# Radiation test case **URL:** \ **Category:** General Questions\ **Created:** [September 3, 2024, 7:31am UTC](https://prepomax.discourse.group/t/radiation-test-case/1979 "2024-09-03T07:31:02Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![PierreAntonetti](https://avatars.discourse-cdn.com/v4/letter/p/f1d935/32.png) [@PierreAntonetti](https://prepomax.discourse.group/u/PierreAntonetti)\ **Post date:** [September 3, 2024, 7:31am UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/1 "2024-09-03T07:31:02Z")
Hello, I’m a brand new user, sorry if i missed something important. I want to reproduce the well-known triangle cavity radiation test case detailed in this [pdf](https://doc.comsol.com/5.6/doc/com.comsol.help.models.heat.cavity_radiation/models.heat.cavity_radiation.pdf) Unfortunately I don’t get the right temperature/flux values I’m not sure about the radiation BCs cause of the thin temperatures requested, guess : - I must set cavity=Yes, so that thin temperature is not ? - all radiations bcs of a cavity must have the same name ? [prepomax file](https://drive.google.com/file/d/1lgi1q1m1TpewjC5S2KyMLoPtIgBtuCf8/view?usp=sharing) Thanks for helping ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [September 3, 2024, 7:45am UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/2 "2024-09-03T07:45:19Z")
I made a very similar test in this tutorial, check if it helps you: [![](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/e/e27f70c10d1d5ada9ac90caee8708c971578fb7f.jpeg "PrePoMax (CalculiX FEA) - Tutorial 25 - Cavity (surface-to-surface) radiation") ](https://www.youtube.com/watch?v=gyyy2XoTDLg) ---
**Author:** ![PierreAntonetti](https://avatars.discourse-cdn.com/v4/letter/p/f1d935/32.png) [@PierreAntonetti](https://prepomax.discourse.group/u/PierreAntonetti)\ **Post date:** [September 3, 2024, 8:34am UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/3 "2024-09-03T08:34:23Z")
Hello, That tutorial helps ! I did exactly the same as in the tutorial (I missed the negative sink temperature), I can’t get the convergence… [file](https://drive.google.com/file/d/1uHqSPfivAuHm5YnpnQkUnh91tEECCcD0/view?usp=drive_link) Thanks for helping ---
**Author:** ![arnie](https://avatars.discourse-cdn.com/v4/letter/a/ba9def/32.png) [@arnie](https://prepomax.discourse.group/u/arnie)\ **Post date:** [September 3, 2024, 9:34am UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/4 "2024-09-03T09:34:35Z")
Seems that you are using Plane Stress elements (CPS3 & CPS4) ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/a/a4479c0fad7c2bf8da107e93955cd249fb30b111.jpeg) ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [September 3, 2024, 10:04am UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/5 "2024-09-03T10:04:26Z")
What’s wrong with that ? Those elements can be used in pure thermal studies too. ---
**Author:** ![arnie](https://avatars.discourse-cdn.com/v4/letter/a/ba9def/32.png) [@arnie](https://prepomax.discourse.group/u/arnie)\ **Post date:** [September 3, 2024, 12:13pm UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/6 "2024-09-03T12:13:26Z")
Ahh, not just plane stress analysis. Thanks for clarifying. I get the analysis to run by changing radiation sink temperatures to anything above (or equal to) Absolute Zero (0K) - perhaps the solver no longer allows negative Kelvin ? ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/d/d8082d40405d1864b6f40ac7bf62928950dd0674.png) ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [September 3, 2024, 12:25pm UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/7 "2024-09-03T12:25:37Z")
