Modeling and Simulation Rev Lengkap (1)

Modeling and SimulationModeling and Simulation

Agus PriyonoFakultas Teknologi Industri

Institut Sains dan Teknologi Nasional, Jakarta

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Modeling and SimulationModeling and SimulationLecture Note 1

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PENDAHULUAN• A model is an abstraction from reality used to

help understand the object or system being modeled. People use modeling all the time to make decisions in their everyday lives although they usually don’t do so in a formal way.

• A simulation of a system is the operation of a model of the system. Simulation is used before an existing system is altered or a new system built, to reduce the chances of failure to meet specifications, to eliminate unforeseen bottlenecks, to prevent under or over-utilization of resources, and to optimize system performance

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For instance, simulation can be used to answer questions like:

• What is the best design for a new telecommunications network?

• What are the associated resource requirements? • How will a telecommunication network perform

when the traffic load increases by 50%?• How will a new routing algorithm affect its

performance? • Which network protocol optimizes network

performance? • What will be the impact of a link failure?

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Basic Concept

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Modelling – Simulation Morphism

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Challenges in Embedded System Design

References

Textbook: •Banks,Carson, Nelson & Nicol, “Discrete Event System Simulation”, Prentice Hall, 2001. •Averill M. Law & W David Kelton, “Simulation, Modeling and Analysis”, 3rd Ed. Mc Graw Hill.•Supplemental: “OMNET++user manual”, available online, as a part of the free software package: http://www.omnetpp.org/

Software

Software: OMNET++: event driven simulator - required •Free software for academic use, download from http://www.omnetpp.org/, use the quick download link on the right hand side of the web page (currently version 3.0)

– Download from pipeline web page for class, version 2.3. •MS.VisualC++6.0:you can obtain a copy from Steven swhichhasa license for undergraduates. Installation of OMNET++, requires that you have previously installed MS. Visual C++ 6.0. •Matlab may also be used occasionally top lot various results–not required – examples may be presented in class, that are generated with Matlab

– Free similar program: Euler Software: - not personally tested http://mathsrv.ku-eichstaett.de/MGF/homes/grothman/euler/index.html

– Matlab compatible free software: Octave – not personally tested http://www.octave.org

Systems

What is a What is a system?system?

System

A system is any set of interrelated components acting together to achieve a common objective.

Definition covers systems of different types Systems vary in size, nature, function,

complexity,… Boundaries of the system is determined by

the scope of the study Common techniques can be used to treat

them

System

A system exists and operates in time and space.

Systems Battery

Consists of anode, cathode, acid and other components

These components act together to achieve one objective

Car Electrical system Consists of a battery, a generator, lamps,… Achieve a common objective

Kopaja (transportation company) Consists of Buses, drivers, stations,… Achieves a common objective

The Boundaries of the system is determined by the scope of the study

Systems

INPUT OUTPUT

PROSES

Figure 2 : System Representation

Systems Inputs (excitations):

signals that cause changes in the systems variables.

Represented by arrows entering the system Outputs (responses) :

measured or calculated variables Shown as arrows leaving the system

Systems (process) Defined the relationship between the

inputs and outputs Represented by a rectangular box

Systems

Figure 3 : Water Tank System Representation

Input

Output

System terminology• State: A variable characterizing an attribute in the

system such as level of stock in inventory or number of jobs waiting for processing.

• Event: An occurrence at a point in time which may change the state of the system, such as arrival of a customer or start of work on a job.

• Entity: An object that passes through the system, such as cars in an intersection or orders in a factory. Often an event (e.g., arrival) is associated with an entity (e.g., customer).

• Queue: A queue is not only a physical queue of people, it can also be a task list, a buffer of finished goods waiting for transportation or any place where entities are waiting for something to happen for any reason.

System terminology• Creating: Creating is causing an arrival of a

new entity to the system at some point in time.• Scheduling: Scheduling is the act of assigning a

new future event to an existing entity.• Random variable: A random variable is a

quantity that is uncertain, such as interarrival time between two incoming flights or number of defective parts in a shipment or an artificially generated random variable

• Distribution: A distribution is the mathematical law which governs the probabilistic features of a random variable.

A Simple Example:Building a simulation gas station with a single pump served by a single service man. Assume that arrival of cars as well their service times are random. At first identify the:•states: number of cars waiting for service and number of cars served at any moment•events: arrival of cars, start of service, end of service•entities: these are the cars•queue: the queue of cars in front of the pump, waiting for service•random realizations: interarrival times, service times•distributions: we shall assume exponential distributions for both the interarrival time and service time

The choice of inputs/outputs/process depends on the purpose of the study

Some Possible Inputs Inlet flow rate Temperature of entering material Concentration of entering material

Some Possible Outputs Level in the tank Temperature of material in tank Outlet flow rate Concentration of material in tank

What inputs and outputs are needed when we want to model the temperature of the water in the tank?

t, l Controled Liquid Example

Ordinary Differential Equation (ODE) model

Trajectories

FSA Formalism Model

Behavior Morphism

Clasification of System

Clasification of System

Experimental FrameExperimental Frame. When one studies a system in the real world, the experimental frame (EF) describes experimental conditions (context), aspects, . . . within which that system and corresponding models will be used. As such, the Experimental Frame reflects the objectives of the experimenter who performs experiments on a real system or, through simulation, on a model. In its most basic form an Experimental Frame consists of two sets of variables, the Frame Input Variables and the Frame Output Variables, which match the system or model terminals.

System vs Experimental Frame

Figure 1 : System vs Experimental Frame