Low-frequency broadband underwater acoustic structure design method based on cylindrical cavity series connection technology

Abstract

The invention discloses a low-frequency broadband underwater acoustic structure design method based on a column cavity series connection technology. The method comprises the steps that the frequency range, the average sound absorption coefficient threshold value # imgabs0 #, efficient sound absorption # imgabs1 #, the efficient sound absorption frequency proportion threshold value # imgabs2 # and the frequency threshold value # imgabs4 # reaching # imgabs3 # for the first time are determined; the structure is decomposed into n layers of cylindrical inclusion layers; setting structural unit cell width, matrix material parameters of each layer, thickness of each layer, and cylindrical inclusion type and diameter; calculating the impedance of each layer of base material, and if the impedance gradient condition is not met, redesigning the parameters of the base material; the layers are connected in series, and a layer of back plate is arranged on the back of the series-connected structure; the average sound absorption coefficient # imgabs5 #, the high-efficiency sound absorption bandwidth proportion # imgabs6 # and the frequency # imgabs8 # reaching the high-efficiency sound absorption # imgabs7 # for the first time within the frequency range are calculated through simulation; if the requirements of # imgabs9 #, # imgabs10 # and # imgabs11 # are not met at the same time, the number of layers is increased, and parameters are reset; otherwise, the designed underwater sound structure meets the sound absorption requirement of the low-frequency broadband. According to the invention, an efficient acoustic stealth effect of a target frequency band is realized in a limited space.

Description

Technical Field

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

[0002] In the field of underwater vehicles, acoustic stealth performance is crucial for underwater vehicles. However, with the continuous advancement of underwater detection technology, the lower limit of underwater detection frequency has expanded to hundreds of hertz, which puts higher requirements on traditional anechoic coatings. The design of traditional underwater acoustic structures usually adopts the method of embedding various cavities in homogeneous rubber or polyurethane to improve the low-frequency absorption effect. When the incident wave approaches the monopole resonance frequency of the cavity, an enhanced scattered wave is generated, which promotes the conversion of longitudinal waves to shear waves and achieves energy attenuation. However, the low-frequency sound absorption effect of this structure relying on a single cavity mainly depends on the volume of the cavity, and the sound absorption bandwidth is narrow. Summary of the invention

[0003] In view of the problems that traditional underwater acoustic structures have a narrow sound absorption bandwidth, poor low-frequency sound absorption, and require large cavities, the present invention proposes a low-frequency and broadband underwater acoustic structure design method based on column cavity series technology. The underwater acoustic structure designed by this method can achieve low-frequency and broadband efficient absorption of sound waves, and thus achieve efficient acoustic stealth effect in the target frequency band in a limited space.

[0004] The technical solution adopted by the present invention is: A low-frequency broadband underwater acoustic structure design method based on column cavity series technology includes the following steps: S1. Determine the frequency range to be calculated , and the average sound absorption coefficient threshold within this frequency range , efficient sound absorption , high-efficiency sound absorption frequency ratio threshold , reaching for the first time Frequency threshold ; S2, decomposing the structure into n layers of columnar inclusions, each layer comprising a base material, a plurality of columnar cavities are provided on the base material, and columnar inclusions are embedded in the columnar cavities; S3. Set the width of the structural unit cell, the material parameters of each layer of the matrix, the thickness of each layer, the type and diameter of the columnar inclusions; S4, through theoretical calculation of the matrix material impedance of each layer of columnar inclusion layer, determine whether the matrix material impedance of each layer of columnar inclusion layer meets the impedance gradient condition: if yes, enter S5, otherwise re-enter S3 to design the parameters of the i-th layer matrix material, i=1~n; S5, designing each layer in series, arranging them in order from the sound wave incident point to the sound wave transmission point as the 1st to the nth columnar inclusion layers, to obtain a structure after series connection, and setting a back plate at the back of the structure after series connection, and the back of the back plate is air; S6, through simulation calculation of the structure after series connection The average sound absorption coefficient , efficient sound absorption bandwidth ratio , achieving efficient sound absorption for the first time Frequency ; S7. Comparison and , and , and Size: If not satisfied at the same time , , , then increase the number of layers, that is, n=n+1, and re-enter S2; if both meet , , , it means that the designed hydroacoustic structure meets the low-frequency and broadband sound absorption requirements.

[0005] In the above scheme, for the sake of simplicity in design, the number of columnar cavities opened on each layer of base material is equal and the centers of the cavities are aligned, and the width of the structural unit cells of each layer of columnar inclusion layers is equal.

