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Complicated Geometry (complicated + geometry)
Selected AbstractsVolume determination for bulk materials in bunkersINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2004S. A. Ahmed Abstract A simple model for the determination of the shape of large granular piles in complicated geometries is discussed. An eikonal formulation of the problem is proposed. Two distinct cases arise. In cylindrical geometries, i.e., if both container and possible obstacles have vertical walls, the problem is equivalent to a two-dimensional travel time problem with obstacles, while in general geometries, this analogy breaks down. In the first case, classical one-sided discretizations are generalized to handle obstacles without loss in accuracy. In the second case, a fast and efficient numerical method is proposed, implemented and tested. The discrete problems are solved through fast marching. Copyright © 2004 John Wiley & Sons, Ltd. [source] A lattice Boltzmann-BGK algorithm for a diffusion equation with Robin boundary condition,application to NMR relaxationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2009A. Hiorth Abstract We present a lattice Boltzmann-BGK (LBGK) algorithm for a diffusion equation together with a Robin boundary condition, which we apply in the case of nuclear magnetic resonance relaxation. The boundary condition we employ is independent of the direction of the wall. This makes the algorithm very suitable for complicated geometries, such as porous media. We discuss the effect of lattice topology by using, respectively, an eight-speed and a four-speed lattice. The numerical algorithm is compared with analytical results for a square and an equilateral triangle. The eight-speed lattice performs well in both cases. The four-speed lattice performs well for the square, but fails in the case of an equilateral triangle. Comparison with a random walk algorithm is also included. The LBGK algorithm presented here can also be used for a convective diffusion problem if the speed of the fluid can be neglected close to the boundary. Copyright © 2008 John Wiley & Sons, Ltd. [source] A new formulation of Signorini's type for seepage problems with free surfacesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2005H. Zheng Abstract A new variational inequality formulation for seepage problems with free surfaces is presented, in which a boundary condition of Signorini's type is prescribed over the potential seepage surfaces. This makes the singularity of seepage points eliminated and the location of seepage points determined easily. Compared to other variational formulations, the proposed formulation can effectively overcome the mesh dependency and significantly improve the numerical stability. A very challenging engineering example with complicated geometry and strong inhomogeneity is investigated in detail. Copyright © 2005 John Wiley & Sons, Ltd. [source] Non-reflecting artificial boundaries for transient scalar wave propagation in a two-dimensional infinite homogeneous layerINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2003Chongbin Zhao Abstract This paper presents an exact non-reflecting boundary condition for dealing with transient scalar wave propagation problems in a two-dimensional infinite homogeneous layer. In order to model the complicated geometry and material properties in the near field, two vertical artificial boundaries are considered in the infinite layer so as to truncate the infinite domain into a finite domain. This treatment requires the appropriate boundary conditions, which are often referred to as the artificial boundary conditions, to be applied on the truncated boundaries. Since the infinite extension direction is different for these two truncated vertical boundaries, namely one extends toward x ,, and another extends toward x,- ,, the non-reflecting boundary condition needs to be derived on these two boundaries. Applying the variable separation method to the wave equation results in a reduction in spatial variables by one. The reduced wave equation, which is a time-dependent partial differential equation with only one spatial variable, can be further changed into a linear first-order ordinary differential equation by using both the operator splitting method and the modal radiation function concept simultaneously. As a result, the non-reflecting artificial boundary condition can be obtained by solving the ordinary differential equation whose stability is ensured. Some numerical examples have demonstrated that the non-reflecting boundary condition is of high accuracy in dealing with scalar wave propagation problems in infinite and semi-infinite media. Copyright © 2003 John Wiley & Sons, Ltd. [source] A mesh patching method for finite volume modelling of shallow water flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2006Keming Hu Abstract A new mesh-patching model is presented for shallow water flow described by the 2D non-linear shallow water (NLSW) equations. The mesh-patching model is based on AMAZON, a high-resolution NLSW engine with an improved HLLC approximate Riemann solver. A new patching algorithm has been developed, which not only provides improved spatial resolution of flow features in particular parts of the mesh, but also simplifies and speeds up the (structured) grid generation process for an area with complicated geometry. The new patching technique is also compatible with increasingly popular parallel computing and adaptive grid techniques. The patching algorithm has been tested with moving bores, and results of test problems are presented and compared to previous work. Copyright © 2005 John Wiley & Sons, Ltd. [source] The direct simulation Monte Carlo method using unstructured adaptive mesh and its applicationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2002J.