Search Results (754)

To address the limited understanding of the aerodynamic characteristics of bird-inspired flapping-wing aircraft across different flight phases and the unclear flow field interaction mechanisms between the wings and tail, this study performs three-dimensional numerical simulations based on a self-developed prototype using ANSYS Fluent and the overset mesh method. The aerodynamic effects of key tail parameters under different flight conditions are quantitatively evaluated, and the mechanisms of bidirectional wing–tail aerodynamic coupling are investigated. The results show that tail twist has a negligible influence on instantaneous lift and thrust during level flight, with a maximum variation of only 0.2 N, but significantly affects the overall aerodynamic moments of the aircraft. When the tail twist angle increases from 15° to 20°, the pitching moment increases by 6%. In contrast, during climbing flight, the tail pitch angle has a pronounced effect on lift and thrust, and its aerodynamic influence depends strongly on the aircraft angle of attack. At an aircraft angle of attack of 15°, the difference between the maximum and minimum cycle-averaged pitching moments reaches 0.2 N·m. Further analysis of vorticity fields and pressure distributions confirms the existence of distinct wing–tail aerodynamic coupling. The tail not only directly modifies the aerodynamic forces and moments acting on the aircraft but also alters the wing-generated flow structures, while the wing wake simultaneously influences the aerodynamic effectiveness of the tail. This bidirectional wing–tail aerodynamic coupling plays a critical role in shaping the aerodynamic response of the aircraft under different flight conditions. These findings clarify the aerodynamic roles of key tail parameters and reveal the underlying flow field interaction mechanisms across different flight phases, providing a theoretical basis for motion-parameter optimization and precise attitude control of bird-inspired flapping-wing aircraft. Full article

The accurate prediction of resistance and running attitudes of high-speed planing crafts is of great significance for the improvement of ship hydrodynamics. In this study, the lab model tests and computational fluid dynamics (CFD) methods are employed to investigate the effects of volumetric Froude number and longitudinal center of gravity (LCG) position on the resistance performance, motion characteristics, and free-surface wave patterns for a planing craft. The capability of the CFD model was validated through towing tank resistance tests conducted under various LCG conditions. A systematic analysis of the influence mechanism of LCG variation on the hydrodynamic performance of the craft was conducted. The results indicate that an aftward LCG position can improve the resistance performance; however, it also leads to an increase in the pitch angle. These findings can provide a foundation for the optimization design of high-speed planing craft. Full article

To address the problems of state estimation bias, dynamic threat response lag, and insufficient safety margin in formation coordination caused by the mismatch between the three-dimensional continuous motion model and the discrete sampling characteristics of sensors in UAV multi-aircraft collaborative inspection missions under complex dynamic environments, this paper studies a trajectory planning method that integrates model predictive control and multi-constraint optimization. By constructing a three-dimensional continuous motion model of the UAV and discretizing it using the Euler integral method, the mapping deviation between the continuous motion characteristics and the discrete working mechanism of the airborne system is solved. Based on the model predictive control method, a patrol trajectory tracking planning model is designed, and state increment and integral augmentation strategies are introduced to transform global reference trajectory tracking into a constrained quadratic programming problem in the rolling time domain, achieving high-precision closed-loop tracking. Furthermore, a dynamic environment model coupling static terrain height field and sudden spherical threat is constructed to systematically characterize the static obstacles and random dynamic threats faced by the UAV in complex scenarios such as mountains and hills. On this basis, multiple constraints such as flight altitude, pitch angle, horizontal turning angle, terrain safety margin, and multi-aircraft collision avoidance are integrated to establish a comprehensive objective function that includes range cost, attitude penalty, and safety cost. Through a collaborative mechanism of global optimization and local online correction, a reference trajectory that meets the requirements of formation safety and flight efficiency is generated and used as the input command for the tracking planning model, forming a closed-loop architecture of global optimization generation, local closed-loop tracking, and dynamic real-time correction for trajectory planning. Experimental results show that the success rate of dynamic obstacle avoidance in complex dynamic environments is always higher than 99.9%, and the mean square error of trajectory tracking is stable in the range of 0.02–0.04 km, which verifies its significant advantages in dynamic adaptability, tracking accuracy and formation safety. Full article

