Applying Periodic boundary conditions 1

[Rameel]

Hi All,
I am working on a unit cell of a composite and model is a 3D cube. Because its a small part of a very big part so i need to apply PBC.
I know its possible with *Equation,,,, i am trying to write it in inpit file.FOr that I created node sets of all six faces of unit cell.and now have to apply *Equation between node sets of opposit faces.
But now the problem is, input file writes the node sets in assending numbering and hence its different than nodes order in the faces. So i want them in the same order in the node sets as in faces.Is there any method to reorder/renumber the nodes.
Any suggestions to overcome this problem will be highly appreciated.
Thanks

 

[rstupplebeen]

I may be confused however don't you just need symmetry planes or tie constraints causing the faces to remain planar?

Rob Stupplebeen

 

[Rameel]

I have to find out the shear modulus from a 3D cube unit cell of composit and for that I want to made two models
1- By applying homoganeous boundary conditions (faces remain palne)
2_ By applying Periodic boundary conditions, in this case opposit faces should have similar deformation, so that when it is kept in tray of other unit cells no face of unit cells penetrarte each other or overlap.

And what i understand *Tie constarine is only applied between the surfaces which are in contact or very near to each other,,, but in my case i have to apply between two opposit faces of cell.
May be the approach you are mentioning useful fro first case,,,, could you please elaborate it more.
thanks

 

[rstupplebeen]

The method I proposed would work for the first case. The second case is more difficult and a brute force technique as you are proposing may be most appropriate. If you post your model I will try to give it a look. I hope this helps.

Rob Stupplebeen

 

[Rameel]

Dear rstupplebeen thanks for your reply,

I have attached the input file.

Because I have two materials in composit and both have different stiffness so dont get equal deformation but i want that palne should remain plane.
The problem i am facing for plane remain plane case is that i cant apply tie because they are opposite faces of cube.
Secondly i get overconstraints at the edges when i try it with rigid surfaces.

Regards

 

[rstupplebeen]

Please see the attached file showing how to keep the 2 faces planar. You may want to constrain them to be planar to each other also. I hope this helps.

Rob Stupplebeen

 

[Rameel]

Dear Rob,
Thanks a lot this really helped me much.
It works very fine when i have to make Plane Z =0 and Plane Z=L planer.But i am getting problem when i have to make plane X=0 and Plane X=L planer. For this case i am applying following boundary conditions

Plane u1 u2 u3 ur1 ur2 ur3

X=0 C F F C C C

X=L C F F C C C

Y=0 F 0 0 F F F


Y=L F 0 0 F F F


Z=0 0 0 0 F F F


Z=L .002 0 0 F F F

Where
F= free
0= NO displacement(Restrained)
C= Coupled with refernce node

When i run the program firstly get following warnings
"Whenever a translation (rotation) dof at a node is constrained by a kinematic coupling definition the translation (rotation) dofs for that node cannot be included in any other constraint including mpcs, rigid bodies, etc.

MPCS (EXTERNAL or INTERNAL, including those generated from rigid body definitions), KINEMATIC COUPLINGS, AND/OR EQUATIONS WILL ACTIVATE ADDITIONAL DEGREES OF FREEDOM

Boundary conditions are specified on inactive dof of 184 nodes. The nodes have been identified in node set WarnNodeBCInactiveDof."


And these 184 nodes with inactive dof are nodes on edges of plane X=0 and Plane X=L.and its because i make u1 coupled with reference nodes in these planes.

Secondly I also see some disturbances at the edges.

I am attaching here my input file as well, i hope you can propose me some good solutions.

Thanks in advance

 

[Rameel]

Dear Rob,

Please if you get some time then have a look on my problem.
I shall be very greatfull to you for this kindness.

Best Regards
Ali