Multi Mesh Models

[Big Al]

I apologise if this topic has been covered before. When using multiple meshes should all the mesh boundaries be open; or should it just be the external boundaries that are open and the mesh boundaries that are adjacent to each other remain closed or deleted.

[Charlie Thornton]

I can think of three cases relating to mesh boundaries:

(1) A mesh boundary that does not touch another mesh (i.e. simulation domain boundary)

In this case, the mesh boundary behaves like a solid wall. I believe it takes it's properties from MISC:SURF_DEFAULT if no VENT is applied. The default surface is almost always INERT.

(2) A mesh boundary that adjoins another mesh

In this case, the two boundaries will be "connected" and heat, particles, etc will be exchanged between the two meshes. There should not be a vent between the two meshes. (is this what you meant by deleted?)

(3) A mesh boundary appears inside another mesh (e.g. mesh A is embedded within a larger mesh B)

It used to be that this was just a waste of cells. I'm not sure how it's handled in the current version of FDS.

When you talk about open, closed, or deleted it sounds like you are talking about VENTs that have been placed on the boundaries of the mesh. In this case, if the VENT's surface is the special OPEN surface it will be "open" to ambient conditions. There is also a special surface called MIRROR that isn't used very often. Other than those two, any VENT surfaces will also "close" the boundary.