A method for identifying performance parameters of kapok mixed fiber porous material

Abstract

A method for identifying the performance parameters of a kapok hybrid fiber porous material disclosed by the present invention includes: manufacturing a test specimen; testing the normal incidence sound absorption coefficient α of the test specimen; identifying the tortuosity α ∞ ; calculating the equivalent mass density of the kapok hybrid fiber porous material #imgabs0# calculating the elastic parameters P, Q, R of the kapok hybrid fiber porous material; calculating the complex wave numbers δ1 and δ2 of two longitudinal waves in the porous material; calculating the characteristic impedance #imgabs1# of the fluid two-phase wave and the characteristic impedance #imgabs2# of the solid two-phase wave in the porous material; characterizing the kapok hybrid fiber porous material with the Johnson-Champoux-Allard-Lafarge model and calculating the theoretical value α of its normal incidence sound absorption coefficient S ; adopting a genetic algorithm to identify the viscous characteristic length Λ and the thermal characteristic length Λ′ by minimizing the error between the theoretical value α S of the normal incidence sound absorption coefficient and the experimental value α. According to the identification results of the tortuosity α ∞ , the viscous characteristic length Λ and the thermal characteristic length Λ′, the present invention can predict the acoustic performance of the kapok hybrid fiber flat plate, effectively reduce the number of tests, and provide a reference basis for the optimized design of the kapok hybrid fiber flat plate.

Description

Technical Field

[0001] The invention belongs to the field of parameter identification of porous materials, and relates to a method for identifying performance parameters of a kapok mixed fiber porous material, and in particular to a method for identifying the tortuosity, viscosity characteristic length and thermal characteristic length of the kapok mixed fiber. Background Art

[0002] Parameter identification is an important area of ​​porous material research. The parameters of porous materials include fluid phase parameters and solid phase parameters. Fluid phase parameters include flow resistivity, porosity, tortuosity, viscous characteristic length and thermal characteristic length, and solid phase parameters include density, Young's modulus, Poisson's ratio and structural loss factor. The accuracy of these parameters is directly related to the accuracy of the established porous material model and whether its acoustic behavior can be accurately predicted. Tortuosity, viscous characteristic length and thermal characteristic length are three important parameters for calculating the sound insulation and sound absorption performance of porous materials. In actual engineering applications, they are often tested by ultrasonic measurement technology.

[0003] Ultrasonic measurement technology requires the use of two gases, one is air and the other is helium or argon. The high-frequency behavior of the refractive index is used to extract the tortuosity, viscous characteristic length and thermal characteristic length of porous materials. However, the workload of ultrasonic measurement technology is large and the testing cost is high. Therefore, it is of great significance to obtain the tortuosity, viscous characteristic length and thermal characteristic length of porous materials through theoretical calculation methods.

[0004] To obtain the tortuosity, viscous characteristic length and thermal characteristic length of porous materials through theoretical calculation methods, the thickness, density, flow resistivity, porosity and normal incidence sound absorption coefficient of the material must be determined first. At present, the most commonly used method is to use commercial software for parameter inversion. According to the thickness, density, flow resistivity, porosity and normal incidence sound absorption coefficient of the porous material, the Johnson-Champoux-Allard model and nonlinear least squares method are used to identify the tortuosity, viscous characteristic length and thermal characteristic length. However, this software is only applicable to the parameter identification of a single porous material, such as glass wool, rock wool and foam materials, and is not applicable to porous materials mixed with multiple fiber materials. Researchers at Shanghai University of Engineering Science proposed a genetic algorithm to derive the parameters of open-cell foam materials. The parameters derived by this method include the material's flow resistivity, porosity, tortuosity, viscous characteristic length, thermal characteristic length, density, Young's modulus, Poisson's ratio, structural loss factor, and static thermal permeability, a total of 10. This technology has three shortcomings. First, the genetic algorithm itself has the disadvantage of being prone to premature convergence and is not suitable for multi-objective optimization. The results of using the genetic algorithm to derive 10 parameters may not be accurate. Second, the author only verified the derivation results of flow resistivity, porosity, Young's modulus, Poisson's ratio and structural loss factor, and the derivation results of other parameters were not verified for accuracy. Third, this method is still for open-cell foam materials and is not suitable for kapok mixed fiber materials. Therefore, it is necessary to propose a parameter identification method suitable for kapok mixed fiber materials. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a method for identifying the performance parameters of a kapok mixed fiber porous material, and gives the tortuosity α of the kapok mixed fiber porous material. ∞ , viscous characteristic length Λ and thermal characteristic length Λ′. Using the high-frequency average value α of the normal-incident sound absorption coefficient of the material high and porosity φ to identify tortuosity α ∞ The Johnson-Champoux-Allard-Lafarge model is used, and Young's modulus E, Poisson's ratio ν and loss factor η are introduced to calculate the theoretical value of the normal incidence sound absorption coefficient α S Calculate the theoretical value of the normal incidence sound absorption coefficient α S The error with the test value α is optimized using a genetic algorithm to find the minimum error, and finally the viscous characteristic length Λ and the thermal characteristic length Λ′ are output.

