Underwater sound absorption covering layer

Abstract

The invention relates to the technical field of underwater sound absorption material structure design, in particular to an underwater sound absorption covering layer. The underwater sound absorption covering layer comprises a plurality of sound absorption cell elements arranged periodically, and each sound absorption cell element comprises a rigid back plate, a damping layer, a rigid vertical plate, a second-order Helmholtz resonator and an oscillator assembly. The damping layer is divided into two parts by the rigid vertical plate, the resonator is embedded into the first part for capturing and dissipating low-frequency sound energy, and the oscillator assembly is embedded into the second part for dissipating medium-high-frequency sound energy. The covering layer consumes energy synergistically through local resonance and viscoelastic shear deformation, within the incidence angle range of 0-45 degrees, the sound absorption coefficient at the frequency band of 116 Hz to 10 kHz is not lower than 0.8, and the sound absorption coefficient at the frequency band of 1.4 kHz to 10 kHz is not lower than 0.95; the maximum deformation under the hydrostatic pressure of 3 MPa does not exceed 4 mm, and the sound absorption coefficient at the frequency band of 215 Hz to 10 kHz is not lower than 0.8; and the overall thickness does not exceed 50mm. According to the invention, the problems of insufficient low-frequency sound absorption, limited bandwidth, poor oblique incidence adaptability and weak anti-pressure ability are solved.

Description

Technical Field

[0001] This invention relates to the field of underwater sound-absorbing material structure design technology, specifically to an underwater sound-absorbing covering layer. Background Technology

[0002] Underwater acoustic coatings are a core technology for enhancing the acoustic stealth performance of submarines and other underwater equipment, and are widely used in critical scenarios such as noise control and sonar detection and avoidance. With the development of sonar technology towards broadband and low-frequency frequencies, and the increasing operating depth of underwater equipment, higher demands are placed on the performance of acoustic coatings: they must not only maintain a high sound absorption coefficient over a wide frequency range, but also possess excellent oblique incidence adaptability and resistance to deep-sea hydrostatic pressure.

[0003] Existing underwater sound-absorbing materials and structures face the following core technological bottlenecks: 1. Insufficient low-frequency sound absorption: Traditional cavity-type covering layers have a significantly reduced sound absorption coefficient in the low-frequency range below 1kHz, and it is especially difficult to achieve efficient acoustic attenuation in the ultra-low frequency range of around 500Hz, which is insufficient for avoiding modern low-frequency active sonar; although local resonant covering layers can improve low-frequency performance, they have the problem of deterioration of sound absorption in the non-resonant frequency range, which makes it difficult to cope with modern low-frequency sonar detection.

[0004] 2. Limited effective bandwidth: The sound absorption bandwidth of a single resonant structure is narrow and cannot cover a wide frequency detection range within 10kHz. The narrow-band sound absorption characteristics are difficult to meet the stealth requirements of the entire frequency band. Existing wideband designs mostly use multiple resonant cavities in series / parallel, which easily leads to a thick structure and increased equivalent density, which contradicts the lightweight requirements of underwater equipment.

[0005] 3. Poor adaptability to oblique incidence: In actual marine environments, sound waves are mostly obliquely incident. Traditional covering layers are prone to exciting Rayleigh-Lamb plate waves at incident angles above 30°, which leads to enhanced sound wave reflection and a significant decrease in sound absorption performance, making it difficult to meet the needs of practical applications.

[0006] 4. Weak resistance to hydrostatic pressure: Under the hydrostatic pressure of 3MPa in the deep sea, the structure deforms greatly and the stress is concentrated. The maximum deformation of the traditional steel base covering layer can reach 6.86mm. The structural deformation and changes in material parameters lead to impedance mismatch and significantly deteriorate the sound absorption performance. Existing high pressure resistance designs are mostly achieved by increasing the structural thickness, which increases the manufacturing cost and further exacerbates the contradiction between lightweight and sound absorption performance.

[0007] 5. Insufficient synergistic performance: Existing improvement solutions mostly focus on single performance optimization (such as only improving low-frequency sound absorption or high-pressure resistance), making it difficult to meet multi-dimensional requirements such as wide frequency range, oblique incidence adaptation, and hydrostatic pressure resistance. For example, although some structures can achieve low-frequency sound absorption, high-frequency attenuation is obvious, or low-frequency performance deteriorates under high pressure.

[0008] Therefore, developing an underwater acoustic covering layer that combines low-frequency broadband high sound absorption, wide-angle adaptability, hydrostatic pressure resistance, and a compact structure has become a key direction for upgrading the acoustic stealth technology of underwater equipment. Summary of the Invention

[0009] In view of the shortcomings of the existing technology, the purpose of this invention is to provide an underwater sound-absorbing covering layer based on the synergistic effect of an oscillator and a second-order Helmholtz resonator, which achieves ultra-low frequency-wideband high sound absorption, excellent oblique incidence adaptability and hydrostatic pressure resistance.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides an underwater sound-absorbing covering layer comprising a plurality of periodically arranged sound-absorbing cells, each of the sound-absorbing cells comprising: Rigid backplate for connection to the surface of underwater equipment; A damping layer covers the upper surface of the rigid back plate; A rigid vertical plate is disposed on the upper surface of the rigid back plate, and the damping layer is divided into two independent first parts and second parts; A second-order Helmholtz resonator, embedded in the first part of the damping layer, is used to generate local resonance under acoustic excitation in order to capture and dissipate low-frequency acoustic energy. An oscillator assembly, embedded within a second portion of the damping layer, is used to induce viscoelastic shear deformation of the damping layer under acoustic excitation in order to dissipate mid-to-high frequency acoustic energy.

[0011] As a preferred embodiment of the present invention, the second-order Helmholtz-like resonator includes: A narrow slit, connecting to the external waters; A frustum-shaped cavity is disposed below and communicates with the slit; A closed cavity is independently located below the frustum cavity and adjacent to the rigid back plate.

