Search Results (3,353)

This paper tests whether reinforcement learning improves monthly commodity-sector rotation once the experiment is reconstructed from investable instruments, strong active benchmarks, realistic costs, and strictly chronological validation. Total returns for energy (DBE), gold (GLD), agriculture (DBA), and base metals (DBB) are obtained from CRSP; GSG and DBC are investable broad-commodity benchmarks. Twelve lagged market-state features generate month-$t+1$ decisions. The initial training sample contains 132 targets through December 2018, the original holdout contains 72 months through December 2024, and a frozen-policy temporal extension adds 17 months through May 2026. All active results deduct 10 basis points per unit of drift-adjusted turnover, and Sharpe ratios use contemporaneous Treasury-bill returns. Six-month momentum earns an 18.6% CAGR and 1.112 excess Sharpe; a fixed 10-seed PPO ensemble earns 9.6% and 0.438. An expanding supervised expert selector earns 16.0% and 0.755. In an explicitly exploratory memory-window sensitivity, a 60-month rolling selector reaches 23.4% and 1.033, but its mean advantage over momentum is not statistically established ($p=0.323$). The pattern is consistent with time variation, but it neither identifies an optimal window nor establishes that older observations are harmful. PPO’s temporal-extension surge is concentrated in March 2026 and reverses when that month is removed. Direct deep RL therefore does not robustly dominate; constrained expert selection remains a research candidate whose memory sensitivity requires prospective confirmation. Full article

Triboelectric nanogenerators (TENGs) are promising for harvesting low-frequency mechanical energy, but rotating TENGs (R-TENGs) driven by low-speed water flow remain constrained by limited driving torque, sliding-contact losses, and rotating-system stability. Here, a three-dimensional (3D) riveted complementary-structure rotating triboelectric nanogenerator (RCSR-TENG) is proposed for low-speed water-flow energy harvesting. A semi-analytical formulation incorporating a force-dependent real-contact fraction is developed to describe the coupled relationships among output voltage, transferred charge, rotation angle, and contact force. Because the contact parameters were not independently calibrated, the formulation is used for sensitivity and trend analysis rather than as a quantitatively validated predictive model. For the single prototype tested for each configuration, at 1000 rpm under the fixed effective measurement load of 9 MΩ, the RCSR-TENG produced a peak output power of 544 μW, compared with 304 μW for the flat R-TENG, representing an increase of approximately 79%. The same RCSR-TENG prototype maintained a stable voltage amplitude of over 150,000 rotation cycles. When coupled to a fully passive flapping-foil collector in a 0.55 m s⁻¹ water flow, the system generated periodic electrical output with a peak area-normalized power exceeding 5000 μW m⁻². These results demonstrate the structural-performance advantage of the riveted complementary design and its proof-of-concept applicability to low-speed water-flow energy harvesting. Full article

This paper presents a modified two-degree-of-freedom wave buoy with an embedded tunable magnetic-spring electromagnetic energy harvester. The proposed device is modeled as a branched kinematic chain composed of a rotational–rotational buoy mechanism and a rotational–prismatic harvester branch sharing the first revolute joint. Two harvester orientations are considered and compared. The mathematical model is formulated using homogeneous transformations, velocity Jacobians and Lagrange equations. Particular attention is paid to the structure of the inertia matrix and to the way in which its inverse transmits generalized forces between the rotational coordinates and the translational motion of the moving magnet. The model is implemented in MATLAB/Simulink R2024b and evaluated under free-response, regular-wave, and bidirectional frequency-sweep excitation scenarios. Under regular-wave excitation, Config. 1 produces approximately 19.3 and 2.98 times greater average load power than Config. 2 for moving-assembly masses of 5 g and 268 g, respectively. The frequency-sweep results show that the preferred harvester orientation depends on the excitation frequency and moving-assembly mass. No resolved sweep-direction dependence is observed for 5 g, whereas for 268 g the identified hysteresis intervals are approximately 0.53 rad/s for Config. 2 and 0.64 rad/s for Config. 1. These results provide design guidelines for selecting the harvester orientation and moving mass in compact wave-excited buoy systems. Full article

The Luzon Strait is a critical generation site for global internal tides. Their generation and propagation are significantly modulated by background currents, including the Kuroshio Current and mesoscale eddies. This study investigates nonlinear effects of these background currents on low-mode (modes 1–3) internal tides using a high-resolution numerical simulation. We apply the Taylor–Goldstein equation considering the Earth’s rotation and background currents to perform modal decomposition, and utilize a nonlinear internal tidal energy equation to quantify three crucial energy pathways: inter-modal energy conversion, nonlinear energy exchange with background currents, and nonlinear advection effects. Results demonstrate that while stationary mode-1 internal tides dominate in the generation region of the Luzon Strait, non-stationary energy increases significantly in the western and eastern propagation regions, driven largely by seasonal variability of the Kuroshio Current. Inter-modal energy conversion follows a cascade from lower to higher modes, with conversion efficiency increasing with mode number. Nonlinear exchanges between background currents and internal tides are one order of magnitude smaller than inter-modal conversions but exhibit a bidirectional transfer, where advection redistributes internal tidal energy within the eddy structures. This study provides a quantitative framework for understanding multiscale energy pathways of internal tides under complex ocean dynamics. Full article