[0006] In order to achieve the purpose of the present invention, the tortuosity α of the kapok mixed fiber porous material provided by the present invention is ∞ , a method for identifying a viscosity characteristic length Λ and a thermal characteristic length Λ′, comprising the following steps:

[0007] (1) Preparing test samples: kapok fiber is mixed with two other fiber materials to prepare a kapok mixed fiber porous material, and then the kapok mixed fiber porous material is pressed into a flat sample; and test samples of different sizes are cut from the flat sample using a cutter;

[0008] (2) Obtain the thickness h and density ρ of the test sample m , flow resistivity σ, porosity φ, Young's modulus E, Poisson's ratio ν, structural loss factor η: The thickness h of the sample is obtained by testing with a laser thickness gauge; the weight of the sample is obtained by testing with an electronic scale, and the density ρ of the sample is obtained by dividing the weight by the volume m ; The flow resistance σ of the sample is measured by the flow resistance test system; the porosity φ of the sample is measured by the porosity test system; the Young's modulus E, Poisson's ratio ν and structural loss factor η of the sample are measured by the quasi-static mechanical analyzer;

[0009] (3) Equipment connection and sample installation: Use an impedance tube test system, which includes two sizes of test tubes, large and small. Install the sample of the corresponding size at one end of the test tube. When installing, the sample should not be overly compressed so that it is installed too tightly and bulges in the middle, nor should it be too loose so that there is a large gap around the sample and the test tube. Apply vaseline to seal the small gaps around the sample. Install two microphones at the front end of the sample, and connect the microphones to the signal acquisition front end and the digital spectrum analysis system. Connect the signal generator to the power amplifier, and the power amplifier to the sound source.

[0010] (4) Test the normal incidence sound absorption coefficient curve of the sample: First, use a large tube to test the normal incidence sound absorption coefficient of the sample in the medium and low frequency bands; then use a small tube to test the normal incidence sound absorption coefficient of the sample in the medium and high frequency bands; use the signal acquisition front end to collect the test data; use the digital spectrum analysis system to merge the test data of the large tube and the small tube to obtain the normal incidence sound absorption coefficient of the sample in the full frequency band;

[0011] (5) Identify the tortuosity α ∞ :The porosity φ of the kapok mixed fiber porous material and the high-frequency average value α of the normal incidence sound absorption coefficient obtained by impedance tube test high , the tortuosity α is calculated according to the following empirical formula ∞ ;

[0012] α ∞ =[φ(2-α high ) / α high ] 2 (1)

[0013] (6) Calculation of the equivalent mass density of kapok mixed fiber porous materials The calculation formula is

[0014]

[0015]

[0016]

[0017] In the formula, is the dynamic density of the kapok mixed fiber porous material characterized by the Johnson-Champoux-Allard-Lafarg model, and the calculation formula is

[0018]

[0019] In the formula, ρ 0 is the air density, P 0 is the atmospheric pressure, ω is the angular frequency, γ is the specific heat ratio of air, μ is the dynamic viscosity of air, κ is the thermal conductivity of air, C p is the specific heat of air at constant pressure, Λ is the viscous characteristic length, Λ′ is the thermal characteristic length, k 0 ′ is the static thermal permeability;

[0020] Static thermal permeability k′ 0 The calculation formula is

[0021]

[0022] Where a is the equivalent radius of the fiber.

