I don't even know how to phrase this, let alone which forum it should go in. I'm trying to design a valve, like in a blood vessel. I want to ensure that the design "works" i.e. the shape of the valve will be determined by the volume of fluid moving through it. So, what shape will it take over time? See attached really rough diagram of just a few steps. Two vessels are crossing at right angles and the valve (a very long, wavy, tentacle) is alternately letting red or blue fluid pass. It doesn't really have to make sense to you - I'm just trying to show you that, for example, the area of the contained fluid will have to remain constent once it's closed off, and that will affect the shape. Note: this need only be designed in 2 dimensions. A 3D calculation is another ball of wax. So: what tools do I use to get these shapes down, at least roughly? I'm currently using pencil and eraser to guess, but I can't calculate areas. Simulation software? Calculus? Analog simulation (marbles)? Anybody want to take a crack at it?