I'm trying to model pressure inside of a cylinder. I put an ourward pointing pressure on the ID of the cylinder and place roller fixtures at the end. When I try and run it, I'm give a generic error complaining about boundary conditions. Is the problem that I'm only restraining the cylinder in the z axis, but not the x and y? How would I constrain the cylinder in the x and y without distorting the analysis? For example, I tried fixing the ends (and thus constraining in all dimensions), but the solutions balloons in the middle but not the edges. I want to model this cylinder without any distortion due to fixtures. Any ideas? Thanks.