Effects Of Gusts Research Articles

Rapid flow separation for transient inflow conditions versus accelerating bodies: An investigation into their equivalency

The possibility of simulating gusts or flow disturbances by accelerating the body rather than the oncoming fluid has been investigated. In this study the effect of a two-dimensional compound gust is considered, defined as the variation of both axial and lateral flow disturbances. The force histories of gust-induced loads on a flat-plate model were compared to those on an equivalent model accelerated within a uniform flow. It was shown that the contribution to force history from fluid acceleration could not be neglected, even at a relatively low reduced frequency. However, differences between gust loads and accelerating-model loads were not proportional to model acceleration. Rather, when differences in the fluid velocity fields were examined, the force histories were differentiated primarily by the distribution of vorticity in the wake, caused by changes in the effective incidence and effective velocity at the trailing-edge of the model.

Dynamics and swing control of mobile boom cranes subject to wind disturbances

Operating cranes is challenging because payloads can experience large and dangerous oscillations. The oscillations are induced by both intentional motions commanded by the human operator and by external disturbances. Although significant progress has been achieved by using command shaping to reduce operator-induced vibration, less success has been achieved on reducing oscillations induced by external disturbances, such as wind. The disturbance-rejection task is more challenging because it requires accurate sensing of the crane payload. This study presents a combined command shaping and feedback control architecture. The input shaper eliminates the payload oscillation caused by human-operator commands, and the feedback controller reduces the effect of wind gusts. Simulations of a large range of motions are used to analyse the dynamic behaviour of boom cranes using the proposed controller. Experimental results obtained from a small-scale boom crane validate the simulated dynamic behaviour and the effectiveness of the controller.

Stochastic modeling the effect of wind gust on dust entrainment during sand storm

After the passage of a cold front, spring in northern China the outbreak of strong wind is often accompanied by dust emissions. Owing to the coherent structure of wind gust, dust particles can effectively overcome the systematic descending air motion and penetrate into the middle and upper levels of the atmospheric boundary layer, and then propagate further and diffuse into the troposphere where ascending air motion prevails. Here, we consider the coherent structure of wind gust in LS models, and construct a model suitable for the dust entrainment under the dust-storm canopy. With the parameter of gust, we simulate the dust entrainment during dust storms, and test that the coherent structures of wind gust make the sand particles to reach the upper of the boundary layer.

Experimental method for studying gust effects on micro rotorcraft

Micro rotorcraft have a great potential for both civilian and military applications, but for successful deployment, they must operate robustly in real-world environments including flight in winds. Due to their small size, common wind fields in and around buildings can represent a large percentage of the vehicle’s full flight envelope resulting in highly non-linear motion. An experimental method has been developed to evaluate the capabilities of micro rotorcraft in realistic wind conditions to aid in the design and evaluation of these vehicles. A synthetic wind generation system is used to create repeatable and controllable gust excitations, and a motion capture system is used for precise measurement of vehicle response. Performance metrics associated with the accuracy of position tracking and angular rate excursions are proposed to quantify vehicle capabilities at different excitation levels for design assessment and cross-platform comparison. To demonstrate the experimental method, test results are shown to evaluate the capabilities of a micro coaxial helicopter in realistic winds as a function of gust excitation level and vehicle size. For this example system, light wind gusts degrade hover hold accuracy by a factor of 3 compared to a situation with quiescent winds.

Impact of wind gusts on sea surface height in storm surge modelling, application to the North Sea

Storm surge models usually do not take into account the explicit effect of wind gusts on the sea surface height. However, as the wind speed enters quadratically into the shallow water equations, short-term fluctuations around the mean value do not average out. We investigate the impact of explicitly added gustiness on storm surge forecasts in the North Sea, using the WAQUA/DCSM model. The sensitivity of the model results to gustiness is tested with Monte Carlo simulations, and these are used to derive a parametrisation of the effect of gustiness on characteristics of storm surges. With the parametrisation and input from the ECMWF model archive, we run hindcasts for a few individual cases and also the 2007–2008 winter storm season. Although the explicit inclusion of gustiness increases the surge levels, it does not help to explain, and hence reduce, the errors in the model results. Moreover, the errors made by ignoring gustiness are small compared to other errors. We conclude that, at present, there is no need to include gustiness explicitly in storm surge calculations for the North Sea.

