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Kaiserslautern, Germany

Linden S.,University of Kaiserlautern | Linden S.,Fraunhofer Institute for Industrial Mathematics | Hagen H.,University of Kaiserlautern | Wiegmann A.,Math2Market GmbH
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2014

We introduce a novel multi-dimensional space partitioning method. A new type of tree combines the advantages of the Octree and the KD-tree without having their disadvantages. We present in this paper a new data structure allowing local refinement, parallelization and proper restriction of transition ratios between cells. Our technique has no dimensional restrictions at all. The tree's data structure is defined by a topological algebra based on the symbols A = {L, I, R} that encode the partitioning steps. The set of successors is restricted such that each cell has the partition of unity property to partition domains without overlap. With our method it is possible to construct a wide choice of spline spaces to compress or reconstruct scientific data such as pressure and velocity fields and multidimensional images. We present a generator function to build a tree that represents a voxel geometry. The space partitioning system is used as a framework to allow numerical computations. This work is triggered by the problem of representing, in a numerically appropriate way, huge three-dimensional voxel geometries that could have up to billions of voxels. © Springer-Verlag 2014. Source


Fallet A.,Constellium | Lhuissier P.,French National Center for Scientific Research | Salvo L.,French National Center for Scientific Research | Martin C.L.,French National Center for Scientific Research | And 2 more authors.
Scripta Materialia | Year: 2013

Random hollow sphere stackings present good performance for the seemingly contradictory requirements of a light structural material and good acoustic damping properties. A way to optimize the architectured materials parameters is described. The structural properties of random hollow sphere stacking have been measured using X-ray tomography and compared to an Artz compaction model. The mechanical properties are optimized according to the architectural parameters by way of coupled finite elements and discrete elements simulations, and acoustical properties are discussed based on tube absorption models. © 2012 Published by Elsevier Ltd. Source


Kling T.,Karlsruhe Institute of Technology | Huo D.,Stanford University | Schwarz J.O.,Johannes Gutenberg University Mainz | Schwarz J.O.,Math2Market GmbH | And 3 more authors.
Solid Earth | Year: 2016

Various geoscientific applications require a fast prediction of fracture permeability for an optimal workflow. Hence, the objective of the current study is to introduce and validate a practical method to characterize and approximate single flow in fractures under different stress conditions by using a core-flooding apparatus, in situ X-ray computed tomography (CT) scans and a finite-volume method solving the Navier-Stokes-Brinkman equations. The permeability of the fractured sandstone sample was measured stepwise during a loading-unloading cycle (0.7 to 22.1MPa and back) to validate the numerical results. Simultaneously, the pressurized core sample was imaged with a medical X-ray CT scanner with a voxel dimension of 0.5 × 0.5 × 1.0mm3. Fracture geometries were obtained by CT images based on a modification of the simplified missing attenuation (MSMA) approach. Simulation results revealed both qualitative plausibility and a quantitative approximation of the experimentally derived permeabilities. The qualitative results indicate flow channeling along several preferential flow paths with less pronounced tortuosity. Significant changes in permeability can be assigned to temporal and permanent changes within the fracture due to applied stresses. The deviations of the quantitative results appear to be mainly caused by both local underestimation of hydraulic properties due to compositional matrix heterogeneities and the low CT resolution affecting the accurate capturing of sub-grid-scale features. Both affect the proper reproduction of the actual connectivity and therefore also the depiction of the expected permeability hysteresis. Furthermore, the threshold value CTmat (1862.6HU) depicting the matrix material represents the most sensitive input parameter of the simulations. Small variations of CTmat can cause enormous changes in simulated permeability by up to a factor of 2.6±0.1 and, thus, have to be defined with caution. Nevertheless, comparison with further CT-based flow simulations indicates that the proposed method represents a valuable method to approximate actual permeabilities, particularly for smooth fractures (<35μm). However, further systematic investigations concerning the applicability of the method are essential for future studies. Thus, some recommendations are compiled by also including suggestions of comparable studies. © 2016 Author(s). Source


Janousch C.,Aalen University of Applied Sciences | Winkler R.,Aalen University of Applied Sciences | Wiegmann A.,Math2Market GmbH | Pannert W.,Aalen University of Applied Sciences | And 2 more authors.
Materialwissenschaft und Werkstofftechnik | Year: 2014

Customers nowadays regard the noise and vibration behavior as an essential product property. Cellular character materials, in particular hollow sphere structures, are predestined to absorb sound in a very efficient manner due to their cellular character. Depending on the constituent material, the geometric parameters like the diameter of the spheres, the thickness of the walls and the assembling schema of single spheres, the absorption coefficient can be reduced to very low levels. In contrast to other cellular materials, the frequency and bandwidth can actively be influenced by the variation of the above mentioned parameters. In order to predict the acoustic behavior of a structure, FE or CFD analyses are used as standard tools. In addition, there exist some parameter based models, e.g. the BIOT theory, which characterizes the absorption, transmission and reflection coefficients using a few macroscopic parameters. Within this contribution, the acoustic properties of hollow sphere structures are investigated by a so-called virtual material laboratory GeoDict (by Math2Market GmbH, originally by the Fraunhofer Institute for Industrial Mathematics). The results for the absorption and reflection coefficients are compared to those gained by classical analysis methods and experiments based on Kundt's tube. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Maus S.,University of Bergen | Leisinger S.,Swiss Federal Institute of forest | Matzl M.,Swiss Federal Institute of forest | Schneebeli M.,Swiss Federal Institute of forest | Wiegmann A.,Math2Market GmbH
Proceedings of the International Conference on Port and Ocean Engineering under Arctic Conditions, POAC | Year: 2013

Oil entrapment in drifting sea ice may lead to release of oil far away from spilling locations, when the ice finally melts at the end of its drift. The entrapment process hence needs to be understood properly to evaluate the environmental risks of oil spills in ice-covered waters. However, field studies of oil-in-ice processes are sparse, while laboratory tests do not necessarily represent natural sea ice in terms of growth conditions, time scales and, in particular, microstructures. In this study we consider the role that the microstructure of sea ice may play for oil entrapment. We discuss oil migration into the sea ice pore space on the basis of 3-d images of young winter sea ice, obtained by X-ray micro-tomography. Simulating fluid flow through these images we obtain the vertical distribution of sea ice permeability and pore size distributions, the basic parameter for the prediction of migration of oil into the ice. We compare the analysis with published results from laboratory experiments of oil entrapment in laboratory-grown ice of similar age. Our analysis suggests that care must be taken when interpreting laboratory experiments, due to limited oil amounts released. Furthermore, we perform a similar analysis of older and thicker summer ice that has similar porosity yet coarser pores. The potential of the old ice to entrap oil is expected to be an order of magnitude larger than indicated by results with young laboratory-grown ice. Due to the importance of sea ice microstructure to predict oil entrapment and transport, future approaches should include models of sea ice microstructure evolution with growth and melt conditions. Source

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