Floating blade installation

Abstract

The demand for blade installation and maintenance is increasing with each additional installed offshore wind turbine. In 2017, 560 additional turbines were installed in Europe, reaching 4149 turbines in total. Currently, they are serviced with cost and time inefficient methods, such as rope access and jack-up vessels. Rope access is slow and requires the deployment of expensive technicians in dangerous environments. Jack-up vessels are overqualified, expensive and not readily available. Identifying the short comings of these methods, TWD saw an opportunity to design a dedicated tool for blade installation. This resulted in the floating Blade Installation Tool (BIT). The BIT is a state-of-the-art solution that allows for blade installation from a floating platform. By incorporating motion compensation and decoupling it can mitigate the vessel motions, thereby reducing the relative motion of the top element of the BIT. After the BIT is connected to the tower, a blade handling kart can safely transport and install the blades to and from the nacelle. The goal of this thesis is to gain insight in the dynamic behaviour of the system, with the focus on the interaction between the turbine and the BIT. For this purpose, a numerical model is created for the governing plane of motions, the vertical plane on the longitudinal axis of the vessel. Using this model, several simulations are performed under a variety of conditions to assess the BIT for the following sub-questions: Are the interface forces on the tower acceptable in conditions comparable to the operational limits of jack-up vessels? What is the relation between the vessel-tower distance and the interface forces? How much does the significant wave height affect the forces and stresses on the tower? The results show that the BIT’s motion compensation system will effectivelymitigate the first order wave force induced motions of the vessel. However, it also shows that at multiple stages of the lifting process the BIT will exert a force exceeding the allowable force limits. To satisfy the constraints imposed by the tower manufacturers, adaptations to the design of the BIT must be made. Some of the possible solutions to be explored are as follows: The increase in contact surface area between the BIT and tower. The stresses, which is the limiting factor, are reduced allowing for higher interface forces. Applying additional mechanical systems, such as winches and hydraulic cylinders, to add an additional layer of control to the system. TThis is expected to be a necessary option, although it will increase the complexity
of the tool.