Current service and installation activities to offshore wind turbines (OWTs) are mainly carried out by jack-up vessels. These vessels are less susceptive to disturbances caused by sea waves when they lift their hull from the water level by jacking down multiple legs to the seabed. An alternative is a crane mounted on a floating vessel, which has the benefits of being faster regarding sailing time, cheaper in operation, able to locate multiple times around the same offshore site and able to operate in deep waters. However floating crane vessels have a significant lower workability in comparison to jack-up vessels and are therefore not deployed in OWT activities yet.
Huisman initiated the three-dimensional (3D) motion compensated crane (MCC) project to improve the workability of crane vessels in offshore operations - thereby focusing on the performance of the equipped cranes - such that floating crane vessels will be able to install and service OWTs during an sufficiently large operational window. But to date MCCs have never been realized for offshore wind industry, which makes it difficult to estimate their performance beforehand and evaluate whether they are feasibile.
This thesis describes the development of a procedure to assess the feasibility of motion systems from a mechatronic design perspective and the motion compensation system of the Huisman 3D MCC is used as a case study. Several aspects of the MCC have been studied into more detail because these aspects are an determining factor regarding feasibility. These aspects are the influence of actuator type and crane boom flexibility and the performance during realistic offshore conditions. To investigate these aspects the system dynamics of the conceptual design are modelled, a controller is designed for the model and parameters are identified. Next the model is evaluated on its disturbance rejection capability because this is an important performance indicator for motion compensation, its robustness is examined and whether the OWT installation requirements are fulfilled.