On the generalized Calder\'on formulas for closed- and open-surface elastic scattering problems

TL;DR

This paper investigates the theoretical properties of elastodynamic Calderón formulas for elastic scattering problems on closed and open surfaces, providing a foundation for developing efficient boundary integral methods.

Contribution

It establishes the Fredholm property of Calderón formulas for closed surfaces and analyzes weighted operators for open surfaces, including spectral properties and invertibility.

Findings

Calderón formula is a second-kind Fredholm operator for closed surfaces.

Weighted integral operators are compact perturbations of invertible operators for open surfaces.

Spectral accumulation points are characterized for the operators involved.

Abstract

The Calder\'on formulas (i.e., the combination of single-layer and hyper-singular boundary integral operators) have been widely utilized in the process of constructing valid boundary integral equation systems which could possess highly favorable spectral properties. This work is devoted to studying the theoretical properties of elastodynamic Calder\'on formulas which provide us with a solid basis for the design of fast boundary integral equation methods solving elastic wave problems defined on a close-surface or an open-surface in two dimensions. For the closed-surface case, it is proved that the Calder\'on formula is a Fredholm operator of second-kind except for certain circumstances. Regarding to the open-surface case, we investigate weighted integral operators instead of the original integral operators which are resulted from dealing with edge singularities of potentials corresponding to the elastic scattering problems by open-surfaces, and show that the Calder\'on formula is a compact perturbation of a bounded and invertible operator. To complete the proof, we need to use the well-posedness result of the elastic scattering problem, the analysis of the zero-frequency integral operators defined on the straight arc, the singularity decompositions of the kernels of integral operators, and a new representation formula of the hyper-singular operator. Moreover, it can be demonstrated that the accumulation point of the spectrum of the invertible operator is the same as that of the eigenvalues of the Calder\'on formula in the closed-surface case.