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Author: Grafiati
Published: 6 September 2023

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1

Cheng, P. W., and W. A. A. M. Bierbooms. "Extreme Gust Loading for Wind Turbines during Operation." Journal of Solar Energy Engineering 123, no. 4 (July 1, 2001): 356–63. http://dx.doi.org/10.1115/1.1413218.

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One of the extreme load cases treated in the wind turbine certification is the extreme gust loading during operation. In the certification codes, it is treated in a deterministic way. A method of generating stochastic extreme gusts that includes the turbulence properties of the wind is described in this paper. For the moment, only the horizontal along wind direction of the wind speed is considered. The stochastic gusts are used to determine the gust responses. The gust responses are processed together with the probability density of the gust amplitude and mean wind speed to obtain the gust response distribution. Different distribution types, namely Rayleigh, Weibull, and Gumbel distributions, are applied to fit the distribution of the extreme gust responses. The estimated distributions are analyzed with statistical methods to determine the required number of simulations to obtain a reliable estimate of the statistical parameters of the distribution. The resulting structural responses to the stochastic gusts are compared to the gust response to the extreme operating gust specified in the IEC (International Electrotechnical Commission) design standard. The results show that the extreme gust response can differ significantly depending on the control concept. The response of the deterministic gust proposed in the IEC design code can also deviate considerably from the response of the stochastic gust depending on the turbine configuration. The aim of this work is to provide a rational approach to determine the extreme gust response. This theoretical method has not yet been verified with extensive measurements.
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2

Letson, Frederick, Rebecca J. Barthelmie, Weifei Hu, and Sara C. Pryor. "Characterizing wind gusts in complex terrain." Atmospheric Chemistry and Physics 19, no. 6 (March 25, 2019): 3797–819. http://dx.doi.org/10.5194/acp-19-3797-2019.

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Abstract. Wind gusts are a key driver of aerodynamic loading, especially for tall structures such a bridges and wind turbines. However, gust characteristics in complex terrain are not well understood and common approximations used to describe wind gust behavior may not be appropriate at heights relevant to wind turbines and other structures. Data collected in the Perdigão experiment are analyzed herein to provide a foundation for improved wind gust characterization and process-level understanding of flow intermittency in complex terrain. High-resolution observations from sonic anemometers and vertically pointing Doppler lidars are used to conduct a detailed study of gust characteristics with a specific focus on the parent distributions of nine gust parameters (that describe velocity, time, and length scales), their joint distributions, height variation, and coherence in the vertical and horizontal planes. Best-fit distributional forms for varying gust properties show good agreement with those from previous experiments in moderately complex terrain but generate nonconservative estimates of the gust properties that are of key importance to structural loading. Probability distributions of gust magnitude derived from vertically pointing Doppler lidars exhibit good agreement with estimates from sonic anemometers despite differences arising from volumetric averaging and the terrain complexity. Wind speed coherence functions during gusty periods (which are important to structural wind loading) are similar to less complex sites for small vertical displacements (10 to 40 m), but do not exhibit an exponential form for larger horizontal displacements (800 to 1500 m).
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Länger-Möller, Annika. "Simulation of transient gusts on the NREL 5 MW wind turbine using the URANS solver THETA." Wind Energy Science 3, no. 2 (July 6, 2018): 461–74. http://dx.doi.org/10.5194/wes-3-461-2018.

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Abstract. A procedure to propagate longitudinal transient gusts through a flow field by using the resolved-gust approach is implemented in the URANS solver THETA. Both the gust strike of a 1−cos⁡() gust and an extreme operating gust following the IEC 61400-1 standard are investigated on the generic NREL 5 MW wind turbine at rated operating conditions. The impact of both gusts on pressure distributions, rotor thrust, rotor torque, and flow states on the blade are examined and quantified. The flow states on the rotor blade before the gust strike at maximum and minimum gust velocity are compared. An increased blade loading is detectable in the pressure coefficients and integrated blade loads. The friction force coefficients indicate the dynamic separation and re-attachment of the flow during the gust. Moreover, a verification of the method is performed by comparing the rotor torque during the extreme operating gust to results of FAST rotor code.
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4

Yigili, I., M. A. Andirin, M. T. Akpolat, O. Baskan, M. Percin, and O. Uzol. "Design of a gust generator and comparison of model wind turbine and porous disc wake flows in a transverse gust." Journal of Physics: Conference Series 2265, no. 2 (May 1, 2022): 022108. http://dx.doi.org/10.1088/1742-6596/2265/2/022108.

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Abstract This paper outlines the similarities and differences between the wake characteristics of a porous disc and model wind turbine under transverse gust loading which is generated via a two-vane wind tunnel gust generator. Phase-locked two-dimensional two-component (2D2C) particle image velocimetry (PIV) measurements show that the capability of a porous disc in representing a wind turbine increases under gust loading. Compared to the uniform inflow case, normalized streamwise velocity plots of the porous disc and model turbine are in a better agreement under gusty inflow condition particularly in the near wake region. Comparison of the wake centerlines reveals a similar wavy wake pattern with no significant phase lag suggesting that the gust dynamics is the dominant factor in the determination of the wake dynamics.
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5

Berger, Frederik, Lars Neuhaus, David Onnen, Michael Hölling, Gerard Schepers, and Martin Kühn. "Experimental analysis of the dynamic inflow effect due to coherent gusts." Wind Energy Science 7, no. 5 (September 8, 2022): 1827–46. http://dx.doi.org/10.5194/wes-7-1827-2022.

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Abstract. The dynamic inflow effect describes the unsteady aerodynamic response to fast changes in rotor loading due to the inertia of the wake. Fast changes in turbine loading due to pitch actuation or rotor speed transients lead to load overshoots. The phenomenon is suspected to be also relevant for gust situations; however, this was never shown, and thus the actual load response is also unknown. The paper's objectives are to prove and explain the dynamic inflow effect due to gusts, and compare and subsequently improve a typical dynamic inflow engineering model to the measurements. An active grid is used to impress a 1.8 m diameter model turbine with rotor uniform gusts of the wind tunnel flow. The influence attributed to the dynamic inflow effect is isolated from the comparison of two experimental cases. Firstly, dynamic measurements of loads and radially resolved axial velocities in the rotor plane during a gust situation are performed. Secondly, corresponding quantities are linearly interpolated for the gust wind speed from lookup tables with steady operational points. Furthermore, simulations with a typical blade element momentum code and a higher-fidelity free-vortex wake model are performed. Both the experiment and higher-fidelity model show a dynamic inflow effect due to gusts in the loads and axial velocities. An amplification of induced velocities causes reduced load amplitudes. Consequently, fatigue loading would be lower. This amplification originates from wake inertia. It is influenced by the coherent gust pushed through the rotor like a turbulent box. The wake is superimposed on that coherent gust box, and thus the inertia of the wake and consequently also the flow in the rotor plane is affected. Contemporary dynamic inflow models inherently assume a constant wind velocity. They filter the induced velocity and thus cannot predict the observed amplification of the induced velocity. The commonly used Øye engineering model predicts increased gust load amplitudes and thus higher fatigue loads. With an extra filter term on the quasi-steady wind velocity, the qualitative behaviour observed experimentally and numerically can be caught. In conclusion, these new experimental findings on dynamic inflow due to gusts and improvements to the Øye model enable improvements in wind turbine design by less conservative fatigue loads.
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6

