fakeplasticpumpkin
I'm am trying to solve a Poisson equation problem, I need to find out how to apply a ground to a boundary or point in Comsol script, I cannot do this as the all the other points in the geometry are automatically made a 0*u_test (the dependant variable). This does not help me as I need to determine the impulse response of my geometry which I cannot do without some kind of grounding... I desparately need help...

fakeplasticpumpkin
Thanks to my girlfriend Suzanne for giving me the answer for this one...
In case anyone is interested (doubtful), It was my boundary conditions that were wrong. I had everything defined as Neumann boundaries but I actually needed the ground area to be defined as Dirichlet conditions. That's why it didn't work and now it works! Goodie!
fakeplasticpumpkin
How do you delete a topic?
cristinaaniro
Hi!

I am a beginner in working with COMSOL.
I want to ask how can I use a function in defining a global expression.

For example I have several functions, depending on the space: fHx, fBx, fQx =f(x), which I take it from a .txt file.

1. first question
I use them to define some other parameters. I write in global expressions like this:
fvx = fQx(x)/(fHx(x)*fBx(x))
fDx = fBx(x)/(fvx*constant)

COMSOL is computing, but I am not sure is k, because in the end when I want to plot fvx and fDx, form Global variables plot it gives an error: 8032 fvx is not a valid globla expression.
This means that there is the possibility also to compute it wrong along x axis.

2.
I want to calculate a parameter in one point (x=103), depending on the functions I implemented. In global expression I write
c_103 = (fQx(103)*c+constant)/(fQx(103)+constant)

c is the dependent variable of the model.
The expression is computed, but I don't trust is k. The same warning when I try to plot it.

Any suggestions would be of great help!

Regards
Cristina
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