Combined acoustic black hole sound absorber structure and design method

Abstract

The application relates to a combined acoustic black hole sound absorption body structure and a design method. The structure comprises a cross-shaped partition plate, a cylindrical cavity, a bottom plate, four groups of 1 / 4 annular thin plate arrays, the number ratio of the four groups of 1 / 4 annular thin plate arrays is 30:25:20:17, the plate thickness and the interval are equal, the cross-shaped partition plate divides the cylindrical cavity into four independent 1 / 4 cylindrical cavities with equal volumes, the four groups of 1 / 4 annular thin plate arrays are respectively located in the four 1 / 4 cylindrical cavities, and the bottom plate is located at one end of the 1 / 4 annular thin plate without an annular partition plate with the smallest inner diameter and seals the end. The application calculates the sound absorption coefficient of the combined acoustic black hole sound absorption body by constructing a transfer matrix model of a single 1 / 4 acoustic black hole sound absorption body, and optimizes the structure length of the single 1 / 4 acoustic black hole sound absorption body and the number of 1 / 4 annular thin plates, so that the structure can stably absorb the medium and high frequency noise. The application has the advantages of simple structure, low cost and stable wideband sound absorption.

Description

TECHNICAL FIELD

[0001] The present application belongs to a wideband sound absorption structure designed by optimizing combination of acoustic black hole sound absorbers with different sizes, and particularly relates to a combined acoustic black hole sound absorber structure and a design method. BACKGROUND

[0002] With the increasing attention to noise pollution, wideband noise reduction has become one of the key problems of noise control. Currently, noise control can be divided into active control and passive control. Active control has the disadvantage of narrow sound absorption band. If passive control is to achieve wideband noise reduction, a larger structure volume and mass are required. In recent years, the acoustic black hole sound absorber structure has good wideband sound absorption characteristics. By adjusting the size parameters of the acoustic black hole sound absorber, the sound absorption range of the acoustic black hole sound absorber structure can be changed. However, the sound absorption coefficient of the acoustic black hole sound absorber will have a large fluctuation with the change of frequency in the medium frequency range. In order to improve its sound absorption effect, many scholars have carried out extensive research. For example, in the invention patent application with the application number 202110976044.8, a micro-perforated plate is arranged inside the acoustic black hole sound absorber structure to achieve high-efficiency low-frequency ultra-wideband sound absorption. In addition, the improved acoustic black hole sound absorber structure with micro-porous plates embedded in multiple resonant cavities can also achieve stable sound absorption in medium and high frequencies ([1] Liang X, Liang H, Chu J, et al. A modified sonic black hole structure for improving and broadening sound absorption, Applied Acoustics, 2023, 210: 109440.).

[0003] It is noted that there are mainly two methods to improve the sound absorption effect of the acoustic black hole sound absorber at present. One is to optimize the structure of the acoustic black hole sound absorber, and the other is to combine the sound absorption material or sound absorption structure with the acoustic black hole sound absorber. However, both methods are prone to increase the volume and mass of the structure. The present application combines acoustic black hole sound absorbers with different sound absorption frequency bands to provide a combined acoustic black hole sound absorber structure with simple structure and stable sound absorption effect in medium and high frequencies, which is used for wideband noise control. SUMMARY

[0004] The present application proposes a combined acoustic black hole sound absorber structure for different structure sizes of acoustic black hole sound absorbers with different sound absorption frequency bands. The structure not only has simple structure, but also has stable wideband sound absorption effect in medium and high frequencies.

[0005] The present application is implemented by the following technical solutions.

[0006] A combined acoustic black hole sound absorption structure, comprising a cross-shaped partition, a cylindrical cavity, a bottom plate, four groups of 1 / 4 annular thin plate arrays, the number of plates of the four groups of 1 / 4 annular thin plate arrays is in a ratio of 30:25:20:17, and the plate thickness and the spacing are equal, the cross-shaped partition divides the cylindrical cavity into four independent and equal-volume 1 / 4 cylindrical cavities, the four groups of 1 / 4 annular thin plate arrays are respectively located in the four 1 / 4 cylindrical cavities, and the bottom plate is located at one end of the 1 / 4 annular thin plate without annular thin plate with the smallest inner diameter and seals the end. By constructing a transfer matrix model of a single 1 / 4 acoustic black hole sound absorption structure, the sound absorption coefficient of the combined acoustic black hole sound absorption structure is calculated, and by optimizing the structure length of the single 1 / 4 acoustic black hole sound absorption structure and the number of 1 / 4 annular thin plates, stable absorption of medium and high frequency noise by the structure is realized.

