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Elite Sttes stem [151 3,676,02 [451 ,By 11, 1972 Murphree et al. [s41 SUB -- §~~r 1 E PROPELLER CAVITATION NOISE 'l‘‘- 6% F ATOR 3,311,868 3,341,697 [72] _ Inventors: Francis J. Murphm, Wmter Park; Paul 3Cami", Orlando, both of Fla- 3,464,016 8/1969 3,482,113 12/1969 3,564,407 2/1971 [73] Assignee: The United States of America as 3/1967 9/1967 I represented by the Secretary of the Navy [22] Filed: June 21, 1971 [21] Appl. No.: 155,053 Cupp et al. ............. ..340/3s4 E x Kaufman et al.. ...... ..235/l84 Kerwin et Heesh ............. .. Metcalf et al. 328/133 X ..332/9 T ux ........ .328/144 x _ Primary Exammer—-Alfred L. Brody Attorney-Richard S. Sciascia et al. [57] ABSTRACT Simulation of submarine propeller cavitation as it varies with [52] U 8 Cl 332/9R 235/184 307/251 [51] ' ' ' """"""""""""""" " Int Cl I 58] “Cid 1528/‘ 44 540/384 E’ ’ Gosh 3/10 """""""""" """""""" 3,165,734 frequency proportional to blade rate to a counter which is periodically read out and reset at a rate proportional to the n 44 13} square root of pressure. The read out is used to control noise /384 E1 235’/184_ 30§/25 1’ ’ [56] speed and depth of submergence is effected by feeding a attenuator means including a one of N decoder and N attenua ’ tors scaled to provide relative noise according to a curve characteristic of the submarine to be simulated. The noise out - References Cited UNITED STATES PATENTS 1/1965 put is modulated in pulse width and repetition rate by a func tion generator also controlled by the counter read-out. Grodzinsky et al ............... ..340/384 E '0 20 3O \ 4 Claims, 6 Drawing Figures 32 34 7/; PRESSURE 40 3e voLT. TO P 44 ONE FREQ. CONV, SHOT / 4o 52 5O BLADE 48 45 54 RATE voLT. TO BINARY FREQ. coNv. coUNTER 22 22a 104 \ 50a _ VOLT To > FREQ. CONV, DELAY L (D2) 50b /soc f/sod 46/ 70 PARALLEL AND GATE MEANS DELAY (0|) 66 i‘ I06 / 94o94b —\ \ /60o A/GOb/GOc /60d 68 94c \ 94m 9e 62 +1 IQ‘TI 42 ' _I'l_// FUNCTION HOLD CIRCUIT GENERATOR /44G 98% I00 VOLTAGE 620/62b/62c / VAR‘ABLE - | 2 / 9 10s 1/“ 7s QNE- oF-TEN Passe" BAND 62d ___ 1o "' H4 76‘ /‘/76u //76b /,/ / 76 1 I . LIMITED NOISE GATE 24 / ___ "4° ‘'0 H4b ‘iii-1'3: 1141 78a 78b 80a 240 1/ 80b ____ 82 84 \ _ CAVITATEON ,- NOISE OUT . 78i 80i 7e] so) 52/’ 86 0 es 92 Patented My 11, m2 3,6748% 4 3 Sheets-Sheet l 3o ‘OE 2O 34 / 32 7/; PRESSURE 4o / / V 36 voLT. TO FREQ. CONV. P 44 / W ONE SHOT / 4o 52 BLADE 5o / RATE 54 voLT. TO ‘* 45 / / 4s BINARY FREQ. CONV. / I D2) /5 (If/50b /50c //50d I04 II \ // voLT. To PARALLEL AND GATE MEANS 9401 E 94th 94c? / 600 // 60b I / 66 I I FUNCT‘ON 60c 60d / , / 68 62 ? EFT‘ I’ M42 HOLD cIRcuIT GENERATOR DELAY (0|) 7 94m 96 46 70 ~ FREQ. CONV. I06 DELAY $4 COUNTER A T 981 440 / ‘ IOO VOLTAGE /62cI/62b / (SEC/62d T VARIABLE 76 ‘T’ PULSE WIDTH ONEE‘COOFD'EEEN oNE-sHoT // ' I 2 9 IO __ BAND / LIMITED Noli; 24 //76a //76b //7sI “4 k GATE "O/ -—H40 / ‘ 78a |l4b ' 800 ‘lit 78b 80b " 78i II4I ’ 80i 78] 88 801 o 92 240 s2\ s4 —: INVENTORS FRANCIS J. MURPHREE PAUL S. CATANO -—» SSYS'TEAB'STN 274241374X M FIG. / % Mad ATTORNEYS 3,676,802 Patent? July 11, 1972 3 Sheets-Sheet 5 % / _ - _ OU E O Um / _M Emlm Q DC 8 9/ . W. 440 O_4 0H.OO lwiEm /w.9_0| 0ND _ ER _FD mm4 b..TRbCbi UNw I20 120d — 122 E VO I300 FIG. 4 0N2I4xm o 40 9 30 SPEED, KNOTS INVENTORS (PRESSURE, ATM) l/2 FRANCIS J. MURPHREE PAUL S. CATANO | ATM 1'33 FT WATER F163 BY ATTORNEYS 1 3,676,802 SUBMARINE PROPELLER CAVITATION NOISE SIMULATOR BACKGROUND OF THE INVENTION This invention relates to the art of sonar simulation for 2 the apparatus 10 is graphically shown in FIG. 2a as a series of noise pulses 12a having an overall amplitude excursion 14a and each having a duration which is short relative to the periodicity of occurrence 16 thereof. The periodicity is, of course, the reciprocal of the blade rate. FIG. 2b shows an ex training purposes or the like, and more particularly to im ample of noise pulses 12b when cavitation is well established. proved apparatus for simulating propeller cavitation noise. Propeller cavitation noise is usually simulated by modulat This example, wherein the period 16b is the same as 16a while the amplitude 14b and the duration of each pulse is notably greater, is indicative