SiM Chapter1

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Concepts System Activities

System Models

Sapan H.Mankad

July 22, 2010
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System Concepts

A system is defined as an aggregation or assemblage of objects

joined in some regular interaction or interdependence.

Flight Simulators to train pilots Aircraft Systems

Nuclear Power Plant

Emulators

Factory
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Simulation Modeling

Paradigm that creates simplified representations of

complex systems

Generates system histories and observes system behavior

and statistics over time

Goals are understanding system performance and

improving system design

Computer simulations vary from computer programs that run a

few minutes, to network-based groups of computers running forhours, to ongoing simulations that run for days.
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System Example I

Figure: An Aircraft under AutoPilot Control
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System Example II

Figure: A Factory System

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System and its simplification-model

Figure: Transforming a system to a model

C S A
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System Parameters

Entities also refered to as objects.

Properties also referred to as attributes.

Activity any process that causes changes in the system.

State denotes a description of all entities, attributes and

activities as they exist at one point of time.

The progress of the system is studied by following the changes

in the states of the system.

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Identifying System Parameters

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Identifying System Parameters

Can you find a few systems in your surroundings and identify

its parameters?

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System Environment

A system is often affected by changes occuring outside the

system, called System Environment. It is very essential to decide upon the boundary between

the system and its environment.

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System Activities

Endogenous describes the activities occuring within the system.

Exogenous describes the activities in the environment that

affect the system.

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Co c s S s c v s

Deterministic Activities

Where the outcome of an activity can be described

completely in terms of its input, the activity is said to be

Deterministic.

A deterministic system is a system in which no randomnessis involved in the development of future states of the

system.

A deterministic model will thus always produce the same

output from a given starting condition or initial state.

Physical laws that are described by differential equations

represent deterministic systems.

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Stochastic Activities

Where the effects of the activity vary randomly over various

possible outcomes, the activity is said to be Stochastic.

The random output can often be measured and describedin the form of a Probability Distribution.

If an activity is truly stochastic, there is no knownexplanation for its randomness.

Elevator System

Seatbelt Controller

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Classification of Systems

Systems such as aircrafts, in which the changes are

predominantly smooth, are called Continuous systems.

Systems such as Factory Systems, in which changes are

predominantly discontinuous, are called Discrete Systems.

Some systems are intrinsically continuous but information

about them is only available at discrete points in time.

They are called Sample Data Systems.

Very few systems are wholly continuous or discrete.

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System Modeling

The objective of many system studies is to predict how a

system will perform before it is built.

One way is to experiment with the system itself.

Another alternative is to construct a number of prototypesand test them.

An expensive & time consuming way

System studies are generally conducted with a model of the

system.

A model is not only a substitute for a system,but also itssimplification.
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