Search Results (977)

Small multirotor UAVs frequently operate in crosswind conditions, yet the aerodynamic interaction between windward and leeward propeller pairs remains incompletely understood. This study investigates the performance of a quadcopter propeller system under lateral crosswind using steady-state RANS simulations with the Transition SST turbulence model, validated against wind tunnel measurements (thrust and torque deviations within $5.4\%$). A parametric matrix of five rotational speeds (8000–12,000 RPM) and six freestream velocities (0–10 m/s) is systematically examined. While thrust and power coefficients of all propellers increase monotonically with freestream velocity, the figure of merit ($FM$) of leeward propellers exhibits a previously unreported non-monotonic response: it decreases from hover, reaches a minimum near $6 \mathrm{m}/\mathrm{s}$, and partially recovers at higher velocities. Windward propellers show no such degradation. Our velocity contour and streamline analyses reveal that this behavior originates from windward wake ingestion into the leeward inflow region, which peaks at intermediate freestream velocities and is progressively alleviated as the stronger crosswind convects the wake downstream. The non-monotonic $FM$ response is therefore a direct consequence of the competition between wake-induced inflow degradation and freestream-driven aerodynamic augmentation. Our findings provide a systematic aerodynamic dataset essential for crosswind attitude control and propulsion system design in multirotor UAVs. Full article

To address the strong coupling among engine geometry, propulsion performance, aerodynamic response, flight trajectory, and manufacturing cost, this study establishes an integrated propulsion–aerodynamics–trajectory–cost design framework for high-speed, long-range rocket-boosted vehicles. Six chamber and nozzle geometric parameters are selected as design variables. An engine performance model is first used to calculate propulsion responses, including thrust, chamber pressure, and specific impulse. A mass and configuration update model then transfers the effects of engine parameter variations to the overall vehicle characteristics, while aerodynamic data and a two-dimensional point-mass trajectory model are introduced to obtain mission-level indicators, including maximum velocity, maximum altitude, and range. An existing manufacturing cost decomposition model for solid rocket motors is extended by coupling the cost response with component masses, geometric dimensions, and parameter-update relationships, thereby enabling the simultaneous evaluation of mission performance and manufacturing cost within the integrated computational chain. Kriging surrogate models are constructed for rapid prediction of the coupled system responses, entropy-weighted TOPSIS is used to screen feasible candidates, and SQP is employed for continuous constrained refinement. Compared with the baseline design, the comprehensive evaluation index increases from 0.4861 to 0.6110. The maximum velocity, maximum altitude, and range increase by 8.29%, 26.81%, and 21.24%, respectively, while the manufacturing cost increases by only 0.48%. The evaluation index is also 15.68% higher than that of the engine-level optimized design. These results demonstrate that the integrated consideration of propulsion, aerodynamics, trajectory, and manufacturing cost improves mission-level performance–cost trade-offs and provides a system-level design approach for mission-oriented and cost-aware solid rocket motor development. Full article

This study presents the design, fabrication, and experimental validation of the Hermes reusable model rocket platform integrating additive manufacturing, onboard sensing, and telemetry capabilities for low-cost aerospace experimentation. The rocket was manufactured using modular Polyethylene Terephthalate Glycol (PETG) components produced through fused filament fabrication to achieve a lightweight and structurally robust configuration suitable for repeated flight operations. A custom flight computer based on a Raspberry Pi Zero 2W was developed to acquire in-flight data from an inertial measurement unit, barometric pressure sensor, and Global Positioning System module, while an onboard camera enabled post-flight trajectory assessment. Aerodynamic performance and stability were evaluated using OpenRocket simulations, and propulsion was provided by a cluster of Klima D9-5 solid rocket motors. Four experimental flights were conducted to evaluate the integrated system architecture, assess telemetry and sensor performance, and compare experimental flight data with simulation predictions. The recorded measurements successfully captured the primary flight phases, including launch, ascent, apogee, descent, and recovery. The experimental results showed qualitative agreement with the simulated flight profiles; however, deviations in apogee altitude, acceleration, and flight duration were observed due to aerodynamic drag, environmental disturbances, motor-performance variability, and implementation-related limitations. The flight campaigns additionally identified practical challenges associated with wireless telemetry reliability, GPS signal acquisition, electronic protection, and parachute deployment, leading to iterative system improvements. From a sensing perspective, the flight campaigns demonstrate the operation and limitations of a low-cost embedded acquisition architecture under dynamic conditions, including the effects of sampling rate, sensor calibration, synchronization, wireless-link interruption, and local data preservation on the quality of the recorded flight measurements. The presented platform demonstrates the feasibility of combining low-cost additive manufacturing techniques with commercially available embedded electronics for reusable aerospace testing and educational applications. The proposed system further provides a flexible experimental framework for flight-data acquisition, simulation validation, and iterative development in academic and amateur rocketry research. Full article