[0012] As a preferred embodiment of the present invention, at least two frustum cavities connected in series are provided, with the bottom diameter of the upper frustum cavity being larger than the bottom diameter of the lower frustum cavity.

[0013] As a preferred embodiment of the present invention, the frustum cavity is filled with water when working underwater, and the sealed cavity is filled with air.

[0014] As a preferred embodiment of the present invention, the oscillator assembly includes a cylindrical oscillator and a helical oscillator located below it, both of which are in close contact with the damping layer.

[0015] As a preferred embodiment of the present invention, the axial direction of the cylindrical oscillator is consistent with the thickness direction of the underwater sound-absorbing covering layer, and the cylindrical oscillator and the helical oscillator are coaxially spaced apart.

[0016] As a preferred embodiment of the present invention, the damping layer is made of viscoelastic damping material, the second-order Helmholtz resonator and oscillator assembly are made of metal or carbon fiber composite material, and the rigid back plate and rigid vertical plate are made of steel.

[0017] As a preferred embodiment of the present invention, within the range of sound wave incident angles from 0° to 45°, the underwater sound-absorbing covering layer has a sound absorption coefficient ≥0.8 in the frequency band from 116Hz to 10kHz and a sound absorption coefficient ≥0.95 in the frequency band from 1.4kHz to 10kHz.

[0018] As a preferred embodiment of the present invention, under a hydrostatic pressure of 3 MPa, the maximum deformation of the underwater sound-absorbing covering layer structure does not exceed 4 mm, and the sound absorption coefficient is ≥0.8 in the frequency band from 215 Hz to 10 kHz.

[0019] As a preferred embodiment of the present invention, the overall thickness of the underwater sound-absorbing covering layer does not exceed 50 mm.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The synergistic energy dissipation mechanism significantly improves broadband sound absorption performance: In the low-frequency range (below 1kHz), sound energy is efficiently captured through the local resonance of the second-order Helmholtz-like resonator. In the mid-to-high frequency range (1kHz-10kHz), sound energy is dissipated by the viscoelastic shear deformation of the rubber layer caused by multiple oscillators, thus achieving ultra-low frequency to broadband full-range synergistic sound absorption with a stable and excellent sound absorption coefficient.

[0021] 2. Strong adaptability to oblique incidence: The structural design can excite low-order global horizontal modes and promote the conversion of longitudinal waves to shear waves. Even under 45° oblique incidence conditions, it can still maintain a high sound absorption coefficient. The first sound absorption peak shifts to low frequencies, further expanding the low-frequency sound absorption range and meeting the application requirements of random sound wave incidence in actual marine environments.

[0022] 3. Outstanding hydrostatic pressure resistance: The rigid support of multiple oscillators effectively disperses the hydrostatic load, reducing structural deformation. The maximum deformation under 3MPa hydrostatic pressure is only 3.54mm, significantly lower than the 6.86mm of the traditional steel base. Moreover, the stress distribution is uniform, avoiding the deterioration of sound absorption performance caused by local stress concentration.

[0023] 4. Compact and lightweight structure: The overall thickness is ≤50mm, which can achieve high pressure resistance and wide frequency sound absorption without the need for additional thickening structure, meeting the requirements of lightweight and miniaturization of underwater equipment, and the manufacturing cost is controllable.

[0024] 5. High parameter adjustability: By optimizing parameters such as the radius / height of the cylindrical oscillator, the number of turns / pitch of the helical oscillator, and the radius / height of the second-order Helmholtz resonator, it is possible to accurately match the sound absorption requirements of different frequency bands and adapt to diverse application scenarios. Attached Figure Description

[0025] Figure 1 This is a three-dimensional structural diagram of the underwater sound-absorbing covering layer of the present invention.

[0026] Figure 2 This is a schematic cross-sectional view of the underwater sound-absorbing covering layer of the present invention.

[0027] Figure 3 This is a schematic cross-sectional view of a single sound-absorbing cell in this invention.

[0028] Figure 4 This is a schematic diagram illustrating the parameter annotations of a single sound-absorbing cell in this invention.

[0029] Figure 5 The following diagrams are provided for the configuration: (a) is a schematic diagram of the decomposition of the equivalent calculation model of a single sound-absorbing cell in this invention; (b) is an electroacoustic analog diagram of a second-order Helmholtz resonator; (c) is a diagram of the average sound absorption coefficient of each frequency band of the three models; and (d) is a diagram comparing the sound absorption coefficients of the models.

[0030] Figure 6 The diagram shows the structural evolution process of the present invention; wherein, (a) is the structural evolution path of a single sound-absorbing cell of the present invention, and (b) is the sound absorption coefficient diagram of different structures during the evolution process.

[0031] Figure 7 The diagram shows the analysis of the present invention under oblique incidence; where (a) is a schematic diagram of oblique incidence of plane wave, and (b) is a sound absorption curve diagram of four angles.

[0032] Figure 8 This is an analysis diagram of the present invention under static pressure.

[0033] Figure 9 The diagram shows the static pressure results of the present invention; where (a) is the deformation diagram of the present invention, and (b) is the sound absorption coefficient diagram at 0MPa and 3MPa.

[0034] In the figure: 1. Sound-absorbing cell; 11. Rigid back plate; 12. Rigid vertical plate; 13. Damping layer; 14. Second-order Helmholtz resonator; 15. Oscillator assembly; 101. Slit; 102. Frustum cavity; 103. Closed cavity; 104. Cylindrical oscillator; 105. Helical oscillator. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that the accompanying drawings are for illustrative purposes only and should not be construed as limiting the present patent. For better illustration of this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable that some well-known structures and their descriptions may be omitted in the drawings for those skilled in the art. The positional relationships described in the drawings are for illustrative purposes only and should not be construed as limiting the present patent.