A numerical model for wind-borne compact debris trajectory estimation: Part 2 – Simulated vertical gust effects on trajectory and mass momentum

In a companion paper [1], the trajectory of compact debris was estimated by accounting for the many uncertainties associated with debris flight. Compact debris are objects possessing non-negligible mass but negligible moment of inertia (e.g., a particle-type object); the wind-driven motion of the debris is predominantly controlled by aerodynamic drag with a limited influence of aerodynamic lift or moment. A numerical algorithm for investigating the probability of wind-borne compact debris impacting on the vertical façade of tall buildings was discussed.In this study, the effect of a “sudden” vertical gust on the trajectory of compact objects was analyzed. Since at initial stages of the flight the effect of turbulence may have an influence on the trajectory, a “Küssner-like” Gust model was proposed, incorporated in the loading model and used in conjunction with the equations of the motion. The numerical simulations, accounting for this simulated vertical gust, indicate that the effect of a simplified vertical turbulence scenario may often be neglected for estimating the trajectory of a compact object. Nevertheless, some effect of this simulated gust on “Iso-probability Impact Contours” and “Universal Probability Curve”, described in [1], was observed and quantified.

Damage assessment in CFRP laminates exposed to impact fatigue loading

Demand for advanced engineering composites in the aerospace industry is increasing continuously. Lately, carbon fibre reinforced polymers (CFRPs) became one of the most important structural materials in the industry due to a combination of characteristics such as: excellent stiffness, high strength-to-weight ratio, and ease of manufacture according to application. In service, aerospace composite components and structures are exposed to various transient loads, some of which can propagate in them as cyclic impacts. A typical example is an effect of the wind gusts during flight.This type of loading is known as impact fatigue (IF); it is a repetition of low-energy impacts. Such loads can cause various types of damage in composites: fibre breaking, transverse matrix cracking, de-bonding between fibres and matrix and delamination resulting in reduction of residual stiffness and loss of functionality. Furthermore, this damage is often sub-surface, which reinforces the need for more regular inspection.The effects of IF are of major importance due its detrimental effect on the structural integrity of components that can be generated after relatively few impacts at low force levels compared to those in a standard fatigue regime. This study utilises an innovative testing system with the capability of subjecting specimens to a series of repetitive impacts. The primary subject of this paper is to assess the damaging effect of IF on the behaviour of drilled CFRP specimens, exposed to such loading. A detailed damage analysis is implemented utilising an X-ray micro computed tomography system. The main findings suggested that at early stages of life damage is governed by o degree splits along the length of the specimens resulting in a 20% reduction of stiffness. The final failure damage scenario indicated that transverse crasks in the 90 degree plies are the main reason for complete delamination which can be translated to a 50% stiffness reduction.

Flight Control Experiment of Multipurpose-Aviation-Laboratory-alpha In-Flight Simulator

This paper reports the results of experimental verification of flight controllers for the multipurpose-aviation-laboratory-α (MuPAL-α) in-flight simulator. The flight controller design requirements are twofold: to suppress the effects of gusts on MuPAL-α motions and to realize a wide range of maneuverability, i.e., handling characteristics, without controller redesign. Using a previously proposed two-step design method for two-degrees-of-freedom model-matching controllers, flight controllers were designed for the linearized longitudinal and lateral-directional motions of MuPAL-α, and their performance was examined by hardware-in-the-loop simulations and flight tests with several maneuverability models. These experiments confirmed that MuPAL-α with our controllers achieves gust suppression and is capable of simulating various types of handling characteristics simply by replacing the model that defines the characteristics to be examined.

