Fuzzy reliability in conceptual design

Conceptual design´s intrinsic uncertainty and influence on product life cycle cost make reliability engineering tools during early design phases important. However, typically poor knowledge bases make the prediction of component failure and system performance challenging. Fuzzy techniques are used here during initial conceptual design stages to quantify imprecision and uncertainty in reliability and risk analysis. More specifically, a fuzzy approach is compared to the probabilistic approach presented in Reliability prediction models to support conceptual design by Ormon, et al. (2002). Triangular fuzzy numbers instead of triangular probability distributions represent unknown failure rates here. Two examples of fuzzy reliability analysis in conceptual design are presented where system reliability is evaluated at the subsystem level: The first is to familiarize the reader with fuzzy reliability subsystem level analysis. The second demonstrates fuzzy reliability prediction models for conceptual design tradeoffs. Examples include subsystems operating with active and standby redundancy. In the first example, defuzzified system reliability is a more conservative prediction than that found probabilistically. Recommendations in Example 2 do not differ from those based on the probabilistic models of Ormon, et al.