[Getdp] Floquet BCs

cgeuzaine at ulg.ac.be cgeuzaine at ulg.ac.be
Sun Nov 23 15:31:40 CET 2014


> On 23 Nov 2014, at 14:50, Danny Holstein <dgholstein at embarqmail.com> wrote:
> 
> All,
> 
> Does GetDP support Floquet BCs for periodic structures?  I'd like to apply this to EM fields in traveling wave tubes such as helix and coupled cavity structures, etcetera.  I don't see why Floquet conditions wouldn't be similarly applicable to other wave propagation in periodic structures, such as phonons in a crystal.
> 

Sure - see e.g. http://onelab.info/wiki/Bloch_modes_in_periodic_waveguides for an example 




> Of course, there is the separate issue of whether GMSH supports the generation of such a mesh, though I'm sure it wouldn't be a complicated workaround.  The 2D mesh at the origin would have to match the mesh at the periodic boundary but with all the nodes translated by that period.
> 
> Let's say the periodicity is in Z, if we define one 2D mesh at Z = 0, and the same mesh at Z = L (same node and element numbers), then the element calculations just to the one side of L would have to do the calculations with translated values of Z (and, of course, the phase-shifted values from the surface mesh).
> 
> Regards,
> Dan
> 
> BTW:  An alternative is to include several periods of the structure and identify the eigenstates.  Computation times are horribly longer and this solution doesn't provide a continuum to DC (or omega -> 0). 
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