Search Results (447)

Autonomous navigation and mooring in confined waters require a navigation solution that remains reliable when individual sensing channels are delayed, unavailable, or environmentally degraded. A risk- and integrity-aware architecture was developed for joint processing of RTK-GNSS, inertial and heading measurements, short-range radar, LiDAR, camera, AIS, ultrasonic ranging, propulsion feedback, environmental, and mooring-line tension data. Asynchronous time alignment is combined with sensor-quality assessment, innovation-based fault detection and isolation, covariance adaptation, active-set reconfiguration, protection-level monitoring, and risk-dependent allocation of authority between automation and the operator. The system was evaluated during a five-day campaign comprising 40 runs, four operational phases, 480 synchronized evaluation epochs, and 16 controlled single-sensor or combined sensor-degradation events. Under nominal conditions, horizontal-position and heading RMSE were 0.043 m and 0.176°, respectively. All 64 fault-active diagnostic records were identified; mean event-log detection and controlled-recovery latencies were 3.17 s and 6.34 s. Horizontal protection-level coverage was 99.3% for single-fault epochs and 100% for combined-fault epochs. One combined-fault docking run contained five consecutive aborted decision epochs, while no unsafe-autonomy event was recorded. The measurements therefore indicate bounded degradation of the navigation solution and conservative transfer of authority when sensing integrity decreases. Because all injected-fault runs were acquired under adverse weather whereas nominal runs were acquired under calm or moderate conditions, the condition-class RMSE differences reported below are descriptive and must not be interpreted as isolated causal effects of sensor faults. Full article

Advancements in solid rocket propulsion have intensified the demand for higher specific impulse. Incorporating high-density, high-calorific metal additives into propellant formulations offers a viable pathway to meet these performance targets. Nevertheless, the ablation response of C/C-SiC thermal protection systems (TPS) exposed to high-temperature, high-velocity, dense gas-particle flows remains inadequately characterized. To address this, we employ high-fidelity numerical simulations to resolve the gas-side ablation behavior under extreme multiphase conditions. By calibrating against experimental data, we quantify the erosive mechanisms induced by boron-laden exhaust plumes and derive an empirical correlation for the linear ablation rate. This model serves as a predictive tool for TPS design in severe operational environments. Parametric investigations were conducted across three key variables: particle diameter (30–50 μm), condensed-phase mass loading (28–68%), and impact angle (18–27°). Validation against ground testing yielded a mean deviation of 3.87%, confirming its applicability to the conditions studied in this paper. Results indicate a positive correlation between ablation rate and particle concentration, impact velocity, incident angle (within the tested range), and particle size. During sensitivity analyses, a single-variable control protocol was enforced to isolate individual parameter effects. Full article

Conceptual design is a critical phase in the development of propulsion plants. Its aim is to explore multidimensional design spaces to provide guidelines for the detailed design phase. This exploration is necessarily broad in scope and shallow in fidelity. Lately, developments in computing hardware have allowed the use of simplified computational fluid dynamics (CFD) models for conceptual design purposes, thereby increasing significantly the amount of data to be processed and generalised. In this context, the present work benchmarks two specific surrogate-model implementations for the conceptual design of a rocket-type pulse detonation engine: a tensor-based method based on high-order singular value decomposition (HOSVD) and a fully connected feed-forward neural network (NN). Two complementary comparisons were considered: HOSVD versus NN, using the same factorial databases to assess the effect of the surrogate method; and factorial versus low-discrepancy sampling, using the same NN architecture to assess the effect of the database distribution. The benchmark, which involved five input architecture parameters and five output operation parameters, was performed for both the direct analysis problem (outputs obtained from inputs) and the inverse design problem (inputs obtained from outputs). Three different situations were considered in the comparison—dimensionally balanced, overdetermined, and underdetermined—to simulate conditions that typically arise in these design phases. Three databases of different sizes were generated for the comparison. The results provide a case-specific assessment of the performance of the two implementations under the conditions considered and may provide useful guidance on the application of these data-analysis approaches in conceptual design. Full article

