New Research resources at the David Taylor Model Basin

AERODYNAMICS

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STRUCTURAL MECHAN ICS

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4 4 £ &l. A & by

Captain E.A. Wright, USN

RESEARCH AND DEVELOPMENT REPORT

HYDROMECHANICS NEW RESEARCH RESOURCES AT THE

DAVID TAYLOR MODEL BASIN

o

APPLIED MATHEMATICS

NEW RESEARCH RESOURCES AT THE DAVID TAYLOR MODEL BASIN

by

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

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 tow-point 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

wave-maker 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 con-tra-rotating propellers, and seakeeping and rotating-arm basins add new

dimen-sions 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 architecture

are often inaccessible without inspired

develop-ments in laboratory instrudevelop-ments and facilities.

Because technical knowledge is exploding radially,

laboratories are in contact with these frontiers on a rapidly increasing perimeter. The purposes of of this paper are (a) to describe briefly recent and forthcoming resources for research at the David Taylor Model Basin, and (b) to indicate thereby

some of the current pressure points on the

un-known. Rudder Flutter

Except for singing propellers,

hydrodynam-ically-excited flutter has fortunately been rare in

naval architecture. Indications are, however, I Commanding Officer and Director, David Taylor

Model Basin, Washington, D. C.

For presentation at the Spring Meeting, Old Point Com-fort, Va., June 2-3, 1958, of THE SOCIETY OF NAVAL

ARCHITECTS AND MARINE ENGINEERS.

that higher speeds and higher performance control

surfaces are already touching the fringes of this

phenomenon, for long well known and explored in aeronautics.

The considerable body of research in air is not fully applicable to naval design because of

differ-ences in the Strouhal number, Mach number, viscosity effects, cavitation, virtual mass, and

structural damping. Hence a comprehensive study is being made theoretically and

experi-mentally [1].2

Apparatus has been developed for exploratory

rudder flutter investigations under the 60-knot

towing carriage. A spade rudder supported by a

stiff shaft, Fig. 1, is free to rotate in a cage, in which torsion springs determine the natural

fre-quency in rotation. The cage is supported by

horizontal flexures from a frame bolted directly

I Numbers in brackets designate the References at the end of the paper.

Fig. I Control-surface flutter apparatus.3

to the structure of the towing carriage.

Not shown in the figure is a large surface plate which simulates the ship hull over the rudder.

As an essential condition for flutter is that the energy dissipated by the system must be equal to or less than the energy extracted from the flow, the former has been kept low in the design of this apparatus. The mass balance of the rotatable

system can be shifted relative to the rudder axis. A controllable eddy-current damper is provided

for both translational and rotational motion.

Metalectric strain gages transmit amplitude

sig-nals to recorders on the carriage. This equipment

was designed by Reed Research, Incorporated

[2], to DTMB basic specifications and built in the

Model Basin shops.

Rudder-Measuring System

A twin-rudder positioning control and

force-measuring system is now in use for maneuvering tests of surface ship models, Fig. 2.

All photographs are Official, U.S. Navy, unless other-wise credited.

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

rud-der 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 con-trol 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.

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, separates the various command signals, and dis-tributes them to the proper propulsion and

rud-der channels. Simultaneously, a telemetering

transmitter in the model is sending back data

which are displayed at the console as dial readings.

Thus the operator has continuous direct

indica-tions before him of the actual values of the quan-tities he is controlling by the radio link, and the

feel of the over-all system is the same as though he

were controlling through direct wire connections. The propulsion system in the model will

con-sist of 1 to 4 series d-c propulsion motors, powered

by I or 2 variable-voltage d-c generators in motor-generator sets, the m-g sets in turn being driven

by high-capacity nickel-cadmium batteries. Such a system, though seemingly elaborate, is necessary

to obtain the required fineness of speed control

and constancy of speed during a run, both to

better than i per cent.

The rudder control and force-measuring dy-namometer will be used in the model.

Addi-tional radio control and data-handling channels

from model to shore are provided for tailoring to the particular experiment.

Fig. 2 Rudder dynamometer for positioning and force measurements

Free-Running Submarine Models

Turning and maneuvering tests employing free-running dynamically-scaled models have become an essential part of the procedure for predicting the handling qualities of new submarines during the early design stages. This is especially true for submerged maneuvers in the horizontal plane

where, because of coupled motions and other

corn-plex effects, it may be difficult or cumbersome to evaluate performance by analytical methods.

The model is

equipped for remote control

through drop cords extending from the carriage boom down through a tube into the model, Fig. 4. The cable tube also carries lights which are pho-tographed to record the model path. The model

is run in a flooded condition and carries a

pro-pulsion motor, rudder-actuator mechanism,

stern-plane control mechanism, vertical gyro, horizontal

and rate gyros, and ballast and trim tanks. All

recording is done on the towing carriage.

The helmsman and stern-plane operators find they must be highly alert and practiced, because the time scale is compressed by the square root of the linear ratio of ship to model. Good

correla-tions have been obtained between prediccorrela-tions by

this technique and full-scale behavior.

12-Ft Submarine Pressure Tank

The increase in size, structural complexity, and versatility of modern submarines has led to still another submarine pressure tank in the series of

these facilities at Carderock. The latest

addi-tion will be 12 ft diam, more than 30 ft long, and

capable of applying pressures of over 1500 psi [3].

The new facility will be the largest tank in the

United States for liquid pressure tests of this

magnitude.

Submarine structural models weighing up to

25 tons are secured vertically in the tank to avoid gravity bending forces, and hydrostatic pressure

is applied to the exterior of the model, Fig. 5. Actually, oil is used as the pressure medium to

eliminate the need for waterproofing the 250 to 300 wire resistance strain gages used in each test.

