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CIEHRIHGHOIISC POR PEDE'JAL SCIENTIFIC AND

TECHK ^*. INFORMATION HardoopT Klcroflalw ^^^ jp

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U. S. NAVY

MARINE ENGINEERING LABORATORY

Annapolis, Md ;') •:*.*&

Dedicated To PROGRESS IN MARINE ENGINEERING

Distribution of this document is unlimited.

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DEDICATED TO PROGRESS IN MARINE ENGINEERING

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the discovery of fundamental knowledge, the

development of new and unique equipment to meet

and anticipate new naval requirements, analysis

of Fleet machinery failures, and evaluation of

prototypes to insure high performance and relia-

bility in the fleet. Dedicated to progress in

naval engineering, the Marine Engineering Lab-

oratory contributes to the technical excellence

and superiority of the Navy today - and tomorrow.

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Vibration Transmission of Flexible Pipe Couplings Influenced by the Elements of

a Trim-Pump System

Assignments 67 102 & 72 105 MEL R&D Report 263/66

September I966

By Ronald C. Hirsch

O

RONALD C. HIRSCH

Approved by:

J. M. VALL1LLO Ship Silencing Division

r\4 a *<rfU. .«-<»_ ~t l.\.l~ J_.

MEL Report 263/66

attribution List

NAVSH1PS (SHIPS 2021) (2) NAVBHIP8 (SHIPS 442) (Mr. John Vasta) NAV8HIP8 (SHIPS 436) (Mr. A. P. Astt l^32!IJ£!(SHIPS525AN) <Mr- R- B. Ifartsig) NAVSHIP8 fRRIPS 031) Addrcas«« (5) l^VBEC (Code 6648) (Mr. H. Kraut) (5) DDC (20) v ' COONR, London (2) NRL (Dr. R, Bdshelm) NHL (Mr. 0«ne Hemmers) ÜEBD, KORVA (Dr. H. Schauer) NSL (Mr. Q. M. Coleman) NAV8HIPYD PTSMH NAVBHIPyD MARE S^SS^H !rHAN <Mr- c- Schrader) NAV8HIPYD 8FRAN (Mr. L. 8. Jue) SSJS' S.0RVA L^' D- Cohen) DTMB (Mr. P. Schloss) DTMR (Dr. A« Powell) NAV6ECPHOLADIV Dr. R. Plunkett

Univ. of Minnesota iutltute of Technology MlnneapoUs 14, Minn.

Dr. M. Junger Cambridge Acoustical Assoc. Cambridge, Mass»

Dr. E. Kerwin fiolt, Baranek & Newman, Inc. SO Moulton St. Cambridge 38, Mass.

Soimd tt Vibration Wctton, R&D Dept. Slaetrlc Boat Dlv. Ctaneral Dynamics Corp. Oroton, Conn«

ü?1^1^8!*^00* <Mr- Robert Strasser) Mr. 0. V. Wright Westlnghouse Electric Corp. Pittsburgh 35, Pa.

Mr. F. Clngel Weetlnghouse Electric Corp. Defense tt Space Center Baltimore, Md.

11

MEL Report 263/66

ABSTRACT

An analyttcal-experimental study was performed to de- Wrmuie the sound transmission characteristics of a nexihle «oupling in a trim-pump system. Mechanical impedance methods were used to compare the structural path to the hull via resilient mounts and foundation to the structural path via flteibie coupling and pipe hanger. Also investigated were the vibration characteristics of an Electric Boat and MEL flexible Coupling under pressurized and unpressurized conditions.

Results showed that the sound transmission via flexible eoupling and pipe hanger exceeded the sound transmission via the mount and foundation and would negate the Isolation effectlvenesa of the primary mounting system. The results of comparing the two types of flexible coupling showed that the Electric Boat Coupling exhibited better total noise attenuation characteristics than did the MEL coupling. However, the MEL coupling showed a unique inherent characteristic of improved attenuation capabilities with increased pressure loading.

ill

MEL Report 263/66

ADMINISTRATIVE INFORMATION

Thii Inveattgatlon was authorized by reference (a) under NAVSHIPS (formerly BUSHIP8) Sub-project S-F013 11 08, Task 01352, and by reference (b) under NAVSHIPS Sub-project 8-F113 11 09, Task 03955.

Iv

MEL Report 263/66

TABLE OF CONTENTS

Page DISTRIBUTION LIST ,. ABSTRACT " ADMINISTRATIVE INFORMATION /„ INTRODUCTION Y

Problem: The Noise Transmission Path i Prior Work t Objectives :

INVESTIGATION J Mathematical Mobility Model o Utilization of Solutions 2 Resilient Mount-Foundation-Hull Transmission Path 2 Data Acquisition 3

COMPARISON OF TWO TYPES OF FLEXIBLE COUPLINGS 4 Approach Flexible Pipe Coupling Description 4

VERIFICATION OF EXPERIMENTA^ANALYTICAL TECHNIQUE 4 Direct Experimental Measurement 4 Experimental-Analytical Method R

RESULTS J Flexible Coupling Force Ratios 5 System Force Ratios g System Transfer Impedances 5 Comparison of Flexible Coupling Types 6 Comparison of Transfer Impedance Methods A

DISCUSSION J Limitation ^ System Corrective Measures 7 Flexible Coupling Modifications

CONCLUSIONS AND RECOMMENDATIONS FUTURE PLANS LIST OF FIGURES

Figure 1 - Curve, Schematic ol Discharge Side of Trim Pump System Figure 2 - Curve, Mounted Ttim Pump and Foundation Figure 3 - Photograph, Flexible Pipe Coupling Configuration Figure 4 - Curve, Schematic of Instrumentation System Figure 6 - Curve, Flexible Coupling Force Transfer Function, T7* Figure 6 - Curve, Flexible Coupling Force Transfer Function, Te* Figure 7 - Curve, Flexible Coupling Force Transfer Function, To* Figure 6 - Curve, System Force Transfer Function, Tte) 14* Figure 9 - Curve, System Transfer Impedance, Z/s» ,4* Figure 10- Curves, Flexible Coupling Force Transniisslbility, T7* Figure 11 - Curves, Flexible Coupling Force Transmisslblllty, To* Figure 12 - Curves, Flexible Coupling Force Transmissiblllly, tl* Figure 13 - Curves, Flexible Coupling Blocked Transfer Impedance, Z7* Figure 14 - Curves, Flexible Coupling Blocked Transfer Impedance, Zg*

