Coupled analysis

[yingying]

I am currently having some trouble running a coupled analysis of an earth dam.

The uncoupled analysis using quad elements ran fine and showed reasonable results. However changing the quad elements to Four Node Quad u-p Elements (element quadUP) gives QNAN errors during the dynamic analysis (the gravity analysis seems to run fine).

Other than changing the ndf to 3, updating the pwp fixities, and adding the properties required for the quadUP elements, the file is the same as the uncoupled analysis.

Are there any obvious changes I have missed out or things I should be looking for in my script in order for the dynamic analysis to work?

[selimgunay]

Have you done an eigenvalue analysis and have you assigned masses to the nodes? OpenSees does not automatically convert gravity forces to mass.

[yingying]

What will the eigenvalue analysis do?

I have assigned masses to the surface nodes where they are submerged under the water table - is this correct?

[yingying]

I believe I have made some improvements to the script and am getting closer to solving this problem:

I defined a gwt by assigning nodes above it with fixed pwp, and nodes below it with free pwp.
For the gravity analysis, I have assigned the permeabilities to be 1 (to ensure hydrostatic conditions), and then I have updated the permabilities for the dynamic analysis.

This runs fine if I do an elastic analysis, i.e. I don't update the material stage to 1. However when I try to run a plastic gravity analysis after the elastic gravity analysis, the script does not run and I get QNAN errors.

What is it that I am still missing? Or could i be defining some parameters incorrectly?