[0023] (7) Calculate the elastic parameters P, Q, and R of the kapok mixed fiber porous material: The calculation formula is:

[0024]

[0025]

[0026]

[0027] In the formula, N is the intermediate quantity, The dynamic density of the kapok mixed fiber porous material characterized by the Johnson-Champoux-Allard-Lafarge model can be calculated according to the following formula;

[0028]

[0029]

[0030] (8) Calculation of the complex wave number δ of two longitudinal waves in the porous material of kapok mixed fiber 1 and δ 2 :The calculation formula is

[0031]

[0032]

[0033] Where Δ is the intermediate quantity, which can be calculated according to the following formula;

[0034]

[0035] (9) Calculation of the characteristic impedance of two longitudinal waves in the fluid phase of the kapok mixed fiber porous material and the characteristic impedance of two longitudinal waves in the solid phase The calculation formula is

[0036]

[0037]

[0038]

[0039]

[0040] In the formula, ζ 1 , 2 is an intermediate quantity and can be calculated according to the following formula;

[0041]

[0042]

[0043] (10) Calculate the theoretical value α of the normal incidence sound absorption coefficient S :The calculation formula is

[0044]

[0045]

[0046] In the formula, A and B are intermediate quantities and can be calculated according to the following formula;

[0047]

[0048]

[0049] (11) A genetic algorithm is used to minimize the theoretical value of the normal incidence sound absorption coefficient α S The error from the experimental value α identifies the viscous characteristic length Λ and the thermal characteristic length Λ′.

[0050] Furthermore, in step (1), the kapok fiber test sample is prepared by mixing kapok fiber with at least one other fiber material.

[0051] Furthermore, the other at least one fiber material includes any one or more of polyester fiber, glass fiber, and soybean protein fiber.

[0052] Furthermore, the iterative process of the genetic algorithm is as follows:

[0053] Step 1: Binary encode the viscosity characteristic length Λ and the thermal characteristic length Λ′ to generate the initial population, and then decode and convert them into decimal numbers;

[0054] Step 2: The tortuosity α calculated in step (5) ∞ , and the thickness h and density ρ obtained by testing m , flow resistivity σ, porosity φ, Young's modulus E, Poisson's ratio ν, and structural loss factor η are substituted into the Johnson-Champoux-Allard-Lafarge model, and the theoretical value of the normal incidence sound absorption coefficient α is calculated according to steps (6)-(10): S ;

[0055] Step 3: Set the objective function to be, and calculate the objective function value according to formula (25). Theoretical value of normal incidence sound absorption coefficient α S The smaller the error with the test value α, the smaller the objective function value;

[0056]

[0057] Step 4: The genetic algorithm selects individuals in the population that make the objective function value smaller for crossover, mutation, and selection to generate a new population, which is then substituted into the Johnson-Champoux-Allard-Lafarge model to calculate the theoretical value α of the normal incidence sound absorption coefficient according to steps (6)-(10): S ;

[0058] Step 5: Calculate the objective function value again. If the change in the objective function value calculated by two adjacent generations of populations is less than C, stop the calculation and output the viscosity characteristic length Λ and thermal characteristic length Λ′ at this time; if not, continue to return to step 4;

[0059] Furthermore, step (2) uses samples of different sizes to test thickness h, density ρ m , flow resistivity σ, porosity φ, Young's modulus E, Poisson's ratio ν, structural loss factor η, and take their average values ​​as the final test results of the parameters.

[0060] Furthermore, in step (4), samples of different sizes are used to test the normal incidence sound absorption coefficient, and the average value is taken as the final test result of the normal incidence sound absorption coefficient.

[0061] Furthermore, step (11) imposes the following constraints on the viscous characteristic length Λ and the thermal characteristic length Λ′:

[0062] 1≤Λ≤2000

[0063] 1≤Λ′≤2000

[0064] Λ≤Λ′

[0065] Compared with the prior art, the present invention has at least the following positive effects:

[0066] 1) According to the tortuosity α ∞ The identification results of the viscous characteristic length Λ and the thermal characteristic length Λ′ can predict the acoustic performance of the kapok mixed fiber flat plate, effectively reduce the number of tests, and provide a reference for the optimal design of the kapok mixed fiber flat plate.

[0067] 2) The present invention has a tortuosity α ∞ In the identification calculation, the calculation method is applicable to the tortuosity calculation of most porous materials used to make acoustic packages in daily life.

