Hello Bernd,

This PR is about a fem example: frequency analysis for a cylindrical shell.

I made this shell frequency analysis which generates pretty well results. These results can be verified using the cylindrical shell theory with about 1% error (thickness = 10 mm, see forum: https://forum.freecadweb.org/viewtopic.php?f=18&t=65382#p564156)

Since there is currently no example of such a model yet (frequency analysis for a cylindrical shell with quad4 element type). I hope this example could help other users if they encounter a similar model or as a reference for shell frequency analysis.

I am still working on different types of shell analysis using FEM Wb. If there is any question or suggestion, please feel free to contact me. 

Best regards,
Han (forum name: chlai)

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