Hi,
When I am performing pressure driven analysis (PDA), using piecewise linear function, negative pressure values are not obtained at any node in the system even when the water level at the reservoir is set to be lower than the elevation of most of the nodes. It seems that (at least in the case that I had run) when the actual demand in a node become zero the pressure head is forced to be equal to zero and can not become negative.
To better clarify my problem, I run another scenario: I assign zero demand to all the nodes in the network. I run the case with both demand driven analysis (DDA) and PDA, with same the hydraulic and physical conditions. The pressure values in some nodes become negative using demand driven analysis while, the pressure values calculated for these nodes are zero and no negative values were observed using PDA. I was thinking maybe the way that the pressure demand function is defined is causing this limitation to PDA. I would like to know your idea about this issue and if there is any way to fix this issue?
Thanks
Mark