I’m having some trouble getting my head around part of the radiation enclosure problem so I’ve tried to summarise in a small example. I have a flat plate with a temperature boundary condition on one edge, and an enclosure radiation surface across the whole thing. As I understand it, when the view factors don’t add up to 1 (which they won’t), the remaining view factor is taken up with an effective black body with a temp of 0 to remove the effective net heat flow.
Now I want to turn this effective loss to space off, so that the radiation exchange only considers other enclosure radiation elements. I was under the impression I could do this with the RADLST card where I collect all the CHBDYG cards and set the radiation exchange matrix type to 4 for a conservative radiation matrix.
In my example, the plate temperature would tend to the boundary condition of 200, as the radiation surface can’t find any other elements with a delta T. But the results don’t change so there still seems to be radiation coupling between the enclosure radiation surface and the .
I don’t really want to use an ambient element as I understand that this will have an impact on the radiation exchange as it needs a fixed temperature.
The reason I want to do this is that in my real model, I don’t want to make every surface part of the radiation enclosure. Mainly due to computational time when (I feel!) I know which radiation surfaces drive the system due to their significantly higher emissivity and in addition there are some surfaces which are conductively coupled to the radiation surface that they will anyway be at the same temperature so aren’t really needed as part of the radiation exchange calculation.
As an aside, if anyone knows how to assign the RADLST card (or solve this problem in another way) in the FEMAP GUI then let me know. I have to write it in the preview at the moment.
I’ve attached the simple model. Any help is appreciated. I’ve been using Nastran quite a long time but am new to the thermal analysis so go easy if I'm asking the wrong questions!