VIBRATION AND TOWING CHARACTERISTICS OF SURFACE-SUSPENDED HYDROPHONE SYSTEMS HYDROMECHANICS by Chester O. Walton and Mervin M. Merriam AERODYNAMICS STRUCTURAL MECHANICS HYDROMECHANICS LABORATORY RESEARCH AND DEVELOPMENT REPORT nee, Ee rC MATIGS Vs) o AUGUST i961 REPORT 1558 no. 1458 = vE a (Rev. 3-58) Hai 1OHM/Taiy VIBRATION AND TOWING CHARACTERISTICS OF SURFACE-SUSPENDED HYDROPHONE SYSTEMS by Chester O. Walton and Mervin M. Merriam AUGUST 1961 REPORT Alb ois es boy es noes i! , iu ye ir a iM aay aM ina r ied i fh ” _ i " ‘ . - , 7 ’ i ‘e - - a TABLE OF CONTENTS Page ABSTRACT INTRODUCTION GENERAL CONSIDERATIONS EXPERIMENTAL PROGRAM SHALLOW-WATER TOWING TESTS OPEN-WATER TOWING TESTS EVALUATION TESTS AT SEA PRESENTATION AND DISCUSSION OF RESULTS CONC LUSIONS AND RECOMMENDATIONS REFERENCES oor hN NN & - = c@ N ii Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Pigure Figure Figure Figure ao PF WN & 10 i: V2 13 14 LIST OF FIGURES Schematic Diagram of a Hydrophone Array Karman Vortex Trail Sketch of Hydrophones Used in Basin Tests Towing Configuration Used in Basin Tests Diagram of Towing Configuration Used in Open-Water Tests Instrument Housing and Fairing Assembly Fairing and Hydrophone Assembly Used in Acoustic Tests Diagram of an Experimental Directivity Hydrophone System Diagram of the Modified Experimental Directivity Hydrophone System A Comparison of the Relative Noise Levels Received from an AX-58 Hydrophone Tested in the Basin under Various Conditions Comparison of Computed and Actual Configuration of the Experimental Array Used in Open-Water Tests Strouhal Number as a Function of Reynolds Number Comparison of Computed and Experimental Frequencies for System Used in Open- Water Tests Comparison of Measured and Computed Cable Configurations for the Experimental Directivity Array iil ~] 10 15 15) i 16 3 s bei) aed win’ a — - » ‘st oh ere dito sb ake a ph iacuey he ; ‘y j ad if i TaN t ae ‘sy Vestas | ie ty eo on oat ‘Blea ie Pi f quish rel ‘t & pee 5s he 0 bey fs aah MDS % +e ee AG “ nh Oe jal oKisshactaes ctr deal 0 Fa ons ome: Pi mn ivan hte boa } nie tie. A i : 5 1 — ih, enor! orrby Hig rar ws er i im ile, re | ee if). 4 A Srohe 19. nc ‘ ie ey) SOTERA eA “oF tecoyihas ie a an wee “iT i : 7 : F fe A i ie, wie Siar ie Bip ps ; Be eat AES f5D vd nee. © My aa : Yds Daten d oy vind SCTE ES Stan SI ela Nt ere! 5 fe : _ L, ey. - bd : ‘ 7 z : - re = \ i = a ~ ell ni . € Aen ABSTRACT An experimental investigation was conducted to determine the sources and methods of reducing cable vibrations in acoustic measuring systems, to provide information concerning full-scale towing behavior, and to accurately define the towing configuration of such systems. The results of this investi- gation including comparisons with theory and recommendations for improving towed acoustic systems are given in this report. INTRODUCTION The use of towed hydrophone systems to measure radiated noise from submarines has led to many problems which must be alleviated if such systems are to fully serve their purpose. Specifically, the vibration of the cables is believed to be one of the major sources of the high level of back- ground noise in the low frequency bands which has been associated with such measurements. Furthermore, insufficient data concerning the resistance of these kinds ofarrays have made it difficult to determine the configuration of the array and, consequently, the orientation of the hydrophones. Accordingly, an experimental program was established under the Funda- mental Hydromechanics Program at the David Taylor Model Basin to study the cause and effects of these flow-created problems as they pertain to typical surface-suspended hydrophone systems. The specific objectives of the pro- gram were: to investigate the capabilities of such systems with regard to speed, depth, and steadiness of tow; to determine how well the behavior of full-scale systems can be predicted for a range of operable conditions; and to provide information which is required to accurately define the configuration of a given system. The facilities which are necessary to carry out tests of a complete system under highly controlled conditions and at a large enough scale required for accurate representation are not available. Consequently, the approach used was to carry out the program in the following three phases: shallow-water towing tests in the towing basins at the Taylor Model Basin to determine sources and magnitudes of low-frequency noise components in the acoustic system, open- water tests in the Chesapeake Bay to provide data on the effects of cable scope and fairing on vibrations and towing attitude of the system, and tests at sea to evaluate the characteristics of a full-scale system proposed for submarine radiated-noise measurements. This