Sound absorption and insulation integrated composite underwater acoustic structure and preparation method

Abstract

The sound absorption and insulation integrated composite underwater acoustic structure comprises a sound absorption layer, the sound absorption layer comprises a sound absorption layer mechanical frame, and the sound absorption layer mechanical frame is of a lattice structure; the lattice structure comprises a three-dimensional curved surface structure with the volume fraction gradually changing in a gradient mode and internally provided with a preset hole cavity. The generation method comprises the steps that S1, a three-dimensional space corresponding to the preset hole cavity is discretized into a specific area NaN; s2, determining an implicit function g (x, y, z) of the three-dimensional curved surface structure; s3, carrying out volume fraction gradual change through an interpolation algorithm, calculating values of different contour surfaces, and realizing linear and exponential nonlinear volume gradual change; s4, calculating values t of different contour surfaces of the implicit function to enable the implicit function to meet g (x, y, z) 2-t2 = 0; and S5, drawing a contour surface and a sealing cover, performing triangulation, and outputting a. Stl file. According to the invention, the defects that the mechanical bearing performance of the current underwater sound absorption polymer is weak, the boundary impedance of the composite structure is difficult to match, and the sound absorption and sound insulation performance cannot be considered are overcome, and a new technical scheme is provided for the design of the composite underwater sound absorption structure.

Description

Technical Field

[0001] The present invention belongs to the field of underwater sound-absorbing materials, and particularly relates to a sound absorption and insulation integrated composite underwater acoustic structure and a preparation method thereof. Background Art

[0002] The concealment of an underwater platform is one of the core indicators for its performance evaluation. To reduce the sound target strength, the outer surface of the platform is usually covered with an acoustic covering layer, which is used to absorb sonar sound waves and suppress the outward propagation of internal noise. The performance of the acoustic covering layer depends on the damping characteristics of the sound-absorbing material and the acoustic structure design. Common underwater sound-absorbing materials are low-modulus viscoelastic polymers, such as modified rubber and polyurethane, which enhance the sound-absorbing effect by adjusting the elastic and damping characteristics. At the same time, through the design of specific acoustic structures inside the material, such as introducing cavities and resonance units, the low-frequency sound-absorbing performance can be effectively improved.

[0003] However, the hydrostatic pressure resistance of the sound-absorbing polymer and its cavity composite structure is poor. In deep water, both the polymer and the cavity will be squeezed by the hydrostatic pressure and harden and deform, resulting in a rapid decline in the sound-absorbing performance. Therefore, it is necessary to design a mechanical support structure to bear and decompose the hydrostatic pressure. For example, a frame made of hard materials (such as aluminum alloy, fiberglass, etc.) is used to limit the deformation of the sound-absorbing material to maintain its sound-absorbing performance. The foam structure and the lattice structure have great potential in improving the mechanical bearing performance. The foam structure has the characteristics of high strength and light weight, and can provide mechanical support for the acoustic material and structure. However, in practical applications, the foaming process control of the foam material is difficult, the porosity and pore size distribution are difficult to accurately control, and internal structural defects are likely to occur during the manufacturing process. At the same time, the fatigue strength and fracture toughness of the foam structure are relatively low, and it is prone to failure especially under cyclic loading, which restricts its wide application in some fields. In contrast, the lattice structure has higher design flexibility and controllability through the array design of unit cells. The geometric shape and arrangement of the lattice structure can be precisely adjusted to optimize the mechanical properties. In addition, the uniformity of the structure can be better controlled during the manufacturing process of the lattice structure, and defects can be reduced. With the help of advanced technologies such as additive manufacturing, the lattice structure can achieve complex internal structure designs, making it have significant advantages in lightweight and high-performance engineering applications.

[0004] Mechanical support structures are usually made of rigid materials to limit the deformation of the sound-absorbing materials. However, the acoustic impedance of these materials often shows significant differences between the sound-absorbing layer and the surrounding water environment. The strong impedance mismatch will cause sound waves to reflect at the layer interface, thus reducing the overall sound-absorbing effect. In addition, the geometric design and material properties of the support structure may also introduce additional sound scattering and multi-path propagation effects, further increasing the difficulty of impedance matching. Therefore, when designing the acoustic covering layer, while meeting the structural strength requirements, it is challenging to minimize the negative impact caused by impedance mismatch through optimizing the material combination and interface design.

[0005] In the process of reducing the acoustic target strength of underwater platforms, it is not only necessary to reduce the reflection of external sonar waves, but also to prevent the internal noise from spreading outwards. Sound absorption and sound insulation are two different functions. Excellent sound-absorbing performance of materials does not mean equally good sound-insulating performance. At present, most acoustic covering layers can only perform well in either sound absorption or sound insulation, and it is difficult to achieve excellent performance in both sound absorption and sound insulation. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide an integrated sound absorption and insulation composite underwater acoustic structure and its preparation method, to solve the shortcomings such as the weak mechanical bearing performance of current underwater acoustic absorption polymers, the difficulty in matching the boundary impedance of composite structures, and the inability to balance sound absorption and sound insulation performance, and to provide a new technical solution for the design of composite underwater acoustic absorption structures.

