A porous material-based acoustic superstructure muffler and methods of use thereof

Abstract

The application discloses a kind of acoustic superstructure muffler based on porous material and its use method, including one or more sound-absorbing structures, when multiple sound-absorbing structures, multiple sound-absorbing structures are connected in series;The sound-absorbing structure includes the perforated plate with uniform opening around the end of outer wall, spacer;The perforated plate with uniform opening around the end of outer wall is located in the pipeline inside;The spacer is connected in one side of the pipeline;The perforated plate with uniform opening around the end of outer wall, the pipeline and the spacer form sound-absorbing back cavity with uniform opening around the end of outer wall.The application not only has good high-frequency sound absorption performance, but also has better low-frequency performance of muffler, wider sound absorption frequency, and is suitable for multiple harmonic frequency noise, simultaneously combines porous material with acoustic superstructure, respectively in high, low frequency fusion sound absorption noise reduction method provides a new idea for solving pipeline noise reduction.

Description

Technical Field

[0001] The present invention relates to the field of pipeline noise reduction, and in particular to an acoustic superstructure muffler based on porous materials and a method for using the same. Background Art

[0002] When many large-scale equipment are working, they will generate mechanical noise and aerodynamic noise, including a large amount of low-frequency noise. Low-frequency noise is more difficult to control than high-frequency noise due to its longer wavelength, low attenuation rate, longer propagation distance and strong penetration rate. Porous materials are the most commonly used thermal insulation and sound insulation materials in noise reduction projects. However, whether it is the traditional porous material glass fiber cotton or the new foam material melamine, its sound absorption performance is mainly manifested in the high-frequency part, and the absorption effect on medium and low-frequency sound waves is not obvious. Therefore, the sound reduction performance of resistive silencers in the low-frequency stage needs to be improved. In recent years, the development of acoustic metamaterials and acoustic superstructure design has provided a new solution to low-frequency noise pollution.

[0003] Acoustic metastructures are artificially designed unit structures with subwavelength thickness that can achieve properties not possessed by ordinary materials in nature, such as negative equivalent mass density, negative elastic modulus, double negative properties, negative refractive index, and near-zero refractive index. Structurally, the surfaces of acoustic metastructures are often arranged periodically, which can achieve control of the reflected sound field of sound waves, sound absorption and noise reduction, and regulation of sound wave transmission. Although acoustic metamaterials can be artificially designed to have excellent low-frequency noise reduction capabilities, their main performance is basically single-frequency sound absorption, and their structure is relatively complex, making it difficult to achieve broadband sound absorption effects through metastructures alone. Porous materials have a broadband mid- and high-frequency noise absorption effect. Therefore, by integrating the design of acoustic metastructures with porous materials, improving the sound absorption performance of silencers within a wide frequency band has become a feasible and significant project. Moreover, there is currently little research on the use of low-frequency sound-absorbing metamaterials in noise reduction in mufflers. Combining acoustic metastructures and porous materials to replace the pure foam structure of traditional resistive mufflers is more important for improving the muffler's sound absorption bandwidth, sound absorption amplitude and low-frequency sound absorption effect. Summary of the Invention

[0004] To improve the low-frequency noise absorption of existing pipe silencers, this invention leverages the superior high-frequency sound absorption of porous materials and incorporates an acoustic metamaterial into its structure. This improves the absorption of low-frequency noise, achieving broadband noise absorption and noise reduction. Compared to conventional pipe silencers, this invention not only offers superior high-frequency sound absorption but also offers superior low-frequency performance, with a wider operating frequency range and compatibility with multi-harmonic noise. The combination of porous materials and acoustic metastructures provides a novel approach to noise reduction, offering integrated sound absorption at both high and low frequencies.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] An acoustic superstructure muffler based on porous materials includes one or more muffler structures. When there are multiple muffler structures, the multiple muffler structures are connected in series.

[0007] The sound-absorbing structure includes a bulkhead and a perforated plate with uniform openings around the end of the outer wall; the perforated plate with uniform openings around the end of the outer wall is located inside the pipe; the bulkhead is connected to one side of the pipe;

[0008] The outer wall end is surrounded by a perforated plate with evenly opened holes, and the pipe and the partition frame form a sound-absorbing back cavity.

[0009] Furthermore, the interior of the perforated plate with uniform openings around the end of the outer wall is a cavity structure, a perforated plate is provided inside the cavity structure, and porous foam is filled between the perforated plates with uniform openings around the end of the outer wall.

