Design method of underwater sound-absorbing blanket based on cavity resonance and localized resonance coupling

Abstract

The application discloses a design method of underwater sound-absorbing covering layer based on cavity resonance and local resonance coupling. The method comprises the following steps: firstly, constructing an initial configuration of sound-absorbing unit cell; then, discretizing the cavity in the initial configuration of sound-absorbing unit cell into a plurality of unit cavity layers with equal height in the axial direction, so as to obtain a discrete configuration of sound-absorbing unit cell, and constructing a prediction function; again, based on the prediction function, optimizing the discrete configuration of sound-absorbing unit cell to obtain a primary optimized configuration of sound-absorbing unit cell; then, placing a resonance body between two adjacent unit cavity layers in the primary optimized configuration of sound-absorbing unit cell, so as to form a complete configuration of sound-absorbing unit cell and construct a black box function; based on the black box function, using an optimization method to optimize the complete configuration of sound-absorbing unit cell, so as to obtain a final configuration of sound-absorbing unit cell. The underwater sound-absorbing covering layer designed by the method can simultaneously realize low-frequency sound absorption and wide-frequency sound absorption, and the average sound absorption coefficient is increased to 86%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of underwater sound-absorbing material design, and particularly relates to a design method of an underwater sound-absorbing coating based on cavity resonance and localized resonance coupling. BACKGROUND

[0002] In underwater environments, underwater acoustics plays an irreplaceable important role and is widely used in many key fields such as ocean monitoring, underwater communication, resource exploration and military defense. Due to the special nature of the water medium, the propagation speed and attenuation characteristics of underwater sound waves are significantly different from those of sound waves in air, specifically manifested as changes in sound speed and significant slowing down of the attenuation process. This characteristic makes underwater acoustic signals able to propagate over a longer distance, but at the same time brings complex sound reflection, scattering and interference problems, resulting in a very complex underwater acoustic environment. In such an environment, efficient sound absorption technology is particularly crucial, which can help reduce noise levels, reduce signal interference, improve the performance and reliability of acoustic equipment, and has important significance for maintaining the acoustic order of the underwater environment and ensuring the smooth progress of various underwater activities.

[0003] However, traditional underwater sound-absorbing materials and technologies have many limitations. For example, although the early Alberich acoustic sound-absorbing coating laid the foundation for the field of underwater sound absorption, its sound-absorbing performance is often poor at low frequencies, and it is difficult to achieve ideal sound-absorbing effect in a wide frequency range. With the continuous expansion of underwater acoustic application scenarios, the demand for materials that can simultaneously meet low-frequency and wideband sound-absorbing performance is increasingly urgent. In addition, existing technologies also face challenges in structure height control. Higher structure height not only increases the manufacturing cost and complexity of the material, but also may limit its application in space-limited environments, such as inside compact underwater devices or on the surface of underwater structures with specific shapes.

[0004] Therefore, it is necessary to propose a design method that can design an underwater sound-absorbing coating that can simultaneously meet low-frequency and wideband sound-absorbing performance. SUMMARY

[0005] In view of the deficiencies in the background art, the purpose of the present application is to provide a design method of an underwater sound-absorbing coating based on cavity resonance and localized resonance coupling. The underwater sound-absorbing coating designed by the method of the present application can simultaneously realize low-frequency sound absorption and wideband sound absorption.

[0006] To achieve the above-mentioned purpose, the technical solution of the present application is as follows:

[0007] I. A design method of an underwater sound-absorbing coating based on cavity resonance and localized resonance coupling

[0008] S1: Construct an initial configuration of sound-absorbing unit cell;

[0009] S2: discretize the cavity in the initial configuration of the sound-absorbing single cell into a plurality of unit cavity layers with equal height in the axial direction, thereby obtaining a discrete configuration of the sound-absorbing single cell; and constructing a prediction function by using the transfer matrix method, taking the cavity porosities of all the unit cavity layers as inputs of the prediction function, and taking the average sound absorption coefficients in a preset frequency range as outputs of the prediction function;

[0010] S3: obtaining a primary optimization configuration of the sound-absorbing single cell based on the prediction function and after optimization of the discrete configuration of the sound-absorbing single cell.

[0011] S4: adding a resonator to the primary optimization configuration of the sound-absorbing single cell and placing the resonator between two adjacent unit cavity layers, thereby forming a complete configuration of the sound-absorbing single cell; taking the number, thickness and radius of the resonator as inputs of a black box function, and taking the average sound absorption coefficients in a preset frequency range as outputs of the black box function; and obtaining a final configuration of the sound-absorbing single cell by using an optimization method to optimize the complete configuration of the sound-absorbing single cell based on the black box function.

