CN108133700B - An acoustic black hole vibration and noise reduction device - Google Patents

Abstract

The invention discloses a vibration reduction and noise reduction device. The vibration reduction and noise reduction device comprises a disc-shaped structure with a distance between upper and lower surfaces gradually decreasing from a central axis to an outer edge. The disc-shaped structure includes a black hole area, so The distance between the upper and lower surfaces of the black hole region changes in the form of a power exponential in the direction from the central axis to the outer edge. There is no need to weaken the thickness of the noise-reduced structure, which avoids the limitation of local high dynamic response and the reduction of the structural strength of the noise-reduced structure.

Description

An acoustic black hole vibration and noise reduction device

technical field

The invention relates to the field of vibration reduction and noise reduction, in particular to an acoustic black hole vibration reduction and noise reduction device.

Background technique

Noise in acoustic media such as air and water originates from the elastic wave propagation effect in the structure on the one hand, and the mutual coupling between structural elastic waves and the surrounding acoustic medium (structure sound), and on the other hand, due to the interaction of sound waves in the sound field (air Voice). Therefore, the control of noise in the acoustic medium should be carried out from the above two directions, that is, the elastic wave behavior in the structure and the acoustic wave in the air are manipulated, so as to achieve vibration reduction and noise reduction in the acoustic space. Wave manipulation methods can be divided into two categories: active methods and passive methods. Active methods generally require external energy supply, the system implementation is more complex, and there is still a certain distance from practicality, so the passive method is generally used in the current engineering structure. Existing passive methods mostly use damping materials, and sound-absorbing materials attenuate bending waves and sound waves. However, with the development of technology and society, people have more and more needs for comfort, reliability, safety, and durability of equipment. High, such as the low noise of civil aircraft, the stealth performance of military aircraft, etc. Therefore, the existing passive methods can no longer meet the design requirements. Especially under the current national strategic development needs of "comprehensively improving the technical level of major equipment" in my country, it is even more necessary to vigorously develop new theories, new methods and new technologies for structural vibration and noise reduction. The proposal of the concept of acoustic black hole has opened a new chapter for the research on "manipulating wave propagation in elastic media and structures", and also provided a new opportunity for theoretical and technological breakthroughs in structural vibration and noise reduction.

Acoustic black hole (ABH) is to introduce the concept of black hole in astrophysics into the field of wave and vibration, and propose it as a brand new concept. The acoustic black hole effect is actually a wave trap made by changing the structural form. Through the change of the structural impedance, the phase velocity and group velocity of the wave propagating in the structure change, and the wave is concentrated in the local area of the structure.

The main way to achieve the acoustic black hole effect is to change the thickness of the structure. Using the propagation characteristics of flexural waves in variable-thickness structures, when the thickness of the structure decreases according to a certain power function, the phase and group velocities of the flexural waves also decrease accordingly. Ideally, when the thickness is reduced to zero, the wave speed at the edge of the structure can be reduced to zero, reaching zero reflection of the wave, concentrating all the wave energy at the tip of the structure, through the damping of the structure and the additional on the structure. Damping material to achieve the purpose of energy absorption or vibration reduction and noise reduction. A two-dimensional ABH is obtained by cutting the thickness of the thin plate structure according to a certain form, forming a wave trap similar to a lens or a black hole, and concentrating the energy propagating in the structure at a specific position.

However, the traditional acoustic black hole achieves its goal by weakening the thickness of the noise-reduced structure. In this way, the reduction of the thickness will bring about a serious problem, which will lead to stress concentration and reduce the strength of the noise-reduced structure, which cannot be applied in practical engineering.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an acoustic black hole vibration and noise reduction device in order to avoid the limitation of local high dynamic response and reduction of structure strength of the noise-reduced structure.