report describes the various experimental investigations, presents the results of measurements to determine vibration characteristics, and in- cludes pertinent observational data. The towing configuration of a proposed system is briefly described,and curves and sketches are provided to define its towing configuration. Recommendations are made on how to improve such systems as well as for future studies which are necessary for further devel- opment. GENERAL CONSIDERATIONS . . ° 2 : : Submarine radiated-noise measurements’’ “ are presently being obtained with a hydrophone array in which the cables are bundled,and the system is allowed to drift with the listening ship in the manner shown in Figure 1. Be- cause of ocean currents and winds, the system is set into motion and the cables move relative to the water which results in the formation ofa'Karman Vortex Trail.""* Above certain velocities, eddies break off alternately on either side of the cable in a periodic fashion, as indicated in Figure 2. Thus a staggered, stable arrangement or trail of vortices is formed behind the cylinder. This alternate shedding produces periodic forces normal to the un- disturbed flow which act first in one direction, and then in the opposite direc- tion. The alternating forces cause the hydrophone cables to vibrate and the cable vibrations are either received directly by the hydrophones.as sound waves or cause an actual acceleration in the sensitive hydrophone elements which also results in noise. The resulting signals are of high amplitude and tend to mask out lower-level noise components present in the low frequency portion of the spectrum. Attempts to reduce the vibrations have been made by sliding loose plastic tubing over the single cable (see Figure 1) to break up the flow around the cable. This technique has been partially successful, pun not to the degree necessary for accurate sound analysis. The motion of the system through the water also causes the hydrophone array to tow in a catenary so that the hydrophones are neither at desired depths nor in a true vertical plane with respect to the noise source. Since the depth and configuration of the present type of array is difficult to predict, the assumptions made with respect to the position of the hydrophones in the anal- ysis of data are sometimes far from accurate. EXPERIMENTAL PROGRAM As mentioned in the Introduction, the experimental program was restricted by limitations of test facilities at the Taylor Model Basin as to size, depth, and background noise. Therefore, this investigation was conducted in three phases: 1. Shallow-water towing tests to determine the magnitudes and sources of vibrations or low-frequency noise components in the acoustic system, 2. Open-water tests to determine the effects of cable scope and fairing in the reduction of vibrations and to obtain information relative to the towing attitude of the system, and 3. Evaluation tests at sea to determine the towing behavior and con- figuration of a proposed system for submarine radiated noise measurements. 1References are listed on page 18. N poe 1 be any 5 UE, Mere aN - thy aa) = Water Surface PS ONC Coa, SM = = foes es 5 Cables — 4 Cables ————e 2.Cab|¢s._——————————— Plastic Tubing Figure 1 — Schematic Diagram of a Hydrophone Array * =Ee - 9 Figure 2 — Karman Vortex Trail OED es ad Pr eRUR Tt ‘5 cartel : alll | : . ene Dense get ee Te RS met orh eer ase e my Saf - f - = 2: oa an) =a a 4 mt! i - 1 i . ; - 7 : 1e em TR nt —— me — - 7 x a : ; A ‘ : 7 7 ‘ ' . 7) iy i -“ a i : * i ; ung _*-- a a A. oo 7 ¥ 7 ia a ay - en's © a 7 A acl ’ ant. “ - i a i Bo » i = * Ul - nd an ; = 1 ’ 5 1 7 7 - it a 7! a i" 7 - j : - SHALLOW-WATER TOWING TESTS The shallow-water tests were conducted in the towing basins at the Taylor Model Basin primarily to ascertain whether the interference in the acoustic measurement systems was due to cable vibration or to hydrophone oscillations. This preliminary investigation was intended to set the basis for possible solutions of the problems affecting acoustic measurements. The initial tests conducted in the basin were made using AX-58 type hydrophones, as shown in Figure 3a. A shroud-ring tail similar to that shown in Figure 3b was attached to the hydrophone to minimize oscillatory motions. Each hydrophone was towed ona 9/16-inch diameter, rubber covered, elec- trical cable, as shown in Figure 4. The cable had a weight of approximately 0.1 pound per foot in water and served as a conductor for the hydrophone signal. The units were towed over a speed range of 0 to 3 knots. Standard type cable fairing was not available for the size cable being used in the basin tests. As a substitute measure, a simulated fairing made from 2-inch plastic tubing, was used for some of these tests. The