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Chapter 5

Chapter 5. Modeling Detailed Operations. An Automative Maintenance and Repair Shop. Current location is in downtown. Additional three-bay facility is to be built in suburb. Appointments for both locations will be from downtown.

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Chapter 5

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  1. Chapter 5 Modeling Detailed Operations

  2. An Automative Maintenance and Repair Shop • Current location is in downtown. Additional three-bay facility is to be built in suburb. • Appointments for both locations will be from downtown. In the suburb, appointments can be made upto 3 working days in advance. • If a customer is unable to schedule an appointment during this period, they call back the next day or may schedule the work to be performed in downtown. • Customer arrivals follows a stationary poisson process with mean rate 29 calls/day. MIS 463-Asli Sencer

  3. 55% callers asks an appointment for the next day, 30% for two days after 15% for three days after If an appointment can not be scheduled in the chosen day, 90% will ask to schedule for the following day. • 80% customers leave their car the entire day 20% wait with car and they are given an approximate waiting time=book time(i.e., approx. Serv. Time)+1hr. Book time distr. is (44+90*BETA(2,3)) Actual Service time distr. is GAMM( Book time/1.05,1.05) • No more than 5 appointments for waiting customers/day! • The number of appointments/day is limited by max. book time hours scheduled/day=8 hrs/day/bay max. actual service time scheduled/day=24 hrs/day MIS 463-Asli Sencer

  4. Cost Issues • Assume 5 workdays/week/bay and 8 hrs/day Capital and labor Cost =$45/hr for each bay Customer charge=$78/hr * book time • To compensate for the service time variability, each service bay can stay open at most 3 extra hrs/day. The overtime cost=$120/hr for each bay If an already-started service can not be completed in that day, it will be completed the next day and customer will be provided a loaner vehicle. Loaner vehicle cost=$35/day If the service can not be even started for a vehicle on its scheduled day, the customer takes his car and brings it the next day. No loaner vehicle is given in this case. • Every day, the first hr is used to allocate future appointments, so resources are not available!! MIS 463-Asli Sencer

  5. Required Statistics • Daily profit • Daily Book Time • Daily Actual Service Time • Daily Overtime • Daily number of wait appointments not completed on time. MIS 463-Asli Sencer

  6. SETS • Group similar objects (resources, sequences, pictures, other) together under a single name • Define: Sets module from Basic Processes • Refer to objects in a Set by their original name and by an index Ex: Operators{Lynn, John, Sue}, In Arena, Operators(2)=John • An object can be a member of more than one Set (or not be in any Sets) Ex: Setup{Lynn, Fred}, Lynn is common in both sets • There can be sets of sets MIS 463-Asli Sencer

  7. Sets (cont.’d) • Perhaps the most common Sets: Resources • Allows dissimilar resources to be grouped — more general than multi-Capacity single Resources, where they all have to be identical • Entities can choose among members of a Resource Set according to preferences, rules • Can animate individual Resources in Set (state, picture) — unlike multi-Capacity single Resources • Also group entity pictures into sets for ease of access (via part-type number) • In our model: Define resource set: Bays {Bay1, Bay2, Bay3} Define entity picture set: Customers{Picture.red entity, Picture.blue entity} Define vehicle picture set: Vehicle {Picture.red car, Picture.blue car} MIS 463-Asli Sencer

  8. Variables Module • A data module in the Basic Process panel. • Some parameters of the model can be set as a global variable so that if they has to be modified in the future it will be easier. Ex: Transfer time in model 4.2 can be a variable • Can be a scalar, vector, or 2-dim. matrix, but any entity can change the value of a variable during simulation. • Allow re-use of the same number(s) in different places • Cannot involve arithmetic expressions, entity attributes, other Variables, or distributions. • In our model: Define “Day” variable to keep track of the current day of the week. MIS 463-Asli Sencer

  9. Expressions Module • A data module in the Advanced Process panel. • Can be a scalar, vector, or 2-dim. Matrix., but the form of the expression cannot be changed during the simulation • Similar motivation to Variables — re-use the same “thing” in several places in the model • A fixed “formula” or function that can involve arithmetic, entity attributes, other Variables, and distributions — very general • Expressions do not store values, name of the expression corresponds to a mathematical expression and its value is returned • In our model: Define expressions to generate the Book time, the actual service times, type of appointment request (wait or leave) MIS 463-Asli Sencer

  10. Submodels • Large models can be partitioned into smaller models by submodels, which may or may not interact. • In our model: Generate appointment calls, Make appointment Service activity Update performance variables Control logic MIS 463-Asli Sencer

  11. Batching and Seperating Entities • Use Batch and Seperate in basic process panel to create dublicate entities • Often used as control enities that can perform variety of functions. • Batch of entities, then split the batch • In our model: Dublicate entities to represent the incoming calls requesting appointments. MIS 463-Asli Sencer

  12. Holding Entities • Hold entities at some place until a specified condition is satisfied. Two different methods: • Hold and signal modules • Hold the entity until a signal to proceed is sent by another activity. • Hold entities until some condition exists • In our model: entities will be held until the day of scheduled service. MIS 463-Asli Sencer

  13. Simulation Replication Data • Project replication parameters • Run/Setup dialog – Replication Parameters tab • 10 Replications of 20 days each • Four options for Initialization Between Replications: • Initialize system (yes), initialize statistics (yes) • 10 independent and identical replications – no calls carried over • Reports for each day separately • Initialize system (yes), initialize statistics (no) • 10 independent replications – no calls carried over • Cumulative summary reports (day 1, days 1-2, days 1-3, …, days 1-10) • Initialize system (no), initialize statistics (yes): Selected • 200 continuous days – calls carried over • Reports are by replication (after each 20 day) • Initialize system (no), initialize statistics (no) • 200 continuous days – calls carried over • Cumulative summary reports MIS 463-Asli Sencer

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