Roof instability in the heading area of fully mechanized excavation roadways, together with insufficient coordinated operation between excavation and support, severely restricts tunneling safety and construction efficiency. A novel track-mounted advanced support equipment structure with an articulated curved roof beam is proposed in this study. Considering actual underground working conditions, including uneven roof contact, eccentric loading and local support failure, a three-degree-of-freedom dynamic model covering vertical, pitch and roll motions is established based on Lagrange’s equations. Dynamic characteristics under varying load amplitudes, excitation frequencies, static load offsets and typical support failure modes are systematically analyzed. The results reveal that only vertical vibration emerges under the full support condition, and the resonance frequency of the system is approximately 10 Hz. The maximum steady-state vertical displacement reaches 0.6406 mm with an RMS of 0.5472 mm under an intact support state. The pitch vibration amplitude caused by the failure of the first support group is three times that of the second group, proving front supports dominate anti-overturning capacity. Side beam failure triggers remarkable roll-coupled vibration, while middle beam failure mainly enlarges vertical displacement. This paper clarifies the vertical–pitch–roll coupling vibration mechanism induced by local support failure. Parameter sensitivity analysis reveals that static load offset has the highest sensitivity, while excitation frequency (within 4–6 Hz) and damping ratio exhibit negligible influence on the steady-state response. The obtained quantitative results can provide a reliable theoretical reference for structural optimization, stability regulation and safety monitoring of track-mounted advanced support facilities. Full article

This paper presents a novel approach to design an attitude motion control strategy of a vehicle to mitigate lateral or longitudinal inertial forces acting on the passenger during cornering, braking, and acceleration maneuvers. The collaboration of active suspension system and active airfoil substantially enhances the attitude motion of a vehicle. By incorporating integral control action for both the desired body attitude roll or pitch angle and zero dynamic tire deflection within the performance index, the optimal controller maintains the ideal roll or pitch angle while preserving the road holding capability. The computer simulations were conducted to evaluate the dynamic performance of the proposed system in comparison with various other suspension systems based on a 4-degree-of-freedom half-car model. Four scenarios for rolling and pitching motions were simulated as follows: the first case examines the rolling response to a one-sided bump input applied to a lateral half-car model during straight-line driving. The second case investigates the rolling performance during a cornering maneuver. The third and fourth cases analyze the pitching responses to braking and acceleration using a longitudinal half-car model. The simulation results demonstrate that the proposed system maintains the ideal body attitude, attenuates the effect of the lateral or longitudinal inertial forces and keeps an ideal road holding capability. As a result, the proposed control system substantially improves ride comfort while enhancing the dynamic safety of the vehicle. Full article

Optimizing flapping-foil kinematics for underwater propulsion is challenging due to strong temporal coupling and nonlinear fluid–structure interactions. Most existing approaches rely on parameterized motion profiles, which restrict the accessible design space. A non-parametric kinematic optimization framework based on the discrete adjoint method is developed, enabling direct optimization of time-resolved motions without predefined functional forms. A Morison-based low-order hydrodynamic model, calibrated against Computational Fluid Dynamics (CFD), is employed for efficient evaluation within a validated regime. Results show that optimized motions substantially enhance propulsion performance over conventional sinusoidal motions, yielding non-sinusoidal, high-efficiency kinematics. In thrust-maximization cases, the optimized kinematics achieve a 50.29% increase in mean thrust by redistributing heave and pitch amplitudes and timing. Under balanced thrust–power conditions, the optimized motions consistently outperform sinusoidal counterparts. In power-minimization cases, a “generator-like” regime emerges, indicating a reversal of net energy transfer enabled by the non-parametric formulation. These results demonstrate that non-parametric optimization provides enhanced design flexibility and improved propulsion performance, offering a practical framework for biomimetic underwater propulsion design. Full article