2

4

7

8 8 e

MEL Report 263/66

TABLE OF CONTENTS (Continued)

Figure 15 - Curves, Flexible Coupling Blocked Transfer Impedance, ZQ* Figure 16 - Curve, Experimental Verification of Computed Method. ZT/A

APPENDIXES '/H

Appendix A - Development of System Response Matrix (3 pages) Appendix B - Development of Mount-Foundation-Hull Vibration Response

Equation Appendix C - Free Mobility and Impedance Measurements of System

Elements (7 pages) Appendix D - Technical References

vl

MEL Report 263/66

VIBRATION TRANSMISSION OF FLKXIBLE PIPE COUPLINGS INFLUENCED BY Till. KEEMFNTS OF

A TRIM-PUMP SYSTEM

1.0 INTRODUCTION

Designing submarine machinery components to withstand deep submergence vet maintaining uncompromising efiorts in effecting proper structurebome vibration isolation, is a problem of dominant importance to the Navy.

1'1 Problem: The Noise Transmission Path. Submarine radiated waterborne noise caused by vibration transmission from machinery to hull via foundations has been ef- fectively controlled by use of resilient vibration isolation mounts. Due to the effectiveness of these Isolators, alternate sound transmission paths, such as electrical power cable bundles, flexible pipe couplings, flexible exhaust stacks, and pipe hangers were revealed. The relatively high rigidity of these elements "short circuit" and negate the effectiveness of the principal isolators to an extent sufficient to cause the transmitted noise to dominate a portion of the radiated noise spectrum.

1.2 Prior Work. Experimental evaluation of isolation devices Is deemed possible1.2 if the measuredtransfer Impedance across the Isolation device is small compared to the driving point impedance at both interfaces where the Isolation device terminates. Vibration t/ansmission studies of two isolation devices, a flexible snorkel exhaust joint-* and ar electrical power cable bundle4 have been made. The transfer impedance of the elements, when compared to the transfer impedance of the principal Isolation mount used in the system, showed that both the exhaust Joint and the power cable bundle possessed sufficient rigidity to become the controlling factor In the Isolation effectiveness of the resillently mounted machinery system.

1.3 Objectives. Deep submergence submarines impose greater reliability demands on sea-water piping systems because they must withstand the stresses induced by the depth pressures. These demands require structurally stronger flexible pipe couplings. Strength, in turn, tends to increase the vibration transmission properties of this type of isolation device. One objective of this investigation was to perform a system analysis to determine the overall vibration transmission properties of a flexible coupling in- serted in a typical trim-pump system. Another objective was to compare the vibration transmission characteristics of two 4-inch flexible pipe coupling assemblies under pressurized and unpressurized conditions. A third objective was to verify, experimen- tally, the analytical-experimental approach used to fulfill the first two objectives.

2.0 INVESTIGATION

The experimental-analytical approach, based on the work of Smith,5»6 was used to investigate the vibration transmission properties of flexible pipe couplings when

Superscripts refer to similarly numbered entries in Appendix D.

which

MEL Report 263/66

^«eTSrraSS^- l^6 ' 1S a 5<:hema,"; '»P^entatlon of the dls.

V5 | |V61 (1)

T;5. ^where n-. ^[rqi^rpr (2)

vibration characteristics. ^^^S yieiaea simplified yet meaningful system

by the resülent mouS. founitio^aLd LT ^^"S t?8 f th! P.ath described

sldered the dominant sound transmission nkth A ft ' ^tÜ ,recently. had been con- Darby ^proposed ameans ote^mü^V^fc^^^Z 0f "* *0rk 0f XVri^'1

items, taking Into consideration C «™.nT^w 5, .tion of mounted machinery mount and foundation ^d the pa hs toX Si W^Ä^ f?0t t0 hul1 vla ^^tion devices. A less rigorous attach Is ^Zl^letZ:^» 'Äi.e

MEL Report 263/66

data. However, a meaningful comparison of the structural noise transmission between the two paths can be made to show the, drastic "short circuiting" effects of flexible Dine couplings and to provide possible criteria for future flexible coupling design. The development of the vibration response equations defining the mount-foundation-hull oath is presented in Appendix B. Figure 2 Is a sketch of a trim pump mounted at four points on a symmetrical foundation. The approach used the known transfer impedance characteristics of the resilient mount, Zab; measured impedance characteristics of the foundation, Zbc (between foundation input. Terminal b, and foundation - hull interface Ternunal c); and the driving point impedance of the hull, Zcc. Solution of the equation resulted in a power-summed transfer impedance, defined by the forces developed at the foundation - hull interface by a unity velocity excitation applied to the four mount injiHixs i

[ab cc * Z„= 2 ■ - ,

T ZH„ O)

I T^t* c°mParison of Equation (3) with the power-summed transfer impedances of the flexible piping system. Equation (1), indicates the controlling sound path and pro- äronhe thf ^ ^ inCreaSe in waterborne noise as a result of the domination of

2.4 Data Acquisition. Solutions of Equations (1) through (3) were obtained usinir ex- penmentally measured mobility responses of the flexible pipe coupling, trim pump and pipe hanger and assumed piping impedance parameters. Representative hull termination and foundation Impedances were collected from published material. All exoerl- mental and assumed data appears in Appendix C.

f'ti1 Experimental Measurements. One of the two flexible pipe couplings, arranged in the three planar contlguration, ib shown in Figure 3 resiliently suspended and free from end constraints. Sinusoidal excitation was applied along three orthogonal axes designated by Terminals 4, 5, and 6. The three free driving-point mobilities mj mgg. and m66. were measured with a Wilcoxon Model 820 impedance head. The nine remaining transfer mobilities were obtained using the force-measuring element of the impedance head and Clevite 2ÖD21 accelerometers oriented at the output end of the con- hguration at the orthogonal terminals. 7. 8. and 9. The acceleration signals were time-integrated ratioed with the force signals, and processed by the electronic system, the schematic of which is shown in Figure 4. Digitized mobility magnitudes and phase angles were recorded by the analog to digital instrumentation. In a similar manner the three driving point mobilities at the trim-pump output flange were measured and digitized. The magnitudes and phase angles were used in the digital programminK tech- mque« to solve the coupled system response matrix. Equation (A8) and Equations (1)

2.4.2 Given Data. The hull and foundation data necessary for the solution of Equation (ö), i.e.. zcc and Zbc, are representative of measurements on a Heet-type submarine However, the curves were smoothed and averaged and do not represent responses for any particular submarine trim-pump foundation - hull combination. The blocked transfer impedance of the 6E2000 resilient mount, loaded to H50 pounds, was usedlo dX ^ab. Ihe foundation, hull, and mount data are shown in Appendix C.

