Square honeycomb structure acoustic covering layer with embedded air layer and hybrid sound absorbers

Abstract

A square honeycomb structure acoustic covering layer embedded with an air layer and a hybrid sound absorber relates to the technical field of underwater acoustic stealth, the covering layer comprises a plurality of sound absorption unit cells arranged periodically, and each sound absorption unit cell comprises an upper end side panel, a lower end side panel, a square honeycomb, the hybrid sound absorber embedded in the honeycomb and the air layer; wherein the hybrid sound absorber is formed by alternately stacking polyurethane and chloroprene rubber and connected with the inner wall of the honeycomb through glue, and the air layer is located on the lower portion of the hybrid sound absorber. According to the invention, the effective sound absorption performance of the deep sub-wavelength low-frequency broadband under high water pressure is realized, the deformation amount is very small under the water pressure of 4MPa, the stability of the sound absorption performance can be kept, modular design can be carried out for sound absorption frequency bands under different working conditions, and an important reference is provided for developing a novel underwater acoustic covering layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater acoustic stealth, and specifically relates to a square honeycomb configuration acoustic covering layer embedded with an air layer and a hybrid sound absorber. Background Art

[0002] The covering layer is generally composed of polymer materials and is usually laid on the outer surface of a submarine to absorb the sound waves detected by an active sonar. It is the first external barrier for a submarine to achieve acoustic stealth. Currently, the truly engineering-applied sound-absorbing covering layer is still in a traditional configuration, such as a uniform material covering layer and a cavity-type covering layer.

[0003] Due to its advantages such as high sound absorption efficiency within a specific frequency range, flexibility in modular combination design, and simple structure and easy manufacturing, the traditional cavity-type acoustic covering layer has been widely used in the field of underwater sound absorption. However, due to the poor mechanical strength, stability, and durability of the cavity structure, under the action of high water pressure loads in the deep sea, the cavity is prone to large deformation, which changes its original resonance characteristics and significantly reduces the sound absorption performance. In addition, the matrix material may crack under pressure, further causing damage to the overall structure.

[0004] For the cavity-type covering layer to achieve broadband sound absorption performance, the loss factor of its sound-absorbing base material should be as close to or greater than 1 as possible. In reality, it is difficult to prepare such high-damping materials. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention proposes a square honeycomb configuration acoustic covering layer embedded with an air layer and a hybrid sound absorber. By setting hybrid material layers with different stiffness and damping and a bottom cavity, the constraint of the viscoelastic body is released, providing space for its longitudinal vibration and facilitating the generation of a low-frequency sound absorption peak. At higher frequencies, a transverse shear region will occur at the junction of the two materials, causing longitudinal waves to be converted into transverse waves and dissipating a large amount of sound energy.

[0006] The square honeycomb configuration acoustic covering layer of the present invention, the covering layer includes a plurality of periodically arranged sound absorption unit cells; the sound absorption unit cell is composed of an upper panel, a square honeycomb, a lower panel, a hybrid sound absorber, and an air layer; the upper surface of the square honeycomb is provided with an upper panel, the lower surface is provided with a lower panel, the hybrid sound absorber is arranged inside the square honeycomb, and the hybrid sound absorber is composed of a first PU layer of the hybrid sound absorber, a second CR layer of the hybrid sound absorber, a third PU layer of the hybrid sound absorber, and a fourth CR layer of the hybrid sound absorber from top to bottom; the air layer is arranged below the hybrid sound absorber.

[0007] Further, the upper panel and the lower panel are adhesively connected to the square honeycomb, and the outer boundary of the hybrid sound absorber is adhesively connected to the inner wall of the square honeycomb.

[0008] Furthermore, the square honeycomb material is aluminum alloy, and the materials of the upper panel and the lower panel are both neoprene.

[0009] Furthermore, the cross-section of the square honeycomb is square, the side length of the honeycomb is 40 mm, the wall thickness of the honeycomb is 2 mm, and the thickness of the honeycomb does not exceed 50 mm.

[0010] Furthermore, the upper panel and the lower panel have the same size, and the thickness of both is 2 mm.

[0011] Furthermore, the total thickness of the first PU layer and the third PU layer of the hybrid sound absorber is 1 - 10 mm, the total thickness of the second CR layer and the fourth CR layer of the hybrid sound absorber is 1 - 10 mm, and the total thickness of the hybrid sound absorber does not exceed 44 mm.

