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This paper studies the scaling of airplane dynamic response to stochastic wind gusts, with focus on the relationship between airplane size and airspeed variations. The results have applications in the design and control of small-scale aircraft for robustness with respect to turbulence. Using linearized equations of motion and the Dryden model of gusts, the paper presents analytical and numerical scaling laws for the phugoid natural frequency and damping ratio, and the variances of the airspeed and flight-path angle. The results show that small aircraft are more susceptible to high frequency gusts, that the phugoid damping ratio does not depend directly on airplane size, that the airspeed and flight-path angle variances can be parameterized by the ratio of the phugoid natural frequency to a characteristic turbulence frequency, and that the coefficient of variation of the airspeed decreases with increasing airplane size. Numerical examples validate the results using models of 11 different airplanes, particu...

probability, that a steady ight state can be maintained when stochastic wind gusts act upon an airplane. First we linearize the airplane dynamic equations and present them as a linear time invariant system with the airplane’s velocity and angular velocity as the state and gust velocity as the input. We then treat the gust velocity as a stationary random process and append the dynamics of a coloring lter to the linearized airplane equations so that the input is Gaussian white noise. We analyze the eect of the noise on the airplane’s dynamics, using the resulting equations to quantify the eects of stochastic wind gusts on an airplane’s steady ight envelope. During the analysis we introduce the notion of stationary ight and a stationary ight envelope to guarantee, within a specied probability, steady ight under such conditions. We also present a numerical example of a general aviation aircraft in steady level ight through moderate turbulence. In the example, the airplane’s cruise speed uctuates with a variance of 1.2 m 2 /s 2 and we show examples of stationary ight envelopes for this case.

International audience; This paper concerns the problem of aircraft control during the takeoff roll in the presence of severe wind gusts. It is assumed that the aircraft moves on the runway with a constant axial acceleration from a stationary position up to a specific speed at which the aircraft can go into flight. The lateral motion is controlled by the steering wheel and the rudder and affected by side wind. The aim of control is to prevent rolling out of the aircraft from the runway strip. Additionally, the lateral deviation, lateral speed, yaw angle, and yaw rate should remain in certain thresholds during the whole takeoff roll. The problem is stated as a differential game with state constraints. A grid method for computing the value function and optimal feedback strategies for the control and disturbance is used. The paper deals both with a nonlinear and linearized models of an aircraft on the ground. Simulations of the trajectories are presented.

A physically based gust parameterisation is added to the atmospheric mesoscale model FOOT3DK to estimate wind gusts associated with storms over West Germany. The gust parameterisation follows the Wind Gust Estimate (WGE) method and its functionality is verified in this study. The method assumes that gusts occurring at the surface are induced by turbulent eddies in the planetary boundary layer, deflecting air parcels from higher levels down to the surface under suitable conditions. Model simulations are performed with horizontal resolutions of 20 km and 5 km. Ten historical storm events of different characteristics and intensities are chosen in order to include a wide range of typical storms affecting Central Europe. All simulated storms occurred between 1990 and 1998. The accuracy of the method is assessed objectively by validating the simulated wind gusts against data from 16 synoptic stations by means of "quality parameters". Concerning these parameters, the temporal and spatial evolution of the simulated gusts is well reproduced. Simulated values for low altitude stations agree particularly well with the measured gusts. For orographically exposed locations, the gust speeds are partly underestimated. The absolute maximum gusts lie in most cases within the bounding interval given by the WGE method. Focussing on individual storms, the performance of the method is better for intense and large storms than for weaker ones. Particularly for weaker storms, the gusts are typically overestimated. The results for the sample of ten storms document that the method is generally applicable with the mesoscale model FOOT3DK for mid-latitude winter storms, even in areas with complex orography.

