Honeycomb edge-folded structure film acoustic metamaterial
阅读说明：本技术 一种蜂窝折边式结构薄膜声学超材料 (Honeycomb edge-folded structure film acoustic metamaterial ) 是由 崔洪宇 朱帅 胡昊明 刘承韬 胡召平 于 2020-07-02 设计创作，主要内容包括：本发明属于用于低频噪声控制的声学超材料技术领域,一种蜂窝折边式结构的薄膜声学超材料,其结构单元由薄膜和折边形式的蜂窝结构组合而成；薄膜声学超材料通过改变折边角度来调节隔声峰对应的频率向低频移动。本发明设计的一种带薄膜结构的蜂窝折边式声学超材料,其六边形蜂窝框架结构可采用轻质的碳纤维、树脂等材料,与传统的金属材料相比,其结构重量轻,而且可以满足整个结构的强度设计要求。(The invention belongs to the technical field of acoustic metamaterials for controlling low-frequency noise, and relates to a film acoustic metamaterial with a honeycomb folded edge type structure, wherein a structural unit of the film acoustic metamaterial is formed by combining a film and a honeycomb structure in a folded edge mode; the film acoustic metamaterial adjusts the frequency corresponding to the sound insulation peak to move towards low frequency by changing the angle of the folded edge. According to the honeycomb folded edge type acoustic metamaterial with the thin film structure, the hexagonal honeycomb frame structure can be made of light carbon fibers, resin and the like, compared with the traditional metal material, the structure is light in weight, and the strength design requirement of the whole structure can be met.)
1. The film acoustic metamaterial with the honeycomb folded edge structure is characterized by being formed by connecting a plurality of structural units, wherein each structural unit is formed by combining a film and a honeycomb frame structure in a folded edge mode; the film acoustic metamaterial adjusts the frequency corresponding to a sound insulation peak to move towards low frequency by changing the angle of the folded edge;
the film divides the folded honeycomb cavity into an upper part and a lower part from the middle in the height direction; the upper layer structure is a first unit, the lower layer structure is a second unit, the film is a third unit, and the film is positioned between the first unit and the second unit;
in the structure, the matrix material of the honeycomb regular hexagon structure is carbon fiber or resin, the side length of the honeycomb regular hexagon is a, and the thickness is t1The folding angle is alpha, the folding length is b, and the first unit height is h1The second unit height is h2Film thickness of t2The number of the folded edges is n.
2. The thin film acoustic metamaterial of a honeycomb folded-edge structure as claimed in claim 1, wherein the specific dimensional parameters of the structure are adjustable, and the adjustment is performed according to the specific requirements of sound insulation so as to meet the sound insulation requirements under different environments.
3. The thin film acoustic metamaterial of a honeycomb folded-edge structure as claimed in claim 1 or 2, wherein the thin film is made of silica gel or nylon and is adhered between the first unit and the second unit, and the thickness and the prestress of the thin film are set according to specific requirements.
4. The thin film acoustic metamaterial of a honeycomb folded structure according to claim 1 or 2, wherein the thin film acoustic metamaterial is prepared by the following steps: the film is obtained by 3D printing, and is bonded with the honeycomb frame structure by glue after being prestressed; if a model of the mass is applied, the mass is stuck in the center of the membrane unit.
5. The thin film acoustic metamaterial of claim 3, wherein the thin film acoustic metamaterial is prepared by the following steps: the film is obtained by 3D printing, and is bonded with the honeycomb frame structure by glue after being prestressed; if a model of the mass is applied, the mass is stuck in the center of the membrane unit.
Technical Field
The invention belongs to the technical field of acoustic metamaterials for controlling low-frequency noise, and particularly relates to a honeycomb folded edge type structure film acoustic metamaterial.
Background
With the development of science and technology, the problems of vibration and noise are more prominent than before due to the high speed, large size and light weight of ships. The structures such as the plate, the stiffened plate and the like are widely applied to ship structures, and generate vibration under the excitation action of mechanical external force, so that radiation noise is caused. The vibration can not only damage the engineering structure and influence the service life thereof, reduces the sensitivity of instruments and meters, but also can easily be detected and found by enemies due to overlarge radiation noise, influences the action distance and the precision of a sonar system of a ship body, reduces the stealth performance of the ship, and also has great influence on the comfort of working and living environments of workers on the ship. Therefore, suppressing the vibration of the ship structure and controlling the noise of the structure are becoming one of the most important issues.
The traditional sound insulation material has larger sound insulation amount when the noise frequency is higher and the material thickness is larger because the traditional sound insulation material follows the law of mass action. Effective isolation of low frequency noise is often not practical in many situations at the expense of increased material weight. In order to break through the limitation of the law of mass action, the acoustic metamaterial is the focus of attention.
