Acoustic covering layer system suitable for multi-water-depth environment and sound absorption regulation and control method

Abstract

The invention discloses an acoustic covering layer system suitable for a multi-water-depth environment and a sound absorption adjustment method, and the acoustic covering layer system suitable for the multi-water-depth environment introduces a pneumatic regulation and control mechanism for the first time based on a structure-material coupling response principle, thereby achieving the active adjustment of sound absorption performance and environment self-adaption. A solution which is simple in structure, stable in performance and efficient in regulation and control is provided for acoustic invisibility of the underwater platform under the working conditions of multiple water depths and variable pressure; compared with an existing underwater acoustic covering layer which depends on external loading pieces such as bolts and inhaul cables to apply additional pressure, the underwater acoustic covering layer is actively regulated and controlled through internal air pressure, the structural form is remarkably simplified, and the system integration complexity and the overall weight are reduced. Meanwhile, a related regulation and control system can be directly compatible with common depth perception and air source management devices of the underwater platform, complex special assemblies do not need to be added, and good integration and operation and maintenance convenience are achieved.

Description

Technical Field

[0001] This invention pertains to acoustic materials and structural technologies within the field of underwater acoustic engineering. Specifically, it relates to an acoustic covering layer system suitable for underwater environments, with wide applications in underwater target stealth noise reduction, background noise control, and communication sound field optimization. More specifically, this invention proposes an underwater sound-absorbing covering layer structure based on aerodynamic control mechanisms. By adjusting the internal air pressure of the cavity, the sound absorption performance can be adjusted to adapt to changes in hydrostatic pressure caused by different water depths. This structure exhibits significant advantages in water pressure adaptability, low-frequency sound absorption stability, and system integration capabilities, overcoming several limitations of traditional underwater acoustic covering layers. Background Technology

[0002] Underwater acoustic coatings (also known as underwater sound-absorbing layers) are functional structural materials applied to the outer surface of underwater platforms. They are widely used in ships, underwater vehicles, and communication nodes to absorb and attenuate incident underwater acoustic waves, serving as a crucial technology for achieving underwater acoustic stealth. This structure can significantly reduce the platform's radiated sound intensity, improve stealth performance, and possess a certain degree of noise shielding capability, contributing to the optimization of the acoustic quality of the underwater communication environment. With the development of marine exploration and underwater warfare technologies, the comprehensive performance requirements of coatings under complex conditions such as multi-depth, high-maneuverability, and long-distance deep-sea diving continue to increase, posing significant challenges to traditional solutions.

[0003] Current mainstream underwater acoustic coating designs typically need to balance three key performance aspects: first, high-efficiency sound absorption across a wide frequency range, especially in the low-frequency range; second, lightweight construction to meet platform maneuverability requirements; and third, pressure resistance and stability in deep-water environments. Low-frequency sound absorption is a core indicator of stealth and noise reduction performance; however, due to the long wavelength and slow attenuation of low-frequency sound waves, conventional materials struggle to achieve effective dissipation. Lightweight construction is crucial for platform buoyancy control and propulsion efficiency; excessive coating mass significantly increases system load and limits platform performance. Deep-water pressure resistance is fundamental to system availability; the acoustic structure must withstand high hydrostatic pressure over extended periods without instability or performance degradation.

[0004] Currently, common solutions often use high-modulus rubber as the matrix material, combined with periodically arranged resonant cavity structures (such as conical cavities and membrane cavity composites) to enhance the local resonance absorption of low-frequency sound waves. This type of "rigid matrix + resonant cavity" structure has long been widely used as the mainstream solution due to its mature technology and stable manufacturing process. However, with the significant enhancement of low-frequency detection capabilities in modern sonar systems, the absorption efficiency of such covering layers over a wide low-frequency band has gradually become insufficient. Simultaneously, the higher water pressure requirements for deep-sea platforms have also exposed the limitations of its structural response capabilities. Existing research shows that under the influence of deep-water pressure, the resonant cavity of traditional structures is prone to significant deformation, causing the resonance conditions to deviate from the design state, thus leading to a significant decrease in sound absorption performance.

[0005] To enhance low-frequency absorption, some studies have attempted to introduce soft materials with low modulus and high loss characteristics as a matrix to improve the material's internal friction performance. However, these materials are soft and have low mechanical strength, making them difficult to withstand high hydrostatic pressure on their own, resulting in insufficient stability of the overall structure in deep-water conditions. To address this issue, some solutions introduce rigid frames or sandwich structures to provide additional support, constructing a composite structural system of "soft matrix + rigid reinforcement." While these solutions have achieved some success in improving pressure resistance, they inevitably increase structural mass and are complex to manufacture and integrate, making them difficult to meet the lightweight and structural simplicity requirements of modern underwater platforms. In complex marine environments such as varying pressure at different depths, the stability and adaptability of such structures in terms of sound absorption performance remain poorly validated, and their control methods are mostly based on static design, limiting their active adaptability.

[0006] To address the aforementioned issues, the inventors previously proposed an underwater acoustic covering layer design based on the coupling of a low-modulus soft material and a periodic cavity structure (Patent Document 1: CN 202210993993.1). This scheme systematically analyzes the nonlinear deformation response of soft materials under high hydrostatic pressure and, based on theoretical modeling, finite element simulation, and experimental verification, constructs a sound-absorbing structure with characteristics of "low modulus – high loss – controllable deformation". In terms of structural design, by optimizing the cavity size and spatial layout, the matrix exhibits non-uniform and anisotropic deformation under pressure, effectively stimulating local resonant modes and achieving a "the higher the pressure, the stronger" performance evolution, meaning that the sound absorption performance in deep water is better than in shallow water, breaking through the physical bottleneck of "high pressure weakening performance" in conventional structures. Furthermore, to maintain stable performance in shallow water conditions, this scheme proposes to use additional external loading devices (such as bolts, cables, etc.) to simulate hydrostatic pressure, improving the system's adaptability in non-high-pressure environments. While maintaining a lightweight design, the overall structure significantly improves sound absorption performance and adaptability to various working conditions, demonstrating excellent engineering potential and application prospects.

