Seventh Copper Mountain Conference on Multigrid Methods

The Seventh Copper Mountain Conference on Multigrid Methods was held on 2-7 Apr. 1995 at Copper Mountain, Colorado. This book is a collection of many of the papers presented at the conference and so represents the conference proceedings. NASA Langley graciously provided printing of this document so that all of the papers could be presented in a single forum. Each paper was reviewed by a member of the conference organizing committee under the coordination of the editors. The multigrid discipline continues to expand and mature, as is evident from these proceedings. The vibrancy in this field is amply expressed in these important papers, and the collection shows its rapid trend to further diversity and depth

Numerical modeling of the leak through semipermeable walls for 2D/3D Stokes flow: Experimental scalability of dual algorithms

The paper deals with the Stokes flow subject to the threshold leak boundary conditions in two and three space dimensions. The velocity-pressure formulation leads to the inequality type problem that is approximated by the P1-bubble/P1 mixed finite elements. The resulting algebraic system is nonsmooth. It is solved by the path-following variant of the interior point method, and by the active-set implementation of the semi-smooth Newton method. Inner linear systems are solved by the preconditioned conjugate gradient method. Numerical experiments illustrate scalability of the algorithms. The novelty of this work consists in applying dual strategies for solving the problem.Web of Science922art. no. 290

Reorthogonalization-based stiffness preconditioning in FETI algorithms with applications to variational inequalities

A cheap symmetric stiffness-based preconditioning of the Hessian of the dual problem arising from the application of the finite element tearing and interconnecting domain decomposition to the solution of variational inequalities with varying coefficients is proposed. The preconditioning preserves the structure of the inequality constraints and affects both the linear and nonlinear steps, so that it can improve the rate of convergence of the algorithms that exploit the conjugate gradient steps or the gradient projection steps. The bounds on the regular condition number of the Hessian of the preconditioned problem, which are independent of the coefficients, are given. The related stiffness scaling is also considered and analysed. The improvement is demonstrated by numerical experiments including the solution of a contact problem with variationally consistent discretization of the non-penetration conditions. The results are relevant also for linear problems.Web of Science22699898