[0068] 3) In the identification and calculation of the viscous characteristic length Λ and the thermal characteristic length Λ′, the present invention takes into account the Young's modulus E, Poisson's ratio ν and loss factor η of the porous material, so the calculation method is also applicable to the case where the material thickness is thin.

[0069] 4) The method of the present invention can more accurately identify the tortuosity α of the material ∞ , viscous characteristic length Λ and thermal characteristic length Λ′, thus saving part of the cost of parameter testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 This is the principle diagram of the normal incidence sound absorption coefficient of the impedance tube test sample;

[0071] Figure 2 is a simplified flow chart of steps for identifying the viscous characteristic length and the thermal characteristic length;

[0072] FIG3( a ) is a graph of the normal incidence sound absorption coefficient of sample 1 obtained by experimental testing;

[0073] FIG3( b ) is a graph of the normal incidence sound absorption coefficient of sample 2 obtained by experimental testing;

[0074] FIG3( c ) is a graph of the normal incidence sound absorption coefficient of sample 3 obtained by experimental testing;

[0075] FIG3( d ) is a graph of the normal incidence sound absorption coefficient of sample 4 obtained by experimental testing;

[0076] Figure 4It is a schematic diagram of the model established by finite element software for calculating the normal incidence sound absorption coefficient of porous materials. DETAILED DESCRIPTION

[0077] In order to make the objectives, technical solutions and advantages of the present invention more clear and explicit, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0078] The present invention provides a method for identifying performance parameters of a kapok mixed fiber porous material, comprising the following steps:

[0079] Step 1: Prepare kapok mixed fiber test samples: mix kapok fiber with other fiber materials to prepare kapok mixed fiber porous materials, and then press the kapok mixed fiber porous materials into flat sample pieces; cut test samples of different sizes from the flat sample pieces.

[0080] In some embodiments of the present invention, kapok fiber is mixed with at least one other fiber material (polyester fiber, glass fiber, soy protein fiber, etc.) and an air-laid process is adopted to make a kapok mixed fiber porous material; a high-temperature molding process is adopted to press the kapok mixed fiber porous material into four groups of flat sample pieces of different thicknesses; and a cutter is used to cut three test samples of different diameters from the four groups of flat sample pieces of different thicknesses.

[0081] Step 2: Obtain the thickness h and density ρ of the test sample m , flow resistivity σ, porosity φ, Young's modulus E, Poisson's ratio ν, and structural loss factor η.

[0082] In some embodiments of the present invention, the test samples are grouped according to thickness, each thickness is a group, a total of four groups, each group contains three groups of test samples with different diameters; the test samples in each group are numbered, and the thickness h, density ρ of each test sample in the same group are tested separately. m , flow resistivity σ, porosity φ, Young's modulus E, Poisson's ratio ν, structural loss factor η, and calculate their average values ​​as the parameter values ​​of this group of test samples.

[0083] In some embodiments of the present invention, a laser thickness gauge is used to measure the thickness h of the test sample; an electronic scale is used to measure the weight of the test sample, and the density ρ of the test sample can be obtained by dividing the weight by the volume. m ; The flow resistance σ of the test sample is tested using a flow resistance test system; the porosity φ of the test sample is tested using a porosity test system; the Young's modulus E, Poisson's ratio ν and structural loss factor η of the test sample are tested using a quasi-static mechanical analyzer.

[0084] Step 3: Equipment connection and sample installation:

[0085] See also Figure 1 , an impedance tube test system is used, which includes two sizes of test tubes, a large tube and a small tube; the test sample of the corresponding size is installed at one end of the test tube; when installing, the test sample cannot be overly compressed so that it is installed too tightly and bulges in the middle, nor can it be too loose so that there is a large gap around the test sample and the test tube; the small gaps around the test sample are sealed by applying vaseline; two microphones are installed at the front end of the test sample, and the microphones are connected to the signal acquisition front end and the digital spectrum analysis system; the signal generator is connected to the power amplifier, and the power amplifier is connected to the sound source.

[0086] Step 4: Test the normal incidence sound absorption coefficient curve of the sample: First, use a large tube to test the normal incidence sound absorption coefficient of the sample in the low and medium frequency bands; then use a small tube to test the normal incidence sound absorption coefficient of the sample in the medium and high frequency bands; use the signal acquisition front end to collect the test data; use the digital spectrum analysis system to combine the test data of the large and small tubes to obtain the normal incidence sound absorption coefficient of the sample in the full frequency band.

