Complex Modal Analysis of Non-Modally Damped Wind Turbine Blade

2015 ◽  
Author(s):  
Xing Xing ◽  
Brian F. Feeny
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Original System ◽  
Wind Turbine Blade ◽  
Modal Damping ◽  
Complex Modes ◽  
Aeroelastic Model ◽  
Vibration Model ◽  
Out Of Plane ◽  
Effects Of Rotation

The vibration model of a wind turbine blade can be approximated as a rotating pretwisted nonsymmetric beam, with damping and gravitational and aeroelastic loading. In this work, the out-of-plane (flapwise) and in-plane (edgewise) motion are examined with simple aeroelastic damping effects. The aeroelastic model used is based on a simple quasisteady blade-element airfoil theory. The linear velocity dependent terms are isolated and incorporated into the damping, which then turns out to be generally non modal (non Caughey). The complex modes are analyzed while neglecting the effects of rotation to single out the effect that aerodynamic damping may have on the modes. The analysis is done by first discretizing the system with assumed modes, and then solving an eigenvalue problem for the state-variable description of the discretized system. The eigen modes are recombined with the assumed mode functions to approximate the modes in the original system. The analysis is performed on the National Renewable Energy Laboratory (NREL) 23-meter blade, the NREL 63-meter blade, and the Sandia 100-meter blade. The effects of nonproportional damping are seen to become more significant as the blade size increases. The results provide some experience for the validity of making modal damping assumptions in blade analyses.

Modeling and Design Method for an Adaptive Wind Turbine Blade With Out-of-Plane Twist

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Hamid Khakpour Nejadkhaki ◽  
John F. Hall
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Energy Production ◽  
Full Range ◽  
Unsteady Aerodynamics ◽  
Wind Turbine Blade ◽  
Torsional Stiffness ◽  
Angle Distribution ◽  
Modeling Framework ◽  
Out Of Plane

A modeling framework to analyze a wind turbine blade subjected to an out-of-plane transformation is presented. The framework combines aerodynamic and mechanical models to support an automated design process. The former combines the National Renewable Energy Lab (NREL) aerodyn software with a genetic algorithm solver. It defines the theoretical twist angle distribution (TAD) as a function of wind speed. The procedure is repeated for a series of points that form a discrete range of wind speeds. This step establishes the full range of blade transformations. The associated theoretical TAD geometry is subsequently passed to the mechanical model. It creates the TAD geometry in the context of a novel wind turbine blade concept. The blade sections are assumed to be made by additive manufacturing, which enables tunable stiffness. An optimization problem minimizes the difference between the practical and theoretical TAD over the full range of transformations. It does so by selecting the actuator locations and the torsional stiffness ratios of consecutive segments. In the final step, the blade free shape (undeformed position) is found. The model and design support out-of-plane twisting, which can increase energy production and mitigate fatigue loads. The proposed framework is demonstrated through a case study based on energy production. It employs data acquired from the NREL Unsteady Aerodynamics Experiment. A set of blade transformations required to improve the efficiency of a fixed-speed system is examined. The results show up to 3.7% and 2.9% increases in the efficiency at cut-in and rated speeds, respectively.

Flutter Limit Investigation for a Horizontal Axis Wind Turbine Blade

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Mennatullah M. Abdel Hafeez ◽  
Ayman A. El-Badawy
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Turbine Blade ◽  
Nonlinear Partial Differential Equations ◽  
Stability Limit ◽  
Wind Turbine Blade ◽  
Horizontal Axis ◽  
Horizontal Axis Wind Turbine ◽  
Centrifugal Stiffening ◽  
Aeroelastic Model

This work presents a new aeroelastic model that governs the extensional, chordwise, flapwise, and torsional vibrations of an isolated horizontal axis wind turbine blade. The model accounts for the sectional offsets between the shear, aerodynamic, and mass centers. The centrifugal stiffening effects are also accounted for by including nonlinear strains based on an ordering scheme that retains terms up to second-order. Aerodynamic loading is derived based on a modified Theodorsen's theory adapted to account for the blade rotational motion. A set of four coupled nonlinear partial differential equations are derived using the Hamiltonian approach that are then linearized about the steady-state extensional position. The finite element method (FEM) is then employed to spatially discretize the resulting equations with the aim of obtaining an approximate solution to the blade's dynamic response, utilizing state space techniques and complex modal analysis. Investigation of the blade's flutter stability limit is carried out. Effects of parameters such as wind speed and blade sectional offsets on the flutter limit and dynamic response are also investigated.

Multi-axial large-scale testing of a 34 m wind turbine blade section to evaluate out-of-plane deformations of double-curved trailing edge sandwich panels within the transition zone

2020 ◽  
pp. 0309524X2097840
Author(s):  
Jacob P Waldbjørn ◽  
Andrei Buliga ◽  
Christian Berggreen ◽  
Find Moelholt Jensen
Keyword(s):  
Wind Turbine ◽  
Transition Zone ◽  
Turbine Blade ◽  
Plane Deformation ◽  
Wind Turbine Blade ◽  
Transverse Cracks ◽  
Trailing Edge ◽  
Root Section ◽  
Out Of Plane ◽  
Plane Deformations

Transverse cracks in the double curved trailing edge panels within the transition zone are among one of the increasingly encountered in-field damages found on wind turbine blades today. Believed to be root cause of these transverse cracks, are the out-of-plane deformation of the double curved trailing edge pressure side panels. These deformations are evaluated on the inner 15 m section of a 34 m wind turbine blade – referred to here as the root section. Through a parametrical study the free end of the root section is loaded in the quasi-static regime comprising edgewise loading (Fy) and torsional moment (Mz) around the longitudinal axis of the blade. The root section is through a multi-scale numerical analysis found to exhibit representative structural behavior in terms of out-of-plane deformations within the area of interest. A combination between Fy and Mz are found to generate the highest peak-to-peak out-of-plane deformation of 15.9 mm.

Noise analysis of the wind turbine blade

2013 ◽  
Author(s):  
Gwochung Tsai ◽  
Yita Wang ◽  
Yuhchung Hu ◽  
Jaching Jiang
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Noise Analysis ◽  
Wind Turbine Blade

DYNAMIC ANALYSIS OF THE FLUID FLOW OVER A WIND TURBINE BLADE

2017 ◽  
Author(s):  
Aldemir Ap Cavalini Jr ◽  
João Marcelo Vedovoto ◽  
Renata Rocha
Keyword(s):  
Fluid Flow ◽  
Dynamic Analysis ◽  
Wind Turbine ◽  
Turbine Blade ◽  
Wind Turbine Blade
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