A wide low-frequency sound-absorbing damping cover layer structure and design method

Abstract

The application belongs to the technical field of preparation and determination of aviation equipment absorbing material, and discloses a wide low-frequency sound absorption and vibration reduction covering layer structure and a design method. The design method comprises the following steps: by changing the geometric parameters of a single unit composed of an embedded neck hole diameter d, an embedded neck length l and a cavity wall plate height L, the strong non-local coupling between a plurality of embedded rubber Helmholtz resonators is changed, the impedance of the embedded rubber Helmholtz resonator is changed, and the overall structure of the wide low-frequency sound absorption and vibration reduction covering layer structure of the sound absorption metasurface array is obtained by the weak coupling resonance sound absorption mechanism; the embedded rubber Helmholtz resonator is composed of an embedded neck, a damping rubber coating layer and a sound absorption cavity. The non-local coupling between the plurality of embedded rubber Helmholtz resonators in the multi-element metasurface array is adjusted, effective broadband impedance modulation is realized, and strong dissipation of broadband sound energy is realized at very low frequency.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of preparation and determination of aviation equipment absorbing materials, and particularly relates to a wide low-frequency sound-absorbing and vibration-reducing covering layer structure and a design method. BACKGROUND

[0002] The most commonly used control measure to solve the problems of noise and vibration occurring inside aviation equipment during flight is to control noise and vibration from the transmission path, such as sound insulation, vibration isolation, sound barrier, and sound absorption. The traditional noise reduction method is to change the structure position, geometric parameters or materials to optimize the structure vibration noise on the basis of analyzing the vibration and acoustic characteristics of the existing structure, to consume sound energy through the interaction of noise sound waves and acoustic materials, so as to achieve the purpose of reducing noise.

[0003] The implementation of noise control often needs to rely on the structure itself. The sound absorption and vibration isolation method of general aviation and aerospace equipment is to use a multi-layer structure, and to place elastic plates, air layers and multi-layer sound absorption materials in a staggered manner. However, such a method can effectively control medium and high frequency noise, but it is ineffective for low frequency noise. According to classical acoustic theory, the thickness of the acoustic material (structure) is usually comparable to the working wavelength. Therefore, for low frequency noise, there is a limitation that it is difficult to use small size structure to efficiently regulate and control large wavelength sound waves. Simply stacking excellent vibration reduction materials and noise reduction materials together will cause performance mismatch of the materials, making the vibration reduction and noise reduction effect worse, and further leading to an increase in the thickness of the material, affecting its practicality. SUMMARY

[0004] To overcome the problems in the related art, the present application provides a wide low-frequency sound-absorbing and vibration-reducing covering layer structure and a design method, specifically a low-frequency, wideband, vibration-reducing sound-absorbing covering layer design method based on a metamaterial array. The purpose of the present application is to provide a coupled embedded aperture Helmholtz cavity type and negative Poisson's ratio array structure multi-unit metamaterial array, and on this basis, to form a design scheme of a wide low-frequency sound-absorbing and vibration-reducing covering layer structure.

[0005] The technical solution is as follows: a wide low-frequency sound-absorbing and vibration-reducing covering layer structure, which adjusts the Helmholtz resonance cavity coefficient to design sound absorption of different frequencies, realizes wideband sound absorption through the coupling resonance of multiple cavities, and uses the coupled structure of the embedded aperture Helmholtz cavity type and the negative Poisson's ratio array for vibration reduction and sound absorption; the structure comprises:

[0006] a cavity wall plate placed between the perforated cover plate and the bottom plate and closely attached to form multiple sound absorption cavities inside;

[0007] A plurality of different lengths, different aperture embedded neck, installed in the perforated cover plate directly below, the neck of the embedded neck channel cross section and the perforated cover plate perforated cross section size and concentric;

[0008] The negative Poisson's ratio array base is the same size as the bottom plate and is arranged in close contact with the bottom plate; the negative Poisson's ratio array structure is formed by closely arranging a plurality of negative Poisson's ratio structures, and a damping rubber coating layer of different thicknesses is uniformly applied to the inner wall of the sound absorption cavity.

[0009] In one embodiment, the perforated cover plate is the same size and shape as the bottom plate; the chamber wall plate is a square cross-section shell with upper and lower through holes, the plate thickness of the chamber wall plate is uniform and consistent, and the thickness of the perforated cover plate and the bottom plate is the same; the damping rubber coating layer is uniformly applied to the inner wall bottom surface and the four side wall surfaces of the sound absorption cavity.

[0010] In one embodiment, the perforated cover plate and the bottom plate are regular polygon structures.

[0011] The perforated cover plate and the bottom plate are thin plate structures.

[0012] In one embodiment, the length and aperture size of the embedded neck, the height of the chamber wall plate and the cross-sectional area of the surrounded sound absorption cavity, and the thickness of the damping rubber coating layer are adjusted to adjust the absorption peak frequency and the absorption frequency bandwidth.

[0013] In one embodiment, the bulk modulus, shear modulus, density, and loss factor of the damping rubber coating layer are adjusted to adjust the absorption peak frequency and the absorption frequency bandwidth.

