Using Simulation and Cost Calculations

This section provides instructions on how to use simulation to compare potential maintenance strategies based on cost and/or availability.

Note: For a general explanation of how to create and edit task records, refer to the Tasks topic. For instructions on how to use a predefined maintenance task selection logic to choose the appropriate maintenance strategy refer to Using Maintenance Task Selection Logic.

If you are using the simulation and cost calculations approach, you will be able to define different types of tasks, simulate the operation of the equipment for a specified time and then compare the results to select which task(s) will be most cost-effective in addressing the failure mode.

The following sections describe the steps for using this approach:

1. Define the URD for the failure mode.

   1. Define the probability of occurrence for the failure mode.

   2. Define the corrective maintenance scenario.

   3. Define the preventive maintenance scenario(s).

2. Perform simulation.

3. Compare the maintenance strategies and assign the tasks.

Define the Probability of Occurrence for the Failure Mode

The model assigned to the cause record (via the URD assigned to the cause record) is used to define the probability that the item will fail due to the particular failure mode. (For information about using the exponential distribution, refer to A Note About the Exponential Distribution (Failure Rate or MTBF).)

Although models can be assigned at various levels in the analysis via the FMRA, you must have a model assigned at the failure mode level in order to use simulation to compare potential maintenance strategies based on cost and/or availability.

Define the Corrective Maintenance Scenario

The corrective maintenance scenario is defined by assigning a corrective task to the URD that is assigned to the cause record. This information is used to estimate the average availability and cost per operating time that could be expected from a run-to-failure maintenance strategy (i.e., performing corrective maintenance only) and it is also required for the simulations of any preventive maintenance strategies that you define.

The following corrective task properties are considered when simulating the run-to-failure maintenance strategy:

• Whether or not the failure mode is detectable. This is based on your selection in the Start corrective task field; select Upon item failure if the failure mode is detectable or When found failed during an inspection if the failure is undetectable.

• The Task duration, which is the amount of time that the equipment is expected to be down for each corrective maintenance action. This may include logistical delays and actual repair time.

• Whether the task brings the system down, in addition to bringing the item down. This is defined using the Task Consequences properties.

• How much the task restores the equipment, specified using the Restoration properties.

• The costs associated directly with the task, as specified in the Additional Costs to Consider properties. This may include downtime costs, labor costs, material costs and any other miscellaneous costs. (Note that if you have provided information on crews and/or spare part pools for the task, then labor costs and material costs may be accounted for via those resources.)

Define the Preventive Maintenance Scenario(s)

In order to use simulation to compare potential maintenance strategies based on cost and/or availability, you will need to define a task record for each potential maintenance strategy that you are considering. Any scheduled task can be part of the preventive maintenance strategy. Authorized users can define the task types that will be used for this portion of the analysis.

Scheduled tasks can be assigned to the URD that is assigned to the cause record either via the Task Manager or via the URD window.

Perform Simulation

Once you have defined the probability of occurrence for the failure mode, the corrective task and the possible scheduled tasks, you can click Simulate in the Task Manager. You will be asked to define the simulation settings. the software will then simulate the operation of the equipment for the specified operating time, given the reliability and maintainability characteristics that you have specified.

In the middle of the Task Manager, the cost per operating time and the average availability associated with a run-to-failure maintenance strategy will be displayed. At the bottom of the Task Manager, the table will display the same metrics for each proposed scheduled task.

Compare the Maintenance Strategies and Assign the Tasks

The final step when using the simulation and cost calculations method is to compare the results from the potential maintenance strategies and choose which task(s) will be performed. For each task that you choose not to add to the scheduled maintenance plan, you can either remove the task from the URD or, if it is not used anywhere else, you can delete the task resource entirely.