Background

Finite element models that contain several volume regions may sometimes be exported with each region being a separate finite element mesh. Such disconnected mesh regions have to be connected into a single finite element mesh before ProTOp can run any optimization procedures.

█ Merging procedure

In ProTOp the mesh merging tool operates in three stages as follows.

• Analysis stage
  In the analysis stage, the tool identifies the number of disconnected regions and computes some mesh parameters.
  
  
• Connecting stage
  In the connecting stage, the tool searches for close FE node pairs lying on the surfaces of two different regions. Two nodes are considered to be close, if the distance between them is less than the specified merge tolerance. The nodes identified as close are connected by inserting special elastic connection finite elements which exhibit a relatively high stiffness. The stiffness of these connection elements can be adjusted by the user by adjusting the corresponding connector FEA parameters during optimization.
  
  
  
• Finalization stage
  In the finalization stage, the complete ProTOp FEA model is updated so that the new connections are properly accounted for.

NOTE. Connecting two mesh regions by elastic connection elements is only an approximation of actually physically merging two disconnected mesh regions. One of the consequences of this fact are various phenomena like spurious stress field variations in the vicinity of the imposed connections. So, the FEA model obtained by the mesh merge operation in ProTOp has to be carefully verified to be good enough for the planned optimization task.