[0014] In one embodiment, the perforated cover plate, the embedded neck, the chamber wall plate, the bottom plate, and the negative Poisson's ratio array base are made of the same metal material.

[0015] In one embodiment, the perforated cover plate, the embedded neck, the chamber wall plate, the bottom plate, and the negative Poisson's ratio array base are formed by metal 3D printing, CNC machining, and sheet metal machining processes.

[0016] The damping rubber coating layer is processed by chemical modification and composite filling process; the processed damping rubber coating layer is preliminarily formed in the sound absorption cavity with an extrusion die, and is adhered to the surface of the sound absorption cavity by an adhesive, and is extracted in a vacuum heating furnace and solidified.

[0017] In one embodiment, the number of sound absorption cavities is 4-20; the number of negative Poisson's ratio structures included in the negative Poisson's ratio array base is 100.

[0018] Another object of the present application is to provide a design method for a wide low-frequency sound absorption and vibration reduction coating layer, which is made of the wide low-frequency sound absorption and vibration reduction coating layer structure, and the design method comprises:

[0019] By changing the geometric parameters of a single unit consisting of an embedded neck hole diameter d, an embedded neck length l, and a chamber wall plate height L, the non-local coupling between multiple embedded rubber Helmholtz resonators is changed, the impedance of the embedded rubber Helmholtz resonator is changed, a wide low-frequency sound absorption and vibration reduction cover structure is obtained by a weakly coupled resonance sound absorption mechanism, and the overall structure of the sound absorption metasurface array; the embedded rubber Helmholtz resonator is composed of an embedded neck, a damping rubber coating layer and a sound absorption cavity.

[0020] In one embodiment, the impedance of the embedded rubber Helmholtz resonator is expressed as:

[0021] .

[0022] wherein, is the overall impedance of the array after being connected in parallel, respectively, are the impedances of the four units; the four units are units freely combined after arbitrary selection of the geometric parameters of the embedded neck hole diameter d, the embedded neck length l, and the chamber wall plate height L.

[0023] In combination with all the above technical solutions, the advantages and positive effects of the present application are: the present application couples vibration and noise generation mechanisms and proposes an integrated vibration and noise reduction structure to achieve effective vibration reduction and high sound absorption performance with small structure thickness. The wide, low-frequency sound absorption and vibration reduction cover structure proposed by the present application can achieve effective broadband impedance modulation by adjusting the non-local coupling between multiple embedded rubber Helmholtz resonators in the multi-element metasurface array, thereby achieving strong dissipation of broadband sound energy at very low frequencies. Through the negative Poisson's ratio characteristics of the negative Poisson's ratio array base, efficient broadband vibration reduction effect can be achieved.

[0024] As positive effects of the present application, the following important aspects are also embodied: (1) The technical solution of the present application can be applied to multiple fields such as aviation equipment shells, urban buildings, and vehicles, which not only improves the service life and safety of products, but also increases the comfort of passengers, residents or staff, thus bringing huge commercial value and social benefits. (2) The technical solution of the present application can effectively solve the noise and vibration problems in multiple scenarios such as flying, driving, and accommodation, thereby promoting the technological progress of related industries. (3) The control of low-frequency noise and vibration has always been a common technical problem in multiple fields, and the technical solution of the present application can effectively solve these problems at the same time. (4) Since the present application adopts the Helmholtz weak coupling resonance theory and the co-body design of the negative Poisson's ratio structure array and the sound absorption cover structure, it also overcomes the technical bias in traditional materials and design methods, and promotes innovation and development in related fields. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure;

[0026] Figure 1 is a wide low frequency sound absorption and vibration reduction cover layer structure provided by the embodiment of the present application;

[0027] Figure 2 is a wide low frequency sound absorption and vibration reduction cover layer structure design principle diagram provided by the embodiment of the present application;

[0028] Figure 3 is a schematic diagram of an embedded rubber Helmholtz resonator and a negative Poisson's ratio array base provided by the embodiment of the present application; (a) is a perforated cover plate, (b) is a cavity structure, and (c) is a negative Poisson's ratio array base, which are placed in order to form a sound absorption and vibration reduction common body structure;

[0029] Figure 4 is a sound absorption coefficient curve diagram of a sound absorption cover layer formed by periodic arrangement of a four-unit sound absorption metasurface array provided by the embodiment of the present application;

[0030] Figure 5 is a verification mode schematic diagram based on impedance analysis provided by the embodiment of the present application;

[0031] Figure 6 is a sound absorption coefficient curve diagram of a sound absorption cover layer formed by periodic arrangement of a four-unit sound absorption metasurface array provided by the embodiment of the present application;

[0032] Figure 7 is a vibration reduction coefficient schematic diagram of an embedded rubber Helmholtz resonator and a negative Poisson's ratio array base provided by the embodiment of the present application;

[0033] In the figure: 1, perforated cover plate; 2, embedded neck; 3, cavity wall plate; 4, damping rubber coating layer; 5, bottom plate; 6, sound absorption cavity; 7, negative Poisson's ratio array structure base; 8, negative Poisson's ratio structure. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below in combination with the drawings. In the following description, a large number of specific details are set forth in order to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0035] This invention addresses the problem of low-frequency noise caused by aerodynamic factors in aviation equipment damaging the durability of airborne systems and posing a health hazard to occupants. It analyzes and optimizes acoustic metamaterial vibration reduction and noise reduction technologies, completes the construction and optimization of vibration reduction and noise reduction metamaterial structures, and uses a designed embedded Helmholtz resonant cavity metamaterial for efficient sound absorption of low-frequency sound waves. It also utilizes the superior performance of negative Poisson's ratio mechanical vibration reduction metamaterials for low-frequency noise reduction in aircraft.

