SWMM56

The skip steady state periods uses the last computed flows in the conveyance system instead of computing new flows. In the sample graphs you can see where the change in lateral flow is below 0.05 cfs (the blue arrow in the second image). The network solution used the steady flows about 27 percent of the time. The time step summary in the text output file tells you how often the model was in steady state. Skip Steady State Periods Checking this option will make the simulation use the most recently computed conveyance system flows during a steady state period instead of computing a new flow routing solution. A time step is considered to be in steady state if the change in external inflow at each node is below 0.5 cfs and the relative difference between total system inflow and outflow is below 5%.

Introduction : If you have a lead and lag pump connecting the same upstream and downstream nodes the normal behavior for the two pumps is to have the the lead pump turn on first followed by the lag pump. The turn on and turn off depths for the pumps determine when the pumps turn of. The pump will work as a simple lead and lag pump based on a wet well elevation without any real time controls. If you want to add real time controls (RTC) to the lead and lag pumps you can add more sophisticated controls. For example, if you wanted to turn on and off the lead pump at successive time steps then you can add these RTC rules ; New Real Time Control (RTC) Rules RULE RULE-1 IF PUMP LEAD_PUMP STATUS = ON AND PUMP LAG_PUMP STATUS = ON THEN PUMP LEAD_PUMP STATUS = OFF PRIORITY 1.000000 RULE RULE-2 IF PUMP LEAD_PUMP STATUS = OFF AND PUMP LAG_PUMP STATUS = ON THEN PUMP LEAD_PUMP STATUS = ON PRIORITY 1.000000 RULE RULE-3 IF PUMP LEAD_PUMP STATUS = OFF AND PUMP LAG_PUMP STATUS = ON THEN PUMP LEAD_PUM...

These three graphs show how the number of iterations to solve the St. Venant equation in SWMM 5 changes during the course of the simulation based on rapidly changing inflow, steady inflow and decreasing inflow. This example allows up to ten iterations and a tighter head tolerance to better illustrate how the number of iterations increase at the beginning of the simulation and during rapid inflow. Normally, in SWMM 5 the number of iterations will be between a minimum of 2 and a maximum of 4 iterations. In the first graph the outflow is in blue and the number of iterations at each time step is shown in red. In the second graph the bubble size is based on the number of iterations and the y axis is outflow of the network. The third graph shows the number of iterations used at each link in the model at a particular time step. The more the flow changes the more iterations are needed to keep the flow in balance.

The overall continuity error at any time during the simulation is simply the total inflow minus the total outflow. The total inflow is the dry weather, wet weather, groundwater, I&I inflow, external inflow and the initial network storage. The total outflow is the amount of surface flooding, outfall flow, reacted flow and the final storage. Continuity error = Total Inflow - Total Outflow The continuity error can be variable over time as this graph of the total inflow, total outflow and continuity error over time shows for the classic extran example from SWMM 3 and SWMM 4. The continuity error can be negative or positive at each saved time step and it tends to balance out over time. As you can imagine depending on how long the simulation lasts the continuity error may be much greater than zero. If you can the simulation to dry weather flow is reached in the sanitary network or the stormwater network has drained the continuity error will be better. You can see that the CE increases at...

If you use the conduit lengthening option under the dynamic tab the shorter lengths will be lengthened internally during the simulation and the results will be a smoother.

Note: It is often important to compare the results for your link flows, node heads and system variables between SWMM 5 versions to help you calibrate the new version based on the old version results. If you run a SWMM 5 model in an older version, save the .rpt and .out file and then open up the SWMM 5 input file in a newer version of SWMM 5 you should see a active graph symbol. The active symbol means that you can plot the results of the old model in the newer SWMM 5 GUI. For example, you can plot one of the system variables and then save ALL of the system variables to either a clipboard or a system calibration file. You can then use the Calibration dialog of SWMM 5 to compare the older results with the simulation results of a new version of SWMM 5.

Comment: A really nice water analogy for the field properties Divergence, Curl and Gradient from the Blog Starts With a Bang ....it's pretty mathematically intensive, but what's missing from most textbooks and E&M courses are physical explanations of what the mathematics means. For instance, I've started teaching about fields, and pretty much every textbook out there goes on and on about the properties of fields. They say you can do three things to fields, take the gradient , divergence , or curl of them. (Are you asleep yet? I'm sorry!) What do these things mean? An easy way to picture it is in terms of water. If you placed a drop of water anywhere on, say, Earth , the magnitude and direction of how it rolls down is the gradient of the Earth's elevation. If you let that drop of water flow, as it goes downhill, it can either spread out or converge to a narrower stream. When we quantify that, that's what the divergence of the field is. And finally, w...