2-step simulation for pre-stretch structure

I check it and find you are right. If I use one input file, there is no problem like this.
But I am sure I change the Step1.rout file into Step2.rin and then run Step2. Why it happened?

This would mean that the approach with restart is questionable. But make sure that it’s really the case by saving output at every increment and comparing the results from the last frame of the first step and the first frame of the second step.

Oh, I found why.!!

If you remove any load from Step2 the system will recover its initial position. It’s like you suddenly release the prestress.
If the time step at the Step2 is not small enough and pre-stretch is large , the first time step in Step2.inp will contain certain amount of recover.
I guess one should keep time step small enough at least for the starting point.

I have never try FSI (maybe I try now) but I can anticipate some issues due to this effect. If pressure doesn’t rise fast enough to stabilize or one doesn’t use some damping on the membrane you can have a crazy oscillating system.


Right and, from what I’ve noticed, CalculiX doesn’t save the 0 frame of the second step.

I would also suggest adding plasticity to this model, just in case.

Here’s what it looks like in Abaqus, where 0 frames are saved too:

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You are right. I decrease the time step of Step1 into 0.001. The initial displacement of step2 become 1.311mm.

Can I think that the effect of this can be eliminated if the time step is small enough?

You need to decrease the time step anyway to be accurate. Check the first oscillating mode of this membrane to get a proper idea of time step.

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I got it. Thanks for your notice.

Don’t you mean the second Step2.inp?¿?

Yes, I decrease the time step in Step2.inp. I made a writing mistake.