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Commonly used methods for identifying modal parameters under environmental excitations assume that the unknown environmental input is a stationary white noise sequence. For large-scale civil structures, actual environmental excitations, such as wind gusts and impact loads, cannot usually meet this condition, and exhibit obvious non-stationary and non-white-noise characteristics. The theoretical basis of the stochastic subspace method is the state-space equation in the time domain, while the state-space equation of the system is only applicable to linear systems. Therefore, under non-smooth excitation, this paper proposes a stochastic subspace method based on RDT. Firstly, this paper uses the random decrement technique of non-stationary excitation to obtain the free attenuation response of the response signal, and then uses the stochastic subspace identification (SSI) method to identify the modal parameters. This not only improves the signal-to-noise ratio of the signal, but also improves the computational efficiency significantly. A non-stationary excitation is applied to the spatial grid structure model, and the RDT-SSI method is used to identify the modal parameters. The identification results show that the proposed method can solve the problem of identifying structural modal parameters under non-stationary excitation. This method is applied to the actual health monitoring of stadium grids, and can also obtain better identification results in frequency, damping ratio, and vibration mode, while also significantly improving computational efficiency. [ABSTRACT FROM AUTHOR] more...

Given that the variable-camber continuous trailing-edge flap can enhance the environmental adaptability of wings, this study experimentally investigates the gust response of an airfoil with a flexible trailing edge. The flexible trailing edge comprises 30% of the airfoil chord length and can adaptively undergo chordwise deformation under flow pressure. The unsteady lift, surrounding flow field, and deformation of the flexible trailing edge are synchronously measured. Compared with the rigid airfoil, the time-averaged lift coefficient of the flexible airfoil increases under gust incoming condition, whereas the standard deviation of the lift coefficient decreases. In the case of a low angle of attack, two representative flow structures with distinct frequencies may be obtained, corresponding to the shear layer and shedding vortex. The shear layer above the upper surface of airfoil fluctuates at gust frequencies. The high-frequency vortex shedding in the wake region is significantly affected by the shear layer. The oscillation of the flexible trailing edge is fully coupled with nearby flow fluctuations, which is divided into four stages in one gust cycle. Additionally, compared with the rigid airfoil, the amplitudes of the shear-layer and velocity fluctuations for the flexible airfoil decrease, indicating that the flexible trailing edge can reduce the influence of gusts on the flow field. At a high angle of attack, dynamic stall occurs. A leading-edge vortex develops above the flexible trailing edge. The induced negative pressure causes the flexible trailing edge to deflect significantly upward, thereby weakening the strength of the leading-edge vortex and alleviating the gust load. [ABSTRACT FROM AUTHOR] more...

Regarding the dynamic magnification effect of structure stiffness on the gust analysis of civil aircraft, the following three methods are presented: rigid modes analysis, secondary processing based on elastic modes, and analysis with enlarged stiffness. These methods provide consistent gust load and address the challenge of extracting internal gust loads of rigid aircraft. The coupling resonant effects of the inertial force, the aerodynamic force, and the gust-induced aerodynamic force at different frequencies are examined. The response of flexible aircraft is nonlinearly related to frequency. It exhibits a significant increase in the inertial force and the aerodynamic force at higher frequencies, while a quasi-rigid response at very low frequencies shows the importance of sufficient analysis time. In addition, compared with rigid aircraft, flexible aircraft experiences a delay in the occurrence of extreme gust loads with the delay interval proportional to the frequency. The maximum gust load of flexible aircraft under a certain range of frequencies exceeds that of rigid aircraft, although this is not necessarily the case at the specific frequency. The dynamic magnification factor is 1.25 for the model in this study, which is almost constant and reaches its maximum value together with the gust loads when the frequency coincides with the frequency of the first bending mode. [ABSTRACT FROM AUTHOR] more...

An architecture for a UV wind lidar dedicated to measuring vertical and lateral wind in front of an aircraft for gust load alleviation is presented. To optimize performance and robustness, it includes a fiber laser architecture and a Quadri Mach–Zehnder (QMZ) interferometer with a robust design to spectrally analyze the backscattered light. Different lidar parameters have been selected to minimize the standard deviation of wind speed measurement projected onto the laser axis, calculated through end-to-end simulations of the instrument. The optimization involves selecting an emission–reception telescope to maximize the number of collected photons backscattered between 100 and 300 m , a background filter to reduce noise from the scene, and photomultiplier tubes (PMTs) to minimize detection noise. Simulations were performed to evaluate lidar performance as a function of laser parameters. This study led to the selection of three laser architectures, a commercial solid-state laser, a design of a fiber laser, and a hybrid fiber laser, resulting in standard deviations of projected wind speed of 0.17, 0.16, and 0.09 ms-1 , respectively, at 10 km altitude. To reconstruct the vertical and lateral wind on the flight path, the lidar is directed along four different directions to measure four different projections of the wind. We analytically calculate (and validate through simulations) the directed angle with respect to the flight direction that minimizes the root mean square error (RMSE) between the reconstructed vertical and lateral wind components and the actual ones, assuming turbulence that follows the von Kármán turbulence model. We found that the optimum angle for an estimation at 100 m is about 50°, resulting in an improvement of about 50 % compared to an angle of 15–30° typically used in current studies. [ABSTRACT FROM AUTHOR] more...

As part of the Ultra High Aspect Ratio Wing Advanced Research and Designs (U-HARWARD) project, funded by CS2JU, various gust load alleviation (GLA) technologies have been developed and studied. GLA plays a crucial role in the development of new generation ultra-high aspect ratio wings (UHARWs), as it reduces gust loads, thereby decreasing the structural weight of the wing and, consequently, the entire aircraft. This weight reduction enhances overall aircraft efficiency, enabling a higher aspect ratio. GLA technologies are categorized into passive systems, which require no active intervention, and active systems, where control surfaces redistribute the aerodynamic loads. In this study, passive GLA was implemented using a folding wing tip (FWT) developed by the University of Bristol, while active GLA employed a Static Output Feedback controller developed by Politecnico di Milano. Both approaches were compared against a baseline aircraft configuration. A flutter assessment confirmed that FWT does not introduce aeroelastic instabilities, ensuring the aircraft remains flutter-free across its flight envelope. A thorough comparison of load envelopes, based on nearly 2000 load cases across different flight points and mass configurations, was conducted in compliance with CS25 regulations, examining both positive and negative gust conditions. The results show a possible 15% reduction in the dynamic load envelope for both passive and active solutions. Using NeOPT, a hybrid finite element (FE) model was developed, with a detailed global FEM (GFEM) for the wingbox and stick elements for other components. Linear gust analyses in Nastran, with the hinge locked and released, provided high-fidelity results, comparing wing failure indexes and demonstrating the effectiveness of the FWT solution. [ABSTRACT FROM AUTHOR] more...

