What Constraint can I impose?

1

Hi:

I wanted to model the a bottom clamped cylindrical shell under side loading. While under loading, I wonder what constraint can I add to make the top circle remain as a circle when I it is under loading? It can’t be Dirichlet as the the top displacement is unknown.

Yuxiang

2

Hi, can you upload your input file or maybe a picture showing your boundary conditions and model?

3

tank (2)
tank (2)945×625 7.87 KB

I 've found rigid body card may do the job, but I found it’s hard to converge for calculix

4

I don’t undersand how/why you could keep it cilindrical if you are loading it in radial direction.

5

you can assume there is a rigid roof on this cylinder, the side forces are acting on the side

6

I got the idea, thanks.

7

I used the solid body card, but the residual cannot converge after some time showing without converging to to 0.005*time averaged force, I found the residual force cannot go further small. Is there any control method to let the solver to iterate fixed number without error on showing diverge or too many iteration needed?

8

Hi,

Use keywords:
*COUPLING
*KINEMATIC

Couple top nodes to the reference point - a node in the cylinder’s center.

9

Thanks for your reply, Imirzov.

I wonder if this reference point in the cylinder’s center will move? If it will not move basically we are imposing Dirichlet BC on the top.

10

Don’t wonder. Just do ))
Without additional boundary conditions the reference node WILL move.

11

Thanks.

I tried setting the top rim as rigid body before,What is the different with setting it kinematic coupling? The rigid body card seems work but ultimately will diverge somehow

12

In coupling constraint you can choose which DOF to couple:

https://abaqus-docs.mit.edu/2017/English/SIMACAECSTRefMap/simacst-c-kinematiccoupling.htm

13

Hi, Imirzov:

I created a center point of upper top rim and put reference point there under coupling card, but the calculix shows ERROR in cascade: zero coefficient on the dependent side of an equation dependent node:…, I guess it’s because the the created center point is a standalone point and does not associated with any equation? The geometry I use is a pure cylindrical shell with no roof element

Any advise would be appreciated!
Yuxiang

14

Advice: ANSA by BETA CAE Systems is very good preprocessor. You can create coupling constraints there within a few clicks. Abaqus CAE is worse, but still good enough for your needs.
Good luck!

15

The reference node in *COUPLING, *KINEMATIC can be unused by any other equations or elements so that won’t be the problem. That error sounds like what you sometimes get with MPCs on shells. Shells can be trouble because their MPCs conflict with those generated by features like *COUPLING, etc.

I would use 20 node solids if you can or add a ring of elements with a high stiffness material to approximate being rigid. Sometimes these idealizations are more trouble that just modeling the thing itself.