An underwater acoustic metasurface structure for low-frequency broadband sound absorption and a design method thereof

Abstract

The present application belongs to the technical field of acoustic metasurface design, and discloses a kind of underwater acoustic metasurface structure and design method for low-frequency broadband sound absorption.The structure includes a plurality of array arranged unit cells, each unit cell is in strip shape, including metal material and non-metal material, the non-metal material is the filling material of unit cell, the cross section of the metal material is a plurality of connected head-to-tail regular hexagons, which is arranged in the non-metal material to form a regular hexagonal honeycomb skeleton, the two sides of the metal material are provided with a plurality of cavities for low-frequency sound absorption, and the sound-incident surface of the unit cell is provided with a cavity below.The design method of the cavity is also disclosed.By the present application, the problem of not being able to guarantee the thin-walled and miniaturization of the structure while achieving efficient absorption of underwater low-frequency sound waves is solved.

Description

Technical Field

[0001] This invention belongs to the technical field of acoustic metasurface design, and more specifically, relates to a hydroacoustic metasurface structure and design method for low-frequency broadband sound absorption. Background Technology

[0002] Acoustic metasurfaces are a type of acoustic functional structure formed by artificially designed subwavelength structural units arranged in a predetermined manner. They can achieve acoustic response characteristics that are difficult to achieve with traditional natural materials, such as effective control over sound wave reflection, refraction, deflection, focusing, and wavefront distribution. Depending on the working medium and application environment, acoustic metasurfaces can generally be divided into air acoustic metasurfaces and underwater acoustic metasurfaces.

[0003] Existing anechoic tiles used for underwater submarine acoustic concealment struggle to improve sound absorption performance at low frequencies. Furthermore, existing sound-absorbing metasurfaces are mostly designed for specific frequencies with narrow bandwidths, making them unsuitable for broadband multi-receiver sonar systems. The main reasons for this are: low-frequency sound waves have long wavelengths and slow attenuation, requiring traditional materials to be quite thick to achieve effective absorption, which contradicts the need for thinner and smaller underwater structures; simultaneously, the high density and acoustic impedance of water further complicate the achievement of low-frequency sound absorption underwater.

[0004] Therefore, how to achieve efficient absorption of low-frequency underwater sound waves while ensuring the structural thinning and miniaturization has become a pressing technical problem to be solved in this field. Overcoming the bottlenecks of the above-mentioned underwater acoustic metasurface design would be of great significance for improving the acoustic stealth capabilities of submarines. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a subsurface structure and design method for low-frequency broadband sound absorption, which solves the problem of not being able to achieve efficient absorption of low-frequency sound waves underwater while ensuring the structure is thin-walled and miniaturized.

[0006] To achieve the above objectives, according to one aspect of the present invention, a subsurface acoustic structure for low-frequency broadband sound absorption is provided. The structure includes a plurality of arrayed unit cells, each unit cell being elongated and comprising a body and a skeleton. The body is filled with a non-metallic material, and the skeleton is made of a metallic material. The cross-section of the skeleton is a plurality of hexagons connected end to end, which are arranged in the body to form a hexagonal honeycomb skeleton. A plurality of cavities for low-frequency sound absorption are provided between the skeleton and the body. At the same time, a cavity is provided below the acoustic surface of the unit cell.

[0007] More preferably, the density of the bulk material is in the range of 900 kg / m³. 3 ~1500 kg / m 3The Young's modulus ranges from 1 MPa to 50 MPa, the Poisson's ratio ranges from 0.30 to 0.4999, and the isotropic loss factor ranges from 0.01 to 0.50; the density of the skeleton material ranges from 2700 kg / m³. 3 ~8900 kg / m 3 The Young's modulus ranges from 60 GPa to 210 GPa, and the Poisson's ratio ranges from 0.28 to 0.36.

[0008] More preferably, the material of the body is rubber, silicone rubber or polyurethane elastomer; the material of the skeleton is titanium, aluminum, steel or copper.

[0009] More preferably, the thickness of the unit cell ranges from 40 mm to 60 mm, and the width ranges from 10 mm to 20 mm.

[0010] More preferably, all cavities are closed cavities filled with air.

[0011] More preferably, the structure is applied to the absorption of plane incident sound waves in the 300 Hz to 1000 Hz range.

