I am trying to define a project in Flow Sim 2010 SP2.1 on a fairly large internal flow design. The assembly has a full 3 axis gimbaled device enclosed in a weldment with a fan and heat exchanger at the bottom. The gas to be included in the analysis is air. I have made trial assemblies of the outer structure alone and Flow Sim does create a fluid volume, added the first gimbal structure which originally would not create a fluid volume but miraculously did the second time I ran Check Geometry. Now adding the the second gimbal structure, the Check Geometry will not create a fluid volume and the Invalid Contacts does not high-light the problem areas that I can see. These inner structures do have small gaps, but the first did eventually allow a fluid volume to be defined. Any ideas?