Does pylith have boundary condition like winkler-foundation?
The cell of the model with viscoelastic material collapses in gravity field.
To prevent this, I used initial stress as in step 2 of the 7.17.5 chapter in manual. I want to observe the stress that occurs in my model due to the density difference.
However, when using the power-law viscosity, it seems that the desired viscosity was not applied due to the influence of the initial stress.
So, I wonder if there is a winkler_foundation boundary condition to prevent cell collapses.
PyLith does not presently have a Winkler foundation boundary condition; however, I am not sure this would do what you want. A Winkler foundation adds an additional term to part of the diagonal of the stiffness matrix, acting as a 1D spring. You would still get some collapse of your domain, although the amount might be decreased. The question is what you are trying to observe. It sounds as though you want to observe the viscoelastic relaxation that occurs after you ‘turn on’ gravity. That is not a realistic initial condition within the earth, however. Looking at your question again, it appears that you want to observe the stresses due to a density contrast. In that case, you could apply initial stresses due to a single density. The out of balance stresses will then correspond to those due to the density contrast. There is a PyLith example that does this (I believe there is a 2D gravity example).