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AN UNMANNED SYSTEM FOR

RECORDING STRESSESAND

ACCELERATIONS ON SHIPS AT SEA

SSC-150

BY

D. J. FRITCH AND F. C. BAILEY

,

SHIP STRUCTURE COMMITTEE

Distribdecl by

U.S. DEPARTMENT OF COMMERCE

OFFICE OF TECHNICAL SERVICES

WAFJ-!INGTON 25, D. C.

-. .—

SHIP STRUCTURE C(3MMlTTEE

MEMBER AGENCIES:

❑ UREAU OF SHIPS, DEPT. OF NAVY

MlL17ARy SEA TRANSPORTATION SERVICE, DEPT. OF NAVY

UNITED STATES COAE.T GUARD, TREASURY DEPT

MARITIME ADMINISTRATION, DEPT. OF COMMERCE

AMERICAN BUREAU OF SHIPPING

ADDRESS CORRESPONDENCE To:

SECRETARY

SH:F STRUCTURE COMMITTEE

U. S COAST GUARD 7-HEADQUARTERS

WASHINGTON 25, D, c,

3 June 1963

Dear Sir:

One of the most critical needs in ship des!g-1 is to learn the

actual long-term stress history of ships . The Ship Structure Com-

mittee is currently sponsoring a project at Lessens and As socitites,

Inc., that is measuring the vertical bending moments on ocean-going

ships. The ~nitlal phase of this study Involved the development and

performance testing of the data re cording system.

Herewith is a copy of the first progress report, SSC-1 50, &

Unmanned System for Reco~dinq Stres -and Acce ierations on Ships

at Sea by D. J. Fritch and F. C. Bailey.

The project was conducted under the advisory guidance of

the Committee on Ship Structural Design of the Niational Academy of

Sciences-National Research Council.

Please address any comments

Secretary, Ship Structure Committee.

concerning this report to the

Sincerely yours,

F . J. Fabik

Rear Admiral, U. S. Coast Guard

Chairman, Ship Structure

Committee

Serial No. SSC-150

First Progress Reporton

Project SR-153

to the

SHIP STRUCTURE COMMITTEE

on

AN UNMANNED SYSTEM FOR RECORDINGSTRESSES AND ACCELERATIONS ON SHIPS AT SEA

by

D. J. Fritch and F. C. BaileyLessens and Associates, IrIc.

under

Bureau of ShipsDepartment of the NavyContract NOhs-77139

transmitted through

Committee on Ship Structural DesignDivision of Engineering and Industrial Research

National Academy of Sciences-National Research Council

under

Department of the NavyBureau of Ships Contract NObs-84321

Washington, D. C.U. S. Department of Commerce, Office of Technical Services

3 June 1963

-..

ABSTRACT

In order to obtain long-term statistical data on wave-induced

bending moments, two dry-cargo ships have been equipped with stress

transducers and automatic magnetic–tape recording instrumentation.

One of these ships has also been equipped with accelerometers to

provide information on seaway-induced loads on cargo. The trans-

ducers and their installation are described, as well as the data con-

ditioning units, the tape recorder, and the programmer which allows

sampling of the data at pre– se lected intervals and continuous record-

ing when pre-set stress levels are exceeded.

The system has performed beyond expectation; data have been

obtained on 36 round-trip voyages representing almost three ship-

years of operation. Versatility of the unit in handling a variety of

data inputs and adapting to various data reduction methods has been

demonstrated. In addition, the data tapes are available for future

analysis in a broad spectrum of naval design applications. Experi-

ence gained to date will permit future installations to be handled

expeditiously and at minimum expense, with a high degree of relia-

bility of the unit assured in service.

CONTENTS

E!9E

1INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . .

BASIC SYSTEM REQUIREMENTS AND COMPARISON WITHEXISTING DEVICES . . . . .

General . . . . . . . . . . . .Previous Work . . . . . . . .Basis for Selection of Tape

DESCRIPTION OF SYSTEM . . . . . . .

General . . . . . . . . . . . .

. . . . . . ● ✎ ✎ ✎ ✎ ✎ ✎ ✎ ✎ 1

12

3

. . . . . . . . . . . . . . .

. . . . . .

Recorder. . . . . . . . .

System . . . .

6. . . . . . . . . . . . . . .

69

121314

. . . . . . . . . . . . . . .

Transducers and Data Conditioning Units . . . . .Recording System . . . . . . . . . . . . . . . . . . . .Program ming Unit . . . . . . . . . . . . . . . . . . . .Auxiliarie s . . . . . . . . . . . . . . . . . . . . . . . .

PERFORMANCE OF EQUIPMENT . . . . . . . . . . . . . . . . . . . 16

1617

GeneralBending

. . . . . . . . . . . . . . . . . . . . . . . . . . .

Moment Calibration . . . . . . . . . . . . .

CONCLUDING REMARKS . . . . . . . . . . . . . . . . . . . . . . . 17

18ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . .

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

A. Project 22: Statistical Studies of SeawayLoads Aboard Ship . . . . . . . . . . . . . . .

B. Detailed Specifications on System Corn -ponents . . . . . . . . . . . . . . . . . . . . . .

19

20

SR-153 PROJECT ADVISORY COMMITTEE

“Ship Response Statistics”

for the

COMMITTEE ON SHIP STRUCTURAL DESIGN

Chairman:

C. O. DohrenwendRensselaer Pol~echnic Institute

Members:

J. P. Den HartogMassachusetts Institute of Technology

N. H. JasperU. S. Naval Mine Defense Laboratory

E. V. LewisWebb Institute of Naval Architecture

R. L. McDougalLockheed Aircraft Corp.

Wilbur MarksOceanics, Inc.

INTRODUCTION

The rational design of ship structures mustbe based on knowledge of the magnitudes andcombined effects of the loads to which the shipis subjected in service. Some of these loadsarise from locked-in stresses, diurnal tempera-ture variations, local heating or cobling, s“till-water cargo loadlng, low–frequency wav~-bending load, slamming, and local vibratoryeffects. Rather than attempt a simultaneousstudy of the combined effects of all of the a-bove loads, and because of the statisticalnature of some of them, it is most convenientto investigate each type of loading in detailand then establish the effects of combinedloadings.

This project deals specifically with thedetermination of low-frequency wave-bendingloads . The approach is aimed at establishinginformation on max~mum attainable wave-induced bending moments for various types ofships operating on a number of routes. Thisimmediate ly implies a comparatively “ longrange” program. By contrast, one could ap-proach the problem by simultaneously studyinga larger number of variables such as bendingmoment loads, wave proportions, cargo load-ing, speed and ship motions on extensivelyinstrumented ships. Problems of instrumenta-tion and data reduction dictate that studies ofthis type be “ short range” in nature, and ofva he primarily in establishing interrelationsbetween the recorded parameters as opposed toestablishing knowledge of the probable rangeof, say, bending moment, under most opsrat-ing conditions.

In all structural response studies, it isdesirable to obtain simultaneous informationon cause and effect. Using the full-scaleship as a moving instrument platform, as wellas the structure under investigation, it is quiteconvenient to measure seaway loads in termsof their effect on the ship, but quite difficu It,as yet, to simultaneously determine the en-viro nme nt. Consequently, information of valuecan be obtained, but an important link in proto-type ship structural research still is missing.

