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JPH10197328

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JPH10197328
[0001]
The present invention relates to an outer plate of a hull during traveling, a water channel, a
pipeline of a plant, etc., which is in contact with fluid externally or internally and where the fluid
flows. The present invention relates to a sound pressure detection device in a flow field applied
to measurement of a sound pressure fluctuation of fluid at a contact surface such as a surface, a
water channel, or a pipe wall surface.
[0002]
2. Description of the Related Art In the prior art, when measuring the sound pressure fluctuation
at the contact surface with the flowing fluid, such as the outer shell plate or the wall surface of
the pipe, as shown in FIG. , Etc., or a device where the sound pressure detector 21 such as a
hydrophone is housed in a holder 24 as shown in FIG. It is attached to the contact surface with
the fluid, and the sound pressure fluctuation is detected.
[0003]
In the embodiment shown in FIG. 2, the holder 14 and the through hole 19A of the flow path wall
19 are attached to the outer wall surface of the flow path wall 19 such as the hull plate and pipe
wall via a plurality of bolts 18. A sound pressure detector 11 such as a hydrophone is disposed
inside the fluid field 10 so as to protrude, and a position (hereinafter referred to as an acoustic
center) 11a at which the sound pressure fluctuation is detected is a contact surface between the
flow path wall 9 and the fluid. Sound pressure is detected in accordance with the inner surface of
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a certain flow path wall.
Reference numeral 16 denotes an O-ring interposed between the holder 14 and the sound
pressure detector 11.
[0004]
In such a case as shown in FIG. 2, when the flow velocity v of the fluid increases, the fluid
pressure field 11 is disturbed by the sound pressure detector 11 such as a hydrophone
projecting in the fluid field, and a pressure fluctuation newly occurs. It is not possible to detect
true pressure fluctuations at the interface with the fluid.
[0005]
In order to solve the above problems, as shown in FIG. 3, in order to smooth the tip and prevent
the flow field from being disturbed, an acoustic window 22 substantially matching the acoustic
characteristics with the fluid such as acrylic is attached to the tip. The inside of the holder 24 is
filled with the same fluid 23 as the object to be measured, and the sound pressure detector 21
such as a hydrophone or the like, and the inward tip 24a of the holder 24 The pressure
fluctuation is detected by being installed in the through hole 29A of the flow path wall 29 so as
to correspond to the contact surface of the flow path wall 29 and the fluid.
Reference numeral 26 denotes an O-ring interposed between the sound pressure detector 21 and
the holder 24, and 26 'denotes an O-ring interposed between the holder 24 and the through hole
29A of the flow path wall 29. Further, reference numeral 28 denotes a plurality of bolts for
attaching the flange 27 of the holder 24 to the outer wall surface of the flow path wall 29.
[0006]
However, in such a case as shown in FIG. 3, since the acoustic center 21a of the sound pressure
detector 21 such as a hydrophone is inside the holder, the space from the holder tip 24a to the
acoustic center 21a forms a sound field. In the frequency range near the resonance frequency of
this space, accurate sound pressure can not be detected.
[0007]
The present invention is intended to provide a sound pressure detection device in a flow field
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that can solve the above problems.
[0008]
In the flow field of the present invention, a sound pressure detection apparatus according to the
present invention comprises a plate-like piezoelectric element, a wall covering the surface of the
piezoelectric element, and a surface forming a flow path, and no sound pressure. It is
characterized by having an acoustic window transmitted to the piezoelectric element.
[0009]
In the present invention, since the surface of the acoustic window containing the piezoelectric
element is smooth with the wall surface forming the flow path, the sound pressure fluctuation
can be detected without disturbing the flow of the fluid field.
[0010]
Further, the acoustic center which is a position to detect the sound pressure of the sound
pressure detection device of the present invention is the surface of the piezoelectric element, and
by using the plate-like piezoelectric element, the acoustic center and the wall surface forming the
flow path The space between the acoustic center and the wall that forms the flow path (the
interface between the fluid and the wall that forms the flow path) can be reduced to set the
resonance frequency high. It is possible to detect sound pressure fluctuations in the flow field
accurately up to high frequencies.
[0011]
DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will
be described with reference to FIG.
The reference numeral 10 denotes a fluid field through which the fluid at the flow velocity v
flows, and the inner wall surface (upper wall surface) of the horizontally disposed channel wall 9
such as an outer shell plate or a pipeline wall contacts the fluid to form a channel It is a wall.
[0012]
In the vertical through hole 9A provided in the flow path wall 9, the inward (upper) tip is inserted
in the same plane as the inner wall surface of the flow path wall 9 to make the holder 4 smooth.
