SWMM 5 uses 2 to 4 iterations to solve the node continuity and link momentum/continuity equation at each time step. Nodes ALWAYS use 4 iterations but links may use only 2 iterations if BOTH the upstream and downstream nodes are converged. If the upstream and downstream nodes are converged then the link flow calculations are bypassed for one or two iterations. This speeds up the SWMM 5 engine because most of the time is used in calculating the link flows and not the node depths.
- Links in SWMM 5 bypass the link calculations if BOTH the upstream and downstream nodes are converged AND there has been at least two iterations. There is a maximum of 4 possible iterations in SWMM 5.
- A node is converged if the current iteration value and the last iteration value of the node depth is less than 0.005 feet (the internal units for SWMM 5 are American Standard Units).
- If a node is no longer converged on the 3rd and 4th iteration the flow computations for the links will resume.
- In a typical model 50 to 70 percent of the link iterations after
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| Figure 1. Iterations in SWMM 5 |