The deflections of the model as the pressure is

increased are scanned by a probe, amplified me-chanically, and plotted automatically on a

turn-table. _{The deflector neter is removed prior to} collapse of the cylinder.

The 12-ft pressure tank was fabricated by the

Norfolk Naval Shipyard of steel with a yield

strength of 100,000 psi. The main tank body and lower ellipsoidal head weigh 56 tons and the

re-movable head 16 tons.

The site for the

Sub-marine Structures Facility

is adjacent to the

Underwater Explosions Test Pond and Air Blast Pits for dynamic investigations of hull structures,

Fig. 6.

40,000-Pound Vibration Generator

Through years

of development and

appli-cation, the David Taylor Model Basin has

ac-quired probably the most complete set of

vi-bration generators in existence, Table 1. These

Table i Vibration Generators at the David Taylor Modal Basin

Fig. 3 Console for radio control of maneuvering ship

models

machines are used to generate sinusoidal forces

and couples for the purpose of exciting flexural and

torsional vibration of ship hulls, machinery, and equipment [4].

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 sinu-soidal 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

struc-tures. A 3-mass 5000-Ib generator has been built

for submarine vibration studies; the machine and

its controls are designed to pass through

sub-marine 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

sinu-soidal 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

The ship-vibration electrical analog models the

flexural modes of

vibration and critical

fre-quencies of complex mechanical systems like ship

hulls and shipboard machinery assemblies 15]. Recently, this facility has been redesigned and re-built, Fig. 8.

An extensive array of passive electrical elements

MACMINE TUB MIDGET 440-LB

LOSONHAUSEN LAZAN BERNHARD TUB 5000-LB

1MO 3-MASS 5000-LB TUB 3-MASS 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 Not Applicable 9,400 8500 120,000 Overload Rating 16 2140 320 37,500 8500 120,000 Frequency Range, cpm 200-9400 300-3000 0-3400 75-3000 60-1500 50-2000 40-1200 Weight, lb 14 140 160 308 5,000 2000 12,500 Dirirensions,

L i W,< H, in. 9i,9l4,584 19i4x 15ko 10'îsv 1294,,11la6lb 2014o16 5349o25 63i 12 16 I086044

Voltage

Re ured OID AC 120 or 240 DC 110 AC 110 AC or DC

TUB Diesel Gen.

or 22O-440-60-3.

220 oC or 22O-44D-60».3

TUB Diesel Gen.

ai

22O-44D-6O 3. Power Regd,

watts 150 1000 DO 8000 30,000

Fig. 4 Free-running submarine model making a turn in the J-basin at Carderock

of resistance, capacitance, and inductance

repre-sents the mechanical equivalents of springs,

masses, and damping. Points of resonance and

various modes of vibration in different parts of the

network are easily determined by varying the

frequency of the alternating-current input. The

electrical analog has broad ability to solve coni-plex problems involving coupled bending, shear, sectional rotation, and torsion.

Vibration generators can be used to excite ship components during construction and so provide

observed vibratory characteristics for input. Typical problems are the critical frequencies of lateral vibration or whipping of a propeller-shaft

system, a prediction of hull vibration including

effects of entrained water, rotary inertia, bending, torsion, shear, and sprung niasses, and the longi-tudinal and torsional vibration of ship-propulsion

systems.

Thrust-Transient-Vibration Dynamometer

As companion techniques to the use of vibration

generators and vibration analogs, several methods

are available for measuring propeller exciting

forces on model scale. One such method is to

measure the transient-pressure fields on the model

hull and appendages in way of the propellers;

another is to cut the stern of the model free and

then to cancel the propeller excitation by small

vibration generators. The newest system at the Taylor Model Basin for measuring transient axial propeller forces depends upon a thrust transient

dynamorneter, Fig. 9.

The differential-reluctance type of transducer operates by flexing under load to increase one air gap and decrease another [6]. Thereby one

mag-netic circuit is weakened and the other strength-ened, resulting in a net output from the secondary

coils

proportional to the applied force.

The

thrust transient dynamotneter embodies this prin-ciple in a thrust transducer called a magnithrust. Annular slots are cut in an enlarged section of the

propeller shaft to form a compression spring. To keep the frequency response high, the flexure was

made very stiff; the natural frequency is 240 cps 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

amplifier in conjunction with a vibration analyzer.

The dynamometer is quite small, 1.12 in. diam by 4.5 in. long. It has served as the shaft strut

barrel of a large model, representing the nuclear-powered carrier Enterprise, to measure the thrust transients excited by the rudders (luring turning

maneuvers.

Bleed Line

Aper

Rnq

Oil Line To

Fig. 5 Diagram of submarine pressure tank showing

defiectometer in model

Transmission Dynamometers

Culminating a period of significant break-throughs in the design of ship model propulsion instruments, the DTMB transmission

dynamorn-eter is the latest addition to the family which

began with the pendulum reaction-type

dyna-mometer having a self-contained propulsion motor

[6]. Model propeller-shaft torque, thrust, and

revolutions are the basic variables measured. Transmission dynamometers are so-called

be-cause they are fitted into the shafts between the drive motors and the propellers. Sorne

advan-tages of this type are that their natural

fre-quency in thrust and torque is relatively high,

response is insensitive to model motions compared

to the pendulum type, propeller shafts may be

synchronized mechanically, slip rings are elimi-nated, small size and freedom from drive motor permit flexibility in location, and motors can be different types to simulate full-scale power-plant characteristics.