Cheney, Jorn A., Jonathan P. J. Stevenson, Nicholas E. Durston, Jialei Song, James R. Usherwood, Richard J. Bomphrey, and Shane P. Windsor. "Bird wings act as a suspension system that rejects gusts." Proceedings of the Royal Society B: Biological Sciences 287, no. 1937 (October 21, 2020): 20201748. http://dx.doi.org/10.1098/rspb.2020.1748.

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Musculoskeletal systems cope with many environmental perturbations without neurological control. These passive preflex responses aid animals to move swiftly through complex terrain. Whether preflexes play a substantial role in animal flight is uncertain. We investigated how birds cope with gusty environments and found that their wings can act as a suspension system, reducing the effects of vertical gusts by elevating rapidly about the shoulder. This preflex mechanism rejected the gust impulse through inertial effects, diminishing the predicted impulse to the torso and head by 32% over the first 80 ms, before aerodynamic mechanisms took effect. For each wing, the centre of aerodynamic loading aligns with the centre of percussion, consistent with enhancing passive inertial gust rejection. The reduced motion of the torso in demanding conditions simplifies crucial tasks, such as landing, prey capture and visual tracking. Implementing a similar preflex mechanism in future small-scale aircraft will help to mitigate the effects of gusts and turbulence without added computational burden.
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7

Naaim-Bouvet, Florence, Mohamed Naaim, Hervé Bellot, and Kouichi Nishimura. "Wind and drifting-snow gust factor in an Alpine context." Annals of Glaciology 52, no. 58 (2011): 223–30. http://dx.doi.org/10.3189/172756411797252112.

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AbstarctWind-transported snow is a common phenomenon in cold windy areas, creating snowdrifts and contributing significantly to the loading of avalanche release areas. It is therefore necessary to take into account snowdrift formation both in terms of predicting and controlling drift patterns. Particularly in an Alpine context, drifting snow is a nonstationary phenomenon, which has not been taken into account in physical modeling carried out in wind tunnels or in numerical simulations. Only a few studies have been conducted to address the relation between wind gusts and drifting-snow gusts. Consequently, the present study was conducted at the Lac Blanc pass (2700ma.s.l.) experimental site in the French Alps using a snow particle counter and a cup anemometer in order to investigate drifting-snow gusts. First, it was shown that the behavior of the wind gust factor was coherent with previous studies. Then the definition of wind gust factor was extended to a drifting-snow gust factor. Sporadic drifting-snow events were removed from the analysis to avoid artificially high drifting-snow gust factors. Two trends were identified: (1) A high 1 s peak and a mean 10 min drifting-snow gust factor, greater than expected, were observed for events that exhibited a gamma distribution on the particle width histogram. The values of drifting-snow gust factors decreased with increasing gust duration. (2) Small drifting-snow gusts (i.e. smaller than or of the same order of magnitude as wind gusts) were also observed. However, in this case, they were systematically characterized by a snow particle size distribution that differed from the two-parameter gamma probability density function.
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8

Zhou, Yin, and Ahsan Kareem. "Gust Loading Factor: New Model." Journal of Structural Engineering 127, no. 2 (February 2001): 168–75. http://dx.doi.org/10.1061/(asce)0733-9445(2001)127:2(168).

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9

Solari, Giovanni. "Turbulence Modeling for Gust Loading." Journal of Structural Engineering 113, no. 7 (July 1987): 1550–69. http://dx.doi.org/10.1061/(asce)0733-9445(1987)113:7(1550).

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10

Verheij, F. J., J. W. Cleijne, and J. A. Leene. "Gust modelling for wind loading." Journal of Wind Engineering and Industrial Aerodynamics 42, no. 1-3 (October 1992): 947–58. http://dx.doi.org/10.1016/0167-6105(92)90101-f.

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11

Bruni, Claudia, James Gibert, Giacomo Frulla, Enrico Cestino, and Pier Marzocca. "Energy harvesting from aeroelastic vibrations induced by discrete gust loads." Journal of Intelligent Material Systems and Structures 28, no. 1 (July 28, 2016): 47–62. http://dx.doi.org/10.1177/1045389x16642533.

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This article evaluates the amount of energy that can be extracted from a gust using an aeroelastic energy harvester composed of a flexible wing with attached piezoelectric elements. The harvester operates in a subcritical flow region. It is modeled as a linear Euler–Bernoulli beam sandwiched between two piezoceramics. The extended Hamilton’s principle is used to derive the harvester’s equations of motion and an eigenfunction expansion is used to form a three-degree-of-freedom reduced-order model. The degrees of freedom retained in the model are two flexural degrees for the in-plane and out-of-plane displacements, and a torsional degree for the rotational displacement. Wagner and Küssner functions are used to represent the unsteady aerodynamic and gust loading, respectively. The amount of energy extracted from the system is then compared for two different deterministic gust profiles, 1-COSINE and two sharp-edged gusts forming a square gust, for various magnitudes and durations. The results show that the harvester is able to extract more energy from the square gust profile, although for both profiles the harvester extracts more power after the gust has subsided.
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12

Manwaring, S. R., and S. Fleeter. "Rotor Blade Unsteady Aerodynamic Gust Response to Inlet Guide Vane Wakes." Journal of Turbomachinery 115, no. 1 (January 1, 1993): 197–206. http://dx.doi.org/10.1115/1.2929207.

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A series of experiments is performed in an extensively instrumented axial flow research compressor to investigate the fundamental flow physics of wake-generated periodic rotor blade row unsteady aerodynamics at realistic values of the reduced frequency. Unique unsteady data are obtained that describe the fundamental unsteady aerodynamic gust interaction phenomena on the first-stage rotor blades of a research axial flow compressor generated by the wakes from the inlet guide vanes. In these experiments, the effects of steady blade aerodynamic loading and the aerodynamic forcing function, including both the transverse and chordwise gust components, and the amplitude of the gusts, are investigated and quantified.
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13

Milford, R. V. "Gust loading factors for lighting masts." Engineering Structures 11, no. 2 (April 1989): 62–68. http://dx.doi.org/10.1016/0141-0296(89)90014-x.

