Sound barrier noise reduction structure and design method thereof

Abstract

The present application relates to a kind of sound barrier noise reduction structure and its design method, comprising: the high-frequency valley of high-frequency noise of the measured noise spectrum is determined as the valley frequency of the high-frequency sound insulation amount of the resonant unit, the low-frequency peak of low-frequency noise is determined as the peak frequency of the low-frequency sound insulation amount of the composite waveguide layer, according to the number of low-frequency peak determines the number of Helmholtz cavity;According to valley frequency, obtain the thickness of micro-perforated plate layer, the diameter of small hole on micro-perforated plate layer, the thickness of hollow cavity layer and its cross-sectional size parameter relationship formula, so as to optimize the selection of relevant parameters;According to each peak frequency, respectively calculate and obtain the volume of corresponding Helmholtz cavity, and the effective area, cross-sectional length relationship of its corresponding throat pipe, so as to optimize the selection of effective area.The structure designed by resonance system controls high-frequency noise, utilizes the Helmholtz cavity of composite waveguide layer to control low-frequency noise, realizes selective sound insulation in large frequency range.

Description

Technical Field

[0001] This invention relates to the field of sound insulation and noise reduction technology, and in particular to a sound barrier noise reduction structure and its design method. Background Technology

[0002] With the widespread application of electric motors in fields such as diesel generator sets, automobiles, and construction machinery, the resulting noise pollution has become increasingly serious. During normal operation, electric motors often generate discrete low-frequency noise and high-frequency continuous noise. Due to the long wavelength of low-frequency noise, the use of traditional sound insulation materials to control low-frequency noise has always been a key and challenging area in noise control, and a hot topic in acoustic research.

[0003] In existing technologies, the emergence of acoustic metamaterials and phononic crystals has provided new approaches to solving the problem of low-frequency noise control, but freely designable noise suppression structures remain scarce. The main problems are: 1. Controlling low-frequency noise often requires large structural dimensions, while practical applications demand that the structural size not be too large. 2. Sound-absorbing materials often have complex structures, making them inconvenient to process and manufacture. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a noise reduction structure for a sound barrier and its design method, which improves the effectiveness of the noise reduction structure in simultaneously isolating low-frequency discrete noise and high-frequency continuous noise, and enhances the flexibility of the design method in selecting optimized parameters.

[0005] The technical solution adopted in this invention is as follows:

[0006] A noise reduction structure for a sound barrier includes a noise reduction unit. The noise reduction unit comprises a micro-perforated plate layer, a hollow cavity layer, and a composite waveguide layer arranged sequentially. The micro-perforated plate layer has several through holes arranged vertically. The hollow cavity layer and the micro-perforated plate layer constitute a resonant unit, jointly participating in the modulation of high-frequency noise. The composite waveguide layer is used to participate in the modulation of low-frequency noise and consists of a main acoustic waveguide and at least one Helmholtz cavity. The main acoustic waveguide and at least one Helmholtz cavity are connected by a throat tube extending into the Helmholtz cavity. The main acoustic waveguide penetrates the composite waveguide layer and is connected at one end to the hollow cavity layer. The at least one Helmholtz cavity is distributed circumferentially around the main acoustic waveguide.

[0007] The cross-section of the acoustic main waveguide is circular. When there is only one Helmholtz cavity, its cross-section is an annular shape with the center of the acoustic main waveguide as the center. The cross-section of the corresponding throat is also an annular shape with the center of the acoustic main waveguide as the center.

[0008] The cross-section of the acoustic waveguide is circular. When there are at least two Helmholtz cavities, their cross-section is a fan-shaped shape with the center of the acoustic waveguide as the center. The cross-section of the corresponding throat is also a fan-shaped shape with the center of the acoustic waveguide as the center. The Helmholtz cavity and the throat connected to it have the same central angle.

[0009] A design method for the aforementioned sound barrier noise reduction structure includes:

[0010] The noise spectrum is measured, and the high-frequency valley of the high-frequency noise in the measured noise spectrum is determined as the valley frequency of the high-frequency sound insulation of the resonant unit composed of the hollow cavity layer and the micro-perforated plate layer. The low-frequency peak of the low-frequency noise in the measured noise spectrum is determined as the peak frequency of the low-frequency sound insulation of the composite waveguide layer. The number of Helmholtz cavities is determined according to the number of low-frequency peaks.