The procedure to estimate the amplitude of the special wind events according to IEC 61400‐1 as proposed by Larsen is reviewed. Corrections are specified that yield larger amplitudes for the extreme operating gust (EOG) and the extreme coherent gust with simultaneous direction change (ECD). For the ECD case, distributions for longitudinal and lateral gust amplitudes are derived and applied in simulations to derive the load distribution, from which the 50‐year extreme load can be found. Results are compared with the calculation with the conventional ECD: In the example calculation, the 50‐year values of both blade root bending moment and tip deflection are smaller than the conventional values. [ABSTRACT FROM AUTHOR] more...

Thunderstorm downbursts are transient in nature and have been responsible for a variety of structural damages in recent years. Currently, the researchers have done several works on the characteristics of downburst wind speed. Nonetheless, rare attention has been placed on the structural aerodynamics characteristics subjected to downburst winds. Based on this, an experimental investigation is performed to reproduce downburst-like winds physically and to study the transient surface pressures (SPs) on a 5:1 rectangular cylinder (RC). The experiment is conducted within a multiple-fan active control wind tunnel (MFACWT) and mainly focuses on simulating the transient characteristics of downburst-like flow, including time-varying mean (TVM) wind speed and nonstationary wind fluctuation. The resulting SPs are measured to understand the influence of transient wind on the aerodynamic behavior of bluff bodies. The spatiotemporal characteristics of the SPs are analyzed using wavelet transform and Priestley's classic spectral theory. The results indicate that the transient nature of the downburst-like flow can be physically reproduced by a MFACWT. The instantaneous pressures of a RC are illustrated by both the turbulence parameters of the transient flow and the flow-separation characteristics. The pressure coefficients normalized by the TVM of the downburst-like winds remain constant, which provides a more appropriate way to estimate the transient gust loading in a quasi-steady manner. Interestingly, the phenomenon of the time-varying phase shift and time-varying correlation of chordwise SPs is observed when the turbulent velocity changes dramatically. In addition, the normalized surface pressure can be regarded as a stationary stochastic process, which provides a significant basis for further establishing the theoretical model of nonstationary gust-loading. [ABSTRACT FROM AUTHOR] more...

Identifying gusts and turbulence events is of primary importance for designing future gust load alleviation systems, calculating airframe load, and analysing incidents. Due to the impossibility of their direct measurement, indirect methods are used and ad hoc experiments are necessary to validate the methodology. This paper employs Convolutional Neural Network and Long Short Term Memory (CNN-LSTM) as well as CNN models for in-flight gust identification. Two aeroelastic models, with different levels of fidelity, representative of a civil and commercial aircraft, are used to generate gust responses to train and test the Deep Learning (DL) models. The results highlight the capability of both LSTM-CNN and CNN models in reconstructing gusts across the entire flight envelope of a civil commercial aircraft. The CNN model demonstrated its ability to identify gusts and turbulence when they occur concurrently, similar to real-world scenarios, in a significantly shorter amount of time. Furthermore, its application to wind tunnel gust response measurements, where the inflow has previously been characterised, demonstrated the effectiveness of the proposed methodology for experimental measurements. • CNN-LSTM and CNN models employed for accurate gust identification. • Methods rigorously applied to both numerical and experimental data. • Utilizing aeroelastic aircraft models with varied fidelity for identification • Identified gusts compared with those from gust generator characterization. • Results showcase significant capability in accurate gust prediction. [ABSTRACT FROM AUTHOR] more...

In this research article, Python programming has been used to model the dynamic wind loading on the structures by using the Gust factor approach. The evaluation has included the design wind velocity and pressure, the Gust factor, and wind loads, which are in sync with the stability criteria as outlined in the IS 875 (Part 3), 2015. One practical numerical problem has been addressed to assess the accuracy and reliability of the developed functions, by providing a detailed step-by-step explanation of the programming process and algorithm. The results thus obtained have demonstrated a very good agreement with the results which have been obtained by using the analytical approach. The observations have indicated that the windward loads exhibit higher magnitudes than those in the across-wind direction. Notably, it has also been observed that the wind loads decrease with the height due to reductions in the tributary area and the top mean floor height. [ABSTRACT FROM AUTHOR] more...

Mitigation of gust-induced separation and aerodynamic loads using a high-frequency blowing/suction slot is demonstrated using high-order implicit large eddy simulation (LES). This approach was previously shown to be effective at alleviating dynamic stall on pitching wings. A NACA0012 wing section operating at a transitional chord-based Reynolds number of Rec=500,000⁠, subsonic freestream Mach number of M∞=0.1 ⁠, and angles of attack of α = 4 deg and 12 deg is subjected to discrete 1-cos transverse gusts. Gust-induced stall is demonstrated and then active flow control (AFC) is applied to cases vulnerable to gust-induced stall. The flow control strategy is shown to be effective at stall suppression during gust encounter, thereby providing partial alleviation of gust induced loads. This approach is most effective at attenuating pitching moment increment. [ABSTRACT FROM AUTHOR] more...

Traditional pressure measurements fail to determine the buffeting force on bridge decks with complex configurations, such as truss or box girders with two slabs. The high-frequency force balance (HFFB) provides an efficient way to solve this aerodynamic issue. This work aims to clarify the spatial distribution characteristics of gust loading acting on a strip of a bridge deck with a projecting slab using force measurements with double-HFFBs. Based on Ribner’s three-dimensional (3D) spectral tensor theory, the relationship between the buffeting forces on an equivalent strip and segment can be derived. The three-dimensional aerodynamic admittance (3D) can be identified considering the 3D effect of turbulence, which can be decoupled into 2D AAF and spanwise correction factor. The results show that the influences of segment lengths and turbulence on the 2D AAF and coherence of the equivalent strip can be eliminated, indicating the validity of the proposed approach. Finally, the applicability of strip theory in estimating the buffeting response of long-span cable-stayed bridges is investigated using finite element analysis. [ABSTRACT FROM AUTHOR] more...

Supersonic aircraft is defined as aircraft that can travel at speeds above the speed of sound (M > 1). For these aircraft, correct dimensioning is essential to enable them to withstand the high aerodynamic loads they face. This study evaluates the impact of internal architecture, boundary conditions, and material on the dimensioning of the vertical tailplane when subjected to a gust load. The optimal configuration is the one that achieves a balance between weight and structural performance. Titanium alloy Ti 6AI‐4 V and carbon/carbon composites are selected as the most suitable materials for this application due to their known high‐temperature resistance. The best configuration, although it weighs 20% times more than the composite configuration, manages to achieve a reduction in tip displacement of 80%, significantly improving strength and instability performance. [ABSTRACT FROM AUTHOR] more...

