Search

Multi-Megawatt wind turbines have long, slender and heavy blades that can undergo extremely wind loadings. Aeroelastic stability of wind turbine blades is of great importance in both power production and load carrying capacity of structure. This paper investigates the aeroelastic stability of wind turbine blades modeled as thin walled composite box beam, utilizing unsteady incompressible aerodynamics. The structural model incorporates a number of non-classical effects such as transverse shear, warping inhibition, non-uniform torsional model and rotary inertia. The unsteady incompressible aerodynamics based on Wagner’s function is used to determine the aerodynamic loads. Governing differential equations of motion are obtained using Hamilton’s principle and solved using extended Galerkin’s method. The results obtained in this paper, related to clarification of the effects of angular velocity and wind speed on the aeroelastic instability boundaries of the thin-walled composite beams. The obtained results are expected to be useful toward obtaining better predictions of the aeroelastic behavior of composite rotating blades.

Abstract: Axial–torsional vibrations of rotating pretwisted thin-walled composite box beams exhibiting primary and secondary warping are investigated. Considering the nonlinear strain–displacement relations, the coupled nonlinear axial–torsional equations of motion are derived using Hamilton's principle. Ignoring the axial inertia term leads to differential equation of motion in terms of elastic torsion in the case of axially immovable beams. Centrifugal load in the presence of material anisotropy and pretwist angle leads to an induced static torque. The nonlinear equation should be linearized about the corresponding equilibrium state to obtain the linear differential equation of motion. Extended Galerkin's method is utilized to achieve the proper eigenvalue problem. The results obtained in this paper seek to clarify the individual and collective effects of axial loading, pretwist, stagger and fiber angles on the torsional behavior of the non-uniform thin-walled composite blades. The results are compared to available analytical and experimental results in the literature which reveals excellent agreements. The outcomes of this study are expected to offer better predictions of the dynamic behavior of this kind of structures in general, and in design of rotor blades of turbo-machinery, in particular. [Copyright &y& Elsevier]

In this work, the structural response of thin-walled composite beams with pretwist angle is investigated by using a mixed beam approach that combines the stiffness and flexibility methods in a unified manner. The Reissner's semi-complimentary energy functional is used to derive the stiffness matrix that approximates the beam in an Euler–Bernoulli level for extension and bending and Vlasov level for torsion. The bending and torsion-related warpings induced by the pretwist effects are derived in a closed form. The developed theory is validated with available literature and detailed finite element structural analysis results using the MSC/NASTRAN. Pretwisted composite beams with rectangular solid and thin-walled box sections are illustrated to validate the current approach. Acceptable correlation has been achieved for cases considered in this study. The effects of pretwist and fiber orientation angles on the static behavior of pretwisted composite beams are also studied. [ABSTRACT FROM AUTHOR]

• Nonlinear dynamics and internal resonance are studied for pretwisted rotating plate. • Governing equations of motion are established for pretwisted rotating cantilever plate. • Method of multiple scales is applied to obtain averaged equations. • Pretwisted rotating blade exhibits hardening and softening nonlinear behaviors. • Periodic, quasi-periodic and chaotic vibrations exist. This paper investigates the complex nonlinear vibrations and internal resonance of the rotating blade subjected to the aerodynamic force, which is simplified to a pretwisted rotating cantilever rectangular plate with the varying cross-section and varying rotating speed. Considering the effects of the cross-section warping, pretwisted and presetting angles, the nonlinear partial differential governing equations of motion are established based on the third-order shear deformation theory, von Karman large deformation theory and Hamilton principle. Two-degree-of-freedom nonlinear ordinary differential equations of motion are obtained by using Galerkin method. The method of multiple scales is applied to obtain the averaged equations under the case of the primary parametric resonance-1/2 subharmonic resonance and 1:2 internal resonance. Numerical simulations are performed to portray the amplitude-frequency response and amplitude-force response curves, bifurcations and chaotic dynamics of the pretwisted rotating cantilever rectangular plate by discussing the influences of the aerodynamic force and rotating speed perturbation. The bifurcation diagrams, maximum Lyapunov exponents, phase portraits, waveforms and Poincare maps are utilized to illustrate the complex nonlinear vibrations of the pretwisted rotating cantilever rectangular plate. [ABSTRACT FROM AUTHOR]

Power loss due to the aeroelastic effect of the blade is becoming an important problem of large-scale blade design. Prior work has already employed the pretwisting method to deal with this problem and obtained some good results at reference wind speed. The aim of this study was to compensate for the power loss for all of the wind speeds by using the pretwisting method. Therefore, we developed an aeroelastic coupling optimization model, which takes the pretwist angles along the blade as free variables, the maximum AEP (annual energy production) as the optimal object, and the smooth of the twist distribution as one of the constraint conditions. In this optimization model, a PSO (particle swarm optimization) algorithm is used and combined with the BEM-3DFEM (blade element momentum—three-dimensional finite element method) model. Then, the optimization model was compared with an iteration method, which was recently developed by another study and can well compensate the power loss at reference wind speed. By a design test, we found that the power loss can be reduced by pretwisting the origin blade, whether using the optimization model or the iteration method. Moreover, the optimization model has better ability than the iteration method to compensate the power loss with lower thrust coefficient while keeping the twist distribution smooth. [ABSTRACT FROM AUTHOR]