[0036] Example 1, as Figures 1-3 As shown, this embodiment of the invention provides a wide low-frequency sound absorption and vibration reduction covering layer structure. By adjusting the Helmholtz resonant cavity coefficient, sound absorption at different frequencies is designed. Wide frequency sound absorption is achieved through the coupling resonance of multiple cavities. The purpose of vibration reduction and sound absorption is achieved by designing a Helmholtz cavity shape with embedded aperture and a negative Poisson's ratio array structure in a co-structure. Specifically, it includes a perforated cover plate 1, an embedded neck 2, a cavity wall panel 3, a damping rubber coating layer 4, a base plate 5, a sound absorption cavity 6, and a negative Poisson's ratio array structure base 7.

[0037] In one embodiment of the present invention, the perforated cover plate 1 and the bottom plate 5 are the same size and shape; the chamber wall plate 3 is a square cross-section shell with through holes at the top and bottom, and the plate thickness is uniform and the same as the thickness of the perforated cover plate 1 and the bottom plate 5.

[0038] The chamber wall panel 3 is placed between the perforated cover plate 1 and the base plate 5, and is tightly fitted to the perforated cover plate 1 and the base plate 5, forming multiple sound-absorbing cavities 6 inside; multiple embedded necks 2 of different lengths and different aperture sizes are installed directly below the perforated cover plate, and the circular cross-section of the inner channel of the neck is the same size as the circular cross-section of the perforation of the perforated cover plate 1 and is concentric; the negative Poisson's ratio array base 7 is the same size as the base plate 5 and is fitted to the base plate; the negative Poisson's ratio array structure 7 is composed of multiple identical negative Poisson's ratio structures 8 arranged closely, and damping rubber coating layers 4 of different thicknesses are evenly applied to the inner wall of the sound-absorbing cavity 6, and the coating surface includes the bottom surface and four side wall surfaces, for a total of five surfaces.

[0039] Preferably, the perforated cover plate 1 and the base plate 5 are both square or other regular polygonal structures, which can be combined with the chamber wall plate 3 to form a sound-absorbing cavity 6.

[0040] The perforated cover plate 1 and the base plate 5 are thin-layer plate structures with a thickness of 2 mm.

[0041] Preferably, at the geometric level, adjusting the length of the embedded neck 2, the aperture size, the height of the chamber wall panel 3, the cross-sectional area of ​​the enclosed sound-absorbing cavity 6, and the thickness of the damping rubber coating layer 4 can adjust the absorption peak frequency and the absorption bandwidth.

[0042] As preferred, at the material property level, the damping rubber coating layer 4 belongs to a viscoelastic material, and by adjusting its bulk modulus, shear modulus, density, and loss factor, the absorption peak frequency and the absorption band width can be adjusted.

[0043] As preferred, the perforated cover plate 1, the embedded neck 2, the chamber wall plate 3, the bottom plate 5, and the negative Poisson's ratio array base 7 are made of the same metal material, such as steel, iron, copper, etc.

[0044] The perforated cover plate 1, the embedded neck 2, the chamber wall plate 3, the bottom plate 5, and the negative Poisson's ratio array base 7 can be formed by metal 3D printing, CNC machining, sheet metal machining, etc.

[0045] As preferred, the rubber material required by the damping rubber coating layer 4 needs to be processed by chemical modification, composite filling, etc. on the basis of the rubber matrix material according to the specific sound absorption effect requirements. The processed rubber material is in a fluid state, needs to be preliminarily formed in the sound absorption cavity 6 with the cooperation of an extrusion die, and is adhered to the metal wall surface by an adhesive, and air is extracted and solidified in a vacuum heating furnace.

[0046] As preferred, the number of the sound absorption cavities 6 is 4-20. The negative Poisson's ratio array base 7 includes 100 negative Poisson's ratio structures 8.

[0047] As preferred, the wide low-frequency sound absorption and vibration reduction covering layer structure is directed to the absorption of incident sound waves in the very low frequency (below 100 Hz), and the overall thickness of the wide low-frequency sound absorption and vibration reduction covering layer structure is controlled in the range of 45.6 mm.

[0048] As preferred, the strong non-local coupling between multiple embedded rubber Helmholtz resonators composed of the embedded neck 2, the damping rubber coating layer 4, and the sound absorption cavity 6 is utilized in the use frequency band to realize the wide, low-frequency sound absorption covering layer wide frequency impedance regulation and the ultra-thin thickness.