[0011] Based on the valley frequency, a first relationship is calculated regarding the thickness of the micro-perforated plate layer, the diameter of the small holes on the micro-perforated plate layer, the thickness of the hollow cavity layer, and its cross-sectional dimensions. Using the first relationship as a constraint, the thickness of the micro-perforated plate layer, the diameter of the small holes on the micro-perforated plate layer, the thickness of the hollow cavity layer, and its cross-sectional dimensions are optimized.

[0012] Based on each peak frequency, a second relationship is calculated regarding the volume of the corresponding Helmholtz cavity, the effective area S of its corresponding larynx, and the cross-sectional length L. Using this second relationship as a constraint, the effective area S is optimized, where the effective area S is the area of ​​the outer arc surface of the sector-shaped cube formed by the larynx, and the cross-sectional length L = r neck -d / 2,r neck d is the limiting radius of the throat, and d is the diameter of the acoustic waveguide.

[0013] Based on the valley frequency, a first relationship is calculated regarding the thickness of the micro-perforated plate layer, the diameter of the pores on the micro-perforated plate layer, the thickness of the hollow cavity layer, and its cross-sectional dimensions, including:

[0014] Calculate the angular frequency ω corresponding to the valley frequency, and substitute it into the following theoretical calculation formula to obtain the first relational expression.

[0015]

[0016] in, t is the thickness of the microperforated plate layer, d MPP It is the diameter of the pores in the microperforated plate. ρ0 is the density of air, μ = 1.983 × 10⁻⁶ -5 Pa*s is the viscosity coefficient of air, σ is the porosity of the micro-perforated plate layer, c0 is the speed of sound in air, and D is the thickness of the hollow cavity layer.

[0017] Based on each peak frequency, a second relationship is calculated regarding the volume of the corresponding Helmholtz cavity, the effective area S of the corresponding larynx, and the cross-sectional length L. Using this second relationship as a constraint, the effective area S is optimized, including:

[0018] Calculate the angular frequency ω corresponding to the peak frequency, and substitute it into the following theoretical formula to obtain the second relationship.

[0019]

[0020] Among them, M HR C HR These are the acoustic quality and acoustic volume of the Helmholtz cavity, respectively. ρ0 and c0 are the density of air and the speed of sound, respectively, V0 is the volume of the Helmholtz cavity, and M... HR =ρ0L / S;

[0021] Based on the relationship between the effective area S and the cross-sectional length L, numerical points are selected within the range of (0,L]. Through simulation calculations, the numerical point corresponding to the optimal noise reduction effect is obtained as the optimal value Re for the throat tube to extend into the Helmholtz cavity, thereby obtaining the optimal value of the effective area S.

[0022] The beneficial effects of this invention are as follows:

[0023] The noise reduction structure of this invention uses a resonant system composed of a micro-perforated plate layer and an intermediate cavity layer to insulate high-frequency noise. It utilizes the Helmholtz cavity of the composite waveguide layer to control low-frequency noise, achieving selective sound insulation functions for low-frequency discrete sound insulation in the 200-1000Hz range and high-frequency continuous sound insulation above 1000Hz. At the same time, the subwavelength size of the noise reduction structure is guaranteed by utilizing the sound attenuation characteristics of the micro-perforated plate, the intermediate cavity layer, and the multi-parallel Helmholtz cavity, as well as their mutual coupling effects.

[0024] The design method of the noise reduction structure of this invention determines the valley frequency point of the high-frequency sound insulation based on the noise spectrum as the resonant frequency point of the resonant system, and determines the geometric parameters such as the diameter and thickness of the micro-perforated plate layer, the thickness and side length of the intermediate cavity layer. The low-frequency sound insulation frequency point is determined based on the noise spectrum as the resonant frequency point of the Helmholtz cavity, and the number of Helmholtz cavities is determined by the number of low-frequency sound insulation frequency points, thereby determining the preferred value R of the throat tube. e This allows for the determination of the effective area of ​​the throat, enabling flexible design for low-frequency noise peaks at different frequencies.

[0025] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a sound barrier noise reduction structure with a Helmholtz cavity, according to an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of a sound barrier noise reduction structure with two Helmholtz cavities, according to an embodiment of the present invention.

[0028] Figure 3 for Figure 2 A sectional view along section AA.

