DuMu(x)3-an open-source simulator for solving flow and transport problems in porous media with a focus on model coupling

We present version 3 of the open-source simulator for flow and transport processes in porous media DuMu(x). DuMu(x) is based on the modular C++ framework DUNE (Distributed and Unified Numerics Environment) and is developed as a research code with a focus on modularity and reusability. We describe recent efforts in improving the transparency and efficiency of the development process and community-building, as well as efforts towards quality assurance and reproducible research. In addition to a major redesign of many simulation components in order to facilitate setting up complex simulations in DuMu(x), version 3 introduces a more consistent abstraction of finite volume schemes. Finally, the new framework for multi-domain simulations is described, and three numerical examples demonstrate its flexibility. (C) 2020 The Authors. Published by Elsevier Ltd.