A Low-Frequency Broadband Underwater Acoustic Structure Design Method Based on Column Cavity Series Technology

Abstract

This invention discloses a low-frequency broadband underwater acoustic structure design method based on column cavity series technology. The method determines the frequency range, average sound absorption coefficient threshold, high-efficiency sound absorption, high-efficiency sound absorption frequency ratio threshold, and the first frequency threshold reached. The structure is decomposed into n columnar inclusion layers. The unit cell width, matrix material parameters for each layer, layer thickness, and the type and diameter of the columnar inclusions are set. The impedance of each matrix material is calculated; if the impedance gradient condition is not met, the matrix material parameters are redesigned. The layers are connected in series, and a backplate is placed on the back of the seriesd structure. Simulation calculations are used to determine the average sound absorption coefficient, high-efficiency sound absorption bandwidth ratio, and the first frequency to achieve high-efficiency sound absorption within the frequency range. If these conditions are not met simultaneously, the number of layers is increased and the parameters are reset; otherwise, the designed underwater acoustic structure meets the low-frequency broadband sound absorption requirements. This invention achieves efficient acoustic stealth within a limited space for the target frequency band.

Description

Technical Field

[0001] This invention relates to the field of underwater sound-absorbing structure technology, and in particular to a low-frequency broadband underwater acoustic structure design method based on column cavity series technology. Background Technology

[0002] In the field of underwater vehicles, acoustic stealth performance is crucial. However, with the continuous advancement of underwater detection technology, the lower limit of underwater detection frequencies has expanded to several hundred hertz, placing higher demands on traditional anechoic coatings. Traditional underwater acoustic structures typically employ the method of embedding various cavities within homogeneous rubber or polyurethane to enhance low-frequency absorption. When the incident wave approaches the cavity's monopole resonant frequency, enhanced scattered waves are generated, promoting the conversion of longitudinal waves to transverse waves and achieving energy attenuation. However, the low-frequency sound absorption effect of this structure, relying on a single cavity, depends primarily on the cavity's volume, and its absorption bandwidth is relatively narrow. Summary of the Invention

[0003] This invention addresses the problems of narrow sound absorption bandwidth, poor low-frequency sound absorption, and the need for large-size cavities in traditional underwater acoustic structures. It proposes a low-frequency broadband underwater acoustic structure design method based on column-cavity series technology. The underwater acoustic structure designed by this method can achieve efficient low-frequency broadband absorption of sound waves, thereby achieving efficient acoustic stealth effect in the target frequency band within a limited space.

[0004] The technical solution adopted in this invention is:

[0005] A low-frequency broadband underwater acoustic structure design method based on column cavity series technology includes the following steps:

[0006] S1. Determine the frequency range to be calculated. The average sound absorption coefficient threshold within this frequency range Highly efficient sound absorption High-efficiency sound absorption frequency ratio threshold First time reaching frequency threshold ;

[0007] S2. Decompose the structure into n layers of columnar inclusions. Each layer includes a matrix material. Several columnar cavities are opened on the matrix material, and columnar inclusions are embedded in the cavities.

[0008] S3. Set the structural unit cell width, matrix material parameters for each layer, thickness of each layer, and type and diameter of columnar inclusions;

[0009] S4. Calculate the matrix material impedance of each columnar inclusion layer theoretically and determine whether the matrix material impedance of each columnar inclusion layer meets the impedance gradient condition. If yes, proceed to S5; otherwise, re-enter S3 and design the matrix material parameters of the i-th layer, i=1~n.

[0010] S5. The layers are designed in series, and the columnar mixed layers are arranged sequentially from the sound wave incident point to the sound wave transmission point as the first to nth layers to obtain the series structure. A back plate is set on the back of the series structure, and the back of the back plate is air.

