JPS6249516B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an underwater sound silencer that eliminates the pulsating sound of water passing through a water conduit.

``Prior Art'' Generally, a water conduit system as shown in FIG. 1 is required to be equipped with an underwater sound silencer. That is, in this water pipe system, for example, the pulsating sound of the water caused by the rotation of the blades of the impeller pump 1 is transmitted to the pipe, and this is transmitted to the support fitting 2 of the pipe, and the sound is transmitted to the building. This is because noise is generated as a result of vibrating walls and slabs. Note that 3 in the figure indicates a flexible joint.

Incidentally, various structures have been proposed and implemented as underwater sound silencers (also referred to as "pipe silencers") to be installed in water pipe systems as described above.

For example, as disclosed in Japanese Patent Publication No. 55-44280 (Fluid Direction Switching Pipe), one or more fluid supply pipes are connected to one main pipe and the flow within the main pipe is switched between forward and reverse directions. In a fluid direction switching pipe having a valve, the on-off valve is provided at a position an odd number times a quarter wavelength of the pulsation to be muffled from the connection point at the end, or As disclosed in Japanese Patent Publication No. 56-27760 (merging main pipe), in a merging main pipe in which a plurality of control pipes are connected at intervals, the fluid inlet side end of the merging main pipe is closed. When the wavelength of vibration to be formed and damped is λ, λ/4 from the closed end
For example, a configuration in which the control tube is connected to a position that is an odd multiple of .

``Problems to be Solved by the Invention'' However, in the former case, in such a conventional underwater sound silencer, the installation position of the on-off valve with respect to the main pipe, the relative position of the on-off valve and the fluid supply pipe, and even the fluid supply Since the relative positions of the pipes are inevitably determined in relation to the wavelength of the pulsation, it is difficult to install these on-off valves and fluid supply pipes in arbitrary positions according to the structure of the building, etc. This poses a problem in that it is not possible to do so and is therefore subject to significant design constraints.

In the latter case, the distance from the connecting position of the controlling pipe to the merging main pipe to the closed end, as well as the relative positions of the controlling pipes to each other, are inevitably determined by the relationship with the wavelength of the pulsation, so the design is similar to the former. The problem is that it is subject to the major restrictions above.

Furthermore, in all conventional methods, the solution is to select the relative distance between the closed end or the extreme end and each component based on the pulsation wavelength.
Due to position determination based on other factors, the effective band of wavelengths that exert a silencing effect is narrow, and therefore, even small fluctuations in wavelength may not produce a sufficient silencing effect. .

This invention has been made in view of the above circumstances, and has a relatively arbitrary installation position in the water pipe, is less subject to design restrictions, and has an excellent sound-dampening effect even if the wavelength varies slightly. The purpose is to provide an underwater sound silencer.

"Means for Solving the Problems" Therefore, in the present invention, in an underwater sound silencer that suppresses the pulsating sound of water passing through a water conduit, the water conduit is provided with a wavelength of a pulsating wave of water passing through the water conduit. Approximately 1/8
A plurality of air chambers communicating with the inside of the water conduit are provided at intervals of .

Here, the air chamber includes a bulging space provided in the water pipe and bulging outward from inside the water pipe, and an elastic air enclosure held in the bulging space and sealing air inside. It is desirable to have a

``Function'' Since there are multiple air chambers that communicate with the water pipe at intervals, the pulsating waves of water passing through the water pipes will reach the trough position of the pulsating waves in the area of the air chamber located λ/8 ahead. is adjusted. Since the air chambers are spaced approximately 1/8 wavelength apart, when the pulsating waves pass through these air chambers, they are most likely to be attenuated, resulting in effective noise reduction. be done. In addition, by providing multiple air chambers in this way, the silencing effect is achieved simply by organically combining the air chambers.
Its function works effectively no matter where it is installed in the water pipe.
Therefore, there are almost no design restrictions.

``Example'' Hereinafter, an example of the present invention will be described with reference to FIGS. 2 to 13.
This will be explained based on the diagram.

Reference numeral 4 in the figure is a water conduit installed in the water conduit system, the left end of which is connected to the discharge side of the pump, and the water is supplied from the right end to the subsequent water conduit via a flexible joint 5. It is meant to lead. T-joints 6 are connected to both sides of the water conduit 4, and air chambers A and B are formed on both sides of the water conduit 4 using these T-joints 6. The water conduit 4 and each T-joint 6 are made of steel or plastic, for example.