This paper presents a positioning control method for underactuated unmanned surface vehicles (USVs) subject to environmental disturbances and wave-contaminated measurements. In underactuated dynamic positioning, surge motion and yaw motion can be directly regulated by the propulsion system, whereas sway motion cannot be directly controlled by an independent lateral thrust. Therefore, the lateral environmental-force component is utilized to induce the vehicle’s dynamic response to sway. To achieve this objective, a position-keeping guidance system taking into account the desired heading and the lateral positioning error is introduced in this paper. With this guidance mechanism, the lateral environmental-force component can drive the USV to reduce the cross-track error, thereby enabling underactuated positioning. A rotated coordinate system is established around the desired position, and the positioning error is decomposed into along-track and cross-track components. To improve the transient response, an error-rate feedback term is introduced into the rotated-angle update law for yaw-heading guidance design, which enhances the damping of the cross-track dynamics. Meanwhile, a wave-filtering observer is designed to make low-frequency position and velocity estimates for feedback control. Simulation results under multiple operating conditions show that the proposed observer reduces the amplitude and high-frequency variation of the control signals compared with the existing wave-filtering observer, and the proposed positioning control method achieves smaller positioning errors than the existing nonlinear positioning control (NPC). The comparative results also indicate that the proposed method is suitable for position keeping under constant or slowly varying environmental loads, moderate model uncertainty, and wave-contaminated measurements, whereas rapidly varying load directions may degrade the positioning accuracy. Full article

Autonomous subterranean mobility remains one of the least unified domains in robotics because locomotion emerges from coupled interactions among deformable geomaterials, structural mechanics, energy dissipation, and environment-dependent sensing constraints. This foundational pioneer technical review synthesizes 35 years of research on burrowing and underground robotic systems through a terradynamic and multiphysics perspective. Following PRISMA guidelines, 143 peer-reviewed studies were analyzed across granular soils, cohesive sediments, saturated media, fractured geomaterials, and extraterrestrial regolith analogs. The review evaluates six dominant locomotion classes, including peristaltic, undulatory, fluidization-assisted, excavation-based, tip-extension, and hybrid architectures. Results demonstrate that locomotion performance is governed primarily by regulation of substrate response rather than propulsion generation alone. Across all architectures, mobility depends on the coupled evolution of confinement-dependent stress redistribution, yielding mechanics, pore-pressure dynamics, fracture propagation, structural stability, thermomechanical loading, and energy partitioning. The analysis further reveals a convergence toward stress-regulated locomotion, where successful systems minimize drag accumulation, control force-chain evolution, and adapt to changing terradynamic conditions. Major unresolved challenges include the absence of transferable scaling laws, standardized benchmarking methodologies, predictive terradynamic models, and multi-medium autonomy. The review concludes by proposing the foundations of a unified multiphysics terradynamic robotics paradigm capable of linking robot design, substrate mechanics, control, and deployment across terrestrial and planetary subsurface environments. Full article

Rack railway systems operating on steep-gradient routes rely on rack-and-pinion propulsion mechanisms that generate substantial vibrational excitation through cyclic gear mesh contact, adversely affecting passenger comfort and long-term mechanical reliability. Conventional integrated steel gears transmit propulsive forces without inherent vibration attenuation, and a systematic design methodology for optimising the internal rubber spring configuration of elastic gears for such applications has not been established. This study develops a kinematic spring-mass model for both conventional steel and elastic rubber gear configurations in a Korean rack railway propulsion system and validates it through controlled experimental testing. A high-speed rail–wheel contact simulator was employed to measure vertical vibrational accelerations under rigid–rigid (steel–steel) and rigid–resilient (steel–rubber elastic gear) contact conditions, with a load simulating steep-gradient operational forces applied to the gear assembly. The elastic gear achieved a 25.1-fold reduction in vertical vibrational acceleration relative to the steel gear baseline (6.4 m/s² vs. 160.7 m/s²). Time-domain statistics (mean, RMS, standard deviation and peak envelope) are reported for both configurations from repeated runs. Analysis of the normalised effective stiffness as a function of the number of rubber springs predicts that four springs represent a practical optimum, beyond which the incremental stiffness change falls below 0.5%; experimental validation of intermediate spring counts is identified as future work. A spring-number optimisation framework is proposed that returns both a spring count and a rubber compound specification, balancing vibration attenuation against load distribution, torque-transmission capacity and component fatigue life. Full article

