Underwater sound absorption covering layer design method based on coupling of cavity resonance and local resonance

Abstract

The invention discloses an underwater sound absorption covering layer design method based on cavity resonance and local resonance coupling. Comprising the following steps: firstly, constructing an initial configuration of a sound absorption unit cell; then dispersing a cavity in the initial configuration of the sound absorption unit cell into a plurality of unit cavity layers with the same height in the axial direction so as to obtain a discrete configuration of the sound absorption unit cell, and constructing a prediction function; based on a prediction function, optimizing the discrete configuration of the sound absorption unit cell to obtain an initial optimized configuration of the sound absorption unit cell; then, the resonance body is placed between two adjacent unit cavity layers of the sound absorption unit cell initial optimization configuration, so that a sound absorption unit cell complete configuration is formed, and a black box function is constructed; and based on the black box function, optimizing the complete configuration of the sound absorption unit cell by using an optimization method to obtain a final configuration of the sound absorption unit cell. The underwater sound absorption covering layer designed through the method can achieve low-frequency sound absorption and broadband sound absorption at the same time, and the average sound absorption coefficient of the underwater sound absorption covering layer 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 enables underwater acoustic signals to propagate over a longer distance, but at the same time brings about 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, as it 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 effects in a wide frequency range. With the continuous expansion of underwater acoustic application scenarios, there is an increasing demand for materials that can simultaneously meet low-frequency and wideband sound-absorbing performance. 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 achieve 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: One, a design method of an underwater sound-absorbing coating based on cavity resonance and localized resonance coupling S1: Constructing an initial configuration of sound-absorbing unit cells; S2: discretize the cavity in the initial configuration of the sound-absorbing single cell into several unit cavity layers with equal height in the axial direction, thereby obtaining a discrete configuration of the sound-absorbing single cell; then, a transfer matrix method is used to construct a prediction function, taking the cavity porosity of all 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: based on the prediction function, the sound-absorbing single cell discrete configuration is optimized to obtain a sound-absorbing single cell initial optimization configuration; S4: add a resonator to the sound-absorbing single cell initial optimization configuration and place the resonator between two adjacent unit cavity layers to form a sound-absorbing single cell complete configuration, take the number, thickness and radius of the resonator as the input of the black box function, and take the average sound absorption coefficient in the preset frequency range as the output of the black box function; based on the black box function, the sound-absorbing single cell complete configuration is optimized by using an optimization method to obtain a sound-absorbing single cell final configuration.

[0007] The initial configuration of the sound-absorbing single cell includes 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.

[0008] The viscoelastic matrix includes 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, the inside of the viscoelastic middle layer is hollow and forms a 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.

[0009] The S3 is specifically: A plurality of optimization methods respectively optimize and solve the prediction function by changing the porosity of all unit cavity layers to obtain a solution vector of optimal porosity, and then generate a first sound-absorbing single cell candidate configuration based on the solution vector of optimal porosity, and select the optimal one from the several first sound-absorbing single cell candidate configurations and mark it as the sound-absorbing single cell initial optimization configuration.

[0010] In the S3, the optimization method includes 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.

[0011] In the S3, the first sound-absorbing single cell candidate configuration obtained by solving different optimization methods based on the solution vector of optimal porosity includes: The solution vector of optimal porosity obtained by solving each optimization method is converted into the radius of all unit cavity layers, the unit cavity layer with 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.

[0012] The step of selecting the best one from among several first sound absorbing unit cell candidate configurations and recording it as the first optimized configuration of the sound absorbing unit cell comprises: First, a candidate configuration of the first sound-absorbing unit cell is selected, in which the frequency of the first sound-absorbing peak is low and the sound absorption coefficient after the first sound-absorbing peak is stable above a preset confidence level. Then, the configuration with the least unit cavity layer among the selected candidate configurations of the first sound-absorbing unit cell is used as the initial optimization configuration of the sound-absorbing unit cell.

[0013] In S4, the black box function is obtained after encapsulating the finite element software. After optimizing and solving the black box function using a simulated annealing algorithm that is not based on gradients, the number, thickness and radius of the resonant bodies are obtained, thereby obtaining the final configuration of the sound-absorbing unit cell.

