A film type Helmholtz muffler

Abstract

The present invention proposes a novel thin-film Helmholtz muffler, which changes the position of the muffler frequency band by changing the number of thin films in the muffler, and effectively moves the muffler frequency closer to the low frequency without changing the cavity volume. By setting multiple Helmholtz cavities in the muffler, the muffler frequency band range can be further increased, effectively solving the problem of too narrow muffler frequency range.

Description

Technical Field

[0001] The invention relates to the technical field of low-frequency silencing devices, in particular to a thin-film Helmholtz silencer, which acts on the surface of a submarine and plays a role of low-frequency silencing within a certain frequency range. Background Art

[0002] Traditional Helmholtz silencers usually consist of a closed cavity and a long neck. Since the volume of the neck is much smaller than the volume of the cavity, the neck fluid can be approximately considered incompressible. However, the volume of the cavity can be compressed and can be regarded as a spring. When the excitation frequency is close to the resonance cavity frequency, the bulk modulus type response will be excited, thereby achieving the purpose of noise reduction. Due to the simple structure and high noise reduction of the traditional Helmholtz silencer, it is widely used to suppress sound propagation in ship ventilation and air-conditioning pipelines and diesel engine intake and exhaust pipelines, and the effect is very significant. Figure 1 The figure shows the schematic diagram of the traditional Helmholtz resonance muffler structure. Figure 2 It is its acoustic finite element model. However, due to structural limitations, the traditional Helmholtz type muffler has a narrow muffler frequency range and the muffler frequency position cannot be adjusted. In actual engineering, if you want to reduce the muffler frequency and achieve low-frequency muffler, you must increase the cavity volume or increase the length of the connecting pipe. These are difficult to achieve due to the compact layout of the equipment in actual engineering applications.

[0003] like Figure 3 , 4 As shown in the figure, Su Shengli, Zhang Miao, Cao Weiwu and other researchers changed the neck of the Helmholtz silencer into a contracted or expanded shape, and connected the Helmholtz silencers in series and parallel, which can effectively widen the range of the silencing frequency band. However, due to the significant structure, the position of the silencing frequency band cannot be controlled, and its applicability in practical applications is very narrow and is significantly affected by environmental factors. Summary of the invention

[0004] In view of the problem that the muffler range of the Helmholtz muffler is too narrow and the muffler position cannot be adjusted, the present invention proposes a new type of thin film type Helmholtz muffler, which changes the position of the muffler frequency band by changing the number of thin films in the muffler, and effectively moves the muffler frequency closer to the low frequency without changing the cavity volume. By setting multiple Helmholtz cavities in the muffler, the muffler frequency band range can be further increased, effectively solving the problem of the muffler frequency range being too narrow.

[0005] To achieve the above-mentioned purpose, the present invention provides a thin film type Helmholtz silencer, which includes a cylindrical tube body with a diameter of r, and the middle part of the cylindrical tube body is a rectangular middle pipe; a plurality of thin film layers are coaxially arranged inside the cylindrical tube body along the axial direction of the tube body, and the inside of the cylindrical tube body is cut along the axial direction of the tube body to be divided into a plurality of Helmholtz chambers.

[0006] Furthermore, the intermediate pipe runs through the cylindrical tube body, and its length is greater than the thickness of the cylindrical tube body.

[0007] Furthermore, the cylindrical tube body includes four equally divided Helmholtz cavities.

[0008] As a preferred embodiment, the cylindrical tube body is provided with less than or equal to three thin film layers coaxially along the axial direction of the tube body.

[0009] Compared with the prior art, the advantages of the present invention are:

[0010] The present invention proposes a novel thin-film Helmholtz muffler, which changes the position of the muffler frequency band by changing the number of thin films in the muffler, and effectively moves the muffler frequency closer to the low frequency without changing the cavity volume. By setting multiple Helmholtz cavities in the muffler, the muffler frequency band range can be further increased, effectively solving the problem of too narrow muffler frequency range.

[0011] Furthermore, by increasing the number of films, the anechoic frequency position is moved to a low frequency. The main principle is to reduce the resonance frequency inside the Helmholtz cavity, thereby reducing the frequency required to excite the bulk modulus and lowering the solid anechoic frequency response. Figures 7 (a) to 7 (c) are the results of COMSOL simulation.

[0012] This is a schematic diagram of the four Helmholtz cavities being opened. When the four Helmholtz cavities are opened, as long as the volume of the four cavities is the same, the neck length and area are the same, the four different anechoic peaks originally generated will overlap into one, thereby effectively widening the anechoic range and being more effective in practical applications. Figure 8 For its simulation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the structure of a traditional Helmholtz resonance muffler;

[0014] Figure 2 It is the acoustic finite element model of the traditional Helmholtz resonance muffler;

[0015] Figure 3 Schematic diagram of the Helmholtz resonator structure when it contracts or expands along a long tube;

[0016] Figure 4It is a schematic diagram of the series structure of the Helmholtz resonator;

[0017] Figure 5 It is a schematic diagram of the internal structure of the muffler of the present invention;

[0018] Figure 6 It is a schematic diagram of the external structure of the muffler of the present invention;

[0019] Figure 7 (a) to Figure 7 (c) are transmission loss diagrams of the Helmholtz cavity muffler with different numbers of membranes.

[0020] Among them, Figure 7 (a) shows one membrane in the cavity, Figure 7 (b) shows two membranes in the cavity, and Figure 7 (c) shows three membranes in the cavity;

[0021] Figure 8 This is the sound transmission loss diagram when four Helmholtz cavities are opened;

[0022] Fig. 9 Simplified model diagram for system theory;

[0023] Figure 10 (a) - Figure 10 (c) Schematic diagram of sound absorption frequency calculated by MATLAB.

