module 8- simulation
TRANSCRIPT
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Technical Note 16
Simulation
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Definition of Simulation
Simulation Methodology
Proposing a New Experiment Considerations When Using Computer
Models
Types of Simulations
Desirable Features of Simulation Software
Advantages & Disadvantages of Simulation
OBJECTIVES
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Simulation
Defined
A simulationis a computer-based model used
to run experiments on a real system
Typically done on a computer
Determines reactions to different operating rules
or change in structure
Can be used in conjunction with traditionalstatistical and management science techniques
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Major Phases in a
Simulation Study
Start
Define Problem
Construct Simulation Model
Specify values of variables and parameters
Run the simulation
Evaluate results
Validation
Propose new experiment
Stop From Exhibit TN16.1
Lets look at each
of these steps in
turn
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Simulation Methodology:Problem
Definition
Specifying the objectives
Identifying the relevant controllable and
uncontrollable variables of the system to
be studied
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Constructing a Simulation Model
Specification of Variables and Parameters
Specification of Decision Rules
Specification of Probability Distributions
Specification of Time-Incrementing Procedure
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Data Collection & Random No. Interval
Example Suppose you timed 20 athletes running the100-yard dash and tallied the information
into the four time intervals below
Seconds0-5.99
6-6.99
7-7.99
8 or more
Tallies Frequency4
10
4
2
You then count the tallies and make a frequency
distribution
%20
50
20
10
Then convert the frequencies into percentages
Finally, use the percentages to develop the random number intervals
RN Intervals00-19
20-69
70-89
90-99
Accum. %20
70
90
100
You then can add the frequencies into a cumulative distribution
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Specify Values of Variables and
Parameters
Determination of starting conditions
Determination of run length
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Run the Simulation
By computer
Manually
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Evaluate Results
Conclusions depend on
the degree to which the model reflects the realsystem
design of the simulation (in a statistical sense)
The only true test of a simulation is how wellthe real system performs after the results ofthe study have been implemented
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Validation
Refers to testing the computer program to
ensure that the simulation is correct
To insure that the model results are
representative of the real world systemthey seek to model
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Considerations When Using Computer
Models Computer language selection
Flowcharting
Coding
Data generation
Output reports
Validation
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Types of Simulation Models
Continuous Based on mathematical equations
Used for simulating continuous values for all
points in time Example: The amount of time a person spends in
a queue
Discrete Used for simulating specific values or specific
points
Example: Number of people in a queue
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Desirable Features of Simulation Software
Be capable of being used interactively as well as allowing
complete runs
Be user-friendly and easy to understand
Allow modules to be built and then connected
Allow users to write and incorporate their own routines
Have building blocks that contain built-in commands
Have macro capability, such as the ability to develop
machining cells
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Desirable Features of Simulation Software
Have material-flow capability
Output standard statistics such as cycle times,
utilization, and wait times
Allow a variety of data analysis alternatives for both
input and output data
Have animation capabilities to display graphicallythe product flow through the system
Permit interactive debugging
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Advantages of Simulation
Often leads to a better understanding of the real
system
Years of experience in the real system can be
compressed into seconds or minutes Simulation does not disrupt ongoing activities of the
real system
Simulation is far more general than mathematical
models
Simulation can be used as a game for training
experience
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Advantages of Simulation (Continued)
Simulation provides a more realistic replication of a
system than mathematical analysis
Simulation can be used to analyze transient
conditions, whereas mathematical techniques usually
cannot
Many standard packaged models, covering a wide
range of topics, are available commercially
Simulation answers what-if questions
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Disadvantages of Simulation
There is no guarantee that the model will, in fact,provide good answers
There is no way to prove reliability
Building a simulation model can take a great deal of
time Simulation may be less accurate than mathematical
analysis because it is randomly based
A significant amount of computer time may be
needed to run complex models The technique of simulation still lacks a standardized
approach
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End of Technical Note 16