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Coarse Meshes (coarse + mesh)

Distribution by Scientific Domains

Engineering	82%
Information Science and Computing	11%

Selected Abstracts

Wrinkling Coarse Meshes on the GPU

COMPUTER GRAPHICS FORUM, Issue 3 2006
J. Loviscach
The simulation of complex layers of folds of cloth can be handled through algorithms which take the physical dynamics into account. In many cases, however, it is sufficient to generate wrinkles on a piece of garment which mostly appears spread out. This paper presents a corresponding fully GPU-based, easy-to-control, and robust method to generate and render plausible and detailed folds. This simulation is generated from an animated mesh. A relaxation step ensures that the behavior remains globally consistent. The resulting wrinkle field controls the lighting and distorts the texture in a way which closely simulates an actually deformed surface. No highly tessellated mesh is required to compute the position of the folds or to render them. Furthermore, the solution provides a 3D paint interface through which the user may bias the computation in such a way that folds already appear in the rest pose. Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Animation, I.3.7 [Computer Graphics]: Color, shading, shadowing, and texture [source]

Nonlinear transient dynamic analysis by explicit finite element with iterative consistent mass matrix

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 3 2009
Shen Rong Wu
Abstract Various mass matrices in the explicit finite element analyses of nonlinear transient dynamic problems are investigated. The matrices are obtained as a linear combination of lumped and consistent mass matrices. An iterative procedure to calculate the inverse of the consistent and the mixed mass matrices in the framework of explicit finite element method is presented. The convergence of the iterative procedure is proved. The inverse of the consistent and mixed mass matrices is approximated by the iteration and is used to compare the results from the lumped mass matrix. For the impact of a structural component and a vehicle, some difference in the results by using coarse mesh is observed. For the component using fine mesh, no significant difference is found. Copyright © 2008 John Wiley & Sons, Ltd. [source]

On the L2 and the H1 couplings for an overlapping domain decomposition method using Lagrange multipliers

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2007
P.-A. Guidault
Abstract In this paper, a comparison of the L2 and the H1 couplings is made for an overlapping domain decomposition method using Lagrange multipliers. The analysis of the local equations arising from the formulation of the coupling of two mechanical models shows that continuous weight functions are required for the L2 coupling term whereas both discontinuous and continuous weight functions can be used for the H1 coupling. The choice of the Lagrange multiplier space is discussed and numerically studied. The paper ends with some numerical examples of an end-loaded cantilever beam and a cracked plate under tension and shear. It is shown that the continuity enforced with the H1 coupling leads to a link with a flexibility that can be beneficial for coupling a very coarse mesh with a very fine one. To limit the effect of the volume coupling on the global response, a narrow coupling zone is recommended. In this case, volume coupling tends to a surface coupling, especially with a L2 coupling. Copyright © 2006 John Wiley & Sons, Ltd. [source]

The extended finite element method for rigid particles in Stokes flow

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2001
G. J. Wagner
Abstract A new method for the simulation of particulate flows, based on the extended finite element method (X-FEM), is described. In this method, the particle surfaces need not conform to the finite element boundaries, so that moving particles can be simulated without remeshing. The near field form of the fluid flow about each particle is built into the finite element basis using a partition of unity enrichment, allowing the simple enforcement of boundary conditions and improved accuracy over other methods on a coarse mesh. We present a weak form of the equations of motion useful for the simulation of freely moving particles, and solve example problems for particles with prescribed and unknown velocities. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Contribution of small insects to pollination of common buckwheat, a distylous crop

ANNALS OF APPLIED BIOLOGY, Issue 1 2009
Hisatomo Taki
Abstract Crop pollination by animals is an essential ecosystem service. Among animal-pollinated crops, distylous plants strongly depend on animal pollination. In distylous pollination systems, pollinator species are usually limited, although flowers of some distylous plants are visited by diverse animals. We studied the pollination biology of common buckwheat (Fagopyrum esculentum), a distylous crop mainly pollinated by honeybees and visited by many insect species, to evaluate the effects of non-honeybee species on pollination services. We focused on insects smaller than honeybees to determine their contribution to pollination. We applied pollination treatments with bags of coarse mesh to exclude flower visits by honeybees and larger insects and compared the seed set of bagged plants with that of untreated plants for pin and thrum flower morphs. We found a great reduction of seed set only in bagged pin flowers. We also confirmed that small insects, including ants, bees, wasps and flies, carried pin-morph pollen. These small insects transfer pollen from the short anthers of pin flowers to the short styles of thrum flowers, leading to sufficient seed set in thrum flowers. Consequently, small, non-honeybee insects have the potential to maintain at least half of the yield of this honeybee-dependent distylous crop. [source]

