Fwd: Issue about FEA mesh and rigid body contacts

[ZHAOYUAN CAO]

Dear all, 

Excuse me.When  I tried to solve FEA mesh and rigid body contacts, maybe there is a difference between the theoretical solution and the results. Could you help me?

I am solving the problem of a sliding block sliding down a slope under the action of gravity. But when I tried to solve it with the small-scale slider model, I encountered a question where there was a significant difference between the theoretical solution and the results.

The FEA mesh is C3D4, which is from abaqus. And the rigid plate is built  by chrono  or imported from *.obj file  which rotates 30 degrees along the z-axis.

First，the length, width, and height of this slider model are 1.4m，0.52m and1.4m respectively. The calculation results of acceleration of node are as follows: ax is -2.0427, ay is -1.1785, and az is 1.2e-5. The theoretical solutions are as follows: ax is -2.0385，ay is -1.1768, az is zero. Compare two results, acceleration of nodes is quite similar to the theoretical solution when stable contacts occurred.

And then ,I tried to scale the FEA mesh to one tenth.But the calculation results of acceleration acceleration of node when stable contacts occurred are as follows: ax is -1.3986, ay is -0.7985, and az is 0.0045. The difference is significant between the theoretical solution and the results.

The attachment is my code and fea mesh.

And the second question is as follows.  The default unit system is SI in ProjectChrono. Can I change the unit system, for example changing length unit to mm, changing density to tonne/mm^3, changing elastic modulus to MPa ?

 

I hope you understand my questions.

Cheers johncao

[Alessandro Tasora]

dear Johncao

sorry I do not have time to test your code, but I can give you few hints:

- have you tried to change the setings of the ADMM solver? it is strange that the large block is almost exactly the analytical solution and the small one is failing..

- projectchrono is dimensionless, so you can assume whatever unit system you prefer. For example once I simulated wrist watch mechanisms, and I assumed length unit to be mm.  Remember that also forces, accelerations, torques, densidies, gravity acc. etc. must be adjusted accordingly to your choice.

alessandro tasora

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