[0014] In 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, radius and average sound absorption coefficient of resonators is generated through finite element batch simulation. The sample library is used to train the neural network until the training is completed, and the trained neural network is used as the proxy model.

[0015] The number of the resonators is determined according to the number of unit cavity layers in the initial optimized configuration of the sound absorbing unit cell.

[0016] 2. A computer device The computer device includes a memory and a processor. The memory stores a computer program. When the processor executes the computer program, the steps of the method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance are implemented.

[0017] 3. A computer-readable storage medium The computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance.

[0018] 4. A computer program product The computer program product includes a computer program / instruction, which, when executed by a processor, implements the steps of the method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention introduces a coupling mechanism of local resonance and cavity resonance by adding a resonator into 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.

[0020] 2. The present invention obtains the final configuration of the sound-absorbing unit cell under specific materials based on the cavity resonance principle and transfer matrix design. The underwater sound-absorbing covering layer prepared based on the final configuration of the sound-absorbing unit cell has very excellent low-frequency sound absorption capability.

[0021] 3. All components of the sound absorbing unit cell of the present invention are of central symmetrical structure, which is simple and convenient for production and processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of laying an underwater sound-absorbing covering layer on an acoustic impedance tube in an embodiment of the present invention.

[0023] Figure 2 Schematic diagram of finite element modeling of sound-absorbing unit cells.

[0024] Figure 3 Schematic diagram of the change of the sound absorbing unit cell configuration during the design process of the present invention.

[0025] Figure 4 : These are cross-sectional views of the four candidate configurations of the first sound-absorbing unit cell obtained in the embodiment; (a) is the candidate configuration view of the first sound-absorbing unit cell obtained by the PS algorithm, (b) is the candidate configuration view of the first sound-absorbing unit cell obtained by the GA algorithm, (c) is the candidate configuration view of the first sound-absorbing unit cell obtained by the SG algorithm, and (d) is the candidate configuration view of the first sound-absorbing unit cell obtained by the PSM algorithm.

[0026] Figure 5 for Figure 4 Comparison of the sound absorption curves of the four first sound-absorbing unit cell candidate configurations and the traditional configuration at 0.1-10kHz.

[0027] Figure 6 These are the candidate configuration diagrams of the sound-absorbing unit cell of pure polyurethane rubber (A1), polyurethane rubber with only cavities added (A2), polyurethane rubber with only resonators added (A3), and polyurethane rubber with both cavities and resonators added (A4).

[0028] Figure 7 The following is a comparison chart of the sound absorption curves of pure polyurethane rubber, polyurethane rubber with only cavities added, polyurethane rubber with only resonators added, and polyurethane rubber with both cavities and resonators added.

[0029] Figure 8 Figure 3 is the mode displacement diagram of 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.

[0030] Figure 9The energy dissipation density diagram of 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.

[0031] Figure 10 Schematic diagram of the structure of converting a cylindrical unit into a regular hexagonal prism unit; (a) is a three-dimensional schematic diagram of converting a cylindrical unit into a regular hexagonal prism unit, and (b) is a top view of converting a cylindrical unit into a regular hexagonal prism unit.

[0032] Figure 11 Comparison of sound absorption curves of cylindrical elements, regular hexagonal prism elements, and regular hexagonal prism elements with periodic boundary conditions.

[0033] Figure 12 Flow chart of the method of the present invention.

[0034] In the figure: 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 DESCRIPTION

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflicting with each other.

[0036] In addition, in the description of the present invention, it should be noted that terms such as "top", "bottom", "up", "down", "left", "right", "vertical", "horizontal", "inside", and "outside" indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the products of the present invention are usually placed when in use. This is merely a simplified description for the convenience of describing the present invention, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be understood as a limitation on the present invention.

[0037] The underwater sound-absorbing coating is placed between the water and the submarine's hull. Due to the impedance difference between the water and the submarine's hull, sound waves are reflected at the interface, causing target leakage or other hazards. The present invention aims to minimize the reflection of incident sound waves, thereby protecting the submarine from detection.