[0007] While the aforementioned solutions have achieved positive results in terms of structural response mechanisms and sound absorption performance, several technical challenges remain. First, current loading methods primarily rely on external mechanical components to apply additional pressure. Although this can simulate environmental pressure effects to some extent, the loading method is relatively localized, easily leading to stress concentration and resulting in inhomogeneity in structural deformation and performance. Second, the introduction of additional structural components increases the system's integration complexity, placing higher demands on platform installation accuracy and maintenance capabilities, and also weakening the system's lightweight and flexibility to some extent. Therefore, how to maintain structural simplicity and lightweight while achieving more efficient, uniform, and adjustable loading methods to actively adjust and stably maintain sound absorption performance under multi-depth water conditions remains a critical technical problem that urgently needs to be solved. Summary of the Invention

[0008] This invention provides a pneumatically controlled acoustic covering layer system suitable for multi-depth environments, aiming to solve the technical bottlenecks of existing technologies, such as unstable sound absorption performance, complex structure, insufficient adjustment capability, and the difficulty in balancing lightweight and pressure resistance. Based on the structure-material coupling response principle, this invention introduces a pneumatic control mechanism for the first time, achieving active adjustment of sound absorption performance and environmental adaptability. It provides a simple, stable, and highly efficient solution for acoustic stealth of underwater platforms under multi-depth and variable pressure conditions.

[0009] Specifically, the covering layer consists of a matrix of low-modulus, high-loss soft material, with multiple periodically embedded resonant cavities. An air duct network system connected to an external air source is introduced to regulate the internal air pressure, thereby establishing a controllable "water pressure-air pressure" field. Under this composite stress field, the soft material matrix undergoes non-uniform, anisotropic compaction deformation, and the resonant cavity configuration adjusts accordingly, forming a structure-material synergistic response mechanism. This effectively excites local resonant modes and enhances the absorption capacity of low-frequency sound waves.

[0010] First, the introduction of air pressure counteracts the increasing hydrostatic pressure in deep water environments, effectively suppressing excessive structural compression and deformation. This ensures the structural configuration remains close to its design state at different water depths, guaranteeing the basic stability of the sound-absorbing structure. Further research shows that within a specific pressure difference range, the structural deformation response produces a low-frequency enhancement effect that differs from conventional passive sound-absorbing structures and is difficult to predict directly through conventional experience. Specifically, pressure difference control can trigger stronger low-frequency resonant modes. This phenomenon significantly improves low-frequency sound energy dissipation and effectively expands the sound absorption bandwidth, providing a new structural control path for optimizing low-frequency sound absorption performance. Second, by regulating the internal air pressure through the air pressure control system, the system can automatically adjust to the optimal sound absorption state according to different water depths, exhibiting good environmental adaptability. For example, in Example 1, when the internal air pressure is slightly higher than the water pressure, forming a positive pressure difference of approximately 1 MPa, the system's sound absorption performance reaches its optimal state. This optimal pressure difference range can be flexibly set based on material parameters, structural dimensions, and configuration characteristics, without being limited to a fixed value.

[0011] Furthermore, unlike existing underwater acoustic coatings that rely on external loads such as bolts and cables to apply additional pressure, this invention significantly simplifies the structure and reduces system integration complexity and overall weight through active internal air pressure regulation. Simultaneously, the related control system is directly compatible with common depth sensing and air source management devices on underwater platforms, eliminating the need for complex dedicated components and offering excellent integrability and ease of maintenance.

[0012] In summary, this invention, by introducing an aerodynamic control mechanism, establishes an adjustable and controllable structural response platform while ensuring lightweight structure and platform adaptability. This enables the stable maintenance and active enhancement of wide-band low-frequency sound absorption performance under various water depth conditions. This invention overcomes the inherent limitations of traditional designs that struggle to coordinate lightweight, pressure-resistant, and wide-band low-frequency performance, possessing broad technical prospects and application value, and is suitable for multiple underwater acoustic engineering fields such as military stealth, underwater communication, and deep-sea exploration.

[0013] This invention is based on a soft material-cavity coupling system. Under natural operating conditions without pneumatic control, its sound absorption performance exhibits a "weaker with increasing water pressure" characteristic. To address the performance degradation revealed by this "weaker with increasing pressure" behavior, this invention proposes a controllable air pressure loading mechanism to establish a composite stress field of "water pressure-air pressure," providing internal pressure support for the resonant structure and significantly improving its mechanical stability and frequency response in deep-water environments. By precisely adjusting the air pressure to form an optimal pressure difference range, the system can excite enhanced low-frequency resonant modes, achieving active adjustment and enhancement of acoustic performance, thereby constructing a stable and efficient sound absorption mechanism suitable for various water depths. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort, and this application can be applied to other similar scenarios based on the provided drawings. Unless obvious from the linguistic context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0015] Figure 1 A schematic diagram of a pneumatically controlled underwater acoustic coating layer structure;

[0016] Figure 2 A side view of a cover tile unit and its side;

[0017] Figure 3 The loss factor frequency distribution of S-SBR material;

[0018] Figure 4 The sound absorption performance of the pneumatically controlled underwater acoustic coating layer;

[0019] Figure 5 The deformation behavior and sound absorption performance of the acoustic covering layer under different hydrostatic pressures;

[0020] Figure 6 This refers to the deformation behavior and sound absorption performance of the acoustic covering layer when the internal and external pressures are balanced.

