A sound-absorbing structure and design method for an underwater mid-to-low frequency Helmholtz resonator

Abstract

This invention relates to the field of underwater noise control technology, and in particular to an underwater mid-to-low frequency Helmholtz resonator sound-absorbing structure and its design method. It comprises M×N identical sound-absorbing units; multiple sound-absorbing units are stacked to form a coupling structure; several coupling structures are combined to form a single-layer sound-absorbing structure; multiple single-layer sound-absorbing structures are stacked to form a resonator sound-absorbing structure; and the incident wave is perpendicular to the resonator sound-absorbing structure. Each sound-absorbing unit consists of a cylindrical throat, a cuboid cavity, and a cuboid-shaped custom composite material base connected in series; the three are fixed and tightly connected by a fixing material; the center of the throat's cross-section coincides with the geometric center of the cuboid cavity, and the cross-sections of the cuboid cavity and the cuboid-shaped custom composite material are identical, fitting tightly together. This invention enables efficient sound absorption over a relatively wide frequency range. Through the design process of this invention, the dimensions of the sound-absorbing unit are designed according to noise requirements, allowing for adjustment of the operating frequency.

Description

Technical Field

[0001] This invention relates to the field of underwater noise control technology, and in particular to an underwater mid-to-low frequency Helmholtz resonator sound-absorbing structure and its design method. Background Technology

[0002] In today's rapidly developing marine industry and shipping technology, underwater noise generated by propeller cavitation, underwater blasting, and mechanical vibration in activities such as shipping, marine resource development, and offshore wind farm construction seriously disrupts the behavior patterns, reproduction, and migration of marine life, and even threatens the survival of endangered species. For example, the pulse noise generated by offshore wind power piling operations can cause mass mortality of large yellow croakers within 500 meters, while the low-frequency noise from ship navigation can travel over thousands of kilometers, affecting the sonar navigation and communication of cetaceans. In certain special scenarios such as ship navigation, a structure that can both absorb sound and adjust the operating frequency is needed. Traditional sound-absorbing and insulating materials mainly rely on rubber-based sound-absorbing tiles, polyurethane coatings, etc., which often need to be tens of centimeters thick to achieve mid-to-high frequency sound absorption, but their absorption efficiency for mid-to-low frequency noise drops sharply. In addition, deep-sea engineering requires materials that are both resistant to high pressure (such as 4.5 MPa hydrostatic pressure) and corrosion-resistant, but traditional materials are prone to deformation and failure under high pressure, leading to a decline in acoustic performance. With the research on acoustic metamaterials by researchers in the past decade or so, sound-absorbing and sound-insulating metamaterials have achieved thin and light sound absorption and insulation performance at a deep subwavelength size. Many metamaterials or metasurfaces based on thin films or Helmholtz resonators have also been proposed. However, they usually work at a single frequency, or in order to achieve broadband effects, they connect many working units with different sound absorption and insulation frequencies in series in the direction of sound propagation. The structure is long and it is difficult to meet the compactness requirements of deep-sea equipment. Summary of the Invention

[0003] The purpose of this invention is to address the problems existing in the background technology by proposing a double-layer Helmholtz resonator sound-absorbing structure with a small structural thickness and high efficiency sound absorption over a wide frequency band in the mid-low frequency range (400-1000 Hz). It can be widely used in scenarios such as noise control during offshore wind farm construction and noise reduction for underwater vehicles.

[0004] The technical solution of the present invention, the first aspect of the present invention provides an underwater mid-low frequency double-layer Helmholtz resonator sound absorption structure, comprising M×N identical sound absorption units; Multiple sound-absorbing units are stacked together to form a coupling structure; several coupling structures are combined to form a single-layer sound-absorbing structure; multiple single-layer sound-absorbing structures are stacked together to form a resonator sound-absorbing structure; and the incident wave is perpendicular to the resonator sound-absorbing structure. Each sound-absorbing unit consists of a cylindrical throat, a rectangular cavity, and a custom-designed rectangular composite material base connected in series; the three are fixed and tightly connected by a fixing material. The center of the cross-section of the throat tube coincides with the geometric center of the cuboid cavity. The cross-sections of the cuboid cavity and the customized cuboid composite material are the same, and the two fit together tightly.

[0005] Preferably, both the cylindrical throat and the cuboid cavity are filled with water.

[0006] Preferably, each coupling unit consists of nine sound-absorbing units, forming a 3×3 array, with equal gaps formed by a fixed material between each sound-absorbing unit.

[0007] Preferably, the length of the cylindrical throat is fixed, but the radius and cross-sectional area of ​​the cavity are not exactly the same.

