System Modeling

KMP5703 Design of Manufacturing Systems

SYSTEM MODELING Aziana

(GS#####)

Harlina binti Ngah

(GS25434)

Azazi Ngatiman

(GS24816)

Haspirudin Basiron

(GS25050)

M. Maaroff Bahurdin

(GS25258)

Overview 1.What is modeling? 2.What is simulation? 3.What is simulation modeling and analysis? 4.What types of problems are suitable for simulation? 5.How to select simulation software? 6.What are the benefits and pitfalls in modeling and simulation? 2

WHAT IS MODELING?

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SYSTEM MODELING

WHAT IS MODELING?

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Modeling Definition 

Modelling is the process of producing a model which:

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 Representation of the construction and working of some system of interest;  Similar to but simpler than the system it represents;  Enable the analyst to predict the effect of changes to the system;  A close approximation to the real system and incorporate most of its salient features; and  Not so complex that it is impossible to understand and experiment with it.

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 Simulation practitioners recommend increasing the complexity of a model iteratively.  Model validation techniques (important issue) include simulating the model under known input conditions and comparing model output with system output.  A model intended for a simulation study is a mathematical model developed with the help of simulation software.  Mathematical model classifications include deterministic or stochastic; and static or dynamic; Ø Deterministic (input and output variables are fixed values) Ø Stochastic (at least one of the input or output variables is probabilistic) Ø Static (time is not taken into account) Ø Dynamic (time-varying interactions among 5 variables are taken into account)

WHAT IS SIMULATION?

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System modeling

WHAT IS SIMULATION?

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Simulation 

A simulation of a system is:

Øan analysis tool for understanding the system. Øthe operation of a model of the system.

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Shannon [1975] defines simulation as an experimental and applied methodology which seeks to: i. describe theories or the behavior of systems;. ii.construct hypotheses that account for the observed behavior; iii.use these theories to predict future behavior, that is, the effects that will be produced by

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Simulation is used before an existing system is altered or a new system built. To reduce the chances of failure to meet specifications

WHY?

To eliminate unforeseen bottlenecks To prevent under or overutilization of resources To optimize system performance 8

Simulation Study Schematic

ØHuman decision making is required in: Model development Experiment design Output analysis Conclusion formulation Making decisions to alter the system under study *Human intervention is not required while running the simulations.

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Strengths of Simulation Time compression – the potential to simulate

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years of real system operation in a few minutes or seconds. Component integration – the ability to integrate system components to study interactions Risk avoidance – hypothetical or potentially dangerous systems can be studied without the financial or physical risks that may be involved in building and studying a real system Physical scaling – the ability to study much larger or smaller versions of a system Repeatability– the ability to study different systems in identical environments or the same system in different environments 10 

Stages in Simulation

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WHAT IS SIMULATION MODELING AND ANALYSIS?

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System modeling

WHAT IS SIMULATION MODELING AND ANALYSIS? 12

Simulation Modeling & Analysis Ø System modeling is a technique to express, visualize, analyze and transform the architecture of a system Ø A system may consist of software components, hardware components, or both and the connections between these components Ø It can increase reliability and reduce development cost by making it easier to build systems, to reuse previous built components within new systems, to change systems to suit changing requirements such as functional 13 enhancement and platform changes, and

Simulation Modeling & Analysis Ø The purpose of analyzing existing systems is to understand how the system does what it does Ø Whether the system is maintained or it is prepared to be transformed, e.g. to another hardware platform, the emphasis of system analysis lies on understanding of which components it is built and how they interact Ø A system model as the result of this analysis, again, aids to the

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Simulation Study Simulation Study: (1)Human decision making is required  - All stages, namely, model development, experiment design, output analysis, conclusion formulation, system altering (2) Human intervention is not required  - Running of the simulation 

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SIMULATION STUDY SCHEMATIC Real World

Simulation Study

System Under Study

11 Steps

Simulation Model Simulation Experiment

Altered System

Simulation Analysis Conclusions

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Simulation Model Ø Consist of the following components: o system entities o input variables o performance measures o functional relationships 

