### Divergence Stokes solver with mesh refinement

Posted:

**26 Jul 2023, 10:10**Hi there,

I am running a transient simulation to make a diagnostic of a Scandinavian glacier.

I use a solver which compute the mass balance in function of elevation in the glacier and then actualise the free surface elevation with the free surface solver.

I made some tests with a resolution of 100 m x 100 m and everything works, I can do my simulation with 59 time-steps as I want. Nevertheless, I want to refine my mesh with a resolution of 40 m x 40 m and did not get a convergence with the Stokes solver. I tried different combination with direct and iterative solvers.

Here is the parameters used with the resolution of 100 m x 100 m:

For the refine mesh, I removed the newton iterations, which allow to have a convergence for few more iterations but not enough. I tried to used :

I use a parallel computation, so I also try the simulation with a non-split mesh.

Unfortunately, all these try did not change the solution anymore.

Until know, when I got convergence problem, it was for the bigger mesh as well and once the problem was solved, I could refine the mesh then.

So I am wondering if anyone have a solution to this problem ? For information, the area of the glacier is only 2.77 kmĀ².

Thanks in advance for your help.

Best,

Olivier

I am running a transient simulation to make a diagnostic of a Scandinavian glacier.

I use a solver which compute the mass balance in function of elevation in the glacier and then actualise the free surface elevation with the free surface solver.

I made some tests with a resolution of 100 m x 100 m and everything works, I can do my simulation with 59 time-steps as I want. Nevertheless, I want to refine my mesh with a resolution of 40 m x 40 m and did not get a convergence with the Stokes solver. I tried different combination with direct and iterative solvers.

Here is the parameters used with the resolution of 100 m x 100 m:

Code: Select all

```
Solver 5
Equation = "Stokes-Vec"
Procedure = "IncompressibleNSVec" "IncompressibleNSSolver"
!linear settings:
!------------------------------
Linear System Solver = Direct
Linear System Direct Method = mumps
!Non-linear iteration settings:
!------------------------------
Nonlinear System Max Iterations = 50
Nonlinear System Convergence Tolerance = 1.0e-08
Nonlinear System Newton After Tolerance = 1.0e-03
!------------------------------
! steady-statte settings
!------------------------------
Steady State Convergence Tolerance = Real 1.0e-4
! 1st iteration viscosity is constant
Constant-Viscosity Start = Logical True
End
```

Code: Select all

`Stokes Flow = logical true`

I use a parallel computation, so I also try the simulation with a non-split mesh.

Unfortunately, all these try did not change the solution anymore.

Until know, when I got convergence problem, it was for the bigger mesh as well and once the problem was solved, I could refine the mesh then.

So I am wondering if anyone have a solution to this problem ? For information, the area of the glacier is only 2.77 kmĀ².

Thanks in advance for your help.

Best,

Olivier