Home About us Contact
|
Home About us Contact | ||
|
|
||
Numerical Tools (numerical + tool)
Selected AbstractsScalable Numerical Tools for Flow and Pressure Drop Computation in Fibrous Filter MediaCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 5 2009F. Strauß Abstract The prediction of flow behavior and pressure drop in fibrous filter media is challenging due to the complexity of the nonuniform fiber structure. Numerical calculation tools can considerably contribute to pressure drop determination for inhomogeneous filter structures. A numerical solution approach based on the finite element method to simulate 2D and 3D filter structures is considered. As numerical examples, computer designed homogeneous and inhomogeneous 2D cases where the numerical approach is validated by analytical models are investigated. Furthermore, the capability of the numerical method to simulate real 3D structures corresponding to more than 25 million degrees of freedom of the related algebraic system is demonstrated. The large systems involved require the use of dedicated techniques related to high performance computing. [source] Computational form-finding of tension membrane structures,Non-finite element approaches: Part 1.INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2003Use of cubic splines in finding minimal surface membranes Abstract This paper, presented in three parts, discusses a computational methodology for form-finding of tension membrane structures (TMS), or fabric structures, used as roofing forms. The term ,form-finding' describes a process of finding the shape of a TMS under its initial tension. Such a shape is neither known a priori, nor can it be described by a simple mathematical function. The work is motivated by the need to provide an efficient numerical tool, which will allow a better integration of the design/analysis/manufacture of TMS. A particular category of structural forms is considered, known as minimal surface membranes (such as can be reproduced by soap films). The numerical method adopted throughout is dynamic relaxation (DR) with kinetic damping. Part 1 describes a new form-finding approach, based on the Laplace,Young equation and cubic spline fitting to give a full, piecewise, analytical description of a minimal surface. The advantages arising from the approach, particularly with regard to manufacture of cutting patterns for a membrane, are highlighted. Part 2 describes an alternative and novel form-finding approach, based on a constant tension field and faceted (triangular mesh) representation of the minimal surface. It presents techniques for controlling mesh distortion and discusses effects of mesh control on the accuracy and computational efficiency of the solution, as well as on the subsequent stages in design. Part 3 gives a comparison of the performance of the initial method (Part 1) and the faceted approximations (Part 2). Functional relations, which encapsulate the numerical efficiency of each method, are presented. Copyright © 2002 John Wiley & Sons, Ltd. [source] Computational form-finding of tension membrane structures,Non-finite element approaches: Part 2.INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2003Triangular mesh discretization, control of mesh distortion in modelling minimal surface membranes Abstract This paper, presented in three parts, discusses a computational methodology for form-finding of tension membrane structures (TMS), or fabric structures, used as roofing forms. The term ,form-finding' describes a process of finding the shape of a TMS under its initial tension. Such a shape is neither known a priori, nor can it be described by a simple mathematical function. The work is motivated by the need to provide an efficient numerical tool, which will allow a better integration of the design/analysis/manufacture of TMS. A particular category of structural forms is considered, known as minimal surface membranes (such as can be reproduced by soap films). The numerical method adopted throughout is dynamic relaxation (DR) with kinetic damping. Part 1 gave a background to the problem of TMS design, described the DR method, and presented a new form-finding methodology, based on the Laplace,Young equation and cubic spline fitting to give a full, piecewise, analytical description of the surface. Part 2 describes an alternative and novel form-finding method, based on a constant tension field and faceted (triangular mesh) representation of the minimal surface. Techniques for controlling mesh distortion are presented, and their effects on the accuracy and computational efficiency of the solution, as well as on the subsequent stages in design, are examined. Part 3 gives a comparison of the performance of the initial method (Part 1) and the faceted approximations (Part 2). Functional relations, which encapsulate the numerical efficiency of each method, are presented. Copyright © 2002 John Wiley & Sons, Ltd. [source] Numerical methods for large-eddy simulation in general co-ordinatesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2004Gefeng