wind turbulence
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2022 ◽  
Author(s):  
Xiaodong Zhang ◽  
Anand Natarajan

Abstract. Uncertainty quantification is a necessary step in wind turbine design due to the random nature of the environmental loads, through which the uncertainty of structural loads and responses under specific situations can be quantified. Specifically, wind turbulence has a significant impact on the extreme and fatigue design envelope of the wind turbine. The wind parameters (mean and standard deviation of 10-minute wind speed) are usually not independent, and it will lead to biased results for structural reliability or uncertainty quantification assuming the wind parameters are independent. A proper probabilistic model should be established to model the correlation among wind parameters. Compared to univariate distributions, theoretical multivariate distributions are limited and not flexible enough to model the wind parameters from different sites or direction sectors. Copula-based models are used often for correlation description, but existing parametric copulas may not model the correlation among wind parameters well due to limitations of the copula structures. The Gaussian mixture model is widely applied for density estimation and clustering in many domains, but limited studies were conducted in wind energy and few used it for density estimation of wind parameters. In this paper, the Gaussian mixture model is used to model the joint distribution of mean and standard deviation of 10-minute wind speed, which is calculated from 15 years of wind measurement time series data. As a comparison, the Nataf transformation (Gaussian copula) and Gumbel copula are compared with the Gaussian mixture model in terms of the estimated marginal distributions and conditional distributions. The Gaussian mixture model is then adopted to estimate the extreme wind turbulence, which could be taken as an input to design loads used in the ultimate design limit state of turbine structures. The wind turbulence associated with a 50-year return period computed from the Gaussian mixture model is compared with what is utilized in the design of wind turbines as given in the IEC 61400-1.


2022 ◽  
Vol 924 (2) ◽  
pp. 92
Author(s):  
G. Q. Zhao ◽  
Y. Lin ◽  
X. Y. Wang ◽  
H. Q. Feng ◽  
D. J. Wu ◽  
...  

Abstract Based on the Parker Solar Probe mission, this paper presents the observations of two correlations in solar wind turbulence near the Sun for the first time, demonstrating the clear existence of the following two correlations. One is positive correlation between the proton temperature and turbulent magnetic energy density. The other is negative correlation between the spectral index and magnetic helicity. It is found that the former correlation has a maximum correlation coefficient (CC) at the wavenumber k ρ p ≃ 0.5 (ρ p being the proton thermal gyroradius), and the latter correlation has a maximum absolute value of CC at k ρ p ≃ 1.8. In addition, investigations based on 11 yr of Wind observations reveal that the dimensionless wavenumbers (k ρ p ) corresponding to the maximum (absolute) values of CC remain nearly the same for different data sets. These results tend to suggest that the two correlations enhanced near the proton gyroradius scale would be a common feature of solar wind turbulence.


2022 ◽  
Vol 924 (2) ◽  
pp. 53
Author(s):  
M. Terres ◽  
Gang Li

Abstract At scales much larger than the ion inertial scale and the gyroradius of thermal protons, the magnetohydrodynamic (MHD) theory is well equipped to describe the nature of solar wind turbulence. The turbulent spectrum itself is defined by a power law manifesting the energy cascading process. A break in the turbulence spectrum develops near-ion scales, signaling the onset of energy dissipation. The exact mechanism for the spectral break is still a matter of debate. In this work, we use the 20 Hz Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) magnetic field data during four planetary flybys at different heliocentric distances to examine the nature of the spectral break in the solar wind. We relate the spectral break frequencies of the solar wind MHD turbulence, found in the range of 0.3–0.7 Hz, with the well-known characteristic spectral bump at frequencies ∼1 Hz upstream of planetary bow shocks. Spectral breaks and spectral bumps during three planetary flybys are identified from the MESSENGER observations, with heliocentric distances in the range of 0.3–0.7 au. The MESSENGER observations are complemented by one Magnetospheric Multiscale observation made at 1 au. We find that the ratio of the spectral bump frequency to the spectral break frequency appears to be r- and B-independent. From this, we postulate that the wavenumber of the spectral break and the frequency of the spectral bump have the same dependence on the magnetic field strength ∣B∣. The implication of our work on the nature of the break scale is discussed.


2022 ◽  
Vol 924 (2) ◽  
pp. L21
Author(s):  
J. Zhang ◽  
S. Y. Huang ◽  
J. S. He ◽  
T. Y. Wang ◽  
Z. G. Yuan ◽  
...  