Basic elements are a torque transducer or

mag-nitorque, thrust transducer or magnithrust, and

revolution counter, Fig. 10. The differential-reluctance type of transducer for torque operates

by the same principle as the magnithrust

de-scribed under the thrust transient dynamometer.

The propeller shaft is necked-down and rings at-tached to produce a differential movement of air gaps in a circumferential direction. The revolu-tion counter is simply a copper disk with 10 radial

slots which pulse the induced voltage.

For contra-rotating propeller tests in models, a dynamometer has been designed to measure

thrust up to 50 lb, torque up to 50 lb-in., and rev-olutions 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 dy-namometer. 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

Developments in dynamometer transducers

and circuitry have made possible a large degree

of automation in

self-propulsion experiments.

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

instrument for pulses originating from (a) the slot-ted-disk shaft-revolution pickups in each of four propeller dynamometers for a 4-shaft ship model,

(b) an electromagnetic pulse generator on the

idler wheel of the towing carriage, and (c) a

pre-cision tuning-fork-controlled oscillator which

pro-duces timing pulses at the rate of 1000 per sec.

For the preselected time interval of the test, pulse

totals are accumulated in six 4-decade decimal

counting units, and translated if need be into pro-peller revolutions per second and carriage speed in feet per second.

During this same interval, thrust and torque

values from each of the four propeller shafts are recorded graphically or displayed on digital

indi-cators. At the end of the test interval the average

rps for each shaft, average carriage speed, time

duration of the run, and a sequential test number

are all automatically tabulated on an

adding-machine-type printer.

General-Purpose Digital Computers

The automatic handling and digitizing of model

test observations lead directly to reduction of

these data in general-purpose digital computers, Fig. 13. The Ship Powering Division in collab-oration with the Applied Mathematics Laboratory at the Model Basin has now programmed all

rou-tine calculations of effective horsepower, shaft

horsepower, and propeller characterizations,

markedly reducing the time and man-hours for

Fig. 6 12-ft submarine pressure tank arrives at facility site

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

Naval mathematics is, in fact, pervading naval

architecture on a wide front, particularly as a partner to the developments described in this

paper [7]. For example, general-purpose digital

computers are being used to calculate the

buck-ling strength of submarine models subjected to external pressure, the equations of motion for

emergency control of a damaged submarine,

Fig. 9 Thrust-vibration dynamometer for measuring

transient axial loads in model propeller shafts

Fig. 8 Ship-vibration electrical analog

critical frequencies of a planetary-gear

propul-sion system, power spectrum analysis of ocean-wave records and of ship model motions in irreg-ular seas, equilibrium configuration of a flexible cable in a uniform stream, boundary-layer devel-opment, inception of cavitation on bodies of

rev-olution, stress distributions in propeller blades, pressure distribution on propeller-shaft struts,

neutron-flux distributions in reactors, and

re-sponse of ship hulls to harmonic driving forces.

The Sperry Rand Corporation is developing

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

Fig. 11 Contra-rotating propeller dynamometer

Fig. 12 Recorders on the towing carriage for self-propulsion tests

for the Atomic Energy Commission and the

Bureau of Ships a general-purpose digital com-puter considerably faster and more versatile than

the two UNIVAC which have been the work-horses at Carderock. The large automatic re-search calculator (LARC) will operate at a speed of 100,000 multiplications per sec, and will have an internal memory of 30,000 words in the ma-chine planned for the Taylor Model Basin. It is a solid-state design with transistors and magnetic-core memory. LARC will be a two-headed

sys-tem; one computer does the staff work such as

automatic programming while the other computer proceeds with the main calculation without

inter-New Research Resources at DTMB 9

ruption. Many hitherto untouchable problems

in naval architecture will become possible when

LARC is added to the DTMB Applied

Mathe-matics Laboratory.

Propeller Boat

The purpose of the double-ended aluminum

propeller boat is to characterize single or

contra-rotating propellers in open water, Fig. 14.

The boat is supported from the floating girder

of either of the deep-water-basin towing carriages,

and the shaft centerline submerged to the desired

depth between 8 and 14 in. depending on the pro-peller diameter. Maximum test speed is 8 knots

Fig. 13 General purpose digital computers complement developments in ship-model facilities

and runs can be made in either or both directions.

One end of the boat is equipped with

contra-rotating shafts, the inner 3/ in. in diam and the

outer shaft l-in. diam. A single propeller can be tested on either outer or inner shaft. The other end of the boat is iltted with a single 3'-in. solid

shaft. Any DTMB propulsion dynamometer,

either pendulum or transmission type, can be used.

35-Horsepower Propeller Dynamometer

Supplementing the propeller boat, equipment is now available for open-water characterization of propellers up to about 20 in. diam and 35 hp. It was designed by the DTMB staff and built by the Norfolk Naval Shipyard.

The 35-hp propeller dynamometer consists of an underwater body housing a transmission-type dynamometer which measures torque, thrust and rpm of a test propeller [8]. The test propeller is

supported on a sting, well forward of the main

body to avoid interference, Fig. 15. This under-water assemblage is supported by struts from the

towing carriage over either the high-speed or

deep-water basins. The dynamometer drive motor is

located above water and drives through a

ver-tical shaft and right-angle gear box located in the

underwater body. The transmission

dynamom-eter employs differential transformers combined with elastic elements. Signals from the trans-ducer elements are handled through slip rings.

Readings are obtained by a manual null balancing system which may be supplemented by a

direct-writing oscillograph when dynamic conditions are

present.