[0006] In the above scheme, the parameters of the i-th layer matrix material include: density , elastic modulus , Poisson's ratio , loss factor , i=1~n.

[0007] In the above solution, the base material is a viscoelastic material such as rubber or polyurethane.

[0008] In the above solution, the columnar inclusion type is air or metal vibrator.

[0009] In the above scheme, in step S4, the method for theoretically calculating the impedance of the matrix material of the i-th columnar inclusion layer is: In the i-th (i=1~n) layer, the longitudinal wave velocity of the matrix material is for (1) In the formula, , , 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 base material for (2) The impedance gradient condition is (3) When i=1, is the impedance of water, where , are the density of water and the speed of sound respectively.

[0010] 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, the parameters of the matrix material of the i-th layer are redesigned, including the density , elastic modulus , Poisson's ratio , loss factor , i=1~n.

[0011] In the above solution, in step S5, the material of the back plate is a rigid material such as steel or aluminum.

[0012] In the above scheme, in step S6, according to the law of conservation of energy, the average sound absorption coefficient for: (8) In the formula, W in is the incident sound power, W out is the transmitted sound power, It is the reflected energy of sound waves.

[0013] In the above scheme, the incident sound pressure in the background pressure field is When , the incident sound intensity is (4) In the formula, is the incident sound intensity, p in is the incident sound pressure, is the wave impedance of the medium where the incident sound field is located; The incident sound power is (5) In the formula, W in is the incident sound power, I in is the incident sound intensity, is the upper surface of the structure in contact with the incident domain; Similarly, the transmitted sound power is (6) In the formula,W out is the transmitted sound power, is the surface of the backplane in contact with the 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, the sound wave will be reflected at the interface due to the different impedances of the fluid medium and the solid medium. The reflected energy is (7) In the formula, is the sound wave reflection energy, for The transmitted sound intensity of the surface incident on the structure.

[0014] The beneficial effects produced by the present invention are: The low-frequency broadband hydroacoustic structure design method based on column cavity series technology proposed in the present invention firstly allows the acoustic energy to enter the deep part of the structure by designing the impedance gradient of the matrix. And by connecting multiple layers of columnar inclusions in series, the columnar inclusions can be cavities or metal oscillators. The two different inclusions have different efficient sound absorption frequency bands. Connecting the two in series can achieve a resonant coupling effect to regulate the sound waves inside the structure, so that the sound waves are strongly scattered and converted into waveforms on the surface of the cavity and the oscillator, and low-frequency broadband efficient sound wave absorption is achieved. Finally, by setting multiple parameter thresholds, a hydroacoustic structure that meets actual engineering needs is designed to achieve an efficient acoustic stealth effect in the target frequency band in a limited space. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 It is a flow chart of the low-frequency broadband underwater acoustic structure design method based on column cavity series technology of the present invention; Figure 2 is a schematic diagram of a hydroacoustic structure designed in an embodiment of the present invention; Figure 3 Schematic diagram of the structural unit cell size of the i-th columnar inclusion layer in an embodiment of the present invention; Figure 4 1 is a schematic diagram comparing the calculation results of the sound absorption coefficient in the embodiment of the present invention with a single inclusion (air or steel). DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] It should be noted that the illustrations provided in the embodiments of the present invention are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout type may also be more complicated.

[0019] like Figure 1 As shown, the present invention proposes a low-frequency broadband underwater acoustic structure design method based on column cavity series technology, comprising the following steps: S1. Determine the frequency range to be calculated , and the average sound absorption coefficient threshold within this frequency range , efficient sound absorption , high-efficiency sound absorption frequency ratio threshold , reaching for the first time Frequency threshold .

[0020] In this embodiment, the frequency range is [100 Hz, 10000 Hz], and the average sound absorption coefficient threshold =0.7, efficient sound absorption , high-efficiency sound absorption frequency ratio threshold , reaching for the first time Frequency threshold .

[0021] S2. Decomposing the structure into n layers of columnar inclusions, each layer includes a base material, a plurality of columnar cavities are opened on the base material, and columnar inclusions are embedded in the columnar cavities.

[0022] In this embodiment, Figure 2 As shown, the structure is decomposed into three layers of columnar inclusions, each layer including a rubber matrix with five columnar cavities formed on the rubber matrix and columnar inclusions embedded in the columnar cavities.

[0023] S3. Set the width of the structural unit cell, the material parameters of each layer of the matrix, the thickness of each layer, the type and diameter of the columnar inclusions.