This paper introduces three new gust load alleviation control strategies, which are based on variable camber technology, to achieve the design requirements for the safety, economy, and comfort of modern civil aircraft. These strategies involve adjusting the inner and outer flap differential of wings, spoilers, and ailerons to alter the aerodynamic shape of the aircraft structure, resulting in drag reduction and gust load alleviation during stepped cruise flights. Furthermore, a logic design is provided for both the cruise drag reduction function and the gust load alleviation function. To validate the effectiveness of the proposed gust load alleviation control strategies, simulation results are presented, utilizing ride quality and wing root bending moment changes as the evaluation criteria. The presented approaches ultimately lead to the development of an optimal scheme that meets the desired design requirements. [ABSTRACT FROM AUTHOR] more...

When tower cranes are applied in coastal engineering, the wind-induced vibration under complex wind loads along the coast will be exceptionally obvious. It is increasingly important to explore the wind-induced vibration characteristics of different sections of tower cranes under full wind angles. This paper first establishes a three-dimensional numerical wind tunnel model that can be used for the simulation of tower cranes under full wind angles and analyzes the aerodynamic load variation of the tower crane under full wind angles. Secondly, the tower crane structure is divided into sub-regions, and the AR model method in the linear filtering method is used to simulate the three-dimensional wind speed time history. Further, the wind speed time history is applied to the finite element transient analysis, and based on the Newmark-β method, the acceleration and displacement responses of different sections of the tower crane structure under fluctuating wind are systematically studied. Finally, the equivalent static wind load of different sections of the tower crane is evaluated by using the gust load factor method. The results indicate that the wind load of the tower crane exhibits an obvious three-dimensional effect, and the crosswind load cannot be ignored in the analysis of wind stability. The different sections of the tower crane structure show low-frequency vibration characteristics, and the low-frequency band is dominated by down-wind vibration, while the high-frequency band often experiences crosswind vibration. The amplification effect of the tower crane on fluctuating wind loads will increase with the increase of the height of the tower crane and the length of the jib, and the amplification effect on fluctuating wind loads in the crosswind direction is more obvious. The equivalent static wind load on the top of the tower crane reaches the maximum when the angle between the jib and the incoming wind is 60◦ . [ABSTRACT FROM AUTHOR] more...

This document is an editorial introducing a special issue of the journal Aerospace on the topic of gust influences on aerospace. The editorial highlights the importance of studying gusts in aerospace engineering, as they can have adverse effects on aircraft and their control systems. The special issue includes eight peer-reviewed papers that cover various aspects of gust research, such as numerical investigations of flow control, experimental approaches on propeller blade geometries, and simulations of rotor aerodynamic performance. The authors express their gratitude to the contributors and reviewers for their contributions to the special issue. [Extracted from the article] more...

The cable-suspended PV system has gained increasing popularity due to its large span and good site adaptability. However, this structure is quite sensitive to wind actions, and wind-induced module damage and structure failure have been frequently reported. Therefore, in this study, we carried out wind tunnel tests to study wind load effects on PV arrays with different lengths and widths. Considering the wind sheltering effects of upstream modules, reduction factors for the wind load were proposed in different array zones. Numerical simulations of wind-induced vibration and equivalent static analysis were conducted to yield gust loading factors for the PV array. This study showed that the maximum wind suction and pressure for the middle zone occurred at 0° and 180°, respectively, while those for the outermost zone appeared under oblique flows (e.g., 30° and 150°). For the PV modules beyond the windward fourth row, the reduction factors of the wind loads were 0.4 (maximum suction) and 0.2 (maximum pressure) for the middle zone and 0.5 (maximum suction) and 0.75 (maximum pressure) for the outermost zone. The gust loading factors for the typical wind directions of 0° and 180° varied from 2.2 to 2.7 for the middle zone and from 1.3 to 1.5 for the outermost zone. [ABSTRACT FROM AUTHOR] more...

Based on measured gust information, a multi-input multi-output (MIMO) adaptive feed-forward control scheme for gust load alleviation (GLA) on a semi-span flying-wing aircraft using multiple control surfaces is proposed. In order to remedy weight drift and biased estimation problems that are commonly encountered in adaptive control, the circular leaky LMS (CLLMS) algorithm is employed, which utilizes gust measurement information, filtered reference signals, and error signals to update controller parameters online. The results demonstrate that good load reductions are achieved in both continuous and discrete gust environments. For instance, the designed GLA control system leads to an 80.72% reduction in the root-mean-square (RMS) values of wing-root bending moment in the Dryden gust environment and a 77.59% reduction of its maximum value in the 1-cos discrete gust condition. Based on the limited power of the actuator and the limited authority for control surface deflections when integrating GLA into the flight control system, a weight-updating algorithm with deflection angle and rate constraints on control surfaces is proposed. The simulation results show that the strict constraints on control surface deflections will degrade the GLA performance. Finally, the influence of the partial jamming fault of actuators on GLA performance is studied. It is found that good GLA performance can be preserved despite the degraded performance during the initial stage of the actuator jamming fault. This is due to the robustness brought about by multiple control surfaces and the adaptability of the control algorithm. [ABSTRACT FROM AUTHOR] more...

This paper investigates the effect of wingtip bending morphing on gust-induced aerodynamics based on the fluid–structure interaction (FSI) method at Re = 40 000. First, an explicit spatiotemporal numerical model for a wingtip bending morphing on a wing with a semi-aspect ratio of 4 is deduced, considering geometrical nonlinearity under large morphing amplitude. A modal-based FSI framework is developed to consider the elastic deformation, active wingtip morphing, and gust. The shear-stress transport-γ model is introduced. The above FSI method is validated by gust response experimental results. The mitigation effects of active bending morphing on gust-induced aerodynamics at different phase offset, gust ratios (GR), and flare angles are investigated. Under GR = 0.2 and flare angle = 0, wingtip bending morphing achieves the best mitigation effect when the phase offset is π/2. As GR increases to 0.4, the optimum phase offset shifts to π/3 and the alleviation rate decreases. The mitigation rate increases with the flare angle. Under GR = 0.4 and flare angle = 30°, the optimum phase offset is π/6, in which case the lift response is reduced by 37%, and wing root bending moment response is reduced by 73% relative to the baseline case. The flow field and vortex evolution result infers that the wingtip bending morphing decreases the spanwise width of the leading-edge vortex and reduces the area of low-pressure zones on the suction side, thereby mitigating gust-induced aerodynamics. The results indicate that active wingtip bending morphing has great potential for gust load alleviation for future aircraft. [ABSTRACT FROM AUTHOR] more...