Near-seabed contact operations with underwater hexapod robots can require one leg to execute a contact task, which reduces the stability of the remaining asymmetric five-legged support. To address this problem, this study proposes a five-legged asymmetric coordinated stability control method that integrates gait rhythm planning with attitude feedback. The method decouples the left middle leg from support, propulsion, and CPG phase evolution to form a ‘5+1’ asymmetric support base. This configuration creates an asymmetric support base intended for future task execution while the reserved leg is maintained in a prescribed safe/task posture in the present simulations. Meanwhile, a five-legged Hopf-CPG rhythm maintains continuous gait under asymmetric support. Low-bandwidth attitude feedback modulation is introduced between the CPG-generated foot trajectory and the inverse-kinematics input to balance attitude correction with foot-contact continuity. Full-degree-of-freedom Webots simulations, rather than physical near-seabed experiments, show that, at a longitudinal flow speed of 0.8 m/s, the method reduces combined attitude RMS by 41.52% relative to the no-feedback strategy. Relative to high-gain PD control, it reduces the RMS rate of change of the control output by 71.32%. These results demonstrate improved command smoothness and metric-level compatibility with the five-legged CPG rhythm under a prescribed task-reserved leg posture, with a moderate trade-off in transient attitude suppression. The method therefore provides a simulation-verified control strategy for balancing attitude regulation and gait rhythm continuity under asymmetric five-legged support. Full article

Numerous studies indicate that a flapping-foil thruster installed at a ship’s bow can convert wave energy into propulsive power and reduce added wave resistance while improving dynamic stability. Based on the preliminary exploration of the drag reduction mechanism of an elastic bow-flapping-foil system in waves, this paper further compares the effects and universality of this system on the resistance and motion response of different ship types under similar operating conditions, using three classic ship types (DTMB 5415, KCS, and Wigley) as research objects. Using the ISIS-CFD solver in NUMECA software, the study simulates the ship coupled with a semi-active elastic flapping foil in head waves, analyzing the influences of spring stiffness, foil size, installation position, and encounter phase on system performance. Numerical results show effective wave energy harvesting, boosting propulsion and stability. Under optimized parameters, ship pitch and heave amplitudes decrease by up to 20.14%, resistance reduction reaches 9.60%, and DTMB 5415 achieves a comprehensive drag-reduction and thrust-increase ratio of 31.39%. Further analysis reveals that thrust performance does not rise proportionally with spring stiffness, whereas drag and heaving reduction improve with increasing stiffness. The system performs best at a wavelength-to-ship-length ratio of 1.2 and a foil encounter phase of −90°. This work supports parameter optimization for such systems based on practical application scenarios and requirements. Full article

Background: The current evidence regarding the impact of augmented reality (AR) rehabilitation on motor function in children with cerebral palsy (CP) remains limited. Objectives: This study aimed to evaluate whether integrating AR motor training (ARMT) into conventional rehabilitation enhances gait and balance outcomes compared to conventional rehabilitation alone. Methods: Forty children aged 7 to 12 years with unilateral or bilateral spastic CP were randomly assigned to receive either ARMT integrated into a 4-week conventional rehabilitation program (n = 20) or conventional rehabilitation alone (n = 20). The ARMT replaced 20–30 min of standard motor therapy five days per week. Gait and balance were assessed pre- and post-intervention using an instrumented 10 m walk test with the G-Walk sensor, the MABC-2 one-leg balance task, and the Pediatric Balance Scale. Due to unavailability of data from five control-group participants, analyses were conducted on 35 children using available-case mixed-model approaches. Results: Nominally significant between-group differences in pre- to post-intervention changes were observed for left stride cycle duration (mean difference: −0.083 s; 95% confidence interval [CI]: [−0.166, −0.0002]; p = 0.049), right stride cycle duration (−0.095 s; 95% CI: [−0.185, −0.006]; p = 0.038), the coefficient of variation of the first double-support phase on the right side (−8.91 percentage points; 95% CI: [−17.39, −0.44]; p = 0.040), and the left propulsion index (2.42 m/s²; 95% CI: [0.39, 4.45]; p = 0.021). No statistically significant differences were detected between groups for balance measures, gait speed, stride length, gait quality, or symmetry. Conclusions: Incorporation of four weeks of ARMT into conventional rehabilitation did not yield substantial additional benefits for gait or balance in this cohort. The observed effects on gait timing, variability, and propulsion are exploratory and warrant validation in larger, adequately powered studies with pre-specified primary outcomes. Full article

