Optimal Operation and Depot Maintenance of Repairable Systems

Project originally titled: Reliability, Maintenance and Optimal Operation of Repairable Systems with Application to a Smart Charging Microgrid.

This project started in 2012 and was completed in 2015.

Most engineering systems are repairable. Their components can be repaired or renewed, if system failure occurs, so that the system can be put back into service. The classical reliability theory however, captures only limited aspects of the performance of these systems. Reliability may become equal to one after repairs. Based on the timing and quality of repairs, different reliability curves can be realized for the same system. The commonly used metrics of Mean-Time-Between-Failures (MTBF) and availability do not provide complete statistical information. MTBF is a widely used concept but only captures the mean. Availability may be misleading because a system that needs constant repair but takes only a short time to repair has a very high availability. Such a system however, has a very small practical use. These observations indicate that classical reliability theory may be inadequate in representing the performance of repairable systems. Over time, many components in a system get old or repaired and the frequency of system breakdown increases. Therefore, a predefined planning horizon (or lifecycle) must be considered. Repairs are performed only within the planning horizon and the system is retired at the end of the planning horizon.

In this project, we developed techniques to deduce the system architecture (reliability block diagram) from limited data, and also determine 1) which system architectures lead to the best cost-performance tradeoff, 2) what performance metrics can best assess the reliability of a repairable system, and 3) how we can manage spare-parts inventory so that a repairable system can be put back to use with minimal interruption without carrying too much inventory and without frequent resupply. We explored a utility-theoretic method and a Pareto front method for the optimal design of a repairable system. Repair assumptions such as “same-as-old,” “good-as-new,” “better-than-old-but-worse-than-new” and “worse-than-old” as well as technical obsolescence are accounted for using the concept of effective age. These repair assumptions are essential for depot maintenance and optimal operation of repairable systems.

Modeling technical obsolescence and repair assumptions is directly relevant to the implementation of “reset.” The topic is of high interest to the Army in general, and to PEO CS & CSS (Combat Support and Combat Service Support) in particular, because most ground vehicle fleets will continue to be used for decades and the Army needs tools to help make fleet planning decisions and develop depot maintenance strategies that will help reduce O&S costs while ensuring that the vehicle fleets maintain their required performance levels.

Research in this topic continues in another ARC project.

Publications:

• V. Pandey, Z.P. Mourelatos, E. Nikolaidis, M. Castanier and D. Lamb, “System Failure Identification using Linear Algebra: Application to Cost-Reliability Tradeoffs under Uncertain Preferences,” Proceedings of SAE International, World Congress, Detroit, MI, April 2012, Paper 2012-01-0914.
• V. Pandey, A.G. Skowronoska, Z.P. Mourelatos, D. Gorsich and M. Castanier, “Reliability and Functionality of Repairable Systems using a Minimal Set of Metrics: Design and Maintenance of a Smart Charging Microgrid,” Proceedings ASME 2013 Design Engineering Technical Conferences, Paper DETC2013-12376, Portland, OR, August 2013.
• V. Pandey and Z.P. Mourelatos, “A New Method for Design Decisions using Decision Topologies,” Proceedings ASME 2013 Design Engineering Technical Conferences, Paper DETC2013-12360, Portland, OR, August 2013. Accepted after revision, ASME Journal of Mechanical Design, August 2014.
• A.G. Skowronoska, D. Gorsich, J. Mange, A. Dunn, V. Pandey and Z.P. Mourelatos, “Global Strategies for Optimizing the Reliability and Performance of US Army Mobile Power Transfer Systems,” Proceedings NDIA 2013 Ground Vehicle Systems Engineering and Technology Symposium (GVSETS), Power & Mobility Mini-Symposium, Troy, MI, August 2013.
• V. Pandey, Z.P. Mourelatos and M. Castanier, “Decision Topology Assessment in Engineering Design under Uncertainty,” Proceedings ASME 2014 Design Engineering Technical Conferences, Paper DETC2014-34244, Buffalo, NY, August 2014.
• V. Pandey, A. Skowronska, Z.P. Mourelatos, D. Gorsich and M. Castanier, “Incorporating Flexibility in the Design of Repairable Systems – Design of Microgrids,” Proceedings ASME 2014 Design Engineering Technical Conferences, Paper DETC2014-34294, Buffalo, NY, August 2014.
• A.G. Dunn, J.B. Mange, A.G. Skowronoska, D.J. Gorsich, V. Pandey and Z.P. Mourelatos, “Simulation of Microgrid and Mobile Power Transfer System Interaction Using Distributed Multiobjective Evolutionary Algorithms,” Proceedings NDIA 2014 Ground Vehicle Systems Engineering and Technology Symposium (GVSETS), Modeling & Simulation, Testing and Validation (MSTV) Mini-Symposium, Novi, MI, August 2014.
• A. Skowronska, D. Gorsich, V. Pandey and Z.P. Mourelatos, “Optimizing the Reliability and Performance of Remote Vehicle-to-Grid Systems Using a Minimal Set of Metrics,” ASME Journal of Energy Resources Technology, 137(4), 041204 (7 pages), 2015