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Ocean Systems Engineering
  Volume 6, Number 4, December 2016 , pages 377-400

Risk free zone study for cylindrical objects dropped into the water
Gong Xiang, Lothar Birk, Linxiong Li, Xiaochuan Yu and Yong Luo

    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. Proper planning of lifting operations requires the knowledge of the risk-free zone on the sea bed to protect underwater structures and equipment. To this end a three-dimensional (3D) theory of dynamic motion of dropped cylindrical object is expanded to also consider ocean currents. The expanded theory is integrated into the authors\' Dropped Objects Simulator (DROBS). DROBS is utilized to simulate the trajectories of dropped cylinders falling through uniform currents originating from different directions (incoming angle at 0o, 90o, 180o, and 270o). It is found that trajectories and landing points of dropped cylinders are greatly influenced by the direction of current. The initial conditions after the cylinders have fallen into the water are treated as random variables. It is assumed that the corresponding parameters orientation angle, translational velocity, and rotational velocity follow normal distributions. The paper presents results of DROBS simulations for the case of a dropped cylinder with initial drop angle at 60 through air-water columns without current. Then the Monte Carlo simulations are used for predicting the landing point distributions of dropped cylinders with varying drop angles under current. The resulting landing point distribution plots may be used to identify risk free zones for offshore lifting operations.
Key Words
    dropped cylindrical object; landing point distribution; Monte Carlo simulation; risk free zone; current
Gong Xiang, Lothar Birk and Xiaochuan Yu: School of Naval Architecture and Marine Engineering, University of New Orleans, New Orleans, LA, USA
Linxiong Li: Department of Mathematics, University of New Orleans, New Orleans, LA, USA
Yong Luo: School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China

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