of operation at a shallower depth than in ing the output of a random noise source at the blade rate which is proportional to the number of propeller blades and 10 the prior example. In the example of FIG. 20 the cavitation has the shaft RPM of the ship or vessel being simulated. Provision is normally made for accentuating the pulse representing one of the blades inasmuch as it has generally been observed that the actual sound from a ship's propeller is usually charac terized by such accentuation. The noise spectrum selected is, of course, chosen to resemble that of a known ship or class of ships. U.S. Pat. No. 3,341,697 of Kaufman et al. and U.S. Pat. No. 3,165,734 of Grodzinsky et al. are representative of the art of propeller noise simulation of the character mentioned. In the case of simulating the propeller noise of submarines progressed to a general condition wherein the amplitude 14c and the duration of the pulses 12c is still greater and noise 18 occurs between the pulses 12c resulting from cavitation from the vessel hull appurtenances other than the propeller. This last example is indicative of still shallower operation. Of course, if depth were held constant, and speed were in creased from that of FIG. 2a, the cavitation noise would in crease from that of FIG. 2a to that'of FIG. 2b, but the period important, namely the effects of depth on the inception and degree of cavitation, the principal source of propeller noise. It has been shown by R. Urick in his book"‘Principles of Un 16b would be decreased. The analogy can be pursued by further increases of speed at the same depth to reach general cavitation as shown in FIG. 2c, but compressed into still shorter periods. Referring to FIG. 3, the relative noise generated by a submarine can be plotted as a function of the 25 ratio of speed in knots (related of course to blade rate) to the derwater Sound for Engineers” published by McGraw-Hill, 1967, that the shaft speed at which propeller cavitation begins dicated by curve C. The particular shape of curve C will vary an additional factor, not heretofore known to be considered, is square root of the static water pressure P in atmospheres as in from submarine to submarine, and the curve shown is a is approximately proportional to the square root of the static hypothetical one for purposes of example rather than a curve water pressure. He has also shown that the relative noise out put can be plotted as a function of the ratio of the speed in 30 representative of any actual submarine. The apparatus 10, in addition to effecting the desired modulation of noise, serves to knots to the square root of the static water pressure in at provide simulation wherein the relative noise is a desired func mospheres. tion of the ratio of the speed or blade rate to the square root of SUMMARY OF THE INVENTION static pressure. I 35 Reverting to FIG. 1, the apparatus 10 receives as its prin With the foregoing in mind, it is a principal object of this in vention to provide improved apparatus for simulating propeller cavitation noise and which is particularly well suited to simulating the propeller noise of a submerged submarine. As another object this invention aims to provide such im proved apparatus which serves to provide a signal simulative of propeller cavitation noise as a function of vessel or shaft speed and the depth at which a simulated submarine vessel is cipal inputs an analog voltage via line 20 representative of static water pressure P at the depth of simulated operation, an analog voltage via line 22 representative of blade rate, and band limited noise via line 24 from a suitable noise source. The apparatus 10 comprises means 30 for providing as an out put on line 32 a voltage proportional to the square root of the pressure represented by the voltage input on line 20. A voltage to frequency converter 34 is connected to receive Still another object is to accomplish the foregoing in a 45 the output on line 32 and provides a frequency output fl on line 36 where f1 = k, The voltage to frequency converter manner which is compatible for use with either analog or 34 may be of any conventional construction but conveniently digital simulation systems and can take advantage of the comprises a voltage