Safety Assessment Of Offshore Substation Platform In Ice Zone

With the development of wind energy in the world, offshore wind farms are planning and constructing in large scale in china. The installed power capacity of a wind farm have reached to 200-300 MW. According to international standard, for the offshore wind farm that the distance from the coast is more than 15 km, an offshore substation is proposed to build.Offshore substation collecting and transforming electric power is the control center of offshore wind farms. An offshore substation platform is subjected to environmental loadings due to wave, current and wind. For the offshore structure located in a special region, earthquake and ice have to be taken into account. In this thesis, the static and dynamic responses, fatigue assessment and the plastic collapse of an actual offshore substation are studied. The contents of the research include:(1) Using SACS, a three-dimensional (3D) numerical model is established. Combined with meteorological data and marine hydrological data, hydrodynamic loads induced by wind, wave and current are calculated. The influences of tide, marine growth and seabed scouring are taken into account as well. The control case and control load direction of offshore substation are determined.(2) The influence of earthquake on the performance of offshore substation platform is studied. Using the methods such as response spectrum and dynamic time-history, sesimic response of offshore substation platform is computed, and the safety is evaluated.(3) Based on the mechanism of self-excited vibration induced by dynamic ice force, the self-excited vibration condition of the offshore substation subjected to ice is obtained. Based on the model test in the State Key Laboratory of Coastal and Offshore Engineering, the histories of ice forces applied to the four legs are measured. Considering three different ice attacking angles including 0°,90° and-60?, the dynamic response of offshore substation subjected to ice is calculated.(4) On the base of the probability distribution of wave direction, wave height and ice loading, omnidirectional fatigue analysis of the offshore substation platform is conducted. The fatigue life of the tubular joints of the jacket structure and pile foundation is evaluated in light of theory of linear cumulative damage.(5) The collapse analysis of offshore substation platform is performed in SACS. The safety reserve coefficients under extreme ice load and earthquake are obtained, respectively.