This study aims to investigate the influence of turbulent three-dimensional (3D) and distortion effects on the unsteady lateral buffeting force of trains on a streamlined deck and propose a closed form equation for the 3D aerodynamic admittance function (AAF). Six fluctuating wind fields were simulated to analyze the influences of different turbulence characteristics on the lateral force of trains through pressure measurement tests. In addition to a train on a bridge, a plain ground scenario was simulated as a reference. The results show that the lateral force correlation of the train is always greater than that of the fluctuating wind. As Lu/D increases, the lateral force coefficient and spanwise correlation of the lateral force increase, and the 3D effect weakens. The AAF is sensitive to Lu/D at high frequencies, and the wind exhibits a clear distortion effect during turbulence flow on the train. A difference exists between the aerodynamic characteristics of trains on the ground and on a bridge. The turbulence intensity has little influence on the lateral aerodynamic characteristics of a train. To correct the uncertainty caused by the 3D and distortion effects, a generalized AAF model was proposed to accurately estimate the gust loading on a train. [ABSTRACT FROM AUTHOR] more...

This paper studies the aeroelastic behavior of a rectangular, cantilever wing equipped with the spanwise morphing trailing edge (SMTE) concept. The SMTE consists of multiple trailing edge flaps that allow controlling the spanwise camber distribution of a wing. The flaps are attached at the wing's trailing edge using torsional springs. The Rayleigh–Ritz method is used to develop the equations of motion of the wing-flap system. The use of shape functions allows for representing the wing as an equivalent 2D airfoil with generalized coordinates that are defined at the wingtip. Strip theory, based on Theodorsen's unsteady aerodynamic model, is used to compute the aerodynamic loads acting on the wing. A representative Padé approximation for Theodorsen's function is utilized to model the aerodynamic behaviors in a state-space form allowing time-domain simulation and analysis. The model is validated using a rectangular cantilever wing and the data are available in the literature. A comprehensive parametric comparison study is conducted to assess the impact of flap stiffness on the aeroelastic boundary. In addition, the potential of the SMTE to provide load alleviation and flutter suppression is assessed for a wide range of flight conditions, using a discrete (1-cosine) gust. Finally, the implementation and validation of a controller for a wing with SMTE for gust load alleviation are studied and controller parameters are tuned for a specific gust model. [ABSTRACT FROM AUTHOR] more...

This paper presents the design of an innovative wingtip device actively actuated to control the aeroelastic loads, with a focus on the gust load alleviation. It summarizes the work carried out in the Clean Sky 2 AIRGREEN2 project, where the device was developed from scratch and reached a relevant technology readiness level with the full-scale prototype manufacturing and testing, compulsory to obtain the permit to fly. This paper describes the overall design of the devices, covering the structure, the aero-servo-elasticity characteristics of the whole aircraft, the actuation system design, the scaled wind tunnel testing, and the full-scale structural qualification tests. The paper proves how the development of a new item involves several disciplines simultaneously, remarking on the importance of an integrated approach to the new generation aircraft design. [ABSTRACT FROM AUTHOR] more...

A wing travelling at a constant angle of attack, α , experiences a large lift spike when subjected to a high-amplitude transverse gust. This study analyses the capability of a low-order model, which uses Wagner and Küssner theory, to calculate a pitch motion profile that mitigates such a lift increase. The model's pitch profiles are tested experimentally by towing a wing at a constant α towards a top-hat transverse gust. Throughout the gust encounter, the wing is pitched with a profile predetermined by the model. Force and flow measurements are analysed for gust ratios of 0.5 and 1.0 and angles of attack of 0, 10, 20 and 45 degrees. In addition, two gust directions are analysed: upwards where the gust velocity is in the direction of positive lift, and downwards (in the opposite direction). The latter produces a large negative lift spike that can be especially dangerous for flying vehicles. Experimental results demonstrate strong mitigation, around 85%, of the gust loads up to an effective angle of attack of 60 degrees, independently of gust direction. The theories used achieve mitigation even at large perturbations and separated flows, where the assumptions used on their derivation are clearly invalid. The mitigation approach does, nevertheless, not mitigate the secondary lift peak that emerges after gust exit when the initial wing incidence exceeds 10 degrees. This secondary peak is a result of attached flow around the wing right after gust exit, which eventually develops into a LEV that sheds from the wing. [ABSTRACT FROM AUTHOR] more...

Wind stability and design loads of long-span bridges are assessed applying experimental and theoretical methods. The commonly used approach entails the extraction of fundamental aerodynamic data of key structural elements such as the deck, towers, and cables, either experimentally or numerically, and the application of theoretical models for evaluation of structural responses to turbulent winds. This phenomenon called buffeting is extremely complex and, to date, there is no closed-form theoretical model to reproduce how the wind converts to structural responses and loads which the bridge must resist. The objective of this paper is to explore the base of the problem, namely the transformation of wind gusts to actual loads, and the response estimations. The time domain response approach has been adopted for solution of the generalized equations of motion allowing the exploration of details in the performance of various theoretical interpretations. Starting from the classic quasi-static linear model, theoretical simplifications are removed toward a more complete model of buffeting loads. Non-linear and aerodynamic coupling effects on response predictions are examined specifically aiming at improved buffeting load representations within the framework of the currently available experimental data. A new concept called stack state-space analysis has been introduced for the response solution to wind buffeting. Aerodynamic and structural data of Pierre-Laporte Bridge in Québec City, and the IABSE Working Group 10, long-span bridge validation example, are utilized as representative cases in this study. Avenues for further experimental and numerical validations of the presented new solution approach are suggested toward more accurate predictions of wind response and design loads of long-span bridges. [ABSTRACT FROM AUTHOR] more...

This paper proposes an incremental nonlinear control method for an aeroelastic system's gust load alleviation and active flutter suppression. These two control objectives can be achieved without modifying the control architecture or the control parameters. The proposed method has guaranteed stability in the Lyapunov sense and also has robustness against external disturbances and model mismatches. The effectiveness of this control method is validated by wind tunnel tests of an active aeroelastic parametric wing apparatus, which is a typical wing section containing heave, pitch, flap, and spoiler degrees of freedom. Wind tunnel experiment results show that the proposed nonlinear incremental control can reduce the maximum gust loads by up to 46.7% and the root mean square of gust loads by up to 72.9%, while expanding the flutter margin by up to 15.9%. [ABSTRACT FROM AUTHOR] more...

SensorCraft is an intelligence, surveillance, and reconnaissance (ISR) system that integrates unmanned flight platforms and airborne antenna arrays. Under gust loads, the high–aspect–ratio, light–wing structure of SensorCraft has considerable bending and torsion deformation, affecting the flight performance of unmanned flight platforms and leading to the loss of antenna arrays' electromagnetic performance. Taking SensorCraft as the background, a wing conformal antenna array was designed, an aircraft model with a passive wingtip device was established, a control law was developed by the LQG/LTR method, and a gust alleviation active–passive combined control method of a "LQG/LTR active controller + passive wingtip device" was proposed. By constructing an unsteady aerodynamic reduced–order model (ROM) based on the Volterra series and a conformal array pattern fast method based on the modal form, the effectiveness of the gust alleviation active–passive combined control method on the aircraft platform and antenna array was analyzed. The results show that structural deformation of the wing conformal antenna leads to changes in the main lobe gain, beam direction, and sidelobe level. The active–passive gust alleviation method has obvious advantages. Compared with the LQG/LTR active gust alleviation method, the peak value of wingtip displacement is reduced by 15.6%, and the peak value of the gain loss is reduced by 0.72 dB, which is conducive to better performance of the airborne conformal antenna array. [ABSTRACT FROM AUTHOR] more...

