JP2021182092A - Underwater silencer - Google Patents

Abstract

To provide an underwater silencer which suitably reduces noise propagating in water with a simple configuration.SOLUTION: In a ship 1, an underwater silencer 10 includes a shroud portion 14 which at least partially surrounds a noise source 12. The shroud portion is isolated from external space where a noise generation source is located, and is configured to demarcate internal space in which a medium having an acoustic impedance different from that of a main body of the shroud portion is accommodated or decompressed from external space.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an underwater silencer.

In recent years, the level of noise propagating in water has been regulated in consideration of the influence on the surrounding environment and marine organisms. As a source of such noise, for example, in a ship navigating on or under water, there are a propeller (screw) that is rotationally driven underwater, a water flow power generation facility that receives a water flow in water with a turbine, and generates electricity.

Since there is a limit to reducing the noise level itself at the noise source, a muffling device capable of reducing noise in water may be used. As a sound deadening device of this type, a sound absorbing material is generally used, but since the sound absorbing material has a significantly reduced sound absorbing performance in a low frequency range, a significant level reduction cannot be expected. Therefore, Patent Document 1 proposes a noise reduction device capable of reducing noise in water by outputting anti-noise having a phase opposite to the noise waveform generated by the noise source.

Japanese Unexamined Patent Publication No. 2003-173191

However, in a noise reduction device as in Patent Document 1, it is necessary to actively output anti-noise having an opposite phase to the noise, which complicates the device configuration.

At least one embodiment of the present disclosure has been made in view of the above circumstances, and an object of the present invention is to provide an underwater silencer capable of suitably reducing noise propagating in water with a simple configuration.

The underwater silencer according to at least one embodiment of the present disclosure is to solve the above problems.
It has a shroud that at least partially surrounds the noise source.
The shroud portion is isolated from the external space in which the noise generation source is arranged, and a medium having an acoustic impedance different from that of the main body of the shroud portion is housed inside, or the inside is decompressed from the external space. Is configured to define.

According to at least one embodiment of the present disclosure, it is possible to provide an underwater silencer capable of suitably reducing noise propagating in water with a simple configuration.

It is sectional drawing which shows the part of the ship which carries out the underwater silencer which concerns on one aspect. It is a partially enlarged view of FIG. 1 which schematically shows the muffling effect by the underwater muffling device. It is a figure which shows the density, sound velocity and acoustic impedance of air, water and iron. This is an example of analysis of the distribution range of underwater noise by an underwater silencer. This is an analysis result showing the relationship between the first parameter of the underwater silencer and the volume reduction. This is an analysis result showing the relationship between the second parameter of the underwater silencer and the volume reduction. It is a schematic diagram which shows the candidate position of the noise generation source corresponding to FIGS. 5A and 5B. It is a modification of FIG.

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as embodiments or shown in the drawings are not intended to limit the scope of the present invention to this, but are merely explanatory examples. No.
For example, expressions that represent relative or absolute arrangements such as "in one direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric" or "coaxial" are exact. Not only does it represent such an arrangement, but it also represents a tolerance or a state of relative displacement at an angle or distance to the extent that the same function can be obtained.
For example, expressions such as "same", "equal", and "homogeneous" that indicate that things are in the same state not only represent exactly the same state, but also have tolerances or differences to the extent that the same function can be obtained. It shall also represent the existing state.
For example, the expression representing a shape such as a quadrangular shape or a cylindrical shape not only represents a shape such as a quadrangular shape or a cylindrical shape in a geometrically strict sense, but also an uneven portion or a chamfer within the range where the same effect can be obtained. It shall also represent the shape including the part and the like.
On the other hand, the expressions "equipped", "equipped", "equipped", "included", or "have" one component are not exclusive expressions excluding the existence of other components.

The underwater silencer 10 according to at least one aspect of the present disclosure can be widely applied to reduce the sound propagating in water. In the following description, as an example of such an underwater silencer 10, the underwater silencer 10 that can be mounted on a ship capable of navigating on or under water will be specifically described. As another application destination of the underwater silencer 10, for example, there is a water flow power generation facility that generates power by a turbine driven by a water flow. In the water flow power generation facility, underwater noise is generated by the rotational drive of the turbine, so such underwater noise can also be suitably reduced by the underwater silencer 10.

