viewFactorCoeffs

RobinZ · June 12, 2015, 09:56

Hello Foamers,

i have a question to the viewFactorCoeffs from the radiationProperties when the viewFactor model is selected.
I had a look in the viewFactor.C and i'm not sure if there is a bug or i misunderstood the code, but i see no difference in calculating the radiation when i set constantEmissivity to true or false. I run a testcase and the results are also the same.
Can anybody explain what this option does and what it is for?

Thanks for your help!

best regards

Robin

Astrodan · June 12, 2015, 10:36

As far as I understand the Code there is the difference that in the constant case the CLU is computed only in the first iteration (Line 552) and kept constant for all following calculations, in which other things might happen in the geometry. Apart from the the calculation is the same, yes. Concerning your test case I can't tell you much because I don't know how the model works, but I guess we need at least a hint how you tried to determine the differences

. Might dependt on the case.

As to the CLU, I just copied this abbr, from the code, and have no clue yet what it means. It seems to be related to the constantEmission in a way I haven't yet understood, but I don't care much about the ViewFactors model.

RobinZ · June 12, 2015, 10:48

Hello Timm,
At first thanks very much for your help.
I interpret the code as following:
CLU is the inverted matrix of C. And i think C is the CoeffMatrix for the viewFactors or the radiation. Until now i'm not really sure.
If the constantEmissivity is true CLU is calculated and used to calculate q.
If it's false C is used to calculated q.
But both calculation are equal.
So q do not differ. I change the source code of the viewFactor.C complied it new and gave me q out.
And q is the same. No difference. I also looked on CLU and C and they are also the same. I don't know why...

best regards

Robin

RobinZ · June 15, 2015, 02:22

Hi Timm,
now i see what you mean. You are right. When the constantEmissivity is set to true, the CLU matrix is only generated one time(at Iteration 0). When it is set to false, C is genereated each number of steps one have specified for solverFreq in the radiationProperties.
Thanks very much!

best regards
Robin

June 12, 2015, 09:56	viewFactorCoeffs	#1
RobinZ New Member RobinZ Join Date: Apr 2014 Posts: 19 Rep Power: 11	Hello Foamers, i have a question to the viewFactorCoeffs from the radiationProperties when the viewFactor model is selected. I had a look in the viewFactor.C and i'm not sure if there is a bug or i misunderstood the code, but i see no difference in calculating the radiation when i set constantEmissivity to true or false. I run a testcase and the results are also the same. Can anybody explain what this option does and what it is for? Thanks for your help! best regards Robin

June 12, 2015, 10:36		#2
Astrodan Member Timm Severin Join Date: Mar 2014 Location: Munich Posts: 63 Rep Power: 12	As far as I understand the Code there is the difference that in the constant case the CLU is computed only in the first iteration (Line 552) and kept constant for all following calculations, in which other things might happen in the geometry. Apart from the the calculation is the same, yes. Concerning your test case I can't tell you much because I don't know how the model works, but I guess we need at least a hint how you tried to determine the differences . Might dependt on the case. As to the CLU, I just copied this abbr, from the code, and have no clue yet what it means. It seems to be related to the constantEmission in a way I haven't yet understood, but I don't care much about the ViewFactors model. __________________ PhD Student at the Institute of Biochemical Engineering at TU München Modelling of fluid dynamics in open photobioreactors. System: OpenFOAM 2.3.x, 64bit, 8 Core Xeon Workstation

June 12, 2015, 10:48		#3
RobinZ New Member RobinZ Join Date: Apr 2014 Posts: 19 Rep Power: 11	Hello Timm, At first thanks very much for your help. I interpret the code as following: CLU is the inverted matrix of C. And i think C is the CoeffMatrix for the viewFactors or the radiation. Until now i'm not really sure. If the constantEmissivity is true CLU is calculated and used to calculate q. If it's false C is used to calculated q. But both calculation are equal. So q do not differ. I change the source code of the viewFactor.C complied it new and gave me q out. And q is the same. No difference. I also looked on CLU and C and they are also the same. I don't know why... best regards Robin

June 15, 2015, 02:22		#4
RobinZ New Member RobinZ Join Date: Apr 2014 Posts: 19 Rep Power: 11	Hi Timm, now i see what you mean. You are right. When the constantEmissivity is set to true, the CLU matrix is only generated one time(at Iteration 0). When it is set to false, C is genereated each number of steps one have specified for solverFreq in the radiationProperties. Thanks very much! best regards Robin