[0029] Figure 4 This is a schematic diagram illustrating the dimensional parameters of a sound barrier noise reduction structure with a Helmholtz cavity, according to an embodiment of the present invention. Detailed Implementation

[0030] The specific embodiments of the present invention are described below with reference to the accompanying drawings.

[0031] See Figure 1 The embodiments of this application provide a sound barrier noise reduction structure, including a noise reduction unit. The noise reduction unit includes a micro-perforated plate layer 1, a hollow cavity layer 2, and a composite waveguide layer 3 arranged sequentially. The micro-perforated plate layer 1 has a plurality of vertically penetrating holes 11. The hollow cavity layer 2 and the micro-perforated plate layer 1 constitute a resonant unit and jointly participate in the modulation of high-frequency noise. The composite waveguide layer 3 is used to participate in the modulation of low-frequency noise and is composed of a main acoustic waveguide 31 and at least one Helmholtz cavity. The main acoustic waveguide 31 and at least one Helmholtz cavity are connected by a throat tube that extends into the Helmholtz cavity. The main acoustic waveguide 31 penetrates the composite waveguide layer 3 and is connected at one end to the hollow cavity layer 2. At least one Helmholtz cavity is distributed in a circumferential direction with the main acoustic waveguide 31 as the center.

[0032] Specifically, the acoustic main waveguide 31 is an acoustic wave channel with a circular cross-section.

[0033] like Figure 1 As shown, when there is only one Helmholtz cavity, it is denoted as A Helmholtz cavity 36, and its cross-section is an annular shape with the center of the main acoustic waveguide 31 as the center. The corresponding throat is denoted as A throat 37, and its cross-section is also an annular shape with the center of the main acoustic waveguide 31 as the center.

[0034] like Figure 2 and Figure 3As shown, when there are at least two Helmholtz cavities, they are denoted as B Helmholtz cavity 32 and C Helmholtz cavity 33, respectively. The cross-section of each is a fan-shaped shape with the center of the main acoustic waveguide 31 as the center. The corresponding throats are denoted as B throat 34 and C throat 35, respectively. Their cross-sections are also fan-shaped with the center of the main acoustic waveguide 31 as the center. B Helmholtz cavity 32 and B throat 34 connected to it have the same central angle, and C Helmholtz cavity 33 and C throat 35 connected to it have the same central angle.

[0035] Specifically, the low-frequency noise insulation performance of the composite waveguide layer, which isolates noise, can be designed through the optimization of the effective area S of the throat, i.e., the area of ​​the outer arc surface of the fan-shaped cube formed by the throat. In this embodiment, the geometric parameters of the Helmholtz cavity have almost no impact on the effective area S; therefore, the specific geometric parameters of the Helmholtz cavity can be set according to the size of the space and the requirements of the ring size of the noise reduction structure.

[0036] Specifically, the resonant unit composed of the hollow cavity layer and the micro-perforated plate layer isolates the high-frequency part of the noise. The structural parameters of the resonant unit can be designed for the specific noise valley part in different usage environments, including the thickness of the hollow cavity layer, the thickness of the micro-perforated plate layer, and the diameter of the small holes.

[0037] Specifically, the silencing unit can be encapsulated into a single cylindrical structural unit.

[0038] In actual use, multiple silencing units can be connected in series to form a silencing assembly as needed.

[0039] Embodiments of this application also provide a design method for the aforementioned sound barrier noise reduction structure, comprising:

[0040] (1) Measure the noise spectrum, determine the high-frequency valley of the high-frequency noise in the measured noise spectrum as the valley frequency of the high-frequency sound insulation of the resonant unit composed of the hollow cavity layer and the micro-perforated plate layer, determine the low-frequency peak of the low-frequency noise in the measured noise spectrum as the peak frequency of the low-frequency sound insulation of the composite waveguide layer, and determine the number of Helmholtz cavities according to the number of low-frequency peaks.

