I’m trying to solve COMSOL’s example problem involving cavity radiation in CalculiX. I’ve obtained correct results in Abaqus but CalculiX still gives me too low temperatures. The picture below shows the assumptions of this analysis:
As you can see, there’s a triangular cavity with each of its surfaces having different emissivity. Blocks outside of the cavity are used to apply boundary conditions and loads - the bottom one has a prescribed temperature while the other two have different prescribed fluxes. The goal is to find the temperatures of cavity faces 2 and 3. According to analytical calculation, they should be around 641 K and 600 K, respectively. However, in CalculiX I get the maximum temperature of 523 K:
Here’s part of my input file:
*Physical constants, Absolute zero=0, Stefan Boltzmann=5.67038E-08 *Material, Name=Material-1 *Conductivity 400 *Solid section, Elset=eall, Material=Material-1 1 *Initial conditions, Type=Temperature nall, 300 *Step *Heat transfer, Steady state *Boundary outer1, 11, 11, 300 *Dflux outer2, S, 2000 *Dflux outer3, S, 1000 *Radiate, cavity=cav inner1_S3, R1CR, 300, 0.4 *Radiate, cavity=cav inner2_S3, R1CR, 300, 0.6 *Radiate, cavity=cav inner3_S3, R1CR, 300, 0.8 *Node file NT, RFL *El file HFL *End step
I uploaded the whole input file here: Dropbox - cav_rad.inp - Simplify your life
I’ve tried defining negative temperatures for cavities (-300), as mentioned in the documentation, but the analysis failed to converge.
Do you know what can be wrong here ? Is that a bug or have I just missed something ?