[0021] Figure 7 The deformation behavior and sound absorption performance of the acoustic covering layer when the internal and external pressure difference is "+1 MPa";

[0022] Figure 8 The influence of different matrix material moduli on the deformation behavior and sound absorption performance of the capping layer;

[0023] Figure 9 The sound absorption performance of the covering layer after proportional scaling of the single-cell structure;

[0024] Figure 10 A comparison of simulation and experimental results of the sound absorption performance of the reference structure;

[0025] Figure 11 Deformation behavior and sound absorption performance of the sound-absorbing covering layer when supported by steel. Detailed Implementation

[0026] This invention proposes a pneumatically controlled acoustic covering layer system suitable for multi-depth environments, including a covering layer 1, a backplate 2, and an air pressure control system.

[0027] Covering layer 1 is a plate-like structure, such as Figure 1and Figure 2 As shown, its thickness direction is basically consistent with the main propagation direction of underwater sound waves. To adapt to the curved surface configurations of different underwater platforms, it can be flexibly designed according to the spherical, cylindrical, or free curvature characteristics of the target surface to achieve a good fit. To facilitate industrial production and on-site installation, the covering layer 1 can be divided into tile units 10 with an in-plane size of approximately 200–800 mm (e.g., Figure 2 As shown in (a), it is used to cover the platform surface in a tiling manner in the application.

[0028] The capping layer 1 is mainly composed of a low-modulus, high-loss elastomer matrix 11, an embedded resonant cavity 12, and a through-type air channel network 13 (e.g., Figure 2 (As shown). Figure 1 (c) This section shows the structural morphology and dimensional parameters of the covering layer 1 under natural operating conditions (i.e., no water pressure and no applied internal air pressure). The overall thickness of the covering layer is denoted as h1, and its specific design should comprehensively consider key factors such as the sound absorption performance of the target frequency band, the available installation space of the platform, structural strength requirements, and the response range of aerodynamic control. Multiple approximately columnar sealed cavities 12 are periodically embedded inside the substrate 11 to form a resonant structure. The resonant cavities 12 should be distributed as evenly as possible, with an arrangement period of 2a. The specific arrangement is not limited and can be as follows: Figure 1 (a), (b) and Figure 2 The hexagonal dot matrix shown in (a) can also be a square or other regular dot matrix.

[0029] To more clearly describe the structural details and facilitate numerical modeling, the cladding layer 1 can be considered as a periodic array of multiple unit cells 100. Each unit cell 100 includes a portion of the substrate 11, a resonant cavity 12, and a section of the airway network 13 (e.g., Figure 2 As shown). Figure 1 As shown in (b), the unit cell has a regular hexagonal cross-section with a side-to-side distance of 2a, forming a solid hexagonal prism structure. Figure 1 As shown in (c) and (d), the base portion of each unit cell 100 can be artificially divided into a main body 110, a near-water end 111, and a far-water end 112, which are connected sequentially. Each resonant cavity 12 can be artificially divided into a main body 120, a near-water end 121, and a far-water end 122, which are connected sequentially. The main body 120 is frustum-shaped with an upper base radius of [missing information]. The radius of the lower base is Height is The near-water end 121 and the far-water end 122 are hemispherical shapes that smoothly transition into the main body 120, and are preferably radii of [missing information]. and A hemispherical shape. Usually chosen. This is to achieve a gradual change in acoustic impedance along the sound wave propagation path, thereby enhancing the acoustic energy coupling efficiency. The distance between the top of the near-water end 121 and the top surface of the substrate 11 is... The distance from the bottom of the far end 122 to the bottom surface of the base 11 is To control the overall structural thickness and facilitate the integration of the air guiding network, the resonant units are arranged in a single layer along the thickness direction. All resonant cavities are integrally formed directly in the tile unit 10 using a mold, eliminating the need for a separate shell and ensuring good airtightness and structural stability. The preferred ranges for each parameter are as follows: , , , , , .

[0030] The substrate for the cover layer is typically made of low-modulus, high-loss elastomer materials, such as solution-polymerized styrene-butadiene rubber (S-SBR), ethylene propylene diene monomer (EPDM), or high-loss polyurethane elastomers (PU). These materials possess good acoustic impedance matching capabilities, stability in underwater service environments, and excellent molding adaptability, making them suitable for constructing complex geometries and meeting diverse operational requirements for underwater sound-absorbing structures. The Young's modulus range for typical materials is... Poisson's ratio is between Between these values, the loss factor (η) ranges from 0.9 to 1.2 within the 0.5–10kHz frequency band. Figure 3 As shown. Material selection also needs to comprehensively consider its aging resistance, thermal stability and process compatibility to ensure the structural consistency and performance stability of the cover layer during large-area installation and actual service.

[0031] An air duct network 13 is provided inside the cover layer substrate to achieve air pressure regulation. The air duct network 13 is connected to the cavity inlet of each resonant cavity 12. The cavity inlet is preferably located at the center of the bottom surface of the far end 122 of each resonant cavity and adopts a sealed venting interface to ensure airtightness. The air duct network 13 adopts a centralized and converging layout in each tile unit 10, that is, the cavity inlets of all resonant cavities in the tile unit are uniformly guided to a main air duct 131, and then the main air duct 131 passes through a single through hole in the back plate to connect to an external air source. This design can effectively reduce the number of openings in the back plate, improve structural integrity and sealing reliability, and also facilitate modular air connection and piping during subsequent laying.

[0032] The cover layer tile units can be manufactured using well-known rubber processing techniques such as compression molding, transfer molding, and injection molding. During the molding process, the resonant cavity and air channel network can be integrally formed directly within the cover layer substrate, eliminating the need for subsequent inserts or assembly operations. This integrated structural design simplifies the manufacturing process, improves manufacturing precision and sealing consistency, and is suitable for mass production, meeting the engineering application requirements of acoustic cover layers for underwater platforms.