[0038] It should be noted that since underwater sound-absorbing coatings are generally continuous in planar form and exhibit periodic structural variations, it is not necessary to optimize the entire coating. Instead, it is necessary to extract and optimize the periodically varying units within the coating. Since the structural variations of the entire coating are primarily manifested in the longitudinal section, structural optimization can be performed on the longitudinal section of a single periodic unit within the coating.

[0039] In a preferred embodiment of the present invention, the underwater sound-absorbing coating 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 sound-absorbing units have the same structure, so the following mainly describes the structure of a single sound-absorbing unit in detail. In a preferred embodiment of the present invention, Figure 12 As shown, the present invention proposes a method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance, which specifically includes the following steps: S1: Preset the radius and height of the viscoelastic top layer 9, the viscoelastic middle layer 10, and the viscoelastic bottom layer 11. Construct the initial configuration of the sound absorbing unit cell.

[0040] 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 along the axial direction is trapezoidal, 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.

[0041] The viscoelastic matrix 3 includes a viscoelastic top layer 9, a viscoelastic middle layer 10, and a viscoelastic bottom layer 11. The viscoelastic top layer 9 and the viscoelastic bottom layer 11 are arranged on both sides of the viscoelastic middle layer 10, respectively. 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 interior of the viscoelastic middle layer 10 is hollow, and a cavity with a trapezoidal cross-section is formed inside the viscoelastic middle layer 10, and its thickness is 50 mm. 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 FIG. Figure 3 As shown in the first sub-figure, the surface of the viscoelastic top layer 9 close to the cavity contacts the cavity, and the surface of the viscoelastic bottom layer 11 close to the cavity contacts the cavity.

[0042] S2: The cavity in the initial configuration of the sound-absorbing unit cell is discretized into 50 unit cavity layers with equal height in the axial direction, thereby obtaining a discrete configuration of the sound-absorbing unit cell; in the discrete configuration of the sound-absorbing unit cell, the thickness of each unit cavity layer is 1 mm, and the porosity of each layer is the cavity radius of the layer divided by the unit cell radius, where the unit cell radius is 15 mm. A step is formed between two adjacent unit cavity layers, such as Figure 3In order to simplify the schematic diagram in this embodiment, Figure 3 The second subgraph plots the radius of seven or eight consecutive unit cavity layers as identical. In practice, the radii of each of the 50 discretized unit cavity layers are different. The transfer matrix method is then used to construct a prediction function, using the porosity of all unit cavity layers as input and the average sound absorption coefficient (AAC) in the frequency range of 0.1-10 kHz as output.

[0043] It should be noted that the use of the transfer matrix method to calculate the sound absorption coefficient of a structure at a certain frequency is an existing technology. By substituting the porosity of each layer in order and the operating frequency into the transfer matrix method, the sound absorption coefficient of the structure at the frequency can be obtained.

[0044] It should be noted that within the frequency range of 0.1-10 kHz, a total of 100 points were averaged with a step size of 0.1 kHz and used as the output average sound absorption coefficient.

[0045] It should be noted that the frequency band studied in this embodiment is 0.1-10 kHz, so a new function is constructed based on the transfer matrix method so that it can accept 50 layers of porosity and output the average sound absorption coefficient (AAC) at 0.1-10 kHz. Then, by changing the 50 layers of porosity to vector v, the prediction function f () of the average sound absorption coefficient can be obtained, that is, AAC=f (v).

[0046] S3: Based on the prediction function, the discrete configuration of the sound-absorbing unit cell is optimized to obtain the initial optimized configuration of the sound-absorbing unit cell.

[0047] S3 specifically: The Genetic Algorithm (GA), Pattern Search Method (PS), Particle Swarm Method (PSM), and Surrogate Model Method (SG) respectively optimize and solve the prediction function by changing the porosity of all unit cavity layers to obtain the solution vector of the optimal porosity corresponding to the maximum average sound absorption coefficient. Based on the solution vector of the optimal porosity, candidate configurations of the first sound-absorbing unit cell obtained by different optimization methods are generated. The optimal one is selected from several candidate configurations of the first sound-absorbing unit cell and recorded as the initial optimized configuration of the sound-absorbing unit cell.