[0012] Furthermore, the air layer is located at the lower part of the hybrid sound absorber and at the bottom of the square honeycomb, and the thickness of the air layer is not less than 1 mm.

[0013] An application of the square honeycomb configuration acoustic covering layer with an embedded air layer and a hybrid sound absorber. The square honeycomb configuration acoustic covering layer with an embedded air layer and a hybrid sound absorber is used as an acoustic absorption layer of an underwater vehicle.

[0014] Furthermore, the sound absorption unit cells of the covering layer are vertically attached to the surface of the underwater vehicle hull.

[0015] Furthermore, the sound absorption unit cells of the covering layer are vertically attached to the surface of the underwater vehicle hull, and the lower panel of the covering layer is fixedly connected to the steel backing on the surface of the underwater vehicle hull.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The traditional acoustic covering layer not only has poor pressure resistance, but also requires viscoelastic materials with high damping performance to improve the sound absorption effect, and the improvement effect on the sound absorption in the low-frequency band is limited. The square honeycomb configuration acoustic covering layer with an embedded air layer and a hybrid sound absorber proposed by the present invention uses a square aluminum alloy honeycomb as the skeleton, embeds a hybrid sound absorber and an air layer inside the honeycomb, and uses a CR panel to encapsulate the ends of the honeycomb. The present invention can achieve excellent low-frequency broadband sound absorption performance with a sound absorption coefficient always greater than 0.8 after 1082 Hz, and the average sound absorption coefficient from 10 - 10000 Hz can reach 0.898, and the sound absorption performance is maintained stable under a water pressure of 4 MPa. The loss factors of the two viscoelastic materials used in the present invention are both less than 0.5, and high-efficiency sound absorption effect is achieved with low damping performance.

[0018] At the same time, the present invention also has the following advantages:

[0019] 1. When the detection sound wave of the active sonar is incident, the upper panel of CR with water impedance similar to that of water can allow the sound wave to fully enter the sound-absorbing body of the honeycomb. In addition, the good stiffness of CR can achieve the ability to resist deformation under large water pressure.

[0020] 2. The square honeycomb not only provides pressure resistance and load-bearing capacity. Due to the stiffness difference between the aluminum alloy and the viscoelastic material, the sound-absorbing viscoelastic body and the honeycomb can be regarded as a "spring-mass block" model, and the sound-absorbing elastic body will generate shear behavior to dissipate sound energy.

[0021] 3. The air layer can release the bottom constraint of the hybrid sound-absorbing body. Under the excitation of low-frequency sound waves, the middle part of the hybrid sound-absorbing body will generate longitudinal vibration downward along the z-axis, enabling the sound wave to continue to propagate in the viscoelastic body after incidence and being gradually absorbed in the path, and the sound energy is converted into kinetic energy and dissipated.

[0022] 4. Due to the stiffness difference between PU and CR, the vibration distributions of the PU layer and the CR layer in every two layers of the hybrid sound-absorbing body show an antisymmetric form in both the transverse x-direction and the y-direction, generating a composite transverse shear motion of "pulling and squeezing", which enhances the dissipation effect of sound energy.

[0023] 5. By optimizing and regulating the thickness of each layer in the hybrid sound-absorbing body, the sound-absorbing performance in different frequency bands can be improved, meeting the effect of absorbing sound waves of the desired target frequency. Description of the Drawings

[0024] Figure 1 It is an explosion diagram of the underwater sound-absorbing single cell of the present invention;

[0025] Figure 2 It is a schematic cross-sectional view of the underwater sound-absorbing single cell of the present invention;

[0026] Figure 3 It is a schematic structural diagram of the underwater square honeycomb configuration acoustic covering layer attached to the steel back lining of the present invention;

[0027] Figure 4 (a) is the frequency-dependent storage modulus and loss factor of PU in the embodiment of the present invention, Figure 4 (b) is the frequency-dependent storage modulus and loss factor of CR in the embodiment of the present invention;

[0028] Figure 5 (a) is the sound absorption coefficient of the embodiment of the present invention under water pressures of 1 MPa, 2 MPa, 3 MPa, and 4 MPa, Figure 5 (b) is the deformation displacement nephogram of the embodiment of the present invention under water pressures of 1 MPa, 2 MPa, 3 MPa, and 4 MPa;