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The holder 14 is attached to the outer wall surface (lower wall surface) of the flow path wall 9 by
a plurality of bolts 8 penetrating flanges 7 which project to both sides.
[0013]
The portion of the holder 4 in the through hole 9A is hollow, and the upper portion of the hollow
portion is provided with a convex portion 4a extending from one side of the hollow portion to the
other side in the horizontal direction. At a portion above the convex portion 4 a of the holder 4, a
concave portion 5 a whose upper side opens to the fluid field 10 is formed.
[0014]
A plate-like piezoelectric ceramic, a piezoelectric rubber, a polymer piezoelectric film, etc.,
mounted horizontally in the recess 5a so as to be integral with the protrusion 4a and having
electrodes 2, 2 'at the top and bottom A piezoelectric element 1 is arranged which generates a
voltage proportional to the working pressure.
[0015]
Lead wires 3, 3 'are attached to the electrodes 2, 2' attached to the upper and lower sides of the
piezoelectric element 1, respectively, so that the voltage generated in the piezoelectric element 1
can be taken out of the holder 4 ing.
[0016]
An acoustic rubber 5 as an acoustic window is filled in the recess 5 a of the holder 4 in which the
piezoelectric element 1 is disposed so as to cover the piezoelectric element 1, and the upper
surface of the acoustic rubber 5 forms a flow path. It is in the same plane as the inner surface of
the flow path wall 9 as the wall surface and the inward tip end of the holder 4 and is smooth.
As the acoustic rubber 5, one whose specific acoustic characteristic substantially matches that of
the fluid field 10 is used.
[0017]
Further, the distance l between the surface (the acoustic center) of the piezoelectric element 1
and the tip of the holder 4 (the tip of the acoustic rubber 5 and the inner wall of the flow path
wall 9) is the sound between the piezoelectric element 1 and the tip of the holder 4 It is set short
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to satisfy the following equation so that the lowest natural frequency of the field is sufficiently
lower than the frequency to be detected.
[0018]
l << c / 4f where c: sound velocity of the fluid field f: frequency to be measured or, further, an Oring 6 for sealing is disposed between the holder 4 and the through hole 9A of the flow path wall
9 ing.
[0019]
In the present embodiment configured as described above, the upper surfaces of the acoustic
rubber 5 and the holder 4 are in the same plane as the inner wall surface of the flow path wall 9
in contact with the fluid and are smooth. The sound pressure fluctuation can be detected by the
piezoelectric element 1 without disturbing the flow 10.
[0020]
Further, by using the plate-like piezoelectric element 1 and integrating it with the convex part 4a
of the holder 4 forming the concave part 5a, as described above, the surface of the piezoelectric
element 1 as the acoustic center and the flow path wall The distance to the inner wall surface of
9 can be shortened, thereby reducing the space between the surface of the piezoelectric element
1 which is the acoustic center and the inner wall surface of the flow path wall 9 which is the
interface between the fluid and the fluid. Since the resonance frequency of the sound field
formed by the same space can be set high, the sound pressure fluctuation can be accurately
detected by the piezoelectric element 1 up to the high frequency range.
[0021]
As described above, according to the present invention, there is provided a plate-like
piezoelectric element, an acoustic window which covers the piezoelectric element and forms a
flow path on its surface, and which transmits no sound pressure to the piezoelectric element.
Therefore, the sound pressure fluctuation can be detected without disturbing the flow of the fluid
field.
[0022]
In addition, by providing a plate-like piezoelectric element and an acoustic window for covering
the piezoelectric element and covering the piezoelectric element, the distance between the
surface of the piezoelectric element that is the acoustic center and the wall surface forming the
flow path is shortened. Since the space between the acoustic center and the wall surface forming
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the flow path, which is the interface of the fluid, can be reduced to set the resonance frequency
in the same space high, the piezoelectric element can accurately detect the sound in the flow field
up to the high frequency range Pressure fluctuations can be detected.
[0023]
Brief description of the drawings
[0024]
1 is a cross-sectional view of an embodiment of the present invention.
[0025]
2 is a cross-sectional view of an example of the sound pressure detection device in the
conventional flow field.
[0026]
3 is a cross-sectional view of another example of the sound pressure detection device in the
conventional flow field.
[0027]
Explanation of sign
[0028]
DESCRIPTION OF SYMBOLS 1 piezoelectric element 2, 2 'electrode 3, 3' lead wire 4 holder 4a
convex part 5 acoustic rubber 5a recessed part 6 O ring 7 flange 8 bolt 9 flow path wall 10 fluid
field
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