## 4 Case Studies
### Retaining Ring Exchange via INP  
The second example is the transfer of a retaining ring model. The freeware program Gmsh 4.8.4 (developed by [PERSON] and [PERSON]) is widely used for finite element mesh generation. We use it to create a grid structure of the retaining ring [57]. As export settings, we choose the INP format with default settings. Standard linear tetrahedra (element type C3D8) build up the mesh. To perform a linear-static analysis based on the exported mesh, we import the INP file into the freeware program Z8 Aurora V5 (Engineering Design and CAD, University of Bayreuth, Bayreuth, Germany). The latter software is utilized in the field of finite element method (FEM) [58]. Again, we have chosen standard import settings. However, loading the model is not possible, even if all relevant information is available in the exchange file. Figure 11 illustrates this process.  
Figure 10: Adapted, compatible sketch coloring for an error-free import into Catia.  
We trace the exchange error back to faulty element sets. Comparing the SSI from Figure 12 with the TSI from Figure 13, we note that the preprocessor in Gmsh exports unwanted line and surface element blocks (ELSET attl.1 to exclusively attl.1+y) in addition to the relevant volume elements (ELSET form inclusively attl.1+y). However, the postprocessor of Z88 does not expect line and surface elements. It also demands only one volume element set block.  
In the second step, we assign conditions based on the structures from the previous step. We classify the additional line and surface element sets as negative because they must be removed to ensure error-free importing of the considered INP file in Z88. Notably, deleting element sets leads to peculiarity. There may be nodes that do not appear in any element set. Unused nodes should be evaluated as negative since they must be removed from the INP file to ensure an error-free data transfer. A merging of the remaining volumes is necessary to ensure compatibility, and we only need to keep the first keyword line of the volume element set blocks. We rank the remaining keyword lines as negative since we must delete them from the file to ensure compatibility. The concrete specification of the node numbers of each element set and their references must be kept, which is why we classify them as homogeneous. Furthermore, we rate the introductory comment line as neutral since the postprocessor ignores the line.  
In the third step, we adapt the incompatible items. Figure 14 shows an example of a modified element-set block. All line and area element sets are no longer part of the item,  
Figure 11: Failed data exchange of a retaining ring model between the finite element mesh generator Gmsh and FEM software Z88.  
Figure 12: Source system (Gmsh) conforms to the item structure of the element set blocks.  
Figure 13: Target system (Z88) conforms to the item structure of the element set blocks.  
and all remaining volume element sets are merged by removing all keyword lines except the first one. The replacement of the element set block extracted from the original INP file, and replacing it with the adapted block shown in Figure 14 ensures an error-free import. The process allows a structural mechanics analysis of the retaining ring model in Z88.