[0007] To achieve the above purpose, the present invention provides an integrated sound absorption and insulation composite underwater acoustic structure, including a sound-absorbing layer, and the sound-absorbing layer includes a sound-absorbing layer mechanical framework, and the sound-absorbing layer mechanical framework is a lattice structure; The lattice structure includes a three-dimensional curved surface structure with a gradually changing volume fraction and preset cavities inside, and the generation method includes the following steps: S1. Discretize a specific area of the three-dimensional space corresponding to the preset cavity into NaN; S2. Determine the implicit function g(x, y, z) of the three-dimensional curved surface structure, and adopt a three-dimensional minimal surface or catenoid surface with zero mean curvature such as Gyroid, Diamond or Primitive; S3. Perform a gradual change of the volume fraction through an interpolation algorithm, calculate the values of different isosurfaces, and realize a uniform change or a change along the exponential function trend of the volume fraction; specifically: set the starting value and the ending value of the volume fraction gradual change, and determine the volume fraction corresponding to each position in the discretized three-dimensional space through the gradient gradual change function; where z is the z-axis coordinate, is the volume fraction at one end of the geometric structure in the z-axis coordinate, is the volume fraction at the other end of the geometric structure in the z-axis coordinate; S4. Calculate the values t of different isosurfaces of the implicit function, so that the implicit function satisfies g(x, y, z) 2 -t 2 = 0; S5. Draw the isosurface and the cover, perform triangulation, and output as a.stl file.

[0008] Furthermore, step S1 is specifically: determine the range of the three-dimensional space and perform discretization processing on it, and set the points within the target range to NaN, that is, "not a number", which do not participate in the subsequent structure generation, and this area corresponds to the space of the preset cavity.

[0009] Furthermore, step S5 is specifically: in the MATLAB software, use the isosurface function and the isocaps function to draw the isosurface of the three-dimensional corrugated surface according to the implicit function in the discrete coordinate dataset [x, y, z], use the triangulation function to perform triangular mesh division on the isosurface, and obtain the corresponding face and vertex data [F, V] and output it for the structural modeling analysis.

[0010] Furthermore, the lattice structure of the acoustic absorption layer mechanical framework is a three-dimensional curved surface structure with a gradually changing gradient of volume fraction and containing a preset cavity inside. The shape and size of the preset cavity are parametrically designed to reserve space for the acoustic absorption cavity and the mass block.

[0011] Furthermore, the underwater acoustic structure includes a plurality of periodically arranged unit cells. The unit cell is in the form of a multi-layer structure, including an upper surface layer, an acoustic absorption layer, and a sound insulation layer; the acoustic absorption layer is located between the upper surface layer and the sound insulation layer; Furthermore, the acoustic absorption layer includes an acoustic absorption layer mechanical framework and a viscoelastic acoustic absorption polymer filled in the mechanical framework. The mechanical framework adopts a lattice support structure. The acoustic absorption polymer is provided with internal cavities and mass blocks to achieve a multi-source acoustic absorption structure; the sound insulation layer is a sandwich structure of anisotropic lattices. By integrating the acoustic absorption structure and the sound insulation structure, the integration of acoustic absorption and sound insulation is achieved; the composite underwater acoustic structure is applicable to the environment where both ends are immersed in water medium. When the sound wave is incident from the upper surface, it shows acoustic absorption and sound insulation effects, and when the sound wave is incident from the sound insulation layer, it shows a sound insulation effect.

[0012] Furthermore, the polymer inside the acoustic absorption layer has internal cavities and steel resonant mass blocks with specific external dimensions; the mechanical framework is a lattice structure, and the volume fraction of the mechanical framework shows a uniform distribution or a gradually changing gradient distribution. When showing a gradually changing gradient distribution, the volume fraction at one end close to the upper surface layer of the unit cell is the smallest, so that the impedance matches the water medium, and more incident sound waves enter the composite structure. At the same time, the volume fraction gradually increases along the sound wave transmission direction and reaches the maximum when approaching the sound insulation layer, so that the sound energy is continuously dissipated in the gradually changing gradient structure.

[0013] Furthermore, the internal cavity of each cell unit includes two frustum-shaped cavities arranged vertically, namely the first cavity located above and the second cavity located below. The shape of each cavity is a frustum with a smaller diameter on the upper surface than on the lower surface. The cylindrical mass block is located between the first cavity and the second cavity and has a gap between the lower surface of the first cavity and the upper surface of the second cavity.

[0014] Furthermore, the sound insulation layer is an anisotropic honeycomb lattice sandwich panel structure, including an upper layer, a lower layer, and a honeycomb lattice beam frame in the middle. All three parts are made of aluminum alloy material, and an air cavity is formed inside the honeycomb lattice.

[0015] On the other hand, the present invention provides a preparation method for an integrated sound absorption and insulation composite underwater acoustic structure, and the method includes the following preparation steps: S1. Obtain a lattice structure frame with characteristic wall thickness and external dimensions and an anisotropic honeycomb lattice sandwich sound insulation layer through additive manufacturing; S2. Layer the cavities and mass blocks inside the sound absorption layer, and use a mold to pour each layer separately; after each layer is completed, bond them in sequence to form a sound absorption module, and combine and assemble the sound absorption module and the lattice structure frame to obtain a lattice structure core material containing cavities and mass blocks; S3. Use a modified polymer to pour the lattice structure core material containing cavities and mass blocks at the frame part, and after the polymer is cured at room temperature or by heating and then demolded, obtain a lattice structure embedded with a solid viscoelastic polymer, thereby forming the sound absorption layer of the integrated sound absorption and insulation structure; S4. Stick the pre-made fiber-reinforced resin material panel on the upper surface of the sound absorption layer, and stick the sound insulation layer on the lower surface of the sound absorption layer to obtain an underwater integrated sound absorption and insulation structure.

[0016] The effective benefits of the present invention are as follows: 1. The present invention proposes an integrated sound absorption and insulation composite underwater acoustic structure and its preparation method. Using a periodic lattice structure as the mechanical load-bearing frame of the sound absorption layer, it has excellent design flexibility and controllability. The geometric shape and internal budget cavity of the lattice structure can be parametrically adjusted, and through mechanical property optimization, the specific strength, specific stiffness, and durability are improved. In addition, the lattice structure can control the acoustic performance by adjusting the unit size and shape, so as to further enhance the sound absorption and insulation effects while meeting the mechanical requirements.