[0012] The initial configuration of the sound-absorbing single cell comprises a viscoelastic matrix and a cavity arranged inside the viscoelastic matrix, the initial configuration of the sound-absorbing single cell is an axisymmetric structure, the cross section of the cavity is a trapezoid, and the radius of the cavity away from the surface of the applied object is smaller than the radius of the cavity close to the surface of the applied object.

[0013] The viscoelastic matrix comprises a viscoelastic top layer, a viscoelastic middle layer and a viscoelastic bottom layer, the viscoelastic middle layer is arranged with the viscoelastic top layer and the viscoelastic bottom layer on both sides respectively, the inside of the viscoelastic middle layer is hollow and forms the cavity with a trapezoidal cross section, and the radius of the cavity close to the viscoelastic top layer is smaller than the radius of the cavity close to the viscoelastic bottom layer.

[0014] The S3 is specifically:

[0015] The plurality of optimization methods respectively optimize and solve the prediction function by changing the porosities of all the unit cavity layers, obtain a solution vector of optimal porosity, and generate a first sound-absorbing single cell candidate configuration solved by different optimization methods based on the solution vector of optimal porosity, and select the optimal one from the plurality of first sound-absorbing single cell candidate configurations and mark it as the primary optimization configuration of the sound-absorbing single cell.

[0016] In the S3, the optimization methods include a genetic algorithm, a pattern search algorithm, a particle swarm algorithm, a surrogate model algorithm, a multi-objective optimization algorithm, a Pareto optimization algorithm and a simulated annealing algorithm.

[0017] In the S3, the first sound-absorbing single cell candidate configuration solved by different optimization methods based on the solution vector of optimal porosity comprises:

[0018] Convert the solution vector of the optimal porosity obtained by each optimization method into the radius of all unit cavity layers, delete the unit cavity layers with too small radius, and compose the first sound absorption single cell candidate configuration corresponding to the optimization method from the viscoelastic matrix and the remaining unit cavity layers in the viscoelastic matrix.

[0019] The optimal one is selected from the plurality of first sound absorption single cell candidate configurations and is recorded as a sound absorption single cell primary optimization configuration, which comprises:

[0020] Firstly, a first sound absorption single cell candidate configuration with a lower frequency of the first sound absorption peak and a sound absorption coefficient stable above the preset reliability after the first sound absorption peak is selected, and then the configuration with the least unit cavity layer in the selected first sound absorption single cell candidate configuration is taken as the sound absorption single cell primary optimization configuration.

[0021] In S4, the black box function is obtained by encapsulating the finite element software, and the number, thickness and radius of the resonator are obtained by optimizing and solving the black box function using the gradient-free simulated annealing algorithm, so as to obtain the final configuration of the sound absorption single cell.

[0022] In S4, the black box function is a proxy model, and the construction process of the proxy model is as follows:

[0023] Firstly, a sample library containing the number, thickness and radius of the resonator to the average sound absorption coefficient is generated by batch simulation of the finite element, and a neural network is trained using the sample library until the training is completed, and the trained neural network is taken as the proxy model.

[0024] The number of resonators is determined according to the number of unit cavity layers in the sound absorption single cell primary optimization configuration.

[0025] II. A computer device

[0026] The computer device comprises a memory and a processor, the memory stores a computer program, and the processor implements the steps of the method for designing an underwater sound absorption cover layer based on cavity resonance and local resonance coupling when executing the computer program.

[0027] III. A computer readable storage medium

[0028] The computer readable storage medium stores a computer program, and the computer program implements the steps of the method for designing an underwater sound absorption cover layer based on cavity resonance and local resonance coupling when executed by a processor.

[0029] IV. A computer program product

[0030] The computer program product includes a computer program / instruction that, when executed by a processor, implements the steps of the underwater sound-absorbing covering layer design method based on cavity resonance and local resonance coupling.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] 1. This invention introduces a local resonance and cavity resonance coupling mechanism by adding a resonator to the structure of the sound-absorbing unit cell, thereby improving the problem of poor mid-frequency sound absorption efficiency when the cavity structure exists alone.

[0033] 2. Based on the cavity resonance principle and transfer matrix design, this invention obtains the final configuration of the sound-absorbing unit cell under a specific material. The underwater sound-absorbing covering layer prepared based on this final configuration of the sound-absorbing unit cell has excellent low-frequency sound absorption capability.