[0048] The objective function of the four optimization algorithms described above is AAC = f (v). The ultimate optimization goal is to maximize this objective function, that is, to maximize the average sound absorption coefficient (AAC). Once the optimal porosity solution vector v is obtained, it can be converted into the radius of each unit cavity layer, thereby forming the initial optimized configuration of the sound-absorbing unit cell with the optimal cavity shape.

[0049] Based on the optimal porosity solution vector, candidate configurations of the first sound-absorbing unit cell are generated by different optimization methods, including: The optimal porosity solution vector obtained by each optimization method is converted into the radius of all unit cavity layers. Unit cavity layers with too small a radius are deleted, and the first candidate sound-absorbing unit cell configuration corresponding to that optimization method is formed by the viscoelastic matrix and the remaining unit cavity layers within the viscoelastic matrix (the space corresponding to the deleted unit cavity layers 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. Therefore, cavities with a radius less than 0.5 mm are deleted, that is, the unit cavity layers that are not conducive to manufacturing are deleted.

[0050] The best one is selected from several candidate configurations of the first sound-absorbing unit cell and recorded as the initial optimized configuration of the sound-absorbing unit cell, including: First, a candidate first-cell configuration is selected, one with a low frequency of first absorption peaks and a stable absorption coefficient above a preset confidence level (e.g., 95%). This ensures that the absorption coefficient at high frequencies (5kHz-10kHz) is sufficiently high to allow for the subsequent addition of resonators within the structure to improve the absorption at low frequencies (0-5kHz). Because the introduction of cavities reduces the rigidity of the entire structure, the number of cavity layers should be minimized. Therefore, the configuration with the fewest cavity layers among the selected first-cell candidate configurations is selected as the initial optimized configuration to enhance the structure's compressive strength and ensure its stability and durability in practical applications.

[0051] Figure 4 (a) is the first candidate configuration diagram of the sound-absorbing unit cell obtained by the PS algorithm. Figure 4 (b) is the first candidate configuration diagram of the sound-absorbing unit cell obtained by the GA algorithm. Figure 4 (c) is the first candidate configuration diagram of the sound-absorbing unit cell obtained by the SG algorithm. Figure 4 (d) is the candidate configuration diagram of the first sound-absorbing unit cell obtained by the PSM algorithm. Figure 5 for Figure 4Comparison of the sound absorption curves of the four candidate first sound-absorbing unit cell configurations and the traditional configuration at 0.1-10kHz, where the traditional configuration used as a control is the sound-absorbing 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 f ber honeycomb, Journal of Sound and Vibration 479 (2020) 115375. The sound absorption curves of the first sound-absorbing unit cell candidate configurations obtained by the four optimization algorithms using the transfer matrix method (denoted as TM in the legend) and the sound absorption curves obtained by the finite element method (denoted as FE in the legend), as well as the sound absorption performance of the traditional configuration (denoted as Wang, 2020 in the legend) are shown. In the figure, the sound absorption curve of the traditional configuration cavity resonance reaches the lowest frequency of 0.8 at 8kHz, but the sound absorption performance of the four first sound absorption unit cell candidate configurations of the present invention are significantly improved.

[0052] In this example, the PS algorithm was selected as the first candidate sound-absorbing unit cell configuration based on its significant advantages in terms of average sound absorption coefficient and structure. Firstly, the PS algorithm-generated configuration maintains a sound absorption coefficient above 0.95 after 5kHz, allowing subsequent optimization efforts to focus on the low-frequency region. Secondly, the PS algorithm requires fewer cavity layers than the GA algorithm-derived cavity configuration, which improves the structural rigidity under high hydrostatic pressure. With the exception of the 1st, 30th, and 50th layers, the porosity of the remaining layers in the PS algorithm-derived cavity configuration is almost negligible, meaning that the remaining layers can be considered to contain no cavities.

