32,894 research outputs found
A review of resonance response in large horizontal-axis wind turbines
Field operation of the Mod-0 and Mod-1 wind turbines is described. Operational experience shows that 1 per rev excitation exists in the drive train, high aerodynamic damping prevents resonance response of the blade flatwise modes, and teetering the hub substantially reduces the chordwise blade response to odd harmonic excitation. These results can be used by designer as a guide to system frequency placement. In addition it is found that present analytical techniques can accurately predict wind turbine natural frequencies
Well-posed Bayesian inverse problems and heavy-tailed stable quasi-Banach space priors
This article extends the framework of Bayesian inverse problems in
infinite-dimensional parameter spaces, as advocated by Stuart (Acta Numer.
19:451--559, 2010) and others, to the case of a heavy-tailed prior measure in
the family of stable distributions, such as an infinite-dimensional Cauchy
distribution, for which polynomial moments are infinite or undefined. It is
shown that analogues of the Karhunen--Lo\`eve expansion for square-integrable
random variables can be used to sample such measures on quasi-Banach spaces.
Furthermore, under weaker regularity assumptions than those used to date, the
Bayesian posterior measure is shown to depend Lipschitz continuously in the
Hellinger metric upon perturbations of the misfit function and observed data.Comment: To appear in Inverse Problems and Imaging. This preprint differs from
the final published version in layout and typographical detail
Well-posedness of Bayesian inverse problems in quasi-Banach spaces with stable priors
The Bayesian perspective on inverse problems has attracted much mathematical
attention in recent years. Particular attention has been paid to Bayesian
inverse problems (BIPs) in which the parameter to be inferred lies in an
infinite-dimensional space, a typical example being a scalar or tensor field
coupled to some observed data via an ODE or PDE. This article gives an
introduction to the framework of well-posed BIPs in infinite-dimensional
parameter spaces, as advocated by Stuart (Acta Numer. 19:451--559, 2010) and
others. This framework has the advantage of ensuring uniformly well-posed
inference problems independently of the finite-dimensional discretisation used
for numerical solution. Recently, this framework has been extended to the case
of a heavy-tailed prior measure in the family of stable distributions, such as
an infinite-dimensional Cauchy distribution, for which polynomial moments are
infinite or undefined. It is shown that analogues of the Karhunen--Lo\`eve
expansion for square-integrable random variables can be used to sample such
measures on quasi-Banach spaces. Furthermore, under weaker regularity
assumptions than those used to date, the Bayesian posterior measure is shown to
depend Lipschitz continuously in the Hellinger and total variation metrics upon
perturbations of the misfit function and observed data.Comment: To appear in the proceedings of the 88th Annual Meeting of the
International Association of Applied Mathematics and Mechanics (GAMM), Weimar
2017. This preprint differs from the final published version in pagination
and typographical detai
Crack growth measured on flat and curved surfaces at cryogenic temperatures
Multiple element continuity gage measures plane stress crack growth plus surface crack growth under plane strain conditions. The gage measures flat and curved surfaces and operates at cryogenic temperatures
Evaluation of a Stirling engine heater bypass with the NASA Lewis nodal-analysis performance code
In support of the U.S. Department of Energy's Stirling Engine Highway Vehicle Systems program, the NASA Lewis Research Center investigated whether bypassing the P-40 Stirling engine heater during regenerative cooling would improve engine performance. The Lewis nodal-analysis Stirling engine computer simulation was used for this investigation. Results for the heater-bypass concept showed no significant improvement in the indicated thermal efficiency for the P-40 Stirling engine operating at full-power and part-power conditions. Optimizing the heater tube length produced a small increase in the indicated thermal efficiency with the heater-bypass concept
Simplified modeling for wind turbine modal analysis using NASTRAN
A detailed finite element model of the MOD-0 wind turbine tower was reduced to six beam elements (stick model). The method used to calculate the properties of the beam elements in the stick model was explained and the accuracy of the stick model in predicting natural frequencies and mode shapes was examined. Computer times were compared and several applications where the stick model was used are described. From results obtained from the MOD-0 tower it is concluded that a tower of this type can be modeled as a simple cantilever beam for modal analysis. However, this model should be limited to tower torsional modes and tower bending modes where the mode shape resembles a cantilever beam first bending mode shape
Structural qualification testing and operational loading on a fiberglass rotor blade for the Mod-OA wind turbine
Fatigue tests were performed on full- and half-scale root end sections, first to qualify the root retention design, and second to induce failure. Test methodology and results are presented. Two operational blades were proof tested to design limit load to ascertain buckling resistance. Measurements of natural frequency, damping ratio, and deflection under load made on the operational blades are documented. The tests showed that all structural design requirements were met or exceeded. Blade loads measured during 3000 hr of field operation were close to those expected. The measured loads validated the loads used in the fatigue tests and gave high confidence in the ability of the blades to achieve design life
Effect of vortex generators on the power conversion performance and structural dynamic loads of the Mod-2 wind turbine
Applying vortex generators from 20 to 100 percent span of the Mod-2 rotor resulted in a projected increase in annual energy capture of 20 percent and reduced the wind speed at which rated power is reached by nearly 3 m/sec. Application of vortex generators from 20 to 70 percent span, the fixed portion of the Mod-2 rotor, resulted in a projected increase in annual energy capture of about half this. This improved performance came at the cost of a small increase in cyclic blade loads in below rated power conditions. Cyclic blade loads were found to correlate well with the change in wind speed during one rotor revolution
Standard model explanation of a CDF dijet excess in Wjj
We demonstrate the recent observation of a peak in the dijet invariant mass
of the Wjj signal observed by the CDF Collaboration can be explained as the
same upward fluctuation observed by CDF in single-top-quark production. In
general, both t-channel and s-channel single-top-quark production produce
kinematically induced peaks in the dijet spectrum. Since CDF used a Monte Carlo
simulation to subtract the single-top backgrounds instead of data, a peak in
the dijet spectrum is expected. The D0 Collaboration has a small upward
fluctuation in their published t-channel data; and hence we predict they would
see at most a small peak in the dijet invariant mass spectrum of Wjj if they
follow the same procedure as CDF.Comment: 3 pg., 2 figs, revtex, minor clarifications, to appear in Phys. Rev.
Relationship science and interventions: Where we are and where we are going
Relationship distress and divorce often have profound effects on couples and their children. Relationship science has long sought to prevent and alleviate relationship distress; this chapter is a summary of many important recent developments in the field. Ongoing challenges in studying and assisting intimate relationships are also discussed
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