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Normal derivative on boundary in PDE Coefficient Form Mode
Posted Nov 5, 2011, 2:14 p.m. EDT Version 3.5a 0 Replies
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I am solving a 2-dimensional time depending PDE using the Coefficient Form of the PDE mode. The only dependent variable is u. For post-processing I want to calculate an integral along one boundary for every time step. The integral contains the derivative normal to this boundary. The bounday is along the x axis, so the normal derivative is along y.
What I tried: I have defined a boundary integration variable on the specific boundary. The expression is 0.5*cos(x)*ncu, where ncu shlould be the normal derivative to the boundary.
The user guide says: ncui: Normal components of the c*grad(ui) vector (Coefficient Form only). Only available when solving using coefficient form as solution form.
However, evaluating the exrpession after solving the PDE results in an error:
Error 6142
Cannot evaluate all expressions on any domain
Failed to evaluate variable
Variable: ncu....
I tried then different names for the normal derivative, ncu1, ncu_c, but I am getting the same error.
Any idea what I am doing wrong? Any hint is much appreciated.
Jorg
Hello Jorg Strutwolf
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