Page 250 - DCAP601_SIMULATION_AND_MODELING

Simulation and Modelling

Notes
Figure 13.5: Approaches to Discrete Event Simulation

There are also three approaches to describing the discrete simulation, see the Diagram above
[Pidd, 1992].
1. Event: This approach describes an instantaneous change, usually from a stop event to a
start event. This is the most common one used, easy to understand and efficient and is
acceptable to implement.
2. Activities: Represents duration. Essentially groups a number of events in order to describe
an activity carried out by an entity e.g. a machine loading. This approach is easy to
understand and to implement but is not efficient.

3. Process: These approach groups activities to describe the life cycle of an entity e.g. a
machine. This is less common and more difficult to plan and implement, but is generally
thought to be the most efficient.

More Common Uses of DES

1. Diagnosing Process Issues: Simulation approaches are particularly well equipped to help
users diagnose issues in complex environments. The Goal (Theory of Constraints) illustrates
the importance of understanding bottlenecks in a system. Only process ‘improvements’ at
the bottlenecks will actually improve the overall system. In many organizations bottlenecks
become hidden by excess inventory, overproduction, variability in processes and
variability in routing or sequencing. By accurately documenting the system inside a
simulation model it is possible to gain a bird’s eye view of the entire system.
A working model of a system allows management to understand performance drivers. A
simulation can be built to include any number of performance KPIs such as: worker
utilization, on-time delivery rate, scrap rate, cash cycles, and so on.
2. Hospital Applications: An operating theater is generally shared between several surgical
disciplines. Through better understanding the nature of these procedures it may be possible
to increase the patient throughput. Example: If a heart surgery takes on average four
hours, changing an operating room schedule from eight available hours to nine will not
increase patient throughput. On the other hand, if a hernia procedure takes on average
twenty minutes providing an extra hour may also not yield any increased throughput if
the capacity and average time spent in the recovery room is not considered.
3. Custom Order Environments: Many systems show very different characteristics from day
to day depending on the order mix. Many small orders may cause bottle-necks due to

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