[0049] The coupling of multiple embedded rubber Helmholtz resonators is a way to widen the sound absorption band;

[0050] The multiple negative Poisson's ratio structures 8 are a way to reduce noise vibration.

[0051] In Example 2, as another embodiment of the present application, a design method of a wide low-frequency sound absorption and vibration reduction covering layer is provided, which includes but is not limited to the following specific examples, the impedance of the embedded rubber Helmholtz resonator can be changed by changing the geometric parameters of a single unit, such as the embedded neck 2 hole diameter d, the embedded neck 2 length l, and the chamber wall plate 3 height L, and the overall structure of the wide low-frequency sound absorption and vibration reduction covering layer structure of the sound absorption metasurface array is obtained by the weak coupling resonance sound absorption mechanism. Thus, different effects can be designed as needed.

[0052] In this embodiment, asFigure 1 and Figure 2 As shown in the figure, the sound waves are incident from above the perforated cover plate 1, and the lateral boundary of the sound absorption super surface array is the periodic boundary. When the sound absorption super surface array is periodically arranged, the sound absorption cover layer is formed.

[0053] The sound absorption super surface array includes four sound absorption cavities 6. By adjusting the length of the embedded neck 2, the aperture size, the height of the cavity wall plate 3, and the thickness of the damping rubber coating layer 4, the volume modulus, shear modulus, density, and loss factor of the damping rubber coating layer 4 can be adjusted to design the absorption peak frequency and absorption bandwidth. Such a sound absorption cover layer based on non-local coupling of multiple resonance units breaks through the technical barrier and realizes broadband and efficient absorption of sound waves in the very low frequency band through deep sub-wavelength structures. By combining multiple negative Poisson array structures 8 as negative Poisson array bases 7 and combining multiple unit non-local coupling, an integrated vibration and noise reduction structure is realized to achieve effective vibration reduction and high sound absorption performance with small structure thickness.

[0054] In another embodiment of the present application, a wide low frequency sound absorption and vibration reduction cover layer structure based on non-local coupling of multiple resonance units is designed. The theoretical calculation results and finite element simulation results show that the structure has a sound absorption coefficient of 0.9 or more and a vibration reduction coefficient of 20db or more in the very low frequency band of 300-450Hz. More importantly, thanks to the good adjustment of the impedance conditions provided by the wide low frequency sound absorption cover layer structure based on non-local coupling of multiple resonance units, a broadband and smooth sound absorption coefficient curve can be obtained even with a single unit sound absorption coefficient that is not high. Breaking the limitation of low frequency sound absorption effect and longer Helmholtz resonator cavity length, the wide low frequency sound absorption and vibration reduction cover layer structure can achieve sound absorption of low frequency sound waves with smaller thickness. By combining multiple negative Poisson array structures 8 as negative Poisson array bases 7 and the embedded rubber Helmholtz resonator technology, an integrated vibration and noise reduction structure is constructed to achieve effective vibration reduction and high sound absorption performance with small structure thickness. The overall thickness of the wide low frequency sound absorption cover layer structure is only 45.6mm.

[0055] For the wide low frequency sound absorption cover layer structure based on non-local coupling of multiple resonance units, the sound energy is efficiently attenuated and absorbed without reflection. To analyze the total acoustic impedance of the proposed wide low frequency sound absorption cover layer based on non-local coupling of multiple resonance units, the impedance of a typical embedded rubber Helmholtz resonator is first calculated.

[0056] To achieve sound absorption and vibration reduction, the sound absorption coefficient of a single super surface material can be determined by its (normal) acoustic impedance. The sound absorption effect of the sound absorption super surface array is based on the weak coupling resonance sound absorption mechanism, and the negative Poisson array base 7 produces a vibration reduction effect by arranging multiple negative Poisson ratio structures 8 in the array.

[0057] In this embodiment, the sound absorption metasurface array is constructed by connecting four units in parallel and adjusting the impedance of the whole, which is another embodiment of the present application Figure 3 . The thickness t of all the hole cover plate 1, chamber wall plate 3 and bottom plate 5 is 2 mm, the side length D of the square cross section of the sound absorption cavity 6 is 32 mm, the thickness h of the negative Poisson's ratio array 7 is 5.6 mm, and the thickness T of the damping rubber coating layer 4 is 0.2 mm. By adjusting the height L of the chamber wall plate 3, the length l of the embedded neck 2 and the hole diameter d, the sound absorption coefficients of the four different units are all below 0.9 at different frequencies in the low frequency band. The geometric parameters of the four units are shown in Table 1.

[0058] Table 1 Related adjustable parameters of samples

[0059] .

[0060] As shown in Figure 4 , the four different unit samples reach the absorption peak at 300 Hz, 345 Hz, 375 Hz and 420 Hz respectively after parameter optimization. Moreover, the thickness L is only about 1 / 1250 of the wavelength of the lowest frequency absorption peak frequency, which means that it has a deep subwavelength scale.

[0061] In order to illustrate that the present application is suitable for wideband sound wave absorption, this embodiment constructs a metasurface array, i.e. a sound absorption metasurface array, by connecting four units in parallel and adjusting the impedance of the whole. The sound absorption cover layer composed of periodic arrays is also illustrated.

