Helmholtz silencer based on quasi-zero stiffness element

Abstract

The utility model provides a Helmholtz silencer based on a quasi-zero stiffness element, which belongs to the technical field of pipeline silencers and comprises an air cavity, a panel is mounted in the air cavity and connected with the air cavity through a vibrating diaphragm, a boss is fixedly mounted on the panel, and the vibrating diaphragm is connected with the boss. The boss is connected with one end of the supporting spring in the radial direction of the main pipeline, the other end of the supporting spring is connected with the air cavity, the two ends, in the axial direction of the main pipeline, of the boss are connected with one end of the pre-compression spring respectively, and the other end of the pre-compression spring is connected with the air cavity. The low-frequency noise in the pipeline is effectively controlled, the low-frequency noise control device has the advantages of being compact in structure, small in size and the like, and if noise of different frequencies needs to be controlled, only the compression amount of the pre-compression spring needs to be adjusted to change the overall rigidity of the structure; under the condition of the same neck area, a smaller air cavity volume can be adopted, the rigidity of each spring can be freely adjusted, and the height of the back cavity is greatly reduced.

Description

Technical Field

[0001] This utility model belongs to the technical field of pipeline silencers, specifically relating to a Helmholtz silencer based on a quasi-zero stiffness element. Background Technology

[0002] Water pipelines are widely used in shipbuilding, hydraulic systems, hydropower stations and other fields. Due to the presence of water pumps, there will be line spectrum noise in the pipelines. The noise frequencies are the pump shaft frequency and blade frequency (corresponding to the pump speed and number of blades). The presence of noise not only affects the working state of the pipeline, but also causes acoustic-structure coupling effect, resulting in structural vibration. This can not only cause acoustic fatigue to the machine structure, thereby reducing its service life, but also cause serious industrial accidents.

[0003] To reduce the impact of noise on piping systems, various types of silencers are often used to reduce noise propagation. For example, reactive silencers, including 1 / 4 wavelength tubes, interference silencers, and Helmholtz silencers, etc.

[0004] As attached Figure 1 As shown, the noise reduction principle of a quarter-wavelength tube is that when the length of the side branch tube corresponds to 1 / 4 of the wavelength of a certain frequency, it can achieve a good noise reduction effect for that frequency. (See attached image.) Figure 2 As shown, the noise reduction principle of the interference silencer is as follows: During sound wave propagation, it travels simultaneously from branch pipe 2 and main pipe 1. Since the propagation path lengths of the branch pipe and the main pipe are different, when the length of the branch pipe minus the length of the main pipe is exactly half the wavelength of a certain frequency, the noise at that frequency can be significantly controlled. A quarter-wavelength tube interference silencer can only eliminate high-frequency noise; controlling low-frequency noise requires a large volume, making it unsuitable for applications with limited space.

[0005] As attached Figure 3 As shown, the silencing principle of a Helmholtz muffler is that the fluid in the neck is analogous to mass M, and the cavity filled with air can be equivalent to acoustic stiffness K. The entire structure is analogous to a single-degree-of-freedom mass spring system. As a traditional pipeline muffler, the Helmholtz muffler features a wide silencing frequency range and excellent high-frequency silencing effect, and is widely used in automotive manufacturing, aerospace, and other fields. Where M = ρL c S, K = ρc²S² / V. ρ is the density of the fluid medium, c is the speed of sound in the fluid, and V is the volume of the cavity. The silencing frequency is:

[0006]

[0007] L c S cThese represent the length and cross-sectional area of ​​the neck, respectively. It can be observed that the control frequency of the Helmholtz silencer is related to the cross-sectional area of ​​the neck, the neck length, and the volume parameters of the back cavity. To achieve noise control at different frequencies, these parameters need to be adjusted. However, to control low-frequency noise using a Helmholtz silencer, the volume of the back cavity needs to be made very large (reducing stiffness) or the neck needs to be made very large (increasing mass). In practical engineering, the space for silencer placement is always limited, restricting the application of this structure in low-frequency noise. This structure is commonly used in engineering for mid-to-high frequency noise control. Therefore, the problem of controlling low-frequency noise within pipelines urgently needs to be solved. Utility Model Content

[0008] The purpose of this invention is to provide a Helmholtz silencer based on a quasi-zero stiffness element, which enables the control of low-frequency noise in pipelines using a small-volume structure.

