Computer Modelling and Design
of Non-Woven acoustical Trim

H. Andrä and Dr. A. Wiegmann

Fraunhofer Institute for Industrial Mathematics (ITWM)
Kaiserslautern, Germany

To comply with upcoming laws in the European Union that require up to
95% of an automobile's weight to be recycled it is desirable to rapidly 
develop acoustic trim made from the least amount possible of single, easily
recyclable material. The goal of the "Integrated Product Policy" (IPP) 
Project at the Fraunhofer Research Institute for Industrial Mathematics
(ITWM) and the partners Audi, Sandler and Faurencia is to develop improved 
acoustic trim by running computer simulations for fiber geometry, fluid 
dynamics and acoustic and calibrating them with acoustic experiments
performed on real trim.

A computer model with few probabilistic parameters such as fiber density, 
fiber radii and fiber orientation represents the non-wovens in the GEODICT 
fiber geometry simulation software package. Fluid dynamical properties of 
the non-woven are simulated using the ITWM's fluid dynamics package PARPAC. 
Based on the fluid dynamics, acoustic measurements on the trim in the 
Kundt-tube are simulated using the ITWM's 1D acoustic simulation package 
AKUDICT. Acoustic measurements inside 3D cavities (for example the alpha-cabin)
are simulated with statistical energy analysis (AutoSEA2) where the output 
of the previous simulations is used as input.

Next, the 3 stage sequence of simulations is inverted. To achieve the desired 
acoustic behavior, AutoSEA2 performs the evaluation of the objective function 
in the optimization to find desired fluid dynamical properties of the acoustic 
trim. To achieve the fluid dynamical properties, appropriate stochastic 
properties of the non-wovens are found. These are finally translated into 
production parameters. 

IPP is sponsored by the IPP initiative of the Bavarian State Ministry for 
Regional Development and Environmental Affairs.

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