In this paper we give new results on domain decomposition preconditioners for GMRES when computing piecewise-linear finite-element approximations of the Helmholtz equation −∆u − (k2 + iε)u = f , with absorption parameter ε ∈ R. Multigrid approximations of this equation with ε 6= 0 are commonly used as preconditioners for the pure Helmholtz case (ε = 0). However a rigorous theory for such (so-ca...

Acoustic waves interact with the human body, head and ears, before reaching the tympanic membranes in the ear canals. In this project we will develop an analytical method to calculate how these acoustic interactions occur. This is a highly nontrivial problem, because the acoustic wave equation (or, for harmonic waves, the Helmholtz equation) has to be solved on the complex geometry of the bound...

We present a new high-order integral algorithm for the solution of scattering problems by heterogeneous bodies under TE radiation. Here, a scatterer is represented by a (continuously or discontinuously) varying refractive index ( ) within a two-dimensional (2-D) bounded region; solutions of the associated Helmholtz equation under given incident fields are then obtained by high-order inversion o...

A general dark-soliton solution of the Helmholtz equation (with defocusing Kerr nonlinearity) that has on- and off-axis, gray and black, paraxial and Helmholtz solitons as particular solutions, is reported. Modifications to soliton transverse velocity, width, phase period, and existence conditions are derived and explained in geometrical terms. Simulations verify analytical predictions and also...

Exterior boundary-value problems for the Helmholtz equation can be reduced to boundary integral equations. It is known that the simplest of these fail to be uniquely solvable at certain ‘irregular frequencies.’ For a single smooth scatterer, it is also known that irregular frequencies can be eliminated by using a modified fundamental solution, one that has additional singularities inside the sc...

The frequency-domain finite-difference (FD-FD) methods have been successfully used to obtain numerical solutions of the twodimensional (2-D) Helmholtz equation. The standard second-order accurate FD-FD scheme is known to produce unwanted numerical spatial and temporal dispersions when the sampling is inadequate. Recently compact higher-order accurate FD-FD methods have been proposed to reduce t...

Motivated by the paraxial narrow–angle approximation of the Helmholtz equation in domains of variable topography that appears as an important application in Underwater Acoustics, we analyze a general Schrödinger-type equation posed on two-dimensional variable domains with mixed boundary conditions. The resulting initialand boundary-value problem is transformed into an equivalent one posed on a ...

We are interested in determining the electromagnetic fields within closed perfectly conducting cavities that may contain dielectric or magnetic materials. The vector Helmholtz equation is the appropriate partial differential equation for this problem. It is well known that the electromagnetic fields in a cavity can be decomposed into distinct modes that oscillate in time at specific resonant fr...

We give a brief overview of some new results in Helmholtz soliton theory. Firstly, fundamental considerations are made in terms of new contexts for Helmholtz solitons that arise directly from Maxwell’s equations. We then detail applications of Helmholtz solitons in material interface geometries: generalising Snell’s law to nonlinear beams and reporting new qualitative phenomena. Novel families ...

The Sommerfeld integral inversion method for the Helmholtz equation in an angular region with diierent boundary values leads to boundary value problems in an innnite strip of the complex plane. We investigate a generic system for such boundary value problems and give existence and uniqueness results with optimal growth estimates on the solution. We also give the solutions of the Dirichlet probl...