Search Results (1,443)

The aerodynamic calculation model of a high-speed train on the embankment under crosswind is built according to computational fluid dynamic (CFD) theory in order to obtain the aerodynamic forces on the train, and the running process of a high-speed train on the embankment is simulated on basis of multi-body dynamic theory. Furthermore, the crosswind aerodynamic performance and running reliability of a high-speed train on the embankment are studied. Considering the randomness of wind load, the influence of the embankment height, the embankment slope coefficient and the position of the upper/lower wind line, the aerodynamic characteristics of the train are analyzed. At the same time, taking the aerodynamic load as input, considering the different embankment heights, slope coefficients, mean wind velocities and train speeds, the change rules of failure probability for train operation with embankment height, train speed and wind velocity are analyzed, and then the probabilistic characteristic wind curve of the train and running safety area for the train under different embankment heights are obtained. The results show that the aerodynamic coefficients of the train gradually increase as the embankment height increases. When the embankment slope coefficient is the same, the absolute value of aerodynamic factor of the leading car is the largest. The aerodynamic factor of the train running on the downwind line is higher than on the upwind line. If the failure probability is given, the maximum operating speed of the train when the wind speed reaches a certain value can be determined through the probabilistic characteristic wind curve. Full article

Landing underactuated quadrotors on inclines is challenging as sudden contact transients convert translational kinetic energy into critical edge-tipping moments. Conventional controllers struggle to mitigate these sub-second impacts without computationally intensive prior terrain models or payload-restricting mechanical shock absorbers. This paper introduces a stabilization approach combining a Zero Moment Point (ZMP)-guided anchoring strategy with an impact-resilient Model Reference Adaptive Control Neural Network (MRAC-NN). The ZMP serves as a proactive geometric threshold. Evaluating overturning moments directly in the body frame before physical tilt occurs triggers immediate asymmetric bidirectional thrust. This artificially augments the surface normal force, thereby securing the vehicle on steep inclines that exceed natural static friction limits. Concurrently, the computationally efficient MRAC-NN suppresses unstructured aerodynamic disturbances and high-frequency impact shocks. To prevent parameter wind-up during sudden kinematic arrest at touchdown, the neuro-adaptive law is structurally augmented with robust bounding and dynamic state-locking mechanisms, mathematically guaranteeing Uniform Ultimate Boundedness (UUB). The framework is validated through high-fidelity simulations that incorporate Linear Complementarity Problem (LCP) rigid-impact constraints and stick–slip friction. Results demonstrate the architecture effectively suppresses post-impact bouncing and transforms critical tipping moments into controlled planar slides, reducing stabilization penalties by up to $47.5\%$ and expanding the survivable flight envelope to ${60}^{\circ }$ inclines where classical methods fail. Full article

Environmental regulations and stricter emission limits are driving the development of advanced fuel supply systems. Precise fuel metering under varying engine loads has become critical, with modern strategies using multiple injections of very short duration. However, injector behavior, particularly nonlinear flow characteristics, is not fully understood. This study presents an experimental analysis of the flow characteristics Q = f (t_inj) and opening dynamics of five low-pressure gas injectors with different valve system designs. The tests were conducted for injection times t_inj = 0–20 ms. For t_inj > 2.5 ms, the characteristics were very well described by a linear model (R² > 0.995), whereas for t_inj < 2.5 ms, there was a clear deviation from the linear relationship between flow rate and injection time. Analysis of the electrical signals, outlet pressure, and body vibrations made it possible to identify the mechanistic sources of the observed nonlinearity. It was demonstrated that the initial lack of flow results from an electromechanical delay associated with the rise in current and the electromagnetic force required to overcome the spring force, friction, and inertia of the valve element. The subsequent movement of the valve contributing factors a dynamic change in the flow cross-sectional area and, consequently, a nonlinear change in flow rate. Additionally, the change in the position of the valve element affects the inductance of the coil and the nature of the electromagnetic force. Near the maximum lift, the element bounces off the stop, causing a momentary change in its position and a local decrease in flow rate. Only after the valve element’s motion stabilizes does the flow transition to a nearly linear relationship. The response times of the injectors ranged from 0.60 to 1.30 ms, and the times to reach full opening ranged from 1.08 to 2.14 ms, corresponding, respectively, to the onset and the transition to the steady-state region of the characteristic curve. The results indicate that the nonlinearity of the short-time portion of the characteristic has a mechanistic, electromechanical nature and results from the coupling of electromagnetic phenomena, the motion of the valve element, and the varying flow cross-section. This means that accurately modeling it requires taking into account the actual dynamics of valve-opening, particularly in the case of strategies that use short and repeated injection pulses. These findings highlight a significant limitation in fuel dosing precision and emphasize the need to incorporate nonlinear injector models or dynamic corrections in ECU control algorithms—an essential step for further reducing exhaust emissions. Full article

