Fast Ewald summation for Stokes flow with arbitrary periodicity

TL;DR

This paper introduces a fast, spectrally accurate Ewald summation method for 3D Stokes flow potentials that works efficiently under any periodic boundary conditions, improving computational speed and accuracy for fluid simulations.

Contribution

It extends the Spectral Ewald method to arbitrary periodicity, deriving new kernels and error estimates, and provides an automated parameter selection procedure.

Findings

Computational time scales as O(N log N) for N sources and targets.

The method is fastest in fully periodic cases, with higher efficiency for uniform source distributions.

Achieves high accuracy and efficiency in simulating Stokes flow with arbitrary periodicity.

Abstract

A fast and spectrally accurate Ewald summation method for the evaluation of stokeslet, stresslet and rotlet potentials of three-dimensional Stokes flow is presented. This work extends the previously developed Spectral Ewald method for Stokes flow to periodic boundary conditions in any number (three, two, one, or none) of the spatial directions, in a unified framework. The periodic potential is split into a short-range and a long-range part, where the latter is treated in Fourier space using the fast Fourier transform. A crucial component of the method is the modified kernels used to treat singular integration. We derive new modified kernels, and new improved truncation error estimates for the stokeslet and stresslet. An automated procedure for selecting parameters based on a given error tolerance is designed and tested. Analytical formulas for validation in the doubly and singly periodic cases are presented. We show that the computational time of the method scales like O(N log N) for N sources and targets, and investigate how the time depends on the error tolerance and window function, i.e. the function used to smoothly spread irregular point data to a uniform grid. The method is fastest in the fully periodic case, while the run time in the free-space case is around three times as large. Furthermore, the highest efficiency is reached when applying the method to a uniform source distribution in a primary cell with low aspect ratio. The work presented in this paper enables efficient and accurate simulations of three-dimensional Stokes flow with arbitrary periodicity using e.g. boundary integral and potential methods.