Dear Jonathan, many thanks for your quick reply.
I figured out that the convective flux crossing the left side of the element W is in your equation - rho * v * (phi_W + phi(X=0))/2 and in my equation - rho * v * phi(X=0) That is the difference. Why is it necessary to interpolate the value of phi at the left side between phi_W and phi(X=0)? The value of phi is known at this position, because it is the boundary condition. Warm regards, Alex Am 06.03.20 um 21:30 schrieb Guyer, Jonathan E. Dr. (Fed) via fipy: > My guess is that you got the sign of the outward-facing normal wrong > somewhere. I posted my derivation to > https://gist.github.com/guyer/3b77bbf32d90ef314754f0d76a7e04cc. > > >> On Mar 6, 2020, at 4:09 AM, Alexander Tismer >> <alexander.tis...@ihs.uni-stuttgart.de >> <mailto:alexander.tis...@ihs.uni-stuttgart.de>> wrote: >> >> Dear Users, >> >> my question concerns the implementation of the boundary conditions in >> FiPy. >> I would like to solve a 1D Conv-Diff-Equation with 3 control volumes >> using CentralDifferenceConvectionTerm and DiffusionTerm of FiPy. >> >> For me, it is not clear why the first row of the matrix of the linear >> equation system is >> > 9.000000 -2.500000 --- >> and the right hand side is >> > 6.5 >> >> The case is the following. Each control volume (W, C and E) has the >> length 1/3. All coefficients (gamma, u, rho) in the equation is set to 1: >> >> o---> x >> |-D=1/3-|-D=1/3-|-D=1/3-| >> x=0 x=1 >> phi=1 phi=0 >> v v >> +-------+-------+-------+ >> | W | C | E | >> o---x---o---x---o---x---o >> | | | | >> +-------+-------+-------+ >> >> If I discretize the equation in the first control volume (W), I get >> for the matrix row >> > 10.000000 -2.500000 --- >> and for the right hand side >> > 7.0 >> >> So this is a little bit different from FiPy. Is there any mistake from >> my side? >> >> Please find attached my notes on how calculating my matrix >> coefficients (fipy_0.png) and my python script for fipy (fipy.py). >> >> Warm regards, >> Alex >> <fipy_0.png><fipy.py>_______________________________________________ >> fipy mailing list >> fipy@nist.gov <mailto:fipy@nist.gov> >> http://www.ctcms.nist.gov/fipy >> [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] > > > _______________________________________________ > fipy mailing list > fipy@nist.gov > http://www.ctcms.nist.gov/fipy > [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] > -- Alexander Tismer Institut für Strömungsmechanik und Hydraulische Strömungsmaschinen Universität Stuttgart Pfaffenwaldring 10 70550 Stuttgart Tel.: +49 (0) 711 / 685 63007 Fax: +49 (0) 711 / 685 63255 eMail: alexander.tis...@ihs.uni-stuttgart.de http://www.ihs.uni-stuttgart.de _______________________________________________ fipy mailing list fipy@nist.gov http://www.ctcms.nist.gov/fipy [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ]