I was using transient analysis, the OPs one is steady-state. If I were him, I would start from my setup and then introduce his changes one by one. It should work if the inputs are realistic. ---
**Author:** ![PierreAntonetti](https://avatars.discourse-cdn.com/v4/letter/p/f1d935/32.png) [@PierreAntonetti](https://prepomax.discourse.group/u/PierreAntonetti)\ **Post date:** [September 3, 2024, 10:43pm UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/8 "2024-09-03T22:43:05Z")
Hello Thank for helping ! I did exactly what @FEAnalyst did in the tutorial 25 modulo set the radiation sink temperature to 0K as mentionned by @arnie (i just use CPS3 elements) and perform a steady-state simulation. A still can’t get the right values but i noticed the results depends a lot on the initial temperature (set to 300K) and also to the copper conductivity which is not normal Thanks a lot. ---
**Author:** ![ANYS](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/anys/32/7737_2.png) [@ANYS](https://prepomax.discourse.group/u/ANYS)\ **Post date:** [September 4, 2024, 7:41am UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/9 "2024-09-04T07:41:17Z")
Steady State analisys doesn’t work with RADIATION. > [@PierreAntonetti](#): > > the results depends a lot on the initial temperature (set to 300K) and also to the copper conductivity which is not normal When performing the transient be sure to provide enough time to the system so it can reach the steady solution. With negative environment temperature on the Kelvin Scale, you can force that view factors add up to 1. For example, Sink= -10 °K Where are you looking the temperature ( inside or outsideof the cavity) to compare results? ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [September 4, 2024, 7:53am UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/10 "2024-09-04T07:53:22Z")
> [@ANYS](#): > > Steady State analisys doesn’t work with RADIATION. Theoretically, it can work, at least in Abaqus - CalculiX may not have it implemented so well: > The exact cavity radiation equations are solved whether parallel decomposition is allowed or not; however, when parallel decomposition is active, Abaqus/Standard may require more iterations to obtain a solution. This slower rate of convergence comes from an approximation to the Jacobian (the linearization of the radiation fluxes) that is based on small changes of the irradiation (any part not due to emission from the surface). Models involving surfaces with low emissivities and steady-state analyses might be especially affected. If you encounter convergence problems with parallel decomposed cavities, you may consider > > - changing the analysis from steady-state to transient Uncoupled Heat Transfer Analysis or > - allowing more solver iterations per time increment. But, as I said before, the OP should use transient analysis here like I did in my tutorial. I also used that approach with -10 K. From ccx manual: > Sometimes, it is useful to specify that the radiation is closed. This is done by specifying a value of the environment temperature which is negative if expressed on the absolute scale (Kelvin). Then, the viewfactors are scaled to one exactly. ---
**Author:** ![ANYS](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/anys/32/7737_2.png) [@ANYS](https://prepomax.discourse.group/u/ANYS)\ **Post date:** [September 4, 2024, 8:22am UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/11 "2024-09-04T08:22:22Z")
Being closer to the problem BC used to obtain the Analitical means T=307ºK and all BC applied to the inner faces. ![imagen](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/6/65951c995bea05f8cb09711f727e79d5108f602c.png) ![imagen](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/b/b2323596fc5a0144064c002e9aba364f2da83be5.jpeg) | | Result [ºC] | Result [ºK] | Expected | Deviation | | --- | --- | --- | --- | --- | | T2 | 366.3 | 639.3 | 641 | 0.3% | | T3 | 321.2 | 594.2 | 600 | 1.0% | ---
