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JPH08313622

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DESCRIPTION JPH08313622
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
underwater receiver, and more particularly to an underwater receiver used for towing in water
for acoustic measurement in the ocean.
[0002]
2. Description of the Related Art Heretofore, in this type of underwater wave receiver, an
electroacoustic transducer is accommodated in an acoustically transparent housing such as a
rubber hose, and the underwater wave receiver is filled with an insulating fluid which is an
acoustic medium. The electroacoustic transducer is covered with a rigid case having an acoustic
entrance in order to prevent the insulating fluid that vibrates from directly colliding with the
electroacoustic transducer when the housing is towed.
[0003]
With such a configuration, even if the fluid filled inside vibrates due to the vibration caused by
the turbulent flow generated on the surface of the housing when towing the underwater receiver,
the vibration fluid first collides with the rigid case Therefore, the rigid case prevents the direct
collision with the electroacoustic transducer as a shield.
[0004]
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1
However, noise generated during towing is generally referred to as flow noise, and noise (voltage
output) is caused by pressure fluctuation due to turbulence generated on the surface of the
casing being transmitted to the pressure-sensitive type electroacoustic transducer. It is believed
to be).
Therefore, according to the prior art having the above-described configuration, the noise
generated in the electroacoustic transducer when the housing having acoustic transparency is
towed is caused by the collision of the vibrated fluid with the electroacoustic transducer. In the
low frequency band which is not affected by resonance in Helmholtz resonators, the pressure
outside the rigid case and the pressure inside the rigid case around the acoustic entrance are the
same, so the noise reduction effect is not exhibited. There was a problem.
[0005]
In view of the above problems, the present invention changes the shape and arrangement
position of the electroacoustic transducer by obtaining a configuration in which pressure
fluctuation due to turbulent flow generated on the surface of the casing is difficult to propagate
to the pressure-sensitive type electroacoustic transducer. It is an object of the present invention
to provide an inexpensive and reliable operation of an underwater receiver by reducing flow
noise.
[0006]
[Means for Solving the Problems] In order to achieve the above object, the present invention is
characterized in that the flow noise generated by the turbulent boundary layer is a pseudo-sound
and it is difficult to propagate far away (Kyoritsu Publishing, Inc. Principles of underwater
acoustics Chapter 11) is used to lengthen the propagation path of pressure fluctuation from the
turbulent flow generation surface to the electroacoustic transducer.
[0007]
That is, according to the present invention, a hollow rigid case having an acoustic entrance is
supported in a case having sound transmission, an electroacoustic transducer is provided inside
the rigid case, and the inside of the case and the rigid case is an acoustic medium In the
underwater receiver filled with the liquid, the acoustic entrance is provided at a position where
the distance from the turbulent flow generation surface is longer than the distance to the sensing
part of the electroacoustic transducer.
[0008]
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2
According to the present invention having the above configuration, when the underwater wave
receiver is towed, a turbulent boundary layer is generated on the surface of the casing and
pressure fluctuation occurs, but at a position away from the turbulent flow generation surface It
is sufficiently reduced or annihilated while propagating to the acoustic entrance, and only the
pressure fluctuation at the position of the acoustic entrance is transmitted to the electroacoustic
transducer.
[0009]
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a side sectional view showing a first embodiment of the present invention.
An acoustically transparent rubber sheet 2 is stretched on the side of the towing body 1 and the
inside is filled with an insulating liquid 3 which is an acoustic medium.
In the liquid 3, a cylindrical rigid case 5 containing a piezoelectric electroacoustic transducer 4
therein is installed so as to be perpendicular to the rubber sheet surface.
[0010]
The rigid body flanges 6 and 7 are fixed to both ends of the rigid body case 5, and among the
two rigid body flanges 6 and 7, the rigid body flange 6 near the rubber sheet 2 blocks the rigid
body case 5. An acoustic entrance 8 is open at the center of the far rigid flange 7.
The position of the sound inlet 8 is set to a position where the distance from the turbulent flow
generation surface is longer than the distance to the sensing part of the electroacoustic
transducer.
[0011]
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The inside of the rigid case 5 is filled with the same liquid 3 as the outside.
A cable 9 for outputting a signal is connected to the electroacoustic transducer 4, and is further
connected to a processor 10 inside the towing body via a terminal provided in the rigid case 5.
