Search Results (962)

A demand-oriented spatial reinforcement scheme was developed for circular anti-slide piles subjected to a known dominant direction of landslide thrust. Based on the depth-dependent bending-moment and shear-force demands, the proposed scheme integrates uniformly distributed full-length base bars, supplementary longitudinal reinforcement concentrated within the principal tension sector, depth-dependent termination of longitudinal bars, and variable-pitch spiral reinforcement. A three-dimensional nonlinear finite-element model was established to compare the proposed scheme with a conventional circumferentially uniform reinforcement arrangement under identical geometrical, material, loading, and boundary conditions. The results showed that the proposed scheme reduced the total reinforcement volume from 1.243 to 1.041 m³, corresponding to a reduction of 16.3%. At 40% of the design load, the pile-head displacement increased slightly by 3.96%, indicating a minor reduction in initial stiffness. Under the full design load, however, the pile-head displacement, maximum longitudinal-bar stress, and maximum equivalent plastic strain decreased by 5.48%, 15.7%, and 34.5%, respectively. The concrete damage distribution also became more localized and discontinuous near the critical region. These results demonstrate that demand-oriented spatial reinforcement can improve reinforcement utilization, reduce local response concentration, and enhance deformation control under high load levels while achieving substantial steel savings. Full article

This study employs a Contracted and Loaded Tip (CLT) propeller to replace the conventional pump-jet rotor, and a comparative analysis is conducted using the Detached Eddy Simulation (DES) method. The reliability of the numerical method is first validated through open-water tests. The CLT pump-jet propulsors are systematically investigated in two series: the varying endplate width (CW) and varying endplate length (CL). The results indicate that varying the endplate width has a significant impact on the hydrodynamic performance. A smaller width leads to a more pronounced decrease in the thrust coefficient, torque coefficient, and efficiency. In contrast, varying the endplate length primarily affects the efficiency at high advance coefficients. Regarding the vortical characteristics, the gap region is dominated by the tip leakage vortex (TLV) and tip separation vortex (TSV), whose intensity and evolution are influenced by the endplate structure. A reduced endplate width expands the low-velocity region within the gap, while an increased length contributes to a more stable vortex development. In terms of the noise performance, the varying-width designs effectively suppress pressure fluctuations and achieve noise reduction. Specifically, the CW3 model exhibits maximum reductions in the overall sound source level of 5.7 dB and 4.0 dB at distances of 1 m and 20 m, respectively. Conversely, the varying-length designs intensify the pressure fluctuations and show no significant noise reduction effect. Full article

Hydrostatic spindles are key components in high-precision grinding machines. In this paper, an internal feedback radial–thrust combined hydrostatic bearing is proposed to improve the load-carrying performance of conventional hydrostatic spindles. The throttling structure is integrated into the bearing inner surface, and an internal feedback throttling configuration is developed to enhance pressure regulation and reduce nterference between oil pockets. Based on fluid lubrication theory and the hydraulic resistance network method, a theoretical model of the combined bearing is established, and a systematic parameter design method is developed. The governing equations of flow, pressure, load-carrying capacity, and stiffness are derived for performance prediction and structural design. Furthermore, finite element simulations are conducted to investigate the effects of key parameters. The simulation results show that, at a supply pressure of 4 MPa, the radial stiffness reaches 2559.3 N/μm and the axial stiffness reaches 423.1 N/μm. The simulation results are compared with the theoretical predictions, showing good agreement and providing numerical verification of the proposed theoretical model. Full article

Background/Objectives: Low-back pain (LBP) is a common musculoskeletal disorder, with a lifetime prevalence reported to be as high as 84%. Chuna manipulative therapy (CMT), a Korean style of manual therapy for correcting joint misalignment, has rarely been evaluated in randomized controlled trials (RCTs). This study primarily aimed to evaluate the feasibility of a future large-scale, multicenter RCT comparing thrust and non-thrust CMT; preliminary clinical and safety data were collected as secondary, exploratory objectives. Methods: This multicenter, assessor-blinded pilot RCT randomized 30 participants with non-acute LBP and pelvic deviation into thrust (n = 15) or non-thrust (n = 15) CMT groups for a 4-week treatment. Feasibility outcomes (eligibility, recruitment, adherence, retention, data completeness, and treatment fidelity) were the primary endpoints. Preliminary clinical effects (Numeric Rating Scale (NRS), Oswestry Disability Index (ODI)) and adverse events were assessed over 24 weeks as exploratory outcomes. Results: Of the 35 screened, 30 (85.7%) were randomized, and the planned 15 per center was achieved at both sites. Twenty-nine (96.7%) received at least the minimum number of sessions and were retained to week 24, with complete outcome data and no protocol deviations in intervention delivery. In exploratory analyses, both groups improved from baseline and between-group differences favored thrust CMT, but as the trial was not powered to compare effectiveness, these findings are preliminary only. Nine mild adverse events resolved spontaneously. Conclusions: A large-scale, multicenter RCT comparing thrust and non-thrust CMT in pelvic deviation is feasible. The observed feasibility outcomes can inform its progression criteria, whereas the exploratory clinical findings require confirmation in an adequately powered definitive trial. Full article

