Acoustic black hole vibration absorber for connecting rib ring of unmanned underwater vehicle and vibration isolation rib ring

Abstract

The invention discloses an acoustic black hole vibration absorber for an unmanned underwater vehicle connecting rib ring and a vibration isolation rib ring, and belongs to the technical field of underwater detection equipment.The acoustic black hole vibration absorber comprises an acoustic black hole component, an oscillating beam and an oscillating component, and the acoustic black hole component forms a wedge-shaped plate with the thickness decreasing progressively in the sound wave propagation direction; the oscillating beam is connected to the acoustic black hole component and extends along the thickness decreasing direction of the acoustic black hole component; the oscillation part is installed on the oscillation beam and located in the thickness reduction direction of the acoustic black hole component, the oscillation part is provided with a tip part opposite to the acoustic black hole component, and a gap is formed between the tip part and the acoustic black hole component. According to the acoustic black hole vibration absorber, through the multi-layer energy dissipation mechanism, the broadband vibration absorption characteristic and the efficient structural design, a high-performance and wide-adaptability solution is provided for vibration control, and the acoustic black hole vibration absorber has important practical value in engineering application.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater detection, and particularly relates to an acoustic black hole vibration absorber and a vibration isolation rib ring for an unmanned underwater vehicle connecting rib ring. Background Art

[0002] An unmanned underwater vehicle is a high-tech equipment that can autonomously or remotely execute underwater tasks without human operation, and is widely used in fields such as ocean exploration, military reconnaissance, environmental monitoring, seabed resource exploration, and underwater search and rescue. Unmanned underwater vehicles usually adopt hydrodynamic optimization design to reduce underwater resistance and improve navigation efficiency, and are equipped with high-precision inertial navigation systems, sonars, camera devices, and various environmental sensors to achieve precise positioning and data collection. With the development of artificial intelligence, energy technology, and underwater communication, the performance of UUVs has been continuously improved, and their application scope has been gradually expanded, providing important support for marine scientific research, national defense security, and marine economic development.

[0003] Currently, the rib ring vibration isolation technology plays a key role in the vibration control of unmanned underwater vehicles, but there are still many problems and deficiencies, which restrict its application in more complex marine environments. First, traditional rib rings mainly rely on the stiffness and damping characteristics of the material itself to suppress vibration, and often use metal or composite material structures. Although these materials may be effective in the low-frequency band, their attenuation effect on medium- and high-frequency vibrations is limited. Especially under high-frequency excitation, local resonance may occur in the rib ring, resulting in the amplification of vibration in a specific frequency band rather than being effectively absorbed and dissipated. Second, existing passive vibration isolation methods usually use elastic supports or damping layers for energy dissipation, such as attaching rubber pads, elastic layers, or composite damping materials to the rib ring. However, these methods often have problems of low energy dissipation efficiency when facing multi-directional complex vibrations, especially for non-linear vibration modes, and traditional damping materials are difficult to provide sufficient vibration absorption effects. In addition, due to the long-term aging, fatigue of elastomer materials, and the influence of environmental factors (such as temperature and pressure), their vibration isolation performance will decrease over time, resulting in the attenuation of the vibration control effect of the underwater vehicle during long-term missions.

[0004] In the aspect of acoustic vibration absorption design, as a new vibration absorption means, the acoustic black hole structure can use the thickness reduction in the form of a power-law curve to reduce the noise wave speed, thereby dissipating vibration energy. However, the current acoustic black hole design still faces multiple challenges. On the one hand, traditional acoustic black holes are mainly applied to flat plates or simple structures, while ribbed rings usually have complex geometric shapes, including multi-layer connections, radial supports, etc., which increases the difficulty of designing and manufacturing the acoustic black hole structure. On the other hand, the vibration absorption ability of acoustic black holes is relatively limited in the low-frequency band, and the vibration sources of unmanned underwater vehicles often cover multiple frequency bands from low to high, making it difficult for a single acoustic black hole structure to meet the full-band vibration absorption requirements. In addition, the actual vibration absorption effect of acoustic black holes is greatly affected by materials, geometric parameters, and installation methods. The optimization design process is complex, and existing research mainly focuses on theoretical analysis and laboratory environments, and the actual engineering applications are still limited.