In pressurized irrigation networks, water-intake hydrants combine flow regulation, shutoff and metering in a single cast body, and the resulting coupled resistance obscures how much each function costs. The conventional body of a DN100 (nominal diameter 100 mm) hydrant and a redesigned production variant were solved with an incompressible Reynolds-averaged Navier–Stokes (RANS) model in three functional configurations (bare body, +regulator, +metering line) at five inlet velocities (1–5 m s⁻¹, Re ≈ 1.0 × 10⁵–5.0 × 10⁵). The mesh was selected after a four-level refinement study, and the quarter-symmetry assumption was verified against two full-domain calculations with both symmetry planes removed: the reduced domain costs 1.0% in pressure drop, and the transverse forces and the net moment on the regulator vanish in the time mean, leaving the axial thrust as the only physically meaningful regulator load. The redesigned body lowers the bare-body loss coefficient by 30.9% and raises K_v by 20.3%. Adding the regulator removes that advantage—ξ becomes 3.0% worse and the full-device axial thrust 11.9% higher—and adding the metering line widens the gap to 37.0% in loss and 60.8% in thrust. Loss and mechanical load therefore reverse sign together at integration, so a body improvement demonstrated in isolation cannot be assumed to survive assembly. The decomposition also acted as a consistency check: a negative metering-line increment in the conventional device, impossible for a passive addition, was traced to a 23.5% passage enlargement present in the supplied full-device geometry rather than to the flow. Wall data give a minimum static pressure of 0.20 bar and a local cavitation number of 1.39, a margin five times narrower than a lumped estimate suggests. Flow-bench measurements on the finished product provide an independent order-of-magnitude reference rather than a validation. The configuration-additive decomposition and the axial-thrust indicator together form an evaluation approach transferable to other devices that combine sub-functions in one body, subject to confirmation on further geometries and Reynolds ranges. Full article

Background/Objectives: Maintaining a stationary manual wheelchair wheelie is a highly demanding dynamic postural control task that can be biomechanically modeled as an inverted pendulum. Although skilled wheelchair users employ a Proactive Balance Strategy (PBS) characterized by small rhythmic wheel movements, its underlying biomechanical control mechanism remains incompletely understood. This study investigated whether the PBS serves as a functional analogue of the human standing ankle strategy by examining the dynamic relationships among wheelchair orientation, center of pressure, and center of mass dynamics. Methods: Forty healthy adults with prior wheelchair wheelie training performed stationary wheelie trials on a force platform while three-dimensional kinematic and kinetic data were collected simultaneously. Results: Cross-correlation analysis demonstrated a strong inverse relationship between wheelchair pitch angle and rear-wheel displacement (r = −0.73, phase lag = 0.032 s). A moderate inverse relationship was also observed between the horizontal center of pressure (COP_x) and horizontal center-of-mass acceleration (COM_accx) (r = −0.61) with a near-zero mean phase lag (−0.003 s). Conclusions: These findings support a functional biomechanical analogy between PBS and the ankle strategy during standing balance. The coordinated kinematic and kinetic relationships indicate that stationary wheelie balance is maintained through continuous regulation of rear-wheel position, which changes the wheel–ground contact point and thereby modulates the COP and whole-body dynamics. The observed biomechanical coupling is compatible with the proactive characteristics proposed for PBS. Although this study involved healthy adults with prior wheelie experience rather than daily wheelchair users, the findings provide a quantitative biomechanical framework for understanding stationary wheelchair wheelie balance and may inform future wheelchair skills training and rehabilitation strategies. Full article

