Effects Of Gusts Research Articles

Dynamics of a knuckle crane carrying a load subjected to wind pressure

AbstractThe paper presents the authors’ model of a knuckle crane offshore type that takes into account the flexibility of boom and drives, which is used to analyze the effect of constant wind pressure or cyclical gusts on the dynamics of the crane and the load. The mathematical model of the crane is derived using a formalism of joint coordinates, homogeneous transformation matrices, and Lagrange equations. Using this model, the influence of wind pressure on the torques and forces in the crane drives and on the accuracy of load positioning is investigated. The results show that the influence of wind on the accuracy of load positioning should not be assessed by limiting the observation to the movement of its gravity center but by observing the movement of characteristic points, the corners of the load. Root mean squared (RMS) indicators are used to quantitatively assess this impact on the driving torque and forces, and appropriate indicators are proposed to assess the accuracy of load positioning.

Aeroacoustic analysis of fixed- and variable-pitch controlled multirotors and noise reduction via rotor phase control

This research conducts a comparative analysis of the aerodynamic and aeroacoustic characteristics of fixed-pitch and variable-pitch controlled multirotors (i.e., revolution per minute and collective pitch control). The study encompasses hovering and forward flight conditions, considering wind gust effects. Specifically, high-resolution time-frequency analysis is conducted to investigate the interference and modulation effects of multirotor noise. The analysis reveals significant variations in spectral characteristics depending on the control method. Notably, the frequencies of tonal noise from variable-pitch controlled multirotor do not exhibit short-periodic modulation, in contrast to those of fixed-pitch controlled multirotor. Considering the distinctive spectral characteristics of variable-pitch controlled multirotor, this study explores the effectiveness of noise reduction in variable-pitch controlled multirotor by implementing rotor phase control methods. To validate the noise reduction in time series simulations, a deep learning model is employed to determine the dynamically optimized rotor phases. A multilayer perceptron neural network was trained to derive the optimal rotor phase angles over time, considering the target observer points and flight conditions. The results demonstrate a substantial reduction in noise at the target observer points.

Increased rupture of cypress pollen type due to atmospheric water in central and southeastern Spain

This study aims to investigate the meteorological variables determining Cupressaceae pollen grain disruption in the environment. A parallel sampling of pollen grains and disrupted Cupressaceae pollen grains was performed in six cities using two Spanish aerobiological networks. The pollen concentrations, disrupted pollen concentrations, percentage of disrupted pollen and number of days when the percentage of disrupted pollen was above or equal to 50 % were quantified during two pollen seasons. The concentrations were determined following the standardised method EN 16868. Results show that the concentrations of pollen grains and disrupted pollen grains were not determined by geographical features and rarely by bioclimatic variables or indexes but by the ornamental use of the specimens in the vicinity of the pollen sampler, highlighting the possibility of using management practices to reduce exposure to allergens in the cities. African dust outbreaks coincided with higher concentrations of pollen grains and disrupted pollen grains, but the reduced percentage of disrupted pollen grains pointed to a non-causal relationship with long-distance transport. The effect of wind and maximum gusts remained negligible. The triggering factor for pollen disruption was the amount of water in the atmosphere, mainly reported as relative humidity. Rainfall increased the effect of disruption due to pollen grain swelling caused by its wash-out effect. The higher the relative humidity, the higher the disrupted pollen concentrations. This aligns with the mechanism of Cupressaceae reproduction since the family needs a water medium in the form of pollination droplets for the pollination tube to develop and the pollen grain to perform its biological function. Therefore, people that develop allergic symptoms to Cupresaceae pollen should avoid exposure during days with high relative humidity in the main pollen season.