[0053] S4: Inserting a resonant body into the viscoelastic matrix will produce a local resonance effect, causing the first absorption peak of the sound absorption curve of the underwater sound-absorbing covering layer to shift to a low frequency. The resonant body is added to the initial optimized configuration of the sound-absorbing unit cell and is placed between two adjacent unit cavity layers to form a complete configuration of the sound-absorbing unit cell. The number of resonant bodies between the two unit cavity layers is one or more. The number, thickness, and radius of the resonant bodies are used as the input of the black box function, and the average sound absorption coefficient in the frequency range of 0.1-10kHz is used as the output of the black box function. Based on the black box function, the complete configuration of the sound-absorbing unit cell is optimized using an optimization method to obtain the final configuration of the sound-absorbing unit cell. The final configuration of the sound-absorbing unit cell is also an axisymmetric structure, that is, all resonant bodies and unit cavity layers are coaxially arranged, and the shape of all resonant bodies and unit cavity layers is cylindrical. Based on the final configuration of the sound-absorbing unit cell, the corresponding sound-absorbing unit cell is prepared, and then an underwater sound-absorbing covering layer is prepared and applied to the surface of the application object to achieve sound absorption of the underwater object.

[0054] The black box function is obtained by encapsulating the finite element software, and the finite element software is specifically COMSOL Multiplphysics software.

[0055] A black box function can also be a proxy model. The construction process of the proxy model is as follows: First, a sample library containing the number, thickness, radius and average sound absorption coefficient of resonators is generated through finite element batch simulation. The sample library is used to train the neural network until the training is completed, and the trained neural network is used as the proxy model.

[0056] Since the continuity of the black-box function is uncertain, the non-gradient-based simulated annealing algorithm (SA) is used to optimize and solve the black-box function. The number, thickness, and radius of the resonant bodies with the maximum average sound absorption coefficient are obtained, thereby obtaining the final configuration of the sound-absorbing unit cell.

[0057] It should be noted that simulating and calculating the average sound absorption coefficient within a target frequency band using finite element technology belongs to the existing technology. Figure 2 This is a schematic diagram of the finite element modeling of a single cell of an underwater sound-absorbing cover. Constructing the finite element model is a key step. When constructing the finite element model based on the physical model of the acoustic reflection problem, it is necessary to set hard acoustic boundaries and low-reflection boundaries at the top and bottom, respectively. Symmetrical boundaries are then set on both sides. Within the geometric range of these four boundaries, a perfectly matched layer, a water medium layer, a pressure acoustics and solid coupling boundary, and an underwater sound-absorbing cover are then set from top to bottom. The underwater sound-absorbing cover can be constructed by importing a viscoelastic material model containing a cavity.

[0058] The number of resonators is determined based on the number of unit cavity layers in the initially optimized configuration of the sound-absorbing unit cell. The number of resonators is equal to the number of unit cavity layers minus one, meaning that only one resonator is placed between two adjacent unit cavity layers. In this embodiment, the number of resonators is set to two. The resonators are made of a rigid metal material, preferably stainless steel or cast iron.

[0059] It should be noted that the above optimization process is aimed at optimizing the half-section of a three-dimensional cylinder.

[0060] The shape of the viscoelastic matrix includes a cylinder, a regular hexagonal prism, a square, other regular shapes or irregular shapes.

[0061] During the preparation of the sound absorbing unit cell structure, the viscoelastic matrix and the resonant body are connected by one or more of bonding, dipping and injection molding.

[0062] The material of the viscoelastic matrix 3 is a composite material composed of one or more viscoelastic materials, or a composite material obtained by adding a metal dopant to one or more viscoelastic materials. The viscoelastic material includes polyurethane rubber and polyurethane resin.

[0063] In the final configuration of the sound-absorbing unit cell, the unit cavity layer is filled with gas, meaning it is not in a vacuum state. The gas can be air, helium, hydrogen, or other gases. The gas types in different unit cavity layers can be the same or different.

