Search Results (446)

In this paper, a special air-ground system consisting of multiple tail-sitters and ground vehicles are constructed under switching topologies and uncertain communication links. For the air-ground system, the ground vehicles serve as the take-off and landing platforms for the tail-sitters. A robust time-varying pinning coordinated controller is developed for the heterogeneous system. The effects of parameter/link uncertainties and external disturbances are effectively attenuated via the devised control law. The robust performance of the air-ground cooperative control system with switching topologies is rigorously validated with the Lyapunov stability criterion. The steady-state tracking deviations satisfy uniform ultimate boundedness and converge within an infinitesimal region around the origin. Simulation tests are carried out to verify that the developed control scheme achieves satisfactory coordination under time-varying cases, with tracking deviations noticeably lower in comparison with conventional control schemes. Full article

In this paper, the fixed-time fault-disturbance estimation problem for an emergency rescue quadrotor UAV during the takeoff–mission execution–landing process is investigated. Considering the complex operating conditions of rescue missions, actuator efficiency loss, actuator bias faults, rescue-environment airflow disturbances, payload-induced disturbances, near-ground aerodynamic effects, and unmodeled dynamic uncertainties are uniformly represented as a lumped fault disturbance entering the angular-velocity dynamic channel. A multi-stage disturbance model is first established according to the takeoff stage, mission execution stage, and landing stage. Then, a fixed-time fault-disturbance estimator with stage-dependent gains is designed to estimate the lumped disturbance. Based on matrix Lyapunov functions and fixed-time stability theory, it is proven that the angular-velocity estimation error and the lumped fault-disturbance estimation error can enter and remain in a small bounded neighborhood within a fixed time independent of the initial conditions. Moreover, the bounded disturbance jumps at the stage-transition instants are analyzed, and the post-transition recovery property of the estimator is established. The simulation results under a practical emergency rescue scenario show that the proposed estimator can reconstruct the main variation trends of the roll, pitch, and yaw channel lumped disturbances, keep the estimation error bounded, and recover after stage-transition-induced disturbance variations. Full article

Quick Access Recorder (QAR) data provide high-dimensional onboard flight records that are increasingly used for data-driven aviation safety analysis. As flight operations become more complex, conventional manual monitoring and threshold-based exceedance detection are often insufficient for identifying evolving risks in a timely and interpretable manner. This paper reviews QAR data-driven methods for flight anomaly detection and risk warning from the perspective of statistical learning and aviation data science. First, the main characteristics of QAR data are summarized, including multi-source heterogeneity, temporal dependence, missing values, noise, and severe class imbalance. Common preprocessing techniques, such as missing-value imputation, trajectory correction, feature engineering, downsampling, and imbalanced-data handling, are then reviewed. Second, existing methods are organized into four groups: statistical monitoring and rule-based methods, clustering and unsupervised anomaly detection, Bayesian and probabilistic risk reasoning, and hybrid machine learning with explainable AI. Representative approaches include statistical process control, association rules, Gaussian mixture models, CurveCluster, Fast-DTW, Bayesian networks, dynamic Bayesian networks, VAE-LSTM, MAD-XFP, and XGBoost with SHAP interpretation. The review further discusses typical applications in landing risk warning, takeoff risk assessment, flight operation pattern recognition, and aviation noise prediction. Finally, key challenges are summarized, including model interpretability, real-time deployment, cross-aircraft and cross-airport generalization, data quality, causal reasoning, and privacy-preserving collaboration. This review provides a structured reference for using QAR data to support aviation safety assessment, risk warning, and operational decision-making. Full article

This report presents an experimental study focused on parametric optimization of an electric vertical take-off and landing (eVTOL) wing–propeller lifting system. The experiments were conducted in a wind tunnel equipped with a Particle Image Velocimetry (PIV) system, and a wing–propeller thrust and power measurement test stand was used. The total mission flight energy was evaluated and compared for three different propeller-to-wing gross area ratios and three mission profiles. Two principal configurations of the wing–propeller lifting system were considered, corresponding to the hovering and cruising stages of flight. In these configurations, both the propellers and the tilting wing sections were oriented according to the requirements of hover and cruise operation. The total flight energy was adopted as the figure of merit and was calculated for all design points. The figure of merit was then analyzed as a function of the propeller-to-wing gross area ratio. The results allowed the determination of optimal configurations for different hover times. Finally, the total flight energy obtained from the experiments was calculated and compared with the corresponding simulation results. Full article

