Dear sir/madam,
I have two questions about the mesh size in the dynamic analysis. While we are studying on a dynamic analysis model consists of a multilayered soil profile with varying Vs values and includes some tight structural elements at the center of the ground of the model:
1) -Calculating the critical mesh size according to soil layer with minimum Vs value, applying this mesh size to all geometry to have a uniform mesh size and determining the sub step number according to this critical mesh size?
-Calculating the critical mesh size for all layers according to their Vs values separately and setting the mesh size of soil layers by changing their coarseness factors and determining the sub step number according to the most critical mesh size of the all layers?
Which one of the options presented above is more accurate about the mesh size of the model and what can be done to have an optimum model for a faster calculation?
2) Is it correct to apply the mesh by changing the relative element sizes from the expert settings to have a uniform mesh? I'm asking this because automatic mesh procedure is setting the mesh size according to the geometry and there can be significant differences in the mesh sizes in the model.
Thanks and best regards.
Nuri
Dear Nuri,
1) You must ensure that any element in your model does not miss the seismic wave. Naturally, the wave travels differently in rock and soil or hard soil and soft soil, etc..
This means that the Vs is different in each case, which allows you to have a much coarser mesh where large shear velocity values are to be expected and a finer mesh where lower velocity values are to be expected.
I would go for #2 as you would save a lot of calculation time while ensuring that your finite element mesh does not miss any parts of the signal.
About the time step please read this article about Time step used in dynamic calculation .
2) Indeed, when the global setting cannot help, you should apply local coarseness factors per polygon. That is precisely why this option exists to allow for such flexibility.
Answer Verified By: Nuri Taştekin