Wind gusts are calculated in a collection of simulated atmospheric flows in complex terrain. This study focuses on a region in West-Iceland during February to April 2007 which includes several windstorms. The atmospheric data is a subset in a large collection of realtime numerical simulations used for forecasting in Iceland. It is generated at horizontal resolutions of 9 and 3 km, and in two sensitivity tests at 1 km. The gust prediction method is based on turbulence kinetic energy, static stability and wind speed in the atmospheric boundary layer. The gust prediction method is implemented as post-processing. The calculated gust strength is compared with wind gust observations from several automatic weather stations. The estimated gusts are strongly dependent on the quality of the simulated flow and are on average well captured when the mean winds are correctly simulated. Maximum gusts in downslope windstorms are however frequently underestimated. The error is presumably related to an inadequate simulation of the downslope surface winds which are also too weak. The windstorms in the current study appear to be related to gravity wave activity aloft and are better reproduced at higher resolutions than at coarse resolution. There are cases of overestimated gusts on the upstream side of mountains, which may be related to an inadequate simulation of the upstream deceleration of the flow and overestimated surface winds. Gustiness in mountain wakes is frequently too great, which appears to be related to overestimated turbulence in the wakes.

This paper examines the practical importance of convective gusts for operators of wind-sensitive systems and for designers of Wind-sensitive structures. The mechanics of gusts associated with turbulence (driven by momentum) and convective eddies (driven by buoyancy) are discussed-Statistical analysis of gusts and gust factors is presented. This shows that extreme gust factors are always produced by the convective mechanism whereas extreme gusts can be produced by either mechanism. Severe convective gusts are shown to have important consequences for operators of Wind-sensitive systems because they defy precise prediction, they can be isolated in their occurrence, they can occur in quite moderate mean winds and they can be associated with sudden changes of wind direction. Extreme convective gusts are of less importance to designers of wind-sensitive structures. They are shown to have a relatively small influence on the magnitude of the predicted extreme gusts taken as design criteria for such structures. Nevertheless, there is a significant chance that when such extreme gusts occur, they are produced by the convective mechanism. When this occurs, the predicted aerodynamic effect may be underestimated, to some extent, because of inertial forces which change the nature of the flow and may increase the loading.

A probabilistic method has been applied to determine the extreme response of pitch regulated wind turbines caused by wind speed gusts. It is assumed that the extreme loading for pitch regulated turbines is caused by gusts with an extreme rise time rather than an extreme gust amplitude. A special kind of wind field simulation, so-called constrained stochastic simulation, is dealt with in order to generate the desired gusts. It can be stated that the stochastic gusts produced in this way are, in a statistical sense, not distinguishable from gusts selected from a (very long) time series. The theoretical mean gust shape, as well as the probability of occurrence of gusts, has been verified by measurements for modest gusts; but not, as yet, severe gusts. For the reference turbine the 50-year blade root flapping moment turned out to be much higher than the response on the IEC operating gust; this should be verified for commercial turbines. The method is formulated in such a way that it can easily be implemented in state-of-the-art design packages for wind turbine design as used by the industry. It should be possible to extend the method to a spatial gust. The proposed more accurate description of extreme loading will enable wind turbine manufacturers to build more reliable and optimised wind turbines.

A new method, so called constrained stochastic simulation, has been developed in order to generate extreme gust time series, to be used to calculate the extreme loading of wind turbines. A constrained simulation corresponds to the addition, in a special manner, of turbulence and a deterministic part (which resembles the auto correlation function of turbulence). The stochastic gusts produced in this way has been denoted NewGust and it is proved that they are, in a statistical sense, not distinguishable from gusts selected from a (very long) stochastic time series, with the same amplitude. The NewGust method forms a part of on overall probabilistic method to determine the distribution of the wind turbine response on gusts. This new probabilistic method enables wind turbine manufacturers to build more reliable and optimised wind turbines. The theoretical mean gust shape, as well as the probability of occurrence of gusts, has been verified by measurements. In addition preliminary comparisons between numerical load simulations and wind turbine load measurements have been carried out.

