Dear all,
I have some problem with Lagrange multipliers: Maybe I misinterpret my
results, but somehow they don't have the effect I expected.
Looking at the solution of systems_of_equations_ex3, (using paraview) I
see the (real part of) pressure r_p to be 0 at time step 0 and than it
jumps to ~10, where it stays for the rest of the simulation. But isn't
it actually enforced to stay at 0 "forever"?
I also tried to change its value to some other fixed (and
time-dependent) ones:
diff --git
a/examples/systems_of_equations/systems_of_equations_ex3/systems_of_equations_ex3.C
b/examples/systems_of_equations/systems_of_equations_ex3/systems_of_equations_ex3.C
index b626203..f576138 100644
---
a/examples/systems_of_equations/systems_of_equations_ex3/systems_of_equations_ex3.C
+++
b/examples/systems_of_equations/systems_of_equations_ex3/systems_of_equations_ex3.C
@@ -614,8 +614,15 @@ void assemble_stokes (EquationSystems & es,
// negative one. Here we do not.
for (unsigned int i=0; i<n_p_dofs; i++)
{
- Kp_alpha(i,0) += JxW[qp]*psi[i][qp];
- Kalpha_p(0,i) += JxW[qp]*psi[i][qp];
+ // original: set p=0
+ //Kp_alpha(i,0) += JxW[qp]*psi[i][qp];
+ //Kalpha_p(0,i) += JxW[qp]*psi[i][qp];
+ // lets fix the pressure to some finite value:
+ //Kp_alpha(i,0) += JxW[qp]*psi[i][qp]-1.*JxW[qp];
+ //Kalpha_p(0,i) += JxW[qp]*psi[i][qp]-1.*JxW[qp];
+ // lets make the pressure growing with time.
+ Kp_alpha(i,0) += JxW[qp]*psi[i][qp]-theta*dt*JxW[qp];
+ Kalpha_p(0,i) += JxW[qp]*psi[i][qp]-theta*dt*JxW[qp];
for (unsigned int j=0; j<n_u_dofs; j++)
{
Kpu(i,j) += JxW[qp]*psi[i][qp]*dphi[j][qp](0);
However, even though the values change a bit, the general behaviour
stays the same.
Could someone please help me clarifying, what is wrong here?
Thanks in advance,
Tobias
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