Some principal characteristics are thrust 700

lb ahead to 200 lb astern, speed 2500 rpm maxi-mum, power 35 hp maximum from 1000 to 2500 rpm, weight 3000 lb complete, and depth of

sub-mergence 48 in. to centerline of propeller.

36-Inch Variable-Pressure Water Tunnel

The versatility of variable-pressure water

tunnels has been well established by the variety

of investigations over the past 15 years in the

DTMB 24-in, tunnel [0], but likewise the limi-tations in many directions have become apparent. It is anticipated that most of the limitations will be overcome in the 36-in, tunnel currently under construction, Fig. 16.

The new tunnel, Fig. 17, will have two

remov-able dynamometer shafts, one from each direction,

so that either the upstream or downstream shaft can be used, or both in the case of contra-rotating

propellers [10]. Pressure in the test section will

be variable from 2 to 60 psi absolute, and the water

velocity up to a maximum of 50 knots. Both

closed-jet and open-jet test sections will be

pro-vided, and it is anticipated that propellers up to 24 in. diam can be tested in the latter, Fig. 18.

Test-section conditions were explored on a 6-in.

pilot model by the St. Anthony Falls Hydraulic

LabQratory [Il].

Every effort is being made to achieve a low

am-bient noise level for experiments involving the

Fig. 14 Double-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

re-turn to the test section.

To provide pressure as well as time for this process, the resorber ex-tends 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 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 national defense by providing a large precision instrument able to tow full-scale weapon, minesweeping and anti-submarine devices that developed loads on the carriages and rails of thousands of pounds.

To extend full-scale testing of these defense

developments to higher speeds, a 60-knot towing

Fig. 15 35-hp open-water propeller dynamorneter

carriage was designed and the high-speed basin was extended from 1168 to 2968 ft on the water,

Fig. 20. A further requirement was that the

facility have a low noise level for acoustic experi-ments. The carriage is driven by 12 d-c niotors, weighing 1300 lb apiece and rated at 400 hp each for short duration, with their armatures connected

Fig. 16 Building to house 36-in, variable-pressure water tunnel

Oynarnorneter

Shaft 1000 SHP

3-d'lo. l6"I.D.

Open - Jet Test Section 9,-0,,

o ID.

Honey

arid Screens Contraction _e'-oLO. Diffuser

in series to equalize loads. Speed is controlled by

an automatic feedback system to plus or minus 0.03-knot over the range.

Acceleration with steel tires requires more

trac-tive effort than could be obtained by gravity

loading alone, and so side drivers squeezing the

682" Resorber 25' 01.0. Bed Rack Propeller Pump 2887 SHP Oynarnometer Shaft 000 SHP

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

circuit

rail head are used in this arrangement. Presently

the 16 drive wheels are fitted with rubber tires

having steel cords and inflated with water to 280

psi; their greater coefficient of friction is sufficient

for acceleration without side drivers. Normal

Fig. 18 Open-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 re-moved 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,

hydro-foils, and parachutes.

Auxiliary Towing Carriage

When ships are maneuvering in close proximity,

such as in replenishment-at-sea operations,

com-plex interaction forces are created. To study

such effects systematically, it was necessary to design an auxiliary carriage to tow two models alongside each other at various relative speeds,

Courtesy Washington Evening Sta,

Fig. 19 View from research pit looking skyward

distances apart, yaw angles and rudder positions,

and to measure the forces between them [14].

The box-shaped auxiliary towing carriage is

mounted on rollers which ride along two machined

Fig. 20 60-knot towing carriage wich rubber-tired wheels

aluminum I-beams attached to the underside of a main towing carriage. The line of motion of the

two models can be adjusted up to 10 ft

trans-versely. A motor-powered cable provides up to

2 knots relative speed of the auxiliary carriage. Provision is made to yaw the model. Various

rudder angles can be used to determine

equilib-ritmi conditions at different positions, speeds

over-the-ground, and relative speeds of the two

models, Fig. 21.

Interaction forces are measured by modular

block gages of the variable reluctance type with

capacities of 50, 100 and 300 pounds. Three

gages are attached to the dynamometer beam,

two at the forward towpoint and one at the after

towpoint, to measure drag and side forces. A

sum-and-difference network is used to convert the

side forces into moments about the center of

gravity of the model.

Restricted-Channel Instrumentation

An interaction dynamometer of the type used in measuring forces between two ship models is

employed also in measuring drag and yawing

forces on models in restricted channels.

On tests of supertankers in a channel simulating

the narrow portion of Gaillard cut in the Panama

Canal, the yaw angles and rudder angles necessary

to obtain equilibrium have been measured as a

function of distance from the channel wall [15].

Tugboat forces necessary to check the swing of the

model when it sheers across the channel are also

measured.

For the Panama Canal tests, a special

plat-form was suspended below the towing carriage, and the floor of the high-speed basin used as the channel bottom, Fig. 22. The box girder

carry-ing the model could be positioned transversely

or angularly, and the outputs from the three

variable-reluctance gages carried to recorders on

the platform. Rudder-angle settings and

pro-peller rpm were controlled remotely from the re-cording area. Trim and sinkage were measured by multiplying pulleys to indicating scales.

Miniature Model Basin

A model basin only 57 ft long overall and with a 2-ft square cross section has been built for fun-damental hydromechanics research, particularly the dynamics of geometrical forms. It has been

used, for example, to study the forces on bodies of revolution in waves, to observe the action of hydrofoils with and without wave action, and to measure the fluctuating lift and drag forces acting on a cylinder moving in a stream [16].

The tank has a pneumatic wavemaker at the

far end, and a beach at the near end, Fig. 23. At mid-length, 10-ft glass panels in the bottom and sides permit lighting and viewing the flow

con-ditions.