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14

LAROSE, G. L., and J. MANN. "GUST LOADING ON STREAMLINED BRIDGE DECKS." Journal of Fluids and Structures 12, no. 5 (July 1998): 511–36. http://dx.doi.org/10.1006/jfls.1998.0161.

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15

SHI, J., and D. HITCHINGS. "FINITE ELEMENT SIMULATION OF GUST LOADING." International Journal for Numerical Methods in Fluids 23, no. 11 (December 15, 1996): 1197–210. http://dx.doi.org/10.1002/(sici)1097-0363(19961215)23:11<1197::aid-fld467>3.0.co;2-p.

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16

Hannesdóttir, Ásta, Albert Meseguer Urbán, Filip Spasov, and Antoine Larvol. "Optimum gust detection by nacelle-based lidar: A study on the Vestas V52." Journal of Physics: Conference Series 2265, no. 2 (May 1, 2022): 022072. http://dx.doi.org/10.1088/1742-6596/2265/2/022072.

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Abstract In this study we use lidar measurements from a four-beam nacelle mounted lidar, together with wind turbine load measurements, to analyse events that cause extreme blade flapwise loading on the Vestas V52 at Risø campus. We define a simple gust detection algorithm that is based on fitting a linear model to the line of sight velocity measurements in order to detect changes and fluctuations in the incoming wind field. The detection algorithm is run on a whole year of measurements and we perform an iterative parameter sweep using different values for two parameters of the gust detection method. These parameters are a slope threshold and slope duration of the linear fit. The blade loads that are associated with the detected gusts are analysed to find the optimum settings of the gust detection parameters. It was found that the most extreme observed blade load was detected for a range of parameters and by setting the slope threshold to 1.2 m/s2 and duration to 4 s, we could achieve the highest average load within the parameter range. On the other hand, the highest average blade load was found by setting the slope threshold to 1.4 m/s2 and duration to 8.5 s, though the most extreme load was not detected with those settings. The gust detection method shows potential to be used as an add-on solution to a traditional wind turbine controller to mitigate extreme loading during operation.
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17

Manwaring, S. R., and D. C. Wisler. "Unsteady Aerodynamics and Gust Response in Compressors and Turbines." Journal of Turbomachinery 115, no. 4 (October 1, 1993): 724–40. http://dx.doi.org/10.1115/1.2929308.

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A comprehensive series of experiments and analyses was performed on compressor and turbine blading to evaluate the ability of current, practical, engineering/analysis models to predict unsteady aerodynamic loading of modern gas turbine blading. This is part of an ongoing effort to improve methods for preventing blading failure. The experiments were conducted in low-speed research facilities capable of simulating the relevant aerodynamic features of turbomachinery. Unsteady loading on compressor and turbine blading was generated by upstream wakes and, additionally for compressors, by a rotating inlet distortion. Fast-response hot-wire anemometry and pressure transducers embedded in the airfoil surfaces were used to determine the aerodynamic gusts and resulting unsteady pressure responses acting on the airfoils. This is the first time that gust response measurements for turbines have been reported in the literature. Several different analyses were used to predict the unsteady component of the blade loading: (1) a classical flat-plate analysis, (2) a two-dimensional linearized flow analysis with a ‘frozen gust’ model, (3) a two-dimensional linearized flow analysis with a “distorted gust” model, (4) a two-dimensional linearized Euler analysis, and (5) a two-dimensional nonlinear Euler analysis. Also for the first time, a detailed comparison of these analyses methods is made and the importance of properly accounting for both vortical and potential disturbances is demonstrated. The predictions are compared with experiment and their abilities assessed to help guide designers in using these prediction schemes.
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18

Hoa, Le Thai, and Nguyen Dong Anh. "Spectral proper transformation and application to gust response prediction of structures." Vietnam Journal of Mechanics 29, no. 1 (March 31, 2007): 25–36. http://dx.doi.org/10.15625/0866-7136/29/1/5588.

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Random turbulent loading on engineering structures which immersed in the atmospheric turbulent flow is often represented as the multi-dimensional and/ or multivariate Gaussian random loading processes. Gust response prediction, however, usually burdens a lot of computational difficulties due to turbulent loading projection on the generalized structural coordinates. In these cases, the decomposition techniques must be required to decouple the multi-variate turbulent loading into the independently generalized turbulent forces, then is associated with the generalized structural modes. This paper will present the proper orthogonal decomposition using the spectral proper transformation in the frequency domain to decouple the multi-variate turbulent loading processes. New approach in the gust response prediction of structures will be formulated with numerical example of cable-stayed bridge.
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19

Kareem, Ahsan, and Yin Zhou. "Gust loading factor—past, present and future." Journal of Wind Engineering and Industrial Aerodynamics 91, no. 12-15 (December 2003): 1301–28. http://dx.doi.org/10.1016/j.jweia.2003.09.003.

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20

Gurley, Kurtis, and Ahsan Kareem. "Gust loading factors for tension leg platforms." Applied Ocean Research 15, no. 3 (January 1993): 137–54. http://dx.doi.org/10.1016/0141-1187(93)90037-x.

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21

Manwaring, S. R., and S. Fleeter. "Inlet Distortion Generated Periodic Aerodynamic Rotor Response." Journal of Turbomachinery 112, no. 2 (April 1, 1990): 298–307. http://dx.doi.org/10.1115/1.2927654.

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Fundamental inlet distortion-generated rotor blade row unsteady aerodynamics, including the effects of both the detailed aerodynamic forcing function for the first time and steady loading are experimentally investigated in an extensively instrumented axial-flow research compressor. A two-per-rev forcing function with three gust amplitude ratios is generated. On the rotor blade pressure surface, the unsteady pressure nondimensionalization compresses the magnitude data with mean flow incidence angle. This is not the case on the higher camber suction surface. These pressure surface unsteady data are primarily affected by the steady loading level, whereas the suction surface unsteady data are a function of the steady loading level and distribution as well as the gust amplitude ratio. In addition, a design inlet distortion blade surface unsteady pressure correlation is considered.
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22

Henderson, G. H., and S. Fleeter. "Forcing Function Effects on Unsteady Aerodynamic Gust Response: Part 1—Forcing Functions." Journal of Turbomachinery 115, no. 4 (October 1, 1993): 741–50. http://dx.doi.org/10.1115/1.2929309.