[0033] The backplate is located at the far end of the acoustic cover layer, primarily providing structural rigidity and serving as the interface foundation for connecting the air duct network to the external air source. Its material can be selected from aluminum alloy, stainless steel, or fiberglass-reinforced composite materials, depending on the specific application requirements. In engineering applications, the cover layer can be directly attached to the surface of the underwater platform's outer shell, using the platform shell as a substitute for the backplate; alternatively, a separate backplate can be installed and integrated with the cover layer. At the main air duct location, the backplate has pre-drilled through holes, combined with flexible sealing rings or embedded interface components, to ensure connection stability and sealing performance in high-pressure underwater environments. Besides bearing the mechanical stress of the cover layer, the backplate, together with the cover layer substrate, constitutes a boundary constraint system. Its in-plane stiffness and mass significantly adjust the resonant frequency of the resonant cavity. Therefore, the thickness and stiffness of the backplate can be synergistically optimized based on the target frequency band and structural response requirements; the preferred backplate thickness h2 is 10–20 mm.

[0034] The air pressure control system typically includes a miniature air pump, pressure regulating valve, depth sensor, pressure sensor, and control module. It can be integrated into the general energy system of an underwater platform or deployed as a standalone module. The through-holes on the backplate connect to the air pump via air channels (such as flexible air ducts), forming a complete air path: air from the air pump outlet, through the backplate through-holes, enters the main air channel of the cover layer, and is further distributed to the internal air channel network and the cavity inlets of each resonant cavity, achieving modular air pressure control. Regarding the control strategy, the air pressure can be statically set according to a preset water depth before the mission begins, or it can be dynamically adjusted in real time based on data collected by the depth sensor, thus adapting to changes in hydrostatic pressure at different water depths and ensuring the continuous effectiveness of sound absorption performance.

[0035] During operation, this system actively controls the resonant frequency by adjusting the positive pressure difference (typically 0–6 MPa) between the air pressure inside the resonant cavity and the external water pressure. An appropriate pressure difference helps maintain the cavity geometry close to its design state, effectively suppressing structural compression, resonant frequency drift, and sound absorption performance degradation caused by external hydrostatic pressure. The setting of the positive pressure difference should comprehensively consider the geometric dimensions of the sound-absorbing unit, the mechanical properties of the materials, and the overall configuration characteristics, and should ideally be optimized through multiphysics modeling and simulation analysis. Practice shows that when the air pressure inside the cavity is slightly higher than the external water pressure (e.g., generating a positive pressure difference of approximately 1 MPa), superior structural stability and sound absorption performance are usually achieved.

[0036] In underwater operating environments, external hydrostatic pressure acting on the elastic matrix material easily induces non-uniform compressive deformation, leading to a reduction in the volume and geometric distortion of the resonant cavity. This, in turn, causes resonant frequency shift, a decrease in resonant amplitude, and unstable sound absorption performance. To mitigate these effects, this invention introduces a positive pressure differential. By adjusting the air pressure inside the resonant cavity to be higher than the external water pressure, the stability of the cavity's geometry is effectively maintained, ensuring reliable operation of the structure within the target resonant range. Specifically, this aerodynamic control mechanism not only helps maintain the resonant absorption peak value but also allows for a controllable shift towards lower frequencies, thereby expanding the overall absorption bandwidth. However, research has also found that while the positive pressure differential enhances low-frequency resonance, it may cause the frequency corresponding to the minimum absorption coefficient (i.e., the absorption valley) in some frequency bands to shift to lower frequencies, thus affecting the stability of broadband absorption performance. To address this issue, this invention significantly suppresses the unfavorable shift of the absorption valley frequency through synergistic optimization design of the resonant cavity configuration parameters and the pressure adjustment strategy. This ensures that the minimum absorption coefficient at the corresponding frequency point is always maintained above 0.8, guaranteeing good performance of the structure across a wide frequency range. Figure 4 As shown, the experimental results verify that the structure of the present invention generally has a sound absorption coefficient of over 0.8 in the frequency band of 1.15–10kHz within the hydrostatic pressure range of 0–6MPa, demonstrating excellent wide low-frequency absorption capability and adaptability to multi-depth water environments.

[0037] The pneumatically controlled acoustic covering system described in this invention possesses excellent compatibility. The backplate structure and air pressure control system can be modularly integrated with existing structures or equipment on submarines or other underwater platforms (such as hull strength frames, in-cabin air supply systems, and environmental control units). This design eliminates the need for bulky or heavy independent devices, effectively avoiding system redundancy while ensuring functional integrity, simplifying the overall architecture, reducing overall structural weight, and facilitating lightweight design and flexible deployment of the covering layer. This significantly enhances the system's engineering adaptability and practicality.

[0038] In summary, this invention proposes an underwater acoustic structure based on a triple coupling mechanism of "voltage regulation-deformation-resonance," constructing a functional system with nonlinear response capabilities and dynamic adjustment characteristics. Through collaborative design of "structure-material-load," the covering layer maintains stable geometry and resonant performance under various water depth conditions, achieving efficient sound absorption and adaptive control. This technical solution combines engineering adaptability and service reliability, providing a theoretical basis and engineering implementation path for the development of intelligent and controllable underwater acoustic covering layers, and possesses good application prospects and promotional value.

[0039] To ensure that numerical simulations have a realistic physical basis and accurately predict sound absorption performance, this invention systematically obtains the static and dynamic mechanical parameters of the matrix material through a combination of experimental measurement and theoretical fitting. Static parameters are obtained through low-speed uniaxial tensile experiments. The linear segment of the stress-strain curve is used to extract Young's modulus, and then the basic mechanical parameters such as shear modulus and Poisson's ratio are derived. The tensile rate is controlled in the experiment to reduce the viscous effect, making the results closer to the quasi-static service state of the underwater structure. Dynamic response is measured using dynamic thermomechanical analysis (DMA). The storage modulus (G′) and loss modulus (G″) are obtained at different temperatures and frequencies. Based on the time-temperature superposition principle, a master curve of the dynamic modulus is constructed, extending the effective frequency range to the mid-to-high frequency band required for sound absorption analysis. On this basis, the uniaxial tensile response is derived in the frequency domain using a neo-Hookean material model. By fitting the master curve with a complex function, frequency-related viscoelastic parameter functions are extracted to accurately characterize the viscoelastic dissipation characteristics of the material. The obtained parameters provide a solid basis for material modeling and performance prediction in multiphysics simulations.

