Chapter 12
Conducting Simulation Studies
12.1 A Successful Simulation Study
What is the definition of a
successful simulation project?
Solve the problem?
Meet the objectives?
Satisfy the boss?
In most cases, success in simulation means
that the study met the objectives set forth by the decision makers (management
in most cases).
How do we know if the objectives
are met?
Metrics - thus we must fully understand the meaning of terms
and how the data will be collected.
In many cases, management wants the process
to "run better". What does that mean?
Does it mean reduce WIP by 30%, cycle time
by 20%, or something else?
What is your budget to make the process
better?
What are your constraints? (such as access to operators, deadline of project, money to
conduct study, etc..)
12.2 Problem Formulation
You must clearly define the problem to be
solved. This goes along with understanding the objectives/constraints/metrics.
The first step is open and frequent
communication with the customer.
Often the customer comes to you with a
problem, but after several long discussions, you discover that the problem is
something entirely different than the customer originally thought.
Determine the metrics needed to simulate the
process. Note that one metric at a high level may have several metrics that
contribute to it.
12.3 Solution Methodology
Match the level of detail of the problem to
the solution methodology.
12.4 System and Simulation Specification
Use team approach if possible. This means:
People are allowed to participate
You have time to use the team approach
Note questions on pp.507-508
In team meetings - remember the 70/20/10 Rule:
70% of the time - the customer team will have the complete answer or
the information
20% of the time - the team will not know the answer, but they know how
to get it
10% of the time - the team will not know the answer, and does not
know where to find it
Establish a contact person. Without a
contact person, your project has little change of going anywhere, because you
will need access to data, personnel, machines, and to facility on a regular
basis. With the increased security at
most facilities, an escort is needed.
12.5 Model Formulation and Construction
Before building the model in ARENA, take
time to consider:
Remember the information needed for the
model in Chapter 6.
Approach - start at a high level with
constant times then add detail as you verify the model's logic.
Be open minded to
the elements, tools and options you use in ARENA. You learned on Project 2 that
I may require you to learn or use something we have not covered.
12.6 Verification and Validation
Verification (debugging) - making sure the model behaves as you intended
Validation - making sure the model behaves like the real world
process
Use animation
Use constant values
Predict outcome on paper, then model
Show model to team for validation
12.7 Experimentation and Analysis
12.8 Presenting and Preserving the
Results
Know your audience. This will dictate the
parameters of the presentation, such as the level of detail, graphics, length,
etc…
Be prepared to develop more alternatives
after presenting
Document what you did for use in future models and future modelers.
In the ideal case you will use the model as
a "living model" where decisions about operations are based in part
on the model as time progresses.
12.9 Disseminating the Model
Dr. Underdown' Simulation Approach
Lego Scenario:
I am a manager who wants to improve the
performance of the process that manufactures airplanes. I want better quality,
lower cost and faster cycle times.
I have asked you to analyze the process and
make suggestions to improve the process.
Let me give you a little history of the
company….
We have had engineers looking at this
process trying to reduce cost but we have had minimal results.
We constantly have to rework parts and
repair planes before they are delivered to the customer.
We are constantly behind schedule
Now go to Simulation:
Tell students they are now assembly workers
in the company. They are to build airplanes and observe the process for
simulation purposes. Ask people to participate in the game.
After the game is complete:
Ask students "what's next"? Ask
them the next step of conducting a process improvement study.
(They should respond by saying they need to
follow the 10-Step approach, starting with Understand the Assignment.)
Step 1 - Understand the
Assignment = Assignment Statement
Assignment
Reduce cycle time 20% within 6 months
Improve quality 20% within 6 months
Reduce costs 20% within 6 months
Step 2 - Identify all processes
List all processes involved in producing the
product or service
Step 3 - Identify opportunities
- identify those processes that
provide the most "bang for the buck" or the greatest chance of
producing successful results that will benefit the company
Step 4 - Bound the process
Determine the beginning and ending points of
the process using the process identification worksheet. Where does the process
start and end? This may seem easy at first, but after talking to several people
who work in the process, making this distinction will not be as easy. Process
improvement efforts tend to expand over time unless you can bound
the process effectively.
Step 5 - Identify relationships
Determine how the process you are
improving relates to other processes in the company. Perform SIPOC (Suppliers,
Inputs, Process, Outputs, Customers) analysis
Step 6 - Document the process
Develop physical representation of the
process, such as a flowchart or scaled model.
Step 7 - Determine the current condition of the
process
Collect data about the process.
Determine the following:
Once you have the data, use scientific
methods of analysis such as statistics and problem solving tools to determine
the opportunities for improvement.
Constraints
Budget minimal - I am not sure what money is
available. (make a point to students that in many
cases, managers do not have an exact number for the budget and the engineers
may have to assume that the budget is "low" and go on)
People - Do not want hire any more people
Machines - very little money available for
new machines
Physical building - minor changes allowed
Materials - may be able to change delivery
schedule
Step 8 - Determine what customers want from the
process
Ask customers informally or
conduct a survey
You must understand the needs of the
customer to determine how to prioritize the process improvement efforts.
Internal customers like top managers and supervisors what certain performance
improvements while the external customer a certain set of performance criteria
that may be different than internal customers. Students must consider both sets
of customers when making improvements to the process.
External Customer needs:
Quality planes - quality is more important
than price or delivery
Delivered when promised
Plane made to exact specifications
Internal Customer needs:
Plane made to exact specifications
Schedule of operations updated regularly
Quick communication about problems
Step 9 - Identify problems with current process
Prepare cause and effect diagrams
to reveal root causes, determine constraints on process
Step 10 - Understand and Improve Product -
You must understand those product characteristics
that make it unique and valuable to the customer. Understanding those product
characteristics important to the customer will limit the alternatives students
have to improve the process. In many cases, making a change to the design of a
product will assist in improving the process. Improvement ideas in this area
must not impact those characteristics that the customer desires.
Product
Engineered to military specifications
Very expensive
Must be extremely reliable
Attention to detail is crucial
Step 11 - Design a new process
Make changes to the process based
on what customers want and problems that were identified
I suggest developing several new designs to
provide management with an opportunity to see variations of the process you
have developed.
Step 12 - Implement the new process
Prepare an action plan for
testing and implementing the new process
Step 13 - Determine the impact of the changes on the
process
Collect data about the new
process and continuously improve the process