[0034] 3. All components in the sound-absorbing unit cell of the present invention are centrally symmetrical structures, which are simple in structure and easy to manufacture. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of laying an underwater sound-absorbing covering layer on an acoustic impedance pipe in an embodiment of the present invention.

[0036] Figure 2 A schematic diagram of the finite element model of a sound-absorbing unit cell.

[0037] Figure 3 This is a schematic diagram illustrating the changes in the sound-absorbing unit cell configuration during the design process of this invention.

[0038] Figure 4 The figures are cross-sectional views of the four candidate configurations of the first sound-absorbing unit cell obtained in the embodiments; wherein (a) is the candidate configuration of the first sound-absorbing unit cell obtained by the PS algorithm, (b) is the candidate configuration of the first sound-absorbing unit cell obtained by the GA algorithm, (c) is the candidate configuration of the first sound-absorbing unit cell obtained by the SG algorithm, and (d) is the candidate configuration of the first sound-absorbing unit cell obtained by the PSM algorithm.

[0039] Figure 5 for Figure 4 A comparison of the sound absorption curves of the four candidate configurations of the first sound-absorbing unit cell obtained in the 0.1-10kHz range with the traditional configuration.

[0040] Figure 6 Candidate sound-absorbing unit cell configurations for pure polyurethane rubber (A1), polyurethane rubber with only cavities (A2), polyurethane rubber with only resonators (A3), and polyurethane rubber with both cavities and resonators (A4).

[0041] Figure 7Comparison of sound absorption curves for pure polyurethane rubber, polyurethane rubber with only cavities, polyurethane rubber with only resonators, and polyurethane rubber with both cavities and resonators.

[0042] Figure 8 The modal displacement diagrams are shown for pure polyurethane rubber, polyurethane rubber with only cavity added, polyurethane rubber with only resonator added, and polyurethane rubber with both cavity and resonator added at 3.4kHz.

[0043] Figure 9 The energy dissipation density plots at 3.4 kHz are for pure polyurethane rubber, polyurethane rubber with only cavity, polyurethane rubber with only resonator, and polyurethane rubber with both cavity and resonator.

[0044] Figure 10 The diagram shows the structure of converting a cylindrical element into a regular hexagonal prism element; where (a) is a three-dimensional diagram of converting a cylindrical element into a regular hexagonal prism element, and (b) is a top view of converting a cylindrical element into a regular hexagonal prism element.

[0045] Figure 11 Comparison of sound absorption curves for cylindrical elements, regular hexagonal prism elements, and regular hexagonal prism elements with periodic boundary conditions.

[0046] Figure 12 This is a flowchart of the method of the present invention.

[0047] In the diagram: 1. Underwater sound-absorbing cover layer, 2. Sound-absorbing unit cell, 3. Viscoelastic matrix, 4. Upper resonator, 5. Lower resonator, 6. Upper cavity, 7. Middle cavity, 8. Lower cavity, 9. Viscoelastic top layer, 10. Viscoelastic middle layer, 11. Viscoelastic bottom layer. Detailed Implementation

[0048] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in the various embodiments of the present invention can be combined accordingly without mutual conflict.

[0049] In addition, in the description of the present application, it should be noted that similar terms such as "top", "bottom", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship when the product of the present application is commonly placed, which is only for the convenience of the simplified description of the present application, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0050] The underwater sound-absorbing covering layer is arranged between the water and the submarine wall. Due to the impedance difference between the water and the submarine wall, the sound wave is reflected at the interface, causing target leakage or other hazards. The purpose of the present application is to reduce the reflection of the incident sound wave as much as possible to protect the submarine from being discovered.

[0051] It should be noted that since the underwater sound-absorbing covering layer is generally planar and continuous, the structure therein is periodically changed, so it is not necessary to optimize the entire underwater sound-absorbing covering layer, but only the periodically changed unit therein needs to be extracted and optimized. Since the configuration change of the entire underwater sound-absorbing covering layer is mainly reflected in the longitudinal section, the configuration optimization can be performed on the longitudinal section of a single periodic unit in the underwater sound-absorbing covering layer.

[0052] In a preferred embodiment of the present application, the underwater sound-absorbing covering layer based on cavity resonance and local resonance coupling is a continuous layer formed by a series of sound-absorbing units arranged periodically and continuously. All the sound-absorbing unit cells are the same, so the structure of a single sound-absorbing unit cell will be described in detail below. In a preferred embodiment of the present application, as shown in Figure 12 The design method of the underwater sound-absorbing covering layer based on cavity resonance and local resonance coupling proposed by the present application specifically includes the following steps:

[0053] S1: preset the radius and height of the viscoelastic top layer 9, the viscoelastic middle layer 10 and the viscoelastic bottom layer 11. Construct an initial configuration of the sound-absorbing unit cell.