[0036] The present invention will now be described in further detail with reference to the accompanying drawings, illustrating an underwater sound-absorbing covering layer.

[0037] This invention addresses five core technical bottlenecks in existing underwater sound-absorbing coverings: insufficient low-frequency sound absorption, limited effective bandwidth, poor adaptability to oblique incidence, weak resistance to hydrostatic pressure, and difficulty in optimizing multiple performance aspects. Through a modular, partitioned design of periodic sound-absorbing cells, a dual-mechanism synergistic sound absorption system is constructed, combining low-frequency local resonance energy dissipation with mid-to-high-frequency shear deformation energy dissipation. Simultaneously, through a synergistic load-bearing design of a rigid frame and an embedded oscillator, acoustic and mechanical performance are simultaneously optimized. Ultimately, within an ultra-thin thickness of ≤50mm, it achieves a unified performance across multiple aspects, including ultra-low frequency to wideband high sound absorption, wide-angle incidence adaptability, and deep-sea high-pressure resistance, perfectly meeting the acoustic stealth protection requirements of submarines, underwater vehicles, underwater exploration platforms, and other equipment.

[0038] The underwater sound-absorbing covering layer of this invention is composed of a core of multiple sound-absorbing cells arranged in a periodic, continuous array within a horizontal plane (xy plane). In practical engineering applications, the planar shape, array quantity, and arrangement of the sound-absorbing cells can be adaptively adjusted according to the external curvature, size, and operating environment of the target equipment: for large planar / regular curved surface structures such as submarine pressure hulls, square or regular hexagonal cells can be used for seamless array splicing; for irregular curved surface structures such as the head and tail of underwater vehicles, the planar dimensions of individual sound-absorbing cells can be scaled proportionally, or irregularly shaped cells can be used to adapt to the curvature of the surface, ensuring complete adhesion between the covering layer and the outer wall of the equipment, and avoiding the risk of acoustic performance attenuation and structural detachment due to splicing gaps or poor adhesion.

[0039] In embodiments of the present invention, such as Figures 1-3As shown, a single sound-absorbing cell 1 is a composite structure, specifically including: a rigid back plate 11, a damping layer 13, rigid vertical plates 12, a second-order Helmholtz resonator 14, and an oscillator assembly 15. The rigid back plate 11 is located at the bottom of the cell, serving as the load-bearing foundation and acoustic rigid boundary of the entire structure; the damping layer 13 covers the upper surface of the rigid back plate 11 and is the core matrix for sound energy dissipation; three rigid vertical plates 12 are vertically fixed to the upper surface of the rigid back plate 11, dividing the damping layer 13 into two independent first and second parts; the second-order Helmholtz resonator 14 is completely embedded in the first part of the damping layer 13, serving as a low-frequency sound-absorbing functional unit, generating local resonance under sound wave excitation, capturing and dissipating low-frequency sound energy below 1kHz; the oscillator assembly 15 is completely embedded in the second part of the damping layer 13, serving as a mid-to-high-frequency sound-absorbing functional unit, inducing the damping layer 13 to undergo global viscoelastic shear deformation under sound wave excitation, dissipating mid-to-high-frequency sound energy from 1kHz to 10kHz.

[0040] All embedded second-order Helmholtz resonators 14 and oscillator components 15 are integrated with the damping layer 13 through high-temperature vulcanization molding to achieve interference fit and integral bonding. There is no relative sliding gap between the two, which ensures that the vibration energy under sound wave excitation can be efficiently transferred to the damping layer 13 matrix to achieve maximum sound energy dissipation. The rigid vertical plate 12 and the rigid back plate 11 are rigidly connected by welding and integral casting molding, with no relative displacement, forming a stable rigid support frame. At the same time, it realizes vibration isolation between the left and right functional areas, avoids the mutual cancellation of low-frequency resonance and mid-to-high frequency shear vibration, and ensures the synergistic superposition of sound absorption performance across the entire frequency band.

[0041] In this embodiment of the invention, the rigid backplate 11 is located at the bottom of a single sound-absorbing cell 1. It serves as the load-bearing foundation, installation reference, and acoustic rigid boundary of the entire sound-absorbing cover layer. Its core functions include three points: First, by bonding or mechanically connecting, the entire sound-absorbing cover layer is fixed to the surface of the underwater equipment, ensuring the stability of the structure under the environment of high hydrostatic pressure and high-speed water flow in the deep sea. Second, by utilizing its own high rigidity, it simulates the total reflection acoustic boundary of the metal shell of the underwater equipment, preventing incident sound waves from penetrating the cover layer and entering the interior of the equipment, ensuring that all incident sound waves are captured and dissipated within the cover layer structure. Third, it forms a collaborative rigid skeleton with the rigid vertical plate 12 and the oscillator assembly 15, bearing the load of deep-sea hydrostatic pressure, reducing the deformation of the upper damping layer 13 and the resonant structure, and maintaining the stability of acoustic performance under high pressure.

[0042] In this embodiment of the invention, the rigid vertical plate 12 is the core component for achieving zoned synergistic sound absorption and structural reinforcement. It is vertically positioned on the upper surface of the rigid back plate 11, dividing the damping layer 13 into two independent functional areas: a first part and a second part. In this preferred embodiment, the planar dimension ratio of the first part (the main low-frequency resonance zone) to the second part (the main mid-high frequency shear zone) is 1:1. This ratio has been acoustically optimized to achieve a balanced performance in both low-frequency and mid-high frequency sound absorption. The rigid vertical plate 12 is made of steel. In this preferred embodiment, the same grade of marine high-strength steel as the rigid back plate 11 is selected to ensure matching welding performance and consistent mechanical properties, avoiding welding cracks and stress concentration problems caused by material differences.