Physiologically correct animation of the heart

COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2008
Kyoungju Park
Abstract Physiologically correct animation of the heart should incorporate non-homogeneous and nonlinear motions of the heart. Therefore, we introduce a methodology that estimates deformations from volume images and utilizes them for animation. Since volume images are acquired at regular slicing intervals, they miss information between slices and recover deformation on the slices. Therefore, the estimated finite element models (FEMs) result in coarse meshes with chunk elements the sizes of which depend on the slice intervals. Thus, we introduce a method of generating a detailed model using implicit surfaces and transferring a deformation from a FEM to implicit surfaces. An implicit surface heart model is reconstructed using contour data points and then cross-parameterized to the heart FEM, the time-varying deformation of which has been estimated by tracking the insights of the heart wall. The implicit surface heart models are composed of four heart walls that are blended into one model. A correspondence map between the source and the target meshes is made using the template fitting method. Deformation coupling transfers the deformation of a coarse heart FEM model to a detailed implicit model by factorizing linear equations. We demonstrate the system and show the resulting deformation of an implicit heart model. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Energy-adjustable mechanism of the combined hybrid finite element method and improvement of Zienkiewicz's plate-element

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2005
Xiao-ping Xie
Abstract The combined hybrid finite element method for plate bending problems allows arbitrary combinations of deflection interpolation and bending moment approximations. A novel expression of the approach discloses the energy-adjustable mechanism of the hybrid variational principle to enhance accuracy and stability of displacement-based finite element models. For a given displacement approximation, appropriate choices of the bending moment mode and the combination parameter , , (0,1) can lead to accurate energy approximation which generally yields numerically high accuracy of the displacement and bending moment approximations. By virtue of this mechanism, improvement of Zienkiewicz's triangular plate-element is discussed. The deflection is approximated by Zienkiewicz incomplete cubic interpolation. And three kinds of bending moments approximations are considered: a 3-parameter constant mode, a 5-parameter incomplete linear mode, and a 9-parameter linear mode. Since the parameters of the assumed bending moments modes can be eliminated at an element level, the computational cost of the combined hybrid counterparts of Zienkiewicz's triangle are as same as that of Zienkiewicz's triangle. Numerical experiments show that the combined hybrid versions can attain high accuracy at coarse meshes. Copyright © 2005 John Wiley & Sons, Ltd. [source]

FLEXMG: A new library of multigrid preconditioners for a spectral/finite element incompressible flow solver

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2010
M. Rasquin
Abstract A new library called FLEXMG has been developed for a spectral/finite element incompressible flow solver called SFELES. FLEXMG allows the use of various types of iterative solvers preconditioned by algebraic multigrid methods. Two families of algebraic multigrid preconditioners have been implemented, namely smooth aggregation-type and non-nested finite element-type. Unlike pure gridless multigrid, both of these families use the information contained in the initial fine mesh. A hierarchy of coarse meshes is also needed for the non-nested finite element-type multigrid so that our approaches can be considered as hybrid. Our aggregation-type multigrid is smoothed with either a constant or a linear least-square fitting function, whereas the non-nested finite element-type multigrid is already smooth by construction. All these multigrid preconditioners are tested as stand-alone solvers or coupled with a GMRES method. After analyzing the accuracy of the solutions obtained with our solvers on a typical test case in fluid mechanics, their performance in terms of convergence rate, computational speed and memory consumption is compared with the performance of a direct sparse LU solver as a reference. Finally, the importance of using smooth interpolation operators is also underlined in the study. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Improved four-node Hellinger,Reissner elements based on skew coordinates

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2008
K. Wisniewski
Abstract Mixed four-node elements based on the Hellinger,Reissner (HR) functional are developed for stress representations in various coordinates, including the skew, natural and Cartesian ones. The two-field HR functional is used in the classical form and in the incremental form suitable for non-linear materials. We argue that the skew coordinates, not the natural ones, should be associated with the natural basis at the element's center. If 5- and 7-parameter stress representations are assumed in these coordinates, then, for a linear elastic case, the homogenous equilibrium equations and the stress form of compatibility equation are satisfied point-wise. Two mixed four-node elements are developed and tested: 1.An assumed stress element (HR5-S) is developed from the non-enhanced HR functional, for a 5-parameter representation of stresses, formally identical as the one used, for example, in Pian and Sumihara [Int. J. Numer. Meth. Engng 1984; 20:1685,1695], but in terms of skew coordinates. This element is very simple and uses a smaller number of parameters, but is equally accurate as the elements by Yuan et al. [Int. J. Numer. Meth. Engng 1993; 36:1747,1763] and by Piltner and Taylor [Int. J. Numer. Meth. Engng 1995; 38:1783,1808]. 2.An assumed stress/enhanced strain element (HR9) is developed from the enhanced HR functional, for a 7-parameter representation of stress and a 2-parameter enhanced assumed displacement gradient or enhanced assumed strain enhancement. Various forms of 7-parameter representations appearing in the literature are reviewed, and we prove that they are linked by a linear onto transformation. The choice of coordinates for the stress and the enhancement turns out to be the crucial factor, and four combinations of coordinates for which the element performs the best are identified. Both elements are based on the Green strain, and several numerical tests show their good accuracy, in particular, their robustness to shape distortions for coarse meshes. Two update schemes for the multipliers of modes and the incremental constitutive procedure accounting for the plane stress condition for non-linear materials are tested for large deformation problems. Copyright © 2008 John Wiley & Sons, Ltd. [source]