This paper proposes a finite-time adaptive backstepping active suspension control strategy, integrating command filtering and composite learning, to address the degradation of ride comfort and attitude stability in heavy-duty vehicles caused by shifting loads and harsh roads. First, a nonlinear dynamic vehicle model is established, treating multi-source complex disturbances as a single lumped disturbance and accounting for suspension stiffness and damping nonlinearities. To stabilize the body attitude, a tri-axis controller governing the vertical, pitch, and roll motions is developed, incorporating the practical physical constraints of actuators. By employing a composite learning Radial Basis Function neural network, the controller achieves smooth approximation and precise compensation of lumped disturbances, significantly enhancing the system’s active disturbance rejection performance under complex excitations. Furthermore, the finite-time stability of the closed-loop system is rigorously proven using Lyapunov stability theory. Finally, the strategy is evaluated under a 40% load mass mismatch and continuous random road excitations. Results indicate that the proposed strategy effectively curbs the deterioration of suspension nonlinearities during overloads, ensuring smoother dynamic transitions across all three axes. Compared to conventional backstepping control, the proposed approach reduces the root mean square values of vertical, pitch, and roll accelerations by 19%, 13%, and 35%, respectively. Ultimately, this framework effectively improves vehicle stability and disturbance rejection, providing a robust reference for heavy-duty vehicle chassis control. Full article

As robotics technology advances, quadruped robots have become capable of operating in complex environments with varying elevation, including ramps and level changes that are challenging for conventional wheeled platforms. While this terrain adaptability opens new opportunities for inspection, rescue, and exploration tasks, the repetitive impacts, frequent ground-contact transitions, and abrupt postural changes inherent to legged locomotion pose significant challenges for LiDAR odometry. High-frequency gait vibrations and abrupt attitude changes introduce intra-scan motion distortion that conventional single-twist deskewing cannot adequately suppress. In addition, sparse vertical geometric constraints in elevation-varying environments weaken Z-axis observability, allowing vertical drift to corrupt the horizontal pose estimate through Hessian coupling. To address these failure modes within a LiDAR-only framework, we propose a Piecewise-Constant Velocity deskewing scheme that partitions each scan into multiple temporal segments with safety clamping on vertical and attitude components, together with a two-stage ICP that decouples SE(3) optimization into horizontal (x, y, yaw) and vertical (z, roll, pitch) stages and applies observability-aware weighting in the vertical update. The proposed odometry front-end is evaluated on four real-world sequences collected with a Unitree Go2 quadruped robot equipped with a Velodyne VLP-16 LiDAR. Experimental results show consistently lower Absolute Pose Error (APE) than ICP, KISS-ICP, and F-LOAM across all sequences. Vertical drift suppression is most pronounced in the ramp-containing sequences, where baseline methods exhibit substantial Z-axis divergence. Full article

Two methods of accounting for the motion of the bodies—the deforming mesh method and the method of overlapping meshes (or overset mesh method)—are compared using problems with floating bodies, which are typical for the shipbuilding industry. Three problems are considered: oscillation of the cylinder on the water surface, movement of the box under the influence of waves, and heaving and pitching of the ship model in head waves. Numerical computations are carried out in the LOGOS software package, the simulation methodology used is based on the solution of a system of Reynolds-averaged Navier‒Stokes equations, and the Volume of fluid (VOF) method to take into account the free surface. In all problems, the characteristics of the movement of bodies are evaluated; the resistance force of the ship model is also determined in the third problem; control values obtained using two methods of accounting for moving bodies are compared with the available experimental data. The results of numerical simulation have shown that both methods predict body movement parameters well; the accuracy in determining the resistance force in the task of streamlining the ship’s hull is also comparable: the difference between the maximum deviations of the resistance coefficient in the computations with deformation and overlapping computation meshes is 0.5%. In the case of computations of the three-dimensional problem, the time spent when using the mesh-deformation method turned out to be 10% more; therefore, the method of overlapping meshes can be considered more optimal when solving such shipbuilding tasks as self-propelled tests and streamlining the ship’s hull with and without wind and wave loads. Full article