This study takes the Ankang area in the Qinling–Dabashan Mountains on the northern margin of the Yangtze Block as an example to investigate whether effective shale gas preservation conditions can exist in large-scale thrust nappe belts at convergent plate margins—a critical scientific question. The aim is to provide new concepts and models for shale gas exploration in tectonically complex regions. An integrated approach combining surface geological mapping, geophysical surveying (2D seismic and wide-field electromagnetic method), calibration of a key borehole (ZBDR01), and geochemical analysis was employed to reconstruct the deep geological structure and evaluate the hydrocarbon generation potential and reservoir characteristics of the target shale interval. The results reveal a relatively gentle, weakly deformed “structural stability window” beneath the Zhongbao Fault, a major thrust nappe surface. Within this window, strata dip at low angles and faults are sparse, exhibiting a significant stress-shielding effect. The Lower Cambrian Niutitang Formation shale within this window is well preserved, characterized by high total organic carbon (average TOC: 4.26%) and moderate thermal maturity (average R_o = 3.02%), falling within the effective shale gas generation window. In contrast, the Lujiaping Formation shale in the hanging wall of the fault, though widely distributed, shows excessive thermal maturity and poor reservoir properties. The study demonstrates that the “stress-shielding” effect is the core mechanism controlling the formation of this stability window and proposes a new “tectonic shielding” accumulation model. This model elucidates how the thrust nappe body itself acts as a thick regional caprock, which together with lateral sealing by the fault zone forms a composite seal-cap system, ensuring in situ preservation of shale gas under a strongly tectonic background. It is concluded that local preservation units can form in the footwalls of thrust nappe belts at convergent plate margins due to stress shielding, challenging the conventional view that intensely deformed zones are unfavorable for shale gas preservation. This research not only provides a new direction and model for shale gas exploration in the tectonically complex Qinling–Dabashan region but also offers important theoretical and technical insights for unconventional hydrocarbon exploration in similar tectonic settings globally. Full article

Hydrodynamic models underpin Autonomous Underwater Vehicle (AUV) design, motion control, and performance evaluation. Existing methods face two critical bottlenecks: (1) conventional explicit CFD requires predefined trajectories, which fails to capture true motion responses under combined rudder-propeller action and creates a disconnect between simulation and real operations; (2) the widely adopted Standard Submarine Motion Equations (SSME) suffer from high parameter redundancy, while high-precision non-parametric models incur prohibitive computational costs, hindering embedded deployment. To address these gaps, this paper proposes an implicit CFD-driven framework for fully appended AUVs equipped with through-body thrusters. It requires no preset trajectories, directly coupling periodic propeller thrust and rudder angle excitations to achieve 5-degree-of-freedom (5DOF) spatial motion simulations aligned with real navigation states. Parametric and non-parametric models are identified via Least Squares (LS) and Neural Networks (NN), respectively. Sobol global sensitivity analysis reduces SSME dimensionality, yielding a Basic Submarine Motion Equation (BSME) with only 25 key parameters—cutting the parameter count by 55% with negligible accuracy loss. Validation shows the non-parametric NN model reduces prediction error by over 10% compared to its parametric counterpart, while the streamlined BSME enables real-time forecasting in low-power computing scenarios. This approach balances accuracy and efficiency for rapid hydrodynamic prediction during early AUV design and embedded controller deployment. Full article

The influence of blade number and rotor solidity on cyclorotor hover performance remains insufficiently understood because previous studies have generally varied these parameters simultaneously or investigated them through separate one-factor analyses. This work examines their independent effects using a two-dimensional unsteady Reynolds–Averaged Navier–Stokes model in which blade number (2–8) and rotor solidity (0.24–0.60) are varied independently across 26 geometrically feasible design points, at constant rotor radius and rotational speed. The model is validated against published experimental data for the same rotor before the parametric analysis is performed. At fixed rotational speed, increasing solidity raises both the thrust and power coefficients and lowers power loading. Because power loading is disk-loading-dependent even for an ideal rotor, however, this apparent penalty largely reflects a change in operating point rather than a loss of aerodynamic efficiency: compared at matched disk loading, efficiency varies only weakly with solidity except in the corner of the design space that combines high solidity with a long blade chord, and an interior efficiency optimum emerges near $\sigma \approx 0.36$ for blade counts $N=4$–8, reconciling the present results with the chord-to-radius optimum reported in the literature. Blade number has only a secondary influence on mean performance at constant solidity, consistent with classical rotor theory; azimuthally resolved loads, however, show peak-to-mean thrust ratios of 3–4 for two- and three-bladed rotors, a design constraint invisible in cycle-averaged metrics. Full article