The present objective of this project is:

“To obtain statistical records of verticallongitudinal wave bending momenEs experiencedby various types of ships operating on differ-ent trade routes, with the emphasis being

placed on extreme values of external loads.The purpose is to provide information for (a)the direct use of the ship designer, and (b) totest methods of predicting bending moments. “This is based largely on the recommendationfor a project on “Statistical Studies of Seawaybads Aboard Ship, “ which was made in thereport edited by Professors E. V. Lewis andG. Gerard and entitled A Lonq-Ranqe ResearchPioqram in Ship Structural Design. 1 The com-plete recommendation is reproduced in Appen-dix A.

After Project SR-153 had been active forsome time, the Army Transportation Corps(ATC) expressed interest in the program as itmight relate to a study of loads imposed ondelicate cargo as a result of seaway-inducedaccelerations. Although the interest of ATCwas directed at completing a broad survey ofcargo loads encountered in all modes of trans-portation, and consequently had little or nokearing on the initial objectives of the ShipStructure Committee program, it became ap-parent that substantial economies would beeffected by sharing of recording and data re-duc~ion systems.

This report will describe the instrumenta-tion systems developed, and in use, to obtainbending moment and acceleration data. Thebasic recording systems have now accumulatedalmost three ship-years of operating time, andsome manual data analysis has been under-taken. The theoretical and practical aspectsof the data reduction and analysis, and pre-liminary results, will be discussed in subse-quent reparts.

BASIC SYSTEM REQUIREMENTS

Genera 1

At the time this project was initiated,several Investigations had been completed, orwere under way, ‘2 -4 which required instrumen-tation of the general type needed for thisstudy. It was essential, therefore, that de-cisions regarding choice of system be basedon a clear understanding of the capabilitiessof existing instrument designs. Any proposedsystem had to ba assessed in the light of theanticipated complexity, and inherent flexibi 1-ity, of data reduction and analysis systems(external to the recording system) which couldbe utilized. This evaluation was complicatedby the fact that most of the more elaborate

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existing systems presupposed certain statisti-cal relationships in the wave-induced dataand actually accomplished some data reductionprior to recording.

Early in the program, the fo Ilowing generalrequirements were e stabli shed and existingequipments reviewed in this light:

1. Cyclic bending moment only will be s~ud-ied.

2. A sampling device, as opposed to onewhich records continuously, is to be preferred,in view of the data storage problem.

3. “Unmanned” operation for periods of up toa month is desirable.

4.

5.

6.

7.

“Good” reliability.

High accuracy (27.).

Adapted to shipboard environment.

hw cost (initial, maintenance, and datareduction).

8. Immunity to the intentional or accidentalministrations of untrained, unauthori zeal, per-sonne 1.

Previous Work

The principal investigations in the generalfield had been sponsored by the David TaylorModel Basin (DTMB), the Society of NavalArchitects and Marine Engineers (SNAME), TheSwedish Shipbuilding Research Foundation(SSRF) and the British Shipbuilding ResearchAssociation (BSRA). Both SNAME and SSRF usedModel Basin instruments for their work, butSNAME had, in addition, sponsored a programto develop a different type of unit.

One recording technique common to all in-vestigations, to a greater or lesser extent,was the use of strain–gage transducers, andstraightfomvard, manned, o scillographic re-cording equipment. A Iarge proportion of thepublished data has been obtained by thismethod. A1l future discussion will be hmitedto units which have the capability of unmannedoperation.

The DTMB Gaqes and Counters

Over a period of years, DTMB developed aseries of gage and counter systems which couldbe used to record strain, motions, or othercyclic wave-induced phenomena. The mechan–ical strain-cycle gage and counters consistedof a mechanical strain gage having a gagelength of ten inches, with mechanical magnifi-cation through a lever system by a factor of10. As strains were induced In the unit, suc-cessive zone level and amplitude contacts weremade which activated numerical counters. Thelogic in this unit was so constructed as to per-mit deduction of mean strain levels and peak-to-peak strain amplitudes from the number ofcmunts shown for each preselected range.

A later adaptation of this instrument intro-duced considerably more flexibility into thechoice of transducer. The output of an acce~-erometer or strain-gage bridge, suitably ampli–fied, was fed to a patentiometric recorder-contro Uer which had been modified by the ad-dition of contractors to the slide wire. Thesemoving contractors intercepted fixed contacts,the outputs of which were fed to a relay logicunit and then to electro-magnetic counterswhich recorded the number of times the peak-to-peak signal had exceeded the range repre-sented by the counter. This urnt was usedsuccessfully in the SSRF program4 while themechanical unit described briefly abcve wasused in the SNAME investigation. 7

The BSRA Gaqe and Counter

BSRA has for some years sponsored work onthe measurement of wave-induced loads Onmerchant ships. Unfortunately, little has beenpublished on the results of these programs, butthe nature of the BSRA statistical gage isknown .8 Basically, this unit consists of a100 inch mechanical strain gage. Strain in thegage element is transformed to rotary motion,and a system of rotating and fixed contactsenergizes counters at a remote location.Strain-gage bridges have been incorporated in-to several of the units to obtain analogue rec-ords in oscillograph form.

Other Systems

A device has been designed by the Frenchgspecifically for the measure me rrt of strainsaboard ships. This “Statistical Extensometer”again combined a mechanical strain gage

-3-

(11 .8 inch gage length) with mechanical ampli-fication, electrical contacts and counters.

Other systems designed for the measure-ment of amcraft loads and motions were review-ed. These covered a number of well–knownunits and several relatively new proprietarydevices. In general, analog recording wasused on a variety Of tape materials using hotstylus, magnetic, or scratch recording. Ageneral disadvantage of these units was there latlve ly short recording time and the e labo -rate specialized playback equipment requiredwhich was, of course, justified when a largenumber of recording units were to be used.

At the conclusion of this general phase ofthe investigation, it was apparent that thestate of development of electromechanicalstrain–cycle counters was such as to permitthe de sign and construction of a relatively in-expensive unit with a high probability of a–thieving long hfe and reliable operation. Allthat remained was to weigh this type of unitagainst the other possibilit~es.

Basis for Selection of Tape Recorder System

De spite the attractions of an e le ctro -mechanical strain-cycle counter (straightfor-ward design, relatively low cost, possibilityof no vacuum tubes, simple data reduction),several disadvantages are quite apparent.Since a large part of the data analysis is ac-cornphshed by the urut, it 1s not possible,after the fact, to review or reanalyze thebasic strain data by alternate methods. Fur-thermore, instantaneous correlation of straindata with other information (wave height, ac-celerations, motions, etc. ) is not pos slble.

Impliclt in the statement of the objectiveof the present project is the necessity, atsome point, of obtaining simultaneous bend–ing moment and wave height Information. Thiswould then permit the data from full- scaleships 10 be used in correlations with modeldata. A number of shipborne wave-measuringsystems are available or under development,but none of these have advanced to the po~ntwhere they can be considered for this investi–gation from the vlewpolnt of cost, accuracy,and rehabihty. However, the desirability ofobtaining simultaneous information on theload-producing element (the seaway) and theresultant bending moment cannot be over–emphasized. It is recognized that this must

await the development of a suitable shlpbornewave–heigh~ sensor.

The decision was therefore reached that theinstrumentation system be based on use of amulti–channel, magnetic-tape recording unit,in spite of higher initial costs. The sPecificfeatures favor~ng this type of system were:

1. Standard magnetic-tape recording systemswere available which, with slight modifica-tion, could provide 160 hours of continuousrecording of one channe 1 of information on asing le tape.

z. The system would be versatile with regardto the number of data channels “which could beutilized.