Effect of Frontal Gusts on Forward Flapping Flight

The response of a rigid flapping wing in forward flight, at Re = 10,000, subjected to frontal gusts has been investigated. The phasing and duration of the gusts and their impact on the various unsteady mechanisms are analyzed within a single flapping cycle. The gust is characterized by a step function with integral length scale much larger than that of the physical dimension of the micro air vehicle and with time scale much smaller than the flapping time period. The instantaneous lift and thrust profiles were observed to be influenced by a combination of the effective angle of attack, wing rotation, and the leading-edge vortex structures existing in the flow at any given time, with the leading-edge vortices themselves being influenced by the duration and magnitude of the change in effective angle of attack. Frontal gusts applied during the downstroke accelerated the development of the flow, resulting in the formation and detachment of multiple leading-edge vortices on the wing surface that increased the lift and thrust, illustrating the importance of the leading-edge vortex dynamics to force production. The effect of the gust is observed to be diminished when it occurs during rapid supination of the wing. The lift and thrust profiles are found to react in a similar fashion for gusts applied during the downstroke, whereas they experienced opposite effects during the upstroke. During the upstroke, force characteristics are shown to primarily react to effective angle-of-attack changes more than to changes in flow structures.

Stochastic Modeling of Incident Gust Effects on Aerodynamic Lift

The intrusive formulation of polynomial chaos expansion is implemented to determine uncertainty in aerodynamic loads on a rigid airfoil due to imprecise parameters that characterize an incoming gust. The results yield the sensitivity of the lift coefficient to variations in intensities and integral length scales of the gust fluctuations. The results show that lift coefficient fluctuations about the mean of each time step are affected primarily by the intensity ofthe fluctuations of the vertical velocity component, which should be expected. Next in order of importance is the integral length scale of the vertical velocity component. This implementation of the intrusive polynomial chaos expansion provides guidance for future efforts to quantify uncertain gust loads on micro air vehicles with higher fidelity models.

Nonlinear-Aerodynamics/Nonlinear-Structure Interaction Methodology for a High-Altitude Long-Endurance Wing

Nonlinear aeroelastic analysis is essential for high-altitude long-endurance (HALE) aircraft. In the current paper, we have presented a computational aeroelastic tool for nonlinear-aerodynamics/nonlinear-structure interaction. Specifically, a consistent nonlinear time-domain aeroelastic methodology has been integrated via tightly coupling a geometrically exact nonlinear intrinsic beam model and the generalized unsteady vortex-lattice aerodynamic model with vortex roll-up and free wake. The effects of discrete gust as well as flow separation at various angles of attack from attached flow to the stall and poststall ranges are also included in the nonlinear aerodynamic model. A HALE-wing model is analyzed as a numerical example. The trim angle of attack is first found for the wing, and the results show that aeroelastic instability could occur at higher angles of attack. The HALE-wing model under the trim condition is then analyzed for various gust profiles to which it is subject. It is found that for certain gust levels, the elastic deformations of the HALE wing tend to become unstable: notably, the in-plane deflections become very significant. It is noted for the unstable solution of the HALE wing that the flow may be well beyond the stall range. An engineering approach with the use of the nonlinear sectional lift is attempted to consider such stall effects.

A stochastic approach for modeling incident gust effects on flow quantities

The uncertainty in gust loads on a rigid, flat-plate airfoil at zero angle-of-attack due to imprecise knowledge of the gust parameters is quantified. The loads are computed using the unsteady vortex lattice model, which includes temporal variations in wake vorticity and the associated downwash on the airfoil. The non-intrusive formulation of the polynomial chaos expansion in terms of the multivariate Hermite polynomials is employed to quantify the uncertainty in the predicted unsteady lift. The expansion coefficients were estimated through Latin hypercube sampling of the parameters in the vertical and streamwise gust spectra. The first-order chaos expansion in terms of the uncertain spectral parameters was found to be sufficient for representing the stochastic aerodynamic lift, which was found to be most sensitive to imprecision in the standard deviation of the vertical component of the gust. These conclusions were found to be unaffected by ignoring the effects of gusts on the locations of the shed vortices in the airfoil’s wake.

