Sharif Digital Repository

In order to evaluate the dynamic behavior of floating offshore wind turbines, the authors consider two approaches. A numerical method is used to investigate Tension Leg Platform (TLP) offshore wind turbine response behavior under a parked condition. This code considers nonlinearities due to changes in the tension of tethers. The off-diagonal components of stiffness, damping and mass matrices are considered to calculate coupling. This code solves the nonlinear equation of motion at each time step. However, in order to validate the data generated by the code, a scaled-down model was fully tested in the marine laboratory. The importance of these series of experiments is due to the fact that... 

The first notable megawatt class wind turbine, which was the pioneer of improvement in the blade performance in large wind turbines, appeared in Vermont. Nowadays, modern wind turbines are using blades with multi-airfoils at different sections. In this study, in order to indicate the best airfoil profile for the optimum performance in different sections of a blade, five popular airfoils, including S8xx, FFA and AH series, were studied. On the large-scale profile, shear stress transport K–ω model was applied for the simulation of horizontal axis wind turbines for different wind speeds. The aerodynamic simulation was accomplished using computational fluid dynamic method, which in turn is based... 

The present study numerically investigates the feasibility of using multiple dielectric barrier discharge (multi-DBD) plasma actuators as a novel approach for active flow control over a large horizontal axis wind turbine rotor. The National Renewable Energy Laboratory 5 MW offshore wind turbine is used as the baseline case. This turbine uses pitch control system to adjust the generated power above its rated wind speeds, but at lower speeds, this system remains inactive. In this paper, the operational condition speed is considered lower than the rated wind speed. The mathematical electro-static model is implemented to simulate the effects of plasma actuator on the external flow and the... 

Limited fossil resources, daily increasing rate of demand for energy and the environmental pollution fact have made people revert to renewable sources of energy as a solution. One type of renewable energy is offshore wind energy which has high potential without any sound and visual noises. Recently, a lot of researchers have carried out on the issue of offshore wind turbine. Because of incapability of most of software programs to simulate gyroscopic effect of rotating rotors, in this articles a significant effort has been made to fabricate and test an offshore wind turbine under different rotor rotation velocities and different heading angle of wind so as to obtain the effects of these... 

In this paper, the aeroelastic analysis of a large scale wind turbine rotor is performed with the aim of studying transient performance of turbine in extreme wind conditions, such as wind gusts and rapid yaw changes. The effect of the presence and/or lack of blade pitch control system on output power, rotor thrust, and blade deformation in sudden change of wind speed are investigated. The NREL 5 MW offshore wind turbine is used as the baseline case. In this regard, the modal approach is implemented for modeling the flexible blade structure with tension, bending and torsion degrees of freedom. The unsteady vortex lattice method is employed to obtain the aerodynamic loads. Moreover, the... 

Highly dynamic nature of the applied loads on flexible and lightly damped offshore wind turbine (OWT) foundations affects the lifetime and serviceability of the system. In this study, the excessive vibration responses of OWTs are minimized using tuned mass dampers (TMD) and tuned liquid column dampers (TLCD). Due to high efficiency of TLCDs and TMDs for certain loading conditions, a combined TLCD-TMD is also utilized to improve the overall performance in a wide range of loading conditions. First, a parametric study was performed that highlights the sensitivity of these structural control devices. The effect of two devices on fixed offshore wind turbine foundations for the benchmark 5 MW NREL... 

Floating wind turbines are subjected to highly dynamic and complicated environmental conditions leading to significant platform motions and structural vibrations during operation and survival conditions. These motions and vibrations alter the induced loading characteristics; and consequently, affect the dynamic behavior of the system. In order to better understand the influence of such motions and structural vibrations, herein elastic structural disturbance of tower, on the system behavior, the spectral and statistical characteristics of a floating wind turbine dynamic responses under operational and survival conditions are fully explored using a fully coupled... 

In this research, to overcome the challenging problem of the vibration suppression in the wind turbine blade, an active robust adaptive finite-time model reference controller is introduced. First, edgewise vibrations of the wind turbine blade, with consideration of the platform heave displacements, is modeled by Euler-Bernoulli beam theory. Then, the appropriate adaptation laws and control laws are introduced to compensate the uncertainties and guarantee the convergence to the desired reference model. The robustness and convergence of the designed adaptation and control laws are mathematically proved via finite-time Lyapunov theory. Performance of the designed robust adaptive finite-time... 

In this article, the effects of the changes in the mass of the floating wind turbine (as a multi-body system) on its nonlinear vertical vibrations are investigated. The fluctuations of the hydrodynamic added mass of the floating platform and the mass of the vibration absorbers, which added to the structure to mitigate the lateral vibrations, change the mass and consequently the dynamics of the vertical vibrations. In this regard, first, the governing equations of the vertical vibrations of the floating wind turbine are derived. The FAST code is used to validate the proposed model of the dynamics of the vertical vibrations through numerical simulations. Then, derived equations are solved...