Dimensional reduction as a tool for mesh refinement and tracking singularities of PDEs

Abstract

We present a collection of algorithms which utilize dimensional reduction to perform mesh refinement and study possibly singular solutions of time-dependent partial differential equations. The algorithms are inspired by constructions used in statistical mechanics to evaluate the properties of a system near a critical point. The first algorithm allows the accurate determination of the time of occurrence of a possible singularity. The second algorithm is an adaptive mesh refinement scheme which can be used to approach efficiently the possible singularity. Finally, the third algorithm uses the second algorithm until the available resolution is exhausted (as we approach the possible singularity) and then switches to a dimensionally reduced model which, when accurate, can follow faithfully the solution beyond the time of occurrence of the purported singularity. An accurate dimensionally reduced model should dissipate energy at the right rate. We construct two variants of each algorithm. The first variant assumes that we have actual knowledge of the reduced model. The second variant assumes that we know the form of the reduced model, i.e. the terms appearing in the reduced model, but not necessarily their coefficients. In this case, we also provide a way of determining the coefficients. We present numerical results for the Burgers equation with zero and nonzero viscosity to illustrate the use of the algorithms.