Underwater sound absorption covering layer based on synergistic effect of grid structure and micro-crack structure

Abstract

The invention discloses an underwater sound absorption covering layer based on the synergistic effect of a grid structure and a micro-crack structure, and relates to the field of noise control. The underwater sound absorption covering layer is formed by periodically and continuously arranging a plurality of sound absorption cell elements, each sound absorption cell element comprises a rigid back plate, a rigid vertical plate and a viscoelastic body, and the rigid back plate is used for being adhered to a target surface needing to be covered; the bottom of the rigid vertical plate is vertically fixed on the top surface of the rigid back plate, the top of the rigid vertical plate penetrates into and is fixed in the viscoelastic body, a gap is formed between the bottom surface of the viscoelastic body and the top surface of the rigid back plate and forms a closed cavity, a semi-closed cavity is formed in the rigid vertical plate, and the top of the semi-closed cavity is communicated with the outside; and the rigid back plate and the rigid vertical plates jointly form a grid structure framework. The problems that an existing underwater sound absorption material is insufficient in low-frequency performance and limited in bandwidth are solved, the low-frequency broadband sound absorption capacity is achieved, the structure is simple, and the underwater acoustic stealth requirements of submarines, underwater vehicles and other scenes are met.

Description

Technical Field

[0001] The present invention relates to the technical field of underwater sound-absorbing material design, and in particular to an underwater sound-absorbing covering layer based on the synergistic effect of a grid structure and a micro-slit structure. Background Art

[0002] Underwater sound-absorbing coatings are applied to the surface of underwater structures to offset active or passive sonar detection. The rapid development of sonar technology requires that sound-absorbing coatings attached to underwater structures meet the requirements of low-frequency, broadband acoustic stealth capabilities. With the continued advancement of the strategy of building a strong maritime nation, research on the design of underwater acoustic coatings with low-frequency, broadband capabilities has become a key focus. Existing underwater sound-absorbing materials face the following technical bottlenecks: (1) Insufficient low-frequency performance: The sound absorption efficiency of existing materials decreases significantly in the low-frequency band below 500 Hz, making it difficult to meet the detection requirements of modern low-frequency active sonar; (2) Limited effective bandwidth: The sound absorption bandwidth of traditional structures is narrow and cannot cover the broadband detection range of the sonar system, resulting in insufficient stealth capability in the full frequency band.

[0003] (3) Complex structure: Since the sound absorption frequency band of a single structure is usually narrow, researchers generally use multiple structures and multiple cells in series or parallel to achieve broadband sound absorption.

[0004] While grid structures based on the shear dissipation principle offer excellent broadband sound absorption, their low-frequency performance is limited by the limitations of a single structural design. Existing improvements often involve the introduction of multiple structures or cells in series or parallel, significantly increasing manufacturing costs and process complexity.

[0005] Therefore, developing an underwater sound-absorbing covering layer with low-frequency and broadband sound absorption capabilities and a simple structure has become a key technical direction to meet the needs of national defense security, marine engineering, and environmental compliance. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention aims to provide an underwater sound-absorbing covering layer based on the synergistic effect of a grid structure and a micro-slit structure, which can achieve ultra-low frequency sound absorption and broadband sound absorption.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides an underwater sound-absorbing covering layer based on the synergistic effect of a grid structure and a micro-slit structure. The underwater sound-absorbing covering layer is formed by a plurality of sound-absorbing cells arranged periodically and continuously, and is characterized in that: the sound-absorbing cells include a rigid backplate, a rigid vertical plate and a viscoelastic body, the rigid backplate is used to adhere to the target surface to be covered; the bottom of the rigid vertical plate is vertically fixed to the top surface of the rigid backplate, the top of the rigid vertical plate penetrates and is fixed in the viscoelastic body, a gap is provided between the bottom surface of the viscoelastic body and the top surface of the rigid backplate to form a closed cavity, a semi-closed cavity is provided inside the rigid vertical plate, and the top of the semi-closed cavity is communicated with the outside world; the rigid backplate and the rigid vertical plate together constitute a grid structure skeleton.