[0017] 2. In the mechanical framework adopted in the present invention, viscoelastic sound-absorbing polymers are filled, and multi-source sound-absorbing mechanisms are introduced by adding sound-absorbing units such as cavities and mass blocks to improve the low-frequency broadband sound-absorbing performance. At the same time, the volume fraction of the mechanical framework of the sound-absorbing layer can be designed gradiently, so that the impedance of the sound-absorbing composite material changes gradually, thereby effectively reducing the reflection of sound waves on the surface and significantly improving the sound-absorbing efficiency. In addition, the adopted mechanical framework is easy to be processed integrally, enhancing the feasibility and economy of manufacturing.

[0018] 3. The sound-insulating layer of the present invention adopts a highly anisotropic lattice sandwich structure, which has significantly different sound wave propagation characteristics in different directions, changes the propagation path and speed of sound waves in the material, and thus produces different sound wave reflection, scattering and attenuation effects in each direction. This design can effectively reduce the transmitted energy of sound waves. At the same time, the highly anisotropic lattice structure can also generate a sound band gap by designing its internal periodic or aperiodic characteristics, further enhancing its sound-insulating effect.

[0019] An integrated sound absorption and insulation composite underwater acoustic structure and its preparation method proposed by the present invention have easily available raw materials, a mature preparation process, and strong designability of the geometric parameters of the lattice structure. The acoustic and mechanical properties of the underwater sound-absorbing material can be flexibly adjusted to meet the integrated requirements of structural functions such as high hydrostatic pressure resistance, wide-frequency high absorption, low reflection, impact resistance, light weight and high strength, providing support for the design and development of a low acoustic target strength shell for underwater platforms. Brief Description of the Drawings

[0020] Figure 1 is a three-dimensional schematic diagram of the integrated sound absorption and insulation composite underwater acoustic structure arranged periodically in Embodiment 1 of the present invention; Figure 2 is a three-dimensional schematic diagram of the unit cell structure of the integrated sound absorption and insulation composite underwater acoustic structure in Embodiment 2; Figure 3 is a side view of the unit cell structure of the integrated sound absorption and insulation composite underwater acoustic structure in Embodiment 2; Figure 4 is a simulation modeling diagram of the integrated sound absorption and insulation composite underwater acoustic structure in Embodiment 2; Figure 5 is a comparison of the sound absorption, transmission and reflection coefficients of the integrated sound absorption and insulation composite underwater acoustic structure in Embodiment 2 varying with frequency under a water pressure of 2 MPa; Figure 6 is a comparison of the sound insulation amount of the integrated sound absorption and insulation composite underwater acoustic structure in Embodiment 2 varying with frequency under a water pressure of 2 MPa; Figure 7 is the maximum displacement of the upper and lower surfaces of the integrated sound absorption and insulation composite underwater acoustic structure in Embodiment 2 under different hydrostatic pressures; Figure 8 It is a three-dimensional schematic diagram of the sound absorption and insulation integrated composite underwater acoustic structure arranged periodically in Embodiment 1; Figure 9 It is a three-dimensional schematic diagram of the unit cell structure of the sound absorption and insulation integrated composite underwater acoustic structure in Embodiment 1; Figure 10 It is a side view schematic diagram of the unit cell structure of the sound absorption and insulation integrated composite underwater acoustic structure in Embodiment 1; Figure 11 It is a simulation modeling diagram of the sound absorption and insulation integrated composite underwater acoustic structure in Embodiment 1; Figure 12 It is a design flow chart of the gradient-varying Gyroid mechanical framework with a preset cavity in Embodiment 1; Figure 13 It is a comparison of the sound absorption, transmission, and reflection coefficients of the sound absorption and insulation integrated composite underwater acoustic structure with frequency under a water pressure of 2 MPa in Embodiment 1; Figure 14 It is a comparison of the sound insulation amount of the sound absorption and insulation integrated composite underwater acoustic structure with frequency under a water pressure of 2 MPa in Embodiment 1; Figure 15 It is the maximum displacement of the upper and lower surfaces of the sound absorption and insulation integrated composite underwater acoustic structure under different hydrostatic pressures in Embodiment 1; Figure 16 It is a schematic diagram of the sound absorption and insulation integrated structure in Embodiment 3; Figure 17 It is a schematic diagram of the sound absorption layer of the sound absorption and insulation integrated structure in Embodiment 3; Figure 18 It is a schematic diagram of the sound insulation layer of the sound absorption and insulation integrated structure in Embodiment 3; Figure 19 It is a hierarchical schematic diagram of the sound absorption unit part in Embodiment 3; Figure 20 It is the mold used for pouring the first layer of the sound absorption unit in Embodiment 3. Then, a modified polyurethane material is poured into the mold, and after curing and demolding, the first layer of the sound absorption module is obtained as Figure 18 shown; Figure 21 It is the mold used for pouring the second layer of the sound absorption unit in Embodiment 3. The parts of the mold are made by additive manufacturing, as shown in Figure 21 (a). When in use, the parts are assembled into the Figure 21 (b) style. Then, a modified polyurethane is poured into the mold, and after curing and demolding, the second layer of the sound absorption unit is obtained as Figure 18 shown; Figure 22 It is the mold used for pouring the third layer of the sound absorption unit in Embodiment 3. The parts of the mold are made by additive manufacturing, as Figure 22As shown in (a), during use, the parts are combined into Figure 22 (b) style. Then, modified polyurethane is poured into the mold. After curing and demolding, steel mass blocks are placed in the reserved hole positions to obtain the third layer of the sound absorption module as shown in Figure 18 ; Figure 23 is the mold used for pouring the fourth layer of the sound absorption unit in Example 3. The parts of the mold are manufactured by additive manufacturing. As shown in Figure 23 (a), during use, the parts are combined into Figure 23 (b) style. Then, modified polyurethane is poured into the mold. After curing and demolding, the fourth layer of the sound absorption module is obtained, and the complete sound absorption module is combined in the manner shown in Figure 18 ; Figure 24 are the left and right parts of the Gyroid mechanical framework obtained by additive manufacturing in Example 3; Figure 25 is to combine the framework and the sound absorption unit in Example 3 (note the up and down positions of the sound absorption module); Figure 26 is the mold used for pouring the framework gap in Example 3. The mold is manufactured by additive manufacturing; Figure 27 is to place the combined module in the mold for pouring modified polyurethane. After curing and demolding, the sound absorption layer is obtained. Specific implementation mode