controlled oscillator and a divider to pro recent availability of low cost solid state shift registers, coun vide an output frequency fl which is compatible with the ters,.multivibrators, and the like. remainder of the apparatus. The output on line 36 is applied to Other objects and advantages of apparatus embodying the trigger a one-shot 40, the output 42 of which is fed via lines invention will become apparent from the following description 44, 45, a delay element 46, and line 48 to the reset connection of the presently preferred embodiment when read in conjunc of a digital counter 50 having, by way of example only, a four tion with the accompanying sheets of drawings forming a part bit output represented by lines 50a, 50b, 50c, and 50d. hereof. The input to the counter 50 is derived by a voltage to 55 frequency converter 52 which provides a corresponding DESCRIPTION OF THE DRAWINGS frequency f2 on line 54 to the counter 50, where f2 = k2 (shaft FIG. 1 is a diagrammatic illustration, in block form, of a RPM). operating. propeller cavitation noise simulator apparatus embodying the The output lines 50a-50d are connected to a parallel AND gate means 60 having parallel output lines 60a, 60b, 60c and 60 FIGS. 2a, 2b, and 2c are graphical illustrations of various 60d connected as the input to a hold circuit 62. The AND gate levels of output corresponding to different degrees of cavita means 60 is connected to receive an enabling input from the tron; one shot 40 via lines 44, 66, a delay element 68 and line 70. FIG. 3 is a graphic illustration of relative noise level as a The AND gate means 60 may comprise a plurality of in function of vessel speed and depth of operation; and 65 dividual AND gates such that when an enabling pulse exists at FIG. 4 is a diagrammatic illustration, in block form, of a line 70 logical ones existing at any of lines 50a-50d will be function generator forming part of the apparatus of FIG. 1. shifted to the hold circuit 62. The hold circuit 62 is periodi cally reset by the output of the one-shot 40 via line 44. DESCRIPTION OF THE PREFERRED EMBODIMENT The output of the one-shot 40 is in the form of a short pulse In the form of the invention illustrated in FIG. 1 and 70 42 of duration T1 and the delays D1 and D2 imposed respec described hereinafter, there is provided a cavitation noise tively by delay means 68 and 46 are conveniently such that simulator apparatus which is generally indicated at 10 and D2>D,,,+T,. The leading edge of pulse 42 is used to reset the serves to provide an analog output signal which is a function of hold circuit 62, following which the leading edge of the vessel speed and depth of operation. In this regard, when delayed output of means 68 is used to shift the count from representing cavitation noise at the onset thereof the output of 75 counter 50 into the hold circuit, and following which the lead invention; lOl044 047° 3 3,676,802 4 ing edge of the delayed output of means 46 is used to reset the The output of the one-shot 100, represented by line 108 is counter 50. This sequence of events occurs each time the one applied as an enabling signal to a gate 110 which controls a shot 40 is triggered by the output of the converter 34. Inasmuch as the input to counter 50 is supplied by the volt age to frequency converter 52 which generates the output frequency f2 proportional to shaft RPM and blade rate, and portion of the band limited noise input via line 24. Thus, the noise input signal is connected via line 24, gate 110 and lines 114, 114a, 114b — 114j to the plurality of ?eld effect transistors 78a, 78b - 78]‘. The noise input is further connected directly as shown by line 24a to the additional ?eld effect transistors 86 and 88. Referring now to FIG. 4, the function generator 96 may conveniently comprise a hold circuit 120 which periodically holds the binary, four bit input from the counter 50 for use by a one of ten decoder 122 as shown by lines 120a, 120b, 1200, since the counter 50 is read out and reset at a rate f1 which is proportional to y/T, the count shifted out of counter 50 to hold circuit 62 is equal to where n equals the number of propeller blades. Keeping in mind that speed may be measured by blade rate and that depth may be measured