In search of a gust definition

Kristensen, Leif; Casanova, Manuel; Courtney, Michael; Troen, Ib

doi:10.1007/bf00119328

Cited by 53 publications

(60 citation statements)

References 7 publications

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“…In order to analyze the intermittent features of the process, level crossing rates and excess time statistics are introduced, that is, a study of the frequency of level crossings and the duration of time intervals where a realization of the process exceeds some prescribed threshold level. [45][46][47][48][49] This definition will be particularly useful for studies of confinement of hot plasmas, where it may be important to distinguish many short plasma bursts from a few long ones. Although the accumulated time in the bursts can be the same, their consequences will be different as far as, for instance, the heat load on a confining wall is concerned.…”

Section: Introductionmentioning

confidence: 99%

Stochastic modelling of intermittent fluctuations in the scrape-off layer: Correlations, distributions, level crossings, and moment estimation

et al. 2016

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A stochastic model is presented for intermittent fluctuations in the scrape-off layer of magnetically confined plasmas. The fluctuations in the plasma density are modeled by a super-position of uncorrelated pulses with fixed shape and duration, describing radial motion of blob-like structures. In the case of an exponential pulse shape and exponentially distributed pulse amplitudes, predictions are given for the lowest order moments, probability density function, auto-correlation function, level crossings, and average times for periods spent above and below a given threshold level. Also, the mean squared errors on estimators of sample mean and variance for realizations of the process by finite time series are obtained. These results are discussed in the context of single-point measurements of fluctuations in the scrape-off layer, broad density profiles, and implications for plasma--wall interactions due to the transient transport events in fusion grade plasmas. The results may also have wide applications for modelling fluctuations in other magnetized plasmas such as basic laboratory experiments and ionospheric irregularities. Published by AIP Publishing.

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Section: Introductionmentioning

confidence: 99%

Stochastic modelling of intermittent fluctuations in the scrape-off layer: Correlations, distributions, level crossings, and moment estimation

et al. 2016

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“…This is shown to give novel predictions of the intermittent features of plasma fluctuations, in particular the rate of level crossings and excess time statistics, that is, the duration of time intervals where the signal exceeds some prescribed threshold level. [13][14][15][16][17] Although of particular interest for plasma-wall interactions in fusion grade plasmas, the stochastic model is prototypical for many intermittent systems, and the results find applications in a broad range of fields (see for example Ref. 17 and references therein).…”

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confidence: 99%

Level crossings, excess times, and transient plasma–wall interactions in fusion plasmas

Theodorsen

Garcia

2016

Physics of Plasmas

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Based on a stochastic model for intermittent fluctuations in the boundary region of magnetically confined plasmas, an expression for the level crossing rate is derived from the joint distribution of the process and its derivative. From this the average time spent by the process above a certain threshold level is obtained. This provides novel predictions of plasma-wall interactions due to transient transport events associated with radial motion of blob-like structures in the scrape-off layer.

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“…48 Despite these deviations and because of the lack of a better description, the gust, de®ned as the maximum wind speed during a measurement period of 5±60 min, is often calculated using a Gaussian process as an approximation. 49,50 Using assumptions of stationarity and that a wideband process results in a joint Gaussian description of u and du/dt, the expected gust value during time T, where we have ®rst block-averaged data over time t, is…”

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confidence: 99%

Wind power meteorology. Part I: climate and turbulence

Petersen¹,

Mortensen²,

Landberg³

et al. 1998

Wind Energ.

116

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Wind power meteorology has evolved as an applied science firmly founded on boundary layer meteorology but with strong links to climatology and geography. It concerns itself with three main areas: siting of wind turbines, regional wind resource assessment and short‐term prediction of the wind resource. The history, status and perspectives of wind power meteorology are presented, with emphasis on physical considerations and on its practical application. Following a global view of the wind resource, the elements of boundary layer meteorology which are most important for wind energy are reviewed: wind profiles and shear, turbulence and gust, and extreme winds. Copyright © 1998 John Wiley & Sons, Ltd.

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In search of a gust definition

Cited by 53 publications

References 7 publications

Stochastic modelling of intermittent fluctuations in the scrape-off layer: Correlations, distributions, level crossings, and moment estimation

Stochastic modelling of intermittent fluctuations in the scrape-off layer: Correlations, distributions, level crossings, and moment estimation

Level crossings, excess times, and transient plasma–wall interactions in fusion plasmas

Wind power meteorology. Part I: climate and turbulence

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