Explore the vast range of titles available.

This study presents a quasi-steady simulation and optimization framework for ground-generation airborne wind energy systems with soft kites. A novel parameterization of the reel-out phase is introduced, explicitly resolving crosswind maneuvers through a kinematically feasible figure-of-eight trajectory, thereby improving physical representativeness compared to conventional averaged crosswind models. The framework is validated against experimental data from the TU Delft V3 reference kite, showing good agreement in kite kinematics, phase- and cycle-averaged power, while highlighting expected limitations in instantaneous force prediction. The model is subsequently used to optimize pumping-cycle operational parameters under fixed environmental conditions, revealing significant variations in cycle duration and modest gains in average power. The results demonstrate the suitability of the proposed framework for efficient conceptual design studies and operational optimization of airborne wind energy systems.

In this paper, an unpowered return trajectory technique for fixed-wing UAVs is studied, focusing on trajectory design, guidance law design, and simulation verification. The proposed design scheme of the longitudinal trajectory is based on the limitation of the maximum lift-to-drag ratio and the transverse course trajectory of the Dubins curve. We also optimized the trajectory in stages for the landing section. The safety and effectiveness under crosswind conditions are verified by simulation, and the results show that the method can accurately track the trajectory and effectively suppress the wind disturbance, which provides a reference for the unpowered return control and complex task trajectory planning.

The maximum allowable turning speed of an aircraft is a critical factor affecting the safety of civil aviation. Evaluating the maximum permissible taxiing turn speed for civil aircraft is an essential aspect of aircraft design. To ensure that the aircraft does not experience unbalanced forces leading to a lateral rollover due to excessive taxiing speed, an engineering estimation method is employed to study the maximum permissible taxiing turn speed for civil aircraft. This method begins with certain assumptions and calculation scenarios, followed by the derivation of a calculation model based on the analysis of aircraft forces. Lastly, a case study of a specific aircraft’s maximum taxiing turn speed is conducted in conjunction with practical engineering considerations. The study reveals that as crosswind forces on civil aircraft increase, the maximum turning speed decreases. Moreover, for lighter aircraft with a forward center of gravity, the risk of lateral rollovers is higher. These findings underscore the engineering applicability of the estimation method.

The aerodynamic load of high-speed trains (HSTs) undergoes significant changes when they pass through the transition section of the cutting under crosswind conditions. This paper establishes a coupled train-cutting-wind three-dimensional aerodynamic model based on the improved delayed detached eddy simulation turbulence model, focusing on the influence of the cutting depth on the change of aerodynamic load and the deterioration of the train’s aerodynamic performance, while also revealing the mechanism of the evolution of the flow field. The results indicate that at the cutting depth of 6 m, the aerodynamic impact energy of the head train during operation is at its highest. As the train completely enters the next operational scenario, with an increase in the cutting depth, the impact of incoming flow on the aerodynamic loads of the train is diminished, leading to a corresponding reduction in fluctuation amplitude. The magnitude of the head train’s abrupt change in aerodynamic load has a near-linear positive correlation with the wind speed.

Wind farms (WFs) typically operate in derated modes to comply with noise regulations, resulting in a significant loss of profit. However, following a conservative approach, little importance is given to the directivity of WF noise. Several field measurements have shown that wind turbines (WTs) exhibit a strong directivity pattern, with a difference of 4-6 decibels (dB) between downwind and crosswind directions. This paper highlights the potential benefit of leveraging the directivity of WF noise to improve profitability, while maintaining regulation-compliant noise levels at relevant locations. Annual energy production (AEP) increases by ∼2% after considering the noise directivity of a WF featuring 12 IEA 3.4MW WTs in a 3 × 4 layout based on a real site, where the closest settlement to the WF is in the crosswind position of the dominant wind direction. The differences in power gain considering uncertainties in wind direction and WT noise source models are also studied, followed by a discussion on the directivity models.

Flux footprint models are often used for interpretation of flux tower measurements, to estimate position and size of surface source areas, and the relative contribution of passive scalar sources to measured fluxes. Accurate knowledge of footprints is of crucial importance for any upscaling exercises from single site flux measurements to local or regional scale. Hence, footprint models are ultimately also of considerable importance for improved greenhouse gas budgeting. With increasing numbers of flux towers within large monitoring networks such as FluxNet, ICOS (Integrated Carbon Observation System), NEON (National Ecological Observatory Network), or AmeriFlux, and with increasing temporal range of observations from such towers (of the order of decades) and availability of airborne flux measurements, there has been an increasing demand for reliable footprint estimation. Even though several sophisticated footprint models have been developed in recent years, most are still not suitable for application to long time series, due to their high computational demands. Existing fast footprint models, on the other hand, are based on surface layer theory and hence are of restricted validity for real-case applications. To remedy such shortcomings, we present the two-dimensional parameterisation for Flux Footprint Prediction (FFP), based on a novel scaling approach for the crosswind distribution of the flux footprint and on an improved version of the footprint parameterisation of Kljun et al. (2004b). Compared to the latter, FFP now provides not only the extent but also the width and shape of footprint estimates, and explicit consideration of the effects of the surface roughness length. The footprint parameterisation has been developed and evaluated using simulations of the backward Lagrangian stochastic particle dispersion model LPDM-B (Kljun et al., 2002). Like LPDM-B, the parameterisation is valid for a broad range of boundary layer conditions and measurement heights over the entire planetary boundary layer. Thus, it can provide footprint estimates for a wide range of real-case applications. The new footprint parameterisation requires input that can be easily determined from, for example, flux tower measurements or airborne flux data. FFP can be applied to data of long-term monitoring programmes as well as be used for quick footprint estimates in the field, or for designing new sites.