[0005] In summary, although the current ribbed ring vibration isolation technology can suppress vibration to a certain extent, it still faces problems such as insufficient low-frequency vibration absorption, limitations of structural complexity, low space utilization rate, influence of material aging, and great difficulty in design optimization. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the present invention provides an acoustic black hole absorber and a vibration isolation ribbed ring for connecting ribbed rings of an unmanned underwater vehicle.

[0007] The present invention is implemented as follows. An acoustic black hole absorber for connecting ribbed rings of an unmanned underwater vehicle is characterized in that it includes an acoustic black hole component, an oscillating beam, and an oscillating component. The acoustic black hole component forms a wedge-shaped plate with a thickness decreasing along the sound wave propagation direction. The oscillating beam is connected to the acoustic black hole component and extends along the direction of the decreasing thickness of the acoustic black hole component. The oscillating component is installed on the oscillating beam and is located in the direction of the decreasing thickness of the acoustic black hole component. The oscillating component is provided with a tip portion opposite to the acoustic black hole component, and a gap is formed between the tip portion and the acoustic black hole component.

[0008] In the above technical solution, preferably, one end face of the acoustic black hole component is a plane, and the other side face of the acoustic black hole component is a power-law gradient curved surface. This design not only realizes the continuous gradient of acoustic impedance and effectively reduces the reflection and scattering of sound waves at the interface. The plane end face is convenient for connecting with other structures and processing, while the power-law gradient curved surface enables the sound waves to gradually concentrate energy in a local area during transmission, exciting a unique acoustic black hole effect, thereby significantly improving the absorption and dissipation efficiency of low-frequency vibration energy and reflecting the innovative advantages in vibration control and energy management.

[0009] In the above technical solution, preferably, the acoustic black hole member forms a wedge-shaped plate with a thickness decreasing from the middle to both sides. The oscillating beam and the oscillating component are located on one side of the curved surface. The middle of the acoustic black hole member is connected to the oscillating beams extending to both sides respectively, and the oscillating components are installed at both ends of the oscillating beam. This design realizes the efficient regulation and energy dissipation of bidirectional sound waves through the structure of "a symmetric wedge-shaped plate with a thickness decreasing from the middle to both sides". The symmetric wedge layout not only balances the structural stress distribution (avoiding the weakening of strength caused by unilateral thinning), but also reduces the generation of standing waves and secondary noise interference through the extension of the bidirectional sound wave path and the suppression of reflection, and is especially suitable for multi-directional sound source (such as plate structure vibration, enclosed cavity sound field) scenarios.

[0010] In the above technical solution, preferably, it includes two symmetrically arranged acoustic black hole members connected in the middle. The curved surfaces of the acoustic black hole members face each other, and the oscillating beam and the oscillating component are located between the two black hole members. The symmetric layout of the two members balances the vibration modes, suppresses the reflection of sound waves through the interference effect generated by the opposite curved surfaces, reduces the energy escape, and the middle connection point, as a rigid support, not only enhances the structural stability, but also avoids the fatigue fracture of the thin end through stress dispersion, ensuring long-term reliability.

[0011] In the above technical solution, preferably, the oscillating component includes an oscillating housing and damping particles. The oscillating housing is connected to the oscillating beam and forms a cavity inside, and several damping particles are arranged in the oscillating housing.

[0012] In the above technical solution, preferably, the inside of the damping particle is a metal granule, and the outer layer of the damping particle is coated with damping rubber. This design realizes multi-modal broadband energy dissipation and adaptive vibration regulation: the metal granule provides a high-density inertial mass, enhancing the kinetic energy of particle collision, while the outer layer of damping rubber absorbs the impact energy and prolongs the contact time through elastic deformation. The two work together to form a double attenuation mechanism of "collision friction-viscoelastic dissipation"; when the particles flow freely in the cavity, they generate random collisions and shear friction with the vibration excitation, covering a wide-frequency vibration spectrum through non-linear energy transfer (especially effective for medium and high-frequency noise), and at the same time, the self-weight distribution of the particles can dynamically adjust the damping characteristics of the system to adapt to the vibration intensity changes under different working conditions.