MEL Report 263/66

3.0 COMPARISON OF TWO TYPES OF FLEXIBLE COUPLINGS

3.1 Approach. A method sinülar to that summarized in paragraph 2.1 and detailed in Appendix A was used to compare, quantitatively, the vibration characteristics of two types of flexible couplings. Free mobility measurements were taken of each flexible coupling type, unfilled at atmospheric pressure and water filled at 600 psic * To malntaüi consistency with the philosophy reported in other studies of isolation device-

' ' ' .v 0ütpi£ end üf each couPlin8 ^Pe was blocked. In this report, the blockiim' waa mathematically accomplished by setting the velocity response equations, defining the output Interface, to zero. Solutions of the blocked forces, developed at the output Interface, ratioed to velocity and force inputs, yielded blocked transfer impedances and blocked force ratios.

3.2 Flexible Pipe Coupling Description. Two types of 4-inch-diameter flexible pipe couplingB were investigated. One type, developed by Electric Boat (EB) and shown in the three-planar configuration. Figure goffered limited flexibility by means of a "ball SL8*?6* a™*ement. the '^1" or inner pipe spool being isolated and water seeded from the "socket" or outer casing by rubber. The other type, developed by MEL was similar In external appearance to the EB coupling and provided a pressure equllization feature to maintain coupling operation if seal rupture occurred. Flexibility of the coupling was provided by a thin film of sampled pressurized fluid and two rubber "O" ring seals located between "ball" and nylatron lined "socket." Three MEL flexible couplings were arranged in a three-planar configuration.

4.0 VERIFICATION OF EXPERIMENTAL - ANALYTICAL TECHNIQUE

To verify the approach used in this Investigation, it was decided to compare the .rn^fr« tJa^fer ^P^»00 of f

the EB flexible coupling when terminated into a finite ^trS06 t0^e comPuted transfer impedance using the measured free mobility char-

acteristics of the coupling and termination. y

t1 ,i^jrect Experimental Measurement. To measure the transfer impedance directly * methoa previously presented^ 8 waB used. 0ae end of the flexihle u ^ ' ted to a force measuring fixture in which four EB force gages were arranged in such a manner as to sense the forces normal to the plane passing through the flange Interface defined by Terminal 7. The fixture, in turn, was attached to a Wgh-lmpeSce termT- Äf;«!^ o0^8 V!SrfUOin *f™r?or*** attached to the free end of the coupling, T^Si 'J** ai^0iM ^"y ^«nals were measured by a Wilcoxon Model 820 impedance head. The force signals developed at each of the four force gages were in- dividually ratioed to the velocity signals developed at the excited free end Terminal ii ♦ ^e8^tin8 four transfer Impedance curves were power summed to give one over-

Si SÄ' ^P6^0!/ characteristic of the system, and to maintain consistency with the technique employed in previous isolation device Investigations.

"Abbreviations used in this text are from the GPO Style Manual, 1959, unless other- wise noted.

MEL Report 263/66

ttn^fy i a^~^n^^caI.Me-t-^- The experimental-analytical technique utilized the previously measured free drivd-s point and transfer mobilities of the EB flexible couplings. In a manner similar to that described in paragraph 2.1. the velocity response equations involving the free mobility measurements of the flexible coupling and driving point Impedance of the termination fixture were mathematically coupled funTf^lt '^^ tvunsier impedance of the system was computed from the solutions of the coupled forces and velocities.

5.0 RESULTS

♦^ „,. »! f I *Z0Xeh !,are force ratl08 <outPut force/power summed Input force) of the pressurized EB flexible coupling. Figures 8 and 9 are the force ratloa and trana- fer impedances of the trim pump system, influenced by the pipe hanger and plplmr oara-

Se iBan^MÄ11« " 1^°^ 15> the blocked force ratloB a"d transfer ImSSs of the EB and MEL flexible couplings, pressurized and unpressurlzed, are compared

tL FlexlMe Coupling Force Ratios. The force ratios are observed to be Influenced ^the pipe hanger ^nd^lplng constraints imposed upon the flexible coupling ouSlr- nunals. The piping response characteristics were simulated by assigning constant impedance magnitudes to the piping Input terminals to create an enve&eSÄmr

SÄ C FIJCTI r ' ^rmtrfl0T The impedance values arTshSiA^ «™Î ^ t!.;0, F1Kures 5 and 7 8how force ratl08. T7 and To. Since the re- n^^nt Ä nt3dMv1

e C0Upllng in the di«^0"8 indicated by TernünaSs 7 and 9 Is tade- ShnfÄ iP f ^^coâtats. Figure 16. the differences In forceMtlM are attributed solely to the piping parameters. Figure 6 depicts the force ratlos Ta de üning Terminal 8. Little difference can be noticed between force Xs for wS^t and antlresonant pipe responses throughout the frequency spectru^ This cSSls- noCin

1t

8ieêdW9he^tISnfted' FlgUre 7-C' ApnendlxC. t^t thTplÄg« Sng point imi^dance.S Z1313, is consistentiy higher than the resonant plffnSpe<W magnltud«. The constraint offered the flexible coupling by the pioe ffirer doSt« hat contributed by the piping. The dynamic forcJdeyelêdaX^ tTtL- uZ'tlt^l^ ^P611^ of the PiP^ Parameters, but are predoSStiy de%S upon the high Impedance characteristics of the pipe hanger. «epenaeni

