1. How to generate node/segment/solid set in S-ALE?
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!
2. How to specify ambient parts in S-ALE?
S-ALE setup doesn't allow for "ambient parts". PART is either a mesh part which contains no material info, or a material parts which has no mesh. A part can not contain both. This is the most significant difference from generic ALE setup.
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 (note: not *BOUNDARY_AMBIENT_EOS).
3. How to specify part(s) in *INITIAL_HYDROSTATIC_ALE or *AMBIENT_HYDROSTATIC_ALE?
In both cards, ALESID could be a set of solid elements. We need to use this option when using S-ALE.
PART is either a mesh part which contains no material info, or a material parts which has no mesh. A part can not contain both. This is the most significant difference from generic ALE setup.
4. Does *ALE_REFERENCE_SYSTEM_GROUP work with S-ALE?
No. It doesn't. Mesh motion in S-ALE is controled by the origin node (translational) and the local coordinate system (rotational).
1. Mesh trimming feature added in dev.124272
Mesh trimming is to delete S-ALE elements far away from the user's interest. For details please check the manual and 2018 LS-DYNA Conference paper. Example models here and here.
2. TDEATH to turn off ALE simulation while continuing the rest of calculation
Tdeath in *ALE_STRUCTURED_MESH could delete S-ALE mesh and related *CONSTRAINED_LAGRANGE_IN_SOLID + *ALE_COUPLING_NODAL cards. This will effectively kill the ALE run while keep other Lagrangian parts running.
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.
2. 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.