Data-driven transient lift attenuation for extreme vortex gust–airfoil interactions

We present a data-driven feedforward control to attenuate large transient lift experienced by an airfoil disturbed by an extreme level of discrete vortex gust. The current analysis uses a nonlinear machine-learning technique to compress the high-dimensional flow dynamics onto a low-dimensional manifold. While the interaction dynamics between the airfoil and extreme vortex gust are parametrized by its size, gust ratio and position, the wake responses are well captured on this simple manifold. The effect of extreme vortex disturbance about the undisturbed baseline flows can be extracted in a physically interpretable manner. Furthermore, we call on phase-amplitude reduction to model and control the complex nonlinear extreme aerodynamic flows. The present phase-amplitude reduction model reveals the sensitivity of the dynamical system in terms of the phase shift and amplitude change induced by external forcing with respect to the baseline periodic orbit. By performing the phase-amplitude analysis for a latent dynamical model identified by sparse regression, the sensitivity functions of low-dimensionalized aerodynamic flows for both phase and amplitude are derived. With the phase and amplitude sensitivity functions, optimal forcing can be determined to quickly suppress the effect of extreme vortex gusts towards the undisturbed states in a low-order space. The present optimal flow modification built upon the machine-learned low-dimensional subspace quickly alleviates the impact of transient vortex gusts for a variety of extreme aerodynamic scenarios, providing a potential foundation for flight of small-scale air vehicles in adverse atmospheric conditions.

Numerical modelling of aerodynamic response to gusts and gust effect mitigation

Unmanned aerial vehicle (UAV) flights in urban environments are challenging due to the complex flow structures and elevated turbulence around buildings. Consequently, research has shifted towards investigating the impact of gusts on the aerodynamic stability and control of UAVs. This study focuses on enhancing gust numerical modelling capabilities to understand the aerodynamic response, specifically exploring gust mitigation strategies for UAVs operating in turbulent urban environments. The split-velocity method, originally designed for two-dimensional compressible inviscid flows, where the velocity components were decomposed into a prescribed gust velocity and the remaining velocity components, is extended to three-dimensional incompressible viscous flows. To facilitate effective gust mitigation techniques, a radial basis function is applied to the modified split-velocity method to numerically model wings in pitching motions under gust encounters. A novel strategy is proposed to correct the discretized gust velocities and ensure gust flux conservation, showing effective improvement to the numerical predictions. The computed results agreed well with the experimental data available in the public domain, confirming that wing pitch motion can effectively mitigate the effects of gusts.

SoftWind: Software-defined trajectory correction modelling of gust wind effects on internet of drone things using glowworm swarm optimization

The dynamic nature of the atmosphere, especially wind gust, poses a crucial challenge to efficient and real-time drone operations. This article presents a novel MQTT based software-defined drone network for trajectory correction of drone flights in gusty wind conditions using Glowworm Swarm Optimization (GSO). By imposing the GSO to the software-defined drone network, our proposed model SoftWind has optimized the navigation and control capabilities of drones by correcting the trajectories in a gusty wind environment. We have analyzed the trajectories and convergence of drones due to wind gusts. As wind disturbances affect the trajectories of drones, we have corrected it by our trajectory correction model and evaluated the direction of the drones must fly to mitigate the wind gust and the resultant velocity compared to the no-wind environment. This study analyzed the trajectories of 100 drone flights due to various wind gust lengths (i.e., 40 m, 10 m, 6 m, and 3 m) for a fixed gust amplitude of 15 m/s and various gust amplitude (i.e., 0 m/s, 5 m/s, 15 m/s, and 40 m/s) for a fixed gust length 5 m. We observed that all the drones are converged to a single point due to low gust length (≤ 5 m) and high gust amplitude (≥ 35 m/s). It is also found that the direction of the drone must fly 28.87°. East of South to mitigate the effect of wind gusts having 10 m gust length and 15 m/s gust amplitude and the resultant velocity of the drone is 22.38 m/s. The result shows that SoftWind reduces the convergence time by 26 %-54 % as compared to other existing models.

