Composite sound absorption structure with double-porosity back cavity and performance prediction method thereof

Abstract

The invention discloses a composite sound absorption structure with a double-porosity back cavity and a performance prediction method of the composite sound absorption structure. The composite sound absorption structure comprises a micro-perforated plate, a curled space, a structural frame, a porous material, an air channel and a side plate. The micro-perforated plate is mounted at the opening of the structural frame; a closed space defined by the micro-perforated plate, the structural frame and the side plates is a curled space; the porous materials are mounted around the inner surface of the structural frame and are separated from one another to form air channels; the air channels and the porous material form a dual-porosity back cavity. Performance in the performance prediction method is represented by an acoustic absorption coefficient spectrum, and the performance prediction method specifically can be realized through the following steps: calculating surface acoustic impedance of the micro-perforated plate; respectively calculating the effective mass density and the effective volume modulus of the air channel and the effective mass density and the effective volume modulus of the porous material; calculating the surface acoustic impedance of the double-porosity back cavity by using a double-porosity medium theory; and calculating the sound absorption coefficient frequency spectrum of the composite sound absorption structure.

Description

Technical Field

[0001] This invention relates to the field of acoustic noise reduction technology, specifically to a composite sound-absorbing structure with a dual-porosity back cavity and a method for predicting its performance. Background Technology

[0002] Low-frequency noise is ubiquitous in buildings and the environment. Noise sources such as industrial equipment, household appliances, and traffic noise typically exhibit a concentration of sound energy in the low-frequency range.

[0003] Low-frequency noise has a longer wavelength, stronger penetrability, and a slower attenuation rate in the air, which can have a negative impact on people's psychological and physiological health.

[0004] Traditional porous materials often require increased thickness or the addition of a back cavity to improve low-frequency sound absorption performance. This method not only wastes materials but is also not suitable for use in confined spaces.

[0005] The patent specification with publication number CN113362796A discloses a bidirectional rough inner tube type Helmholtz resonant sound absorption structure. The cavity has a height of 20~50mm and a diameter of 20~30mm. The upper surface of the cavity has a small hole, and a bidirectional rough inner tube is installed in the small hole. The bidirectional rough inner tube is connected to the cavity by adhesive bonding or welding. The lower surface of the cavity is fixed to the surface of the object that needs acoustic treatment, forming a bidirectional rough inner tube type Helmholtz resonant sound absorption structure with a sound absorption coefficient greater than 0.99 at a frequency of 100~500Hz.

[0006] Patent specification CN119811345A discloses a parallel Helmholtz resonator with adjustable sound absorption performance, comprising: a main cavity containing several sound-absorbing chambers arranged in parallel, each sound-absorbing chamber having a first sound-absorbing hole and a second sound-absorbing hole spaced apart along a first direction on its top surface; an upper cover plate slidably connected to the main cavity along the first direction, having several connected regions thereon, each connected region having several third sound-absorbing holes and a fourth sound-absorbing hole spaced apart along the first direction; the several sound-absorbing chambers and several connected regions are arranged one-to-one; a PVC gel actuator is connected to the upper cover plate, when not energized, the corresponding first sound-absorbing hole and third sound-absorbing hole overlap and connect, and when energized, it contracts so that the corresponding second sound-absorbing hole and fourth sound-absorbing hole overlap and connect. This patented technology, through the design of parallel sound-absorbing chambers, generates low-frequency broadband sound absorption with multiple absorption peaks, and further achieves low-frequency broadband sound absorption effects for different frequencies without changing the size parameters and structure of the sound-absorbing chambers.

[0007] Traditional resonant sound-absorbing structures also have many shortcomings in controlling low-frequency noise. For example, although the Helmholtz resonator with a coiled back cavity increases the cavity depth and improves low-frequency sound absorption, its bandwidth is very narrow and the actual noise reduction effect is not obvious. Compared with the Helmholtz resonator, the micro-perforated plate has a higher acoustic impedance and can have a wider low-frequency sound absorption bandwidth at the same cavity depth, but its sound absorption performance in the frequency band outside the resonant frequency is still very limited.

