Understanding Failure Mode Base Variables

Each (FMCV-based) failure mode has its own FMCV, which is defined in terms of a specified “base variable”. GoldSim provides four options for base variables:

• Operating time. This is the default base variable for any new failure mode. This base variable accrues time only when the element is Operating.

• Total time. FMCVs using this base variable accrue time from the in-service time of the component, regardless of the element’s status. Total time is useful for modeling failure modes which are independent of operational status, and also for modeling the degradation of standby and backup systems.

• Number of actions completed. This base variable is only available to failure modes for Action elements. This base variable tracks the number of times the action has been triggered and has issued an ActionOK or ActionFailed event.

• User-defined. In some cases, it may be appropriate to define an FMCV which 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, the user-defined base variable will be defined using an Integrator, Reservoir or Pool element.

It is important to note that when using the base variables that are based on time (e.g., total time and operating time), GoldSim can predict the occurrence of the next event (based on the values from the model’s last update at a timestep or event) and will interrupt a timestep for that event. This means that failure modes with static Acceleration Factors are insensitive to the timestep length, at least from a perspective of how the system will evolve. However, you should note that the condition of the system is only recorded at scheduled timesteps.