Two-dimensional Fourier Continuation and applications

Abstract

This paper presents a "two-dimensional Fourier Continuation" method (2D-FC) for construction of bi-periodic extensions of smooth non-periodic functions defined over general two-dimensional smooth domains. The approach can be directly generalized to domains of any given dimensionality, and even to non-smooth domains, but such generalizations are not considered here. The 2D-FC extensions are produced in a two-step procedure. In the first step the one-dimensional Fourier Continuation method is applied along a discrete set of outward boundary-normal directions to produce, along such directions, continuations that vanish outside a narrow interval beyond the boundary. Thus, the first step of the algorithm produces "blending-to-zero along normals" for the given function values. In the second step, the extended function values are evaluated on an underlying Cartesian grid by means of an efficient, high-order boundary-normal interpolation scheme. A Fourier Continuation expansion of the given function can then be obtained by a direct application of the two-dimensional Fast Fourier Transform (FFT). Algorithms of arbitrarily high order of accuracy can be obtained by this method. The usefulness and performance of the proposed two-dimensional Fourier Continuation method are illustrated with applications to the Poisson equation and the time-domain wave equation within a bounded domain. As part of these examples the novel "Fourier Forwarding" solver is introduced which, propagating plane waves as they would in free space and relying on certain boundary corrections, can solve the time-domain wave equation and other hyperbolic partial differential equations within general domains at computing costs that grow sublinearly with the size of the spatial discretization.

FC-based shock-dynamics solver with neural-network localized artificial-viscosity assignment

“…In practice, reference [13] proposes η(e) = u 9)) for the 1D and 2D Euler equations ( 5) and (6). As for the normalization operator, reference [13] proposes N = 1 for the Euler equations and N [e](x, t) = |η(e)(x, t) − η(e)(t)| for the Linear advection and Burgers equations, where η(e)(t) denotes the spatial average of η(e) at time t.…”

“…the Mach 3 forward-facing step case considered in Figure 16a. Extensions to general domains Ω, which could rely on either an embedded-boundary [5,6,28] approach, or an overlapping patch boundary-conforming curvilinear discretization strategy [1,2,4], is left for future work.…”

A fast, high-order scheme for evaluating volume potentials on complex 2D geometries via area-to-line integral conversion and domain mappings

“…Other approaches to extension have traded off adaptivity for high-order accuracy and compatibility with FFTs on uniform grids; one recently introduced technique is the two-dimensional Fourier continuation method [25] which as well as being a general-purpose numerical tool has recently been demonstrated to give accurate smooth periodic extensions suitable for use in elliptic solvers, at least in some simple geometrical contexts. In [26], a function extension scheme based on the use of radial basis functions (RBFs) is proposed, termed as the partition of unity extension (PUX) method.…”