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The fundamental gust modeling assumption is investigated by means of a series of experiments performed in the Purdue Annular Cascade Research Facility. The unsteady periodic flow field is generated by rotating rows of perforated plates and airfoil cascades. In this paper, the measured unsteady flow fields are compared to linear-theory vortical gust requirements, with the resulting unsteady gust response of a downstream stator cascade correlated with linear theory predictions in an accompanying paper. The perforated-plate forcing functions closely resemble linear-theory forcing functions, with the static pressure fluctuations small and the periodic velocity vectors parallel to the downstream mean-relative flow angle over the entire periodic cycle. In contrast, the airfoil forcing functions exhibit characteristics far from linear-theory vortical gusts, with the alignment of the velocity vectors and the static pressure fluctuation amplitudes dependent on the rotor-loading condition, rotor solidity, and the inlet mean-relative flow angle. Thus, these unique data clearly show that airfoil wakes, both compressor and turbine, are not able to be modeled with the boundary conditions of current state-of-the-art linear unsteady aerodynamic theory.
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23

Chiang, Hsiao-Wei D., and Sanford Fleeter. "Cascade aerodynamic gust response including steady loading effects." International Journal for Numerical Methods in Fluids 10, no. 3 (February 1990): 285–303. http://dx.doi.org/10.1002/fld.1650100305.

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24

Saucray, J. M., C. Artigues, G. Squeglia, and J. Guillot. "International standardisation of regulations for gust loading calculations." Aeronautical Journal 95, no. 950 (December 1991): 370–78. http://dx.doi.org/10.1017/s0001924000024313.

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Abstract Analysing the action of atmospheric turbulence on aircraft for the determination of limit and fatigue loads is an essential stage in the structural design process. These calculations are governed by regulations, the evolution of which is of great importance to the aeronautical industry. The aim of this paper is to present the various calculation methods used for the preliminary dimensioning, substantiation and certification of aircraft, and to assess, on the basis of aircraft response studies and comparisons of loads calculated, the repercussions of the progress which has been made in recent years. Moreover, the regulatory requirements currently in force internationally, though often disparate and unbalanced, are now aimed at standardisation as a result of the impetus of both the airworthiness authorities and the aeronautical industry. Against this background, we propose a new calculation method developed on the basis of results obtained at Aerospatiale.
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25

Myers, Matthew R., and E. J. Kerschen. "Influence of incidence angle on sound generation by airfoils interacting with high-frequency gusts." Journal of Fluid Mechanics 292 (June 10, 1995): 271–304. http://dx.doi.org/10.1017/s0022112095001522.

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A theoretical model is developed for the sound generated when a convected vortical or entropic gust encounters an airfoil at non-zero angle of attack. The theory is based on a linearization of the Euler equations about the steady subsonic flow past the airfoil. High-frequency gusts, whose wavelengths are short compared to the airfoil chord, but long compared to the displacement of the mean-flow stagnation point from the leading edge, are considered. The analysis utilizes singular-perturbation techniques and involves four asymptotic regions. Local regions, which scale on the gust wavelength, are present at the airfoil leading and trailing edges. Behind the airfoil a ‘transition’ region, which is similar to the transition zone between illuminated and shadow zones in optical problems, is present. In the outer region, far away from the airfoil edges and wake, the solution has a geometric-acoustics form. The primary sound generation is found to be concentrated in the local leading-edge region. The trailing edge plays a secondary role as a scatterer of the sound generated in the leading-edge region. Parametric calculations are presented which illustrate that moderate levels of airfoil steady loading can significantly affect the sound field produced by airfoil–gust interactions.
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26

Sanni, R. A., D. Surry, and A. G. Davenport. "Wind loading on intermediate height buildings." Canadian Journal of Civil Engineering 19, no. 1 (February 1, 1992): 148–63. http://dx.doi.org/10.1139/l92-015.

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The current gust factor approach in the detailed method of the National Building Code of Canada (NBCC) for the estimation of wind loads on buildings was developed from research work that was largely directed towards very tall and flexible buildings for which resonant responses are very significant; however, the dynamic responses of the majority of intermediate height buildings are dominated by quasi-steady gust loading with little resonant response. This study has been carried out to assess the applicability of the detailed approach of the NBCC to that class of fairly common intermediate height buildings, of which apartment buildings are good examples. For the purposes of this study, these buildings have been defined as buildings whose heights are between 20 and 120 m and whose ratio of height to minimum width is not more than 4. The responses estimated from the detailed approach of the NBCC have been compared with those from wind tunnel tests with a view to verifying and simplifying its application to such intermediate height buildings.Since intermediate height buildings are often arranged in groups, an experimental study of the interference effects between adjacent buildings was also undertaken to assess the effect of an upwind building on the wind-induced overall moments on a downwind building of a similar height. The influence of this interference effect on the member stresses or forces was investigated using the concept of joint action factors.General agreement between the test and the code-estimated responses was obtained in the comparisons. The small resonant responses observed provided a basis for deriving a simplified method for estimating the gust factor in the detailed method without the requirement of knowing the structure's dynamic properties.Significant interference effects were found, particularly for the across-wind and torsional moments on buildings in an open exposure; however, the amplification of the overall wind-induced moments does not necessarily translate into a similar amplification of member forces or stresses. For the buildings studied, the results have shown that for the majority of practical situations, interference effects are not likely to result in amplification of member stresses or forces. A set of additional factors of safety have been proposed, based on the limited experimental data set, to cover load amplification by interference effects for those members that are very sensitive to overall wind-induced torsional moments. Key words: codes, wind loads, wind engineering, intermediate height buildings, interference effects.
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27

Kwon, Dae Kun, Ahsan Kareem, and Kyle Butler. "Gust-front loading effects on wind turbine tower systems." Journal of Wind Engineering and Industrial Aerodynamics 104-106 (May 2012): 109–15. http://dx.doi.org/10.1016/j.jweia.2012.03.030.

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28

Hoyniak, D., and S. Fleeter. "Forced Response Analysis of an Aerodynamically Detuned Supersonic Turbomachine Rotor." Journal of Vibration and Acoustics 108, no. 2 (April 1, 1986): 117–24. http://dx.doi.org/10.1115/1.3269311.

