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https://kluedo.ub.unikl.de/index/index/
Mon, 31 Jan 2005 16:38:20 +0100
Mon, 31 Jan 2005 16:38:20 +0100

Design of acoustic trim based on geometric modeling and flow simulation for nonwoven
https://kluedo.ub.unikl.de/frontdoor/index/index/docId/1602
In order to optimize the acoustic properties of a stacked fiber nonwoven, the microstructure of the nonwoven 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 nonwoven 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 nonwoven. 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 frequencydependent acoustic absorption of the nonwoven in the impedance tube. Using the geometric model, the description of a nonwoven 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.
K. Schladitz; S. Peters; A. ReinelBitzer; A. Wiegmann; J. Ohser
report
https://kluedo.ub.unikl.de/frontdoor/index/index/docId/1602
Mon, 31 Jan 2005 16:38:20 +0100

Diffraction by image processing and its application in materials science
https://kluedo.ub.unikl.de/frontdoor/index/index/docId/1587
A spectral theory for constituents of macroscopically homogeneous random microstructures modeled as homogeneous random closed sets is developed and provided with a sound mathematical basis, where the spectrum obtained by Fourier methods corresponds to the angular intensity distribution of xrays scattered by this constituent. It is shown that the fast Fourier transform applied to threedimensional images of microstructures obtained by microtomography is a powerful tool of image processing. The applicability of this technique is is demonstrated in the analysis of images of porous media.
J. Ohser; K. Schladitz; K. Koch; N. NĂ¶the
report
https://kluedo.ub.unikl.de/frontdoor/index/index/docId/1587
Mon, 29 Nov 2004 15:30:32 +0100

Spectral Theory For Random Closed Sets And Estimating The Covariance Via Frequency Space
https://kluedo.ub.unikl.de/frontdoor/index/index/docId/1490
A spectral theory for stationary random closed sets is developed and provided with a sound mathematical basis. Definition and proof of existence of the Bartlett spectrum of a stationary random closed set as well as the proof of a WienerKhintchine theorem for the power spectrum are used to two ends: First, well known second order characteristics like the covariance can be estimated faster than usual via frequency space. Second, the Bartlett spectrum and the power spectrum can be used as second order characteristics in frequency space. Examples show, that in some cases information about the random closed set is easier to obtain from these characteristics in frequency space than from their real world counterparts.
K. Koch; J. Ohser; K. Schladitz
report
https://kluedo.ub.unikl.de/frontdoor/index/index/docId/1490
Mon, 02 Feb 2004 15:33:30 +0100

The Euler Number Of Discretized Sets  On The Choice Of Adjacency In Homogeneous Lattices
https://kluedo.ub.unikl.de/frontdoor/index/index/docId/1486
Two approaches for determining the EulerPoincarĂ© characteristic of a set observed on lattice points are considered in the context of image analysis { the integral geometric and the polyhedral approach. Information about the set is assumed to be available on lattice points only. In order to retain properties of the Euler number and to provide a good approximation of the true Euler number of the original set in the Euclidean space, the appropriate choice of adjacency in the lattice for the set and its background is crucial. Adjacencies are defined using tessellations of the whole space into polyhedrons. In R 3 , two new 14 adjacencies are introduced additionally to the well known 6 and 26 adjacencies. For the Euler number of a set and its complement, a consistency relation holds. Each of the pairs of adjacencies (14:1; 14:1), (14:2; 14:2), (6; 26), and (26; 6) is shown to be a pair of complementary adjacencies with respect to this relation. That is, the approximations of the Euler numbers are consistent if the set and its background (complement) are equipped with this pair of adjacencies. Furthermore, sufficient conditions for the correctness of the approximations of the Euler number are given. The analysis of selected microstructures and a simulation study illustrate how the estimated Euler number depends on the chosen adjacency. It also shows that there is not a uniquely best pair of adjacencies with respect to the estimation of the Euler number of a set in Euclidean space.
J. Ohser; W. Nagel; K. Schladitz
report
https://kluedo.ub.unikl.de/frontdoor/index/index/docId/1486
Mon, 02 Feb 2004 15:00:22 +0100