Purpose: Excessive drill advancement after cortical breakthrough is a potential safety concern in orthopaedic procedures. We developed a data-driven approach to estimate the drill-tip position relative to the far cortex prior to breakthrough using time-series thrust force and spindle torque signals. Methods: Drilling experiments were performed on 268 porcine cortical bone specimens at a constant feed rate of 0.5 mm/s. A long short-term memory network was trained to estimate the drill-tip position from filtered force and torque signals. The reference position was derived from breakthrough timing confirmed by high-speed imaging and the programmed feed rate. Performance was evaluated using mean absolute error within the −2 to +2 mm peri-breakthrough interval. Two post hoc analyses examined whether model performance exceeded an elapsed-time baseline and whether pre-breakthrough force patterns were more consistent when expressed relative to breakthrough position than to drilling onset time. Results: The combined-input LSTM achieved an MAE of 0.20 mm, compared with 0.23 mm for force alone and 0.24 mm for torque alone. Among the representative architectures evaluated, LSTM showed the lowest regression error. A signal-blind time-only baseline yielded an MAE of 0.54 mm. The association between cortical thickness and force-decline onset was weaker when expressed in spatial coordinates relative to breakthrough than when expressed as time from drilling onset (R² = 23% vs. 74%). These findings suggest that force and torque signals contained information associated with proximity to breakthrough beyond that provided by average drilling duration alone. Conclusion: Converting sensor-derived resistance patterns into spatially anchored positional information may support proactive strategies such as controlled deceleration before penetration. The proposed approach represents a step toward exemplifying the emerging concept of surgeon-assisting Physical AI. Full article

High-speed compound helicopters surpass the forward-speed limits of conventional helicopters and expand the flight envelope, yet close multi-component integration induces complex aerodynamic interference, whose underlying mechanisms and evolution with flight speed must be understood to support integrated aerodynamic design. This study examines the principal aerodynamic interactions in a box-wing, twin-propeller compound helicopter at flight speeds of 30–110 m/s. Time-accurate Reynolds-averaged Navier-Stokes calculations with dynamic overset grids are performed for isolated-component, rotor-airframe, rotor-propeller, and complete configurations. At 30 m/s, direct impingement of the main-rotor wake produces highly non-uniform propeller inflow, pronounced periodic propeller-thrust fluctuations, and substantial lift losses on the advancing-side wing panels. As flight speed increases, the wake is convected downstream and direct interference weakens, although lateral asymmetry persists. When the airframe is included, the lateral propeller thrust-coefficient trend observed in the rotor-propeller configuration is reversed, while box-wing lift is redistributed unevenly among the individual panels. At 90 and 110 m/s, the main-rotor thrust-coefficient ranges in the complete configuration lie entirely below the corresponding isolated-rotor ranges. These findings clarify how flight speed and component integration jointly govern complete-configuration aerodynamics, providing a basis for reliable aerodynamic assessment and configuration optimization of high-speed compound helicopters. Full article

With the continuous expansion of deep-sea resource exploration, marine environmental monitoring, and underwater operations, Autonomous Underwater Vehicles (AUVs) have been increasingly widely applied. Aiming at the demand for high-performance main propulsion systems of Autonomous Underwater Vehicles (AUVs), this paper conducts research on the structural design and hydrodynamic performance of a 30 kW rim-driven thruster (RDT) and its coupling mechanism with AUVs. By combining computational fluid dynamics (CFD) simulations and experimental methods, the influence of the advance coefficient on the open-water performance of the thruster is revealed. An integrated coupling simulation model of the AUV and RDT is established to analyze the performance attenuation law of the thruster and the characteristics of the coupled flow field under wake flow conditions, and to clarify the two-way interaction mechanism between the thruster and AUV. Towing tank tests were carried out at sailing speeds ranging from 1 to 4 kn, which verifies the reliability of the numerical simulation model and the matching performance between the thruster and AUV. The results show that the open-water efficiency of the thruster reaches a peak value of 0.536 at the advance coefficient $\mathrm{J}=0.8$, which is close to the optimal efficiency range with good matching performance of the propulsion system Under wake flow conditions, the attenuation range of the thrust coefficient of the thruster is 12.45–16.53% with the increase in advance coefficient. The main reasons are the uneven inflow velocity and unstable flow field pressure distribution caused by the non-uniform wake flow at the AUV stern. At the ship speeds of 2 kn, 3 kn and 4 kn, the self-propulsion rotational speeds obtained from test fitting are in good agreement with the simulation results, with all relative errors less than 8%. This study provides a theoretical basis and technical reference for the engineering design of medium and high-power rim-driven thrusters as well as the matching optimization of AUV-thruster systems. 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

