To me it seems that the DF-physics are closer to reality than we all thought. It seems, that if the distance between the flowing tiles and the channel is large enough, the dynamic-pressure-behavior disapers as it would in real life. it only accounts for static pressure while the total pressure remains the same.
DF ONLY accounts for static pressure. Dynamic pressure isn't simulated.
by the looks of the spoilers above DF simulates the dynamic pressure as a form of horizontal static pressure - otherwise there wouldn't be a difference between the damned an the flowing river!
The dynamic part of pressure is proportional to fluid velocity. In RL the total pressure of a flowing river is HIGHER than a damned river. So the DF effect that water rises further when tapped to a damned river has nothing to do with reality.
I agree what's described in Diagram A in the wiki is a bit odd. I can find no correlation to real effects, so I'm assuming a programming artefact. (Namely fluid simulation, when having to choose if to put a tile of water at the end of a u-bend or on the outflow of the river, always opts for the outflow.)
If you can name a fluid dynamics effect that would explain the strange behaviour in Diagram A, I will listen. I can say dynamic pressure is not it.
First of all I think we have to consider that DF is only
trying to simulate the behaviour of hydro-pressure, I wasn't saying that the pressure features of DF are even close to reality. Still it seems DF is able to make a difference between standing water and flowing water of the same height - which I found a nice feature given the rather blunt simulation of DF-flow. The real issue is, that rivers in DF do not flow due to elevation but rather due to a artificial water source, where water is generated by the will of Armok. As
spitfire pointed out in real life the water level should rise when a river is damned due to the potential energy of the water upstream diverting its dynamic pressure back into potential energy an therefore applying static pressure on the water below. Due to the lack elevation difference this is impossible to simulate in DF-rivers. What DF seems to do is not accounting for the static pressure of a water tile until no further flow on the same z-level is possible. Therefore DF is simulating something like dynamic pressure...
Back to the original problem: In the first post of jez9999 the question was (I hope I got that right) why the tunnel on the inside end of the u-bend is being flooded, since the water is being taken out of the a flowing river, and on the same z-level as the bottom of the river (therefore the flowing water). The wiki says, that the water shouldn't do so (diagram A). To me this behaviour makes sense (see first paragraph). I believe the flood is happening because DF is able to notice tiles that are not in flowing direction are not accounted as being part of the flow system (maybe flow has something like a pathing-algorithm noticing dead ends). Therefore the dynamic pressure behaviour stated above does not apply to them.
