Journal of Ocean and Wind Energy (ISSN 2310-3604) http://www.isope.org/publications Copyright © by The International Society of Offshore and Polar Engineers Vol. 1, No. 4, November 2014, pp. 193–201 Response Analysis of a Spar-Type Floating Offshore Wind Turbine Under Atmospheric Icing Conditions Mahmoud Etemaddar Department of Marine Technology, Norwegian University of Science and Technology Trondheim, Norway Martin O. L. Hansen DTU Wind Energy, Denmark Technical University Copenhagen, Denmark Torgeir Moan Centre for Autonomous Marine Operations and Systems (AMOS) Norwegian University of Science and Technology, Trondheim, Norway One of the challenges for the development of wind energy in offshore cold-climate regions is atmospheric icing. This paper examines the effects of atmospheric icing on power production, overall performance, and extreme loads of a 5-MW spar-type floating offshore wind turbine during power production, normal and emergency rotor shutdown, extreme gusts, and survival conditions. Atmospheric icing is simulated by using the ice accretion simulation code LEWICE. A CFD method is used to estimate the blade aerodynamic degradation due to icing. The effects of icing on one, two, or three blades are compared, as are the effects of atmospheric icing on land-based and offshore wind turbines. NOMENCLATURE CFD Computational Fluid Dynamics DLC Design Load Case ECD Extreme Coherent gust with Direction change ESS Extreme Sea State EWM Extreme Wind Model FWT Floating offshore Wind Turbine LWT Land-based Wind Turbine NSS Normal Sea State NTM Normal Turbulent Model INTRODUCTION Producing wind energy in cold climates has been a challenge for wind energy development in Europe, North America, and Asia (Ronsten et al., 2012). The icing of wind instruments, such as wind vanes and anemometers, can cause uncertainty in wind power estimation during the initial planning phase of a project, or lead to an underestimation of wind speed for the startup and shutdown of wind turbines during operation. Low-temperature materials, such as low-temperature steel, lubrication oil, and electronics, are required for wind turbines in cold climates. Icing of the rotor is the primary challenge for wind turbine designers because it reduces the efficiency of the wind turbine through aerodynamic degradation and increases the load and vibration during operation. A risk of sea icing and atmospheric icing of the wind turbine exists in offshore cold-climate regions (Battisti et al., 2006), and icing and environmental safety create challenges for onshore wind turbines in cold climates (Seifert et al., 2003); therefore, the safety Received June 4, 2014; revised manuscript received by the editors September 7, 2014. The original version was submitted directly to the Journal. KEY WORDS: Offshore, floating wind turbine, atmospheric icing, CFD, extreme loads, aerodynamic degradation. of O&M personnel and other nearby personnel must be guaranteed in areas at risk of ice shedding. Potential solutions to these challenges have been developed over the last ten years. Knowledge acquired by the aviation industry has been successfully used to solve problems in wind energy production in cold climates. Ice-free anemometers and wind vanes have been successfully tested. Most manufacturers have adapted their low-temperature wind turbines for cold-climate regions. The wind turbines are equipped with anti-icing and deicing systems to prevent icing of the blades, but these alterations increase the power production costs. In addition, if the anti-icing system fails for one or three blades, the wind turbine is again subjected to icing. The problem of sea icing for both moving and stationary marine structures has been studied for many years (Sanderson, 1988). Mathematical models have been developed to calculate the static and dynamic forces from ice on offshore substructures (Mróz et al., 2008). The experience and knowledge obtained from the oil and gas industry can be directly applied to sea icing on offshore wind turbines. The current rules and standards IEC-61400-3 (IEC, 2009) and DNV OS-J101 (DNV, 2004) contain recommendations for the design of offshore wind turbine support structures with respect to ice loads. To study the effects of atmospheric icing on a wind turbine, one must first specify the atmospheric icing conditions and the regions in which a risk of icing exists. While maps have been developed to specify the regions with a high risk of icing in Europe (Ronsten, 2008), Canada, China, and other areas, there is still high uncertainty in the estimation of atmospheric icing parameters due to the complexity of the phenomenon and the lack of measurements. Ice accretion and aerodynamic degradation of the rotor are two results of atmospheric icing. The experience and knowledge gained from the aviation industry have been helpful for investigating these effects. The NASA panel code LEWICE (Wright, 1995), which has been extensively verified for aircraft, has been used by many researchers to simulate the ice accretion on wind turbine rotors. The