Page 419 - ExtendSim User Guide
P. 419

In this example, the pro-
portions for the Diverge
block’s two branches are
set to 1:1. The constrain-
ing rates in the valves are
defined such that the
upstream supply of 10
flow units per time unit
through Valve 1 equals
the cumulative down-
stream demand of 10 set
by Valves 2 and 3.
Because a large enough
supply of flow exists to
satisfy downstream demand, the distributional proportions are ignored and have no impact on the set of effective rates defined for each outflow branch of the Diverge block.
Two examples highlight what happens when the Diverge block is set to Distributional model and there is a “supply scarcity” that causes the upstream supply to be less than the downstream demand:
• IftheconstrainingrateinValve1ischangedfrom10to8,theDivergeblockwillusethe1:1 proportions that have been defined in its dialog to allocate the now limited supply between the two downstream demanding branches. In this case, 4 units of flow per time unit will move through both the top and bottom branches.
• IftheconstrainingrateinValve1issetto9unitsofflowperunitoftime,thesituationisdif- ferent. According to the 1:1 proportions that have been defined in its dialog, the Diverge block should allocate 4.5 units of flow to each of the two downstream demanding branches. However, the constraining rate for Valve 3 is 4 units of flow per time unit and that is all it can accept. The extra 0.5 units of flow will be routed through the top branch because the downstream demand for the bottom branch cannot keep up with the upstream supply (4.0 vs. 4.5) and the Distributional mode will always try to push as much flow as possible.
☞ The Diverge block's Proportional mode is used to resolve discrepancies when downstream demand is greater than upstream supply.
Distributional Mode Merge model
When the blocks are in Distributional mode, the difference between a Merge block and a Diverge block (illustrated above) is that the proportions defined in the Merge block’s table impacts the effective rates for the inflow branches only if there is a downstream “scarcity of demand”. The Distributional Mode Merge model illustrates the use of the Distributional mode when 1) the downstream demand exceeds upstream supply, and 2) downstream demand is less than upstream supply.
☞ The Merge block's Proportional mode is used to resolve discrepancies when upstream supply is greater than downstream demand.
Sensing mode
Similar to the Proportional mode discussed on page 390, the Sensing modes use proportions to calculate the effective rates for the branches. However, unlike the Proportional mode where
Merging, Diverging, and Routing Flow 393
Merging and diverging flow
Distributional Mode Diverge model
Distributional Mode Diverge model
Discrete Rate

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