[0009] The objective of this utility model is achieved through the following technical solution:

[0010] A Helmholtz silencer based on a quasi-zero stiffness element includes: an air cavity, a panel installed inside the air cavity, the panel being connected to the air cavity via a diaphragm, a boss fixedly installed on the panel, the boss being connected to one end of a support spring in the radial direction of a main pipe, the other end of the support spring being connected to the air cavity, and the boss being connected to one end of a pre-compression spring at both ends in the axial direction of the main pipe, the other end of the pre-compression spring being connected to the air cavity.

[0011] Furthermore, the diaphragm is a ring diaphragm.

[0012] Furthermore, the pre-compression spring is a lightweight spring.

[0013] Furthermore, the panel is made of a high-rigidity material.

[0014] Furthermore, the panel surface is equipped with a reinforcing rib structure.

[0015] The beneficial effects of this utility model are as follows:

[0016] This invention effectively controls low-frequency noise within pipelines. Compared to traditional reactive silencers, this structure is compact and small in size. Furthermore, to control noise at different frequencies, only the compression of the pre-compression spring needs to be adjusted to change the overall stiffness of the structure.

[0017] This invention allows for a smaller air cavity volume under the same neck area conditions, and the stiffness of each spring can be freely adjusted, significantly reducing the back cavity height. The use of quasi-zero stiffness adjustment further reduces the inherent characteristics of the structure, thereby achieving low-frequency noise control in the pipeline. Attached Figure Description

[0018] Appendix Figure 1 This is a schematic diagram of the structure of a 1 / 4 wavelength tube in the prior art.

[0019] Appendix Figure 2 This is a schematic diagram of the structure of an interference-type silencer in the existing technology.

[0020] Appendix Figure 3 This is a schematic diagram of the structure of a Helmholtz silencer in the existing technology.

[0021] Appendix Figure 4 This is a schematic diagram of the structure of this utility model.

[0022] Appendix Figure 5 This is a schematic diagram of the stiffness and stress of this utility model.

[0023] Appendix Figure 6 This is a schematic diagram of the transmission loss (TL) curves of the Helmholtz silencer before and after the improvement of this utility model.

[0024] In the attached diagram: 1. Main pipe; 2. Pre-compression spring; 3. Air cavity; 4. Support spring; 5. Boss; 6. Panel; 7. Diaphragm. Detailed Implementation

[0025] The present invention will now be further described with reference to the accompanying drawings.

[0026] This utility model provides a Helmholtz silencer based on a quasi-zero stiffness element, as shown in the attached figure. Figure 1 As shown, it includes: an air cavity 3, a panel 6 installed inside the air cavity 3, the panel 6 being connected to the air cavity 3 via a diaphragm 7, a boss 5 fixedly installed on the panel 6, the boss 5 being connected to one end of a support spring 4 in the radial direction of the main pipe 1, the other end of the support spring 4 being connected to the air cavity 3, and the two ends of the boss 5 in the axial direction of the main pipe 1 being connected to one end of a pre-compression spring 2, the other end of the pre-compression spring 2 being connected to the air cavity 3.

[0027] In this embodiment, two pre-compression springs 2 and one support spring 4 serve as the stiffness source of the Helmholtz muffler, while a boss 5 and a panel 6 serve as the mass source. The boss 5 and the panel 6 are fixed together, and the panel 6 and the air cavity 3 are connected by a folded ring. The diaphragm 7 separates the main pipe 1 and the air cavity 3 and provides a certain stiffness (non-dominant stiffness). The diaphragm 7 is a ring diaphragm.

[0028] Furthermore, one end of the pre-compression spring 2 and the support spring 4 are fixed to the air cavity 3, and the other end is connected to the boss. When the panel is excited by sound waves, it moves up and down. The extension and contraction direction of the support spring is consistent with the displacement direction of the panel, thus providing positive stiffness and restoring force for the structure. The extension and contraction direction of the pre-compression spring forms an angle with the displacement direction of the panel, causing the pre-compression spring to generate a nonlinear restoring force, providing negative stiffness. The combination of these two stiffnesses can reduce the natural frequency of the structure without changing the mass, thus enabling low-frequency noise control.