Investigation of the Internal Flow Characteristics of a Tiltrotor Aircraft Engine Inlet in a Gust Environment

In the vertical take-off and landing (VTOL) state of tiltrotor aircraft, the inlet entrance encounters the incoming airflow at a 90° attack angle, resulting in highly complex internal flow characteristics that are extremely susceptible to gusts. Meanwhile, the flow quality at the inlet exit directly affects the performance of the aircraft’s engine. This work made use of an unsteady numerical simulation method based on sliding meshes to investigate the internal flow characteristics of the inlet during the hover state of a typical tiltrotor aircraft and the effects of head-on gusts on the inlet’s aerodynamic characteristics. The results show that during the hover state, the tiltrotor aircraft inlet features three pairs of transverse vortices and one streamwise vortex at the aerodynamic interface plane (AIP). The transverse vortices generated due to the rotational motion of the air have the largest scale and exert the strongest influence on the inlet’s performance, which is characterized by pronounced unsteady features. Additionally, strong unsteady characteristics are present within the inlet. Head-on gusts mainly affect the mechanical energy and non-uniformity of the air sucked into the inlet by influencing the direction of the rotor’s induced slipstream, thereby impacting the performance of the inlet. The larger head-on gusts have beneficial effects on the performance of the inlet. When the gust velocity reaches 12 m/s, there is a 1.01% increase in the total pressure recovery (σ) of the inlet, a 25.72% decrease in the circumferential distortion index (DC60), and a reduction of 62.84% in the area where the swirl angle |α| exceeds 15°. Conversely, when the gust velocity of head-on gusts reaches 12 m/s in the opposite direction, the inlet’s total pressure recovery decreases by 1.13%, the circumferential distortion index increases by 14.57%, and the area where the swirl angle exceeds 15° increases by 69.59%, adversely affecting the performance of the inlet. Additionally, the presence of gusts alters the unsteady characteristics within the inlet.

Adding Gusts to a Mobile Wind Tunnel: Experimental Setup and Effect of Simulated Gusts on Horizontal Transport

Wind erosivity has an intermittent character due to complicated interactions between air streams, surface characteristics, and sediment particles. To experimentally investigate the effect of a sudden and local gust on sediment entrainment, a simple setup was installed in a mobile wind tunnel. One, three, and five consecutive gusts were applied and compared with standard test conditions with steady wind. The applied wind was characterized by total test duration (s), duration of gust (s), mean velocity, peak velocity (m s−1), gust factor, and transport capacity based on sediment-specific threshold velocity. The eroded material was collected by sediment containers. The results suggest that 1. the application of gusts inside the mobile wind tunnel setup is feasible but related to uncertainty concerning the applied wind conditions, and 2. the horizontal transport rate increased with the number of applied gusts. While the highest rates were measured during five gusts on sand, the relative effect of gusts was most accentuated in the comparison of one gust to no gust on loam. The findings highlight how temporally and spatially limited gust impact causes extreme particle entrainment. These particles may subsequently either start erosion or enter vertical dust transport.

Airfoil response to periodic vertical and longitudinal gusts

Gust response has consistently been a concern in engineering. Critical theories have been proposed in the past to predict the unsteady lift response of an airfoil experiencing vertical gusts by Atassi, and longitudinal gusts by Greenberg. However, their applicability for an airfoil with non-zero angles of attack still needs clarification. Thus, force measurements are conducted to examine these theories’ validity and quasi-steady corrections are applied to compensate potential disparities between the idealised and real flow conditions. Velocity measurements are performed to scrutinise the effect of gusts on the flow around the airfoil, and subsequently to reveal the underlying mechanism governing the airfoil's response to gust-induced perturbations. In the study, two pitching vanes are arranged upstream to generate periodic vertical and longitudinal gusts, whereas a downstream airfoil with angles of attack of 0–12° is subjected to two gust types. It is found that Greenberg's theory demonstrates superior predictive capability in pre-stall regimes, with the potential for its effectiveness to be expanded to post-stall regimes through theoretical refinements. In contrast, Atassi's theory exhibits significant deviations from experimental outcomes across the measured angles of attack. Nevertheless, a modified version of the theory aligns better with experimental results at small angles of attack, whereas substantial discrepancies persist as the angle of attack increases. In the pre-stall regime, the aerodynamic response of the airfoil to vertical gusts displays a linear correlation with the flow angle near the leading edge. In the post-stall regime, the vertical gust induces dynamic stall of the airfoil. The flow angle has an essential effect on the lift coefficient but it alone is inadequate to dictate the trend of the lift coefficient. The vorticity statistics show that negative vortex circulation strongly correlates with the lift coefficient. Thus, further correction of the theory or a new vortex model can be expected to predict the lift variation.

