Hallo.
I need help with ViewFactors.
Thought I had already defined the model correctly, but I do not succeed. The heat transfer in model don´t work correctly. It meets my first post not with "Heat Transfer Work" which I have already posted.
At the same structural model, calculated ViewFactors ELMER FEM one time correctly one time wrong.
For each new calculation, I delete in the folder always the Sif file and the Viewfactor file.
Mesh I did with gmsh.
Inputs for radiation: radiation are diffusive gray, emisivity 0.9
In particular bodys Heat Equation is active, the other possibilities can be in this column is set to none.
For calculation of ViewFactors program calculates the emission values in the first iteration. Iteration 2 - 20 are NaN.
The Question is, Must I change something in the Solver Settning. That Viewfactoren will be calculated.
Many regards.
Josi
ViewFactors help
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Re: ViewFactors help
Hi Josi
There are two possible problems that come to mind:
1) Your normals are not oriented consistantly. Elmer has basically no way of knowing which of the two sides is the radiating one. To overcome this you could give the Emissivity in the Material block rather than in the BC block. The information on which side the Emissivity is found is then used to decide the direction of the normal vector. This feature has been around for perhaps a year and there are still examples around which do not utilize this feature which should make the set-up of complicated radiation problems more straight-forward.
2) If your radiation boundary is not fully closed Elmer will still try to normalize the sum of the view factors to 2PI. This is used to ensure energy conservation and improve accuracy but for partically open boundaries you should disable the feature by setting "Radiation Boundary Open = Logical True".
As you did its always a good idea to remove the old view factors if the case has changed. You can also manually enforce computation of the factors by simply calling "ViewFactors" at the command line.
-Peter
-Peter
There are two possible problems that come to mind:
1) Your normals are not oriented consistantly. Elmer has basically no way of knowing which of the two sides is the radiating one. To overcome this you could give the Emissivity in the Material block rather than in the BC block. The information on which side the Emissivity is found is then used to decide the direction of the normal vector. This feature has been around for perhaps a year and there are still examples around which do not utilize this feature which should make the set-up of complicated radiation problems more straight-forward.
2) If your radiation boundary is not fully closed Elmer will still try to normalize the sum of the view factors to 2PI. This is used to ensure energy conservation and improve accuracy but for partically open boundaries you should disable the feature by setting "Radiation Boundary Open = Logical True".
As you did its always a good idea to remove the old view factors if the case has changed. You can also manually enforce computation of the factors by simply calling "ViewFactors" at the command line.
-Peter
-Peter