Fluvial sand bodies represent one of the most significant reservoir types in hydrocarbon exploration. Restricted by climatic conditions, sedimentary environments and the properties of provenance parent rocks, sedimentary characteristics and sand-body architectures exhibit substantial spatial variations across different river systems and along individual river segments. Research on modern sedimentary processes of the Weihe River provides critical insights for advancing continental fluvial sedimentology theories and reconstructing paleoriver sedimentary models for analogous basins. Integrating high-resolution satellite image interpretation combined with systematic field geological surveys across typical river reaches, this study systematically characterizes the spatial differentiation of river patterns, sedimentary signatures, sand-body architectures and their primary controlling factors within the Weihe Basin. The results reveal a distinct three-segment spatial differentiation pattern of fluvial styles in the Weihe Basin: braided rivers dominate the Baoji–Zhouzhi reach; low-sinuosity meandering rivers occur in the reach from Zhouzhi to Lintong; and high-sinuosity meandering rivers prevail in the downstream segments below Lintong. Unique hydrodynamic regimes associated with each river type control sedimentary partitioning and sand-body development. Braided rivers feature intense hydrodynamic force and coarse-grained sediments, with sedimentary assemblages consisting of gravelly channel deposits, mid-channel bars and floodplain deposits, which form thick stacked sand bodies via multi-stage sedimentary superimposition. Low-sinuosity meandering rivers possess moderate hydrodynamic energy and are dominated by sandy-gravel deposits, yielding a complete sedimentary succession composed of channel fills, point bars, natural levees and floodplains. High-sinuosity meandering rivers are characterized by weak hydrodynamic conditions and fine grain sizes dominated by sandstone and mudstone units, developing diverse sedimentary facies including channels, crevasse splays and oxbow lake deposits. The spatial heterogeneity of the sedimentary system across the Weihe Basin is synergistically controlled by the channel gradient, provenance attributes, sediment grain size and sediment concentration. This study clarifies the sedimentary evolutionary laws of modern rivers under semi-arid and semi-humid climatic conditions, enriches fundamental fluvial sedimentology theories, and supplies a modern sedimentary analog for paleoriver identification, paleoenvironmental reconstruction and hydrocarbon exploration targeting fluvial reservoir systems. Full article

Conformational analysis is commonly centered on potential energy surfaces, whereas changes in the intrinsic metric and topological organization of molecular configuration spaces have received less attention. Here, we introduce a correspondence-preserving framework that directly compares ideal geometric samples with their constrained MMFF94-relaxed realizations. Unlike energy-based conformational analysis, the proposed approach separates changes in pairwise structural geometry from changes in global topological organization. Configuration spaces were constructed for ethane, butane, butadiene, biphenyl, and n-pentane using one- and two-dimensional torsional domains. Pairwise root-mean-square deviation (RMSD) matrices after optimal rigid-body superposition were used to quantify metric deformation, while Vietoris–Rips persistent homology was used to compare the corresponding topological signatures. MMFF94 relaxation produced structured, conformation-dependent patterns of metric expansion and contraction rather than a uniform rescaling of the configuration spaces. Nevertheless, the dominant homological organization was preserved: the one-torsional systems retained $({\beta }_0,{\beta }_1)=(1,1)$, compatible with $S^1$, whereas n-pentane retained $({\beta }_0,{\beta }_1,{\beta }_2)=(1,2,1)$, compatible with ${\mathbb{T}}^2$. Persistence-diagram distances further showed that preservation of these dominant classes does not imply equality of the complete persistence representations. For the molecular systems, sampling schemes, and force-field model considered, the results demonstrate that molecular relaxation can systematically reorganize RMSD geometry without altering the dominant global topological features. The framework therefore provides a quantitative means of distinguishing metric deformation from topological change in corresponding molecular configuration spaces. Full article

Tractor rollover is a persistent worldwide problem that does not yet have a fundamental solution. Adjusting the tractor’s attitude or configuration may enhance mobility under complex terrain conditions to prevent rollover. Therefore, in this study, an attitude adjustment method for offsetting the height difference between the uphill and downhill sides is proposed to adjust a tractor’s posture. Kinematic models are established for front-wheel, four-wheel, and articulated body steering modes. Steering mathematical models are developed for the three modes to describe the effects of posture change on tractor steering instability. This method predicts the steering stability by analyzing tire contact forces. Both the critical slope angle and steering speed are derived and used to predict instability while taking the steering radius into consideration. Considering a tractor’s attitude, simulations are conducted under two conditions; namely, attitude adjustment and level attitude. The results show that attitude adjustment is an effective method to enhance a tractor’s steering stability to avoid overturning. Furthermore, the models presented here provide theoretical references and optimization directions to prevent lateral overturning during tractor steering. Full article