[0043] The core functions of the rigid vertical plate 12 are divided into two main aspects: First, it separates the low-frequency resonance zone from the mid-to-high frequency shear zone, avoiding mutual interference and phase cancellation between the low-frequency local resonance of the second-order Helmholtz resonator 14 and the mid-to-high frequency vibration of the oscillator assembly 15, ensuring that the energy dissipation mechanisms of the two frequency bands occur independently and efficiently, while forming a seamless connection in the frequency domain to achieve synergistic sound absorption across the entire frequency band; Second, it strengthens the structure and disperses the load, forming a vertical rigid support with the rigid back plate 11. In the deep-sea hydrostatic pressure environment, it can evenly distribute the vertical water pressure load to the entire plane of the rigid back plate 11, avoiding local compression deformation of the damping layer 13, while suppressing the horizontal expansion deformation of the damping layer 13, ensuring that the geometric configuration of the embedded resonator and oscillator assembly 15 is not destroyed, thereby maintaining stable acoustic performance under high pressure.

[0044] In this embodiment of the invention, the damping layer 13 is the core sound energy dissipation matrix of the sound-absorbing covering layer of the invention. It covers the upper surface of the rigid back plate 11 and is divided into two independent parts by the rigid vertical plate 12, which respectively embed a second-order Helmholtz resonator 14 and an oscillator assembly 15.

[0045] The damping layer 13 is made of a viscoelastic damping material. In this preferred embodiment, butyl rubber is preferentially selected as the matrix material of the damping layer 13. This material has three core advantages: First, excellent viscoelastic energy dissipation characteristics, with a shear loss factor as high as 0.9. Under the vibration deformation generated by acoustic excitation, it can efficiently convert vibration mechanical energy into heat energy dissipation through the internal friction effect between rubber molecular chains. In particular, the energy dissipation efficiency for shear deformation is much higher than that for compression deformation, perfectly matching the core shear energy dissipation mechanism of this invention. Second, excellent adaptability to marine environments. Butyl rubber has excellent resistance to seawater corrosion, anti-aging properties, and low-temperature resistance. It can maintain stable material performance for a long time in deep-sea high-salt, high-pressure, and temperature environments ranging from -5℃ to 60℃, without problems such as swelling, cracking, hardening, or performance degradation. Third, excellent molding and bonding properties. It can achieve high-strength integrated bonding with metal parts through high-temperature vulcanization, with an interface bonding strength ≥4MPa, and no risk of delamination or separation.

[0046] The damping layer 13 is divided into two independent functional zones: the first part is the main energy dissipation zone for low-frequency resonance, which is embedded with a second-order Helmholtz resonator 14. Under the excitation of low-frequency sound waves, the local resonance generated by the resonator will cause the surrounding damping layer 13 to generate strong local shear deformation. Through the internal friction effect of the damping material, low-frequency sound energy below 1kHz is efficiently captured and dissipated; the second part is the main energy dissipation zone for mid-to-high frequency shear, which is embedded with an oscillator component 15. Under the excitation of mid-to-high frequency sound waves, the multi-mode vibration of the oscillator component 15 will cause the damping layer 13 in the entire region to generate viscoelastic shear deformation, thereby achieving efficient dissipation of mid-to-high frequency sound energy from 1kHz to 10kHz.

[0047] In this embodiment of the invention, the second-order Helmholtz resonator 14 is the core functional unit for achieving ultra-low frequency high-efficiency sound absorption. It is embedded in the first part of the damping layer 13 and is used to generate local resonance under sound wave excitation in order to capture and dissipate low-frequency sound energy. The core structure of the second-order Helmholtz resonator 14 consists of the following components from top to bottom: slit 101, frustum cavity 102, and closed cavity 103. The three components are coaxially arranged to form a complete second-order resonance system.

[0048] The second-order Helmholtz resonator 14 is embedded in the center of the first part of the damping layer 13, with its axis aligned with the thickness direction (z-direction) of the sound-absorbing covering layer. Its top is flush with the upper surface of the damping layer 13, and its bottom extends close to the rigid backplate 11, forming a vertical multi-stage resonant structure. Unlike traditional single-order Helmholtz resonators, the second-order Helmholtz resonator 14 of this invention, through its second-order resonance system design of slit 101 + double-series frustum cavities 102 + closed cavity 103, can significantly reduce the resonant frequency while broadening the low-frequency sound absorption bandwidth, fundamentally solving the defects of insufficient low-frequency sound absorption and narrow bandwidth in traditional single-order resonators.

[0049] The slit 101, located at the top of the second-order Helmholtz resonator 14, is a cylindrical through-hole structure. Its top is flush with the upper surface of the damping layer 13, directly communicating with the external water area. Its bottom is smoothly connected to the frustum-shaped cavity 102 below, without steps or abrupt changes in cross-section, thus avoiding energy loss during the propagation of water flow and sound waves. The slit 101 is the only channel for external sound waves and water flow to enter the resonator. Under the excitation of sound waves, the water column inside the slit 101 forms the acoustic mass unit of the Helmholtz resonator, generating axial reciprocating vibration. This forms an acoustic mass-acoustic stiffness resonance system with the acoustic stiffness unit of the cavity below, which is the core structure for triggering local resonance.

[0050] In this preferred embodiment, two frustum cavities 102 are provided, coaxially connected in series: an upper frustum cavity 102 and a lower frustum cavity 102, which are smoothly connected. The top diameter of the upper frustum cavity 102 is exactly the same as the bottom diameter of the slit 101, achieving a smooth transition. The bottom diameter of the upper frustum cavity 102 is larger than the top diameter of the lower frustum cavity 102, and simultaneously, the bottom diameter of the upper frustum cavity 102 is larger than the bottom diameter of the lower frustum cavity 102, forming a progressively contracting series structure.