**Author:** ![PierreAntonetti](https://avatars.discourse-cdn.com/v4/letter/p/f1d935/32.png) [@PierreAntonetti](https://prepomax.discourse.group/u/PierreAntonetti)\ **Post date:** [September 4, 2024, 5:21pm UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/12 "2024-09-04T17:21:13Z")
Hello @ANYS, I didn’t know calculix does not handle steady-state radiation (hope it’ll be included) Could you share your prepomax file ? Thanks. ---
**Author:** ![ANYS](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/anys/32/7737_2.png) [@ANYS](https://prepomax.discourse.group/u/ANYS)\ **Post date:** [September 4, 2024, 9:05pm UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/13 "2024-09-04T21:05:43Z")
```auto *Node 1, 4.00000000E+003, 4.00000000E+003 2, 4.00000000E+003, 1.00000000E+003 3, 5.00000000E+003, 1.00000000E+003 4, 5.00000000E+003, 4.00000000E+003 5, 4.00000000E+003, 2.50000000E+003 6, 4.50000000E+003, 1.00000000E+003 7, 4.50000000E+003, 2.50000000E+003 8, 5.00000000E+003, 2.50000000E+003 9, 4.50000000E+003, 4.00000000E+003 10, 4.00000000E+003, 0.00000000E+000 11, 4.00000000E+003, 1.00000000E+003 12, 0.00000000E+000, 1.00000000E+003 13, 0.00000000E+000, 0.00000000E+000 14, 2.00000000E+003, 1.00000000E+003 15, 2.00000000E+003, 5.00000000E+002 16, 4.00000000E+003, 5.00000000E+002 17, 0.00000000E+000, 5.00000000E+002 18, 2.00000000E+003, 0.00000000E+000 19, 0.00000000E+000, 1.00000000E+003 20, 4.00000000E+003, 4.00000000E+003 21, 3.40000000E+003, 4.80000000E+003 22, -6.00000000E+002, 1.80000000E+003 23, 1.70000000E+003, 2.90000000E+003 24, 3.70000000E+003, 4.40000000E+003 25, 2.55000000E+003, 3.85000000E+003 26, 2.85000000E+003, 3.45000000E+003 27, -3.00000000E+002, 1.40000000E+003 28, 8.50000000E+002, 1.95000000E+003 29, 5.50000000E+002, 2.35000000E+003 30, 2.00000000E+003, 2.50000000E+003 31, 1.40000000E+003, 3.30000000E+003 ** ** Elements ++++++++++++++++++++++++++++++++++++++++++++++++ ** *Element, Type=CPS6, Elset=right 1, 1, 2, 3, 5, 6, 7 2, 3, 4, 1, 8, 9, 7 *Element, Type=CPS6, Elset=bottom 3, 11, 12, 10, 14, 15, 16 4, 12, 13, 10, 17, 18, 15 *Element, Type=CPS6, Elset=slopped 5, 20, 21, 23, 24, 25, 26 6, 22, 19, 23, 27, 28, 29 7, 19, 20, 23, 30, 26, 28 8, 21, 22, 23, 31, 29, 25 ** ** Node sets +++++++++++++++++++++++++++++++++++++++++++++++ ** *Nset, Nset=Internal_Selection-1_T1 11, 12, 14 *Nset, Nset=Internal-1_Internal_Selection-1_e1 11, 12, 14 *Nset, Nset=Internal-1_Internal_Selection-1_e2 1, 2, 5 *Nset, Nset=Internal-1_Internal_Selection-1_Radiation-1 19, 20, 30 *Nset, Nset=Internal-1_Internal_Selection-1_q2 1, 2, 5 *Nset, Nset=Internal-1_Internal_Selection-1_q3 19, 20, 30 *Nset, Nset=Internal_Selection-1_Init 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 ** ** Element sets ++++++++++++++++++++++++++++++++++++++++++++ ** *Elset, Elset=Internal_Selection-1_Copper right, bottom, slopped *Elset, Elset=Internal-1_Internal_Selection-1_e1_S3 3 *Elset, Elset=Internal-1_Internal_Selection-1_e2_S3 1 *Elset, Elset=Internal-1_Internal_Selection-1_Radiation-1_S3 7 *Elset, Elset=Internal-1_Internal_Selection-1_q2_S3 1 *Elset, Elset=Internal-1_Internal_Selection-1_q3_S3 7 ** ** Surfaces ++++++++++++++++++++++++++++++++++++++++++++++++ ** *Surface, Name=Internal_Selection-1_e1, Type=Element Internal-1_Internal_Selection-1_e1_S3, S1 *Surface, Name=Internal_Selection-1_e2, Type=Element Internal-1_Internal_Selection-1_e2_S3, S1 *Surface, Name=Internal_Selection-1_Radiation-1, Type=Element