[0008] Although porous materials or resonant sound-absorbing structures can improve low-frequency performance by increasing the depth of the back cavity, traditional back cavities are often made of a single air medium. Such back cavities with a single porosity have certain limitations in impedance matching, improving low-frequency sound absorption performance and bandwidth. Summary of the Invention

[0009] To address the aforementioned technical problems and shortcomings in this field, this invention provides a composite sound-absorbing structure with a dual-porosity back cavity and a method for predicting its performance. Based on the theory of dual-porosity media, this invention proposes a performance prediction method for this composite sound-absorbing structure. This method, verified by finite element simulation and experimental measurements, can accurately predict the sound absorption coefficient spectrum of the composite sound-absorbing structure. This invention effectively improves low-frequency sound absorption performance while broadening the sound absorption bandwidth; reducing the width of the air channel further enhances low-frequency sound absorption performance.

[0010] The specific technical solution is as follows: In a first aspect, the present invention provides a composite sound-absorbing structure with a dual-porosity back cavity, comprising a micro-perforated plate, a rolled space, a structural frame, a porous material, an air channel, and a side plate. The micro-perforated plate is installed at the opening of the structural frame; The closed space formed by the micro-perforated plate, the structural frame, and the side plate is the curling space. The porous material is mounted around the inner surface of the structural frame, and the porous materials are separated from each other to form the air channels; The air channel and the porous material form the dual-porosity back cavity.

[0011] Furthermore, in the composite sound-absorbing structure with a dual porosity back cavity, the micro-perforated plate has the same shape and area as the opening of the structural frame.

[0012] Furthermore, in the composite sound-absorbing structure with a dual-porosity back cavity, the micro-perforated plate is flush with the outer surface of the structural frame.

[0013] Secondly, the present invention provides a performance prediction method for the composite sound-absorbing structure with a dual-porosity back cavity as described in the first aspect, wherein the performance is determined by the sound absorption coefficient spectrum. α Characterization, the sound absorption coefficient spectrumα Represented as: Re represents the real part; Im represents the imaginary part; Z S The surface acoustic impedance of the composite sound-absorbing structure with a dual-porosity back cavity is indicated. Z MPP , Z c These represent the surface acoustic impedances of the micro-perforated plate and the dual-porosity back cavity, respectively. f This represents the ratio of the opening width of the structural frame to the length of the structural frame.

[0014] j Represents the imaginary unit; r , m These represent the relative acoustic impedance and relative acoustic mass of the micro-perforated plate, respectively. or Indicates the air viscosity coefficient; t MPP The thickness of the micro-perforated plate; p MPP The perforation rate of the micro-perforated plate; r 0 represents air density; c 0 represents the speed of sound; d MPP The perforation diameter of the micro-perforated plate; oh =2π f Represents angular frequency. f For frequency; This represents the perforation constant of the micro-perforated plate. f For frequency.

[0015] j Represents the imaginary unit; r 0 represents air density; c 0 represents the speed of sound; cot represents the cotangent function in trigonometric functions; L e Indicates the equivalent depth of the curled space; z c This represents the characteristic impedance of a dual-porosity back cavity. k c The acoustic beam representing a dual-porosity back cavity; r e This indicates the effective mass density of the dual-porosity back cavity. K e This represents the effective bulk modulus of the dual-porosity back cavity. oh =2π f Represents angular frequency. f For frequency.

[0016] T Indicates the thickness of the composite sound-absorbing structure; w Indicates the wall thickness of the structural frame; t MPP The thickness of the micro-perforated plate; N Indicates the number of subspaces that make up the curled space; s Indicates the width of the curled space; L e,1 , L e,2 , L e,3 The subscripts 1 and 3 respectively represent the equivalent depths of the subspaces that constitute the curled space. Subscript 1 and 3 respectively represent the subspace ① adjacent to the micro-perforated plate and the subspace ③ farthest from the micro-perforated plate. Subscript 2 represents the other subspaces ② besides subspaces ① and ③.

[0017] f c = l / s The ratio of the width of the air passage to the width of the curling space. l , s These are the width of the air passage and the width of the curling space, respectively. j Represents the imaginary unit; r c Indicates the effective mass density of the air passage; r p Indicates the effective mass density of porous materials; Kc Indicates the effective bulk modulus of the air passage; K p This represents the effective bulk modulus of porous materials. r 0 represents air density; tanh represents the hyperbolic tangent function; c This represents the specific heat of air (a value of 1.4 is acceptable). P 0 represents atmospheric pressure (value can be 1.01 × 10⁻⁶). 5 Pr represents Prandtl's constant (which can take the value 0.71). oh =2π f Represents angular frequency. f For frequency; or Indicates the air viscosity coefficient; , , , , These are the tortuosity, porosity, flow resistance, viscous characteristic length, and thermal characteristic length of porous materials, respectively. , C p These are the thermal conductivity and specific heat capacity of air, respectively.

