> I am trying to solve a system of equations that do this:
> Stokes to solve for v_r and p_r for one fluid (viscous rock), I use these
> solutions on the RHS of a Darcy type equation solved like step-20 for the
> pressure p_f in the fluid in the domain. Using the 3 solutions, I update
> another component (porosity - using a simple time dependent equation like
> dphi/dt = rhs(pr-pf)) and put it back in the Stokes equation and so on....
>
> One of my conditions for the Darcy eqn is that for the top boundary, the
> pressure there equals pr found previously.
>
> Looking at the output, my values for p_f at the top boundary does not equal
> the p_r just found. This is causing a massive issue as my porosity equation
> needs pr-pf to be 0 (or at least very small) at the top boundary, and this
> seems to be causing a real mess. I'm guessing because it's weakly imposed,
> there might be issues.
>
> Does anyone have any suggestions on what to do for this?
>
> My base profile for the equations separately all work and have been verified
> with MMS. With test values of the porosity, I have also verified that the
> profiles separately give me what I expect (which then gives me pr-pf
> monotonic
> at least, but with what is happening at the top, this bit is messed up).
Jane -- the problem as you state it is too difficult to debug. Here's ho to
approach this:
* Pick a problem for which you know the exact solution.
* In the Stokes equation, in all of the places where you currently use the
Darcy solution, use the exact solution instead
* In the Darcy equation, in all of the places where you currently use the
Stokes solution, use the exact solution instead
With this scheme, your iteration needs to converge in one step. If it doesn't,
then you know where to look. If it does, revert the steps above one by one
until the problem stops working.
I hope this helps!
Best
W.
--
------------------------------------------------------------------------
Wolfgang Bangerth email: bange...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/
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