[0029] Wherein: 1. upper panel; 2. honeycomb; 3. lower panel; 4. hybrid sound absorber; 5. first PU layer of hybrid sound absorber; 6. second CR layer of hybrid sound absorber; 7. third PU layer of hybrid sound absorber; 8. fourth CR layer of hybrid sound absorber; 9. air layer. Detailed implementation manners

[0030] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer and more understandable, the spirit of what is disclosed in the present invention will be described in detail below. After any person skilled in the relevant technical field understands the embodiments of the content of the present invention, the techniques taught by the content of the present invention can be changed and modified, which does not depart from the spirit and scope of the content of the present invention.

[0031] The schematic embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0032] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "one side", "one end", "one side", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, in the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0033] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection", and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0034] In the drawings, various schematic structural diagrams according to the disclosed embodiments of the present invention are shown. These figures are not drawn to scale. For the purpose of clear expression, some details are enlarged, and some details may be omitted. The shapes of various regions and layers shown in the figures and their relative sizes and positional relationships are only exemplary. In practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art can design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0035] The present invention provides a square honeycomb configuration acoustic covering layer with an embedded air layer and a hybrid sound absorber, which includes a plurality of unit cells periodically arranged in the x-direction and y-direction. Each unit cell includes a square honeycomb with an embedded air layer and a hybrid sound absorber, an upper panel, and a lower panel, wherein the hybrid sound absorber is embedded in the upper part of the honeycomb, and the air layer is embedded in the bottom of the honeycomb. The hybrid sound absorber is composed of alternately arranged low-damping PU and CR. Through the synergistic action of viscous dissipation between the sound-absorbing hybrid and the honeycomb wall, longitudinal vibration of the sound-absorbing hybrid, transverse shear between the PU layer and the CR layer, and global structural resonance, the sound absorption coefficient is always greater than 0.8 after 1082 Hz, and the average sound absorption coefficient in the range of 100 - 10000 Hz reaches 0.898. The sound absorption performance has no obvious attenuation under a water pressure of 4 MPa, and it has excellent high-pressure-resistant low-frequency broadband effective sound absorption performance.

[0036] Please refer to Figures 1-3 , an acoustic covering layer with a square honeycomb configuration having an embedded air layer and a hybrid sound absorber provided by the present invention is attached to a steel backing and includes a plurality of periodically arranged sound-absorbing unit cells. The structural dimensions of each sound-absorbing unit cell are the same. The sound-absorbing unit cell includes a square honeycomb 2, an upper panel 1, a lower panel 3, a hybrid sound absorber 4, and an air layer 9. The hybrid sound absorber 4 is composed of a first PU layer 5, a second CR layer 6, a third PU layer 7, and a fourth CR layer 8 arranged in sequence alternately.

[0037] Among them, the square honeycomb 2 is adhesively connected to the upper panel 1, the lower panel 2, and the hybrid sound absorber 4.

[0038] Among them, the thickness of each layer in the hybrid sound absorber is 1 - 10 mm, and the total thickness is less than or equal to 44 mm; the thickness of the air layer is greater than or equal to 1 mm, and the sum of the thicknesses of the hybrid sound absorber and the air layer is fixed at 45 mm. The thicknesses of each medium layer can vary randomly within the specified size range.

[0039] The present invention has the following technical effects:

[0040] 1. Excellent deep sub-wavelength low-frequency broadband sound absorption performance, and low-damping materials control large wavelengths: Under standard atmospheric pressure, the starting frequency point of effective sound absorption (sound absorption coefficient greater than or equal to 0.8) of the covering layer proposed by the present invention is as low as 1082 Hz, and the overall thickness (49 mm) is only 3.56% of the corresponding wavelength (1.34 m). The average loss factors of the two viscoelastic materials used are both less than 0.5, which proves that low-damping sound-absorbing substrates can also regulate large-wavelength sound waves; at the same time, the effective sound absorption bandwidth length of the covering layer of the present invention is 8918 Hz (1082 - 10000 Hz), and the average sound absorption coefficient is as high as 0.898. It has obvious advantages in sound absorption compared with other types of acoustic covering layers.

