A honeycomb-microperforated structure with adjustable sound absorption performance and its design method

Abstract

The present invention relates to a honeycomb-microperforated structure with adjustable sound absorption performance, comprising an upper panel and a lower panel and a honeycomb core sandwiched between the upper panel and the lower panel, wherein the upper panel is a microperforated panel, the honeycomb core is retractable, and the honeycomb core is composed of a lower honeycomb core and an upper honeycomb core, wherein the lower end outer diameter of the upper honeycomb core is slightly larger than the upper end inner diameter of the lower honeycomb core, and the purpose of controlling the height of the honeycomb core is achieved by controlling the upper honeycomb core to be pulled out or retracted into the lower honeycomb core, thereby controlling the back cavity height, changing the structural resonance frequency, and absorbing noise of different frequencies. The present invention has a simple structural principle, and only needs to change the height of the honeycomb-microperforated structure honeycomb core to meet the noise reduction requirements of different noise environments, and has a wide range of applications and is easy to operate.

Description

Technical Field

[0001] The invention belongs to a medium and low frequency noise reduction structure and method designed by using a honeycomb-micro perforated plate composite structure, and particularly relates to a honeycomb-micro perforated structure with adjustable sound absorption performance and a design method thereof. Background Art

[0002] With the development of science and technology and the improvement of people's living standards, more and more people choose to travel by safe and high-speed airplanes. While airplanes facilitate people's travel, they also bring a series of aerodynamic problems. Aircraft noise is one of the aerodynamic problems that must be paid attention to. Aircraft noise will affect the comfort of crew members and passengers, the working status of internal instruments and equipment, and even affect the flight life and safety of the aircraft. For aircraft noise reduction, whether it is using sound-absorbing materials or sound-absorbing structures for noise reduction, it must meet the characteristics of lightness and reliability while meeting the sound absorption performance. The honeycomb-microperforated plate structure is widely used in aircraft noise reduction due to its excellent mechanical properties and good sound absorption effect.

[0003] According to the sound absorption principle of micro-perforated plate, the plate thickness and cavity depth of the micro-perforated plate structure directly affect the sound absorption performance of the structure, namely the sound absorption frequency and the sound absorption coefficient. However, when the honeycomb-micro-perforated structure is formed, the sound absorption performance of the structure has also been determined. In order to adjust the sound absorption performance of the structure, the honeycomb part of the honeycomb-micro-perforated structure is designed as a honeycomb core with adjustable height, and the absorption of noise of different frequencies is achieved by changing the height of the honeycomb core. Summary of the invention

[0004] The present invention aims at the honeycomb-microperforated sound absorption structure and designs a honeycomb-microperforated structure with adjustable sound absorption performance by utilizing the telescopic rod principle. By changing the height of the honeycomb core layer of the structure, the structure can absorb noise of different frequencies, thereby effectively improving the sound absorption effect of the single-layer honeycomb-microperforated structure.

[0005] The present invention solves its technical problem by adopting the following technical scheme.

[0006] A honeycomb-microperforated structure with adjustable sound absorption performance comprises an upper panel, a lower panel and a honeycomb core sandwiched between the upper panel and the lower panel, wherein the upper panel is a microperforated panel, and the honeycomb core is retractable. The honeycomb core consists of a lower honeycomb core and an upper honeycomb core, wherein the outer diameter of the lower end of the upper honeycomb core is slightly larger than the inner diameter of the upper end of the lower honeycomb core, and the height of the honeycomb core is controlled by controlling the upper honeycomb core to be pulled out or retracted into the lower honeycomb core, thereby controlling the height of the back cavity, changing the structural resonance frequency, and absorbing noises of different frequencies.

[0007] Preferably, the lower honeycomb core is arranged in a close-packed circular pattern.

[0008] Preferably, the inner wall of the lower honeycomb core is configured to be a cone, the inner diameter of the upper end of the lower honeycomb core is slightly smaller than the inner diameter of the lower end of the lower honeycomb core, and the outer wall of the upper honeycomb core is configured to be a cone, the upper end diameter of the upper honeycomb core is slightly smaller than the lower end diameter of the upper honeycomb core.