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High-performance aircraft engine fan and compressor blades are vulnerable to aerodynamically forced vibrations generated by inlet flow distortions due to wakes from upstream blade and vane rows, atmospheric gusts, and maldistributions in inlet ducts. In this paper, an analysis is developed to predict the flow-induced forced response behavior of an aerodynamically detuned rotor operating in a supersonic flow with a subsonic axial component. The aerodynamic detuning is achieved by alternating the circumferential spacing of adjacent rotor blades. The total unsteady aerodynamic loading acting on the blading, due to the convection of the transverse gust past the airfoil cascade and the resulting motion of the cascade, is developed in terms of influence coefficients. This analysis is then utilized to investigate the effect of aerodynamic detuning on the forced response characteristics of a 12-bladed rotor, with Verdon’s Cascade B flow geometry as a uniformly spaced baseline configuration. The results of this study indicate that for forward traveling wave gust excitations, aerodynamic detuning is generally very beneficial, resulting in significantly decreased maximum amplitude blade responses for many interblade phase angles.
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29

Wissmeier, Ulrike, and Robert Goler. "A Comparison of Tropical and Midlatitude Thunderstorm Evolution in Response to Wind Shear." Journal of the Atmospheric Sciences 66, no. 8 (August 1, 2009): 2385–401. http://dx.doi.org/10.1175/2009jas2963.1.

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Abstract The influence of vertical wind shear on storm development within a tropical environment is studied with the aid of two numerical models and compared with that in simulations of midlatitude storms. The simulations show that larger wind shears are required in a tropical environment than in a midlatitude environment for a storm of given updraft velocity to split. This finding is supported by the experience of forecasters at the Australian Bureau of Meteorology Regional Forecasting Centre in Darwin that the operational storm forecasting tools developed for midlatitude storms overforecast supercells within the tropics. That tropical storms require higher shears to split can be attributed either to the larger gust front speed or to the earlier gust front occurrence compared to those in the midlatitudes. A fast gust front cuts off the storm from the warm moist inflow and the updraft has little or no time to split. In the cases where the midtropospheric relative humidity is larger in the tropics or comparable with that in the midlatitudes, the total liquid water and ice content within the deeper tropical storms is larger than in the midlatitude storms, causing a stronger downdraft. In other words, the main contribution to the negative buoyancy of the downdraft is the water loading rather than the evaporative cooling. When a tropical storm is simulated in an environment with smaller midtropospheric relative humidity than in the midlatitudes, the amount of liquid water and ice within the storm is comparable to that within the midlatitude storm. Intense evaporation within the tropical storm then leads to a stronger negative buoyancy than in the midlatitude storm, causing a stronger downdraft and thus an earlier or a faster-spreading gust front. At higher shears in the tropics, entrainment reduces the storm depth and thus water loading, resulting in a delayed gust front initiation and/or reduction of the gust front speed, which then allows storm splitting to occur.
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30

Brenneman, B. "Random Vibrations Due to Small-Scale Turbulence With the Coherence Integral Method." Journal of Vibration and Acoustics 109, no. 2 (April 1, 1987): 158–61. http://dx.doi.org/10.1115/1.3269408.

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Conventional methods exist for obtaining the random vibration response of a finite-element model to “large-scale” turbulence, such as gust loading on an aircraft. However, this loading is random in time only. This paper presents a finite-element method for obtaining the response to “small-scale” turbulence that is random in space as well as time. Boundary-layer turbulence is an example of this type of loading. The method has been used successfully to find the random response of nonuniform, multispan tubes to inhomogeneous turbulent crossflow.
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CARVALHO, H., G. QUEIROZ, P. M. L. VILELA, and R. H. FAKURY. "Dynamic analysis of a concrete chimney considering the aerodynamic damping." Revista IBRACON de Estruturas e Materiais 12, no. 2 (April 2019): 308–28. http://dx.doi.org/10.1590/s1983-41952019000200006.

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Abstract Usually, the analysis of structures under wind loading is performed using an equivalent static analysis, where the influence of floating response is taken into account by the gust factor. This methodology can be used in case of rigid structures for not presenting a considerable dynamic response. More flexible structures, in particular those lightly damped, may show an important resonant response and their dynamic properties must be considered in the analysis. The aim of this paper is to present a methodology for dynamic analysis of structures under wind loading considering the geometric nonlinearity, the vibration caused by the kinetic energy of wind gusts and the aerodynamic damping due to the relative movement between this structure and the wind. The formulation proposed is applied to a 180-meter-high concrete chimney and the results were compared with those obtained through the recommendation given in the standard ABNT NBR 6123:1988 [2] for the dynamic structural analysis.
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32

Malykhina, O. I. "Analytical solution to approximate equations of the launch vehicle motion under the gust action for the dynamic loading calculation." Advanced Engineering Research 22, no. 1 (March 30, 2022): 30–41. http://dx.doi.org/10.23947/2687-1653-2022-22-1-30-41.

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Introduction. The launch vehicle (LV) in flight and the dynamic components of loads from the impact of a trapezoidal wind gust are considered. It is proposed to determine the dynamic components of the force factors using analytical solutions for the structure points accelerations. The work objective is to create a technique for selecting the duration of the standard gust, under the influence of which maximum loads are provided in the sections of the LV structure.Materials and Methods. The launch vehicle is presented as an uneven beam. The description of its vibrations is reduced to a system of independent ordinary differential equations that determine the motion of an equivalent system of oscillators. The equation of oscillator vibrations under the action of a trapezoidal pulse load is solved by the overlay method, and it is reduced to the calculation of the Duhamel integral. It is proposed to get the parameters of an equivalent system of oscillators based on the results of the calculation of dynamic characteristics for a finite element LV model in the Nastran program.Results. Analytical relations for the LV structure point accelerations under the action of a trapezoidal wind gust are given. For the beam model, test calculations of accelerations were carried out according to the technique proposed in this paper. These data are compared to the results of finite element modeling. With the help of analytical solutions, dependences are constructed that determine the nature of the change in the magnitude of the bending moment for different sections of the launch vehicle when the duration of the wind gust varies.Discussion and Conclusions. The presented technique provides building an equivalent dynamic model of systems with a large number of degrees of freedom on the example of a LV and obtaining analytical solutions for accelerations of points of a mechanical system under trapezoidal external action. These solutions are applicable for the study of dynamic loads. The analysis results enable to select the duration of the wind gust, at which maximum loads are reached in the sections of the LV structure. Calculations based on the analytical solutions are very economical in terms of time spent. They can be used in design calculations for preliminary assessment of loading.
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33

Capece, V. R., and S. Fleeter. "Experimental Investigation of Multistage Interaction Gust Aerodynamics." Journal of Turbomachinery 111, no. 4 (October 1, 1989): 409–17. http://dx.doi.org/10.1115/1.3262288.

