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Normal Velocity (normal + velocity)
Selected AbstractsOn the calculation of normals in free-surface flow problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 5 2004M. A. Walkley Abstract The use of boundary-conforming finite element methods is considered for the solution of surface-tension-dominated free-surface flow problems in three dimensions. This class of method is based upon the use of a moving mesh whose velocity is driven by the motion of the free surface, which is in turn determined via a kinematic boundary condition for the normal velocity. The significance of the method used to compute the normal direction at the finite element node points for a C0 piecewise-polynomial free surface is investigated. In particular, it is demonstrated that the concept of mass-consistent normals on an isoparametric quadratic tetrahedral mesh is flawed. In this case an alternative, purely geometric, normal is shown to lead to a far more robust numerical algorithm. Copyright © 2004 John Wiley & Sons, Ltd. [source] Numerical study of an inviscid incompressible flow through a channel of finite lengthINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2009Vasily N. Govorukhin Abstract A two-dimensional inviscid incompressible flow in a rectilinear channel of finite length is studied numerically. Both the normal velocity and the vorticity are given at the inlet, and only the normal velocity is specified at the outlet. The flow is described in terms of the stream function and vorticity. To solve the unsteady problem numerically, we propose a version of the vortex particle method. The vorticity field is approximated using its values at a set of fluid particles. A pseudo-symplectic integrator is employed to solve the system of ordinary differential equations governing the motion of fluid particles. The stream function is computed using the Galerkin method. Unsteady flows developing from an initial perturbation in the form of an elliptical patch of vorticity are calculated for various values of the volume flux of fluid through the channel. It is shown that if the flux of fluid is large, the initial vortex patch is washed out of the channel, and when the flux is reduced, the initial perturbation evolves to a steady flow with stagnation regions. Copyright © 2008 John Wiley & Sons, Ltd. [source] Geometrical interpretation of the multi-point flux approximation L-methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2009Yufei Cao Abstract In this paper, we first investigate the influence of different Dirichlet boundary discretizations on the convergence rate of the multi-point flux approximation (MPFA) L-method by the numerical comparisons between the MPFA O- and L-method, and show how important it is for this new method to handle Dirichlet boundary conditions in a suitable way. A new Dirichlet boundary strategy is proposed, which in some sense can well recover the superconvergence rate of the normal velocity. In the second part of the work, the MPFA L-method with homogeneous media is studied. A systematic concept and geometrical interpretations of the L-method are given and illustrated, which yield more insight into the L-method. Finally, we apply the MPFA L-method for two-phase flow in porous media on different quadrilateral grids and compare its numerical results for the pressure and saturation with the results of the two-point flux approximation method. Copyright © 2008 John Wiley & Sons, Ltd. [source] Opiate-induced oesophageal dysmotilityALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 5 2010R. E. KRAICHELY Aliment Pharmacol Ther,31, 601,606 Summary Background, Opiates have well characterized (troublesome) untoward effects on the gastrointestinal tract. Opioid bowel dysfunction has been a subject of research and even drug design, but surprisingly little is known with regard to clinical effects of opiates on the oesophagus. Aim, To characterize opiate effects on motor function of the oesophagus in patients presenting with dysphagia. Methods, Retrospective review of 15 patients with dysphagia referred for oesophageal manometry while on chronic opiates. Manometry was completed during opiate use and in three cases, after opiates were discontinued. Results, All patients demonstrated motility abnormalities. Incomplete lower oesophageal sphincter (LOS) relaxation (11.5 ± 1.6 mmHg) was seen in most cases. Ten patients demonstrated nonperistaltic contractions in ,3 of 10 swallows. Additional abnormalities included high amplitude contractions; triple peaked contractions; and increased velocity. The average resting lower oesophageal sphincter (LOSP) met criteria for hypertensive LOS in three patients. These features were suggestive of spasm or achalasia. Repeat manometry off opiates was performed in three cases. LOS relaxation was noted to be complete upon repeat manometry in these cases. There was also improved peristalsis and normal velocity. Conclusions, A range of manometric abnormalities were seen in patients with dysphagia in the setting of opiate use: impaired LOS relaxation, high amplitude/velocity and simultaneous oesophageal waves. These data suggest that the oesophagus is susceptible to the effects of opiates and care must be taken before ascribing dysphagia to a primary oesophageal motility disorder in patients taking opiates. [source] A direct method for solving an anisotropic mean curvature flow of plane curves with an external forceMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 13 2004Karol Mikula Abstract A new method for solution of the evolution of plane curves satisfying the geometric equation v=,(x,k,,), where v is the normal velocity, k and , are the curvature and tangential angle of a plane curve , , ,2 at the point x,,, is proposed. We derive a governing system of partial differential equations for the curvature, tangential angle, local length and position vector of an evolving family of plane curves and prove local in time existence of a classical solution. These equations include a non-trivial tangential velocity functional governing a uniform redistribution of grid points and thus preventing numerically computed solutions from forming various instabilities. We discretize the governing system of equations in order to find a numerical solution for 2D anisotropic interface motions and image segmentation problems. Copyright © 2004 John Wiley & Sons, Ltd. [source] Solution-precipitation creep , micromechanical modelling and numerical resultsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005Sandra Ili Our aim is to present a continuum mechanical model for solution-precipitation creep as well as to compare the numerical results based on that model with experimental observations. The formulation of the problem is based on the minimization of a Lagrangian consisting of elastic power and dissipation. Elastic energy is chosen to be in a standard form but dissipation is strongly adapted to the solution-precipitation process by introducing two new quantities: the velocity of material transport within the crystallite-interfaces and the normal velocity of precipitation or solution respectively. The model enables one to give an analytical solution for the case of a single crystal and numerical solution based on a finite element method for more complex, polycrystalline materials. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||