Reliable launch environment recognition is essential for assisted-takeoff unmanned aerial vehicles (UAVs) because it determines the timing of flight-control activation, motor startup, and mode switching. However, recognition parameters are commonly selected empirically, and their effects on failure rate are rarely quantified. This study proposes a failure-rate-oriented parameter optimization framework integrating Monte Carlo failure-rate modeling, Sobol global sensitivity analysis, and particle swarm optimization (PSO) for UAV launch environment recognition. Three parameters in the sliding-window logic, namely the acceleration threshold $\left(a_{th}\right)$, number of sampling points within the judgment window $\left(n_s\right)$, and threshold-reaching proportion $\left(r\right)$, are analyzed and optimized under low-overload catapult-launch and high-overload gun-launch conditions. Sobol analysis identifies both individual contributions and interaction effects, providing interpretable guidance for parameter design, while PSO searches for parameter combinations that minimize the recognition failure rate. An additional multi-objective optimization was conducted by incorporating recognition delay, false-trigger probability, and sampling frequency to evaluate the trade-off between recognition reliability and response speed. Results showed that $n_s$ dominated the low-overload case, contributing 54.88%, whereas $r$ dominated the high-overload case, contributing 37.06%. PSO reduced the upper limit of the 95% confidence interval of the failure rate by 88.47% and 90.22%, respectively. The multi-objective optimization further reduced the mean recognition delay from 55.8 ms to 45.5 ms under the low-overload condition and from 8.8 ms to 4.1 ms under the high-overload condition while maintaining low false-trigger probability and recognition failure rate. Experimental tests verified successful recognition in six low-overload and six high-overload launches. Runtime comparisons with genetic algorithm (GA), differential evolution (DE), and random search (RS) further demonstrated the offline computational efficiency of PSO. Full article

An adaptive super-twisting algorithm (ASTA)-based variable-damping strategy coordinated with five-vector model predictive current control (FV-MPCC) is proposed for a dual three-phase permanent magnet linear generator (DTP-PMLG) wave energy conversion system. In the upper-level controller, the power take-off (PTO) damping coefficient is adjusted online based on the captured power gradient, and finite-time convergence of the power-gradient variable is established via Lyapunov analysis. In the lower-level controller, four active voltage vectors and one zero voltage vector are applied in each sampling period, so that the d–q–x–y current components are directly included in the action-time calculation. Therefore, q-axis current tracking and x–y harmonic-current suppression are achieved simultaneously. Simulation results under two irregular-wave conditions show that the proposed variable-damping law approaches the optimal fixed-damping performance without requiring prior sea-state-specific damping selection, increasing the mean captured power by 2.38% and 3.44% relative to the optimal fixed-damping cases. Experimental results further confirm that the proposed FV-MPCC reduces the d-axis and q-axis current ripples by 35.92% and 40.66%, respectively, compared with conventional MPCC. Full article

