抛物囚禁下Helmholtz方程的高频界及其在数值分析中的应用
High-frequency bounds for the Helmholtz equation under parabolic trapping and applications in numerical analysis
摘要：
本文研究了当障碍物为陷阱时，在Dirichlet边界条件下，Helmholtz方程在有界障碍物外的实轴上的预解式估计。目前在文献中有两种针对这种情况的预解估计：（i）在椭圆捕获的情况下，适用指数增长性的一般“最坏情况”界限，并且实例表明，这种增长可以通过某些波数序列来实现，（ii）在双曲线俘获的典型情况下，其中亥姆霍兹方程被置于两个严格凸障碍物的外部（或具有附加约束的几个障碍）非捕获预解估计保持对数损失。本文证明了抛物型陷阱的第一预解估计障碍，研究一类障碍的原型例子是两个正方形（在二维），或两个立方体（在三维），其侧面是平行的外部。我们表明，通过发展的向量场/乘数的论点Morawetz和第一次应用这种方法来捕获配置，一个预解估计持有多项式损失的nontrapping估计。我们使用这个界，以及其他捕获预解估计，证明结果的积分方程配方的边值问题的情况下，捕获。将这些边界送入现有的有限元和边界元方法分析框架，我们得到了第一波数显式证明的收敛性数值方法求解Helmholtz方程在外部的一个陷阱障碍。
英文摘要：
This paper is concerned with resolvent estimates on the real axis for the Helmholtz equation posed in the exterior of a bounded obstacle with Dirichlet boundary conditions when the obstacle is trapping. There are two resolvent estimates for this situation currently in the literature: (i) in the case of elliptic trapping the general "worst case" bound of exponential growth applies, and examples show that this growth can be realised through some sequence of wavenumbers, (ii) in the prototypical case of hyperbolic trapping where the Helmholtz equation is posed in the exterior of two strictly convex obstacles (or several obstacles with additional constraints) the nontrapping resolvent estimate holds with a logarithmic loss. This paper proves the first resolvent estimate for parabolic trapping by obstacles, studying a class of obstacles the prototypical example of which is the exterior of two squares (in 2-d), or two cubes (in 3-d), whose sides are parallel. We show, via developments of the vector-field/multiplier argument of Morawetz and the first application of this methodology to trapping configurations, that a resolvent estimate holds with a polynomial loss over the nontrapping estimate. We use this bound, along with the other trapping resolvent estimates, to prove results about integral-equation formulations of the boundary value problem in the case of trapping. Feeding these bounds into existing frameworks for analysing finite and boundary element methods, we obtain the first wavenumber-explicit proofs of convergence for numerical methods for solving the Helmholtz equation in the exterior of a trapping obstacle.
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