[0008] As a further optimization scheme of the present invention, the rigid vertical plate includes two vertical plate units arranged symmetrically on the left and right, each of the vertical plate units is connected by an upper vertical plate close to the outside side and a lower vertical plate close to the rigid back plate side, and the width of the upper vertical plate is greater than the width of the lower vertical plate; there is a gap between the two upper vertical plates and a micro-gap cavity is formed, and there is a gap between the two lower vertical plates and they are separated into an upper cavity and a lower cavity by a middle viscoelastic body, the upper cavity and the micro-gap cavity are connected and combined to form a semi-closed cavity, and the lower cavity is a closed cavity.

[0009] As a further optimized solution of the present invention, the viscoelastic body further includes an external viscoelastic body fixed on the outer wall of the rigid vertical plate.

[0010] As a further optimization solution of the present invention, the side cavities on the left and right sides of the lower cavity are both closed cavities, and the closed cavities are filled with air.

[0011] As a further optimization solution of the present invention, the width of the upper cavity is the same as the width of the lower cavity, and the width of the upper cavity is greater than the width of the micro-slit cavity.

[0012] As a further optimization solution of the present invention, the upper vertical plate and the lower vertical plate are designed to be integrally formed.

[0013] As a further optimized solution of the present invention, the material of the viscoelastic body is a viscoelastic material including rubber, polyurethane, or a composite material based on a viscoelastic material.

[0014] As a further optimization solution of the present invention, the rigid back plate and the rigid vertical plate are both made of rigid metal material or carbon fiber composite material.

[0015] As a further optimization solution of the present invention, the sound absorption coefficient of the underwater sound-absorbing covering layer in the frequency range of 220 Hz to 10,000 Hz exceeds 0.8.

[0016] As a further optimization solution of the present invention, the rigid back plate, rigid vertical plate, cavity and viscoelastic body are all rectangular parallelepiped structures or variable cross-section structures.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The area near the interface between the rigid risers and the viscoelastic body experiences intense shear motion under the action of sound waves. Based on the principle of shear dissipation, the structure exhibits a high sound absorption coefficient over a wide frequency band. Compared to traditional grid structures, the grid structure skeleton proposed in this invention has a larger volume share. By increasing the thickness of the rigid risers and rationally changing their volume share, the surface impedance of the structure can be matched to that of water, further enhancing the structure's broadband sound absorption.

[0018] 2. The rigid risers essentially do not contribute to sound energy dissipation. Designing a micro-slit cavity structure within the rigid risers maximizes space utilization. The semi-enclosed cavity (micro-slit cavity + upper cavity) fills with water when operating underwater, allowing low-frequency sound waves to more easily enter the sound-absorbing cover layer and be dissipated by the viscoelastic structure within the rigid risers. The micro-slit design primarily filters low-frequency sound waves from entering the sound-absorbing cover layer, specifically absorbing low-frequency sound waves below 500Hz while maintaining broadband sound absorption.

[0019] 3. All parts of the sound absorbing cell of the present invention are mirror-symmetrical, with a simple structure, which is convenient for production and processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the three-dimensional structure of the underwater sound-absorbing covering layer of the present invention.

[0021] Figure 2 Schematic diagram of the cross-sectional structure of a single sound-absorbing cell of the present invention.

[0022] Figure 3 This is a diagram of an application scenario of the underwater sound-absorbing covering layer of the present invention.

[0023] Figure 4 The evolution process from the traditional grid structure to the structure of the present invention is shown in Figure 1. Configuration I is the traditional grid structure, Configuration II is the grid structure with thickened rigid vertical plates, and Configuration III is a new structure that combines the grid structure with the micro-slit structure.

[0024] Figure 5 for Figure 4 Comparison curve of the sound absorption coefficient of the three structures changing with frequency.

