Page 420 - ExtendSim User Guide
P. 420

Merging, Diverging, and Routing Flow
Merging and diverging flow
you directly enter or control the proportions for each branch, the proportions for the Sensing modes are derived dynamically from the model as it runs.
• In the case of the Diverge block, Demand Sensing proportions for the outflow branches are calculated as a function of the potential downstream demand. For instance, the downstream demand placed on a particular outflow branch becomes the proportion for that branch.
• Similarly, the Merge block uses the potential upstream supply to define the Supply Sensing proportions for each inflow branch.
☞ Potential demand and supply rates are advanced concepts that are discussed in “Upstream sup- ply and downstream demand” on page 455.
In the Sensing mode, the block's dialog has a table where you must define the maximum possi- ble rate of flow through each branch. This upper bound is used as a way to limit throughput so that the proportions can be determined if the upstream supply or the downstream demand is infinite.
The discussion on page 455 provides reasons why the Sensing mode should be used with extreme caution and some situations where it should be avoided altogether. Given the potential problems, and because similar behavior can be achieved using the Distributional mode, the Sensing mode should be used only as a last resort.
Demand Sensing Mode Diverge model
In this example, the constraining rates in Valves 2, 3, and 4 define the demand for flow downstream of the Diverge block. They therefore define the pro- portions used to distrib- ute the flow across the Diverge block’s outflow branches.
A maximum possible
rate of 1,000 for each
branch is entered in the
Diverge block’s table.
The block’s Results tab
(cloned onto the model
worksheet) displays each branch’s actual outflow rate and the amount of total outflow for the simulation run.
Supply Sensing Mode Merge model
In the Supply Sensing Mode Merge example, the constraining rates in Valves 1, 2, and 3 define the supply upstream of the Merge block. They therefore define the proportions used to distrib- ute flow across the inflow branches.
Neutral mode
Unlike any of the modes discussed previously, the Neutral mode does not allow you to control the effective rates for the branches. This is a passive mode where no branch has a throughput
Demand Sensing Mode Diverge model
Discrete Rate

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