View Factor Fij

[zeljkoT]

Hi

For a simple example I'm comparing the numeric view factor calculated by Elmer with the analytical solution.
Here I'm considering the following two surfaces:

Fij.png

(70.89 KiB) Not downloaded yet

If running "ViewFactors.F90" over cmd, the dF_i->j and dF_j->i are stored in a separate file "ViewFactors.dat".

Question:
Is there a way of getting the fully integrated view factor over the surface Fij and Fji ?

According to this web site, the view factor Fij (large to small surface) should be 0.053857.
https://sites.me.ucsb.edu/~bennett/heat ... alcEx.html

Thx in advance
Cheers

[raback]

Hi

Unfortunately there is no automated way. I understand that it could be useful. It would be very easy also but just hasn't been done...

You need to locate from mesh.boundary the boundary elements "i" and then sum of the view factors related to all "i" related to certain boundary condition.

-Peter

[raback]

Hi,

This is was such a nice idea that I added some code to echo the summed VFs. It requires that "Max Output Level" >= 7. Nothing is saved to files. We just get std out like.

Code: Select all

iewFactors: Printing some lumped information of view factors
ViewFactors: BC 1 with 14 elems perm: 1
ViewFactors: BC 2 with 8 elems perm: 2
ViewFactors: Lumped areas:
ViewFactors:    1.0000000000000000       0.50000000000000000
ViewFactors: Lumped View Factor Matrix:
ViewFactors:    0.0000000000000000        5.3824655895603882E-002
ViewFactors:   0.10764931179120774        0.0000000000000000

This is output from your test case after separating the BCs:

Code: Select all

Boundary Condition 1
  Target Boundaries(1) = 1
  Radiation Boundary Open = True
  Radiation = Diffuse Gray
End

Boundary Condition 2
  Target Boundaries(1) = 7 
  Radiation Boundary Open = True
  Radiation = Diffuse Gray
End

I guess the result is good as the accuracy is ~0.06%

-Peter