Saturday, August 3, 2013

How the State InfoSewer solution solves for the link flow and node heads

Note: State InfoSewer solution solves for the link flow and node heads

Here is an example of how the Steady State InfoSewer solution solves for the link flow and node heads or depths:

•         1ST Flow is computed in each link and d and d/D is calculated based on pipe flow and manhole loading data and not the adjusted data from the 2nd pass.
•         2nd InfoSewer adjusts the link depth based on the manhole head and lists the adjusted depth in the browser and the Report Table after the manhole depths are calculated from downstream to upstream in the network.
•         Result: The HGL graph shows the link d and d/D based on pipe flow not the adjusted depth so you are looking at the results of the 1st pass in the links and the 2nd Pass in the Nodes in a HGL Plot  for a Steady State Simulation.

Here is one example of this sequence of events: The downstream head at the outfall causes a backwater condition in all of the links.  The d/D and q/Q is based on the manhole loading flow in the 1st pass and indicates the pipe is NOT full. However, in the 2nd Pass where the manhole depths are calculated from downstream to upstream the effect of the downstream boundary condition is felt.  The head shows that there is a full downstream boundary condition which is reflected in the condition of backwater and in the adjusted depth value.  The links are now full and the full depth is reflected in the value of the adjusted depth and the graphical presentation.

How to interpret this result:
1.   Based on the manhole loading to the network the pipes are NOT full which is indicated by the value of d/D and q/Q, however
2.   Based on the head calculations which account for downstream boundary conditions the pipes are full due to the backwater effect.  The backwater condition is reflected in the value of the adjusted depth – the adjusted depth shows the pipe to be full.

Figure 1.  Backwater is caused by the downstream boundary condition and shows full pipes but d/D is less than 1 based on the 1st Pass Link Flow Values.
Figure 2. InfoSewer solves for the flows in the links in the 1st pass and the heads at the nodes in the 2nd pass for the Steady State solution.

Figure 3.  Pipe Summary Table Shows the Pipe Adjustments based on 2nd Pass Head calculations and the d/D and q/Q values from the 1st Pass Link Flow Calculations.

Figure 4:  Two Pass Solution for InfoSewer (1) Flow and (2) Head

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