Simulation

What is Simulation?  Imitation  An attempt to duplicate the features, appearance, and characteristics of a real system 1. To imitate a real-world situation mathematically 2. To study its properties and operating characteristics 3. To draw conclusions and make action decisions based on the results of the simulation

Simulation-New Definition • A simulation is 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

–

A given system is copied and the variables and constants associated with it are manipulated in that artificial environment to examine the behaviour of the system

Simulation Example • Aerodynamic Simulation– to study aerodynamic properties of aeroplane

• Driving Simulation– To have the feeling of vehicle driving

• Computer Program Simulation– for layout, financial and market analysis model

Computer Analysis

Simulation Applications Ambulance location and dispatching

Bus scheduling

Assembly-line balancing

Design of library operations

Parking lot and harbor design

Taxi, truck, and railroad dispatching

Distribution system design

Production facility scheduling

Scheduling aircraft

Plant layout

Labor-hiring decisions

Capital investments

Personnel scheduling

Production scheduling

Traffic-light timing

Sales forecasting

Voting pattern prediction

Inventory planning and control

Table F.1

Other Simulation Egs. • Simulation in education and training – war games – animated narrative vignettes (ANV). ANVs are cartoonlike video narratives of hypothetical and reality-based stories involving classroom teaching and learning. ANVs have been used to assess knowledge, problem solving skills and dispositions of children, and preservice and in-service teachers. – case study

• • •

Truck Simulator Healthcare (Clinical) Simulators Interactive models

Other Simulation Egs. • • • • • • •

Computer simulators The "classroom simulators" Financial Planning and Analysis City Simulators / Urban Simulation Flight simulators Marine simulators Engineering (Technology) simulation or Process simulation

The Process of Simulation

Define problem

Introduce variables

Construct model Specify values of variables Conduct simulation

Examine results

Figure F.1

Select best course

Advantages of Simulation 1. Relatively straightforward and flexible 2. Can be used to analyze large and complex real-world situations that cannot be solved by conventional models 3. Real-world complications can be included that most OM models cannot permit 4. “Time compression” is possible -

Years of experience in the real system can be compressed into seconds or minutes

Advantages of Simulation 1. Allows “what-if” types of questions 2. Does not interfere with real-world systems 3. Can study the interactive effects of individual components or variables in order to determine which ones are important

Advantages of Simulation • Often leads to a better understanding of the real system • Simulation is far more general than mathematical models • Simulation can be used as a game for training experience • Simulation provides a more realistic replication of a system than mathematical analysis • Many standard packaged models, covering a wide range of topics, are available commercially

Disadvantages of Simulation 1. Can be very expensive and may take months to develop 2. It is a trial-and-error approach that may produce different solutions in repeated runs - Simulation may be less accurate than mathematical analysis because it is randomly based •

Managers must generate all of the conditions and constraints for solutions they want to examine

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Each simulation model is unique

Disadvantages of Simulation .. • There is no guarantee that the model will, in fact, provide good answers • There is no way to prove reliability • A significant amount of computer time may be needed to run complex models • The technique of simulation still lacks a standardized approach

Inventory Simulation Daily demand for Ace Drill (1) Demand for Ace Drill 0

(2)

(3)

(4) Cumulative Probability .05

(5) Interval of Random Numbers 01 through 05

Frequency 15

Probability .05

1

30

.10

.15

06 through 15

2

60

.20

.35

16 through 35

3

120

.40

.75

36 through 75

4

45

.15

.90

76 through 90

5

30

.10

1.00

91 through 00

300

1.00 Table F.8

Simulation Example 1 Day Random Number Number 1 52 5 Expected 2 37 = 3demand 82i =1 4 69 =98 5 6 96 7 33 8 50 = 9 88 =90 10

Simulated Daily Demand 3 3 (probability of i units) x 4 (demand of i units) 4 (.05)(0) + 5(.10)(1) + (.20)(2) + (.30)(3)5+ (.20)(4) + (.15)(5) 2 3 0 + .1 + .4 + .9 + .8 + .75 5 2.95 tires5 39 Total 3.9 Average

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Using Software in Simulation  Computers are critical in simulating complex tasks  General-purpose languages - BASIC, C++  Special-purpose simulation languages GPSS, SIMSCRIPT 1. Require less programming time for large simulations 2. Usually more efficient and easier to check for errors 3. Random-number generators are built in

Using Software in Simulation  Commercial simulation programs are available for many applications - Extend, Modsim, Witness, MAP/1, Enterprise Dynamics, Simfactory, ProModel, Micro Saint, ARENA  Spreadsheets such as Excel can be used to develop some simulations

Using Software in Simulation