Characterization of coupled body response in random sea

The frequent use of two or more closely positioned vessels during offshore operations makes the study of multi-body hydrodynamics an important topic, especially for the design of deepwater offshore systems. This research investigation studies the response behavior of a coupled mini-TLP / barge system in both head and beam sea conditions. The design sea conditions were selected to represent the combined wind, wave and current conditions for a target location off the coast of West Africa. Both the mini-TLP and the barge were designed to have independent mooring systems. Coupling between the two vessels is introduced through a connection consisting of two breast lines and a fender system. This connection is designed to restrain the horizontal movements of the two vessels while keeping a constant distance between them and avoiding collisions. The main focus of this study is to analyze the experimental data obtained during the model testing, especially the motions of the two bodies and the values related to the fender system, in order to characterize the behavior of the uncoupled and coupled system configurations. A statistical approach is used for the data analysis and interpretation. Statistical parameters are used to provide an overall characterization of system behavior, and Gaussian and Weibull distribution functions are utilized to detect the importance of non-linearity in the data with particular attention to extreme values. Correlations between the two vessels in time domain and frequency domain are investigated. In addition, auto and cross spectrum analyses of the data are used to contrast the motion behavior of the uncoupled and coupled configurations. It is shown that the connection system reduces the horizontal vessel motions; however the forces exerted on the fender system show significant variation depending on sea heading conditions.