Page 482 - ExtendSim User Guide
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456 Advanced Topics
Upstream supply and downstream demand
• Gettinginformationabouttheseratesslowsdownthesimulation.TheExecutivehastomake a lot more LP calculations to extract the potential rate information.
• InsomecasesthepotentialratesasreportedbytheSensorblockarenotaccurate.Depending on how flow is diverged and merged, the potential supply or demand rates could be aggre- gated even if they should not be. This is illustrated in the “Supply & Demand Warning model” described below.
• Merge/DivergeblocksinDistributional,Neutral,andPrioritymodesarenotalwayscompat- ible with Merge/Diverge blocks in Sensing mode. Consequently, models with blocks that mix Sensing mode with Distributional, Neutral, or Priority modes are prone to error.
• AMergeorDivergeblockinSensingmodehasabiasorder.Dependingontheblock’sloca- tion in the Executive’s list of bias orders:
• Theeffectiveratesmightbedifferent.
• The block might not follow the proportions specified by the Sensing mode.
For instance, the effective rates are different in the “Combine Priority Sensing model” and the “Combine Sensing Priority model”, and neither of those models follow the Sensing rule.
Issues when relying on the Sensor to report potential rates
Based on how a model is configured, and the mode selected in a Merge or Diverge block, a Sensor block could report erroneous information.
Supply & Demand Warning model
In this model, the Sensor blocks correctly report the upstream supply. But Sensor A reports an invalid downstream demand of 1400 gallons/minute. The actual downstream demand is 1000 gallons/minute, reported by Sensor C. This is determined by verifying the demand results, compared to what was expected, from right to left.
Supply & Demand Warning model
Evaluating the model from right to left (for the downstream demand rate):
• SensorCreportsademand(DemandC)of1000gallons/minutebecauseValveClimitsflow to 1000 gallons/minute. The Sink at the end of the line doesn't limit the inflow rate at all.
• Demand B1 is 1000 gallons/minute because the Prioritize 2 block has its top priority at branch B1. (Verification: If a Tank with flow is present at branch B1, Prioritize 2 and Valve C would accept 1000 gallons/minute coming from branch B1.)
Discrete Rate

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