What is Link Bypass in SWMM 5?

Subject: What is Link Bypass in SWMM 5?

 

If a link has converged within two iterations then the hydraulic computations will be bypassed for new iterations.  A link is deemed converged if BOTH the upstream and downstream nodes depth has converged between successive iterations as long as two iterations have occurred during the time step.  This is simulation savings step as it my eliminate up to 75 percent of the computational time in a SWMM 5 simulation.  The image below shows that for some links the flow in the link is converged within 2 iterations whereas for others it may take 3 or 4 iterations.  Overall, 37 percent of the link computations are bypassed during the simulation of this particular hydraulic network.

 

Time Step Critical Elements in SWMM 5

Subject:  Time Step Critical Elements in SWMM 5

The time step critical elements in the SWMM 5 report text output file tells you which elements were controlling the time step during the simulation.  If no element was controlling the time step then the program will just use the maximum time step.  For example, if the maximum time step was 10 seconds and the average time step was 9.8 then only a few time steps were set by a link or node that needed a smaller than maximum time step (Figure 1).  If the maximum time step for the same simulation was 30 seconds then many links and nodes will set the time step (Figure 2).

Figure 1.  Most of the time the simulation used the maximum time step of 10 seconds so only a few links were time step critical.

Figure 2.  Most of the time the simulation used less than the maximum time step of 30 seconds so many links were time step critical.

Pump Power Usage in SWMM 5

Subject: Pump Power Usage in SWMM 5


 The pumping summary table (Figure 1) includes a column that tells the user how much power was consumed by the pump in kilowatts by the head loss or head gain of the water flowing through the pump. The power usage equations are shown in Figure 2.


 Figure 1. Pump Summary Table in SWMM 5.0.021

 

 

Figure 2. Pump Power Equations in SWMM in which dt is the time step.

A General Theory of Productivity

Note: A General Theory of Productivity


Mar.17, 2008 in Creativity, Flow, Productivity

A General Theory of Productivity

Here recently I’ve been thinking a lot about what makes people productive in general. What follows is a general theory that captures what I think is going on:

Productivity =  (Creative Energy + Focus + Motivation + Aptitude + Ideal Time)

                      ----------------------------------------------------------------------------------

                                                             (Difficulty + Distractions)

Non Linear Term in the Saint Venant Equation of SWMM 5

Subject:  Non Linear Term in the Saint Venant Equation of SWMM 5

The flow equation has six components that have to be in balance at each time step:

1. The unsteady flow term or dQ/dt

2. The friction loss term (normally based on Manning's equation except for full force mains),

3. The bed slope term or dz/dx

4. The water surface slope term or dy/dx,

5. The non linear term or d(Q^2/A)/dx and

6. The entrance, exit and other loss terms.

All of these terms have to add up to zero at each time step. If the water surface slope becomes zero or negative then the only way the equation can be balanced is for the flow to decrease. If the spike is due to a change in the downstream head versus the upstream head then typically you will a dip in the flow graph as the water surface slope term becomes flat or negative, followed by a rise in the flow as the upstream head increases versus the downstream head.

You get more than the normal flow based on the head difference because in addition to the head difference you also get a push from the non linear terms or dq3 and dq4 in this graph.