[0025] In the figure: 1, underwater sound-absorbing cover layer; 11, sound-absorbing cell; 111, rigid back plate; 112, rigid vertical plate; 1121, vertical plate unit; 1122, upper vertical plate; 1123, lower vertical plate; 113, viscoelastic body; 1131, external viscoelastic body; 1132, middle viscoelastic body; 114, micro-slit cavity; 115, upper cavity; 116, lower cavity; 117, side cavity. DETAILED DESCRIPTION

[0026] To help those skilled in the art better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that the drawings are for illustrative purposes only and are not to be construed as limiting this patent. To better illustrate this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the drawings. The positional relationships described in the drawings are for illustrative purposes only and are not to be construed as limiting this patent.

[0027] The present invention will be described in further detail below with reference to the accompanying drawings, illustrating an underwater sound-absorbing covering layer based on the synergistic effect of a grid structure and a micro-slit structure.

[0028] like Figure 1-4 As shown, the present invention provides an underwater sound-absorbing covering layer 1 based on the synergistic effect of a grid structure and a micro-slit structure. The covering layer is composed of a plurality of sound-absorbing cells 11 arranged periodically and continuously. The sound-absorbing cells 11 include a rigid backplate 111, rigid vertical plates 112, and a viscoelastic body 113. The rigid backplate 111 is adapted to adhere to the target surface to be covered. The bottom of the rigid vertical plates 112 is perpendicularly fixed to the top of the rigid backplate 111, and there is no vibration displacement between the rigid backplate 111 and the rigid vertical plates 112. The top of the rigid vertical plates 112 is inserted into and fixed in the viscoelastic body 113. A gap is formed between the bottom of the viscoelastic body 113 and the top of the rigid backplate 111, forming a closed cavity. The interior of the rigid vertical plates 112 contains a semi-enclosed cavity, the top of which is open to the outside world. The rigid backplate 111 and the rigid vertical plates 112 together form a grid structure skeleton, which enhances the overall rigidity of the cells and prevents structural deformation under water pressure, which would otherwise degrade sound absorption performance.

[0029] In the above scheme, the periodic arrangement of sound-absorbing cells 11 forms an acoustic metamaterial structure. The rigid backplate 111 can be secured to the target surface using epoxy adhesives, mechanical fasteners (such as bolts), or other methods to ensure no relative slip at the interface. The enclosed cavity can be filled with air, and the external viscoelastic body 1131 and the rigid riser 112 experience intense relative motion under the influence of acoustic waves. Due to viscoelastic shear damping, high-frequency sound absorption is particularly effective. The semi-enclosed cavity is open at the top and connected to the external water medium, while the bottom is sealed by the central viscoelastic body 1132, forming an underwater Helmholtz resonator that selectively absorbs low-frequency sound waves.

[0030] In some embodiments, as Figure 2 As shown, the rigid vertical plate 112 includes two vertical plate units 1121 arranged symmetrically on both sides. Each vertical plate unit 1121 is formed by connecting an upper vertical plate 1122 on the side closest to the outside and a lower vertical plate 1123 on the side closest to the rigid back plate 111. The upper vertical plates 1122 and the lower vertical plates 1123 are integrally formed. The width of the upper vertical plate 1122 is greater than that of the lower vertical plate 1123. There is a gap between the two upper vertical plates 1122, forming a micro-slit cavity 114. The two lower vertical plates 1123 are separated by a gap and are divided into an upper cavity 115 and a lower cavity 116 by a central viscoelastic body 1132. The upper cavity 115 and the micro-slit cavity 114 are connected to form a semi-enclosed cavity, while the lower cavity 116 is a closed cavity. Because the dynamic viscosity of water is relatively low, the micro-slit cavity 114 has negligible effect on the dissipation of low-frequency acoustic energy. The middle viscoelastic body 1132 generates a large shear strain under the excitation of the resonant acoustic pressure and dissipates the low-frequency acoustic energy through internal friction.