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The fundamental flow physics of multistage blade row interactions are experimentally investigated at realistic reduced frequency values. Unique data are obtained that describe the fundamental unsteady aerodynamic interaction phenomena on the stator vanes of a three-stage axial flow research compressor. In these experiments, the effect on vane row unsteady aerodynamics of the following are investigated and quantified: (1) steady vane aerodynamic loading; (2) aerodynamic forcing function waveform, including both the chordwise and transverse gust components; (3) solidity; (4) potential interactions; and (5) isolated airfoil steady flow separation.
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34

TERAZAKI, Hiroshi, Akira KATSUMURA, Yasushi UEMATSU, Kazuo OHTAKE, Yasuo OKUDA, Hirotoshi KIKUCHI, Hiroshi NODA, Yuka MASUYAMA, Manabu YAMAMOTO, and Akihito YOSHIDA. "Wind Force Coefficient and Gust Loading Factor for Roof and Eave." Wind Engineers, JAWE 36, no. 4 (2011): 343–61. http://dx.doi.org/10.5359/jawe.36.343.

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35

Huang, Yong, Dongliang Hu, and Xianbin Liu. "Center manifold reduction for the flutter of airfoils with gust loading." Journal of Fluids and Structures 30 (April 2012): 133–40. http://dx.doi.org/10.1016/j.jfluidstructs.2012.02.009.

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36

A. V. Gorle, R. S. Tatwawadi. "Effect of Building Geometry on its Performance Under Earthquake and Wind Loading." Proceeding International Conference on Science and Engineering 11, no. 1 (February 18, 2023): 1019–25. http://dx.doi.org/10.52783/cienceng.v11i1.229.

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Recently new trend generated to resist lateral forces using truss system called as diagrid structure. Diagrid structural system adopted to resist lateral load due to its structural efficiency and flexibility of architectural planning. This study report contain effect of geometry of structure on its performance. To find out effect of geometry of structure on performance. Comparative analysis is done on circular and square shaped diagrid steel structure under earthquake and wind loading. To analyse models under earthquake and wind loading, response spectra method and gust factor method are adopted respectively. E tabs 2015 software used for modelling and analysis of diagrid steel structure. The loading conditions is based on their action of transmission like wind loading acting exposed surface to ground and earthquake loading acting ground to structure. Comparison of structural performance is done on the basis of storey displacement, storey shear, time period, material consumption.
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37

Rodzewicz, Miroslaw, Zdobyslaw Goraj, and Adam Tomaszewski. "Design and testing of three tailless unmanned aerial vehicle configurations built for surveillance in Antarctic environment." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 232, no. 14 (September 4, 2018): 2598–614. http://dx.doi.org/10.1177/0954410018797855.

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The tailless fixed-wing aircraft have a very compact design and therefore are very attractive as portable unmanned aerial vehicle (UAV) platforms. There is a special need for using such platforms in case of operations in such backlands as Antarctica, because very often the equipment necessary for preparing improvised airfields near Antarctic scientific bases and organizing the UAV flights must be hand-carried. The main aim of this paper is to present the design activity and testing of a number of UAV configurations to be used for aerial monitoring in Antarctic areas and collecting data of local ecosystems. Two UAV flying-wing platforms – MONICA-1 and MONICA-2 – were developed, differing largely with respect to wing-loading and weight-to-power ratios. The light-weight Skywalker X-8 built from the kit and used as a baseline configuration was adapted for special photogrammetric missions. It was found that the main advantage of such light UAV consists in a very simple take-off system (i.e. bungee), however due to low wing loading a usage of this UAV is limited to the so-called ‘weather windows’ of relatively low wind, which do not frequently occur in Antarctica. MONICA-1 is much less sensitive to gust but as a heavy platform it is more difficult to handle in harsh Antarctic environment. To be able to operate in much wider range of the wind, vertical gust and heavy turbulence, typical for Antarctic zones, a special UAV platform – called MONICA-2 – was designed and manufactured. MONICA-2 platform of higher wing loading is smaller than the X-8 and at the same time is able to carry the same photogrammetry equipment. The effort of designers focused on achieving low sensitivity to gust and turbulence by increasing the critical angle of attack and natural static and dynamic stability in the whole range of operational speeds. The paper contains the selected design details and some observations from the flight tests.
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38

Bai, Hao, Younes Aoues, Jean-Marc Cherfils, and Didier Lemosse. "Design of an Active Damping System for Vibration Control of Wind Turbine Towers." Infrastructures 6, no. 11 (November 11, 2021): 162. http://dx.doi.org/10.3390/infrastructures6110162.

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The vibration of wind turbine towers is relevant to the reliability of the wind turbine structure and the quality of power production. It produces both ultimate loads and fatigue loads threatening structural safety. This paper aims to reduce vibration in wind turbine towers using an active damper named the twin rotor damper (TRD). A single degree of freedom (SDOF) oscillator with the TRD is used to approximate the response of wind turbines under a unidirectional gusty wind with loss of the electrical network. The coincidence between the wind gust and the grid loss is studied to involve the maximum loading on the structure. The performance of the proposed damping system under the maximum loading is then evaluated on the state-of-the-art wind turbine NREL 5 MW. The effectiveness of the TRD is compared to a passive tuned mass damper (TMD) designed with similar requirements. The numerical results reveal that, at the 1st natural mode, the TRD outperforms the passive TMD by three to six times. Moreover, the results show that the TRD is effective in reducing ultimate loads on wind turbine towers.
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39

Selby, Robert G., and Robert B. Dryburgh. "A comparison of the gust factor method and the patch load method of analysis of guyed towers." Canadian Journal of Civil Engineering 23, no. 4 (August 1, 1996): 862–71. http://dx.doi.org/10.1139/l96-894.

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The Canadian standard CAN/CSA-S37-94 "Antennas, towers and antenna supporting structures" (S37) has introduced as an appendix a quasi-dynamic method of analysis. This patch load method yields a more realistic pattern of forces in a guyed tower, but S37 contains no firm guidelines as to when this new method is required over the conventional static gust factor approach. This paper describes various comparative studies that were made to determine the conditions under which the normally used gust factor approach does not give sufficiently acceptable results so that patch load analyses are required. Results of the parametric studies and the analyses of a large number of actual towers showed that leg loads in the upper few spans tended to be about 15% larger on average in a patch load analysis. Face shears at the guy supports were also about 15% higher on average in the patch load method. The studies revealed no strong trends between the patch load and gust factor correlation and the tower parameters, although there were slight trends suggesting that a patch load analysis was warranted if the tower height was greater than 250 m, the aspect ratio was greater than 120, or the drag area exceeded 2.0 m2/m. The presence of a cantilever accentuated the margin between the results of the two methods. Key words: guyed towers, analysis, wind loading, dynamic effects, patch load, gust factor.
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40

Manwaring, S. R., and S. Fleeter. "Forcing Function Effects on Rotor Periodic Aerodynamic Response." Journal of Turbomachinery 113, no. 2 (April 1, 1991): 312–19. http://dx.doi.org/10.1115/1.2929109.