[0021] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0022] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0023] In the description of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0024] The following will Figures 1 - 27 describe the specific embodiments of the present invention in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0025] The present invention provides an integrated sound absorption and insulation composite underwater acoustic structure and a preparation method thereof. The integrated sound absorption and insulation composite underwater acoustic structure includes a cell unit, and the cell units are arranged periodically. The cell unit presents a multi-layer structure form, and the upper surface layer is a continuous fiber reinforced resin panel. The bottom of the upper surface layer is connected to the sound absorption layer, and the sound absorption layer is composed of a mechanical framework, a viscoelastic sound absorption polymer filled in the framework, a cavity with a specific shape and size inside the polymer, and a steel resonant mass block. The mechanical framework adopts a lattice structure such as a hexagonal framework and a three-dimensional curved surface framework with a preset cavity, and the volume fraction can be set to be gradient-variable. The bottom of the sound absorption layer is connected to the sound insulation layer, and the sound insulation layer is a sandwich structure containing an anisotropic honeycomb lattice. By integrating the sound absorption structure and the sound insulation structure, the integration of sound absorption and sound insulation is realized. The shape of the cell can be a quadrangular prism or a hexagonal prism, and the lattice constant and thickness of the cell can be adjusted according to the wavelength of the incident sound wave.

[0026] The mechanical structure of the sound-absorbing layer can adopt lattice structures such as a hexagonal frame structure (shown in Embodiment 1), a three-dimensional curved surface structure (shown in Embodiment 2), etc. The volume fraction of the lattice structure can be gradually changed in a gradient manner. When the lattice structure shows a gradient change distribution, the volume fraction at one end close to the upper surface layer of the unit cell is the smallest, enabling the impedance to match the water medium, and more incident sound waves can enter the interior of the composite structure. At the same time, the volume fraction gradually increases along the sound wave transmission direction and reaches the maximum at one end close to the sound insulation layer, causing the sound energy to dissipate continuously in the gradient change structure. The processing of the lattice structure framework adopts additive manufacturing technology, and the material can be selected from aluminum alloy, titanium alloy, or high-modulus resins, high-modulus ceramics, etc. with a modulus reaching the order of hundreds of megapascals or even higher. The viscoelastic polymer filled in the lattice structure framework can be rubber, polyurethane, and their modified polymers, which have excellent damping performance and wide-temperature sound absorption performance. The viscoelastic polymer is filled in the lattice structure framework, and the polymer filled in the framework cavity has cavities and mass blocks inside. The upper panel of the unit cell is made of glass fiber-reinforced resin material or carbon fiber-reinforced resin material, which has good sound wave transmission performance. This panel can evenly distribute the external pressure to the lattice structure framework, thereby effectively reducing the structural loss caused by stress concentration and significantly reducing the deformation of the internal viscoelastic polymer. Combining the sound-absorbing structure and the sound-insulating structure together can not only absorb the incident sound waves from above and reduce reflection but also isolate the incident sound waves from below and reduce transmission. In the sound insulation layer, the sound insulation performance can be adjusted by changing the wall thickness of the anisotropic honeycomb lattice. The smaller the wall thickness, the better the sound insulation performance in the low-frequency band, but the structural strength will also decrease. Placing the integrated sound absorption and insulation composite underwater acoustic structure in an environment where both ends are immersed in water medium, when the sound wave is incident from the upper surface, it shows high sound absorption and high sound insulation, and when the sound wave is incident from the sound insulation layer, it shows high sound insulation.

[0027] Embodiment 1 As Figure 8 shown, the integrated sound absorption and insulation composite underwater acoustic structure of Embodiment 1 is a multi-interlayer structure mode, which is formed by the periodic arrangement of multiple quadrangular prism unit cells. Both Embodiment 1 and Embodiment 2 adopt an integrated structure combining a sound-absorbing layer and a sound-insulating layer. As Figure 9 、 10 shown, Embodiment 1 is the same as Embodiment 2 in the upper surface layer 1 and the sound insulation layer 3 parts, and the difference is that Embodiment 1 adopts a different mechanical framework structure for the sound-absorbing layer 2.

[0028] The sound-absorbing layer 2 in this Embodiment 1 adopts a preset pore cavity Gyroid three-dimensional curved surface structure, as Figure 10 shown. The Gyroid support structure 21 is a three-dimensional minimal surface structure, which can achieve high stiffness, high compressive strength, and high surface area. It is made of aluminum alloy material with a density of 2700 kg / m 3, the Young's modulus is 700 MPa, the Poisson's ratio is 0.3, the equivalent isotropic loss factor is 0.001, and the volume fraction of the frame structure 21 gradually changes from 35% to 20% from bottom to top. The viscoelastic polymer 22 uses modified rubber with a density of 960 kg / m 3 , the Young's modulus is 20 MPa, the Poisson's ratio is 0.49, and the equivalent isotropic loss factor is 0.6. The characteristic density of water is 1000 kg / m 3 , and the sound speed is 1500 m / s.

