Failure Mode Control Variables (FMCV)

This model demonstrates the use of failure mode control variables in Reliability function and action elements. Below are 3 examples that show how to define FMCVs in different ways: Total elapsed time, Total operating time, and the number of actions.

One of the Reliability Module's greatest strengths is its ability to represent failure modes in great detail. This is done by clearing the Use simple failure rate instead of failure modes checkbox. When you do this, a Failure Modes tab is added to the dialog which provides access to the Reliability Module's advanced failure mode features. In the advanced failure mode features, it is possible to specified the detailed behavior of Failure Mode Control Variables (FMCV).

Most failure modes are defined relative to a failure mode control variable (FMCV). This is the variable that is referenced by the failure mode to determine when failure occurs. (For those failure modes that are defined as distributions, the control variable represents the x-axis of a failure distribution plot.)

For FMCV-based failure modes, the failure mode calculates the FMCV “age” that will result in its next failure at the start of the realization, after each time the mode is repaired, and after each time the component is replaced. When the FMCV exceeds this value, the failure occurs.

Each (FMCV-based) failure mode has its own FMCV, which is defined in terms of a specified “base variable” (e.g., total simulation time, operating time, mileage). The FMCV for a particular failure mode and the base variable are related as follows:

FMCV(t) = Initial Value + SUM[ (Base Variablei - Base Variablei-1) * Acceleration ]

FMCV(t) represents the value for the FMCV at time t. The sum is made over all the timesteps from the beginning of the realization (or the time the FMCV was reset) to time t. The Initial Value and Acceleration Factor are user inputs for each failure mode. The FMCV calculation can be reset by certain events such as replacement of the component or repair of the failure mode. This is done by resetting the Initial Value (to a specified FMCV value) and restarting the sum.

This model provides examples of customizing the Control Variables for failure modes.

Total Time

The Total time control variable accrues time regardless of whether or not the component is operating. This means failure occurs at 100 days. There is no preventive maintenance.

Operating Time

The Operating time control variable only accrues time while operating.

In this case, the element begins accruing time at 75 days, and accrues time until 125 days, where the failure mode is repaired by a Preventive Maintenance event that lasts 5 days. Failure occurrs 100 operating days later at 230 days.

Number of Completed Actions

The Number of actions completed control variable increases only when the action is successful. This means that the action element accrues no wear until it is turned on at 75 days (as it cannot successfully complete its action if it is off).

To Open the Model File:

1. Start GoldSim
2. Click on the File and select Open Example...
3. Browse to Reliability Examples
4. Select the file called ControlVariables.gsm