[0009] Preferably, the diameter of the lower outer wall of the upper honeycomb core is slightly larger than the diameter of the upper inner wall of the lower honeycomb core, and the slope of the inner wall surface of the lower honeycomb core is the same as the slope of the outer wall surface of the upper honeycomb core.

[0010] A design method for a honeycomb-microperforated structure with adjustable sound absorption performance includes a honeycomb sandwich panel, wherein the honeycomb sandwich panel is composed of an upper panel, a lower panel and a honeycomb core therebetween, and the design steps are as follows:

[0011] The first step is to verify the effect of the change of cavity height on the sound absorption effect of micro-perforation based on the micro-perforated plate theory of Academician Ma Dayou and computer simulation.

[0012] For the micro-perforated plate sound absorption structure, the sound absorption coefficient when the sound wave is incident vertically is:

[0013]

[0014] The sound absorption coefficient of the micro-perforated sound absorber reaches its maximum value when it resonates. At this time, the maximum sound absorption coefficient is:

[0015]

[0016] The frequency at which the sound absorption coefficient reaches the maximum, i.e. the resonance frequency f0, satisfies:

[0017] 2πf0m-cot(2πf0D / c)=0 (3)

[0018] The acoustic resistance r and acoustic mass m are:

[0019]

[0020]

[0021] In the above equations, k is the perforated plate constant

[0022]

[0023] μ is the kinematic viscosity coefficient of air (1.48×10 -5 m 2 / s), t is the plate thickness, d is the perforation diameter, D is the cavity height, p is the perforation rate, f is the sound frequency, and the acoustic impedance of the cavity behind the plate is

[0024] Z D = -jρccot(ωD / c) (7)

[0025] From the above theoretical formula, it can be seen that the change of the cavity height D will change the resonant frequency f0 of the structure, that is, the frequency corresponding to the maximum value of the sound absorption coefficient α0 will change, and the cavity height D will increase, that is, the resonant frequency f0 will move to a low frequency. In other words, theoretically, changing the cavity height D of the micro-perforated plate can adjust the sound absorption frequency of the micro-perforated plate structure.

[0026] In the second step, based on the above-mentioned law of change of the resonant frequency f0 with the cavity height D, a honeycomb-microperforated structure that can adjust the back cavity height is designed. The structure adopts a densely packed circular honeycomb core. By changing the height of the honeycomb core, the purpose of changing the acoustic impedance of the cavity behind the plate is achieved, thereby realizing the absorption of noise of different frequencies.

[0027] The honeycomb-microperforated structure with adjustable sound absorption performance of the present invention has the following advantages:

[0028] 1. The honeycomb-micro-perforated structure described in the invention can achieve the best noise reduction effect by changing the back cavity height for noises of different frequencies;

[0029] 2. The honeycomb-micro-perforated structure described in the invention is simple to manufacture and operate, and has broad application prospects in the field of noise reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a common closely packed circular honeycomb micro-perforated structure;

[0031] Figure 2 It is a schematic diagram of the structure of the present invention;

[0032] Figure 3 is a front view of a single honeycomb core cell of the present invention;

[0033] Figure 4 is a side view of a single honeycomb core cell of the present invention;

[0034] Figure 5 is a top view of a single honeycomb core cell of the present invention;

[0035] Figure 6 Schematic diagram of the original honeycomb core structure in the embodiment;

[0036] Figure 7 is a schematic diagram of a retractable honeycomb core structure after installing the retractable honeycomb core structure;

[0037] Figure 8 is a schematic diagram of the extended honeycomb core structure after the retractable honeycomb core structure is installed;

[0038] Fig. 9 is a diagram of simulation calculation results of an embodiment;

[0039] In the figure: 1. upper panel, 2. closely packed circular honeycomb core, 3. lower panel, 4. lower honeycomb core, 5. upper honeycomb core, 6. honeycomb core. Specific implementation methods

[0040] The present invention is described in detail below in conjunction with the accompanying drawings.