[0013] In the above technical solution, preferably, a damping layer is installed at the end with a small thickness of the acoustic black hole member. Setting a damping layer in the tip region of the wedge-shaped plate can further absorb the vibration energy and improve the vibration attenuation efficiency.

[0014] This acoustic black hole vibration absorber has the following advantages and effects:

[0015] This acoustic black hole vibration absorber has efficient vibration energy dissipation capabilities. A wedge-shaped plate with a thickness decreasing along the sound wave propagation direction serves as its core structure, causing the sound wave to experience a gradually narrowing thickness region during propagation, resulting in a decrease in wave speed and focusing, thereby enhancing the vibration energy dissipation effect.

[0016] This absorber adopts a composite vibration energy conversion and absorption mechanism. The oscillating beam is connected to the acoustic black hole component and extends along the direction of decreasing thickness. Under the action of vibration, it can work together with the acoustic black hole component to spread the vibration energy over a larger range, thereby improving the overall vibration absorption capacity. At the same time, the oscillating component resonates within a suitable frequency range, causing its tip to periodically strike the curved surface of the acoustic black hole component to achieve secondary energy dissipation. This design not only enhances the vibration absorption effect but also effectively reduces equipment damage caused by vibration.

[0017] This absorber has a multi-level vibration attenuation mechanism. First, a small gap is formed between the tip of the oscillating component and the acoustic black hole component. When vibration is transmitted here, the tip continuously strikes the wedge-shaped plate, converting the vibration energy into local deformation and heat energy, improving the energy dissipation efficiency. Second, damping particles are provided inside the oscillating component. As the vibration continues, these particles continuously collide with the inner wall within the cavity, thereby further converting the vibration energy into disordered heat energy to achieve more efficient vibration attenuation. Finally, the impact of the tip will secondarily introduce energy into the acoustic black hole path, forcing more vibration energy to propagate along the direction of decreasing thickness of the wedge-shaped plate to achieve deeper energy dissipation.

[0018] This absorber can be compatible with vibration control in different frequency bands. The design of the decreasing thickness of the acoustic black hole component gives it excellent attenuation effects on low-frequency vibrations, while the resonance and mechanical impact effects of the oscillating component enhance the dissipation ability of high-frequency vibrations, thereby ensuring that the system has good control effects on vibrations in a wide frequency range. In addition, multiple non-linear vibration units, such as oscillating beams, oscillating components, and damping particles, are included inside the system, which can adapt to vibration changes under complex working conditions and improve stability and reliability.

[0019] This absorber has the advantages of a compact structure and strong adaptability. Its compact integrated design makes each vibration absorption unit closely coupled, occupying a small space and being convenient for integration within a limited structure, improving the feasibility of engineering applications. At the same time, this structure is suitable for a variety of installation environments and can be widely applied to fields with high vibration control requirements such as mechanical equipment, aerospace, and rail transit to improve the stability and durability of equipment operation.

[0020] This vibration absorber also has good adjustability and potential for intelligent expansion. By optimizing the mass, stiffness, and damping particle type of the oscillating component, it can be adjusted according to different vibration characteristics to improve the adaptability of the system. At the same time, combined with intelligent materials or adjustable damping mechanisms, this vibration absorber can further achieve dynamic control of vibration energy and has the potential to develop towards an intelligent system.

[0021] In summary, through a multi-level energy dissipation mechanism, broadband vibration absorption characteristics, and efficient structural design, this acoustic black hole vibration absorber provides a high-performance and widely adaptable solution for vibration control and has important practical value in engineering applications. Brief Description of the Drawings

[0022] Figure 1 is a schematic structural diagram of the present invention;

[0023] Figure 2 is a cross-sectional view of the present invention;

[0024] Figure 3 is a perspective view of the present invention;

[0025] Figure 4 is an exploded view of the present invention;

[0026] Figure 5 is a schematic internal structure diagram of the oscillating component in the present invention;

[0027] Figure 6 is a schematic structural diagram of the vibration isolation rib ring described in the second embodiment of the present invention. Detailed Description of the Preferred Embodiments

[0028] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] To solve the problem of poor vibration isolation effect of the current rib ring, the present invention specifically provides an acoustic black hole vibration absorber and a vibration isolation rib ring for connecting the rib ring of an unmanned underwater vehicle. To further illustrate the structure of the present invention, it is described in detail below with reference to the drawings:

[0030] Please refer to Figures 1 - 5 , an acoustic black hole vibration absorber for connecting the rib ring of an unmanned underwater vehicle, including an acoustic black hole component 1, an oscillating beam 2, and an oscillating component 3.