Navigating vortex gust interactions and mitigations by plunging wings

Inspired by the stability achieved by biological flapping-winged fliers in gusty environments, we conducted particle image velocimetry studies on the interactions between plunging wings and large-scale vortex gusts. Our experiments involved a flat plate wing performing sinusoidal plunging motions at various frequencies, resulting in Strouhal numbers (St) ranging from 0 to 0.5 within which biological fliers commonly operate. This range of St corresponded to reduced frequencies (k) between 0 and 0.79 at a chord Reynolds number of 2000. The gust structures, generated periodically by pitching vanes, traveled downstream to the wing. We observed the vortex interactions between wing-induced vortices [particularly the boundary layer and the leading-edge vortex (LEV)] and the gusts. Additionally, we quantified the gusts' effects on the local flow around the wing by calculating the circulation within a control region attached to the plunging wing. The wing-induced vorticity merged momentarily with gusts of the same-sign vorticity. In contrast, opposite-sign gusts not only increased the circulation of the wing-induced vortices but also led to the LEV detaching faster. While gusts had the potential to significantly alter the flow around the wings, the plunging wings sometimes managed to avoid the gusts due to their transverse motion. Furthermore, the prolonged presence of the stronger LEVs near the wing, which are characteristic of plunging wings at higher St and k, could deflect the gusts away, reducing their impact on the vorticity and circulation within the control region. These findings illustrate how robust flapping kinematics can mitigate the effects of vortex gusts.

Exploring the Effect of Meteorological Factors on Predicting Hourly Water Levels Based on CEEMDAN and LSTM

The magnitude of tidal energy depends on changes in ocean water levels, and by accurately predicting water level changes, tidal power plants can be effectively helped to plan and optimize the timing of power generation to maximize energy harvesting efficiency. The time-dependent nature of water level changes results in water level data being of the time-series type and is essential for both short- and long-term forecasting. Real-time water level information is essential for studying tidal power, and the National Oceanic and Atmospheric Administration (NOAA) has real-time water level information, making the NOAA data useful for such studies. In this paper, long short-term memory (LSTM) and its variants, stack long short-term memory (StackLSTM) and bi-directional long short-term memory (BiLSTM), are used to predict water levels at three sites and compared with classical machine learning algorithms, e.g., support vector machine (SVM), random forest (RF), extreme gradient boosting (XGBoost), and light gradient boosting machine (LightGBM). This study aims to investigate the effects of wind speed (WS), wind direction (WD), gusts (WG), air temperature (AT), and atmospheric pressure (Baro) on predicting hourly water levels (WL). The results show that the highest coefficient of determination (R2) was obtained at all meteorological factors when used as inputs, except at the La Jolla site. (Burlington station (R2) = 0.721, Kahului station (R2) = 0.852). In the final part of this article, the complete ensemble empirical mode decomposition adaptive noise (CEEMDAN) algorithm was introduced into various models, and the results showed a significant improvement in predicting water levels at each site. Among them, the CEEMDAN-BiLSTM algorithm performed the best, with an average RMSE of 0.0759 mh−1 for the prediction of three sites. This indicates that applying the CEEMDAN algorithm to deep learning has a more stable predictive performance for water level forecasting in different regions.

