15 research outputs found
Analysis of a Helmholtz preconditioning problem motivated by uncertainty quantification
This paper analyses the following question: let , be
the Galerkin matrices corresponding to finite-element discretisations of the
exterior Dirichlet problem for the heterogeneous Helmholtz equations
. How small must and be (in terms of -dependence) for
GMRES applied to either or
to converge in a -independent number of
iterations for arbitrarily large ? (In other words, for to be
a good left- or right-preconditioner for ?). We prove results
answering this question, give theoretical evidence for their sharpness, and
give numerical experiments supporting the estimates.
Our motivation for tackling this question comes from calculating quantities
of interest for the Helmholtz equation with random coefficients and .
Such a calculation may require the solution of many deterministic Helmholtz
problems, each with different and , and the answer to the question above
dictates to what extent a previously-calculated inverse of one of the Galerkin
matrices can be used as a preconditioner for other Galerkin matrices
Linear continuous interior penalty finite element method for Helmholtz equation With High Wave Number: One-Dimensional Analysis
This article addresses the properties of continuous interior penalty (CIP) finite element solutions for the Helmholtz equation. The h-version of the CIP finite element method with piecewise linear approximation is applied to a one-dimensional (1D) model problem. We first show discrete well posedness and convergence results, using the imaginary part of the stabilization operator, for the complex Helmholtz equation. Then we consider a method with real valued penalty parameter and prove an error estimate of the discrete solution in the H1-norm, as the sum of best approximation error plus a pollution term that is the order of the phase difference. It is proved that the pollution effect can be eliminated by selecting the penalty parameter appropriately. As a result of this analysis, thorough and rigorous understanding of the error behavior throughout the range of convergence is gained. Numerical results are presented that show sharpness of the error estimates and highlight some phenomena of the discrete solution behavior. In particular, we give numerical evidence that the optimal penalty parameter obtained in the 1D case also works very well for the CIP-FEM on two-dimensional Cartesian grids
Wavenumber-explicit convergence of the -FEM for the full-space heterogeneous Helmholtz equation with smooth coefficients
A convergence theory for the -FEM applied to a variety of
constant-coefficient Helmholtz problems was pioneered in the papers
[Melenk-Sauter, 2010], [Melenk-Sauter, 2011], [Esterhazy-Melenk, 2012],
[Melenk-Parsania-Sauter, 2013]. This theory shows that, if the solution
operator is bounded polynomially in the wavenumber , then the Galerkin
method is quasioptimal provided that and ,
where is sufficiently small, and is sufficiently large.
This paper proves the analogous quasioptimality result for the heterogeneous
(i.e. variable coefficient) Helmholtz equation, posed in ,
, with the Sommerfeld radiation condition at infinity, and
coefficients. We also prove a bound on the relative error of the Galerkin
solution in the particular case of the plane-wave scattering problem