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Merging, Diverging, and Routing Flow
Merging and diverging flow
satisfy the downstream demand that has been placed on the top outflow branch first. After that, if supply is still available, the Diverge block will attempt to service subsequent branches. This pattern is repeated until every branch has been satisfied or until the upstream supply of flow runs out, whichever comes first.
Priority Mode Merge model
When the blocks are in Priority mode, the difference between a Merge block and a Diverge block (illustrated above) is that the priorities defined in the Merge block’s table impact the effective rates for the inflow branches if there is a downstream “scarcity of demand”. The Pri- ority Mode Merge model illustrates the use of Priority mode when 1) the downstream demand exceeds upstream supply, and 2) downstream demand is less than upstream supply.
Distributional mode
Similar to the Proportional mode described on page 390, the Distributional mode allows you to define a desired set of proportions for each branch. However, unlike the Proportional mode (but similar to the Priority mode discussed on page 390), these proportions serve as the deci- sion rule for assigning effective rates to the branches only when discrepancies arise between the upstream flow supply and the downstream flow demand.
• In the case of the Diverge block, when the upstream supply is greater than or equal to the downstream demand, the block passes as much flow through each branch as the downstream demand will allow and the proportions are ignored. However, when downstream demand exceeds upstream supply, the proportions assigned to each branch are used as a guide to determine how the limited supply should be distributed across the outflow branches.
• In contrast, the Merge block passes as much flow as possible through each inflow branch when downstream demand exceeds upstream supply, ignoring the proportions entered in the dialog’s table. However, when upstream supply exceeds downstream demand, the propor- tions assigned to each branch are used as guides to determine how the limited demand should be distributed across the inflow branches.
☞ The distributional proportions entered in a Merge or Diverge block’s table are significant only in certain situations; they are ignored otherwise. Proportions do not follow a fixed flow rule; they only impact the effective rates assigned to the branches when discrepancies arise between the upstream flow supply and the downstream flow demand.
Merge/Diverge blocks in Distributional mode are not always compatible with Merge/Diverge blocks in Sensing mode. Consequently, an area of the model with some blocks in Sensing mode and others in Distributional mode are prone to error. See “Cautions when using potential rates” on page 455 for more information.
Discrete Rate

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