[0062] By modifying the geometric parameters of the single unit, i.e. the hole diameter d of the embedded neck 2, the length l of the embedded neck 2 and the height L of the chamber wall plate 3, the impedance of the embedded rubber Helmholtz resonator is changed, and the wide low frequency sound absorption and vibration reduction cover layer structure of the sound absorption metasurface array is obtained by the weak coupling resonance sound absorption mechanism.

[0063] The overall impedance can be represented by the following formula:

[0064] ;

[0065] wherein, is the overall impedance of the array after being connected in parallel, are the impedances of the four units respectively; the four units are units freely combined after the geometric parameters of the hole diameter d of the embedded neck 2, the length l of the embedded neck 2 and the height L of the chamber wall plate 3 are arbitrarily selected, different combinations are achieved by modifying the values of the hole diameter d of the embedded neck 2, the length l of the embedded neck 2 and the height L of the chamber wall plate 3, and the structures of the four units are the same; as shown in Table 1 and Table 2.

[0066] The present application has simple structure and thin thickness, and can realize efficient energy loss of the structure in the corresponding frequency band by adjusting each embedded hole 2, unit sound absorption cavity 6 and damping rubber coating layer 4, so as to achieve the effect of wide-band sound energy loss in a specific frequency band. The negative Poisson's ratio characteristic of the negative Poisson's ratio array base 7 reduces the vibration generated by low-frequency noise. Through experiments and simulation verification, it is found that the sample with a thickness of 45.6 mm has a sound absorption coefficient of more than 0.9 and a vibration reduction coefficient of more than 20 in the frequency range of 300-450 Hz.

[0067] Figure 4 The sound absorption coefficient curve of the sound absorption cover layer formed by the periodic arrangement of the four-unit metamaterial array is given. It can be seen that the sound absorption cover layer realizes wide-band near-perfect sound absorption in the frequency range of 300-450 Hz, and the sound absorption coefficient is greater than 0.9. The deep black solid line is the theoretical calculation result, the circle is the finite element simulation result, and the four light black solid lines with low peak value represent the sound absorption coefficients of each unit. According to the impedance matching principle of perfect sound absorption, a verification method based on impedance analysis is given for the obtained sound absorption coefficient result, as shown in Figure 5 , at the peak of the absorption peak, the impedance imaginary part curve (the lower curve Im( )) passes through 0, and the impedance real part curve (the upper curve Re( )) is close to 1, at this time the impedance is approximately matched, and high-efficiency sound absorption can be realized.

[0068] In example 5, the sample of the metamaterial array in example 4 is demonstrated to illustrate that the present application is suitable for wide-band sound absorption, and can be designed by embedding the impedance of the rubber Helmholtz resonator through the geometric parameters of the individual unit, i.e. the embedded neck hole diameter d, the embedded neck length l, and the cavity wall plate height L, to obtain the overall sound absorption structure of the sound absorption metasurface array by the weak coupling resonance sound absorption mechanism. Thus, different effects can be designed as needed.

[0069] In this embodiment, a metamaterial array is still constructed by connecting 20 units in parallel and adjusting the impedance of the whole. The geometric parameters of the four units, i.e. the embedded neck hole diameter d, the embedded neck length l, and the cavity wall plate height L, are adjusted.

[0070] The geometric parameters of the four units are shown in Table 2, and the other parameters are the same as those in example 1.

[0071] Table 2 Related adjustable parameters of the sample:

[0072] .

[0073] Figure 6The sound absorption coefficient curve of the sound absorption cover layer formed by the periodic arrangement of the four-unit metamaterial array is given, and it can be seen that in the frequency band range of 140Hz-165Hz, the sound absorption cover layer realizes near perfect sound absorption, and the sound absorption coefficient is greater than 0.9. The upper solid line is the theoretical calculation result, the circle is the finite element simulation result, and the four lower peak solid lines represent the sound absorption coefficients of each unit.

[0074] Example by Helmholtz cavity array and negative Poisson ratio array co-body design Figure 3 By setting the coupling surface, the noise vibration calculation is carried out by the Helmholtz cavity sound absorption structure to the negative Poisson ratio array structure, the dynamic response is calculated, the dynamic intensity analysis is carried out, and the structure vibration response is obtained. The displacement Y without action is obtained, and the vibration reduction coefficient of the negative Poisson ratio array and the Helmholtz cavity co-body structure is obtained. Figure 7 The vibration reduction coefficient of the negative Poisson ratio array and the Helmholtz cavity co-body structure is given, and it can be seen that in the frequency band range of 300Hz-1100Hz, the vibration reduction coefficient reaches the lowest 20db effect.

[0075] In order to further illustrate the technical scheme of the present application, the displacement obtained when the negative Poisson ratio array co-body acts is described below The displacement Y without action is obtained, and the vibration reduction coefficient of the negative Poisson ratio array and the Helmholtz cavity co-body structure is obtained.