The film type acoustic metamaterial is a novel artificial composite material, has the advantages of light weight, small volume, flexible arrangement and the like, and shows good sound insulation performance in a low-frequency range. The invention designs a honeycomb folded edge type acoustic metamaterial with a thin film structure by combining the traditional thin film type acoustic metamaterial.
The acoustic metamaterial is a composite material consisting of a periodic subwavelength structure with negative equivalent characteristics, and can show excellent sound insulation performance in a low-frequency range by optimizing the material and structure properties of the material and the structure. The invention designs a film acoustic metamaterial with a honeycomb folded edge structure based on a traditional acoustic metamaterial and by introducing an angle-adjustable folded edge structure.
Disclosure of Invention
The invention aims to solve the problem that low-frequency noise in the field of ships is difficult to effectively isolate at present. The film acoustic metamaterial with the honeycomb folded edge type structure is designed, the frame base body is folded, the angle is adjustable, and the good sound insulation effect in a low-frequency range can be achieved by adding the film structure.
The technical scheme of the invention is as follows:
a film acoustic metamaterial with a honeycomb folded edge structure is characterized in that a structural unit is formed by combining a film and a honeycomb structure in a folded edge mode; the film acoustic metamaterial adjusts the frequency corresponding to a sound insulation peak to move towards low frequency by changing the angle of the folded edge;
the film divides the folded honeycomb cavity into an upper part and a lower part from the middle in the height direction; the upper layer structure is a first unit, the lower layer structure is a second unit, the film is a third unit, and the film is positioned between the first unit and the second unit;
in the structure, the matrix material of the honeycomb regular hexagon structure is carbon fiber or resin, the side length of the honeycomb regular hexagon is a, and the thickness is t1The folding angle is alpha, the folding length is b, and the first unit height is h1The second unit height is h2Film thickness of t2The number of the folded edges is n;
in the structure, specific size parameters are adjustable and are adjusted according to specific sound insulation requirements so as to meet sound insulation requirements in different environments.
In the above scheme, the film can be made of materials such as silica gel and nylon and is pasted between the first unit and the second unit, and the thickness and the prestress of the film can be set according to specific requirements.
In the scheme, the plane acoustic wave is perpendicularly incident to the surface of the film.
In the above scheme, the preparation process of the acoustic metamaterial comprises the following steps: the frame structure can be obtained by 3D printing and other modes, and the film is bonded with the frame structure by glue after being prestressed. A model of a mass is applied, which is glued in the center of the membrane unit.
The invention has the beneficial effects that:
(1) according to the honeycomb folded edge type acoustic metamaterial with the thin film structure, the hexagonal honeycomb frame structure can be made of light carbon fibers, resin and the like, compared with the traditional metal material, the structure is light in weight, and the strength design requirement of the whole structure can be met.
(2) The sound wave, the elastic film and the cavity structure are utilized to cause resonance under different frequencies, so that the effective sound insulation effect in a low-frequency range can be realized.
(3) By adjusting the parameters of the structural unit, when the thickness of the film is 0.4mm, the folding number n is 12, the folding length b is 5mm, and the height h is1＝h2When the folding angle alpha is 45 degrees and the film prestress is 500N/m, the maximum sound insulation amount of the acoustic metamaterial structure can reach 68dB at 320Hz and the average sound insulation amount reaches 31dB in the frequency band range of 50-800Hz through the test of the inventor; after the thin film unit is added with the mass block, two sound insulation peaks appear in the sound insulation frequency band range, and the first sound insulation peak and the second sound insulation peak both move towards low frequency. At 295Hz, the maximum sound insulation reaches 76dB, and the average sound insulation reaches 32dB in the frequency band range of 50-1600Hz (as shown in FIG. 13).
(4) The acoustic metamaterial can change the position of a sound insulation peak by changing structural parameters and material parameters, so that the sound insulation effect of the structure is adjusted and improved.
(5) The single unit structure of the acoustic metamaterial can achieve the purpose of low-frequency control, actual size requirements on site can be met through periodic arrangement of unit cell structures (as shown in figure 1), complex stacking is not needed, and structural arrangement efficiency and structural overall stability are improved. The method can be widely applied to the fields of engineering structures, equipment and the like in ships.
Drawings
Figure 1 is an isometric view of a multi-cell structure according to one embodiment of the design.
Figure 2 is a top view of the multi-cell structure according to one embodiment of the design.
Figure 3 is a top view of the multi-cell structure plus quality blocks of one embodiment of the design.
FIG. 4 is a front view of the cell structure and its dimensions according to one embodiment of the design.
FIG. 5 is a front view of the design after the cell structure plus mass blocks, and its dimensions.
FIG. 6 is a top view of the cell structure and its dimensions according to one embodiment of the design.
FIG. 7 is a side view of a multi-cell structure according to one embodiment of the design.