[0087] In some embodiments of the present invention, the normal incidence sound absorption coefficient of samples of different diameters in each group is tested according to the number: first, the normal incidence sound absorption coefficient of the sample in the frequency band of 50-1600Hz is tested with a large tube; then the normal incidence sound absorption coefficient of the sample in the frequency band of 500-6400Hz is tested with a small tube; the test data is collected using a signal acquisition front end; the test data of the large tube and the small tube are combined using a digital spectrum analysis system to obtain the normal incidence sound absorption coefficient of the sample in the full frequency band; the normal incidence sound absorption coefficient test data of all samples in the same group are collected, and the average value is calculated as the normal incidence sound absorption coefficient of the group of samples. As shown in Figures 3(a) to (d), the normal incidence sound absorption coefficient curves of the four groups of samples obtained by the test.

[0088] Step 5: Identify the tortuosity α ∞ :

[0089] The porosity φ of the kapok mixed fiber porous material and the high-frequency average value α of the normal incidence sound absorption coefficient obtained by impedance tube testing high Calculate the tortuosity α ∞ , the calculation formula is

[0090] α ∞ =[φ(2-α high ) / α high ] 2 (1)

[0091] In the formula, α high is the average value in the frequency range of 5000-6400 Hz in the normal incidence sound absorption coefficient curve of the test sample obtained in step 4;

[0092] Step 6: Calculate the three equivalent mass densities of the kapok mixed fiber porous material in, is the equivalent mass density of the framework part (solid) of the porous material, is the equivalent mass density of the air portion (fluid) in the porous material, is the equivalent mass density of the porous material frame and the air coupling part (fluid-structure interaction):

[0093] The calculation formula is

[0094]

[0095]

[0096]

[0097] In the formula, is the dynamic density of the kapok mixed fiber porous material characterized by the Johnson-Champoux-Allard-Lafarge model, and the calculation formula is

[0098]

[0099] In the formula, ρ 0 is the air density; ω is the angular frequency; μ is the air dynamic viscosity; Λ is the viscous characteristic length, i is the imaginary unit, i 2 =-1,ρ m is the density of the test sample, and σ is the flow resistivity of the test sample.

[0100] Step 7: Calculate the three elastic parameters P, Q, and R of the kapok mixed fiber porous material:

[0101] The calculation formula is

[0102]

[0103]

[0104]

[0105] In the formula, N is the intermediate quantity, The dynamic bulk modulus of the kapok hybrid fiber porous material characterized by the Johnson-Champoux-Allard-Lafarge model can be calculated according to the following formula;

[0106]

[0107]

[0108] Where P0 is the atmospheric pressure; γ is the specific heat ratio of air; κ is the thermal conductivity of air; C p is the specific heat of air at constant pressure; Λ′ is the thermal characteristic length; k′ 0 is the static thermal permeability, calculated as

[0109]

[0110] Where a is the equivalent radius of the fiber.

[0111] Step 8: Calculate the complex wave number δ of the two longitudinal waves in the kapok mixed fiber porous material 1 and δ 2 :

[0112] The calculation formula is

[0113]

[0114]

[0115] Where Δ is the intermediate quantity, which can be calculated according to the following formula;

[0116]

[0117] Step 9: Calculate the characteristic impedance of two longitudinal waves in the fluid phase of the kapok hybrid fiber porous material and the characteristic impedance of two longitudinal waves in the solid phase

[0118] The calculation formula is

[0119]

[0120]

[0121]

[0122]

[0123] In the formula, ζ 1 , 2 is an intermediate quantity and can be calculated according to the following formula;

[0124]

[0125]

[0126] Step 10: Calculate the theoretical value of the normal incidence sound absorption coefficient α S :

[0127] The calculation formula is

[0128]

[0129] c 0 is the speed of sound in air; Z S is an intermediate quantity and can be calculated according to the following formula;

[0130]

[0131] In the formula, A and B are intermediate quantities, which can be calculated according to the following formula;

[0132]

[0133]

[0134] Step 11: Use genetic algorithm to minimize the theoretical value of sound absorption coefficient α S The error between the normal incidence sound absorption coefficient test value α obtained in step 4 identifies the viscous characteristic length Λ and the thermal characteristic length Λ′:

[0135] The iteration process is as follows:

