A high-order accurate upwind compact difference scheme with an optimal control coefficient is developed to track the flame front of a premixed V-flame. In multi-dimensional problems, dispersion effect appears in the f...
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A high-order accurate upwind compact difference scheme with an optimal control coefficient is developed to track the flame front of a premixed V-flame. In multi-dimensional problems, dispersion effect appears in the form of anisotropy. By means of Fourier analysis of the operators, anisotropic effects of the upwind compact difference schemes are analysed. Based on a level set algorithm with the effect of exothermicity and baroclinicity, the flame front is tracked. The high-order accurate upwind compact scheme is employed to approximate the levelset equation. In order to suppress numerical oscillations, the group velocity control technique is used and the upwind compact difference scheme is combined with the random vortex method to simulate the turbulent premixed V-flame. Distributions of velocities and flame brush thickness are obtained by this technique and found to be comparable with experimental measurement. Copyright (c) 2005 John Wiley & Sons, Ltd.
Understanding the stability of fluid interfaces subjected to small vibrations under microgravity conditions is important for designing future materials science experiments to be conducted aboard orbiting spacecraft. D...
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Understanding the stability of fluid interfaces subjected to small vibrations under microgravity conditions is important for designing future materials science experiments to be conducted aboard orbiting spacecraft. During the STS-85 mission, experiments investigating the motion of a large bubble resulting from small, controlled vibrations were performed aboard the Space Shuttle Discovery. To better understand the experimental results, two- and three-dimensional simulations of the experiment were performed using levelset and volume-of-fluid interface tracking algorithms. The simulations proved capable of predicting accurately the experimentally determined bubble translation behavior. Linear dependence of the bubble translation amplitude on the container translation amplitude was confirmed. In addition, the simulation model was used to confirm predictions of a theoretical inviscid model of bubble motion developed in a previous study.
An important class of generalized eigenvalue problems Ax = lambdaBx is those in which A and B are Hermitian and some real linear combination of them is definite. For the quadratic eigenvalue problem (QEP) (lambda(2)A ...
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An important class of generalized eigenvalue problems Ax = lambdaBx is those in which A and B are Hermitian and some real linear combination of them is definite. For the quadratic eigenvalue problem (QEP) (lambda(2)A +lambdaB + C)x = 0 with Hermitian A, B and C and positive definite A, particular interest focuses on problems in which (x*Bx)(2) - 4(x*Ax)(x*Cx) is one-signed for all non-zero x-for the positive sign these problems are called hyperbolic and for the negative sign elliptic. The important class of overdamped problems arising in mechanics is a sub-class of the hyperbolic problems. For each of these classes of generalized and quadratic eigenvalue problems we show how to check that a putative member has the required properties and we derive the distance to the nearest problem outside the class. For definite pairs (A, B) the distance is the Crawford number, and we derive bisection and level set algorithms both for testing its positivity and for computing it. Testing hyperbolicity of a QEP is shown to reduce to testing a related pair for definiteness. The distance to the nearest non-hyperbolic or non-elliptic n x n QEP is shown to be the solution of a global minimization problem with n - 1 dearees of freedom. Numerical results are given to illustrate the theory and algorithms. (C) 2002 Published by Elsevier Science Inc.
For treatment of abdominal aortic aneurysm (AAA) by placement of aortic stent graft device it Is necessary to make accurate AAA measurements in order to choose the stent graft device of appropriate shape and size. In ...
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ISBN:
(纸本)078036466X
For treatment of abdominal aortic aneurysm (AAA) by placement of aortic stent graft device it Is necessary to make accurate AAA measurements in order to choose the stent graft device of appropriate shape and size. In this paper, we propose a novel technique for 3-D segmentation of abdominal aortic aneurysm from computed tomography (CT) angiography images. The technique is based on 3-D deformable model and utilizes the level set algorithm for implementation of the method. The method performs 3-D segmentation of CT images and extracts a 3-D AAA model. Once the 3-D model of AAA is available it is easy to perform all required measurements for appropriate stent graft selection. The method proposed in this paper uses the level-setalgorithm instead of the classical active contour algorithm developed by Kass et al. The main advantage of the level set algorithm is that it enables easy segmentation of complex structures such as bifurcations in arteries. In the levelset approach for shape modeling, a 3-D surface is represented by a real 3-D function that can be viewed as a 4-D surface. The 4-D surface evolves through an iterative process of solving the differential equation of surface motion. The surface motion is defined by velocity at each point. The velocity is a sum of a constant velocity (inflation force), curvature-dependent velocity (internal force), and image-dependent velocity (external force). The image-dependent velocity is computed on the basis of image gradient. The algorithm has been Implemented in MATLAB and C languages. Experiments have been performed using real patient CT angiography images and have shown good results. A 3-D rendering of the segmented region is performed that is useful for aneurysm shape visualization.
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