# Having difficulties in understanding how view factors is used

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 March 8, 2016, 01:16 Having difficulties in understanding how view factors is used #1 New Member   Adkar Join Date: Apr 2015 Posts: 18 Rep Power: 11 Could someone please explain what nFacesInCoarsestLevel in viewfactorsdict means? For example, in viewFactorsDict found in the multiRegionHeater tutorial, the following is seen. writeViewFactorMatrix true; writeFacesAgglomeration true; writePatchViewFactors false; bottomAir_to_heater { nFacesInCoarsestLevel 30; featureAngle 10; } bottomAir_to_leftSolid { nFacesInCoarsestLevel 20; featureAngle 10; } . . . . What do these numbers mean? I am not sure about the featureAngle either. I would appreciate any help! Thank you in advance.

 March 10, 2016, 01:03 Could anyone please help me understand how to calculate View Factors? #2 New Member   Adkar Join Date: Apr 2015 Posts: 18 Rep Power: 11 Hello everyone, I am pretty new to openfoam and I am stuck in a radiation heat transfer problem. I am searching everywhere in the web to calculate the viewfactors, but I could not get any answer. Could anyone tell how to determine viewfactors and calculate radiation heat transfer. Or at least where I can find information on how to implement radiation in openfoam using viewfactors method. I have understood the following after looking through the multiregionHeater tutorial. First, a utility called faceAgglomerate is used to group the faces together using viewFactorsDict (in the fluid region and not in the solid region). This creates a file called 'finalAgglom'. Next, another utility called viewFactorsGen is used to generate viewfactors using finalAgglom. I din't quite understand how this was done since I do not understand the meaning of the two keywords and the meaning of the number (10) in this dictionary. I also did not understand which faces are being grouped together. eg: minX { nFacesInCoarsestLevel 10; featureAngle 10; } Also, in the changeDictionary file, I could not understand the meaning of G and IDefault. Qr is the radiative heat which is suposed to be returned by the function rad.sh (thermo) in the EEqn Any help is highly appreciated. Thank you in advance.

March 30, 2016, 00:24
ChtMultiRegion Radiation - Error while running viewFactorsGen utility.
#3
New Member

Join Date: Apr 2015
Posts: 18
Rep Power: 11
Hello everyone,
I am trying to use viewFactors model in OpenFOAM. Also, there is a very little info on Radiation Heat transfer in OpenFOAM especially using chtMultiRegion. Any help/comments/advice will be highly helpful.

My case setup is simple. It is a square domain (front and back empty similar to icoFoam's cavity tutorial) with a heat source (a smaller square) in the middle of the bigger square cavity given by setFields. The two regions are the middle small square region (which is the source term for heat generation) and the surrounding square domain. I want to use radiation with viewFactors Model along with convection and conduction. Radiation was introduced in the chtMultiRegionSimpleFoam solver and the simulations were run.

According to my knowledge, to use viewFactors model, first I have to use the faceAgglomeration Utility to coarsen the boundary patches and then using these coarsened patches, viewFactorsGen generates the viewfactors.

When I run faceAgglomeration utility, it writes a file called finalAgglom. Next, when I run viewFactorsGen the following is the error what I encounted. Please take a look at the output message.

