Optimal multiple replacement and maintenance scheduling in two-unit systems

Abstract

This paper models and optimizes the replacement and maintenance schedule (RMS) for a heterogeneous two-unit standby system. The system must accomplish a specified amount of work for a successful mission. When one unit executes the specified mission task, the other unit undergoes a certain type of maintenance based on the RMS, followed by staying in a warm standby mode if its next activation time is not up. The mission fails if both units fail before the task completion, or if one unit fails while the other one undergoes maintenance and thus is not ready to be activated and take over the task timely. A probabilistic model-based method is proposed to evaluate the mission success probability (MSP) of the considered system that may undergo multiple preventive replacements and different types of maintenance actions during the mission. The optimal RMS problem is then formulated and solved, which determines durations of operation periods of the activated unit and types of maintenance actions performed by the inactivated unit during its idle time for maximizing the MSP. A detailed case study on an oil transfer system with two heterogeneous pumps is provided to illustrate the proposed methodology and influences of multiple model parameters on the optimal RMS and corresponding MSP.