[0031] The acoustic black hole member forms a wedge-shaped plate whose thickness decreases along the sound wave propagation direction. In this embodiment, the acoustic black hole member forms a wedge-shaped plate whose thickness decreases from the middle to both sides. One end face of the acoustic black hole member is a plane, and the other side face is a power-law gradually changing curved surface. This acoustic black hole vibration absorber includes two symmetrically arranged acoustic black hole members connected in the middle. The ends with larger thicknesses of the two acoustic black hole members are connected, and the curved surfaces of the acoustic black hole members face each other. In this structural design, due to the design that the thickness decreases from the middle to both sides, the entire structure has different resonance frequencies at different positions, thereby forming a wide-band vibration dissipation system. The two symmetrically connected acoustic black hole members interact with each other, further broadening the absorption frequency band and enhancing the adaptability and vibration absorption efficiency of the overall system under actual working conditions.

[0032] The oscillating beam is connected to the acoustic black hole member and extends along the direction in which the thickness of the acoustic black hole member decreases. The oscillating beam and the oscillating component are located on one side of the curved surface. The middle of the acoustic black hole member is connected to the oscillating beams extending towards both sides.

[0033] The oscillating component is installed on the oscillating beam and is located in the direction where the thickness of the acoustic black hole member decreases. The oscillating component is provided with a tip portion opposite to the acoustic black hole member, and a gap is formed between the tip portion and the acoustic black hole member. The oscillating beam and the oscillating component are located between the two black hole members. The oscillating components are respectively installed at both ends of the oscillating beam.

[0034] The oscillating component includes an oscillating housing and damping particles 4. The oscillating housing is connected to the oscillating beam and forms a cavity inside. A number of damping particles are arranged in the oscillating housing. The inside of the damping particle is a metal granule body 4-1, and the outer layer of the damping particle is coated with damping rubber 4-2. Since the metal granule body has a relatively high density and mass, it can form a large inertial response under low-frequency vibration conditions, while the rubber coating layer can adjust the energy loss during the collision process, enabling the entire system to have stronger adaptability to low-frequency vibration. The damping particles inside the oscillating component can effectively reduce the noise energy of vibration transmitted to the vehicle housing through non-linear collision and the absorption effect of the rubber coating layer, reducing underwater noise radiation. This is crucial for the stealth of underwater vehicles, can reduce the risk of being detected by sonar, and improve the concealment and mission execution ability of the vehicle.

[0035] In this embodiment, specifically, this acoustic black hole vibration absorber forms an upper and lower layer symmetric structure, in which the acoustic black hole members in the upper layer and the acoustic black hole members in the lower layer are symmetric up and down, and both ends are in the power-law function H = h0 + εx m(m≥2) realizes the decreasing of the tip thickness. A middle through hole 1-1, a stepped through hole and a limiting groove 1-2 are provided at the part with a large middle thickness of the upper acoustic black hole component. A middle through hole, a threaded hole and a limiting groove are provided at the part with a large middle thickness of the lower acoustic black hole component. After being connected by the corresponding middle through holes, the limiting grooves form a groove for embedding the oscillating beam. The oscillating beam is of a symmetric structure, and through holes are provided in the middle and at both ends. The middle through hole corresponds to the middle through hole of the acoustic black hole component. The oscillating housing is composed of an upper oscillating housing 3-1 and a lower oscillating housing 3-2. Both the upper oscillating housing and the lower oscillating housing are of a spire structure and are hollow structures inside. The damping particles are of a layered structure, with a high-density metal in the inner layer and a high-damping rubber in the outer layer.