Facing strict requirements on reliability, power density, vibration and noise for electrified underwater propulsion (EUP) drive motors, this paper investigates dual three-phase winding selection and structural parameter multi-objective optimization of a 24-slot/22-pole surface-mounted permanent magnet (PM) synchronous motor (PMSM). According to winding function theory and magnetomotive force (MMF) harmonic analysis under normal and faulty operation, a double-layer 30° phase-shifted (DL30°) winding is chosen, which is proven to boost torque output and attenuate torque ripple via finite-element (FE) analysis. Key dimensions are globally optimized by the multi-objective particle swarm optimization algorithm, yielding a 5.36% torque density rise and a 41.46% reduction in torque ripple. Prototype experiments agree well with simulations and validate the design strategy. Full article

Bearing damage caused by electric discharge machining (EDM) is a concern in electric ship propulsion drives, particularly during low-speed operations such as maneuvering and slow steaming. In a modular multilevel converter (MMC) operated with nearest-level modulation (NLM), rounding of the three-phase submodule insertion numbers produces a residual imbalance that appears as common-mode voltage (CMV) and charges the bearing film capacitance. The peak bearing voltage rises from 6.4 V at 60 Hz to 20.0 V at 10 Hz, while the thinning lubricant film lowers the dielectric breakdown threshold. Always-on CMV reduction approaches apply a corrected switching candidate in every control period, including intervals where the bearing voltage stays well below the threshold. This paper proposes a selective NLM correction driven by predicted bearing voltage risk: a reduced-order RC model predicts the bearing voltage the conventional NLM candidate would produce, and a hysteretic controller applies a zero-CMV candidate only when that prediction approaches the insulation threshold. Using a worst-case discharge criterion and thresholds of 5.9–29 V derived from elastohydrodynamic film thickness estimates, simulations at 10 Hz show that the method eliminates EDM events over the full evaluated threshold range. It achieves the same zero-EDM outcome as always-on correction while reducing the correction mode activation ratio from 100% to at most 30.8%, and remains inactive where conventional NLM is already safe. Full article

The propulsion performance and propeller design of ships have traditionally been evaluated mainly under calm-water conditions. However, under actual sea conditions, waves can increase added resistance, change the stern wake distribution, reduce propulsive efficiency, and affect cavitation behavior. This study evaluates the propulsion performance and designs a propeller for an 1800 TEU container ship under regular wave conditions using computational fluid dynamics. Resistance and self-propulsion simulations are conducted for eleven wavelength ratios in the range of $0.5\le \lambda /L_{PP}\le 2.0$, with a fixed wave steepness of $H/\lambda =0.01$. The results show that the required power increases significantly in the resonance wavelength range because of the combined effects of added resistance, wake variation, and reduced propulsive efficiency. The Brake Horsepower (BHP) transfer function obtained from the regular wave simulations is combined with representative sea-state spectra using the spectral method to estimate the Daily Fuel Oil Consumption (DFOC) under actual operating sea states. The total long term DFOC is estimated as 37.084 t/day. For the propeller design, the wake distribution at the propeller plane is analyzed at $\lambda /L_{PP}=1.1$, as a representative wave condition where the ship motion and propulsion performance variation become significant. The wake analysis shows that the instantaneous inflow changes considerably according to the wave phase, which can affect blade loading and cavitation. Based on this analysis, a new propeller geometry is designed with the cavitation performance as the primary consideration while also improving the propulsion performance. The designed propeller reduces the cavity volume over the selected wave phases and decreases the delivered power by approximately 2.1% in calm water and 3.4% in wave conditions. These results demonstrate the importance of considering wake variation and cavitation characteristics in practical propeller design under actual operating conditions. Full article