The miniature towing carriage is driven by an endless cable in continuous speed variations from

0.5 to 9.0 fps. The drive system is equipped with

an electromagnetic brake actuated by a track

trip; in event of failure, the carriage is arrested

Fig. 21 _{A small model under an auxiliary towing carriage maneuvers alongside a large model}

measured by a 30-ft brass speed bar fitted with

insulated plugs. Interruptions of current through a point contactor travelling along the bar permit

speed measurements to an accuracy of ± 0.001

fps. Guide wheels limit the side movement of

the carriage to 0.003 in.

Carriage equipment includes a mechanical

oscil-lator for driving a model in a vertical plane, tow-points on both the forward and after sides of the carriage, and a dynamometer for loads up to 60

lb drag and 250 lb lift. Power to the carriage equipment and readings from the carriage in-strunients are brought in and out by overhead

cables.

Electrolytic Tank

The David Taylor Model Basin, like a number of other hydrodynamic laboratories, found need

for an electrolytic tank to study the potential

flow patterns about two and three-dimensional

bodies [17]. Either a dielectric model

represent-ing the hydrodynamic body is placed in a

semicon-ducting medium so that streamlines correspond to

lines of constant electric flux and equipotential

lines correspond to lines of constant electric po-tential, or a conducting model is placed in a

di-electric medium and the correspondence is reversed.

The tank is steel and is lined with a wax com-pound to inside dimensions of 28 by 46 in. on the bottom;

it may be filled to a depth of 15 in.

Heavy copper electrodes are available for the tank

sides. The probe for exploring the electric field

is carried either on the arm of a pantograph or on

a small carriage, Fig. 24. Double probes are

use-ful in obtaining the pressure and velocity field

away from a body. Precise alignment of the

con-ducting surfaces,

tank boundaries and probe

movement is essential. Model tolerances must

be held to a few thousandths of an inch, and

dielectric models machined out of plastic material.

Low-Turbulence Wind Tunnel

For the investigation of turbulent boundary

layer and wake phenomena related to problems of hydrodynamic noise and frictional resistance,

a wind tunnel has been constructed with low

initial intensity of turbulence

[18]. A

tur-bulence level of about 0.1 per cent is achieved primarily by making the tunnel an open-return

type, by the use of 6 turbulence damping screens

in the settling chamber, and by a contraction

ratio of 12.5:1.

The closed test section is rectangular in cross section, 4 ft high and nominally 2 ft wide. Both

test-section side walls are constructed of flexible sheet steel and can be adjusted so that the section width can be continuously varied from 1 to 3 ft.

In this way a large variety of axial pressure

gradients can be obtained. The position of each side wall is individually controlled by 28

adjust-ing screws, Fig. 25.

A maximum velocity of approximately 140 fps

is obtained in the test section. The air flow is created by an 8-bladed wooden fan, 6 ft diam, located downstream of an 18-ft-long diffuser.

The fan is driven by a direct-coupled 60-hp motor whose speed is

continuously variable up to

1800 rpm.

Transonic Wind Tunnel

Flexible use of aerodynamics facilities for hy-dromechanics research and vice versa has been

a tradition since Rear Admiral Taylor married wind tunnels and towing tanks in 1914. For example, submarine models and underwater cable fairings are tested in wind tunnels, parachutes in a model basin, and stack smoke flow in a circulat-ing water channel.

Fig. 22 Panama Canal tests of a supertanker model

The newest addition to the DTMB

aerody-namics facilities is a transonic wind tunnel with a test section 10 ft wide and 7 ft high. Reynolds

numbers up to 1.2 x 108 can be obtained on a

20-ft submarine model.

The transonic tunnel is a closed-circuit,

single-return type with a contraction ratio of 14.4 to 1

and a diffuser angle of about 3 deg, Fig. 26.

It

is constructed of reinforced concrete, except for

the high-velocity portions which are made of

machined steel. The tunnel is designed to oper-ate over a Mach-number range of approximoper-ately 0.3 to 1.2, and at test section pressures between 0.25 and 1.75 atm. There are two contra-rotat-ing propellers, each driven by a 12,000-hp

con-stant-speed electric motor through a

variable-speed coupling. A continuously operating

desic-cant-type air dryer is capable of maintaining a

dewpoint of - 15° F. A finned-tube radiator in the third corner of the tunnel, combined with a cool-ing tower, is used to control the air temperature. At a flow of 14,000 gal of cooling water per mm,

the stagnation temperature can be maintained

In the test section, Fig. 27, longitudinal slots in the floor and overhead are proportioned to

eliminate choking and to

reduce 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 gradients in the flow field 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

re-corded 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 gases from the stacks of passenger and naval ships.

Fig. 23 Minature model basin and towing carriage

17

Fig. 24 Electrolytic tank, fitted with cross beams and

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

Fig. 26 View looking downstream in the transonic wind tunnel

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

de-sired 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 test

velocities, 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

making towing models at the U.S. Experimental Model Basin and the David Taylor Model Basin,

because the low-temperature soft paraffin wax

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

months in the Washington area. With the

gen-eral development of synthetic products, it has now been possible to develop a suitable

high-temperature hard-wax composition. While the

blending and casting techniques are more com-plicated than foreign methods, considerable

sav-ings in time and cost have been effected (21]. The wax blend developed consists of 30 per

cent refined paraffin, 32.5 per cent hydrogenated castor oil, and 37.5 per cent n-butyl methacrylate.

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

Entirely satisfactory models up to 30 ft in length have been constructed, Fig. 29. Hogging wires

are usually fitted for models 20 ft and longer.