[0011] S6. The cascaded structure is calculated through simulation. Within the range, average sound absorption coefficient High-efficiency sound absorption bandwidth ratio For the first time, it has achieved high-efficiency sound absorption. frequency ;

[0012] S7, Comparison and , and , and Size: If not simultaneously satisfied , , If the number of layers increases, i.e., n = n + 1, then it re-enters S2; if both conditions are met... , , This indicates that the designed underwater acoustic structure meets the low-frequency broadband sound absorption requirements.

[0013] In the above scheme, for the sake of design simplicity, the number of column cavities opened on each layer of matrix material is equal and the centers are aligned, and the structural unit cell width of each columnar inclusion layer is equal.

[0014] In the above scheme, the parameters of the i-th matrix material include: density elastic modulus Poisson's ratio Loss factor , i=1~n.

[0015] In the above scheme, the matrix material is selected from viscoelastic materials such as rubber or polyurethane.

[0016] In the above scheme, the cylindrical inclusion type is an air or metal oscillator.

[0017] In the above scheme, step S4, the method for theoretically calculating the matrix material impedance of the i-th columnar inclusion layer is as follows:

[0018] In the i-th (i=1~n) layer, the longitudinal wave velocity of the matrix material for

[0019] (1)

[0020] In the formula, , , These are the density, elastic modulus, and Poisson's ratio of the matrix material, respectively.

[0021] In the i-th (i=1~n) layer, the impedance of the matrix material for

[0022] (2)

[0023] The impedance gradient condition is

[0024] (3)

[0025] When i=1, Let be the resistance of water, where , These represent the density of water and the speed of sound, respectively.

[0026] In the above scheme, in step S4, if the impedance of the matrix material of each columnar inclusion layer does not meet the impedance gradient condition, then the parameters of the matrix material of the i-th layer are redesigned, including density. elastic modulus Poisson's ratio Loss factor , i=1~n.

[0027] In the above scheme, in step S5, the material of the back plate is selected as rigid material such as steel or aluminum.

[0028] In the above scheme, in step S6, according to the law of conservation of energy, the average sound absorption coefficient is... for:

[0029] (8)

[0030] In the formula, W in For incident sound power, W out For transmitted sound power, This is the energy reflected by sound waves.

[0031] In the above scheme, the incident sound pressure in the background pressure field is When the incident sound intensity is

[0032] (4)

[0033] In the formula, For the incident sound intensity, p in For incident sound pressure, The wave impedance of the medium in which the incident sound field is located;

[0034] Then the incident sound power is

[0035] (5)

[0036] In the formula, W in For incident sound power, I in For the incident sound intensity, The upper surface of the structure in contact with the incident region;

[0037] Similarly, the transmitted sound power is

[0038] (6)

[0039] In the formula, W out For transmitted sound power, The surface of the back panel that is in contact with air. for The transmitted sound intensity at the surface;

[0040] When a plane wave is incident on the interface between a fluid medium and a solid medium, due to the significant difference in impedance between the two media, the sound wave will be reflected at the interface, with the reflection energy being...

[0041] (7)

[0042] In the formula, As sound wave reflection energy, for The transmitted sound intensity incident on the surface of the structure.

[0043] The beneficial effects of this invention are:

[0044] This invention proposes a low-frequency broadband underwater acoustic structure design method based on column-cavity series technology. First, it designs a substrate with gradually varying impedance to allow acoustic energy to penetrate deep into the structure. Then, it connects multiple layers of columnar inclusions in series. These inclusions can be cavities or metal oscillators; the two different inclusions have different high-efficiency sound absorption frequency bands. Connecting them in series achieves a resonant coupling effect, thereby modulating the sound waves inside the structure. This causes strong scattering and waveform conversion of sound waves at the surfaces of the cavities and oscillators, achieving efficient low-frequency broadband sound absorption. Finally, by setting various parameter thresholds, an underwater acoustic structure that meets practical engineering requirements is designed, achieving efficient acoustic stealth within a limited space for the target frequency band. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a flowchart of the low-frequency broadband underwater acoustic structure design method based on column cavity series technology of the present invention;

[0047] Figure 2 This is a schematic diagram of the underwater acoustic structure designed in an embodiment of the present invention;

[0048] Figure 3 This is a schematic diagram of the structural unit cell size of the i-th columnar inclusion layer in an embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram comparing the calculated sound absorption coefficient with that of a single inclusion (air or steel) in an embodiment of the present invention. Detailed Implementation

[0050] 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.