[0008] Preferably, the radius of the throat and the cross-sectional area of ​​the cavity of each sound-absorbing unit can determine the operating frequency of the sound-absorbing unit.

[0009] Preferably, the sound-absorbing units have the same overall height, the throat has a circular cross-section, and the cavity and composite material have rectangular cross-sections that are identical.

[0010] Preferably, each sound-absorbing unit has a defined resonant frequency, and the coupling effect of multiple sound-absorbing units enables the coupling unit to have a wide operating frequency band.

[0011] The second aspect of the present invention provides a design method for an underwater mid-low frequency double-layer Helmholtz resonator sound-absorbing structure, and the manufacturing method of the above-mentioned underwater mid-low frequency double-layer Helmholtz resonator sound-absorbing structure includes the following specific steps: S1. Determine the operating frequency range from which noise needs to be absorbed; S2, the throat radius of the sound-absorbing unit is denoted as... The length is denoted as The width of the cuboid is denoted as . The length is denoted as The height of the rectangular cavity is denoted as . The height of the custom-made rectangular composite material base is denoted as ; S3. Obtain the resonant frequency expression of the sound-absorbing unit through the acoustic-electric analogy method, compare it with the required operating frequency range, and determine the above parameter values; S4. Arrange the 9 sound-absorbing units at intervals of... Arranged in a 3×3 array with fixed material between the gaps, forming a single sound-absorbing structural unit; S5. Arrange N sound-absorbing structural units periodically at intervals of D, with the gaps being fixed materials to form a single-layer structure. S6. Stack M single-layer structures to form an underwater mid-to-low frequency double-layer Helmholtz resonator sound-absorbing structure.

[0012] Preferably, based on acoustic-electric analogy calculations, a theoretical formula for the operating frequency of a single sound-absorbing unit is obtained. This formula can be written as the operating frequency. With dimensional parameters , , , , , The function of the operating frequency of a single sound-absorbing unit is:

[0013] In the formula , ,in This is the density of water, taken as 1000 kg / m^3. This is the density of the customized composite material, with a value of 5500 kg / m^3; The speed of sound in water at 20℃ is taken as 1473 m / s. It is the sound velocity in the custom composite material at 20℃, with a value of 259 m / s.

[0014] Preferably, by adjusting the size parameters , , , , , It can effectively change the resonant frequency of a single sound-absorbing unit and achieve tunability of underwater sound absorption through the coupling effect of multiple sound-absorbing units.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: 1. The structure has a thin thickness dimension, which can achieve thin and light underwater mid-to-low frequency sound absorption, making it suitable for deep-sea environments; 2. The structure has multiple resonant frequencies, thus achieving broadband underwater sound absorption, rather than a single peak. 3. Traditional Helmholtz resonators use water or air as the medium in the cavity, but this structure uses composite materials as the medium, which improves the acoustic impedance and effectively reduces the thickness. 4. This design method allows for adjustment of the operating frequency band by adjusting the dimensions, and also provides corresponding operating mode frequency calculation formulas, allowing for independent modification of structural parameters according to spectrum requirements. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the resonator sound-absorbing structure in an embodiment of the present invention; Figure 2 This is a schematic diagram of a single-layer structure of the resonator sound-absorbing structure in an embodiment of the present invention; Figure 3This is a schematic diagram of the coupling unit in an embodiment of the present invention; Figure 4 This is a schematic diagram of the sound-absorbing unit in an embodiment of the present invention; Figure 5 This is a schematic diagram of the simulation model in an embodiment of the present invention; Figure 6 This is a schematic diagram of the simulation results in an embodiment of the present invention.

[0017] Reference numerals: 01~03: First~third single-layer structure; 0111~0113: 1st~3rd coupling unit on the first single-layer structure; 0121~0122: First~second coupling unit interval in the first single-layer structure; 01111~01119: 1st~9th sound-absorbing unit in the first coupling unit on the first layer structure; 011131: Cylindrical throat in the 3rd sound-absorbing unit in the first coupling unit on the first layer structure; 011132: Cuboid cavity in the 3rd sound-absorbing unit in the first coupling unit on the first layer structure; 011133: Cuboid custom composite material base in the 3rd sound-absorbing unit in the first coupling unit on the first layer structure. Detailed Implementation

