Reliability allocation and optimization for complex systems

During the design phase of a product, reliability engineers are called upon to evaluate the reliability of the system. The question of how to meet a reliability goal for the system arises when the estimated reliability is inadequate. This then becomes a reliability allocation problem at the component level. In this paper, a general model estimates the minimum reliability requirement for multiple components within a system that will yield the goal reliability value for the system. The model consists of two parts. The first part is a nonlinear programming formulation of the allocation problem. The second part is a cost function formulation to be used in the nonlinear programming algorithm. A general behavior of the cost as a function of a component's reliability is assumed for this matter. The system's cost is then minimized by solving for an optimum component reliability, which satisfies the system's reliability goal requirement. Once the reliability requirement for each component is estimated, one can then decide whether to achieve this reliability by fault tolerance or fault avoidance. The model has yielded very encouraging results and it can be applied to any type of system, simple or complex, and for a variety of distributions. The advantage of this model is that it is very flexible, and requires very little processing time. These advantages make the proposed reliability allocation solution a great system design tool. A computer program has been developed and the model is available in a commercial software package called BlockSim/sup TM/.