A new probabilistic method has been developed in order to determine the long-term distribution of the extreme response of wind turbines. The probabilistic method relies on the quick determination of the response to a single gust, with a given amplitude, by means of the so-called constrained simulation. A constrained simulation corresponds to the addition, in a special manner, of turbulence and a deterministic part (which resembles the autocorrelation function of turbulence). The stochastic gusts produced in this way has been denoted NewGust and are, in a statistical sense, not distinguishable from gusts selected from a (very long) stochastic time series, with the same amplitude.

A software program and associated methodology to study gust loading on aircraft exists for a classification of geometrically simplified flexible configurations. This program consists of a simple aircraft response model with two rigid and three flexible symmetric degrees-of - freedom and allows for the calculation of various airplane responses due to a discrete one-minus- cosine gust as well as continuous turbulence. Simplifications, assumptions, and opportunities for potential improvements pertaining to the existing software program are first identified, then a revised version of the original software tool is developed with improved methodology to include more complex geometries, additional excitation cases, and additional output data so as to provide a more useful and precise tool for gust load analysis. In order to improve the original software program to enhance usefulness, a wing control surface and horizontal tail control surface is added, an extended application of the discrete one-minus-cosine gust input is employed, a supplemental continuous turbulence spectrum is implemented, and a capability to animate the total vehicle deformation response to gust inputs is included. These revisions and enhancements are implemented and an analysis of the results is used to validate the modifications.

Extreme gust loading of wind turbines has been treated deterministically as prescribed in the design codes, without taking into account the stochastic property of the wind turbulence. In this paper a rational approach to quantify the variability of the gust loading of a wind turbine is presented and a new approach on the simulation of the extreme gusts with constrained simulations is proposed. The results from simulations with deterministic gusts and stochastic gusts are compared. The distribution of the extreme response due to extreme gust is derived using the constrained gust approach. The influence on response of a spatial gust and a point gust is studied. The effect of the gust centre on the turbine response has also been taken into account. The response distribution at a certain mean wind speed is determined with full-scale time domain simulation and compared to the distribution derived with constrained gusts. The method is demonstrated using the turbine model of a prototype wind turbine; for this reason the result is preliminary and generalization should be made with care.

A new wind gust estimate method (denoted WGE method) is proposed. Contrary to most techniques used in operational weather forecasting, the determination of gusts in this approach is fully based on physical considerations. The main motivation for developing such an approach is to improve the knowledge of the physical processes that control the determination of gusts. The proposed approach assumes that surface gusts result from the deflection of air parcels flowing higher in the boundary layer, which are brought down by turbulent eddies. The WGE method takes into account the mean wind and the turbulent structure of the atmosphere. Moreover, this method includes the computation of a bounding interval around the gust estimate, which provides a range of likely gust magnitudes. The WGE method has been tested on two explosive cyclogenesis events that were satisfyingly simulated with the Modele Atmospherique Regional mesoscale model nested in the ECMWF analysis. Daily maximum gusts are predicted with good accuracy, while the hourly temporal evolution of estimated gusts depends strongly on the accuracy of the meteorological fields generated by the model. Typical error range for the gust estimates range is about 5 m s(-1). The bounding interval is useful for determining the uncertainty around estimated gusts. Statistical evaluation of the WGE method shows that the main features of the climatology of gusts during the period from January to March 1990 are reproduced, even though estimated gusts have a negative bias (from 3% to 10%) compared to observations. An interesting aspect of the WGE method is the reliability of the bounding interval, with 73% of the predicted daily gusts lying in this interval. Compared to other approaches, the WGE method is as good as other methods used in weather forecasting although extensive testing remains to be done.

SUMMARY Estimates of the largest wind gust that will occur at a given location over a specified period are required by civil engineers. Estimation is usually based on models which are derived from the limiting distributions of maxima of stationary time series and which are fitted to data on extreme gusts. In this paper we develop a model for maximum gusts which also incorporates data on hourly mean speeds through a distributional relationship between maxima and means. This joint model is closely linked to the physical processes which generate the most extreme values and thus provides a mechanism by which data on means can augment those on gusts. It is argued that this increases the credibility of extrapolation in estimates of long period return gusts. The model is shown to provide a good fit to data obtained at a location in northern England and is compared with a more traditional modelling approach, which also performs well for this site.