Musculoskeletal injuries are the leading cause of time loss in professional football, yet machine learning models integrating multi-protocol force-plate data for injury-risk classification are absent from the Latin American professional football literature. Purpose: This study aims to develop and internally cross-validate a supervised Random Forest model for injury risk classification using full-season VALD ForceDecks data from a professional Costa Rican club, with thresholds derived from receiver operating characteristic (ROC) analyses. Methods: We utilized an observational longitudinal study (September 2024 to April 2026). One hundred and twenty-six male footballers from five competitive categories underwent 518 dual-force-plate assessments across four protocols (Nordic Hamstring, isometric mid-thigh pull, isometric adductor squeeze, countermovement jump), yielding 21 variables; one assessment per player entered the model. Record linkage against 262 surveillance-documented time-loss events identified 53 players with pre-injury assessments as the positive class (42.1%; ratio 1:1.4). SMOTE (k = 5) was applied within each training fold only. A Random Forest model (500 trees; depth 4) used 5-fold stratified cross-validation. The HIGH boundary was set at the Youden index, and the LOW boundary was set as the first score quartile. Results: The mean AUC-ROC across folds was 0.683 +/− 0.050, the only estimate of generalisation reported. Refitted on the complete dataset and applied back to the same players, the model gave at the Youden cut-point (score ≥ 45.2) an apparent sensitivity of 100% and specificity of 95.9%; these resubstitution values are optimistically biased. The leading predictors were Pull RFD (10.0%), CMJ power per body mass (7.2%) and eccentric CMJ peak force (6.6%). The risk tiers were HIGH 56 (44.4%), MEDIUM 39 (31.0%), and LOW 31 (24.6%). Conclusions: Multi-protocol force-plate data yield moderate internally cross-validated discrimination of injury risk. The near-perfect threshold metrics are apparent values, not generalisation performance. Rate of force development and eccentric force capacity outranked asymmetry indices. Prospective external validation is required before clinical use. Full article

This paper investigates the dynamical behaviour of an infinitesimal mass body moving under the gravitational influence of a heterogeneous triaxial primary body and a secondary body that produces a modified Newtonian gravitational force in the elliptic restricted three-body problem. In this model, the two primary bodies move around their common center of mass in elliptical orbits, while the mass of the third body is assumed to be sufficiently small so that its effect on the motion of the primary bodies can be neglected. The equations of motion of the infinitesimal body are formulated, and the corresponding mean motion of the system is determined by taking into account the triaxial structure and mass heterogeneity of the primary body as well as the modified gravitational field of the secondary. The equilibrium points of the system are then investigated. Both collinear equilibrium points, which lie along the line joining the two primary bodies, and non-collinear equilibrium points, which are located away from this line, are determined analytically. Their linear stability is examined by studying the characteristic equations associated with small perturbations around these points. In addition, the dynamical characteristics of the system are illustrated numerically through potential surfaces, the locations of equilibrium points, permissible regions of motion, periodic orbits, and basins of attraction. These numerical results provide a clear understanding of how the eccentricity of the motion, triaxiality of the primary body, and the modified gravitational force of the secondary influence the motion of the infinitesimal body. The results may be useful in understanding the dynamics of celestial bodies. Full article

On-body robots that travel around a human limb must keep a firm enough grip to avoid slipping or detaching, while never pressing hard enough to hurt—a balance that is hardest to strike precisely when the robot is orbiting the limb and gravity continually redistributes the contact loads. This paper presents an open, non-anthropomorphic robot that wraps around a compliant cylindrical surface with a three-contact grasp: a central traction module with two in-line driven wheels, and two lateral spring-loaded arms with distal wheels. Its central contribution is an actuation-space decomposition in which the two lateral wheel torques, expressed in a common-mode/differential basis, simultaneously drive the orbital motion and regulate the central normal force. We show that this basis diagonalises both the rolling kinematics and the static force balance, so the differential (grip-regulating) channel is provably orthogonal to the common-mode (propulsion) channel: a single pair of actuators perform both tasks without mutual interference and without a dedicated force mechanism. A model-based feedforward law derived from the static contact model, corrected by a PI term fed back from the compliant arms—which double as the force sensor—keeps the central force within a safe band; in a full-revolution simulation the differential command reverses sign to counteract the gravitational load swing while leaving the orbit undisturbed. The same compliant arms yield a closed-form estimate of the cylinder radius and contact geometry, accurate to below one millimetre across a 45–87 mm diameter range, from proprioception alone. Preliminary prototype tests reproduce the predicted behaviour, supporting the approach for future wearable and assistive applications. Full article

This study presents a computational comparison of 24 lattice topologies over their geometrically feasible relative density ranges. Conjugate heat transfer simulations were performed in ANSYS Fluent 2024 R2 using 10 mm unit cells, inlet air at 300 K and 0.05 m/s, a constant base temperature of 312 K, and gravity acting in the negative z direction. The inlet Reynolds number was approximately 32.5. The prescribed temperature difference of 12 K gives a Grashof number of 1.68 × 10³ and a Richardson number of 1.59, indicating that buoyancy and the imposed flow are both relevant. The operating condition was therefore classified as low-speed mixed convection with perpendicular forced flow and buoyancy directions. The hydrodynamic model was benchmarked against published pressure gradient data for a body-centered cubic lattice. Thermal performance was compared using interfacial area, the magnitude of the ANSYS Fluent surface heat transfer coefficient, interfacial heat transfer rate, and interfacial thermal resistance. At 10% relative density, Auxetic gave the lowest resistance, 112.34 K/W, compared with 327.51 K/W for Cube. At 70%, FBCC reached 97.56 K/W, whereas Cube reached 1028.12 K/W. Increasing relative density improved or degraded thermal performance depending on topology. The database provides comparative guidance for lattice selection and subsequent multiscale design optimization of lightweight aerospace and electronic heatsinks. Full article

