# Ask for help in Femlab

1. Apr 7, 2006

### mageer

Hi everyone,
I want to simulate the radiation heat transfer among the solid A,solid B and solid C using Femlab 3.1. The temperature of one solid is affected by the temperatures of the other two solids. So the temperatures of solid A, B and C are different.
I try to solve it by adding one 'general heat transfer' mode. But the temperature and radiation(J) in each equation are the same symbols. How to distinguish them in three solids?
I am wondering if I should add three 'general heat transfer' modes at the beginning of navigator? I can specify solid A in first mode(T1 and radiation J1 for solid A), solid B in 2nd mode(T2 and radiation J2 for solid B), and solid C in 3rd mode(T3 and J3 for solid C). Is it right? How to use coupling function? What is the meaning of and how to use the 'dest' function? How can I solve it?
Thank you very much!
Sincerely,
mageer
My e-mail: mageer@gmail.com

2. Apr 10, 2006

### PerennialII

Hi mageer,

I think you're on the right track, you can use both techniques to solve your problem. If you add geometries you get the 'added variables' you can use to derive boundary conditions for the coupling, but likely the easiest way around it (and I think the one most feasible considering the problem solution overall) would be to use coupling variables between the boundaries of radiation heat transfer. How familiar are you with the extrusion/projection coupling variables, can help you step by step if you like?

3. Apr 11, 2006

### mageer

some questions in using FEMLAB

Hi PerennialII:
Thank you very much for your help.
But I still have some questions in heat radiation using FEMLAB. I am a rookie .
Three tori:co1,co2,co3 are shown in the following fig. The thicknesses of co1 and co2 are very thin(1.5mm). The heat radiation transfers exist between co1 and ambient,co1 and co2, co2 and co3, also in the inside boundary of co3. The convection exists only between the co1 and ambient.
1.What is the difference between the heat transfer function in FEMLAB module, and the heat transfer module?
2.What is the difference among the Lagrange-T2J1,Lagrange-T3J1,Lagrange-T4J1.......in element tab of heat transfer module?
How to solve it?
thanks a lot.

#### Attached Files:

• ###### cross section.jpg
File size:
18.3 KB
Views:
53
Last edited: Apr 12, 2006
4. Apr 12, 2006

### PerennialII

Man you got all the modules .... lucky chap!

The 'basic' heat transfers in both I believe are identical, the heat transfer module having some added options such as surface-to-surface radiation with the radiosity method and lots and lots of related 'candy'.

Lagrange-T2J1 etc. are something specific to the heat transfer module (which I don't have ), might those be the thin conductive shell elements one can use in 3D (and only available in the heat transfer module)?

5. Apr 12, 2006

### mageer

Hi PerennialII:
As for my module comprised of three tori,
1.there are heat convection and heat radiation between the exterior boundary of CO1 and ambient.
1.between interior boundary of CO1 and exterior boundary of CO2;
2.interior boundary of CO2 and exterior boundary of CO3;
3.the interior boundary of CO3.
Should I add three 'general heat transfer modules' as shown in fig.2? One module specifies CO1, one module specifies CO2 and the other module for CO3? How can the CO1,CO2 and CO3 be linked together? Using coupling?
Would you pls how to use 'coupling' parameter?
by the way, what is the difference among:integration coupling,extrusion coupling and projection coupling?
thanks a lot.

#### Attached Files:

• ###### cross section.jpg
File size:
27.8 KB
Views:
49
6. Apr 14, 2006

### PerennialII

With respect to the boundary conditions you need to map the variables from boundary to another. You could do this by doing separate models and solving them coupled as separate (different geometries, different "Ti" - variables etc.), but this I'd say is quite crude. It's easier to either work with weak forms or even better, with the coupling options Femlab/Comsol has to offer.

The couplings -- integration, extrusion and projection coupling give different tools to accomplish just this. Integration gives you an integral of an expression over a domain to be used somewhere, extrusion enables you to map variables between domains and projection is essentially a mix of both of these methods (or in a way generalized extrusion coupling).

I'd think in your application it would be easiest to map the solution from boundary to boundary using extrusion coupling (same dimensions and just mapping a scalar so would be pretty straightforward), and use the generated extrusion coupling variables in the radiation heat flux boundary conditions to define the radiation sink temperature. So you'd define the couplings via "options -> coupling variables" and use the variables when defining "boundary settings" as usual for the radiation term. Interesting case :tongue2: , let me know if can help with the details.

7. Apr 16, 2006

### mageer

Ah,thank you very much.
I'll try to solve it as you suggested. Can I send email to you by msn if I have any questions about it? I have added you to my buddy list in MSN. Thanks a lot.

8. Apr 16, 2006

### PerennialII

Yeah & of course, "bomb" away ! (either via MSN, the board email/PM) It'll be interesting to see how it turns out.

9. Feb 1, 2009

### akshayvohra

Hi All,

I am trying to solve a problem where the solutions are expected to be zero for a very long time.

I have refined the mesh with the maximum element size of 0.002 and am using the GMRES method with preconditioning quality of 0.01.

However, inspite of it, the system is unable to process the solution and gives an error for residual computation citing singular matrix as the problem.

Can anyone please suggest some ways to solve the problem?

Akshay