# FFT-based homogenization on periodic anisotropic translation invariant spaces

## TL;DR

This paper develops a unified mathematical framework for homogenization in elasticity using anisotropic translation invariant spaces, combining Fourier and finite element methods, and introduces a periodised Green operator with proven properties.

## Contribution

It unifies Fourier series and finite element approaches in a common anisotropic translation invariant space framework for homogenization.

## Key findings

- The periodised Green operator is bounded.
- The operator is a projection if generated by a Dirichlet kernel.
- Numerical examples demonstrate framework flexibility.

## Abstract

In this paper we derive a discretisation of the equation of quasi-static elasticity in homogenization in form of a variational formulation and the so-called Lippmann-Schwinger equation, in anisotropic spaces of translates of periodic functions. We unify and extend the truncated Fourier series approach, the constant finite element ansatz and the anisotropic lattice derivation. The resulting formulation of the Lippmann-Schwinger equation in anisotropic translation invariant spaces unifies and analyses for the first time both the Fourier methods and finite element approaches in a common mathematical framework. We further define and characterize the resulting periodised Green operator. This operator coincides in case of a Dirichlet kernel corresponding to a diagonal matrix with the operator derived for the Galerkin projection stemming from the truncated Fourier series approach and to the anisotropic lattice derivation for all other Dirichlet kernels. Additionally, we proof the boundedness of the periodised Green operator. The operator further constitutes a projection if and only if the space of translates is generated by a Dirichlet kernel. Numerical examples for both the de la Vall\'ee Poussin means and Box splines illustrate the flexibility of this framework.