[0012] According to another aspect of the present invention, a method for designing a hollow cavity in a low-frequency broadband acoustic metasurface structure for underwater acoustic absorption, as described above, is provided, the method comprising the following steps: The unit cell is divided into multiple blocks along the height direction, and the cavity radius of each block is set to... The radius of the cavity located below the frontal surface is set to ; Establish the relationship between the radius of each cavity and the sound absorption coefficient, construct an optimization model with the maximum sound absorption coefficient as the objective function, and solve the optimization model to obtain the radius of each cavity.

[0013] More preferably, the objective function is as follows:

[0014] in, The sound absorption coefficient is... The sound pressure of the incident sound field. The sound pressure of the reflected sound field. This indicates that the integral calculation is performed at the surface of the structure.

[0015] More preferably, the constraints of the optimization model are as follows:

[0016]

[0017]

[0018]

[0019] in, The density of the structure is obtained by dividing the total mass of the sound-absorbing structure by the total volume of the structure. The volume shrinkage rate is obtained by dividing the volume of the structure after being subjected to pressure by the volume of the structure before being subjected to pressure.

[0020] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art: 1. This invention employs an array of unit-cell structures. The main body of each unit-cell is filled with non-metallic materials, while the framework is made of metallic materials. Cavities for low-frequency sound absorption are also distributed within the main body. The metallic framework ensures the overall strength and stability of the structure, guaranteeing its pressure resistance. The main body and its internal cavities together constitute a local resonant sound-absorbing structure, providing the structure's sound absorption capability. When sound waves are incident on the underwater acoustic metasurface, the main body vibrates and deforms under sound pressure, coupling with the internal cavities. Due to the low stiffness and damping loss of the non-metallic material, local resonance can occur near specific frequencies, effectively confining the incident sound energy within the unit-cell structure. This energy is dissipated through material damping and structural internal losses, converting into heat energy, thus achieving the absorption of low-frequency sound waves. The cavities located below the acoustic surface, being closer to the area affected by the incident sound waves, preferentially couple with the incident sound field, reducing the difficulty of generating a resonant response in the low-frequency range, thereby improving the structure's response and absorption capabilities for low-frequency sound waves. Furthermore, the remaining cavities are used to further regulate the distribution of equivalent mass and equivalent stiffness within the structure. Since the different sizes and locations of the cavities correspond to different resonant frequencies, the synergistic effect of multiple cavities can form multiple local resonant modes at different frequencies, thereby broadening the effective absorption bandwidth of the structure for low-frequency sound waves. Therefore, the cavity below the acoustic surface is mainly used to enhance the coupling between low-frequency incident sound waves and the structure and induce low-frequency resonance, while the remaining cavities are mainly used to form a multi-frequency resonant response and broaden the sound absorption bandwidth. Their synergistic effect enables this invention to effectively absorb low-frequency sound waves from 300 Hz to 1000 Hz under relatively thin structural dimensions, solving the problem of achieving efficient absorption of underwater low-frequency sound waves while ensuring thin-walled and miniaturized structures.

[0021] 2. In this invention, the body and frame are made of non-metallic and metallic materials, respectively. Low-frequency sound absorption is mainly achieved through the resonant sound absorption of the internally perforated rubber. The selected non-metallic material, with its low Young's modulus, high Poisson's ratio, and large loss factor, easily forms local resonance with the internal cavity under sound wave excitation, effectively dissipating energy during the resonance process, thereby improving the low-frequency sound absorption capability. The metallic material is mainly used to construct the hexagonal honeycomb frame, providing stable support and boundary constraints for the rubber resonance area, and assisting in adjusting the resonance frequency and sound absorption bandwidth through rigid-flexible coupling.

[0022] 3. In this invention, the radius of the cavity is obtained by constructing an optimization model for each cavity radius to obtain the optimal cavity radius corresponding to the maximum sound absorption coefficient. The sound absorption performance of the metasurface structure obtained by this method can meet the requirements, and the calculation is convenient, which can effectively solve the problem of cavity radius optimization.