FIG. 1 is a cross-sectional view showing a part of a ship 1 on which the underwater silencer 10 according to one aspect is mounted, and FIG. 2 is a partially enlarged view of FIG. 1 schematically showing a noise reduction effect by the underwater silencer 10. .. The ship 1 can navigate on or under water, and the engine 4 which is a power source for navigation is mounted inside the hull 2 (inside the ship). The engine 4 is connected to a propeller 8 located outside the ship via a rotating shaft 6. The propeller 8 includes a plurality of rotary blades 8a arranged at substantially equal intervals along the circumferential direction of the rotary shaft 6. The power output from the engine 4 is transmitted to the propeller 8 via the rotating shaft 6, and the rotation of the propeller 8 produces a thrust for the ship to navigate. In such a ship, underwater noise WN including a frequency component corresponding to the rotation speed is generated from the engine 4, the rotating shaft 6 and the propeller 8 in which the exciting force is generated during navigation (or idling).

In the following description, the engine 4, the rotary shaft 6, and the propeller 8 are treated as the noise source 12, but the noise source 12 may include other components of the ship. Further, the noise generation source 12 is arranged in the external space 15 isolated from the internal space 16 of the shroud portion 14, which will be described later. In the present embodiment, the case where the engine 4, the rotary shaft 6, and the propeller 8 are included as the noise source 12 is illustrated. In this case, the noise source 12 is the external space 15 regardless of whether the hull of the ship 1 is inside or outside. It means the arranged space.

Further, the underwater noise WN generated from the noise source 12 includes a frequency component corresponding to the rotation speed of each element constituting the noise source 12. In this embodiment, the engine 4, the rotating shaft 6, and the propeller 8 constituting the noise source 12 can take various rotational speeds according to the navigation state of the ship. Therefore, the underwater noise WN generated from the noise source 12 is included in the underwater noise WN. A wide frequency range is included. Such a frequency band includes, for example, a component having a relatively low frequency of 1000 Hz or less, which is difficult to absorb with a general sound absorbing material, and as will be described later, the underwater noise WN including such a low frequency component. Is suitably reduced by the underwater silencer 10.

Further, the ship 1 is arranged on the outer peripheral side of the propeller 8 and includes a shroud portion 14 that surrounds the propeller 8 along the circumferential direction. The shroud portion 14 is provided over the entire circumference of the propeller 8, and has a function of improving the thrust of the ship 1 by rectifying the water flow generated by the rotational drive of the propeller 8. In the present embodiment, the diameter of the rear side of the shroud portion 14 is slightly smaller than that of the front side with respect to the propulsion direction of the ship 1, so that the water flow generated by the rotational drive of the propeller 8 is increased. It has become.

The underwater silencer 10 is integrally configured with the shroud portion 14 having such a basic configuration. The main body 14a of the shroud portion 14 is formed of a metal material such as iron, and has a hollow structure by being configured to define the internal space 16. The internal space 16 accommodates a medium 18 having an acoustic impedance Z different from that of the main body 14a. The acoustic impedance Z is expressed by the following equation using the material density ρ [kg / m3] and the speed of sound c [m / sec].
Z = ρ × c ... (1)

Here, FIG. 3 is a diagram showing the densities ρ, sound velocity c, and acoustic impedance Z of air, water, and iron. As shown in FIG. 3, water and metal have acoustic impedances relatively close to each other. Therefore, if the shroud portion 14 has a solid structure without the internal space 16, the underwater noise WN incident on the shroud portion 14 from the noise generation source 12 is the surface of the shroud portion 14 composed of water and metal. It is not reflected at the boundary of, and most of it passes through the shroud portion 14 and escapes to the outside (see the dotted arrow WN'in FIG. 2).

On the other hand, in this embodiment, the main body 14a of the shroud portion 14 is provided with an internal space 16 in which a medium 18 having an acoustic impedance Z different from that of the main body 14a is accommodated, so that the noise source 12 is incident on the shroud portion 14. The underwater noise WN generated is reflected in the internal space 16 filled with the medium 18. As a result, the reflected sound RN of the underwater noise WN does not diffuse to the outside of the shroud portion 14, and a good muffling effect can be obtained.

