In some cases, it may be appropriate to define a failure control variable that is defined with respect to a base variable other than time or the number of actions completed (e.g., mileage). Any monotonically increasing function can be specified as a base variable. In most cases, a user-defined base variable will be an Integrator or Reservoir element.
GoldSim samples the change in the control variable required to cause failure, and monitors the change in the variable that you’ve selected. When the change in the control variable (taking into account Acceleration, and Initial Value settings) exceeds that required to cause failure of the mode, the mode fails.
It is important to note that failure modes using user-defined base variables cannot interrupt the simulation at the exact time of failure like failure modes using time-based control variables. Failures can only occur at a scheduled timestep, or when an event occurs (since GoldSim only evaluates the base variables at these times). This means that models that employ user-defined control variables typically require significantly more timesteps to accurately model a system.
The model file Mileage.gsm, found in the Reliability Examples folder in your GoldSim directory directory (accessed by selecting File | Open Example... from the main menu), is a very simple model of a car (one reliability element) that contains a number of failure modes that use the user-defined variable "mileage" as the base variable.
In this case, an Integrator element is used to represent mileage, and a Stochastic element, resampled once per year, is used as the mileage Integrator's rate of change input.
You can see how a User-defined control variable is set up by going to the Failure Modes page of the Car element’s property dialog, selecting a failure mode and clicking the Settings… button:
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