[0076] In order to realize sound absorption, it is necessary to understand the sound absorption coefficient of such structure The sound absorption coefficient of the metasurface material can be determined by its (normal) acoustic impedance The relationship is:

[0077] (1)

[0078] Among them, and are the density and sound speed of air, is the sound absorption coefficient, is the acoustic impedance;

[0079] When considering the thermal viscous loss in the embedded neck 2 and the end correction of the embedded neck 2, the impedance of the embedded neck 2 can be expressed as:

[0080] (2)

[0081] Among them, is the impedance, is a virtual number, is the density of air, is the angular frequency, ; For time, = Wavelength multiplied by distance It is an imaginary number. The perforation ratio at the air and resonator boundaries. , Let be the area of ​​the opening on the perforated cover plate 1. The area of ​​the perforated cover plate 1; yes The thickness of the viscous layer boundary is twice that of the viscous layer boundary. The aerodynamic viscosity coefficient; For the first The first-order Bessel function of the first kind, The diameter of the inset neck opening.

[0082] Based on electroacoustic analogy, the damping rubber coating layer 4 and the sound-absorbing cavity 6 exhibit a clear parallel relationship. The total acoustic impedance of the resonant cavity... It can be represented as:

[0083] (3)

[0084] in, and These represent the impedances of the sound-absorbing cavity 6 and the damping rubber coating layer 4, respectively.

[0085] The impedance of the damping rubber coating layer 4 can be expressed as:

[0086] (4)

[0087] in, Let be the inner cross-sectional area of ​​the sound-absorbing cavity 6. To represent the volume of the sound-absorbing cavity 6;

[0088] The impedance of the sound-absorbing cavity 6 can be expressed as:

[0089] (5)

[0090] in, For the volume of the damping rubber coating layer 4, The velocity of sound is the speed of sound in the damping rubber coating layer 4. The density of the damping rubber coating layer is 4.

[0091] In this embodiment, a resonant unit includes an embedded neck, a damping rubber coating, and a sound-absorbing cavity. The impedance of the resonant unit... It can be expressed by the following formula:

[0092] (6)

[0093] Structural vibration causes changes in noise, which is related to the inherent characteristics of the structure. Therefore, resonance may occur at certain frequencies, further amplifying the noise. Accordingly, this invention proposes to use a unidirectional fluid-structure interaction method to analyze the vibration response of a structure under the action of an external fluid.

[0094] The unidirectional coupling method solves for the fluid and solid separately. It uses CFD calculations to obtain the fluid forces applied to the structure, which are then imported into CSD to calculate the static deformation and dynamic response of the structure. This method considers the fluid's effect on the solid; at the fluid-solid interface, variables such as stress and displacement obey conservation principles, i.e.:

[0095] (7)

[0096] here, These represent the normal stresses at the interface between the fluid domain and the solid domain, respectively. This represents the displacement of the fluid domain and the solid domain at the interface. These represent the heat fluxes at the interface between the fluid domain and the solid domain, respectively. These represent the temperatures at the interface between the fluid and solid domains, respectively. The boundary at the fluid-structure interaction surface must satisfy the requirement that stress and normal velocity are continuous, meaning that surface acoustic load information and vibration response are integrated to calculate noise and vibration noise.

[0097] By introducing the Heaviside function and rewriting the Navier-Stokes equations, we can obtain the FW-H equations:

[0098] (8)

[0099] In the formula, for directional fluid velocity components; Perpendicular to the sound source surface The fluid velocity component; The velocity component of the sound source surface is perpendicular to the direction of the sound source surface. For density, It is the Dirac function; For Hevisai function; For far-field sound pressure; The velocity of sound in the unperturbed fluid in the far field; The sound source surface can be an impermeable solid surface or a permeable data surface that is far from the object surface; The direction of the outward normal to the sound source surface; the subscript 0 indicates the physical quantity of free flow.

[0100] For the Lighthill stress tensor:

[0101] ;

[0102] where, is the compressibility stress tensor, for Stokes fluid:

[0103] (10)

[0104] where, is the velocity classification, indicating the components in different directions; is the sound pressure, is the Dirac function; using the generalized function theory and free space Green function , the solution of FW-H equation can be obtained, that is, Farassat 1A formula:

[0105] (11)

[0106] (12)

[0107] where, is the sound pressure, is the density, is the area, is the mass, is the coefficient of free space Green function;

[0108] (13)

[0109] where:

[0110] (14)

[0111] (15)

[0112] In terms of vibration noise, the vibration response results of space-aircraft under flow excitation are obtained as boundary conditions by CSD, the structural vibration response data are mapped to the corresponding acoustic calculation structure grid, and the frequency domain Fourier transform is carried out at the same time, and then the vibration radiation noise is obtained by solving by finite element method.

[0113] Solving vibration noise radiation, the vibration noise sound pressure level spectrum is obtained.