[0041] like Figure 1 As shown, a common close-packed circular honeycomb micro-perforation is composed of an upper panel 1, a close-packed circular honeycomb core 2, and a lower panel 3, wherein the upper panel is a micro-perforated plate with a certain perforation rate, the honeycomb core adopts a close-packed circular structure, and the lower panel is an ordinary metal sheet.

[0042] The present invention improves the common honeycomb core sandwich structure and configures the honeycomb core structure into a retractable structure.

[0043] like Figures 2 to 5 As shown, a honeycomb-microperforated structure with adjustable sound absorption performance includes an upper panel 1 and a lower panel 3 and a honeycomb core 6 sandwiched between the upper panel 1 and the lower panel 3, wherein the upper panel 1 is a microperforated panel, and the honeycomb core 6 is retractable. The honeycomb core 6 consists of a lower honeycomb core 4 and an upper honeycomb core 5, wherein the outer diameter of the lower end of the upper honeycomb core 5 is slightly larger than the inner diameter of the upper end of the lower honeycomb core 4, and the height of the honeycomb core 6 is controlled by controlling the upper honeycomb core 5 to be pulled out or retracted into the lower honeycomb core 4, thereby controlling the height of the back cavity, changing the structural resonance frequency, and absorbing noises of different frequencies.

[0044] As a preferred embodiment, the lower honeycomb core 4 is arranged in a close-packed circular pattern.

[0045] As a preferred embodiment, the inner wall of the lower honeycomb core 4 is arranged in a frustum shape, the inner diameter of the upper end of the lower honeycomb core 4 is slightly smaller than the inner diameter of the lower end of the lower honeycomb core 4, and the outer wall of the upper honeycomb core 5 is arranged in a frustum shape, and the upper end diameter of the upper honeycomb core 5 is slightly smaller than the lower end diameter of the upper honeycomb core 5.

[0046] As a preferred embodiment, the outer wall diameter of the lower end of the upper honeycomb core 5 is slightly larger than the inner wall diameter of the upper end of the lower honeycomb core 4 and the slope of the inner wall surface of the lower honeycomb core 4 is the same as the slope of the outer wall surface of the upper honeycomb core 5 .

[0047] A single scalable honeycomb core cell such as Figure 3 , Figure 4 and Figure 5 shown. Figure 3 It is a front view of a single honeycomb core cell with adjustable sound absorption performance; Figure 4 It is a side view of a single honeycomb core cell with adjustable sound absorption performance; Figure 5It is a top view of a single honeycomb core cell with adjustable sound absorption performance; wherein the honeycomb core 6 is similar to a fishing rod and is composed of a lower honeycomb core 4 and an upper honeycomb core 5, the inner wall of the lower honeycomb core 4 is set to be a frustum, the inner diameter of the upper end is slightly smaller than the inner diameter of the lower end, the outer wall of the upper honeycomb core 5 is set to be a frustum, the diameter of the upper end is slightly smaller than the diameter of the lower end, the outer wall diameter of the lower end of the upper honeycomb core 5 is slightly larger than the inner wall diameter of the upper end of the lower honeycomb core 4, and the slope of the inner wall surface of the lower honeycomb core 4 should be the same as the slope of the outer wall surface of the upper honeycomb core 5. By controlling whether the upper honeycomb core 5 is pulled out from the lower honeycomb core 4, noises of different frequencies can be absorbed.

[0048] A method for designing a honeycomb-microperforated structure with adjustable sound absorption performance comprises the following steps:

[0049] The first step is to verify the effect of the change of cavity height on the sound absorption effect of micro-perforation based on the micro-perforation plate theory of Academician Ma Dayou and computer simulation.