-S. Wu Abstract The implementation of an adaptive mesh-embedding (h-refinement) scheme using unstructured grid in two-dimensional direct simulation Monte Carlo (DSMC) method is reported. In this technique, local isotropic refinement is used to introduce new mesh where the local cell Knudsen number is less than some preset value. This simple scheme, however, has several severe consequences affecting the performance of the DSMC method. Thus, we have applied a technique to remove the hanging node, by introducing the an-isotropic refinement in the interfacial cells between refined and non-refined cells. Not only does this remedy increase a negligible amount of work, but it also removes all the difficulties presented in the originals scheme. We have tested the proposed scheme for argon gas in a high-speed driven cavity flow. The results show an improved flow resolution as compared with that of un-adaptive mesh. Finally, we have used triangular adaptive mesh to compute a near-continuum gas flow, a hypersonic flow over a cylinder. The results show fairly good agreement with previous studies. In summary, the proposed simple mesh adaptation is very useful in computing rarefied gas flows, which involve both complicated geometry and highly non-uniform density variations throughout the flow field. Copyright © 2002 John Wiley & Sons, Ltd. [source] Modelling of a pin-fin heat converter with fluid cooling for power semiconductor modulesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2003Igor Khorunzhii Abstract This paper presents a way to design a finite-element computer model of cooling system with a complicated geometry. The computer model is developed on the basis of a commercial software package ABAQUS. The steady state forced-convective fluid cooling of a pin-fin heat converter for power (,1 kW heat power) semiconductor module has been investigated on the basis of computer simulation. A phenomenological equation has been used for calculation of the local value of the heat transfer coefficient for the liquid-solid interface. The impacts of the thermal conductivity of the pin-fin sink material, volume flow rate of the cooling liquid and geometrical design of the pin-fin sink on the thermal resistance of the converter are shown. Copyright © 2003 John Wiley & Sons, Ltd. [source] Manufacturing Silicon Carbide Microrotors by Reactive Hot Isostatic Pressing within Micromachined Silicon MoldsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002Jing-Feng Li A novel ceramic microfabrication process,based on the idea of silicon carbide (SiC) reaction sintering within a micromachined silicon mold,has been developed to produce a SiC microroter for miniaturized gas turbines. The new process involves the micromachining of silicon molds; filling the molds with powder mixtures of ,-SiC, graphite, and phenol resin; bonding the molds with an adhesive; reaction sintering by hot isostatic pressing (HIP); and the releasing of a reaction-sintered workpiece from the mold by wet etching. Using this process, we have successfully fabricated SiC microrotors with a diameter of 5 mm, whose complicated geometry was well transferred from the negative shape of the micromachined silicon mold. The reaction-HIPed SiC ceramics within Si molds showed reasonably good mechanical properties, which are comparable to those of the commercialized reaction-sintered SiC ceramics. [source] Asymptotic analysis of flow in wavy tubes and simulation of the extrusion processMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 8 2007A. Ainser Abstract The paper is devoted to the mathematical modelling of an extrusion process. Usually, an extruder has a very complicated geometry. This generates a lot of difficulties for computations of three-dimensional flows. In the present paper, we develop and justify the asymptotic domain decomposition strategy in order to parallelize the computational process and reduce the memory. The error estimates are proved for the Stokes steady-state equation in the two-dimensional and three-dimensional cases. Then, the asymptotic domain decomposition procedure is applied for numerical testing and computations of the non-Newtonian fluid simulating a real process of the polymer extrusion. Copyright © 2007 John Wiley & Sons, Ltd. [source] The hybrid FEM,MOL approach for the analysis of scattering problemsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2002Ying Xiao Abstract In this Letter a hybrid approach combining the finite-element method and the method of lines is presented for solving the scattering problems of irregular geometry and inhomogeneity. In this approach, the FEM is used to treat the region with complicated geometry and inhomogeneous material profile, and the MoL acts as a radiation boundary condition for the FEM. The MoL can also treat layered regions. Because of the flexibility of the FEM and the semianalytical nature of the MoL, the flexibility, efficiency, and accuracy of these two methods are maintained. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 134,138, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10395 [source] | ||||||||||