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Giuseppe Piccardo - One of the best experts on this subject based on the ideXlab platform.

  • a generalized Gust Factor technique for evaluating the wind induced response of aeroelastic structures sensitive to vortex induced vibrations
    Journal of Fluids and Structures, 2017
    Co-Authors: Luisa Pagnini, Giuseppe Piccardo
    Abstract:

    Abstract This paper develops a unified procedure for dealing with Gust-excited vibrations and aeroelastic phenomena on slender structures and structural elements in the framework of the Generalized Gust Factor technique. The structure is arbitrarily inclined and constrained, and excited on its fundamental mode. Galloping phenomenon is taken into account considering linearized effects only; vortex-induced oscillations are simulated through a nonlinear equivalent damping based on the classic Vickery and Basu approach. The effectiveness of the procedure is discussed and verified over a selection of circular-shaped structures, object of extensive experimental measures. The model proposed is fully suitable to reproduce the effective structural aeroelastic behavior, also in the synchronization region at lock-in. Large uncertainties, however, arise from the choice of the model parameters, on which the literature is still poor. Particular attention is devoted to the limiting magnitude (which governs the non-linear aerodynamic damping) and to the peak Factor (which supplies the maximum response), both these quantities having a crucial role in the assessment of vortex-induced vibrations.

  • A generalized Gust Factor technique for evaluating the wind–induced response of aeroelastic structures sensitive to vortex-induced vibrations
    Journal of Fluids and Structures, 2017
    Co-Authors: Luisa Pagnini, Giuseppe Piccardo
    Abstract:

    Abstract This paper develops a unified procedure for dealing with Gust-excited vibrations and aeroelastic phenomena on slender structures and structural elements in the framework of the Generalized Gust Factor technique. The structure is arbitrarily inclined and constrained, and excited on its fundamental mode. Galloping phenomenon is taken into account considering linearized effects only; vortex-induced oscillations are simulated through a nonlinear equivalent damping based on the classic Vickery and Basu approach. The effectiveness of the procedure is discussed and verified over a selection of circular-shaped structures, object of extensive experimental measures. The model proposed is fully suitable to reproduce the effective structural aeroelastic behavior, also in the synchronization region at lock-in. Large uncertainties, however, arise from the choice of the model parameters, on which the literature is still poor. Particular attention is devoted to the limiting magnitude (which governs the non-linear aerodynamic damping) and to the peak Factor (which supplies the maximum response), both these quantities having a crucial role in the assessment of vortex-induced vibrations.

  • 3 d Gust effect Factor for slender vertical structures
    Probabilistic Engineering Mechanics, 2002
    Co-Authors: Giuseppe Piccardo, Giovanni Solari
    Abstract:

    Original studies on Gust Factor buffeting dealt with the alongwind displacement of structures. Research on this topic carried out since the nineties followed two distinct lines: the first determines the maximum effects due to the alongwind response; the second extends the original method from the alongwind response to crosswind and torsional responses. This paper represents the junction point of these research lines with reference to cantilever slender vertical structures. It derives the most relevant effects associated with the three-dimensional (3-D) wind-excited response of this structural type and shows that a suitable definition of one non-dimensional quantity, referred to as the 3-D Gust effect Factor, provides such effects at any level through a wide set of experimental, numerical and analytical procedures. A new definition of a 3-D equivalent static force consistent with this method is also introduced and critically compared with previous analogous statements.

Luisa Pagnini - One of the best experts on this subject based on the ideXlab platform.

  • a generalized Gust Factor technique for evaluating the wind induced response of aeroelastic structures sensitive to vortex induced vibrations
    Journal of Fluids and Structures, 2017
    Co-Authors: Luisa Pagnini, Giuseppe Piccardo
    Abstract:

    Abstract This paper develops a unified procedure for dealing with Gust-excited vibrations and aeroelastic phenomena on slender structures and structural elements in the framework of the Generalized Gust Factor technique. The structure is arbitrarily inclined and constrained, and excited on its fundamental mode. Galloping phenomenon is taken into account considering linearized effects only; vortex-induced oscillations are simulated through a nonlinear equivalent damping based on the classic Vickery and Basu approach. The effectiveness of the procedure is discussed and verified over a selection of circular-shaped structures, object of extensive experimental measures. The model proposed is fully suitable to reproduce the effective structural aeroelastic behavior, also in the synchronization region at lock-in. Large uncertainties, however, arise from the choice of the model parameters, on which the literature is still poor. Particular attention is devoted to the limiting magnitude (which governs the non-linear aerodynamic damping) and to the peak Factor (which supplies the maximum response), both these quantities having a crucial role in the assessment of vortex-induced vibrations.