About 95 per cent of the wax can be salvaged and

reused; savings in construction compared to a standard 20-ft wood model are in the order of

20 man-days productive effort and 2 weeks' time.

Wood models continue to be used widely for such applications _{as maneuvering, seakeeping, and}

submerged models, as well as for final designs.

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

Substantial progress is being made in the use of fiberglass reinforced plastics for model construc-tion, Fig. 30. The higher strengths and thinner skin of fiberglass provides additional weight and space for propulsion equipment and instrumenta-tion, a particular advantage in subsurface models. Fiberglass laminates are being used also for

air-craft models because of the favorable

strength-to-weight ratio compared to wood. This mate-rial is bridging the wide gap that existed between

wood and metal in model construction, both in

regard to cost and physical properties.

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

Planar-Motion-Mechanism System

The hvdrodynamic-stability derivatives in all

six degrees of freedom of deeply submerged models

can be determined by the planar motion

niecha-nism system 122]. Models varying in length from

9 to 23 ft are supported by two struts in tandem, Fig. 31. Force components are measured at each

strut by internal force balances. These balances are individual flexure boxes employing

variable-reluctance displacement gages as transducers.

Static forces and moments associated with hull angles are measured by remotely rotating the tilt

Fig. 31 Planar motion mechanism with subsurface model attached

Fig. 32 Analog computer array for simulating motions and trajectories

Fig. 33 Heaving towpoint facility attached co side of

towing carriage

table carrying the entire model-strut system. The force-balance signals from such tests are recorded by servo-null-balance type of digital indicators.

The data are tabulated automatically by an

electric typewriter.

Dynamic forces and moments are obtained by

oscillating the model in heave with the struts

moving up and down in unison, and then by

oscillating in pitch with the struts moving out of

phase. The sinusoidal signals measured by the

force balances during the oscillation runs are

electronically resolved, rectified, integrated and

recorded, saving many man-months of data

re-duction [23]. Linear acceleration coefficients are

determined by accelerating the towing carriage.

A related apparatus is the pitch and heave

oscillator, designed primarily for determining

experimentally the coefficients for the equations

of mction of a ship in a seaway [24]. Surface

ship models up to 12 ft in length are towed at

constant speed and forced to perform sinusoidal

heaving or pitching oscillations. Amplitudes, forces, amI phase relations are measured.

Simulator Facilities

Studies are made in the simulator facilities of

the stability, control aoci stabilization of sub-marines, surface ships, torpedoes and missiles.

Design variations 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

com-puters used to solve linear and nonlinear

dif-ferential 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

avail-able 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

shown on the instruments in front of the operator, and the cab rotates to the computed pitch angle. The joy stick is moved again to perform the

de-sired maneuver and the cycle repeats.

Mean-while a graphical record of the submarine path is obtained automatically on a plotting board.

Heaving Towpoint

Laboratory experiments to predict full-scale

behavior nearly always involve decisions whether certain variables can be neglected. When a

sub-merged body is towed from a ship, it was suspected

that the ship motions had an appreciable effect

on the behavior of the body, particularly when the

towpoint passed over the ship's stern. To

in-vestigate such effects, a facility was designed to vary methodically the vertical position of a

towpoint [26].

The heaving towpoint facility is attached to an 18-knot towing carriage near the centerline of the deep-water basin, Fig. 33. The towpoint oscil-lates vertically either in a sinusoidal motion with

double-amplitude variable from O to 10 ft and

period from 3 sec to infinity, or in a single-step

function. The maximum loading on the towpoint

side force. The track is readily demountable to avoid interference with other tests.

Pneumatic Wavemaker

Waves in the open ocean have been found to

have a frequency spectrum which varies depending

upon the sea state. For modern studies of sea-keeping in the laboratory, it is necessary to have wavemakers that can be programmed to produce

model seas of this character. The pneumatic

principle of wave generation, first applied at the California Institute of Technology and Lausanne

University in France, is highly suitable for

fre-quency shifting because of the low inertia of the

moving parts.

Development at Carderock began in the

2-ft-wide towing tank, continued in the 10-ft-2-ft-wide

tank, and culminated in the 51-ft-wide

deep-water basin, Fig. 34. Waves are produced by

oscillating the air pressure from positive to nega-tive in a plenum chamber which embraces a strip of the water surface [27]. Wave length is con-trolled by the frequency of shifting valves from pressure to suction, and wave height is varied by adjusting blower speed. Regular waves 5 to 40 ft long and 4 to 24 iti. high can be generated, and are fully stabilized within a travel down the basin of less than 75 ft.

As conventional model basins with wavemakers

permit tests only in long-crested head and

follow-ing seas, a seakeepfollow-ing basin has been designed and

Fig. 34 Pneumatic wavemaker for the deep.water basin

is under construction to provide complex seas

from any relative direction [28].

In the 3'0-scale model of this facility, Fig. 35, pneumatic wavemakers of the type developed for the deep-water basin are arranged in banks of 8

along one end and 13 along an adjacent side.

Short crested seas will be generated not only by intersecting wave trains from the two banks, but also by intersecting circular trains generated by individual wavemakers acting as a point source

[29]. Highly absorbent beaches, developed in

collaboration with the St. Anthony Falls Hydrau-lic Laboratory [30], line the opposite tank sides.

One beach is masked when it is desired to produce

regular or irregular waves in only one direction. The full-scale seakeeping and maneuvering

basin [31] will be 360 ft long by 240 ft wide, Fig.

