| Abstract |
State of the art models of enhanced geothermal systems (EGS) rely on multi-physics simulations, as EGS are driven by complex thermo-hydro-mechanical interactions. Different physical processes are frequently modeled with their own geometry and method, thus their solutions are elements of different function spaces. Fluid behavior, for example, can be simulated with the finite-difference method on uniform structured grids, whereas in mechanics the finite-element method on unstructured grids is often preferred. To transfer physical information across the different spaces, we use a generic variational transfer operator, which has previously been introduced as pseudo-$L^2$-projection. We demonstrate that our transfer operator can be particularly useful for simulating physical processes in rough fractures: First, non-matching surfaces at the contact boundary need to be handled for mechanical contact simulations. Here, the transfer operator acts as a mortar projection and we show how the operator is used to resolve the contact boundary on high resolution rock fracture topologies. This approach enables us to simulate fracture normal stress and closure behavior with high accuracy. We show results using geometries taken from high resolution photogrammetry scans from samples taken from the Grimsel test site in Switzerland. Secondly we present preliminary results of a three dimensional fluid-structure simulation, simulating water flow between rocks with an immersed boundary approach. In this method the solid, which is formulated on an unstructured grid, interacts with the fluid, formulated on a structured grid, by means of a material force in the Navier-Stokes equation. And lastly we show how the transfer operator can be used to efficiently solve elastic contact in rocks: Using our operator we can generate a multilevel hierarchy for the complex geometry of the fracture, enabling us to solve the problem with multigrid efficiency, thus extending the possible size of simulations immensely. |