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### Topological information

Although the major calculations take place in compfluid.c there is one routine placed at the start of nonlingeo.c to collect topological information, which is not changed due to the deformation of the structural components (in fluid-structure interaction calculations). This information includes:

- Storage of all external faces of the mesh (i.e. faces which belong to only one element) in fields nelemface (element number) and sideface (face number). The field nelemface is sorted in ascending order. The face number corresponds to the load face numbering in Section 6.10.2.
- Storage of all solid surface nodes in field isolidsurf in ascending order. A solid surface node is a node for which all velocity components are prescribed to be zero. Solid surface nodes belong to external faces of the mesh. The in-stream neighbor of a solid surface node is stored in field neighsolidsurf, the distance between both is stored in field xsolidsurf. The distance is a geometrical entity and is determined in routine initialcfd.f.
- Storing all freestream nodes in field ifreestream in ascending order. A freestream node is a node belonging to an external face which is not a solid surface node and which does not belong to a cyclic MPC.
- Determining the fluid elements to which a given node belongs and storing them in field iponoel and inoel. For a given node i one fluid element to which it belongs are stored in inoel(1,iponoel(i)). inoel(3,iponoel(i)) is a pointer into field inoel pointing to the next fluid element to which the node belongs. This is continued until inoel(3,inoel(3,inoel(3.....inoel(3,iponoel(i)))))) is zero.

Figure 128: Flow diagram for liquids

Figure 129: Flow diagram for compressible fluids

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