Autonomous takeoff and landing (ATOL) remains one of the most challenging tasks for fixed-wing unmanned aerial vehicles (UAVs), particularly in environments where Global Navigation Satellite System (GNSS) signals are degraded or unavailable. This paper presents an LiDAR-assisted terrain-relative navigation framework for the autonomous takeoff and landing of a 5 kg fixed-wing UAV operating under degraded navigation conditions. The proposed architecture integrates a downward-facing LiDAR rangefinder with barometric altitude sensing, INS/GNSS navigation, optical-flow measurements, and airspeed information within a multi-sensor fusion and flight-control framework. The system combines a Pixhawk-based autopilot with a companion-computer architecture responsible for real-time sensor processing, altitude estimation, mission supervision, and MAVLink-based communication. A dedicated filtering strategy and sensor fusion approach enable reliable terrain-relative altitude estimation during critical low-altitude flight phases, while fault-tolerant command-management mechanisms improve operational robustness in the presence of temporary communication losses and sensor disturbances. The proposed framework was validated through Software-in-the-Loop (SITL), Hardware-in-the-Loop (HITL), and real-flight experiments. Experimental results demonstrated stable and repeatable autonomous landing performance. Comparative analyses showed that the LiDAR sensor provided the most accurate and responsive terrain-relative altitude measurements during takeoff, flare, and landing operations, particularly over irregular and vegetation-covered surfaces. In contrast, barometric sensing provided greater long-term stability during cruise flight, highlighting the importance of multi-sensor fusion for reliable altitude estimation throughout the mission profile. The results confirm that LiDAR-based terrain-relative sensing significantly improves autonomous takeoff and landing performance for fixed-wing UAVs operating in GNSS-degraded environments. The proposed architecture offers a practical and low-cost solution for the autonomous takeoff and landing of fixed-wing UAVs operating in GNSS-degraded environments while demonstrating the benefits of integrating LiDAR, inertial, barometric, and GNSS measurements within a unified multi-sensor autonomous flight framework. Full article

Floating tidal platforms provide a flexible solution for offshore tidal–stream energy exploitation, but their wave-induced motions may affect platform stability, turbine operation and power performance. Integrating wave energy converters (WECs) with a floating tidal platform provides a potential approach to absorb wave energy and modify platform motions. However, the dynamic role of a WEC array attached to a floating tidal platform remains insufficiently understood, especially with respect to array layouts, power take-off (PTO)-induced coupling and absorbed power. This study investigates the effects of WEC array layout on the motion response and absorbed power of a catamaran-type floating tidal platform under irregular wave excitation. Three representative WEC array layouts, namely longitudinal, transverse and hybrid arrangements, were compared with a baseline platform without WECs. A coupled numerical model was established by combining frequency-domain radiation-diffraction analysis and time-domain simulations of mooring system and PTO dynamics based on ANSYS AQWA 2023R2. The hydrodynamic model was verified through code-to-code comparisons with OrcaWave 11.6, and the PTO power model was checked against published numerical results. The results show that the WEC array layout has a significant influence on both platform response and power absorption. Among the investigated layouts, the transverse array provides the most effective overall motion suppression, with average reductions of 36.83% in heave responses and 52.62% in pitch responses compared with the baseline platform. Frequency-domain results indicate that pure multi-body hydrodynamic interaction has a limited influence on the platform response amplitude operators (RAOs) and wave-excited forces, whereas time-domain results reveal much stronger layout-dependent responses once PTO coupling was included. The WECs’ absorbed power was strongly affected by the geometric relationship between the PTO rotation plane and the dominant platform motion plane. When these two planes were aligned in coplanarity, platform motion enhances the relative PTO rotation and increases output power. These findings indicate that, for floating tidal platforms with relatively small displacement, WEC arrays should be treated as distributed dynamic subsystems rather than only as energy-harvesting add-ons. The results can provide useful guidance for the layout design and coupled dynamic assessment of floating hybrid tidal–wave energy converters (HTWEC). Full article

Background: Team sports often involve high-intensity unilateral actions that can lead to neuromuscular asymmetries, increasing injury risk and reducing performance, particularly in young female athletes. Methods: This study quantified and compared inter-limb asymmetries in single-leg countermovement jumps (slCMJ) across sexes and sports in 96 youth elite athletes (16.42 ± 1.03 years; 1.83 ± 0.09 m; 74.36 ± 8.69 kg) from basketball, handball, and volleyball. Using a force plate, asymmetries were assessed, and statistical analyses (t-test, ANOVA) identified differences. Results: Females showed greater asymmetry in jump height (9.64 ± 6.43% vs. 6.48 ± 4.87%, p = 0.01, d = 0.59), whereas males exhibited higher asymmetry in time to take-off (10.32 ± 7.5% vs. 6.4 ± 4.7%, p = 0.003, d = 0.63). Volleyball players displayed the lowest asymmetry in jump height (7.05 ± 4.9%) compared to basketball (8.73 ± 7.2%) and handball (11.88 ± 9.7%, p = 0.05), and in relative maximum power (4.63 ± 3.7%) compared to basketball (7.75 ± 5.3%, p = 0.04) and handball (6.51 ± 4.7%). Conclusions: These findings highlight sex- and sport-specific neuromuscular asymmetry patterns, emphasizing their relevance for injury prevention and performance strategies. However, asymmetries are highly variable, influenced by multiple factors. Full article