[0024] In this embodiment, Figure 3 As shown, the width of the structural unit cell is The parameters of the rubber layer i (i=1~n) include: rubber density , elastic modulus , Poisson's ratio , loss factor . The thickness of the i-th layer , inclusion type is air or steel, diameter Specifically: The first layer of rubber parameters include rubber density , elastic modulus , Poisson's ratio , loss factor . Thickness of the first layer , inclusion type is air, diameter .

[0025] The second layer rubber parameters include rubber density , elastic modulus , Poisson's ratio , loss factor .Thickness of the second layer , inclusion type is steel, diameter .

[0026] The third layer rubber parameters include rubber density , elastic modulus , Poisson's ratio , loss factor .Thickness of the third layer , inclusion type is air, diameter .

[0027] S4. By theoretically calculating the impedance of the matrix material of each layer of columnar inclusions, determine whether the impedance of the matrix material of each layer of columnar inclusions meets the impedance gradient condition: if yes, enter S5, otherwise re-enter S3 to design the parameters of the i-th layer of matrix material, i=1~n.

[0028] The impedance of the i-th (i=1~n) columnar inclusion layer is theoretically calculated, and the theoretical calculation method is as follows.

[0029] In the i-th (i=1~n) layer, the longitudinal wave velocity of the matrix material is for (1) In the i-th (i=1~n) layer, the impedance of the base material for (2) The impedance gradient condition is (3) In particular, when i=1, is the impedance of water, where , are the density of water and the speed of sound respectively.

[0030] In this embodiment, the impedance ratios of each layer are , , If the impedance gradient condition is met, the process goes to step S5.

[0031] S5. Each layer is designed to be connected in series, and arranged in sequence as the 1st to nth columnar inclusion layers from the sound wave incident point to the sound wave transmission point to obtain a structure after series connection, and a back plate is set at the back of the structure after series connection, and the back of the back plate is air.

[0032] In this embodiment, each layer is designed to be connected in series, and the first to third columnar inclusion layers are arranged in sequence from the sound wave incident point to the sound wave transmission point to obtain a structure after the series connection, and a layer of steel plate is added to the back of the structure after the series connection, and the back of the steel plate is air. Figure 2 As shown, the thickness of the steel plate is 10 mm, the material parameters of the steel plate are elastic modulus 205 GPa, and density 7850 kg / m 3 , Poisson's ratio 0.3.

[0033] S6, through simulation calculation of the structure after series connection The average sound absorption coefficient , efficient sound absorption bandwidth ratio , achieving efficient sound absorption for the first time Frequency .

[0034] Specifically, the simulation calculation principle is as follows.

[0035] The incident sound pressure in the background pressure field is When , the incident sound intensity is (4) In the formula, is the incident sound intensity, p in is the incident sound pressure, is the wave impedance of the medium where the incident sound field is located.

[0036] The incident sound power is (5) In the formula, W in is the incident sound power, I in is the incident sound intensity, is the upper surface of the structure in contact with the incident domain.

[0037] Similarly, the transmitted sound power is (6) In the formula, W outis the transmitted sound power, is the surface of the backplane in contact with the air, for The transmitted sound intensity at the surface.

[0038] Furthermore, when a plane wave is incident on the interface between a fluid medium and a solid medium, the sound wave will be reflected at the interface due to the different impedances of the fluid medium and the solid medium. The reflected energy is (7) In the formula, is the sound wave reflection energy, for The transmitted sound intensity of the surface incident on the structure.

[0039] Furthermore, according to the law of conservation of energy, the sound absorption coefficient is (8) In this embodiment, the sound absorption coefficient obtained by simulation calculation is as follows: Figure 4 The average sound absorption coefficient is =0.782, the proportion of efficient sound absorption frequency , achieving efficient sound absorption for the first time Frequency .

[0040] S7. Comparison and , and , and Size: If not satisfied at the same time , , , then increase the number of layers, that is, n=n+1, and re-enter S2; if both meet , , , it means that the designed hydroacoustic structure meets the low-frequency and broadband sound absorption requirements.

[0041] In this embodiment, =0.782> =0.7, indicating that the average sound absorption effect of this example in the target frequency band meets the basic requirements; > , indicating that the high-efficiency sound absorption frequency band of this example exceeds the entire frequency band by 80%, achieving broadband sound absorption; < , indicating that this example has achieved a sound absorption effect of 0.8 at a low frequency of 1600 Hz, achieving low-frequency sound absorption. In summary, the hydroacoustic structure designed in this embodiment meets the low-frequency broadband sound absorption requirements.