Derivation of equivalent gust effect factors for wind loading on low-rise buildings through Database-Assisted-Design approach

The method for the simulation of extreme wind loading on low-rise buildings, currently adopted by most civil engineering Standards, is based on the concept of “gust effect factor” (GEF). The GEF is a dimensionless coefficient that quantifies the effect of turbulence on wind pressure distribution and enables the assessment of maximum external loading and internal forces in the structure from the analysis of the mean wind pressure scenario. The GEF is employed because a direct quantification of unsteady pressures, usually requiring detailed wind tunnel investigation, is sometimes uneconomical for a “simplified” low-rise building. This study analyzes different methods for the assessment of wind loading, utilizing the GEF. These include the approach employed by the Standard of the American Society of Civil Engineers (ASCE-7), the guidelines of the Seventh Edition of the Massachusetts Building Code (780-CMR) and the Database-Assisted-Design (DAD) approach. The DAD, developed by the National Institute for Standard and Technology, is a rational approach for the structural design against extreme winds, which employs a large database of wind tunnel test results. A set of simulated loading scenarios on rectangular low-rise gabled-roof buildings with various floor-plan dimensions and heights was employed. Wind loading analyses were restricted to enclosed buildings and primarily based on external pressures. The performance of the main wind force resisting system was analyzed. Two-dimensional lateral frames were considered. Peak values of the bending moments at critical locations were evaluated through the DAD procedure, and transformed into “equivalent gust effect factors” (EGEF) for comparison with ASCE-7 and 780-CMR. It was found that ASCE-7 always predicts an increment in the GEF with the height of the building, while the DAD estimations suggest that, for a large building, the EGEF should decrease with the height. Moreover, ASCE-7 can under-predict the magnitude of the gust effects is some cases. Finally, a relative increment in the EGEF was recorded between a large and a small floor-plan building, which is partially incompatible with the equivalent reduction of loading indicated by 780-CMR for “one and two family dwellings and townhouses”.

Effect of Side Wind on a Simplified Car Model: Experimental and Numerical Analysis

A prior analysis of the effect of steady cross wind on full size cars or models must be conducted when dealing with transient cross wind gust effects on automobiles. The experimental and numerical tests presented in this paper are performed on the Willy square-back test model. This model is realistic compared with a van-type vehicle; its plane underbody surface is parallel to the ground, and separations are limited to the base for moderated yaw angles. Experiments were carried out in the semi-open test section at the Conservatoire National des Arts et Métiers, and computations were performed at the Ecole Centrale de Nantes (ECN). The ISIS-CFD flow solver, developed by the CFD Department of the Fluid Mechanics Laboratory of ECN, used the incompressible unsteady Reynolds-averaged Navier–Stokes equations. In this paper, the results of experiments obtained at a Reynolds number of 0.9×106 are compared with numerical data at the same Reynolds number for steady flows. In both the experiments and numerical results, the yaw angle varies from 0 deg to 30 deg. The comparison between experimental and numerical results obtained for aerodynamic forces, wall pressures, and total pressure maps shows that the unsteady ISIS-CFD solver correctly reflects the physics of steady three-dimensional separated flows around bluff bodies. This encouraging result allows us to move to a second step dealing with the analysis of unsteady separated flows around the Willy model.

Numerical methods for investigation of destructive wind energy dissipation by bridges

Many bridges are located at especially unfavourable places considering the local wind power and turbulence. Therefore it turns out that finding an optimal balance between structural safety and erection costs depends strongly on a proper wind modelling and investigation. Several aspects must be taken into account for the wind design. The effect of wind gusts and randomly distributed wind velocity and direction must be considered in the framework of a wind buffeting analysis. This requires detailed information about the power spectral density and cross correlation of the local wind events. The air flow pattern strongly influences the resulting forces. Since a fully coupled model for randomly oncoming flow and resulting wind forces is too complex, the forces are derived from steady state CFD calculations in general. In this paper, the theoretical background of the applied analysis methods is outlined and practical examples for different long span bridges are given.

Development of Stable Automated Cruise Flap for an Aircraft with Adaptive Wing

Cruise flaps are devices designed to minimize drag, and previous research has explored using a wing-based pressure differential to automate them. Different presentations of the pressure-differential data tend to lead to the development of different types of controllers for automated cruise flaps. A presentation used by previous researchers led to an unstable drag-minimizing controller, whereas a presentation used in this research leads to a stable controller that implements multiple functions. Techniques previously used for high Reynolds number natural-laminar-flow airfoils are modified for use with the low Reynolds number SD7037 planned for future flight testing. The results of rigid-aircraft simulations are presented, showing the effectiveness of the multifunction controller, which is able to simultaneously reduce drag and alleviate the effects of vertical gusts.

