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Make my model infinite at one direction

Posted Apr 4, 2013, 1:35 p.m. EDT RF & Microwave Engineering, Modeling Tools & Definitions, Parameters, Variables, & Functions, Structural Mechanics Version 3.5a, Version 4.1, Version 4.2, Version 4.2a, Version 4.3, Version 4.3a 2 Replies

Constantinos Tsangarides
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In order to make my block having an infinite length in x-direction

(as it is a stripe of graphene and extends along its length to infinity)

Should I use some specific Boundary Condition??
2 Replies Last Post Jun 25, 2014, 8:26 a.m. EDT
Robert Koslover Certified Consultant
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Posted: 1 decade ago Apr 4, 2013, 10:18 p.m. EDT
If your overall geometry is infinite in any particular direction, then in many cases, that direction can simply be dropped out of the problem entirely. For example, in 3D, if your problem space is infinite along x, and if the variables of interest to you have no dependencies upon x, then you really should be solving a 2D problem (in the y-z plane, in this example) instead.

Alternatively, if there does exist a dependence on x, but if that dependence is periodic, then you might be able to prepare a 3D problem with a finite extent along x, and use periodic boundary conditions on some end-faces perpendicular to x.

Finally, if there is a dependence on x, and it isn't periodic, but you still have infinite extent in x in your problem, then your approach will likely have to be customized to the specific physics in question - you may need to provide the readers here with additional information about your problem.


If your overall geometry is infinite in any particular direction, then in many cases, that direction can simply be dropped out of the problem entirely. For example, in 3D, if your problem space is infinite along x, and if the variables of interest to you have no dependencies upon x, then you really should be solving a 2D problem (in the y-z plane, in this example) instead. Alternatively, if there does exist a dependence on x, but if that dependence is periodic, then you might be able to prepare a 3D problem with a finite extent along x, and use periodic boundary conditions on some end-faces perpendicular to x. Finally, if there is a dependence on x, and it isn't periodic, but you still have infinite extent in x in your problem, then your approach will likely have to be customized to the specific physics in question - you may need to provide the readers here with additional information about your problem.
H.T.M.
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Posted: 1 decade ago Jun 25, 2014, 8:26 a.m. EDT
Hi All

I have similar problem in setting infinite length. My interest is to simulate elasticity problem in 3D for an infinitely long cylinder (Axis along Z direction).

I tried to set Periodic boundary conditions on top and bottom surfaces of the cylinder and do the simulation but displacements (U,V W) become dependent on the axial coordinate Z. I was expecting them to be independent of Z !


So.... are there other options in COMSOL to set the infinite length for 3D problem?

I didnt want to use the 2D modules due to the nature the problem .



Thanks,
H.
Hi All I have similar problem in setting infinite length. My interest is to simulate elasticity problem in 3D for an infinitely long cylinder (Axis along Z direction). I tried to set Periodic boundary conditions on top and bottom surfaces of the cylinder and do the simulation but displacements (U,V W) become dependent on the axial coordinate Z. I was expecting them to be independent of Z ! So.... are there other options in COMSOL to set the infinite length for 3D problem? I didnt want to use the 2D modules due to the nature the problem . Thanks, H.

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