by pressure, it may be stated that the net ef fect of the two inputs (f, and f2) to the counter 50 is to make the count registered at read out directly proportional to speed, and inversely proportional to the square root of pressure at a 120d. The decoder 122 has its output lines 122a — 122j con 15 nected to the control electrodes of ?eld effect transistors 124a - 124j, respectively. These transistors serve as electronic switches to control application of a voltage from a source 128 to respective resistors 130a, 13Gb - 130j. These resistors are connected through a resistor 132 to nominal ground and the output line 98. Selection of the resistors 130a - 130j, only one of which will be connected by its associated transistor to the voltage source at any given time, will result in a desired volt age output on line 98 for a given input to the hold circuit 120. Accordingly, resistors may be selected so that as the blade rate given depth. For example, if speed doubles but pressure in creases by a factor of 4, the count registered remains the same. The readouts from the counter 50 are used to control elec tronic attenuator means about to be described which adjusts the level of a modulated noise signal to provide relative noise 25 increases, the output pulses of the one-shot 100 will be output which varies with speed and depth according to a widened, thereby enabling the gate 110 to pass noise for wider pulses on output line 82. desired curve such as C of FIG. 3. The circuit 62 serves to hold the count shifted thereto while counter 50 is working up a new count. The count being held in The resistors 80a - 80j are selected to attenuate the noise in accordance with a curve such as curve C. For any given analog 62 is, in this example in four bit, binary form and is applied via inputs of pressure and blade rate, only one of the transistors lines 62a, 62b, 62c, and 62d to a one-of-ten decoder 76. The 1 14a - 114j will be rendered conductive and the associated re decoder 76, as its name implies, has 10 output lines 76a, 76b — sistor, together with resistor 84 will provide an appropriate 76j only one of which exhibits a change of voltage for any relative noise level output, modulated of course at the blade given digital combination applied 62a—62d thereof. Such rate by the gate 110 and having pulse widths as determined by decoders are well known to those skilled in the art to which 35 the function generator 96 and one-shot 160. Present information indicates that as the speed of a sub the invention pertains, one example being that marketed by F airchild Semiconductor Division of Fairchild Camera and In strument Corporation, Mountain View, California as their MSl 9301. The output lines 76a - 76] are connected as shown to the control electrodes of a plurality of ?eld effect transistors 78a - marine increases past the threshold of incipient propeller cavitation noise, the propeller beat phenomena becomes less 40 78j which are connected in series with a corresponding plu rality of attenuator resistors 80a-80j. The resistors 80a-80j are connected to a common line 82 from which cavitation 45 noise output is taken, and which is separated from nominal ground by a load resistor 84. One or more of the output lines, e.g. lines 761', 76j, may be connected to the control electrodes noticeable although the level of cavitation noise increases. This is shown in FIG. 2c by the presence of noise between the beat pulses. The purpose, therefore, of additional transistors such as 86 and 88 is to include in the output unmodulated noise at the higher speed to square root of pressure ratios in addition to the propeller beat modulated noise. Obviously many modi?cations and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the ap pended claims the invention may be practiced otherwise than of other ?eld effect transistors such as 86, 88 which are con > nected in series with resistors 90, 92 for a purpose which will 50 as speci?cally described. presently be made apparent. What is claimed is: 1. Apparatus for generating signals simulative of propeller In order to effect the desired modulation of the noise signals cavitation noise from a source of ?rst analog signals represen in accordance with speed or blade rate, the count shifted