[0041] (2) Calculate the angular frequency ω corresponding to the valley frequency and substitute it into the following theoretical calculation formula:

[0042]

[0043] in, Substituting into equation (1), we get:

[0044]

[0045] in, t is the thickness of the microperforated plate layer, dMPP It is the diameter of the pores in the microperforated plate. ρ0 is the density of air, μ = 1.983 × 10⁻⁶ -5 Pa*s is the viscosity coefficient of air, σ is the porosity of the micro-perforated plate layer, c0 is the speed of sound in air, and D is the thickness of the hollow cavity layer, where ρ0 = 1.21 kg / m 3 c0 = 343 m / s;

[0046] Equation (2) is used to obtain the thickness t of the micro-perforated plate and the diameter d of the pores on the micro-perforated plate. MPP The first relationship between the thickness D of the hollow cavity layer and its cross-sectional dimension parameters (specifically, the side length H or diameter of the cross-section) is used as a constraint to optimize the selection of the thickness of the micro-perforated plate layer, the diameter of the small holes on the micro-perforated plate layer, the thickness of the hollow cavity layer and its cross-sectional dimension parameters to obtain suitable geometric parameters.

[0047] (3) Calculate the angular frequency ω corresponding to each peak frequency and substitute it into the following theoretical calculation formula:

[0048]

[0049] Z HR For the acoustic impedance of the corresponding Helmholtz cavity, M HR C HR These represent the acoustic quality and acoustic volume of the corresponding Helmholtz cavity. ρ0 and c0 are the density of air and the speed of sound, respectively, V0 is the volume of the corresponding Helmholtz cavity, and M... HR =ρ0L / S;

[0050] Z HR When the imaginary part is 0, the Helmholtz cavity resonates, thus achieving sound insulation at the corresponding peak frequency, and R n The acoustic impedance is caused by the thermoviscosity effect, which has no effect on the calculation of the resonant frequency and can be ignored. Therefore, equation (3) is transformed into:

[0051]

[0052] According to equation (4), the relationships related to the structural parameters of the Helmholtz cavity and the larynx corresponding to each peak frequency can be obtained, namely, the second relationship regarding the volume of the Helmholtz cavity and the effective area S and cross-sectional length L of its corresponding larynx:

[0053]

[0054] As mentioned earlier, the effective area S is the area of ​​the outer arc surface of the sector-shaped cube formed by the throat, and the cross-sectional length L = r neck -d / 2,rneck Let d be the limiting radius of the throat tube and d be the diameter of the acoustic waveguide. Using the second relationship shown in Equation (5) as a constraint, and based on the relationship between the effective area S and the cross-sectional length L, a numerical point is selected within the range of (0, L]. Through simulation calculation, the numerical point corresponding to the optimal noise reduction effect is obtained as the optimal value Re for the throat tube to extend into the Helmholtz cavity, thereby obtaining the optimal effective area.

[0055] Preferably, the optimal value Re can be obtained through fitting.

[0056] For example Figure 4 For the anechoic unit shown, which has a Helmholtz cavity with a circular cross-section, the effective area S = 2π(R) e +d / 2)W neck W neck The thickness of the trachea; see the symbols for the above parameters for details. Figure 4 The annotation is in Chinese.

[0057] Since the Helmholtz cavity and the connected larynx have the same central angle, the influence on the resonant frequency can be eliminated when calculating the resonant frequency. Therefore, the angle of the central angle has no effect on the resonant frequency of the Helmholtz cavity, and thus will not affect the low-frequency sound insulation frequency.

[0058] The design method in this embodiment uses a different number of Helmholtz cavities to correspond to the different numbers of low-frequency peaks of the low-frequency noise to be reduced. That is, one Helmholtz cavity is used for low-frequency noise with one low-frequency peak, two Helmholtz cavities are used for low-frequency noise with two low-frequency peaks, and so on. Each cavity is distributed to target the low-frequency noise peaks at different frequencies, thereby achieving effective sound insulation of low frequencies by multiple Helmholtz cavities.

[0059] The design method in this embodiment combines the silencing frequency bands of micro-perforated plates with multi-parallel Helmholtz cavities through different structural parameter designs, enabling the noise reduction structure to have selective sound insulation performance. Due to the coupling effect between the interconnected high-frequency and low-frequency sound insulation structures, the sound attenuation of the structure is greatly enhanced. This coupling effect effectively suppresses low-frequency discrete noise and high-frequency continuous noise above 1000Hz, primarily within the 200-1000Hz range. Furthermore, the design method in this embodiment features multi-degree-of-freedom parameter design, making it highly flexible and specific.

