Mathematical models for reliability allocation and optimization for complex systems

RAMS is an acronym for Reliability, Availability, Maintainability and Safety. These four properties concern the application of important methodologies for designing and managing complex technical systems. The present chapter analyses several reliability allocation techniques present in literature. Starting from well-known methodologies, two reliability allocation methods has been proposed and validated: Integrated Factors Method (I.F.M.) and Critical Flow Method (C.F.M.). We focus on the most important conventional methods to discuss their limitations to motivate the current research. The proposed methods supply a logic for the analysis of prototype complex systems during the pre-design phase, even if it presents general characteristics that allow this logic to be extended to different design phases. In particular, the proposed CFM method can resolve the shortcomings of the conventional methods with a new reliability approach useful to series-parallel configurations in order to obtain important cost savings. In fact, the results show that the most conventional reliability allocation methods have one fundamental problem: in general, they are designed for complex system with series-configurations (preliminary phase design) but not for series-parallel configurations. The result is an increase of reliability allocated to units (series configuration) in order to guarantee the reliability target system (extremely low failure rate).