tubing was placed over the cable so that it was free to align itself with the stream and was tested using the hydrophone with and without the shroud-ring tail. In an attempt to further break up the flow around the cable and thus reduce vibrations, the plastic tubing was coated with a cork mixture to roughen the surface. The system with the coated tubing was also towed over the 0-to 3-knot speed range. During each run, noise measurements were made in 1/3-octave bands using a spec- trometer and a sound-level recorder. OPEN-WATER TOWING TESTS The shallow-water tests did not provide adequate information for deter- mining the towing configuration of the hydrophone array as well as the effects of the use of greater cable scopes and standard cable fairing on cable vibration. Consequently, in an attempt to obtain the additional information in an environment having a minimum of background noise, tests were conducted in open water in the Chesapeake Bay. A secondary purpose of these tests was to obtain design in- formation relative to a full-scale hydrophone array. The tests in the Chesapeake Bay were conducted with the configuration similar.to that shown in Figure 5 using a motor boat as the towing vessel. Two 50-foot sections of fairing were used as the main towline. The fairing was of an airfoil shape (TMB No. 7)* made of a two-durometer rubber which normally would enclose the towcable. The 50-foot sections were joined together by junction boxes,as shown in Figure 6. Both at the extreme end and at the junc- tion of the two sections an instrument housing was attached which contained two pendulum angle indicators {one for longitudinal and the other for lateral meas- urements). A 100-pound faired towing weight was attached at the deepest end of the array to provide directional stability. The initial tows were made over the stern, but satisfactory measurements could not be obtained because of propeller wake. The towing arrangement was then modified to permit over-the-side towing. It was then possible to tow the configuration and make pressure and angular measurements over a speedrange 4 boaed =< a y rad k D a) : ue " ( aia a A at o Kae i ke a od i ‘ + = \ of " a PRA Pe hi os¥¥ . . 9,4 Tad i\ OS oe ow dint ae > ¢ ay n be rs Tf ree © 2 vite “ha teal) Gate 3 : 4 1 \ ror a) ee. th leans ty F ee Pe: . Cn Bi \ rae Figure 3a Figure 3b Figure 3 — Sketch of Hydrophones Used in Basin Tests To Instrumentation Carriage Platform Coaxial Cable Plastic Tubing Basin Floor Hydrophone Figure 4 — Towing Configuration Used in Basin Tests 3) i OLEAN x 5 ‘ f ‘e f 7 f, a f : ‘ vA ven er) ele re a ey) ar) real i { fi : ¥ j ; ; i , J 4 a 4) Sp Ha Tay, : i 1 A : ¥ yy | t nt ¥ sy i (ae La nae a% + ly q : at : - 7 4%, —- . oa : - 7 7 ‘ e . ; _ o 7 a) me Pg ' " er OM LER Rites is 3 7 ‘ “A i Gs ) a re I f i ? - - =e Q ~ : a) ' ok 7 + An ' ' 1 - : a , y oo as _ oo aT # ° ' : ; ' ' - ” . ra - C= i i wae rae . i - ‘ a : , et ‘ ar : Towing Reel Towing Vessel Hydrophones 100 |b Faired Weight Figure 5 — Diagram of Towing Configuration Used in Open-Water Tests 6 pomerens ee : a a 23) OFF NIT ty oni pont pa nimi his: ar : zs 5 1 i t a ua a : 9 easy poner See 5 y 7 fj it , . . « te : i i a ” : a ; i. oie ee. ae s ms OM 7 iw cs ~ Instrument Housing Fairing Junction Fairing PSD 92337 Figure 6 — Instrument Housing and Fairing Assembly Fairing » Hydrophone Fairing Junction PSD 92338 Figure 7 — Fairing and Hydrophone Assembly Used in Acoustic Tests of 0 to 4 knots. At 4 knots, the fairing tended to tow in towards the propellers and it was not feasible to tow above this speed. To carry out the tests to determine the vibration characteristics of the faired system, the instrumented housings were replaced with hydrophones, as shown in Figure 7. Two similar hydrophones were attached to an unfaired 5/8-inch (not shown in Figure 5) weighted line. to measure the vibrations for comparison with the faired system. The hydrophones were located at depths of 50 and 100 feet in each system. Tests were made over a speed range of 0 to 4 knots and the hydrophone signals were recorded over the full speed range. y EVALUATION TESTS AT SEA ‘The tests conducted in Chesapeake Bay resulted in information which was applicable to full-scale arrays. Accordingly, an experimental full-scale array for studying submarine radiated-noise patterns was first constructed and then tested at sea off Key West, Florida. The purpose of these tests was to deter- mine stability, towing characteristics, configuration, and acoustic performance ofthe array. It was also desired to obtain information required for design modifications for future arrays. The array used in the first sea tests is shown by the sketch in Figure 8. It is composed of a 100-pound faired towing model, pressure