This paper presents a novel fractional-order hybrid observer framework for robust sensorless control of brushless DC (BLDC) motor drives in unmanned aerial vehicle (UAV) propulsion systems, addressing the fundamental limitations of conventional integer-order observers through the lens of fractional calculus. The proposed architecture synergistically integrates high-frequency square-wave signal injection for zero/low-speed operation with an adaptive fractional-order extended Kalman filter (AFEKF) augmented by online stator resistance and flux linkage estimation, capitalizing on the memory and hereditary properties inherent to fractional-order systems. A minimum-order current observer enables accurate three-phase current reconstruction using a single DC-link sensor, substantially reducing hardware complexity and cost. The complete algorithm is implemented on an STM32H7 microcontroller and experimentally validated on a 1.5 kW drone propulsion testbench and in-flight platform. Results demonstrate reliable startup under 50% rated load, stable operation from standstill to 5000 RPM on the UAV motor (and validated up to 22,000 RPM on a high-speed test motor, <4° electrical position error at 5 kRPM, and strong robustness against 35% stator resistance variation. In-flight tests confirm improved thrust smoothness and hover stability compared to conventional sensorless strategies. The proposed fractional-order architecture offers a practical, resilient, and computationally feasible solution for next-generation autonomous aerial systems, establishing a new paradigm for observer design in electric propulsion. Full article

This paper presents the development of a multi-domain simulation for the Porsche Taycan’s all-wheel-drive (AWD) electric propulsion system to investigate the impact of the rear drive unit’s two-speed transmission on performance and drive quality during maximum acceleration. This study was undertaken independent of the vehicle and propulsion system OEM. A lumped-parameter model of the front and rear electric drive units (EDU) and the high-voltage battery was developed and calibrated against the published data for key benchmarks, including 0–100 kph acceleration times and peak longitudinal acceleration. The mechanical shifting mechanism was reverse-engineered to simulate high-performance shift trajectories. To manage the transition, a clutch control scheme integrates a reduced-order clutch-to-clutch model featuring a feedforward (FF) torque estimator and a closed-loop feedback (FB) controller to achieve target input shaft speeds and shift durations. The study concludes with a comprehensive analysis of the propulsion system’s behavior at a battery state of charge of 96% and 25% and three electric motor speeds at which the upshift is commanded. The simulation results demonstrate that executing an early upshift at 10,700 rpm with 96% of SOC yields a 0.100-s inertia phase shift time, restricts the clutch thermal dissipation to 21 kJ, and achieves an 8-s velocity of 203.4 kph, outperforming the upshift at 15,300 rpm (0.210 s, 34 kJ, and 202.8 kph). Furthermore, the transient regenerative braking on the rear axle during the inertia phase reduces the peak current draw from 675 A to 87 A, recovering the DC bus voltage to enable cross-axle torque boosting on the front axle. Full article

As the drone industry expands rapidly, the demand for high-performance propulsion systems with high power density, superior energy efficiency, and lightweight characteristics has grown significantly. Outer-rotor permanent magnet synchronous motors (OR-PMSMs) are particularly well-suited for drone propulsion, due to their superior torque density and efficient thermal management, compared to inner-rotor structures. However, achieving accurate performance prediction during the initial design phase remains challenging due to complex electromagnetic phenomena. This paper proposes an analytical methodology using the subdomain method to evaluate the electromagnetic performance of OR-PMSMs, specifically accounting for slotting effects caused by stator geometry. Rather than focusing on complex optimization algorithms, this study prioritizes comprehensive performance evaluation and experimental validation. Key electromagnetic parameters and circuit constants—including air-gap flux density, back-EMF, winding resistance, inductance, and electromagnetic torque—are calculated efficiently using the proposed analytical model. To complement the limitations of analytical formulation regarding core saturation and flux leakage, the finite element method (FEM) is conducted for comparative evaluation. Furthermore, a physical prototype of the OR-PMSMs for drone propulsion was fabricated, and experimental tests were performed to validate the analytical and numerical results. The analytical predictions demonstrate strong agreement with both the FEM simulations and experimental measurements, confirming the accuracy and reliability of the proposed framework. Consequently, this study addresses the inherent constraints of conventional analytical methods and provides a computationally efficient, yet precise, evaluation procedure, serving as valuable baseline data for the design and development of high-efficiency, lightweight drone propulsion motors. Full article