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A series of experiments are performed in an extensively instrumented axial flow research compressor to investigate the effects of different low reduced frequency aerodynamic forcing functions and steady loading level on the gust-generated unsteady aerodynamics of a first-stage rotor blade row. Two different two-per-rev forcing functions are considered: (1) the velocity deficit from two 90 deg circumferential inlet flow distortions, and (2) the wakes from two upstream obstructions, which are characteristic of airfoil or probe excitations. The data show that the wake-generated rotor row first harmonic response is much greater than that generated by the inlet distortion, with the difference decreasing with increased steady loading.
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41

Reynolds, Kate V., Adrian L. R. Thomas, and Graham K. Taylor. "Wing tucks are a response to atmospheric turbulence in the soaring flight of the steppe eagle Aquila nipalensis." Journal of The Royal Society Interface 11, no. 101 (December 6, 2014): 20140645. http://dx.doi.org/10.1098/rsif.2014.0645.

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Turbulent atmospheric conditions represent a challenge to stable flight in soaring birds, which are often seen to drop their wings in a transient motion that we call a tuck. Here, we investigate the mechanics, occurrence and causation of wing tucking in a captive steppe eagle Aquila nipalensis , using ground-based video and onboard inertial instrumentation. Statistical analysis of 2594 tucks, identified automatically from 45 flights, reveals that wing tucks occur more frequently under conditions of higher atmospheric turbulence. Furthermore, wing tucks are usually preceded by transient increases in airspeed, load factor and pitch rate, consistent with the bird encountering a headwind gust. The tuck itself immediately follows a rapid drop in angle of attack, caused by a downdraft or nose-down pitch motion, which produces a rapid drop in load factor. Positive aerodynamic loading acts to elevate the wings, and the resulting aerodynamic moment must therefore be balanced in soaring by an opposing musculoskeletal moment. Wing tucking presumably occurs when the reduction in the aerodynamic moment caused by a drop in load factor is not met by an equivalent reduction in the applied musculoskeletal moment. We conclude that wing tucks represent a gust response precipitated by a transient drop in aerodynamic loading.
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42

PEAKE, N., and E. J. KERSCHEN. "Influence of mean loading on noise generated by the interaction of gusts with a flat-plate cascade: upstream radiation." Journal of Fluid Mechanics 347 (September 25, 1997): 315–46. http://dx.doi.org/10.1017/s0022112097006502.

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The sound generated by the interaction between convected vortical and entropic disturbances and a blade row is a significant component of the total noise emitted by a modern aeroengine, and the blade geometry has an important effect on this process. As a first step in the development of a general prediction scheme, we model in this paper just the action of the blade mean loading by treating the blades as flat plates aligned at a non-zero incidence angle, δ, to the oncoming stream, and consider harmonic components of the incident field with reduced frequency k. We then use asymptotic analysis in the realistic limit k[Gt ]1, δ[Lt ]1 with kδ=O(1) to make a consistent asymptotic expansion of the compressible Euler equations. The flow is seen to consist of inner regions around each leading edge, in which sound is generated by the local gust–airfoil and gust–flow interactions, and an outer region in which both the incident gust is distorted according to rapid distortion theory and the out-going sound is refracted by the non-uniform mean flow. The complicated multiple interactions between the sound and the cascade are included to the appropriate asymptotic order, and analytical expressions for the forward radiation are derived. It is seen that even a relatively small value of δ can have a significant effect, thanks to both the O(δk1/2) change in the amplitudes and the O(kδ) change in the phases of the various radiation components, corresponding to the additional source mechanisms associated with the flow distortion around each leading edge and the effects of propagation through the non-uniform flow, respectively. Further work will extend this analysis to include the effects of camber and thickness.
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43

Yu, Yang, Zhengjie Wang, and Shijun Guo. "Efficient Method for Aeroelastic Tailoring of Composite Wing to Minimize Gust Response." International Journal of Aerospace Engineering 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/1592527.

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Aeroelastic tailoring of laminated composite structure demands relatively high computational time especially for dynamic problem. This paper presents an efficient method for aeroelastic dynamic response analysis with significantly reduced computational time. In this method, a relationship is established between the maximum aeroelastic response and quasi-steady deflection of a wing subject to a dynamic loading. Based on this relationship, the time consuming dynamic response can be approximated by a quasi-steady deflection analysis in a large proportion of the optimization process. This method has been applied to the aeroelastic tailoring of a composite wing of a tailless aircraft for minimum gust response. The results have shown that 20%–36% gust response reduction has been achieved for this case. The computational time of the optimization process has been reduced by 90% at the cost of accuracy reduction of 2~4% comparing with the traditional dynamic response analysis.
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44

MYERS, MATTHEW R., and E. J. KERSCHEN. "Influence of camber on sound generation by airfoils interacting with high-frequency gusts." Journal of Fluid Mechanics 353 (December 25, 1997): 221–59. http://dx.doi.org/10.1017/s0022112097007349.

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A theoretical model is developed for the sound generated when a convected disturbance encounters a cambered airfoil at non-zero angle of attack. The model is a generalization of a previous theory for a flat-plate airfoil, and is based on a linearization of the Euler equations about the steady, subsonic flow past the airfoil. High-frequency gusts, whose wavelengths are short compared to the airfoil chord, are considered. The airfoil camber and incidence angle are restricted so that the mean flow past the airfoil is a small perturbation to a uniform flow. The singular perturbation analysis retains the asymptotic regions present in the case of a flat-plate airfoil: local regions, which scale on the gust wavelength, at the airfoil leading and trailing edges; a ‘transition’ region behind the airfoil which is similar to the transition zone between illuminated and shadow regions in optical problems; and an outer region, far away from the airfoil edges and wake, in which the solution has a geometric-acoustics form. For the cambered airfoil, an additional asymptotic region in the form of an acoustic boundary layer adjacent to the airfoil surface is required in order to account for surface curvature effects. Parametric calculations are presented which illustrate that, like incidence angle, moderate amounts of airfoil camber can significantly affect the sound field produced by airfoil–gust interactions. Most importantly, the amount of radiated sound power is found to correlate very well with a single aerodynamic loading parameter, αeff, which is an effective mean-flow incidence angle for the airfoil leading edge.
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45

Azouz, Naoufel, Mahmoud Khamlia, Jean Lerbet, and Azgal Abichou. "Stabilization of an Unconventional Large Airship When Hovering." Applied Sciences 11, no. 8 (April 15, 2021): 3551. http://dx.doi.org/10.3390/app11083551.

