Weakly Nonlinear Estimation of Hydrodynamic Forces and Motions on a Barge Type Floating Body With Moonpools in Waves

Abstract This paper describes nonlinear effects of overtopping and sloshing behaviours of water mass within a moonpool on wave exciting forces and motion responses of a barge floating body with a moonpool for offshore wind. Overtopping and sloshing like behaviours should be a problem in design of the structure. These phenomena give nonlinear problems in predictions of hydrodynamic forces and motion behaviours. Objectives of this study are to investigate nonlinear effects of a barge type floating structure with a moonpool on wave excitations and motions. In order to know the physical phenomena, the study carried out model experiments and numerical calculations with the weakly nonlinear potential theory. The paper takes into account up to the 2nd-order terms as nonlinearity in frequency domain. As a result, the linear wave exciting forces and motions could be reproduced by using the 1st-order potential theory only in small wave heigh conditions in which there were not the overtopping. The 2nd-order motions were also able to be almost reproduced by the 2nd-order potential theory in large wave height conditions even then the overtopping and the sloshing which was strong and complicated. The study adapted a hybrid-boundary-element-method which was an in-house programme code validated. The 2nd-oder theory approach would be useful to estimates motion responses with relatively strong nonlinearity in regular waves.