With the size of the wind turbine and water depth being continually increasing, offshore wind turbine (OWT) installation has become a major challenge for the development of offshore wind energy. The traditional OWT installation methods either use a crane vessel to achieve a single lift installation of the integrated wind turbine onto the pre-installed foundation, or use a jack-up vessel to conduct modular lift installations for the different pieces of OWTs such as the tower, nacelle, and blades. The crane vessel method is limited by the lift capacity and height of the crane vessel, and is sensitive to the environmental excitations. The modular lift method by jack-ups generally entails a large number of offshore lifts and a protracted period for offshore hook-up and commissioning, resulting low installation efficiency and high costs. In addition, the working water depth of the jack-up installation vessels in the market is generally limited to 35 meters. The increasing interests in exploiting offshore wind energy in deeper water may bring new challenges to the installation of OWTs. Therefore, many novel installation methods have been proposed by practitioners and academia. This paper presents a novel integrated mating method based on a ship-type installation vessel with the capacity of transporting 4 integrated wind turbines on one route. By this method, the blades, rotor, nacelle and tower are assembled as one piece at the shipyard, which is then loaded out onto the installation vessel. During transportation, the 4 integrated turbines are horizontally placed on the 8-legged frame mounted on the ship deck. The installation of the integrated turbines involves anchoring and prepositioning of the installation vessel, erection of the integrated turbine by the hydraulic jacking system and mating of the tower stabbing cone with the pre-installed foundation. This installation approach is an analogy to the float-over deck installation method for the offshore platforms. A case study of offshore wind turbine installation onto a pre-installed monopile foundation by the new installation method is conducted in this paper. By using ANSYS-AQWA, numerical simulations are carried out to investigate the hydrodynamic characteristics of the installation vessel and the nonlinear dynamics arising from the mating operations. In addition, parametric studies are performed to study the effects of the motion control systems such as the mooring system, fender system and shock absorber within the monopile, on the vessel motions and mating forces.
|Conference||30th International Ocean and Polar Engineering Conference (ISOPE 2020)|
|Period||11/10/2020 → 16/10/2020|
|Series||Proceedings of the International Offshore and Polar Engineering Conference|