Air chambers A and B are of the same type and are constructed as follows. That is, T extending upward
A short pipe 8 having a flange 7 is screwed inside the opening of the branch pipe portion 6a of the joint 6, and a frame-shaped wire mesh support fitting 9, a frame-shaped packing 10, and a transparent plastic plate are attached to the upper part of the flange 7. 11 and the flange body 12 are sequentially overlapped, bolt 1
3 and a nut 14. The transparent plastic plate 11 is the branch pipe part 6a of the T-joint 6.
The opening of the short pipe 8 is liquid-tightly closed, thereby forming the inside of the short pipe 8 into a bulging space S that bulges upward from the inside of the water conduit 4. Further, the transparent plastic plate 11 allows the interior of the bulging space S to be visually recognized from the outside through the central through-hole 12a of the flange body 12. On the inner peripheral edge of the wire mesh support fitting 9,
A peripheral edge of the opening of a bag-shaped wire mesh 15 that bulges downward is attached. A pneumatic ball 16 made of rubber or plastic is housed within the wire mesh 15.

In this way, the air chambers A and B each hold the air-filled ball 16 in the bulging space S.

By the way, in the present invention, the distance l ₁ between the air chambers A and B in the length direction of the water conduit 4 is set to approximately 1/8 of the wavelength of the pulsating wave of water passing through the water conduit 4. Limited. As a result, the air chambers A and B have a sufficient muffling effect on the pulsating sound of water.

Therefore, next, the significance of limiting the interval _l1 between the air chambers A and B to the above value will be explained.

First, the underwater sound pressure level distribution in a pipe having one air chamber will be explained ("Water Hammer Effect and Pressure Pulsation" by Tokuzo Akimoto). That is, when a sine wave expressed by P・sin2πf(t-x/c) enters a water conduit P having an air chamber C from the left side as shown in FIG. The amplitudes U and U of the underwater sound in the area on the left side of C and the area on the right side of C are expressed by the following formulas.

U=P ・√1+′ ² +2′2・′……(1) m′x=2f/c (L−x+l) U=P・Sa ・√1+ ² +22 ……(2) mx=2f/c (L-x) U: Amplitude of underwater sound inside the pipe (mAq) P: Amplitude of incident wave (mAq) : Frequency (Hz) t: Time (s) c: Speed of sound (m/s) x: Distance ( m) R′L: Reflection coefficient at the position of the air chamber Sa: Passage rate of waves at the position of the air chamber l: Corrected length of pipe length (m) La: Length to the air chamber (m) L : Pipe length (m) RL: Reflection coefficient at the pipe end (right end) Of these, R'LlSa is determined as follows.

R'L=1-4/D(1- ^RL2 )...(3) l=-(L-La)+c/4πtam ^-1 4RLsin2πma+2B(1+ ^RL2 +2RLcos2πma)/4(1
RLcos2πma)-D……(4) D=4 (1+BRLsin2πma) +B ² (1+RL ₂ +2RLcos2πma) B k・2πf/g・c/a ma=2f/c (L−La) k=l/k′・Va/Ha k′: Specific heat ratio Va: Amount of air in the air chamber (m ³ ) Ha: Pressure in the air chamber (mAq) a: Pipe cross-sectional area (m ² ) G: Gravitational acceleration 9.8 (m/s ² ) By the way, underwater sound of water conduit P without air chamber C The amplitude U of is expressed by the following formula.

U=P・√1+ ² 22...(6) mx2f/c(L-x) Next, taking as an example the case where the reflection coefficient RL at the pipe end (right end) is -1, The distribution of underwater sound pressure levels is shown in Figure 6.
That is, as is clear from the above formulas (1) and (6),
In the region , the position of the wave trough does not change depending on the presence or absence of the air chamber C. In addition, in the area of , the position of the trough of the wave moves according to the capacity of the air chamber C, and if the capacity is large enough, the position of the trough will change depending on the capacity of the air chamber C.
, and d=0. By the way, if the value of B (related to the capacity of the air chamber C) in the above equation (4) is 8 or more, the value of d is equal to the half wavelength r of the wave.
It will be around 10%. Note that r does not change.