Combined Effects of Passing Clouds and Wind Gusts on an Interactive Wind-PV System with Battery Storage Using Neural Networks

This article analyzes the combined effects of random clouds and wind gusts on a grid-linked rooftop wind-photovoltaic system (WPS) with battery storage. For short period intervals, the wind speed and the solar radiation are considered as the sole sources of power whose variations influence the system variables. The stochastic nature of gusty winds creates a quasi-permanent transitory environment for the wind power subsystem, where the wind generator voltage and power undergo steep changes in short periods of time. Likewise, passing clouds affect the variables of the photovoltaics. Since both subsystems have different dynamics, their respective responses are expected to impact differently the overall system behavior. The system responses are predicted with artificial neural networks (ANN). Unlike conventional modeling, the ANN simulation does not require the knowledge of system parameters. This allows circumventing two major problems: parameter uncertainty and system non-linearity, which could be high for large systems with multiple components placed in unpredictable environment characterized by turbulent movement of wind and random cloud passage. The dynamics of the system are captured and stored in the connection weights between two consecutive layers. The dispatchability of the battery-supported WPS as well as its stability and reliability during gusts and cloud passage are also discussed.

NONLINEAR ACTUATOR FAULT DETECTION AND ISOLATION FOR A GENERAL AVIATION AIRCRAFT

This paper addresses the problem of detection and isolation of actuator faults for a general aviation aircraft, where the nonlinear simulation aircraft model embeds the effects of wind gusts, atmospheric turbulence and measurement errors. The approach is based on the recently introduced NonLinear Geometric Approach (NLGA) to the Fault Detection and Isolation (FDI) problem. The actuators FDI is performed in a coordinated turn, hence with coupled longitudinal and lateral–directional dynamics. This work represents the first complete NLGA FDI scheme for a general aviation aircraft in a condition with tight–coupled dynamics. The results obtained in the simulation of the faulty behaviour of a nonlinear Piper PA30 aircraft are finally reported.

Restructurable Guidance and Control for Aircraft with Failures Considering Gust Effects

This paper presents a procedure for designing a fault-tolerant guidance and control system for a damaged aircraft using the simultaneous online fault/wind estimation and the nonlinear restructurable guidance and control law. The algorithm employs an extended Kalman filter (EKF) and a nonlinear inverse dynamics (NID) controller with the singular perturbation method. The EKF, which is based on the six-degree-of-freedom nonlinear aircraft equations of motion, simultaneously estimates the aerodynamic derivative changes and the wind-velocity components. The NID controller computes the required control-surface deflections and engine thrust not only to stabilize damaged aircraft but also to enable the aircraft to track the reference trajectory using the estimated results in a gusty environment. The estimation algorithm is evaluated through flight-test data obtained by using the experimental aircraft. Numerical simulations are carried out to verify the guidance and control capability of damaged aircraft under gusty conditions.

Performance factors in ski jumping

Predominant performance factors in ski jumping are: High in-run velocity, high linear momentum perpendicular to the ramp at take-off due to the jumping movement and the utilisation of aerodynamic lift, accurate timing of the take-off jump with respect to the edge of the ramp, appropriate angular momentum at take-off in order to obtain an aerodynamically advantageous and stable flight position as soon as possible, choice of advantageous body and equipment configurations and angles of attack during the entire flight in order to obtain optimum lift and drag values and the ability to control the flight stability. After the transition from take-off to the flight phase the pitching moment has to be balanced close to zero (1) in order to avoid tumbling accidents; this can become extraordinary difficult when gust or other disturbing effects occur. During the flight, the gravitational force F g , the lift force F l, and the drag force F d act upon the athlete and his equipment and determine the flight path of the centre of gravity of a ski jumper with a given set of initial conditions and parameters. During the flight phase the athlete’s position changes. The athlete can strongly influence the aerodynamic forces by changing his posture. He can affect the drag force, the lift force and the torque; the latter enables him to change his flight position and angle of attack with respect to the air stream.