[0029] Preferably, the pre-compression spring 2 can be a standard lightweight spring, which is highly replaceable and easy to maintain. Adjusting the pre-compression of the spring during installation can also change the control frequency of the noise-absorbing structure, achieving noise control at different frequencies without changing the structure, thus expanding the application scenarios of the noise-absorbing structure.

[0030] Preferably, panel 6 can be made of a material or structure with high stiffness. For example, aluminum alloy can be selected as the panel material, and a reinforcing rib can be added to the surface of the panel to increase the natural frequency of the panel (referring only to the panel as a single component) and avoid the appearance of higher-order vibration modes of the panel within the operating frequency of the sound-absorbing structure, thereby affecting the acoustic performance of the structure.

[0031] When using a traditional Helmholtz silencer structure for noise control at 200Hz in a DN100 water-filled pipe, a back cavity of 1.35 × 10⁻⁶ mm is required if the neck radius is 30 mm. -2 m 3 The volume of the back cavity can be reduced by using the structure of this invention, while maintaining the same neck area. The stiffness of each spring can be freely adjusted.

[0032] Traditional Helmholtz silencers, with a back cavity cross-sectional area three times that of the neck, have a height of 1.6m, making installation impossible in limited spaces. The structure provided by this invention significantly reduces the back cavity height. For example, a spring with a wire diameter of 2mm and 5 effective support coils can be used as the support spring, and a spring with a wire diameter of 1mm and 3 effective support coils can be used as the pre-compression spring. The maximum height of the air cavity is the sum of the length of the support spring under static conditions, the height of the boss, and the thickness of the panel.

[0033] As attached Figure 5 As shown in the diagram, F1 and F2 are the restoring forces of the pre-compressed springs, F3 is the restoring force of the supporting springs, and m is the total mass of the structure. The restoring force in the vertical direction is:

[0034]

[0035] Making the above equation dimensionless, we can obtain the expression for the stiffness of the structure:

[0036]

[0037] in, K1 and K2 are the stiffnesses of the pre-compression spring and the support spring, respectively; l0 and l are the original length and the length after compression, respectively; and x0 is the displacement.

[0038] Appendix Figure 6 The diagram shows the transmission loss (TL) curves of the Helmholtz muffler before and after the improvement. The difference between the sound power levels at the inlet and outlet of the muffler indicates that the larger the difference, the better the acoustic performance of the muffler and the better the noise control effect. The peak value of the transmission loss can be observed to shift from high frequency to low frequency, thus achieving control of low frequency noise.

[0039] When sound waves from inside the pipe are transmitted to panel 6, the supporting spring 4 and diaphragm 7 provide support. Due to the introduction of pre-compression spring 2, a recovery force is provided in the vertical direction opposite to that of the supporting spring, reducing the overall stiffness of the structure. According to formula (1), as stiffness K decreases, the resonant frequency shifts to lower frequencies, thus enabling control of low-frequency noise inside the pipe. To achieve noise control at different frequencies, the overall stiffness of the structure can be adjusted by regulating the pre-compression amount of the pre-compression spring, further changing the control frequency.

[0040] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A Helmholtz silencer based on a quasi-zero stiffness element, characterized in that, include: An air cavity (3) is provided, and a panel (6) is installed inside the air cavity (3). The panel (6) is connected to the air cavity (3) via a diaphragm (7). A boss (5) is fixedly installed on the panel (6). The boss (5) is connected to one end of a support spring (4) in the radial direction of the main pipe (1). The other end of the support spring (4) is connected to the air cavity (3). The boss (5) is connected to one end of a pre-compression spring (2) at both ends in the axial direction of the main pipe (1). The other end of the pre-compression spring (2) is connected to the air cavity (3).

2. A quasi-zero stiffness element based Helmholtz silencer according to claim 1, characterized in that, The diaphragm (7) is a ring diaphragm.

3. The quasi-zero stiffness element based Helmholtz silencer of claim 1, wherein, The pre-compression spring (2) is a lightweight spring.

4. The quasi-zero stiffness element based Helmholtz silencer of claim 1, wherein, The panel (6) is made of a high-rigidity material.

5. A quasi-zero stiffness element based Helmholtz silencer according to claim 4, characterized in that, The panel (6) surface is fitted with a reinforcing rib structure.

Images