Abstract

To evaluate the operational safety of a semi-submersible platform in a polar region, a model test of the dynamic positioning (DP) assisted mooring of a platform in the coupling action of wave, current, and artificial ice floes was carried out. The motion responses of the platform positioned by the DP system with and without acceleration feedback were analyzed, demonstrating the effectiveness of the acceleration feedback strategy. A switching positioning point strategy is proposed to eliminate the accumulation of ice floes in front of the column of the semi-submersible platform. The tension of the mooring system is substantially reduced by using this strategy, further improving the operating safety of the platform.

Introduction

In recent years, the engineering demand for drilling platforms in Arctic waters has become higher due to the feasibility studies of scientific expeditions in polar regions, oil and gas resource exploration, and Arctic summer navigation (Hansen et al., 1999; Wright, 1999). Most proven oil and gas resources in polar regions are found in deep water, where fixed structures are unrealistic in terms of economics and feasibility. Therefore, floating structures with dynamic positioning (DP) or mooring systems are appropriate options for polar zone exploration and drilling operations. The positioning system of a floating structure must withstand the dynamic load of an ice floe as well as wind, wave and currents; otherwise, the structure may be pushed away from its desired position and affect production operations, or, in extreme cases, the floating structure may be damaged, which would have a significant impact on the safety and operation of the floating structure (Kjerstad et al., 2015). Therefore, it is important to clarify the loads and the motion response of the floating structure caused by coupling with managed ice, wave, and current loads for the design of a floating structure, the safety calibration of a mooring system, and the development of a DP system.

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