Piezoelectric sensors and actuators have been widely used in many fields. In this study, the reliability of a piezoelectric actuator to alleviate the flutter of a flexible rectangular cantilever beam under wind load is investigated. Firstly, a dynamic calculation model of the cantilever beam underload is derived. Secondly, the derived dynamic calculation model of the cantilever beam is extended with a piezoelectric actuator. Thirdly, two types of wind load on the beam are considered. Finally, the reliability of using one and two actuators to alleviate the flutter of the beam under different wind loads is simulated. The proposed calculation model has practical engineering significance and feasibility for the reliability design and maintenance of unmanned aerial vehicle (UAV) wings and wind power devices. [ABSTRACT FROM AUTHOR] more...

Flap deflections of an aircraft wing for active load alleviation within CFD simulations are realized using pure grid deformation due to time saving and low modeling complexity. In this case, spanwise gaps are neglected, which are present in reality during a flap deflection. Another possibility to realize the deflections is the combination of pure grid deformation and Chimera method, which allows the modeling of the gap between flap and wing or consecutive flaps. The overall aim of this work is the analysis of the aerodynamic effects caused by the different modeling approaches realizing leading and trailing edge flap deflections. The comparison of the modeling methods is investigated on the DLR LEISA configuration, which is a generic wing‐fuselage configuration. For active gust load alleviation, the leading edge flaps are deflected downward and the trailing edge flaps are deflected upward. Due to the downward deflection of the leading edge flaps, vortices are formed using the combined Chimera method as a result of the gap consideration. These vortices lead to a local drag increase resulting in a difference between both modeling methods in the spanwise as well as global drag coefficient. With the pure grid deformation these vortices do not occur. Due to the upward trailing edge deflection, the combined Chimera method leads to a pressure compensation via the effective gap enlargement, which is not present in the pure grid deformation. Overall, the combined Chimera method offers a good possibility to model the induced drag as well as the pressure compensation at a large flap deflection. [ABSTRACT FROM AUTHOR] more...

Microjets arranged on the wing surfaces of civil transport aircraft have been shown to have great potential in suppressing high-frequency gust loads. This paper presents a study of aerodynamic load reduction on a supercritical airfoil using tilted microjets by solving the Reynolds-averaged Navier-Stokes (RANS) equations. The numerical method was first validated against the experimental and previous numerical data. Afterward, the subsonic and transonic flowfields around the supercritical airfoil were simulated with various angled microjets. The results show that both the lift reduction and the power efficiencies significantly increase as the blowing direction shifts downstream to upstream. The movement and weakening of the shock due to the jet are observed at α > 2 ∘ in transonic flow, resulting in a drag reduction compared to the baseline airfoil. However, the transient subsonic results revealed that the upstream jet induces a strong vortex shedding, which is suppressed in transonic flows. During jet deployment, there are three distinct phases: time lag, vortex rolling-up, and rebalancing, in that order. Once it reaches the trailing edge in subsonic flows, the starting vortex rapidly modifies the load and induced a strong roll-up vortex from the pressure surface. Nevertheless, in transonic flow, the rebalancing stage contributes to a greater reduction in lift due to the additional shock movement and weakening effect. [ABSTRACT FROM AUTHOR] more...

To investigate the stochastic characteristics of vehicle-bridge (VB) system under crosswind, an efficient method which combines AutoRegressive Moving Average with eXogenous inputs (ARMAX) model, high-order differencing (HOD) and important sample was proposed in this paper. First, the wind turbulence spectra relative to a moving vehicle and equivalent static gust load method were adopted to simplify the turbulent wind field of VB system, and a wind-vehicle-bridge (WVB) model was established and verified. Then, an analysis framework for WVB system based on ARMAX model was proposed, and HOD method and important sample were used to improve the prediction performance of the surrogate model. Prediction accuracy and calculation efficiency of proposed AMRAX model were verified and compared by Monte Carlo simulation (MCS). Finally, the impacts of vehicle speed and wind velocity on the stochastic characteristics of train response were discussed. Results indicate that the HOD method has significantly improved the prediction performance of ARMAX model for lateral response of trains, and the train responses predicted by ARMAX model based on HOD and important sample show perfect agreement with target results. Compared with MCS, the calculation efficiencies of proposed ARMAX model are improved by about two orders of magnitude. The extreme values of the train response with different vehicle speed and wind velocity gradually obey right skewness distribution, especially the lateral acceleration. [ABSTRACT FROM AUTHOR] more...

Active load alleviation can substantially contribute to decrease structural weight and emissions of future transport aircraft by limiting peak aerodynamic loads that the aircraft experiences during flight. Fluidic actuators, as part of active load alleviation systems, have the potential for faster and more complete gust load reduction. The performance of a dual slot circulation control airfoil for gust load alleviation is investigated experimentally on a supercritical airfoil model. The tests are conducted in a low-speed wind tunnel at a chord-based Reynolds number of Re = 1.5 · 10 6 and M ∞ = 0.14 . The model features an elliptical Coandă geometry integrated into the airfoil's trailing edge to minimize cruise performance penalty, while still allowing for substantial load reduction. Blowing from a single slot, as well as simultaneously from pressure and suction side slots is tested over a range of blowing rates to assess the impact on load modification. Both steady and impulsive activation performance are evaluated based on surface pressure, integral load, and flow field measurements around the Coandă geometry. High control authority is found for upper and lower single slot blowing, with peak changes in lift coefficient of about ± 0.33 and lift-to-equivalent-drag ratio change of up to 100. Similar peak lift changes and reduced equivalent drag are obtained by adding marginal ( < 14 % of total) blowing from the opposite slot, which also reduces pitching moment changes for primary upper and marginal lower blowing. Impulsive jet activation exhibits load control authority comparable to steady actuation and sufficiently short onset times to counteract all gusts defined by certification documentation. [ABSTRACT FROM AUTHOR] more...