Further, the internal space 16 may be decompressed from the external space 15. In this case, the above-mentioned medium 18 may be housed in the internal space 16 under a reduced pressure environment, or the internal space 16 may be configured as a vacuum space in which the medium 18 does not exist. Even in these cases, since the inside of the internal space 16 has an acoustic impedance different from that of the main body 14a, the underwater noise WN is reflected and a good muffling effect can be obtained.

Incidentally, the main body 14a of the shroud portion 14, for example, poly may be constituted of a resin such as vinyl chloride (the acoustic impedance Z of polyvinyl chloride is ^{2.53 × 10 6 [kg / m} 2 s]) .. Also in this case, as in the case where the main body 14a is made of a metal such as iron as described above, the acoustic impedance of the main body 14a and the acoustic impedance of the medium 18 accommodated in the internal space 16 are different. Therefore, a good sound deadening effect can be obtained.

As the medium 18 accommodated in the internal space 16, a medium having an acoustic impedance Z smaller than that of the main body 14a may be adopted. In this case, the underwater noise WN from the noise source 12 is reflected at the free end at the boundary between the main body 14a of the shroud portion 14 and the internal space 16 to become a reflected sound RN whose phase is inverted. As a result, as shown in FIG. 2, the underwater noise WN0 (underwater noise that does not enter the shroud portion 14 and propagates in the water) from the noise source 12 that passes inside the shroud portion 14 is incident on the internal space. The underwater noise WN is canceled by the reflected sound RN reflected at the free end, and a better muffling effect can be obtained.

As shown in FIG. 2, the sum of the propagation distance of the underwater noise WN0 and the propagation distance of the underwater noise WN and the reflected sound RN is not exactly equal, but the sound velocity c in the water is very large, so that both are used. It can be considered to be substantially equal. Therefore, the underwater noise WN0 and the reflected sound RN, which are in opposite phase to each other, cancel each other out, and a good muffling effect can be obtained.

As such a medium 18, for example, air can be used. As shown in FIG. 3 above, air has a very small acoustic impedance Z as compared with water or metal. Therefore, by adopting air as the medium 18, the underwater noise from the noise source 12 can be satisfactorily reflected by the internal space 16.
In order to obtain a sufficient sound deadening effect, for example, the acoustic impedance of the medium 18 is preferably 1/100 or less with respect to water.

Here, FIG. 4 is an analysis example of the distribution range D1 of the underwater noise WN by the underwater silencer 10. In this analysis example, the position of the ship 1 is indicated by the center O, and the distribution of underwater noise WN when the main body 14a of the shroud portion 14 is formed of iron and air is used as the medium 18 accommodated in the internal space 16. The result of analyzing the range D1 by FEM analysis is shown. Further, in FIG. 4, as a comparative example, the distribution range D2 of the underwater noise WN in the ship 1 having the shroud portion 14 having no internal space 16 is shown by the alternate long and short dash line. As is clear by comparing the two, the distribution range D1 is much smaller than the distribution range D2, and it was confirmed that a good muffling effect was obtained by the underwater muffling device 10 of this embodiment.

Further, as the medium 18, another material such as Styrofoam, which has an acoustic impedance Z smaller than that of water, may be used (for example, the acoustic impedance of the foamed styrene is close to that of the above-mentioned air). Styrofoam is more likely to increase the damping of the structure than air, so vibration can be suppressed by using it as the medium 18.

As shown in FIGS. 1 and 2, the main body 14a of the shroud portion 14 has a facing surface 14c facing the noise generation source 12, and the internal space 16 is configured to extend to the facing surface 14c. As a result, the underwater noise WN incident on the shroud portion 14 from the noise generation source 12 is received by a wide area of the internal space 16. As a result, the reflected wave RN can be formed by reflecting the underwater noise WN at the boundary between the main body 14a and the internal space 16. As a result, the underwater noise WN'permeating to the outside of the shroud portion 14 can be reduced more effectively.

Further, the internal space 16 may be formed inside the main body 14a of the shroud portion 14 so as to surround the noise generation source 12 along the circumferential direction of the rotating shaft 6. By forming the internal space 16 in this way, the underwater noise WN from the noise source 12 can be reduced more effectively.