[0114] In ideal fluid, the small amplitude wave equation is:

[0115] (16)

[0116] where, is the sound pressure, c is the sound speed, t is the time, and when the excitation point source in the sound field acts, the Helmholtz equation integral solution is:

[0117] (17)

[0118] where G is a Gaussian kernel function, the sound intensity I corresponding to the surface node of the structural surface is:

[0119] (18)

[0120] Integrating the above formula, we can get:

[0121] (19)

[0122] Radiation sound pressure The radiation sound pressure can be obtained by Rayleigh integral:

[0123] (20)

[0124] where I is the sound intensity, P is the sound pressure, and S is the area;

[0125] Based on the first-order shear theory of Reissner-Mindlin model and the principle of minimum potential energy, the free vibration governing equations of negative Poisson's ratio sandwich are derived. According to the relevant boundary conditions, the Rayleigh-Ritz method is used to construct the generalized displacement to solve the frequency equation. The Lagrange equation of the energy function is constructed, and the numerical solution of the frequency of each order of the structure is obtained by calling the Matlab eigenvalue and eigenvector functions. The relationship between the energy loss of the structure and the basic damping loss factor of the material is explored, and the damping loss factor of each order of the structure is solved based on the modal strain energy method. The suspension method is used to approximate the free-free boundary condition, and the frequency response function of the structure is obtained by the hammering measurement method of multi-point excitation and single-point response, so as to obtain its inherent vibration damping characteristics. Through modal analysis, the natural frequency, modal shape, and unit volume, stress and strain components of each order of the negative Poisson's ratio sandwich structure are obtained and extracted. Based on the modal strain energy method, the damping performance is applied to the damping prediction of the negative Poisson's ratio lattice sandwich structure as a basic parameter. By analyzing the damping contribution factor of the strain energy component of the structure, the damping energy dissipation mechanism of the structure is revealed. And its vibration reduction performance is evaluated:

[0126] (21)

[0127] where, is the displacement of the main mass from the static equilibrium position after installing the damper, is the displacement of the main mass without installing the damper.

[0128] An experiment is performed on the technical solution of example 4: 3D printing is performed by using a laser melting forming (SLM) metal 3D printing technique, and the precision is 0.1 mm. The experiment uses a B&K 4206T impedance tube, and the absorption coefficient is measured strictly according to the impedance tube method of GB / T 18696.1-2004. It is found that the experiment and simulation results are basically consistent. The experiment and simulation verify that the sample with a thickness of 45.6 mm has an absorption coefficient of 0.9 or more and a damping coefficient of 20 or more in the frequency range of 300-450 Hz.

[0129] The application can be applied to the following aspects: an aviation equipment shell: used for controlling the aerodynamic noise and vibration generated by the aviation equipment frequently entering the dense atmosphere and the sparse atmosphere at supersonic speed, reducing the fatigue damage caused, and the negative Poisson's ratio characteristics of the integrated material can also cope with the problem of thermal expansion of the surface of the machine body, which is beneficial to improve the service life of the aviation equipment and increase the safety. Civil aircraft, motor train units and other vehicles: improve the comfort of passengers in the cabin and carriage. City buildings: effectively isolate external city low-frequency noise, effectively protect the health of internal residents or staff, and the unique mechanical properties of the composite material can also increase the strength and bending stiffness of the building structure, and improve the service life. It can also be used for transformer shells, case shells and other directions, used to isolate the generated vibration and low-frequency noise, and prevent it from radiating outward to affect the normal use of other parts.

[0130] In the above embodiments, the description of each embodiment has its own focus, and the parts not described or recorded in a certain embodiment can be referred to the related description of other embodiments.

[0131] The information interaction, execution process and the like between the above devices / units are based on the same concept as the method embodiments of the application, and the specific functions and technical effects brought by them can be referred to the method embodiments part, which will not be repeated here.

[0132] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the above-mentioned division of each functional unit and module is exemplified, and in actual application, the above-mentioned functions can be completed by different functional units and modules according to needs, that is, the internal structure of the device is divided into different functional units or modules to complete all or part of the functions described above. Each functional unit and module in the embodiment can be integrated in one processing unit, or each unit can exist physically, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be realized in the form of hardware or software function unit. In addition, the specific names of each functional unit and module are only for easy distinction, and do not limit the protection scope of the application. The specific working process of the unit and module in the above system can be referred to the corresponding process in the foregoing method embodiments.

[0133] Based on the technical solutions of the embodiments of the present application described above, the following application examples can be further proposed.

[0134] According to the embodiments of the present application, the present application further provides a computer device, comprising at least one processor, a memory, and a computer program stored in the memory and executable on the at least one processor, wherein the processor implements the steps in any of the above method embodiments when executing the computer program.

[0135] The embodiments of the present application further provide a computer readable storage medium, which stores a computer program, wherein the computer program is executable by a processor to implement the steps in any of the above method embodiments.

[0136] The embodiments of the present application further provide an information data processing terminal, which is used to provide a user input interface to implement the steps in any of the above method embodiments when executed on an electronic device, and the information data processing terminal is not limited to a mobile phone, a computer, or a switch.

[0137] The embodiments of the present application further provide a server, which is used to provide a user input interface to implement the steps in any of the above method embodiments when executed on an electronic device.

[0138] The embodiments of the present application further provide a computer program product, which, when executed on an electronic device, enables the electronic device to implement the steps in any of the above method embodiments.

