Maintenance and Breakdowns

Planned maintenance and breakdowns are modelled using the DowntimeEntity, which generates random or scheduled events based on either working time or calendar time.  Normally, a maintenance activity is scheduled to occur at regular intervals based on calendar time.  Breakdowns are normally modelled to occur randomly based on the working time for the object.

The object that will undergo the maintenance or breakdown has a series of keywords that determine how the object responds to a particular maintenance or breakdown event.

Maintenance and Breakdowns Inputs

Keyword

Description

WorkingStateList

A list of states for which the entity is considered to be working.

ImmediateMaintenanceList

A list of DowntimeEntities representing planned maintenance that must be performed immediately, interrupting any work underway at present.

ForcedMaintenanceList

A list of DowntimeEntities representing planned maintenance that must begin as soon as task underway at present is finished.

OpportunisticMaintenanceList

A list of DowntimeEntities representing planned maintenance that can wait until task underway at present is finished and the queue of tasks is empty.

ImmediateBreakdownList

A list of DowntimeEntities representing unplanned maintenance that must be performed immediately, interrupting any work underway at present.

ForcedBreakdownList

A list of DowntimeEntities representing unplanned maintenance that must begin as soon as task underway at present is finished.

OpportunisticBreakdownList

A list of DowntimeEntities representing unplanned maintenance that can wait until task underway at present is finished and the queue of tasks is empty.

Only one breakdown or maintenance activity can occur at any given time.  If multiple breakdown/maintenance activities are scheduled for the same time, they are performed sequentially.  It is possible under some circumstances for a breakdown or maintenance to occur while a threshold is closed.  In this case, the state is set to the appropriate breakdown or maintenance state.

The outputs for maintenance, breakdowns, and thresholds are grouped together as follows.

Maintenance, Breakdowns, and Thresholds Outputs

Output Name

Description

Idle

Returns TRUE if able to work but there is no work to perform.  For an EntitySystem, TRUE is returned if all the entities in the system are idle.

Working

Returns TRUE if work is being performed.  For an EntitySystem, TRUE is returned if any of the entities in the system are working.

Setup

Returns TRUE if setup is being performed.  For an EntitySystem, TRUE is returned if setup is being performed on any of the entities in the system.

Maintenance

Returns TRUE if maintenance is being performed.  For an EntitySystem, TRUE is returned if maintenance is being performed on any of the entities in the system.

Breakdown

Returns TRUE if a breakdown is being repaired.  For an EntitySystem, TRUE is returned if a breakdown is being repaired on any of the entities in the system.

Stopped

Returns TRUE if an operating limit prevents work from being performed.  For an EntitySystem, TRUE is returned if an operating limit prevents work from being performed on any of the entities in the system.

Utilisation

The fraction of calendar time (excluding the initialisation period) that this object is in the Working state.  Includes any completed cycles.

Commitment

The fraction of calendar time (excluding the initialisation period) that his object is in any state other than Idle.  Includes any completed cycles.

Availability

The fraction of calendar time (excluding the initialisation period) that this object is in any state other than Maintenance or Breakdown.  Includes any completed cycles.

Reliability

The ratio of Working time to the sum of Working time and Breakdown time.  All times exclude the initialisation period and include any completed cycles.

Open

Returns TRUE if all the thresholds specified by the ThresholdList keywords are open.

NextMaintenanceTime

The estimated time at which the next maintenance activity will start.

NextBreakdownTime

The estimated time at which the next breakdown will occur.