Design of acoustic trim based on geometric modeling and flow simulation for non-woven

Abstract

In order to optimize the acoustic properties of a stacked fiber nonwoven, the microstructure of the non-woven is modeled by a macroscopically homogeneous random system of straight cylinders (tubes). That is, the fibers are modeled by a spatially stationary random system of lines (Poisson line process), dilated by a sphere. Pressing the non-woven causes anisotropy. In our model, this anisotropy is described by a one parametric distribution of the direction of the fibers. In the present application, the anisotropy parameter has to be estimated from 2d reflected light microscopic images of microsections of the non-woven.After fitting the model, the flow is computed in digitized realizations of the stochastic geometric model using the lattice Boltzmann method. Based on the flow resistivity, the formulas of Delany and Bazley predict the frequency-dependent acoustic absorption of the non-woven in the impedance tube.Using the geometric model, the description of a non-woven with improved acoustic absorption properties is obtained in the following way: First, the fiber thicknesses, porosity and anisotropy of the fiber system are modified. Then the flow and acoustics simulations are performed in the new sample. These two steps are repeatedc for various sets of parameters. Finally, the set of parameters for the geometric model leading to the best acoustic absorption is chosen.

Computation of Thermal Conductivity of Gas Diffusion Layers of PEM Fuel Cells

“…Using spherical coordinates, β characterizes the directional distribution of fibers. The density of the directional distribution is given by Equation (1), (Schladitz et al, 2006) The density is thus independent of φ, i.e. the density exhibits rotational symmetry with respect to the z-axis.…”

3D analysis, modeling and simulation of transport processes in compressed fibrous microstructures, using the Lattice Boltzmann method

“…The idea of representing fiber based material by randomly distributed cylinders was presented by Tomadakis and Sotirchos already in 1993 [48]. A commonly used stochastic model for fiber based GDLs was presented by Schladitz et al [49]. In this model straight fibers of non-woven GDLs are generated by a 3D dilated Poisson line process.…”

“…First, Hao and Cheng created their virtual geometry from the Schladitz model [49] whereas our approach is based on the model from Thiedmann [51] and its extension regarding the binder [52,53].…”

Three-dimensional reconstruction of a random fibrous medium: Geometry, transport, and sound absorbing properties

“…The reconstructed fibrous medium is used as a basis for the computation of its geometrical, transport, and sound absorbing properties. In discussing a range of experimental data on the microstructure of non-woven fibrous materials involving x-ray micro computed tomography and microscopy analysis, previous works had relied on ad hoc "fiber anisotropies" 7,8 or "volume weighted average radius." 9 Here it is shown that, in conjunction with the bulk porosity, these parameters: (1) Contribute to a precise description of the acoustical characteristics of fibrous absorbents.…”