[0054] The initial configuration of the sound-absorbing unit cell includes a viscoelastic matrix and a cavity arranged inside the viscoelastic matrix. The initial configuration of the sound-absorbing unit cell is an axisymmetric structure, that is, the cavity is an axisymmetric structure, the cross section of the cavity in the axial direction is a trapezoid, and the radius of the cavity away from the surface of the application object is smaller than the radius of the cavity close to the surface of the application object.

[0055] The viscoelastic base body 3 comprises a viscoelastic top layer 9, a viscoelastic middle layer 10, and a viscoelastic bottom layer 11, the viscoelastic middle layer 10 is arranged with the viscoelastic top layer 9 and the viscoelastic bottom layer 11 on both sides, the viscoelastic bottom layer 11 is attached to the surface of the application object, and the viscoelastic top layer 9 is arranged away from the surface of the application object. The inside of the viscoelastic middle layer 10 is hollow and forms a cavity with a trapezoidal cross section, and the thickness is 50mm. The cavity radius near the viscoelastic top layer 9 is smaller than the cavity radius near the viscoelastic bottom layer 11, that is, the cavity radius away from the surface of the application object is smaller than the cavity radius near the surface of the application object, as shown in the first subgraph of Figure 3 The surface of the viscoelastic top layer 9 near the cavity is in contact with the cavity, and the surface of the viscoelastic bottom layer 11 near the cavity is in contact with the cavity.

[0056] S2: Discretize the cavity in the initial configuration of the sound absorption unit cell into 50 unit cavity layers with equal height in the axial direction, thereby obtaining a discrete configuration of the sound absorption unit cell; in the discrete configuration of the sound absorption unit cell, the thickness of each unit cavity layer is 1mm, and the porosity of each layer is the cavity radius of the layer divided by the unit cell radius, wherein the unit cell radius is 15mm. The adjacent two unit cavity layers form a step, as shown in the second subgraph of Figure 3 In order to simplify the schematic diagram, Figure 3 In the second subgraph of

[0057] It should be noted that the use of the transfer matrix method to calculate the sound absorption coefficient of the structure at a certain frequency belongs to the prior art. By sequentially inputting each layer porosity and the working frequency into the transfer matrix method, the sound absorption coefficient of the structure at the frequency can be obtained.

[0058] It should be noted that in the frequency range of 0.1-10kHz, 100 points are taken with a step of 0.1kHz, and the average value is taken as the output average sound absorption coefficient.

[0059] It should be noted that the frequency band studied in this embodiment is 0.1-10kHz, so a new function is constructed based on the transfer matrix method, which can accept 50 layer porosities and output the average sound absorption coefficient (AAC) in the frequency range of 0.1-10kHz. Therefore, by changing the 50 layer porosities to a vector v, the prediction function f ( ) of the average sound absorption coefficient can be obtained, that is, AAC=f (v).

[0060] S3: obtaining a first optimization configuration of the sound absorption unit cell based on the prediction function and the optimization of the sound absorption unit cell discrete configuration.

[0061] S3 specifically includes:

[0062] The genetic algorithm (GA), the pattern search method (PS), the particle swarm method (PSM), and the surrogate model method (SG) are respectively used to optimize and solve the prediction function by changing the porosity of all unit cavity layers, to obtain a solution vector of the optimal porosity corresponding to the maximum average absorption coefficient, and to generate a first sound absorption unit cell candidate configuration based on the solution vector of the optimal porosity and the first sound absorption unit cell candidate configuration obtained by solving the different optimization methods. The optimal first sound absorption unit cell candidate configuration is selected from the several first sound absorption unit cell candidate configurations and is recorded as the first optimization configuration of the sound absorption unit cell.

[0063] The objective function of the above four optimization algorithms is AAC=f(v), and the final optimization goal is to maximize the objective function, i.e., to ensure that the average absorption coefficient AAC is maximum. When the solution vector v of the optimal porosity is obtained, the solution vector v of the optimal porosity can be converted into the radius of each unit cavity layer, and the first optimization configuration of the sound absorption unit cell with the optimal cavity shape is formed.

