Design of a Motion Compensation System for Offshore Wind Turbine Installation

Abstract

To reach the Paris Agreement goals, switching from fossil fuels to renewable energy is inevitable. Wind power has proved to play a critical role in this transition. To speed up this transition, the wind industry must keep innovating. The major part of Wind Turbine Generators (WTGs) is installed by a jack-up which not only has its limitations from an engineering point of view, such as water depth, soil characteristics and lifting capacity but also from a financial point of view. To overcome these limitations, this research aimed at developing an innovative concept design for the installation of offshore WTGs.
A vessel dynamic analysis showed that the Mighty Servant 1 is the most suitable Boskalis vessel to install WTGs from. The same dynamic analysis also highlighted that a motion compensation system is required to mitigate wave-induced dynamics and enabling WTG installation in floating conditions. After developing multiple concepts of motion compensation systems, a multi-criteria analysis in the form of an analytic hierarchy process is performed. It is found that the most promising concept should rely on hydraulic actuators. To find the optimal values of the design parameters of the chosen concept, a kinematic multi-objective optimization is carried out by means of a genetic algorithm. The optimal set of design parameters is selected by taking advantage of the Pareto front, which is computed by using three chosen performance indexes. A model is developed in MATLAB and Simulink to simulate the dynamics of the motions compensation system. The simulated results showed that a controller which uses velocity feed-forward and position feedback is the preferred way to go. The results also highlighted that the required amount of hydraulic power has a great impact on the economic feasibility of the system. Therefore, to reduce the hydraulic power and guarantee the feasibility, a passive system based on a hydraulic accumulator is added. Based on the results of this research, it can be concluded that the next generation offshore wind turbine generator can be motion-compensated with hydraulic actuators including hydraulic accumulators. Further research could be carried out by assessing more installation phases in combination with a wider range of load cases.