For design load calculations for wind turbines it is necessary to determine the fatigue loads as well as the extreme loads. An advanced method has been presented previously to incorporate extreme turbulence gusts in wind field simulation, the so-called ‘NewGust’ method. The gust generator works by constraining the random parameters of a stochastic wind field simulator. The present article deals with the verification of the mean shape of extreme gusts. On the basis of a statistical analysis an expression of the mean gust shape is obtained. This theoretical gust shape is compared with the mean gust shape determined from both simulated and measured turbulence. The resemblance is remarkably good, which demonstrates the viability of the NewGust method. Copyright © 1999 John Wiley & Sons, Ltd.

This paper presents results from pilot studies of the use of model-generated hourly soundings to forecast nonconvectively produced strong wind gusts. Model soundings from the operational Eta and Meso Eta Models were used for a period of 14 months in 1996 and 1997. Skill does exist in forecasting strong to damaging surface wind gusts, although the forecasts are at the mercy of the model-based boundary layer stability forecast. The wind gust forecasts are more accurate during the daytime, when the boundary layer depth and stability is more accurately forecasted and also more conducive to vertical mixing of boundary layer winds. The results of this preliminary evaluation show that the model sounding–based forecasts provide a reasonable prediction tool for nonconvective strong wind gusts. Additionally, the results warrant more complete evaluations once the dataset has grown to sufficient size.

Turbulence modelling for aircraft response studies requires adequate representation of atmospheric turbulence to provide for realistic reproduction of turbulence loads on an airframe. The power spectral density method, the traditional tool based on Fourier analysis that has been extensively used, does not account for coherent structures or the gusts so predominant in atmospheric turbulence. The statistical discrete gust (SDG) model was developed to overcome this problem, and the coherent structures are introduced in the form of discrete ramp-gusts. The model defines the associated probability distributions in terms of the amplitude and scale of such discrete gusts with refinements to take care of deviation of real turbulence from self-similar behaviour and scale-dependent intermittency, and provides a more realistic basis for predicting aircraft response to atmospheric turbulence. In the present work, the possibility of using tower-derived atmospheric turbulence data, instead of the commonly used aircraft measured data, for SDG analysis is investigated. The discrete gusts in the data have been detected using two methods, namely the wavelet transform method and the smoothing-differencing method, and the associated amplitudes and scales are extracted. The SDG analysis carried out by varying both the similarity parameter and the fractal dimension of turbulence to account for, respectively, the deviation of atmospheric turbulence from self-similarity and scale-dependent intermittency shows that tower-based data are highly useful to determine the model parameters. The values of the similarity parameter estimated from the data (from both the power spectra and wavelet transform) indicate the need for the incorporation of deviation of atmospheric turbulence from self-similarity and scale-dependent intermittency in the SDG model. The intermittency and intensity parameters involved in the SDG model are estimated from the tower data and show good comparison with those derived from aircraft measured data. The variation of the parameters with height and time is discussed and the relation between the intensity of fluctuations in the data and their intermittency with the corresponding model parameters is elucidated.

This study reports on the ability of the Canadian Regional Climate Model to simulate the surface wind gusts of 24 severe mid-latitude storms in Switzerland during the period 1990–2010. A multiple self-nesting approach is used, reaching a final 2-km grid which is centred over Switzerland, a country characterised by complex topography. A physically-based wind gust parameterization scheme is applied to simulate local surface gusts. Model performance is evaluated by comparing simulated wind speeds to time series at weather stations. While a number of simulated variables are reproduced in a realistic manner, the surface wind gusts show differences when compared to observed values. Results indicate that the performance of this parameterization scheme not only depends on the accuracy of the simulated planetary boundary layer, the vertical temperature, wind speed and atmospheric humidity profiles, but also on the accuracy of the reproduction of the surface fields such as temperature and moisture.