[0064] The first sound absorption unit cell candidate configuration generated based on the solution vector of the optimal porosity and obtained by solving the different optimization methods includes:

[0065] The solution vector of the optimal porosity obtained by solving each optimization method is converted into the radius of all unit cavity layers, the unit cavity layer with a small radius is deleted, and the first sound absorption unit cell candidate configuration corresponding to the optimization method is composed of the viscoelastic matrix and the remaining unit cavity layers in the viscoelastic matrix (the space corresponding to the deleted unit cavity layer is filled with the viscoelastic matrix). In this embodiment, if the cavity radius is less than 0.5 mm, it is not conducive to manufacturing, and therefore the cavity with a radius less than 0.5 mm is deleted, i.e., the unit cavity layer that is not conducive to manufacturing is deleted.

[0066] The optimal first sound absorption unit cell candidate configuration is selected from the several first sound absorption unit cell candidate configurations and is recorded as the first optimization configuration of the sound absorption unit cell, which includes:

[0067] Firstly, the first sound absorption cell candidate configuration with a lower first sound absorption peak frequency and a sound absorption coefficient stable above a preset confidence level (such as 95%) after the first sound absorption peak is selected, so as to ensure that the sound absorption coefficient of the configuration at high frequencies (5 kHz-10 kHz) is high enough, so that the subsequent resonance body is added inside the structure, and the sound absorption effect at low frequencies (0-5 kHz) is improved by the added resonance body. Since the introduction of the cavity will reduce the rigidity of the entire structure, the number of cavity layers introduced should be as few as possible. Therefore, the configuration with the least unit cavity layer in the selected first sound absorption cell candidate configuration is taken as the initial optimization configuration of the sound absorption cell, so as to enhance the compression resistance of the structure and ensure the stability and durability of the structure in practical application.

[0068] Figure 4 (a) is the first sound absorption cell candidate configuration obtained by the PS algorithm, Figure 4 (b) is the first sound absorption cell candidate configuration obtained by the GA algorithm, Figure 4 (c) is the first sound absorption cell candidate configuration obtained by the SG algorithm, Figure 4 (d) is the first sound absorption cell candidate configuration obtained by the PSM algorithm. Figure 5 Figure 4 The sound absorption curves of the four first sound absorption cell candidate configurations obtained in the above and the traditional configuration at 0.1-10 kHz are shown in the following figure, wherein the traditional configuration as a control is the sound absorption unit structure mentioned in Z. Wang, Y. Huang, X. Zhang, L. Li, M. Chen, D. Fang, Broadband underwater sound absorbing structure with gradient cavity shaped polyurethane composite array supported by carbon fiber honeycomb, Journal of Sound and Vibration 479 (2020) 115375. The sound absorption performance of the first sound absorption cell candidate configurations given by the four optimization algorithms (labeled as TM in the figure legend) and the sound absorption curves obtained by the finite element method (labeled as FE in the figure legend) and the sound absorption performance of the traditional configuration (labeled as Wang, 2020) in the figure. The lowest frequency of the sound absorption curve of the traditional configuration cavity resonance in the figure is 8 kHz, but the sound absorption performance of the four first sound absorption cell candidate configurations of the present application is significantly improved.

[0069] ​In this embodiment, the first candidate configuration of the sound absorption unit cell given by the PS algorithm is selected based on its significant advantages in the average sound absorption coefficient and structure. On the one hand, the configuration generated by the PS algorithm maintains the sound absorption coefficient above 0.95 after 5 kHz, and the subsequent optimization work can focus on the low-frequency region. On the other hand, compared with the cavity configuration given by the GA algorithm, the PS algorithm requires fewer cavity layers, which makes the structure have better rigidity under high hydrostatic pressure. In the cavity configuration given by the PS algorithm, the porosity of the remaining layers except the first layer, the 30th layer and the 50th layer can be ignored, that is, it can be considered that the other layers do not contain cavities.

[0070] S4: Inserting the resonator into the viscoelastic matrix produces a local resonance effect, which moves the first absorption peak of the underwater sound absorption cover layer to low frequency. Add the resonator to the initial optimization configuration of the sound absorption unit cell, and place the resonator between the cavities of two adjacent unit cells to form a complete configuration of the sound absorption unit cell. The number of resonators between the two unit cavity layers is one or more. The number, thickness and radius of the resonator are taken as the input of the black box function, and the average sound absorption coefficient in the frequency range of 0.1-10 kHz is taken as the output of the black box function. Based on the black box function, the complete configuration of the sound absorption unit cell is optimized by using an optimization method to obtain the final configuration of the sound absorption unit cell. The final configuration of the sound absorption unit cell is also an axisymmetric structure, that is, all resonators and unit cavity layers are coaxially arranged, and the shapes of all resonators and unit cavity layers are cylindrical. Based on the final configuration of the sound absorption unit cell, a corresponding sound absorption unit cell is prepared, and then an underwater sound absorption cover layer is prepared and attached to the surface of an application object to achieve sound absorption of underwater objects.

