Study of loading policies for unequal strength shared-load system

This paper presents three policies for load assignment among unequal strength units based on: (1) maximizing the mean time between failure (MTBF) of the system (Policy A); (2) requiring all active units to fail simultaneously (Policy B); and (3) simply taking the same load for all active units (Policy C). The traditional shared-load k-out-of-n: G system performs satisfactorily if at least k of the total n units are up, with load being shared among the surviving units. One of the advantages in such a system is that the active units play the role of both an actuator and a sensor. Thus we have enough time to make corrective replacement of failed units while the system is still kept on duty. We use examples to show that policies A and B have almost the same MTBF (the difference is within 1%), which is much more superior than Policy C. Two indices are used for the selection of valve k, with given number of total units. One is called the effectiveness factor, while the other is the tolerance factor. The former concerns with the effectiveness of load assignments among the surviving units. The latter deals with the time buffer when one more unit fails.