A Method for Identifying Tortuosity, Viscous Characteristic Length and Thermal Characteristic Length of Kapok Mixed Fiber Porous Materials 2023-01-1058

Tortuosity, viscous characteristic length and thermal characteristic length are three important parameters for estimating sound insulation and absorption parameters of porous materials, and it is usually measured by ultrasonic measurement technology, which is cost. In this paper, a method for identifying the tortuosity, viscous characteristic length and thermal characteristic length for the mixed porous fiber materials of kapok fiber with low melting fiber and polyester staple fiber is proposed. The tortuosity is calculated by using the porosity and high-frequency sound absorption coefficient of porous materials. Using JCAL (Johnson-Champoux-Allard-Lafarge) model and genetic algorithm, viscous characteristic length and thermal characteristic length are identified by using the measured parameters, the calculated tortuosity and the measured sound absorption coefficient of porous materials under normal incidence. The measured parameters include flow resistivity, porosity, Young's modulus, Poisson's ratio, structural loss factor, thickness and density. The identification results of the tortuosity, viscous characteristic length and thermal characteristic length are compared with experiments, and the proposed method is validated. The relationship between sound absorption performance of kapok mixed fiber porous materials, and tortuosity, viscous characteristic length, thermal characteristic length and static thermal permeability is investigated. Assuming the normal incidence of sound waves, and the frequency range is located between 1000Hz to 4000Hz, taking the average sound absorption coefficient of the material in 1/3 octave frequencies as the objective function, the JCAL model and genetic algorithm are then used to obtain the optimal parameters of kapok mixed fiber porous materials.