[0051] It should be noted that the illustrations provided in the embodiments of the present invention are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0052] like Figure 1 As shown, this invention proposes a low-frequency broadband underwater acoustic structure design method based on column cavity series technology, including the following steps:

[0053] S1. Determine the frequency range to be calculated. The average sound absorption coefficient threshold within this frequency range Highly efficient sound absorption High-efficiency sound absorption frequency ratio threshold First time reaching frequency threshold .

[0054] In this embodiment, the frequency range is [100Hz, 10000Hz], and the average sound absorption coefficient threshold is... =0.7, high-efficiency sound absorption High-efficiency sound absorption frequency ratio threshold First time reaching frequency threshold .

[0055] S2. Decompose the structure into n layers of columnar inclusions. Each layer includes a matrix material. Several columnar cavities are opened on the matrix material, and columnar inclusions are embedded in the cavities.

[0056] In this embodiment, as Figure 2 As shown, the structure is decomposed into three cylindrical inclusion layers. Each layer includes a rubber matrix with five cylindrical cavities, each containing cylindrical inclusions.

[0057] S3. Set the structural unit cell width, matrix material parameters for each layer, thickness of each layer, and type and diameter of columnar inclusions.

[0058] In this embodiment, as Figure 3 As shown, the width of the structural unit cell The parameters of the i-th (i=1~n) layer of rubber include rubber density. elastic modulus Poisson's ratio Loss factor Thickness of the i-th layer The inclusions are of the type of air or steel, with a diameter of Specifically:

[0059] The parameters of the first layer of rubber include rubber density. elastic modulus Poisson's ratio Loss factor The thickness of the first layer The inclusion type is air, and the diameter is... .

[0060] The parameters of the second layer of rubber include rubber density. elastic modulus Poisson's ratio Loss factor The thickness of the second layer The inclusion type is steel, with a diameter of .

[0061] The parameters of the third layer of rubber include rubber density. elastic modulus Poisson's ratio Loss factor The thickness of the third layer The inclusion type is air, and the diameter is... .

[0062] S4. Calculate the impedance of the matrix material of each columnar inclusion layer through theoretical calculation, and determine whether the impedance of the matrix material of each columnar inclusion layer meets the impedance gradient condition. If yes, proceed to S5; otherwise, re-enter S3 to design the matrix material parameters of the i-th layer, i=1~n.

[0063] The impedance of the i-th (i=1~n) columnar inclusion layer is theoretically calculated as follows.

[0064] In the i-th (i=1~n) layer, the longitudinal wave velocity of the matrix material for

[0065] (1)

[0066] In the i-th (i=1~n) layer, the impedance of the matrix material for

[0067] (2)

[0068] The impedance gradient condition is

[0069] (3)

[0070] Specifically, when i=1, Let be the resistance of water, where , These represent the density of water and the speed of sound, respectively.

[0071] In this embodiment, the impedance ratios of each layer are as follows: , , If the impedance gradient condition is met, proceed to step S5.

[0072] S5. The layers are designed in series, and the columnar mixed layers are arranged sequentially from the sound wave incident point to the sound wave transmission point as the first to nth layers to obtain the series structure. A back plate is set on the back of the series structure, and the back of the back plate is air.

[0073] In this embodiment, the layers are designed in series, arranged sequentially as columnar sandwich layers 1 to 3 from the sound wave incident point to the sound wave transmission point, resulting in a series structure. A steel plate is added to the back of the series structure, with air behind the steel plate. The series structure is as follows. Figure 2 As shown, the steel plate is 10mm thick, and the material parameters are: elastic modulus 205GPa, density 7850kg / m³. 3 Poisson's ratio is 0.3.