[0136] Step 1: Binary encode the viscosity characteristic length Λ and the thermal characteristic length Λ′ to generate an initial population; set the range of the viscosity characteristic length Λ and the thermal characteristic length Λ′ to 1≤Λ≤2000, 1≤Λ′≤2000, and Λ≤Λ′; and then decode and convert them into decimal numbers;

[0137] Step 2: The tortuosity α calculated in step 5 ∞ , and the thickness h and density ρ obtained by testing m , flow resistivity σ, porosity φ, Young's modulus E, Poisson's ratio ν, and loss factor η are substituted into the Johnson-Champoux-Allard-Lafarge model, and the theoretical value α of the normal incidence sound absorption coefficient is calculated according to steps 6-10 S ;

[0138] Step 3: Calculate the objective function value according to formula (25). Theoretical value of normal incidence sound absorption coefficient α S The smaller the error with the test value α, the smaller the objective function value;

[0139]

[0140] In the formula, corrcoef(α S ,α) is α S The correlation coefficient with α, n is the number of frequency points.

[0141] Step 4: The genetic algorithm selects individuals in the population that make the objective function value smaller for crossover, mutation, and selection to generate a new population, and then substitutes it into the Johnson-Champoux-Allard-Lafarge model to calculate the theoretical value α of the normal incidence sound absorption coefficient according to steps 6-10. S ;

[0142] Step 5: Calculate the objective function value again. If the change in the objective function value calculated between two adjacent generations of populations is less than the preset value C, stop the calculation and output the viscosity characteristic length Λ and thermal characteristic length Λ′ at this time; if not, continue and return to step 4.

[0143] In some embodiments of the present invention, the preset value C is 10 -6 .

[0144] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for identifying performance parameters of kapok mixed fiber porous materials, Features The following steps are involved: (1) Prepare kapok fiber test samples; (2) Obtain the thickness h and density ρ of the test sample m , flow resistivity σ, porosity φ, Young's modulus E, Poisson's ratio ν, structural loss factor η: (3) Testing the normal incidence sound absorption coefficient curve of the test sample: first, testing the normal incidence sound absorption coefficient of the sample in the low-mid frequency band; then testing the normal incidence sound absorption coefficient of the sample in the high-mid frequency band, and then combining the two test data to obtain the normal incidence sound absorption coefficient of the sample in the full frequency band; (4) Identify the tortuosity α ∞ : The porosity φ of the kapok mixed fiber porous material and the high-frequency average value α of the normal incidence sound absorption coefficient obtained by the test in step (3) are used. high , calculate the tortuosity α ∞ ; a ∞ =[φ(2-a high ) / a high ] 2 (1) (5) Calculation of three equivalent mass densities of kapok mixed fiber porous materials The calculation formula is In the formula, ρ 0 is the air density, ω is the angular frequency, is the dynamic density of the kapok mixed fiber porous material characterized by the Johnson-Champoux-Allard-Lafarge model, and the calculation formula is Where σ is the flow resistivity of the test sample, μ is the dynamic viscosity of air, Λ is the viscous characteristic length, and i is the imaginary unit; (6) Calculate the three elastic parameters P, Q, and R of the kapok mixed fiber porous material: the calculation formula is In the formula, N is the intermediate quantity, The dynamic bulk modulus of the kapok mixed fiber porous material characterized by the Johnson-Champoux-Allard-Lafarge model can be calculated according to the following formula: Where P 0 is the atmospheric pressure, γ is the specific heat ratio of air, κ is the thermal conductivity of air, C p is the specific heat of air at constant pressure, Λ′ is the thermal characteristic length, k 0 ′ is the static thermal permeability; (7) Calculation of the complex wave number δ of two longitudinal waves in the porous material of kapok mixed fiber 1 and δ 2 :The calculation formula is Where Δ is the intermediate quantity, which is calculated according to the following formula; (8) Calculation of the characteristic impedance of two longitudinal waves in the fluid phase of the kapok mixed fiber porous material and the characteristic impedance of two longitudinal waves in the solid phase The calculation formula is In the formula, ζ 1 , 2 It is an intermediate quantity and can be calculated according to the following formula; (9) Calculate the theoretical value α of the normal incidence sound absorption coefficient S :The calculation formula is Where A and B are intermediate quantities, calculated according to the following formula; (10) A genetic algorithm is used to minimize the theoretical value of the normal incidence sound absorption coefficient α S The error identification with the normal incidence sound absorption coefficient test value α obtained in step (3) yields the viscous characteristic length Λ and the thermal characteristic length Λ′.

