Abstract
Abstract. Sea ice disasters seriously threaten the structural safety of oil platforms in the Bohai Sea. Therefore, it is necessary to carry out a risk assessment of sea ice disasters on oil platforms in the Bohai Sea. In this study, a risk assessment of sea ice disasters on fixed jacket platforms in Liaodong Bay, in the Bohai Sea, was performed in five steps. Firstly, the formation mechanisms of sea ice disasters were analyzed and the sources and modes of sea ice risks were summarized. Secondly, according to the calculation formulas of extreme ice force, dynamic ice force, and accumulated force, several ice indices such as thickness, motion, strength, period, and concentration were proposed as the hazard indices, and corresponding values were then assigned to the proposed indices based on ice conditions in the Bohai Sea. Thirdly, based on four structural failure modes – structural overturning by extreme ice force (Mode 1), structural fracture failure caused by dynamic ice force (Mode 2), the damage of facilities caused by dynamic ice force (Mode 3), and structural function failure caused by accumulated ice (Mode 4) – the structural vulnerability index, overturning index, dynamic index, ice-induced vibration index, and function index were proposed, and corresponding values were assigned to the structural vulnerability index of fixed jacket platforms in Liaodong Bay. Fourthly, the weight of each risk index was determined according to previously recorded sea ice disasters and accidents, and the sea ice risk was then calculated with the weighted synthetic index method. Finally, with the above index system and risk assessment methods, the risk assessment of sea ice disasters on 10 jacket platforms in three sea areas in Liaodong Bay was carried out. The analysis results showed that efficient sea ice prevention strategies could largely mitigate the sea ice-induced vibration-related risks of jacket platforms in Liaodong Bay. If steady-state vibration occurs (usually in front of the vertical legged structure) or the structural fundamental frequency is high, the structural vulnerability is significantly increased and the calculated risk levels are high. The sea ice risk assessment method can be applied in the design, operation, and management of other engineering structures in sea ice areas.
Highlights
Optimized selection and safety assessment of engineering structures generally involve a long-term simulation calculation and require a certain calculation basis
This paper focuses on the risk assessment methods of sea ice disasters on jacket platforms
Sea ice disasters have three major risk sources and four structural risk modes (Zhang et al, 2015)
Summary
Optimized selection and safety assessment of engineering structures generally involve a long-term simulation calculation and require a certain calculation basis. During the ice period in 1969, the entire Bohai Sea was covered by sea ice and ice thickness even reached 60 cm During this sea ice disaster, the No 2 well’s living and drilling plat-. The fundamental studies are mainly focused on ice force calculation methods (Sanderson, 1988; Huang and Li, 2011), structural failure mode analysis (Yue et al, 2008), ice force resistance of engineering structures (Wang et al, 2012), and fatigue life calculation (Li et al, 2008; Liu et al, 2006). The previous results might be used as the basic theory for establishing a sea ice risk assessment index system and assessment method of marine structures. This paper focuses on the risk assessment methods of sea ice disasters on jacket platforms. The assessment results indicated that, except for several auxiliary platforms that are in the high risk level, all other platforms are in a healthy condition but that safety management in winter should be further enhanced
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