5.2 System Force Ratios. The force ratios, T*15, are shown In Fifrure 8 When eom. ^ .gUre86and8'itis evident that the forcil'developed at TeSai 8 assJcJaSd ZlXZfoTnTl^ wrt06 Pa.rame/er' mdQtS0 ne^glÄtenuîrle-6' tween 20 and 200 Hertz (Hz). When the system force ratio associated with the hldi antlresonant) piping response Is considered, however, sufficient SffereSeseSfflr ÄÄelbetW«en P/Pe **?*** md Plpe' Fiê 7-C AppenS^ to Se^L sideraUe attenuation from 20 to 800 Hz. For frequencies greater than 800 Hz the forces developed at Terminal 8, for both values of pipe impldWes. we a^nukted f~ Äy •, T1^8 lnd!i1

cate8 that the 8y8tem force ratios. in this f?4queney rZe are relatively independent of either resonant or antlresonant piping VesSefSd are predominantly a function of the pipe hanger characteristics. ^P00868 and are

o;3^Kem T^ter êgdanceg. Figure 9 is a superposition of transfer Impedances of the wo sound transmission paths. Comparison of the Impedance nStudes viSds a quantitative evaluation of the performance of the two isolation ayst^ä The vlbi tional characteristics of the mount-foundation-hull sound ÄlT^ M^ScÄ ness line of approximately 3500 lb per In. from 20 to 170 Hz. At frequeSatove

MEL Report 263/66

170 Hz, the response is predominantly influenced by the ioundation-hull charactcnslios. Reasoning similar to that used in paragraph 5.2 explains the factors controlling the characteristics of the flexible coupling system transfer impedances. The importance of Figure 9 is to show the negating influence of the flexible coupling part of the sysicm on the isolation effectiveness of the primary mounting system. It is seen that the two impedance curves of the flexible coupling-hanger system form an envelope describing the maximum and minimum impedance values possible with the assumed piping impedance parameters. At 100 Hz, the curve associated with the resonant piping condition indicates that maximum forces developed at the pipe hanger-hull interlace exceed those developed at the hull-foundation interface by approximetjly 43 db. At frequencies above 1000 Hz, both curves coincide and extend below the impedance curve describing the primary mounting system.

5.4 Comparison of HexiMe Coupling Types. Figures 10 through 15 are the blocked force ratios and blocked transfer impedances of the two types of flexible pipe coupling preBSurized and unpressurlzed. The curves were smoothed by computer to simplify " comparison. It must be understood, however, that the results give only a comparative evaluation of the two types of flexible coupling and do not indicate performance when in- corporated in a system, since rarely is the coupling terminated by blocked conditions.

5.4.1 The blocked force ratios, Figures 10 through 12, show that pressurizing the MEL flexlUe coupling decreases transmitted forces in the low- and mid-frequency range. This phenomenon can be explained by realizing that the MEL coupling's pressure equalizing feature provides a film of pressurized water between "ball and socket." When the film is considered as a resilient layer in series with the elastic nature of the nylatron "socket, " a combined resilience of lower dynamic spring constant would result, thereby providing some vibration isolation. Above 1000 Hz, however, pressuri- zatlcm causes relatively high force transmission to extend to higher frequencies. The EB flexible coupling force ratio is relatively unaffected by pressure from 20 to 800 Hz However, high force transmission extends into the higher frequency region, similar to that which occurred for the MEL coupling. Comparison of the flexible coupling blocked force ratios, pressurized and unpressurlzed, shows that the EB coupling yields lower force transmission characteristics across the frequency spectrum; the greatest dif- ^n!;e k*^611 the tw0 couplings, approximately 35 db, occurring between 400 and 5000 Hz for the unpressurlzed condition,

5.4.2 Both flexible couplings present similar transfer impedances. Figures 13 through 15, characterized by high antiresonant or blocked force magnitudes at approximately 1400 Hz and rapidly decreasing to minimum impedance magnitudes. Antiresonances or high impedances should be emphasized since, in these,,regions, maximum Mocked forces are developed. If a comparison of Z$, Z|, and Zg for each flexible pipe coupling confl^ration of like loading conditions is made, it is seen that the forces developed at Terminal 7 predominate over most of the frequency spectrum except at the high antiresonant region centered at 1000 Hz, where the forces developed at the three terminals are comparable in magnitude.

5-5 Comparison of Transfer Impedance Methcxls. Figure 16 is a comparison of transfer impedances of the EB flexihle coupling configuration determined by experimental techniques and by the computational methods discussed in this report. Little corro- boration of the two methods is apparant between 20 and 50 Hz. There is Justification

MEL Report 263/66

fcTtüVho T**?that reasonahle correlation exists between the two curves when the fact that the direct measurement involved translational and rotational resoonses whil. the computed techniques consisted only of translational responsesTterrffi ?' Uck fi. e.tteliCtrr0b0,i:aii0a can al80 ^ attributed to the generalized response chTracter- ^«t to tlC

fihÛltfr0n? rWer sum

Jmla?the *™ individual transS^cea in con- trast to the polnt-by-point computed technique which results from the ratiolna ol L«

crete forces and velocities at Terminals 7 and 4. It Is unfortSe that time dW not m^fTnaHTreÄ0Sl1

COinparlSon of technêB. Ass^greclprod^ ^d s^n- ^.lYnf # S6 ** n!lhle couPlln8,8 ^faulty characteristics accuSatdyT for 6 de- £ wS^SSSil^mr 0£ 3» ffee

urbility âsurements woSJKeqJredT tue 12 translational mobUitle«, used In this report, plus 12 rotational and is ^«T

lational-rotatlonal mobültles. A similar series of me"iem^ärfÄnÄ; fixture would be necessary, defining the fixture by a n^Tuô" 2 frTe mSSKf A system of equations of formidable size would result T.H i« Lil, !f ^ * , !f' of the matrix and computation of F7/V4 w^ termlned transfer Impedance, particularly between 20 and 50 Hz. eXper-mentally de-

