System design for integration of cost, reliability and performance using analytical target

Abstract

Since the system design is much about the integration of cost, reliability and performance, the tradeoff should be designed optimally with a systematic method. However, conventional methods have not sufficiently concerned the interactions with a systematic method, and the reliability is often optimized by passive modification on the basis of the previous optimized cost and performance rather than the self-directed search to be optimized by which the defects invalidate the optimality. To address the problem, analytical target cascading (ATC) is proposed to be served as the frame to conduct integrated system design. Differing from other Multidisciplinary Design Optimization (MDO) structure, ATC focuses on the object assigned to each element of its multilevel systematic structure. The appropriate targets would be set for each of the smaller design tasks such that if met, the whole system will be a consistent that meets the top-level system targets. Because of this target oriented character, ATC is more adaptive to design the certain requirement for system. In addition, there indeed exists many uncertainties in the practical system. When involving uncertainties, reliability is widely used by quantifying the probabilistic constraints containing uncertain variables. The conventional method to design a system concerning reliability is in accordance with the reliability targets arbitrarily assigned to each subsystem and each failure mode by user, but the consistency and optimality of system have been broken by the restraints imposed on cost and performance from the prescribed settled reliability target. The better method is to treat each reliability as variable designed by optimizer under the specified overall system reliability target. When implementing in the framework of ATC, the reliability of each subsystem and each failure mode are optimized together with the design variables, which interacts with the cost and performance. However, another systematic condition that the certain reliability goal for each subsystem must be met should be added since there is a reliability limit for holistic system. Thus the system design using ATC results in operating the optimal reliable design and optimal reliability allocation simultaneously. The gist of the paper is to research the integration of cost, reliability and performance in system design, and the interaction among these three properties. When the objective of design optimization is cost, the requirement of performance must be served as one kind of constraints. Likewise performance as objective, cost demand must be regarded as the constraint. In order to achieve the systematic tradeoff and optimality, the effect of any property impacting the remaining two will be illustrated after establishing the system integration. And the comparison would indicate the design inclination and the balance among cost, reliability and performance when design a system.