Towards gradient-based design optimization of fully-flexible tension-leg platform wind turbines

Novel technologies and design methods are needed to enable cost-competitive development of wind turbines with floating foundations. Tension-leg platforms have an established history in the oil and gas industry, though the complexity in coupled analysis of floating wind turbines generally has limited the exploration of novel concepts. The application of efficient, gradient-based optimization models has shown promise to overcome these difficulties and develop innovative designs. The core of this design optimization approach is an efficient coupled aero-hydro-servo-elastic dynamic model for a generic tension-leg platform wind turbine design, referred to as TLPOpt. The equation of motion is defined based on the generalized elastic mode shapes of the combined main column and tower. TLPOpt is implemented in the OpenMDAO framework for optimization, and analytical derivatives are defined throughout to increase efficiency. Stochastic dynamic analysis in the frequency-domain allows for efficient assessment of fatigue and extreme conditions. Verification steps show good agreement between the linearized analysis and higher-fidelity analysis tools. Early optimization studies suggest the optimization is able to improve upon a reference design, though more realistic constraint and objective functions are needed to draw further conclusions.