Internal-1_Internal_Selection-1_Radiation-1_S3, S1 *Surface, Name=Internal_Selection-1_q2, Type=Element Internal-1_Internal_Selection-1_q2_S3, S1 *Surface, Name=Internal_Selection-1_q3, Type=Element Internal-1_Internal_Selection-1_q3_S3, S1 ** ** Physical constants ++++++++++++++++++++++++++++++++++++++ ** *Physical constants, Absolute zero=-273.15, Stefan Boltzmann=5.6704E-11 ** ** Coordinate systems ++++++++++++++++++++++++++++++++++++++ ** ** ** Materials +++++++++++++++++++++++++++++++++++++++++++++++ ** *Material, Name=Copper *Conductivity 400 *Specific heat 385000000 *Expansion, Zero=26.85 1E-12 *Density 8.96E-09 ** ** Sections ++++++++++++++++++++++++++++++++++++++++++++++++ ** *Solid section, Elset=Internal_Selection-1_Copper, Material=Copper 1000 ** ** Pre-tension sections ++++++++++++++++++++++++++++++++++++ ** ** ** Constraints +++++++++++++++++++++++++++++++++++++++++++++ ** ** ** Surface interactions ++++++++++++++++++++++++++++++++++++ ** ** ** Contact pairs +++++++++++++++++++++++++++++++++++++++++++ ** ** ** Amplitudes ++++++++++++++++++++++++++++++++++++++++++++++ ** ** ** Initial conditions ++++++++++++++++++++++++++++++++++++++ ** ** Name: Init *Initial conditions, Type=Temperature Internal_Selection-1_Init, 33.85 ** ** Steps +++++++++++++++++++++++++++++++++++++++++++++++++++ ** ** ** Heat ++++++++++++++++++++++++++++++++++++++++++++++++++++ ** *Step, Inc=1000 *Heat transfer, Solver=Pardiso 10000, 8000000, 1E-05, 10000 ** ** Controls ++++++++++++++++++++++++++++++++++++++++++++++++ ** ** ** Output frequency ++++++++++++++++++++++++++++++++++++++++ ** *Output, Frequency=1 ** ** Boundary conditions +++++++++++++++++++++++++++++++++++++ ** *Boundary, op=New ** Name: T1 *Boundary Internal_Selection-1_T1, 11, 11, 33.85 ** ** Loads +++++++++++++++++++++++++++++++++++++++++++++++++++ ** *Cflux, op=New *Dflux, op=New *Radiate, op=New ** Name: q2 *Dflux Internal_Selection-1_q2, S, 2 ** Name: q3 *Dflux Internal_Selection-1_q3, S, 1 ** Name: e1 *RadiateCavity=cav Internal-1_Internal_Selection-1_e1_S3, R1CR, -283.15, 0.4 ** Name: e2 *RadiateCavity=cav Internal-1_Internal_Selection-1_e2_S3, R1CR, -283.15, 0.6 ** Name: e3 *RadiateCavity=cav Internal-1_Internal_Selection-1_Radiation-1_S3, R1CR, -283.15, 0.8 ** ** Defined fields ++++++++++++++++++++++++++++++++++++++++++ ** ** ** History outputs +++++++++++++++++++++++++++++++++++++++++ ** ** ** Field outputs +++++++++++++++++++++++++++++++++++++++++++ ** *Node file NT, RFL *El file, Output=3D HFL ** ** End step ++++++++++++++++++++++++++++++++++++++++++++++++ ** *End step ``` ---
**Author:** ![Gunnar](https://avatars.discourse-cdn.com/v4/letter/g/ed655f/32.png) [@Gunnar](https://prepomax.discourse.group/u/Gunnar)\ **Post date:** [September 4, 2024, 10:05pm UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/14 "2024-09-04T22:05:21Z")
Under Step control you can edit the number of iterations after which a cutback is made (parameter IR). I changed it from the default (8) to 50, the solution converged after 26 iterations. However, it was also neccessary to change the unit system to SI units (Kelvin). I have no idea if it’s just a coincidence but it worked for this case. ![d](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/7/7594572413d9616913161eb0be8c5ff79065493d.png) comparison with elmer: ![e](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/9/958afd8ca5b9b33926949cd6a1dd81387f2e2e6f.png) ---