[0007] Further, the cross-shaped partition has a thickness not greater than 2 mm, the center line of the cross-shaped partition coincides with the center line of the cylindrical cavity, the cross-shaped partition is fixed inside the cylindrical cavity, and the cylindrical cavity is sealed and separated into four independent 1 / 4 cylindrical cavities, and the length of the cross-shaped partition is not less than the length of the cylindrical cavity.

[0008] Further, the length of the cylindrical cavity is not less than the length of the 1 / 4 annular thin plate array.

[0009] Further, the bottom plate comprises four 1 / 4 circular plates with the same size, the same outer diameter as the inner diameter of the cylindrical cavity, and the same thickness as the annular thin plate, the bottom plate is located at one end of the 1 / 4 annular thin plate without annular thin plate with the smallest inner diameter, is fixed in the cross-shaped partition and the cylindrical cavity, and seals the end, and the distance between the bottom plate and the 1 / 4 annular thin plate with the smallest inner diameter is equal to the spacing between two adjacent annular thin plates.

[0010] Further, the 1 / 4 annular thin plate array comprises a plurality of 1 / 4 annular thin plates with a first function change in the inner diameter, the first function is r1 represents the inner diameter of the 1 / 4 annular sheet with the smallest inner diameter, the minimum inner diameters r1 of the four groups of 1 / 4 annular sheet arrays are the same, R represents the inner diameter of the cylindrical cavity, L represents the total length of the 1 / 4 annular sheet array, the ratio of the total lengths L of the four groups of 1 / 4 annular sheet arrays is 30:25:20:17, x represents the distance between any one 1 / 4 annular sheet in each group of 1 / 4 annular sheet array and the 1 / 4 annular sheet with the largest inner diameter, wherein x≤L, the 1 / 4 annular sheet is perpendicular to the cross-shaped partition plate, the 1 / 4 annular sheets are parallel and uniformly fixed between the cross-shaped partition plate and the cylindrical cavity, the outer diameter of the 1 / 4 annular sheet is equal to the inner diameter of the cylindrical cavity, the four groups of 1 / 4 annular sheet arrays are respectively located in the four 1 / 4 cylinders separated by the cross-shaped partition plate, the thickness of the 1 / 4 annular sheet is not greater than 2mm, and the 1 / 4 annular sheets with the largest inner diameter in the four groups of 1 / 4 annular sheet arrays are located in the same plane.

[0011] Further, the cross-shaped partition plate, the cylindrical cavity, the bottom plate and the four groups of 1 / 4 annular sheet arrays are fixed by using strong glue, welding, or are integrally formed by 3D printing.

[0012] A combined acoustic black hole sound absorber structure design method, characterized by comprising the following steps:

[0013] Firstly, the sound absorption coefficient of a single 1 / 4 acoustic black hole sound absorber when the sound wave is vertically incident is obtained by the transfer function method:

[0014]

[0015] The effective acoustic impedance Z satisfies

[0016]

[0017] The transfer matrix T satisfies

[0018]

[0019] The cavity admittance Y satisfies n satisfies

[0020]

[0021] In the above formulas, Z0 is the impedance of air

[0022] Z0 = p0c0 (13)

[0023] p0 is the density of air, c0 is the speed of sound propagation in air, and k is the wave number

[0024]

[0025] d nis the spacing between the thin plates, is the open area of the 1 / 4 ring-shaped thin plate, V n is the volume of the hollow circular truncated cone part between the adjacent two 1 / 4 ring-shaped thin plates.

[0026] Through parallel coupling design of 4 groups of 1 / 4 acoustic black hole sound absorbers, the sound absorption coefficient of the combination is

[0027]

[0028] In the formula, the effective acoustic impedance Z 总 satisfies

[0029]

[0030] In the formula, Z1, Z2, Z3, Z4 are the acoustic impedances of the 4 groups of 1 / 4 acoustic black hole sound absorbers, S = πR 2 is the total area allowing the vertical incidence of sound waves, and R is the inner diameter of the cylindrical cavity.

[0031] Secondly, based on the change of the impedance value with the structure length of the 1 / 4 acoustic black hole sound absorber, the structure length of the 1 / 4 acoustic black hole sound absorber is designed through parallel coupling design, and the sound absorption coefficient of the combined acoustic black hole sound absorber structure is optimized.

