Model Basin," DTMB Report electronic data handling, reduction and analysis,821, July 1952. by wax-model developments, and by modular 5Edward Kapiloff, "Calculation Of Normal design of dynamometers. Modes and Natural Frequencies Of Ship Hulls This paper has dealt only with new physicalby Means of the Electrical Analog," DTMB resources.Human resources remain the most im-Report 742, July 1954. portant asset of the David Taylor Model Basin. 6 G. J. Norman, M. W. Wilson, and F. B.

27 w

r.1.v

Fig. 40Construction siew, rotating-arm basin to right and maneuvering basin to left

Bryant,"Propeller Dynamometer1 nstrumen- 12 H. E. Saunders, "The David W. Taylor tation at the David Taylor Model Basin," DTMB Model Basin, Parts 1, 2, and 3," Trans. SNAME, Report 1068, July 1956. 1938, 1940, and 1941. 7E. A. Wright, "Naval Mathematics At The 13G. A. De Shazer, . 'An Arc Welded High- David Taylor Model Basin," Journal of theSpeedModel-TowingCarriage,"Design-for- American Society of Naval Engineers, May 1957.Progress Award Program, James F.Lincoln SG. L. Santore, "Dynamic Calibration ofArc Welding Foundation, June 1947. 35-HP Propeller Dynamometer," DTMB Report 14C. G. Moody, "Interaction Between Ships 805, February 1952. During Replenishment-at-Sea Operations," 9A. G. Mumma,'The Variable-PressureDTMB Report in preparation. Water Tunnels at the David W. Taylor Model 15 C. G.Moody, "Restricted Channel Effects Basin," Trans. SNAME, 1941. in Panama Canal Cuts," DTMB Report in prepa- 10W. F.Brownell, "A 36-Inch Variableration. Pressure Water Tunnel," DTMB Report 1052, 16 M. S. Macovsky, "Vortex Induced Vibra- June 1956. tion Studies," DTMB Report 1190 in prepara- 11R. M. Olson, "Model Studies Of a Watertion. Tunnel withanAir-BubbleResorber,"St. 17A. Borden, G. L. Shelton, Jr., and W. E. Anthony Falls Hydraulic Laboratory, UniversityBall, Jr., "An Electrolytic Tank Developed For of Minnesota, Project Report 29, February 1952.Obtaining Velocity and Pressure Distributions

28 About Hydrodynamic Forms," DTMB Report 25D. L. Greenberg, "Submarine Simulation 824, April 1953. Facility at the David Taylor Model Basin," 18R. D. Cooper and M. P. Tulin, "Descrip- DTMB Report in preparation. tion of Low Turbulence Wind Tunnel," DTMB 26S. M. Y. Lum and C. O. Walton, "A Com- Report in preparation. parison of Pitch Measurements on an Oscillating 19H. E. Saunders, C. W. Hubbard, "TheTowed Body Using a Vertical Gyro and a Pen- Circulating Water Channel of the David W.dulum Indicator," DTMB Report 1153, July Taylor Model Basin," Trans. SNAME, 1944. 1957. 20P. C. Pien, N. L. Ficken, and A. L. Real, 27 W. F. Brownell, W. L. Asling and W. "Smoke Ejection Tests for LSD 28 Class Repre-Marks, "A 51-Foot Pneumatic Wavemaker and sented by Model 4552," DTMB Report in pre-Wave Absorber," DTMB Report 1054, August paration. 1956. 21J.B. Hadler and W. B.Hinterthan, 28F. H. Todd, "On A New Facility For "Wax Model Construction At The David W.Testing Ship Models In Waves," Symposium On Taylor Model Basin," DTMB Report 930, JuneThe Behavior of Ships In A Seaway, Netherlands 1955. Ship Model Basin, September 1957. 22.M. Gertler and A. Goodman, "Experi- 29 W. Marks, "On The Status Of Complex mental Techniques and Procedures Used at theWave Generation In Model Tanks," DTMB Re- David Taylor Model Basin to Determine Hydro- port 1069, July 1956. dynamic Stability and Control Coefficients of 30J. B. Herbich, "Experimental Studies of Submerged Bodies," DTMB Report in prepa-Wave Filters And Absorbers," St. Anthony Falls ration. Hydraulic Laboratory, University of Minnesota, 23R. G. Tuckerman, "A Phase ComponentProject Report 44, January 1956. Measurement System," DTMB Report 1139 in 31W. F. Brownell, "A Rotating Arm and preparation. Maneuvering Basin," DTMB Report 1053, July 24P. Golovato, "The Forces and Moments 1956. on a Heaving Surface Ship," Journal of Ship 32E. A. Wright, "Some International As- Research, The Society of Naval Architects andpects Of Ship Model Research," Journal of the Marine Engineers, April 1957. Amer. Soc. of Naval Engineers, February 1958.