Here, FIG. 5A is an analysis result showing the relationship between the first parameter X1 of the underwater silencer 10 and the volume reduction device Y, and FIG. 5B is an analysis showing the relationship between the second parameter X2 of the underwater silencer 10 and the volume reduction Y. As a result, FIG. 6 is a schematic diagram showing candidate positions P1 to P4 of the noise generation source 12 corresponding to FIGS. 5A and 5B.

In FIG. 5A, as the first parameter X1 of the underwater silencer 10, the ratio t / T of the thickness t of the internal space 16 (the vertical length of the facing surface 14c) and the thickness T of the main body 14a of the shroud portion 14 Handle. As shown in FIG. 5A, it was verified that the volume reduction Y of the underwater silencer 10 is less dependent on the first parameter X1 regardless of which candidate positions P1 to P4 the noise generation source 12 is located. This indicates that a good muffling effect can be obtained even when the thickness t of the internal space 16 is small (in other words, by securing the internal space 16 in the main body 14a even a little, the muffling effect can be obtained. Can be expected to improve).

Further, in FIG. 5B, as the second parameter X2 of the underwater silencer 10, the ratio l / of the length l of the internal space 16 (the length along the facing surface 14c) and the length L of the main body 14a of the shroud portion 14 Handle L. As shown in FIG. 5B, it was verified that the volume reduction Y of the underwater silencer 10 tends to increase as the first parameter X1 increases, regardless of which candidate positions P1 to P4 the noise generation source 12 is located. It is shown that as the length of the internal space 16 becomes relatively large with respect to the main body 14a, the underwater noise WN from the noise source 12 is easily reflected by the internal space 16 and the muffling effect is improved. There is. From this, in order to obtain a sufficient sound deadening effect, it is preferable that the length l of the internal space 16 is, for example, about 50% or more of the length L of the main body 14a.

Here, FIG. 7 is a modification of FIG. 2. In this modification, the reinforcing member 20 is provided in the internal space 16. The reinforcing member 20 is configured to connect between the inner walls 16a and 16b that face each other and define the internal space 16. Thereby, by increasing the strength of the internal space 16, for example, good durability against the water pressure received when the shroud portion 14 is immersed in water can be obtained.

The reinforcing member 20 may be erected in a rib shape on either one of the inner walls 16a and 16b. Further, the reinforcing member 20 may be formed over the entire internal space 16 or may be formed in a part of the internal space 16.

As described above, according to each of the above-described aspects, the medium 18 having an acoustic impedance different from that of the main body 14a of the shroud portion 14 is provided in the internal space 16 provided in the shroud portion 14 that at least partially surrounds the noise source 12. By accommodating it, the underwater noise WN from the noise source 12 can be suitably reduced.

In addition, it is possible to replace the components in the above-described embodiment with well-known components as appropriate without departing from the spirit of the present disclosure, and the above-described embodiments may be combined as appropriate.

The contents described in each of the above embodiments are grasped as follows, for example.

(1) The underwater silencer according to one embodiment (for example, the underwater silencer 10 of the above embodiment) is
A shroud portion (for example, the shroud portion 14 of the above embodiment) that at least partially surrounds the noise generation source (for example, the noise generation source 12 of the above embodiment) is provided.
The shroud portion is isolated from the external space in which the noise generation source is arranged, and a medium having an acoustic impedance different from that of the main body of the shroud portion (for example, the medium 18 of the above embodiment) is housed inside, or the inside is housed. It is configured to define an internal space decompressed from the external space (for example, the internal space 16 of the above embodiment).

According to the aspect (1) above, an internal space isolated from the external space in which the noise generation source is arranged is determined in the shroud portion that at least partially surrounds the noise generation source. A medium having an acoustic impedance different from that of the main body of the shroud portion is accommodated in the internal space, or the pressure is reduced from the external space. Therefore, when the shroud portion is placed in water together with the noise generation source, the underwater noise incident from the noise generation source is well reflected at the boundary between the main body of the shroud portion and the internal space. As a result, underwater noise from the noise source is suppressed from penetrating to the outside of the shroud portion, and a good muffling effect can be obtained.

(2) In another aspect, in the above aspect (1),
The medium has a smaller acoustic impedance than the main body.

According to the aspect (2) above, as the medium accommodated in the internal space, a medium having a smaller acoustic impedance than the main body of the shroud portion is used. As a result, the underwater noise from the noise source is reflected at the free end at the boundary between the main body of the shroud portion and the internal space, and the phase is inverted. As a result, the underwater noise from the noise source is canceled by the reflected sound reflected at the free end, and a better muffling effect can be obtained.