[0032] Compared with the existing sound absorption structure, the present application has the advantages that the structure is simple, has wide frequency sound absorption effect in the middle and high frequencies, and the sound absorption coefficient is greater than 0.6 in the middle and high frequencies, the sound absorption coefficient at different frequencies does not change greatly, and the sound absorption effect is stable. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a schematic diagram of the present application;

[0034] Figure 2 is a cross-shaped partition plate of the present application;

[0035] Figure 3 is a cylindrical cavity of the present application;

[0036] Figure 4 is a bottom plate of the present application;

[0037] Figure 5 is a 1 / 4 ring-shaped thin plate array of the present application, the number of thin plates is 30;

[0038] Figure 6 is a 1 / 4 ring-shaped thin plate array of the present application, the number of thin plates is 25;

[0039] Figure 7 is a 1 / 4 ring-shaped thin plate array of the present application, the number of thin plates is 20;

[0040] Figure 8 The present invention comprises a 1 / 4 annular thin plate array with 17 thin plates;

[0041] Figure 9 The curves showing the variation of the sound absorption coefficient and the theoretically calculated sound absorption coefficient with the incident noise frequency in an embodiment of the combined acoustic black hole sound absorber structure of the present invention.

[0042] In the diagram: 1. Thin plate, 2. Cylindrical cavity, 3. Base plate, 4. 1 / 4 annular thin plate array. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and specific examples, but this should not be construed as limiting the present invention.

[0044] like Figures 1 to 8 As shown, a combined acoustic black hole sound absorber structure includes a cross-shaped partition 1, a cylindrical cavity 2, a base plate 3, and four sets of 1 / 4 annular thin plate arrays 4. The ratio of the number of plates in the four sets of 1 / 4 annular thin plate arrays is 30:25:20:17, and the plate thickness and spacing are equal. The cross-shaped partition 1 divides the cylindrical cavity 2 into four independent 1 / 4 cylindrical cavities of equal volume. The four sets of 1 / 4 annular thin plate arrays are located in the four 1 / 4 cylindrical cavities respectively. The base plate 3 is located at the end of the 1 / 4 annular thin plate with the smallest inner diameter that has no annular partition and seals that end. By constructing a transfer matrix model of a single 1 / 4 acoustic black hole sound absorber, the sound absorption coefficient of the combined acoustic black hole sound absorber is calculated. By optimizing the structural length of the single 1 / 4 acoustic black hole sound absorber and the number of 1 / 4 annular thin plates 4, the structure achieves stable absorption of mid-to-high frequency noise.

[0045] Furthermore, the thickness of the cross-shaped partition 1 is no more than 2mm, the center line of the cross-shaped partition 1 coincides with the center line of the cylindrical cavity 2, the cross-shaped partition 1 is fixed inside the cylindrical cavity 2, and the cylindrical cavity 2 is sealed and separated into 4 independent 1 / 4 cylindrical cavities, and the length of the cross-shaped partition 1 is not less than the length of the cylindrical cavity 2.

[0046] Furthermore, the length of the cylindrical cavity 2 is not less than 1 / 4 of the length of the annular thin plate array.

[0047] Furthermore, the base plate 3 includes four quarter-circular plates of the same size with an outer diameter equal to the inner diameter of the cylindrical cavity, and a thickness equal to that of the annular thin plate. The base plate is located at the end of the quarter-circular thin plate 4 with the smallest inner diameter that does not have an annular thin plate, and is fixed inside the cross-shaped partition 1 and the cylindrical cavity 2 and the end is sealed. The distance between the base plate 3 and the quarter-circular thin plate 4 with the smallest inner diameter is equal to the distance between two adjacent annular thin plates.

[0048] Further, the 1 / 4 ring-shaped thin plate array comprises a plurality of 1 / 4 ring-shaped thin plates 4 with a first-order function change in inner diameter, the first-order function is r1 represents the inner diameter of the 1 / 4 ring-shaped thin plate 4 with the smallest inner diameter, the smallest inner diameter r1 of the four groups of 1 / 4 ring-shaped thin plate arrays is the same, R represents the inner diameter of the cylindrical cavity 2, L represents the total length of the 1 / 4 ring-shaped thin plate array, the ratio of the total length L of the four groups of 1 / 4 ring-shaped thin plate arrays is 30:25:20:17, x represents the distance between any one 1 / 4 ring-shaped thin plate 4 in each group of 1 / 4 ring-shaped thin plate array and the 1 / 4 ring-shaped thin plate 4 with the largest inner diameter, wherein x≤L, the 1 / 4 ring-shaped thin plate 4 is perpendicular to the cross-shaped partition 1, the 1 / 4 ring-shaped thin plate 4 is parallel and uniformly fixed between the cross-shaped partition and the cylindrical cavity, the outer diameter of the 1 / 4 ring-shaped thin plate 4 is equal to the inner diameter of the cylindrical cavity 2, the four groups of 1 / 4 ring-shaped thin plate arrays are respectively located in the four 1 / 4 cylindrical cavities separated by the cross-shaped partition 1, the thickness of the 1 / 4 ring-shaped thin plate 4 is not greater than 2mm, and the 1 / 4 ring-shaped thin plate 4 with the largest inner diameter in the four groups of 1 / 4 ring-shaped thin plate arrays is located in the same plane.