6.0 DISCUSSION

nt ^ ^rl8ht|,sl,phÜ080phy ref^rdiae the generation of waterbome sound as a function

of the dynamic forces transmitted to the hull Is reflected In tWs tovestißiüon w£rp the characteristics of the system are defined In terms of Ite devetÄÄ

6.1 Limitation. Darby^ developed an approximation to predict the Increase In radl- a«n.5F^?^d,,dU^t0 the contro11^ effect of one isolation deSfhlgh'mped- ance when It was Installed In a reslllently mounted machinery svstem AoriÄtÄT sign curve of reference 2 at 100 Hz. a 36-db Incr^SateÄwÄnSs^ suits when the flexible coupling transmission path Is Included comired to fhe orlLrv SÄ'r,ni8S!0,lpath/ TemP«ring this Screase wiihthTSStSt^riSS character sties at the terminations of foundation - hull and pipe hanger-huU?M art «v^frV?.1"' i"l8 »âPP'-^nt that a serious limitation Is SSed S the effec- Son A6 ^^^ 1SOlati0n 8yStem by the flexIhle couPlto« - &* Ä tr^-0

6.2 System Corrective Measures. Assuminethat for atrenffth »Hhrd««« «„J u 1

SÄtteüefhle?OUpllngi8o£ optlmum Ä ceXÄectiÄrSÄ'

Ä fthe 8y8tfm element8 t0 reduce the foroe8 transmitted to the hX WrtfoSarlv

for those frequencies at which the piping undergoes resonant conditions. Flwre 7-C £Z â l,

the,cr8tant iaV****<* magnitude describing the lêr iSt (resS^ce con- Ä?^6 t^l re8p0n8,e envelope lles entirely bel*w the driving potot ImSce äû ^ ^ ^ ,hanSer• Zl313- The confitralnt offered by the hangSrlherK Jin^fS.* n ^fPf6»4 of relatively high forces at the pipe ha^SJpe Interface Since, for all practical purposes, the force ratio of a hamreria unftv hJik Slü -t* transmitted to the h^. To reduce the forcesê hÄemÄea'JÄôf sufficlenüy low Impedance to minimize the forces develop at the pSe hSr l3 terminal. As an eMunple, a hanger exhibiting the ImpedSce proÄs^fl Ä r« Ä ^L10^t0 10^ P0™08 WOuld exhlblt a dyrS sprTng^Ä of a^!" matdy 310 lbs per in., Figure 7-c. Its Impedance magnitudes lie below that deseSbina ve!0

PÄ tHflTSM0ndIti0,?' ^^ 0fferin« ^ i80laS P0'^ to tTe^ces de^ veloped at the flexible coupling output terminal. t~ « 1« we iorces ae

MEL Report 263/66

6±. Hexlble Coupling Mediflcatlons. It Is evident, from Figures 10 through 15 that neither type oiüeÄ coupling is a satisfactory isolation device. The MEL coupling fr^'^Ä lmpr0Ved !f0lSf0n cha^^8tics when pressurized, shows po/' tential if modifications are made. Improved isolation properties would te feasible if Mat^n 1Äf0fn,Ing ^ ^^ 3urface ln «ach casing or "soXt" were rep Led £r wodd nÄVÄ; T5e CTbintd efleCt between P^ssurized water im and rub- Xenttv «^lÄ lmpr0Ve .damP nS. but also result in a lower dynamic stiffness than presently exists between water film and nylatron liner.

'. 0 CONCLUSIONS AND RECOMMENDATIONS

7.1 The conclusions derived from this study are:

^K—«* T1if bl0ck rubber P1?6 hanger and piping responses predominantly affect the ?JiS;?ÄSeri9*iCfl ?f *? aexiUe CWPlln« ty***- With the PS ^dergoing XTr™™'^ *** ^ l8 ,ne£feCtIVe ln reduc1^ the Ä- f-ce 'ratios

r,ihiv.^Sefcter reduction of, the system-transmitted forces would result if the block rubber pipe hanger were replaced by an Isolation device of low dynamic stiftaess terminated directly to the hull frame or a rigid structural member;

m-w To J« transfer impedance of the flexible coupling system exceeds that of the pri- oTSÄS Ss? 8y8tem' ^^ ^^the n0i8e attenuati0n âcterisSs

MEL aJuLel^Sg* COUPllng eXhiblted better VlbratIOn characterl8tlca than did the

tAn,.0««.Tif*i,M1EL fleXi5le ow&tog offers the unique feature of Improved vibration at-

tenuation with increased pressure loading. The combined effect of replacing the nvla- ÄÄIJLtnnrUb^ "? thf P,re88Ure 9en8ltlve attenÊelre. shol im^ve the flexible coupling vibration isolation characteristics. , ^î mprove

7.2 Recommendations are as follows:

i».^* ^ ^f ba818 ?f ^ re8ldts of the system analysis, an isolation device of low SÄ;6 md P^rfy termi^ted should be used in lieu of the eSsttag Sck rubber sSsÄVcrrÄ!16^68 are empioyed to o™****the ^- ^ber

.,.«„ * Slnclthe M^1- fle^ble coupling exhibited favorable pressure-dependent attenuation properties efforts should be continued In its development for swXS use

feristics. ^^ al80 Pre8ent8 faVOrahle 8trength ^d shoTresis^t c^frac-

MEL Report 263/66

8.0 FUTURE PLANS .

«„cfoJ? ^ PlaTd « conti1nue *e Investigation of flexible couplings as influenced by

system elements. Since the trim pump system lends itself to realistic modeling a Ä^Ä? thKnf£8tem elementS f0r mlnlmum sound transmission Sd fnclude fntn .^ ? m0^ity ^«"r^ents of various types of flexible couplings and hoses into the system matrix, along with Improved pipe hanger characteristics.

