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Fatigue case study and reliability analyses for wind turbines
Modern wind turbines are fatigue critical machines used to produce electrical power. To insure long term, reliable operation, their structure must be optimized if they are to be economically viable. The fatigue and reliability projects in Sandia`s Wind Energy Program are developing the analysis tools required to accomplish these design requirements. The first section of the paper formulates the fatigue analysis of a wind turbine using a cumulative damage technique. The second section uses reliability analysis for quantifying the uncertainties and the inherent randomness associated with turbine performance and the prediction of service lifetimes. Both research areas are highlighted with typical results
Damage measurements on the NWTC direct-drive, Variable-Speed Test Bed
The NWTC (National Wind Technology Center) Variable-Speed Test Bed turbine is a three-bladed, 10-meter, downwind machine that can be run in either fixed-speed or variable-speed mode. In the variable-speed mode, the generator torque is regulated, using a discrete-stepped load bank to maximize the turbine`s power coefficient. At rated power, a second control loop that uses blade pitch to maintain rotor speed essentially as before, i.e., using the load bank to maintain either generator power or (optionally) generator torque. In this paper, the authors will use this turbine to study the effect of variable-speed operation on blade damage. Using time-series data obtained from blade flap and edge strain gauges, the load spectrum for the turbine is developed using rainflow counting techniques. Miner`s rule is then used to determine the damage rates for variable-speed and fixed-speed operation. The results illustrate that the controller algorithm used with this turbine introduces relatively large load cycles into the blade that significantly reduce its service lifetime, while power production is only marginally increased
Breakdown of Luttinger liquid state in one-dimensional frustrated spinless fermion model
Haldane hypothesis about the universality of Luttinger liquid (LL) behavior
in conducting one-dimensional (1D) fermion systems is checked numerically for
spinless fermion model with next-nearest-neighbor interactions. It is shown
that for large enough interactions the ground state can be gapless (metallic)
due to frustrations but not be LL. The exponents of correlation functions for
this unusual conducting state are found numerically by finite-size method.Comment: 3 pages, 4 figures, RevTe
Luttinger model approach to interacting one-dimensional fermions in a harmonic trap
A model of interacting one--dimensional fermions confined to a harmonic trap
is proposed. The model is treated analytically to all orders of the coupling
constant by a method analogous to that used for the Luttinger model. As a first
application, the particle density is evaluated and the behavior of Friedel
oscillations under the influence of interactions is studied. It is found that
attractive interactions tend to suppress the Friedel oscillations while strong
repulsive interactions enhance the Friedel oscillations significantly. The
momentum distribution function and the relation of the model interaction to
realistic pair interactions are also discussed.Comment: 12 pages latex, 1 eps-figure in 1 tar file, extended Appendix, added
and corrected references, new eq. (53), corrected typos, accepted for PR
Myocyte Enhancer Factor 2 and Class II Histone Deacetylases Control a Gender-Specific Pathway of Cardioprotection Mediated by the Estrogen Receptor
Gender differences in cardiovascular disease have long been recognized and attributed to beneficial cardiovascular actions of estrogen. Class II histone deacetylases (HDACs) act as key modulators of heart disease by repressing the activity of the myocyte enhancer factor (MEF)2 transcription factor, which promotes pathological cardiac remodeling in response to stress. Although it is proposed that HDACs additionally influence nuclear receptor signaling, the effect of class II HDACs on gender differences in cardiovascular disease remains unstudied
Extended Aharonov-Bohm period analysis of strongly correlated electron systems
The `extended Aharonov-Bohm (AB) period' recently proposed by Kusakabe and
Aoki [J. Phys. Soc. Jpn (65), 2772 (1996)] is extensively studied numerically
for finite size systems of strongly correlated electrons. While the extended AB
period is the system length times the flux quantum for noninteracting systems,
we have found the existence of the boundary across which the period is halved
or another boundary into an even shorter period on the phase diagram for these
models. If we compare this result with the phase diagram predicted from the
Tomonaga-Luttinger theory, devised for low-energy physics, the halved period
(or shorter periods) has a one-to-one correspondence to the existence of the
pairing (phase separation or metal-insulator transition) in these models. We
have also found for the t-J model that the extended AB period does not change
across the integrable-nonintegrable boundary despite the totally different
level statistics.Comment: 26 pages, RevTex, 16 figures available on request from
[email protected], to be published in J. Phys. Soc. Jpn 66 No.
7(1997), We disscus the extended AB period of strongly correlated systems
more systematically by performing numerical calculation for the t-J-J' model
and the extended Hubbard model in addition to the 1D t-J model and the t-J
ladde
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