Computational methods based on this decomposition are presented, for both inviscid and viscous flows. It is shown that the solutions for viscous attached high-Reynolds-number flows and for inviscid flows are close to each other, provided that the Kutta-Joukowski trailing-edge condition is satisfied for inviscid flows.
The incompressible-flow formulation is then extended to compressible flows. It is shown that the Helmholtz decomposition is not convenient for the boundary element analysis of compressible flows, because the rotational source terms are different from zero in the irrotational region. A new decomposition, called the Poincare decomposition, is introduced, for which the rotational source terms are equal to zero in most of the irrotational region.
This makes the decomposition appealing for the boundary element solution of compressible viscous flows. The origin of this coordinate system lies at the end of each line segment lk, and the x' axis is directed along the line segment itself, in the counterclockwise direction of the boundary F.
The boundary integrals in eqn 17 is evaluated by using the same procedure that is used for evaluating UB and VB. The vector wB represents the boundary integral contribution in eqn The geometric coefficients matrices depend only on the relative location between the grid notes and are independent of the solution variables u, v, and w and of the boundary conditions.
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This feature has several advantages resulting in a drastic reduction in the required time and storage. In addition, these matrices need not to be computed repeatedly from iteration to iteration during the iterative procedure for solving the governing equations. This method accurately simulates the local generation of vorticity on the solid surface.
In the present work, the tangential prescribed velocity values at the boundary are used to compute the boundary vorticity. As indicated by Wu, 16 the use of both velocity values, the tangential and the normal velocity components in determining the boundary vorticity will overspecify the problem. More details can be found in Ref. The overall numerical procedure to advance the solution by one iteration loop, consists of kinetic steps as well as kinematic steps. In this section, a general procedure for solving integral flow problems with arbitrary boundaries is presented.
The velocities ub and Vb at the boundary nodes are assumed to be known. Starting with known values of the w7 at the iteration level n at the interior domain nodes N - Nb , the following steps constitute one iteration loop. Using the above iteration loop, it is found necessary to employ a point under-relaxation technique to obtain convergent solutions. Usually, e is set in the range o f 10 -4 to for interior flow cases.
The under-relaxation parameter R depends on the flow Reynolds number. In the present work R is taken to be 0. However, both solutions are not in good agreement, quantitatively. Both the T P B E M and the experimental flow patterns show a secondary vortex near the lower left corner. In Fig.
VISCOUS FLOW AND HEAT TRANSFER WITH MOVING PHASE BOUNDARY. — the Research Networking System
It is clear in the figure that the two solutions are in better agreement than that between the T P B E M grid 40 x 40 and the present F D M grid 40 x Results for this case are compared with those obtained by finite difference method developed in the present work. The comparison is conducted for two values o f Reynolds number and The present F D M uses a semi-implicit finite difference scheme to approximate the flow kinematics and kinetics. The convective terms are approximated by using the second-order Adams Bashforth time stepping explicit scheme while the diffusive terms are approximated by employing the Crank-Nicholson implicit scheme.
Mesh refinement numerical tests were carried out to predict the optimum mesh sizes Ax and Ay. El-Refaee FIll Fig. The comparison is shown in Fig. The numerical solutions as well as the experimental data can be said to be in good agreement with the present TPBEM velocity profiles.
ExperimentalData[ Fig. T h e convective-diffusion flow p r o b l e m is described by two integral e q u a t i o n s ; a kinematical integral e q u a t i o n a n d a kinetical integral e q u a t i o n. T h e present T P B E M is expected to give efficient solutions for p r o b l e m s with large convective d o m a i n such as external flow since the present m e t h o d deals explicitly with interior u n k n o w n s. Velocity profiles at the cavity centerline comparison among the present BEM and other models.
The work started before the invasion of the Iraqis to the State of Kuwait. Brebbia, C. Pineridge Press, Swansea, Wu, J. Integral representations of field variables for the finite element solution of viscous flow problems in Proc. Snyder, M. Boundary integral equation analysis of anisotropic cracked plates, Int.
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About this book
Combination of boundary finite elements in elastostatics. Martinez, J. Steady state potential problems are problems where the primary variable is a scalar and the results are independent of time. The chapter discusses the implementation and shows examples ranging from confined to unconfined seepage problems. In this chapter, we discuss the implementation for static linear solid mechanics.
On several examples in 2-D and 3-D, we investigate the efficiency of the implementation and the accuracy that can be obtained. Trimmed surfaces introduce several challenges for analysis, and their treatment is the focus of this chapter.
SIAM Journal on Numerical Analysis
The following techniques are problem-independent in principle. As examples, we consider their application in the context of isogeometric BEM simulations of the problem types presented in the previous chapters, i. With boundary integral equations alone we cannot consider effects that occur inside the domain and therefore can only deal with linear problems and homogeneous domains, with effects on the boundary only. In this chapter, we introduce effects inside the domain, also known as body forces. The BEM relies on the availability of fundamental solutions of the governing differential equations, which are only available for homogeneous domains.
As this would restrict the practical application of the method, we explore here the possibility of considering inhomogeneities. This chapter deals with the implementation of non-linear material behavior, in particular plasticity. The BEM is ideally suited for applications in geomechanics because it can handle infinite domain problems without truncation.
This chapter shows how the theory outlined so far can be applied to practical problems, in this case the simulation of underground excavations. In this chapter, we discuss the implementation of the isogeometric BEM for steady state viscous incompressible flows. Here we re-introduce time effects. Which can be either transient or harmonic. We discuss transient problems for potential flow in 2-D first and then show an example of a harmonic problem, namely acoustics.
This chapter summarizes the contents of the book and provides an outlook of future developments.