[0029] As Figure 11 shown, the finite element model of the integrated sound absorption and insulation composite underwater acoustic structure includes a water area 41 and a composite acoustic structure 42. In this case, the finite element method is used to model the acoustic characteristics of the unit cell structure in the water backing environment at both the acoustic wave incident end and the outgoing end, and analyze its water pressure resistance performance and the sound absorption and insulation performance of the structure under the action of hydrostatic pressure.

[0030] Among them, the design method of the preset cavity Gyroid frame with a gradient change in the volume fraction of the sound absorption layer is as Figure 12 shown, including the following steps: ① Discretize a specific area of the three-dimensional space corresponding to the preset cavity as NaN. Specifically: determine the range of the three-dimensional space and perform discretization processing on it, and set the points within the target range as NaN, that is, "not a number", which does not participate in the subsequent structure generation, and this area corresponds to the space of the preset cavity.

[0031] ② Determine the implicit function of the surface. Specifically: determine the implicit function g(x,y,z) of Gyroid, as shown below.

[0032] Among them, the parameters a, b, and c are the dimensions of the unit cell in the x, y, and z axis directions respectively.

[0033] ③ Perform volume fraction gradient change through the interpolation algorithm and calculate the values of different isosurfaces. Specifically: set the starting value and ending value of the volume fraction gradient change, and determine the volume fraction corresponding to each position in the discretized three-dimensional space through the gradient change function.

[0034] Among them, z is the z-axis coordinate, is the volume fraction of the geometric structure at one end of the z-axis coordinate, is the volume fraction of the geometric structure at the other end of the z-axis coordinate.

[0035] ④ Calculate the values of different isosurfaces of the implicit function so that the implicit function satisfies g(x,y,z) 2 -t 2= 0. In this Example 1, the volume fraction shows a linear gradient change with respect to the z - coordinate in the range of 20 vol% to 35 vol%, that is .

[0036] ⑤ Draw the isosurface and capping, perform triangulation, and output as a.stl file. Specifically: In the MATLAB software, use the isosurface function and isocaps function to draw the isosurface of the three - dimensional corrugated surface according to the implicit function in the discrete coordinate dataset [x, y, z], use the triangulation function to perform triangular mesh division on the isosurface, obtain the corresponding face and vertex data [F, V] and output them for the structural modeling analysis.

[0037] Figure 13 Shows the variation of the sound absorption, reflection, and transmission coefficients of the sound absorption and insulation integrated composite underwater acoustic structure with frequency under a water pressure of 2 MPa. It can be seen that the composite underwater acoustic structure has excellent water pressure resistance. For sound waves in the range of 1 kHz to 3 kHz, the average sound absorption coefficient is greater than 0.55; for sound waves in the range of 3 kHz to 10 kHz, the sound absorption coefficient is greater than 0.85.

[0038] Figure 14 Shows the variation of the sound insulation amount of the sound absorption and insulation integrated composite underwater acoustic structure with frequency under a water pressure of 2 MPa. It can be seen that the underwater sound insulation performance of the composite underwater acoustic structure is excellent. The average sound insulation amount for sound waves in the range of 1 kHz to 3 kHz is greater than 5 dB. The sound insulation amount reaches local peaks at 4 kHz and 8 kHz respectively. This may be because some structural units of the composite structure start to resonate with sound waves of specific frequencies, thereby absorbing or scattering sound waves, resulting in an increase in the sound insulation amount. For sound waves in the range of 1 kHz to 10 kHz, although the variation of the sound insulation amount has fluctuations, the overall trend is still upward.

[0039] Figure 15 Gives the variation of the maximum displacement of the upper and lower surfaces of the sound absorption and insulation integrated composite underwater acoustic structure under different hydrostatic pressures, which is used to analyze the water pressure resistance performance of the material. It can be seen that the underwater acoustic material can effectively bear a hydrostatic pressure of 10 MPa, and the bearing performance is excellent. The maximum deformation of the material increases approximately linearly with the increase of the hydrostatic pressure, indicating that the material is in the elastic deformation range and no damage has occurred.

[0040] In summary, the underwater sound absorption material proposed by the present invention has good low - frequency broadband sound absorption performance. When the sound absorption material is directly placed under the condition of being immersed in water at both ends, the underwater acoustic material has high sound absorption, low reflection, and high sound insulation performance.

[0041] Example 2 As Figure 1 shown, according to the sound absorption and insulation integrated composite underwater acoustic structure of the present invention, this structure is a multi - sandwich structure mode, which is formed by the periodic arrangement of multiple hexagonal prism cell units. AsFigure 2 , 3 As shown in 3 , the cell unit of the integrated sound absorption and insulation composite underwater acoustic structure includes an upper surface layer 1, a sound absorption layer 2, and a sound insulation layer 3. Among them, the upper surface layer 1 is a continuous fiber-reinforced resin panel. The sound absorption layer 2 is located between the upper surface layer 1 and the sound insulation layer 3 and is formed by arranging multiple hexagonal cell units periodically. It includes a mechanical framework 21 and a viscoelastic sound absorption polymer 22 filled in the mechanical framework. An internal cavity 23 and a mass block 24 are provided in the sound absorption polymer 22. In this embodiment 2, the mechanical framework 21 is a hexagonal lattice support structure made of aluminum alloy, and the volume fraction is a fixed value. The sound insulation layer 3 is an anisotropic honeycomb lattice sandwich structure, including honeycomb lattice beams 31, cavities 32, and panels 33. The integrated sound absorption and insulation composite underwater acoustic structure in Embodiment 2 is a hexagonal prism with a lattice constant of 29.5 mm and an overall thickness of 80 mm. The cylinder is a sandwich structure including an upper surface layer, a sound absorption layer, and a sound insulation layer. The upper panel is a fiber-reinforced resin with a thickness of 2 mm. The fiber-reinforced resin panel is a glass fiber-reinforced resin with an elastic modulus of 1800 MPa, a Poisson's ratio of 0.15, and a density of 1600 g / cm 3 .