The complex and nonlinear load characteristics of Hall thrusters remain a key challenge in the design of propulsion power-supply output stages. In existing power-supply simulations for electric propulsion systems, the Hall thruster is often simplified as a fixed impedance or a prescribed current source, which makes it difficult to capture the time-synchronized interaction during simulation between the power-supply output stage and the thruster discharge process. To address this issue, this study encapsulates a one-dimensional discharge model as an externally callable thruster slave and proposes a HallThruster.jl–Simulink–Saber co-simulation method. The proposed method enables synchronized bidirectional exchange between the power-port voltage $V_{cmd}$ and the thruster discharge current $I_{out}$. The results show that the discharge current under the co-simulation condition exhibits a sustained low-frequency response at approximately 15.0 kHz. Compared with a fixed-voltage standalone simulation, the co-simulation preserves the same principal oscillation band and overall internal-field structures, while small but observable differences remain in instantaneous phase, local waveform shape, harmonic amplitudes, and high-gradient regions of the internal fields. The proposed method provides a computational framework for investigating dynamically coupled port behavior between a Hall thruster and a representative power-supply output stage. Full article

Sustainable aviation fuel is among the most practical near-term routes for aviation decarbonization because it can be used in existing aircraft, engines, and airport fuel systems with limited infrastructure changes while minimizing disruption to the aviation fuel supply chain. This review examines SAF applications in aerospace propulsion systems, focusing on production pathways, aero-engine compatibility, property prediction, and fuel heat sink potential. It compares hydroprocessed esters and fatty acids (HEFA), Fischer–Tropsch (FT), alcohol-to-jet (ATJ), synthesized iso-paraffins (SIP), and power-to-liquid (PtL) fuels in terms of feedstock type, process complexity, product composition, and blending constraints. It also assesses how molecular composition governs density, cold-flow behavior, thermal stability, coking propensity, seal compatibility, and emissions. Recent advances in molecular dynamics, machine learning, spectroscopic analysis, and uncertainty quantification show a shift from empirical estimation toward composition-based prediction, prescreening, and fuel design. For high-thermal-load propulsion systems, SAF is further evaluated as a fuel heat sink in active regenerative cooling. Current evidence points to advantages in thermal stability and low coking tendency, but important gaps remain in transcritical and supercritical heat transfer, pyrolytic heat absorption, wall-material effects, coke deposition, and heat sink capacity modeling across wide operating ranges. Full article

Unmanned aerial vehicles (UAVs) increasingly demand higher flight speeds, longer endurance, improved payload capacity, and greater operational flexibility across a wide range of applications. While battery-electric propulsion systems dominate small UAV platforms, their limited energy density significantly constrains range and mission duration. Consequently, turbine-based propulsion systems, including micro turbojets, turboprops, turboshafts, and hybrid-electric gas turbine architectures, are attracting growing attention as alternatives for advanced UAV operations. Unlike previous reviews that primarily focus on propulsion technologies or individual subsystem performance, this review provides an integrated assessment of the multidisciplinary challenges associated with turbine-powered UAVs, encompassing thermal, structural, aerodynamic, acoustic, operational, and stealth considerations within a unified framework. The presented synthesis identifies current knowledge gaps and emerging research directions, providing a comprehensive reference for the design and development of next-generation turbine-powered unmanned aerial platforms. Full article

As a paradigm-shifting hypervelocity propulsion technology, electromagnetic rail launch (EMRL) is fundamentally constrained by armature/rail (A/R) interface degradation, which directly erodes its service longevity and operational reliability. Small-caliber circular bore electromagnetic launchers (SCCB-EMRL) offer superior structural integration and ballistic stability over traditional rectangular bores. Their inherently lower self-centering capability imposes strict requirements on interfacial contact stability. This study investigates the physicochemical evolution of the A/R interface at extreme loading. Consecutive repetitive launch experiments were conducted, and samples were prepared by typical areas of rail according to the current curve. Characterization was performed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. Results revealed a bimodal non-uniform thickness distribution of the deposition layer along the launch direction. The maximum deposition thickness reached 60.6 μm within the acceleration-startup zone. The deposited material comprises transferred Al, oxidized phases (Al₂O₃), Al-Cu intermetallic, and a mixed carbonaceous system containing amorphous and graphitized carbon. Initial launches triggered rapid material accumulation and increased start-up times, after which the interface reached a dynamic equilibrium. This work reveals the evolution patterns of elemental composition and thickness distribution of the deposition layer at the armature/rail interface in small-caliber circular-bore electromagnetic launching and provides experimental reference for the design of anti-deposition coatings to extend the service lifespan of SCCB-EMRL systems. Full article