[0051] Compared to traditional cylindrical cavities, this progressively contracting series frustum structure has several key advantages: First, the variable cross-section structure allows sound waves to undergo multiple reflections, refractions, and scatterings within the cavity, significantly extending the sound wave propagation path and improving sound energy capture efficiency. Simultaneously, it ensures that sound wave energy is evenly distributed across the damping layer 13 surrounding the entire cavity, expanding the low-frequency energy dissipation area. Second, the two series-connected frustum cavities 102 form two series-connected acoustic capacitive structures, which, combined with the acoustic quality of the slit 101, form a second-order resonant system. This system can generate two adjacent resonant absorption peaks in the low-frequency band, significantly broadening the low-frequency absorption bandwidth and completely solving the core problem of single-peak absorption and narrow bandwidth in traditional single-order Helmholtz resonators.

[0052] In underwater operation, water from the external water area completely fills the two series-connected frustum cavities 102 through the top slit 101, forming a continuous water column structure. This water column structure generates axial reciprocating vibrations under the excitation of low-frequency sound waves, coupling with the damping layer 13 and the air in the enclosed cavity 103. This efficiently transfers the energy of the low-frequency sound waves to the surrounding damping layer 13, dissipating the sound energy through the shear deformation of the damping material. Simultaneously, the variable cross-section design of the series-connected frustum cavities 102 allows the water column to vibrate at different velocities at different cross-sections, inducing multi-regional shear deformation in the surrounding damping layer 13, further enhancing the low-frequency sound energy dissipation efficiency.

[0053] In this preferred embodiment, the enclosed cavity 103 is an independent cylindrical enclosed structure located directly below the lower frustum cavity 102. It is completely isolated from the lower frustum cavity 102 by a damping layer 13 material, with no connecting channels, ensuring the complete airtightness of the enclosed cavity 103. The bottom of the enclosed cavity 103 is directly adjacent to the upper surface of the rigid back plate 11, and a damping layer 13 of a certain thickness is reserved between the top and the bottom of the lower frustum cavity 102 to prevent the vibration of the high-pressure water column from directly impacting the enclosed cavity 103, thus ensuring the stability of the cavity structure. The air inside the enclosed cavity 103 forms the core acoustic stiffness unit of the second-order Helmholtz resonator 14 of the present invention, which forms a mass-spring resonance system coupled with the acoustic mass of the water column in the upper frustum cavity 102. When the frequency of the incident sound wave is consistent with the natural frequency of the resonance system, it will induce strong local resonance, and the reciprocating vibration amplitude of the water column will reach its peak value, which will drive the surrounding damping layer 13 to generate strong shear strain, thereby efficiently converting low-frequency sound energy into heat energy dissipation.

[0054] In this embodiment of the invention, the oscillator component 15 is the core functional unit for achieving high-frequency wideband high sound absorption in the invention, and is also a key support structure for improving the structure's resistance to hydrostatic pressure. It is embedded in the second part of the damping layer 13 and is used to induce viscoelastic shear deformation of the damping layer 13 under acoustic excitation in order to dissipate high-frequency acoustic energy. The oscillator assembly 15 is fully embedded in the central axis of the second part of the damping layer 13, making complete and tight contact with the damping layer 13 without gaps or air bubbles. This integrated design is achieved through vulcanization molding. Unlike traditional single oscillator structures, the oscillator assembly 15 of this invention employs a coaxial combination of a cylindrical oscillator 104 and a helical oscillator 105, spaced coaxially. This allows for the formation of multiple continuous resonance peaks in the mid-to-high frequency range of 1kHz-10kHz, achieving high sound absorption without troughs across the entire mid-to-high frequency band. Simultaneously, it provides rigid support for the entire structure, significantly improving its resistance to hydrostatic pressure.

[0055] The cylindrical oscillator 104 is a solid cylindrical rigid structure, with its axis aligned with the thickness direction (z-direction) of the sound-absorbing covering layer, and is coaxially positioned at the central axis of the second part of the damping layer 13. A certain thickness of damping layer 13 is reserved between the top of the cylindrical oscillator 104 and the upper surface of the damping layer 13, and a certain thickness of damping layer 13 is reserved between the bottom of the cylindrical oscillator 104 and the top of the helical oscillator 105, forming a coaxially spaced structure. This structure can avoid mutual interference and phase cancellation between the vibration modes of the two, and can also ensure that the vibration of both can induce shear deformation of the surrounding damping layer 13, achieving full coverage of the vibration energy dissipation range.

[0056] In this preferred embodiment, the cylindrical oscillator 104 can form stable resonance in the mid-to-high frequency range, causing strong shear deformation in the surrounding damping layer 13. The cylindrical oscillator 104 is a solid rigid structure with a density much greater than the rubber material of the damping layer 13. Under acoustic excitation, its vibration inertia is greater, and its vibration phase differs significantly from the matrix of the damping layer 13, resulting in a strong relative displacement between them. This, in turn, generates strong shear strain in the surrounding damping layer 13, achieving efficient dissipation of mid-to-high frequency acoustic energy. Simultaneously, the cylindrical oscillator 104 is axially arranged along the thickness direction, forming continuous rigid support in the vertical direction. In the deep-sea hydrostatic pressure environment, it effectively bears the vertical pressure load, reducing the compressive deformation of the damping layer 13. Together with the rigid vertical plate 12 and the rigid back plate 11, it forms a collaborative load-bearing skeleton, significantly improving the structure's resistance to hydrostatic pressure.

[0057] In this preferred embodiment, the helical oscillator 105 is located directly below the cylindrical oscillator 104 and is coaxially arranged with the cylindrical oscillator 104. A damping layer 13 of a certain thickness is reserved between the bottom of the helical oscillator 105 and the upper surface of the rigid back plate 11. The whole is a cylindrical helical rigid structure, similar to the continuous helical configuration of a spring.