Lidars have gained a lot of popularity in the field of wind energy, partly because of their potential to be used for wind turbine control. By scanning the oncoming wind field, any threats such as gusts can be detected early and high loads can be avoided by taking preventive actions. Unfortunately, lidars suffer from some inherent weaknesses that hinder measuring gusts; e.g., the averaging of high-frequency fluctuations and only measuring along the line of sight). This paper proposes a method to construct a useful signal from a lidar by fitting a homogeneous Gaussian velocity field to a set of scattered measurements. The output signal, an along-wind force, acts as a measure for the damaging potential of an oncoming gust and is shown to agree with the rotor-effective wind speed (a similar control input, but derived directly from the wind turbine’s shaft torque). Low data availability and the disadvantage of not knowing the velocity between the lidar beams is translated into uncertainty and integrated in the output signal. This allows a designer to establish a control strategy based on risk, with the ultimate goal to reduce the extreme loads during operation.

The present study ivestigated in detail a serie of 184 wind gusts events originally discarded by Ferreira e Nascimento (2015), which presented a behavior not consistent with local convective activity by persist for several hours. This study aims to confirm or not the convective nature of these wind gusts. Using hourly data from automated weather stations maintained by Brazil National Weather Service (INMET), satellite imagery from the Geostationary Operational Environmental Satellite (GOES 12 and 13), weather radars data and final analysis data from the National Centers for Environment Prediction (NCEP) Global Forecast System (GFS-FNL) the 184 intese wind gusts episodes was analysed, some recorded by weather stations located at high elevations and other in the coastal region of brazilian south. After a detailed analysis only 9 wind gusts events were confirmed as convective origin. For the weather stations located in high altitudes the most frequently forcing mechanism to explain intense wind gusts persisting for several hours was not convective activity, but the presence of a flow from north-northeast like a low-level jet (LLJ). In the coastal stations the most wind gusts originated from low pressure systems in synoptic scale located near the coast of southern Brazil, as extratropical cyclones.

The meteorological conditions for high wind speeds and gusts are reviewed; it is pointed out that whereas wind engineers focus their attention on shear-generated turbulent flows produced in the presence of high synoptic pressure gradients, meteorological forecasters for mid-latitude climates are equally concerned with the production of gusts by the combined action of the boundary layer dynamics and thermal convection above it. Radar data, radiosonde observations and mean wind and gust measurements largely confirm the working hypotheses of forecasters. The theoretical analysis for how the upper level convective downdrafts interact with the boundary layer is developed in Section 3. The forecasting of extreme winds and other weather variables using ensemble techniques is now statistically significant for periods of up to 15 days ahead; recent results are reviewed in Section 4. Finally, in Section 5, using the results of different Global Climate Models, the effects of climate change on the frequency, intensity and tracks of storms and hurricanes are considered, in order to estimate how climate change might affect extreme surface winds.

A surface monitoring system that can detect turbulence aloft would benefit wind turbine damage prevention, aircraft safety, and would be a new probe to study the atmospheric boundary layer. Previous research indicated that elevated velocity events may trigger pressure fluctuations on the ground. If that is true, it should be possible to monitor elevated wind gusts by measuring these pressure fluctuations. The goal of this project was to develop a ground based detection method that monitors pressure fluctuations on the ground for indicators that a gust event may be taking place at higher altitudes. Using gust data generated with a convective boundary layer large eddy simulation, cross-correlation analysis between the time evolution of the frequency content corresponding to elevated wind gusts and the pressure on the ground below were investigated. Several common features of the pressures caused by elevated gusts were identified. These features were used to develop a tracking program that monitors fast movi...

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.

Velocity measurements of wind blowing near the North Sea border of Northern Germany and velocity measurements under local isotropic conditions of a turbulent wake behind a cylinder are compared. It is shown that wind gusts - measured by means of velocity increments - do show similar statistics to the laboratory data, if they are conditioned on an averaged wind speed value. Clear differences between the laboratory data and the atmospheric wind velocity measurement are found for the waiting time statistics between successive gusts above a certain threshold of interest.

