Fatigue Life Assessment and Lifetime Management of Aluminum Ships Using Life-Cycle Optimization

Abstract

The development of aluminum ship structures has been promoted in the context of the rapid evolution of high-speed and light-weight vessels. Under the repeated and/or fluctuating application of stresses during voyages, fatigue damage of structural ship members is accumulated. For this reason, fatigue reliability analysis has to be conducted for assessing and predicting lifetime performance of aluminum ships. This assessment offers the opportunity to optimally perform the lifetime ship structural management planning. To allocate limited financial resources required to balance the lifetime reliability of ship structural details and the life-cycle cost, single-or multi-objective optimization can be used. The multi-objective optimization problem has several competing objectives such as:(minimizing the life-cycle maintenance cost,maximizing the fatigue reliability of details with welded attachments, andminimizing the fatigue damage. The S-N (stress vs. number of cycles) approach and available sea loading information are used to evaluate the time-dependent fatigue reliability. In this paper, the estimated fatigue reliability is incorporated into a life-cycle cost optimization problem to find the optimal inspection and repair interventions. The proposed approach is illustrated on an aluminum ship detail.