3. A complete, permanent, analog record ofthe desired information would be available atthe completion of each voyage.

4. Type, method, and scheduling of analysis

would not be re strlcted.

5. Ali seaway-induced stresses would &recorded, including slamming (whipping)stresses which result from longitudinal vibra-tion of the hull at its lowest natural frequency.(Although the se stresses are not of primaryinterest on this project, other investigatorsare pursuing this problem. )

6. A variety of high–speed automatic data re-duction techruques would be available.

In addition, the contemplated ‘cape-recording system, as initially installed, orwith slight modification, could obtain data ofinterest to a number of other active or sug–gested research programs . Some of these arelisted below. (Project numbers are those usedin Lewis and Gerard, pages 220 and 221 .)l

~olect No.— Title and Comment

3 Routine Collection and Dis-semination of Synoptic WaveData (Deduction 01 sea spectraby analysis of ship responseand use of transfer function).

11 Long Range Determination ofExpected Sea Conditions forShip Design Purposes (sea datafrom ship response using

-4-

FIG. 1. S . S . HOOSIER STATE

SS HQOS/ER STATE

W -

FIG. Z . S. S. HOOSIER STATE: VOYAGE 123 (EAST); VOYAGE 124 (WEST);NOV. -DEC . 1960.

——

DATA LOG

SHIP ——.— ———.—

VOYAGE_ ———— FROM–—___— TO DATES TO———m.., n ———— .—--— ———

I

1ndex0.

r————.—-——.Date (IvI, D, Y)Time (GMT)

anlr1- -— ——.-,- ,.. - —-.. . .=—-—--, ,-- —. .—.I “-- Al/g. AWJ. ,

Time ‘ Noon Speed <Meter

:g=~z

–++=7- ~-—.

WI ii U

Lzx ,Air 7Nind W ndTemp.

ISpeed Dir.

‘d

Weather Initials

—-i--.+

kl———

l-+

=+===-

--( --–1----~l.—..

FIG. 3, DATA FORM FOR RECORDING SHIP SPEED AND WEATHER CONDITIONS .

DATA LOG

! 71’ ,Avg . ]Avg . Avg. Estimate Average I Barometer Rem arks

Beaufort I True I Wave ]Wave Wave Length in Feet I Reading & (Changes of Course, Changes of

Index Sea State I Direction ] Height 1period Length & ‘i’rue Direction Sea Photo Speed, Changes of Ballasting,

No. Number I of Advance ! Ft. ~Sec. , Ft. of Swell Number Slamming, Rewind Recorder)

pp==f=Ff-’‘=~=+===1~-~-~+=p{--==:~:===j————.—

L_–. — -L -.1-—— ——_—_— —d

FIG, 4. DATA FORM FOR RECORDING SEA STATE CONDITIONS.

-b-

Project No,

18

19

21

26

27

34

39

41

Title and Comment.—

transfer function. )

Case Studies of Seaway Loadsaboard Ship. (Same basicrecording system; additionaltransducers requmed. )

Correlation of Full-Scale Bend-ing Lmds with Model and The-oretical Predictions .

Trends of Be nd~ng and ShearLoads in Irregular Seas.

Transverse Bending hads (Re-arrangement of strain-gagebridge connections. )

Loads Resulting from Motionsof Internal Liquids .

Observation of Slamming badsat Sea (Data already availableon tape. )

Compiling Data and ObservingSea and Pir Ternpsratures andSolar Radiation on VariousTrade Routes (Extensive logdata now recorded; all ~nforma-tion could be placed on a sin-gle channel of tape. )

Statistical Data on ExtremeTemperature gradien~s in ShipHulls (Diurnal thermal stressvariations can be observed onmagnetic tape records. )

Speclflc details of the complete magnetic-tape system follow.

DESCRIPTION OF SYSTEM

General

At the present time two instrumentationsystems are in operation on dry–cargo vessels]n the North Atlantic service. ~n~ ship has

been instrumented for the unmanned recordingof wave–induced stresses on magnetic tape.The instrument aboard the second ship in-cludes channe 1s for recording wave-inducedaccelerations in addition to stresses.

cargo vessels, operated by States MarineLines. Figure 1 is a photograph of ths S. S.HOOSIER STATE docked in Bremerhaven, Ger-many. The selection of the two sister shipswas based on the wilhng cooperation ofStates Marine Lines and the desmabihty ofcollecting a iarge quantity of data on a givenship type and trade route within the shortestpossible elapsed t~me.

The ships operate between East CoastU. S. ports and Northern European ports. Theroute of a typical voyage IS Illustrated InFig. 2.

The sh~p’s watch officers maintain a datalog book for the project which includes con-current data on ship position operating con-ditions, local weather and sea condlhons.The log entr~es can Later be related to givensamples of the reduced data. T.hs officersalso rewind and replace the data tapes on themagne’tic-tape recorder.

The States Marine Line ships participatein the collection of data for the U. S. WeatherBureau. Tha watch officers are therefore ac-

customed to gathering the type of weather andsea- state data wh~ch are included in the logsheets. Samples of the data log sheets areprovided in Figures 3 and 4. The first col-umn, “Index Number, “ ties together the dataon the two paces which correspond to a givenwatch period. The “Time Meter R@adlng” isobtained from an indicator assocla L’ed with themagnetic tape recorder and serves to ident~f ythe corresponding data record on the magnetictape. The other column h~adings are self-explanatory.

Figure 5 illustrates In block diagram formthe complete system for recording ocean-wavs-induced stress which has been placed aboardthe S.S. HOOSIER STATE. It is also repre-sentative of the stress channel of the expandedsixess and acceleration recording system onbaard the S. S. WOLVERINE STATE.

Figure 6 is a functional block diagramrepresenting o~.e channel typical of the sevenacce Ieration reccmchng chanmls of the S. S.WOLVERINE STATE SYSTEM .

-7-

DATA RECORD’NG 5YSTEM(57J’?K55 CHBNNEL)

——

TW!MSDUCEi? BALWCE WD D-C/9/WPL/f/ER— — — ‘~flDsMT~

~7RK5S G@ “ CAL/BRR7/ON‘ GAYN=200C/RCL7/TS

A

Elii/TAVONPRO GRA~/WER

LRECORDERON S’2MI’&/4h’#PJR/0.O24 Vofz.fw 2.ZERO CH&CK l/W/N

3. CHLIBRR7L /P91/V4. CONT/NuQU5ABoVE 7HR.E5h’oLD

2Z0 v //5 v -D-C -: /WOTOR ALTERA49TORSET /4-c

SHIPPOWER 70 /Ns7RuMEN75

FIG. 5. DATA WCORD~NG SYSTEM (STRESS CHANNEL)

DAT/9 /f.fCORLYIVG 5YSZEZ(A CCELERRT/O& LliW+YEL)

IPhWGRRA7MER

@w’ww - LRE(CORDER ON 32/WIl@+QP&WOD2. ZERO CHECK /MIN3. CAUIBR#TE //1+’/Nq CONTINUOUS @BoVE Ti%RE.%foLD

220 v 115vD.< + : /’1/70TOR /f TERtiA’TOR 5ET

SHIP Po tiERR-c -

70 /NsTRum@JT5

FIG . 6. DATA RECORDING SYSTEM (ACCELERATION CI-IANNEL)

~!~/ REPRODUCE 5Y5T.6M

,R...yf===p==p=FM CO~PENSAT/ON LXZR/W/W970R

5#mzcH

FIG . 8. WIRING LAYOUT STRAIN GAGE CIRCUITS,CLI

FIG. 9. INSTRUMENTATION CABLE AND TERMINAL BOX IJ+YOUT, S . S . WOLVERINE STATE.