Tang Abstract Large scale unsteady motions in many practical engineering flows play a very important role and it is very unlikely that these unsteady flow features can be captured within the framework of Reynolds averaged Navier,Stokes approach. Large-eddy simulation (LES) has become, arguably, the only practical numerical tool for predicting those flows more accurately since it is still not realistic to apply DNS to practical engineering flows with the current and near future available computing power. Numerical methods for the LES of turbulent flows in complex geometry have been developed and applied to predict practical engineering flows successfully. The method is based on body-fitted curvilinear co-ordinates with the contravariant velocity components of the general Navier,Stokes equations discretized on a staggered orthogonal mesh. For incompressible flow simulations the main source of computational expense is due to the solution of a Poisson equation for pressure. This is especially true for flows in complex geometry. A multigrid 3D pressure solver is developed to speed up the solution. In addition, the Poisson equation for pressure takes a simpler form with no cross-derivatives when orthogonal mesh is used and hence resulting in increased convergence rate and producing more accurate solutions. Copyright © 2004 John Wiley & Sons, Ltd. [source] Modeling UHMWPE wear debris generationJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2007H. Baudriller Abstract It is widely recognized that polyethylene wear debris is one of the main causes of long-term prosthesis loosening. The noxious bioreactivity associated with this debris is determined by its size, shape, and quantity. The aim of this study was to develop a numerical tool that can be used to investigate the primary polyethylene wear mechanisms involved. This model illustrates the formation of varying flow of polyethylene debris with various shapes and sizes caused by elementary mechanical processes. Instead of using the classical continuum mechanics formulation for this purpose, we used a divided materials approach to simulate debris production and release. This approach involves complex nonlinear bulk behaviors, frictional adhesive contact, and characterizes material damage as a loss of adhesion. All the associated models were validated with various benchmark tests. The examples given show the ability of the numerical model to generate debris of various shapes and sizes such as those observed in implant retrieval studies. Most of wear mechanisms such as abrasion, adhesion, and the shearing off of micro-asperities can be described using this approach. Furthermore, it could be applied to study the effects of friction couples, macroscopic geometries, and material processing (e.g. irradiation) on wear. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007 [source] The geometric minimum action method: A least action principle on the space of curvesCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 8 2008Matthias Heymann Freidlin-Wentzell theory of large deviations for the description of the effect of small random perturbations on dynamical systems is exploited as a numerical tool. Specifically, a numerical algorithm is proposed to compute the quasi-potential in the theory, which is the key object to quantify the dynamics on long time scales when the effect of the noise becomes ubiquitous: the equilibrium distribution of the system, the pathways of transition between metastable states and their rate, etc., can all be expressed in terms of the quasi-potential. We propose an algorithm to compute these quantities called the geometric minimum action method (gMAM), which is a blend of the original minimum action method (MAM) and the string method. It is based on a reformulation of the large deviations action functional on the space of curves that allows one to easily perform the double minimization of the original action required to compute the quasi-potential. The theoretical background of the gMAM in the context of large deviations theory is discussed in detail, as well as the algorithmic aspects of the method. The gMAM is then illustrated on several examples: a finite-dimensional system displaying bistability and modeled by a nongradient stochastic ordinary differential equation, an infinite-dimensional analogue of this system modeled by a stochastic partial differential equation, and an example of a bistable genetic switch modeled by a Markov jump process. © 2007 Wiley Periodicals, Inc. [source] Minimum action method for the study of rare eventsCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 5 2004Weinan E The least action principle from the Wentzell-Freidlin theory of large deviations is exploited as a numerical tool for finding the optimal dynamical paths in spatially extended systems driven by a small noise. The action is discretized and a preconditioned BFGS method is used to optimize the discrete action. Applications are presented for thermally activated