gages, hydro- phones, buoys, float material, and a network of cables. All three legs of the system (horizontal and two vertical legs) are composed of 0.7-inch diameter cable with 26 twisted pairs of conductors and a strength member. The inter- mediate cables suspended from the horizontal leg are 0.3-inch in diameter. The horizontal leg is supported by flotation material. Hydrophones and depth gages were located at the points indicated in the sketch. Junctions were pro- vided for additional hydrophones and depth gages to be located every 100 feet along the vertical legs. The system was towed over a speed range of 0 to 3 knots while pressure measurements and hydrophone signals were recorded. On a subsequent sea trial, the array shown by the diagram in Figure 9 was used. The added 500-pound faired towing weight in the second system was intended to provide greater depth and more vertical area in the loop formed by the array. PRESENTATION AND DISCUSSION OF RESULTS The results of the shallow-water tests are presented in Figure 10 as dif- ferences in relative noise level versus frequency for three of the test con- ditions. Since the results with the fourth condition (simulated fairing with a roughened surface) were approximately the same as those with a smooth sur- face they are not presented. It may be seen from Figure 10 that, for the very low speeds (0.1 to 0.25 knots), there are no significant differences in noise P So WMeres aa a ‘ js orn! ohana 1 oe 4A i. :. et te oi ST ek ear rn i ay ten j ah - ” : = LAr ee Vite gS 2 is te at ee 7 Fe 5 Z hen ows & ve \ ; cc ven qj ¥ in Shoes eee - - i Oe i wip) bare & : (Was $5.) She 2a) e r ieee! ? de 2 A aS ee ws ae cto Pe 1) oe ' a4 Par i are a aes On SS ; #7 Bb athe. fe) 6 Hr m2 + ee oe hee fe behave “ani . = dy Pub syyte “4g 5 > Ut? te Pt, yap Mag eto ee Wy tant t j= | 4 \ i § eS bukiige, “te Milelagcy: che i a ‘ee ae) a me fee), > i i Prk oak sty 4 7 s “ ‘ (inte A ietey Vi enw) .b* fy lel PS ’ j - ; ize ore : . : a t ‘fey 7 ‘ 4 x : : : 7 gS) Scr: Pa Bech x VN mys aw ed ; A 7 a ee See 2 Tats) eigi't oe : 5 . een Lee if hele 2 Pe Orey 7e48 ‘ oan ‘ . y : erie - - % 7 wae : — = Wh - A, - - ty he ; 7 , ae i : «Te ' ib ooah } i u = Towing Tie 300 11 — ai * by 9h a Ee : le “ ¢ ie CA a OY ? ay ge sy ur, yl + op Blige i a i -_ a : Pa ; re —t y : a i : i ‘ o* $e) = : os ; 7 7 - . = - : - ’ : —_— ’ ; be! 4 1 - A : ° SUOIIPUOD SNolIVA JopuN UISeg OY} UI poysey, eUoYdoIpA}y BG-XY Ue WIJ peAToIEY S[eAS] OSION OAT}V[oY ey} JO UostIedWOD Y — OL 9insIy sdo uy Aouanbeay sdo uz Asuenbeay O7= a 1 [s) N ! °o rt ' 002 Oot O9meEOS o7 O€ 02 OT 002 OOT 09 «60S 07 o€ oz OT —— = TH8L - BupszBy O—O 7 | TFBL - 4upsted G—O TF8L ON - SuTIpey (-}—1) _ TF8L ON - Supapeqg C—O TBL ON - eTQBD arBy O——O THB8L ON - aTQeD ereY O—O qoux SL°O 70UH 0S°O —— — I}8L - Suyapey O—D 1¥B8L ON - Suptayey (-—) TTBL ON - eTQBQ euegG O-—O youy Sz°O TH8L - Buyapey O—D TTBL ON - Buyazey O—O TFBL ON - 91QB8D e1Bg O——O youx 1°O BTEQTOap UT [eve] eaTzeToY 81 eq}oep UF [eve] eATzBTSY 10 Leg hee asiediet ates jt, - me lie 4 MA ee VT of Bastiaans ‘ae a (penutjuos) OT aInst 7 sdo uf Aouanbery sdo uy Aouanbesy oo0z OOT 09 #OS oF o€ oe OI 002 OOT 09 OS oF o€ oz Ot T o7- TreL - Fupsped O—O TFBL - 2uyatey O— TFB8L ON - SuyspeyY O—O) TF8L ON - Supsyey O-—) TIPL ON - ETQBD ereg O—O LTBL ON - eTQe9 aaegO—Of | ‘a alia O€- SOUH O°E szouy 0°? T 9 E IFBL - Bupapey O—D T¥eL ~ Burated O—O ITPL ON - Butateyg OO) THBL ON - Sutsted (-—) ITBL ON - aTQBeQ e1egG O—O ike aa | THB8L ON - eTQBD e4Bg O——O | syOUX S*T youx O°T S[aqyoep UF [eas] PATIBTAY B[aqyoap UT [eae] aATzBTIy Wal : ‘ aed ; Pony aeons ony 7 : F ; ) , tv y ial f ee DY, levels among the conditions tested. However, observations made during the tests indicated that the bare cable vibrated at these speeds and that these vi- brations appeared to influence the motion of the hydrophone as well as its signal as seen on an oscilloscope. The vibrations at these speeds are of such low frequency that they do not appear in the analysis, since the lowest 1/3-octave band on the spectrometer is centered at 16 cycles per second. At speeds between 0.5 and 2.0 knots, the noise levels for the bare cable condition are from 5 to 20 decibels higher in the low frequency bands (16 to 125 cycles per second) than for the faired cable condition. All test conditions produced high-noise levels for speeds above 2.0 knots. The addition of plastic tubing (fairing) reduced cable vibration at allspeeds and seemed to completely eliminate the vibrations at the low speeds. The shroud-ring tail on the hydrophone greatly reduced the very low-frequency os- cillation of the hydrophone at all speeds. The effect of the reduction does not appear in the analysis because the frequency of the oscillations is below the frequency range of