[0010] Furthermore, the interior of the perforated plate is a cavity structure, and the cavity structure inside the perforated plate forms an air flow channel for gas to pass through.

[0011] Furthermore, the cross-sectional shape of the air flow channel is square or circular.

[0012] Furthermore, the porous foam is made of sound-absorbing material, and its cross-section is annular.

[0013] Furthermore, the porous foam has a plurality of pores that penetrate each other from the surface to the inside.

[0014] Furthermore, the perforated plate with uniform openings around the end of the outer wall is made of a rigid material by punching holes at one end.

[0015] Furthermore, the cross-sectional shape of the sound-absorbing back cavity is annular.

[0016] Furthermore, the connection between the bulkhead and the pipeline is riveted.

[0017] A method for using an acoustic superstructure muffler based on a porous material comprises the following steps:

[0018] The length, number of noise reduction structures and thickness are determined based on the noise frequency in the pipeline. The determined noise reduction structures are installed in the pipeline to be noise-reduced. When the noise passes through the air flow channel, the noise reduction structures absorb medium and low frequency noise. By changing the length, number of noise reduction structures and thickness, multi-peak noise reduction or broadband noise reduction can be achieved.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention provides an acoustic superstructure muffler based on porous materials, which has the characteristics of good low-frequency sound absorption and wide sound absorption frequency band. At the same time, the low-frequency performance of the muffler is targeted and the operating frequency is wide. The number of sound absorption modules, the thickness of the sound absorption back cavity, and the thickness of the porous foam can be adjusted according to the actual size of the pipeline and the noise reduction required to achieve the target requirements. It is suitable for high-volume systems such as substations, gas turbines, aircraft engine test benches, mines, tunnels, subways, and building ducts.

[0021] Furthermore, the present invention makes the perforated plate into a cavity structure, and sets the cross-sectional shape of the air flow channel to a square or a circle, so that the air flow can pass through the muffler smoothly, thereby improving the noise reduction effect.

[0022] Furthermore, the present invention adopts porous foam made of melamine and glass fiber cotton, which can improve the absorption effect of medium and high frequency noise.

[0023] Furthermore, the present invention connects the bulkhead and the pipe by riveting, which can improve the stability of the internal structure of the muffler.

[0024] The present invention also provides a method for using an acoustic superstructure silencer based on porous materials. First, the frequency range of the target noise is determined, and different measures are taken according to the frequency of the noise: for medium and high frequency noise, the internal interlayer foam can achieve almost perfect absorption; for medium and low frequency noise, the peak frequency of its main distribution is selected, and the length of the sound-absorbing back cavity is calculated according to the selected frequency. The obtained structure can be used to absorb the noise of this frequency; for noise with multiple peak frequencies or wide frequency, multiple cavities can be combined to perform multi-peak silencer or wide-band silencer. Compared with general pipe silencers, it not only has good high-frequency sound absorption performance, but also has better low-frequency performance of the silencer. The sound absorption working frequency is wider and can be applied to multi-harmonic frequency noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic structural diagram of an acoustic superstructure muffler based on porous materials provided in an embodiment of the present invention;

[0026] Figure 2 A cross-sectional view of an acoustic superstructure muffler based on porous materials provided by an embodiment of the present invention;

[0027] Figure 3 Schematic diagram of the simulation structure of an embodiment of the present invention;

[0028] Figure 4 Only the TL curve of the muffler cavity is shown for the embodiment of the present invention;

[0029] Figure 5TL curve diagram of the resistive muffler and the muffler with a sound-absorbing cavity added in the embodiment of the present invention.

[0030] Reference numerals:

[0031] Air flow channel-01; perforated plate-02; porous foam-03; perforated plate with uniform openings around the end of the outer wall-04; pipe-05; bulkhead-06. DETAILED DESCRIPTION

[0032] The present invention provides an acoustic superstructure muffler based on porous materials, comprising one or more muffler structures. When there are multiple muffler structures, the multiple muffler structures are connected in series. The muffler structure is located at the end of the outer wall of the pipe 05, and has a perforated plate 04 with uniform holes around it, and a partition frame 06 connected to one side of the pipe 05.

[0033] The sound-absorbing structure further includes a sound-absorbing back cavity, which is surrounded by a perforated plate 04 with uniform openings around the end of the outer wall, the pipe 05 and the partition frame 06.

[0034] The present invention also proposes a method for using an acoustic superstructure muffler based on a porous material, which comprises the following steps:

[0035] S1: Determine the length, number and thickness of the silencer structure based on the noise frequency in the pipeline;

[0036] S2: Install the determined silencer structure in the pipe to be silenced.

