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Periodic Boundary Conditions

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Hi,

does any body know how do I set periodic boundary conditions in a simple 3D cube if I want to lunch a plane wave (from one the faces) with different angles comparing to propagation axis?
I appreciate your help.

Farhad

5 Replies Last Post Nov 26, 2009, 10:12 a.m. EST

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Posted: 1 decade ago Jul 8, 2009, 8:28 p.m. EDT
It sounds like you want floquet periodic boundary conditions (PBCs) for the sides from which the plane wave starts.

For example, if you want a plane wave going only in the x direction, select floquet PBCs for the sides of the cube on the x-axis in the boundary mode. For the xyz inputs, you can put a variable 'kx' in the x slot and 0 in the y and z slots.

You can then vary kx to, e.g., look at a band structure if you're computing eigenfrequencies.
It sounds like you want floquet periodic boundary conditions (PBCs) for the sides from which the plane wave starts. For example, if you want a plane wave going only in the x direction, select floquet PBCs for the sides of the cube on the x-axis in the boundary mode. For the xyz inputs, you can put a variable 'kx' in the x slot and 0 in the y and z slots. You can then vary kx to, e.g., look at a band structure if you're computing eigenfrequencies.

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Posted: 1 decade ago Jul 11, 2009, 3:55 a.m. EDT
Thanks a lot was a great help.

Thanks a lot was a great help.

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Posted: 1 decade ago Sep 22, 2009, 5:41 a.m. EDT
Thanks for the info.
What would be the changes required for PBCs with oblique waves?
Thanks for the info. What would be the changes required for PBCs with oblique waves?

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Posted: 1 decade ago Sep 28, 2009, 2:21 p.m. EDT
I am attempting to create the band structure plots for a square lattice of circular cylinders in 2d. Essentially these plots consist of listing the degenerate eigan solutions for the first brillouin zone i.e., the reciprocal lattice. My understanding is that people create these plots by sampling a continuum of wave vectors (or altering the direction of the incident plane waves) and plotting these wave vectors against freq.

My question is this: I am using Comsol to solve Helmholtz's equation for the all of the eigan frequency solutions of the reciprocal unit cell of my lattice near the location of the principle stop band. It then returns a bunch of frequencies, some with only one degenerate and others with more. This is fantastic and all but how do I extract the wave vector direction from these solutions to assign an x-axis position to the band structure plot given that the eigan value approach uses no source terms?

see attached plot for example of what I want to create

I am using periodic boundary conditions see attached sim file
I am attempting to create the band structure plots for a square lattice of circular cylinders in 2d. Essentially these plots consist of listing the degenerate eigan solutions for the first brillouin zone i.e., the reciprocal lattice. My understanding is that people create these plots by sampling a continuum of wave vectors (or altering the direction of the incident plane waves) and plotting these wave vectors against freq. My question is this: I am using Comsol to solve Helmholtz's equation for the all of the eigan frequency solutions of the reciprocal unit cell of my lattice near the location of the principle stop band. It then returns a bunch of frequencies, some with only one degenerate and others with more. This is fantastic and all but how do I extract the wave vector direction from these solutions to assign an x-axis position to the band structure plot given that the eigan value approach uses no source terms? see attached plot for example of what I want to create I am using periodic boundary conditions see attached sim file


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Posted: 1 decade ago Nov 26, 2009, 10:12 a.m. EST
Hi,

I am looking for applications in chemical engineering that covers the topic of periodic boundary conditions. Does anyone know or has a chemical engineering model in Comsol that applies this concept?

your help will be greatly appreciated...

regards
Luis
Hi, I am looking for applications in chemical engineering that covers the topic of periodic boundary conditions. Does anyone know or has a chemical engineering model in Comsol that applies this concept? your help will be greatly appreciated... regards Luis

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