[0040] To systematically reveal the sound absorption performance response characteristics of underwater acoustic covering layers under different working conditions and analyze the control effects of material parameters and geometric configuration, this invention constructs an incremental finite deformation numerical simulation method based on supervisoelastic theory. This method takes into account the finite large deformation behavior of the structure under hydrostatic pressure and internal pressure, as well as the propagation characteristics of perturbational sound waves in the deformation background field, and can accurately characterize the dynamic response mechanism of soft material sound-absorbing structures under pressure. In the modeling process, the covering layer as a whole is regarded as a small perturbation superposition system based on quasi-static large deformation. The elastic response of the matrix is ​​described by the neo-Hookean model, and the viscoelastic dissipation characteristics of the material are introduced through frequency-dependent complex relaxation functions. For the structural configuration evolution and material parameter changes caused by finite deformation, the effective stiffness tensor under the current configuration is constructed by push-forward formulation under the deformation tensor, and the equivalent elastic modulus is formed by combining the frequency domain viscoelastic response, realizing the unified modeling of elastic response and dissipation effect. This method can not only accurately predict the resonant frequency drift and absorption performance evolution caused by changes in water pressure and cavity pressure, but also support multi-parameter sensitivity analysis and structural optimization, providing a solid theoretical and numerical foundation for the design and performance improvement of underwater soft material acoustic structures.

[0041] The numerical experiments used in this invention are based on a commercial finite element platform and employ a two-step method for acoustic performance analysis. The first step involves finite deformation calculations under hydrostatic pressure to obtain the steady-state deformation field and corresponding deformation gradient tensor of the structure at its actual service water depth. The second step, based on this, applies a periodic perturbation sound pressure boundary and performs frequency-domain acoustic-structure interaction analysis to solve for the dynamic response of the structure to incident sound waves, ultimately obtaining the frequency-absorption coefficient (FAB). The relationship curve. To control computational resources while maintaining accuracy, a two-dimensional axisymmetric model is used for modeling during the simulation (e.g., Figure 1 As shown in (c) and (d), computational efficiency is significantly improved while effectively preserving key structural features and physical mechanisms. This modeling strategy has been widely applied in related research, and its accuracy and applicability have been verified by comparison with 3D simulation and experimental data. The "two-step method" combined with the axisymmetric strategy adopted in this invention not only greatly improves simulation efficiency but also provides a repeatable and generalizable numerical experimental basis for structural response analysis and parameter optimization under different working conditions. In the reference embodiment one, the relevant simulation results have been verified by comparison with existing experimental data and 3D simulation results, further demonstrating that this method has good accuracy and engineering feasibility, and can be widely applied to structural parameter design, performance evaluation, and optimization analysis.

[0042] Example 1: Unit structure design and performance verification of pneumatically controlled underwater acoustic coating

[0043] Example 1 selects a typical unit in the acoustic covering layer structure as the research object and examines its performance under different hydrostatic pressures ( The deformation response and sound absorption performance changes under certain conditions were studied, focusing on verifying the practical effect of the aerodynamic control mechanism in maintaining the stability of the cavity configuration and improving broadband sound absorption performance. The geometric configuration, material parameters, and loading method of the unit structure all follow the aforementioned design principles and are set in conjunction with theoretical models and existing experimental data to ensure the representativeness and engineering adaptability of the simulation results.

[0044] The cladding structure used is a flat, sheet-like form, with the internal resonant cavity embedded in the elastic matrix in a hexagonal lattice configuration. The overall configuration is similar to... Figure 1 The structure shown is consistent. To establish an accurate simulation model, its key structural parameters are listed in Table 1. The above structure has been described in detail in the "Detailed Implementation" section and will not be repeated here.

[0045] Table 1. Key structural parameters of pneumatically controlled underwater acoustic coating

[0046]

[0047] The matrix material selected in this embodiment is solution-styrene-butadiene rubber (S-SBR), specifically model VSL5025-0. This material is a typical low-modulus, high-loss elastomer, commonly used in underwater sound-absorbing structures. Its static Young's modulus... The pressure is approximately 4 MPa, and the Poisson's ratio is close to 0.49. Frequency response characteristics measured based on DMA experiments indicate that the equivalent loss factor of this material ranges from 0.9 to 1.2 in the 0.5–10 kHz frequency band. (See details...) Figure 3 .

[0048] Under conditions without internal pressure, the structural deformation behavior and sound absorption performance of the overburden layer in a water depth range of 0–300 m (corresponding to a hydrostatic pressure of 0–3 MPa) are as follows: Figure 5 As shown. Figure 5 (a) shows that as water depth increases, the matrix material undergoes significant compression under hydrostatic pressure, resulting in a marked distortion of the overall configuration (where the black frame represents the initial configuration of the material, and the grayscale image represents the deformed configuration. The degree of offset of the grayscale image relative to the frame reflects the overall deformation amplitude, with darker colors indicating more severe local compression). The cavity structure exhibits significant collapse, with stress concentration in local areas, and some locations even showing a tendency to become unstable. Figure 5 (b) shows the sound absorption coefficient of the cover layer under different water pressure conditions. The relationship between frequency and absorption peak frequency is shown. The results indicate that as the water depth increases, the resonant structure gradually deviates from the original design state, with the absorption peak frequency shifting and the amplitude attenuating, leading to a significant decrease in overall sound absorption performance and severe damage to the acoustic function of the covering layer.

