Journal of Cold Regions Engineering

Oil and gas exploration and production and other maritime activities are rapidly increasing in the Bohai Sea. Since sea ice occurs every winter in this region, it poses serious threats to these activities. The presence of sea ice has caused severe damages to offshore structures and losses of production in this region. Sea ice is an important marine environmental factor to be considered in the planning, design, and construction of offshore structures in the Bohai Sea and northern Yellow Sea. This paper gives an overview of ice conditions in the Bohai Sea and the northern Yellow Sea.

The sea ice model for simulating ice growth, decay, and drift in the Bohai Sea was developed based on the ice conditions in the Sea and on existing sea ice models. Both dynamic and thermodynamic processes of sea ice are incorporated into the model. The viscous-plastic constitutive law is applied to estimate the internal ice stress. The thermodynamic growth rates are determined from the effect of thermodynamic forcing from atmosphere and ocean, which are parameterized according to the heat exchanges at the air/ice, air/water, and ice/water interfaces. This model is coupled with an oceanic model and is linked to a numerical weather prediction model for forecasting ice conditions in the Bohai Sea and the northern Yellow Sea. Statistical verification was used to make an objective assessment of the model. This paper summarizes the development of the sea ice model and its application in Bohai Sea ice forecast.

Full-scale tests of ice-structure interaction were conducted on three multileg jacket platforms in Bohai Sea. Two of them were installed with ice-breaking cones on each of their four legs to reduce ice force and mitigate ice-induced vibration. The other is a three-leg platform with cylindrical piles without ice-breaking cones. Dynamic responses of these structures were recorded continuously, the variations in ice force were measured by load panels, and the failure processes of ice acting on cones and cylindrical pile were observed by video cameras. For the structure with ice-breaking cones, the ice sheet fails in bending, but the breaking frequency could coincide with the natural frequency of the structure at a fast ice speed and significant dynamic amplifying could be induced. For the cylindrical structure, two types of vibration are classed. At a high ice speed, the amplitude of structure response is uneven and ice fails with the brittle flanking model. At a medium ice speed, the event of steady-state vibration could take place. The explanation of ice-induced steady-state vibration is presented based on failure processes of ice within the ductile-brittle transition zone. Field observations reveal that sea ice can induce the offshore jacket structure to vibrate in resonance regardless of the fact that ice-breaking cones have been installed.

Sea ice monitoring and forecasting in the Bohai Sea is an operational task of the National Research Center for Marine Forecasts (NRCMEF), China. An overview of current satellite image receiving and processing systems at NRCMEF in relation to the Bohai Sea ice monitoring, including the use of NOAA-AVHRR, GMS, SAR of ERS-1, Radarsat, and SeaWiFS data, is presented.