Fatigue Approach for WAPS

Abstract

In the context of climate change and limiting the global temperature rise, wind assisted propulsion systems (WAPS) appear as innovative emission reduction mechanisms, utilizing the thrust force generated by the wind to reduce fuel consumption. So, to assure the safety for the vessel and the equipment, these must follow a series of standards and guidelines, defined by classification societies not only to guide and ease their work, but also to assist the designer in evaluating the equipment’s robustness. The implementation of such equipment, however, require new standards, because, although previous knowledge with structures mounted on ships may be useful, WAPS differ from many of them regarding the fact that they are in operation while the ship is navigating. Moreover, since WAPS rely on wind to operate, wind loads should also be considered carefully. This complex problem can be extended for the whole WAPS, but, since such systems vary considerably, this would require an individual analysis. However, the connection between system and ship can be regarded as similar for most cases and, for this reason, a standard approach could be developed. Therefore, the present work, then, aimed to identify the relevant loads for fatigue in WAPS and to develop a standard approach for estimating fatigue damage for these systems in a rule context, focusing on the attachment of the WAPS to the hull. A review on WAPS and on their present rules was carried to understand how such systems work and how the problem should be approached. Moreover, similarities to offshore wind turbines were drawn to better explore the problem, also considering further aspects relevant for a moving ship. The basis for the work was completed with an overview of the general fatigue assessment procedure. Then, the loads and stresses acting on WAPS, resulting from winds and waves, as well as their combination, were approached at different levels of complexity. This required a series of assumptions to be made and proved for calculating the loads their combinations for the different procedures and levels of detail. In the end, the whole knowledge was gathered and summarized to present a fatigue approach for WAPS.