[0018] The performance prediction method for the composite sound-absorbing structure described in this invention is based on the sound absorption coefficient spectrum. α The representation can be achieved through the following steps: Calculate the surface acoustic impedance of a micro-perforated plate Z MPP ; Calculate the effective mass density of the air channels separately. r c and effective bulk modulus K c and the effective mass density of porous materials. r p and effective bulk modulus K p ; The surface acoustic impedance of the dual-porosity back cavity was calculated using dual-porosity medium theory. Z c ; Calculate the sound absorption coefficient spectrum of the composite sound-absorbing structure α .

[0019] Compared with the prior art, the beneficial effects of this invention are as follows: Compared with a back cavity with a single porosity, this invention effectively improves and broadens the low-frequency sound absorption performance, while also having wide-band high sound absorption performance in the mid-to-high frequency range; reducing the ratio of the air channel width to the curled space width, or reducing the perforation rate of the micro-perforated plate, can further improve the low-frequency sound absorption performance. Attached Figure Description

[0020] Figure 1 A schematic diagram of a composite sound-absorbing structure with a double-porosity back cavity; Figure 2 A finite element simulation model of a composite sound-absorbing structure with a double porosity back cavity; Figure 3 A schematic diagram of an experimental setup for a composite sound-absorbing structure with a double-porosity back cavity; Figure 4 Photograph of an experimental sample of a composite sound-absorbing structure with a dual-porosity back cavity; Figure 5 A verification diagram for the sound absorption performance prediction method of a composite sound-absorbing structure with a dual-porosity back cavity; Figure 6 The sound absorption coefficient spectrum is shown for different composite sound absorption structure embodiments. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0022] Example 1: like Figure 1 As shown, a composite sound-absorbing structure with a dual-porosity back cavity includes a micro-perforated plate, a curled space, a structural frame, porous material, air channels, and side plates. The micro-perforated plate is installed at the opening of the structural frame, having the same shape and area as the opening, and is flush with the outer surface of the structural frame. The closed space formed by the micro-perforated plate, the structural frame, and the side plates is the curled space. The porous material is installed around the inner surface of the structural frame, and the porous materials are separated from each other to form air channels; the air channels and the porous material form a dual-porosity back cavity. In this embodiment, the curled space has three subspaces: red dashed line ① represents the equivalent depth of the subspace adjacent to the micro-perforated plate, red dashed line ③ represents the equivalent depth of the subspace farthest from the micro-perforated plate, and red dashed line ② represents the equivalent depth of the other subspaces besides subspaces ① and ③.

[0023] Example 2: A method for predicting the performance of composite sound-absorbing structures, wherein the performance is determined by the sound absorption coefficient spectrum. α Characterization is achieved through the following steps: Step 1: Calculate the surface acoustic impedance of the micro-perforated plate Z MPP The calculation formula is: j Represents the imaginary unit; r , m These represent the relative acoustic impedance and relative acoustic mass of the micro-perforated plate, respectively. or Indicates the air viscosity coefficient; t MPP The thickness of the micro-perforated plate; p MPP The perforation rate of the micro-perforated plate; r 0 represents air density; c 0 represents the speed of sound; d MPP The perforation diameter of the micro-perforated plate; oh =2π f Represents angular frequency. f For frequency; This represents the perforation constant of the micro-perforated plate. f For frequency.

[0024] Step 2: Calculate the effective mass density of the air channels respectively. r c Effective bulk modulus K c and the effective mass density of porous materials. r p Effective bulk modulus K p The calculation formula is: r 0 represents air density; tanh represents the hyperbolic tangent function; j Represents the imaginary unit; c To represent the specific heat of air, take 1.4; P 0 represents atmospheric pressure, taken as 1.01 × 10⁻⁶. 5 Pr represents Prandtl's constant, which is 0.71. l Indicates the width of the air passage; oh =2π f Represents angular frequency. f For frequency; or Indicates the air viscosity coefficient; , , , , These are the tortuosity, porosity, flow resistance, viscous characteristic length, and thermal characteristic length of porous materials, respectively. , C p These are the thermal conductivity and specific heat capacity of air, respectively.

