Fluid-structure interaction

Fluid-structure interaction (FSI) simulations are coupled CFD (fluids) and FEM (mechanics) cases. FSI is a part of mulitphysics simulations and an actual main focus in CFD development. As these solvers use different methods and codes, the transfer of the boundary conditions at the interface is an important feature of an FSI solution.

Coupling

1-way FSI

1-way FSI typically describes the pure mapping of physical properties resulting from the analysis of a CFD-/FE-model to another FE-model. The two models typically do not rely on matching meshes (e.g. mapping aerodynamic pressure distribution onto a structural Finite Element model). However in the case of 1-way FSI the mapping of the physical properties does not include the modification of any of the meshes.

2-way FSI

In the case of 2-way FSI the mapping is done in an iterative loop i.e. the results of the first model are mapped to the second model and these results are mapped back to the first model and so on until convergence is found or the process is stopped manually. Very often in the case of 2-way FSI one of the mapping steps involves the modification/morphing of the mesh of one or both of the models (e.g. mapping deformations coming from aerodynamic loads back to the CFD-model and re-evaluating the CFD-model in the deformed configuration).

Mesh Morphing

In most cases FSI is quite simple to realize even employing meshes not matching. However as soon as mesh-morphing is needed the whole process gets much more difficult and only few software solutions are around that can handle this. They key-problems with mesh-morphing are:

• Performance: Typical CFD-models as employed today in Formula 1 or Aerospace require very efficient morphing algorithms. A lot of the straight-forward approaches are not able to handle CFD-models consisting of several millions of cells.
• Surface Quality: For calculating pressure distributions in aerodynamics the surface quality in terms of continuity has to be quite high. Otherwise one starts to observe oscillations in the pressure fields. This is namely a challenge in the case where the mesh providing the deformation (typically the structural FE-mesh) is significantly coarser then the surface mesh of the CFD-model (which is quite common).

Applications

• Biomechanical Engineering
• Airfoil Aerodynamics
• Aero-elasticity