-9-

electrical signals suitable for graphical recoi+ing or subsequent analysis.

Figure 8 indicates the transducer cablingwhich was added to the S .S. HOOSIER STATE.It shows the general location of the Port andstarboard stress transducers with respect tothe instrumentation room in which the record–ing equipment was located.

Figure 9 indicates the transducer cablingwhich was installed on the S.S. WOLVERINESTATE and shaws the location of the acce ler-ation transducers at the lmw, stern, and amid-ships. The port and starhard stress gages

are located near junction koxes 3 and 7 re–spectively.

The following sections of this report con–tain descriptions of the various componentsof the data collection system. Detailedspecification on the individual components areincluded in the Appendix.

Transducers and Data Conditioning Units

Stress Channel

Stress Gaqe. A stress measuring trans–ducer was developed by cementing etched-foil electrical strain gages to the inside ofthe ship’s side plates six inches below theweather deck. Plating thickness was 0.90inches; transverse frames are 30 inches apartat this section. A similar stress gage wasplaced amidships on both the port and star–board sides of the ship. The gages wereoriented to re spend only to Lhe longitudinalcomponent of the bending stress. The out-puts of the two stress gages were combinsdelectrically to form a full bridge circuit inwhich horizontal components cancel so thatonly the vertical components of the lonqitudi–nal bending stress appear in the output.Figure 10 illustrates the completed instaHa-tion of one of the stress gages in the midshipcargo spaces.

Tatna 11 Metal Film Strain Gages TyPeC6-181,were used in the S.S. HOOSIER STATEinstallation. Eight gages were used to formthe four-arm brj dge circuit. The active arms

of ~he bridge, on opposite sides of the ship,consis[ed of two gages electrically connectedin series and positioned against the sideplate to form a vee– shaped dyadic siressgage? 0 with the centerline of the vee orienl’ed

nG . 10. STRESS GAGE INSTALLATION IN

MIDSHIP CARGO SPACE .

in the fore and aft dir~ ct’io n. Ths angle of thevee is selected to compensa~e for the Poissoneffect in the steei side plate. A poisson ratioof O.26 was used for the mild ship steel.

Baldwin–Lima– Hamilton Stres s–Straingages, type FAB28-S6 were used ID the S.S.WOLVERINE STATE installation. These were anew development which had just become a-vailable in the fall of 1961, at Lhe time thesecond shipboard insta Hation took place.The se units combine two axial- skain-sensingelements, having different electrical re si st-ance and oriented at right angles, into a sin-gle unit to provide a measurement of truestress along the principal gage axis. Theseunits are designed to compensate for a Pois-son’s ratio of O.28 for mild steel.

The temperature compensating (inactive)bridge arms consist of an e Iectrical straingage or pair of strain gages identical 10 thatwhich was used in the active arms. The secompensating gages are cemented to blocksof mild– stee 1 ship plate which are held byspring loading against the ship’s side plate.The blocks are thus exposed to the same sideplate temperatures as the active gages, but tonone of the forces which act on the side plates.

The stress gages are protected in place bya steel hausing. Fig. 11 illustrates the Pr-otective housing with strain gages, strain-gageconnectors, and compensating block in place.The housing consists of a steel ring and acover with O–rjng seals between the open

-1o-,,,..,,

FIG. 11. COMPONENT PARTS FOR STRESSGAGE INSTALLATION .

bottom of the r~ng and the ship’s side platesand the top of the ring and the cover. Thehousing IS suppcwted in place between twoframes of the ship by means of the angle-u-onstructure shown in Fig . 10. A flex- link con-nection is used between frames and ang le-mon structure to Insure ihat the structure doesnot provide a load path para lle 1 to the side

shell plating on which th”e transducer ismounted, A metal screen protects the elec-trical cable which is attached to the housing.

After final assembly the housing is filledwith Dow Corrung Compound Number 3, aslhcone grease which provides electrical in-sulal’ion and protection against moisture, andIs harmless to natural and synthctlc rubbercables. Then sufficient s~hcone grease ispumped In through a grease fitting to producea s hght positive pressure which excludes airand moisture from the housing.

Slnc~ the strain gage is located on onefac~ of the side shell plating, any local bend-ing effects would be additive to the basiccenter timckness longitudinal stress. Inspec-tion shows no initial unfairness of the platingin this region, This, coupled with the generallocation of the gages near the gunwale angle,the plating thickne SS, and transverse stiffenerspacing (31) Inches), lead to the conclusion thatlocal bending effects will result in rmgligibleerror in the recorded stresses. This will beestablished, ~nsofar as possible, by static“calibration” of the vessel throughout theanticipated seaway induced stress range.

Strain Gaae Module A compact, sh-ain-—-.gage module, type SRB200RGH, which con-tains a solld-state regulated 24-volt d-cbridge excitation pawer supply, bridge bal-anclng and calibration circuits was purchased

m

‘1

FIG . 12. AUTOMATIC DATA RECORDING UNIT

from Video Instruments Incorporated of Cali-forrm (now a div~ sion of End~vco Corporation).The calibration pormon of the urut can be re-motely operated from the syst~m programmingunit describ=d later. This module includes

the blocks marked EXCITATION 24 VOLTS D-Cand BALANCE AND CALH3RATION CIRCUITS ofFig. 5. It appears as ‘the left-hand unit inthe upp~r panel of the recording system shownlrl i%. 12.

Strain Gaqe Amplifier. A chopper-stabilized, transistorized d-c amplifier (VideoInstruments Division, Endevco CorporahonModel 602A) has been incorporated in thesystem to raise the low level output signalsfrom the strain gage module to a level whichmatches [he input requmembnts of the tape re–corder. This amplifier has the hqhly desrrablecharacteristics of low noise and very goodlong-term gain and zero-stability. The strain-gage amplifier appears as the second unit infrom th~ left-hand side on the top panel of thecomplete recording system, as shown in Fig. 12.

Stress Meter . At the center of the top—panel of the recording system, Fig . 12, is ameter which monitors the output of the straingage amplifier. The meter is an AssemblyProducts, Inc. contact making meter-relaywith adjustable high- and low- lim~t contacts.

The meter is used during the voyage as anindicator of satisfactory system operation,since it swings to the left and right of centerscal~ as the wave–induced stresses vary froma positive to nsqative value with respect totheir still water value. The limit contacts canb= positioned on the meter scale so that therec~rding system will be turned on when thewavz-induced stresses exceed selcscted pre-set values. In this manner extra data sampleswill be gathered during periods of rough seaconditions.

The meter 1s also used during the routineequipment checkout visit, at the end of eachvoyage, to indicate satisfactory cali bra Lionand balance of the various data channe 1s ofthe system. For this purpose, the stresschannel and each of the acceleration channelscan be fed in turn through the strain-gageamplifier by means of a selector switch on theprogramming unit.

Acceleration Chanrm 1s

The data recording .syst@m on board theS.S. WOLVERINE STATE utilizes seven ad-ditional tape recorder chanrm 1s to record theoutput of seven linear accelerometers at vari-ous locations on the ship. Three acceler-

ometers are located at the bow oriented tomeasure linear accelerations in the vertical,transverse (athwartship), and fore-and-aftdire ctions. Three accelerometers having the

FIG. 13. COMPLETED INSTALLATION OF A

MOISTURE-PROOF BOX CONTAINING STR41N-GAGE ACCELEROMETERS ,

same orientation are 10cated at the stern. Asingle accelerometer measuring transverseaccelerations is mounted amidships. All ac-ce lerometers are located on the center hne ofthe sh~p and at the same level i.n the ship,just below the midship weather deck.

