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MIE360 10 Pilot Runs - MIE360 Computer Modeling and...

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MIE360 Computer Modeling and Simulation Lecture Notes Lecture 10– Make Pilot Runs Yes Determine # of replications No Determine the run lengths Terminating Simulation Determine the Warm-up period No Include Transient Yes Determine # of replications The Warm-Up period In many real life situations we rarely start the system from scratch. When plants close, its status is frozen as is until it opens up again the next day. Or it runs 24/7 shifts. When we simulate such systems in a computer model, there is an initial period which resembles the operation of the plant when it first started many years ago. In order to ensure that the initial simulation period is representative of the steady state operation of a system, we have to wait some time until the simulation itself reaches this steady state. Until it reaches steady-state the results have to be ignored. We can only start tracking the states and counters once this stead state period is reached. Computer simulation languages always allow a user to specify a warm-up period. For now we delay dealing with this issue, by assuming that we wish to include the transient. Terminating vs. Non-terminating Simulations A terminating simulation is one that has a natural end point, such as a closing time or natural cycle. A non-terminating simulation is one that has no such natural end-point. Clearly the problem of the run length only exists for non-terminating simulations - for terminating simulation the run length is decided upon by the user or situation. While there are very sophisticated methods for determining the run lengths for non-terminating simulations, these are beyond the scope of introductory simulation courses, and common practice. The standard practice in simulation is for the analyst to negotiate a run-length with the client that is considered “appropriate” and thus to negotiate the client into using a terminating simulation. Daniel Frances © 2010 1
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