[0050] For the micro-perforated plate sound absorption structure, the sound absorption coefficient when the sound wave is incident vertically is:

[0051]

[0052] The sound absorption coefficient of the micro-perforated sound absorber reaches its maximum value when it resonates. At this time, the maximum sound absorption coefficient is:

[0053]

[0054] The frequency at which the sound absorption coefficient reaches the maximum, i.e. the resonance frequency f0, satisfies:

[0055] 2πf0m-cot(2πf0D / c)=0 (3)

[0056] The acoustic resistance r and acoustic mass m are:

[0057]

[0058]

[0059] In the above equations, k is the perforated plate constant

[0060]

[0061] μ is the kinematic viscosity coefficient of air (1.48×10 -5 m 2 / s), t is the plate thickness, d is the perforation diameter, D is the cavity height, p is the perforation rate, f is the sound frequency, and the acoustic impedance of the cavity behind the plate is

[0062] Z D = -jρccot(ωD / c) (7)

[0063] From the above theoretical formula, it can be seen that the change of the cavity height D will change the resonant frequency f0 of the structure, that is, the frequency corresponding to the maximum value of the sound absorption coefficient α0 will change. The increase of the cavity height D will move the resonant frequency f0 to a low frequency. In other words, theoretically, the sound absorption frequency of the micro-perforated plate structure can be adjusted by changing the cavity height D of the micro-perforated plate.

[0064] In the second step, based on the above-mentioned law of change of the resonant frequency f0 with the cavity height D, a honeycomb-microperforated structure that can adjust the back cavity height is designed. The structure adopts a densely packed circular honeycomb core. By changing the height of the honeycomb core, the purpose of changing the acoustic impedance of the cavity behind the plate is achieved, thereby realizing the absorption of noise of different frequencies.

[0065] Example

[0066] A single scalable honeycomb core cell such as Figure 3 , Figure 4 and Figure 5 As shown. The dimensions of the honeycomb core are as follows: the lower honeycomb core 4 has an outer diameter of 6 mm, a height of 30 mm, a bottom wall thickness of 0.5 mm, and an upper wall thickness of 1 mm; the upper honeycomb core 5 has an inner diameter of 4 mm, a height of 30 mm, a bottom wall thickness of 1.04 mm, and an upper wall thickness of 0.54 mm; this embodiment calculates the original honeycomb core structure (such as Figure 6 As shown), install the retractable honeycomb core structure and then stretch the honeycomb core (as shown Figure 8 as shown) and shrink honeycomb core (as shown Figure 7 The sound absorption coefficient is shown in Figure 2.

[0067] First, the sound absorption coefficient of the original structure is calculated. The original structure is set to a cylindrical shape with a diameter of 29mm to facilitate measurement in the impedance tube. At this time, the diameter of the honeycomb core is 6mm, the wall thickness is 0.5mm, and the height is 30mm. Then the honeycomb core structure is replaced with a retractable honeycomb core to measure the sound absorption coefficient when stretched and contracted. When the honeycomb core is stretched, the overall height of the structure is 60mm. The heights of the lower honeycomb core 4 and the upper honeycomb core 5 are both 30mm. However, to avoid pulling out the upper honeycomb core 5, the lower end outer diameter of the upper honeycomb core 5 is slightly larger than the upper end inner diameter of the lower honeycomb core 4. When the upper honeycomb core 5 is pulled out 28mm, it cannot be pulled out again. Panel 1 is a micro-perforated plate with a pore diameter of 0.5mm, a perforation rate of 3%, and a plate thickness of 1mm. Panel 3 is a thin plate with a plate thickness of 1mm.

[0068] Fig. 9 The sound absorption effects of the three structures are as follows: Figure 6 As shown), changing the honeycomb core and then stretching the honeycomb core structure (as shown Figure 8 As shown) and the shrink honeycomb core structure (as Figure 7The measurement results are shown in Figure 2. The measurement found that the resonance frequency of the original structure was around 1300Hz. When the honeycomb core of the original structure was replaced with a retractable honeycomb core structure and the honeycomb core was shrunk, the resonance frequency basically remained unchanged. When the honeycomb core was stretched out, the resonance frequency moved to around 800Hz, and the resonance frequency dropped by 500Hz. That is, the peak value of the structural sound absorption coefficient moved 500Hz to the low frequency, and the structure had a wider sound absorption bandwidth. Therefore, using this structure, noise of different frequencies can be effectively absorbed.