FIG. 8 is an isometric view of the frame of the cell structure of one embodiment of the design.
FIG. 9 is a diagram of a straight-sided model comparing the cell structure of an embodiment of the design.
FIG. 10 is a model diagram of a finite element cell simulation of the cell structure of one embodiment of the design in COMSOL Multiphysics 5.4.
FIG. 11 is a finite element cell simulation model of the cell structure plus the quality block in COMSOL Multiphysics5.4 according to one embodiment of the design.
FIG. 12 shows an embodiment of the design, in which the thickness of the film is 0.4mm, the number of folds n is 12, the length of the folds b is 5mm, and the height h is1＝h221.21mm, folding angle alpha 45 degrees, film prestress 500N/m sound insulation curve.
FIG. 13 is a graph comparing the sound insulation of the cell structure of the embodiment of the design shown in FIG. 12 after applying a mass with the parameters unchanged.
FIG. 14 is a graph comparing the sound insulation of one embodiment of the design shown in FIG. 12 with the straight model shown in FIG. 9.
Fig. 15 is a graph showing the comparison of the sound insulation when the folding angle α is 20 °, 30 ° or 45 ° in the unit cell structure of the embodiment of the design shown in fig. 12, with the other parameters being kept unchanged.
In the figure: 1, an upper layer structure; 2, a film; 3, a lower layer structure; 4 perfect matching layer; 5 background pressure field; 6 pressure acoustic domain; 7 pressure acoustic domain; 8 mass blocks; 9 pressure acoustic domain.
Detailed Description
The following describes the embodiments of the present invention in detail with reference to the drawings.
Fig. 1 shows an embodiment of a honeycomb folded-edge structure thin film acoustic metamaterial according to the present invention.
The invention adds a layer of film on the basis of the variable-angle folded frame structure, and utilizes the resonance generated by sound waves, the cavity and the film, thereby realizing good sound insulation effect in a low-frequency range.
Fig. 1 shows a multi-cell structure of the acoustic metamaterial, which includes an
Fig. 2 is a top view of the acoustic metamaterial multi-cell structure, which has a cross section of a regular hexagon with a side length of a.
Fig. 3 is a top view of the multi-cell model of the acoustic metamaterial after a mass block is added to the center of the unit cell structure film.
FIG. 4 is a front view of a unit cell structure of the acoustic metamaterial, which may be arranged periodically to form the multi-cell structure shown in FIG. 1; as shown in the figure, the upper frame height of the model unit cell structure is h1The height of the lower frame is h2Film thickness of t2Total height h1+h2+t2The side length of the folded edge is b, and the structural wall thickness is t1The folding angle is alpha; the specific size can be adjusted according to the actual sound insulation requirement.
Fig. 5 is a front view of a unit cell structure of the acoustic metamaterial after a mass is applied to the center of a thin film, which can be arranged periodically to form the multi-cell structure shown in fig. 3. The structural size is the same as that described in figure 4, and the height of the mass block is h3。
FIG. 6 is a top view of the unit cell structure of the acoustic metamaterial, the cross section of the unit cell structure is a regular hexagon, and the side length is a.
Fig. 7 is a side view of the acoustic metamaterial multi-cell structure, the height dimension of the acoustic metamaterial multi-cell structure is the same as that of fig. 4, and a folded edge form of the acoustic metamaterial multi-cell structure can be clearly seen.
Fig. 8 is a three-dimensional isometric view of the acoustic metamaterial unit cell structure.
FIG. 9 is a side view of a straight-sided model compared to the unit cell structure of the acoustic metamaterial, with the same structural dimensions as described in FIG. 4, with only the edgefold form modified to a straight-sided form.
FIG. 10 is a simulation model diagram of the unit cell structure of the acoustic metamaterial.
To further understand the present invention, a finite element simulation study was conducted on the simulation model depicted in FIG. 10 to obtain its sound insulation characteristics.
By way of non-limiting example, the preferred geometric parameters of the simulation model of the present invention are: a is 10mm, t1＝1.6mm,h1＝h2＝21.21mm,t20.4mm, 12 n and 45 deg. The material of the frame structure is carbon fiber with elastic modulus E of 50 × 109Pa; a Poisson ratio of 0.31; density rho 1800kg/m3]The film is a silicone rubber film [ elastic modulus E ═ 2X 10%5Pa; a Poisson ratio of 0.49; density rho 1200kg/m3]。
The "acoustic-solid coupling, frequency" module in the large commercial software COMSOL multiphysics5.4 performs the calculations. Wherein 1 and 3 are solid mechanical domains, 2 is a thin film domain, 4 is a perfect matching layer, 5 is a background pressure field, and 6, 7 and 9 are pressure acoustic domains; and setting the boundary conditions of the model as periodic boundary conditions so as to accurately simulate the actual size and installation conditions of the acoustic metamaterial.