[0060] It will be understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of designing a noise reducing structure for a sound barrier, characterized by, The sound barrier noise reduction structure comprises a sound absorbing unit, the sound absorbing unit comprises a micro-perforated plate layer, a hollow cavity layer and a composite waveguide layer arranged in sequence, a plurality of up-down penetrating holes are arranged on the micro-perforated plate layer, the hollow cavity layer and the micro-perforated plate layer constitute a resonance unit and jointly participate in the adjustment of high-frequency noise, the composite waveguide layer is used for participating in the adjustment of low-frequency noise and is composed of a sound main waveguide and at least one Helmholtz cavity, the sound main waveguide and the at least one Helmholtz cavity are connected in communication through a throat pipe, the throat pipe extends into the Helmholtz cavity, the sound main waveguide penetrates the composite waveguide layer and one end of the sound main waveguide is in communication with the hollow cavity layer, and the at least one Helmholtz cavity is distributed in a circumferential direction with the sound main waveguide as the center. The design method comprises: measuring a noise spectrum, determining a high-frequency valley value of high-frequency noise of the measured noise spectrum as a valley frequency of a high-frequency sound insulation amount of the resonance unit constituted by the hollow cavity layer and the micro-perforated plate layer, determining a low-frequency peak value of low-frequency noise of the measured noise spectrum as a peak frequency of a low-frequency sound insulation amount of the composite waveguide layer, and determining the number of Helmholtz cavities according to the number of the low-frequency peak values; according to the valley frequency, a first relationship formula about the thickness of the micro-perforated plate layer, the diameter of the hole on the micro-perforated plate layer, the thickness of the hollow cavity layer and the cross-sectional size parameters thereof is obtained, comprising: calculating the angular frequency ω corresponding to the valley frequency, and substituting the following theoretical calculation formula to obtain the first relationship formula, wherein t is the thickness of the micro-perforated plate layer, d MPP is the diameter of the holes of the micro-perforated plate layer, p0 is the density of air, μ = 1.983 x 10 -5 Pa*s is the viscosity of air, σ is the porosity of the micro-perforated plate layer, c0 is the speed of sound of air, D is the thickness of the hollow cavity layer; taking the first relationship formula as a constraint, the thickness of the micro-perforated plate layer, the diameter of the hole on the micro-perforated plate layer, the thickness of the hollow cavity layer and the cross-sectional size parameters thereof are selected and optimized; According to each of the peak frequencies, a second relationship is obtained for the volume of the corresponding Helmholtz cavity, and the effective area S and the cross-sectional length L of its corresponding throat, where the effective area S is the area of the outer arc surface of the sector-shaped cube formed by the throat, and the cross-sectional length L = r neck - d / 2, r neck is the limit radius of the throat, and d is the diameter of the acoustic main waveguide.

2. The design method of claim 1, wherein the cross section of the sound main waveguide is circular, and the cross section of the Helmholtz cavity is a circular ring shape with the center of the sound main waveguide as the center when the Helmholtz cavity is one, and the cross section of the corresponding throat pipe is also a circular ring shape with the center of the sound main waveguide as the center.

3. The method of claim 1, wherein the cross section of the sound main waveguide is circular, and the cross section of the Helmholtz cavity is a sector shape with the center of the sound main waveguide as the center when the Helmholtz cavity is at least two, and the cross section of the corresponding throat pipe is also a sector shape with the center of the sound main waveguide as the center, and the Helmholtz cavity and the throat pipe connected therewith have the same central angle.

4. The method of claim 1, wherein, according to each peak frequency, a second relationship formula about the volume of the corresponding Helmholtz cavity, and the effective area S and the cross-sectional length L of the corresponding throat pipe are respectively calculated, the effective area S is selected and optimized according to the second relationship formula as a constraint, comprising: calculating the angular frequency ω corresponding to the peak frequency, and substituting the following theoretical calculation formula to obtain the second relationship formula, where M HR , C HR are the acoustic mass and the acoustic compliance of the Helmholtz cavity, respectively, ρ0, c0are the density and the sound speed of air, respectively, V0is the volume of the Helmholtz cavity, M HR = ρ0L / S; according to the relationship between the effective area S and the cross-sectional length L, a numerical point in the range of (0, L] is selected, the optimal sound absorbing effect is obtained through simulation calculation, the numerical point is taken as the optimal numerical value Re of the throat pipe extending into the Helmholtz cavity, and the optimal effective area S is obtained.

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