Page 74 - ExtendSim User Guide
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Simulation Concepts
Modeling methodologies
Factor
What causes a change in state
Time steps
Characteristics of what is modeled
Ordering
Routing
Statistical detail
Typical uses
Continuous
A time change
Interval between time steps is constant. Model recalculations are sequential and time-dependent.
Track characteristics in a database or assume the flow is homoge- neous.
FIFO
Values need to be explicitly routed by being turned off at one branch and turned on at the other (values can go to multiple places at the same time.).
General statistics about the system: amount, efficiency, etc.
Scientific (biology, chemistry, physics), engineering (electron- ics, control systems), finance and econom- ics, System Dynamics.
Discrete Event An event
Interval between events is dependent on when events occur. Model only recalcu- lates when events occur.
Using attributes, items are assigned unique characteristics and can then be tracked throughout the model.
Items can move in FIFO, LIFO, Priority, time-delayed, or cus- tomized order.
By default, items are automatically routed to the first available branch (items can only beinoneplaceata time.)
In addition to general statistics, each item can be individually tracked: count, utiliza- tion, cycle time.
Manufacturing, ser- vice industries, busi- ness operations, networks, systems engineering.
Discrete Rate An event
Interval between events is dependent on when events occur. Model only recalcu- lates when events occur.
Track characteristics in a database or assume the flow is homoge- neous.
FIFO
Flow is routed based on constraint rates and rules that are defined in the model (flow can be divided into multi- ple branches.)
In addition to general statistics, effective rates, cumulative amount.
Manufacturing of pow- ders, fluids, and high speed, high volume processes. Chemical processes, ATM trans- actions. Supply chains.
Some systems, especially when a portion of the flow has a delay or wait time, can be modeled using any of the three styles. In this case, you would generally choose how to model the system based on the level of detail required. Discrete event models provide much more detail about the workings of these types of systems than continuous models. Continuous and discrete rate models, on the other hand, usually run faster than discrete event models.
Remember that you may combine blocks from different libraries within the same model. For example, it is quite common to use continuous blocks from the Value library when creating a discrete event model. However, the discrete event blocks in the Item library and the discrete rate blocks in the Rate library can only be used in event-driven (non-continuous) models. If
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