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 ]
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