On Tue, Jun 5, 2012 at 12:59 PM, Matej Svejda <[email protected]> wrote:
>> OK. My comments still stand. The discrepancies do not have the appearance of
>> a "bad" solution, but rather that they are not solutions to the same
>> equation and/or boundary conditions.
>>
>> Are you solving the same equation and boundary conditions? How do you know?
>
> So the equation I am trying to solve is:
>
> \frac{1}{D_r} * \frac{\partial \varphi(\alpha, t)}{\partial t} =
> \frac{\partial^2 \varphi(\alpha, t)}{\partial \alpha^2} +
> \frac{\partial}{\partial \alpha} (\frac{1}{K * T} * \frac{\partial H(\alpha,
> t)}{\partial \alpha} * \varphi(\alpha, t))
>
> Where D_r, K, T are constants. My FiPy equation is:
>
> equation = TransientTerm(coeff = (1. / self.p.Dr)) == \
> DiffusionTerm() + ExponentialConvectionTerm(coeff = (1 / (self.p.K *
> self.p.temp)) * H.getFaceGrad())
>
Matej, The equation looks good.
> The boundary conditions of my problem are:
> \varphi(\alpha, 0) = p_0(\alpha)
> \varphi(-\frac{\pi}{2}, 0) = \varphi(\frac{\pi}{2}, 0) = 0
>
> Where p_0 is a known function.
>
> In FiPy I represent them as:
>
> prob.setValue(self._p_zero(alpha - math.pi / 2))
> boundaries = (FixedValue(faces=alphaMesh.getFacesRight(), value=0.0), \
> FixedValue(faces=alphaMesh.getFacesLeft(), value=0.0))
Read the FAQ here
<http://www.ctcms.nist.gov/fipy/documentation/FAQ.html#i-can-t-get-the-fixedvalue-or-fixedflux-boundary-condition-objects-to-work-right-what-do-i-do-now>.
I'm concerned that maybe the boundary conditions are not working as
you might expect in version 2.1. We have since corrected some issues
by implementing the boundary conditions in a different way. This may
or may not be the issue.
Another thing is that H.getFaceGrad() does not see the boundary
condition (again this is something that has been corrected in the
upcoming release). One way to get round this in version 2.1 is to make
the centers of the end cells the boundaries of the domain and use
source terms to set the value of \varphi to zero in these end cells
using a really large implicit source term just for the end cells. This
will avoid all the boundary issues. Try that and see if it helps.
Good luck.
--
Daniel Wheeler
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