Large-scale sinusoidal gust effect on aerodynamic pressures and forces on a square cylinder

Aerodynamic pressures and forces on a two-dimensional square cylinder were experimentally investigated in large-scale sinusoidal gusts. The effects of streamwise and transverse gusts with a wide range of gust amplitudes were studied at a Reynolds number of Re = 2.1 × 104. To enhance our understanding of the large-scale sinusoidal gust effect, the pressure fields and global aerodynamic forces of the square cylinder in large-scale gusts were compared with those in smooth and grid-generated turbulent flows. This study shows that both large-scale streamwise and transverse gusts can promote early pressure recovery, resulting in larger mean pressures on the side and leeward surfaces. The root mean square (RMS) of the pressures on the side surface increased and decreased with an increase in the streamwise and transverse gust amplitudes, respectively. The mean drag on the square cylinder was reduced under the effects of large-scale streamwise and transverse gusts. The increase in the streamwise and transverse gust amplitudes significantly affected the RMS of the drag and lift on the square cylinder, respectively. A proper orthogonal decomposition (POD) analysis showed that the contribution of the first POD mode switched from fluctuating lift to drag when the streamwise gust amplitude was very high. The spectral analysis demonstrated that the alternating von Kármán vortex-shedding process still dominated the fluctuating lift under the effect of large-scale gusts. In addition, the spanwise correlations of drag were significantly strong under the effects of large-scale streamwise gusts. However, the spanwise correlations of lift were reduced under the effects of large-scale gusts with high gust amplitudes.

Turbulence regimes in the nocturnal roughness sublayer: Interaction with deep convection and tree mortality in the Amazon

We investigated the influence of seasonality and proximity to the forest canopy on nocturnal turbulence regimes in the roughness sublayer of a Central Amazon forest. Since convective systems of different scales are common in this region, we also analyzed the effect of extreme wind gusts (propagated from convective downdrafts) on the organization of the turbulence regimes, and their potential to cause the mortality of canopy trees. Our data include high-frequency winds, temperature and ozone concentration at different heights during the dry and wet seasons of 2014. In addition, we used critical wind-speed data derived from a tree-winching experiment and a modeling study conducted in the same study site. Two different turbulence regimes were identified at three heights above the canopy: a weakly stable (WS) and a very stable regime (VS). The threshold wind speeds that mark the transition between turbulence regimes were larger during the dry season and increased as a function of the height above the canopy. The turbulent fluxes of sensible heat and momentum during the WS accounted for 88% of the entire nighttime flux. Downdrafts occurred only in the WS and favored a fully coupled state of wind flow along the canopy profile. The destructive potential of winds was four times higher than on nights without downdrafts.

Gust response analysis based on a nonlinear structural model and the unsteady aerodynamics of a flexible aircraft

Purpose This study aims to simulate gust effects on the aeroelastic behavior of a flexible aircraft. The dynamic response of the system for different discreet gust excitations is obtained using numerical simulations. Design/methodology/approach Coupled dynamics, including rigid and flexible body coordinates, are considered for modeling the dynamic behavior of the aircraft. Wing is considered flexible and other parts are considered rigid. Wing is modeled with nonlinear Euler Bernoulli beam. Moreover, unsteady aerodynamics based on the Wagner function are used for aerodynamic loading, and the results are compared with those of quasi-steady aerodynamics. Findings Von Kármán continuous gust is applied to this aircraft. In addition, the discrete “1- cosine” gust with different gust lengths is applied to the aircraft, and the maximum and minimum accelerations are computed. It is shown that the nonlinear modeling of the system represents the actual behavior and causes limit cycle oscillation phenomena. Originality/value This methodology can yield a relatively simple dynamic model for high aspect ratio aircrafts to provide insights into the vehicles’ dynamics, which can be available early in the design cycle.