[0023] 4. The underwater acoustic metasurface of the present invention is designed based on the principle of interaction between acoustic waves and structures. Unlike metamaterials or metasurfaces realized by the principle of impedance matching between materials, it has relatively low requirements for material properties and therefore has greater flexibility in structural design. Attached Figure Description

[0024] Figure 1 This is a geometric schematic diagram of the underwater acoustic metasurface structure constructed according to a preferred embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of a numerical simulation model of an underwater acoustic metasurface constructed according to a preferred embodiment of the present invention.

[0026] Figure 3 This is a schematic diagram of the structural geometry of a unit block in an underwater acoustic metasurface constructed according to a preferred embodiment of the present invention.

[0027] Figure 4 This is a graph showing the sound absorption coefficient of the underwater acoustic metasurface constructed according to a preferred embodiment of the present invention at 300 Hz to 1000 Hz.

[0028] Figure 5 The displacement cloud diagrams of the underwater acoustic metasurface constructed according to a preferred embodiment of the present invention under different hydrostatic pressures are shown.

[0029] Figure 6 This is a three-dimensional structural illustration of a hydroacoustic metasurface structure for low-frequency broadband sound absorption constructed according to a preferred embodiment of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] like Figure 1 As shown, a subsurface structure for low-frequency broadband sound absorption is provided, which is suitable for absorbing planar incident sound waves of 300Hz to 1000Hz underwater.

[0032] The underwater acoustic metasurface structure is a multi-layered periodic structure. It exhibits periodicity in the width direction and is composed of multiple tightly arranged unit cells. In the thickness direction, it can be divided into multiple equal unit blocks stacked together. The thickness of each unit cell is much smaller than the wavelength of the incident sound wave.

[0033] Furthermore, each unit cell contains three types of materials: a metallic material called titanium; a non-metallic material called rubber; and finally, air.

[0034] Furthermore, the metallic material in the underwater acoustic metasurface can be titanium, aluminum, steel, or copper, and the metallic material is arranged in the middle of each unit block in the form of a hexagonal honeycomb skeleton.

[0035] Furthermore, the non-metallic materials in the underwater acoustic metasurface are rubber, silicone rubber, and polyurethane elastomer, and the non-metallic materials fill the area outside the honeycomb skeleton in the form of internal cavities.

[0036] Furthermore, except for the unit block where the frontal surface is located, all the unit blocks have the same topological configuration, namely a central honeycomb skeleton, cavities on both sides of the metal skeleton, and the rest filled with rubber; the unit block where the frontal surface is located is different from other unit blocks in that it has an additional cavity below the frontal surface.

[0037] Furthermore, a steel backplate is provided behind (below) the underwater acoustic metasurface structure.

[0038] Furthermore, underwater acoustic metasurface structures are suitable for frequencies f Sound wave absorption from 300 Hz to 1000 Hz corresponds to wavelengths... λ = 1.5 m ~ 5 m. The speed of sound in seawater is c =1500 m / s, wavelength λ ,frequency f speed of sound c The relationship between them is satisfied c = λf .

[0039] Preferably, the underwater acoustic metasurface achieves optimal acoustic absorption performance at a frequency of 710 Hz.

[0040] The present invention will be further described below with reference to specific embodiments.

[0041] like Figure 1 As shown, this invention provides a hydroacoustic metasurface structure for low-frequency broadband sound absorption. The metasurface is a multi-layered periodic structure, exhibiting periodicity in the width direction. Figure 1 Only one periodic unit is shown. There are 6 unit blocks in the thickness direction, each unit block is 12 mm wide and 10 mm thick, and the back plate thickness can be 5 mm.

[0042] In embodiments of the present invention, the unit block comprises three types of materials: a metallic material, titanium; a non-metallic material, rubber; and air. The density of the metallic material titanium... ρ M Equals 4500 Young's modulus E M Equals 108 Poisson's ratio μ M Equal to 0.34; density of non-metallic material rubber ρ N Equals 1100 Young's modulus E N Equal to 10 Poisson's ratio μ N Equal to 0.49933, isotropic loss factor η N =0.3; air is represented as empty material, with density, Young's modulus and Poisson's ratio taken as 0.

[0043] The metallic material titanium is arranged in the middle of each unit block in the form of a hexagonal honeycomb skeleton, while the non-metallic material rubber is filled in the area outside the honeycomb skeleton in each unit block in the form of embedded cavities.