[0031] In the above scheme, the upper vertical plate 1122 is relatively wide, forming a micro-slit cavity 114; the lower vertical plate 1123 is relatively narrow, forming an upper cavity 115. The micro-slit cavity 114 and the upper cavity 115 are connected to form a "neck-cavity" structure, equivalent to a Helmholtz resonator. The bottom of the Helmholtz resonator is a flexible wall (the middle viscoelastic body 1132). Low-frequency sound absorption peaks can be optimized by adjusting the slit width, cavity size, and the dimensions of the middle viscoelastic body 1132. The middle viscoelastic body 1132 is positioned between the upper cavity 115 and the lower cavity 116. When low-frequency sound waves enter the semi-enclosed cavity, the middle viscoelastic body 1132 undergoes shear deformation, dissipating sound energy through internal friction. This is particularly effective in the frequency range below 500 Hz.

[0032] In some embodiments, the viscoelastic body 113 comprises an outer viscoelastic body 1131 and a middle viscoelastic body 1132. The outer viscoelastic body 1131 is fixed to the outer wall of the rigid riser 112, while the middle viscoelastic body 1132 is fixed between the two lower risers 1123. The outer viscoelastic body 1131 primarily absorbs medium- and high-frequency sound waves through shear friction of the damping material; the middle viscoelastic body 1132 absorbs low-frequency sound waves through Helmholtz resonance, broadening the sound absorption bandwidth. The viscoelastic body 113 is connected to the rigid risers 112 using one or more of bonding, injection molding, or injection molding.

[0033] In some embodiments, the side cavities 117 on the left and right sides of the lower cavity 116 are both closed cavities filled with air. The width of the upper cavity 115 is the same as that of the lower cavity 116 , and the width of the upper cavity 115 is greater than that of the micro-slit cavity 114 .

[0034] In some embodiments, the viscoelastic body 113 is made of a viscoelastic material including rubber, polyurethane, or a composite material based on a viscoelastic material. The viscoelastic body 113 is preferably made of rubber.

[0035] In some embodiments, the rigid back plate 111 and the rigid riser 112 are both made of a rigid metal material or a carbon fiber composite material with a large elastic modulus and corrosion resistance.

[0036] In some embodiments, the rigid back plate 111, the rigid vertical plate 112, the cavity and the viscoelastic body 113 are all rectangular structures or variable cross-section structures. Unless otherwise specified, all components are rectangular structures. If necessary, variable cross-section processing can be appropriately adopted to meet the impedance matching or assembly fixation of the structure. The dimensions of the cavity, the rigid vertical plate 112 and the viscoelastic material can be arbitrarily changed as long as the size of the sound-absorbing covering layer allows. The size of the sound-absorbing covering layer in the xy plane is not limited. The smaller the height in the z direction, the better, usually not exceeding 50 mm. After the underwater sound-absorbing covering layer 1 is actually spliced and covered with the target object, the lower cavity 116 and the side cavity 117 will naturally form a closed cavity, leaving only the top opening of the micro-slit cavity 114 to communicate with the outside world.

[0037] The materials of the viscoelastic body 113, rigid risers 112, cavity, and rigid backplate 111 in the above structure can be modified based on actual conditions. For example, the grid material can be made of carbon fiber composite material. The width and height of the viscoelastic body 113, rigid risers 112, and cavity can be modified as appropriate, and the number of viscoelastic bodies 113, rigid risers 112, and cavities within the periodically arranged cells can also be arbitrarily varied. This demonstration configuration is merely a special case.

[0038] Figure 4The evolution from a traditional grid structure to the structure of the present invention is shown in Figure 1. Configuration I is a traditional grid structure, Configuration II is a grid structure with thickened rigid vertical plates 112, and Configuration III is a novel structure that combines the synergistic effects of a grid structure and a micro-slit structure. Based on Configuration II, this structure incorporates a micro-slit sound-absorbing structure within the thickened rigid vertical plates 112.