36. Spanning the basin will be a 376-foot steel bridge weighing about 230 tons, Fig. 37.

Run-ning on the underside of the bridge will be a

car-riage for test personnel and instruments, and to

tow or guide captive models with limited degrees of freedom. The carriage will be a

welded-alumi-num, tubular truss structure, supported and

guided by steel wheels, and driven through

rubber-tired wheels preloaded against the vertical faces of a traction rail. _{Acceleration rates up to 0.4 g} can be obtained thereby and maximum speeds of 15 knots. The bridge will be positionable from

o to 45 deg to the long axis of the basin which, coupled with a 90-deg choice of wavemakers,

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

will permit the carriage to run under the bridge

at any angle relative to a wave system.

Basin depth will be 20 ft generally, except for a trench 50 ft wide and 35 ft deep adjacent to the

beach on the long side. In this deep portion, it is

planned to operate free-running submarine models

and to observe their behavior through a series of

underwater windows in the basin wall. Loop

filling and draining connections have been made

to the existing 3,000,000-gal per day filtration plant to provide suitable conditions for

under-water photography.

Rotating-Arm Basin

Housed under the same 695-ft by 373-ft

column-free roof as the seakeeping and maneuvering

basin will be a rotating-arm basin, Fig. 38. The

two facilities will be functionally independent of each other except for certain supporting services

[31 J.

Rotary coefficients for the differential equations of motion of surface ships and submarines are best

obtained in a rotating-arm basin designed for the

purpose. Here constrained models are towed in

circular paths of different radii and the resultant

forces and moments measured at different drift

angles. The need for experimental observations of this nature to analyze and predict directional stability and control has been recognized in

ter-nationally by the construction of 7 rotating-arm basins in different countries [32].

The DTMB rotating arm basin will be 260 ft

diam and 21 ft deep. The arm will pivot iii the center of the basin on tapered roller bearings de-signed for a centrifugal force of 145,000 lb, and will be supported by and driven from a peripheral track. The rotating arm is a tubular aluminum

structure, Fig. 39, weighing about 37,500 lb and having natural frequencies in the vertical,

hori-zontal and torsional modes exceeding 3 cps. The drive system is designed to accelerate the arm to 30 knots at the 120-ft radius in half a revolution. Thereby surface ships models can be brought up to speed and readings taken before meeting their

own wake. Traction is through two 30-in, steel

wheels preloaded against the track surface to a

normal force of over 60,000 lb per wheel, and di-rect connected to 400-hp motors capable of 230

per cent overload during acceleration. A

con-trol console will be located on the inner bay of the rotating arm near the island pivot.

The models will be attached to a towing

car-riage which can be positioned remotely on the

underside of the rotating arm at any radius from

about 12 to 120 ft. Surface-ship models will be

attached to a beam, and submerged models to struts supported by a yaw table. A balance will measure concurrently the forces and moments

Fin. Grade Approximate Surface Top of Rock D E D

Carriage Ç_ Bottom Chord

Stop

about 3 axes. A drydock 26 ft long by 16 ft

wide and 18 ft deep, supported by rails on the

basin floor, will be movable to carry subsurface

models out under the rotating arm, to attach

them at any desired radius, and to make model

changes and adjustments between tests.

Both the rotating-arm basin and maneuvering

basin are still in the heavy construction stage,

Fig. 40, proceeding toward a tentative completion

date of late calendar 1959. It is hoped that these

important facilities for ship research will be in

operation by the time of the 1960 Spring Meeting of this Society, presently planned for the

Wash-ington area. Conclusions

These developments in facilities and

instrumen-tation at the David Taylor Model Basin are

in-dicative of several trends in ship research:

(a) The laboratory approach to problems of

Ç_Bridge Ç_Top Chord Elevation

-I

#=

₌₁

Stop Plan

Fig. 36 Plan and elevation of the seakeeping and maneuvering basin

Bridge in Extreme"\

Rotational Position

Ali. II

-

376-O"

-Drive Arresting Engine

(Ç_Pivots)

Truck Platform \ Electrical Equip.Platform

Submarine Trench Water Depth 35-O"\ Bridge in Extreme Transverse _{Ç_ Bridge}

PsThon Ill to il Ç_Track Stop Control Platform

ship design has become highly imfettered and

attack is from many different directions.

The wisdom of building functional test

facilities for seen and unseen future demands has

been reaffirmed strongly.

Theories are more often reflected in ex-periments, which are planned either to make spot

checks or to provide coefficients.

Motions and maneuvers of free bodies are studied widely in six deg of freedom.

Dynamic experiments have become the rule, markedly increasing the scope and

versa-tility of model testing.

Model size varies throughout the range

from very small to full scale.

Analog computers permit modeling elec-trically a broad diversity of problems in ship

de-sign.

Automation of routine model experiments, 25

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

both the data taking and data reduction, is

in-creasing rapidly.

Digital computers are opening hitherto

un-touchable fields of analysis and mathematical

modeling.

Continued miniaturization of instrumen-tation will lead to further applications in model

experiments.

Versatile and accurate differential

reluc-tance transducers and strain-gage flexures arc

revolutionizing the design of dynamometers, both transient and steady state.

(i) Research in underwater acoustics exerts

a broad and rapidly growing influence on facilities

and instrumentation.

Seakeeping theory and experiment are

bringing into the laboratory all the complex hut

orderly environment of surface mariners.

No longer is the aeronautical industry

more forward looking or acting in research than

our own profession.

Substantial savings in cost,

time, and

engineering manpower have been effected by

electronic data handling, reduction and analysis,

by wax-model developments, and by modular

design of dynamometers.

