Effect of the Turret’s Rotational Damping on the Heading Stability of a Turret-Moored FPSO

Abstract

Certain types of facilities operating offshore need to maintain their position, for which diverse mooring systems are employed, such as single point mooring (SPM), spread mooring, and turret mooring systems (TMSs). TMSs are widely used in relatively harsh environments. The use of a turret allows a vessel to rotate towards a predominant external load to reduce its effective load. However, floaters equipped with a turret might experience a fish-tailing phenomenon in specific conditions, and in severe cases, the motion will worsen. Since turrets are widely utilized, abundant research has been accomplished, which has mainly been about the yaw behavior or factors related to heading stability. Various causes have been suggested as factors in yaw motion of turret-moored floaters, but the underlying causes still need to be verified. Munipalli et al. (2007) examined the response of the heading under conditions with multiple regular waves and fixed steepness from head sea. They found that large yaw motion occurred for a shorter wave period. Cho et al. (2013) experimented with the yaw motion of a turret-moored floating body in regular waves with fixed wave steepness. Studies have examined the effect of the distance between the turret and the center of gravity ( ) of a system and the distance between   and the center of the turret ( ). The maximum yaw angle in regular waves was analyzed, and it was found that when the turret is closer to   , the yaw motion is larger (Yadav et al., 2007). Sanchez-Mondragon et al. (2018) compared the results of a similar study with different configurations and wave steepness. The configuration and the environmental conditions were varied, and the turret position and the mooring stiffness influenced the specific wave period between 15.0 and 19.0 s. Kaasen et al. (2017) concluded that the interaction between yaw and sway is most important in their research on the heading control of turret-moored floating production storage and offloading (FPSO), which they performed with a simplified model. Garza-Rios and Bernitsas (1999) presented a mathematical model for the nonlinear dynamics of slow motions in the horizontal plane of a TMS in terms of the equation of motion. They proved that if the friction moment