[0041] 2. Good hydrostatic pressure bearing performance and sound absorption performance under high pressure: The covering layer proposed in the present invention only undergoes slight deformation under a hydrostatic pressure of 4 MPa. The aluminum honeycomb transfers most of the stress, effectively reducing the stress and deformation inside the sound absorber. The average sound absorption coefficient at 4 MPa is 0.868, which only decreases by 3.34% compared to that under atmospheric pressure.

[0042] 3. Engineering modular design: The covering layer proposed in the present invention is formed by parallel connection of several sound absorption single cells. To meet the sound absorption requirements in different frequency bands, the filler and the size of the air layer in each single cell can be optimized specifically to meet the engineering application requirements under various sound absorption conditions.

[0043] The sound absorption mechanism of the present invention is as follows:

[0044] 1. The stiffness of the viscoelastic material is much smaller than that of the aluminum alloy. When sound waves are incident, the sound absorption hybrid and the honeycomb wall can be regarded as a "mass-spring-rigid plate" system. Shear deformation will occur in the contact area between the hybrid and the honeycomb, and low-frequency sound energy is dissipated viscously.

[0045] 2. The large stiffness of the honeycomb restricts the longitudinal deformation at the boundary of the sound absorption hybrid. The air layer releases the bottom constraint of the hybrid. Therefore, after the sound waves are incident, intense longitudinal vibrations will occur at the bottom of the middle part of the hybrid, and the sound energy is converted into vibration energy, and more sound waves are gradually absorbed along the propagation direction.

[0046] 3. Due to the differences in elasticity and stiffness between CR and PU, transverse shear deformation is excited at the interface between the CR layer and the PU layer, and longitudinal waves are converted into transverse waves for propagation, and the sound energy is dissipated.

[0047] 4. The synergistic effect of shear energy dissipation, global resonance, viscous loss, and longitudinal-transverse wave conversion results in effective absorption and attenuation of a large amount of sound waves.

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components described and shown in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0049] Materials used in the embodiments:

[0050] Water: density 1000 kg / m 3, the speed of sound is 1489 m / s.

[0051] Air: density 1.29 kg / m 3 , the speed of sound is 343 m / s.

[0052] Aluminum alloy: density 2700 kg / m 3 , Young's modulus 70 GPa, Poisson's ratio 0.3.

[0053] Steel: density 7850 kg / m 3 , Young's modulus 210 GPa, Poisson's ratio 0.28.

[0054] PU: density 1100 kg / m 3 , storage modulus E PU = 6.367 + 1.084f^0.293 MPa, Poisson's ratio 0.485, loss factor η PU = 0.012 + 0.083f^0.147. (Note: The value range of f is 10 - 10000 Hz)

[0055] CR: density 1680 kg / m 3 , storage modulus E CR = 45.298 + 5.466f^0.3388 MPa, Poisson's ratio 0.495, loss factor η CR = -0.863 + 1.027f^0.0328. (Note: The value range of f is 10 - 10000 Hz)

[0056] Structural dimensions of the embodiment:

[0057] Side length of the square honeycomb (unit cell lattice constant) L = 40 mm.

[0058] Wall thickness of the square honeycomb t = 2 mm.

[0059] Thickness of the upper and lower panels h0 = 2 mm.

[0060] Honeycomb thickness H = 45 mm.

[0061] Thickness of the first layer of the sound-absorbing hybrid h1 = 3.8 mm, thickness of the second layer of the sound-absorbing hybrid h2 = 8.5 mm, thickness of the third layer of the sound-absorbing hybrid h3 = 21.9 mm, thickness of the fourth layer of the sound-absorbing hybrid h1 = 4.5 mm. Thickness of the air layer h5 = 6.3 mm.

[0062] The modeling and calculation of the embodiment of the present invention are based on COMSOL finite element software. A plane sound wave with a sound pressure of 1Pa is incident vertically into the cover layer, and the calculation frequency range is 100-10000Hz, with an interval frequency of 100Hz. The hydrostatic pressure is applied to the contact surface between the upper panel and the incident water area, and the calculation water pressure load range is 1-4MPa, with an interval load of 1MPa.

[0063] The embodiment of the present invention can achieve excellent low-frequency broadband sound absorption performance under standard atmospheric pressure, with the sound absorption coefficient always being greater than 0.8 after 1082Hz and the average sound absorption coefficient of 100-10000Hz reaching 0.898. Under a high water pressure of 4MPa, the maximum displacement of the structure is only 3.5mm, the strain rate does not exceed 7.5%, and the sound absorption performance maintains good stability. Thus, the superior performance of taking into account both pressure resistance and low-frequency broadband effective sound absorption is achieved.

