As offshore wind energy moves to cold regions, existence of floating ice sheet is taken as a key technological challenge for offshore wind turbine design. How to estimate dynamic ice loads exposed by wind turbine tower at the waterline remains a question. This paper aims to present a numerical model which considers non-simultaneous ice crushing failure acting on vertical structure of wind turbine tower. The ice crushing force acting at local structure nodes are calculated and summed up to derive global force. The boundary of ice sheet is updated at each time step. Validation of dynamic ice loads against model tests in the ice basin are performed. It seems that the proposed model could capture the main trend of ice- wind turbine tower interaction at the vertical slope and is helpful in assisting the initial design of wind turbine towers in cold waters.
As a renewable energy, offshore wind turbine is developing fast and widely used in the recent years. When it comes to cold regions, it may be challenged by the severe environmental impact from technical aspect. In shallow waters, bottom-fixed wind turbine is often used. Ice loads should be taken as one of important environmental impacts in addition to aerodynamic load. However, the dynamic effect of ice loads on the design of icebreaking structure of offshore wind turbine is not well known due to lack of standards and guidelines. Therefore, the challenges due to ice loads on offshore wind turbine should be investigated in depth. The turbine is operating under constant wind speed and floating freshwater ice loading, as shown in Fig.1.
Dempsey et al. (2001) and Johnston et al. (1998) found that global ice pressures were significantly lower than local ice pressures during full-scale ice crushing against structures at medium to high speed. Sanderson (1988) also indicated that global ice pressures decreased with increasing area based on different scales ranging from laboratory tests to full-scale ice-structure interactions. The reason is that the ice failure does not occur simultaneously in discrete local zones. Although crushing failure may occur over the width of structure, it is likely to concentrate in a few zones across the width due to irregular ice structure contact.