[0074] S6. The cascaded structure is calculated through simulation. Within the range, average sound absorption coefficient High-efficiency sound absorption bandwidth ratio For the first time, it has achieved high-efficiency sound absorption. frequency .

[0075] Specifically, the simulation calculation principle is as follows.

[0076] The incident sound pressure in the background pressure field is: When the incident sound intensity is

[0077] (4)

[0078] In the formula, For the incident sound intensity, p in For incident sound pressure, The impedance of the medium in which the incident sound field is located.

[0079] Then the incident sound power is

[0080] (5)

[0081] In the formula, W in For incident sound power, I in For the incident sound intensity, The upper surface of the structure is in contact with the incident region.

[0082] Similarly, the transmitted sound power is

[0083] (6)

[0084] In the formula, W out For transmitted sound power, The surface of the back panel that is in contact with air. for The transmitted sound intensity at the surface.

[0085] Furthermore, when a plane wave is incident on the interface between a fluid medium and a solid medium, due to the significant difference in impedance between the two media, the sound wave will be reflected at the interface, with the reflection energy being...

[0086] (7)

[0087] In the formula, As sound wave reflection energy, for The transmitted sound intensity incident on the surface of the structure.

[0088] Furthermore, according to the law of conservation of energy, the sound absorption coefficient is...

[0089] (8)

[0090] In this embodiment, the sound absorption coefficient obtained through simulation calculation is as follows: Figure 4 As shown. The average sound absorption coefficient is =0.782, high-efficiency sound absorption frequency ratio For the first time, it has achieved high-efficiency sound absorption. frequency .

[0091] S7, Comparison and , and , and Size: If not simultaneously satisfied , , If the number of layers increases, i.e., n = n + 1, then it re-enters S2; if both conditions are met... , , This indicates that the designed underwater acoustic structure meets the low-frequency broadband sound absorption requirements.

[0092] In this embodiment, =0.782> =0.7 indicates that the average sound absorption effect of this example in the target frequency band meets the basic requirements; > This demonstrates that the high-efficiency sound absorption frequency band in this example exceeds 80% of the entire frequency band, achieving broadband sound absorption; < This demonstrates that this example achieves a sound absorption effect of 0.8 at a low frequency of 1600Hz, realizing low-frequency sound absorption. In summary, the underwater acoustic structure designed in this embodiment meets the requirements for low-frequency broadband sound absorption.

[0093] Figure 4 The diagram illustrates a comparison of the sound absorption coefficients of the present invention (two types of inclusions) with those containing only air inclusions and those containing only steel inclusions. As can be seen from the figure, the sound absorption performance of the air-only inclusion significantly decreases to a low level after the low-frequency absorption peak, resulting in a narrow sound absorption bandwidth. The steel-only inclusion maintains a low level across the entire sound absorption frequency range, failing to achieve good sound absorption. In contrast, the present invention, containing two types of inclusions, can significantly broaden the sound absorption bandwidth through the resonant coupling effect of the two, achieving broadband sound absorption at low frequencies.