Acce leromet~. Unbended strain-gagelirmar accelerometers (Statham Instruments,Inc. Modal A3) having a range of +2.5 g anda natural frequency of 55 cycles p=r secondhave been used in all accelerometer loca-tions. Strain-gage accelerometers were se-lected because of the very low frequenciesencountered in wave-induced accelerat~ons.The useful fr~quency range of thes~ acceler-om~ters is from 0 (d–c) to 33 cycles per sec–ond . The accelerometers arc calibrated cl~c-

tr~cally In the same manner as an electricalresistance strain-gage bridge, that 1s, byshunting one arm of the st’rain-gage bridgewith a calibration resistor of the proper value .Figure 13 illustrates the compk Led installa-

-lz-

tion of a moisture-proof bcx containing strain-gage accelerometers, their associated signalamplifiers, and remotely operated calibratingcircuits. The boxes are bolted to stee 1 platesthat have previous ly bzen welded to the

overhead.

Figure 14, provides an interior view of theaccelerometer housing. In the center is seena machined steel block with three mutuallyperpendicular sides LOwhich are attached thethree linear acce barometers. Through bo Itsattach this block firm ly to the steel plate pre-viously mentioned so “that the accelerometersare in intimate contact with the ship’s struc–ture. The accelerometer signs 1 amplifiers arelocated in front of the accelerometer mountingblock and the remote calibration r~lay is seen

at the rear of the box.

FIG. 14. INTERIOR VIEW OF THE AC-CELEROMETER HOUSING .

Accelerometer Amplifiers. Transistorizedaccelerometer signal amplifiers (Statham 1n.struments, Inc. Model CA9–!i6) are employedto supply excitation to the strain–gage ac–ce lerometers and amplify the transducer outputto a level which matches the input requirementsof the tape recorder.

The acce ~erometers are used in a carriersystem. Tcr, ki Ioc ycle p.zr second carrierexcitation is supplied by the amplifier unit tothe s ‘u-ain-g+ge bridge in the acce lerorneter.The acce Icrorneter bridge output is then de–modulated in the amplifier unit and amplifiedto the proper leve 1. Since the amplifier unitsare located adjacent to the accelerometers,only the d–c Dower required to operate theamplifier and the low–frequency signals fromthe acce lerome L’ers are ca~ied by the ship–beard instrumentation cables.

Recording System

The shiplmard magnstic–taps data-re cord-ing system is illustrated in the system blockdiagrams, Fiq. 5 and 6, and the photographFig. 12. The cabinet is 27 x 27 x 70 inches.The system is based on the Model 3168 tapetransport fnanufactured by Mirmeapolis-Honeywe 11 Regulator Company of Denver,Co lorad~. The system uses 10 1/2 inch reelsof one inch wide magnetic tape having a 1-mi 1,(0.001 “) mylar backing. A 14-track IRIGstandard magnetic recording head permits therecording of LIP to 14 channe 1s on the one inchwide tape, and provides compatibility y fcrplayback of the tapes on other standard ma-chines. A tape speed of 0.3 inches per sec–ond permits the recording of forty hours ofdata on a single pass of the tape. The fre-quency rnoduiation recording technique is usedto provide a system frequency response O (d-c)to 50 cycles per second. (The lFHG standardcenter frequency at 0.3 inches per second is270 cycles per second. )

Bacau se of the very slow tape speed, thesystem incorporates electronic compensationfor the noise re suiting from irregularitiess oftape motion. A constant frequency is recordedon one of the tracks of the tape. During play-back, variations in the frequency which is re-corded on this track, resulting from motionirregularities (f Iut Ler and wow), produce sig-nals which are subtracted from the outputs ofthe data channe 1s to improve the overall sys-tem signal-lo–noise ratio.

The recording system aboard the S. S.HOOSIER STATE records one chanrm 1 of dataand the compensation signal during each passof the tape. % the end of each pass, theship’s Second Officer rewinds the tape andswitches the two active recording chanrm 1S tothe next pair of recording heads. This action

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IL/..

I —. ) I

I

I

.—— — .—.— ——— ——— ——

171G. 15. PROGRAMMER WIRING SCHEMATIC S . S . WOLVERINE STATE,

can be repeated four times to produce eighttracks on a single reel of tape, recorded lwoat a ~ime, for a total data record of 160 hourstotal elapsed time.

The recording system on board the S. S.WOLVERINE STATE utilizes 10 of the 14 avail-ablc tracks (one stress channel, seven ac-ce leration channels, one comp~nsation chan-nel, and one spare channe 1). At the end ofeach forty hours of record the sh~p’s SecondOfficer rewinds the tape and replaces it witha new reel.

Proqramminq Un~

A programming unit developed by the in-ve stigators has been incorporated to providethe automatic operation of the shipbaard re–cording system. The functions of this unitare indi cated in the system block diagrams,Fig. 5and6. A schematic diagram of ‘the pro-

gramming unit aboard the S. S. WOLVEIUNESTATE is included aS Fig. 15. The front panelof the programming unit appaars al the top afthe complete recording system cabinet, seephotograph, Fig. 1z. This panel includes theStrain-Gage Module, the Strain-Gage Ampli-fier, the Stress Meter, and an elapsed-timemeter which serves as a taps footage counter.

The fundamental purpose of the program-ming unit is to turn the recording system on

regularly at four-hour interva 1s to obtain a

data record of thirty minutes duratio’n. At thekgirming of each of these records the unitperforms a calibration sequence. The poweris removed from all transducers for a one-rninute system zero-check. Then, during ase mnd minute, calibration resisters are alter–nately shunted and removes from across onearm of the strain gage bridge in eech trans-ducer. The calibration sequence provideschecks on system zero drift and calibration

Io

I//w//Y

FIG. 16. SKETCH OF TYPICAL DATA SAMpLE .

changes, and also provides timing markersalong the tape record since the sequence isrepeated at r~gular four-hour intervals. Asketch of a typical interval of data record isshown m Fig. 16. As noted in this figure andin Fig. 17 (a) and (b), stress and acceleration

Si9nals are superimposed upon the calibrationsignals. The change of level occurring at thebeginning and end of the calibration pulse’sserve to indicate the calibration lev~l. Thestress channels are calibrated for a stresschange of 10, 000 psi. The acceleration chan-nels are calibrated for an acceleration changeofo.5g.

IrI addition to obtaining regular records offixed length and providing calibration signals,the programming unit will also obtain extendedrecords of data when the sea condit~ons are ex-tremely bad. Adjustable contact on the StressMeter can be set to sekcted threshold valuesat which the programming unit can b: trig-gered to turn on the recorder and obtain rec-ords in fifteen minute increments in additionto the regular records of one–half hour dura-tion. A stress level attained above the pre-set threshold will turn the recorder on. Anautomatic ‘mmer w1ll turn the recorder off atthe end of fifteen minutes unless stressescontinue abave the preset level.

