# How to check if a model is fully constrained? Model does not reach equilibrium

Hi all,

I have run simulations on a pressure hull model with face sealing. The goal is to test if the design can tolerate a given pressure magnitude. The hull is symmetrical about 2 planes, so just a quarter of it is represented.

The hull is mounted to a plate which is attached to a bigger structure, so just part of it is included in the model. I assume that the far end of the plate is fixed, forcing deformations to be zeros.

I break boundary conditions into 2 steps; the first is applying bolt clamping force, and the second is applying pressure on the external surfaces of the hull. The simulation results of face calculations on faces of the clamping bolts and the stud are off. For example, the clamping force exerted between the lid and the hull disappears at the time step where pressure is applied (total clamping force of the hull seal face is 4400 N)

and the forces between the stud and the stud boreholes do not converge. As shown below, the force in x direction skyrockets, reflecting increasing pulling from the lid of the pressure hull which is pressed down by the pressure.

Due to these observations, I am thinking that maybe the model is not well constrained. How do I check if a model is fully constrained? Any suggestions on contacts and boundary conditions will be greatly appreciated.

Here is the link to my project. You can look at “Run2” of “static mesh 2”. If you look at different time steps, you will be able to see that the solution is diverging.

Boris

Hey Boris!

One thing that came into my head was this post from my colleague @rszoeke: No contacts were defined for some sub-assemblies - #3 by rszoeke - check it out and let us know if that helped you. Tagging the @fea_squad in any case.

Best,

Jousef