reversal in the Ginzburg-Landau model in one and two dimensions, and for noise induced excursion events in the Brusselator taken as an example of non-gradient system arising in chemistry. In the Ginzburg-Landau model, the reversal proceeds via interesting nucleation events, followed by propagation of domain walls. The issue of nucleation versus propagation is discussed and the scaling for the number of nucleation events as a function of the reversal time and other material parameters is computed. Good agreement is found with the numerical results. In the Brusselator, whose deterministic dynamics has a single stable equilibrium state, the presence of noise is shown to induce large excursions by which the system cycles out of this equilibrium state. © 2004 Wiley Periodicals, Inc. [source] Transient solution for multilayered poroviscoelastic media obtained by an exact stiffness matrix formulationINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 18 2009A. Mesgouez Abstract The authors propose a semi-analytical approach to studying wave propagation in multilayered poroviscoelastic grounds due to transient loads. The theoretical development is based on the exact stiffness matrix method for the Biot theory coupled with a matrix conditioning technique. It is developed in the wavenumber frequency domain after a Fourier transform on the surface space variables and the time variable. The usual methods yield a poorly conditioned numerical system. This is due in particular to the presence of mismatched exponential terms. In this article, increasing exponential terms are eliminated and only decreasing exponential terms remain. Consequently, the method can be applied to a large field of configurations without restriction concerning high frequencies, large Fourier transform parameters or large layer thicknesses. Validation and efficiency of the method are discussed. Effects of layering show that the layer impedance influence on solid and fluid displacements. Moreover, this approach can be of interest for the validation of numerical tools. Copyright © 2009 John Wiley & Sons, Ltd. [source] A robust methodology for RANS simulations of highly underexpanded jetsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2008G. Lehnasch Abstract This work aims at developing/combining numerical tools adapted to the simulation of the near field of highly underexpanded jets. An overview of the challenging numerical problems related to the complex shock/expansion structure encountered in these flows is given and an efficient and low-cost numerical strategy is proposed to overcome these, even on short computational domains. Based on common upwinding algorithms used on unstructured meshes in a mixed finite-volume/finite-element approach, it relies on an appropriate utilization of zonal anisotropic remeshing algorithms. This methodology is validated for the whole near field of cold air jets issuing from axisymmetric convergent nozzles and yielding various underexpansion ratios. In addition, the most usual corrections of the k,, model used to take into account the compressibility effects on turbulence are precisely assessed. Copyright © 2007 John Wiley & Sons, Ltd. [source] High-order ENO and WENO schemes for unstructured gridsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2007W. R. Wolf Abstract This work describes the implementation and analysis of high-order accurate schemes applied to high-speed flows on unstructured grids. The class of essentially non-oscillatory schemes (ENO), that includes weighted ENO schemes (WENO), is discussed in the paper with regard to the implementation of third- and fourth-order accurate methods. The entire reconstruction process of ENO and WENO schemes is described with emphasis on the stencil selection algorithms. The stencils can be composed by control volumes with any number of edges, e.g. triangles, quadrilaterals and hybrid meshes. In the paper, ENO and WENO schemes are implemented for the solution of the dimensionless, 2-D Euler equations in a cell centred finite volume context. High-order flux integration is achieved using Gaussian quadratures. An approximate Riemann solver is used to evaluate the fluxes on the interfaces of the control volumes and a TVD Runge,Kutta scheme provides the time integration of the equations. Such a coupling of all these numerical tools, together with the high-order interpolation of primitive variables provided by ENO and WENO schemes, leads to the desired order of accuracy expected in the solutions. An adaptive mesh refinement technique provides better resolution in regions with strong flowfield gradients. Results for high-speed flow simulations are presented with the objective of assessing the implemented capability. Copyright © 2007 John Wiley & Sons, Ltd. [source] Numerical analysis of deformed free surface under AC magnetic fieldsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2004Haruhiko Kohno Abstract A novel numerical scheme for the analysis of large deformation of electrically conducting liquid under