Biomimetic surface texturing provides a promising strategy for regulating the vibration behavior of rolling bearings under starved lubrication. In this study, vein-like, elliptical, semi-elliptical, and composite textures inspired by Monstera deliciosa leaves were fabricated on the shaft-washer raceways of thrust cylindrical roller bearings at depths of 4 μm, 8 μm, and 12 μm. Tangential and normal vibration signals were analyzed using time-domain parameters, frequency spectra, power spectral density, and time–frequency maps. The results showed that both texture morphology and depth strongly affected vibration stability. Most textured bearings exhibited lower vibration responses than the smooth bearing after prolonged operation. Among the tested depths, 8 μm produced the most stable response, characterized by lower peak values, smoother root mean square curves, reduced power spectral density levels, and more uniform time–frequency energy distributions. The 8 μm semi-elliptical texture exhibited the best overall performance by suppressing transient impacts and high-frequency energy concentration. These findings indicate that vibration regulation in textured rolling bearings depends primarily on the synergistic matching between texture morphology and depth rather than texture complexity alone. Full article

To addressthe challenge of attitude control in quad-ducted fan unmanned aerial vehicles (UAVs) under coupled disturbances comprising thrust lag, ground effect and a composite wind field during near-ground flight and to mitigate the inherent trade-off between disturbance rejection and noise suppression in fixed-bandwidth extended state observers (ESOs), this paper proposes a robust attitude control method based on a Sigmoid law adaptive-bandwidth extended state observer (AB-ESO). An attitude dynamic model covering the above multi-source disturbances is established, with all uncertainties uniformly treated as lumped disturbances. An adaptive-bandwidth mechanism with filtering and rate-limiting modules is designed for smooth continuous bandwidth tuning. A composite control framework integrating disturbance feedforward, lag compensation and attitude feedback is constructed, and the uniform ultimate boundedness of the closed-loop system is proved. Comparative simulations are conducted against six baseline controllers, including a cascade proportional–integral–derivative (PID) controller, fixed-bandwidth ESOs, incremental nonlinear dynamic inversion (INDI), fast terminal sliding mode control (FTSMC) and a time-varying bandwidth ESO, in a near-ground composite wind scenario. Results show that the proposed method achieves improved comprehensive performance: the three-axis average tracking root mean square error (RMSE) is approximately 72% lower than of the PID controller and 15.8% lower than that of the high-bandwidth ESO, and the control output total variation is reduced by about 27.8%. Monte Carlo verification with 100 random turbulence groups further validates the strong statistical robustness of the proposed method. All validations in this work are based on numerical simulations. This study provides a technical reference for high-precision control of ducted fan UAVs in near-ground environments. Full article

Since the thrust of a single-emitter Field Emission Electric Propulsion (FEEP) thruster is limited to 1–20 µN, a multi-emitter configuration is necessary to increase the thrust capacity. This study proposes a hybrid multi-emitter configuration designed to achieve uniform current distribution, enhanced thrust, and high efficiency. The design consists of linearly arrayed hybrid emitters, dummy emitters, and a slit extractor. Preliminary experiments investigated Taylor cone formation and ion emission characteristics. Capillary emitters exhibited pulse, oscillating, and continuous emission modes depending on the power supply method, whereas hybrid emitters exhibited only continuous emission with well-confined Taylor cone formation and consistent current–voltage characteristics. Key design requirements for the hybrid multi-emitter configuration include axially aligned electric field distribution and a large extractor hole diameter. The proposed configuration generates the required electric field distribution with the aid of dummy emitters, achieving uniform current emission across the emitter array. The calculated maximum thrust and emitter power-to-thrust ratio were 279.0 µN and 160.4 mW/µN, respectively, at an emitter current of 2.86 mA. These results demonstrate the potential of the proposed hybrid multi-emitter configuration as a scalable emitter architecture for FEEP thruster applications requiring uniform ion emission and increased thrust capacity. 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