22. SIMULATION

•Some complex systems can’t be modeled because of,

-random events

-changing operating conditions

-too many interactions

-exact solutions don’t exist

•Simulation is used to determine how these systems will behave

•Simulation typically involves developing a model that includes discrete stations and events that occur with some probable distribution.

•We can then examine the simulation results to evaluate the modeled system. Examples include,

-machine utilization

-lead time

-down time

-etc.

•This is a very effective tool when considering the effect of a change, comparing decision options, or refining a design.

•Some simulation terms include,

System - the real collection of components

Model - a reasonable mathematically (simpler) representation of the system

State - the model undergoes discrete changes. A state is a ‘snapshot’ of the system Entity - a part of the system (eg machine tool)

Attributes - the behavior of an entity

Event - something that changes the state of a machine

Activity - when an entity is going through some activity. (eg, press cycling) Delay - a period of time with no activity

•Good approach to simulation,

1.Determine what the problem is

2.Set objectives for the simulation