  • A generalized Gust Factor technique for evaluating the wind–induced response of aeroelastic structures sensitive to vortex-induced vibrations
    Journal of Fluids and Structures, 2017
    Co-Authors: Luisa Pagnini, Giuseppe Piccardo
    Abstract:

    Abstract This paper develops a unified procedure for dealing with Gust-excited vibrations and aeroelastic phenomena on slender structures and structural elements in the framework of the Generalized Gust Factor technique. The structure is arbitrarily inclined and constrained, and excited on its fundamental mode. Galloping phenomenon is taken into account considering linearized effects only; vortex-induced oscillations are simulated through a nonlinear equivalent damping based on the classic Vickery and Basu approach. The effectiveness of the procedure is discussed and verified over a selection of circular-shaped structures, object of extensive experimental measures. The model proposed is fully suitable to reproduce the effective structural aeroelastic behavior, also in the synchronization region at lock-in. Large uncertainties, however, arise from the choice of the model parameters, on which the literature is still poor. Particular attention is devoted to the limiting magnitude (which governs the non-linear aerodynamic damping) and to the peak Factor (which supplies the maximum response), both these quantities having a crucial role in the assessment of vortex-induced vibrations.

  • A numerical approach for the evaluation of wind-induced effects on inclined, slender structural elements
    European Journal of Environmental and Civil Engineering, 2016
    Co-Authors: Luisa Pagnini
    Abstract:

    The Gust-excited response of structures is usually evaluated by an equivalent static load defined as the product between the wind-induced mean static force and a Gust Factor calibrated on maximum displacements. Advanced formulations provide the 3-D response using Gust Factors calibrated on the generic effect investigated, rather than refer only to displacement, allowing a more accurate description of the actual internal forces. Established procedures are available, by now, concerning vertical cantilever slender structures. Starting from this framework, the present paper generalises the Gust Factor technique supplying a numerical solution for the estimate of shear forces and bending moments of a variegated typology of structural slender elements, generically inclined, elevated above the ground and variously constrained. Accounting for the cross-contributions of different turbulence terms and the wake excitation (in absence of lock-in conditions), the procedure is particularly suitable for dealing with a wi...

Takuji Waseda - One of the best experts on this subject based on the ideXlab platform.

  • The Impact of the Winter Monsoon on Marine Surface-Layer Turbulence
    Boundary-Layer Meteorology, 2015
    Co-Authors: Tomoya Nishida, Takuji Waseda
    Abstract:

    During winter the East-Asia monsoon is the dominant climatological phenomenon in the north-west Pacific, especially around the Japan Islands. Previous studies based on satellite and radiosonde observations revealed that cold and dry strong flow from Siberia over the warm Kuroshio Extension enhances instability of the marine boundary layer and reduces vertical wind shear. Since active convection manifests as intensification of near-surface turbulence, in situ meteorological buoy data were analyzed, confirming that turbulence intensity or equivalently the Gust Factor increases during the winter north-westerly monsoon. Concurrently, a hindcast atmospheric simulation was conducted to quantify the thermal and vapour fluxes in the marine boundary layer. When large Gust Factors or turbulence intensity are observed, the buoyancy production plays an important role in the turbulent kinetic energy budget. To further clarify the respective roles of the sensible and latent heat fluxes at the sea surface, atmospheric model experiments showed that the sensible heat flux predominantly contributes to the increase in turbulence intensity. On the other hand, the latent heat flux mainly affects the generation of clouds at the top of the marine boundary layer.

