U.S. patent number 3,676,802 [Application Number 05/155,053] was granted by the patent office on 1972-07-11 for submarine propeller cavitation noise simulator.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Navy. Invention is credited to Paul S. Catano, Francis J. Murphree.
United States Patent |
3,676,802 |
Murphree , et al. |
July 11, 1972 |
SUBMARINE PROPELLER CAVITATION NOISE SIMULATOR
Abstract
Simulation of submarine propeller cavitation as it varies with
speed and th of submergence is effected by feeding a frequency
proportional to blade rate to a counter which is periodically read
out and reset at a rate proportional to the square root of
pressure. The read out is used to control noise attenuator means
including a one of N decoder and N attenuators scaled to provide
relative noise according to a curve characteristic of the submarine
to be simulated. The noise output is modulated in pulse width and
repetition rate by a function generator also controlled by the
counter read-out.
Inventors: |
Murphree; Francis J. (Winter
Park, FL), Catano; Paul S. (Orlando, FL) |
Assignee: |
The United States of America as
represented by the Secretary of the Navy (N/A)
|
Family
ID: |
22553946 |
Appl.
No.: |
05/155,053 |
Filed: |
June 21, 1971 |
Current U.S.
Class: |
340/384.3; 367/1;
434/6; 708/605; 367/137; 327/313; 327/349; 703/8 |
Current CPC
Class: |
G06F
7/62 (20130101); G09B 9/06 (20130101) |
Current International
Class: |
G06F
7/62 (20060101); G09B 9/06 (20060101); G09B
9/02 (20060101); G06F 7/60 (20060101); G08b
003/10 () |
Field of
Search: |
;332/9R,9T ;328/144,133
;340/384E ;235/184 ;307/251 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brody; Alfred L.
Claims
What is claimed is:
1. Apparatus for generating signals simulative of propeller
cavitation noise from a source of first analog signals
representative of water pressure P, a source of second analog
signals representative of blade rate, and a source of band limited
noise signals, said apparatus comprising:
first means for converting said first analog signals to a first
frequency which is proportional to the square root of P;
second means for converting said second analog signals to a 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 proportional to the
square root of P in response to said first 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
fifth 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 defined in claim 1, and wherein:
said first means comprises first voltage to frequency converter
means;
said second means comprises second voltage to frequency converter
means;
said third means comprises counter means for providing a count in
binary form of input pulses at said first frequency, first gate
means for reading out said count, hold circuit means for holding
said count after read out until a new count is developed, first and
second delay means for effecting read out of each new count after
resetting of 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 corresponding to each count read out of said
counter means, a plurality 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 corresponding one
of said attenuator elements in series with said fourth means.
3. Apparatus as defined in claim 2, and wherein:
said fourth means comprises third voltage to frequency converter
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 variable pulse width one-shot means for
rendering a train 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 attenuator means comprises at least one additional attenuator
element and at least one additional electronic switching means
responsive to condition change at one of said decoder output
connections to connect said additional attenuator element directly
in series with said source of noise signals.
Description
BACKGROUND OF THE INVENTION
This invention relates to the art of sonar simulation for training
purposes or the like, and more particularly to improved apparatus
for simulating propeller cavitation noise.
Propeller cavitation noise is usually simulated by modulating the
output of a random noise source at the blade rate which is
proportional to the number of propeller blades and 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 characterized 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 an
additional factor, not heretofore known to be considered, is
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 Underwater Sound for
Engineers" published by McGraw-Hill, 1967, that the shaft speed at
which propeller cavitation begins is approximately proportional to
the square root of the static water pressure. He has also shown
that the relative noise output can be plotted as a function of the
ratio of the speed in knots to the square root of the static water
pressure in atmospheres.
SUMMARY OF THE INVENTION
With the foregoing in mind, it is a principal object of this
invention 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 improved
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 operating.
Still another object is to accomplish the foregoing in a manner
which is compatible for use with either analog or digital
simulation systems and can take advantage of the recent
availability of low cost solid state shift registers, counters,
multivibrators, and the like.
Other objects and advantages of apparatus embodying the invention
will become apparent from the following description of the
presently preferred embodiment when read in conjunction with the
accompanying sheets of drawings forming a part hereof.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic illustration, in block form, of a
propeller cavitation noise simulator apparatus embodying the
invention;
FIGS. 2a, 2b, and 2c are graphical illustrations of various levels
of output corresponding to different degrees of cavitation;
FIG. 3 is a graphic illustration of relative noise level as a
function of vessel speed and depth of operation; and
FIG. 4 is a diagrammatic illustration, in block form, of a function
generator forming part of the apparatus of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the form of the invention illustrated in FIG. 1 and described
hereinafter, there is provided a cavitation noise simulator
apparatus which is generally indicated at 10 and serves to provide
an analog output signal which is a function of vessel speed and
depth of operation. In this regard, when representing cavitation
noise at the onset thereof the output of 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 example of noise pulses 12b when cavitation is well
established. 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 the prior example. In the example of FIG. 2c the cavitation
has 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 increased
from that of FIG. 2a, the cavitation noise would increase from that
of FIG. 2a to that of FIG. 2b, but the period 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 ratio of speed in knots (related of course to blade
rate) to the square root of the static water pressure P in
atmospheres as indicated by curve C. The particular shape of curve
C will vary from submarine to submarine, and the curve shown is a
hypothetical one for purposes of example rather than a curve
representative of any actual submarine. The apparatus 10, in
addition to effecting the desired modulation of noise, serves to
provide simulation wherein the relative noise is a desired function
of the ratio of the speed or blade rate to the square root of
static pressure.