the instrumentation. The addition of the shroud-ring tail to the hydrophone had no effect in reducing the higher frequency cable vibra- tions. It should Se noted, however, that the results shown in Figure 10 may be influenced by background noise in the basin, and noise and vibration of the tow . carriage. Nevertheless, the data indicate that further investigation into the effects of more refined fairing, greater cable scopes, and other towing con- figurations is warranted. The experimental results obtained from the open-water tests conducted in Chesapeake Bay are presented in Figure 11. The results of theoretical calculations, using the method outlined in Reference 5, are superimposed for comparison. It may be seen that the computed position of the array does not agree very well with the measured portion. Lack of agreement is attributed mainly to the fact the system towed to one side. Using a constrained, flexible, faired section that is not free to swivel, the tow member will cause the towline to develop side forces which deflects the systemtoone side. This occurrence is indicated in this system by lateral angular measurements which approached 45 degrees at 4 knots. The angular records and observations showed that a!l- though the array towed to one side, it remained reasonably steady over the speed range. A qualitative narrow-band frequency analysis was performed on the hydro-~- phone signals recorded during the open-water tests. It was found that for the condition with the hydrophone at 100-foot depth suspended on the faired cable, the interference which might be attributed to cable or fairing vibration in the 0-to 50-cps frequency range was negligible. Thus, the broad-band signal could be amplified so that other noise components such as the firing rate of the boat's engine, signals from a passing tanker, random background noise, etc., could be identified. However, the records from the two hydrophones secured to the unfaired weighted rope were quite different. In particular, the record for the 100-foot depth hydrophone in the latter system showed many interfering high- level noise components in the very low frequency range. The hydrophone was taped directly to the rope which was the vibrating member in this case. 12 ; Hoe fe] 100 60 Depth in feet 40 —— Experimental Speed in Imots Figure 11 — Comparison of Computed and Actual Configuration of the Experimental Array Used in Open-Water Tests ae, oT ' _ T = 1 ra a i os =5 7 \ ie , ie : yh Y, 3 i ¥ 2 ae r Pin: ne 1 Os a i] it f Pos t i be ; beabat : pia as i) \ t i : ' 1 y : ’ i : q | oS i : 1 Je ' s : 44) ; Le | F | , ; f j e . i 1 ¥ } BUN j - = is Re. 1 ] = } i : lane i 7a . mal i * a A - “ FD a = i y : j - 7 sp ‘ : 8 ES re 4 - - ‘ i $c. eet Ny . vs ae ° ie - As ¢ 7 i : 1 - ier, 7 yis P2 i =, i ie i ‘ : . ' ‘ a - ' , ‘ ' i > ‘ 7 ‘* ¥ ak = ’ 7 —_ it “ 7 : ‘ <2: hina ti re eae canara a. eT ee — ‘rl ry 4 i - t } ; | } j i eee = Le igh 10) FT Oita = ey a) a ~ - » Me F , an = - : eee ow j i. ; — Zinman Seeggro ey j 4 yo , t ¢ rene 8 Saree ss cn ' f ‘ } : I i. ope ai The frequency of vibration for arrays of this type can be approximated by using the equation NV f= —— d where f is frequency of vibration, N is Strouhal Number, V is velocity of fluid, and d is diameter of cable. Figure 12 shows the relationship of Strouhal Number and Reynolds Number and can be used to compute the frequency for a series cf speeds and cable diameters. It should be noted that these data refer to rigid cylindrical sections and should be applied with caution to cables. Once an elastic body has been excited, the motion of the body modifies the frequency. Figure 13 compares the frequencies measured on the system used in the open-water tests with values computed by the foregoing method. It may be seen that, in spite of the fact that the computed value is based on rigid cylinders, it compares reasonably well with the low frequency components that were meas- ured. The interfering components seemed to be composed of fundamental fre- quencies and a number of related harmonics. These frequencies changed with towing speed. The noise components were not present for the portion of the re- cord taken when the boat was not moving. When these components were present on the record, they were of such a high level that the broad-band signal could not be amplified to allow the identification of other signals without overloading the analysis instrumentation. The results of the evaluation tests at sea are shown in Figures l4a and 14b, the corresponding theoretical computations are superimposed for comparison. It may be seen that, in these two cases, the theory and experiment are in very good agreement. The system without the weight (Figure 14a) was observed io tow in a reasonably steady manner. A