Oscar: A software library for modelling THM coupled processes

The simulation of thermo-hydro-mechanical (THM) coupled processes, i.e., the prediction of interactions between temperature, fluids and mechanical properties within a repository system, is an essential prerequisite for performing and evaluating preliminary safety analysis in the site selection process.

The presented open-source python software library Oscar is developed at the Federal Office for the Safety of Nuclear Waste Management (BASE) and has been released with its initial revision. The development of an own software library allows for the continuous development of expertise within BASE regarding numerical modelling and the diversification of the testing capabilities regarding the preliminary safety investigations. The choice for an open-source software strategy is motivated by the transparency requirement in the German site selection act and the potential to the provision of appropriately quality-assured and documented simulation tools to the public.

The main goal of this in-house development is to provide a quality-assured, flexible and easy-to-use toolbox for the modelling of THM coupled processes using the finite element method with the following key features:

• Finite element analysis with the usual cell types for 1D, 2D and 3D modellings (edge, triangle, quadrilateral, tetrahedron, hexahedron).

• Generic shape function generator with predefined base-functions for linear, and quadratic elements.

• Script-based interface to the solution of the governing equations for the THM coupled processes in non-dimensional form in a symbolic manner with its strong or weak formulation.

• Predefined process solver classes for frequently used THM processes (e.g., heat conduction, fluid flow, mechanical deformation).

• Growing set of Jupyter notebooks of intensively documented tutorials to the finite element theory and to the usage of the presented software library.

• Growing set of Jupyter notebooks of documented examples and commonly known benchmarks for the modelling of THM coupled processes.

The presented poster shows some key features of the software library and outlines potential applications.