The reflection coefficient RL at the pipe end (right end) and the position of the air chamber C are related to the wave passage rate Sa as follows. That is, as shown in FIGS. 7 and 8, when the air chamber C is at the trough of the standing wave, the passage rate Sa becomes large and the wave attenuation effect disappears; When the distance is more than 1/4r from the wave trough, the passage rate is reduced to 1/
By lowering it to about 10, a sufficient wave attenuation effect can be obtained.

Therefore, the air chamber C is 1/4r from the trough of the standing wave.
It is extremely effective to provide the wave attenuating effect only in the above-mentioned separated positions.

However, it is difficult to predict the position of the trough of the standing wave and reliably provide the air chamber C at the above-mentioned limited position. This is because the position of the trough of the standing wave is determined by the position of the reflecting object and the underwater sound speed, and in particular, the underwater sound speed changes slightly depending on the amount of air in the water.

This is where the significance of the present invention is that the two air chambers A and B are provided at an interval _l1 of approximately 1/8 (1/4r) of the wavelength.

That is, the present invention was made by focusing on the fact that when the capacity of an air chamber is large, the position of the wave trough approaches the air chamber.
By limiting the interval l ₁ of B to the above value,
The combination is such that one air chamber A adjusts the wave trough position, and the other air chamber B effectively dampens the waves.

By the way, if the amount of air in the water increases,
There is a concern that the wavelength of the wave will become smaller and the next trough of the wave will hit the other air chamber B. However, the 9th
As shown in the figure, no trough of the wave is applied to the air chamber B within the range where the wave of half wavelength r shown by the solid line in the figure changes to half wavelength 1/3r.

That is, the condition for the air chamber B to be outside the range of 1/4r from the trough of the wave is expressed by the following formula.

x>r _' /4 It can be seen that sufficient wave attenuation is achieved over a wide range up to a change of /3.

Incidentally, in the embodiment of the present invention shown in Fig. 2, when the water conduit 4 is a steel pipe with an inner diameter of 80 mm and a wave with a frequency of about 100 Hz to 300 Hz of general pump noise is incident inside the pipe, the underwater sound velocity is the same as that of the air in the water. It is considerably smaller than the theoretical value of 1500 m/s because it varies depending on the amount and the molding material of the water conduit 4. For example, when the actual underwater sound velocity in the water conduit 4 is 1200 m/s and the frequency is 150 Hz, l ₁
The value of is 1000mm.

Therefore, it was proved through the following experiment that the underwater sound silencer according to the present invention has an excellent wave damping effect, that is, an excellent pulsating sound muffling effect.

FIG. 10 shows the first experimental setup for this silencer. In the silencer set here, the water conduit 4 is a steel pipe with an inner diameter of 80 mm, and the interval _l1 between the two air chambers A and B is 1300 mm. Also, the dimensions of the water pipe system to which this silencer is installed are: l ₂ = 1600mm, l ₃ = 300mm, l ₄ = 150mm, l ₅
= 200 mm, l ₆ = 3300 mm, and l ₇ = 5550 mm, and an underwater speaker 18 is set in the pipe at the lower end of the silencer. The flexible joint 5 on the upper end of the silencer is made of stainless steel, and the connecting pipe 17 on the lower end of the silencer is a transparent pipe.

In such a first experimental device, four signals of 125Hz, 160Hz, 200Hz, and 250H are output from the underwater speaker 18.
Different types of waves were incident, and the underwater sound level inside each tube was detected by an underwater microphone (not shown). The experimental results are shown in Figures 11a, 11b,
It is shown in FIG. 11c and FIG. 11d. As is clear from the results of these experiments, especially from the underwater sound level at the detection point ~, this silencer achieved an excellent pulsating sound muffling effect.

FIG. 12 shows a second experimental setup for this silencer. In the silencer set here, the water conduit 4 is a steel pipe with an inner diameter of 80 mm, and the interval _l1 between the two air chambers A and B is 600 mm. The dimensions of the water pipe system to which this silencer is installed are l ₈ = 900 mm, l ₉ = 1000 mm, l ₁₀ = 150 mm, l ₁₁ = 300
mm, l ₁₂ =2300 mm, and an underwater speaker 18 is set in the pipe at the lower end of the silencer. The flexible joint 5 on the lower end side of the silencer is made of stainless steel, and the connecting pipe 1
9 is a transparent tube.