[0069] The above description is only a simple embodiment of the present invention, and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A honeycomb-microperforated structure with adjustable sound absorption performance, comprising an upper panel (1) and a lower panel (3) and a honeycomb core (6) sandwiched between the upper panel (1) and the lower panel (3), wherein the upper panel (1) is a microperforated panel, characterized in that: The honeycomb core (6) is retractable. The honeycomb core (6) is composed of a lower honeycomb core (4) and an upper honeycomb core (5). The outer diameter of the lower end of the upper honeycomb core (5) is slightly larger than the inner diameter of the upper end of the lower honeycomb core (4). The height of the honeycomb core (6) is controlled by controlling the upper honeycomb core (5) to be pulled out or retracted into the lower honeycomb core (4), thereby controlling the height of the back cavity, changing the structural resonance frequency, and absorbing noises of different frequencies. The lower honeycomb core (4) is arranged in a closely packed circular pattern. The inner wall of the lower honeycomb core (4) is arranged in a frustum shape, the inner diameter of the upper end of the lower honeycomb core (4) is slightly smaller than the inner diameter of the lower end of the lower honeycomb core (4), and the outer wall of the upper honeycomb core (5) is arranged in a frustum shape, the diameter of the upper end of the upper honeycomb core (5) is slightly smaller than the diameter of the lower end of the upper honeycomb core (5).

2. The honeycomb-microperforated structure with adjustable sound absorption performance according to claim 1, characterized in that: The diameter of the lower outer wall of the upper honeycomb core (5) is slightly larger than the diameter of the upper inner wall of the lower honeycomb core (4), and the slope of the inner wall surface of the lower honeycomb core (4) is the same as the slope of the outer wall surface of the upper honeycomb core (5).

3. A design method for a honeycomb-microperforated structure with adjustable sound absorption performance, characterized in that: The steps include: The first step is to verify the effect of the change of cavity height on the sound absorption effect of micro-perforation based on the micro-perforation plate theory of Academician Ma Dayou and computer simulation. For the micro-perforated plate sound absorption structure, the sound absorption coefficient when the sound wave is incident vertically is: The sound absorption coefficient of the micro-perforated sound absorber reaches its maximum value when it resonates. At this time, the maximum sound absorption coefficient is: The frequency at which the sound absorption coefficient reaches the maximum, i.e. the resonance frequency f0, satisfies: 2πf0m-cot(2πf0D / c)=0 (3) The acoustic resistance r and acoustic mass m are: In the above equations, k is the perforated plate constant μ is the kinematic viscosity coefficient of air, where μ = 1.48 × 10 -5 m 2 / s, t is the plate thickness, d is the perforation diameter, D is the cavity height, p is the perforation rate, f is the sound frequency, and the acoustic impedance of the cavity behind the plate is Z D =-jρccot(ωD / c) (7) From the above theoretical formula, it can be seen that the change of the cavity height D will change the resonant frequency f0 of the structure, that is, the frequency corresponding to the maximum value of the sound absorption coefficient α0 will change. The increase of the cavity height D will move the resonant frequency f0 to a low frequency. In other words, theoretically, the sound absorption frequency of the micro-perforated plate structure can be adjusted by changing the cavity height D of the micro-perforated plate. In the second step, based on the above-mentioned law of change of the resonant frequency f0 with the cavity height D, a honeycomb-microperforated structure that can adjust the back cavity height is designed. The structure adopts a densely packed circular honeycomb core. By changing the height of the honeycomb core, the purpose of changing the acoustic impedance of the cavity behind the plate is achieved, thereby realizing the absorption of noise of different frequencies.

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