Vibration control of horizontal axis offshore wind turbine blade using SMA stiffener

Modern multi-megawatt wind turbines have large flexible blades that often exhibit significant vibration when exposed to turbulent wind. The present study proposes longitudinal stiffening of blades to address this issue using tendon made of shape memory alloy. A reduced order model of the combined system is developed that incorporates blade stiffening. The nonlinear material behavior of the stiffener is modeled by combining the principle of thermodynamics with the constitutive model as proposed in the literature. Thus, super-elastic effects are utilized in active mode (i.e. using Jule heating with the help of current flow) to apply actuation force that opposes blade deformation. Three-dimensional wind field passing through the rotor plane is simulated using TurbSim package freely available from National Renewable Energy Laboratory, USA. Aerodynamic loads are computed using modified Blade Element Momentum theory and wave loads are simulated using Morison's equation where wave time histories are simulated from the JONSWAP spectrum. Using these loads as input, the response of a benchmark wind turbine is simulated to show the performance of the proposed control strategy. Numerical results presented in this paper clearly demonstrate the efficiency and advantage of the SMA based stiffener to improve the vibration characteristics of the large turbine blades.