A simple, generic, simulation math model of a commercial airliner has been developed to study the susceptibility of unrestrained passengers to large, discrete gust encounters. The math model simulates the longitudinal motion to vertical gusts and includes (1) motion of an unrestrained passenger in the rear cabin, (2) fuselage flexibility, (3) the lag in the downwash from the wing to the tail, and (4) unsteady lift effects. Airplane and passenger response contours are calculated for a matrix of gust amplitudes and gust lengths of a simulated mountain rotor. A comparison of the model-predicted responses to data from three accidents indicates that the accelerations in actual accidents are sometimes much larger than the simulated gust encounters.

Progress in computational atmospheric dynamics is exhibiting the ability of numerical simulation to describe instability processes associated with turbulence observed at altitudes between 15 and 25 km in the lower stratosphere. As these numerical simulation tools mature, they can be used to extend estimates of atmospheric perturbations from the present gust database for airplane design at altitudes below 15 km to altitudes between 25 and 50 km where aerospace plane operation would be at hypersonic speeds. The amount of available gust data and number of temperature perturbation observations are limited at altitudes between 15 and 25 km. On the other hand, in-situ gust data at higher altitudes are virtually nonexistent. The uncertain potential for future airbreathing hypersonic flight research vehicles to encounter strong turbulence at higher altitudes could penalize the design of these vehicles by undue cost or limitations on performance. Because the atmospheric structure changes markedly with altitude, direct extrapolation of gust magnitudes and encounter probabilities to the higher flight altitudes is not advisable. This paper presents a brief review of turbulence characteristics observed in the lower stratosphere and highlights the progress of computational atmospheric dynamics that may be used to estimate the severity of atmospheric transients at higher altitudes.

‘‘Wind gusts’’ are actually just very large scale turbulence, generally having spatial dimensions comparable to the thickness of the atmospheric boundary layer (several hundred to several thousand meters). For propagation paths smaller than the dimensions of the wind gusts it is conceptually useful to distinguish between variations in the vertical profiles of wind and temperature along the propagation path (caused by the gusts) and scattering by smaller, wavelength‐scale turbulent eddies. For example, in the case of upwind propagation, the gusts can cause the boundary of a refractive shadow zone to shift in position, whereas the smaller‐scale eddies are responsible for scattering sound energy into the shadow. In this paper a numerical propagation model is used to closely examine the relative roles of the gusts and smaller‐scale eddies for upwind, crosswind, and downwind propagation. The strength of both the gusts and smaller‐scale eddies is modeled with turbulence similarity theory. The gusts are generall...

Case studies of three destructive hurricanes: Carla, Camille, and Celia, as they moved inland, were performed to determine the change in horizontal wind speed distribution. Criteria for determining the storm's intensity were employed to describe storms in sparse data regions, i.e., while over the sea, to conform with their eventual description in relatively data-rich regions while over land. These criteria were considered critically as the storm's winds decreased after landfall. Resulting models of peak gust distribution for each storm are shown. Comparisons are made with Malkin's (1959) factors for wind decrease. Although the storms occurred after Malkin's study, his factors are representative of the synoptic maxima in two storms. For peak gusts other than the synoptic maxima, and for all peak gusts in the third storm, other considerations should be made for engineering estimates.

The theory by Rice for extreme value statistics is used to study the influence of filters in a wind measuring system on the measured gusts. An extension is made to discretely sampled data. Model results are compared with strong wind data from the Cabauw tower. On the basis of this theory a definition is proposed for the duration of gusts. Also a data reduction scheme for standard synoptic and climatological stations is proposed. Such a standardization would enhance the applicability of wind gust climatology.

For economic design of large structures it would be desirable to have maximum wind gust estimates for each direction sector rather than the global estimates at present available. Current observational practice is to record only a single maximum gust daily, together with its direction sector, for each observing station. These data could be used to make directional estimates of extreme gusts only if no significant gusts from any direction are masked by stronger gusts from other directions on the same day. To obtain an indication of whether such masking occurs, twenty-nine years of anemograph charts for a single station were examined. It was found that masking of important gusts did occur for some direction sectors. The data considered also raised questions related to the uncertainty of extreme gust directions.