[0058] The spiral structure of the spiral oscillator 105 has the following advantages: First, a larger contact area and energy dissipation range. The spiral structure has a much larger specific surface area than a solid cylinder, increasing the contact area with the damping layer 13 by more than three times. During vibration, it can induce shear deformation of the damping layer 13 over a wider range, achieving full-range dissipation of mid-to-high frequency sound energy, rather than the localized energy dissipation of traditional structures. Second, multi-mode vibration and broadband sound absorption. The spiral structure can generate multiple torsional vibrations and axial vibrations in different mid-to-high frequency bands, forming multiple continuous resonant sound absorption peaks. The resonance peak of the cylindrical oscillator 104 is perfectly complementary, further broadening the mid-to-high frequency sound absorption bandwidth and ensuring that the sound absorption coefficient is stable above 0.9 in the entire frequency range of 1kHz-10kHz. Thirdly, it has excellent mechanical load-bearing and deformation resistance. The spiral structure has a certain axial elasticity. Under hydrostatic pressure load, it can absorb pressure energy through small elastic deformation, while uniformly distributing the load to the surrounding damping layer 13 and rigid back plate 11, avoiding local stress concentration, further improving the deformation resistance of the structure, and ensuring the structural and performance stability under high pressure environment.

[0059] Under mid-to-high frequency acoustic excitation, the helical oscillator 105 simultaneously generates axial reciprocating vibration and circumferential torsional vibration. These two vibration modes act simultaneously on the surrounding damping layer 13, causing multi-dimensional shear deformation. Compared to single axial vibration, this multi-dimensional deformation more efficiently stimulates the internal friction energy dissipation effect of the damping material, improving the dissipation efficiency of mid-to-high frequency acoustic energy. Furthermore, the coaxial arrangement of the helical oscillator 105 and the cylindrical oscillator 104 allows their vibration modes to couple and superimpose in the mid-to-high frequency range, forming a continuous high sound absorption range within the 1.4kHz-10kHz frequency band, with a stable sound absorption coefficient ≥0.95.

[0060] To clearly illustrate the technical solution and beneficial effects of the present invention, this section provides a complete set of preferred embodiment parameters, such as... Figure 4 As shown, its sound absorption performance is verified by finite element simulation. All parameters are illustrative and not intended to limit the scope of protection of this invention. Those skilled in the art can adjust the parameters according to actual application scenarios, and all such adjustments are within the scope of protection of this invention.

[0061] 1. The damping layer is made of a viscoelastic material, preferably with a density of 900 kg / m³. 3 Butyl rubber with a pressure wave velocity of 1000 m / s, a compression loss factor of 0.3, a shear wave velocity of 100 m / s, and a shear loss factor of 0.9.

[0062] 2. The preferred material for both cylindrical and helical oscillators has an elastic modulus of 2.1 × 10⁻⁶. 11 Pa, density 7850 kg / m³ 3 Steel with a Poisson's ratio of 0.3.

[0063] 3. The rigid backplate uses a steel base, made of high-strength steel, with a preferred thickness h2 of 10mm, which can be adjusted according to actual equipment requirements.

[0064] 4. The overall thickness (z direction) of the underwater sound-absorbing covering layer is 50mm, which meets the requirements for lightweight underwater equipment; the side length d1 of a single cell in the xy plane is preferably 64mm, which can be adjusted according to the periodic arrangement requirements.

[0065] 5. Optimization of key parameters for second-order Helmholtz resonators: cylindrical slit radius ra=2mm, height ha=5mm; upper frustum cavity bottom radius 14.5mm, height 20mm; lower frustum cavity radius 12mm, height 18mm; bottom cylindrical closed cavity radius rd=14.5mm, height hd=3mm.

[0066] 6. Optimization of key parameters for oscillator components: Cylindrical oscillator radius r2=12mm, height h3=37mm, h4=42mm; Helical oscillator number of turns n=6.1, axial pitch p=4.2mm, inner radius rinner=1.67mm, outer radius router=10mm.

[0067] 7. Internal cavity filling: Water is filled into the slit and frustum cavities, while air (density 1.21 kg / m³) is filled into the sealed cavities. 3 (Sound speed 343 m / s).

[0068] 8. Unless otherwise specified, all components have regular geometric structures and may be modified with variable cross-sections as appropriate according to impedance matching or assembly requirements.

[0069] This invention uses the three-dimensional finite element simulation software COMSOL Multiphysics to simulate and verify the full-frequency acoustic performance, oblique incidence adaptability, and hydrostatic pressure resistance of the underwater sound-absorbing covering layer of the above-mentioned preferred embodiment. The simulation model is constructed entirely according to the parameters of the preferred embodiment, as detailed below: like Figure 5 As shown, Model A, a multi-oscillator sound-absorbing structure with excellent pressure resistance, exhibits good sound absorption in the mid-to-high frequency range, but its low-frequency performance is far from ideal. Introducing an air-backed sound-absorbing structure—Model B—at the bottom of the damping layer expands the structure's vibration degrees of freedom, improving low-frequency sound absorption performance, but its low-frequency broadband sound absorption performance needs further enhancement. Furthermore, by embedding a second-order Helmholtz resonator in the main damping layer of Model B, the new sound-absorbing structure, Model D, significantly reduces the equivalent stiffness of the sound-absorbing covering layer, thereby driving the sound absorption peak to shift to lower frequencies, thus achieving a superior low-frequency broadband sound absorption effect. Figure 5 As shown in (d), neither Model B nor Model C alone can significantly improve low-frequency sound absorption performance, but when the two are coupled to construct Model D, a significant low-frequency sound absorption enhancement effect is produced.