  • The Impact of Winter Northwest Monsoon on Gust Factor
    Volume 5: Ocean Engineering, 2013
    Co-Authors: Tomoya Nishida, Takuji Waseda
    Abstract:

    This paper examines temporal variation of ocean wind Gust Factor and turbulence intensity in the Northwest Pacific. Observation data at coastal and open oceans near Japan are analyzed to investigate the relationship between Gust Factor and turbulence intensity, and the seasonal variation of probability distribution of Gust Factor. The contrast of the winter monsoon cold air and relatively warmer sea surface temperature is the trigger for growth of the marine boundary layer. Downdraft by developed convection enhances sea surface Gustiness. The relative significance of sensible heat flux to momentum flux is considered to be the cause of higher Gust Factor in winter. In view of deploying offshore wind turbines around Japan, the result of this study may be more relevant on the Sea of Japan side because the winter monsoon influence there is stronger than that on the Pacific side.Copyright © 2013 by ASME

Carl Fortelius - One of the best experts on this subject based on the ideXlab platform.

  • Gust Factor based on research aircraft measurements: a new methodology applied to the Arctic marine boundary layer
    Quarterly Journal of the Royal Meteorological Society, 2016
    Co-Authors: Irene Suomi, Christof Lüpkes, Jörg Hartmann, Timo Vihma, Sven-erik Gryning, Carl Fortelius
    Abstract:

    There is as yet no standard methodology for measuring wind Gusts from a moving platform. To address this, we have developed a method to derive Gusts from research aircraft data. First we evaluated four different approaches, including Taylor’s hypothesis of frozen turbulence, to derive the Gust length scales that correspond to the Gust time scales, namely, the Gust duration (seconds) and the sample period (typically 10 min). The novelty of our method is in using peak Factors (deviation of the Gust from the mean wind speed normalized by the local turbulence) to convert between the scales. After devising a way to derive the Gust length scales, we calculated the Gust Factors from aircraft observations and tested them against those from four parameterizations originally developed for weather stations. Three of them performed well (R2=0.66 or higher), while the fourth overestimated the Gust Factors in unstable conditions(R2=0.52). The mean errors for all methods were low, from -0.02 to 0.05, indicating that wind Gust Factors can indeed be measured from research aircraft. Moreover, we showed that aircraft can provide Gust measurements within the whole boundary layer, if horizontal legs are flown at multiple levels over the same track. This is a significant advance, as Gust measurements are usually limited to heights reached by weather masts. In unstable conditions over the open ocean the Gust Factor was nearly constant with height throughout the boundary layer, the near-surface values only slightly exceeding those at upper levels. Furthermore, we found Gust Factors to be strongly dependent on surface roughness conditions, which differed between the open ocean and sea ice in the Arctic marine environment. The roughness effect on the Gust Factor was stronger than the effect of boundary-layer stability.

  • On the vertical structure of wind Gusts
    Quarterly Journal of the Royal Meteorological Society, 2014
    Co-Authors: Irene Suomi, Timo Vihma, Sven-erik Gryning, Rogier Ralph Floors, Carl Fortelius
    Abstract:

    The increasing size of wind turbines, their height and the area swept by their blades have revised the need for understanding the vertical structure of wind Gusts. Information is needed for the whole profile. In this study, we analyzed turbulence measurements from a 100 m high meteorological mast at the Danish National Test Station for Large Wind Turbines at Hovsore in Denmark. The site represents flat, homogeneous grassland with an average Gust Factor of 1.4 at 10 m and 1.2 at 100 m level. In a typical surface-layer Gust parametrization, the Gust Factor is composed of two components, the peak Factor and the turbulence intensity, of which the turbulence intensity was found to dominate over the peak Factor in determining the effects of stability and height above the surface on the Gust Factor. The peak Factor only explained 15% or less of the vertical decrease of the Gust Factor, but determined the effect of Gust duration on the Gust Factor. The statistical method to estimate the peak Factor did not reproduce the observed vertical decrease in near-neutral and stable conditions and near-constant situation in unstable conditions. Despite this inconsistency, the theoretical method provides estimates for the peak Factor when comparing Gust durations of 1 and 3 s with averaging period lengths of 10 min and 1 h. A new technique to study the timing of maxima at different levels relative to the maximum Gust at some level was developed. Results showed that a 10 m level maximum Gust was typically preceded by maxima at higher levels and vice versa: a 100 m Gust was usually followed by a maximum at lower levels.

