I'm doing a simulation on an assembly whose internal cavity will be put under vacuum. To simulate this, I am applying a pressure of 101,325 N/m^2 to all exterior surfaces. After I run the simulation, certain areas of the top surface (where there aren't any internal reinforcing ribs) are actually deflecting outward. This doesn't make any sense to me since the pressure should be deflecting these areas inward. If I look at the bottom surface, these areas are deflecting inward like I would expect. Is there something going wrong with the simulation to cause these inexplicable results in the top surface, or am I totally missing/overlooking something? Any help or insight is very much appreciated, thanks!