[0044] In this embodiment, a steel backplate is disposed behind the underwater acoustic metasurface structure. The backplate thickness is 0.5 mm and the density is [not specified]. Young's modulus is 200 The Poisson's ratio is 0.3.

[0045] like Figure 2 As shown, Figure 2 for Figure 1A schematic diagram of the finite element model of the underwater acoustic metasurface. The simulation software and version are COMSOL Multiphysics 6.2. The incident sound wave is a vertically downward plane wave, and the background medium is seawater with a density of [insert density here]. The speed of sound is .

[0046] To characterize the sound absorption performance of metasurfaces, the "sound absorption coefficient" is typically used. This parameter is used for evaluation, and its calculation formula is as follows:

[0047] Among them, physical quantities This represents the reflection coefficient of the structure. The following methods can be used for calculation

[0048] in, This represents the sound pressure level of the reflected sound field. This represents the sound pressure of the incident sound field, with the integration region being the upper boundary of the metasurface. The sound absorption coefficient. It is a scalar value, ranging from 0 to 1, representing the degree to which sound energy is absorbed. When When, it means that all the energy of the incident sound wave is absorbed by the structure; when When this occurs, it means that no sound energy is absorbed by the material or structure at all; here it is defined as when... When this is the case, it indicates that the metasurface has good sound absorption properties.

[0049] like Figure 3 As shown, Figure 3 for Figure 1 One form of the unit block of the aforementioned underwater acoustic metasurface is called a built-in honeycomb titanium skeleton unit cell. In the underwater acoustic metasurface of this invention, the honeycomb titanium skeleton built into the unit cell is a regular hexagonal honeycomb, and its size is smaller than the unit cell size. Therefore, it is not closely spaced in the width direction, meaning it does not contact the skeleton of other unit cells. The cavities inside the rubber are fixed on the left and right sides of the unit cell; the frontal unit cell has an additional cavity on its upper side. The side length of the hexagonal honeycomb skeleton is... l Thickness is t The unit cell is a rectangular unit cell with a length of a , width is b The radius of the internal cavity is r There are a total of 4 geometric parameters. In the underwater acoustic metasurface involved in this invention, the following parameters are taken: a = 12 mm, b = 10 mm, l = 5 mm, t =0.35 mm, cavity radius r It is determined in the following way.

[0050] The cavities on both sides of the unit cell have the same radius and are fixed in position. , The cavity location of the additional opening on the frontal surface is... , The underwater acoustic metasurface involved in this invention has six layers, and the internal cavity dimensions of each unit cell are individually designed. Furthermore, the aperture of the upper side hole of the frontal unit cell is independent of the apertures of other cavities within that unit cell. Accordingly, seven parameters are to be determined. A parameter optimization approach is used to optimize these parameters. In the problem involved in this invention, the parameter optimization problem can be expressed as:

[0051] Among them, For structural geometric parameter vectors, Here, the objective function is obtained from finite element simulation calculation. Defined as the sound absorption coefficient of a metasurface The structural geometry has seven radius variables, each representing the radius of the uppermost individual hole. and the radius of the cavity pore in the 6-layer unit cell Considering that the cavity should not cross the metal frame and the ease of opening, constraints need to be placed on the range of variables: The Nelder-Mead simplex optimization algorithm was used to optimize the parameters, and the optimization results were obtained, which then formed the underwater acoustic metasurface involved in this invention. The optimization results are shown in Table 1.

[0052] Table 1 Optimization results of underwater acoustic metasurface parameters

[0053] Figure 4 This is a graph showing the sound absorption coefficient of the underwater acoustic metasurface involved in this invention at 300 Hz to 1000 Hz, including the average sound absorption coefficient. And the range where the sound absorption coefficient is greater than 0.6. The density of this structure is 1298.6 kg / m³. 3 It meets the constraint requirements. Its average sound absorption coefficient in the range of 300 Hz to 1000 Hz is... The coefficient reached 0.56, greater than 0.5, indicating good average sound absorption performance over a wide low-frequency range. Further analysis showed that this metasurface exhibited a sound absorption coefficient in the frequency band from 555 Hz to 975 Hz. This indicates that it has a good sound absorption effect in this frequency range, which can meet the design requirements of low-frequency broadband sound absorption, thus providing a feasible solution for the engineering application of underwater low-frequency sound absorption structures.