BLANK PAGE

MEL Report 265/66

USN MARINE ENGINEERING LABORATORY

0-

>-l30- PIPE HANGER

TRIM PUMP

-O 1 -O 2

40- JO-

60-

FLEXIBLE COUPLING 2i< v I0O-

^ 11 O- J20-

PIPING

• 14 ISO-j HULL

FLEXIBLE PIPE — ^.COUPLING

^1

PIPING

Figure 1

Schematic of Discharge Side of Trim Pump System

MEL Report 265/66


Figure 2

Mounted Trim Pump and Foundation

MEL Report 263/66

USN


NOTE:

1 - Goodmans Vibration Exciter2 - Impedance Head3 - Suspension Cord4 - EB Flexible Coupling (3-planar Configuration)5 - Accelerometers (Orthogonally Oriented)

IA.’,

Figure 3

Flexible Pipe Coupling Configuration

MEL Report 263/66

o EH

O ffl

H a; w H 2! H

« w H

z D

o o

-YL ^ I

"S 1

Jp 2:

rlbn *-" — < —1

■hr*

t t

I UJ Ä to o

a- 5

O 1- •— _l QC <

o u

O z "- os"~

T

-W

Z ae O üf

CD

^

UJ<2

a.<t UJ UJ O

O

a: O u. O

o

UJ O 0 ^ a. <»- S «1

'-•- o

t t ♦

o 1-1

x z

S

e (U

M

w c 0

•H

c a) E

w c

0

Ü ■H 4-) rfl e (1)

rC u tn

(^ 3

■H

MEL Report 265/66

USN


Figure 5*

Flexible Coupling Force Ratios T 7

MEL Report 265/66

USNMARINE ENGINEERING LABORATORY

-“idE PIPE

COUPLING

0) 0) ^

• fi

PIPING

jj: PIPE HANGES

1--

Hua 0

Figure 6

Flexible Coupling Force Ratios T*3

MEL Report 263/66

USNMARINE ENGINEERING LABORATORY

I .

F- =/;.M'*lFil^|Fj'

f:EXIBU PIPE

"i

iT- ^

PIPING

>-

TiT PIPE hanger L>'<7\|C^

hUtl.©

Figure 7

Flexible Coupling Force Ratios T*^

MEL Report 265/66

USN


f,

/HUH

0

Figure 8

System Force Ratios

MEL Report 265/66

USN


hiV4

hiVs

-COUPLING

'1II

HUlI ©

Figure 9

System Transfer Impedances

MEL Report 265/66


Wflrer EJ 1 Lad

(Appli^j to the ov two curves^ ^s two curves)

FLEXIBLE COUPLING

T*7 = F7 (Blocked) Fi

where Fi =7^1 2 ^P +|F6|2

i

Unfilled at 0 psi

Figure 10

Flexible Coupling Blocked Force Ratio T*-?

MEL Report 263/66

USN


(Applies to the two curves)

1 40—

2 503 60—

FLEXIBLECOUPLING

. F| ( Bloclced )

'•-Ti-------------

wher* \ *1 ‘*'1 h

^8—09

Unfilled at 0 psig

Flexible Coupling Blocked Force Ratio T*0

MEL Report 265/66


water Filled 600 psig


FLEXIBLE COUPLING

7 Fj (Bloclced) Fi

where Fi =/] F4 |2+| F5|2+ | F6|

Unfilled at 0 psic

Flexible Coupling Blocked Force Ratio T*o

MEL Report 265/66


Water Filled 600 psig


O 1 40— FLEXIBLE

1 ? JO—

03 60— COUPLING

2 . .2 . _ .2 f? + h + h V4 v5 V6

>9 yy

y

i;

where F7 is blocked force

Unfilled at 0 psig

Figure 1?

Flexible Coupling Blocked Transfer Impedances, Z*y

MEL Report 263/66


Water pilled 600 psig

^THT

FLEXIBLE COUPLING

4 V

(Applies to the 9« two curves) ^« "

/ . .2 . .2 . .

./ \ t \ + ^

/ V4 v5 Vö

where F, is blocked force

Unfilled at 0 psi

Flexible Coupling Blocked Transfer Impedances, Z*Q

MEL Report 263/66


er Filled ^QO psig^

FLEXIBLE COUPLING H p

1: f.l • f>l • ' u' (Applies to the

two curves)

where F9 is blocked force

Figure 15

Flexible Coupling Blocked Transfer Impedances, Z*Q

MEL Report 263/66


4-

- j ^ I- -

^^i-: ' | ;>- . -1. \ , t-t, :->r

'Hz

Figure 16

Experimental Verification of Computed Results z j/u

MEL Report 263/66

APPENDIX A

Development of System Response Matrix

MEL Report 263/66

REFERENCE

(a) Smith, J. E., "Vibration Transmission through Rubber Block Pipe Hanuers ' MEL rept (in preparation)

A-ii

MEL Report 263/66

The uncoupled velocities and forces at each numbered terminal, and the measured free driving point and transfer mobilities (translational only) of the elements of the system are defined according to the following sets of equations:

Trim Pump at Outlet Flange

Vl = fimii + v01

Vl=f2m22 + V02 (Al)

V2=f3m33 + V03

The v 's are the free velocities that exist at the pump output flange when it is free of connections. They will represent the velocity excitations by the pump on the system when the system elements are united.

flexible Coupling at Input Interface

v4 = f4m44 + f5m45 + f6m46 + f^ + f^ + f9m49

V5 = f4m54 + f5m55 + f6m56 + f7m57 + f8m58 + f9m59 (A2)

V6 ' f4m64 + f5m65 + f6m66 + f7m67 + f8m68 + f9m69

Flexible Coupling at Output Interface

V7 = f4m74 + f5m75 + f6m76 + f7m77 + f8m78 + £9m79

V8 = f4m84 + f5m85 + f6m86 + f7m87 + f8m88 + f9m89 (A3)

V9 = f4m94 + f5m95 + f6m96 + f7m97 + f8m98 + f9m99

Piping Input Interface

vio3fiomioio

Vll =fllmllll

V12 = f12mi212

.(A4)

Pipe Hanger Input Interface

V13 = f13mi313 + f14mi314 (A5)

MEL Report 263/66

Pipe Hanger Output Interface

V14 ' f14ml414 + f 13ml413 (A6)

Hull Input Interface

V15 = f15mi515 (A7)

The measured transfer mobilities between terminals located at the pump outlet interface are low compared to the driving point mobilities; therefore, it is assumed no coupling exists between terminals. A similar assumption was applied to the hull mobility (inverse impedance), therefore, one measurement, misis, was used in a di- rection normal to the hull. The free mobility measurements of the typical block rubber pipe hanger, the vibration properties of which were reported by Smith, reference (a), were assumed to be unidirectional.

