Find time period in dynamic implicit step for a quasi-static problem

[SM1994]

I am modelling a large deformation with hyperelastic material.
Technically I have a quasi-static problem, I inflate a balloon using pressure, but since it is large deformation static general module is not able to solve it; hence I am using dynamic implicit.
Obviously, for a different time period in dynamic implicit, I get different results.
My question is that how can I decide on the right time period? Since my problem is not really dynamic, therefore the duration of inflation cannot be a good factor to consider as time period.
Thanks for your help

 

[IceBreakerSours]

Firstly, in reality, no phenomenon is static - ever! Or, in another words, every phenomenon is dynamic. The relevant time scale may be hours, days, years - but there will be a time scale.

Secondly, assuming the pressure loading is "very slow", then a static simulation should be able to solve it - large deformation or not. Large deformation is a nonlinearity; you just need to enable NLGEOM, if you haven't already.

Thirdly, assuming static analysis is indeed appropriate, you can do an eigenvalue analysis and figure out the lowest and the highest modes of interest and pick a time step size that will capture those frequencies appropriately. Check this and this example out from a code called DIANA.

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[SM1994]

Thanks for your reply, I think that the appropriate step is static for my case, although I have enabled NLGEOM, for a time period of one sec, it cannot converge, and only reaches to 0.5 sec. I have also reduced the mesh size to prevent mesh distortion, but did not help.
Imagine that I inflate a balloon, and in one second, it reaches to the required pressure, but if I use one sec, in dynamic implicit, it does not give the actual resutl, hence I have to change it to some thing like 60 sec.

 

[FEA way]

Try with automatic stabilization enabled. You can find it in step settings. You may also have to refine the mesh and adjust material properties to achieve convergence.

 

[IceBreakerSours]

Can you talk about the actual physical phenomenon? How long does it take to inflate the balloon on the bench? Is the balloon material well-characterized using, say, biaxial tension?

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[IceBreakerSours]

I should add - The argument you make has flaws.

Now, what do you mean by ".. it does not give the actual result.."?

Keep in mind: a) force and acceleration are one and the same thing (related by mass) and b) acceleration is the second derivative of displacement. So, if the applied load/displacement is NOT smooth, the second derivative will have fluctuations which will show up as transient forces.

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