[0037] S3: After the noise passes through the air flow channel, the silencer structure absorbs the medium and low frequency noise. By changing the length, number of silencers used and thickness, multi-peak silencer or broadband silencer can be performed.

[0038] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following clearly and completely describes the technical solutions in the embodiments of the present invention in conjunction with the implementation methods and the accompanying drawings. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0039] The present invention is further described in detail below with reference to the accompanying drawings and embodiments:

[0040] The overall structural diagram of the embodiment is as follows Figure 1As shown, a single or multiple acoustic superstructures are added to the pipeline. This structure consists of a perforated plate 04 with uniform openings around the end of the outer wall, a pipeline 05, and a bulkhead 06. The bulkhead 06 is connected to the end of the perforated plate 04 with uniform openings around the end of the outer wall without openings. The structural parameters are changed according to the required noise reduction frequency, so that the silencer forms a Hertz resonant cavity absorber system with the pipeline air at the operating frequency, thereby improving the noise reduction effect of the pipeline acoustics. The specific implementation plan is as follows:

[0041] The cross-sectional shape of the air flow channel 01 can be square, circular, or other reasonable shapes, as long as the airflow can pass through the silencer smoothly. The material is steel plate or other rigid material formed by punching. The perforated plate 02 serves as the channel for the airflow. At the same time, it and the perforated plate 04 with uniform openings around the end of the outer wall together constitute the filling space of the porous foam 03. The perforated plate 04 with uniform openings around the end of the outer wall is formed by punching one end of a steel plate or other rigid material. At the same time, the perforated plate 04 with uniform openings around the end of the outer wall also serves as one surface of the sound-absorbing back cavity. The porous foam 03 can be made of sound-absorbing materials such as melamine and glass fiber cotton, which can be curled into a ring-shaped filling. The specific use can be considered according to the target sound attenuation amount, actual working conditions, etc. A partition frame 06 is provided on the side of the pipe 05 to play the role of support and sound-absorbing cavity side panel. The connection method can be riveting.

[0042] The following is a detailed description of the muffler's working principle. When noise enters from one end of pipe 05, it enters the surrounding porous foam 03. Because porous foam 03 contains a large number of interconnected micropores, the sound entering the internal voids of the material causes the air and material fibers to vibrate, resulting in friction between the air and the pore walls. The air close to the pore walls and fiber surfaces is difficult to move due to the pore walls. Therefore, this friction and the viscosity between air molecules convert the kinetic energy of the vibration into heat energy, causing most of the sound energy to be converted into heat and dissipated. However, the porous material (porous foam 03) is not ideal for absorbing medium and low frequencies. Therefore, an acoustic superstructure sound absorption cavity (sound absorption back cavity structure) is added to the muffler structure to absorb medium and low frequency noise. When the noise frequency matches the operating frequency of the sound absorption cavity, the corresponding noise in the fluid is absorbed and no longer vibrates, preventing it from transmitting to the pipe outlet, thereby achieving the effect of noise reduction.

[0043] The following details the method for matching noise frequency with the muffler's operating frequency. Since porous materials are good at absorbing mid- and high-frequency noise, the muffler cavity primarily targets mid- and low-frequency noise. First, the design is based on the target noise frequency. Depending on the desired operating frequency, structural parameters such as the thickness, aperture, perforation ratio, and length of the perforated plate (04) with uniform openings around the outer wall end are modified. The dominant parameter is the length of the perforated plate (04) with uniform openings around the outer wall end, which determines the basic design frequency. The remaining parameters can be adjusted to the design frequency, allowing it to absorb noise at the design frequency and control the propagation of noise at a specific frequency. Multiple identical structures are then added and arranged periodically to achieve the desired noise reduction. If there are multiple peak noise levels, mufflers of different lengths can be designed using the above method. By using this designed structure, noise at different frequencies can be eliminated. If the noise is broadband, the broadband noise can be considered as the superposition of multiple peak noise levels. The sound-absorbing cavity can then be designed using the above method to complete the acoustic superstructure design.