by tative of water pressure P, a source of second analog signals the AND gate means 60 out of the counter 50 is also applied as shown by lines 94a, 94b, 94c, and 94d to a function genera 55 representative of blade rate, and a source of band limited noise signals, said apparatus comprising: tor 96. The function generator 96, one satisfactory form of ?rst means for converting said ?rst analog signals to a ?rst which is later described with reference to FIG. 4, provides a frequency which is proportional to the square root of P; voltage output on line 98 to a voltage variable pulse width second means for converting said second analog signals to a , one-shot 100, which voltage is a function of the input count to the function generator. The purpose of this, as will presently be seen, is to control the width of the noise pulses 12a, 12b, 120 such that the pulses are narrow when the threshold for cavitation inception has just been exceeded and such that the pulses increase in width as cavitation progresses toward the 65 general condition. Conversely, of course, the pulses go from wide to narrow as cavitation decreases. To this end, the blade rate analog input on line 22 is also ap plied via line 22a to a voltage to frequency converter 104, the output of which is fed via line 106 as the triggering input to the 70 one-shot 100. The one-shot 100, may conveniently be of the type described in U.S. Pat. No. application Ser. No. 50,259 of Arthur B. Moulton, assigned to the assignee hereof, and is adapted to have its unstable or triggered period controlled in duration by the voltage input from the function generator 96. 75 6532 second frequency which is proportional to blade rate; third means for periodically providing an output which is directly proportional to said blade rate and inversely pro portional to the square root of P in response to said ?rst and second frequencies; fourth means for modulating said noise signals to provide pulses thereof at said blade rate and having a pulse width which is a function of said output of said third means; and ?fth means for attenuating said pulses in amplitude by an amount which is a predetermined function of said output of said third means. 2. Apparatus as de?ned in claim 1, and wherein: said ?rst means comprises ?rst voltage to frequency con verter means; said second means comprises second voltage to frequency converter means; 101044 0473 5 3,676,802 6 said third means comprises counter means for providing a said fourth means comprises third voltage to frequency con verter means for converting said second analog signals to a series of pulses at said blade rate, function generator means for providing a voltage which is a predetermined function of the output of said third means, voltage varia ble pulse width one-shot means for rendering a train of count in binary form of input pulses at said ?rst frequen cy, first gate means for reading out said count, hold cir cuit means for holding said count after read out until a new count is developed, ?rst and second delay means for effecting read out of each new count after resetting of pulses at said blade rate and having widths determined by the output of said function generator means, and second gate means for passing said noise signals to said electronic switching means. 4. Apparatus as defined in claim 3, and wherein: said hold circuit and before resetting of said counter means; and said fifth means comprising one-of-N decoder means for rendering a condition change at a predetermined one of N output connections of said decoder means correspond ing to each count read out of said counter means, a plu rality of attenuator elements, a plurality of electronic switching means each being responsive to a change of condition at one of said connections to connect a cor said attenuator means comprises at least one additional at tenuator element and at least one additional electronic 15 responding one of said attenuator elements in series with said fourth means. 3. Apparatus as defined in claim 2, and wherein: 25 30 35 40 45 55 60 65 70 75 switching means responsive to condition change at one of said decoder output connections to connect said addi tional attenuator element directly in series with said source of noise signals.