The operation of the present embodiment according to the above configuration will be described.
When the towing body 1 is towed in the sea, a turbulent boundary layer A is generated on the
outer surface of the rubber sheet 2. The pressure fluctuation caused by the turbulent boundary
layer A is transmitted to the inside of the rubber sheet 2 and reaches the wave receiver through
the liquid 3 inside, and the sound entrance of the rigid flange 7 provided farthest from the
rubber sheet surface. The voltage (noise) is transmitted from the point 8 to the electroacoustic
transducer 4 inside the rigid case 5. At this time, the pressure is sufficiently reduced or reduced
while propagating to the sound inlet 8 at a position away from the turbulent flow generation
surface, and only the pressure fluctuation at the position of the sound inlet 8 is transmitted to the
electroacoustic transducer 4 It will be.
[0012]
FIG. 2 is a graph comparing the receiving sensitivity characteristic of the receiver of the present
invention with that of a conventional receiver. Here, the size of the hole of the rigid flange 7 and
the internal method and the volume inside the rigid case 5 determine the resonant frequency of
the Helmholtz resonator. The resonance frequency is set to be sufficiently higher than the
working band so that the receiving sensitivity characteristic to the acoustic signal of the receiver
is not adversely affected, and the receiving sensitivity in the working band is covered with a
normal rigid case. Not the same as a receiver. In addition, the use frequency is set to a low
frequency at which the inside of the rigid case 5 can be regarded as an elastic body without the
influence of the diffraction of the rigid case 5.
[0013]
FIG. 3 is a side cross-sectional view showing a second embodiment of the present invention, in
which the underwater wave receiver is housed in a cylindrical towed wave receiving array. A
rubber hose 11 having sound permeability is filled with an insulating liquid 3 as an acoustic
medium, and a receiver and an electronic circuit capsule 12 are accommodated. Here, in the
wave receiver, a piezoelectric type electroacoustic transducer 4 is covered with a cylindrical rigid
body case 5, and the rigid body case 5 is placed parallel to the rubber hose 11 so that its central
axis coincides.
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[0014]
Although rigid body flanges 6 and 7 are fixed to both ends of the rigid body case 5 and the rigid
body flange 6 on one side closes the rigid body case 5, an acoustic entrance 8 is at the center of
the rigid body flange 7 on the opposite side There is. As a result, the acoustic entrance is
disposed at a position farthest from the turbulent flow generation surface, that is, on the central
axis of the rubber hose 1. Of course, the position of such an acoustic entrance 8 is longer than
the distance from the turbulent flow generation surface to the sensing part of the electroacoustic
transducer 4.
[0015]
The inside of the rigid case 5 is filled with the same liquid 3 as the outside. A cable 9 for
outputting a signal is connected to the electroacoustic transducer 4, and is further connected to
the electronic circuit capsule 12 through a terminal provided in the rigid case 5. The operation of
the second embodiment having the above configuration is similar to that of the first embodiment.
[0016]
As described above in detail, according to the present invention, a hollow rigid case having an
acoustic entrance is supported in an acoustically transparent housing, and an electroacoustic
transducer is supported inside the rigid case. In the underwater receiver in which the inside of
the case and the rigid case is filled with a liquid serving as an acoustic medium, the distance from
the sound generation surface to the sound incident port is greater than the distance to the
sensing part of the electroacoustic transducer Since it is provided at a long position, the
propagation path of pressure fluctuation from the turbulent flow generation surface to the
electroacoustic transducer can be made long.
[0017]
This makes it difficult for pressure fluctuations due to turbulence generated on the surface of the
case to propagate to the pressure-sensitive type electroacoustic transducer, and reduces flow
noise without changing the shape or arrangement position of the electroacoustic transducer,
which is inexpensive This has the effect of providing a highly reliable underwater receiver.
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[0018]
Brief description of the drawings
[0019]
1 is a side sectional view showing a first embodiment of the present invention.
[0020]
2 is a graph comparing the wave receiving sensitivity characteristics of the wave receiver of the
present invention with a conventional wave receiver.
[0021]
3 is a side sectional view showing a second embodiment of the present invention.
[0022]
Explanation of sign
[0023]
1 towed body 2 rubber sheet 3 liquid 4 electroacoustic transducer 5 rigid case 6, 7 rigid flange 8
acoustic entrance 9 cable 10 processor
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