A Rational Dynamic Analysis Procedure for Turret Mooring Systems

Abstract

Until recently, most of the turret mooring systems have been designed using the so-called quasistatic approach. There is an increasing awareness that this approach may be deficient for certain applications, and that dynamic analyses are needed. To this end, this paper presents a rational dynamic analysis procedure for designing turret mooring systems. Specifically, practical methods for computing the low frequency motions and dynamic line tensions are presented, based on the latest analytical developments, model tests, and design experience. Model test data are presented for three turret-mooring systems in water depths of 70 metres, 75 metres, and 370 metres, respectively, to substantiate the significance of drag force on mooring lines on the low frequency motions, the modified Rayleigh distribution and the RINA method for interpolating the statistical low frequency responses, and line dynamic behaviour. Finally, this procedure is illustrated using the turret mooring system of a 230K dwt tanker in 370 metre water depth as an example case. The results of the dynamic analyses are compared with model test data and with the results using a quasistatic analysis approach.