[0070] like Figure 6As shown, the initial structure I consists of thin steel and a traditional damping layer. Structure II is a traditional grid-type anechoic layer, composed of a thin rigid support frame and sandwiched damping material. Building upon this, Structure III introduces a cylindrical air backing structure placed below the damping layer, expanding the vibrational degrees of freedom and effectively improving low-frequency sound absorption performance. To further enhance low-frequency sound absorption, Structure IV embeds a second-order Helmholtz-like underwater periodic resonant unit, significantly reducing the equivalent stiffness of the covering layer and causing the sound absorption peak to shift further into the low-frequency region, achieving superior low-frequency broadband absorption. However, while low-modulus damping materials are beneficial for low-frequency sound absorption, they easily cause significant acoustic impedance mismatch. Therefore, Structure V adds two cylindrical steel oscillators to the original configuration to achieve active control and matching optimization of surface impedance. Structure VI further integrates a helical oscillator resonator based on Structure V, and its sound absorption characteristics and hydrostatic pressure resistance under obliquely incident sound waves are systematically investigated.

[0071] Figure 6 The study also showcased the sound absorption coefficients of six acoustic overlay configurations in the 0-10kHz frequency range. Structure I exhibited a relatively low overall sound absorption coefficient, particularly deteriorating in the low-frequency range below 1kHz. Structure II showed a significant improvement over I, maintaining a high sound absorption level in the mid-to-high frequency range. Structure III achieved a high sound absorption coefficient of 0.8 at 900 Hz and broadened the effective sound absorption bandwidth. Structure IV failed to meet expectations in sound absorption performance across the entire frequency range. Structure V, formed by coupling III and IV, achieved a significant resonance peak at 200Hz through a synergistic effect of stiffness modulation, impedance matching, and local resonance energy convergence and dissipation. Its effective sound absorption bandwidth extended to 474.5Hz-10kHz (sound absorption coefficient ≥0.8). Its core mechanism involves a second-order Helmholtz resonator optimizing the equivalent stiffness-mass ratio of the damping layer, combined with the additional vibrational degrees of freedom provided by the air backing, promoting broadband coupling between local resonance and overall vibration modes, significantly improving the efficiency of sound energy conversion to vibrational energy, and ultimately achieving a dual leap in low-frequency sound absorption coefficient and bandwidth. Structure VI maintains excellent high-frequency sound absorption while further improving mid-to-high frequency stability, with a stable sound absorption coefficient ≥0.95 in the 1.4kHz-10kHz frequency range. The evolution from Structure I to VI clearly demonstrates the continuous improvement in low-frequency sound absorption enhancement and wideband control capabilities.

[0072] Figures 7-9 The sound absorption performance under vertical incidence, oblique incidence, and hydrostatic pressure was demonstrated.

[0073] (a) Broadband sound absorption performance under vertical incidence Under conditions of perpendicular sound wave incidence (0° incident angle), the sound-absorbing covering layer of the present invention has a sound absorption coefficient ≥0.8 in the entire frequency range of 146Hz-10kHz, with an average sound absorption coefficient of 0.967 in the entire frequency range; among which, in the mid-high frequency range of 1.4kHz-10kHz, the sound absorption coefficient is stably ≥0.95, with the highest sound absorption coefficient reaching 0.998, achieving efficient sound absorption across the entire frequency range from ultra-low frequency to high frequency.

[0074] Specifically, in the low-frequency range below 1kHz, the structure exhibits its first resonant absorption peak at 146Hz with an absorption coefficient of 0.863, and its second resonant absorption peak at 200Hz with an absorption coefficient of 0.945. This completely solves the problem of insufficient low-frequency absorption below 1kHz in traditional sound-absorbing covering layers and provides excellent avoidance capabilities against modern low-frequency active sonar. In the mid-to-high frequency range of 1kHz-10kHz, the structure's absorption coefficient remains consistently above 0.9 with no obvious absorption troughs, achieving wideband stable sound absorption and fully covering the mainstream operating frequency bands of existing underwater sonar.

[0075] (ii) Sound absorption performance under oblique incidence In real marine environments, incident sound waves are mostly obliquely incident. Traditional sound-absorbing coatings experience significant performance degradation at incident angles greater than 30°, while the structure of this invention exhibits excellent adaptability to wide-angle incident events. Simulation results show: At a 30° sound wave incident angle, the sound-absorbing coating layer of this invention maintains a sound absorption coefficient ≥0.8 in the 131.5Hz-10kHz frequency band, with an average sound absorption coefficient of 0.967 across the entire frequency band, essentially consistent with its performance under perpendicular incidence, showing no significant attenuation. At a 45° sound wave incident angle, the structure's first sound absorption peak shifts to a lower frequency of 116.3Hz. Within the ultra-wide frequency band of 116.3Hz-10kHz, the sound absorption coefficient remains ≥0.8, with an average sound absorption coefficient of 0.958 across the entire frequency band. Only a slight fluctuation in the sound absorption coefficient occurs in the extremely high frequency band above 8kHz, and the overall performance remains excellent. Even at a large incident angle of 60°, the structure maintains a sound absorption coefficient ≥0.7 in the 200Hz-8kHz frequency band, far superior to the performance of traditional sound-absorbing coating layers.

[0076] This superior oblique incidence performance stems from the structural design of this invention, which can excite low-order global horizontal modes, promote the conversion of longitudinal waves into shear waves, and the shear waves can be dissipated more efficiently by the viscoelastic damping layer. Even under large-angle oblique incidence, it can still maintain efficient acoustic energy capture and dissipation capabilities, perfectly adapting to the application scenarios of random acoustic wave incidence in actual marine environments.