[0054] Figure 5The displacement contour maps of the underwater acoustic metasurface involved in this invention under different hydrostatic pressures show the deformation and volume shrinkage rate of the structure under pressures of 0.5 MPa, 1.0 MPa, and 2.0 MPa. The volume shrinkage rate is calculated by the volume ratio before and after deformation. It can be observed that the structure undergoes almost no deformation at 0.5 MPa, with a volume shrinkage rate of only 0.5%; at 1.0 MPa, the volume shrinkage rate is 1.0%, indicating that the structure has good compressive strength. It is noteworthy that at a pressure of 2.0 MPa, the volume shrinkage rate is only 1.9%, within 2.0%, but from the deformation perspective, the constitutive relationship of the non-metallic rubber material is very likely to enter the nonlinear stage. Therefore, it is recommended that the underwater acoustic metasurface be used in environments with water depths less than 100 m (i.e., less than the 1.0 MPa pressure requirement).

[0055] Figure 6 The present invention relates to a three-dimensional model of an underwater acoustic metasurface, showing a three-dimensional model of an underwater acoustic metasurface composed of 10 units.

[0056] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hydroacoustic metasurface structure for low-frequency broadband sound absorption, characterized in that, The structure comprises multiple arrayed unit cells, each unit cell being elongated and including a body and a skeleton. The body is filled with a non-metallic material, while the skeleton is made of metal. The skeleton has a cross-section of multiple hexagons connected end to end, which are arranged in the body to form a hexagonal honeycomb skeleton. Multiple cavities for low-frequency sound absorption are provided between the skeleton and the body. At the same time, a cavity is provided below the frontal surface of each unit cell.

2. The underwater acoustic metasurface structure for low-frequency broadband sound absorption as described in claim 1, characterized in that, The density range of the bulk material is 900 kg / m³. 3 ~1500 kg / m 3 The Young's modulus ranges from 1 MPa to 50 MPa, the Poisson's ratio ranges from 0.30 to 0.4999, and the isotropic loss factor ranges from 0.01 to 0.50; the density of the skeleton material ranges from 2700 kg / m³. 3 ~8900 kg / m 3 The Young's modulus ranges from 60 GPa to 210 GPa, and the Poisson's ratio ranges from 0.28 to 0.

36.

3. A hydroacoustic metasurface structure for low-frequency broadband sound absorption as described in claim 1 or 2, characterized in that, The body is made of rubber, silicone rubber, or polyurethane elastomer; the skeleton is made of titanium, aluminum, steel, or copper.

4. The underwater acoustic metasurface structure for low-frequency broadband sound absorption as described in claim 1, characterized in that, The thickness of the unit cell ranges from 40 mm to 60 mm, and the width ranges from 10 mm to 20 mm.

5. The underwater acoustic metasurface structure for low-frequency broadband sound absorption as described in claim 1, characterized in that, All cavities are closed cavities filled with air.

6. The underwater acoustic metasurface structure for low-frequency broadband sound absorption as described in claim 1, characterized in that, The structure is used for the absorption of plane incident sound waves in the 300 Hz to 1000 Hz range.

7. A design method for a hollow cavity in a low-frequency broadband acoustic metasurface structure for sound absorption as described in any one of claims 1-6, characterized in that, The method includes the following steps: The unit cell is divided into multiple blocks along the height direction, and the cavity radius of each block is set to... The radius of the cavity located below the frontal surface is set to ; Establish the relationship between the radius of each cavity and the sound absorption coefficient, construct an optimization model with the maximum sound absorption coefficient as the objective function, and solve the optimization model to obtain the radius of each cavity.

8. The design method as described in claim 7, characterized in that, The objective function is as follows: in, The sound absorption coefficient is... The sound pressure of the incident sound field. The sound pressure of the reflected sound field. This indicates that the integral calculation is performed at the surface of the structure.

9. The design method as described in claim 7, characterized in that, The constraints of the optimization model are as follows: in, The density of the structure is obtained by dividing the total mass of the sound-absorbing structure by the total volume of the structure. The volume shrinkage rate is obtained by dividing the volume of the structure after being subjected to pressure by the volume of the structure before being subjected to pressure.

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