For achieving the above object, the present invention provides the following scheme:

An acoustic black hole vibration reduction and noise reduction device, the vibration reduction and noise reduction device is arranged on a structure to be noise-reduced, the vibration reduction and noise reduction device comprises a disc-shaped structure, and the upper and lower surfaces of the disc-shaped structure are between the upper and lower surfaces. The distance between them varies gradually from the central axis to the outer edge of the disc-shaped structure, the disc-shaped structure includes a black hole region, and the distance between the upper and lower surfaces of the black hole region is from the central axis to the outer edge. The direction changes exponentially.

The disc-shaped structure further includes a uniform area, which is arranged at the position of the central axis of the disc-shaped structure and is located inside the black hole area, and communicates with the black hole area, and the upper part of the uniform area is located. , the distance between the lower surfaces is constant, and is equal to the maximum distance between the upper and lower surfaces of the black hole region.

The disc-shaped structure further includes an extension area, the extension area is arranged at the outer edge of the disc-shaped structure, is located outside the black hole area, and communicates with the black hole area. The distance between the upper and lower surfaces is constant and equal to the minimum distance between the upper and lower surfaces of the black hole region.

A cavity is provided at the position of the central axis of the lower surface of the disc-shaped structure, a through hole communicating with the cavity is opened on the upper surface of the disc-shaped structure, and the through hole and the cavity are formed acoustic cavity.

The cavity is a cylindrical cavity.

The vibration and noise reduction device further includes an annular damping washer, the outer diameter of the annular damping washer is the same as the outer diameter of the disc-shaped structure, and the annular damping washer is adhered to the the lower surface of the disc-shaped structure.

The vibration and noise reduction device further includes a connecting ring, which is arranged on the lower surface of the disc-shaped structure and is used to connect the disc-shaped structure and the noise-reduced structure.

The material of the connecting ring is a vibration-absorbing and sound-absorbing material.

According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

The invention discloses a vibration reduction and noise reduction device. The vibration reduction and noise reduction device comprises a disc-shaped structure with a distance between upper and lower surfaces gradually decreasing from a central axis to an outer edge. The disc-shaped structure includes a black hole area, so The distance between the upper and lower surfaces of the black hole region changes in the form of power exponential in the direction from the central axis to the outer edge. The controlled structure performs broadband vibration and noise reduction without weakening the thickness of the controlled structure, so as to avoid local high dynamic response and reduction of structural strength of the controlled structure.

At the same time, by setting cavities and through holes on the disc-shaped structure, the cavities and through holes form an acoustic resonance cavity, which can effectively control low-frequency sound waves, thereby realizing full-band noise reduction, making up for the use of traditional acoustic black holes for vibration reduction and reduction. Noise, the limitations of low frequencies that are difficult to achieve.

Description of drawings

In order to describe the embodiments of the present invention more clearly, the accompanying drawings required in the embodiments will be briefly introduced below. Obviously, the accompanying drawing described below is only an embodiment of the present invention, and for those of ordinary skill in the art, other drawings can also be obtained from this accompanying drawing without creative effort.

1 is a structural diagram of a vibration and noise reduction device provided by the present invention;

2 is an installation diagram of a vibration and noise reduction device provided by the present invention on a noise-reduced structure;

3 is an installation diagram in a square enclosed space provided by the present invention;

Fig. 4 is the installation diagram in the enclosed space of irregular cavity cover type provided by the present invention;

5 is a schematic diagram of the propagation of the noise waveform provided by the present invention in the vibration and noise reduction device provided by the present invention;

Fig. 6 is the arrangement diagram of the vibration reduction and noise reduction device provided by the present invention;

FIG. 7 is a comparison diagram of the damping characteristics of the additional vibration and noise reduction device of the present invention and the additional uniform mass damping sheet;

FIG. 8 is a comparison diagram of the acoustic characteristics of the additional vibration and noise reduction device of the present invention and the additional uniform mass damping sheet.

Detailed ways

The purpose of the present invention is to provide an acoustic black hole vibration reduction and noise reduction device, so as to avoid the limitation of local high dynamic response and reduction of structure strength of the noise-reduced structure.

