Session: 02-07-01 Reliability of Renewable Energy Systems

Paper Number: 80511

80511 - Fatigue Assessment of Wind Assisted Propulsion Systems 

With the increasing focus on decarbonization, IMO has introduced a new regime for rating ship emissions. This is divided into a design index for new and existing ships, EEDI or EEXI, and to an operational index CII. Over time, ship owners must adapt to an increasingly strict emissions regime and utilize different strategies to reduce fuel consumption to stay in compliance with regulations, but also to stay competitive. One of the solutions to reduce fuel consumption is to utilize wind and set sails.

While sails have been used for centuries, the new rapidly emerging technologies are not conventional sail rigs like seen on small vessels, but wind assisted propulsion systems particularly developed for large vessels operating in harsh environments and designed for a long operational lifetime. They may be automatically adjusted by a sensor-based control system to achieve optimum performance and safety. Safety associated risks may be high and consequences in case of failures severe. One of the damage modes of concern is fatigue.

Fatigue accumulation may be driven by many sources, and for design assessment the two main sources are ship motions and wind gusts. It is not trivial how to combine these two sources, neither is the dynamic nature of the wind itself. The paper describes the process of how a pragmatic design formula has been derived to find a gust factor that is useful for combination with ship motions to predict fatigue damage in design. This factor is dependent on wind speed, ship motion and distance from the sea surface. Since fatigue assessment may result in requirements to increased strength and dimensions of the sail system, the new formula offers a much less conservative design than gust factors traditionally used for extreme design, thereby saving material resources and installation costs. This may also be relevant for floating offshore wind turbine installations.            

Presenting Author: Gaute Storhaug DNV

Authors:

Gaute Storhaug DNV
Guilherme Romar Borzacchiello Kongstein
Hasso Hoffmeister DNV