Discussion Forum

Hello,
Recently I read a blog about Comsol using skills, and there is a example about how to using global equation to limit the max temperature at a probe.
I built a model followed the blog , the main step is as follows
1. Using Heat Transfer in solids, choose Stationary and the geometry is 1m*1m square ,
2. Add a boundary heat source at one boundary and the heat rate is Q_0, the other three boundary is nature convection boundary and the heat transfer coefficient h=10.
3. Add a max function maxop1 and set T_probe=maxop1(T), add parameter T_max=100[degC]
4. Add a global equation as Name:Q_0 f(u,ut,utt,t): T_probe-T_max

the error message is failed to find a solution Singular matrix.
There are 1 void equation (empty row in matrix) for the variable comp1.Q_0 ...

Clearly the error message shows that there are some errors about Q_0

But is that a wrong initial value problem or the global equation must contains something relative to Q_0 like Q_0t ?
Thanks!

Wesley