[0064] The underwater sound absorbing covering layer 1 is composed of a plurality of sound absorbing cells 2 arranged periodically and continuously. The cells can be arranged at intervals or closely, preferably closely. The cross-sectional shape of the cell can be a cylinder, a regular hexagonal prism, a square, other regular shapes or irregular shapes. Figure 2 As shown, each sound-absorbing unit cell comprises a viscoelastic matrix 3, an upper resonant body 4, and a lower resonant body 5. The viscoelastic matrix 3 is composed of a viscoelastic top layer 9, a viscoelastic middle layer 10, and a viscoelastic bottom layer 11, which are sequentially joined. The viscoelastic middle layer 10 is provided with an upper cavity 6, a middle cavity 7, and a lower cavity 8. The upper resonant body 4 is mounted in the viscoelastic middle layer 10 between the upper cavity 6 and the middle cavity 7, and the lower resonant body 5 is mounted in the viscoelastic middle layer 10 between the middle cavity 7 and the viscoelastic bottom layer 11. The upper resonant body 4, the lower resonant body 5, the upper cavity 6, the middle cavity 7, and the lower cavity 8 are independent of each other and do not contact each other. The upper cavity 6 is in direct contact with the viscoelastic top layer 9, and the lower cavity 8 is in direct contact with the viscoelastic bottom layer 11.

[0065] In this 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, the thickness h3 of the viscoelastic bottom layer 11 is 5 mm, and the radius R of the viscoelastic base 3 is 15 mm.

[0066] 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 midpoint of the upper resonator is 40 mm from the viscoelastic base layer 11, while the midpoint of the lower resonator is 15 mm from the viscoelastic base layer 11.

[0067] The present invention places a resonant body (i.e., a resonator) between the cavities, effectively preventing compression of the cavity top. Simultaneously, the resonator supports the sides of the cavity, preventing the sidewalls from collapsing inward. Therefore, under the action of water pressure, the volume of the viscoelastic matrix and the resonator remains essentially stable. Thanks to the resonator's firm support, the volume of the cavity also remains relatively stable, giving the present invention excellent load-bearing capacity.

[0068] Figure 1 This is a schematic diagram of laying an underwater sound-absorbing covering layer on an acoustic impedance tube in an embodiment of the present invention. The outer circle represents the diameter of the acoustic impedance tube, the honeycomb structure in the middle is the underwater sound-absorbing covering layer, and other areas not covered by the underwater sound-absorbing covering layer are filled and covered with a viscoelastic matrix material.

[0069] The underwater sound-absorbing covering layer 1 prepared by the present invention has an average sound absorption efficiency of 86% within the frequency range of 0.1-10 kHz.

[0070] Figure 6 The candidate configuration diagrams of the sound-absorbing unit cell of pure polyurethane rubber (A1), polyurethane rubber with only cavities added (A2), polyurethane rubber with only resonators added (A3), and polyurethane rubber with both cavities and resonators added (A4) are shown. Figure 7 The sound absorption curves of pure polyurethane rubber, polyurethane rubber with only cavity added, polyurethane rubber with only resonator added, and polyurethane rubber with both cavity and resonator added are shown. Figure 7 It can be seen that when the cavity and the resonator are added at the same time, the average sound absorption coefficient is greatly improved.

[0071] Figure 8 and Figure 9 The vibration mode displacement diagram and energy dissipation density diagram of pure polyurethane rubber, polyurethane rubber with only cavity added, polyurethane rubber with only resonator added, and polyurethane rubber with both cavity and resonator added are shown at 3.4kHz. Figure 8 and Figure 9 As can be seen from the figure, due to the coupling between the cavity and the resonator, incident sound waves (longitudinal waves) undergo waveform conversion near the viscoelastic interface between the two, transforming the longitudinal waves into shear waves, which increases the dissipation of the viscoelastic body. Therefore, it can be seen that waveform conversion contributes significantly to mid-frequency sound absorption (2kHz to 4kHz).

[0072] Taking manufacturing factors into consideration, the cylindrical unit was transformed into a regular hexagonal prism unit during the experimental manufacturing process, such as Figure 10 (a) and Figure 10 As shown in (b), the radius of the inscribed circle of the regular hexagon is 15 mm. Figure 11 The following diagram compares the absorption curves of a cylindrical element, a regular hexagonal prism element, and a regular hexagonal prism element with periodic boundary conditions. It can be observed that the absorption curves remain almost unchanged from the 2D rotational model to the 3D actual manufacturing model.

