Thanks Roman for your answer,

But clarify me : it's holow cylinder, with void, only waves in thickness. Do you specify boundaries faces extremity definied by thickness to specify SRC and DST definitions on comsol ?

Thanks a lot

Roman thanks à lot, excellent explication.I test Floquet, and its work perflectly. I find all dispersion points kz=f(freq), but i can't obtain classe famille definition, to identify family modes : longitudinal, torsion, flex...how to identify them with console? Thanks a lot again

Thanks a lot, that's right the easyway is to look the shape in 3D, the last case you submit can be interesting... need to test .

Roman, thanks a lot, for your time, and very good explication.

I wish you a good year

Friendly Serge