**Author:** ![ANYS](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/anys/32/7737_2.png) [@ANYS](https://prepomax.discourse.group/u/ANYS)\ **Post date:** [September 4, 2024, 10:31pm UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/15 "2024-09-04T22:31:15Z")
Oh!. Nice contribution. In my case I had to increase it up to 200. Steady State has converge in 102 iterations with exactly the same result as in my previous post (but much faster: Total CalculiX Time: 0.664303 s) SUMMARY OF JOB INFORMATION STEP INC ATT ITRS TOT TIME STEP TIME INC TIME 1 1 1 102 0.100000E+01 0.100000E+01 0.100000E+01 ---
**Author:** ![PierreAntonetti](https://avatars.discourse-cdn.com/v4/letter/p/f1d935/32.png) [@PierreAntonetti](https://prepomax.discourse.group/u/PierreAntonetti)\ **Post date:** [September 4, 2024, 10:45pm UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/16 "2024-09-04T22:45:43Z")
Hi everybody Thanks to all your kind answers, I finally get the right results with your help ! To clarify : - I use a steady state “Heat transfer step” (not transient step) - I set all sink temperatures to -10K - i set IR=50 (under edit control-\>Time incrementation), thanks @Gunnar So I guess Calculix handles steadystate radiation ! @Gunnar, how do you manage to set kelvin as temperature unit ? I have some GUI suggestions to make radiation easier to set @Matej ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/f/f661f746ecac200b3412687db5cb12b122828bd2.jpeg) ---
**Author:** ![PierreAntonetti](https://avatars.discourse-cdn.com/v4/letter/p/f1d935/32.png) [@PierreAntonetti](https://prepomax.discourse.group/u/PierreAntonetti)\ **Post date:** [September 4, 2024, 10:47pm UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/17 "2024-09-04T22:47:42Z")
I still have a question : is it possible to calculate the heat flow through an edge (1d-integral of the heat flux on a border) ? In that case, iI need to check the heat flow on T1 (bottom) is 11KW/m ---
**Author:** ![Gunnar](https://avatars.discourse-cdn.com/v4/letter/g/ed655f/32.png) [@Gunnar](https://prepomax.discourse.group/u/Gunnar)\ **Post date:** [September 5, 2024, 5:39am UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/18 "2024-09-05T05:39:20Z")
> [@PierreAntonetti](#): > > @Gunnar, how do you manage to set kelvin as temperature unit ? What I meant is, I used the unit system type “unitless” and entered all values in SI units. I rememberd that it is generally recommended to use an absolute temperature scale for radiation as it being proportional to T^4. ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [September 5, 2024, 7:31am UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/19 "2024-09-05T07:31:11Z")
Being able to switch to Kelvins would be nice. It was requested in the past: [Unit Systems: (m, kg, s, K) and/or (mm, kg, s, K)](https://prepomax.discourse.group/t/unit-systems-m-kg-s-k-and-or-mm-kg-s-k/1032) > [@PierreAntonetti](#): > > I still have a question : is it possible to calculate the heat flow through an edge (1d-integral of the heat flux on a border) ? You can use 1D (e.g. beam) elements in CalculiX for heat transfer but they are expanded to solids anyway and not supported in PrePoMax for now. ---
**Author:** ![ANYS](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/anys/32/7737_2.png) [@ANYS](https://prepomax.discourse.group/u/ANYS)\ **Post date:** [September 5, 2024, 9:54am UTC](https://prepomax.discourse.group/t/radiation-test-case/1979/20 "2024-09-05T09:54:31Z")
> [@PierreAntonetti](#): > > is it possible to calculate the heat flow through an edge (1d-integral of the heat flux on a border) ? The procedure is the same as with reaction forces. In this case FLUX is the requested variable. Check 7.114 \*SECTION PRINT in the manual for more details. Result: ```auto total surface flux (q) for set INNER1 and time 0.1000000E+01 -1.107630E+04 ``` [Next page](https://prepomax.discourse.group/t/radiation-test-case/1979.md?page=2)