[0064] In summary, the square honeycomb configuration acoustic covering layer with an embedded air layer and a mixed sound absorber proposed in the present invention achieves excellent low-frequency broadband sound absorption performance of 1082-10000 Hz through the synergistic effect of multiple mechanisms, and can still ensure the stability of the sound absorption performance under a water pressure of 4 MPa, which provides an important reference for the development of new acoustic covering layers.

[0065] The embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present application, ordinary technicians in this field can also make many forms of implementation methods without departing from the purpose of the present application and the scope of protection of the claims, and these implementation methods are all within the protection of the present application.

Claims

1. A square honeycomb configuration acoustic covering layer with an embedded air layer and a hybrid sound absorber, characterized in that The covering layer described above includes a plurality of sound-absorbing single cells arranged periodically; the sound-absorbing single cell is composed of an upper panel (1), a square honeycomb (2), a lower panel (3), a hybrid sound-absorbing body (4) and an air layer (9); the upper surface of the square honeycomb (2) is provided with an upper panel (1), and the lower surface is provided with a lower panel (3), the hybrid sound-absorbing body (4) is arranged inside the square honeycomb (2), and the hybrid sound-absorbing body (4) is composed of a first PU layer (5) of the hybrid sound-absorbing body, a second CR layer (6) of the hybrid sound-absorbing body, a third PU layer (7) of the hybrid sound-absorbing body and a fourth CR layer (8) of the hybrid sound-absorbing body from top to bottom; the air layer (9) is arranged below the hybrid sound-absorbing body (4).

2. The square honeycomb configuration acoustic covering layer with an embedded air layer and a hybrid sound absorber according to claim 1, characterized in that, The upper panel (1) and the lower panel (3) are adhesively connected to the square honeycomb (2), and the outer boundary of the hybrid sound-absorbing body (4) is adhesively connected to the inner wall of the square honeycomb (2).

3. The square honeycomb configuration acoustic covering layer with an embedded air layer and a hybrid sound absorber according to claim 1, characterized in that, The material of the square honeycomb (2) is aluminum alloy, and the materials of the upper panel (1) and the lower panel (3) are both neoprene rubber.

4. The square honeycomb configuration acoustic covering layer with an embedded air layer and a hybrid sound absorber according to claim 1 or 2, characterized in that, The cross-section of the square honeycomb (2) is square, the honeycomb side length is 40 mm, the honeycomb wall thickness is 2 mm, and the honeycomb thickness does not exceed 50 mm.

5. A square honeycomb configuration acoustic covering layer with an embedded air layer and a hybrid sound absorber according to claim 1, 2 or 3, characterized in that, The upper panel (1) and the lower panel (3) have the same size, and the thickness of both is 2 mm.

6. The square honeycomb configuration acoustic covering layer with an embedded air layer and a hybrid sound absorber according to claim 1, characterized in that, The total thickness of the first PU layer (5) and the third PU layer (7) of the hybrid sound-absorbing body is 1 - 10 mm, the total thickness of the second CR layer (6) and the fourth CR layer (8) of the hybrid sound-absorbing body is 1 - 10 mm, and the total thickness of the hybrid sound-absorbing body (4) does not exceed 44 mm.

7. The square honeycomb configuration acoustic covering layer with an embedded air layer and a hybrid sound absorber according to claim 1, characterized in that, The air layer (9) is located below the hybrid sound-absorbing body (4) and at the bottom of the square honeycomb (2), and the thickness of the air layer (9) is not less than 1 mm.

8. The application of a square honeycomb configuration acoustic covering layer with an embedded air layer and a hybrid sound absorber as claimed in claim 1, characterized in that, The acoustic covering layer of the square honeycomb configuration with the embedded air layer and the hybrid sound-absorbing body is used as the sound-absorbing layer of the underwater vehicle.

9. The application according to claim 8, wherein The sound-absorbing single cells of the covering layer are vertically attached to the surface of the underwater vehicle hull.

10. The application according to claim 8, characterized in that The sound-absorbing single cells of the covering layer are vertically attached to the surface of the underwater vehicle hull, and the lower panel (3) of the covering layer is fixedly connected to the steel backing on the surface of the underwater vehicle hull.

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