JP-10 is a pivotal high-density hydrocarbon fuel for advanced aerospace propulsion systems. Doping aluminum nanoparticles to prepare nanofluid fuels is a promising route to enhance its energy density and combustion performance, yet the droplet formation mechanism of such multiphase fuels remains poorly understood, hindering single-droplet combustion research and atomization system optimization. This work constructed a piezoelectric drop-on-demand (DOD) monodisperse droplet generation platform integrated with phase Doppler anemometry (PDA) and high-speed imaging. Using Al/JP-10/OA nanofluids with aluminum mass fractions of 0.1 wt. %, 0.5 wt. % and 1.0 wt. %, we systematically explored the effects of liquid flow rate, driving frequency and particle concentration on droplet size, size uniformity and ejection velocity. In this work, Al/JP-10/OA nanofluids with aluminum mass fractions of 0.1 wt. %, 0.5 wt. % and 1.0 wt. % were tested under liquid flow rates of 1.1–1.5 mL/min and driving frequencies of 10–50 kHz, with measured droplet diameter ranging from 241.04 μm to 292.26 μm and ejection velocity ranging from 1.65 m/s to 2.45 m/s. The results demonstrate that average droplet diameter increases linearly with flow rate and decreases monotonically with driving frequency. Compared with the 0.1 wt. % nanofluid, the 1.0 wt. % nanofluid shows a 4.4% larger droplet diameter and 12.1% lower ejection velocity, while the 0.1 wt. % sample retains excellent monodispersity with a size Span below 0.098. The multi-scale regulation mechanisms involving viscous variation, shear-thinning rheology and particle agglomeration are further clarified. This study provides fundamental data and theoretical support for atomization design of nanofluid aviation fuels. 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

Background/Objectives: This study investigated the effect of sprint intensity on spatiotemporal variables and joint kinematics during the maximal-velocity phase at each intensity level in experienced sprinters. Methods: Twenty experienced master sprinters (18 men and two women, age: 38.2 ± 12.1 years, height: 1.80 ± 0.06 m, body mass: 81.8 ± 8.8 kg, 100 m PB: 12.65 ± 1.06) performed nine 50 m sprints with increasing intensity each time (60–100%), during which step-by-step spatiotemporal parameters and joint kinematics during the maximal-velocity phase of each sprint were measured. Results: The main findings were that sprint times decreased significantly with each increase in intensity, together with a significant increase in maximal sprint velocity. The spatiotemporal parameters contact and flight times decreased, step frequency increased, while step length increased until 75% and decreased again after 90%. Joint angles of the ankle and knee changed, while those of the hip joint did not change at touchdown and toe-off with increasing intensity. All peak step-by-step angular joint velocities during the maximal-velocity phases increased with increasing sprint intensity. However, the changes in joint kinematics across joints did not occur at the same time between intensity levels. Conclusions: These findings highlight that spatiotemporal variables and joint kinematics do not follow a linear development as intensity increases; rather, they adopt distinct mechanical strategies at very high intensities to accommodate reduced time for force application and limb repositioning. Based on the findings it is suggested that training targeting rapid hip-extension mechanics, efficient limb repositioning, and the ability to maintain effective propulsion under shortened contact times may be particularly beneficial. Full article