[0018] Example 1 This embodiment provides an underwater mid-to-low frequency double-layer Helmholtz resonator sound-absorbing structure. The basic sound-absorbing unit of this structure is formed by connecting a cylindrical throat, a rectangular cavity, and a custom-designed rectangular composite material in series. The throat length is fixed at 10mm, denoted as [missing information]. Its radius is The height of the rectangular cavity is The thickness of the custom-made rectangular composite material is denoted as The center of the cross-section of the throat coincides with the geometric center of the cuboid cavity. The cuboid cavity fits tightly with the composite material, with a consistent cross-section and a width denoted as . The length is denoted as The overall height of this basic unit is ; Furthermore, the nine sound-absorbing units are spaced out in the vertical direction (this vertical direction, and the subsequent horizontal direction, are only for illustrating the splicing process and do not represent the orientation of their working state). Arranged in a 3×3 array, they form a sound-absorbing structural unit; Furthermore, the above M sound-absorbing structural units, each with a spacing length D, are periodically arranged in a plane to form an underwater mid-to-low frequency double-layer Helmholtz resonator sound absorber structure. Furthermore, the sound-absorbing structure has multiple resonant frequencies, namely the respective resonant frequencies of the sound-absorbing units that make up the coupling unit. Under the coupling effect, effective sound absorption can be achieved in a wide frequency range that includes these resonant frequencies. Furthermore, based on acoustic-electric analogy calculations, a theoretical formula for the operating frequency of a single sound-absorbing unit can be obtained, which can be written as the operating frequency. With dimensional parameters , , , , , The function of the operating frequency of a single sound-absorbing unit is:

[0019] In the formula , ,in This is the density of water, taken as 1000 kg / m^3. This is the density of the customized composite material, with a value of 5500 kg / m^3; The speed of sound in water at 20℃ is taken as 1473 m / s. It is the sound velocity in the custom composite material at 20℃, with a value of 259 m / s.

[0020] Example 2 like Figure 1 As shown, the underwater mid-low frequency double-layer Helmholtz resonator sound absorber structure in this embodiment of the invention consists of three single-layer structures (M=3), namely the first to the third single-layer structures (01~03). Each of these three structures is the same, and the details of the single-layer structure are described using the first single-layer structure (01).

[0021] like Figure 1 and Figure 2 As shown, the first single-layer structure consists of coupling units and the intervals between them. In this embodiment, the single-layer structure is formed by N=3 coupling units arranged together, which are the 1st to 3rd coupling units (0111~0113). The distance between the units is D=1mm, and this distance is filled with a fixed material, namely the coupling unit intervals (0121~0122). The structure of the coupling unit is relatively complex, but the structure and size of all coupling units are consistent. Therefore, the details of the coupling unit structure are explained using the first coupling unit (0111) on the first single-layer structure.

[0022] like Figure 2 and Figure 3As shown, the coupling unit 0111 is composed of nine sound-absorbing units (01111~01119) with different structures, arranged in a 3×3 array in a plane. The gaps between the front, back, left, and right sides of the sound-absorbing units are all... =1mm.

[0023] like Figure 3 and Figure 4 As shown, although the dimensions of these sound-absorbing units vary, their general structure is consistent. Taking the third sound-absorbing unit 01113 of the first coupling unit 0111 on the single-layer structure 01 as an example, the sound waves are incident from top to bottom (arrow direction in the diagram). The cylindrical throat (water-filled) has a radius of... The height is A cylindrical cavity (011131); below this cavity is a rectangular cavity (water-filled) (011132), the width of which is... , length is The height is Below the cuboid cavity, a custom-designed cuboid composite material (011133) fits snugly against it. The width of the cuboid is... , length is The height is It should be noted that the cavity is surrounded by a fixed material, which also holds the coupling units together in a 3×3 array to form a sound-absorbing unit, thus constituting an underwater mid-to-low frequency double-layer Helmholtz resonator sound absorber structure.

[0024] Furthermore, based on acoustic-electric analogy calculations, a theoretical formula for the operating frequency of a single sound-absorbing unit can be obtained, which can be written as the operating frequency. With dimensional parameters , , , , , The function of the operating frequency of a single sound-absorbing unit is:

[0025] In the formula , ,in This is the density of water, taken as 1000 kg / m^3. This is the density of the customized composite material, with a value of 5500 kg / m^3; The speed of sound in water at 20℃ is taken as 1473 m / s. It is the sound velocity in the custom composite material at 20℃, with a value of 259 m / s.

[0026] Due to the coupling effect between the nine sound-absorbing units, multiple absorption peaks corresponding to different frequencies can appear in a relatively wide frequency band for the sound-absorbing unit as a whole, thereby achieving a better sound absorption effect in a relatively wide frequency band.

[0027] The analysis was performed using the finite element simulation software COMSOL Multiphysics 6.2, and the model was constructed as follows: Figure 5 As shown.

[0028] A plane acoustic wave with an amplitude of 1 Pa propagating along the negative z-axis is applied to the structure, and the average reflected sound pressure at the entrance is detected using a sound intensity probe. The sound absorption coefficient can be calculated. ,like Figure 6 As shown.

