Specifying the Initial Value for Failure Mode Control Variables

Base variables are independent of failure mode (i.e., they are a property of the Function or Action element). FMCVs, however, are specific to each of the element's failure modes. The FMCV for a particular failure mode is computed by applying a specified Initial Value and an Acceleration Factor to the base variable.

That is, these two parameters convert the base variable (which is independent of the failure mode) to an FMCV, which is specifically applied for each particular failure mode. The Initial Value field is available for FMCV-based failure modes (except Exponential/Poisson).

Note: Although Exponential/Poisson and Defective Component failures are FMCV-based, they are memoryless, since their hazard function is constant with time. As a result, the Initial Value cannot be specified for these failure modes (as it would have no impact).

The Initial Value (which defaults to 0) allows you to model failure modes in which components are not new at the start of the simulation. There are two options for the Initial FMCV value, which are accessible via a drop-list:

If you know the current “age” of the component, it can be directly specified with the User-specified Initial Value option. If the current age of the component is unknown, you can use the Uncertain Initial Value option. In this case, GoldSim will randomly select an “age” between "new" and the value of the FMCV at the next failure of that failure mode.

Note: Although the Initial Value can be defined with an expression or link to another element’s output (and hence could be specified to be a function of time), it is only evaluated at the start of each realization. When the FMCV is reset (due to repair or replacement), it is always reset to the specified Repair Definition, not the Initial Value

Note: Some confusion could potentially occur with regard to Initial Values when creating user-defined base variables. This is because user-defined base variables are likely to be Integrators or Reservoirs, which themselves have Initial Values. With regard to the FMCV, the Initial Value of the base variable itself (i.e., the Integrator or Reservoir) is never used. GoldSim only monitors changes in the base variable and uses the Initial Value specified in the Failure Mode Control Variable dialog to determine the actual value of the FMCV.