Richards flow: numerical instability in calculation of velocity

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Hello,

I am simulating Richards flow in OGS5 using the following conditions:

  1. Initial condition - uniform pressure in the domain

  2. Boundary conditions:

  • Inlet (line)- constant source term (CONSTANT_NEUMANN)
  • Outlet (line)- constant pressure
  1. Numerical solver settings:

"
#NUMERICS
$PCS_TYPE
RICHARDS_FLOW
$ELE_UPWINDING
0.5
$ELE_MASS_LUMPING
1
$ELE_GAUSS_POINTS
3
$LINEAR_SOLVER
; method error_tolerance max_iterations theta precond storage
3 6 1.e-015 5000 1.0 100 4
$NON_LINEAR_SOLVER
; method error_tolerance max_iterations relaxation
PICARD 1.0e-15 5000 0.0
"

The pressure and saturation calculations are stable over time in all tested cases, while the calculation of velocity at each node varies over time (varies up to 3-4% of expected value in some cases). I understand that this might be the case if the solver focuses on precision in the calculation of the primary variable (Pressure in this case), while it does not follow through on the calculation of the secondary variable (velocity in this case). Is this true for OGS5? Is there any way I can address this (maybe change the solver or other parameters in the .NUM file)?

Regards
Swamini

1 Like
2

Hi @swamini.khurana,

how did you come up with the presented set-up?
What did you already tried out?

Please, provide a minimal working example, so other I can try it out.

Best,

3

…What are you trying to model?

1 Like