Hi, I am new to FreeFem and PETSc and need some help. I want to solve a time dependent stokes equation, where the righthandside is updated with the old velocity uold in each iteration step. Until the time loop everything works fine but then I get the error "Error line number 63, in file petsc-stoke…

The error is: 63 : rhs = vPbf(def(u) [u, uB, uC],Wh) error operator <6C_args>, <7E_Array>, <PP5v_fes> The fix is: 63 : rhs = vPbf(0,Wh); Like your line 46.

Thank you for your answer! But if I set 63 : rhs = vPbf(0,Wh); my right-hand side won’t be updated with the computed velocity from the last time step.

Well, you need to update it yourself.

Okay thanks. Is there any documentation why rhs has to be set to vPbf(0,Wh) and can’t be something like vPbf([uold,uoldB,p],Wh)? I am trying to update it myself for the first iteration step (so without the loop): // run with MPI: ff-mpirun -np 4 script.edp load "PETSc" /…

See here: Finite element Note that vPbf(0,Wh) does not set [uold,uoldB,p] to zero. It just tells FreeFEM to evaluate the expression as a linear form rather than a bilinear one.

Stokes with time stepper - PETSc

General Discussion

rirane July 11, 2023, 8:45am 7

Thank you for the clarification. Now everything seems to work fine!
petsc-stokes.edp (1.7 KB)

Unsteady Stokes with PETSc

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Stokes with time stepper - PETSc

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