[0036] A damping layer 5 is installed at the end with a small thickness of the acoustic black hole component. That is, damping layers are pasted at the small-thickness planes of the upper acoustic black hole component and the lower acoustic black hole component to dissipate the tip wave velocity. The upper acoustic black hole component, the oscillating beam and the lower acoustic black hole component are combined in a sandwich form. The position of the oscillating beam is restricted by the limiting grooves of the two acoustic black hole components, and the three are fastened by screws. The upper oscillating housing, the oscillating beam and the lower oscillating housing are also in a sandwich combination. The upper oscillating housing and the lower oscillating housing are fastened by threads and are fixedly connected to both ends of the oscillating beam. A number of damping particles are placed in the internal cavity formed by the combination of the upper oscillating housing and the lower oscillating housing.

[0037] In this absorber, there is a static small gap between the upper oscillating housing and the upper acoustic black hole component and between the lower oscillating housing and the lower acoustic black hole component. When the vibration is transmitted from the bottom of the lower acoustic black hole component, on the one hand, the vibration propagates along the acoustic black hole structure, and part of the energy is dissipated through the decreasing thickness and the damping layer at the tip. On the other hand, the vibration drives the oscillating beam to vibrate. After being transmitted to both ends, the oscillating housing resonance is realized, and the curved surfaces of the upper acoustic black hole component and the lower acoustic black hole component will be continuously hammered. The vibration energy is transmitted to the acoustic black hole component again through the tip of the oscillating housing, realizing the accelerated dissipation of the vibration energy. Among them, the resonance of the oscillating housing will drive the oscillating collision of the damping particles in the inner cavity, further dissipating the vibration energy.

[0038] Embodiment 2

[0039] Please refer to Figure 6, a vibration isolation rib ring, which is a known component and an important part in an autonomous underwater vehicle (AUV) for reducing vibration transmission and enhancing structural stability. It is usually in a ring structure and is installed at the supporting parts of the pressure hull or key equipment. It effectively isolates the mechanical vibration inside the vehicle and the external hydrodynamic disturbance through elastic materials or damping structures. The role of the vibration isolation rib ring is mainly reflected in reducing the impact of the propulsion system, pumps or other high-frequency vibration sources on the overall structure of the vehicle, thereby reducing noise propagation and improving the stealth performance of the vehicle. At the same time, it can also reduce the interference of vibration on sensitive components such as precision electronic equipment and inertial navigation systems, and improve the measurement accuracy and reliability of the instruments. Its structure includes a rib ring body, and the rib ring body includes an outer ring body 6, an inner seat body 7 located inside the outer ring body, and radial connecting frames 8 connecting the outer ring body and the inner seat body. In this embodiment, specifically, the inner seat body is an inner ring body provided with a shaft hole, and the radial connecting frames are four beam-shaped rib plates distributed at intervals in the circumferential direction connecting the inner seat body and the outer ring body. An acoustic black hole absorber described in Embodiment 1 is installed on the radial connecting frames. Specifically, N acoustic black hole absorbers are arranged radially and installed on the radial connecting frames, and the end with a larger thickness of the acoustic black hole component of the acoustic black hole absorber is connected to the radial connecting frames. That is, N acoustic black hole absorbers are arranged and fixedly connected on one side surface of the plate-shaped connecting frame. The plane middle part of the acoustic black hole component of the acoustic black hole absorber is fixed to the radial connecting frame, and the thickness decreasing direction of the acoustic black hole component is perpendicular to the radial direction.

[0040] The acoustic black hole absorber is mainly arranged on the radial connecting frames of the vibration isolation rib ring. The periodic uniform distribution can achieve the concentration and dissipation of vibration energy, and can effectively absorb vibration energy without changing the strength of the rib ring, with the characteristics of light weight and good vibration suppression effect. In addition, from the perspective of the layout structure, this structure enables the vibration energy to be evenly distributed along the ring structure during the propagation process. It can absorb and attenuate vibration energy more evenly, improve the overall vibration isolation effect, reduce the risk of excessive local vibration concentration at the same time, and extend the fatigue life of the structure. Since the thickness decreasing direction of the acoustic black hole component is perpendicular to the radial direction, the vibration energy will inevitably enter the acoustic black hole path during propagation and experience a multi-level energy dissipation process. On the one hand, when the vibration propagates from the rib ring body to the radial connecting frames, it will be actively guided by the acoustic black hole absorber into the black hole structure to achieve the first layer of energy absorption; on the other hand, the oscillating components inside the acoustic black hole absorber can further convert the remaining vibration energy into heat energy and further attenuate it through mechanical shock, friction and damping effects.