Abstract We utilize the data from the Parker Solar Probe mission at its first perihelion to investigate the three-dimensional (3D) anisotropies and scalings of solar wind turbulence for the total, perpendicular, and parallel magnetic-field fluctuations at kinetic scales in the inner heliosphere. By calculating the five-point second-order structure functions, we find that the three characteristic lengths of turbulence eddies for the total and the perpendicular magnetic-field fluctuations in the local reference frame ( L ˆ ⊥ , l ˆ ⊥ , l ˆ ∣ ∣ ) defined with respect to the local mean magnetic field B local feature as l ∣∣ > L ⊥ > l ⊥ in both the transition range and the ion-to-electron scales, but l ∣∣ > L ⊥ ≈ l ⊥ for the parallel magnetic-field fluctuations. For the total magnetic-field fluctuations, the wave-vector anisotropy scalings are characterized by l ∣ ∣ ∝ l ⊥ 0.78 and L ⊥ ∝ l ⊥ 1.02 in the transition range, and they feature as l ∣ ∣ ∝ l ⊥ 0.44 and L ⊥ ∝ l ⊥ 0.73 in the ion-to-electron scales. Still, we need more complete kinetic-scale turbulence models to explain all these observational results.


Author(s):  
Zhiyu Wan ◽  
Dandan Zhang ◽  
Zhenbiao Li ◽  
Shi Mo ◽  
Yu Zhang

Galloping of twin bundled overhead conductors accreted by ice is a frequent phenomenon during freezing weather, which may damage the operation of transmission lines. To analyze the galloping behavior of iced conductors, their aerodynamic characteristics must be studied. In this study, models with two different outlines were designed and tested to determine a more suitable ice-accreted conductor testing model. Subsequently, the influences of the conductor type, ice thickness, wind turbulence intensity, and wake effect of the windward conductor on the aerodynamic coefficients of the conductors with crescent-shape ice are investigated. The results show that the strand outline of overhead conductors must be considered to improve the accuracy of aerodynamic tests. With increasing ice thickness, the aerodynamic stability becomes rapidly deteriorated. Under the wind turbulence intensity of 4%, the aerodynamic stability gets the most enhancement. Moreover, different conductor types have little impact on the aerodynamic coefficients. The wake caused by the windward conductor is the leading cause for the twin bundled iced conductors to have weaker aerodynamic stability than a single conductor. The aerodynamic coefficients determined in this study are essential for predicting the galloping amplitudes of ice-accreted twin bundled overhead conductors under different weather conditions.


2021 ◽  
Vol 9 ◽  
Author(s):  
Mengsi Ruan ◽  
Pingbing Zuo ◽  
Zilu Zhou ◽  
Zhenning Shen ◽  
Yi Wang ◽  
...  

Solar wind dynamic pressure pulses (DPPs) are small-scale plasma structures with abrupt and large-amplitude plasma dynamic pressure changes on timescales of seconds to several minutes. Overwhelming majority of DPP events (around 79.13%) reside in large-scale solar wind transients, i.e., coronal mass ejections, stream interaction regions, and complex ejecta. In this study, the intermittency, which is a typical feature of solar wind turbulence, is determined and compared during the time intervals in the undisturbed solar wind and in large-scale solar wind transients with clustered DPP events, respectively, as well as in the undisturbed solar wind without DPPs. The probability distribution functions (PDFs) of the fluctuations of proton density increments normalized to the standard deviation at different time lags in the three types of distinct regions are calculated. The PDFs in the undisturbed solar wind without DPPs are near-Gaussian distributions. However, the PDFs in the solar wind with clustered DPPs are obviously non-Gaussian distributions, and the intermittency is much stronger in the large-scale solar wind transients than that in the undisturbed solar wind. The major components of the DPPs are tangential discontinuities (TDs) and rotational discontinuities (RDs), which are suggested to be formed by compressive magnetohydrodynamic (MHD) turbulence. There are far more TD-type DPPs than RD-type DPPs both in the undisturbed solar wind and large-scale solar wind transients. The results imply that the formation of solar wind DPPs could be associated with solar wind turbulence, and much stronger intermittency may be responsible for the high occurrence rate of DPPs in the large-scale solar wind transients.


2021 ◽  
Vol 919 (1) ◽  
pp. 19
Author(s):  
N. Andrés ◽  
F. Sahraoui ◽  
L. Z. Hadid ◽  
S. Y. Huang ◽  
N. Romanelli ◽  
...  

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