Fully coupled dynamic analysis of a FPSO and its MWA system with mooring lines and risers

•An innovative mooring system called middle water arch (MWA) is developed for floating production storage and offloading (FPSO).•The time domain simulation of a fully coupled model is executed to illustrate the effectiveness of MWA.•A simplified model of the MWA is established to provide information regarding the preliminary design of such structure.

The middle water arch (MWA) is an innovation that is developed for floating production storage and offloading (FPSO). During simulating structural global motion in time domain, the fully coupled hull, mooring lines, tendons and risers technique is widely recognized as a unique method to understand the accurate hydrodynamic interactions and coupling effects. This paper investigates the dynamic response characteristics of a single point turret-moored FPSO-MWA system under the combined parallel wave, wind and current conditions by using coupled time domain analysis code AQWA. The complex nonlinear issues e.g. forces nonlinearity, mooring nonlinearity, motion nonlinearity are included in the numerical model. To illustrate the hydrodynamic interactions and coupling effects of FPSO, MWA and mooring system, the numerical solutions are systematically compared with those from the single body mooring system without considering the effects of MWA mooring system. The results indicate that the MWA system has not only an important influence on the top tensions and shapes of risers, but also have some contribution to motion responses of the FPSO and mooring lines. Furthermore, the results reveal that the favorable motion performance of MWA in the multi-body system may provide some economic benefits due to the possible decrease of fabrication cost and work-off days.