A Research of the Effect of Heeling And Trimming On a Specific Semi-Submersible Platform With Dynamic Positioning System

Liu, Han-lin (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Wang, Lei (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Chen, Gang (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University)

OnePetro 

ABSTRACT:

This paper starts from the hydrodynamic performance of dynamic positioning system propellers of the semi-submersible platform. According to the relevant standards, provided by the register of shipping, which have set the maximum allowable tilt angle of a semisubmersible platform, a research is taken about the effect on dynamic positioning system under a series of heeling and trimming angles by studying the changes of thruster-thruster interaction patterns. After numerical simulations, the time-domain curves of positioning accuracy and power consumption can come out. 1Finally, an analysis is made about the reasons of the results, besides; some applicable conclusions can be carried out.



INTRODUCTION


Modern offshore industry techniques have been making increasing use of dynamic positioning (DP) systems for vessels especially deep ocean platforms in wave, wind and current environments, even in severe environmental conditions. The DP system controls the vessel’s motion in three horizontal degrees of freedom: surge, sway, and yaw. Generally speaking, the wave induced platform motions can be separated into two major components, namely the first order highfrequency motions and the second order low frequency motions. The DP systems are designed to counter the effects of the latter low frequency component, in addition to the effects of currents and wind. The purpose of DP system is to locate the vessel at relatively fixed position with high positioning accuracy and consuming power as low as possible. Nowadays, many numerical and experimental tests have been taken from various aspects in order to take thruster-thruster and thruster-hull interactions into account. Depending on some experiences from tests of both ships and platforms, the loss of thrust is in the order of 30%-70%. Such loss of thrust could be caused by Coanda effect or interaction efforts, such as thruster-hull, thruster-current and thruster-thruster interactions, which are the results of complex physical phenomena (Nienhuis U, 1992).