Hello,
I’m using the THM model and getting a negative pore pressure for my cavern floor boundary nodes. I have the rock permeability set to 1x10-19 and porosity set to 0.015 to represent salt rock. When the boundaries are dropped to the gas pressure the state of compression reduces due to it being considerably lower than the lithostatic stress. This results in displacement towards the cavern centre, where at its largest point (cavern floor axis of symmetry) it results in a negative pressure.
I’m wondering if anyone has dealt with this negative pressure before? I seen in another post it was recommended to use (Q8P4) elements, where the simulation integration order is set to 3 and the displacement set to 2. I’m using 2nd-order traingular elements with 6 defined points (nodes), and the system integration order is set to 4, displacement 2 and pressure and temperatuer 1…
As I felt this may be related to the permeability I tried afjusting this and it seemed to reduce the effect. The node measure for this is the floor node on the axis of symmetry.
Hello Richard @richardWallace,
I think triangular elements are not capable of dealing with incompressibility constraints. You should convert your triangular mesh to a quad9 element and then use integration order 1 for pressure and 2 for displacement (i.e., Q9P4).
However, based on the pressure plot, there don’t appear to be any shocks, so this might not be the problem. The kinks in the plot suggest that your timestep might be too large; consider reducing it to see if it solves the problem
I hope this helps!
Best,
Pavan