[0024] Among them, Figure 10 (a) shows one membrane in the cavity, Figure 10 (b) shows two membranes in the cavity, and Figure 10 (c) shows three membranes in the cavity;

[0025] In the figure, 1 is the cavity of the Helmholtz structure, 2 is the neck of the Helmholtz structure, 3 is the film, 4 is the internal partition, 5 is the middle pipe of the muffler, and 6 is the external closed structure. DETAILED DESCRIPTION

[0026] In order to better understand the present invention, the technical solution of the present invention is described in detail below with reference to the accompanying drawings, but the present invention is not limited thereto.

[0027] Embodiment 1:

[0028] Figure 5 , Figure 6 As shown, the present invention provides a thin film type Helmholtz silencer, which includes a cylindrical tube body with a diameter of r, and the middle part of the cylindrical tube body is a rectangular middle pipe; a plurality of thin film layers are coaxially arranged inside the cylindrical tube body along the axial direction of the tube body, and the inside of the cylindrical tube body is cut along the axial direction of the tube body to be divided into a plurality of Helmholtz cavities.

[0029] Furthermore, the intermediate pipe runs through the cylindrical tube body, and its length is greater than the thickness of the cylindrical tube body.

[0030] Furthermore, the cylindrical tube body includes four equally divided Helmholtz cavities.

[0031] As a preferred embodiment, the cylindrical tube body is provided with less than or equal to three thin film layers coaxially along the axial direction of the tube body.

[0032] The novel thin-film Helmholtz muffler provided by the present invention changes the position of the muffler frequency band by changing the number of thin films in the muffler, and effectively moves the muffler frequency closer to the low frequency without changing the cavity volume. By setting multiple Helmholtz cavities in the muffler, the muffler frequency band range can be further increased, effectively solving the problem of too narrow muffler frequency range.

[0033] The film type Helmholtz muffler proposed by the present invention is as follows: Figure 5 , Figure 6 As shown, the size of the muffler is , which can be applied to the surface of submarines as a device to absorb enemy sonar. When the sound waves of the enemy sonar are transmitted from the left side of the muffler in the form of sound waves, they pass through the Helmholtz cavity, and the sound waves at this frequency are completely absorbed, so that the sonar detector cannot receive the detection signal, showing the function of acoustic stealth.

[0034] By increasing the number of thin films, the anechoic frequency position is moved to a low frequency. The main principle is to reduce the resonance frequency inside the Helmholtz cavity, thereby reducing the frequency required to excite the bulk modulus and reducing the solid anechoic frequency response. Figure 7 (a) - Figure 7 (c) are the results of COMSOL simulation. Figure 7 (a) - Figure 7 (c) are transmission loss diagrams of the Helmholtz cavity silencer with different numbers of membranes. (a) One membrane in the cavity, (b) Two membranes in the cavity, (c) Three membranes in the cavity.

[0035] When four Helmholtz cavities are opened, as long as the volume of the four cavities is the same, the neck length and area are the same, the four different anechoic peaks originally generated will overlap into one, thereby effectively widening its anechoic range and being more effective in practical applications. Figure 8 For its simulation results.

[0036] Fig. 9 This is a simplified schematic diagram of the interior of the Helmholtz cavity. Since the liquid in the internal cavity is water with a low density, it can be simplified into a spring, the film is simplified into mass, and the external structure is steel, which can also be simplified into a mass block.

[0037]

[0038] When the number of membranes is 0, 1, and 2, the equivalent mass of the system is shown in the above formula. When the frequency of the external excitation makes the equivalent mass of the system negative, the Holmholtz silencer exhibits a sound absorption effect at the sub-frequency. Figure 10 (a)-Figure 10 (c) are the sound absorption frequencies calculated by Matlab (when a resonant cavity is opened). It can also be seen from the theory that with the increase of membranes, the sound absorption frequency moves to low frequency.

[0039] Fig. 10(a)-Fig. 10(c) Sound absorption frequencies calculated by MATLAB for (a) one membrane in the cavity, (b) two membranes in the cavity, and (c) three membranes in the cavity.

[0040] The muffler is processed according to its size. Except for the outer structure of the film, which is printed by 3D printing, the inner film structure is added or reduced according to different environmental requirements and installed inside the Helmholtz cavity by pasting or inserting. The whole structure is installed on the surface of the submarine, covering the entire submarine in an array, so that the submarine can achieve stealth characteristics against foreign sonar.

[0041] The above is a detailed introduction to a thin film Helmholtz muffler provided by the present invention; the description of this embodiment is only used to help understand the method of the present invention. The application mode of the present invention can be adjusted according to actual conditions and is not intended to limit the present invention.

Claims

1. A thin film type Helmholtz muffler, characterized in that: The muffler comprises a cylindrical tube body with a diameter of r, wherein the middle part of the cylindrical tube body is a rectangular middle pipe; a plurality of thin films are coaxially arranged inside the cylindrical tube body along the axial direction of the tube body, and the inside of the cylindrical tube body is cut along the axial direction of the tube body to be divided into a plurality of Helmholtz cavities, and by increasing the number of thin films, the muffler frequency is moved to a low frequency without changing the cavity volume; The intermediate pipe runs through the cylindrical tube body, and its length is greater than the thickness of the cylindrical tube body; The cylindrical tube body includes four equally divided Helmholtz cavities, ensuring that the four cavities have the same volume, diameter length, and area, so that four different anechoic peaks overlap into one, thereby widening the anechoic range.

2. A thin film type Helmholtz muffler according to claim 1, characterized in that: The inside of the cylindrical tube body is coaxially provided with thin film layers of less than or equal to three layers along the axial direction of the tube body.

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