Small unmanned aerial vehicles (UAVs) are widely used in civil and military fields, and their noise problem has always been the industry’s focus. Compared with a traditional propeller fan, a ducted fan offers higher aerodynamic efficiency, lower aerodynamic noise, and greater safety. It has become the key power component of small UAVs. However, due to the rigid restriction on tip clearance, the traditional integral ducted fan is prone to generating a tip leakage vortex, which produces high-intensity aerodynamic noise and significantly reduces propulsion efficiency. To address the above key problem restricting the quiet flight of small UAVs, this paper designs a segmented ducted fan (SDF). It preliminarily explores the influence of the segmented clearance on the fan’s flow field structure and acoustic radiation characteristics. Specifically, the k-ω SST (shear stress transport) turbulence model and the broadband noise source model were used to establish a computational fluid dynamics model, and the effects of fan speed (20,000–40,000 rpm) and duct spacing (0–20 mm) on its aeroacoustic characteristics were systematically studied. The results showed that the SDF’s acoustic power level maximum (APL_max) was significantly higher than that of the traditional integral structure, especially at high speed. At 40,000 rpm, increasing the duct spacing to 20 mm resulted in a sudden increase in APL_max to 194.5 dB, 61.3 dB higher than that of the integral type. Its essence was derived from the three-stage chain amplification mechanism: (1) strong tip leakage vortex induced by geometric clearance; (2) broadband noise caused by vortex impacting the duct wall; (3) resonant coupling of leakage vortex harmonic frequency and duct cavity standing wave. Based on this, a collaborative noise reduction path was proposed: compressing the spacing to ≤10 mm to suppress the intensity of leakage vortex, designing the periodicity of failure vortex combined with the serrated blade tip/inner wall rubber strip, and blocking the acoustic cavity resonance with non-uniform wall stiffness or 8–10 kHz Helmholtz resonator, providing a solution for the low-noise design of UAV propulsion system. Unfortunately, our study cannot currently resolve transient characteristics; only time-averaged velocity/pressure flow-field contours and total acoustic power distribution are obtained for qualitative analysis of macroscopic noise variation laws and flow-sound correlation. Full article

To address the low efficiency and unclear internal loss mechanisms of azimuth waterjet propulsion (AWP) systems operating under shallow and complex flow conditions, this study investigates an AWP unit at 950 rpm with a thrust of 1.63 kN. Steady numerical simulations are conducted under mooring and low-speed conditions, focusing on thrust coefficient, impeller efficiency, pump efficiency, and diffuser flow characteristics, with comparisons to a conventional mixed-flow pump. The results show that the propeller hydraulic efficiency at the design condition is approximately 52%, significantly lower than the 80–93% typical of mixed-flow pumps. The diffuser contributes nearly 80% of the total hydraulic loss, dominated by secondary flow effects. From the perspective of radial equilibrium in the guide vanes, secondary flow development is closely linked to spanwise momentum non-uniformity and deviation from equilibrium. The inclined outflow from the impeller induces strong spanwise imbalance, while the nearly 180° turning in the diffuser suppresses conventional force terms and establishes a pressure-gradient-dominated inertial balance associated with streamline curvature. This mechanism drives transverse migration and entrainment, promoting the formation of counter-rotating vortex pairs and secondary flows. Four major vortex concentration regions are identified, where interactions between secondary flow and recirculation generate complex three-dimensional vortex structures, including induced and spiral separation vortices. These vortices locally block the flow passage, causing pressure fluctuations and energy dissipation. The mid-span region of the guide vanes is identified as the primary location of loss accumulation. These findings provide theoretical and engineering guidance for diffuser optimization in AWP systems. It should be noted that the present study is based solely on numerical simulations, and no experimental validation for the investigated AWP configuration is currently available. Future experimental studies are needed to further verify the predicted hydraulic performance and flow structures. Full article