[0049] Based on this, if an air pressure equal in amplitude to the external hydrostatic pressure is applied inside the resonant cavity, that is, if the air pressure inside the cavity is... With external water pressure Maintaining consistency throughout allows for a balanced state within the structure, effectively counteracting the deformation caused by water pressure. For example... Figure 6 As shown in (a), in Within the water pressure range of MPa, by maintaining The geometry of the covering layer remains almost unchanged, the cavity remains in its designed state, and there is no obvious compression or distortion. Figure 6 (b) shows the sound absorption coefficient under this condition. The curves show that the sound absorption performance is basically consistent with that under no hydrostatic pressure conditions, indicating that the structure can achieve performance stability under different water depths. These results verify that the key factor affecting the sound absorption performance of the covering layer is the pressure difference between the inside and outside of the cavity. It is not the water depth itself, but the depth of the water.

[0050] Furthermore, under conditions where the internal air pressure is slightly higher than the hydrostatic pressure, for example, by applying approximately... A positive pressure difference can cause the structure to produce a moderate reverse expansion effect. For example... Figure 7 As shown in (a), the cavity morphology is restored to a more ideal state, the local equivalent stiffness is improved, and the resonant frequency is effectively controlled. Figure 7 (b) shows the sound absorption coefficient under this condition. The curves show that a positive pressure difference causes the absorption peak to shift towards lower frequencies, thereby expanding the effective absorption bandwidth and significantly improving low-frequency performance. Although studies have found that a moderate positive pressure difference, while enhancing low-frequency absorption, also causes the absorption valley frequency to shift synchronously towards lower frequencies, resulting in a decrease in the sound absorption coefficient in some frequency bands, this invention, through the synergistic optimization of the aforementioned structural configuration and voltage regulation strategy, effectively suppresses the low-frequency drift of the absorption valley, ensuring that its minimum sound absorption coefficient remains stably above 0.8, thus guaranteeing the stability and efficiency of broadband sound absorption performance.

[0051] The comparison results of sound absorption performance show that, Under positive pressure differential control conditions, the acoustic coating layer in Maintains stable sound absorption performance under hydrostatic pressure. The sound absorption coefficient remains above 0.8 and the equivalent density is below 0.8 throughout the frequency band. The results verify the comprehensive advantages of the structure of the present invention in terms of bandwidth, efficiency, lightweight and pressure resistance, and show that it has better underwater adaptability and sound absorption performance than traditional fixed structure sound-absorbing coverings.

[0052] In summary, this embodiment systematically demonstrates the structural stability and adjustable sound absorption performance of a pneumatically controlled underwater acoustic coating under hydrostatic pressure conditions, verifying the effectiveness of achieving multi-depth adaptability and sound absorption bandwidth expansion by adjusting the internal pressure of the resonant cavity. This technical solution can effectively cope with deep-water, high-pressure conditions while maintaining the lightweight nature of the coating, achieving wide-range, low-frequency, and high-efficiency absorption, meeting the engineering requirements of "lightweight – low-frequency – pressure-resistant," and possessing significant application value and engineering promotion prospects.

[0053] Example 2: The regulating effect of matrix material modulus on the sound absorption performance of the capping layer

[0054] This embodiment aims to analyze the influence of the elastic modulus of the cover layer matrix material on the sound absorption performance, and propose an optimized material selection strategy accordingly. During the simulation, except for the matrix elastic modulus parameter, other structural configuration parameters and material properties remained consistent with those in Embodiment 1 to ensure comparability of results and the relevance of the analysis.

[0055] In an underwater hydrostatic environment, the substrate material of the capping layer needs to possess appropriate deformation capacity to effectively adjust the structural resonance characteristics. To investigate the effect of changes in elastic modulus on sound absorption performance, this embodiment uses the substrate material from Embodiment 1, setting its Young's modulus to be... ,in This is the baseline modulus of the material used in Example 1. The scaling factor is adjusted accordingly. The response characteristics of materials ranging from softer to harder were simulated using values ​​of 0.5, 1.0, 1.5, and 2, respectively. Simulation analysis was conducted under positive differential pressure loading to systematically evaluate the regulatory trend of matrix modulus changes on structural response and sound absorption performance.

[0056] The structural response and sound absorption performance of the capping layer under different matrix material modulus conditions are as follows: Figure 8 As shown. Figure 8 (a) indicates that as the material modulus decreases, the overall thickness of the structure expands significantly, the volume of the resonant cavity increases, and this expansion is more pronounced at lower moduli ( Under extremely soft material conditions, significant distortion may occur in localized areas, causing the resonant unit configuration to deviate from its design state. This structural instability weakens the stability of the resonance mechanism and is detrimental to maintaining sound absorption performance. Conversely, excessively high material modulus (…) When the structure is subjected to positive pressure difference, there is almost no obvious deformation, the cavity volume remains unchanged, and it is difficult to trigger the frequency regulation mechanism dominated by the geometry configuration. Figure 8 (b) shows the frequency response characteristics of the sound absorption coefficient under different modulus conditions. For materials with excessively low modulus, the sound absorption coefficient is generally below 0.7, and the broadband sound absorption performance is severely degraded, especially in the low-frequency range. When the modulus is too high, although the sound absorption coefficient is improved in some mid-to-high frequency ranges, the low-frequency absorption capacity is significantly weakened, and the sound absorption spectrum exhibits high-frequency drift characteristics. At this time, the structure is sluggish in response to positive pressure differential regulation, and the tuning mechanism is difficult to play its role. Comprehensive analysis shows that the modulus of the matrix material has a significant impact on the structural response and regulation performance of the capping layer. A balance needs to be sought between "deformation capability" and "structural stability" to achieve the optimal sound absorption effect.