(3) In another aspect, in the above aspect (1) or (2),
The main body has a facing surface facing the noise generation source (for example, the facing surface 14c of the above embodiment).
The interior space is defined so as to extend along the facing surface.

According to the aspect (3) above, the water from the noise source is provided by providing the internal space capable of reflecting the underwater noise so as to extend along the facing surface facing the noise source. Noise can be effectively reduced.

(4) In another aspect, in any one of the above (1) to (3),
The internal space is defined so as to surround the noise source along the circumferential direction of the rotation axis.

According to the aspect (4) above, by providing an internal space capable of reflecting underwater noise so as to surround the noise generation source as described above, underwater noise from the noise generation source can be effectively reduced.

(5) In another aspect, in any one of the above (1) to (4),
A reinforcing member (for example, the reinforcing member 20 of the above embodiment) that defines the internal space of the shroud portion and connects the inner walls facing each other (for example, the inner walls 16a and 16b of the above embodiment) is further provided.

According to the aspect (5) above, by providing the reinforcing member in the internal space, good strength can be ensured even when the shroud portion is subjected to water pressure when it is immersed in water, for example.

(6) In another aspect, in any one of the above (1) to (5),
The noise source generates sound containing a frequency component of 1000 Hz or less.

According to the above aspect (6), even noise containing a relatively low frequency component of 1000 Hz or less, which is difficult to absorb with a general sound absorbing material, can be satisfactorily reduced.

(7) In another aspect, in any one of the above (1) to (6),
The body contains metal or resin and
The medium is air.

According to the above aspect (7), a good sound deadening effect can be obtained by using air whose acoustic impedance is much smaller than that of the metal or resin constituting the main body as the medium accommodated in the internal space.

(8) In another aspect, in any one of the above (1) to (6),
The body contains metal or resin and
The medium is Styrofoam.

According to the aspect (8) above, a good sound deadening effect can be obtained by using styrofoam having a very small acoustic impedance as compared with the metal or resin constituting the main body as the medium accommodated in the internal space. .. Further, since Styrofoam tends to increase the damping of the structure as compared with the air hit, it is possible to suppress the vibration of the underwater silencer by using it as a medium.

(9) In another aspect, in any one of the above (1) to (8),
The noise generation source is a propeller (for example, the propeller 8 of the above embodiment) for outputting navigational power of a ship (for example, the ship 1 of the above embodiment).

According to the above aspect (9), by mounting the underwater silencer of each of the above aspects on a ship, it is possible to effectively reduce the noise generated from the propeller for outputting the navigation power.

1 Ship 2 Hull 4 Engine 6 Rotating shaft 8 Propeller 8a Rotor 10 Underwater silencer 12 Noise source 14 Shroud part 14a Main body 14c Facing surface 16 Internal space 16a Inner wall 18 Medium 20 Reinforcing part

Claims (9)

It has a shroud that at least partially surrounds the noise source.
The shroud portion is isolated from the external space in which the noise generation source is arranged, and a medium having an acoustic impedance different from that of the main body of the shroud portion is housed inside, or the inside is decompressed from the external space. An underwater silencer configured to define. The underwater silencer according to claim 1, wherein the medium has a smaller acoustic impedance than the main body. The main body has a facing surface facing the noise source, and the main body has a facing surface facing the noise source.
The underwater silencer according to claim 1 or 2, wherein the internal space is defined so as to extend along the facing surface. The underwater silencer according to any one of claims 1 to 3, wherein the internal space is defined so as to surround the noise source along the circumferential direction of the rotation axis. The underwater sound deadening device according to any one of claims 1 to 4, further comprising a reinforcing member that defines the internal space of the shroud portion and connects the inner walls facing each other. The underwater silencer according to any one of claims 1 to 5, wherein the noise source generates sound containing a frequency component of 1000 Hz or less. The body contains metal or resin and
The underwater silencer according to any one of claims 1 to 6, wherein the medium is air. The body contains metal or resin and
The underwater silencer according to any one of claims 1 to 6, wherein the medium is styrofoam. The underwater muffling device according to any one of claims 1 to 8, wherein the noise generation source is a propeller for outputting power for navigation of a ship.

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