This paper has dealt only with new physical

resources. Human resources remain the most

im-portant asset of the David Taylor Model Basin.

Fig. 39 Aluminum truss rotating arm under construction

Together they create a sound and productive

pattern for research in naval architecture. Acknowledgment

Many individuals in all laboratories and

depart-ments of the David Taylor Model Basin con-tributed to the developments described in this

paper.

References

i

R. T. McGoldrick and D. A. Jewell, "A

Control Surface Flutter Study in the Field of

Naval Architecture,' DTMB Report 1222 in

preparation.

2 Reed Research, Inc., "Design Calculations

for Rudder Vibration Test Gear,' Project

RR-1097, February 1957.

3 M. E. Lunchick, "A New Facility for the

Structural Testing Of Submarine Models," Society

of Experimental Stress Analysis, Washington

Area Section, May 1958.

4 Q. R. Robinson, "Vibration Machines at the David W. Taylor Model Basin," DTMB Report

821, July 1952.

5 Edward Kapiloff, "Calculation Of Normal

Modes and Natural Frequencies Of Ship Hulls

by Means of the Electrical Analog," DTMB

Report 742, July 1954.

6

G. J. Norman, M. W. Wilson, and F. B.

w

r.1.v

:i

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

Bryant, "Propeller Dynamometer 1 nstrumen-tation at the David Taylor Model Basin," DTMB

Report 1068, July 1956.

7 E. A. Wright, "Naval Mathematics At The

David Taylor Model Basin," Journal of the

American Society of Naval Engineers, May 1957. S

G. L. Santore, "Dynamic Calibration of

35-HP Propeller Dynamometer," DTMB Report 805, February 1952.

9

A. G. Mumma,

'The Variable-Pressure

Water Tunnels at the David W. Taylor Model

Basin," Trans. SNAME, 1941.

10

W. F.

Brownell, "A 36-Inch Variable Pressure Water Tunnel," DTMB Report 1052,

June 1956.

11 R. M. Olson, "Model Studies Of a Water

Tunnel with

an Air-Bubble Resorber," St.

Anthony Falls Hydraulic Laboratory, University of Minnesota, Project Report 29, February 1952.

12 H. E. Saunders, "The David W. Taylor Model Basin, Parts 1, 2, and 3," Trans. SNAME,

1938, 1940, and 1941.

13 G. A. De Shazer, . 'An Arc Welded

High-Speed Model-Towing Carriage,"

Design-for-Progress Award Program, James F.

Lincoln

Arc Welding Foundation, June 1947.

14 C. G. Moody, "Interaction Between Ships During Replenishment-at-Sea Operations," DTMB Report in preparation.

15 C. G.Moody, "Restricted Channel Effects in Panama Canal Cuts," DTMB Report in prepa-ration.

16 M. S. Macovsky, "Vortex Induced Vibra-tion Studies," DTMB Report 1190 in

prepara-tion.

17 A. Borden, G. L. Shelton, Jr., and W. E. Ball, Jr., "An Electrolytic Tank Developed For Obtaining Velocity and Pressure Distributions

About Hydrodynamic Forms," DTMB Report

824, April 1953.

18 R. D. Cooper and M. P. Tulin, "Descrip-tion of Low Turbulence Wind Tunnel," DTMB Report in preparation.

19

H. E. Saunders, C. W. Hubbard, "The

Circulating Water Channel of the David W.

Taylor Model Basin," Trans. SNAME, 1944.

20 P. C. Pien, N. L. Ficken, and A. L. Real,

"Smoke Ejection Tests for LSD 28 Class

Resented by Model 4552," DTMB Report in

pre-paration.

21 _J.

B. Hadler and W. B.

_Hinterthan,

"Wax Model Construction At The David W.

Taylor Model Basin," DTMB Report 930, June

1955.

22.

M. Gertler and A. Goodman,

"Experi-mental Techniques and Procedures Used at the

David Taylor Model Basin to Determine

Hydro-dynamic Stability and Control Coefficients of Submerged Bodies," DTMB Report in

prepa-ration.

23 R. G. Tuckerman, "A Phase Component Measurement System," DTMB Report 1139 in

preparation.

24 _{P. Golovato, "The Forces and Moments}

on a Heaving Surface Ship," Journal of Ship

Research, The Society of Naval Architects and

Marine Engineers, April 1957.

25 D. L. Greenberg, "Submarine Simulation

Facility at the David Taylor Model Basin,"

DTMB Report in preparation.

26 S. M. Y. Lum and C. O. Walton, "A Com-parison of Pitch Measurements on an Oscillating Towed Body Using a Vertical Gyro and a

Pen-dulum Indicator," DTMB Report 1153, July

1957.

27 W. F. Brownell, W. L. Asling and W.

Marks, "A 51-Foot Pneumatic Wavemaker and

Wave Absorber," DTMB Report 1054, August

1956.

28

F. H. Todd, "On A New Facility For

Testing Ship Models In Waves," Symposium On The Behavior of Ships In A Seaway, Netherlands

Ship Model Basin, September 1957.

29 W. Marks, "On The Status Of Complex

Wave Generation In Model Tanks," DTMB

Re-port 1069, July 1956.

30 J. B. Herbich, "Experimental Studies of

Wave Filters And Absorbers," St. Anthony Falls Hydraulic Laboratory, University of Minnesota, Project Report 44, January 1956.

31

W. F. Brownell, "A Rotating Arm and

Maneuvering Basin," DTMB Report 1053, July

1956.

32

E. A. Wright, "Some International

As-pects Of Ship Model Research," Journal of the

Amer. Soc. of Naval Engineers, February 1958.