[0039] The present invention provides a set of cell structure parameters and material parameters to verify the beneficial effects of the present invention, including the following: (1) The width of the sound absorbing cell excluding the rigid back plate is 50 mm and the height is 50 mm.

[0040] (2) Since the rigid backplate is a fixed constraint, the height of the rigid backplate can take any value. The demonstration model sets its height to 1mm and width to 50mm.

[0041] (3) The width of the upper cavity inside the rigid vertical plate is 16 mm, the width of the micro-slit cavity is 2 mm, and the width of the cavities on both sides of the rigid vertical plate is 15 mm. The height of the upper cavity connected to the outside world is 5 mm, and the height of the micro-slit cavity is 39 mm. The height of the lower cavity where the bottom contacts the rigid back plate is 1 mm.

[0042] (4) The narrower area at the bottom of the rigid vertical plate is 2 mm wide and 11 mm high. The wider area at the top of the rigid vertical plate is 9 mm wide and 39 mm high.

[0043] (5) The external viscoelastic body on both sides of the rigid vertical plate has a width of 15 mm and a height of 49 mm. The central viscoelastic body inside the rigid vertical plate has a width of 16 mm and a height of 5 mm.

[0044] (6) The viscoelastic material is rubber, and its elastic modulus is ,density , Poisson's ratio , loss factor , the rigid vertical plate and rigid back plate are made of stainless steel, and its elastic modulus is ,density , Poisson's ratio ; The cavity material is air, and its density , the speed of sound ; Water material density , the speed of sound .

[0045] (7) Correspondingly, in configuration I, the width of the rigid vertical plate is 2 mm and the height is 50 mm. The viscoelastic layer on both sides of the rigid vertical plate is 24 mm wide and 49 mm high. The cavity is 1 mm high and 24 mm wide. In configuration II, the width of the rigid vertical plate is 20 mm and the height is 50 mm. The viscoelastic layer on both sides of the rigid vertical plate is 15 mm wide and 49 mm high. The cavity is 1 mm high and 15 mm wide. The material properties are consistent with those of configuration III.

[0046] (8) The sound absorption coefficient can be obtained by solving the finite element model using COMSOL Multiphysics software. Figure 5 The following figure compares the sound absorption of three structures. It can be seen that the traditional grid structure has significant shortcomings in both low-frequency and broadband sound absorption, with the sound absorption coefficient failing to exceed 0.8 across a significant portion of the frequency band. Increasing the thickness of the rigid vertical panels significantly improves the structure's broadband sound absorption performance (see Curve II). By further incorporating a micro-slit structure, Structure III (the sound-absorbing cell 11 designed in the present invention) further enhances low-frequency sound absorption, achieving a sound absorption coefficient exceeding 0.8 across the 220Hz-10,000Hz frequency range.

[0047] In summary, the present invention fully combines and amplifies the respective advantages of the grid structure and the micro-slit structure, and obtains excellent low-frequency and broadband sound absorption performance.

[0048] Based on the description and illustrations of the technical solution of the present invention, those skilled in the art can easily implement and apply this underwater sound-absorbing coating that combines the synergistic effects of the grid structure and the micro-slit structure, and can achieve the acoustic performance optimization and technical benefits described in the specification. It should be noted that the specific implementation methods of this technical solution are not limited to the exemplary embodiments listed in the specification. While maintaining the core innovative principles (i.e., the acoustic impedance matching mechanism and multi-stage dissipation mechanism of the grid-micro-slit composite structure), relevant technical personnel can make improvements through equivalent replacement of technical elements, reasonable adjustment of the structural form, or adaptive optimization of process parameters. Such modified implementation methods that meet the design points of this technical solution should be included in the scope of protection of the patent claims.

