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Tracking Algorithms (tracking + algorithms)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

Modeling three-dimensional crack propagation,A comparison of crack path tracking strategies

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 9 2008
P. Jäger
Abstract The development of a new finite element technique for the simulation of discontinuous failure phenomena in three dimensions is the key objective of this study. In contrast to the widely used extended finite element technique, we apply a purely deformation-based strategy based on an independent interpolation of the deformation field on both sides of the discontinuity. This method has been applied successfully for two-dimensional crack propagation problems in the past. However, when it comes to three-dimensional failure phenomena, it faces the same difficulties as the extended finite element method. Unlike in two dimensions, the characterization for the three-dimensional failure surface is non-unique and the tracking of the discrete crack can be performed in several conceptually different ways. In this work, we review the four most common three-dimensional crack tracking strategies. We perform a systematic comparison in terms of standard algorithmic quality measures such as mesh independency, efficiency, robustness, stability and computational cost. Moreover, we discuss more specific issues such as crack path continuity and integratability in commercial finite element packages. The features of the suggested crack tracking algorithms will be elaborated by means of characteristic benchmark problems in failure analysis. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Numerical errors of the volume-of-fluid interface tracking algorithm

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2002
Gregor, erne
Abstract One of the important limitations of the interface tracking algorithms is that they can be used only as long as the local computational grid density allows surface tracking. In a dispersed flow, where the dimensions of the particular fluid parts are comparable or smaller than the grid spacing, several numerical and reconstruction errors become considerable. In this paper the analysis of the interface tracking errors is performed for the volume-of-fluid method with the least squares volume of fluid interface reconstruction algorithm. A few simple two-fluid benchmarks are proposed for the investigation of the interface tracking grid dependence. The expression based on the gradient of the volume fraction variable is introduced for the estimation of the reconstruction correctness and can be used for the activation of an adaptive mesh refinement algorithm. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Ground truth hardware phantoms for validation of diffusion-weighted MRI applications

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2010
Pim Pullens MSc
Abstract Purpose: To quantitatively validate diffusion-weighted MRI (DW-MRI) applications, a hardware phantom containing crossing fibers at a sub-voxel level is presented. It is suitable for validation of a large spectrum of DW-MRI applications from acquisition to fiber tracking, which is an important recurrent issue in the field. Materials and Methods: Phantom properties were optimized to resemble properties of human white matter in terms of anisotropy, fractional anisotropy, and T2. Sub-voxel crossings were constructed at angles of 30, 50, and 65 degrees, by wrapping polyester fibers, with a diameter close to axon diameter, into heat shrink tubes. We show our phantoms are suitable for the acquisition of DW-MRI data using a clinical protocol. Results: The phantoms can be used to succesfully estimate both the diffusion tensor and non-Gaussian diffusion models, and perform streamline fiber tracking. DOT (Diffusion Orientation Transform) and q-ball reconstruction of the diffusion profiles acquired at b = 3000 s/mm2 and 132 diffusion directions reveal multimodal diffusion profiles in voxels containing crossing yarn strands. Conclusion: The highly purpose adaptable phantoms provide a DW-MRI validation platform: applications include optimisation of acquisition schemes, validation of non-Gaussian diffusion models, comparison and validation of fiber tracking algorithms, and quality control in multi-center DWI studies. J. Magn. Reson. Imaging 2010;32:482,488. © 2010 Wiley-Liss, Inc. [source]

Maximizing power production in a stack of microbial fuel cells using multiunit optimization method

BIOTECHNOLOGY PROGRESS, Issue 3 2009
Lyne Woodward
Abstract This study demonstrates real-time maximization of power production in a stack of two continuous flow microbial fuel cells (MFCs). To maximize power output, external resistances of two air,cathode membraneless MFCs were controlled by a multiunit optimization algorithm. Multiunit optimization is a recently proposed method that uses multiple similar units to optimize process performance. The experiment demonstrated fast convergence toward optimal external resistance and algorithm stability during external perturbations (e.g., temperature variations). Rate of the algorithm convergence was much faster than in traditional maximum power point tracking algorithms (MPPT), which are based on temporal perturbations. A power output of 81,84 mW/LA (A = anode volume) was achieved in each MFC. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source]