[0042] Figure 4 The comparison of the sound absorption coefficients of the examples of the present invention (two kinds of inclusions) and those containing only air inclusions and only steel inclusions is shown. As can be seen from the figure, the sound absorption performance of the air inclusions alone drops significantly to a lower level after the sound absorption peak is generated at low frequency, and the sound absorption bandwidth is narrow; the steel inclusions alone are at a lower level in the entire sound absorption frequency band and do not have a good sound absorption effect; while the examples of the present invention contain two kinds of inclusions, which can significantly broaden the sound absorption bandwidth through the resonance coupling effect of the two, and achieve low-frequency broadband sound absorption.

[0043] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, and two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0044] The order of execution of each step in the above embodiment does not mean the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0045] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A low-frequency broadband underwater acoustic structure design method based on column cavity series technology, characterized in that: The following steps are involved: S1. Determine the frequency range to be calculated , and the average sound absorption coefficient threshold within this frequency range , efficient sound absorption , high-efficiency sound absorption frequency ratio threshold , reaching for the first time Frequency threshold ; S2, decomposing the structure into n layers of columnar inclusions, each layer comprising a base material, a plurality of columnar cavities are provided on the base material, and columnar inclusions are embedded in the columnar cavities; S3. Set the width of the structural unit cell, the material parameters of each layer of the matrix, the thickness of each layer, the type and diameter of the columnar inclusions; S4, through theoretical calculation of the matrix material impedance of each layer of columnar inclusion layer, determine whether the matrix material impedance of each layer of columnar inclusion layer meets the impedance gradient condition: if yes, enter S5, otherwise re-enter S3 to design the parameters of the i-th layer matrix material, i=1~n; S5, designing each layer in series, arranging them in order from the sound wave incident point to the sound wave transmission point as the 1st to the nth columnar inclusion layers, to obtain a structure after series connection, and setting a back plate at the back of the structure after series connection, and the back of the back plate is air; S6, through simulation calculation of the structure after series connection The average sound absorption coefficient , efficient sound absorption bandwidth ratio , achieving efficient sound absorption for the first time Frequency ; S7. Comparison and , and , and Size: If not satisfied at the same time , , , then increase the number of layers, that is, n=n+1, and re-enter S2; if both meet , , , it means that the designed hydroacoustic structure meets the low-frequency and broadband sound absorption requirements.

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

3. The low-frequency broadband underwater acoustic structure design method based on column cavity series connection technology according to claim 1 is 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 connection technology according to claim 1 is characterized in that: The matrix material is a viscoelastic material.

5. The low-frequency broadband underwater acoustic structure design method based on column cavity series connection technology according to claim 1 is characterized in that: The columnar inclusion type is air or metal vibrator.

6. The low-frequency broadband underwater acoustic structure design method based on column cavity series connection technology according to claim 1 is characterized in that: In step S4, the method for theoretically calculating the impedance of the matrix material of the i-th columnar inclusion layer is: In the i-th (i=1~n) layer, the longitudinal wave velocity of the matrix material is for （1） In the formula, , , 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 base material for （2） The impedance gradient condition is （3） When i=1, is the impedance of water, where , are 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 connection technology according to claim 1 is characterized in that: In step S4, if the impedance of the matrix material of each columnar inclusion layer does not meet the impedance gradient condition, the parameters of the matrix material of the i-th layer are redesigned, including the 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 connection technology according to claim 1 is 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 connection technology according to claim 1 is characterized in that: In step S6, according to the law of conservation of energy, the average sound absorption coefficient for: （8） In the formula, W in is the incident sound power, W out is the transmitted sound power, It is the reflected energy of sound waves.

10. The low-frequency broadband underwater acoustic structure design method based on column cavity series connection technology according to claim 9 is characterized in that: The incident sound pressure in the background pressure field is When , the incident sound intensity is （4） In the formula, is the incident sound intensity, p in is the incident sound pressure, is the wave impedance of the medium where the incident sound field is located; The incident sound power is （5） In the formula, W in is the incident sound power, I in is the incident sound intensity, is the upper surface of the structure in contact with the incident domain; Similarly, the transmitted sound power is （6） In the formula, W out is the transmitted sound power, is the surface of the backplane in contact with the 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, the sound wave will be reflected at the interface due to the different impedances of the fluid medium and the solid medium. The reflected energy is （7） In the formula, is the sound wave reflection energy, for The transmitted sound intensity of the surface incident on the structure.

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