Effects Of Gusts Research Articles

The effect of wind gusts, moisture content and fetch length on sand transport on a beach

This paper reports on an analysis of instantaneous sediment transport in relation to wind gusts, moisture content and fetch length from a field study carried out at Skallingen, Denmark. Wind speeds were measured with cup anemometers and instantaneous sediment transport with vertical traps coupled to electronic balances. Moisture content was measured gravimetrically using samples taken along a beach profile at intervals of 1 to 2 h. Sediment transport and wind speeds were sampled at 1 Hz and a 5-s running mean was used to smooth the data from the trap because of limitations of the balance resolution. Three measures of the threshold of sediment motion—the intermittency threshold, minimum threshold and maximum threshold—were explored using data from five runs carried out on October 26, 2000. The intermittency threshold and maximum threshold were largely insensitive to wind speed but varied spatially along the fetch distance. The minimum threshold increased significantly with increasing mean wind speed as a result of reduced time for drying of the surface layer. Examination of time series for instantaneous wind speed and sediment transport for a number of runs on October 26 and November 6, 2000 showed close agreement between fluctuations in wind speed and fluctuations in sediment transport. Cross spectral analysis of instantaneous wind speed and sediment transport for one run on each day where there was continuous transport showed high coherence between the two variables over a range of frequencies from 0.2 Hz to <0.01 Hz. Plots of all non-zero instantaneous sediment transport values versus wind speed show considerable scatter. In general, transport rates are highest for traps located further from the upwind non-erodible boundary (i.e. along the fetch). Best fit power relationships show R 2 values generally ranging from 0.4 to 0.6 and exponents ranging from 4.5 to 6.94—i.e. much higher than the traditional value of 3 found in most transport equations. Traps located close to the upwind boundary had lower R 2 values and exponents <2.5.

Reliability analysis of composite wing subjected to gust loads

An aerospace vehicle in atmospheric flight can be exposed to random air turbulence which may cause critical structural failure. Especially, for high aspect ratio wing, the effect of gust becomes more significant and its response to random gust need to be analyzed precisely. In this paper, the reliability analysis is conducted for composite wing subject to gust loads. For this, the probability distribution function of bending moment from random gust is calculated by power spectral analysis and the material properties of composite skin are assumed to be normal random variables to consider uncertainty. With these distributions of random variables, the probability of failure of the wing structure is calculated by Monte Carlo simulation.

Unbalanced wind buffeting effects on bridges during double cantilever erection stages

This paper is focused on the torsional effects that are induced on bridge piers by unbalanced windrnbuffeting on the deck during double cantilever erection stages. The case of decks with variable cross section isrnconsidered in particular as this characteristic is typical of most frame bridges that are built by the cantileverrnmethod. The procedure outlined in the paper is basically an application of the method that Dyrbye and Hansenrn(1996) have illustrated for decks with constant cross section. This format was chosen because it is suitable forrndesign purposes and may easily be implemented in structural codes. As a complement, the correspondence withrnthe format that is adopted in the Canadian code (NBCC 1990) for the gust factor is established, which might bernuseful to bridge designers used to the North-American approach to the gust effects on structures. Onlyrnalongwind turbulence and horizontal movements of the deck are considered. The combination of torsional andrnbending effects is also discussed and it is illustrated with an example of application.

Special Studies for Vasco da Gama Bridge

The importance and structural characteristics of the Vasco da Gama Bridge led to the development of some special studies to achieve a more detailed analysis of its structural behavior. The studies reported in this paper concern the following subjects: (1) Analysis of the behavior of the deck under a “design ship fire”; (2) study of an elastoplastic damping system to control the seismic response; and (3) analysis of the aerodynamic behavior of the bridge (computational fluid dynamics analysis of the deck and dynamic analyses of the structure to assess the effects of wind gusts). These studies gave technical support to some important decisions that were undertaken, such as the installation of two vertical baffles under the deck to improve the aerodynamic stability and eight hysteretic damping devices in the connections between the deck and the towers to reduce the seismic displacements.