Effect of Macroscopic Turbulent Gust on the Aerodynamic Performance of Vertical Axis Wind Turbine

Vertical Axis Wind Turbines (VAWTs) have proven to be suitable for changing wind conditions, particularly in urban settings. In this paper, a 2D URANS (Unsteady Reynolds-Averaged Navier Stokes) numerical analysis is employed for an H-Darrieus VAWT. A turbulent domain is created through systemically randomising the inlet velocity to create macro-turbulence in front of the VAWT. The parameters for spatial and temporal randomisation of velocity and its effects on the turbine performance are studied for a mean free stream velocity, U∞ = 10 m/s, and a tip speed ratio (TSR) of 4.1. The mean Coefficient of power (Cp) for randomised fluctuation of 2 m/s and half-cycle randomisation update frequency is 0.411 and for uniform inlet velocity is 0.400. The Cp vs. Tip Speed ratio plot suggests that the optimal tip speed ratio for operation is around 4.1 for this particular wind turbine of diameter 1 m, chord 0.06 m, and NACA 0018 airfoils. The effect of randomisation for tip speed ratio λ = 2.5, 3.3, 4.1, and 5.3 on the performance of the turbine is studied. Turbine wake recovers at a faster rate for macro-turbulent conditions and is symmetric when compared to wake generated by uniform velocity inlet. The maximum velocity deficit for a distance behind the turbine, x/d = 8 at TSR (λ) = 4.1 is 46% for randomised inlet and 64% for uniform inlet. The effect of randomisation for λ = 2.5 to 5.3 on the performance of the turbine is analysed. A time-varying gust based on International Electrotechnical Commission (IEC) Extreme Operating Gust is used to study the effect of fluctuating wind conditions in a turbulent environment. Since real-time conditions often exceed gust factors mentioned by IEC, winds with large gust factors such as 1.50, 1.64, and 1.80 are analysed. With an increase in gust amplitude, Ugust = 6 m/s to Ugust = 12 m/s on a free stream velocity of U∞ = 10 m/s, the mean Cp decreases from 0.41 to 0.35 since the wind turbine operates under tip speed ratios outside optimal range due to large fluctuations in incoming velocity.

Aeroelastic response of an elastically mounted 2-DOF airfoil and its gust-induced oscillations

The paper is concerned with numerical investigations on the effect of vertical wind gusts on airfoils in a parameter range relevant for Micro-Air Vehicles. Using a simplified substitute model instead of an elastic wing, a rigid but elastically mounted airfoil with two degrees of freedom (heave and pitch) is considered. The coupled problem is tackled by a partitioned fluid–structure interaction coupling scheme based on the large-eddy simulation (LES) technique and a rigid-body solver. In order to describe the effect of deterministic 1-cosine gusts of different gust lengths and gust strengths, the split velocity method (SVM) is incorporated into the simulation framework relying on the Arbitrary Lagrangian–Eulerian (ALE) formulation on temporally varying control volumes. First the flow fields and the corresponding aerodynamic forces during the direct airfoil–gust interaction are compared for a fixed and an elastically mounted airfoil. The intrinsic study on the elastic case includes nine different gust scenarios in the transitional Reynolds number regime in order to investigate the resulting flow fields and motion patterns and to answer the question whether limit-cycle oscillations (LCO) or even flutter can be induced. The results show that in seven of the studied cases, the airfoil–gust interaction leads to sustained heave and pitch oscillations of bounded amplitudes (i.e., LCO). Further investigations clarify that this can be physically attributed to the laminar separation taking place on the upper and lower surfaces of the airfoil. The two strongest gust cases, however, excite the airfoil to levels above its critical angle of attack and triggered a pitch-induced diverging flutter. An energy analysis of both characteristic scenarios (i.e., LCO and flutter) further elucidates the differences between both cases. The former case is driven by the heave motion, whereas the pitch DOF acts as an energy sink. Contrarily, in the case of flutter the pitching motion is powering the coupled system, whereas the heave motion dissipates energy.

