& CO CLUSIO SPracticable life extension of engineering systems would be a remarkable application of prognostics. Although considerable research has been devoted to developing prognostics algorithms, rather less attention has been paid to post-prognostic issues such as maintenance decision making. This research investigates the use of prognostic data to mobilize the potential residual life. In this respect, a multiobjective optimization model is presented for a typical power generation unit. This model proves the ability of prognostic models to balance between power generation and life extension. The results of the optimization models quantitatively indicated that maximizing the service life of bearings requires lower shaft speed and longer maintenance time.
I TRODUCTIOAn effective prognostic system should play a significant role in improving the durability of engineering systems. In essence, limited investment capitals and the need for Returnon-investment (ROI) are the motivations for life extension in engineering systems. Power generation systems are an excellent example of capital-intensive engineering systems that are expected to operate safely and efficiently beyond their nominal design life. It is to be noted that applying prognosis for extending the operable life of power generating systems has been noticeably lacking in published literature.A critical aspect in the evaluation of economic viability of power generation system is the difference between the market value of energy and the energy generation costs. In effect, the operations and maintenance (O&M) costs are a major contributor to the energy generation costs. For instance, the O&M costs of offshore wind farms contribute about 25-30% to the energy generation costs [1]. It should be emphasized that the maintenance strategy is the main contributor to the O&M costs. As indicated by Lu et al. [2], if the maintenance strategy does not work appropriately, the cost of replacement related to a failed bearing in wind turbines would jump from $5000 to $250,000. In essence, O&M costs can be minimized through improved reliability of the turbine's components, condition-based maintenance (CBM) and optimal management of maintenance requirements. Diagnostics and prognostics are two important aspects of a comprehensive CBM program. In essence, decision-making and planning for O&M need to take diagnostic and prognostic systems into account. The primary objective of this research is to develop a prognostic-based lifeextending methodology in order to improve the current PHM practices for a typical wind-based power generation unit (PGU).The first and foremost element of an efficient lifeextending methodology is effective and robust diagnosis. Next, real-time estimates of remaining useful life (RUL) need to be used in order to characterize and quantify the life extension practices. Useful life can be defined as the ability for power generation to fully or partially meet demands. RUL is the time that a component or system is able to operate with the same predefined specifi...