An auto repair shop has three technicians (Emma, Ava, and James). Cars arrive according to an
exponential interarrival-time distribution with mean 8 hours, with the first car’s arriving at time
0. Before a new car can start processing, it must be put on a car lift, and this lifting operation
takes 10 minutes (there are four car lifts available, and obviously each lift can be used only for
one car at a time). Every repair process on any car starts with Emma, continues with Ava and
ends with James (each technician is responsible for part of the whole repair process of every car,
so in this case we are dealing with a Serial Processing – Specialized Separated Work method). The
car remains on the lift until it completes processing by all three technicians, at which time it is
removed from the lift (this removal operations takes 10 minute), after which the lift becomes
available for another car that might be waiting for it.
Service times of Emma follow a triangular operation time with minimum 4, mode 7, and
maximum 9 hours. Ava’s service times have a uniform distribution between 5 and 10 hours and
service times of James have a triangular operation time with minimum 5, mode 6.5, and
maximum 9 hours.
Run your simulation for a single replication of length 10 days and observe the time-average and
maximum total work in process (WIP) in the whole system. For each technician separately,
observe the average and maximum queue lengths, and the resource utilization. Also observe the
utilization of the four lifts as a group, as well as the time-average and maximum number of cars
that are waiting for a lift (before they can even get going into the system for processing). Add a
plot for the total WIP and by-technician queue lengths, all on the same set of axes; add a second
plot showing the number of lifts that are in use. Put in a text box with the numerical results
requested. What appears to be the bottleneck in this system preventing better efficiency?
HINT: Remember that an entity can have multiple different resources Seized at the same time,
and that the Process module has “Action” options other than the usual Seize-Delay-Release.
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