qualitative frequency analysis of samples of hydrophone signals for th1-c towing speed conditions was made. The records showed that there was con- siderable interference due to cable vibration in the low frequency region at all speeds. The frequency of vibration in these cases is proportional to the flow velocity divided by the diameter of the cable. This was substantiated by the records which showed that the frequencies received by the same hydrophone became higher both with increased towing speeds for fixed diameter, and with decreased cable diameter for fixed speed. The signals from hydrophones on the weighted leg were higher in amplitude than those from the non-weighted leg. This was attributed to the fact that the weighted leg was a better carrier for the flow-induced vibrations than was the non-weighted leg. 14 Ey 89 espero sy 3H att ( sangre oC aaa 1 bore ACU NG if = ax : B Frequency of Generation of Eddies Diameter of Cylinder Speed of Cylinder 4 Kinematic Viscosit 0.25 ee ill || 2|> © 0.20 ao 2 Ee =) 2 re) Ould 2 7) 0.05 ———— L Je NAW 10 [ee 10 10 Reynolds Number, yan Figure 12 — Strouhal Number as a Function of Reynolds Number 24 Computed 20 Experimental om Frequency in cps (0) | 2 &) 4 Speed in knots Figure 13 — Comparison of Computed and Experimental Frequencies for System Used in Open-Water Tests 15 ty 1 is Distance Aft in feet 1000 800 600 400 200 te) | 200 400 vey oO ® G & a rs) Q, 600 & 800 @ Pressure Gage Depth © Computed Depth 1000 Figure i4a — Without Weight Distance Aft in feet 800 600 400 200 ry) v é 2.6 knots L 400 2 @® ) | . = = § s a |_— 600 A Se Le 1.3 knots eal 1 — 800 zi |e ennai eats See e @® Pressure Gage Depth 0.6 knots © Computed Depth 1000 Figure 14b — With 100-Pound Weight Figure 14 - Comparison of Measured and Computed Cable Configurations for the Experimental Directivity Array 16 Bom Se Peemeee-: Paes ae ee tasted ae nya i { : +y i i mAs ‘ ’ vie i : _ ; 7 iy 1 : yh HNP) ne S a : x } ‘ ip ahd lopescete ree it ‘ 7 if , ae i = re i t j ui ; 7 H “ & : — 7 Sv - oy ; 4 Nit on i t % ‘ art > a i a r 4 i | ee Maes ee alt i Le Mul avn f Samer n'y an y oH ~ jeccmt : gs rs : ee 2 f = ee oy a z| 5 t 2 } F | i] | 4 ri ' . } bit Patt 7 ! f ae J 7 r 7 7 i } a i 1 / } A zo eS s 1 Te ee ee ie i 7 en he : lt i i : . J J i : - [oN ve : H A f i * ‘ : if °) m a ; oo y! aoe y webs 40 oe « CONCLUSIONS AND RECOMMENDATIONS On the basis of experimental and theoretical investigations of typical surface-suspended hydrophone systems, it is concluded that: 1. Any movement of sensitive non-acceleration cancelling hydro- phones such as the AX-58, whether due to cable vibrations or to hydrophone oscillations, affects the acoustic signal in the low frequency range. 2. By stabilizing the hydrophone with the addition of a shroud-ring tail the very low frequency oscillations are substantially reduced for the range of towing speeds which are usually encountered during submarine radiated- noise measurements. 3. Single hydrophone cables in a flow environment tend to vibrate due to vortex shedding of the Von Karman vortex street type. The vibrations of the single cables interfere with acoustic measurements in the lower end of the frequency range of interest. In general, bundling a number of cables, thereby increasing the effective size of the cylinder, decreases the frequency of vibration below the range of interest. 4. Fairing hydrophone cables reduces cable vibration, aids in ob- taining greater operating depth and speed, and improves the stability of the system. 5. The configurations of arrays similar to the ones investigated can be predicted with reasonable accuracy. 6. To obtain maximum depth at speeds above one knot, vertical cables in array systems must be weighted. However, this may increase the acoustic interference. 7. The overall towing attitude of the full-scale array is satisfactory. Based on the foregoing conclusions, it is recommended that: 1. Hydrophones in surface-suspended array systems be stabilized to reduce the oscillations and vibrations. 2. The vibratory motions of the array lines be reduced by fairing methods. 3. Further tests be made to determine the type of cable fairing most suitable for these kinds of arrays. 4, The amount of fairing required to eliminate or reduce cable vibration should be determined either experimentally or theoretically. 5. Techniques for improved fabrication, launching,and storage of complete array systems should be investigated. 17 iain, t REFERENCES David Taylor Model Basin Report C-987, SECRET. David Taylor Model Basin Report C-1153, SECRET. Binder, R. C., PHD, "Fluid Mechanics," Prentice-Hall, Inc. , (1955), Fehlner, Leo F. and Pode, Leonard,"'The Development of a Fairing for Tow Cable," David Tayler Model Basin Report C-433 (January 1952) CONFIDENTIAL. Pode, Leonard, ''Tables for Computing the Equilibrium Configuration of a Flexible Cable in a Uniform Stream, '' David Taylor Model Basin Report 687 (March 1951). Relf, E. F. andSimmons, B. A., 'The Frequency of the Eddies Generated by the Motion of Circular Cylinders Through a Fluid," A.R.G.; R& M No. 917 (June 1924). 