Background: Very-long-baseline interferometry (VLBI) is a technique employed in radio astronomy where a signal from a planetary radio source is collected on earth at multiple radio antennae. Working in a network, the time difference of the radio signal reception by the antennae is employed to achieve an effective aperture allowing for the development of a significantly high-resolution images of the space. However, the signal clarity of each individual antenna is dependent on its structural response under environmental conditions. This paper proposes a design optimization framework for VLBI antennae for their performance maximization under aerodynamic gust employing structural geometric nonlinearities. Purpose: The dynamic aeroelastic response of the antenna is attenuated by optimizing actuation length changes in active structural elements to improve the pointing accuracy of the VLBI antenna under wind gust loads. No framework currently exists in the open literature that leverages the principles of tensegrity structures for vibration attenuation of VLBI antenna using control actuations, therefore, the need for such a framework has been established to design high-performance VLBI ground stations. Methods: Dynamic aeroelastic gust analysis is performed considering the Power Spectral Density (PSD) with the Davenport spectrum (DS) statistical model and Tuned Discrete Gust analysis with a One-Minus Cosine gust profile. Analyses are performed for two different operating conditions using time-consistent loads (TCL) and time-consistent displacements (TCD). Additionally, the effect of a varying number of active elements for control actuations is analyzed in the boomarm subsystem of the VLBI antenna while minimizing both the pointing error and total strain energy using an optimization framework employing a Multi-Objective Genetic Algorithm (MOGA). Results: A case study was presented to showcase the proposed framework. A reduction of 82.6% with a total strain energy increase of 292.5% was obtained for the primary operating case under PSD gust excitation. On the other hand, at the increased mean wind speeds of the secondary operating case, the developed design algorithm was able to reduce the total pointing error by 80.9% but with a total strain energy increase of 825.3%. Similarly, for TDG analysis with the OMC excitation profile the optimization algorithm reduced the total pointing error by 51.6% with a TSE increase of 2098.1% and 80.5% with a TSE increase of 48.7% for the primary and secondary operating conditions, respectively, when compared to the uncontrolled response. Conclusion: It is found that in all subcases analyzed the developed optimization framework successfully found the best response of the antenna using the utopian point method. These results confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR] more...

Featured Application: Gust load control, aircraft weight reduction, aircraft drag reduction. Effective control of aerodynamic loads, such as maneuvering load and gust load, allows for reduced structural weight and therefore greater aerodynamic efficiency. After a basic introduction in the types of gusts and the current gust load control strategies for aircraft, we outline the conventional gust load alleviation techniques using trailing-edge flaps and spoilers. As these devices also function as high-lift devices or inflight speed brakes, they are often too heavy for high-frequency activations such as control surfaces. Non-conventional active control devices via fluidic actuators have attracted some attention recently from researchers to explore more effective gust load alleviation techniques against traditional flaps for future aircraft design. Research progress of flow control using fluidic actuators, including surface jet blowing and circulation control (CC) for gust load alleviation, is reviewed in detail here. Their load control capabilities in terms of lift force modulations are outlined and compared. Also reviewed are the flow control performances of these fluidic actuators under gust conditions. Experiments and numerical efforts indicated that both CC and surface jet blowing demonstrate fast response characteristics, capable for timely adaptive gust load controls. [ABSTRACT FROM AUTHOR] more...

The European H2020 project SLOWD is aimed to investigate the fuel sloshing damping effect to reduce the design loads on aircraft wings. Wings house the fuel tanks and are highly flexible structures that can significantly deform under gust loads. In the recent experiment by Martinez-Carrascal and González-Gutiérrez ["Experimental study of the liquid damping effects on a SDOF vertical sloshing tank," J. Fluids Struct. 100, 103172 (2021)], the complex problem of the fuel sloshing inside a flexible wing structure was significantly simplified by considering a partially filled vertically heaving tank attached to a system of springs. In the present research, a smoothed particle hydrodynamic model was adopted to evaluate the energy dissipated in the three-dimensional sloshing flow obtained using the same tank motions. From a numerical point of view, the simulation of such a violent flow is rather challenging, the involved vertical accelerations being as large as 10 g. The resulting flow is extremely complex because of the severe turbulence developed, the violent impacts, and the considerable fragmentation of the air–liquid interface. The role of the viscosity is investigated by taking into account two different liquids. Finally, some comparisons between three-dimensional results and previous two-dimensional studies are also discussed. [ABSTRACT FROM AUTHOR] more...

• A novel state-space aeroelastic model is derived for permeable airfoils. • Static and dynamic aeroelasticity of permeable airfoils are studied. • A novel parametric analysis is presented to assess the effects of permeability. • The effects of the boundary conditions are addressed. This work addresses the aeroelasticity of airfoils with permeable trailing sections which is a topic that has not been studied in the literature before. There has been an increasing interest in the past few years regarding the analysis of permeable airfoils from the aerodynamics and aeroacoustics points of view. So, this work adds a new aspect to the analysis by considering the airfoil elasticity and flexibility effect. Two types of airfoils are considered: membrane airfoils and flexible-chord airfoils. Both static and dynamic aeroelastic studies of permeable airfoils are presented through a parametric analysis to investigate the effects of the permeable section length, permeability factor, boundary conditions represented by the membrane fixed or elastic supports and the elastic center position of flexible-chord airfoils, and the elastic properties of the airfoils like the bending rigidity of flexible-chord airfoils and the tension coefficient of membrane airfoils. The aeroelastic model of permeable airfoils is derived using the Hamilton's variational principle and the finite element method. The finite element system of equations is presented in a time domain nonlinear form to account for the nonlinear stiffening of membrane airfoils. The seepage flow through the permeable section is modeled using Darcy's law. The effects of permeability on the static aerodynamic coefficients, the dynamic response under a sinusoidal gust, and the aeroelastic instabilities (divergence and flutter) are investigated. The study aims at the aeroelastic performance of permeable airfoils subjected to incompressible airflows at small angles of attack and moderate to high Reynolds numbers, so the potential flow theory is adopted for the aerodynamic modeling. The analysis shows that permeability can have a significant effect on the aeroelastic responses of airfoils. The trailing permeable section changes the pressure distribution which changes the lift curve slope and the aerodynamic center position which in turn affects the aeroelastic instabilities and responses. This permeability effect strongly depends on the airfoil's stiffness represented by the bending rigidity of the flexible-chord airfoils and the tension in the membrane airfoils. [ABSTRACT FROM AUTHOR] more...