An improved three-dimensional, nonrecursive model for atmospheric turbulence has been developed that provides for simulation of both instantaneous gusts and gust gradients along the flight path of the Space Shuttle. The one-dimensional gust and gust gradient spectral models, which form the basis for the simulation scheme, are developed from three-dimensional, von Karman spectra, integrated over finite limits based on the characteristic dimensions (length, width, and thickness) of the flight vehicle. By means of the simulation process, nondimensional time series for both gusts and gust gradients have been generated and stored on a series of magnetic tapes for four altitude bands ranging from 0 to 10,000 m. These Shuttle Simulation Turbulence Tapes (SSTT) have been validated by means of spectral and statistical analyses with very satisfactory results. The dimensionless form of the time series, coupled with the use of a von Karman spectral model (as opposed to a Dryden model), distinguish the SSTT from earlier turbulence simulation concepts.

Recent research in the UK on the subject of turbulence modelling for aircraft assessment and certification has emphasised the importance of considering ordered structures existing in apparently disordered air motions. A consequence of the existence of such order within disorder is that probability distributions of velocity gradients and associated velocity increments are often strongly non-Gaussian, even in so-called continuous turbulence. This non-Gaussian characteristic of turbulence (which may be related to the phenomenon of “intermittency”) is a source of dissatisfaction with the widely-used power-spectral method for modelling turbulence and is the main incentive for developing an alternative.

Parameter optimization techniques are utilized to explore the performance limits of a set of simplified radioinertial lateral path guidance systems subject to stochastic gusts, radio measurement noise and a constraint on rms control surface activity. The hybrid systems are shown to have rms lateral path errors less than half those of the pure radio systems for equivalent effector activity. The systematic generation of optimized solutions is shown to be particularly valuable in providing a performance bound for a system, against which the performance of a realizable configuration may be measured

Recent Royal Aircraft Establishment research on gusts has been particularly concerned with severe gusts and the situations in which they occur. In the stratosphere, mountain wave conditions and the vicinity of thunderstorm tops have been investigated. At lower altitudes, gusts in and near thunderstorms have also been studied, as have wind and gust effects likely to be significant during takeoff and landing. The mathematical modeling of severe gusts relevant to aircraft design is described, and the effects of pilot control activity during flight through gusts are considered briefly. Particular emphasis has been placed on two aspects of the work: (1) the study of possible means by which severe gusts might be avoided in aircraft operations and (2) the limitations of existing mathematical models of gusts that are used in aircraft design. Suggestions are made for models that may prove to be both more accurate and more physically plausible.

Light rigid civil aircraft response to continuous atmospheric turbulence estimated using two rigid body degrees of freedom method for vertical and lateral gusts

Preliminary estimates are presented of the number of occurrences of large amplitude gusts for use in the design of wind energy conversion systems. Existing turbulence information has been combined with an assumed wind speed distribution to arrive at the estimates. The number of large amplitude gusts per year is treated as a function of the annual mean wind speed and terrain roughness. This treatment is based upon the assumptions that the atmosphere has neutral stability during high winds and that the gustiness is induced by flow over surface roughness elements. Large gusts during thunderstorms and other severe weather phenomena are not treated. The results of the study are presented in tabular form as a function of gust amplitude and hourly average wind speed.

The results of a NASA investigation of a claimed Overlap between two gust response analysis methods: the Statistical Discrete Gust (SDG) Method and the Power Spectral Density (PSD) Method are presented. The claim is that the ratio of an SDG response to the corresponding PSD response is 10.4. Analytical results presented for several different airplanes at several different flight conditions indicate that such an Overlap does appear to exist. However, the claim was not met precisely: a scatter of up to about 10 percent about the 10.4 factor can be expected.