[0071] The black box function is obtained by encapsulating the finite element software, and the finite element software is COMSOL Multiplphysics software.

[0072] The black box function can also be a proxy model, and the construction process of the proxy model is as follows:

[0073] First, a sample library containing the number, thickness and radius of the resonator to the average sound absorption coefficient is generated by batch simulation of the finite element, and a neural network is trained using the sample library until the training is completed. The trained neural network is used as a proxy model.

[0074] Since it is uncertain whether the black box function is continuous or not, the number, thickness and radius of the resonator under the maximum average sound absorption coefficient are obtained by optimizing and solving the black box function using a gradient-free simulated annealing algorithm (SA), thereby obtaining the final configuration of the sound absorption unit cell.

[0075] It should be noted that simulating and calculating the average sound absorption coefficient in the target frequency band by the finite element technology belongs to the prior art. Figure 2The schematic diagram of the finite element modeling of the single cell of the underwater sound absorbing cover layer, wherein the construction of the finite element model is a key step. When the finite element model is constructed based on the physical model of the sound reflection problem, a hard sound field boundary and a low reflection boundary are respectively arranged above and below, and then symmetrical boundaries are arranged on both sides. In the geometric range of the four boundaries, a perfect matched layer, a water medium layer, a pressure acoustic and solid coupling boundary, and an underwater sound absorbing cover layer are sequentially arranged from top to bottom. The underwater sound absorbing cover layer can be introduced into a viscoelastic material model containing a cavity for construction.

[0076] The number of resonators is determined according to the number of unit cavity layers in the initial optimization configuration of the sound absorbing single cell. The number of unit cavity layers minus one is equal to the number of resonators, that is, only one resonator is arranged between two adjacent unit cavity layers. In this embodiment, the number of resonators is set to 2. The resonator is made of rigid metal material, and is preferably stainless steel or cast iron.

[0077] It should be noted that the above optimization process is for optimizing the three-dimensional cylindrical half-section.

[0078] The shape of the viscoelastic matrix includes a cylinder, a regular hexagonal prism, a square, other regular shapes or irregular shapes.

[0079] In the preparation process of the sound absorbing single cell structure, the viscoelastic matrix and the resonator are connected by one or more of bonding, plastic dipping, and injection molding.

[0080] The material of the viscoelastic matrix 3 is a composite material composed of one or more viscoelastic materials, or a composite material in which a metal dopant is added to one or more viscoelastic materials. The viscoelastic material includes polyurethane rubber and polyurethane resin.

[0081] In the final configuration of the sound absorbing single cell, the unit cavity layer is filled with gas, that is, not in a vacuum state. The gas is air, helium, hydrogen or other gas. The types of gas in different unit cavity layers are the same or different.

[0082] The underwater sound absorbing cover layer 1 is periodically and continuously arranged by a plurality of sound absorbing single cells 2. The single cells can be arranged with intervals or closely arranged, and are preferably closely arranged. The cross-sectional shape of the single cell can be a cylinder, a regular hexagonal prism, a square, other regular shapes or irregular shapes. For example, Figure 2As shown, each sound-absorbing unit cell comprises a viscoelastic matrix 3, an upper resonator 4 and a lower resonator 5, wherein the viscoelastic matrix 3 is composed of a viscoelastic top layer 9, a viscoelastic middle layer 10 and a viscoelastic bottom layer 11 in sequence. The viscoelastic middle layer 10 is provided with an upper layer cavity 6, a middle layer cavity 7 and a lower layer cavity 8 in sequence. The upper resonator 4 is installed in the viscoelastic middle layer 10 between the upper layer cavity 6 and the middle layer cavity 7. The lower resonator 5 is installed in the viscoelastic middle layer 10 between the middle layer cavity 7 and the viscoelastic bottom layer 11. The upper resonator 4, the lower resonator 5, the upper layer cavity 6, the middle layer cavity 7 and the lower layer cavity 8 are independent of each other and do not contact each other. The upper layer cavity 6 directly contacts the viscoelastic top layer 9. The lower layer cavity 8 directly contacts the viscoelastic bottom layer 11.

[0083] In the embodiment, the thickness h1 of the viscoelastic top layer 9 is 5 mm, the thickness h2 of the viscoelastic middle layer 10 is 50 mm, and the thickness h3 of the viscoelastic bottom layer 11 is 5 mm. The radius R of the viscoelastic matrix 3 is 15 mm.