A cut-cell non-conforming Cartesian mesh method for compressible and incompressible flow

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2007
J. Pattinson
Abstract This paper details a multigrid-accelerated cut-cell non-conforming Cartesian mesh methodology for the modelling of inviscid compressible and incompressible flow. This is done via a single equation set that describes sub-, trans-, and supersonic flows. Cut-cell technology is developed to furnish body-fitted meshes with an overlapping mesh as starting point, and in a manner which is insensitive to surface definition inconsistencies. Spatial discretization is effected via an edge-based vertex-centred finite volume method. An alternative dual-mesh construction strategy, similar to the cell-centred method, is developed. Incompressibility is dealt with via an artificial compressibility algorithm, and stabilization achieved with artificial dissipation. In compressible flow, shocks are captured via pressure switch-activated upwinding. The solution process is accelerated with full approximation storage (FAS) multigrid where coarse meshes are generated automatically via a volume agglomeration methodology. This is the first time that the proposed discretization and solution methods are employed to solve a single compressible,incompressible equation set on cut-cell Cartesian meshes. The developed technology is validated by numerical experiments. The standard discretization and alternative methods were found equivalent in accuracy and computational cost. The multigrid implementation achieved decreases in CPU time of up to one order of magnitude. Copyright © 2007 John Wiley & Sons, Ltd. [source]

A practical large-strain solid finite element for sheet forming

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2005
Jue Wang
Abstract An alternative approach for developing practical large-strain finite elements has been introduced and used to create a three-dimensional solid element that exhibits no locking or hourglassing, but which is more easily and reliably derived and implemented than typical reduced-integration schemes with hourglassing control. Typical large-strain elements for forming applications rely on reduced integration to remove locking modes that occur with the coarse meshes that are necessary for practical use. This procedure introduces spurious zero-energy deformation modes that lead to hourglassing, which in turn is controlled by complex implementations that involve lengthy derivations, knowledge of the material model, and/or undetermined parameters. Thus, for a new material or new computer program, implementation of such elements is a daunting task. Wang,Wagoner-3-dimensions (WW3D), a mixed, hexahedral, three-dimensional solid element, was derived from the standard linear brick element by ignoring the strain components corresponding to locking modes while maintaining full integration (8 Gauss points). Thus, WW3D is easily implemented for any material law, with little chance of programming error, starting from programming for a readily available linear brick element. Surprisingly, this approach and resulting element perform similarly or better than standard solid elements in a series of numerical tests appearing in the literature. The element was also tested successfully for an applied sheet-forming analysis problem. Many variations on the scheme are also possible for deriving special-purpose elements. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Numerical study of grid distribution effect on accuracy of DQ analysis of beams and plates by error estimation of derivative approximation

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2001
C. Shu
Abstract The accuracy of global methods such as the differential quadrature (DQ) approach is usually sensitive to the grid point distribution. This paper is to numerically study the effect of grid point distribution on the accuracy of DQ solution for beams and plates. It was found that the stretching of grid towards the boundary can improve the accuracy of DQ solution, especially for coarse meshes. The optimal grid point distribution (corresponding to optimal stretching parameter) depends on the order of derivatives in the boundary condition and the number of grid points used. The optimal grid distribution may not be from the roots of orthogonal polynomials. This differs somewhat from the conventional analysis. This paper also proposes a simple and effective formulation for stretching the grid towards the boundary. The error distribution of derivative approximation is also studied, and used to analyze the effect of grid point distribution on accuracy of numerical solutions. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Multi-material incompressible flow simulation using the moment-of-fluid method,