Despite the rapid expansion of unmanned aerial vehicle (UAV) applications across precision agriculture, logistics, infrastructure inspection, disaster response, and aerial surveying, objective and quantitative hardware evaluation criteria for UAV components remain insufficiently developed. This paper proposes quantitative key performance indicators (KPIs) for thirteen core hardware subsystems, including airframe and propulsion, battery and power supply, flight control, wireless communication, imaging (camera), Global Positioning System (GPS)/Global Navigation Satellite System (GNSS) positioning, thermal management, acoustic and vibration characteristics, AI-based autonomous flight, electromagnetic compatibility (EMC), cybersecurity, and reliability and environmental qualification, together with LiDAR payload evaluation criteria. International standardization activities by 3GPP (Release 15/17), IEEE (1936–1958 series), American society for photogrammetry and remote sensing (ASPRS), and national regulatory frameworks are synthesized to define measurable performance metrics and recommended test methods for each subsystem. An integrated KPI matrix maps application-domain-specific performance targets—encompassing surveying (real-time kinematic (RTK) horizontal accuracy ≤ 2 cm root-mean-square error (RMSE), ground sample distance (GSD) ≤ 2 cm/px), infrastructure inspection (LiDAR payload up to 8 kg, beyond visual line-of-sight (BVLOS) latency ≤ 140 ms), and logistics delivery (payload ≥ 2 kg, precision landing ≤ 50 cm)—demonstrating that no universal platform can simultaneously satisfy all domain requirements. A fuzzy-AHP weighting procedure and inter-subsystem coupling analysis are introduced to address size, weight, and power (SWaP) trade-off relationships that purely additive scoring models cannot capture. The proposed evaluation framework is intended to contribute practically to UAV standardization, certification, and quality management across the full design–procurement–operation lifecycle. Full article

The decarbonisation of short-sea passenger shipping is a central challenge within the broader transition toward intelligent and sustainable transportation systems. This paper presents a model-based design and techno-economic assessment of a Battery Energy Storage System (BESS) retrofitting a hybrid diesel-electric regional ferry operating the Naples-Ischia route (~19 nautical miles). An experimentally validated Equivalent Circuit Model (ECM) of a commercial LiFePO₄ cell, parameterised through Hybrid Pulse Power Characterisation (HPPC) tests at 10 °C, 25 °C, and 40 °C and validated via Extended Kalman Filter State-of-Charge (SOC) estimation, is embedded into a full-vessel dynamic model. This last encompasses propulsion, power generation, electrical distribution and battery subsystems. Two energy management strategies are evaluated against the conventional diesel-electric baseline: Strategy 1 (S1), combining in-port BESS discharge with shore-grid recharging; Strategy 2 (S2), adding controlled in-navigation recharging when SOC falls below 20%. S1 is found to achieve a 17% annual CO₂ reduction, while S2 yields superior 20-year economics, with annual net savings of ~€470,000, a simple payback period of 3.72 years, and ~6 battery replacements versus ~9 under S1. Also, adopting S2 allows maintaining a shallower average Depth of Discharge (DoD), namely ~40% vs. ~70% of S1. A multi-objective optimisation confirms that the proposed BESS layout occupies only 5% of the available garage area and satisfies Load Line Convention constraints without reducing commercial payload capacity. The presented integrated framework provides a replicable, multidisciplinary tool for BESS deployment across the Mediterranean short-sea ferry sector, directly contributing to the advancement of sustainable maritime transportation. Full article

Electric ducted fans (EDFs) have emerged as promising propulsion systems due to their compact design, high thrust density, and enhanced operational safety. Accurate prediction of aerodynamic thrust is essential for EDF design and performance evaluation; however, existing numerical studies have not yet provided a systematic comparison of the thrust-prediction capability of different k−ω-based turbulence models in micro-EDF applications. In this study, a dedicated thrust-measurement platform was developed for a 120 mm EDF, and experimental thrust data were obtained under three representative hover operating conditions. Based on these measurements, six turbulence models, including SST, SK$\omega$, BSL, GEKO, EARSM, and SST-$\gamma$(alg.), were evaluated using three-dimensional CFD simulations. The numerical model was assessed through thrust validation, centerline velocity comparison, power-consistency analysis, grid independence verification, and qualitative flow-field interpretation. A two-factor full-factorial analysis was further conducted to quantify the effects of rotational speed and turbulence model on prediction accuracy and computational cost. The results show that the turbulence model has a stronger influence on the normalized thrust-prediction error than the rotational speed factor over the investigated operating range. The SST-$\gamma$(alg.) model achieves the highest thrust-prediction accuracy, with an average relative deviation of 0.47%, but requires the highest computational cost. In comparison, the SST model provides a favorable balance between accuracy and efficiency, with an average relative deviation of 1.79% and an average computation time of 184.33 min, approximately 33% lower than that of the SST-$\gamma$(alg.) model. The centerline velocity and power-consistency results further support the comparative model assessment. Overall, this study provides an experimentally validated comparative reference for turbulence model selection in simulations of similar 120 mm EDF under hover conditions. Considering both prediction accuracy and computational efficiency, the SST model can serve as a practical turbulence model choice for engineering parameter optimization of similar micro-EDF configurations. Full article