On 10/16/2017 09:23 AM, Mark Ma wrote:
It almost looks to me like you're applying both Dirichlet values (via
the ConstraintMatrix) and Neumann boundary values (via a boundary
integral). But then I haven't taken a look at the code, so I can't
really say for sure.
I think I only applied Dirichlet values via ConstraintMatrix. There
is no boundary integrals, so I believe Neumann BC is not
implemented.
My guess came from the fact that a Neumann boundary condition would act
like a boundary heat source. It looks like you have a heat source in the
last layer of cells around the boundary.
I don't know whether that is true, but it's a place I'd try to
investigate in debugging.
But may be you are right since for most of the case, heat equations
are solved assuming an adiabatic process, that is dT/dx = 0 at
boundaries. This zero values is automatically satisfied.
That's a different question. Whether one may *physically* want a
different equation is besides the point -- you have chosen one equation
you'd like to solve, but the numerical solution is wrong. It's
worthwhile trying to understand why that is before thinking about
*other* equations.
I think the problem comes from the way of setting Boundary values
using constraint method, which in dealii it makes some kind of
constraints at vertex of boundaries, i.e. x22 = x1/2 + x2/2,
Hm, that would be the constraint of a hanging node. Do you have hanging
nodes in your problem? If you do, may I suggest to simplify the problem
and see if you have the same problem on uniform meshes?
Best
W.
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Wolfgang Bangerth email: [email protected]
www: http://www.math.colostate.edu/~bangerth/
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