alternating current magnetic fields is presented. The main features are characterized by two numerical tools; the level set method to calculate deformed free surface stably and the hybrid finite element method and boundary element method to discretize the electromagnetic field efficiently. Two-dimensional numerical simulation of conducting drop deformation is carried out to demonstrate the effectiveness of the present scheme, and the oscillatory behaviour, which depends on the magnitude of surface tension and Lorentz force, is investigated. Copyright © 2004 John Wiley & Sons, Ltd. [source] Normal form representation of control systemsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 5 2002Daizhan Cheng Abstract This paper is to investigate the normal form representation of control systems. First, as numerical tools we develop an algorithm for normal form expression and the matrix representation of the Lie derivative of a linear vector field over homogeneous vector fields. The concept of normal form is modified. Necessary and sufficient conditions for a linear transformation to maintain the Brunowsky canonical form are obtained. It is then shown that the shift term can always be linearized up to any degree. Based on this fact, linearization procedure is proposed and the related algorithms are presented. Least square linear approximations are proposed for non-linearizable systems. Finally, the method is applied to the ball and beam example. The efforts are focused on the numerical and computer realization of linearization process. Copyright © 2002 John Wiley & Sons, Ltd. [source] A comprehensive experimental study and numerical modeling of parison formation in extrusion blow molding,POLYMER ENGINEERING & SCIENCE, Issue 1 2007Azizeh-Mitra Yousefi Parison dimensions in extrusion blow molding are affected by two phenomena, swell due to stress relaxation and sag drawdown due to gravity. It is well established that the parison swell and sag are strongly dependent on the die geometry and the operating conditions. The availability of a modeling technique ensures a more accurate prediction of the entire blow molding process, as the proper prediction of the parison formation is the input for the remaining process phases. This study considers both the simulated and the experimental effects of the die geometry, the operating conditions, and the resin properties on the parison dimensions using high density polyethylene. Parison programming with a moving mandrel and the flow rate evolution in intermittent extrusion are also considered. The parison dimensions are measured experimentally by using the pinch-off mold technique on two industrial scale machines. The finite element software BlowParison® developed at IMI is used to predict the parison formation, taking into account the swell, sag, and nonisothermal effects. The comparison between the predicted parison/part dimensions and the corresponding experimental data demonstrates the efficiency of numerical tools in the prediction of the final part thickness and weight distributions. POLYM. ENG. SCI., 47:1,13, 2007. © 2006 Society of Plastics Engineers [source] Numerical Analysis of a Cyclical Loaded Construction under Corrosion DegradationPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005W. Dudda A contribution for analytical and numerical tools that permits of a deterministic evaluation of structure behavior in external conditions, under multiparameter and/or cyclic mechanical, thermal and chemical loads, is the aim of this paper. Particular structure elements undergo the plastic and corrosion degradation and they dissipate energy, which consists of irreversible contributions, like a work on the inelastic strains. The construction and its unit lifetime are estimated according to a dissipated energy criterion. The paper emphasizes the modeling and numerical implementation of degradation effects, such as cyclic plasticity, generated by mechanical and thermal loads, stress corrosion, electrochemical corrosion and low-cyclic corrosion. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Numerical Calculations of Spray Roasting Reactors of the Steel Industry with Special Emphasis on Fe2O3 -Particle FormationCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2007M. Beck Abstract This work presents numerical calculations for the lay-out of spray roasting reactors for the steel industry. In these reactors, a pickling liquor based on water and HCl containing FeCl2 is regenerated in a combustor leading to the formation of Fe2O3 particles. For the lay-out of these reactors, detailed knowledge of the flow and temperature field, the associated gas phase reactions, and especially, of the formation of the Fe2O3 particles is required. An extended particle formation model is presented which is based on earlier work. Finally, results for an industrial spray roasting reactor are given showing the potential of the numerical tools developed for the improvement of the technical lay-out of such thermal reactors. [source] | |||||||||||||