Code:
```\$ viewFactorsGen -region etc

/*---------------------------------------------------------------------------*\

| =========                 |                                                 |

| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |

|  \\    /   O peration     | Version:  2.3.x                                 |

|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |

|    \\/     M anipulation  |                                                 |

\*---------------------------------------------------------------------------*/

Build  : 2.3.x-ccc06b4581b5

Exec   : viewFactorsGen -region etc

Date   : Mar 29 2016

Time   : 23:47:29

Host   : "lab5-6.cheng.es"

PID    : 12942

nProcs : 1

sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).

fileModificationChecking : Monitoring run-time modified files using timeStampMaster

allowSystemOperations : Allowing user-supplied system call operations

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

Create time

Create mesh etc for time = 0

Creating single cell mesh...

Created single cell mesh...

Total number of coarse faces: 8

View factor patches included in the calculation : 5(0 1 2 3 5)

*** glibc detected *** viewFactorsGen: free(): invalid next size (normal): 0x000000000210d510 ***

======= Backtrace: =========

/lib64/libc.so.6[0x371de75f4e]

/lib64/libc.so.6[0x371de78cf0]

viewFactorsGen[0x41553c]

viewFactorsGen[0x4166f1]

viewFactorsGen[0x42fea3]

/lib64/libc.so.6(__libc_start_main+0xfd)[0x371de1ed5d]

viewFactorsGen[0x415355]

======= Memory map: ========

00400000-00449000 r-xp 00000000 08:02 2642904                            /opt/OpenFOAM/OpenFOAM-2.3.x/platforms/linux64Gcc47DPOpt/bin/viewFactorsGen

00649000-0064b000 rw-p 00049000 08:02 2642904                            /opt/OpenFOAM/OpenFOAM-2.3.x/platforms/linux64Gcc47DPOpt/bin/viewFactorsGen

01a80000-02e7b000 rw-p 00000000 00:00 0                                  [heap]

371da00000-371da20000 r-xp 00000000 08:02 1966164                        /lib64/ld-2.12.so

371dc1f000-371dc20000 r--p 0001f000 08:02 1966164                        /lib64/ld-2.12.so

371dc20000-371dc21000 rw-p 00020000 08:02 1966164                        /lib64/ld-2.12.so

371dc21000-371dc22000 rw-p 00000000 00:00 0

371de00000-371df8a000 r-xp 00000000 08:02 1998162                        /lib64/libc-2.12.so

371df8a000-371e18a000 ---p 0018a000 08:02 1998162                        /lib64/libc-2.12.so

371e18a000-371e18e000 r--p 0018a000 08:02 1998162                        /lib64/libc-2.12.so

371e18e000-371e18f000 rw-p 0018e000 08:02 1998162                        /lib64/libc-2.12.so

371e18f000-371e194000 rw-p 00000000 00:00 0

371e200000-371e202000 r-xp 00000000 08:02 1998179                        /lib64/libdl-2.12.so

371e202000-371e402000 ---p 00002000 08:02 1998179                        /lib64/libdl-2.12.so

371e402000-371e403000 r--p 00002000 08:02 1998179                        /lib64/libdl-2.12.so

371e403000-371e404000 rw-p 00003000 08:02 1998179                        /lib64/libdl-2.12.so

371e600000-371e617000 r-xp 00000000 08:02 1998177                        /lib64/libpthread-2.12.so

371e617000-371e817000 ---p 00017000 08:02 1998177                        /lib64/libpthread-2.12.so

371e817000-371e818000 r--p 00017000 08:02 1998177                        /lib64/libpthread-2.12.so

371e818000-371e819000 rw-p 00018000 08:02 1998177                        /lib64/libpthread-2.12.so

371e819000-371e81d000 rw-p 00000000 00:00 0

371ea00000-371ea83000 r-xp 00000000 08:02 1998164                        /lib64/libm-2.12.so

371ea83000-371ec82000 ---p 00083000 08:02 1998164                        /lib64/libm-2.12.so

371ec82000-371ec83000 r--p 00082000 08:02 1998164                        /lib64/libm-2.12.so

371ec83000-371ec84000 rw-p 00083000 08:02 1998164                        /lib64/libm-2.12.so

371ee00000-371ee15000 r-xp 00000000 08:02 1998166                        /lib64/libz.so.1.2.3

371ee15000-371f014000 ---p 00015000 08:02 1998166                        /lib64/libz.so.1.2.3

371f014000-371f015000 r--p 00014000 08:02 1998166                        /lib64/libz.so.1.2.3

371f015000-371f016000 rw-p 00015000 08:02 1998166                        /lib64/libz.so.1.2.3

371f200000-371f207000 r-xp 00000000 08:02 1998192                        /lib64/librt-2.12.so

371f207000-371f406000 ---p 00007000 08:02 1998192                        /lib64/librt-2.12.so

371f406000-371f407000 r--p 00006000 08:02 1998192                        /lib64/librt-2.12.so

371f407000-371f408000 rw-p 00007000 08:02 1998192                        /lib64/librt-2.12.so

3724600000-3724608000 r-xp 00000000 08:02 1590138                        /usr/lib64/libnuma.so.1

3724608000-3724808000 ---p 00008000 08:02 1590138                        /usr/lib64/libnuma.so.1

3724808000-3724809000 rw-p 00008000 08:02 1590138                        /usr/lib64/libnuma.so.1

372de00000-372de02000 r-xp 00000000 08:02 1998188                        /lib64/libutil-2.12.so

372de02000-372e001000 ---p 00002000 08:02 1998188                        /lib64/libutil-2.12.so

372e001000-372e002000 r--p 00001000 08:02 1998188                        /lib64/libutil-2.12.so

372e002000-372e003000 rw-p 00002000 08:02 1998188                        /lib64/libutil-2.12.so

3730400000-3730416000 r-xp 00000000 08:02 1969094                        /lib64/libnsl-2.12.so

3730416000-3730615000 ---p 00016000 08:02 1969094                        /lib64/libnsl-2.12.so

3730615000-3730616000 r--p 00015000 08:02 1969094                        /lib64/libnsl-2.12.so

3730616000-3730617000 rw-p 00016000 08:02 1969094                        /lib64/libnsl-2.12.so

3730617000-3730619000 rw-p 00000000 00:00 0

7fc474000000-7fc474021000 rw-p 00000000 00:00 0

7fc474021000-7fc478000000 ---p 00000000 00:00 0

7fc47a1c7000-7fc47b089000 rw-p 00000000 00:00 0

7fc47b089000-7fc47b095000 r-xp 00000000 08:02 1966182                    /lib64/libnss_files-2.12.so

7fc47b095000-7fc47b295000 ---p 0000c000 08:02 1966182                    /lib64/libnss_files-2.12.so

7fc47b295000-7fc47b296000 r--p 0000c000 08:02 1966182                    /lib64/libnss_files-2.12.so

7fc47b296000-7fc47b297000 rw-p 0000d000 08:02 1966182                    /lib64/libnss_files-2.12.so

7fc47b2be000-7fc47b2cc000 rw-p 00000000 00:00 0

7fc47b2cc000-7fc47b2f0000 r-xp 00000000 08:02 2642698                    /opt/OpenFOAM/OpenFOAM-2.3.x/platforms/linux64Gcc47DPOpt/lib/libthermophysicalFunctions.so

7fc47b2f0000-7fc47b4ef000 ---p 00024000 08:02 2642698                    /opt/OpenFOAM/OpenFOAM-2.3.x/platforms/linux64Gcc47DPOpt/lib/libthermophysicalFunctions.so

7fc47b4ef000-7fc47b4f1000 rw-p 00023000 08:02 2642698                    /opt/OpenFOAM/OpenFOAM-2.3.x/platforms/linux64Gcc47DPOpt/lib/libthermophysicalFunctions.so

7fc47b4f1000-7fc47baec000 r-xp 00000000 08:02 2642704                    /opt/OpenFOAM/OpenFOAM-2.3.x/platforms/linux64Gcc47DPOpt/lib/libreactionThermophysicalModels.so

7fc47baec000-7fc47bcec000 ---p 005fb000 08:02 2642704                    /opt/OpenFOAM/OpenFOAM-2.3.x/platforms/linux64Gcc47DPOpt/lib/libreactionThermophysicalModels.so

7fc47bcec000-7fc47bd15000 rw-p 005fb000 08:02 2642704                    /opt/OpenFOAM/OpenFOAM-2.3.x/platforms/linux64Gcc47DPOpt/lib/libreactionThermophysicalModels.so

7fc47bd15000-7fc47bd17000 rw-p 00000000 00:00 0

7fc47bd17000-7fc47bd4e000 r-xp 00000000 08:02 2642697                    /opt/OpenFOAM/OpenFOAM-2.3.x/platforms/linux64Gcc47DPOpt/lib/libsolidSpecie.so

7fc47bd4e000-7fc47bf4d000 ---p 00037000 08:02 2642697                    /opt/OpenFOAM/OpenFOAM-2.3.x/platforms/linux64Gcc47DPOpt/lib/libsolidSpecie.soAborted (core dumped)```
When I used face agglomeration, it works alright making the finalAgglom file.
This file is attached as the zip file, please take a look at it.

This is the output message of faceAgglomerate utility.
Code:
```/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.x                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
Build  : 2.3.x-ccc06b4581b5
Exec   : faceAgglomerate -region etc -dict constant/viewFactorsDict
Date   : Mar 29 2016
Time   : 23:44:40
Host   : "lab5-6.cheng.es"
PID    : 12905
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster
allowSystemOperations : Allowing user-supplied system call operations

