Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
setting periodic boundary condition in structural mechanics problem
Posted Jan 10, 2010, 11:14 p.m. EST 4 Replies
Please login with a confirmed email address before reporting spam
Hi,
How do you set periodic boundary conditions for a 3D structural mechanics model like if you have a unit cell? Is this different from using symmetry boundary conditions?
Thanks!
How do you set periodic boundary conditions for a 3D structural mechanics model like if you have a unit cell? Is this different from using symmetry boundary conditions?
Thanks!
4 Replies Last Post May 19, 2010, 8:24 a.m. EDT
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Hi
For me it should be rather rather similar, you have an example (mixed physics) in the smemodlib.pdf for the SAW gas sensor p434 for V3.5a, and some generic explanation in the chapter on "Using Periodic Boundary Conditions" in the "guide.pdf" p257 (v3.5a).
But there are some restrictions such as "use homogeneous Neumann boundary condition", but this I understand is a general restritcion, not linked particularly to SM.
You will also find further cliues in the modelling.pdf "Using Identity Conditions" p430 (V3.5a)
do an indexed search on the COMSOL documentation, this helps to locate interesting features that are scattered around in all the docs,
And do not forget to search the model library, there are lots of goodies asnd inspiration source therein
Good luck
Ivar
For me it should be rather rather similar, you have an example (mixed physics) in the smemodlib.pdf for the SAW gas sensor p434 for V3.5a, and some generic explanation in the chapter on "Using Periodic Boundary Conditions" in the "guide.pdf" p257 (v3.5a).
But there are some restrictions such as "use homogeneous Neumann boundary condition", but this I understand is a general restritcion, not linked particularly to SM.
You will also find further cliues in the modelling.pdf "Using Identity Conditions" p430 (V3.5a)
do an indexed search on the COMSOL documentation, this helps to locate interesting features that are scattered around in all the docs,
And do not forget to search the model library, there are lots of goodies asnd inspiration source therein
Good luck
Ivar
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
this was very helpful... I have already set up my model.. so we'll see if it'll work. thanks so much!
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Hi Jihan,
Does your model work properly?
I have same problems as you had.. I have a unit cell and I need to set periodic boundary conditions to assume it like a layer..
Then I need to simulate a compression and define stiffness..
I set periodic BC in terms u,v,w but it doesn't work as it should-one boundary bends too much and almost nothing happens with other.. but it can't be true in periodic layer structure.. (contacting boundaries should behave in the same way)
I thought I need to set BC in terms of pressure but I dont know how... just replacing u,v,w on p gives nothing...
how did you set up your BC?
best regards,
Alex
P.S: my unit cell with pBC is attached.
Does your model work properly?
I have same problems as you had.. I have a unit cell and I need to set periodic boundary conditions to assume it like a layer..
Then I need to simulate a compression and define stiffness..
I set periodic BC in terms u,v,w but it doesn't work as it should-one boundary bends too much and almost nothing happens with other.. but it can't be true in periodic layer structure.. (contacting boundaries should behave in the same way)
I thought I need to set BC in terms of pressure but I dont know how... just replacing u,v,w on p gives nothing...
how did you set up your BC?
best regards,
Alex
P.S: my unit cell with pBC is attached.
Attachments:
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Hi Alex,
I think that the problem comes from a badly defined geometry, and the mesh quality.
The boundary #13 is very distorted because of a low thickness at some point. Plus, there are several small boundaries in the geometry, which may cause some problems. Also, the quality of the mesh is low at these "critical points", so the boundary conditions may not be taken in count propertly (numerical problems).
If you can, change your RUC to avoid those low thicknesses. Shifting it of a few millimeters may really help !
Best regards.
I think that the problem comes from a badly defined geometry, and the mesh quality.
The boundary #13 is very distorted because of a low thickness at some point. Plus, there are several small boundaries in the geometry, which may cause some problems. Also, the quality of the mesh is low at these "critical points", so the boundary conditions may not be taken in count propertly (numerical problems).
If you can, change your RUC to avoid those low thicknesses. Shifting it of a few millimeters may really help !
Best regards.