[0049] Further, the cross-shaped partition 1, the cylindrical cavity 2, the bottom plate 3 and the four groups of 1 / 4 ring-shaped thin plate arrays are fixed by using strong glue, welding, or integrally formed by 3D printing.

[0050] A combined acoustic black hole sound absorber structure design method, characterized by comprising the following steps:

[0051] Firstly, the sound absorption coefficient of a single 1 / 4 acoustic black hole sound absorber when the sound wave is vertically incident is obtained by the transfer function method:

[0052]

[0053] The effective acoustic impedance Z satisfies

[0054]

[0055] The transfer matrix T satisfies

[0056]

[0057] The cavity admittance Y n satisfies

[0058]

[0059] In the above formulas, Z0 is the impedance of air

[0060] Z0=ρ0c0 (21)

[0061] ρ0 is the density of air, c0 is the speed of sound propagation in air, and k is the wave number

[0062]

[0063] d n is the spacing between the thin plates, is the open area of the 1 / 4 annular thin plate, V n is the volume of the hollow circular truncated cone part between the adjacent two 1 / 4 annular thin plates.

[0064] By parallel coupling design of 4 groups of 1 / 4 acoustic black hole sound absorbers, the sound absorption coefficient of the combination is

[0065]

[0066] In the formula, the effective acoustic impedance Z 总 satisfies

[0067]

[0068] In the formula, Z1, Z2, Z3, Z4 are the acoustic impedances of the 4 groups of 1 / 4 acoustic black hole sound absorbers, S = πR 2 is the total area allowing the vertical incidence of sound waves, and R is the inner diameter of the cylindrical cavity.

[0069] Secondly, based on the change of the impedance value with the length of the 1 / 4 acoustic black hole sound absorber structure, the length of the 1 / 4 acoustic black hole sound absorber structure is designed by parallel coupling design, and the sound absorption coefficient of the combined acoustic black hole sound absorber structure is optimized.

[0070] In this embodiment, the experimental model of the combined acoustic black hole sound absorber with a cross-shaped partition thickness of 2mm, a total length of 91mm, a cylindrical cavity outer diameter of 49.5mm, an inner diameter of 47.5mm, a total length of 91mm, a bottom plate thickness of 1mm, a radius of 47.5mm, 4 groups of annular thin plates with a number of 30, 25, 20 and 17 respectively, a thickness of 1mm, an outer diameter of 47.5mm, a spacing between adjacent plates of 3mm, and a maximum thin plate inner diameter of 47.5mm in the 1 / 4 annular thin plate array and a minimum inner diameter of 4.5mm is obtained by 3D printing. The sound absorption coefficient of the experimental model is measured by the impedance tube method, and the sound absorption coefficient of the designed combined acoustic black hole sound absorber is calculated by the transfer function method. The experimental measurement results and the calculation results are shown in Figure 9 It can be found from the comparison results that the experimental measurement results are highly consistent with the theoretical calculation results, the sound absorption coefficient is greater than 0.6 when the frequency is greater than 500Hz, the sound absorption coefficient at different frequencies has no large change at medium and high frequencies, and the sound absorption effect is stable. This indicates that the combined acoustic black hole sound absorber structure has good medium and high frequency sound absorption performance.

[0071] The above merely describes preferred embodiments of the present application, and is not intended to limit the implementation and protection scope of the present application. Those skilled in the art should be able to understand that any equivalent substitutions and obvious changes made according to the present application description and drawings should be included in the protection scope of the present application.