Continuous Variable Speed Wind Turbine: Transmission Concept and Robust Control

This paper presents the theory and design of a novel hybrid mechanical-electrical variable speed wind turbine transmission, and discusses a robust control solution for optimal power output of the wind turbine equipped with such a transmission. The novel, planetary differential transmission would be driven by the variable speed rotor and controlled by a control system to ensure a constant speed of the main generator at a wide range of wind speed variations. Analysis shows that this would lead to an increase in the wind turbine energy output, estimated to be in the range of 15% to 20%, compared to a wind turbine with the same rotor and a fixed transmission. Using robust control design techniques, a single controller is synthesized for efficient operation over the entire anticipated wind speed range. The control system automatically varies the rotor speed to optimize its power output for slow wind speed variation and attenuates high frequency wind gust effects to reduce the resulting fatigue damage. Overall, the new concept provides a cost effective solution for variable speed wind turbine operation. The improved system performance is demonstrated using the results of a numerically simulated dynamic model of the proposed system.

Investigation of Turbulence Effect on Dynamic Behaviour of Aircraft Through Use of JDYNASIM: A Platform Independent Simulation Software

The need of fast and interactive tool to simulate aircraft behaviour is a demand of modern technology. This necessity is more evident when light aircraft and sailplanes are involved.. This paper presents an attempt to give simulation possibility almost to everyone through the use of JDynaSim code, written to meet this goal. JDynaSim is an interactive graphic flight simulation code written in JAVA and VRML languages which practically allows everyone to fly the aeroplane under investigation. This is true due to the fact that JAVA is a language born to work under a generic Internet browser (such as Microsoft Explorer or Netscape) and thus it is independent from the operating system under which it is running. Dynamic motion equations are solved by 12 ordinary non-linear differential equations in which the non-linear forces are input in multidimensional matrix form and are interpolated at each time instant. Advancing in time is performed using a 4th order Runge-Kutta integration scheme. Translation equations of motion are written in a flight path axis system while rotational equations are written on body axis system. An on-purpose written pre-processor has to be used to transform forces to appropriate reference system. The code can interactively read mouse and keyboard inputs as well as files with command laws assigned in function of time. There is the possibility to record the interactive session performed and then to repeat the manoeuvre. This paper presents also the code extension for simulating the effect of gusts generated according to classical theories. In particular investigation has been performed to compare results coming from classical theories on aircraft responses to gusts inputs respect to those coming from JDynSim flight simulator. JDynaSim is available to everybody through Internet at the following URL: http://www.dpa.unina.it/coiro/

99/03822 Neural network modeling of the gust effects on a grid-interactive wind energy conversion system with battery storage: Giraud, F. and Salameh, Z. M. Elec. Power Syst. Res., 1999, 50, (3), 155–161

99/03822 Neural network modeling of the gust effects on a grid-interactive wind energy conversion system with battery storage: Giraud, F. and Salameh, Z. M. Elec. Power Syst. Res., 1999, 50, (3), 155–161

THE RESPONSE OF A SWEPT BLADE ROW TO A THREE-DIMENSIONAL GUST

An analytical expression is obtained for the unsteady loading, acoustic mode amplitude, and sound power output of a three-dimensional rectilinear cascade of blades with finite chord excited by a three dimensional gust. The effects of spanwise wave number and cross-flow are included so that the effect of blade sweep and a gust with a spanwise variation can be considered. The results show that the effect of the spanwise gust and blade sweep are very similar and reduce the effective frequency of the incoming gust. The dominant effect is caused by the cut off of acoustic modes when the trace velocity of the gust along the blade span is subsonic.

Neural network modeling of the gust effects on a grid-interactive wind energy conversion system with battery storage

This paper presents a simplified way to predict accurately the dynamic responses of a grid-linked Wind Energy Conversion System (WECS) to gusty winds using a Recurrent Neural Network (RNN). The RNN is a single-output feedforward backpropagation network with external feedback. High winds, which are stochastic and turbulent by nature, create a quasi-permanent transitory environment for the WECS, putting the system in a seemingly non-equilibrated state. For instance, the generator current at the system output, besides being dependent upon the current excitation signal at the system input, will also greatly be dependent upon the past history of the system. The feedback in the RNN allows past responses to be fed back to the network input. In this model, the WECS parameters need not be known. After proper training, the known and unknown dynamics of the WECS are captured by the network structure and stored in the connection weights between consecutive layers. For that reason, the neural modeling allows us to circumvent two majors problems faced by conventional linear mathematical modeling of system dynamics: parameter uncertainty and system non-linearity, which could be significant in a difficult dynamic environment as in high winds. Moreover, neural modeling is universal, and involves less computational effort. The viability of the battery supported system as dispatchable unit is also discussed. The simulated values are compared with actual values; excellent results have been achieved.

