Discussion Forum

Hi everyone,

I've got simply problem with few questions. I'm working at a heat generation in a disc brake, just like the one from Application Gallery, but more difficult, with a 3d model synchronized from Autodesk Inventor 2014.

www.comsol.com/model/heat-generation-in-a-disc-brake-102

The more sophisticated geometry, the more problems I have. For the first time, I've made everything, step by step from Modeling Instructions which I have found on the page above. With the simplest disc, only vented, everything went fine. Next disc was more complicated and it gives me an error:

Nonlinear solver did not converge.
Time : 0.2662525798149283
Attempt to evaluate non-integral power of negative number.
Function: ^
Failed to evaluate variable.
Variable: comp1.ht.chf1.fLow, Defined as: (((comp1.ht.chf1.Re^0.5)*((0.3387*comp1.ht.chf1.kExtFluid)*(comp1.ht.chf1.Pr^0.33333333333333331)))/(comp1.ht.chf1.L*((1+((0.046800000000000001/comp1.ht.chf1.Pr)^0.66666666666666663))^0.25)))
Failed to evaluate expression.
Expression: nojac((2*((comp1.ht.chf1.hsExprLow*comp1.ht.chf1.fLow)+(comp1.ht.chf1.fHigh*comp1.ht.chf1.hsExprHigh))))
Failed to evaluate variable.
Variable: comp1.ht.chf1.h, Defined as: nojac((2*((comp1.ht.chf1.hsExprLow*comp1.ht.chf1.fLow)+(comp1.ht.chf1.fHigh*comp1.ht.chf1.hsExprHigh))))
Failed to evaluate expression.
Expression: d((comp1.ht.chf1.h*(comp1.ht.chf1.Text-comp1.T)*test(comp1.T))*(dvol),{test180})
Attempt to evaluate non-integral power of negative number.
Function: ^
Failed to evaluate variable.
Variable: comp1.ht.chf1.fLow, Defined as: (((comp1.ht.chf1.Re^0.5)*((0.3387*comp1.ht.chf1.kExtFluid)*(comp1.ht.chf1.Pr^0.33333333333333331)))/(comp1.ht.chf1.L*((1+((0.046800000000000001/comp1.ht.chf1.Pr)^0.66666666666666663))^0.25)))
Failed to evaluate expression.
Expression: nojac((2*((comp1.ht.chf1.hsExprLow*comp1.ht.chf1.fLow)+(comp1.ht.chf1.fHigh*comp1.ht.chf1.hsExprHigh))))
Failed to evaluate variable.
Variable: comp1.ht.chf1.h, Defined as: nojac((2*((comp1.ht.chf1.hsExprLow*comp1.ht.chf1.fLow)+(comp1.ht.chf1.fHigh*comp1.ht.chf1.hsExprHigh))))
Failed to evaluate expression.
Expression: d((comp1.ht.chf1.h*(comp1.ht.chf1.Text-comp1.T)*test(comp1.T))*(dvol),{test138})
Last time step is not converged.

I've found that I must choose Form an Assembly despite Form a Union as a default option. - Is that correct? Should I select "Create pairs" check box?

I have changed Thermal Contact to Pair Thermal Contact, but then phrase "ht.tc1.Qfric/(mu*v(t))" is orange, some boundaries changed and program shows error:

Failed to evaluate variable.
- Variable: ht.tc1.Qfric
- Geometry: 1
- Boundary: 49
Failed to evaluate variable.
- Variable: comp1.ht.ptc1.Tn
- Defined as: ((ht.tc1.Qfric*unit_s_cf)/(unit_m_cf*(v((t/unit_s_cf))*mu)))
Failed to evaluate variable.
- Variable: comp1.ht.ptc1.TnRel
- Defined as: (comp1.ht.ptc1.Tn/comp1.ht.ptc1.Hmic)
Failed to evaluate operator Jacobian.
- Operator: if
- Geometry: 1
- Boundary: 49
Failed to evaluate operator double Jacobian.
- Operator: if
- Geometry: 1
- Boundary: 49

So the main questions are about diffrences how to define all physics and definitions? (maybe the best/fastes way will be to do changes on the example of Heat Transfer in a Disc Brake - both .mph file that work with Form an Assembly or instruction text). Of course if it solve my problem...

www.comsol.com/model/heat-generation-in-a-disc-brake-102

I would be thankful for any help :)