A three-dimensional acoustic black hole structure for structural vibration and air noise reduction

Abstract

The application discloses a three-dimensional acoustic black hole structure for structural vibration reduction and air noise reduction, comprising micro units arranged in a matrix mode, each micro unit comprising a plurality of layers of nested hollow frames and a mass block, the hollow frames are all in a cubic structure, the inside of the hollow frame shell is a hollow structure, the inside of the hollow frame forms a cubic cavity, the hollow frame located in the inner layer is embedded in the cubic cavity of the hollow frame located in the outer layer, each end surface of the hollow frame has an open circular hole, the middle part of each frame edge of the hollow frame is provided with a long hole corresponding to the circular hole, the volume of each layer of hollow frames gradually decreases until the volume of the cubic cavity of the innermost hollow frame is the same as that of the mass block, and the mass block is a solid cubic structure and is embedded in the cubic cavity of the innermost hollow frame. The three-dimensional acoustic black hole has equivalent vibration and noise suppression capacity in x, y and z directions, realizes the attenuation of vibration energy and sound waves, and is convenient to arrange.

Description

Technical Field

[0001] This invention relates to the field of mechanical vibration and noise control technology, and in particular to a three-dimensional acoustic black hole structure for structural vibration reduction and air noise reduction. Background Technology

[0002] Vibration reduction, noise reduction, and lightweighting have always been important requirements in the aerospace field. For example, in equipment such as electric vertical takeoff and landing aircraft, the cabin structure space is very limited and the mass constraints are strict, while structural vibration reduction and aerodynamic noise reduction must be taken into account simultaneously. However, existing passive vibration reduction and noise reduction technologies, such as adding damping layers, sound-absorbing materials, or dynamic vibration absorbers, can significantly reduce acoustic and vibration responses, but usually require additional materials or devices; at the same time, these methods are mostly designed for single vibration or noise problems, and have limited ability to coordinate the control of structural vibration and aerodynamic noise.

[0003] Acoustic black hole tubes offer a novel technical approach to addressing the aforementioned problems. An acoustic black hole tube is a variable cross-section acoustic structure based on the slow-sound effect. Its inner diameter can gradually decrease along the axial direction according to a power law, or it can form an acoustic channel with an approximate gradually changing inner diameter by embedding rings of different sizes into the inner wall of the tube. When sound waves propagate within it, the wave velocity gradually decreases, the wavelength is compressed, and sound energy concentrates in a localized area, thereby achieving broadband noise reduction. However, existing acoustic black hole tubes are mainly arranged along a single axis, and their sound wave modulation effect is highly directional, typically only effective for sound propagation in a specific direction. This makes it difficult to meet the comprehensive requirements of engineering equipment for multi-directional structural vibration reduction and airborne noise reduction. Therefore, there is an urgent need for a three-dimensional acoustic black hole structure with good noise reduction effect, capable of vibration and noise reduction in multiple directions, and easy to arrange. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and to provide a three-dimensional acoustic black hole structure with good noise reduction effect, capable of vibration reduction and noise reduction in multiple directions, and easy to arrange.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] A three-dimensional acoustic black hole structure for structural vibration reduction and air noise reduction includes micro-units arranged in a matrix. Each micro-unit includes a multi-layered nested hollow frame and a mass block. The hollow frames are all cubic structures with a hollow interior forming a cubic cavity. The inner hollow frame is fitted into the cubic cavity of the outer hollow frame. Each end face of the hollow frame has an open circular hole, and each edge of the hollow frame has an elongated hole corresponding to the circular hole. The volume of each hollow frame decreases progressively until the cubic cavity of the innermost hollow frame has the same volume as the mass block. The mass block is a solid cube fitted into the cubic cavity of the innermost hollow frame.

[0007] Furthermore, each frame of the hollow frame is provided with two elongated holes.

[0008] Furthermore, the micro-units are configured with at least eight units forming a cube matrix.

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] The micro-units in this invention introduce a multi-layered structure within a three-dimensional cubic frame. By progressively stacking the cubic cavities of individual hollow frames, cavities with gradually varying inner diameters are formed, giving the structure equivalent vibration and noise suppression capabilities in the x, y, and z directions. Simultaneously, the principle of local resonance is utilized to attenuate vibration energy and sound waves. Furthermore, by periodically arranging the micro-units along the three directions to form a matrix structure, the interaction between adjacent micro-units further enhances the suppression of noise and vibration, resulting in a significant propagation suppression effect within a specific frequency band. Ultimately, this achieves multi-directional, wide-bandwidth coordinated control of airborne noise reduction and structural vibration reduction within a limited space. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the matrix structure of the present invention;

[0012] Figure 2 This is a schematic diagram of the structure of a single micro-unit in this invention;

[0013] Figure 3 This is a diagram showing the internal structure of a single micro-unit in this invention;

[0014] Figure 4 This is a schematic diagram of the structure of a single hollow frame in this invention;

[0015] Figure 5 This is a diagram showing the internal structure of a single hollow frame in this invention;

[0016] Figure 6 for Figure 5 Side view;

[0017] Figure 7 This is a schematic diagram of the elastic wave bandgap and acoustic wave bandgap in the embodiment.

