Modal properties and stability of  bend–twist coupled wind turbine blades

Stäblein, Alexander R.; Hansen, Morten Hartvig; Verelst, David Robert

doi:10.5194/wes-2-343-2017

Cited by 26 publications

(26 citation statements)

References 24 publications

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“…When the blades flex into and out of the wind, the rotor interacts with its own vorticity, calling the accuracy of the design assumptions into question. Additionally, structural dynamics of blades incorporating composite materials, built-in curvature and sweep, and large nonlinear deflection (including torsion and bend-twist coupling) further complicate models of the physics (69) and the assessment of crucial design aspects such as stability (70,71). In fact, although aeroelastic stability has typically not been a key design driver for rotor blades up to now, the situation may change for future highly flexible and large rotors.…”

Section: First Grand Challenge: Improved Understanding Of Atmosphericmentioning

confidence: 99%

Grand challenges in the science of wind energy

Veers

Dykes

Lantz

et al. 2019

Science

712

342

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Harvested by advanced technical systems honed over decades of research and development, wind energy has become a mainstream energy resource. However, continued innovation is needed to realize the potential of wind to serve the global demand for clean energy. Here, we outline three interdependent, cross-disciplinary grand challenges underpinning this research endeavor. The first is the need for a deeper understanding of the physics of atmospheric flow in the critical zone of plant operation. The second involves science and engineering of the largest dynamic, rotating machines in the world. The third encompasses optimization and control of fleets of wind plants working synergistically within the electricity grid. Addressing these challenges could enable wind power to provide as much as half of our global electricity needs and perhaps beyond.

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Section: First Grand Challenge: Improved Understanding Of Atmosphericmentioning

confidence: 99%

Grand challenges in the science of wind energy

Veers

Dykes

Lantz

et al. 2019

Science

712

342

View full text Add to dashboard Cite

show abstract

“…Steady operational points are defined by steady wind speed, pitch angle, and rotor angular speed. It performs modal analysis around a stationary deflected position of the blades with or without aerodynamic stiffness and damping terms . The normal (undamped) blade mode shapes were calculated in HAWCStab2 for different steady conditions, including the load effects such as centrifugal stiffening and without gravity, aerodynamic stiffness and aerodynamic damping effects.…”

Section: Methods and Implementationmentioning

confidence: 99%

Representation of wind turbine blade responses in power production load cases by linear mode shapes

Gözcü

Stolpe

2020

Wind Energy

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The wind turbine industry is designing large MW size turbines with very long blades, which exhibit large deflections during their operational life. These large deflections decrease the accuracy of linear models such as linear finite element and modal-based models, in which the structure is represented by linear mode shapes. The aim of this study is to investigate the competence of the mode shapes to represent the large blade responses in normal operation load cases. For this purpose, blade deflections are projected onto the linear modal space, swept by mode shape vectors. The projection shows the contribution of each mode and the projection error. The blade deflections are calculated by a nonlinear aero-servo-elastic solver for power production fatigue load cases with normal turbulence. The mode shapes are calculated at the steady-state deflected blade position computed at different wind speeds. Three reference turbine blades are used in the study to evaluate the effects of various blade design parameters such as length, stiffness, mass, and prebend. The results show that although the linear mode shapes can represent the flapwise and edgewise deflections accurately, axial and torsional deflections cannot be captured with good accuracy. The geometric nonlinear effects are more apparent in the latter directions.The results indicate that the blade deflections occur beyond the linear assumptions. KEYWORDSgeometric nonlinearity, structural dynamics, wind energy, wind turbine aeroelasticity, wind turbine loads INTRODUCTIONThe wind turbine design process requires a wide range of different simulations including load and stability analysis and design optimization.Although, some analyses need models with only one uncoupled turbine property such as aerodynamic and structure, others need coupled models which have couplings between the structure, the aerodynamics, and the controller. Coupled turbine analyses generally use low fidelity models because of the high computational cost and difficulties in the coupling process. For example, turbine load analyses are generally performed by the blade element momentum (BEM) 1 method for the aerodynamic part and beam solvers or reduced order models for the structural part. The structural model can be geometrically linear or nonlinear depending on the solver capabilities and available computation resources. The focus of this study is to assess the capabilities of using linear mode shapes in reduced order structural models in stability, aeroelastic, and load analysis of modern turbines.Linear modes constitute a simple and fundamental modeling alternative for most of the linear dynamic problems. Small size, cost effective, and reliable reduced order models 2-6 can be constructed by the mode shapes to calculate the structural response. It is also the key part of the stability analysis. Therefore, reduced order models are also preferred in wind turbine load and stability analysis. 7,8 Although, these models work very well for the structures with small deflections, their accuracy decreases as...

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“…The optimisation of blade twist and its resultant effects have been extensively studied for pitch-to-feather and fixed-pitch stall configurations using a number of methods [9][10][11]. In such instances, the design criteria commonly focuses on maximising the power coefficient and reducing blade vibrations and fatigue.…”

Section: Introductionmentioning

confidence: 99%

“…In such instances, the design criteria commonly focuses on maximising the power coefficient and reducing blade vibrations and fatigue. Stäblein et al [10] achieved increased platform damping, and hence, reductions in tower fore-aft moment from blade twist modifications. For fixed-stall blades, a back twist was employed (the blade twists back towards feather at the tip for a proportion of the blade's length) which resulted in the air flow remaining attached at the blade tip for higher wind speeds, thus increasing the power production capabilities of these sections of the blade [9].…”

Section: Introductionmentioning

confidence: 99%

Reducing Tower Fatigue through Blade Back Twist and Active Pitch-to-Stall Control Strategy for a Semi-Submersible Floating Offshore Wind Turbine

2019

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The necessity of producing more electricity from renewable sources has been driven predominantly by the need to prevent irreversible climate chance. Currently, industry is looking towards floating offshore wind turbine solutions to form part of their future renewable portfolio. However, wind turbine loads are often increased when mounted on a floating rather than fixed platform. Negative damping must also be avoided to prevent tower oscillations. By presenting a turbine actively pitching-to-stall, the impact on the tower fore–aft bending moment of a blade with back twist towards feather as it approaches the tip was explored, utilizing the time domain FAST v8 simulation tool. The turbine was coupled to a floating semisubmersible platform, as this type of floater suffers from increased fore–aft oscillations of the tower, and therefore could benefit from this alternative control approach. Correlation between the responses of the blade’s flapwise bending moment and the tower base’s fore–aft moment was observed with this back-twisted pitch-to-stall blade. Negative damping was also avoided by utilizing a pitch-to-stall control strategy. At 13 and 18 m/s mean turbulent winds, a 20% and 5.8% increase in the tower axial fatigue life was achieved, respectively. Overall, it was shown that the proposed approach seems to be effective in diminishing detrimental oscillations of the power output and in enhancing the tower axial fatigue life.

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Modal properties and stability of bend–twist coupled wind turbine blades

Cited by 26 publications

References 24 publications

Grand challenges in the science of wind energy

Grand challenges in the science of wind energy

Representation of wind turbine blade responses in power production load cases by linear mode shapes

Reducing Tower Fatigue through Blade Back Twist and Active Pitch-to-Stall Control Strategy for a Semi-Submersible Floating Offshore Wind Turbine

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