Autonomous UAV landing on dynamic unmanned surface vessel platforms is affected by deck motion and degraded visual observations, which may lead to unsafe final descent decisions. This paper proposes a fully decentralized reliability-enhanced predictive landing method that combines probabilistic perception, visual quality assessment, and model predictive control. Target posterior probability, perception uncertainty, and task-oriented image quality are fused into an online observation reliability index, which is used to adapt observation noise, constrain phase switching, and penalize unreliable descent opportunities. FFT-based dominant-mode identification and Kalman correction are also used to predict deck roll and pitch for landing-window selection. Simulation results show that the proposed method achieves a 90% small-angle landing success rate and keeps the touchdown attitude angle within 5°. Compared with standard MPC, landings within a 15° deck inclination increase from 24% to 82%, and the 80th-percentile touchdown inclination decreases by 9°. Compared with SHMPC, the average solution time decreases from 913 ms to approximately 104 ms per iteration. These results indicate that the proposed reliability-aware framework can reduce unsafe descent decisions and improve landing robustness while maintaining real-time feasibility under degraded maritime visual conditions. Full article

This study presents a comprehensive numerical investigation of a modified backward bent duct buoy (BBDB) floating oscillating water column (FOWC) system, with emphasis on coupled hydrodynamic response and power take-off (PTO) representation. A fully integrated computational framework is developed using SIEMENS STAR-CCM+, ANSYS AQUA and ANSYS CFX, and three-dimensional CFD, incorporating free-surface wave modeling (VOF), six-degree-of-freedom (6-DOF) body motion, and mooring system interaction under realistic offshore wave conditions (H_s = 3.0 m, T = 9.0 s). A key contribution of this work is the development of an orifice-based PTO surrogate calibrated to replicate turbine-equivalent pressure-drop behavior. Comparative analysis demonstrates that the selected 0.30D orifice reproduces turbine response with deviations below 10% in pressure and flow characteristics, while maintaining superior numerical stability. Hydrodynamic analysis confirms that the modified BBDB-FOWC exhibits stable and bounded motion, with dominant heave-driven response and controlled pitch behavior. The influence of viscous damping is quantified through free-decay analysis and incorporated into the coupled simulations. Results show that damping enhances pressure development by ~25% and flow throughput by ~20%, leading to a significant increase in energy extraction potential. Dimensionless analysis further reveals that the system operates in a turbulent, inertia-dominated regime, governed by nonlinear oscillatory flow dynamics. The combined results demonstrate that the proposed methodology enables accurate, stable, and computationally efficient modeling of floating OWC systems with realistic PTO behavior. The findings provide a scalable framework for future optimization and support the development of high-performance offshore wave energy converters. Full article

Wearable sensors like inertial measurement units (IMUs) can quantify sport technique in natural settings, yet field hockey-specific skill analyses remain limited. This exploratory study investigated how relative foot placement, stick orientation, and lower body kinematics at impact relate to performance of the field hockey sweep skill. Eight experienced female participants performed sweeps under three foot positions relative to the ball (in front, in line, and behind) while IMUs recorded body segment and stick motion. Sweep performance was characterized by accuracy, bounciness, and ball speed. Placing the foot in front of the ball was associated with reduced ball speed and a trend toward lower accuracy relative to the in-line reference, whereas placing the foot behind the ball did not differ from in line on any outcome. Stick roll at impact emerged as a consistent trial-level predictor, with a more open face associated with a greater likelihood of a bouncy sweep and slightly increasing ball speed. Stick pitch and lower limb joint angles were not significant within-participant predictors. However, between-participant analyses indicated that larger knee angles and smaller hip angles were associated with greater accuracy, while smaller average pitch was associated with faster ball speed. Together, these findings indicate that some aspects of sweep performance are amenable to immediate technique adjustments whereas others reflect stable individual movement tendencies. These findings provide a foundation for future work on offering evidence-based guidance for technique refinement and potential implications for injury risk reduction. Full article