Auxl harles

&hipboard Cables. Prior to the actual m-installation of the recording systems akoard

ship, cabhng from the instrumem~ation room. tothe transducer locations, and from the lnstru–mentatlon room LOthe source of shipboard220-volt d-c Poiwer was added to each ship.S~nce it was required that this wiring meetCoast Guard approval, the wiring was install-ed by m.arlne contractors under the super-vis~on of the Investigators. Figures 8 and 9illustrate the instrumentation cabling which

was added LOeach ship. The p~wer to operatethe recording system, about 1500 watts, wasdrawn from the hnes to Lhe forward quartersvermilation system.

Motor-lilternator Set. A conversion devicewas needed to convert the 220-volt d-c ship-board power to I i O-volt 60-cycle a-c powerto operate the recording system . Surplus ship-koard motor-a kernator sets with the requiredstarting and protective circuits were purchasedand installed aboard each of the sh~ps. Themotor-alternator sets were conservative lyrated for increased reliability. A 41WA unitwas installed aboard the S. S. HOOSIER STATEand a 7, 5KVA unit was installed aboard theS. S. WOLVERINE STATE. The function of theseunits is lndicatcd in the system block d~ag’rams,Fig. 5and6.

~emote Indicating Instruments for ShipQhart Room. As part of the data log maintainedfor this project, the officer on watch recordsthe reading from an elapsed time meter. ThisProvides the tol~ 1 time that the re @rder hasrecorded data dur~ng the previous four hours,

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FIG. 17 (a). VISUAL RECORD OF STRESS AND ACCELEROMETER SIGNALS.

,,. .,:, ,, ., ‘,”, ;“,$,’ --

“c... .... . ..:: “

,,!,, .

,, . . . TQQQQ

L._? --..,.-..—..—.,., ,.,-.— .. . . ,-”.,-—........,.”.....--...,..,”,-—-..—--. .,,-—...-” ! ,. .......... , ,.-.

,,,.,“ ..”,,,;, - ‘“

FIG. 17 (b). ENLARGED VIEW OF CALIBRATED SECTION.

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,,d,

,,,,, ;, If”

‘1’I ‘, ~“1, ,.. .,, ,, “<’;!~’: $,

FIG 18. INDICATORS IN CHART ROOM.

and serves to tie the tape record to the data109. To observe this meter, the watch officermust leav~ the bridge and go two decks belowto the recording equipment. Because of thisinconvenience, the Second Officer of the S. S.HOOSIER STATE reque steal that a remote indi–eating meter be located in the Chart Room.

The investigators agreed that a remote in-dicating running time meter would be installedin the Chart Roam. It was also decided, sincethe additional cost was slight, to include a re-mote indicating stress meter. The ship elec-trician installed a four-conductor cable he-tween the recording equipment and the ChartRoom during the tenth voyage so that the in-struments could be installed when the shipreturned. The resulting installation is pic-tured in Fig. 18.

The ship personnel were instructed to taketheir time meter readings from this remote run-ning time meter in the Chart Room, and to resetit to zero when tape is rewound to agree withthe meter on the recording equipment.

A similar remote ] ndicator has been as-sembled for installation aboard the S. S.WOLVERINE STATE in the near future.

‘,, ,,-. .”.” .. I.,”’. J!..‘.L .,

UWkck System. ~ system for pkiy-ing back the data tapes is located in the in-

vestigators’ laboratory. This system is com-patible with the shipb~ard recording units in

that it accommodates 10 1/2 inch reels of one–inch-wide magne”tic tape which have been re-corded using freguency modulation techniquesin the standard 14-track I RIG configuration.The purpose of tl:is system is to reconstruct theoriginally recorded data in the form of e iec-trical signals which can be used as inputs tographical recorders or automatic data analysissystems. Figure 7 is a functional block dia-gram illustrating the operation of reproducinga typical channe I of magnetic-taps recordeddata.

PERFORMANCE OF EQUIPMENT

General

The original installation was made aboardthe S.S. HOOSIER STATE in November of 1960.The second installation was made abnard theS.S. WOLVERINE STATE in December 1961. UpLOOctober 1962, useful data have been ob–tained from 17 out of the 20 round-trip voyagesof the S. S. HOOSIER STATE and from 8 out of 9

round-trip voyages of the S. S. WOLVERINESTATE .

A regular maintenance check is made a-koard each ship, approximately once a month,at the completion of a round-trip voyage .During the se visits the operation of the record-ing system and the condition of all transducersis che eked; any needed repairs are made; androutine preventative maintenance is performed.

After the initial two months of operation,moisture entered the stress-gage housings a–beard the S. S. HOOSIER STATE. Corrosionthe n caused the compensation strain gages onImth sides of the ship to develop short cir-cuits. The resu It was an overload which dama-ged the strain-gage amplifier and, by a chainreaction, damaged the F-M recording oscilla-tor in the tape recorder. Because of delays inshipping schedules and the need for sufficienttime to renew the transducer installation, thesystem was inoperative for nearly three months.

After removal of the stress gage, the pro-tective housing was filled with Dew- CorningNo. 3 compound (silicone grease) under slightpressure to exclude moisture, and a “dike” ofelectrical direct-sealing mmpound was formedaround the outside of the housing adjacent tothe ship’s side plate. In the original instal-lation the housing was hard packed with thesilicone grease aqd reliance was nlaccd u~on

the O-ring seal between Lhe housing and theship side plate.

Since the” repair, the stress gages on theS. S. HOOSIER STATE have operated satisfac-torily for 16 months. The revised installationtechniques were employed on the S.S. WOL-VERINE STATE stress gages. These have beenoperated satisfactorily with no evidence ofdeterioration during the nine months of opsra-tion since they were installed.

There have been some minor system dif -iiculties from time to time, but these haveeither occurred toward the end of a voyage orhave not been of a serious enough nature tocause the loss of a significant quantity ofdata. Examples of these difficukies would in-clude several failures of the strain gage amp-lifiers, a relay failure in one of the taps re–ccmders, and failure of the motor– a lternatorspeed control aboard the S. S. HOOSIER STATE.

I7-

Bending Moment Calibration

It is desirable to obtain a direct bendingmoment vs. stress calibration for each sixess–gage installation. To date, it has been pos-sible to obtain only one such calibration. onthe S. S. HOOSIER STATE and none on the S .S.WOLVERINE STATE .

The S. S. HOOSIER STATE calibration wasaccomplished during night bunkering in Broolt–lyn, N. Y., in November of 1960. A total of1369. I tons of fuel -were taken aboard in thethree midship double–bottom tanks, resuliingin a calculated bending-moment change at thegage cross section of 35,666 ft-tons (sag).Using the section modulus at the gage loca-

tion (43, 120 in.2 -ft), the computed stresschange al the gages was -1, 853 psi. Th~scompared to a stress of -1, 750 psi measuredat the recorder, a difference of OniY 5.5 Per-cent. It should be noted that the addition ofriveted deck straps to the vessel, subsequentto the calibration, increased the section mod–UIUS at the gages to 47,365 ins –ft.

It was possible to observe stress changesin the S. S. WOLVERINE STATE during dry-docking . The change in stress from the stillwater condition prior to drydocking, to thedrydocked condition (on blocks, dock pumped)was -9000 psi. This compares to the maxi–mum observed (to date) seaway–induced peak-to-peak stress value of 8300 psi.

CONCLUDING REMAR.KS

The performance of the two “unmanned”tapz recording systems to date has been ex-cellent . The versatility of the unit has beendemonstrated by the ease with which addi-tional transducer input’s were handled in thecase of the S. S. HOOSIER STATE. Tha ac-quisition of data reduction and analysisequipment will result in a completely inte-grated system for acquisition of data from anumber of units, with analysis being Pzr-formed at a central faciLity.