[0057] In summary, the elastic modulus of the matrix material has a significant impact on the structural response and aerodynamic control effect. When the material modulus is too low, the structure is prone to excessive expansion and local distortion, which undermines the stability of the resonant system and severely weakens the sound absorption performance. Conversely, when the modulus is too high, the structural deformation capacity is limited, making it impossible to form an effective frequency shift, and the control mechanism is difficult to function. Therefore, controlling the elastic modulus within a certain range is crucial. interval (i.e.) The matrix material of S-SBR, while ensuring structural stability, possesses excellent adjustable response capabilities, which can significantly improve sound absorption performance and system adaptability. Based on the above analysis, S-SBR material and other rubber-like elastomers with similar mechanical properties can be used as preferred matrix materials for the acoustic covering layer of this invention. Under the action of aerodynamic control mechanism, the adjustable advantages of the resonant structure can be fully utilized to significantly improve the broadband absorption capability and engineering application performance in multi-depth water environments.

[0058] Example 3: The regulating effect of matrix structural parameters on the sound absorption performance of the capping layer

[0059] To further clarify the performance variation trend of underwater acoustic coatings at different structural scales and analyze the influence of structural dimensions on aerodynamic control, this embodiment introduces an overall scale factor based on Embodiment 1. The main structure of the overlay layer is scaled proportionally in all directions to create a series of structural styles with different thicknesses (such as...). Figure 9 (as shown in (a)). In all comparative structures, the unit cell configuration, periodic arrangement, porosity, and backing material remained unchanged; only the scale of the cover layer matrix was adjusted. Specifically, the structural scale factor n took values ​​of 0.5, 1, 1.5, and 2, corresponding to four typical cases: shrinking to 50% of the original volume, maintaining the original size, enlarging to 150% of the original volume, and enlarging to 200%, respectively. This setup ensured that, under the premise of consistent geometric proportions, the response differences were introduced only through dimensional changes, thereby systematically exploring the influence of cover layer thickness on sound absorption performance and control capability.

[0060] like Figure 9 As shown in (b)–(e), each structure is in zero pressure difference and The sound absorption performance under a positive pressure difference of MPa exhibits a significant scale dependence. Specifically, when At that time, the overall thickness of the structure decreases and the cavity becomes thinner, only under zero pressure difference... Good absorption is achieved at kHz; the cavity volume increases slightly under positive pressure difference, low-frequency resonance is enhanced, and the absorption band extends to [a certain value]. kHz; when (In the original structure) it was already covered under zero pressure difference. kHz, the positive pressure difference is further extended to kHz; when At that time, it can be achieved at zero pressure difference. Wideband sound absorption of kHz, and positive pressure difference further extend low-frequency performance to approximately kHz. kHz; when At that time, the absorption bandwidth expands to [value missing] under positive pressure difference. kHz, achieving extremely wideband sound absorption.

[0061] The above results indicate that structural scaling can effectively reduce the intrinsic resonant frequency of the system, thereby enhancing its low-frequency absorption capability. However, increasing the structural size also leads to a significant increase in material usage and coating thickness, resulting in increased overall weight and manufacturing costs. Furthermore, a significant size effect is observed in aerodynamic control capabilities: for smaller structures, the deformation induced by positive pressure difference is more pronounced, resulting in significant control effects; while in larger structures, their inherent low-frequency resonant capability partially offsets the additional structural response induced by pressure regulation, leading to gradual saturation of the control gain and a weakening of the marginal effect.

[0062] In summary, under the current configuration, the preferred range for the thickness of the capping layer matrix is ​​as follows: It can achieve coordinated optimization of structural compactness, lightweight design, and control efficiency while ensuring wideband sound absorption performance.

[0063] Example 1: Sound absorption performance of the covering layer without aerodynamic control or structural optimization

[0064] To verify the incremental finite deformation theory used in this invention and its accuracy and applicability in the analysis of coupled large deformation structures and underwater acoustic fields, and to further analyze the sound absorption performance of the structure without the introduction of aerodynamic control mechanisms, this reference example selects a typical spherical cavity rubber matrix structure as the case study object, with the configuration as follows: Figure 10 As shown in (a). This structure originates from the experimental and three-dimensional finite element simulation study reported in reference 2 (Yang H, Zhao H, Wen J. Theory and numerical method for the effects of hydrostatic pressure on sound absorption of underwater acoustic coatings with air cavities[J]. Journal of Sound and Vibration, 2022, 533: 116985.), with the model being a thickness A mm-sized axially symmetric rubber matrix layer, with several spherical cavities symmetrically embedded within it along the axial direction, the cavity radius being... mm, embedding depth mm, outer diameter of the matrix mm.

[0065] In terms of materials, the matrix is ​​a highly elastic rubber, and the shear modulus is set to... MPa, Poisson's ratio is The viscoelastic parameters were obtained by fitting experimental data from the literature. To adapt to the modeling strategy in this paper, the structure was constructed using a two-dimensional axisymmetric model, and the material model was adjusted from the Mooney–Rivlin form in the original paper to a neo-Hookean model. Based on this, the frequency-related storage modulus and loss modulus were obtained by fitting its dynamic response characteristics.

[0066] The simulation results of this invention are compared with the three-dimensional simulation and experimental test data reported in Reference 2, and the results are as follows: Figure 10 As shown in (b), the three methods exhibit high consistency in key indicators such as the frequency, peak amplitude, and bandwidth of the main absorption peak, and their absorption coefficient curves almost overlap, verifying the reliability of the numerical method used in this invention in terms of accuracy and engineering applicability.

[0067] Further analysis of the structure's water depth response characteristics under conditions without aerodynamic control reveals that its sound absorption performance is significantly affected by changes in hydrostatic pressure. As water depth increases, the hydrostatic pressure rises, causing compression deformation of the cavity and a shift in its internal resonance characteristics. This results in drift or performance degradation of the originally optimized sound absorption frequency band. Simulation results show that the low-frequency absorption peak shifts towards higher frequencies, and the overall sound absorption coefficient decreases, indicating that this type of structure struggles to maintain stable sound absorption performance in complex underwater environments.

