Learning Forum

[Rana Nasser]

Hi everyone,

I have a problem in modeling the soil using mohr-coulomb material model. The behavior of the soil in the transient analysis is good, but when I'm trying to do a modal analysis to the same structure the error in the attached image appears although the model is not in a superposition case. A small trial model is attached in the archived file below. 

Many thanks!  

[peteroznewman]

Hi Rana,

The attached image shows a Warning, not an error. It is telling you that Modal analysis is a linear analysis, but you have nonlinear contact in your model. In order to do the linear analysis it has taken the initial contact status and used that for the Modal analysis.  For frictional contact, if the contact was initially closed, then it behaves as bonded during the Modal analysis. If the contact was initially open, then there is no contact during the Modal analysis.

Kind regards,

Peter

[Rana Nasser]

Hi Peter,

Thank you for your quick response - as usual-, an error occurred after the previous warning and the model couldn't show any results ( the error message is attached below, sorry for forgetting it in the previous attachment). I tried to run the same model using orthotropic stress limits to simulate the soil and its weakness in tension and the model has worked and there are some extracted mode shapes shows that the soil and the wall have separated. I can't understand why the modal analysis could solve the problem with the ortotropic stress limits ,but it couldn't solve with the mohr-coulomb matrial model? could you please explain it in more details?!     

[peteroznewman]

You can't solve a Modal analysis with Mohr-Coulomb because that is not supported by the material model.

The reason is probably because the material model can't represent unlimited tensile stresses. Since a Modal analysis has arbitrary deformation magnitudes, the maximum tensile stress can't be guaranteed to remain in the valid region, so ANSYS turned off the ability to use that material in any solution but the two shown above.