In order that the objectives of the projectmay be fully realized, it is necessary thatinformation be obtained on a number of shiptypes operating on a variety of routes. It isto be hoped that, with satisfactory instru-mentation now available, sufficient intere Stwill be exhibited to psrmit equipping othership types. For example, it would seem de-

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Sirable that one or more C-4 MARINER ?lassv~ssels, operating on the northern trans–Pacific run, be instrumented. These arerelatively fast sh~ps operating on one of themore unpleasant routes, as regards weatherand sea conditions . At some point in the nearfuture, a large tanker, operating on as un-friendly a route as possible, should be stud-ied.

The data tapes are being stored at theinve sligators’ faci hty. Inqulries relative tothese tapes, or to shiplmard ~ns’tallations,can be drrecled either to the irwe stigalors orto the Secretary, Ship Structure Committee,U. s. Coast Guard Headquarters, Washing-ton 25, D. C.

ACKNOWLEDGEMENTS

This project is sponsored by the ShipStructure Committee and is under the guid-ance of an advisory committee of the Gom -mlttee on Ship Structural Design of the Na-tional Academy of Sciences-National ResearchCouncil. The who lehearted cooperahon andcontinu~ng assistance of the States MarineLnes, and in particular of Messrs. E. p.Bainbridge, Nell Miller, and the officers andmen of the S.S. HOOSIER STATE and the S.S.WOLVERINE STATE, has been a major factorin the success of the Investigation to date.The contribution of States Marine Lines in theform of shipboard wiring and instrument in-stallation is deepiy appreciated.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

REFERENCES

Lewis, E. V., and Gerald, G., eds. , ~@rig- Range Research Proqram in Ship Struc-~ura 1 De siqn (Ship Structure Committee Re-port Serial No. SSC-124) . Washington:National Academy of Sciencss-NationalResearch Council, November 30, 1959.

Jasper, N. H., and Brooks, R. L., &Tests of the USCGC UNHVLAK “Statistical—c..— .Presentation of the Motions, Hull BendingMoments, and Slamming Pressures forShips of the AVP Type, “ (Part 2),, (DTMBReport 977). Washington: David TaylorModel Basin, April 1957.

Jasper, N. H., et al Statistical Presenta-J ——— —tion of Motions and~ll Bendinq Moments—.—of Essex Glass Aircraft Carriers (DTMBReport 1251 ). Washington: David TaylorModel Basin, June 1960.

Bennett, R., &ress and~otion Mea~-ments on Ships at Sea (Report No. 13).—.The Swedish Shipbuilding Research Founda-tion, 1958.

Jasper, N. H., “The TMB Strain CycleGage and Counter, “ Proc. SESA, vol. X,.—no. 1, p. 87,

Jasper, N, H., The TMB .%tomatic Ships~on Recorder (DTMB Report 777).Washington: David Taylor Model Basin,October 1951.

“Stress Data Obtained on SS IVIOR.MACMAILand SS IMORMACPENN (Letter Report No.605). Ho”wken, N. J.: Stevens Instituteof Te chno log y, Experimental Towing Tank,October 1957.

Communication dated 20 November 1959from Mr. RI. Lackenby, BSRA.

de Lems, H., “La Determination Statis -tique des Contraintes Subies Par LeMavler A La Mer, “ Association TechniqueMaritme et Aeronauhque, 1956 Session.

Murray and Stein, Strain Ga~Te chniques——(Part I). Cambridge, Mass. : M. I. T.,p. 49, 1956.

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APP2NDIX A

-cT 22: st~t~sticgl stu~o~s~Loads Aboard Ship

Objective: To obtain statistical records ofvertical longitudinal wave bending momentsexperienced by various types of ships opera-ting on different trade routes, with the em-phasis being placed on extreme values ofexternal loads.

IYoqram: Carry out a long-range statisticals~udy of longitudinal wave bending momentson approximately 15 to 20 ships of differentsizes, speeds and types operating on impor-tant routes. Sea and weather data should becompiled concurrently. Reports of accumu-lated results in tabular and graphical formshould be issued periodically. StatisticalsL’udles shou~d be made, leading prlmarlly toinformation on distributions of extreme loadvalues. (Short-range case studies entailingmore complete seaway load measurement’s andmeasurement of wave patterns are covered inProject 18. )

Suqqested Technluues: Two strain gage in-stallations mounted on the strength deck amid-ships, one port and one starboard, should beinstalled on all ships. They should k tem-perature-compensated and connected In seriesi~ order to give a mean reading. Calibrationof each ship in t~rms of vertical longitudinalbending moment would be obtained by fillingand emptying ship tanks in calm water to pro–vide known bending moments . Records at seawould be obtained by suitable instruments de-signed to require a minimum of attention, suchas strain–cycle counters, automatic samphngrecorders, or instruments for recording averageand maximum values during fixed time inter-vals. The instruments should be designed soas not to respond to h~gh-frequency strainvariations caused by slamminy, engine vibra–tion, etc. , for such effects should be con-sidered separately under another project.

Statistical analysis should be made of allload data; in particular, “extreme value” theoryshould be applied to the study of trends ofmaximum values. (See also Project 23. ) Ifsufficient data are obtained, analysis of trendsshould also be obtained in the manner ofJasper .10

being obtained by the HUII Structure Committeeof the SNAME (Panel S–10), DTMB, BritishShipbuilding Research Association, the SwedishShip Research Institute, the Laboratory for ShipStructure Research, De lft Technical University,and the Association Technique Maritime etAw-onautique, France (de Leirls5 3,. The ShipStructure Committee has initiated a project(SR-1 53) with Lessens and Associates, Inc.,for a portion of this study.

Re suits Expe~: Further supporting data onstatistical trends of hull bending moments.After five or more years, statistically valuableinform ation on extreme loads for different ser-vices and different ship types should emerge.

Taken from Reference 1.

&e&earch in P;oqress: Some stress data are

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APPENDIX B

Detailed Specifications on System Components

1. Transducers

a. Stress Gages

i. Budd/Tatna 11 Me’talfi lm Strain Gage,Type C6-181 (See Reference No. 9for stress gage configuration)Manufacturer: The Budd Company,P. O. Box 245, Phoenixvllle,Penris ylvaniaResistance: 120 + O.2 ohmsGage Factor: 2,01 + O. 5%

Temperature Compe&ation: com-pensated for use on mild steelGage Length: 0.5 inchesGage Width: 0.5 inchesOverall Length: 1.005 inchesOverall Width: O.5 inchesResistance Material: AdvanceBacking Material: Epoxy

Ii. Baldwin-Lima-Hamilton Stress-Strain Gage Type FAB28-S6Manufacturer: Baldwin- Lima Hami 1-ton, Waltham, MassachusettsResistance: Element 1: 350 ohms

Element 2: 98 ohmsMaterial Poisson Ratio: . Z8Material Coef. of Expansion: 6micro inch\inch/aF (Mild Steel)Gage Material: Resistance FoilBacking Material: Phenollc

b. Strain Gage Cement

Manufacturer: Armstrong ProductsCompany, Argonna Road, Warsaw,IndianaType: Armstrong Adhesive A-1Epoxy resin formulation with in-organic filler and amine typecatalySt

c. Dmw Corning 3 Compound (SiliconeGrease)

