Hydrodynamic analysis of a hybrid modular floating structure system under different wave directions

The present work reports a novel hybrid modular floating structure (HMFS) system consisting of a certain number of outermost box-type modules and inner semi-sub modules. Semi-sub modules are connected with ball joints in both longitudinal and transverse directions. Box-type modules are connected with adjacent semi-sub modules with pitch hinges. Outermost box-type modules mainly function as wave energy converters (WECs) and breakwaters. Based on the rigid module and flexible connector (RMFC) method, the effects of different wave directions, longitudinal expansion, positions of modules and connectors on hydrodynamic responses of the HMFS system are emphatically investigated under typical sea conditions. The results indicate that for the layout of the HMFS system, the transverse direction is recommended to be consistent with wave direction with the highest occurrence probability in terms of comprehensive consideration of module motions, connector loads, mooring forces as well as wave energy power. The HMFS system shows good longitudinal expansibility for mild marine environments. The positions of modules and connectors have significant effects on their hydrodynamic responses, and the corresponding mechanism has been preliminary clarified. In addition, the statistic information of extreme hydrodynamic responses under representative wave directions has been comparatively analyzed for the ultimate limit state design of the HMFS system.