Reverting to FIG. 1, the apparatus 10 receives as its principal
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 output 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 the
output on line 32 and provides a frequency output f.sub.1 on line
36 where f.sub.1 = k.sub.1 .sqroot.P. The voltage to frequency
converter 34 may be of any conventional construction but
conveniently comprises a voltage controlled oscillator and a
divider to provide an output frequency f.sub.1 which is compatible
with the remainder of the apparatus. The output on line 36 is
applied to trigger a one-shot 40, the output 42 of which is fed via
lines 44, 45, a delay element 46, and line 48 to the reset
connection of a digital counter 50 having, by way of example only,
a four bit output represented by lines 50a, 50b, 50c, and 50d.
The input to the counter 50 is derived by a voltage to frequency
converter 52 which provides a corresponding frequency f.sub.2 on
line 54 to the counter 50, where f.sub.2 = k.sub.2 (shaft RPM).
The output lines 50a-50d are connected to a parallel AND gate means
60 having parallel output lines 60a, 60b, 60c and 60d connected as
the input to a hold circuit 62. The AND gate means 60 is connected
to receive an enabling input from the one shot 40 via lines 44, 66,
a delay element 68 and line 70. The AND gate means 60 may comprise
a plurality of individual AND gates such that when an enabling
pulse exists at line 70 logical ones existing at any of lines
50a-50d will be shifted to the hold circuit 62. The hold circuit 62
is periodically reset by the output of the one-shot 40 via line
44.
The output of the one-shot 40 is in the form of a short pulse 42 of
duration T.sub.1 and the delays D.sub.1 and D.sub.2 imposed
respectively by delay means 68 and 46 are conveniently such that
D.sub.2 >D.sub.1 +T.sub.1. The leading edge of pulse 42 is used
to reset the hold circuit 62, following which the leading edge of
the delayed output of means 68 is used to shift the count from
counter 50 into the hold circuit, and following which the leading
edge of the delayed output of means 46 is used to reset the counter
50. This sequence of events occurs each time the one-shot 40 is
triggered by the output of the converter 34.
Inasmuch as the input to counter 50 is supplied by the voltage to
frequency converter 52 which generates the output frequency f.sub.2
proportional to shaft RPM and blade rate, and since the counter 50
is read out and reset at a rate f.sub.1 which is proportional to
.sqroot.P, 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 effect of the two inputs
(f.sub.1 and f.sub.2) 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 given
depth. For example, if speed doubles but pressure increases by a
factor of 4, the count registered remains the same.
The readouts from the counter 50 are used to control electronic
attenuator means about to be described which adjusts the level of a
modulated noise signal to provide relative noise output which
varies with speed and depth according to a 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 62
is, in this example in four bit, binary form and is applied via
lines 62a, 62b, 62c, and 62d to a one-of-ten decoder 76. The
decoder 76, as its name implies, has 10 output lines 76a, 76b - 76j
only one of which exhibits a change of voltage for any given
digital combination applied 62a-62d thereof. Such decoders are well
known to those skilled in the art to which the invention pertains,
one example being that marketed by Fairchild Semiconductor Division
of Fairchild Camera and Instrument Corporation, Mountain View,
California as their MS1 9301.
The output lines 76a - 76j are connected as shown to the control
electrodes of a plurality of field effect transistors 78a - 78j
which are connected in series with a corresponding plurality of
attenuator resistors 80a - 80j. The resistors 80a -80j are
connected to a common line 82 from which cavitation 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 76i, 76j,
may be connected to the control electrodes of other field effect
transistors such as 86, 88 which are connected in series with
resistors 90, 92 for a purpose which will presently be made
apparent.
In order to effect the desired modulation of the noise signals in
accordance with speed or blade rate, the count shifted by 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 generator 96. The
function generator 96, one satisfactory form of which is later
described with reference to FIG. 4, provides a voltage output on
line 98 to a voltage variable pulse width 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, 12c 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 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 applied
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 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.
The output of the one-shot 100, represented by line 108 is applied
as an enabling signal to a gate 110 which controls a 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 field effect transistors 78a, 78b - 78j. The
noise input is further connected directly as shown by line 24a to
the additional field 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, 120c, 120d. The decoder 122 has
its output lines 122a - 122j connected to the control electrodes of
field 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, 130b -
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 voltage output on line 98 for a given input to the hold
circuit 120. Accordingly, resistors may be selected so that as the
blade rate increases, the output pulses of the one-shot 100 will be
widened, thereby enabling the gate 110 to pass noise for wider
pulses on output line 82.
The resistors 80a - 80j are selected to attenuate the noise in
accordance with a curve such as curve C. For any given analog
inputs of pressure and blade rate, only one of the transistors 114a
- 114j will be rendered conductive and the associated resistor,
together with resistor 84 will provide an appropriate relative
noise level output, modulated of course at the blade rate by the
gate 110 and having pulse widths as determined by the function
generator 96 and one-shot 100.
Present information indicates that as the speed of a submarine
increases past the threshold of incipient propeller cavitation
noise, the propeller beat phenomena becomes less 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 modifications 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 appended
claims the invention may be practiced otherwise than as
specifically described.
* * * * *