[0094] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0095] The order of the steps in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0096] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A low-frequency broadband underwater acoustic structure design method based on column cavity series technology, characterized in that, Includes the following steps: S1. Determine the frequency range to be calculated. The average sound absorption coefficient threshold within this frequency range Highly efficient sound absorption High-efficiency sound absorption frequency ratio threshold First time reaching frequency threshold ; S2. Decompose the structure into n layers of columnar inclusions. Each layer includes a matrix material. Several columnar cavities are opened on the matrix material, and columnar inclusions are embedded in the cavities. S3. Set the structural unit cell width, matrix material parameters for each layer, thickness of each layer, and type and diameter of columnar inclusions; S4. Calculate the matrix material impedance of each columnar inclusion layer theoretically and determine whether the matrix material impedance of each columnar inclusion layer meets the impedance gradient condition. If yes, proceed to S5; otherwise, re-enter S3 and design the matrix material parameters of the i-th layer, i=1~n. S5. The layers are designed in series, and the columnar mixed layers are arranged sequentially from the sound wave incident point to the sound wave transmission point as the first to nth layers to obtain the series structure. A back plate is set on the back of the series structure, and the back of the back plate is air. S6. The cascaded structure is calculated through simulation. Within the range, average sound absorption coefficient High-efficiency sound absorption bandwidth ratio For the first time, it has achieved high-efficiency sound absorption. frequency ; S7, Comparison and , and , and Size: If not simultaneously satisfied , , If the number of layers increases, i.e., n = n + 1, then it re-enters S2; if both conditions are met... , , This indicates that the designed underwater acoustic structure meets the low-frequency broadband sound absorption requirements.

2. The low-frequency broadband underwater acoustic structure design method based on column cavity series technology according to claim 1, characterized in that, The number of column cavities opened on each layer of matrix material is equal and their centers are aligned, and the structural unit cell width of each columnar inclusion layer is equal.

3. The low-frequency broadband underwater acoustic structure design method based on column cavity series technology according to claim 1, characterized in that, The parameters of the i-th layer matrix material include: density. elastic modulus Poisson's ratio Loss factor , i=1~n.

4. The low-frequency broadband underwater acoustic structure design method based on column cavity series technology according to claim 1, characterized in that, The matrix material is selected from viscoelastic materials.

5. The low-frequency broadband underwater acoustic structure design method based on column cavity series technology according to claim 1, characterized in that, The cylindrical inclusions are of the type of air or metal oscillators.

6. The low-frequency broadband underwater acoustic structure design method based on column cavity series technology according to claim 1, characterized in that, In step S4, the method for theoretically calculating the matrix material impedance of the i-th columnar inclusion layer is as follows: In the i-th (i=1~n) layer, the longitudinal wave velocity of the matrix material for （1） In the formula, , , These are the density, elastic modulus, and Poisson's ratio of the matrix material, respectively. In the i-th (i=1~n) layer, the impedance of the matrix material for （2） The impedance gradient condition is （3） When i=1, Let be the resistance of water, where , These represent the density of water and the speed of sound, respectively.

7. The low-frequency broadband underwater acoustic structure design method based on column cavity series technology according to claim 1, characterized in that, In step S4, if the matrix material impedance of each columnar inclusion layer does not meet the impedance gradient condition, the matrix material parameters of the i-th layer are redesigned, including density. elastic modulus Poisson's ratio Loss factor , i=1~n.

8. The low-frequency broadband underwater acoustic structure design method based on column cavity series technology according to claim 1, characterized in that, In step S5, the back plate is made of a rigid material.

9. The low-frequency broadband underwater acoustic structure design method based on column cavity series technology according to claim 1, characterized in that, In step S6, according to the law of conservation of energy, the average sound absorption coefficient is... for: （8） In the formula, W in For incident sound power, W out For transmitted sound power, This is the energy reflected by sound waves.

10. The low-frequency broadband underwater acoustic structure design method based on column cavity series technology according to claim 9, characterized in that, The incident sound pressure in the background pressure field is: When the incident sound intensity is （4） In the formula, For the incident sound intensity, p in For incident sound pressure, The wave impedance of the medium in which the incident sound field is located; Then the incident sound power is （5） In the formula, W in For incident sound power, I in For the incident sound intensity, The upper surface of the structure in contact with the incident region; Similarly, the transmitted sound power is （6） In the formula, W out For transmitted sound power, The surface of the back panel that is in contact with air. for The transmitted sound intensity at the surface; When a plane wave is incident on the interface between a fluid medium and a solid medium, due to the significant difference in impedance between the two media, the sound wave will be reflected at the interface, with the reflection energy being... （7） In the formula, As sound wave reflection energy, for The transmitted sound intensity incident on the surface of the structure.

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