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The service facility she is planning has 3 service bays, each staffed by a sin-
gle mechanic that works exclusively in each bay (see Exhibit 8.15). There is a large
parking lot associated with the facility that can accommodate a very large number of
parked vehicles. Inez has decided that the fleet operators will be required to deliver
their autos to the lot every morning before the shop opens at 9:00 am. The autos are
parked in the next available slot for the type of service required and then service
is performed on a first-come-first-served basis. Although the hours of operation are
9:00 am to 7:00 pm, if at the end of the day an automobile has service started before
7:00 pm, service will be completed on that auto. Also, the autos need to be removed
from the lot by fleet owners by the close of business; Inez wants to avoid the legal
liability of insuring that the autos are safe overnight. As we have already stated,
there are three types of service that are handled at Autohaus— engine/electrical
diagnostics , mechanical diagnostics , and oil change service.
Wolfgang, her trusted head mechanic, has many years of experience, and he has
kept mental records regarding the time that each service demand type requires. As a
former modeling and simulation professional, Inez will find her expertise to be quite
valuable for constructing a model of Autohaus. It is Inez’s goal to understand the
general behavior of this new business model in terms of the various types of service
demand Autohaus will experience and the operations design that she is contemplat-
ing. This is a very reasonable goal if she is to organize the business for the highest
possible return on investment. Inez decides that the first step in the assessment of the
business model is to simulate the operation. She decides to have a conversation with
Wolfgang to better understand the current business, and to get his input on impor-
tant simulation design issues. The following are questions she wants to discuss with
Wolfgang to assist in step 6a and 6b of the simulation process:
1. Are the general arrival rates (autos/hour) for the arrival of customers seeking
service at Autohaus different for different hours? Wolfgang has noted that the
arrival rate for the early time period, 5:00-7:00 am, is different from the later
time period, 7:00–9:00 am.
2. She also wants to understand the uncertainty associated with the business model.
a. The first type of uncertainty is associated with the arrival of autos. When
and how many autos arrive and enter the facility? What type of services do
arriving autos request?
b. The second type of uncertainty is associated with service provision. Will the
requested service type be available? What is the service time required for
each auto arrival?
After considerable discussion with Wolfgang, she arrives at a flow diagram of
the process, shown in Exhibit 8.16. The process begins with autos arriving prior to
the facility’s start of operation at 9:00 am. (This assumption greatly simplifies the
operation of the simulation model as we will see in Table 8.2). The process flow ele-
ments in diamonds represent uncertainty. The Autos Arrive with
process element
indicates that autos arrive in unknown quantities and within one of two contiguous
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