[0025] Step 3: Calculate the surface acoustic impedance of the dual-porosity back cavity Z c The calculation formula is: f c =l / s The ratio of the width of the air passage to the width of the curling space. l , s These are the width of the air passage and the width of the curling space, respectively. j Represents the imaginary unit; r 0 represents air density; c 0 represents the speed of sound; cot represents the cotangent function in trigonometric functions; L e Indicates the equivalent depth of the curled space; z c This represents the characteristic impedance of a dual-porosity back cavity. k c The acoustic beam representing a dual-porosity back cavity; r e This indicates the effective mass density of the dual-porosity back cavity. K e This represents the effective bulk modulus of the dual-porosity back cavity. r c Indicates the effective mass density of the air passage; r p Indicates the effective mass density of porous materials; K c Indicates the effective bulk modulus of the air passage; K p This represents the effective bulk modulus of porous materials. oh =2π f Represents angular frequency. f For frequency.

[0026] T Indicates the thickness of the composite sound-absorbing structure; w Indicates the wall thickness of the structural frame; t MPP The thickness of the micro-perforated plate; N Indicates the number of subspaces that make up the curled space; s Indicates the width of the curled space; L e,1 , L e,2 , L e,3 The subscripts 1 and 3 respectively represent the equivalent depths of the subspaces that constitute the curled space. Subscript 1 and 3 respectively represent the subspace ① adjacent to the micro-perforated plate and the subspace ③ farthest from the micro-perforated plate. Subscript 2 represents the other subspaces ② besides subspaces ① and ③.

[0027] Step 4: Calculate the sound absorption coefficient spectrum of the composite sound-absorbing structure α The calculation formula is: Re represents the real part; Im represents the imaginary part; Z S The surface acoustic impedance of a composite sound-absorbing structure with a double porosity back cavity is represented. Z MPP , Z c These represent the surface acoustic impedance of the micro-perforated plate and the curled space (double porosity back cavity), respectively. f This represents the ratio of the opening width of the structural frame to the length of the structural frame.

[0028] like Figure 2 As shown, a finite element simulation model of the composite sound-absorbing structure is established. The cross-sectional width of the virtual impedance tube is the same as that of the composite sound-absorbing structure. A plane wave is incident from the left side of the impedance tube. Points 1 and 2 are the positions of two virtual microphones used to measure the complex sound pressure of the standing wave field inside the tube, with a distance of 50 mm between them and the surface of the composite sound-absorbing structure, respectively, which are 650 mm and 600 mm away. The micro-perforated plate is regarded as the internal impedance boundary, the tube wall of the impedance tube is set as the hard sound field boundary, and the domain where the porous material is located is set as the porous acoustic domain.

[0029] like Figure 3As shown, an experimental measurement device for constructing a composite sound-absorbing structure is presented. A signal processor sends a swept-frequency signal, which is transmitted through a power amplifier to a loudspeaker located at one end of the impedance tube, emitting a plane wave that propagates to the test sample at the other end of the impedance tube. The sound wave is reflected at the sample surface, and two microphones are used to measure the complex sound pressure at two locations on the inner wall of the impedance tube. After the microphones collect the sound pressure signals, they are transmitted back to the signal processor and computer for sound absorption coefficient spectral analysis.

[0030] In such Figure 4 The parameters of the microperforated plate in the test sample shown are: p MPP = 3.8%, d MPP = 0.6 mm, t MPP =0.4 mm; the porous material uses melamine foam with a thickness of 12 mm; the air channel width is 7.3 mm, and the curled space has 3 sub-spaces; the structural frame wall thickness is 1.5 mm, and the external dimensions are 100 mm × 100 mm × 60 mm. For example... Figure 5 As shown, within the effective frequency range of 100~1000 Hz, the experimental measurements, theoretical predictions, and finite element simulations of the sound absorption coefficients of the test samples show good agreement, verifying the accuracy of the performance prediction method for composite sound absorption structures.

[0031] Example 3: Based on the composite sound absorption structure performance prediction method of Example 2, two composite sound absorption structures with different structural parameters were designed, and their sound absorption coefficient spectra are as follows: Figure 6 As shown. For Case 1, its resonant absorption peak is located at 215 Hz, and its absorption coefficient is higher than 0.5 in the frequency range of 140~390Hz. Case 2 connects two composite sound-absorbing structures in parallel, and its resonant absorption peak is located at 360 Hz, with an absorption coefficient higher than 0.5 in the frequency range of 220~1000 Hz, achieving low-frequency sound absorption performance while broadening the sound absorption bandwidth.

