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Failed to evaluate variables and Jacobian variables

Posted Jan 5, 2017, 12:02 p.m. EST Computational Fluid Dynamics (CFD) Version 5.2a 4 Replies

Babak Ebrazi Bakhshayesh
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Hi COMSOL Users,

I an new to using COMSOL 5.2a and perhaps because of that I am missing something simple. I have tried to model evaporation of water, which is part of modeling a new toilet technology we are proposing for developing countries, but I get several errors when trying to model the second study in the toilet system.

The problem that noticed is due to the domain number . Once it is removed from the geometry, the second study is done successfully, while adding this domain results in the following errors:

Undefined variable.
- Variable: comp1.c
- Geometry: geom1
- Domain: 2
Failed to evaluate Jacobian of expression.
- Expression: comp1.c
Failed to evaluate Jacobian of operator.
- Operator: mean
- Geometry: geom1
- Boundary: 9
Failed to evaluate Jacobian of variable.
- Variable: comp1.c
- Geometry: geom1
- Boundary: 9
Failed to evaluate Jacobian of expression.
- Expression: dvol*(r*(pi*((2*comp1.ht.bhs1.Qb)*comp1.ht.d)))
Failed to evaluate Jacobian of expression.
- Expression: (2*comp1.ht.bhs1.Qb*test(comp1.ht.bhs1.Tvar)*comp1.ht.d*pi*r)*(dvol)


I have attached my model to this post just in case.

Has anyone had problems like the above ones? How can fox these issues?

Thanks in advance,
Babak

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4 Replies Last Post Jan 6, 2017, 2:47 p.m. EST
Sohan Birla
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Posted: 8 years ago Jan 6, 2017, 10:44 a.m. EST
Remove boundary 9 from both concentration and heat source boundary.
Remove boundary 9 from both concentration and heat source boundary.
Babak Ebrazi Bakhshayesh
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Posted: 8 years ago Jan 6, 2017, 11:01 a.m. EST
Hi Sohan,

Thanks for your response. I did that and this time simulation did not have any errors.

But, I have been dealing with a question regarding a variable definition in my model. The variable is saturated water vapor concentration, C_sat, used in Transport of diluted species interface in concentration 2 boundary condition.

Its definition is ht.fluid1.fpsat(T)/(R_const*T) in which fluid1 is air domain in the model.

The first things that I have not been able to figure out yet is that whether temperature used in this expression is exactly the temperature of the water surface or not. Since the fluid 1 is for air and I am wondering maybe temperature here in this expression is not the water surface temperature.

I also tried to use fluid 2 in above expression instead of fluid1 but the model does not recognize this variable.

What can be the reason based on your knowledge?

Thanks,
Babak
Hi Sohan, Thanks for your response. I did that and this time simulation did not have any errors. But, I have been dealing with a question regarding a variable definition in my model. The variable is saturated water vapor concentration, C_sat, used in Transport of diluted species interface in concentration 2 boundary condition. Its definition is ht.fluid1.fpsat(T)/(R_const*T) in which fluid1 is air domain in the model. The first things that I have not been able to figure out yet is that whether temperature used in this expression is exactly the temperature of the water surface or not. Since the fluid 1 is for air and I am wondering maybe temperature here in this expression is not the water surface temperature. I also tried to use fluid 2 in above expression instead of fluid1 but the model does not recognize this variable. What can be the reason based on your knowledge? Thanks, Babak
Sohan Birla
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Posted: 8 years ago Jan 6, 2017, 1:33 p.m. EST
Remove boundary 9 from both concentration and heat source boundary.
Remove boundary 9 from both concentration and heat source boundary.
Sohan Birla
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Posted: 8 years ago Jan 6, 2017, 2:47 p.m. EST
This is a interface boundary temperature. I recommend you to add also the Acrylic sheet domain in heat transfer as solid. Also add the water in laminar flow to take into account of natural convention caused by evaporative cooling.
This is a interface boundary temperature. I recommend you to add also the Acrylic sheet domain in heat transfer as solid. Also add the water in laminar flow to take into account of natural convention caused by evaporative cooling.

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