In order to make the above objects, features and advantages of the present invention more clearly understood, the technical invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 1 , the present invention provides an acoustic black hole vibration and noise reduction device, the vibration and noise reduction device A1 is arranged on the noise-reduced structure A2, and the vibration and noise reduction device includes a disc-shaped structure, The distance between the upper and lower surfaces of the disc-shaped structure gradually decreases from the central axis of the disc-shaped structure to the outer edge, and the disc-shaped structure includes a black hole region 2, and the black hole region 2 The distance between the upper and lower surfaces of , changes in the form of a power exponent h(x)=εx ^m (wherein the exponent m is greater than or equal to 2) in the direction from the central axis to the outer edge.

The disk-shaped structure further includes a uniform region 3, which is arranged at the position of the central axis of the disk-shaped structure and is located inside the black hole region 2, and communicates with the black hole region. The distance between the upper and lower surfaces of the region 3 is unchanged, and is equal to the maximum distance between the upper and lower surfaces of the black hole region 2 .

The disc-shaped structure A1 further includes an extension region 1, and the extension region 1 is arranged at the outer edge of the disc-shaped structure, and is located outside the black hole region 2, and communicates with the black hole region 2, The distance between the upper and lower surfaces of the extended region 1 is unchanged, and is equal to the minimum distance between the upper and lower surfaces of the black hole region 2 .

Specifically, the disk-shaped structure is a rotationally symmetric structure, so the acoustic black hole region is actually a ring body with a radius of r _ABH , and the extension region 1 is a ring with a radius of r ₁ .

A cavity 6 is provided on the central axis of the lower surface of the disc-shaped structure A1, and a through hole 7 communicating with the cavity 6 is opened on the upper surface of the disc-shaped structure A1. The through hole 7 and the cavity 6 to form an acoustic resonance cavity. The volume of the cavity 6 and the size of the through hole 7 are designed according to the frequency of the noise of the noise-reduced structure.

The cavity 6 is a cylindrical cavity.

The vibration damping and noise reduction device further includes an annular damping washer 5, and the outer diameter of the annular damping washer 5 is the same as the outer diameter of the disc-shaped structure. Adhered to the lower surface of the disc-shaped structure; the thickness of the annular damping gasket 5 is six times the distance between the upper and lower surfaces of the extension area 1 . The material of the annular damping gasket is damping material, specifically including high polymer and polymer.

The vibration and noise reduction device further includes a connecting ring 4, which is disposed on the lower surface of the disc-shaped structure and is used to connect the disc-shaped structure and the noise-reduced structure.

The material of the connecting ring 4 is a vibration-absorbing and sound-absorbing material, specifically fiber, rubber, and the like.

On the one hand, for typical enclosed spaces (such as cavities, aircraft cabins, etc.), as shown in Figures 3 and 4, the fluctuating energy of the noise-reduced structure A2 can be transferred to the acoustic black hole vibration and noise reduction device through the connecting ring 4 A1. The acoustic black hole vibration and noise reduction device of the present invention is based on the fact that the propagating flexural wave in the solid medium decreases according to a certain power function with the thickness of the structure, and its corresponding phase velocity and group velocity also decrease, so that on a certain spatial scale, the The broadband bending waves are concentrated in the area where the thickness of the structure becomes thinner. As shown in Figure 5, in the uniform area of the acoustic black hole vibration and noise reduction device, the wave propagation speed of a certain frequency does not change, and the wavelength does not change. In the region of an acoustic black hole, the propagation velocity of the wave decreases as the power exponent of the thickness decreases, the wavelength decreases, and the vibration amplitude increases. By combining the annular damping gasket, most of the bending wave energy is consumed, so as to achieve the purpose of high-efficiency energy absorption or vibration reduction and noise reduction. The acoustic structure adopted by the acoustic black hole vibration reduction and noise reduction device of the present invention is an epitaxial type, and the weak wave speed of the structure occurs at the outermost end of the structure, and the outer end is less constrained by the structure, the deformation is easier, and the acoustic black hole effect is easier occur. On the other hand, for low-frequency wave energy, the modal density of the noise-reduced structure A2 in a typical enclosed space (cavity, aircraft cabin) is often very small at low frequencies, and the vibration radiation noise is mainly distributed at a few discrete frequencies. The black hole vibration and noise reduction device combines the characteristics of the Helmholtz resonance muffler. When multiple acoustic black hole vibration and noise reduction devices are used at the same time, the design can be optimized to achieve noise reduction of multiple frequencies at the same time. Therefore, the design based on the above two mechanisms can realize full-band noise reduction.