A program to obtain gust gradient measurements over the span of an airfoil is being conducted by NASA. Data have been collected from four areas of the United States (Denver, Colorado; Edwards, California; Huntsville, Alabama; and Norman, Oklahoma). The background program development data collection, and some data analysis efforts of the gust gradient effort have previously been presented (Houbolt, 1979; Camp, et al., 1983; Campbell, 1983; Campbell, et al., 1983; Frost, et al., 1983; and Painter and Camp, 1983). The purpose of this paper is to discuss briefly the animation of a gust gradient data set that was collected during the summer of 1982 at Denver, Colorado.

An improved three-dimensional, nonrecursive model for atmospheric turbulence has been developed which provides for simulation of both instantaneous gusts and gust gradients along the flight path of the Space Shuttle. The one-dimensional gust and gust gradient spectral models, which form the basis for the simulation scheme, are developed from three-dimensional, von Karman spectra, integrated over finite limits based on the characteristic dimensions (length, width, and thickness) of the flight vehicle. By means of the simulation process nondimensional time series for both gusts and gust gradients have been generated and stored on a series of magnetic tapes for four altitude bands ranging from 0 to 10,000 meters. These Shuttle Simulated Turbulence Tapes (SSTT) have been validated by means of spectral and statistical analyses with satisfactory results. The dimensionless form of the time series coupled with the use of a von Karman spectral model (as opposed to a Dryden model) distinguish the SSTT from earlier turbulence simulation concepts.

This paper presents the analytical models most in use at present for the description of the structure of turbulence in the surface atmospheric boundary layer. The study gives maximum prominence to the degree of uncertainty involved in these models, showing that a detailed forecast of the configuration of turbulence is very often fallacious. In the light of this consideration, two straightforward expressions of the power spectrum and of the coherence function are proposed that are particularly apt for the evaluation of the actions of wind on constructions such as buildings, towers, and chimneys. The use of each of these equations calls for the assignment of only one parameter, the best choice and the variability field of which are discussed.

This paper discusses the application of three statistical methods in combination to model wind gusts for use in aircraft flight simulation. The approach combines principal components analysis, time series analysis and probability distribution model to analyze and simulate wind gust components. Comparisons are given between wind gust components generated by the model and components measured onboard an aircraft.

Forecasting the occurrence of operationally critical values of strong surface winds with accompanying gusts presents a major problem at Grand Forks AFB, N. Dakota. This investigation was conducted to develop an objective aid for forecasting such critical values.

Due to the small-scale and non-stationary nature of the convective wind gusts usually associated with thunderstorms, there is a considerable lack of knowledge regarding their characteristics and statistics. In an effort to remedy this situation, we investigated in this study a set of 110 climate stations of the German Weather Service between 1992 and 2014 to analyze the temporal and spatial distribution, intensity, and occurrence probability of convective gusts. Similar to thunderstorm activity, the frequency of convective gusts decreases gradually from southern to northern Germany. No further spatial structures, such as a relation to orography or climate conditions, can be identified regarding their strength or likelihood. Rather, high wind speeds of above 30 m s−1 can be expected everywhere in Germany with almost similar occurrence probabilities. A comparison of the 20-year return values of convective gusts with those of turbulent gusts demonstrates that the latter have higher frequencies, especially in northern Germany. However, for higher return periods, this effect can be reversed at some stations. The values of the convective gust factors are mainly in a range between 1 and 4 but can even reach values up to 10. Besides the dependency from the averaging time period of the mean wind, the values of the gust factors additionally depend on the event duration and the storm type, respectively.

Surface wind gusts are studied by analyses of the properties of gust distributions. The data come from a set of anemometers that acquires data continuously at Sydney Airport. Probabilistic techniques are developed to identify landing and take-off directions under the greatest risk of along- and cross-track gusts. At Sydney Airport, along-track gusts are found to be more severe than cross-track gusts, and operations in runway direction 07 are found to pose the greatest risk. Conditions of strong synoptically generated wind are considered as well as days on which thunderstorms occurred. The techniques developed should be applicable to data acquired from a ground-level anemometer network at any airport.