Automotive Maintenance and Repair Shop Expansion

1
Automotive Maintenance and Repair Shop Expansion

• Presentation by
• Steve Roberson
• For
• CST 5306 Modeling and Simulation

2
Model Building Steps

• Define the scope of the model
• Define the data to be used in the model
• Define any submodels that may be needed to break
  up the complexity
• Build the submodels
• Add animation
• Run the simulation

3
Step 1Scope - General

• 3 bay facility
• Appointments scheduled at one location
• Appointments made up to three working days in
  advance No same day service

4
Step 1Scope - Statistics

• Average service calls 29 per day following a
  Poisson distribution
• 55 schedule for next day, 30 two days in
  advance and remaining 15 three days in advance
• If appointment cant be scheduled for the
  requested day, 90 chance will be scheduled for
  following day
• 80 leave vehicles, 20 wait on service
• Wait time is service time 1 hour (allowance
  factor)
• No more than five waiting customers will be
  scheduled in one day
• Standard service times are in a BETA distribution
  Actual service times are in a GAMMA distribution

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Arena Statistical Distributions

• Beta
• Continuous
• Discrete
• Erlang
• Exponential
• Gamma
• Johnson

• Lognormal
• Normal
• Poisson
• Triangular
• Uniform
• Weibull

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Step 1Scope - Costs

• 24 hours of availability 3 bays at 8 hours per
  day
• Cost per bay - 45 per hour
• Customer charged - 78 per hour base on standard
  service time
• Overtime
• Limited to 3 hours extra per day per bay
• Charge is 120 per hour per bay
• If work not completed by end of day, customer
  given loaner car at a dealership cost of 35 per
  day

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Step 1Scope Statistics Collected

• Daily profit
• Daily standard service times
• Daily actual service times
• Daily overtime
• Daily number appointments not completed on time

8
New Modeling Methods

• Multiple-way decisions
• Sets
• Variables and expressions
• Submodels
• Duplicating entities
• Holding entities
• Statistics and animation
• Terminating or steady-state

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Step 2Define the Data

• Define resources (3 bays)
• Define sets
• Bay resource set
• Customer entity set (customer who waits)
• Vehicle entity set (vehicles left for service)
• Define variables (15 determined)
• Define expressions
• Formula to determine inter-arrival time
• Formula to determine service time
• Formula to determine if customer has to wait for
  service
• Final statistics (costing, overtime, service
  times and waiting times)

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Step 3Define Submodels

• Complete Model

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Step 4Build Submodels

• Generate Appointment Calls

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Step 4Build Submodels

• Make Appointment

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Step 4Build Submodels

• Service Activity

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Step 4Build Submodels

• Update Performance Variables

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Step 4Build Submodels

• Control Logic

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Step 4Build Submodels

• In Arena, the model can be checked for errors
• Errors are flagged to assist with troubleshooting

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Step 5Add Animation

• Animated Service Center

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Step 6Run Simulation

• Run simulation
• Observe results
• Analyze results

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Model Enhancements
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Redefining the Scope

• Not all jobs done by all bays
• Bays 2 3 can handle all jobs
• Bay 1 can only handle 40 of the jobs
• Not all customers arrive at start of day
• Some never show up
• 60-70 arrive on time (follows uniform
  distribution)
• Remaining arrive randomly over next two hours

21
Sets and Resource Logic

• Additional Resource Set

22
Model Change

• Service Activity

23
Model Change
Control Logic
24
Re-run Simulation

• Observe results
• Analyze results