The Stability Analysis of FOAM-X Software in Porous Fiber Absorption Material 2015-01-2210

Five parameters are often used in acoustic modeling of porous absorption material, which are air flow resistivity σ, porosity φ, tortuosity α∞, viscous and thermal characteristic lengths Λ and Λ′. These parameters are not easy to be directly tested, especially the latter three parameters. One software capable of identifying inversely these parameters from impedance tube test results becomes increasingly popular. However, its detail stability analysis is rarely reported till now. This paper studies its stability on those porous fiber materials generally applied in vehicle interior trim, such as PET fiber, shoddy, PP/PET mixed fiber.

Some conclusions are obtained. (1) The identification of α∞, Λ and Λ′ is always stable when σ and φ are assumed in advance. Furthermore, high correlation coefficient is obtained if σ and φ are assumed reasonably, which means high precision of identification. (2) The identification of φ, α∞, Λ and Λ′ is stable in most cases when σ is assumed in advance. However, the identified porosity is often 1.0 for high porosity material. In this case, it might as well assume φ to be 0.99. (3) Given φ only in advance, the identification of other parameters is sensitive to the fluctuation of frequency span, but insensitive to the fluctuation of vacuum bulk density. (4) Assumed that all parameters are unknown in advance, the identification becomes more sensitive. In the latter two cases, the identified parameters should be carefully checked combining with a prior knowledge about fibrous material, so as to meet high correlation coefficient.