2. The method for identifying performance parameters of a kapok mixed fiber porous material according to claim 1, Features: In step (1), the kapok fiber test sample is prepared by mixing kapok fiber with at least one other fiber material.

3. The method for identifying performance parameters of a kapok mixed fiber porous material according to claim 2, Features: The at least one other fiber material includes any one or more of polyester fiber, glass fiber, and soybean protein fiber.

4. The method for identifying performance parameters of a kapok mixed fiber porous material according to claim 1, Features: In step (2), kapok mixed fiber test samples of different sizes are used to test the thickness h and density ρ m , flow resistivity σ, porosity φ, Young's modulus E, Poisson's ratio ν, structural loss factor η, and take their average values ​​as the final test results of the parameters.

5. The method for identifying performance parameters of a kapok mixed fiber porous material according to claim 1, Features: In step (2), a laser thickness gauge is used to measure the thickness h of the test sample; an electronic scale is used to measure the weight of the test sample, and the weight is divided by the volume to obtain the density ρ of the test sample. m ; The flow resistance σ of the test sample is measured by the flow resistance test system; the porosity φ of the test sample is measured by the porosity test system; The Young's modulus E, Poisson's ratio ν and structural loss factor η of the test sample were obtained using a quasi-static mechanical analyzer.

6. The method for identifying performance parameters of a kapok mixed fiber porous material according to claim 1, Features: In step (3), the normal incidence sound absorption coefficient is tested for test samples of different sizes, and the average value is taken as the final test result of the normal incidence sound absorption coefficient.

7. The method for identifying performance parameters of a kapok mixed fiber porous material according to claim 1, It is characterized in that Before step (3) of testing the normal incidence sound absorption coefficient curve, the method further includes the following steps: installing the test sample in an impedance tube test system, installing a microphone at the front end of the test sample, the microphone being connected to a signal acquisition front end and a digital spectrum analysis system; connecting a signal generator to a power amplifier, and connecting the power amplifier to a sound source.

8. The method for identifying performance parameters of a kapok mixed fiber porous material according to claim 1, Features: In step (5), the static thermal permeability k 0 The calculation formula of ′ is Where a is the equivalent radius of the fiber.

9. The method for identifying performance parameters of a kapok mixed fiber porous material according to claim 1, Features: Step (10) imposes the following constraints on the viscous characteristic length Λ and the thermal characteristic length Λ′: 1≤Λ≤2000 1≤Λ′≤2000 Λ≤Λ′.

10. A method for identifying performance parameters of a kapok mixed fiber porous material according to any one of claims 1 to 9, Features: In step (10), the viscous characteristic length Λ and the thermal characteristic length Λ′ are identified by using a genetic algorithm. The iterative process includes: Step 1: Binary encode the viscosity characteristic length Λ and the thermal characteristic length Λ′ to generate the initial population, and then decode and convert them into decimal numbers; Step 2: Set the tortuosity α ∞ and the thickness h and density ρ of the test specimen m , flow resistivity σ, porosity φ, Young's modulus E, Poisson's ratio ν, and structural loss factor η are substituted into the Johnson-Champoux-Allard-Lafarge model, and the theoretical value of the normal incidence sound absorption coefficient α is calculated according to steps (5)-(9): S ; Step 3: Calculate the objective function value F according to formula (25) 1 , the theoretical value of normal incidence sound absorption coefficient α S The smaller the error with the test value α, the smaller the objective function value; In the formula, corrcoef(α S ,α) is α S The correlation coefficient with α, n is the number of frequency points; Step 4: The genetic algorithm selects individuals in the population that make the objective function value smaller for crossover, mutation, and selection to generate a new population. The new population is then substituted into the Johnson-Champoux-Allard-Lafarge model and the theoretical value α of the normal incidence sound absorption coefficient is calculated according to steps (5)-(9). S ; Step 5: Calculate the objective function value again. If the change in the objective function value calculated between two adjacent generations of populations is less than the preset value C, stop the calculation and output the viscosity characteristic length Λ and thermal characteristic length Λ′ at this time; if not, return to step 4.

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