Claims

1. An underwater sound-absorbing covering layer based on the synergistic effect of a grid structure and a micro-slit structure, wherein the underwater sound-absorbing covering layer (1) is formed by a plurality of sound-absorbing cells (11) arranged periodically and continuously, and is characterized by: The sound absorbing cell (11) comprises a rigid back plate (111), a rigid vertical plate (112) and a viscoelastic body (113), wherein the rigid back plate (111) is used to adhere to a target surface to be covered; the bottom of the rigid vertical plate (112) is vertically fixed to the top surface of the rigid back plate (111), the top of the rigid vertical plate (112) is penetrated into and fixed in the viscoelastic body (113), a gap is provided between the bottom surface of the viscoelastic body (113) and the top surface of the rigid back plate (111), and a closed cavity is formed; a semi-closed cavity is provided inside the rigid vertical plate (112), and the top of the semi-closed cavity is communicated with the outside; the rigid back plate (111) and the rigid vertical plate (112) together form a grid structure skeleton.

2. The underwater sound-absorbing covering layer based on the synergistic effect of the grid structure and the micro-slit structure according to claim 1 is characterized in that: The rigid vertical plate (112) comprises two vertical plate units (1121) arranged symmetrically on the left and right, each vertical plate unit (1121) being connected by an upper vertical plate (1122) on the side close to the outside and a lower vertical plate (1123) on the side close to the rigid back plate (111), the width of the upper vertical plate (1122) being greater than the width of the lower vertical plate (1123); a gap is provided between the two upper vertical plates (1122) to form a micro-slit cavity (114), and a gap is provided between the two lower vertical plates (1123) to form an upper cavity (115) and a lower cavity (116) through a middle viscoelastic body (1132), the upper cavity (115) and the micro-slit cavity (114) are connected and combined to form a semi-enclosed cavity, and the lower cavity (116) is a closed cavity.

3. The underwater sound-absorbing covering layer based on the synergistic effect of the grid structure and the micro-slit structure according to claim 2 is characterized in that: The viscoelastic body (113) further includes an external viscoelastic body (1131) fixed on the outer wall of the rigid vertical plate (112).

4. The underwater sound-absorbing covering layer based on the synergistic effect of the grid structure and the micro-slit structure according to claim 2 is characterized in that: The side cavities (117) on the left and right sides of the lower cavity (116) are both closed cavities, and the closed cavities are filled with air.

5. The underwater sound-absorbing covering layer based on the synergistic effect of the grid structure and the micro-slit structure according to claim 2 is characterized in that: The width of the upper cavity (115) is the same as the width of the lower cavity (116), and the width of the upper cavity (115) is greater than the width of the micro-slit cavity (114).

6. The underwater sound-absorbing covering layer based on the synergistic effect of the grid structure and the micro-slit structure according to claim 2 is characterized in that: The upper vertical plate (1122) and the lower vertical plate (1123) are designed to be integrally formed.

7. The underwater sound-absorbing covering layer based on the synergistic effect of the grid structure and the micro-slit structure according to claim 1 is characterized in that: The material of the viscoelastic body (113) is a viscoelastic material including rubber, polyurethane, or a composite material with a viscoelastic material as a matrix.

8. The underwater sound-absorbing covering layer based on the synergistic effect of the grid structure and the micro-slit structure according to claim 1 is characterized in that: The rigid back plate (111) and the rigid vertical plate (112) are both made of rigid metal material or carbon fiber composite material.

9. The underwater sound-absorbing covering layer based on the synergistic effect of the grid structure and the micro-slit structure according to claim 1 is characterized in that: The underwater sound-absorbing covering layer (1) has a sound absorption coefficient exceeding 0.8 in the frequency range of 220 Hz to 10,000 Hz.

10. The underwater sound-absorbing covering layer based on the synergistic effect of the grid structure and the micro-slit structure according to claim 1 is characterized in that: The rigid back plate (111), the rigid vertical plate (112), the cavity and the viscoelastic body (113) are all rectangular parallelepiped structures or variable cross-section structures.

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