Vertical take-off and landing (VTOL) configurations incur a structural weight penalty that reduces payload fraction and endurance compared to conventional fixed-wing and multirotor aircraft of comparable gross weight. To extend the endurance of VTOL UAVs, this work presents the design, analysis and control of a novel unmanned tilt trirotor aircraft with tandem wings, named Gong-H, featuring VTOL capability and high aerodynamic efficiency. A prototype of this aircraft was built with the rotor system mounted between tandem wings with a high wing coverage rate, which can achieve a more compact structure than other VTOL aircraft. The control forces and torques are provided not only by the rotor system in VTOL flight mode and the two tandem wings in cruise mode, but also by both the rotor system and wings in transition mode. Additionally, Computational Fluid Dynamics (CFD) simulations are conducted to optimize the wing configuration to improve the efficiency of cruise mode. Moreover, an airspeed-scheduled hybrid control framework based on incremental nonlinear dynamic inversion (INDI) and PID is adopted for different flight modes to improve the robustness of control and the stability of flight mode switching. Hover experiments confirm improved power efficiency compared to tilt quadrotor configuration, which extends endurance time and increases range. Additionally, complete flight cycle field experiments were conducted to demonstrate the aerodynamic feasibility of the prototype, including VTOL flight, cruise flight, and transition flight modes. Control surface redundancy tests and comparative INDI-PID validation under asymmetric disturbances further verify the practical robustness of the control framework. This work provides a design concept of VTOL aircraft and a practical solution for VTOL applications. Full article

Dynamic bipedal jumping is highly sensitive to takeoff momentum and landing configuration, making the direct execution of purely offline-optimized trajectories unreliable on full-sized humanoid robots in the presence of modeling inaccuracies and execution uncertainties. A key challenge is the gap between dynamic feasibility predicted offline using simplified models and executability on physical hardware, because such models cannot fully capture full-body dynamics, actuator behavior, contact transitions, and execution uncertainty. This paper proposes an offline-to-online planning and whole-body control framework for robust in-place jumping of full-sized humanoid robots. The framework integrates phase-consistent offline trajectory optimization, lightweight online reference reshaping, constraint-aware whole-body control, and actuator-level command mapping to improve execution robustness without online re-optimization. In the offline stage, centroidal-dynamics-based trajectory optimization generates jumping references subject to kinematic-consistency and contact-feasibility constraints. During execution, these references are adapted online using real-time state estimates to compensate for takeoff deviations and regulate the landing state; a weighted quadratic-programming whole-body controller then tracks the adapted references. Hardware experiments on a 79.5 kg humanoid robot demonstrate repeatable in-place vertical jumps with a height of approximately 30 cm and stable landings. The results show that robust jumping on a full-sized humanoid robot can be achieved by combining offline nominal trajectory generation with online execution adaptation rather than relying on exact reproduction of the offline trajectories. Full article

Surface congestion and taxiing delays at high-density airports increasingly constrain aviation sustainability, as ground-phase fuel consumption and emissions constitute a significant share of total airport emissions. Existing studies typically decouple air traffic flow management from ground resource scheduling, hindering coordinated optimization of punctuality, environmental benefits, and resource utilization. This paper proposes a multi-objective optimization method for runway-taxiway systems oriented toward air–ground collaborative decision-making, integrating Calculated Take-Off Time (CTOT) compliance constraints. A tri-objective mixed-integer programming model is formulated to minimize CTOT deviation, total taxiing time, and runway workload imbalance. A hybrid intelligent algorithm, SSA-SCA-NSGA-II, is designed with a bidirectional elite feedback mechanism to address this NP-hard problem. Validation uses real operational data of 58 departure flights during a peak period at Beijing Daxing International Airport. The results demonstrate that the proposed method achieves effective trade-offs on the Pareto front: CTOT compliance rate increased from 77.6% to 89.7–96.6%; total taxiing time decreased from 692 min to 551–635 min; and dual-runway utilization imbalance declined from 5.2% to 1.7–3.8%. These improvements translate into quantifiable sustainability gains: fuel consumption is reduced by 1425–3525 kg and CO₂ emissions by 4503–11,139 kg per peak hour, alongside a 19-percentage point improvement in punctuality that lowers passenger delay costs and reduces controller coordination workload. By simultaneously advancing environmental sustainability (carbon footprint reduction), economic sustainability (fuel and operational cost savings), and social sustainability (service punctuality and labor efficiency), the framework provides a measurable, monitorable, and policy-relevant decision-support tool for green airport surface operations aligned with sustainable development goals (SDGs). Full article