Ocean spray and the thermodynamics of tropical cyclones

Serious gaps in knowledge about ocean spray at wind speeds over 40m/s remain difficult to fill by observation or experiment; yet refined study of the thermodynamics of Tropical Cyclones (including typhoons and hurricanes) requires assessment of the hypothesis that 'spray cooling' at extreme wind speeds may act to reduce (i) the initial temperature of saturated air rising in the eyewall and so also (ii) the input of mechanical energy into the airflow as a whole. Such progressive reductions at higher speeds could, for example, make any possible influence of future global warming on Tropical Cyclone intensification largely self-limiting. In order to help in extrapolation of knowledge on ocean spray to extreme wind speeds, a probabilistic analysis is introduced which allows for the effects of gusts, gravity and evaporation on droplet distributions, yet in other respects is as simple as possible. Preliminary indications from this simplified analysis appear to confirm the potential importance of spray cooling.

The effectiveness of viscous-damping walls for controlling wind vibrations in multi-story buildings

To investigate the behavior and effectiveness of viscous-damping (VD) walls in controlling wind-induced vibrations in multi-story buildings, an aeroelastic building model with VD wall units was constructed for the experimental study. Wind tunnel testing of the model included conditions of simulated gust. In addition to being effective in reducing the effects of wind gust in the along-wind direction, the experimental results showed that VD walls were also effective in the cross-wind direction. The damping action of the VD walls in the rotational mode was also investigated.

Numerical Wind Studies for the Vasco da Gama Bridge, Portugal

This paper presents numerical studies to the aerodynamic behaviour of the Vasco da Gama Bridge. The configuration initially proposed for the deck was prone to wind instability problems. To overcome this situation, an innovative Computational Fluid Dynamics (CFD) analysis of the deck was performed in conjugation with wind tunnel tests. The structural effects of wind gusts on the bridge were also studied. These effects were evaluated by an analysis in the frequency domain and by another analysis in the time domain. In the latter, a nonlinear analysis of the stays was performed to evaluate the amplitudes of oscillation induced by deck movements due to wind gusts.

Numerical modelling of gust effect on wind-driven rain

The weather resistance design of building facades requires adequate knowledge on the wind and rain environments around the building. Wind-driven rain intensity on building faces was first studied with on site measurements. More recently numerical method using computational fluid dynamics technique were proposed. However, the method was based on a mean flow condition without taking the effect of gusts into account. In the present paper a numerical method for the simulation of wind-driven rain around a building with the effect of gust incorporated is proposed. Some preliminary results on the effects due to two types of gust simulation (a) small uncorrelated gust and (b) large correlated gust are presented.

A probabilistic model for estimating ocean-spray distribution in extreme tropical cyclone winds

ABSTRACT. Serious gaps in knowledge about ocean spray at wind speeds over 28 m/s remain difficult to fill by observation or experiment; yet refined study of the thermodynamics of Tropical Cyclones (including typhoons and hurricanes) requires assessment of the hypothesis that ‘spray cooling’ at extreme wind speeds may act to reduce (i) the initial temperature of saturated air rising in the eyewall and so also (ii) the input of mechanical energy into the airflow as a whole. Such progressive reductions at higher speeds could, for example, make any possible influence, of future global warming on Tropical Cyclone intensification largely se1f-limiting. In order to help in extrapolation of knowledge on ocean spray to extreme wind speeds, a probabilistic analysis is introduced which allows for the effects of gusts, gravity and evaporation on droplet distributions yet all other respect is as simple as possible. Preliminary indications from this simplified analysis appear to confirm the potential importance of spray cooling.&#x0D; &#x0D;

Background and main features of the Romanian standard on wind action

Background and main features of the most recently endorsed Romanian standard on wind action, STAS 10101/20-90 are presented. Research carried out on summarizing the developments of some reference codes, on zonation of Romania, on the dynamic effects of wind gusts and on structural safety is briefly presented. The most characteristic features of STAS 10101/20-90 are then summarized. Some suggestions on further developments in this field are finally presented.

