Two block problem

[Narissa]

Hello there.

I got issue running my model. In my model, I have a hyper-elastic block on top of the biphasic block with contact. The block is fixed at the bottom of the biphasic block and a pressure load is applied on top of the hyper-elastic block. I would like to run a biphasic analyses but it kept giving me the Negative Jacobian error. I did run separate biphasic analyses where I only have a hyper-elastic block, it still gave me same error. Any advice on how to deal with the error?

Warm Regards,
Narissa

[ateshian]

Hi Narissa,

You need to first push the blocks together a little bit using displacement control (or create your model such that the blocks overlap a little bit initially). Once they overlap a little bit, you can switch to load control (such as the pressure you apply at the top). Otherwise, the contact interface is not initially engaged if the surfaces don't overlap. So the finite element analysis fails because there is a pressure applied on one side of the block, but that pressure cannot be balanced by the contact on the other side since the program doesn't detect any contact in the first iteration. So the loaded block goes to infinity and the analysis fails.

Best,

Gerard

[Narissa]

Hello Gerard.

Thank you for your help. Is there any other way in which I can use pressure instead of displacement?

Regards,
Narissa

[ateshian]

Hi Narissa,

Yes, within PreView, you can translate one block by a small amount to overlap a little bit with the other block. So, at the start of the analysis, FEBio will detect contact and should proceed with the solution properly.

Best,

Gerard