Claims

1. A combined acoustic black hole sound absorber structure, characterized in that... It includes a cross-shaped partition (1), a cylindrical cavity (2), a bottom plate (3), and four sets of 1 / 4 annular thin plate arrays (4). The ratio of the number of plates in the four sets of 1 / 4 annular thin plate arrays is 30:25:20:17, and the plate thickness and spacing are equal. The cross-shaped partition (1) divides the cylindrical cavity (2) into four independent 1 / 4 cylindrical cavities with equal volume. The four sets of 1 / 4 annular thin plate arrays are located in the four 1 / 4 cylindrical cavities respectively. The bottom plate (3) is located at the end of the 1 / 4 annular partition with the smallest inner diameter without annular partition and seals that end. The 1 / 4 annular thin plate array comprises several 1 / 4 annular thin plates (4) whose inner diameters vary according to a linear function, wherein the linear function is... r1 represents the inner diameter of the smallest 1 / 4 annular plate (4). The smallest inner diameter r1 of the four groups of 1 / 4 annular plate arrays is the same. R represents the inner diameter of the cylindrical cavity (2). L represents the total length of the 1 / 4 annular plate array. The ratio of the total lengths L of the four groups of 1 / 4 annular plate arrays is 30:25:20:

17. x represents the distance between any 1 / 4 annular plate (4) in each group of 1 / 4 annular plate arrays and the 1 / 4 annular plate (4) with the largest inner diameter, where x≤L. 4) Perpendicular to the cross-shaped partition (1), the 1 / 4 annular thin plates (4) are parallel and uniformly fixed in the cross-shaped partition and the cylindrical cavity (2). The outer diameter of the 1 / 4 annular thin plate (4) is equal to the inner diameter of the cylindrical cavity (2). The four sets of 1 / 4 annular thin plate arrays are respectively located in the four 1 / 4 cylinders separated by the cross-shaped partition (1). The thickness of the 1 / 4 annular thin plate (4) is not greater than 2mm. The 1 / 4 annular thin plate (4) with the largest inner diameter in the four sets of 1 / 4 annular thin plate arrays are all located in the same plane. The thickness of the cross-shaped partition (1) is no more than 2 mm. The center line of the cross-shaped partition (1) coincides with the center line of the cylindrical cavity (2). The cross-shaped partition (1) is fixed inside the cylindrical cavity (2) to seal and separate the cylindrical cavity (2) into 4 independent 1 / 4 cylindrical cavities. The length of the cross-shaped partition (1) is not less than the length of the cylindrical cavity (2).

2. The combined acoustic black hole sound absorber structure according to claim 1 is characterized in that the length of the cylindrical cavity (2) is not less than 1 / 4 of the length of the annular thin plate array.

3. The combined acoustic black hole sound absorber structure according to claim 1 is characterized in that the base plate (3) is a 1 / 4 circular plate with an outer diameter the same as the inner diameter of the cylindrical cavity, and a thickness the same as the thickness of the annular thin plate. The base plate (3) is located at the end of the 1 / 4 annular thin plate (4) with the smallest inner diameter without the annular thin plate, and is fixed in the cross-shaped partition (1) and the cylindrical cavity (2) and the end is sealed. The distance between the base plate (3) and the 1 / 4 annular thin plate (4) with the smallest inner diameter is equal to the distance between two adjacent annular thin plates.

4. The combined acoustic black hole sound absorber structure according to claim 1 is characterized in that the cross-shaped partition (1), the cylindrical cavity (2), the bottom plate (3) and the four sets of 1 / 4 annular thin plate arrays are fixed by using strong glue or welding, or integrally formed by 3D printing.

5. A design method for a combined acoustic black hole sound absorber structure, characterized in that, Includes the following steps: The first step is to obtain the sound absorption coefficient of a single 1 / 4 acoustic black hole absorber when the sound wave is incident perpendicularly, using the transfer function method: Effective acoustic impedance Z satisfies The transfer matrix T satisfies Cavity admittance Y n satisfy In the above equations, Z0 represents the resistance of air. Z0=ρ0c0 (5) ρ0 is the density of air, c0 is the speed of sound in air, and k is the wave number. d n For the spacing between thin plates, V is 1 / 4 of the opening area of ​​the annular thin plate. n This represents the volume of the hollow frustum between two adjacent 1 / 4 annular plates. By designing four sets of 1 / 4 acoustic black hole sound absorbers in parallel coupling, the combined sound absorption coefficient is: In the formula, the effective acoustic impedance Z 总 satisfy In the formula, Z1, Z2, Z3, and Z4 are the acoustic impedances of the four sets of 1 / 4 acoustic black hole absorbers, and S = πR 2 R is the inner diameter of the cylindrical cavity, representing the total area that allows sound waves to be incident perpendicularly. The second step involves designing the length of the 1 / 4 acoustic black hole absorber structure based on the aforementioned impedance value variation with the length of the 1 / 4 acoustic black hole absorber structure through parallel coupling design, thereby optimizing the absorption coefficient of the combined acoustic black hole absorber structure.

Images