Hi Marco,
Thanks for your question.
1) Exporting .xlsx files is not supported yet. We'll add this feature soon.
2) S3hark create an effective stress site response analysis finite element model, with dashpots at the base.
There are two options to solve the FE model:
In the 'Configure' tab, if you left the OpenSees path empty by default, S3hark will solve the model internally.
If you provided the OpenSees path there, S3hark will create a tcl file and call your OpenSees to run it.
This tcl file can be found in
macOS: ~/Library/Application Support/SimCenter/s3hark/analysis/
Windows: C:/Users/<USER>/AppData/Roaming/SimCenter/s3hark/analysis/