If you have a large network and especially if you are doing continuous simulation then you want to have many tools for helping you understand the network and the simulation results.
- In InfoSWMM and H2OMAP SWMM you can have a Base Network with many differenct Child Scenaio generations. A Child can be either based on the Base Scenario of a different generation Child Scenario.
- Facility Manager allows you to make inactive and active sets areas of your network, which makes simulating larger and smaller models a snap to do in InfoSWMM. Run Manager lets you control which areas of the model network gets save to the binary graphics file (Figure 1).
- The Process Control in Run Manager (similar to the process control in SWMM 5) allows the modeler to control which processes are simulation to help in her model calibration.
Time Step Selection in InfoSWMM
1st The time step you use in InfoSWMM is controlled from the top by the rainfall interval (Figure 3):
1. All of your time steps should be less than the rainfall interval,
2. The hydrology time step should be less than or equal to the smallest raingage rainfall interval in your network,
3. The hydraulic time step should be less than or equal to the hydrology time step and should be based on the hydraulic needs of the your network. Short length links, pump and weirs may require a smaller maximum hydraulic time step.
2nd The report time step controls what you see in the graphics output of InfoSWMM. If you see a large difference between that you see in the graphics output and the report text file it is because you have a large difference between the report time step and the average time step used during the simulation.
Solution: If there is a large discrepancy in the graphics and report text file then the best solution is to reduce the maximum time hydraulic time step so it is closer to the average time step and also to make the report time step closer to the Maximum time step (Figure 4).
How to Speed Up your InfoSWMM Simulation by examining the Minimum Time Step, the Average Time Step and the Maximum Time Step.
Minimum Time Step (sec) 0.984
Average Time Step (sec) 9.071
Maximum Time Step (sec) 30.000
Percent in Steady State (%) 0.000
Average Iterations per Time Step 4.821
Use a maximum time that will lower your average iterations per time step to speed up the simulation,decrease the maximum time step to lower the number of iterations, use equivalent conduit lengthening to increase
the minimum time step, the model is fastest if the minimum and maximum time steps are not too small or large compared to the average time step. Adjust the stopping toleranceand the number of iterations if you can to speed up your model
You can also decrease the number of iterations or the stopping tolerance to speed up the model or improve the continuity error of the model. If you are doing a continuous simulation then you can have a reduced graphical output data set to speed up the simulation
If you have a duo or quad core computer another option to speed up the simulations is to use 1, 2, 3 or 4 cores for the simulation
Note: A rough approximation of the time step you need for an InfoSWMM model can be found by finding the mean link length using the field statistics tool for the length in the Conduit DB Table and then estimating the time step from the mean length, mean full depth velocity and mean full depth wave celerity.
The time step actually used during the simulation is related to this velocity and the safety adjustment factor. The larger the safety adjustment factor the larger the mean time step listed in the Routing Time Step Suggestion.
Variables for Controlling the Continuity Error in InfoSWMM compared to SWMM 5
Time step is always a key parameter in SWMM 5 as it is the main parameter for a user to adjust in case of a significant continuity error. InfoSWMM has additional flexibility and allows the user to control the number of Picard iterations and the Node continuity stopping tolerance. SWMM 5.0.022 has the number of iterations fixed at 8 and the stopping tolerance fixed at 0.005 feet. The stopping tolerance is important because it controls the number of iterations during a time step. For example, if all of the Nodes have a current and former iteration depth difference (absolute) less than 0.005 feet then the time step is deemed converged and the node and link flow computations are stopped for that time step. In SWMM 5 since the stopping tolerance is fixed then your main option is to reduce the time step. In InfoSWMM you can also decrease the stopping tolerance, increase the number of iterations or decrease the time step. In most models it is best to alter all three parameters for the fastest model. For example, a slightly smaller maximum time step or a smaller variable time step adjustment factor, more iterations and a smaller tolerance will normally work better than just lowering the time step (Figure 6).