FAQs:
Node/Segment/Solid set
There are two new options SALEFAC, SALECPT in *SET_NODE/SEGMENT/SOLID_GENERAL. SALEFAC picks all nodes/segments/solids at the S-ALE mesh face. SALECPT picks the entities inside the box (I1,J1,K1) and (I2,J2,K2) in control_points.
NOTE: All other options in *SET_?_GENERAL do not work with S-ALE mesh!
Ambient
S-ALE setup doesn't allow for "ambient parts". An "ambient part" contains both the mesh and material properties. This contradicts the rule that in S-ALE part only serves one role, either mesh or material.
S-ALE has "ambient elements" instead. Certain part of S-ALE mesh are grouped as solid element set and prescribed as "ambient elements" by using *BOUNDARY_AMBIENT (Not *BOUNDARY_AMBIENT_EOS).
Mesh Motion
*ALE_REFERENCE_SYSTEM_GROUP is NOT supported in S-ALE. Mesh follows motion of the origin translationally and rotates with the local coordinate system. Or it can follow the rigid body motion of certain fluids by using *ALE_STRUCTURED_MESH_MOTION.
Notable points on ALE/FSI:
The order in *ALE_MULTI-MATERIAL_GROUP
The "material part" serves as a wrapper to encapsulate *MAT+*EOS+*HG. They are listed in *ALE_MULTI-MATERIAL_GROUP card to tell the solver:
1. How many fluids (AMMGs) flow in the ALE domain("mesh part").
2. Each AMMG's material property --> (*MAT+*EOS+*HG)
There is also a function, overlooked very often, that frequently leads to failed ALE/FSI analysis. That is: the order in which those parts are listed in *ALE_MULTI-MATERIAL_GROUP plays a crucial role. It determines the order in which material interfaces are constructed in mixed elements. Simply speaking, in a mixed element, the solver would do interface construction for AMMG1, then AMMG1+AMMG2, then AMMG1+AMMG2+AMMG3, so on and forth.
This means, to correctly reconstuct the fluid interfaces, we need to make sure neighboring materials are listed next to each other under *ALE_MULTI-MATERIAL_GROUP card. Please refer to the slide here for a detailed explanation.
FSI: LAG/ALE 1:1 mesh size
We prefer the ALE mesh size to be around the same as the LAG mesh. In interface reconstruction for mixed ALE cells, we only do 1 cut, i.e. we assume the interface is a plane intersecting the ALE cell. So finer LAG mesh won't do any good. Instead it might cause the two interfaces (LAG/ALE) not conciliable.