[0084] The upper resonator is a cylinder with a thickness of 3.4 mm and a radius of 13.3 mm. The lower resonator is a cylinder with a thickness of 16.7 mm and a radius of 12.6 mm. The distance between the midpoint of the upper resonator and the viscoelastic bottom layer 11 is 40 mm. The distance between the midpoint of the lower resonator and the viscoelastic bottom layer 11 is 15 mm.

[0085] The resonator (i.e. resonant body) is placed between the cavities in the present application, effectively preventing the compression of the top of the cavity; at the same time, the resonator also supports the side of the cavity, so that the side wall is also difficult to fold inward. Therefore, under the action of water pressure, the volume of the viscoelastic matrix and the resonator is basically stable, and the volume of the cavity can also be relatively stable due to the stable support of the resonator, thereby giving the present application excellent load-carrying capacity.

[0086] Figure 1 It is a schematic diagram of laying the underwater sound-absorbing cover layer on the acoustic impedance pipe in the embodiment of the present application. The outer circle represents the pipe diameter of the acoustic impedance pipe, and the honeycomb structure in the middle is the underwater sound-absorbing cover layer. The areas not covered by the underwater sound-absorbing cover layer are filled and covered with the material of the viscoelastic matrix.

[0087] The underwater sound-absorbing cover layer 1 prepared in the present application has an average sound absorption efficiency of 86% in the frequency range of 0.1-10 kHz.

[0088] Figure 6 The sound-absorbing unit cell candidate configuration diagrams of pure polyurethane rubber (A1), polyurethane rubber only added with cavities (A2), polyurethane rubber only added with resonators (A3) and polyurethane rubber added with both cavities and resonators (A4) are shown. Figure 7The sound absorption curves of the pure polyurethane rubber, the polyurethane rubber with only cavities added, the polyurethane rubber with only resonators added and the polyurethane rubber with both cavities and resonators added are shown; it can be seen from Figure 7 that the average sound absorption coefficient is greatly improved after the cavities and resonators are added simultaneously.

[0089] Figure 8 and Figure 9 are respectively the mode shape displacement diagrams and the energy dissipation density diagrams of the pure polyurethane rubber, the polyurethane rubber with only cavities added, the polyurethane rubber with only resonators added and the polyurethane rubber with both cavities and resonators added at 3.4 kHz; it can be seen from Figure 8 and Figure 9 that due to the coupling effect of the cavities and resonators, after the sound wave (longitudinal wave) is incident, wave shape conversion occurs near the viscoelastic interface between the two, the longitudinal wave is converted into a shear wave, thereby increasing the dissipation of the viscoelastic body. Therefore, it can be seen that the wave shape conversion greatly contributes to the mid-frequency (2 kHz-4 kHz) sound absorption.

[0090] Considering the manufacturing factors, the cylindrical unit is changed into a regular hexagonal prism unit during the experimental manufacturing process, as shown in (a) of Figure 10 and (b) of Figure 10 , and the inscribed circle radius of the regular hexagon is 15 mm. Figure 11 The sound absorption curve comparison diagram of the cylindrical unit, the regular hexagonal prism unit and the regular hexagonal prism unit with periodic boundary conditions is shown. It can be observed that the sound absorption curve is almost unchanged from the two-dimensional rotating model to the three-dimensional actual manufacturing model.

[0091] The above-described embodiments are only a preferred scheme of the present application, and are not intended to limit the present application. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application. Therefore, any technical scheme obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present application.

Claims

1. A design method of an underwater sound absorbing cover layer based on cavity resonance and local resonance coupling, characterized in that, The method comprises the following steps: S1: constructing an initial configuration of the sound-absorbing single cell; S2: discretizing the cavity in the initial configuration of the sound-absorbing single cell into a plurality of unit cavity layers with equal height in the axial direction, thereby obtaining a discrete configuration of the sound-absorbing single cell; and constructing a prediction function by using the transfer matrix method, taking the cavity porosity of all the unit cavity layers as the input of the prediction function, and taking the average sound absorption coefficient in a preset frequency range as the output of the prediction function; S3: obtaining a primary optimized configuration of the sound-absorbing single cell based on the prediction function and optimization of the discrete configuration of the sound-absorbing single cell; S4: adding a resonator to the primary optimized configuration of the sound-absorbing single cell and placing the resonator between two adjacent unit cavity layers, thereby forming a complete configuration of the sound-absorbing single cell, taking the number, thickness and radius of the resonator as the input of a black box function, and taking the average sound absorption coefficient in a preset frequency range as the output of the black box function; Based on the black box function, the complete configuration of the sound-absorbing single cell is optimized by using an optimization method, and a final configuration of the sound-absorbing single cell is obtained.

