1.
What is simulation?
Simulation is
the imitation of the operation of a real-world process or system over time.
Simulation involves the generation of an artificial history of the system, and
the observation of that artificial history to draw inferences concerning the
operating characteristics of the real system that is represented.
Simulation is
the numerical technique for conducting experiments on digital computer, which
involves logical and mathematical relationships that interact to describe the
behavior and the structure of a complex real world system over extended period
of time.
The process of
designing a model of a real system, implementing the model as a computer
program, and conducting experiments with the model for the purpose of
understanding the behavior of the system, or evaluating strategies for the
operation of the system.
The behavior of
a system is studied by developing a simulation model. This model usually takes
the form of a set of assumptions concerning the operation of the system. These
assumptions are expressed in mathematical, logical, and symbolic relationships
between the entities, or object of interest, of the system. Such developed
model when validated then is used to investigate a variety of ‘what if’
questions about the real-world system. Thus, simulation modeling can be used
both as an analysis tool and design tool.
2.
System Concepts
A system is
defined as a group of objects that are joined together in some regular
interaction or interdependence for the accomplishment of some task. For
example: Production system for
manufacturing automobiles.
A system is
usually considered as a set of inter–related factors, which are described as entities
activities and have properties or attributes. Processes that cause system changes
are called activities. The state of a system is a description of all entities, attributes
and the activities at any time.
Example: A
factory system shown as follows:
Components
of system
2.1 Entity,
attribute and activities
An entity
represents an object that requires explicit definition. An entity can be
dynamic in that it moves through the system, or it can be static in that it
serves other entities. In the example, the customer is a dynamic entity,
whereas the bank teller is a static entity.
An entity may
have attributes that pertain to that entity alone. Thus, attributes
should be considered as local values. In the example, an attribute of the
entity could be the time of arrival. Attributes of interest in one investigation
may not be of interest in another investigation. Thus, if red parts and blue
parts are being manufactured, the color could be an attribute.
Processes that
cause system changes are called activities or events.
In the bank
example, events include the arrival of a customer for service at the bank, the
beginning of service for a customer, and the completion of a service.
There are both
internal and external events, also called endogenous and exogenous events,
respectively. For instance, an endogenous event in the example is the beginning
of service of the customer since that is within the system being simulated. An
exogenous event is the arrival of a customer for service since that occurrence
is outside of the simulation.
2.2 State
variables
The state of a
system is defined to be that collection of variables necessary to describe the
system at any time, relative to the objectives of the study. In the study of a
bank, possible state variables are the number of busy tellers, the number of
customers waiting in line or being served, and the arrival time of the next
customer.
So the system
state variables are the collection of all information needed to define what is
happening within the system to a sufficient level (i.e., to attain the desired
output) at a given point in time.
No comments:
Post a Comment