[0029] Simulation experiments demonstrate that the underwater mid-to-low frequency double-layer Helmholtz resonator sound absorber structure of the embodiment can achieve a sound absorption coefficient greater than 0.9 in the 400-960Hz range.

[0030] As can be seen from the examples, by reasonably designing the dimensional parameters... , , , , , The operating frequency of a single sound-absorbing unit can be obtained according to equation (1). Multiple sound-absorbing units form a coupled sound absorption frequency range, thereby achieving a tunable broadband sound insulation effect. It is worth noting that the parameters M and N only determine the overall length and width of the structure and do not affect the sound absorption frequency. Appropriate sizes of M and N can be selected according to the requirements.

[0031] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A design method for an underwater mid-low frequency Helmholtz resonator sound-absorbing structure, which manufactures any underwater mid-low frequency Helmholtz resonator sound-absorbing structure and applies it to noise control during offshore wind farm construction or noise reduction for underwater vehicles, wherein the sound-absorbing structure comprises M×N identical sound-absorbing units. Multiple sound-absorbing units are stacked together to form a coupling structure; several coupling structures are combined to form a single-layer sound-absorbing structure; multiple single-layer sound-absorbing structures are stacked together to form a resonator sound-absorbing structure; and the incident wave is perpendicular to the resonator sound-absorbing structure. Each sound-absorbing unit consists of a cylindrical throat, a rectangular cavity, and a custom-designed rectangular composite material base connected in series; the three are fixed and tightly connected by a fixing material. The center of the cross-section of the throat tube coincides with the geometric center of the cuboid cavity. The cuboid cavity and the cuboid-shaped custom composite material base have the same cross-section, and the two fit together tightly. Its characteristic is that... The design method includes the following specific steps: S1. Determine the operating frequency range from which noise needs to be absorbed; S2, the radius of the throat of the sound-absorbing unit is denoted as... The length is denoted as The width of the cuboid cavity and the cuboid-shaped custom composite material is denoted as... The length is denoted as The height of the rectangular cavity is denoted as . The height of the custom-made rectangular composite material base is denoted as ; S3. Obtain the resonant frequency expression of the sound-absorbing unit through the acoustic-electric analogy method, compare it with the required operating frequency range, and determine the values ​​of each parameter in step S2. Based on acoustic-electric analogy calculations, a theoretical formula for the operating frequency of a single sound-absorbing unit is obtained. This formula is written as the operating frequency. With dimensional parameters , , , , , The function of the operating frequency of a single sound-absorbing unit is: ； In the formula , ,in This is the density of water, taken as 1000 kg / m³. 3 , This is the density of the customized composite material, with a value of 5500 kg / m³. 3 ; The speed of sound in water at 20℃ is taken as 1473 m / s. The velocity of sound in the custom composite material at 20°C is 259 m / s. S4. Arrange the 9 sound-absorbing units at intervals of... Arranged in a 3×3 array with fixed material between the gaps, forming a single sound-absorbing structural unit; S5. Arrange N sound-absorbing structural units at intervals of D periodically, with the gaps made of fixed material, to form a single-layer structure. S6. Stack M single-layer structures to form an underwater mid-to-low frequency Helmholtz resonator sound-absorbing structure.

2. The design method of an underwater mid-to-low frequency Helmholtz resonator sound-absorbing structure according to claim 1, characterized in that, Both the cylindrical throat and the rectangular cavity are filled with water.

3. The design method of an underwater mid-to-low frequency Helmholtz resonator sound-absorbing structure according to claim 1, characterized in that, The length of the cylindrical throat is fixed.

4. The design method of an underwater mid-to-low frequency Helmholtz resonator sound-absorbing structure according to claim 1, characterized in that, The radius of the throat and the cross-sectional area of ​​the cavity of each sound-absorbing unit can determine the operating frequency of the sound-absorbing unit.

5. The design method of an underwater mid-to-low frequency Helmholtz resonator sound-absorbing structure according to claim 1, characterized in that, The sound-absorbing units have the same overall height, the throat tube has a circular cross-section, and the cavity and the composite material base have identical rectangular cross-sections.

6. The design method of an underwater mid-to-low frequency Helmholtz resonator sound-absorbing structure according to claim 1, characterized in that, Each sound-absorbing unit has a defined resonant frequency, and the coupling effect of multiple sound-absorbing units gives the coupling unit a wide operating frequency band.

7. The design method of an underwater mid-to-low frequency Helmholtz resonator sound-absorbing structure according to claim 1, characterized in that, By adjusting the size parameters , , , , , It can effectively change the resonant frequency of a single sound-absorbing unit and achieve tunability of underwater sound absorption through the coupling effect of multiple sound-absorbing units.

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