Guidelines for Solving Surface-to-Surface Radiation Problems
The following guidelines are helpful when selecting solver settings for models that involve surface-to-surface radiation. First check the Jacobian contribution setting in the Jacobian Contribution section of the Surface-to-surface Radiation interface. The default value, Only local contributions to radiosity, results in a lumped Jacobian matrix and reduces a lot the required amount of memory. There a few configurations where this formulation may lead to poor convergence. In this case, using the Include contributions from total irradiation option should fix the issue at the price of a much larger memory consumption use, in particular using the Direct area integration or Hemicube method. In this case:
•
the Jacobian matrix of the discrete model is partly filled as opposed to the usual sparse matrix. The additional nonzero elements in the matrix appear in the rows and columns corresponding to the radiosity degrees of freedom. It is therefore common practice to keep the element order of the radiosity variable, J, low. By default, linear Lagrange elements are used irrespective of the shape-function order specified for the temperature. When you need to increase the resolution of your temperature field, it might be worth considering raising the order of the temperature elements instead of refining the mesh.
•
The Assembly block size parameter (found in the Advanced solver feature) can have a major influence on memory usage during the assembly of problems where surface-to-surface radiation is enabled. When surface-to-surface is detected, the solver sets the assembly block size at 100. Using a smaller block size also leads to more frequent updates of the progress bar.
Introduction to Solvers and Studies and Advanced in the COMSOL Multiphysics Reference Manual