Pak Wai Chan - One of the best experts on this subject based on the ideXlab platform.

  • Vertical wind profiles for typhoon, monsoon and thunderstorm winds
    Journal of Wind Engineering and Industrial Aerodynamics, 2017
    Co-Authors: Qiusheng Li, Y.c. He, Pak Wai Chan
    Abstract:

    Abstract The vertical profiles of mean wind speed within the atmospheric boundary layer have always been a focus of attention in wind engineering. In particular, the characteristics of wind speed profiles associated with different wind phenomena are of great significance in many engineering fields. Hence, this study presents a comparative analysis on the wind profile characteristics in connection with typhoon, monsoon and thunderstorm winds respectively, in which the wind profiles are constructed by synchronizing the wind measurements taken from a surface cup-anemometer and a Doppler radar profiler equipped at a coastal weather station in Hong Kong. For each type of wind phenomenon, the shape of the wind speed profiles is examined, and the fitting parameters contained in the logarithmic-law and the power-law model are derived. In addition, some other characteristic parameters associated with the wind speed profiles, such as wind shear coefficient and Gust Factor, etc, are determined as well to enhance the understanding of the characteristics of wind profiles in connection with different wind phenomena.

  • Gust Factors for tropical cyclone, monsoon and thunderstorm winds
    Journal of Wind Engineering and Industrial Aerodynamics, 2015
    Co-Authors: Z.r. Shu, He Yuncheng, Pak Wai Chan
    Abstract:

    Abstract Gust Factor, defined as the ratio of peak Gust wind (of a given duration) to mean wind speed (for a given averaging time), is an important parameter for describing the turbulence characteristics of wind flows. Such information is useful for structural design, prevention of air pollution, air ventilation assessment and prospection of wind farms, etc. This study presents a comprehensive investigation on the characteristics of Gust Factor in tropical cyclones, monsoons and thunderstorms. Based on a 6-year wind database recorded at 6 meteorological stations in Hong Kong, the relations of Gust Factor with various wind parameters are explored. It is found that, in general, the variation of Gust Factor depends greatly on mean wind speed. This paper focuses on the comparison of Gust Factor in connection with tropical and extra-tropical winds, which shows that the deviation of Gust Factors is related to topographic condition and wind speed. The characteristics of Gust Factor associated with thunderstorm events are also investigated, and it is found that thunderstorms may generate larger statistic maximum values of Gust Factor when compared with those during strong synoptic winds. The dependence of Gust Factor against different Gust durations are comparatively established, which implies that the time scales for thunderstorms are markedly different from those of tropical cyclones and monsoons. Finally, the correlation of Gust Factor with turbulence intensity is presented and discussed.

  • Wind characteristics over different terrains
    Journal of Wind Engineering and Industrial Aerodynamics, 2013
    Co-Authors: He Yuncheng, Pak Wai Chan
    Abstract:

    Abstract This paper presents an investigation of wind characteristics over several typical terrain conditions based on a 6 years’ database from four surface meteorological stations in Hong Kong. Basic weather elements such as wind speed, air temperature, and air pressure are discussed first to present an overall description of the regional climate. Fractal dimension is introduced to quantify the fluctuations of these weather elements. Wind quantities are presented and discussed subsequently, which mainly include turbulence intensity, Gust Factor, spectra, and turbulence integral length scale. Gust Factors under different terrain conditions such as open sea terrain and hilly terrain, and in high wind events such as tropical cyclones and monsoons are discussed, and the associated comparative study is conducted. The analyzed results from tropical cyclones and monsoons under neutral conditions demonstrate little difference. The relationship between Gust Factor and turbulence intensity is studied and fitted by a linear model, in which the peak Factor is found to be 3.1. Gust-duration dependence of Gust Factor values is also investigated. Two kinds of empirical models are presented for open sea and built-up exposures. The von Karman spectrum is found to be suitable to depict the energy distributions in low frequency range. Based on the spectral analysis results, turbulence integral length scale and standard deviations of fluctuating wind speeds are estimated and discussed. The findings of this comprehensive study can be used as references for wind loading estimation, wind energy assessment and air pollution prevention over different terrains.