The acoustic black hole vibration and noise reduction device of the present invention can be arranged in different ways according to the different vibration characteristics of the elastic structure during use, as shown in Figure 6, including a matrix arrangement, b character arrangement, and c free arrangement , often a reasonable arrangement can further improve the noise reduction efficiency.

The following is an example, which verifies the effectiveness of the acoustic black hole vibration and noise reduction device by means of simulation.

Example:

1. Computational model

A square pipe with a side length of 200mm and a length of 0.6m is selected as the structure to be noise-reduced. The two ends of the square pipe simulate the non-reflection condition, and three acoustic black holes are added axially at equal intervals on the inner surface of the pipe elastic wall. The vibration and noise reduction device is 120mm in diameter, 20mm in thickness, and 0.2mm in edge thickness, and is also designed with aluminum. The annular damping gasket on the acoustic black hole vibration reduction and noise reduction device is arranged in a 1.2mm thickness butyl rubber ring, and the acoustic black hole vibration reduction and noise reduction device is 8% of the mass of the original elastic wall structure. At the same time, in order to do a comparative study, the inner surface of the elastic wall is attached with a uniform mass-damping sheet with the same dimension and quality as the acoustic black hole vibration and noise reduction device.

The dynamic model of the structure is built in Abaqus by using the FEM method, and then the damping and its vibration characteristics are calculated in Virtual.lab, and then the BEM is established based on the vibration response to calculate the acoustic characteristics.

2. Analysis of calculation results

1) Damping characteristic analysis

As shown in Figure 7, the biggest characteristic of the acoustic black hole vibration and noise reduction device of the present invention is that it can greatly improve the inherent damping of the structure. Compared with adding the same mass-damping sheet to the structure, the damping is improved by 10-20 times, and the damping characteristics of only a few modes below 250Hz are not good. Overall, the additional ABH structure can greatly improve the damping characteristics of the plate, which has potential benefits for vibration damping of elastic structures without a significant increase in mass.

2) Analysis of vibration and noise control characteristics

The system surface vibration and acoustic radiation power of the acoustic black hole vibration and noise reduction device and the damping sheet structure (with uniform mass damping material of the same size added at the same position) are calculated, so as to prove that the acoustic black hole vibration and noise reduction device of the present invention is effective in reducing vibration. The benefits of noise reduction.

The acoustic characteristics are evaluated mainly through the simulation results of its radiated sound power. As shown in Figure 8, the sound power of the acoustic black hole vibration reduction and noise reduction device in the entire frequency band is reduced by more than 5dB, and some frequency bands (1500-2500Hz) even reach 35dB. The amount of noise reduction, the results are very impressive. And some frequencies are flattened due to the local modal damping effect, for example, at 2750Hz, when the frequency is higher, all the formants will become very flat, which can effectively suppress sound radiation. For low frequencies such as 700Hz, the noise reduction is mainly due to the Helmholtz resonance characteristics. In addition, the elastic radiation sound power in the entire broadband is investigated. The acoustic black hole vibration reduction and noise reduction device is 104.1dB and the reference structure is 112.0dB, which is a full reduction of 8dB. This is very beneficial for improving the acoustic characteristics during practical application.