[0018] Figure label:

[0019] 1-Micro unit, 2-Hollow frame, 3-Circular hole, 4-Elongated hole, 5-Cube cavity, 6-Mass block. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] like Figures 1 to 6 As shown, a three-dimensional acoustic black hole structure for structural vibration reduction and air noise reduction includes micro-units 1 arranged in a matrix. Each micro-unit 1 includes a multi-layered nested hollow frame 2 and a mass block 6. The hollow frame 2 is a cube structure with a hollow interior forming a cube cavity 5. The inner hollow frame 2 is fitted into the cube cavity 5 of the outer hollow frame 2. Each end face of the hollow frame 2 has an open circular hole 3. The middle of each frame edge of the hollow frame 2 is provided with an elongated hole 4 corresponding to the circular hole 3. The volume of each layer of hollow frame 2 decreases gradually until the volume of the cube cavity 5 of the innermost hollow frame 2 is the same as that of the mass block 6. The mass block 6 is a solid cube fitted into the cube cavity 5 of the innermost hollow frame 2.

[0022] The hollow frame 2 has two elongated holes 4 on each side, so that each circular hole 3 corresponds to four elongated holes 4. This structure can simultaneously achieve air noise reduction and structural vibration reduction. For air noise reduction, the hollow frame 2 increases the propagation path of sound waves in the air. When air passes through the elongated holes 4, the impedance increases, suppressing sound wave propagation. Hollow frames 2 with elongated holes 4 of different sizes correspond to different effective frequency bands, thereby widening the frequency range of noise reduction and improving noise reduction capability. At the same time, since each circular hole 3 corresponds to four elongated holes 4, and the four elongated holes 4 are located in four directions, each end face of the hollow frame 2 can suppress the propagation of sound waves from different directions.

[0023] like Figures 2 to 4 As shown, in this example, the outermost cubic structure of micro-unit 1 has a side length of 30 mm. The overall design employs a four-layer hierarchical structure, with the innermost mass block 6 being a solid cube with a side length of 9 mm. All other layers are composed of hollow frames 2. Each hollow frame has a radial width of 3.5 mm, an inner wall thickness of 0.5 mm, and elongated holes with a width of 2.5 mm and a length of 4 mm. The radius of the circular holes 3 within the hollow frame 2 is determined by the outer frame dimensions of the layer and the interlayer thickness; for example, the radius of the outermost cylinder is 11.5 mm. Figure 5As shown, in order to facilitate the inner hollow frame 2 to be fitted into the cube cavity 5 of the outer hollow frame 2, a single micro unit 1 can be made into a split structure. First, the mass block 6 located in the center is placed into the innermost hollow frame 2, and then the hollow frames 2 are spliced ​​together step by step.

[0024] The hollow frames 2 and the central mass block 6 of each micro-unit 1 together form a vibration damping unit. When the simple harmonic excitation force acts on the outer hollow frame 2, the central mass block 6 will generate vibration in the opposite direction to the outer frame. The resulting reaction force on the frame will offset the externally applied excitation force, thereby suppressing the vibration transmission of the frame structure.

[0025] The micro-units 1 are arranged in a cube matrix of at least eight. By periodically arranging the micro-units 1 along the x, y, and z directions, the interaction between adjacent micro-units 1 further enhances the suppression of noise and vibration. This not only enables the structure to achieve a significant propagation suppression effect within a specific frequency band, but also provides equivalent vibration and noise suppression capabilities in the x, y, and z directions, as well as in the corresponding directions of the six end faces of the matrix. Compared to existing acoustic black hole tubes arranged along a single axis, this invention can achieve multi-directional, wide-band air noise reduction and structural vibration reduction synergistic control within a limited space.

[0026] like Figure 7 As shown, the dispersion relation of this structure was calculated using the finite element method combined with Bloch periodic boundary conditions. The elastic wave bandgap is 3462–5498 Hz, and the acoustic wave bandgap is 6421–6604 Hz. The dispersion curves are shown below. Figure 4 As shown in the figure. The results show that the structure can achieve solid-domain vibration suppression in the 3462–5498 Hz frequency band and air-domain acoustic attenuation in the 6421–6604 Hz frequency band.

[0027] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A three-dimensional acoustic black hole structure for structural vibration reduction and air noise reduction, characterized in that: The system includes micro-units (1) arranged in a matrix. Each micro-unit (1) includes a multi-layered nested hollow frame (2) and a mass block (6). The hollow frame (2) is a cube structure. The interior of the shell of the hollow frame (2) is hollow. A cube cavity (5) is formed inside the hollow frame (2). The inner hollow frame (2) is fitted into the cube cavity (5) of the outer hollow frame (2). Each end face of the hollow frame (2) has an open circular hole (3). The middle part of each frame edge of the hollow frame (2) is provided with an elongated hole (4) corresponding to the circular hole (3). The volume of each layer of hollow frame (2) decreases step by step until the volume of the cube cavity (5) of the innermost hollow frame (2) is the same as that of the mass block (6). The mass block (6) is a solid cube and is fitted into the cube cavity (5) of the innermost hollow frame (2).

2. The three-dimensional acoustic black hole structure for structural vibration reduction and air noise reduction according to claim 1, characterized in that: The hollow frame (2) has two elongated holes (4) on each side of its frame.

3. The three-dimensional acoustic black hole structure for structural vibration reduction and air noise reduction according to claim 1, characterized in that: The micro-unit (1) is configured with at least eight units forming a cube matrix.

Images