Air cell-based wheelchair seat cushions are widely used for pressure ulcer prevention in individuals with limited mobility. However, the influence of ambient pressure variations on the mechanical surface pressure acting on users has not been systematically investigated. This study presents a dedicated measurement concept to quantify these effects under controlled laboratory conditions. Surface pressure was quantified using a dual-range FSR sensor calibration, achieving a minimum resolution of 0.0012 N/cm² per digit. Five representative scenarios were investigated, covering ambient pressure reductions between 30 hPa (elevator rides) and 250 hPa (aircraft takeoff). Measurements were conducted across 150 series, combining five initial internal cushion pressures and six load levels. Ambient pressure reductions led to measurable increases in surface pressure across all conditions, ranging from 11.2 ± 11.0% (30 hPa) to 62.0 ± 45.3% (250 hPa). Risk assessment based on a pressure–time cell death model revealed risk category changes in up to 66.7% of all conditions. Mean reductions in time to cell death ranged from 16 min (30 hPa) to 55 min (250 hPa), following a logarithmic relationship (adjusted R² = 0.984). These findings highlight ambient pressure variation as a previously unrecognized influencing factor on pressure ulcer risk in wheelchair users with air cell-based seat cushions. Full article

This study examines the development of urban air mobility, which requires the creation of vertiports capable of ensuring the safe operation of electric vertical takeoff and landing (eVTOL) systems. Key operational constraints include unstable power supply, external climatic conditions, and reliance on battery systems. This study aims to develop a risk-based model for vertiport planning those accounts for the stochastic nature of eVTOL operational safety. A continuous-time Markov model incorporating nominal operational characteristics, system constraints, and transitions into emergency and catastrophic flight modes is proposed. State transitions within the model are primarily driven by climatic indicators, power supply reliability, battery parameters, maintenance quality, and diagnostic coverage. To interpret the low probabilities of transitioning to a catastrophic mode, this study introduces a safety index (integrated safety index), which facilitates the comparison of various operational scenarios and regulatory maturity levels. The practical importance of the research lies in applying the proposed model to precisely select vertiport locations; assess energy infrastructure requirements; and organize onboard monitoring, robotic preflight inspection systems, and decision support systems. The results demonstrate that eVTOL operational safety is assessed not only through spatial and infrastructure metrics but also through an integrated indicator encompassing power supply, climate, battery degradation, diagnostics, and hardware–software reliability of the entire vertiport system. Full article

The distinct engineering advantages of Oscillating Water Column (OWC) systems have driven substantial academic interest lately. This work examines the onshore U-shaped OWC (U-OWC), selected for its cost-effective installation integrated with existing coastal infrastructure and its superior broadband response to diverse wave climates. Time-domain CFD simulations, incorporating the scaling-rematched approach, were conducted to quantify key hydrodynamic and air-compressibility coefficients, including the amplitude of the wave exciting force, fluid damping coefficient, added mass, absorption factor, and the effective PTO (power take-off) damping and air-compressibility coefficients. These parameters collectively elucidate the underlying hydrodynamics and how they are interwoven with the compressibility of the air in the plenum chamber, thereby impacting the U-OWC’s energy-capture performance under incident waves. A principal finding is the identification of a C+ interval wherein air compressibility enhances capture performance in the lower wave-period range examined (<8.0 s). The added mass of the present U-OWC exhibits a remarkably pronounced decrease around the wave period of 8.0 s, which can be verified by a simple resonance formula of heave buoys to underline its strong near-resonance behavior. Full article