|Title: Design Considerations of DP- Systems for Offshore Windpark Installation Vessels|
|Written by: Stefan Krüger, Hendrik Vorhölter|
|in: IMDC, Glasgow, Scotland 2012|
Abstract: The political decision in Germany to escape from nuclear power generation has lead to a severe pressure on the German offshore wind industry. A large number of wind turbines shall be installed in a short time. As these offshore wind parks have to be erected quite far away from the German coastline, the wind turbine installation vessels have to operate in a potentially harsh environment. Prior to the jacking process, the vessel has to keep exactly its position, where wind forces, current forces and wave forces act on the vessel. During the concept design phase of such vessels, these forces have to be determined quickly and with a sufficient accuracy to serve as input basis for the DP- system. Such DP- systems consist of several maneuvering components which are alternatively used for propulsion purposes. Typically, lateral thrusters are combined with azimuthing units to achieve the highest DP- flexibility. However, this often leads to the situation where the DP- system has much more degrees of freedom than possible equations which makes it difficult to develop a control algorithm for the system. Moreover, there is a strong interaction between the DP- components as such and between the individual components and the hull. This can result in forbidden zones for each DP- component, which makes the development of the control system even more challenging. Therefore an alternative method for the design of the DP- system and the hull form was used during the concept design of the Type 187 Offshore Wind Farm Transport and Installation Vessel of Sietas Shipyard, which was on order for a Dutch client. For this DP system, experiences from the crabbing requirement of twin screw ferries were used to design a DP system which has less degrees of freedom, but a higher efficiency, as the single DP components can more efficiently used. At the same time, the DP task was introduced into the hull form design from the very beginning of the project. Further, due to its simplicity, the DP system is quite cost effective and easy to maintain. The paper will show that the use of appropriate computational methods during the first phase of the ship design process will lead to efficient and simple solutions. Further it will be shown that such methods need to be used especially by the responsible building yard to ensure that the final product will meet the desired purpose in the desired quality. The paper is original and the subject for the first time presented in public.