Manufacturer: Dow Corning Cor-poration, Midland, MichiganA non-melting silicon dielectric andlubricant. Effective from 40 to4CIO”F

d. Accelerometers

Manufacturer: Statham Instruments,Inc., 12401 Olympic Boulevard, LosAngeles 64, CaliforniaModel: A3-2 .5-350Range: ~2.5gNominal Bridge Resistance: 350 ohmsMaximum Excitatiofl: 11 volts d-c ora-c (rms)Full Scale Output (open circuit): ~20mv.Approximate Natural Frequency: 55 CPSDamping (Viscous Fluid): O.7 -t 0.1critical at room temperature -Direction of Sensitivity: Perpendicu-lar EC baseOverioad: Three times rated rangeTransverse Acce Ieration Response:O. 02~ per g up to rated rangeNonlinearity and Hysteresis: Lessthan + 170 of full scale outputWeight: Approximate ly 2 1/2 ounces

2. Strain Gage Conditioning Equipment

Manufacturer: Video InstrumentsDivision, Endevco Corporation,161 East Cahfornia Boulevard,Pasadena, CaliforniaModel: SRB-200RCH Strain GageModuleOutput for Bridge Excitation: 0-24volts d-cCurrent Range: 0- ZOOmaOutput ~mped~~ce: LeSS than 0.2 ohm

Line Regulation, 95-1 35V. a-c: 0.170Load Regulation, ~-Full kad: O. 17’oRipple, 95-135V. a-c: 1 mv. rmsInput Power: 115 + 20V. a-c 50-400—CpsUnit contains contro 1s for calibration,bridge balance and excitation leve 1.Internal relays permit removal of trans-ducer excitation and operation of cah-bration circuits by remote contro 1.

3. Amplifiers

a. Strai~~ Gage AmPlffier

Manufacturer: Video InstrumentsDivision, Endevco Corporation,161 East California Boulevard,Pasadena, CaliforniaModel: 602A Sclid State AmplifierInput: Differential or single ended

—

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Input-Cases Isolation, ohms, 10, 000Meg.Output: Single ended, isolated frominput and groundOutput-Case Isolation, ohms: 100Meg.Gain Range: 1-1, 000Gain Steps: 7Gain Vernier: Variable between stepsDC Gain Accuracy: 1~0Gain Stability: . 04’?7024 hrs.Gain Temperature Coeff., Y’o/°F: .02Zero Stabi iity: .04YoF. S. 24 hrs.Zero Temperature Coeff., Y’oF.S ./°F:.005D.C. Linearity, F. S.: .05Input Impedance, ohms: 1 Meg.Max. Safe Input Signal, Volts: ~ 10Max. Source Impedance: 1KMax. Source Unbalance: 10KD .C. Common Mode Rejection, db:16060 CPS Common Mode Rejection, db:120Max. Safe Common Mode Signal,volts: ~200Bandwidth, Relative to D. C. output:lo- lqo; 100- 3dbMax. Overload Recovery Time: 1/2S5C.Total Output Noise, Wide Band,Including Chopper RiPPle, at Max.Gain, mv Rrns: 3Full Scale Output Volts: ~loMax. Output Current: 200Max. D. C. output Impedance, ohms:.5Max. Capacitive Load, Wide Band:Infinite up to rated output current.Operating Temperature Range, “F:+40 to +120Power Requirement: 115 ~ 10’7’. VAC,50-400-40 watts

b. Accelerometer Amplifier

Manufacturer: Statham Instruments,Inc. , 12401 West Olympic Boulevard,LOS Angeles 64, CaliforniaModel: CA9-56 Strain Gage SignalAmplifierPower Requirements: 30 mi llamperesat 28 volts DC +100/ooutput : -2.5 to-+2.5 DCTransducer excitation: 4.5 to 5.5volts peak-to–peak (square wave)Frequency: 10 kc

Frequency response: Flat ~5~0 (ref-erenced to DC), from zero to 2000 CPSRipple: Less than 0.1570 rms.Sensitivity: Designed to operate withtransducers with rated sensitivity from1.5 rev/v to 10 rev/vBalance control: From -2.5 to I-2.5volts d-cGain Stability: +0. 4% over a period of8 hours after 15 ~inute warm-upInput Impedance: Designed to operatewith transducers with bridge resistancegreater than 200 ohms and less than500 ohmsOutput Impedance: Less than 4, 000ohms (100K ohms minimum recommendedload)Non-Linearity and Hysteresis: Less

than +0. 3~o of full scaleTemperature range: Opsrating -65“Fto +180-R Non-operating -75 “F to+230”Thermal coeff. of sensitivity: O.015%per degree FThermal zero shift +0. 005’% of fullscale output per de~ree FVibration tolerance: Constant dis-placement of 0.75 double amplitudefrom 5 to 30 cps. Constant acce lera-tion of 35g from 30 to 2, 000 cps.Vibration applied along any major axisStatic acceleration: 100g along anymajor axis

4. Tape Recording System

Manufacturer: Mirmeapo lis - Honeywe 11

Regulator Company, Heiland Division,4800 East Dry Creek Road, Denver 10,ColoradoTape Transport: Type 3167, 0.3 and0.6 lPS tape speed, for 1 inch taPe,10 1/2 reelsRecording Head: IRIG Standard record

head stack assembly (2 heads inter-leaved, 14 tracks per inch) 14 tracks.Recording Oscillator: Dual FM Re-cording Oscillator, Type 4206. 0.27 kccenter frequencySystem Performance:

Input Level: 0.5 to 25 volts rms for+40 percent carrier deviation. Ad-~ustable by means of front panelco ntro 1Input Imps dance: 10, 000 ohms, un-balanced to groundFrequency Response and Signalfioise

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Ratio: DC - 50 CPS, 0.27kc, 36(compensation improves S/N ratio by20db)Total Harmonic Distortion: Less than270DC Linearity: No more than O. 5%deviation from best straight line(~40Yo deviation system)Drift Sensitivity: Less than +0 .27’0 offull scale in six hours after 1-/2 hourwarmupDC Drift: No more than O. ZYOof fullscale per hour warmup (+40% devia-tion system)Output Leve 1: 4 volts peak maximumfor full scale deviationOutput Current: 30 milliamps maxi-mum (standard output)Output Impsdance: Less than 1 ohmOut put Character sties: Balance,short- circuit proof; can be operatedwith one side grounded. Output re–turns to zero with no input signalpres~nt (squelch) or with over-modulation (adjustable from + 50~odeviation) for oscillograph g=lva-norneter protection.Ibw Pass Filters: Type 523z, FlatFrequency Response: dc to maximumspecified cutoff frequency, + O.5 db.—overshoot unspecified.

* U.S. GOVERNMENT PRINTING OFFICE ,563 0-69! .’733

NATIONAL ACACEMY OF SCIEi7TCES-NATI ONAL RESEARCH COUNCIL

Committee on Ship Structwal Design

ChairmaA: N. J. HoifDept. of Aeronautics & AstronauticsStanford University

Vice Chairman:M. G. ForrestGibbs and Cox, Inc.

Members:C. O. I)ohrenwendRensselaer Polytechnic Institute

;. Harvey EvansDept. of Naval Arc hitectu:re and

Marine EngineeringMassachusetts Institute C)fTechnoJo9Y

D. K, FelbeckDepartment of Mechankal EnglileerktgUniversity of .Mic higan

J. M. FrarddandMechanics DivisionNational Bureau of Standards

William PragerBrown University

J. J. StokerDepartment of MathematicssNew York University

——.. —.— —

Arthur R. Lytle R. W. Rumke

Director Executive Secretary