Reply To: Apply prestress with the inistate command, for a hyperelastic material (Yeoh)

[peteroznewman]

Hello Charlotte,

The result with inistate and gravity is closer to horizontal than the result with gravity only. It’s not going to return to a perfectly horizontal state like the mesh with no load on it because the equilibrium is different without gravity.

I’m still not clear on why you are trying to read inistate onto a mesh of different geometry than the one the inistate was written from.

One reason is to export the deformed shape of the mesh from the gravity load, which may have taken hundreds of nonlinear iterations to converge, and begin a new analysis with gravity and have step 1 converge in just a few iterations. In that case, the deformed mesh would not not move hardly at all when converged. One reason you may want that is so in a second step, you can apply other loads and measure the deformation from step 1. While you could do a two step solution starting with the undeformed beam, the deformation at the end of step 2 is measured from the undeformed beam.  Using inistate and a deformed mesh, you can measure deformation at the end of step 2 from the nodal positions at the end of step 1 with just gravity.

On a related topic, sometimes only the deformed shape of a structure is known along with the loads and supports that were applied, but the undeformed shape with no load is not known and that is the desired output. This happens in biology where a CT scan captures the deformed shape of some structure in the body and the pressure on that body is known because it can be measured. There is a procedure called Inverse Analysis where the deformed body is meshed then loads and supports are applied and the solution in a deformation plot shows the body with no load. One limitation to this analyisis is that it is for linear analysis only.

Regards,
Peter