With the growing demand for precise absolute pose estimation of landers in lunar exploration missions, crater database-based navigation technology has become a core path to achieving this goal, but it faces challenges of low efficiency in large-scale data retrieval and insufficient matching robustness. To address these issues, a coarse-to-fine crater matching framework with database fast searching and robust triangle similarity matching is proposed. A Geo-KD search algorithm is designed to realize fast and accurate retrieval of craters within the field of view by combining Geohash and KD-tree. A robust triangle similarity matching algorithm is constructed through local neighborhood crater screening, triangle similarity matching, and mismatching elimination based on Random Sample Consensus (RANSAC) and Local Motion Consistency (LMC). Experiments show that the algorithm achieves an average retrieval time of 20 ms with an F₁-score of 0.8 for the global lunar database with 1.29 million craters. It has an F₁-score more than 0.746 and a single-frame matching time less than 1.005 s under lunar orbital phase, landing phase, and different camera pitch angles, outperforming other advanced algorithms and meeting on-orbit real-time requirements, providing reliable support for the absolute pose estimation of lunar probes. Full article

Solar energy is one of the fastest-growing contributors to the global energy market. Floating photovoltaic (FPV) systems have emerged as a promising solution to the land-use challenges faced by conventional solar farms. However, the extension of FPV systems to offshore environments is hindered by dynamic wave–structure interactions. Inspired by air-cushion vessels, this study proposes and experimentally validates a novel FPV platform supported by an inflatable air cushion that provides adjustable stiffness and passive damping through air compressibility and wave-induced volumetric deformation. The investigated platform adopts a symmetric structural configuration, which inherently mitigates asymmetric roll and yaw coupling to maintain a balanced hydrodynamic response and stable power generation under wave action. Wave tank experiments were conducted to evaluate the coupled hydro-elastic response, mooring loads, and power generation stability under varying wave heights. The results show that the air-cushion design can significantly reduce peak mooring loads by over 50% compared with the catamaran benchmark. The highest pressure of 20 mbar increases structural stiffness but causes wave-induced losses of up to 30%. Conversely, the lowest pressure of 5 mbar results in excessive compliance that amplifies pitch and heave motion. A moderate pressure of 10 mbar acts as the optimal damping condition within the tested pressure range, suppressing motion resonance while maintaining power output stability. These findings demonstrate the potential of air-cushion integration for offshore FPV adaptability. Full article

In this study, the energy harvesting mechanism of a two-degree-of-freedom (2-DOF) oscillating foil under near-surface conditions and the underlying influence of structural parameters are systematically investigated. Numerical simulations are conducted using the open-source CFD platform OpenFOAM and the waves2Foam toolbox. The free surface is captured using the volume of fluid (VOF) method, while the heave and pitch motions of the foil are simulated via the overWaveDyMFoam solver, coupling 6-DOF dynamic equations with the overset grid technique. The results demonstrate that the periodic evolution and shedding of the leading-edge vortex (LEV) fundamentally drive the self-sustained oscillation of the foil. Moreover, the phase synchronization between the fluid-induced force and the kinematic response serves as the core mechanism for efficient energy extraction. Structural parameters critically regulate these characteristics: stiffness coefficients dictate the natural frequency and phase coordination, thereby modulating the overall motion response. Notably, a local resonance occurs when the system’s natural frequency approaches the fluid’s vortex shedding frequency, inducing the maximum kinematic response. Within the investigated parameter space, the system achieves a peak energy harvesting efficiency of 45.6% and a maximum average power coefficient of 1.15. Finally, the damping coefficients are found to primarily govern the response amplitude and the viscous dissipation of the system. Full article