[0073] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance, characterized in that: The following steps are involved: S1: construct the initial configuration of the sound-absorbing unit cell; S2: Discretize the cavity in the initial configuration of the sound-absorbing unit cell into several unit cavity layers with equal height in the axial direction, thereby obtaining the discrete configuration of the sound-absorbing unit cell; then use the transfer matrix method to construct a prediction function, using the cavity porosity of all unit cavity layers as the input of the prediction function and the average sound absorption coefficient within the preset frequency range as the output of the prediction function; S3: Based on the prediction function, the discrete configuration of the sound absorbing unit cell is optimized to obtain the initial optimized configuration of the sound absorbing unit cell; S4: Add the resonant body to the initial optimized configuration of the sound absorbing unit cell and place the resonant body between two adjacent unit cavity layers to form a complete configuration of the sound absorbing unit cell. The number, thickness and radius of the resonant body are used as the input of the black box function, and the average sound absorption coefficient within the preset frequency range is used as the output of the black box function. Based on the black box function, the complete configuration of the sound-absorbing unit cell is optimized using the optimization method to obtain the final configuration of the sound-absorbing unit cell.

2. The method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance according to claim 1, characterized in that: 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, the cross-section of the cavity is trapezoidal, 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.

3. The method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance according to claim 2, characterized in that: The viscoelastic matrix includes a viscoelastic top layer, a viscoelastic middle layer and a viscoelastic bottom layer. The viscoelastic top layer and the viscoelastic bottom layer are respectively arranged on both sides of the viscoelastic middle layer. The interior of the viscoelastic middle layer is hollow and a cavity with a trapezoidal cross-section is formed inside the viscoelastic middle layer. 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 method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance according to claim 1, characterized in that: The S3 is specifically: Multiple optimization methods are used to optimize and solve the prediction function by changing the porosity of all unit cavity layers to obtain the corresponding optimal porosity solution vector. Then, based on the optimal porosity solution vector, the first sound-absorbing unit cell candidate configurations obtained by different optimization methods are generated. The optimal one is selected from several first sound-absorbing unit cell candidate configurations and recorded as the initial optimized configuration of the sound-absorbing unit cell.

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

6. The method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance according to claim 4, characterized in that: In S3, the first sound absorbing unit cell candidate configurations obtained by solving different optimization methods based on the solution vector of the optimal porosity are generated, including: The solution vector of the optimal porosity obtained by each optimization method is converted into the radius of all unit cavity layers. The unit cavity layers with too small radius are deleted, and the first sound-absorbing 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.

7. The method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance according to claim 4, characterized in that: The step of selecting the best one from among several first sound absorbing unit cell candidate configurations and recording it as the first optimized configuration of the sound absorbing unit cell comprises: First, a candidate configuration of the first sound-absorbing unit cell is selected, in which the frequency of the first sound-absorbing peak is low and the sound absorption coefficient after the first sound-absorbing peak is stable above a preset confidence level. Then, the configuration with the least unit cavity layer among the selected candidate configurations of the first sound-absorbing unit cell is used as the initial optimization configuration of the sound-absorbing unit cell.

8. The method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance according to claim 1, characterized in that: In S4, the black box function is obtained after encapsulating the finite element software. After optimizing and solving the black box function using a simulated annealing algorithm that is not based on gradients, the number, thickness and radius of the resonant bodies are obtained, thereby obtaining the final configuration of the sound-absorbing unit cell.

9. The method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance according to claim 1, characterized in that: In 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, radius and average sound absorption coefficient of resonators is generated through finite element batch simulation. The sample library is used to train the neural network until the training is completed, and the trained neural network is used as the proxy model.

10. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method for designing an underwater sound-absorbing covering layer based on the coupling of cavity resonance and local resonance as described in any one of claims 1 to 9 are implemented.

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