Delay - EMSE 235: Systems Thinking and Policy Modeling I...

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EMSE 235: Systems Thinking and Policy Modeling I
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EMSE 235: Systems Thinking and Policy Modeling I 2 • Material Delays – Mixed item delays (system dynamics) – Traditional material delays (traditional OR models) • Information Delays – Exponential smoothing – Nth order exponential smoothing
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EMSE 235: Systems Thinking and Policy Modeling I 3 • The delay of a process is the time lag between the process input and the output. • We model two types: – A material delay captures the physical flow of material, e.g. a supply chain, building construction, etc. – An information delay captures the gradual adjustment of perceptions or beliefs, e.g., perception of a change in demand. Input Output Delay
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EMSE 235: Systems Thinking and Policy Modeling I 4 • Many management problems can be stated as delay related problems: – Inventory control – Capacity planning – Process improvement / reengineering – Time to market / product development – Project management • Delays are sources of oscillation and complex dynamic behavior .
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• Controlling the shower temperature. A first model: • But old houses will take a long time to get water to the shower… EMSE 235: Systems Thinking and Policy Modeling I 5 Temperature in Shower Desired Temperature Discrepancy Adjustment Adjustment Time INIT Temperature_in_Shower = 32 Discrepancy = Desired_Temperature-Temperature_in_Shower Adjustment = Discrepancy/Adjustment_Time Adjustment_Time = 2 Desired_Temperature = 75
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• Modeling a delay in the pipes… EMSE 235: Systems Thinking and Policy Modeling I 6 Temperature in Shower Desired Temperature Discrepancy Adjustment Adjustment Time To Shower Temperature Change in Pipe INIT Temperature_Change_in_Pipe = 32 INIT Temperature_in_Shower = 32 Discrepancy = Desired_Temperature-Temperature_in_Shower Adjustment = Discrepancy/Adjustment_Time To_Shower = DELAY(Adjustment,10) Adjustment_Time = 15 Desired_Temperature = 75
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EMSE 235: Systems Thinking and Policy Modeling I 7 12:52 PM Tue, Oct 28, 2008 Shower Dynamics Page 1 0.00 30.00 60.00 90.00 120.00 Months 1: -20 50 120 Temperature in Shower: 1 - 2 - 3 - 4 - 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 AD=6 AD=8 AD=10 AD=15
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EMSE 235: Systems Thinking and Policy Modeling I 8 Delays are modeled with the aid of one or more stocks Delay Input Output Pending Homeworks New assignments Finished Assignments Packets in Transit Sent Packets Packets that Arrived Quality Perception of Adjustment to Perception Material Delays Information Delays
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EMSE 235: Systems Thinking and Policy Modeling I 10 Delays are modeled with the aid of one or more stocks in tandem . Pending Homeworks New assignments Finished Assignments Packets in Transit Sent Packets Packets that Arrived Material Delay Input Output
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EMSE 235: Systems Thinking and Policy Modeling I 11 • Having defined the stock and flow structure of delay, we need to define an equation for the outflow.
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Delay - EMSE 235: Systems Thinking and Policy Modeling I...

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