Ø Almost all simulation software packages provides constructs to model each of the above components 17

Simulation Model Steps Involved: (1)Identify the problem (2)Formulate the problem (3)Collect the process real system data (4)Formulate & develop a model (5)Validate the model (6)Document model for future use 

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Simulation Experiment It is a test or series of test, meaningful changes are made to the input variables We can observe and identify the reasons of change in the performance measures Steps Involved: (7) Select appropriate experimental design (8) Establish experimental conditions 

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Simulation Analysis Most simulation packages provide run statistics on the performance measure

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Steps Involved: (10) Interpret and present result (11) Recommend further course of action 

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WHAT TYPES OF PROBLEMS ARE SUITABLE FOR SIMULATION?

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System modeling

WHAT TYPES OF PROBLEMS ARE SUITABLE FOR SIMULATION? 21

Types of problems to simulate 

Situations in which simulation modeling and analysis is used include the following: Ø It is impossible or extremely expensive to observe certain processes in the real world, e.g., next year‘s cancer statistics, performance of the next space shuttle, and the effect of Internet advertising on a company's sales. Ø Problems in which mathematical model can be formulated but analytic solutions are either impossible (e.g., job shop scheduling problem, high order difference equations) or too complicated (e.g. complex systems like the stock market, and large scale queuing models). Ø It is impossible or extremely expensive to 22 validate the mathematical model

Areas suitable for simulation  Applications of simulation abound in the areas of : 

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HOW TO SELECT SIMULATION SOFTWARE?

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System modeling

HOW TO SELECT SIMULATION SOFTWARE? 24

Types of simulation software

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Types of simulation software General purpose programming lan 

ØBut Available over a wide variety when compared with Simu ØLess expensive Package ØGreater flexibility may require more “programming ØEasier development lead to “longer and “higher ØLess cost: totime” obtain ØE.g. Visual Basic, C++ 26

Types of simulation software Using simulation packages

Øreduced programming requirements But when compared with built in features Øconceptual guidance: GPL: Øanimation Øautomated ss known gathering of statistics ss flexible Øgraphic symbolism for communication gher cost Øflexibility to change the model nger Ø execution Ø 27

Simulation language

Offer more flexibility than the applicationoriented simulators  But languages require varying amounts of programming expertise

easier to learn and have modeling constructs closely related to the application  incorporate animation which is excellent for communication and can be used to debug the simulation program; a 28

Simulation language

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Application orientedsimulators

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Metric for evaluations

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WHAT ARE THE BENEFITS AND PITFALLS IN MODELING AND SIMULATION?



System modeling

WHAT ARE THE BENEFITS AND PITFALLS IN MODELING AND SIMULATION? 32

The benefits of simulation & analysis ü Obtain a better understanding of the system ü Test hypotheses about the system for feasibility ü Experiment with new or unknown situations about which only weak information is available ü Identify bottlenecks in the flow of entities (material, people, etc.) or information ü Employ a systems approach to problem solving ü Develop well designed and robust systems and reduce system development time. 33

Pitfalls to guard against in simulation Unclear objective Using simulation when an analytic solution is appropriate. Invalid model Simulation model too complex or too simple Erroneous assumptions. Using the wrong input probability distribution Using the wrong performance measure Bugs in the simulation program Poor schedule and budget planning Poor communication among the personnel involved in the simulation study 34

MANUFACTURING MODEL EXAMPLE USING WITNESS

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System Modeling

MANUFACTURING MODEL EXAMPLE USING WITNESS 35

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References 1. Maria, A. INTRODUCTION TO MODELING AND SIMULATION. in 1997 Winter Simulation Conference. 1997 2. Bakry, S.H., SIMULATION SOFTWARE. 1996. 3. Miller, S. and D. Pegden. INTRODUCTION TO MANUFACTURING SIMULATION. in 2000 Winter Simulation Conference. 2000.

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