[0042] In Embodiment 2, Figure 3 is a side view of the structure of a single cell unit. The obtained hexagonal mechanical framework 21 includes 6 rectangular side walls, and each side wall has a hollow structure. A mass block 24 is provided at the center of each hexagonal framework. An internal cavity 23 is provided above and below the mass block 24 respectively. The internal cavity 23 and the mass block 24 are formed in the sound absorption polymer 22 and do not contact the framework. The internal cavity of each cell unit includes two frustum-shaped cavities arranged vertically, namely the first cavity located above and the second cavity located below. The diameter of the circular upper surface of each cavity is smaller than the diameter of the circular lower surface. The design of the cavity shape utilizes the impedance matching principle. Compared with a cylindrical cavity, the frustum cavity has better sound absorption performance. The cylindrical mass block is located between the first cavity and the second cavity and has a gap between the lower surface of the first cavity and the upper surface of the second cavity. The diameter of the circular lower surface of the first cavity is smaller than the diameter of the circular upper surface of the second cavity; the height of the first cavity is smaller than the height of the second cavity; the height of the cylindrical mass block is smaller than the height of the first cavity; the diameter of the cylindrical mass block is larger than the diameter of the circular upper surface of the second cavity; preferably, the diameter of the cylindrical mass block is equal to the diameter of the circular lower surface of the second cavity.

[0043] The material of the hexagonal framework 21 is aluminum alloy, and the specific parameters are a density of 2700 kg / m 3 , a Young's modulus of 7000 MPa, a Poisson's ratio of 0.3, and an equivalent isotropic loss factor of 0.001. The viscoelastic sound absorption polymer uses modified rubber with a density of 960 kg / m 3, the Young's modulus is 20 MPa, the Poisson's ratio is 0.49, and the equivalent isotropic loss factor is 0.6. The characteristic density of water is 1000 kg / m 3 , and the sound speed is 1500 m / s.

[0044] The sound insulation layer 3 adopts an anisotropic honeycomb lattice sandwich structure, including upper and lower faceplates 33 and honeycomb lattice beams 31 in the middle. The overall thickness is 20 mm. The upper and lower layers are aluminum alloy faceplate layers 33, and the honeycomb lattice beams 31 are made of aluminum alloy. Cavities 32 are formed inside the honeycomb lattice. The inside of the cavity 32 is air. The main axis of the honeycomb lattice in this structure is inclined to the horizontal direction, which makes the acoustic wave propagation characteristics in different directions significantly different. This design has a low acoustic impedance and forms an impedance mismatch with water, which can effectively reduce the transmitted energy of acoustic waves.

[0045] As Figure 4 shown, the finite element model of the integrated sound absorption and insulation composite underwater acoustic structure includes a water area 41 and a composite acoustic structure 42. In this case, the acoustic characteristics of the unit cell structure are modeled under the water backing environment at both the acoustic wave incident end and the outgoing end to analyze its water pressure resistance performance and the sound absorption and insulation performance of the structure under hydrostatic pressure.

[0046] Figure 5 Shows the variation of the sound absorption, reflection, and transmission coefficients of the integrated sound absorption and insulation composite underwater acoustic structure with frequency under 2 MPa water pressure. It can be seen that the water pressure resistance performance of the composite underwater acoustic structure is excellent. For acoustic waves in the range of 1 kHz to 3 kHz, the average sound absorption coefficient is greater than 0.55; for acoustic waves in the range of 3 kHz to 10 kHz, the sound absorption coefficient is greater than 0.8.

[0047] Figure 6 Shows the variation of the sound insulation amount of the integrated sound absorption and insulation composite underwater acoustic structure with frequency under 2 MPa water pressure. It can be seen that the underwater sound insulation performance of the composite underwater acoustic structure is excellent. The average sound insulation amount for acoustic waves in the range of 1 kHz to 3 kHz is greater than 5 dB. The sound insulation amount reaches local peaks at 3 kHz, 5 kHz, and 6.5 kHz respectively. This may be because some structural units of the composite structure start to resonate with acoustic waves of specific frequencies, thereby absorbing or scattering acoustic waves, resulting in an increase in the sound insulation amount. After the acoustic wave frequency is greater than 4 kHz, although the variation of the sound insulation amount fluctuates, the overall trend is still upward.

[0048] Figure 7 Gives the variation of the maximum displacement of the upper and lower surfaces of the integrated sound absorption and insulation composite underwater acoustic structure under different hydrostatic pressures, which is used to analyze the water pressure resistance performance of the material. It can be seen that the underwater acoustic material can effectively bear a hydrostatic pressure of 10 MPa, and the bearing performance is excellent. The maximum deformation of the material increases approximately linearly with the increase of the hydrostatic pressure, indicating that the material is in the elastic deformation range and no damage occurs.

[0049] In summary, the underwater sound-absorbing material proposed by the present invention has good low-frequency broadband sound-absorbing performance. When the sound-absorbing material is directly placed in the environment immersed in water media at both ends, it has high sound absorption, low reflection, and high sound insulation performance.

[0050] Example 3 According to the preparation method of the integrated sound absorption and insulation composite underwater acoustic structure of the present invention, the exemplary structure is as Figure 16 shown, in which the structures of the sound-absorbing layer and the sound-insulating layer are respectively shown in Figure 17 and Figure 18 .