The vibration transmission properties of the flexible coupling in shipboard systems are largely a function of the termination offered by the piping system, the physical arrangement of which is often dependent on available compartment space. No typical impedance measurements are available, therefore, to define this boundary condition. To compensate for the lack of detail, response values, defining the envelope between antiresonant and resonant conditions, were assigned to the fictional piping system by assuming constant impedance magnitudes as parameters. Terminals 11 and 12 were designated as radial orthogonal axes having equal impedance response magnitudes, and Terminal 10 was assigned as the longitudinal axis of the piping defined by a different and higher constant Impedance magnitude. Two sets of constant values were assigned to the terminals, thereby covering a dynamic range of 5000 to 1.0 lb- sec per in., a reasonable response envelope for an arbitrary piping system.

Equations (Al) through (A7) describe the uncoupled responses of each element un- constrained at its interfaces. To connect the elements mathematically into a machinery system, boundary conditions were imposed at the interfaces, the assumption being made that all interface connections were rigid. Therefore, referring to Item (b) Figure 1 of the text, it can be stated that v. = v., f, + f, = 0; v0 = v-, f0 + fc = 0; v0 = v

1*14 2 5 2 5 3 6 k+ fg = 0. Since the terminals of the flexible pipe coupling, piping, and pipe hanger

ve dbmmon axes when connected, Vg = vn = v13 and f8 + ^ + f = o. Also v = v , f7 + f10 = 0' v9 = vi2 and f9 + fl2 = ^ When the connection between pipe hanger and hull are formed, it can be stated that v14 = v15 and f14 + f^ = 0. When these boundary

conditions are applied to Equations (Al) through (A7) and when unity free velocity is assigned to voi, v02 and VAO, (since the investigation was made with the pump not ope- rating) a system of simultaneous linear equations evolve from which solutions of the coupled forces and velocities at each terminal can be obtained. The matrix form of this system of linear equations can be written as [v] = [m] x [f ] or in expanded form clSl

A-2

MEL Report 265/66

"44 T "'a

m54

me4

m74

mH4

"«4

m«4

"K T '"22

m

"'40

Btm,

m76

"■so

47

"57

^ + mi2I2

m«9

0

0

0

0

nmi 0

0

0

0

0

0

0

"1313 -»HH

"1413 ml51ätlnl.

(8)

To reduce the 36 flexitde-coupline free mnhii,-+„ ™ define the matrix to a number 1 es!'for mi ^hity measurements needed to rigorously were applied. The Mlow^Tis a LôTthe fle^h?^ 1^ ^ StrUCtUral ^^r/ used to solve Equation (A8): eXlble couPllng êe mobility equalities

m^ = m„ ^4 '"77

m 4g-mc/1=-m, 54 79 "in97

m56 - m65 = -m89 = " m98

ln59=m95

m^ = m 46 - mr,4 = -m78 = ■m 87 mô = m. 69 - ra96 - -m58 = -m

85 m = m_. 47 74

m4S=m84=m67=m76

m49 - m94 " -m57 = -m 75

m.r = m 5a "99

m66 = m88

m68=m86

It is also assumed that the piping mobilities m 1 o, „ A written as inverse impedances 1/Z 2io and x/^ 12. mllll <which ^ also be metry of the piping. 1212 v<cllll)> are equal due to the radial 1 sym-

A-^

BLANK PAGE

MEL Report 263/6G

APPENDIX B

Development of Mount- Foundation - Hull Vibration Response Equation

MEL Report 263/66

REFERENCE

(a) Wright. D. V.. and A. C. Hagg, "Practical Calculations and Control of Vibration Transmission through Resilient Mounts and Basic Foundation Structures " Westinghouse Research Lab, BUSHIPS Contr NObs-72326, Dec 1959

B-ii

MEL Report 263/66

Figure 2 of the text is a sketch of a trim pump mounted at four points on a symmetrical foundation. Lack of data prevents inclusion of three degrees of freedom at the mount-foundation interfaces, therefore, it is assumed that translational iorces, developed along the x, y axes, generate negligihle forces at the hull, Terminal c. Refer- ring to the dynamics along the z axis only, the forces generated at the foundation-mount Interface, Terminal b, can be defined as a product of the velocity of the machine foot and the blocked transfer impedance of the isolation mount, reference (a),

^"•^ab (B1)

The insertion factor or ratio of dynamic forces at the hull, Terminal c, to the forces at the foundation input, Terminal b, can be derived from the ratio of the measured hull driving point Impedance, Z without the foundation attached, to the transfer impedance of the foundation, Zbc, when attached to the hull. In equation form

Z f v f cc _ c c _ c Zbc " vc fb " fb (B2)

Combining Equations (B2) and (Bl) results in a transfer impedance which defines the path from mount input to hull-foundation interface,

f Z . Z 7 _ c _ ab cc ^~\"~i^r ^

Equation (B3) is a valid estimate of the vibration transmission through each foundation leg if the following assumptions are made:

• The hull driving point impedance at each hull-foundation interface is low compared to the transfer impedances between the locations.

• Attachment of the foundation to the hull, at Terminal c, applies nedlglhle constraint to the hull response.

• Dynamic coupling between mounting locations is negligible.

• The four isolation mounts have identical transfer impedance characteristics.