Aerodynamic characteristics of aircraft under side gust

Wind-tunnel tests were conducted to investigate the aerodynamic characteristics of an aircraft when exposed to side gust resulting from microburst windshear. External airstream was supplied through the test section side wall such that it was normal to the flight pathline and parallel to the ground. The effect of side gust was studied in terms of the model performance in undisturbed flight compared to its response during side flow. The model aerodynamic characteristics were examined at several sideslip angles as well as during straight flight. The wind-tunnel results of the straight-flight mode indicated that as side gust was introduced, there was a slight but consistent drop in lift, considerable accumulation of drag, increase in nose-up pitching moment, and constant lateral drift. The loss of lift became more appreciable at negative sideslip angles. In remedy, this situation was associated with a minimal amount of added-on drag. It was demonstrated that such loss of lift could be minimized by yawing the aircraft in the opposite direction, i.e., as the gust direction became closer to being head wind. However, this configuration of positive sideslip yielded higher accumulation of drag. Severe nose-up pitching moment was experienced during side gust exposure at negative sideslip orientations. It is found that while the trim condition was displaced, the stability margin was retained unaffected.

The Effect of Nonlinear Drag on the Motion and Settling Velocity of Heavy Particles

Abstract The effects of nonlinear drag on the motion and settling velocity of heavy particles in a turbulent atmosphere are investigated. The authors approach the problem rather systematically by first considering the response of particles to much simpler fluid motions that are subprocesses of the more complex turbulent field. The authors first consider the motion and time response of particles falling under gravity in still fluid. Then the effects of a sudden gust or step change in relative velocity between a falling particle and its surrounding fluid are investigated. The authors demonstrate that horizontal relative motion produced by a sudden gust tends to reduce the settling velocity of a panicle. In simple oscillating fluids it is shown that the reduction of settling velocity increases with increasing amplitude of fluid oscillation. The authors also explore the effects of oscillation frequency on the settling velocity and show that if the period of fluid oscillation is less than the particle response...

Acoustic radiation from a thin airfoil in nonuniform subsonic flows

Noise resulting from the interaction of a three dimensional gust is modeled directly from unsteady aerodynamic codes. This paper provides bench mark results for the case of a thin airfoil for comparison with the more complex case of a loaded airfoil. It is shown that the acoustic pressure pattern strongly depends on the value of a certain reduced frequency. The effects of an oblique gust are examined and shown to significantly reduce the acoustic power for certain gust parameters range. The Acoustic power versus the gust frequency exhibits a maximum. High frequency and non-compact source effects are also investigated.

Unsteady aerodynamics of a Wortmann wing at low Reynolds numbers

The unsteady effects of turbulence and gusts on the performance of a full-scale Wortmann FX 63-137 wing for remotely piloted vehicle applications were studied by conducting experiments in the atmospheric boundary layer. The wing, which had an aspect ratio of 6, was mounted on an instrumented truck equipped for force/ moment and wind measurements. The vehicle remained stationary, and the wing was aligned with the prevailing wind. The wing experienced predominantly a plunging rather than a pitching motion, together with sweeping and longitudinal oscillations, due to the unsteady three-dimensional wind Held. The chord Reynolds number ranged from 250,000 to 450,000, and the turbulence intensity ranged from 8% to about 20%. From the spectra of the wind components, the reduced frequencies experienced by the wing may be up to 0.1 or higher, indicating that unsteady effects are important. The results show significant lift overshoot, resulting in an increase in the maximum lift coefficient and stall angle. The aerodynamic coefficients do not show pronounced hysteresis loops. A significant reduction of the minimum drag coefficient was also observed, consistent with the theory of a rigidwing plate undergoing plunging oscillation. It was concluded that the fluctuating wind field significantly improved the wing's maneuverability and endurance.

Gust effects on a flexible aircraft

Aircraft response to atmospheric turbulence is a basic problem in aeronautical design. Several uncertainties still exist about the most adequate mathematical model for it. A recent investigation conducted by AGARD revealed that different users follow very different criteria.The reasons for this diversity in analysis methods is only partially due to the randomness of the phenomenon. Three elements are the ingredients: structure, aerodynamics and turbulence distribution. No special problems arise from the first element, since structural dynamics and programs relevant to it are well established. For the aerodynamic model, the only choice is between quasi-steady and unsteady formulation, the latter being by far heavier than the former. For turbulence distribution, as is well known(2-4), two different approaches are used, time history and power spectral density (PSD); both are used in the regulations of national certifying agencies. For the latter the turbulence power spectrum must be given, and the aircraft response is evaluated through the classical theory of random vibrations.