Modeling Random Failures

Modeling How-To's > Modeling Downtimes > Modeling Random Failures

Modeling Random Failures

An activity randomly fails, interrupting the current entity being processed. When it is repaired, the current entity resumes its activity.

The model used for this example, as well as all of the modeling "how-to" examples, can be found in the ProModel Solutions Café (http://www.promodel.com/solutionscafe/howto/). A video demonstrating this solution can be found here.

Solution A (If you only know roughly the percentage of time the activity is available (i.e., not down)

Enter the percent availability in the Availability field of the activity Properties dialog.

Solution B (If you have a good idea of the time between failures and the time to repair)

In the activity Properties dialog, click on the Downtimes tab.
In the first (Basis) field of the Downtimes table, select Usage, since most equipment failures occur only while in use.
Complete the rest of the data for the downtime. Since this is a random failure, the Interrupt option should be selected.

Example

A printing machine in a publishing process goes down randomly every 10 minutes exponentially distributed. The repair time is roughly triangularly distributed with a min, mode and max of 1, 4 and 15 minutes respectively.

Solution

The Downtimes tab shows the entries which define this random failure for the Printer activity.