This study investigates the compression and impact responses of three brachistochrone-inspired lattice topologies, namely, Gyroid, Body-Centered Cubic (BCC), and Interconnected Wavelet Packet (IWP), fabricated by additive manufacturing using Elastic 50A Resin V2. Quasi-static compression tests were performed to characterize the force–displacement response of each topology, and drop-weight tests were conducted to measure the corresponding acceleration histories under impact loading. Based on the compression data, two restoring-force descriptions were evaluated for dynamic prediction: a fractal dynamic model with polynomial restoring force and the Equivalent Energy Spring Model (EESM). The results show that lattice topology strongly affects deformation mode, compressive stability, and energy absorption. The B-IWP lattice exhibited the highest energy-absorption capacity but also showed greater susceptibility to buckling, whereas the B-BCC topology provided a more balanced combination of structural stability and impact-mitigation capability. Comparison with the experimental impact responses showed that both modeling approaches reproduced the main features of the measured acceleration histories, while the EESM generally provided better agreement with the experimental data. These findings demonstrate that compression-derived restoring-force models provide an effective framework for predicting the impact behavior of brachistochrone-inspired lattices and support their design for protective packaging and other impact-critical applications. Full article

Background: The aim was to investigate the stride-by-stride development of spatiotemporal parameters, joint kinematics, kinetics, and electromyographic (EMG) activity during a 50 m sprint, providing a comprehensive analysis of the biomechanical and neuromuscular changes throughout the entire sprint. Methods: Fifteen male sprinters (age 20.5 ± 1.3 years, body mass 66.8 ± 4.5 kg, body height 1.74 ± 0.06 m, 100 m personal best: 11.24 ± 0.34 s) performed a 50 m sprint, while the spatiotemporal parameters, joint kinematics, kinetics, and EMG activity of nine muscles were measured. Results: The main findings were that the 50 m sprint could be divided into three phases: initial acceleration, transition and maximal velocity and involve tightly coordinated changes across multiple biomechanical domains. The initial acceleration (the first 3–5 strides) was dominated by rapid increases in stride frequency, rapid changes in joint angles, and rising EMG activity in key muscles. In the transition phase (up to ~30–35 m), continued increases in stride length, decreasing contact time, and stabilization of kinematics and EMG activity were the main characteristics. In the maximal-velocity phase, a plateau in velocity, increased flight time, greater reliance on vertical force (an increase in vertical force relative to the horizontal forces), and stabilized neuromuscular patterns were observed. Conclusion: The phased progression supports contemporary biomechanical models of sprinting and emphasizes the importance of both mechanical and neuromuscular efficiency in achieving optimal sprint performance. Full article

Accurate actuator-space tracking is an important engineering requirement for repeatable motion delivery by parallel rehabilitation mechanisms, but controller performance should also be assessed under configuration-dependent dynamics and modeling uncertainty. This study evaluates a bounded fuzzy-supervised proportional–integral–derivative (FSPID) controller for a three-chain 3STC+S parallel rehabilitation mechanism. CAD-derived inverse kinematics generated the three prismatic-joint reference trajectories, while closed-loop behavior was simulated using a Simscape Multibody model including rigid-body mass and inertia properties, gravity, closed-loop constraints, and external force/moment loading. Three fixed-gain PID loops formed the baseline. The FSPID supervisor used zero-order Sugeno inference to adjust proportional and derivative gains within prescribed bounds, while the integral action remained fixed and was implemented with a leaky integrator. Under the nominal 1° trajectory at 0.2 Hz, FSPID reduced mean root-mean-square error (RMSE), maximum absolute error, and integral absolute error (IAE) by 0.25%, 0.37%, and 0.21%, respectively. Under sustained external loading, maximum-error reductions reached 9.33–10.20%, with mean actuator-wise peak-force changes within approximately ±2%. Additional simulations examined trajectory amplitude, synthetic measurement noise, viscous damping, and combined nonidealities. The results support FSPID as a conservative simulation-level refinement of fixed-gain PID; experimental validation remains necessary. Full article