[0051] The preparation steps are as follows: S1. Obtain a lattice structure framework with characteristic wall thickness and external dimensions and an anisotropic honeycomb lattice sandwich sound-insulating layer through additive manufacturing (3D printing). The sound-insulating layer can be completed by one printing, while the lattice structure framework of the sound-absorbing layer needs to be embedded with sound-absorbing units such as cavities and mass blocks. In Example 1, the sound-absorbing layer uses a preset cavity Gyroid framework and needs to be printed in two parts. If the hexagonal framework in Example 1 is used, it can be completed by one printing; S2. The cavities and mass blocks inside the sound-absorbing layer are stratified, as Figure 19 shown. The sound-absorbing modules inside the sound-absorbing layer are divided into four layers. The bottom layer is the first layer, the second layer is above the first layer, the second layer contains the second cavity, the third layer is above the second layer, the third layer contains the mass block, the fourth layer is above the third layer, and the fourth layer contains the first cavity. Use the Figures 20 - 23 shown first to fourth molds to pour each layer respectively. Finally, the four cast layers are glued together in sequence to form a sound-absorbing module, and the sound-absorbing module and the lattice structure framework are assembled together to obtain a lattice structure core material containing cavities and mass blocks, as Figure 25 shown; at this time, there is still a gap between the sound-absorbing module and the lattice structure framework.

[0052] S3. Place the assembled lattice structure core material in the fifth mold as Figure 26 shown. The fifth mold is a circular ring structure. Then, as Figure 27 shown, use a modified polymer for pouring. After the polymer is cured at room temperature or by heating and demolded, a lattice structure embedded with a solid viscoelastic polymer is obtained, that is, the sound-absorbing layer of the integrated sound absorption and insulation structure; S4. Stick the pre-made fiber-reinforced resin material panel on the upper surface of the sound-absorbing layer, and stick the sound-insulating layer to the lower surface of the sound-absorbing layer, then the underwater integrated sound absorption and insulation structure of the present invention is obtained.

[0053] Among them, in step S2, the following steps are further included: S201. Use Figure 20The first mold used for pouring the first layer of the sound-absorbing unit. In this embodiment, the first mold is a circular ring structure, and the first mold can be fabricated by additive manufacturing. Pour the modified polyurethane material into the first mold, and after curing and demolding, the first layer of the sound-absorbing module as shown in Figure 19 is obtained.

[0054] S202. Fabricate two parts that can be combined into the second mold by additive manufacturing. The specific structure is as shown in Figure 21 (a). One of the parts is a circular ring, and the other part is a bottom plate adapted to the circular ring. The bottom plate is provided with a number of frustum-shaped protrusions having the same structure as the second cavity structure. When in use, the two parts are combined into the second mold with an integral structure as shown in Figure 21 (b), and the second mold is used for pouring the second layer of the sound-absorbing unit. Pour the modified polyurethane into the second mold, and after curing and demolding, the second layer of the sound-absorbing unit as shown in Figure 19 is obtained.

[0055] S203. Fabricate two parts of the third mold by additive manufacturing, as shown in Figure 22 (a), including a circular ring and a bottom plate adapted to the circular ring. The bottom plate is provided with a number of protrusions having the same structure as the mass block structure. When in use, the parts are combined into an integral structure, thereby forming the third mold used for pouring the third layer of the sound-absorbing unit, as shown in Figure 22 (b). Then pour the modified polyurethane into the third mold, and after curing and demolding, place the steel mass block in the reserved hole position to obtain the third layer of the sound-absorbing module as shown in Figure 19 .

[0056] S204. Fabricate two parts of the fourth mold by additive manufacturing, as shown in Figure 23 (a), including a circular ring and a bottom plate adapted to the circular ring. The bottom plate is provided with a number of protrusions having the same structure as the first cavity structure. When in use, the two parts are combined into an integral structure, thereby forming the fourth mold used for pouring the fourth layer of the sound-absorbing unit, as shown in Figure 23 (b). Then pour the modified polyurethane into the fourth mold, and after curing and demolding, the fourth layer of the sound-absorbing module is obtained, and the complete sound-absorbing module is combined in the manner as shown in Figure 19 .

[0057] The sound-absorbing layer structures of Embodiment 1 and 2 are both realized by this method.

[0058] Any process or method description, whether in the flowchart of the present invention or described in other ways herein, can be understood to represent a module, segment, or portion of code including one or more executable instructions for implementing a specific logical function or process, which can be implemented in any computer-readable medium for an instruction execution system, apparatus, or device. The computer-readable medium can be any medium that contains, communicates, propagates, or transports a program for use by the instruction execution system, apparatus, or device, including read-only memory, magnetic disks, or optical disks, etc.

[0059] In the description of this specification, the description referring to terms such as "embodiment", "example", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. In addition, those skilled in the art can combine or combine different embodiments or examples described in this specification and the features therein without contradiction.

[0060] Although the above content has shown and described the embodiments of the present invention, it can be understood that the above embodiments are exemplary and cannot be construed as limitations on the present invention. Those of ordinary skill in the art can perform update operations such as changes, modifications, substitutions, and variations on the above embodiments within the scope of the present invention.