[0139] The integrated unit, if realized in the form of a software function unit and sold or used as an independent product, can be stored in a computer readable storage medium. Based on such understanding, the present application can implement all or part of the processes in the above embodiments by a computer program to instruct related hardware, and the computer program can be stored in a computer readable storage medium. The computer program, when executed by a processor, can implement the steps in any of the above method embodiments. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or some intermediate form. The computer readable medium at least includes any entity or device capable of carrying the computer program code to a photographing device / terminal device, recording medium, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal, and software distribution medium. For example, U disk, mobile hard disk, magnetic disk or optical disk, etc.

[0140] The above merely describes the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any modification, equivalent replacement and improvement within the technical range disclosed by the present application and within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A wide low frequency sound absorbing and vibration damping cover layer structure, characterized by, The structure is designed to absorb sound of different frequencies by adjusting the Helmholtz resonance cavity coefficient, realizes wide-frequency sound absorption by coupling resonance of multiple cavities, and is used for vibration absorption and sound absorption by designing the Helmholtz cavity type with embedded apertures and the negative Poisson's ratio array structure; the structure comprises: A chamber wall plate (3) is placed between the perforated cover plate (1) and the bottom plate (5) and closely adheres to form multiple sound absorption cavities (6) inside; Multiple embedded necks (2) with different lengths and different apertures are installed directly below the perforated cover plate (1), and the neck inner passage circular section of the embedded neck (2) is the same size as and concentrically arranged with the perforated cover plate (1) perforated circular section; A negative Poisson's ratio array base (7) is the same size as the bottom plate (5) and is arranged in close contact with the bottom plate (5); the negative Poisson's ratio array structure (7) is formed by closely arranging multiple negative Poisson's ratio structures (8), and a damping rubber coating layer (4) with uniform thickness is uniformly coated on the inner wall of the sound absorption cavity (6); The perforated cover plate (1) and the bottom plate (5) are the same size and the same shape; the chamber wall plate (3) is a square section shell with upper and lower through holes, the plate thickness of the chamber wall plate (3) is uniform and consistent, and the thickness is the same as that of the perforated cover plate (1) and the bottom plate (5); the damping rubber coating layer (4) is uniformly coated on the inner wall bottom surface and the four side wall surfaces of the sound absorption cavity (6); The length and aperture size of the embedded neck (2), the height of the chamber wall plate (3) and the cross-sectional area of the surrounded sound absorption cavity (6), and the thickness of the damping rubber coating layer (4) are adjusted to adjust the absorption peak frequency and the absorption frequency band width; The volume modulus, shear modulus, density, and loss factor of the damping rubber coating layer (4) are adjusted to adjust the absorption peak frequency and the absorption frequency band width.

2. The broad low frequency sound absorbing and damping overlay structure according to claim 1, wherein, The perforated cover plate (1) and the bottom plate (5) are regular polygon structures; the perforated cover plate (1) and the bottom plate (5) are thin plate structures.

3. The broad low frequency sound absorbing and damping overlay structure of claim 1, wherein, The perforated cover plate (1), the embedded neck (2), the chamber wall plate (3), the bottom plate (5), and the negative Poisson's ratio array base (7) are made of the same metal material.

4. The broad low frequency sound absorbing and damping overlay structure of claim 1, wherein, The perforated cover plate (1), the embedded neck (2), the chamber wall plate (3), the bottom plate (5), and the negative Poisson's ratio array base (7) are formed by metal 3D printing, CNC machining, and sheet metal machining processes; The damping rubber coating layer (4) is processed by chemical modification and composite filling process; the processed damping rubber coating layer (4) is preliminarily formed in the sound absorption cavity (6) by cooperating with an extrusion die, and is adhered to the surface of the sound absorption cavity (6) by an adhesive, and air is extracted in a vacuum heating furnace and solidified.

5. The broad low frequency sound absorbing and vibration damping overlay structure of claim 1, wherein, The number of the sound absorption cavities (6) is 4-20; the negative Poisson's ratio array base (7) comprises 100 negative Poisson's ratio structures (8).

6. A method of designing a wide low frequency sound absorbing and vibration damping overlay, characterized by, The design method is made of the wide low-frequency sound absorption and vibration reduction coating structure of any one of claims 1-5, and the design method comprises: By changing the geometric parameters of the single unit composed of the hole diameter d of the embedded neck (2), the length l of the embedded neck (2), and the height L of the chamber wall plate (3), the non-local coupling between multiple embedded rubber Helmholtz resonators is changed, the impedance of the embedded rubber Helmholtz resonator is changed, a wide low-frequency sound absorption and vibration reduction covering layer structure of the sound absorption metasurface array is obtained by the weak coupling resonance sound absorption mechanism; the embedded rubber Helmholtz resonator is composed of an embedded neck (2), a damping rubber coating layer (4), and a sound absorption cavity (6).

7. The method of designing a broad low frequency sound absorbing and vibration dampening overlay of claim 6, wherein, The impedance of the embedded rubber Helmholtz resonator is expressed as: ； wherein, Ztot is the overall impedance of the parallel array, Z1, Z2, Z3, and Z4 are the individual impedances of the four units, respectively; the four units are the units freely combined after the geometric parameters of the inner embedded neck (2) hole diameter d, the inner embedded neck (2) length l, and the chamber wall plate (3) height L are arbitrarily selected.

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