Running problem of sfsi model in webinar25

[Charon]

4. The acceleration results of my analysis runs show a weird trend（As shown in the picture）. The acceleration at the deepest part of the soil is quite small, and the acceleration at the shallower part gets larger, which I know should be the rule, but the acceleration peaks at the deepest and shallowest parts are off by several orders of magnitude! In my perception, the deepest acceleration should be approximately equal to the peak of the UniformExcitation input (0.2) Can you see how this works? Or is there something wrong with the way I input seismic waves?

You are using Uniform Excitation so it make sense. The output will be relative acceleration(relative to the fixed nodes at the bottom level)

Thanks to the STKO team for the quick reply. In my case, how do I get the absolute acceleration of the soil nodes?

Best wishes，
Charon

[STKO Team]

Just extract the acceleration (relative) and sum the applied uniform excitation.

[Charon]

Just extract the acceleration (relative) and sum the applied uniform excitation.

That is, the acceleration results extracted by STKO plus the results of the applied seismic waves?
In geotechnical engineering, do we mean absolute acceleration (those acceleration time graphs in the paper)?

[STKO Team]

It depends and what the author wants to show.
Just read the paper and see how they describe the values shown in their graphs

[Charon]

Dear STKO Team，

Thanks for your quick reply!
Do you have any suggestions on the parameters for ZeroLengthContactASDimplex Element when acting between the pile and the soil?
I browsed other posts and I know that Kn and Kt should be quite large, as you set Kn to 1e10 and Kt to 7.14e7 in Webinar25.
However, in my model, if Kn and Kt are too large(For example, 1e8), the model requires a larger value of Rayleigh damping to continue the operation. And in the results, both the acceleration time course curve and the pore water pressure time course curve have a large oscillation component.
Therefore, my current results are running with a relatively small Kn and Kt. What do you think this will do to the results? What should I do to make it run with larger Kn and Kt?

Best wishes，
Charon

[STKO Team]

Large means "large compared to the typical stiffness of the bodies in contact".
1.0e8 can be large or small depending on your model.
Try to evaluate a typical stiffness as E*Lch (where E is the young's modulus and Lch is the approximate size of the mesh).
Then set Kn and Kt to that value increased by 1 or 2 order of magnitude

[xiaojitututu02]

I have also encountered the same issue: The curve of the soil pore water pressure is also strange, as the pore water pressure does not rise with vibration. Have you managed to find a solution?

[Charon]

I have also encountered the same issue: The curve of the soil pore water pressure is also strange, as the pore water pressure does not rise with vibration. Have you managed to find a solution?

The surface layer of the soil has to fix the pore water pressure.
The permeability coefficient of the UP unit should be set very large at the beginning (e.g. 100) and later updated to the true permeability coefficient value before inputting seismic waves. Try different permeability coefficients.

I think of these for now, others are welcome to add

[xiaojitututu02]

Thank you very much. I will come back to provide further updates and engage in further discussion if I make any new discoveries later on.

[STKO Team]

You're welcome