According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

The acoustic black hole vibration reduction and noise reduction device of the present invention is attached to the noise reduction structure, and is an additional acoustic black hole vibration reduction and noise reduction structure, which breaks through the traditional acoustic black hole by weakening the thickness of the noise reduction structure, resulting in a high dynamic response, and Limitations to reduce the strength of the denoised structures. Moreover, it is based on the fact that the flexural wave propagating in the solid medium decreases according to a certain power function with the thickness of the structure, and its corresponding phase velocity and group velocity also decrease, so that the broadband flexural wave can be concentrated on a certain spatial scale. A structure in a region where the thickness of the structure becomes thinner.

The acoustic black hole vibration and noise reduction device of the present invention includes an extended area, the acoustic structure adopted is an epitaxial type, the area with weak structure and large vibration amplitude occurs at the outermost end of the structure, and the outer end is less constrained by the structure, so deformation is easier, Acoustic black hole effects are also more likely to occur.

The acoustic black hole vibration and noise reduction device of the present invention has a small additional mass, is easy to meet engineering applications, and has the characteristics of high efficiency.

The acoustic black hole vibration and noise reduction device of the present invention skillfully combines the characteristics of the acoustic resonance cavity to perform low-frequency noise reduction, thereby broadening the limitations of traditional acoustic black holes. The acoustic resonant cavity of the present invention can be designed according to the noise frequency of the noise reduction device, and at the same time, multiple acoustic black hole vibration reduction and noise reduction devices are arranged on the same noise reduction device to generate the characteristics of phononic crystals, which can further improve the low frequency. The characteristics of the ABH effect and dynamic vibration absorption are used to realize the effect of broadband vibration control.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other.

The technical principles and implementations are described herein by using specific examples. The descriptions of the above embodiments are only to help understand the technical methods and core ideas of the present invention. The described embodiments are only examples of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims (7)

1. An acoustic black hole vibration and noise reduction device is characterized in that the vibration and noise reduction device is arranged on a noise reduction structure and comprises a disc-shaped structure, the distance between the upper surface and the lower surface of the disc-shaped structure gradually decreases from the central axis of the disc-shaped structure to the outer edge of the disc-shaped structure, the disc-shaped structure comprises a black hole area, and the distance between the upper surface and the lower surface of the black hole area changes in a power exponent form from the central axis to the outer edge direction;

the vibration-damping and noise-reducing device further comprises a connecting ring, wherein the connecting ring is arranged on the lower surface of the disc-shaped structure and used for connecting the disc-shaped structure with the noise-reduced structure.

2. An acoustic black hole vibration and noise reduction device according to claim 1, wherein said disc-shaped structure further comprises a uniform region, said uniform region is disposed at the position of the central axis of said disc-shaped structure and inside said black hole region, and is communicated with said black hole region, and the distance between the upper and lower surfaces of said uniform region is constant and equal to the maximum distance between the upper and lower surfaces of said black hole region.

3. An acoustic black hole vibration and noise reduction device according to claim 1, wherein the disc-shaped structure further comprises an extension region, the extension region is disposed at an outer edge position of the disc-shaped structure and located at an outer side of the black hole region, and is communicated with the black hole region, and a distance between an upper surface and a lower surface of the extension region is constant and is equal to a minimum distance between the upper surface and the lower surface of the black hole region.

4. An acoustic black hole vibration and noise reduction device according to claim 1, wherein a cavity is disposed at a central axis of a lower surface of the disc-shaped structure, a through hole communicated with the cavity is disposed on an upper surface of the disc-shaped structure, and the through hole and the cavity form an acoustic resonant cavity.

5. An acoustic black hole vibration and noise reduction device according to claim 4, wherein said cavity is a cylindrical cavity.

6. The acoustic black hole vibration and noise reduction device according to claim 1, further comprising a circular ring-shaped damping shim having an outer diameter identical to that of the disc-shaped structure, wherein the circular ring-shaped damping shim is adhered to the lower surface of the disc-shaped structure.

7. An acoustic black hole vibration and noise reduction device according to claim 1, wherein the material of said connection ring is vibration absorbing and sound absorbing material.

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