Different physical field modules are arranged for different geometric domains, wherein the air domain is arranged to be a pressure acoustic module, the frame structure is arranged to be a solid mechanical module, and the membrane domain is processed by using a membrane unit. The finite element model of the acoustic metamaterial therefore mainly comprises four types of elements:
1) a fluid unit consisting of an air layer;
2) a solid unit consisting of a frame structure;
3) a nonlinear unit composed of a thin film structure;
4) a fluid-solid coupling unit at an interface of a fluid and a structure (including a membrane).
Different physical fields are set, and the finite element software can automatically perform coupling calculation on the different physical fields.
When the plane sound wave enters the frame cavity structure from the vertical incidence of the background pressure field and passes through the film domain, a part of the sound wave is reflected back to be absorbed by the perfect matching layer, and a part of the sound wave continuously transmits forwards through the film until being absorbed by the perfect matching layer on the other side. The perfect matching layer eliminates the influence of boundary reflection on the calculation result, so that the calculation result is more accurate.
In the process, the incident sound pressure, the reflected sound pressure andtransmission sound pressure is pi，prAnd ptIntegrating the incident surface and the emergent surface respectively as shown in the following
wherein WinFor incident acoustic energy, WoutIs transmitted acoustic energy; rho0Is the density of air at normal temperature; c. C0Is the propagation velocity of sound wave in air at normal temperature, rho0c0The characteristic impedance of air at normal temperature is 415 N.s/m3。
The amplitude of incident sound pressure of a background pressure field is defined to be 1Pa, the frequency scanning range is 50-1600Hz, and the calculation step length is 5 Hz. Due to the presence of the thin film, a graph of the sound insulation of the model in the frequency band range can be obtained by using geometric non-linear analysis, and is shown in fig. 12.
As can be seen from fig. 12, when the frequency is about 320Hz, the sound insulation curve has a peak value, and the maximum sound insulation reaches 68 dB; in the range of 50-800Hz of the whole sound insulation frequency band, the average sound insulation amount reaches 31dB, and good sound insulation effect in a low frequency range is realized.
FIG. 11 shows a simulation model of a honeycomb folded-edge structure of a thin film acoustic metamaterial according to the invention after a mass block is added to the center of the thin film. The diameter and height h of the mass block are 5mm32mm, 0.3g, and Nd-Fe-B magnet (elastic modulus E1.6 × 10)11Pa; a Poisson ratio of 0.28; density rho 7400kg/m3]. The simulation procedure is the same as that described in fig. 10, and the mass block is
As can be seen from fig. 13, after the mass block is applied, the peak value of the sound insulation peak is increased, the second sound insulation peak moves obviously to the low frequency, and the moving amplitude of the first sound insulation peak to the low frequency is small, mainly because the first sound insulation peak is caused by the resonance of sound waves and the cavity, and the mass block is applied to have little influence on the first sound insulation peak. The second sound insulation peak is caused by the resonance of sound waves and the film, and after the mass block is applied, the mass block has great influence on the first resonance mode of the film, and the second sound insulation peak is formed by the resonance of the sound waves and the film
Fig. 14 explores a comparison graph of the sound insulation calculated by the straight-side comparison model of the designed acoustic metamaterial when the folding angle α is 45 °. As shown in the figure, the sound insulation capacity curves of the two models are basically consistent, and the sound insulation peak frequencies are respectively 320Hz and 345 Hz. Compared with a straight-side model, the flanging structure of the invention moves 25Hz to the low frequency compared with the first sound insulation peak of the common straight-side structure, thereby having better low-frequency sound insulation performance.
Fig. 15 researches the influence of the folding angle alpha on the sound insulation of the designed acoustic metamaterial under the condition that the folding angle alpha is changed only while other structural parameters are kept unchanged. As can be seen from the figure, in the process that α increases from 20 ° to 45 °, the sound insulation peak gradually moves to a low frequency, and when α is 30 °, the sound insulation amount is slightly higher than the other two angles; when alpha is 45 degrees, the frequency corresponding to the sound insulation quantity is the lowest, and the low-frequency sound insulation effect is the best.
The film acoustic metamaterial with the honeycomb folded edge structure can be used for replacing traditional materials with poor low-frequency sound insulation effect. Through the design of hem formula, can realize that low frequency sound insulation is effectual, the structural parameter is adjustable, advantages such as sound insulation peak value is adjustable. The structure can be used in ship equipment, reduces, isolates and controls low-frequency noise, and serves high-end manufacturing industry in ship and ocean engineering.
The above described preferred embodiments are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and any obvious modifications or simple variations which may be made to the acoustical metamaterial structures described herein are intended to be included within the scope of the present invention.
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