[0068] In summary, this reference example verifies the applicability and accuracy of the numerical simulation experimental method involved in the present invention in acoustic modeling of rubber-like soft structures. On the other hand, it also reveals the limitations of traditional uncontrolled structures in terms of insufficient stability of sound absorption performance under hydrostatic pressure changes, demonstrating the important value of the aerodynamic control mechanism of the present invention in improving low-frequency stability and structural adaptability, and providing strong support for the advantages of subsequent solutions.

[0069] Comparative Example 1: Sound absorption performance of the covering layer when supported by steel

[0070] To verify the effectiveness of the pneumatic control mechanism proposed in this invention and to reveal the performance of the classic steel-supported sound-absorbing structure in the application scenario of this invention, this comparative example replaces the pneumatic control unit with a steel support structure based on the material and structure of the pneumatically controlled underwater sound-absorbing covering layer, thus constructing a comparative model without active control capability, such as... Figure 11 As shown in (a). Specifically, a cylindrical steel support rod with a radius of [missing information] is introduced at the center of the overburden layer. mm, height mm, its bottom end is fixed to the steel back plate, and its top end passes through the conical cavity and is embedded in the rubber matrix; at the same time, at a distance of from the bottom end Set a radius at mm mm, thickness A steel disc measuring mm was used to enhance the overall resistance to deformation.

[0071] like Figure 11 As shown in (a), the steel support structure is Severe cavity crushing occurred under MPa hydrostatic pressure, resulting in poor sound absorption performance. Figure 11 (b) Significant decrease, only in It exhibits limited absorption in the kHz range, which is significantly lower than the broadband sound absorption performance of the aerodynamic control structure under the same operating conditions.

[0072] The results in summary clearly demonstrate that the aerodynamic control mechanism has significant advantages in improving the compressive stability and low-frequency absorption capacity of the sound-absorbing covering layer structure, making it a key design strategy for dealing with complex water depth conditions. In contrast, traditional steel-supported structures, lacking active control capabilities, struggle to adapt to changes in external water pressure, resulting in insufficient stability in sound absorption performance. This comparative result, from the opposite perspective, verifies the core value of the aerodynamic control mechanism in ensuring wideband, high-efficiency sound absorption and structural adaptability, providing strong support for the rationality and superiority of the proposed solution.

Claims

1. An acoustic covering layer system suitable for environments with varying water depths, characterized in that: This includes the cover layer, back panel, and air pressure control system; The covering layer includes an elastomer matrix, a resonant cavity, and an airway network; Both the resonant cavity and the air passage network are located inside the substrate. The resonant cavity has a cavity inlet, and the air passage network is connected to the cavity inlet of the resonant cavity. The backplate is disposed at the far end of the cover layer; the air pressure regulation system includes an air source and a control module; the air channel network is connected to the air source, the control module controls the air source, and controls the air pressure in the resonant cavity through the air channel network.

2. The acoustic covering layer system suitable for multi-depth water environments as described in claim 1, characterized in that, The resonant cavity includes a main body, a near-water end, and a far-water end, which are connected in sequence. The main body is frustum-shaped, and the base radius r1 of the main body connected to the near-water end is smaller than the base radius r2 of the main body connected to the far-water end. The near-water end and the far-water end are hemispherical shapes that smoothly transition to the main body.

3. The acoustic covering layer system suitable for multi-depth environments as described in claim 2, characterized in that, The thickness h1 of the cover layer is 75-150mm, the distance h3 between the top of the near-water end and the top surface of the substrate is 6.25-12.5mm, the distance h4 between the bottom of the far-water end and the bottom surface of the substrate is 6.25-12.5mm, r1 is 2.5-5mm, r2 is 3.75-7.5mm, and the thickness h2 of the back plate is 10-20mm.

4. The acoustic covering layer system suitable for multi-depth environments as described in any one of claims 1-3, characterized in that, The resonant cavities are periodically arranged within the substrate, preferably with an arrangement period 2a of 18.75-37.5 mm.

5. The acoustic covering layer system suitable for multi-depth environments as described in any one of claims 1-3, characterized in that, The substrate material of the capping layer satisfies at least one of the following conditions: a) The elastic modulus is 4-6 MPa. b) Poisson's ratio is between between, c) The loss factor ranges from 0.9 to 1.2 within the 0.5-10kHz frequency band. d) The substrate material of the cover layer is solution polymerized styrene-butadiene rubber (S-SBR), ethylene propylene rubber (EPDM), or high-loss polyurethane elastomer (PU).

6. The acoustic covering layer system suitable for multi-depth environments as described in any one of claims 1-3, characterized in that, The cavity inlet is located at the center of the bottom surface at the far end of the resonant cavity.

7. The acoustic covering layer system suitable for multi-depth environments as described in any one of claims 1-3, characterized in that, The covering layer is formed by multiple tile units, each tile unit having multiple resonant cavities, and preferably the in-plane dimensions of the tile unit are 200-800 mm.

8. The acoustic covering layer system suitable for multi-depth environments as described in claim 7, characterized in that, The tile unit has only one main air channel, and the cavity inlets of all resonant cavities in the tile unit are uniformly guided to this main air channel, which is connected to the air source.

9. The acoustic covering layer system suitable for multi-depth environments as described in any one of claims 1-3, characterized in that, The air pressure control system also includes a depth sensor, a pressure regulating valve, and / or a pressure sensor.

10. A method for controlling sound absorption based on the system described in any one of claims 1-9, characterized in that, The air pressure regulation system makes the air pressure inside the resonant cavity higher than the water pressure outside the covering layer, preferably generating a positive pressure difference of about 1 MPa.

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