Aerodynamics modelling of floating offshore wind turbines

An unsteady Blade Element Momentum (uBEM) method is presented for the analysis of Floating Offshore Wind Turbines (FOWTs).FOWTs allow wind turbines to be placed in deeper waters with stronger and more consistent winds.However, the floating platform motions result in motions of the wind turbine not found in fixed-bottom wind turbines, thus the widely-used blade element momentum (BEM) method, a static analysis method, cannot be used to calculate wind turbine blade forces.Different unsteady aerodynamic phenomena associated with FOWTs are analysed, with corrective models developed for an accurate analysis of FOWT aerodynamics.The NREL 5MW virtual wind turbine was studied in axial flow and sinusoidal surge motions at different frequencies and amplitudes, using full-3D computational fluid dynamics simulations.The effects studied include the unsteady airfoil effect, stall delay effect, tip-loss, and transient wake states.The unsteady airfoil effect is studied based on experimental data from the Ohio State University, and a modified Beddoes-Leishman model is presented based on airfoil shape parameters and an optimisation-based methodology.The stall-delay effect was accounted for using the Du & Selig model, and a novel methodology for real-time stall delay incorporating the unsteady airfoil effect is presented.A novel correction and modelling methodology is presented for tip-losses, through a correction to Glauert's implementation of the Prandtl tip-loss factor, which incorporates changes in tip speed ratio as well as changes in wake state.Buhl's version of the Glauert correction for the turbulent wake state was used as a basis to model the propeller and propeller brake states of the wind turbine, which are rare for fixed-bottom wind turbines but can be expected to occur periodically for FOWTs.The dynamic wake model of Øye is optimised to take into account the level of unsteadiness found in FOWTs and work in conjunction with other unsteady models.Finally, these models are incorporated into the uBEM method and a FOWT aerodynamics analysis tool is created with low computational time, and more realistic force predictions.Future studies can extend these methodologies to more motion degrees of freedom.i The 52nd Dai Al Mutlaq of the Dawoodi Bohra Community, my spiritual father, Dr Syedna Mohammed Burhanuddin (RA), had always taught me that knowledge is the true path to salvation, and urged his followers to excel in their own fields.He has been a constant source of blessings, strength and inspiration.His successor and beloved son, the 53rd Dai Al Mutlaq, Syedna Mufaddal Saifuddin (TUS) has taught me to aim for the highest peak, and to get there through perspiration, and that the highest calling for Man is the pursuit of knowledge and constant innovation.His humility has been a great example and inspiration.I would like to thank my supervisor Associate Professor Ng Yin Kwee, who still hasnt stopped believing in me and always has an encouraging word to keep me going, my co-supervisor Dr Narasimalu Srikanth who always pushed a me little bit harder to achieve more, and the Energy Research Institute @ NTU (ERI@N) for all the opportunities.I would like to thank the Economic Development Board (EDB), who have given the opportunity for this industrial postgraduate programme.I would like to especially thank the Lloyds Register Global Technology Centre, Singapore, especially Dr Johan Gullman-Strand, Mr Anand Bahuguni and Mr Krishna Sivalingam for their advice and support.Peter Davies has provided a lot of input and advice for the direction of this research.Janaab Badrul Jamali Bhaisaheb Najmuddin has been a source of guidance and wisdom, and his advice had led me to embark on this PhD.My family has put up with all my shenanigans.Mum and Dad, always with a word of support or a listening ear, my brother Hozefa, sister-in-law Umme Hani and niece, Insiyah, who always manages to cheer me up after a long day.My wife, Fatema has only observed my life as a PhD student, since we were married just before I embarked on this journey.She has been a constant rock, doing everything she could to make sure I got through.In my final year of research, she gave me the greatest gift of all: our daughter Ruqaiyyah.Ruqaiyyah, thank you for coming into my life, and making it so special.You are my world.