Imposing different boundary conditions for thermal computational homogenization problems with FFT- and tensor-train-based Green's operator methods

To compute the effective properties of random heterogeneous materials, a number of different boundary conditions are used to define the apparent properties on cells of finite size. Typically, depending on the specific boundary condition, different numerical methods are used. The article at hand provides a unified framework for Lippmann–Schwinger solvers in thermal conductivity and Dirichlet (prescribed temperature), Neumann (prescribed normal heat flux) as well as periodic boundary conditions. We focus on the explicit jump finite-difference discretization and discuss different techniques for computing the discrete Green's operator. These include Fourier-type methods, that is, based on discrete sine, cosine and Fourier transformations, as well as low-rank tensor methods, that is, the tensor-train approximation, whose computational prowess was demonstrated recently. We use the developed computational technology to investigate a number of interesting random materials and assess different microstructure-generation techniques in terms of their compatibility with the prescribed boundary conditions.