Assessment of Research Needs for Wind Turbine Rotor Materials Technology (1991) / Chapter Skim
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2 STRUCTURAL LOADING CHARACTERISTICS
2 STRUCTURAL LOADING CHARACTERISTICS
Pages 25-34
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From page 25... ...
Similarly, even in the absence of an external energy source, aerostatic tailoring itself uses a form of control law to modify the behavior of a structure. In addition to being a form of passive control, structural tailoring provides a method to optimize the performance of actively controlled structures.
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From page 26... ...
Various wind turbine configurations have been studied and tried, such as horizontal axis wind turbines (HAWTs} versus vertical axis wind turbines (VAWTs) , stall- versus pitch-controlled turbines, fixed- versus free-yaw turbines, up- versus down-wind rotors, constant versus variable rpm, high~olidity slow running versus low-solidity fast running, stiff versus flexible, and different manners of overspeed protection.
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From page 27... ...
Part of the fatigue problem with wind turbine rotors is manifested an leading and trailing edge cracks that form as the blades undergo continual use. Research has shown that, because early design efforts focused almost entirely on blade flapping moments and gave inadequate attention to inplane {chordwise or lead-lag)
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From page 28... ...
The new designs did not come without cost, however, and any significant change in the way wind turbine" are designed will likely require years of research. Helicopter rotor blades spin at a relatively high angular speed and, although flexible, are effectively stiffened by centrifugal forcer.
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From page 29... ...
Also, with blades made of isotropic materials, simple engineering beam theories will usually suffice in the determination of beam stiffness. Except for torsional stiffness, the stiffness constants are simply integrals of modulus-weighted geometric quantities over the cross section.
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From page 30... ...
analytical warping; thin-walled; uniaxial "tree" Worndle - uniaxial stress Germany 2-D finite field; no re- element strained warping section plane by finite elements in order to obtain the properties. (The term quasi-three-dimensional indicates that the axial coordinate is handled analytically.)
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From page 31... ...
Flap bending/twiat coupling could provide small outboard blade angle changes to help a constant-rpm machine retain optimum efficiency over the low wind range, but variable rpm provides a much more effective and versatile way of doing shim, and it in on the near horizon. Using extension-twi~t coupling to provide overspeed limitation for fixed-pitch rotors may be the most potent near-term use of elastic tailoring, as it could simplify rotor construction while removing a lot of rotor cost and also be much more reliable than current mechanical latch mechanisms.
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From page 32... ...
To accomplish this in an accurate and computationally efficient manner will require additional research. The resulting tools may likely be in the spirit of Rehfield/Nixon but with additional wind turbine parameters included, such as initial curvature, initial twist, and taper and with additional attention given to obtaining shear stiffness more accurately and accounting for restrained warping.
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From page 33... ...
1989. Finite Element Based Modal Analysis of Helicopter Rotor Blade-.
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From page 34... ...
1985. Design Analysis Methodology for Composite Rotor Blades.
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