18 healt talhade: ne ' iy 5 Ce re AP 9 om : mL Ny t NS ce op ; INITIAL DISTRIBUTION Copies Chief Bureau of Ships 2 Technical Information Branch (Code 335) 1 Technical Assistant (Code 106) 1 Laboratory Management (Code 320) 1 Ship Silencing Branch (Code 345) 1 Antisubmarine Warfare and Ocean Surveillance Division (Code 370) 1 Sonar Branch (Code 688) 1 Chief, Bureau of Naval Weapons, Code RUDC 5 2 Office of Naval Research 1 Underseas Warfare Branch (Code 466) 1 Acoustics Branch (Code 411) Z. Director U.S. Naval Research Laboratory Technical Information Division Washington 25, D. C. 1 (Sound Division) (Code 5560) 1 Commanding Officer Office of Naval Research Branch Office Box 39 Navy #100, Fleet Post Office New York, New York it Commander U.S. Naval Ordnance Laboratory Acoustic Division, White Oak Silver Spring, Maryland 1 Commanding Officer and Director U.S. Navy Electronics Laboratory San Diego 52, California 1 Director U.S. Navy Underwater Sound Reference Laboratory Office of Naval’ Research, P. O.. Box 8337 Orlando, Florida 1 Commanding Officer and Director U.S. Navy Underwater Sound Laboratory Fort Trumbull New London, Connecticut Ne eas oe iy, be ; 4 43 1 iy ey: ‘ f Ty i > ae | iar n ‘ Fees oa} ROT Asien fanaa ze S705 ¥ Sie 2 Bie ae ike ; tM a ew, on we Hsia s leh Sa hes ~ = Wf , 3 ne 7 r & - : : an . - 3 é ; a ‘ = 5 7 oo ‘ 7 ‘ Copy 1 Commander U.S. Naval Air Development Center Johnsville, Pennsylvania 1 Director National Bureau of Standards Connecticut Ave & Van Ness Street, N. W. Washington 25, D. C. Attn: Chief of Sound Section 1 Superintendent U.S. Navy Postgraduate School Monterey, California 1 Commanding Officer U.S. Navy Mine Defense Laboratory Panama City, Florida 1 U.S. Navy SOFAR Station APO 856 c/o Postmaster New York, N. Y. Attn: “Miss 1G. Rs Hamilton 1 Defense Research Laboratory University of Texas Austin, Texas Attn: Dr. C.H. McKinney 1 Institute for Defense Analyses Communications Research Division Princeton, New Jersey 1 Commander Submarine Development Group 2 c/o Fleet Post Office New York, N. Y. Attn: CDRA. Jerhert 1 Brown University Department of Physics Providence 12, Rhode Island 1 University of California Marine Physical Laboratory of the Scripps Institution of Oceanography San Deigo 52, California Attn: Dr. F.N. Spiess 20 ; 1 : — r ® te ay ; if i te A. vat Sone t i rn ' i e ' i | i “ « nai i i = > . Pct yy ’ ‘el ws ous : yee ee, Biccct: enope yes i rs F 7 a i : ! ; 1 : 7 1 —- C er ie ea ns) ; i Sn ee i Se ‘v i ae = 7 ea E Y ari - tii 7 ual 2Ra ok ! 7 : iz 1 a : +6 > - 7 yc A } ae ie 4 LS Ww] i TEL nin! i 7 ‘ a ‘ : a Ca | Poee - » be PAs, eo y bie 7 sy i . be oe rs pot . ; cs m4 < — ~ i ms bye A rr: + pow ~ ve ' Ys 7 . ¥ . * i e po Us ¥ ‘ ‘5 . i > : oa : Sots) gS vs ae : : =o H * 4 _bu, 7 - a> a4"! ' . ‘' aoa 7 meat) 8 wee — »,;, ie ‘ ~ MU = 7 ia ‘= oe . yy uber oe on i } =e ¥ - 7 ; : -_ Ls Hi - A ’ - i { ' 0 A Re foal a i, (ae ea v i 7 as SA: Rat haves pe) Copy 10 Director Columbia University Hudson Laboratories 145 Palisades Street Dobbs Ferry, N. Y. Woods Hole Oceanographic Institution Woods Hole, Massachusetts Stanford Research Institute Menlo Park, California Attn: Dr. Vincent Salmon Chesapeake Instrument Corporation Shadyside, Maryland ASTIA 21 a con Pep ieae aie het pe ‘ “W UTAIOW ‘OreTEW “TT *O 107804 ‘uOyTeM “] quew -OINSBOW--SOUBUIOJIE J --smiejshs O1jSNOOy “fF sentpiqudsy --smeqsks oNsnooy ‘¢ uoNBains yuo0D--sme}sks sUIMO]--SseuoydoipAy *g woNB1qIA--Sequo SUIMOT,--SeuoqdoipAy. “T “W UTAIOW ‘ureTeW “]] “O JezSeyH “uoyTeM “J quew -OINSBOW--SOUBULIOJIE g --smeyshs otjsnooy “pF sentiqudey --suieysks osnooy “¢ ao1yBind yuoD--sme4sks sUIMO]--Souoydoaphy °Z UOTWBIqIA--So[quo sulmoy--seuoydoipAy “Tt *q10dei Sty} UI UeAID O18 sUe}SAS O1VSNODB peMo} SutAosdui Jo} suotspuewuooes pus Joey) YIM suostied “WOO FUIPNJOUL UONBATSOAUT SIY) JO SyJnsei ey, *suezshs yons Jo TONBINSTyUOO FUIMO) Oy} eUTJep AToyBINDO¥ 07 PUB ‘IOIABYOq SUTMOY @[BOS-[[Nj Fulu1e uo. uoNeMIojuL eprAoad oy ‘sweqshs Fursnsvew O19SNOO’ UI SUOTIBIGIA E[Ged Dutonpas jo spoyjyow pus soeoinos 0} SUIWIOJep 07 poJONpuod sBM UONBSISeAUT [eyUeWLIedxe uy . GaIHISSVTONN gejos ‘sydvad ‘*suseip ‘-snqt “dig ‘Mt “T96T Say “were ‘J ULAIE; pus UOTE “O JoySeYD Aq ‘SWHLSAS ANONdOUGAH GAGNAasNs “HOVAUNS AO SOMLSIUALOVUVHO ONIMOL GNV NOILVUGIA “QSS1 $day -urspg jepow 40jADy piang *qaodei Sty} UT UeAIT eae sWoySXs OSNOOR pemo} SurAoiduyt Joy suolyepuowwooes pus Asooy) YIM suostied “WOO SUIPNJOUL UONBATSeAUT SIY} JO SyJnsel