Mapped Mesh for a High Aspect Ratio Geometry

Hello,

I am working on a geometry that has a very high aspect ratio and need to create mapped mesh for one of the domains and free triangular mesh for the others.

I am facing couple of issues:

1. When trying to mesh one of the domains with a mapped mesh, it says "Isolated element found" or "Inverted element". How can I solve this issue?

2. On meshing the entire domain with free traingular mesh and using Laminar Flow and Heat Transfer modules, the computation doesn't terminate and gives an error: "Singular Matrix Found" What might have gone wrong?

Thanks in Advance!