[0044] The finite element simulation software COMSOL Multiphysics is used to calculate the transmission loss (TL) after the muffler is installed. The cross-sectional size of pipe 05 is 420mm×420mm and the length is 2700mm. Two sound absorbing structures 1 and two sound absorbing structures 2 are installed in series in pipe 05. The length of sound absorbing structure 1 is 900mm, with a perforated plate with uniform openings around the end of the outer wall 04 perforation length The cross-sectional dimensions are 380mm×380mm, which means that the thickness of the sound absorption cavity is The perforation rate is 20 mm, and the perforation rate is 04 in the perforated part of the perforated plate with uniform openings around the end of the outer wall. is 25%, aperture 2mm, plate thickness The parameters of the perforated plate 02 are consistent with those of the perforated plate 04 with uniform openings around the end of the outer wall. The cross-sectional shape of the porous foam 03 is a ring-shaped sandwich of the perforated plate 04 with uniform openings around the end of the outer wall with a cross-sectional size of 380mm×380mm and the perforated plate 02 with a cross-sectional size of 260mm×260mm. This means that the thickness of the porous foam is 60mm. Similarly, except for the structural parameters of the perforated plate 04 with uniform openings around the end of the outer wall, the sound-absorbing structure 2 is consistent with the structure 1 in terms of length and the structural parameters of the perforated plate 04 with uniform openings around the end of the outer wall. The length of structure 2 is 450mm, and the perforation length of the perforated plate 04 with uniform openings around the end of the outer wall is 100mm. Its perforation rate, plate thickness, and aperture are consistent with those of structure 1. In order to accurately simulate the actual situation, a perfect matching layer simulating an infinite space area was added during the finite element analysis to act as an almost ideal absorber. The model in the finite element software COMSOL is as follows Figure 3 As shown, Figure 4 This is the transmission loss of the muffler structure when no foam material is added, that is, only the transmission loss of the sound absorption cavity. It can be seen that the operating frequencies of the two structures of the muffler, structure 1 and structure 2, are 118Hz and 230Hz, and their respective TLs can reach 61.5Hz and 41.0Hz respectively. Figure 5 The TL curves for a resistive muffler and one with an added sound-absorbing cavity show that the sound transmission loss is effectively improved by up to 9dB at operating frequencies near the sound-absorbing cavity, 118Hz and 230Hz, including between 118Hz and 230Hz. In practical applications, the structural length and the structural parameters of the perforated plate with a hole at one end can be varied to adjust the operating frequency. The thickness of the sound-absorbing cavity and the foam can also be adjusted to achieve the optimal noise reduction. Furthermore, additional sound-absorbing structures can be added to further reduce noise.

[0045] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's description and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An acoustic superstructure muffler based on porous materials, characterized in that: It includes one or more noise reduction structures. When there are multiple noise reduction structures, the multiple noise reduction structures are connected in series. The sound-absorbing structure comprises a bulkhead (06) and a perforated plate (04) having uniform openings around the end of the outer wall; the perforated plate (04) having uniform openings around the end of the outer wall is located inside the pipe (05); the bulkhead (06) is connected to one side of the pipe (05); The end of the outer wall is surrounded by a perforated plate (04) with uniform openings, the pipe (05) and the partition frame (06) to form a sound-absorbing back cavity; The perforated plate (04) with uniform openings around the end of the outer wall has a cavity structure inside, a perforated plate (02) is provided inside the cavity structure, and porous foam (03) is filled between the perforated plate (04) with uniform openings at the end of the outer wall and the perforated plate (02); The porous foam (03) is made of sound-absorbing material, and its cross-section is annular. The porous foam (03) has a plurality of holes that are interconnected from the outside to the inside. The interior of the perforated plate (02) is a cavity structure, and the cavity structure inside the perforated plate (02) forms an air flow channel (01) for gas to pass through.

2. The porous material-based acoustic superstructure muffler according to claim 1, characterized in that: The cross-sectional shape of the air flow channel (01) is square or circular.

3. The porous material-based acoustic superstructure muffler according to claim 1, characterized in that: The perforated plate (04) with uniform openings around the outer wall end is made of a rigid material by punching holes at one end.

4. The porous material-based acoustic superstructure muffler according to claim 1, characterized in that: The cross-section of the sound-absorbing back cavity is annular.

5. The porous material-based acoustic superstructure muffler according to claim 1, characterized in that: The connection method between the bulkhead (06) and the pipe (05) is riveting.

6. A method for using an acoustic superstructure muffler based on porous materials, characterized in that: An acoustic superstructure muffler based on a porous material according to any one of claims 1 to 5, comprising the following steps: The length, number of noise reduction structures and thickness are determined based on the noise frequency in the pipeline. The determined noise reduction structures are installed in the pipeline to be noise-reduced. When the noise passes through the air flow channel, the noise reduction structures absorb medium and low frequency noise. By changing the length, number of noise reduction structures and thickness, multi-peak noise reduction or broadband noise reduction can be achieved.

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