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2010
Samuel P. Schofield
Abstract This paper compares the numerical performance of the moment-of-fluid (MOF) interface reconstruction technique with Youngs, LVIRA, power diagram (PD), and Swartz interface reconstruction techniques in the context of a volume-of-fluid (VOF) based finite element projection method for the numerical simulation of variable-density incompressible viscous flows. In pure advection tests with multiple materials MOF shows dramatic improvements in accuracy compared with the other methods. In incompressible flows where density differences determine the flow evolution, all the methods perform similarly for two material flows on structured grids. On unstructured grids, the second-order MOF, LVIRA, and Swartz methods perform similarly and show improvement over the first-order Youngs' and PD methods. For flow simulations with more than two materials, MOF shows increased accuracy in interface positions on coarse meshes. In most cases, the convergence and accuracy of the computed flow solution was not strongly affected by interface reconstruction method. Published in 2009 by John Wiley & Sons, Ltd. [source]

A lattice Boltzmann method for solute transport

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2009
Jian Guo Zhou
Abstract A lattice Boltzmann method is developed for solute transport. Proper expressions for the local equilibrium distribution functions enable the method to be formulated on rectangular lattice with the same simple procedure as that on a square lattice. This provides an additional advantage over a lattice Boltzmann method on a square lattice for problems characterized by dominant phenomenon in one direction and relatively weak in another such as solute transport in shear flow over a narrow channel, where the problems can efficiently be approached with fine and coarse meshes, respectively, resulting in more efficient algorithm. The stability conditions are also described. The proposed method on a square lattice is naturally recovered when a square lattice is used. It is verified by solving four tests and compared with the analytical/exact solutions. They are in good agreement, demonstrating that the method is simple, accurate and robust for solute transport. Copyright © 2008 John Wiley & Sons, Ltd. [source]

URANS computations for an oscillatory non-isothermal triple-jet using the k,, and second moment closure turbulence models

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2003
M. Nishimura
Abstract Low Reynolds number turbulence stress and heat flux equation models (LRSFM) have been developed to enhance predictive capabilities. A new method is proposed for providing the wall boundary condition for dissipation rate of turbulent kinetic energy, ,, to improve the model capability upon application of coarse meshes for practical use. The proposed method shows good agreement with accepted correlations and experimental data for flows with various Reynolds and Prandtl numbers including transitional regimes. Also, a mesh width about 5 times or larger than that used in existing models is applicable by using the present boundary condition. The present method thus enhanced computational efficiency in applying the complex turbulence model, LRSFM, to predictions of complicated flows. Unsteady Reynolds averaged Navier,Stokes (URANS) computations are conducted for an oscillatory non-isothermal quasi-planar triple-jet. Comparisons are made between an experiment and predictions with the LRSFM and the standard k,, model. A water test facility with three vertical jets, the cold in between two hot jets, simulates temperature fluctuations anticipated at the outlet of a liquid metal fast reactor core. The LRSFM shows good agreement with the experiment, with respect to mean profiles and the oscillatory motion of the flow, while the k,, model under-predicts the mixing due to the oscillation, such that a transverse mean temperature difference remains far downstream. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Multiscalet basis in Galerkin's method for solving three-dimensional electromagnetic integral equations

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 4 2008
M. S. Tong
Abstract Multiscalets in the multiwavelet family are used as the basis and testing functions in Galerkin's method. Since the multiscalets are orthogonal to their translations under the Sobolev inner product, the resulting Galerkin's method behaves like a collocation method but possesses the ability of derivative tracking for unknown functions in solving integral equations. The former makes the method simple in implementation and the latter allows to use coarse meshes in discretization. These robust features have been demonstrated in solving two-dimensional (2D) electromagnetic (EM) problems, but have not been exploited in three-dimensional (3D) scenarios. For 3D problems, the unknown functions in the integral equations are dependent on two coordinate variables. In order to preserve the use of coarse meshes for 3D cases, we realize the omnidirectional derivative tracking by tracking the directional derivatives along two orthogonal directions, or equivalently tracking the gradient. This process yields a nonsquare matrix equation and we use the least-squares method (LSM) to solve it. Numerical examples show that the multiscalet-based Galerkin's method is also robust in solving for 3D EM integral equations with a minor cost increase from LSM. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Modelling electrospinning of nanofibres

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009
Tomasz A. Kowalewski
Electrospinning is based on so-called bending instability which results in an erratic spiralling motion of the liquid jet as it proceeds towards a collecting electrode, where it is eventually deposited as a mat of micro/nanosized fibres. Most electrospinning models formulated within the slender approximation rely, however, on an inconsistent description of electrostatic interactions which renders them grossly inappropriate whenever the discretization is either too coarse or too fine. The present work aims at proposing a discrete slender model which is numerically consistent (allowing use of arbitrary fine meshes) and remains accurate even for coarse meshes. At the same time, efficient numerical techniques based on hierarchical charge clustering are introduced that drastically decrease computational times. Finally, a versatile boundary value method is implemented to enforce fixed-potential boundary conditions, allowing realistic electrode configurations to be investigated. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]