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In this paper, we present the stabilization of an unconventional unmanned airship above a loading and unloading area. The study concerns a quad-rotor flying wing airship. This airship is devoted to freight transport. However, during the loading and unloading phases, the airship is very sensitive to squalls. In this context, we present in this paper the dynamic model of the airship, and we propose a strategy for controlling it under the effects of a gust of wind. A feedforward/feedback control law is proposed to stabilize the airship when hovering. As part of the control allocation, the non-linear equations between the control vectors and the response of the airship actuators are highlighted and solved analytically through energy optimization constraints. A comparison with classical numerical algorithms was performed and demonstrated the power and interest of our analytic algorithm.
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46

Munk, David J., David W. Boyd, and Gareth A. Vio. "SIMP for Complex Structures." Applied Mechanics and Materials 846 (July 2016): 535–40. http://dx.doi.org/10.4028/www.scientific.net/amm.846.535.

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Designing structures with frequency constraints is an important task in aerospace engineering. Aerodynamic loading, gust loading, and engine vibrations all impart dynamic loads upon an airframe. To avoid structural resonance and excessive vibration, the natural frequencies of the structure must be shifted away from the frequency range of any dynamic loads. Care must also be taken to ensure that the modal frequencies of a structure do not coalesce, which can lead to dramatic structural failure. So far in industry, no aircraft lifting surfaces are designed from the ground up with frequency optimisation as the primary goal. This paper will explore computational methods for achieving this task.This paper will present a topology optimisation algorithm employing the Solid Isotropic Microstructure with Penalisation (SIMP) method for the design of an optimal aircraft wing structure for rejection of frequency excitation.
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47

Kareem, A., and J. Zhao. "Analysis of Non-Gaussian Surge Response of Tension Leg Platforms Under Wind Loads." Journal of Offshore Mechanics and Arctic Engineering 116, no. 3 (August 1, 1994): 137–44. http://dx.doi.org/10.1115/1.2920142.

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The nonlinearity in the wind loading expression for a complaint offshore structure, e.g., a tension leg platform (TLP), results in response statistics that deviate from the Gaussian distribution. This paper focuses on the statistical analysis of the response of these structures to random wind loads. The analysis presented here involves a nonlinear system with memory. As an improvement over the commonly used linearization approach, an equivalent statistical quadratization method is presented. The higher-order response cumulants are based on Volterra series. A direct integration scheme and Kac-Siegert technique is utilized to evaluate the response cumulants. Based on the first four cumulants, the response probability density function, crossing rates, and peak value distribution are derived. The results provide a good comparison with simulation. A nonlinear wind gust loading factor based on the derived extreme value distribution of nonlinear wind effects is formulated.
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48

Marzocca, Piergiovanni, Liviu Librescu, and Gianfranco Chiocchia. "Aeroelastic response of 2-D lifting surfaces to gust and arbitrary explosive loading signatures." International Journal of Impact Engineering 25, no. 1 (January 2001): 41–65. http://dx.doi.org/10.1016/s0734-743x(00)00033-6.

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49

Newman, James C. "Rainflow-on-the-Fly Methodology: Fatigue-Crack Growth under Aircraft Spectrum Loading." Advanced Materials Research 891-892 (March 2014): 771–76. http://dx.doi.org/10.4028/www.scientific.net/amr.891-892.771.

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Crack-growth-rate tests were conducted on compact, C(T), specimens made of 7075-T7351 aluminum alloy over a wide range of constant-amplitude loading (R = Pmin/Pmax = 0.1 to 0.9) to establish the baseline crack-growth-rate curve for life-prediction analyses. Both compression precracking and load-reduction methods were used. A crack-closure analysis was used to collapse the ΔKeff-rate data into a fairly narrow band over many orders of magnitude in rates using an appropriate plane-strain constraint factor. Life predictions were made on C(T) specimens using the FASTRAN Version 5.42 life-prediction code. Some improvements had been made in the code and the predictions were made under cycle-by-cycle simulations. Life predictions under Christmas-Tree-type loading using the rainflow-on-the-fly methodology were very good. And the predicted results on three different aircraft spectrum loading histories (a modified Falstaff, modified Mini-TWIST (Level III), and a modified Wing-Gust-Maneuver spectrum), agreed to within 20% of the test data.
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50

Mashiko, Wataru, Hiroshi Niino, and Teruyuki Kato. "Numerical Simulation of Tornadogenesis in an Outer-Rainband Minisupercell of Typhoon Shanshan on 17 September 2006." Monthly Weather Review 137, no. 12 (December 1, 2009): 4238–60. http://dx.doi.org/10.1175/2009mwr2959.1.

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Abstract On 17 September 2006, three tornadoes occurred along the east coast of Kyusyu Island in western Japan during the passage of an outer rainband in the right-front quadrant of Typhoon Shanshan. To clarify the structure of the tornado-producing storms and the mechanism of tornadogenesis, quadruply nested numerical simulations were performed using a nonhydrostatic model with an innermost horizontal grid spacing of 50 m. Several simulated convective storms in the outermost rainband exhibited characteristics of a minisupercell. One storm had a strong rotating updraft of more than 30 m s−1 and a large vertical vorticity exceeding 0.06 s−1. This storm spawned a tornado when the low-level mesocyclone intensified. The tornado was generated on the rear-flank gust front near the mesocyclone center when a secondary rear-flank downdraft (RFD) surge advanced cyclonically around the low-level mesocyclone and overtook the rear-flank gust front at its left-front edge. Backward trajectories and vorticity budget analysis along the trajectories indicate that the secondary RFD surge played a key role in tornadogenesis by barotropically transporting the large streamwise vorticity associated with the environmental low-level veering shear toward the surface. When the secondary RFD outflow surge boundary reached the rear-flank gust front, the horizontal convergence was enhanced, contributing to the rapid amplification of the vertically tilted streamwise vorticity. The diagnostics of the vertical momentum equation and several sensitivity experiments demonstrated that precipitation loading in the area of a hook-shaped precipitation pattern was crucial to the behavior of the RFD and the subsequent tornadogenesis.
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