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[151
3,676,02
[451 ,By 11, 1972
Murphree et al.
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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
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332/9R 235/184 307/251
[51]
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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
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INVENTORS
FRANCIS J. MURPHREE
PAUL S. CATANO
-—» SSYS'TEAB'STN
274241374X
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FIG. /
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ATTORNEYS
3,676,802
Patent? July 11, 1972
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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.