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A sharp relative-error bound for the Helmholtz h-FEM at high frequency

机译:高频亥姆霍兹 h-FEM 的尖锐相对误差边界

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摘要

For the h-finite-element method (h-FEM) applied to the Helmholtz equation, the question of how quickly the meshwidth h must decrease with the frequency k to maintain accuracy as k increases has been studied since the mid 80's. Nevertheless, there still do not exist in the literature any k-explicit bounds on the relative error of the FEM solution (the measure of the FEM error most often used in practical applications), apart from in one dimension. The main result of this paper is the sharp result that, for the lowest fixed-order conforming FEM (with polynomial degree, p, equal to one), the condition "h(2)k(3) sufficiently small" is sufficient for the relative error of the FEM solution in 2 or 3 dimensions to be controllably small (independent of k) for scattering of a plane wave by a nontrapping obstacle and/or a nontrapping inhomogeneous medium. We also prove relative-error bounds on the FEM solution for arbitrary fixed-order methods applied to scattering by a nontrapping obstacle, but these bounds are not sharp for p >= 2. A key ingredient in our proofs is a result describing the oscillatory behaviour of the solution of the plane-wave scattering problem, which we prove using semiclassical defect measures.
机译:对于应用于亥姆霍兹方程的 h 有限元法 (h-FEM),自 80 年代中期以来,人们一直在研究网格宽度 h 必须随频率 k 减小多快才能随着 k 的增加而保持精度的问题。然而,除了在一维上之外,文献中仍然不存在任何关于有限元解的相对误差(实际应用中最常使用的有限元误差的度量)的 k 显式边界。本文的主要结果是,对于最低的定阶一致性有限元(多项式阶数,p,等于1),条件“h(2)k(3)足够小”足以使2维或3维有限元解的相对误差可控地小(与k无关),以便通过非捕获障碍物和/或非捕获的非均匀介质散射平面波。我们还证明了应用于非捕获障碍物散射的任意固定阶方法的有限元解的相对误差边界,但这些边界对于 p >= 2 并不清晰。我们证明的一个关键因素是描述平面波散射问题解的振荡行为的结果,我们使用半经典缺陷测量来证明这一点。

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