Study of the Trajectory and Landing Points of Dropped Cylindrical Object with Different Longitudinal Center of Gravity

摘要

Dropped objects are among the top ten causes of fatalities and serious injuries in the oil and gas industry (DORIS, 2016). Objects may accidentally fall down from platforms or vessels during lifting or any other offshore operation. The accurate prediction of the landing points of the dropped objects may protect underwater structures and equipment from being damaged. In this paper, the authors propose a three-dimensional (3D) theory to numerically simulate the dynamic motion of a dropped cylindrical object under the water and to investigate the influence of the longitudinal center of gravity (LCG) on the motion. A numerical tool called Dropped Objects Simulator (DROBS) has been further developed on the basis of this 3D theory. It is initially applied to a dropped cylinder with its center of gravity at the center of volume (cylinder #1, LCG = 0) falling from the surface through calm water. The calculated trajectories match very well with both the experimental and numerical results published in Aanesland (1987). Then DROBS is further utilized to simulate two dropped cylinders with positive LCG (cylinder #2) and negative LCG (cylinder #3), respectively. The simulated results from DROBS show better agreement with the measured data than the numerical results given in Chu et al. (2005). This comparison again validates and indicates the effectiveness of the DROBS program. Finally, the simulation is applied to investigate the effects of varying LCGs on the trajectory and landing points. The newly developed DROBS program can be used to simulate the distribution of the landing points of dropped cylindrical objects in order to predict risk-free zones for offshore operations.