[0077] (III) Resistance to hydrostatic pressure High hydrostatic pressure in deep-sea environments is a key factor affecting the performance of sound-absorbing covering layers. Traditional covering layers exhibit significant structural deformation and markedly deteriorate sound absorption performance under hydrostatic pressure of 3 MPa (corresponding to a water depth of approximately 300 meters). This invention, through a synergistic support design of a rigid frame and oscillator components, possesses excellent resistance to hydrostatic pressure.

[0078] Simulation results show that under a hydrostatic pressure load of 3 MPa, the maximum deformation of the sound-absorbing covering layer structure of the present invention is only 3.54 mm, which is much lower than the maximum deformation of 6.86 mm of the traditional steel base covering layer. At the same time, the stress distribution of the structure is uniform, with the maximum stress concentrated at the connection between the rigid vertical plate and the rigid back plate. The stress value is much lower than the yield strength of the steel, and there is no risk of structural damage or yield deformation.

[0079] In terms of acoustic performance, under a hydrostatic pressure of 3MPa, the sound-absorbing covering layer of this invention still maintains a sound absorption coefficient ≥0.8 in the frequency band of 215.1Hz-10kHz, with an average sound absorption coefficient of 0.93 across the entire frequency band. Only the first sound absorption peak in the low-frequency band shows a slight high-frequency shift, while the sound absorption performance in the mid-to-high frequency band remains essentially unchanged. The sound absorption energy dissipation mechanism remains stable: the sound energy dissipation in the low-frequency band is still concentrated in the damping layer around the second-order Helmholtz resonator, while the sound energy dissipation in the mid-to-high frequency band covers the entire damping layer. This completely solves the problem of deterioration in the sound absorption performance of traditional covering layers under high pressure, and can meet the application requirements of deep-sea operations within a water depth of 300 meters.

[0080] Through the above-described structural design and implementation method, this invention completely solves the core technical bottlenecks of existing underwater sound-absorbing covering layers, such as insufficient low-frequency sound absorption, limited effective bandwidth, poor adaptability to oblique incidence, weak resistance to hydrostatic pressure, and insufficient multi-performance synergy. It achieves four core advantages: First, the synergistic energy dissipation mechanism significantly improves broadband sound absorption performance, achieving high sound absorption in the ultra-wide frequency range of 116Hz-10kHz; second, it has strong adaptability to oblique incidence, maintaining high sound absorption across the entire frequency range even at a 45° incident angle; third, it has outstanding resistance to hydrostatic pressure, with a maximum deformation of only 3.54mm under 3MPa hydrostatic pressure, and stable sound absorption performance; fourth, it has a compact and lightweight structure, with an overall thickness of ≤50mm, meeting the lightweight requirements of underwater equipment.

[0081] The above are merely specific embodiments of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. An underwater sound-absorbing covering layer, comprising a plurality of periodically arranged sound-absorbing cells (1), characterized in that, Each of the aforementioned sound-absorbing cells (1) includes: Rigid backplate (11) for connection to the surface of underwater equipment; Damping layer (13) covers the upper surface of the rigid back plate; A rigid vertical plate (12) is disposed on the upper surface of the rigid back plate (11) and divides the damping layer (13) into two independent first parts and second parts; A second-order Helmholtz resonator (14), embedded in the first part of the damping layer (13), is used to generate local resonance under acoustic excitation to capture and dissipate low-frequency acoustic energy. An oscillator assembly (15), embedded in a second portion of the damping layer (13), is used to induce viscoelastic shear deformation of the damping layer (13) under acoustic excitation in order to dissipate mid-to-high frequency acoustic energy.

2. The underwater sound-absorbing covering layer according to claim 1, characterized in that, The second-order Helmholtz resonator (14) includes: The slit (101) connects to the external waters; A frustum cavity (102) is disposed below and communicates with the slit (101); A closed cavity (103) is independently located below the frustum cavity (102) and adjacent to the rigid back plate (11).

3. The underwater sound-absorbing covering layer according to claim 2, characterized in that, At least two frustum cavities (102) connected in series are provided, with the bottom diameter of the upper frustum cavity (102) being larger than the bottom diameter of the lower frustum cavity (102).

4. The underwater sound-absorbing covering layer according to claim 2, characterized in that, The frustum cavity (102) is filled with water when working underwater, and the closed cavity (103) is filled with air.

5. The underwater sound-absorbing covering layer according to claim 1, characterized in that, The oscillator assembly (15) includes a cylindrical oscillator (104) and a helical oscillator (105) located below it, both of which are in close contact with the damping layer (13).

6. The underwater sound-absorbing covering layer according to claim 5, characterized in that, The axial direction of the cylindrical oscillator (104) is consistent with the thickness direction of the underwater sound-absorbing covering layer, and the cylindrical oscillator (104) and the spiral oscillator (105) are arranged coaxially at intervals.

7. The underwater sound-absorbing covering layer according to claim 1, characterized in that, The damping layer (13) is made of viscoelastic damping material, the second-order Helmholtz resonator (14) and oscillator assembly (15) are made of metal or carbon fiber composite material, and the rigid back plate and rigid vertical plate (12) are made of steel.

8. The underwater sound-absorbing covering layer according to claim 1, characterized in that, Within the range of sound wave incident angles from 0° to 45°, the underwater sound-absorbing coating has a sound absorption coefficient ≥0.8 in the frequency band from 116Hz to 10kHz and a sound absorption coefficient ≥0.95 in the frequency band from 1.4kHz to 10kHz.

9. The underwater sound-absorbing covering layer according to claim 1, characterized in that, Under a hydrostatic pressure of 3 MPa, the maximum deformation of the underwater sound-absorbing covering layer structure does not exceed 4 mm, and the sound absorption coefficient is ≥0.8 in the frequency band from 215 Hz to 10 kHz.

10. The underwater sound-absorbing covering layer according to claim 1, characterized in that, The overall thickness of the underwater sound-absorbing covering layer does not exceed 50mm.

Images