[0041] From the perspective of spatial layout, the layout described in this embodiment avoids the waste of space inside the vehicle and achieves efficient vibration absorption without increasing the additional occupied space. It is particularly suitable for compact AUVs or underwater vehicles with high requirements for equipment integration. In addition, its layout will not encroach on the core equipment area inside the vehicle, such as the battery compartment, control module or propulsion system. This structure optimizes the functional zoning inside the vehicle, ensures a more reasonable overall layout of the vehicle, and improves the maintainability and scalability of the equipment. Improve the vibration absorption efficiency per unit volume. Compared with traditional decentralized or centralized vibration absorption solutions, this layout can absorb more vibration energy in the same volume, making the vibration control effect of the entire machine more uniform and efficient.

[0042] Traditional vibration isolation rib rings mainly rely on their own materials and shapes for structural support, but in this design, after the acoustic black hole vibration absorbers are fixed on the radial connecting frame, these vibration absorbers themselves can also play a certain role in enhancing the stiffness of the rib ring. The acoustic black hole component is fixed in the middle of the plane of the radial connecting frame, so that it can provide additional structural support when subjected to vibration, reduce the deformation of the connecting frame, and improve the overall mechanical strength and durability.

[0043] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An acoustic black hole vibration absorber for the connecting rib ring of an unmanned underwater vehicle, characterized in that: It includes an acoustic black hole member, an oscillating beam, and an oscillating component. The acoustic black hole member forms a wedge-shaped plate with a thickness decreasing along the sound wave propagation direction; the oscillating beam is connected to the acoustic black hole member and extends along the direction in which the thickness of the acoustic black hole member decreases; the oscillating component is mounted on the oscillating beam and is located in the direction where the thickness of the acoustic black hole member decreases. The oscillating component is provided with a tip portion opposite to the acoustic black hole member, and a gap is formed between the tip portion and the acoustic black hole member.

2. The acoustic black hole vibration absorber for the connecting rib ring of the unmanned underwater vehicle according to claim 1, wherein: One end face of the acoustic black hole member is a plane, and the other side face of the acoustic black hole member is a power-law gradient curved surface.

3. The acoustic black hole vibration absorber for the connecting rib ring of the unmanned underwater vehicle according to claim 2, characterized in that: The acoustic black hole member forms a wedge-shaped plate with a thickness decreasing from the middle to both sides. The oscillating beam and the oscillating component are located on one side of the curved surface. The middle of the acoustic black hole member is connected to the oscillating beams extending respectively to both sides, and the two end portions of the oscillating beam are respectively mounted with the oscillating components.

4. The acoustic black hole vibration absorber for the connecting rib ring of the unmanned underwater vehicle according to claim 3, characterized in that: It includes two symmetrically arranged acoustic black hole members connected in the middle. The curved surfaces of the acoustic black hole members face each other, and the oscillating beam and the oscillating component are located between the two black hole members.

5. The acoustic black hole vibration absorber for the connecting rib ring of the unmanned underwater vehicle according to claim 1 or 4, characterized in that: The oscillating component includes an oscillating housing and damping particles. The oscillating housing is connected to the oscillating beam and forms a cavity inside, and several damping particles are arranged in the oscillating housing.

6. The acoustic black hole vibration absorber for the connecting rib ring of the unmanned underwater vehicle according to claim 5, characterized in that: The inside of the damping particle is a metal granule body, and the outer layer of the damping particle is coated with damping rubber.

7. The acoustic black hole vibration absorber for the connecting rib ring of the unmanned underwater vehicle according to claim 6, characterized in that: A damping layer is installed at the end of the acoustic black hole member with a small thickness.

8. A vibration isolation rib ring, comprising a rib ring body, the rib ring body including an outer ring body, an inner seat body located inside the outer ring body, and a radial connecting frame connecting the outer ring body and the inner seat body, characterized in that: The acoustic black hole absorber according to claim 7 is mounted on the radial connecting frame.

9. The vibration isolation rib ring according to claim 8, wherein: N acoustic black hole absorbers are arranged radially and mounted on the radial connecting frame. The end of the acoustic black hole member of the acoustic black hole absorber with a large thickness is connected to the radial connecting frame.

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