[0032] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A composite sound-absorbing structure with a dual-porosity back cavity, characterized in that, It includes micro-perforated plates, curled spaces, structural frames, porous materials, air channels, and side plates; The micro-perforated plate is installed at the opening of the structural frame; The closed space formed by the micro-perforated plate, the structural frame, and the side plate is the curling space. The porous material is mounted around the inner surface of the structural frame, and the porous materials are separated from each other to form the air channels; The air channel and the porous material form the dual-porosity back cavity.

2. The composite sound-absorbing structure with a dual-porosity back cavity according to claim 1, characterized in that, The micro-perforated plate has the same shape and area as the opening in the structural frame.

3. The composite sound-absorbing structure with a dual-porosity back cavity according to claim 1 or 2, characterized in that, The micro-perforated plate is flush with the outer surface of the structural frame.

4. The performance prediction method for the composite sound-absorbing structure with a dual-porosity back cavity according to any one of claims 1 to 3, characterized in that, The performance is determined by the sound absorption coefficient spectrum. α Characterization, the sound absorption coefficient spectrum α Represented as: Re represents the real part; Im represents the imaginary part; Z S The surface acoustic impedance of the composite sound-absorbing structure with a dual-porosity back cavity is indicated. Z MPP , Z c These represent the surface acoustic impedances of the micro-perforated plate and the dual-porosity back cavity, respectively. φ This represents the ratio of the opening width of the structural frame to the length of the structural frame.

5. The performance prediction method for the composite sound-absorbing structure with a dual-porosity back cavity according to claim 4, characterized in that: j Represents the imaginary unit; r , m These represent the relative acoustic impedance and relative acoustic mass of the micro-perforated plate, respectively. η Indicates the air viscosity coefficient; t MPP The thickness of the micro-perforated plate; p MPP The perforation rate of the micro-perforated plate; d MPP The perforation diameter of the micro-perforated plate; ρ 0 represents air density; c 0 represents the speed of sound; ω =2π f Represents angular frequency. f For frequency; This represents the perforation constant of the micro-perforated plate. f For frequency.

6. The performance prediction method for the composite sound-absorbing structure with a dual-porosity back cavity according to claim 4, characterized in that: j Represents the imaginary unit; ρ 0 represents air density; c 0 represents the speed of sound; cot represents the cotangent function in trigonometric functions; L e Indicates the equivalent depth of the curled space; z c This represents the characteristic impedance of a dual-porosity back cavity. k c The acoustic beam representing a dual-porosity back cavity; ρ e This indicates the effective mass density of the dual-porosity back cavity. K e This represents the effective bulk modulus of the dual-porosity back cavity. ω =2π f Represents angular frequency. f For frequency.

7. The performance prediction method for the composite sound-absorbing structure with a dual-porosity back cavity according to claim 6, characterized in that: T Indicates the thickness of the composite sound-absorbing structure; w Indicates the wall thickness of the structural frame; t MPP The thickness of the micro-perforated plate; N Indicates the number of subspaces that make up the curled space; s Indicates the width of the curled space; L e,1 , L e,2 , L e,3 The subscripts 1 and 3 respectively represent the equivalent depths of the subspaces that constitute the curled space. Subscript 1 and 3 respectively represent the subspace ① adjacent to the micro-perforated plate and the subspace ③ farthest from the micro-perforated plate. Subscript 2 represents the other subspaces ② besides subspaces ① and ③.

8. The performance prediction method for the composite sound-absorbing structure with a dual-porosity back cavity according to claim 6, characterized in that: φ c = l / s The ratio of the width of the air passage to the width of the curling space. l , s These are the width of the air passage and the width of the curling space, respectively. j Represents the imaginary unit; ρ c Indicates the effective mass density of the air passage; ρ p Indicates the effective mass density of porous materials; K c Indicates the effective bulk modulus of the air passage; K p This represents the effective bulk modulus of porous materials. ρ 0 represents air density; tanh represents the hyperbolic tangent function; γ Indicates the specific heat of air; P 0 represents atmospheric pressure; Pr represents Prandtl's constant; ω =2π f Represents angular frequency. f For frequency; η Indicates the air viscosity coefficient; , , , , These are the tortuosity, porosity, flow resistance, viscous characteristic length, and thermal characteristic length of porous materials, respectively. , C p These are the thermal conductivity and specific heat capacity of air, respectively.

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