2. The design method of an underwater sound absorbing cover layer based on cavity resonance and local resonance coupling according to claim 1, characterized in that, The initial configuration of the sound-absorbing single cell comprises a viscoelastic matrix and a cavity arranged inside the viscoelastic matrix, the initial configuration of the sound-absorbing single cell is an axisymmetric structure, the cross section of the cavity is a trapezoid, and the radius of the cavity away from the surface of the applied object is smaller than the radius of the cavity close to the surface of the applied object.

3. The design method of an underwater sound absorbing cover layer based on cavity resonance and local resonance coupling according to claim 2, characterized in that, The viscoelastic matrix comprises a viscoelastic top layer, a viscoelastic middle layer and a viscoelastic bottom layer, the viscoelastic middle layer is arranged on both sides of the viscoelastic top layer and the viscoelastic bottom layer, the inside of the viscoelastic middle layer is hollow and forms the cavity with a trapezoidal cross section, and the radius of the cavity close to the viscoelastic top layer is smaller than the radius of the cavity close to the viscoelastic bottom layer.

4. The design method of an underwater sound absorbing cover layer based on cavity resonance and local resonance coupling according to claim 1, characterized in that, The S3 is specifically: A plurality of optimization methods respectively optimize and solve the prediction function by changing the porosity of all the unit cavity layers, obtain a solution vector of optimal porosity corresponding to each optimization method, and generate a first sound-absorbing single cell candidate configuration obtained by solving the prediction function by using different optimization methods based on the solution vector of optimal porosity, and select the optimal one from the plurality of first sound-absorbing single cell candidate configurations and mark it as the primary optimized configuration of the sound-absorbing single cell.

5. The design method of an underwater sound absorbing cover layer based on cavity resonance and local resonance coupling according to claim 4, characterized in that, In the S3, the optimization methods include genetic algorithm, pattern search algorithm, particle swarm algorithm, surrogate model algorithm, multi-objective optimization algorithm, Pareto optimization algorithm and simulated annealing algorithm.

6. The design method of an underwater sound absorbing cover layer based on cavity resonance and local resonance coupling according to claim 4, characterized in that, In the S3, the first sound-absorbing single cell candidate configuration obtained by solving the prediction function by using different optimization methods based on the solution vector of optimal porosity comprises: The solution vector of optimal porosity obtained by solving the prediction function by using each optimization method is converted into the radius of all the unit cavity layers, the unit cavity layer with a too small radius is deleted, and the first sound-absorbing single cell candidate configuration corresponding to the optimization method is composed of the viscoelastic matrix and the remaining unit cavity layers in the viscoelastic matrix.

7. The design method of an underwater sound absorbing cover layer based on cavity resonance and local resonance coupling according to claim 4, characterized in that, The selection of the optimal one from the plurality of first sound-absorbing single cell candidate configurations and the marking of the primary optimized configuration of the sound-absorbing single cell comprise: First, a first sound-absorbing single cell candidate configuration with a low first sound absorption peak frequency and a sound absorption coefficient stable above a preset reliability after the first sound absorption peak is selected, and then the configuration with the least unit cavity layers in the selected first sound-absorbing single cell candidate configuration is taken as the primary optimized configuration of the sound-absorbing single cell.

8. The design method of an underwater sound absorbing cover layer based on cavity resonance and local resonance coupling according to claim 1, characterized in that, In the S4, the black box function is obtained after encapsulating the finite element software, and the number, thickness and radius of the resonator are obtained after the black box function is optimized and solved by using a gradient-free simulated annealing algorithm, so that the final configuration of the sound absorption unit cell is obtained.

9. The design method of an underwater sound absorbing cover layer based on cavity resonance and local resonance coupling according to claim 1, characterized in that, In the S4, the black box function is a proxy model, and the construction process of the proxy model is as follows: First, a sample library containing the number, thickness and radius of the resonator to the average sound absorption coefficient is generated by batch simulation of the finite element, a neural network is trained by using the sample library, and the trained neural network is used as a proxy model until the training is completed. 10.A computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the computer device is configured to perform the method according to any one of claims 1-9. The processor executes the computer program to realize the steps of the underwater sound absorption cover layer design method based on cavity resonance and local resonance coupling in any one of claims 1 to 9.

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