In such a second experimental device, four types of waves of 125 Hz, 160 Hz, 200 Hz, and 250 Hz were input from the underwater speaker 18, and the underwater sound level in each pipe was detected by an underwater microphone (not shown). . The experimental results are shown in Figure 13a, Figure 13b, and Figure 1.
3c and 13d. As is clear from the results of these experiments, particularly from the underwater sound level at the detection point ~, the present silencer achieved excellent pulsating sound muffling effects similar to the first experimental results.

In each of the above embodiments, the air chambers A and B are configured by holding the air ball 16 in the bulging space S, but the configuration of the air chambers A and B is not limited in any way, and the design may be changed as appropriate. For example, ball 1
6, an air-filled air bag 20 or a diaphragm 21 as shown in FIG. 14a or 14b may be held in the bulging space S. The former air bag 20 has an air-tight space formed inside by heat-pressing the circumferential parts of plastic or metal-deposited film plastic, which is difficult for air to pass through, and the latter diaphragm 21 is made of, for example, stainless steel or the like. It has a sealed air space inside.

"Effects of the Invention" As explained in detail above, according to the underwater sound silencer according to the present invention, a plurality of air chambers are provided in the water conduit at limited intervals of approximately 1/8 of the wavelength of the pulsating wave. By the cooperation of each air chamber, pulsating noise can be surely and effectively silenced. By the way, when compared with the most advanced conventional silencer of this type, it was found that the silencing effect was greater than 20 dB depending on the frequency.

In addition, by limiting only the mutual spacing between multiple air chambers, an excellent noise reduction effect can be achieved, so as long as this limiting condition is satisfied, the installation position of each air chamber with respect to the water pipe can be arbitrary. The silencing effect does not decrease depending on the mounting position of each air chamber.

In addition, since it has a simple structure of just providing an air chamber in the water pipe and can be easily manufactured using general piping materials, the silencer itself can be made compact, and it can be easily made by simply combining air chambers with each other. Since the air chamber is designed to exhibit a silencing effect, its function can be effectively performed no matter where in the water conduit the air chamber is provided, and there are almost no restrictions on the design.

Furthermore, by adjusting the position of the trough of the pulsating wave,
Since the air chamber can be set at a position where the silencing effect is most effective, the silencing effect can be fully exerted even if the wavelength fluctuates somewhat.

In addition, in the space that bulges outward from the inside of the water conduit,
If an air chamber is constructed by holding an elastic air enclosing body such as an air-filled ball, an air bag, or a diaphragm, various effects can be obtained, such as the ease of maintenance of the air chamber by replacing the air enclosing body.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an example of a water conduit system with a pump, Fig. 2 is an external view showing an embodiment of the present invention, Fig. 3 is an enlarged sectional view of the air chamber portion, and Fig. 4 is 5 to 8 are cross-sectional views of the wire mesh inside the air chamber, and FIGS. 5 to 8 are diagrams showing the operation of one air chamber for explaining the principle of operation of this invention. FIG. 9 is a view for explaining the operation of this invention. FIG. 10 is a configuration diagram of the first experimental apparatus of the present invention, FIGS. 11 a to d are diagrams showing experimental results using the first experimental apparatus, and FIG.
The figure is a configuration diagram of the second experimental apparatus of this invention, No. 13
Figures a to d are diagrams showing experimental results using the second experimental device, and Figures 14a and 14b are longitudinal cross-sectional views showing other examples of the air-enclosed body, respectively. 4...Water conduit, 16, 20, 21...Air enclosure, A, B...Air chamber, S...Bulging space.

Claims (1)

[Scope of Claims] 1. In an underwater sound silencer that eliminates the sound of pulsating water passing through a water conduit, the water is placed in the water conduit at intervals of approximately 1/8 of the wavelength of the pulsating waves of water passing through the water conduit. An underwater sound silencer characterized by having a plurality of air chambers communicating within a conduit. 2. The air chamber includes a bulging space provided in the water pipe and bulging outward from inside the water pipe, and an elastic air enclosure held within the bulging space and sealing air inside. An underwater sound silencer according to claim 1.