Simulation Based Optimization of Layered Non-wovens as Acoustic Trims

V. Schulz, H. Andrä, and K. Steiner, Fraunhofer-Institut für Techno- und Wirtschaftsmathematik, Kaiserslautern, Germany

Background
Over the last years, the prediction of the acoustic absorption of non-wovens used as acoustic trims has been established. 
For example, the calculation (or measurement) of the flow resistivity of a non-woven and the corresponding absorption 
curve over the frequency is a common procedure for the optimal acoustic trim material selection. Beside the acoustic 
behaviour, a non-woven has to fulfil other demands when used in the automotive industry. These properties for example are 
a small weight combined with a high stiffness. Therefore, the material selection has to be seen as a compromise between 
different properties leading into opposite directions.

Approach
Against the background of this problem, we present in this talk the potential of layered structures used as acoustic trims. 
In our approach, the acoustic absorption of each layer is simulated separately by the model of Allard and Johnson. This 
model requires the determination of five parameters:
Flow resistivity
Porosity
Tortuosity
Viscous characteristic length
Thermal characteristic length
All these 5 parameters are computed entirely from the 3D microscopic fibre structure which is generated virtually. Thus, 
in our approach there is no need to measure any data in order to predict the acoustic properties of the non-woven. Even 
better, there is no need to produce a non-woven prototype.

Practical application
As a benefit of our method, we present for the first time a systematic investigation about the Allard-Johnson parameters 
and 3D fibre structures of real non-wovens. Additionally, we show how the computer simulation can be used in order to 
design multi-layered non-wovens with desired absorptions as light weight construction.


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