Sorry, its hard for me to explain. But, I was just giving an idea that I had tested successfully with my professor, no need to bash on me. And I had .15mm wall flex, not .5mm, mistype.
The flex method involves "the control of expanding and contracting of the walls in order to control the expanding and contracting capabilities of the sub". You are able to use the (expanded wall's) contraction force to your advantage.
For the U-port, it just has to be done to be shown. To sum it up, it tries to keep a constant air volume in the box, and moves air in and out ONLY when it needs to (like a vent). It's trial-and-error for the calculations and hands-on attempt.