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BlenderFDS Rough Notes
These are notes on getting started with BlenderFDS. At this point there is no organization to the notes. I am just putting things down as I encounter problems and come up with solution.
I usually build objects up through boolean operations of Mesh objects. Then when I go to Edit mode I find that the original Mesh object still exists. Luckily, in 2.92 I found this handy trick: Object >> Apply >> Visual Geometry to Mesh.
I often run into a problem when trying to export the GEOM lines, with "Bad geometry" errors. Suggest adding the 3D Print toolkit in Edit >> Preferences; search on "mesh". With this toolkit you can "make manifold" and "clean up" to remove duplicate edges and vertices.
The cleanup operations are usually done in Edit mode. It seems that you need to switch to Object mode in order to view the FDS Code.
With Blender 2.8, make sure to import the DXF format reader in Edit >> Preferences >> Addons.
This has me vexed for several hours. Maybe I just somehow knew how to do with with 2.7, but in 2.8 it was not obvious to me that you have first click the "+" to generate an additional slot for the the material, then select the faces and assign. So, think in terms of: 1. how many materials will this object need---add that many slots for that object; 2. next, make sure you have all the materials defined (or do this first, in BlenderFDS, many are predefined); 3. Assign the materials.
To remove a material from the dropdown list, first remove it from all objects. It will then have a 0 next to it (the number tells you how many objects us it, F is for stored materials). Save the .blend file and re-open it. The material will be gone.
When doing a boolean union between two objects make sure both objects have the same list of available materials so that faces of the new mesh have the origin materials retained.
The current version of BlenderFDS has a simplified the Blender interface. In order to see the Units panel in the Properties Editor you need to go back to the normal Blender interface. Open File > User Preferences ..., go to the Add-Ons tab and expand BlenderFDS. Uncheck the Simplify Blender User Interface option. Then you probably want to Save User Settings.
To set the units to English (Imperial) go to the Scene Properties Editor. Expand the Units dialog and set to Imperial. IMPORTANT: Make sure the Unit Scale remains 1.000. If not, BlenderFDS will not correctly convert to meters for the FDS input file.
Bug: Export fds case gives nonsensical error message when the only problem is not specifying a SURF for the GEOM
Would be nice if we could give a sensible error trap for this case.
When you go to export the GEOM you may get an error such as "self intersection". This usually happens when you have duplicate edges (and hence vertices) in your mesh. This following link seems to work well to fix this problem.
Loops cuts turn out to be a useful feature to use. Open the "+" panel on the left, in the Tools tab goto Add: Loop Cut and Slide. Use your cursor to place the cut and set orientation. Hit Enter. You can then increase the number of cuts using the left panel. There are also hot keys such as Ctrl + R.
I often run into a situation where I have a surface that I need to subdivide and extrude. This tutorial explains how to do that. In Edit Mode do: Mesh >> Extrude >> ....
You will want to think about how many faces get created when you introduce a new mesh object in Blender. For example, you have to the opportunity to control the number or sides a cylinder has when it is created. Later you will not be able to change this, and small features can lead to a lot of triangles getting exported to FDS that are not doing anything to improve your geometry.
Ctrl + M in object mode.
If you create nurbs surface, before you can do anything else with it you will probably need to turn it into a mesh object. In Object Mode, select the surface and then goto Mesh > Convert to (Ctrl + C).
I ran into this when making a large sheet. I started from a simple box, so I knew the geometry was closed. I made a thin sheet, about 1/4 inch thick and somewhere between 5.3 ft and 5.4 ft wide I started to get a self-intersection error, which was preventing me from getting output from BlenderFDS. The problem turned out to be related to the very skinny triangles that I was implicitly creating along the length of the sheet (it was a corrugated plate, I had used about 100 loop cuts in the other direction for the corrugations). The fix was to add a few loop cuts in the perpendicular direction to make the triangles more reasonable.
When adding a Mesh > Cylinder object, do yourself a favor and right at the beginning do the following: (1) set the number of sides to something minimal and (2) set the Cap Fill Type to "Triangle Fan". This makes the triangles at the end caps much nicer than the "Ngon" version.
In Edit Mode, do Select > Select Similar > Co-planar. This allowed me to select all the fuel ports in an otherwise round pipe (there were 100s) all one stroke.
When working with the CERN facility case we were handed a single .stl file for the whole facility. It turns out this facility had 300+ objects. A handy trick to separate these objects so that can be exported independently to different FDS GEOM lines is the following: In Edit Mode, do P > By Loose. (Thanks to Nikolas Kilian for this tip.)
If you have two objects that need to be merged into a single manifold object, go to Modifiers > Boolean > Union. Then I sometimes need to check Properties > 3D Printing (left panel).