With the above assumptions, a description of the total sound transmission path can be estimated by a power summation of the four identical transfer impedances re- sulting in '

-o I ^ab cc I ZT ~M~Zrri .....(B4)

MEL Report 265/66

Appendix C

Free Mobility and Impedance Measurements of System Elements

MEL Report 265/66


f ^ I I#- - i •- ** ' —

(Applies to the three curves)

-rv ^:r-i

H-4-441 ilii, -1■f *s®* ' • m

oL-f’Tir^»i 1«r

«»

1 4^^r^i T“ ;

\Ei■ j4:-: . - ■

’■h—L-^t:l^-' :'>-4--f-rfJ-rn*'^ ni4-2rf-: I-.;;.. -f'vi 4--• ...: ..

mil

n ]—

J4li l1iiiwiili V if: 1 iiiiiii^

m55

Figure 1-CFree Mobility Measurements of Trim Pump

Pump at Outlet Flange

C-1

MEL Report 265/66


\ ■■'■'■

(Applies uo the three curves)

1: '^^-ffff;- ^r-e W-tf-! ■ffP'>f-;; L 4-

ill t~ri- -:: -; _;; _ -+---j_ ^-C.; ij/fi. ■''tl-f't-'-'-

./"v-^T

-iJJi

irM

m55

1 m66

Figure 2-C, Free Mobility Measurements of EB Flexible Coupling Configuration, Water Filled at 600 psig

C-2

MEL Report 265/66



" feb^^H'^r "^-t^-^f^^^-vt^:

Figure J-C, Free Mobility Measurements of EB Flexible Coupling Configuration, Water Filled at 600 psig

C-5

MEL Report 263/66


4 5 6

FLEXIBLE COUPLING

-o 7 -o 8 -o 9


.-4-J-"

iwrnpi^i/WA/j^-r

Figure 4-C, Free Mobility Measurements of EB Flexible Coupling Configuration, Water Filled at 600 psig

c-4

•f

i

*»

i

MEL Report 265/66


50- FLEXIBLECOUPLING ^ 8

-o 9(Applies to the three curves)

> I ■I I

■V "

‘:: : U :: Im86

PMIMM' -

i's/f ^;i-;T ’ r"

**eMK< -

m96

rhJi■1!

Figure 5-C, Free Mobility Measurements of EB Flexible Coupling Configuration, Water Filled at 6OO psig

C-5

MEL Report 263/66


Figure 6-C

Free Driving Point and Transfer Mobility Measurements of Block Rubber Pipe Hanger

Legend applies to the two curves

«■ •Tl» ■ ■■'-'

no: \.tm^^ _^ wn Lwnwri

TT -iJ?— f^m -^ g^ j^__L T 1HI|. •,(■ HMHIULUMTKT —j- 1- ' o'

1 - IS b i SüBiä

r-^-L ^-^X ii —- Pff'- I • ■^

■^^^H—

?a ^p ̂ 5

^^ 3 k' ^ "'' SI ife M

i —. >— " 71 ~ KRIS B»>Yl» K'ttl ■ 'H«W|I

iltl ■ fill« "- « c^--_—- J ~ = *

- '' - -^ ^1 -*.'' ^ .. | ■ ' -

T

1 1J3. ̂ ti Sr-_—- --—^-^-^ -~.

T ii ^-if^Ta^'wf^-^

-^^^ ̂ ■^-r' ^ ^-^jF-trH ■—r^ ̂ ~h~1 ^S^-" T^ ^ ̂ ^

fcfciti tlKia* riCTiti ^J!^ ^H

Figure 7-C

Comparison of Piping Parameters and Isolator Characteristics

C-6

MEL Report 265/66


Figure 8-C

Hull Driving Point Impedance — and Z ml515 cc

(Drawing applies to Figures 8-C and 9-C)

LLTL^ ":__ ; ■ • ; : ITU - ! - ^ i1 ( -

Figure 9-C, Power Summed Foundation Transfer Impedance, Zbc

C-7

Sfinnly Classificalion Unclassified

DOCUMENT CONTROL DATA R&D iSecurily clmitiflion ol rill«, body ol nbttrmcl mid indeiinj unnolntlon mu«! lit «nlwd whtn Iht overall repoff It rlftlllmd:

I ORIGINATING AC Ti vi TV ^Corporal* «ulhor;

Navy Marine Engineering Laboratory Annapolis, Maryland

3 REPORT TITLE

2«. RtPORT »ECUftlTV C U*«HFIC A TION

Unclassified ib. GROUP

Vibration Transmission of Flexible Pipe Coupling Influenced by the Elements of a Trim-Pump System

4 DESCRIPTIVE NOTCS fTVp» ol reporr «nd/nclualv« cf«le«>

5 AUTHORISI (Fittt nmmt, mlddla inlllml, tm*t nmm*)

Ronald c. Hirsch 6 REPORT DATE

Sept 1966 7a. TOTAL NO Of PAOEl lb. NO OF Rirt

2__ Sa. CONTRACT OR GRANT NO.

6. PROJECT NO SPOIJ 11 09

SF013 11 08 Task 03955

»a. oniaiNATOR'i REPORT NuMitRiti

263/66

9b. OTMt« ««PORT NOOI (Any o(ft«r numfta that may ha maatanad thla raport) v

Assigt 72 105 and 6? 102 10. DISTRIBUTION tTATCMCNT

Distribution of this document is unlimited.

II. SUPPLEMENTAHV NOTCt 12- SPONtORlNO MILt T AAV ACTIVITY

NAVSHIPS

13. ABSTRACT

An analytical-experimental study was performed to determine the sound transmission characteristics of a flexible coupling in a trim- pump system. Mechanical impedance methods were used to compare the structural path to the hull via resilient mounts and foundation to the structural path via flexible coupling and pipe hanger. Also investigate were the vibration characteristics of an Electric Boat and MEL flexible coupling under pressurized and unpressurized conditions. Results showed that the sound transmission via flexible coupling and pipe hanger exceeded the sound transmission via the mount and foundation and would negate the isolation effectiveness of the primary mounting system. The results of comparing the two types of flexible coupling showed that the Electric Boat Coupling exhibited better total noise attenuation characteristics than did the MEL coupling. However, the MEL coupling showed a unique inherent characteristic of improved attenuation capabilities with increased pressure loading.

( Author)

DD .FN0ORVM..1473 (PAGE,, Unclassified s/M oini. «07.finni TTK

security ci»»»ification Unclassified

(E Y wo n DS

Submarines Piping systems Structureborne vibration Flexible couplings Radiated waterborne noise Foundations, machinery Hull resonance Isolation mounts Trim pump systems

DD.,r'..1473 e«, (PAGE 2)

Unclassified Security Classification

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