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create mesh etc for time = 0

Agglomerating patch : etc_to_solid

Agglomerating patch : minX

Agglomerating patch : minY

Agglomerating patch : maxX

Agglomerating patch : maxY

Writing facesAgglomeration
End

And the following is my viewFactorsDict.

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
FoamFile
{
version     2.0;
format      ascii;
class       dictionary;
object      viewFactorsDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

writeViewFactorMatrix     true;
writeFacesAgglomeration   true;
writePatchViewFactors     false;

debug                     1;

etc_to_solid
{
nFacesInCoarsestLevel     0;
featureAngle              0;
}

minX
{
nFacesInCoarsestLevel     0;
featureAngle              0;
}

minY
{
nFacesInCoarsestLevel     0;
featureAngle              0;
}

maxX
{
nFacesInCoarsestLevel     0;
featureAngle              0;
}

maxY
{
nFacesInCoarsestLevel     0;
featureAngle              0;
}

//minmaxZ
//{

//nFacesInCoarsestLevel     0;
//featureAngle              0;
//}

// ************************************************************************* //```
My problem is the viewFactorsGen utility is giving me this error message when I run it.
Attached Files
 finalAgglom.zip (164.6 KB, 22 views)

Last edited by wyldckat; May 1, 2016 at 15:15. Reason: Added/repaired [CODE][/CODE] markers

 May 24, 2018, 05:24 #4 Member   chengan.wang Join Date: Jan 2016 Location: china Posts: 47 Rep Power: 10 Dear Adkar, If you solved the problem? Could you post your calculating case here? best regards, Chengan

 June 12, 2018, 06:15 hello! thread #5 New Member   wing Join Date: Feb 2018 Posts: 3 Rep Power: 8 Dear Adkar, As chengan.wang said,If you solved the problem,Could you post your calculating case here?I have the same problem. best regards! Steben