Claims

1. An integrated sound absorption and insulation composite underwater acoustic structure, characterized in that, It includes an acoustic absorption layer, and the acoustic absorption layer includes an acoustic absorption layer mechanical framework, and the acoustic absorption layer mechanical framework is a lattice structure; The lattice structure includes a three-dimensional curved surface structure with a gradually changing volume fraction and preset cavities inside, and the generation method includes the following steps: S1. Discretize a specific area of the three-dimensional space corresponding to the preset cavity into NaN; S2. Determine the implicit function g(x, y, z) of the three-dimensional curved surface structure, and use a three-dimensional minimal surface or catenoid surface with zero mean curvature such as Gyroid, Diamond or Primitive; S3. Perform a gradual change in volume fraction through an interpolation algorithm, calculate the values of different isosurfaces, and achieve a uniform change or a change along the exponential function trend of the volume fraction; specifically: set the starting value and ending value of the volume fraction gradient change, and determine the volume fraction corresponding to each position in the discretized three-dimensional space through the gradient change function; where z is the z-axis coordinate, is the volume fraction at one end of the geometric structure in the z-axis coordinate, is the volume fraction at the other end of the geometric structure in the z-axis coordinate; S4. Calculate the values \(t\) of different isosurfaces of the implicit function, such that the implicit function satisfies \(g(x,y,z)\) 2 -t 2 = 0; S5. Draw the isosurface and capping, perform triangulation, and output as an.stl file.

2. The integrated sound absorption and insulation composite underwater acoustic structure according to claim 1, characterized in that Step S1 is specifically: determine the range of the three-dimensional space and perform discretization processing on it, and set the points within the target range to NaN, that is, "not a number", which does not participate in the subsequent structure generation, and this area corresponds to the space of the preset cavity.

3. The integrated sound absorption and insulation composite underwater acoustic structure according to claim 1, wherein Step S5 is specifically: draw the isosurface of the three-dimensional corrugated curved surface according to the implicit function in the discrete coordinate data set [x, y, z], perform mesh division on the isosurface using a triangular mesh, and obtain the corresponding face and vertex data [F, V] and output it for the modeling analysis of the structure.

4. The integrated sound absorption and insulation composite underwater acoustic structure according to claim 1, characterized in that The lattice structure of the acoustic absorption layer mechanical framework is a three-dimensional curved surface structure with a gradually changing volume fraction and preset cavities inside, and the shape and size of the preset cavities are parametrically designed to reserve space for the acoustic absorption cavity and the mass block.

5. The integrated sound absorption and insulation composite underwater acoustic structure according to claim 1, characterized in that The underwater acoustic structure includes a plurality of periodically arranged unit cells, and the unit cell is in the form of a multi-layer structure, including an upper surface layer, an acoustic absorption layer and a sound insulation layer; the acoustic absorption layer is located between the upper surface layer and the sound insulation layer.

6. The integrated sound absorption and insulation composite underwater acoustic structure according to claim 5, characterized in that The acoustic absorption layer includes an acoustic absorption layer mechanical framework and a viscoelastic acoustic absorption polymer filled in the mechanical framework. The mechanical framework adopts a lattice support structure. The acoustic absorption polymer is provided with internal cavities and mass blocks to realize a multi-source acoustic absorption structure; the sound insulation layer is a sandwich structure of anisotropic lattices. By integrating the acoustic absorption structure and the sound insulation structure, the integration of acoustic absorption and sound insulation is realized; the composite underwater acoustic structure is applicable to an environment where both ends are immersed in water media. When the sound wave is incident from the upper surface, it shows acoustic absorption and sound insulation effects, and when the sound wave is incident from the sound insulation layer, it shows a sound insulation effect.

7. The integrated sound absorption and insulation composite underwater acoustic structure according to claim 1, characterized in that, The polymer inside the acoustic absorption layer has internal cavities and steel resonant mass blocks with specific external dimensions; the mechanical framework is a lattice structure, and the volume fraction of the mechanical framework shows a uniform distribution or a gradually changing gradient distribution. When showing a gradually changing gradient distribution, the volume fraction at one end close to the upper surface layer of the unit cell is the smallest, so that the impedance matches the water medium, and more incident sound waves enter the composite structure. At the same time, the volume fraction gradually increases along the sound wave transmission direction and reaches the maximum when approaching the sound insulation layer, so that the sound energy is continuously dissipated in the gradually changing gradient structure.

8. The integrated sound absorption and insulation composite underwater acoustic structure according to claim 7, characterized in that, The internal cavity of each cell unit includes two frustum-shaped cavities arranged vertically, namely the first cavity located above and the second cavity located below. The shape of each cavity is a frustum with a smaller upper surface diameter than the lower surface diameter. The cylindrical mass block is located between the first cavity and the second cavity and has a gap between the lower surface of the first cavity and the upper surface of the second cavity.

9. The integrated sound absorption and insulation composite underwater acoustic structure according to claim 1, characterized in that The sound insulation layer is an anisotropic honeycomb lattice sandwich panel structure, including an upper layer, a lower layer, and a honeycomb lattice beam frame in the middle. All three parts are made of aluminum alloy material, and an air cavity is formed inside the honeycomb lattice.

10. The preparation method of the integrated sound absorption and insulation composite underwater acoustic structure according to any one of claims 1-9, characterized in that, The preparation method includes the following steps: S1. Obtain a lattice structure frame with characteristic wall thickness and external dimensions and an anisotropic honeycomb lattice sandwich sound insulation layer through additive manufacturing; S2. Layer the cavities and mass blocks inside the sound absorption layer, and use a mold to pour each layer separately; after each layer is completed, bond them in sequence to form a sound absorption module, and combine and assemble the sound absorption module and the lattice structure frame to obtain a lattice structure core material containing cavities and mass blocks; S3. Use a modified polymer to pour the frame of the lattice structure core material containing cavities and mass blocks. After the polymer is cured at room temperature or by heating and then demolded, a lattice structure embedded with a solid viscoelastic polymer is obtained, thereby forming a sound absorption layer with an integrated sound absorption and insulation structure; S4. Stick the pre-made fiber-reinforced resin material panel on the upper surface of the sound absorption layer, and stick the sound insulation layer on the lower surface of the sound absorption layer to obtain an underwater integrated sound absorption and insulation structure.

Images