Although a reduction in lift-induced drag by having larger wing spans potentially improves aircraft performance and fuel consumption, it could bring about structural and maneuverability challenges. Folding Wing-Tip (FWT) devices offer a solution by enabling higher aspect ratios during cruise while being folded to meet the size constraints on the ground or other flight conditions. This study investigates active control of Flared FWT (FFWT) for Gust Load Alleviation (GLA) as well as limit cycle oscillations (LCOs) suppression of flexible wings, while addressing the limitations of previous passive approaches. To this end, an enhanced aeroelastic model is developed that incorporates unsteady aerodynamics via Theodorsen's theory to capture the nonlinear dynamic effects. Proportional-Integral-Derivative (PID) and Linear Model Predictive Control (LMPC) strategies are designed to minimize the Wing Root Bending Moment (WRBM) by adjusting the wingtip tab angle. Simulations demonstrate the LMPC outperforms PID controller by reducing peak WRBM by around 10% on average against various gust scenarios in comparison with the passive case. Both controllers effectively eliminated sustained LCOs beyond the bifurcation point. The present work extends previous FFWT studies by introducing active control and improved aerodynamic modeling in the control design process. The demonstrated ability to alleviate gust loads and expand stable flight regime paves the way for potential implementation of the proposed active FFWT control to enhance aircraft efficiency while mitigating structural impacts. • An improved aeroelastic model incorporating unsteady aerodynamics is developed. • Nonlinear dynamics including limit cycle oscillations are captured. • PID and linear MPC controllers are designed for gust load alleviation (GLA). • Active control effectively reduces wing root bending moment (WRBM) under gust inputs. • LMPC outperforms PID, reducing peak WRBM around 10% on average for different gust scenarios. [ABSTRACT FROM AUTHOR] more...

• Future sustainable aviation Goals: truss-braced wing (TBW) configurations, compatible with traditional or novel propulsion technologies, have been proposed to support sustainable aviation, necessitating an understanding of propulsion system design impacts. • Integrated propulsion system Sensitivities: coupled aerodynamic, flight dynamics, and structural dynamics models reveal that TBW configurations are more sensitive to powerplant location compared to conventional aircraft, highlighting the importance of such architectural design considerations. • Dynamic load Response: TBW configurations exhibit increased coupling between powerplant swing and wing bending modes, significantly influencing their dynamic response under gust loading scenarios. • Distinct sensitivities for propulsion Types: conventional TBW systems are more sensitive to powerplant mass, whereas hybrid-electric TBW systems are more influenced by pylon stiffness variations, underscoring the need for tailored structural optimisation. Strut-, or Truss-Braced Wing configurations, compatible with traditional or more novel propulsion technology, have been proposed to meet future sustainable aviation goals. However, an understanding of how propulsion system performance and/or design is impacted by such novel architectural changes is required to develop an optimal integrated propulsion system solution. With a focus on the structural characteristics of the propulsion system, this paper details how major architectural parameters (mass, stiffness and location of powerplant and airframe integration) impact the key structural response of the propulsion system. Coupled aerodynamic (DLM) – Flight Dynamics (FD) – Structural Dynamics (SD) whole aircraft models have been created for conventionally powered (TBW) and hybrid electric (TBWe) Truss-Braced Wing configurations. Models facilitate evaluation of key structural responses, of both airframe and powerplant, under a range of static and dynamic load cases. Sensitivity analysis concluded that Truss-braced Wing configurations were more sensitive to variation in powerplant spanwise location than a conventional Tube-and-Wing aircraft. Increased coupling between powerplant swing and wing bending modes is evident, influencing dynamic response under gust loading. Moreover, differences in the mass and stiffness characteristics of the conventional and electric propulsion system features has also yielded contrasting dominant parameter sensitivities – TBW is more sensitive to variation in powerplant mass, while TBWe is more sensitive to variation in pylon stiffness. [ABSTRACT FROM AUTHOR] more...

The passive flow-control application section is closed by the transient analysis undertaken on cruise missiles' submerged inlet by Zhang and Mi [[5]]. In AFC applications, five parameters need to be optimized, and despite the fact that parametric optimizations can be quite useful, the use of optimizers based on Genetic Algorithms (GA) or gradient-based methods appear to be a much more precise way to accurately tune the required parameters. A parametric optimization considering three AFC parameters on an NACA-8412 airfoil at an Angle of Attack (AoA) pf 15 degrees and Reynolds number of 68.5*10 SP 3 sp is undertaken by Couto and Bergadà [[9]]. [Extracted from the article] more...

This paper presents a practical model predictive control (MPC) framework for gust load alleviation of a flexible flying wing. Both the controller solving and state estimation are based on a reduced-order model, which features a linear parameter-varying (LPV) form, avoiding online linearization and reducing the scale of the corresponding quadratic programming problem. An improved modeling and model reduction process is used to enhance modeling efficiency and ensure that the reduced-order model can accurately capture the rigid-flexible coupled characteristics of the flexible flying wing under arbitrary gusts. By reconstructing the output of the control-oriented model to include both rigid-body motion and flexible vibrations, the rigid-flexible coupled multi-objective control is established as an MPC problem for reference tracking. The online optimization is formulated in a sparse fashion and combined with an iterative algorithm based on predicted trajectories, describing the variation of model dynamics within the prediction horizon more accurately. With a time-varying Kalman estimator for state updating, the closed-loop simulations are performed for gust alleviation performance validation. Additionally, the real-time potential of the proposed MPC framework is demonstrated through Monte Carlo simulations. • Comprehensive modeling, model order reduction, and control design for flexible aircraft. • An extended unsteady vortex lattice model to improve aerodynamic modeling efficiency. • A reduced-order model-based control and state estimation framework suitable for engineering practice. [ABSTRACT FROM AUTHOR] more...

• A gust response alleviation approach is investigated for the supersonic wing aeroelastic systems. • Effect of the nonlinear energy sink (NES) on the aeroelastic gust response is studied. • Influence of NES parameters on the dynamic response amplitude is discussed. • The optimal relative distance for the installation of NES is found. • Influence of nonlinear energy sink on the targeted transfer of vibration energy is analyzed. In order to reduce the gust response level of the aircraft wing aeroelastic systems in supersonic flows, the nonlinear energy sink (NES) is introduced into the aeroelastic system, and the effect of the nonlinear energy sink on the aeroelastic gust response is studied. The gust response dynamic model without and with NES is established by Lagrange equation, considering the cubic nonlinear characteristics of both plunge and pitch stiffness. The piston theory model as well as the '1-cos' model are employed to describe the unsteady aerodynamic load and the gust velocity, respectively. Besides, the comparison study of the gust response amplitude and energy characteristics of the wing aeroelastic systems with and without NES are analyzed. For systems with NES, the amplitude of gust dynamic response decreases rapidly, while vibration can be transmitted to the NES mechanism and causing its vibration. From an energy perspective, about 72.15 % of the original vibration energy has been transferred into NES, and further consumed through its damping. The influence of NES parameters, such as frequency ratio, mass ratio, damping ratio, and installation position on gust response, is discussed. Numerical simulations demonstrate that: as the frequency ratio, damping ratio and mass ratio increase, the dynamic response amplitude of the aeroelastic system decays faster, and the energy transferred from the wing system also increases. In addition, an optimal relative distance for the installation of NES can be found with best gust alleviation effect. The influence of nonlinear energy sink on the targeted transfer of vibration energy in aeroelastic systems are analyzed under different working conditions. The NES shows great gust alleviation effect and good robustness under different flight speeds, gust intensities, and gust lengths. [ABSTRACT FROM AUTHOR] more...