High Crosswind-Tolerance Airplane by Adjusting Dihedral Angle and Vertical Tail Volume

The present authors proposed the “quasi-neutral dihedral-effect and directional-stability” (QNDD) airplane, which is a modified neutral dihedral-effect and directional-stability (NDD) airplane for its realization. The QNDD airplane provides a superior tolerance to crosswinds compared to a conventional one by modifying geometric properties: dihedral angle of a main wing and vertical tail volume to achieve small values of and , which results in a small effect of crosswind gust on an airplane’s attitude. While the QNDD airplane yields small and , the NDD airplane yields and equal to zero. When the changes of and due to the wing deformations are considered, the NDD airplane is ideal, while the QNDD airplane is more practical. The QNDD airplane had four real eigenvalues rather than classically two reals and one pair of complex conjugates. The eigenvalues seen in a conventional airplane as a Dutch roll mode were seen to be reals in a QNDD airplane, and the mode was overdamped, which is different from a set of eigenvalues of a conventional one. From the Bode diagrams and unsteady simulations with a discrete gust applied as a crosswind, it was confirmed that the QNDD airplane had a higher tolerance to the crosswind.

Aerodynamic Response of a Serpentine Inlet to Horizontal Periodic Gusts

Gust is a common atmospheric turbulence phenomenon encountered by aircraft and is one major cause of several undesired instability problems. Although the response of aircraft to the incoming gust has been widely investigated within the subject of external-flow aerodynamics in the past decades, little attention is paid to its effects on the internal flow within aircraft engines. In this paper, a newly implemented Field Velocity Method (FVM) in OpenFOAM is used to simulate the flow field and aerodynamic responses of a serpentine inlet exposed to non-stationary horizontal sinusoidal gusts. Validations are performed on the results obtained based on the baseline Computational Fluid Dynamics (CFD) solver and the gust modeling method. Finally, the flow field and aerodynamic characteristics of the serpentine inlet under horizontal sinusoidal gust conditions are comprehensively investigated. It is found that the gusts not only significantly change the flow structure but also play an unfavorable role in the total pressure distortion of the serpentine inlet. This finding shows the necessity to consider gust effects when designing and evaluating the performance of aircraft engines.

A Wireless Transient Attenuated-Exponential Overpressure Beamforming With for Far-Field Blast Source Localization

Time-domain beamforming is more suitable for blast wave transient signal than frequency-domain beamformer because wideband spectrum of noise makes the beamforming image less clear. To avoid the gust effects and enable the location of blast source accurately, this article proposes a new 1-D far-field delay-and-sum (DAS) beamforming method with an attenuate exponential function model for wireless overpressure transient signal. In addition, we design wireless overpressure peak and root-mean-square (rms) directional estimators to assess the performance of the proposed new DAS beamforming method. Furthermore, the effects of the wireless pressure sensor node (WPSN) spacing, the number of WPSNs, and sidelobe level brought from noise on the beamwidth are investigated in the two estimators. The proposed formula is verified by a uniformly spaced linear sensing array, and the results verify the feasibility of the proposed method in blast source localization. This article is conducted to provide new insight into blast source localization algorithm and further open a door for transient blast overpressure source localization scenarios in future.

Effect of Rotor Tilt on the Gust Rejection Properties of Multirotor Aircraft

In order to operate safely in windy and gusty conditions, multirotor VTOL aircraft require gust resilience. This paper shows that their gust rejection properties can be improved by applying a small amount of fixed outward rotor tilt. Standard aerodynamic models of the rotors are incorporated into two dynamic models to assess the gust rejection properties. The first case is a conceptual birotor planar VTOL aircraft. The dependence of the trim and stability on the tilt angle are analyzed. The aircraft is stabilized using a pole-placement approach in order to obtain consistent closed-loop station-keeping performance in still air. The effect of gusts on the resulting response is determined by simulation. The second case study is for a quadrotor with a 10° outward rotor tilt. The aerodynamic coefficients are analyzed for trimmed station-keeping over a range of steady wind speeds. An LQR controller is used to apply station-keeping that includes integral action, and the gust responses are again obtained using simulation. The results show that the outward rotor tilt causes the aircraft to pitch down into a lateral gust, providing lateral force that opposes the gust and so significantly improving the gust rejection properties.