| Sea ice occurs in about10%of the world ocean’s surface, growing, melting, and drifting under the influence of solar, atmospheric, oceanic, and tidal forcing. As a formidable obstacle, sea ice poses a threat at many levels to oil and gas platform, navigation, fishery industry and scientific expedition. In sizeable basins, solid sea ice lids are statically unstable and break into fields of ice floes forming drift ice, which is able to reach to relatively high velocity and quickly change flow direction. So this makes the management of this barrier difficult.In order to lower the sea ice hazard, this thesis develops a sea-ice forecast system, which can be taken advantage of to manage sea ice for engineering activities in ice-covered regions. Fundamentally, this system is the combination of research results of physical and mechanical properties, observed dynamical characteristics, and numerical method for dynamics and thermodynamics of sea ice. Those aspects will be studied as following chapters with different ways.Firstly, the flexural strength, uniaxial compression strength and confined compression strength of sea ice as the function of stress rate and brine volume are experimentally studied around the Bohai Sea. Based on the experimental data, the statistical functions are obtained to express the relationship between the strength and brine volume and stress rate. Furthermore, two enveloping lines for the uniaxial compression strength are computed referring to the brine volume and the temperature and the influence of the confined stress on compression strength is analyzed. As a summary, the representation of sea ice strengths under the influences of brine volume and stress rate is unified.Secondly, the data of dynamic properties of sea ice are collected accurate and successive enough from the field observation with the assistance of the digital and radar images processing and analyzing system. Based on those data, the phenomenon of flow ice is deeply understood after the concentration, area, velocity, fracture of sea ice is intuitively captured. The results show the magnitude and direction of flow ice appear Gaussian distribution and Rayleigh distribution, respectively; and the joint probability distribution for both of them is also concluded. Moreover, the relationship between ice-induced vibration and sea ice dynamic properties is given depending on the collected data.Thirdly, the sea ice numerical model includes DEM (discrete element method) for dynamic part and energy-conserving method for thermodynamic part. The energy-conserving method is used to modify the computing grids after growth or melting of sea ice, which is also applicable to the change of thickness because of dynamic factor. Then the numerical dynamic performances under the vortex wind and regular boundary are given and the numerical result is also compared with analytical solution to testify the model. After that, the application of DEM for sea ice into the Bohai Sea and the comparison results with the observed data from the JZ20-2validate the numerical model.In this study, three computational approaches, finite element model, Duhamel integration of simplified structure and statistical analysis based on field data, are developed to analyze the ice-induced vibration of jacket platform with ice-breaking cones. MUQ platform located in the JZ20-2oil field of Liaodong Bay is taken as an example. The ice-induced vibration is simulated and compared with the above three approaches. Then by integrating the research achievements mentioned above, this thesis makes an employment of the sea ice forecast system for engineering activities. And the application of the system into the management of sea ice in the Liaodong bay, where a number of oil and gas platforms appear, significantly enhances the warning ability of sea ice disaster for platform structure and navigation.Finally, Summary of all the research aspects relating to this thesis is concluded and directions for future research are suggested. |
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