Motion Characteristics of a Floating Model With Moonpools for VAWTs

Abstract This paper describes motion behaviors of a floating body and water regions of moonpools. The floating model to be focused in this study has moonpools and is for offshore wind turbine system with two vertical axis wind turbines. Motion behaviors of water region in moonpools strongly affect on motion characteristics of a floating body itself. Often the effects lead to non-linear motion of the floating body. Besides, when the floating body is a system of vertical axis offshore wind turbines, the system becomes more complicated. This study conducted theoretical calculations and model experiments in a wave tank. Behaviors of moonpools were measured in regular waves and we measured wave exciting forces, radiation forces on heave and motion responses of the floating model. Also, the study considered effects of Vertical Axis Wind Turbine (VAWT) model’s rotation on the motion. From the results behaviors of moonpools were often nonlinear to incident waves and the behaviors affected on motion responses of the floating model. The experimental results were compared with the calculation results. When non-linearity due to overtopping of water from moonpools was found, the calculations could not reproduce hydro forces but they are able to estimate motion responses. The study confirmed reduction effects due to the moonpools on motion responses comparing with a conventional pontoon with identical displacement.