I wish to apply Floquet boundary condition at left-right ends and up-down ends, and the wish to find out the dispersion relation for the unit cell.
But I fail to find any option of Periodic condition in the list. If I make this an area-type geometry or a volume-type geometry, I can find the option, but not for the geometry provided (see attached image).
Please help me on how to do it. Thanks in advance.
Symmetry boundaries are used to reduce the extent of your computational model, they are used when the physical geometry,
Mohammed H.Ali Thanks for the reply, but I could not understand your statement. It seems to be incomplete.
I wish to apply the Periodic Condition which is different from the Symmetry Condition. Although, the former is not applicable for a 1D geometry in a 2D space (modelled as beams). But this paper (see link) uses the Floquet Periodic Condition on a 1D geometry, which is what I am trying to do in COMSOL.
Article Phononic properties of hexagonal chiral lattices
Floquet-Bloch periodic BC in COMSOL is applied on surfaces in 3D or edges/lines in 2D. This is because the source point is computed using a rotation of the position relative to the destination, i.e. rotation matrix R is computed. This is usually evaluated from the cross product of the source and destination boundary normal directions. Since normal directions are not defined for a point (which is exactly what you intend to select in your particular FE setup), the software does not provide that option.
Read more in detail here: https://doc.comsol.com/5.5/doc/com.comsol.help.comsol/comsol_ref_modeling.10.67.html
The "Spadoni et al., Wave Motion, 40(7) (2009)" paper uses the discretized FE model approach by treating the rigidly connected lattice links as Timoshenko beams. In fact, the best way would be to model the 2D/3D geometry of the unit cells without making an assumption of rigid connectors/beam theories.
Check below the two papers that model periodic BCs of the auxetic unit cells, one uses the beam model approach while the other uses full geometry:
Article 3D auxetic lattice materials for anomalous elastic wave polarization
Article 3D Auxetic Microlattices with Independently Controllable Aco...
Snell's low is applied depending on vector analysis of geometry for short wave of incidents
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