The influence of environmental steady aerodynamic loads on the both carbody hunting motion and bogie hunting motion stability of high-speed trains (HSTs) is presented in this paper. A lateral HST dynamics model with 17 degrees of freedom (DOFs) is established to reflect the dynamic characteristics of carbody hunting and bogie hunting motions. The nonlinear creep force saturation and variable friction coefficient nonlinear characteristics are considered in the model. Then the continuous modal tracking method and numerical simulation method are used to evaluate the hunting stability and acquire the bifurcation diagram, respectively. The linear hunting stability and bifurcation behavior, subject to different wheel/rail match equivalent conicity and friction coefficient conditions, are investigated in detail for both the carbody and bogie hunting motions. The results show that crosswind aerodynamic loads will change the normal wheel/rail force and quasi-static contact position. Additionally, the creep coefficient and creep force saturation modified coefficient, which are closely related to hunting stability, will also be affected. The crosswind aerodynamic loads can significantly impact the hunting stability and bifurcation characteristics, especially under condition of small friction coefficient. The double grazing phenomenon with occurrence of carbody hunting motion will change to single grazing phenomenon when the crosswind aerodynamics loads are large enough.

Large bodies of water represent major obstacles for the migration of soaring birds because thermal updrafts are absent or weak over water. Soaring birds are known to time their water crossings with favourable weather conditions and there are records of birds falling into the water and drowning in large numbers. However, it is still unclear how environmental factors, individual traits and trajectory choices affect their water crossing performance, this being important to understand the fitness consequences of water barriers for this group of birds. We addressed this problem using the black kite Milvus migrans as model species at a major migration bottleneck, the Strait of Gibraltar. We recorded high‐resolution GPS and triaxial accelerometer data for 73 birds while crossing the Strait of Gibraltar, allowing the determination of sea crossing duration, length, altitude, speed and tortuosity, the flapping behaviour of birds and their failed crossing attempts. These parameters were modelled against wind speed and direction, time of the day, solar irradiance (proxy of thermal uplift), starting altitude and distance to Morocco, and age and sex of birds. We found that sea crossing performance of black kites is driven by their age, the wind conditions, the starting altitude and distance to Morocco. Young birds made longer sea crossings and reached lower altitude above the sea than adults. Crosswinds promoted longer sea crossings, with birds reaching lower altitudes and with higher flapping effort. Birds starting at lower altitudes were more likely to quit or made higher flapping effort to complete the crossing. The location where birds started the sea crossings impacted crossing distance and duration. We present evidence that explains why migrating soaring birds accumulate at sea passages during adverse weather conditions. Strong crosswinds during sea crossings force birds to extended flap‐powered flight at low altitude, which may increase their chances of falling in the water. We also showed that juvenile birds assume more risks than adults. Finally, the way in which birds start the sea crossing is crucial for their success, particularly the starting altitude, which dictates how far birds can reach with reduced flapping effort. Soaring birds engage in flap‐powered flight during sea crossings, which is fatiguing and can lead to drowning due to exhaustion. Using state‐of‐art tracking technology, the authors determined precise indicators of sea crossing performance. They found that sea crossing performance is driven by age, wind conditions and the starting trajectory.

To reduce the crosswind effect on high-speed trains, in this paper, by using the Improved Delayed Detached Eddy Simulation (IDDES) method and the SST turbulence model, a novel blowing measure is studied and compared by considering different positions of blowing slots on the train surface. The concerned blowing positions on the train surface include the top position (Top); windward side (WWS): the upper position (WU), middle position (WM), and lower position (WL); and leeward side (LWS): the upper position (LU), middle position (LM), and lower position (LL). The results show that in regard to the rolling moment coefficient around the leeward rail, C Mx lee , the mitigation effect with LM for the head car is the largest, and the mitigation effect with WL for the middle car and tail car is superior to other cases. The corresponding drop percentages are 18.5%, 21.7%, and 30.8% for the head car, middle car, and tail car, respectively. The flow structures indicate that the blowing positions on the lower half of WWS and upper half of LWS would form a protective air gap to weaken the impact of coming flows and delay the vortex separation on LWS, and thus the train aerodynamic performance is improved.

The power generation efficiency of photovoltaic (PV) modules is significantly compromised by dust deposition, with wind direction emerging as a critical determinant of particle trajectory, spatial distribution and deposition rate of dust particles on PV surfaces. This study systematically investigates wind direction effects on dust deposition characteristics through numerical simulations of three representative wind conditions: windward, crosswind, and leeward. The findings reveal that dust deposition rates exhibit distinct wind speed dependencies based on orientation: under both windward and crosswind conditions, deposition rates increase monotonically with wind speed, demonstrating a strong positive correlation. Conversely, leeward conditions show an inverse relationship, where elevated wind speeds lead to progressively lower deposition rates. The maximum deposition rates for windward, crosswind, and leeward were 30.24%, 11.04%, and 4.39%, with peak particle sizes of 300 μm, 300 μm, and 5 μm, respectively. These findings provide valuable insights for optimizing the spatial layout of PV modules in order to minimize the efficiency loss associated with dust.