• Review basic ideas and developments of calculation methods for ESWLs. • ESWL analysis methods are classified whether one target or true distribution. • Summarize applications of ESWLs in standards. This paper reviews the basic ideas, developments, and codification practices of different calculation methods for equivalent static wind load (ESWL) in the past about sixty years. From the landmark work of Davenport's Gust Loading Factor (GLF), Kasperski's Load-Response-Correlation (LRC), and Katsumura, Tamura's Universal-ESWL (U-ESWL), the development thread of ESWL is clarified. The ESWLs are classified based on the number of target load effects (Single-target or Multiple-target) and on actuality (Realistic or Unrealistic). GLF is representative as a "Single-target Unrealistic" ESWL, which has been adopted in many international codes and standards for building design and is extended into many approaches considering different targets (e.g. base bending moment), and different components (along-wind, crosswind, torsional). The LRC method identifies a realistic wind load distribution that causes one target maximum/minimum load effect, is a representative of "Single-target Realistic" ESWL, is well adopted as a background component ESWL, and is further developed to consider the dynamic resonant effect. The U-ESWL simultaneously reproduces maximum/minimum load effects in multiple structural members with only two sets of load distributions, is a "Multiple-target Unrealistic" ESWL, and has also been developed and employed in a wind load code for roof structures. [ABSTRACT FROM AUTHOR] more...

[Display omitted] • An efficient system monitoring approach able to track small changes in damping intensity is proposed. • The proposed approach utilizes a numerically efficient bootstrap technique and a Bayesian conjugate model. • Automatic detection of free-response transients during intermittent operation. • Efficient damping and uncertainty estimation from a short free-response signal using Bayesian conjugate prior. Monitoring mechanical systems that are exposed to dynamic loads during operation requires a technical indicator that provides reliable information on degradation. In this paper, the damping ratio is used as an indicator and can be obtained from monitoring data such as acceleration. Its change from the initial value highly correlates with the system change that can lead to failure. The damping ratio can be relatively easily estimated from the free response data. Such events occur frequently for systems that are subjected to environmental loads such as wind gusts on structures, or sudden stops and changes in the operational cycle. The problem addressed by this research is the fully autonomous detection of these free-response events and the subsequent estimation of the damping ratio, including uncertainty. Therefore, a novel monitoring approach is proposed, utilising the Bootstrap technique and Bayesian analysis. Bootstrap provides automatic free response detection without monitoring the excitation force. Once the event is detected as a valid free response, Bayesian analysis in the form of a gamma-exponential conjugate prior is applied to estimate the damping ratio. As damping estimation is in the form of distribution, uncertainty is also quantified, which is a required feature when monitoring the degradation process and remaining useful life prediction. The monitoring approach is demonstrated and verified numerically and experimentally on a single degree of freedom air-bearing testbed as well as on multiple degrees of freedom beam system. As shown, the combination of the Bootstrap technique and Bayesian analysis provided satisfactory results, demonstrating that the degradation process can be reliably monitored by the proposed approach. [ABSTRACT FROM AUTHOR] more...

Large wind turbine rotors are becoming more common in utility-scale wind power, especially for offshore wind plants. However, the trend toward large rotors can be limited by their ability to manage dynamic and extreme loads. To provide a safety margin for the rotor design and avoid catastrophic events such as tower strikes, extreme loads need to be controlled. The objective of this study is to develop and evaluate a feedback control system to alleviate extreme loads and reduce blade deflections under gust events using active flow control devices. We also propose a modification in the turbine controller to achieve further reduction in extreme loads. The extreme load reductions are evaluated under gust wind conditions with direction changes according to the IEC standard. The effects of the gust alleviation controller on turbine performance and fatigue loads are investigated as well. With the deployment of the gust alleviation controller and modified turbine baseline controller, the extreme loads and deflections reduce by up to 23%. The energy captured by the turbine is not affected by the proposed gust alleviation controller. The fatigue loads of various wind turbine components are either reduced or remain unchanged. [ABSTRACT FROM AUTHOR] more...

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This paper presents an aeroelastic analysis of a polymorphing wing capable of active span extension and passive pitch variation. The wing is split into two segments: an inboard segment responsible for span extension/retraction and an outboard segment capable of pitch variation. The two segments are connected through an overlapping spar and a torsional spring. A finite element aeroelastic model is developed where the wing structure is discretized into Euler–Bernoulli beam elements and the aerodynamic loads are calculated using Theodorsen's unsteady model. A comprehensive parametric analysis is carried out with and without span extension to analyze the effect of varying critical design parameters, such as elastic axis position of outboard section and torsional spring rigidity, and conditions for aeroelastic phenomena of flutter and divergence are studied. A gust load analysis is carried out to quantify the capability of the outboard wing passive twist mechanism to alleviate loads. Finally, a nonlinear analysis is carried out by replacing the linear torsional spring with a nonlinear cubic spring to study the effects of cubic hardening and softening on the aeroelasticity of the polymorphing wing. [ABSTRACT FROM AUTHOR] more...

In recent years, load alleviation technologies have been more widely used in transport aircraft. For aircraft already in service, load alleviation can contribute in extending the fatigue life, or enable small configurational changes. If load alleviation is considered in the aircraft design process, the structural mass of the aircraft can be reduced. This paper investigates various maneuver and gust load alleviation algorithms as well as potential future technologies regarding flight operation, turbulence forecast and material science, and it evaluates the mass reduction that can be achieved. In doing so, a long-range transport aircraft was taken as the reference, and the considered load case conditions were 1-cos gusts, maneuvers and quasi-steady landing. Based upon the loads, the composite structure of the lifting surfaces was optimized, while the secondary masses as well as the wing planform were kept unchanged. With all technologies implemented, a reduction of the wing box mass by 26.5% or 4.4% of the operating empty mass could be achieved. [ABSTRACT FROM AUTHOR] more...

We report on the development of a novel direct-detection Doppler wind lidar (DD-DWL) within the strong requirements of an aeronautic feed-forward control application for gust load alleviation (GLA). This DD-DWL is based on fringe imaging of the Doppler-shifted backscatter of ultraviolet laser pulses in a field-widened Michelson interferometer (FW-FIMI) using a fast linear photodetector. The double approach of detailed simulation and demonstrator development is validated by field measurements with reference wind sensing instrumentation. These experiments allow us to establish wind determination precision at a high repeat rate, short range resolution and close distance of approximately 0.5 m/s, which is in accordance with the dedicated simulations. These findings lead us to the conclusion that this FW-FIMI-based Doppler wind lidar is a pertinent development meeting the special requirements of this aeronautics application. Second, the developed simulators are well suited (given their validation) to be used in the overall and full analysis as well as the optimization of the lidar-based GLA control scheme. [ABSTRACT FROM AUTHOR] more...