ey], “suoyshs yons jo UONBANsIjuOD FuIMoy oy} euryep AJoywinoow 0} puE ‘IOIABYOq SUIMO} @]BOS-[[NJ DuluJooUOD UONBUAOJUT OptAoad oy ‘suo,Shs sulinsvow O14SROde UT SUONBIGIA [Gud Furonpes jo Spoyyow pus seoanos OY} SUTWIOJep 07 poJONpUOD SYM UONBSySEAUT [ByUeWIIedxe uy » GHIMISSV'TONN 38303 ‘sydeid “saderp “snqyr “dTZ “It “T96T Soy ‘werasoyy “Jy UTAIEyy PUB UOTE “O J0zSeY4D Aq ‘SWALSAS ANONdUOUGAH GAGNaasns “HOVAUNS AO SOMLSIUALOVAVHO DNIMOL GNV NOILLVUAIA “8SG1 soday urspg japow s0)A0y plang “W UTAJeN SoreteW “]] *O J91SEYD ‘uOyTEM *T quew -OINSBOW--SOUBUIIOJIO J --Suie}sks o1SNooy “F sontyiqedey --sweysks osnooy ‘¢ uonBingd yuog--suleysAs SUIMO],--SouoydoipAy] *Z uoT}BIq IA --SOTquo sdurmoy--seuoydospAy *T “W UlAIeW\ ‘UreIEW *]] *O JoySOYH ‘UOyTBA *] quew -OINSBOW--SOUBUIOJI0 J --sueysXs OSNOOy “F sentiqudey --sweysks osnooy ‘¢ wowing 1yuog--smeyshs suIMOT--souoydoipAy] ° UOTyBAq IA --Se]quo suIMOy--seuoydoipAy *T *y10de1 Sty} UT UeATS EIB SUeySAS O1SNODB pemoy Sutaosduy 10} suoryepueuuiooes pus Arooy YIM suostied “WOO SUIPNJOUT UOVASeAUr Sty} JO Sy[Nse1 eyy, “sweyshs yons jo BoNBinsijuos Fumo, ey euyap Ajeqvsno08 0} pue ‘IOIABYeq SUIMO} 8[89S-][NJ Futusooucs uonyeuoyor eptaoad oy ‘suoysXs Furmnsvew O14SNOd¥ UL SUOTPBIGIA O[Gvd SuToONpad jo Spoyjyow pus seoanos 8Y} EUTUIEJEp 07 peJONpUod SBA LONBSIYSEAUI [BUOTIIIOdxe uy . GHIAISSYTONA “ajol ‘sydvas ‘-sadeip ‘snqpt “dtg ‘tt “T9¢gT ny “UBIO “J\ UAE PUB UCIT *O JeySeYD Aq ‘SWALSAS ANOHdOUGAH GAGNAdsns “HOVAENS AO SOMLSIYALOVUVHO DNIMOL GNV NOILLVUSIA “8SG| $oday ‘uispg japow sopADy pang *y40do1 S14} Ul UeATT e1y suieysAS OFSN008B peso) Sutaoidwr Joy suotepuemmooes pue AJoey) YIM suostaed “WOO FUIPNJOUL UOIBAT}SEAUT SIY} JO S}{NSeI oY, “sweyss Yons Jo UOWBANTIJUOD FUIMO} oY} EUTJOp AToqBINDOB 07 PLB ‘JOTABYeq SUTMO} 8]8OS-[[NJ FutuJeou0d uorewsojUI eprAosd oy ‘suiezss Surmnsvew d19SNOdB UT SUOTIBIGIA B[qvo Sulonpal jo Spoyjzou puw soeoinos 84} SUTMIJEJep 07 poJONpUOS SBA UONBSSOAUI [VyUeWMTJedxe uy . GHIHISSVTONN “sjel ‘sydvad ‘*saderp ‘snyjr “d[g ‘it “T96T Sny ‘were ‘fy UIAIOWy puw UOZTBA “O JoyseyD Aq ‘SWHLSAS ANOHAOUGAH GAANAdsNs “HAOVAUNS AO SOILSIMALOVUVHO DNIMOL GNV NOILVUGIA "8GS| doday -ursog japow 10,40] pang “W UlAIeW\ ‘orereyy *]] *O JoqysoyD ‘uojq[em *] quew -ONS¥EW--EdUBUIIOJIOg --suie}shs o1jsnooy “pF sentiqudey --sweysks oysnooy *¢ uoeaingd tju07--sme}shs duIMO]--souoydoiphy °Z wor}B1qIA--Se[qeo suIMO]--seuoydoipAy -T *qaodor Sty} UI UeAIT e’e SWOySAS O1SNOODR peMoy Sutaoidut 10j suoryepueuwoses pus k1oey) YIM suostied “WOO FUIPNJOU! UONBATSOAUT SIy) Jo S}[NSeI EY, “swaySks yons jo UOHeand1juOD BUIMO) ey) oUTJep AToywInoD¥ 0} puL ‘JOIABYoq FuIMO} 9[BOS-[[Nj FuluJo.uOD uOBUMACJUT OprAojd oy ‘suoySshs sutinsvew O14SNOde Ul SUONBAGIA O[G¥ud Fulonpes Jo Spoyyow pus seoanos 94} OUTUIOZep 07 poJONpuOD SYM UONBSTSOAUT [ByUOWTIedxe uy » GHIAISSVTONN “sjel ‘sydeas ‘-sadvrp ‘snqpt “dig ‘tt ‘T96T Sny “WBIMOEW ‘JY UIAIEW PUB UOTE “O JOWSEY4D Aq ‘SWALSAS ANONdOUGAH GAGNAasns “HOVAUNS AO SOMLSIUALOVUVHO DNIMOL GNV NOILVUAIA "BSSL Hoday -uysog japow 40jA40) prang “W UlAIEW ‘urBIey “]] *O qejseyD ‘uy[em *] queuw -OINSBEW--SeoUBUIIOJIO J --Swoysks onsnooy “F sontiqedep --swejshs onsnooy “¢ woNBind1ju09--suleysAs sduIMO],--souoydospAy °*g uon]Baq IA --Se[quo dutmoy--souoydoapAyy “7 “W UlALe\ ‘orerey “]] *O 19}80YD ‘UOTE “] quow -OINSBOW--SdUBUIOJI0 J --smeyshs O1SNooy “PF sontiqudey --swoeysks osnooy ‘¢ WOI}BINT1yUOD--suleysAs dUIMOT--SouoydoipAyy °g UOT}BIG TA --SE]qvO sUIMOy--seuoydoipAy *T ‘y40de1 Sty] UT UeATS EIB SUO;SAS O1YSNODB peo; Sutaoidut 10} suotyepueuuiooes pus Aroey} YQIM suostied “WOO FUIPNJOUL UOBATSEAUT SIy} JO S}[NSeI ey], “suleySshs yons jo UOHBaNs1ju0S FuIMo) oy} eurjap AJeqzwand08 0} puB ‘IOTABYoq FUTMO} @[BOS-[][NJ Fuluseou0s uoyewsojut epraoid oy ‘sueisfs dulinsvew O14SNOOB UL SUOT}BAGIA O[Gd DuTONpal JO Spoyjow pus seoinos 84} SUIUJE}ep 07 poJONpUOd SYM UONBSTySOAUI [ByUEMTIedxe uy . GHIISSY TONN sos ‘sydvad ‘*saderp ‘snqyt “dig ‘tt “T96T Sny ‘wets “JW UIAIOW PUB UOTE *O 3eISeYD Aq ‘SWALSAS ANOUAOUGAH GAGNAadsNs “HOVAENS AO SOMLSIUALOVUVHO DNIMOL GNV NOILLVASIA "BSS| Hodey ‘uysog japoy 40)ADy prang “q10dei Siq) UI WeATS e18 smeysds omsnooe peMo} duraoiduit 10} suoyyepuewmosel pues As0ey) YIM suOsTied “WOd FUIPNJOUL UONBATSEAUT SIy} JO SyINsei OY, “steysAs yons Jo UoNBANFIyUOD FuTAo} ey} eutjep ATeqBIND08 0} pLB ‘IOIABYaq SUIMO} 9][8OS-][NJ FutuseouCs uONBMIOJUI eprAold Oj ‘smesAs Fulnsvew O19SNOOw UT SUOTIBAGIA O][qQ¥O SuToNped JO Spoyjow puB seoinos OY} SUTWIEJep 0} poJONpUOD SBA UOT}BSySeAUI [eyueWIIedxe uy » GHIAISSVTONN “sjod ‘sydvad ‘-sudetp “snqt “dig ‘tt “T96T Sny “WUBILIOW\ “JY UAE PUB UOFTBA\ “O JoySeYD Aq ‘SWALSAS ANOHAOUGAH GAANAasAS “HOVAANS AO SOMLSIUALOVUVHO DNIMOL GNV NOILVUGIA "BSG Hodey “uysog japow 40}4D) prang