Wearable electronic systems require compact and sustainable power sources together with reliable motion-sensing functions. This study presents a gear-driven plantar energy harvester that integrates biomechanical energy conversion with self-sensing locomotion recognition. The device converts low-frequency vertical foot loading into rotary motion through a wedge–lever transmission and amplifies the rotational speed using a multistage gear train with a total transmission ratio of 12. A one-way bearing enables directional power transmission during loading and prevents reverse rotation during recovery. The generated voltage serves both as the electrical output and as the sensing signal for locomotion recognition. Human-subject experiments were conducted under six locomotion modes: walking at 1, 2 and 3 m/s; running; ascending; and descending. Voltage signals were sampled at 2000 Hz and segmented into overlapping sequences. A CNN–LSTM model was used to extract local waveform features and temporal dependencies from the nonstationary signals. The model achieved an overall recognition accuracy of 98.8%, with most errors occurring between ascending and descending. The results demonstrate that a single plantar device can simultaneously harvest biomechanical energy and provide motion-related information, offering a compact solution for integrated energy harvesting and self-sensing in wearable systems. Full article

This study investigates the effects of different graded crushing durations in a blade crusher on the crushing mechanics of wheat and the properties of the resulting flour. Mechanical models were established for blade–particle collisions, radial sliding of particles along the blade surface, and particle–chamber wall collisions. Under reasonable simplifying assumptions, the models analytically characterize the theoretical relationships of impact force and crushing energy with blade rotational speed, rotational radius, and particle incidence angle. The models were used to provide a qualitative mechanistic interpretation of the experimental trends rather than to quantitatively predict flour particle size distribution or damaged starch content. Two graded crushing processes were evaluated, with crushing durations of 10 s per pass (F10) and 15 s per pass (F15). Observation of particle-size evolution during the crushing of wheat particles showed that as the number of crushing passes increased, the proportion of coarse particles continuously decreased, the proportion of fine particles gradually increased, and the proportion of intermediate-sized particles initially increased and then decreased, demonstrating a progressive coarse-to-fine fragmentation pattern. Particle size analysis of the resulting wheat flour showed that the particle size distribution for the F15 process peaked below 5 μm and shifted toward smaller particle sizes relative to that for the F10 process. Nevertheless, the wheat flour obtained from both processes exhibited relatively concentrated particle size distributions, with Span values ranging from 2.46 to 2.68. Damaged starch content increased significantly with the number of crushing passes and was generally higher for the F15 process than for the F10 process. Moisture content decreased from 14.30% to 12.86% under the F10 process and from 14.25% to 12.73% under the F15 process, whereas ash content ultimately increased to 0.48% under both processes. Protein content initially increased and subsequently decreased under both processes. These findings provide experimental evidence for the effects of graded milling on grain refinement, starch damage, and physicochemical composition of wheat flour. Full article

Four full-scale exterior beam-to-column connections comprising H-section beams and square hollow-section (SHS) columns were tested under low-cycle reversed loading to investigate two engineering-oriented T-stub section configurations and the effects of the presence or absence of triangular stiffeners. Failure modes, moment–rotation response, stiffness degradation, energy dissipation, and cumulative damage were evaluated, together with nonlinear finite element simulations and a modified Park–Ang damage assessment. All specimens progressed from bolt-hole slip through plastic deformation to localized fracture. In the unstiffened connections, damage concentrated near the T-stub flange-to-web junction; stiffeners redistributed critical demand toward the stiffener welds, adjacent T-stub webs, and SHS column walls. The maximum differences in initial rotational stiffness relative to J1A were 15.69% and 15.07% in the positive and negative loading directions, indicating that the elastic-stage response reflected the combined deformability of the T-stub, blind-bolt assembly, and column wall. The maximum increases in yield moment, peak-resistance moment, and ductility coefficient were 20.59%, 43.71%, and 45.91%, respectively. Complete-history energy dissipation varied non-monotonically across the tested configurations. The finite element model reproduced the global and local responses, while the damage-index results showed overall correspondence with the observed failure progression. The findings emphasize stiffness compatibility and rational distribution of plastic demand rather than maximum local stiffness. Full article

Accurate characterization of rock anisotropy is crucial for underground engineering stability assessment. In this study, multi-directional drilling tests were performed on sandy mudstone and argillaceous sandstone, with real-time monitoring of feed force (F), torque (M), rotational speed (n), power (P), drilling velocity (v), and depth (h). Drilling-derived apparent friction angles (φ) in different directions were estimated using a force-equilibrium-based model. Based on drill bit geometry, an energy balance model for hollow drilling was developed, and a unit grinding energy (η_e) was derived. A preliminary drilling-derived anisotropy index ($B_{\phi -{\eta }_e}$), based on the coefficient of variation (CV) and integrating φ and η_e, was proposed. Results show a strong linear correlation between thrust force and torque, both exhibiting a two-stage increase with drilling depth. For the tested drilling orientations, the anisotropy determined using the proposed method decreases in the following order: sandy mudstone 1, sandy mudstone 2, argillaceous sandstone 2, and argillaceous sandstone 1. The proposed index provides a preliminary basis for evaluating directional variations in rock anisotropy. Full article

High-accuracy angular speed measurement using incremental rotary encoders is essential for the optimized operation of electric drives and the improvement of energy efficiency in industrial applications. Conventional encoder-based speed estimation relies on frequency- or period-based methods, whose accuracy is limited to complementary operating regions. Hybrid schemes based on stationary Kalman filters have been proposed to fuse both methods; however, since their noise covariances remain fixed, they achieve near-optimal performance only around a single rotational speed, and their accuracy deteriorates over the rest of the speed range. To overcome this limitation, this work proposes two adaptive Kalman filter variants that fuse frequency- and period-based measurements with online covariance adaptation: the measurement-adaptive Kalman filter (MA-KF) and the dual-adaptive Kalman filter (DA-KF). Both are evaluated in simulation and benchmarked against a stationary Kalman filter (S-KF) and the conventional frequency- and period-based estimators. The results demonstrate that Kalman-based estimators achieve significantly lower relative errors than classical methods across the entire speed range, with the maximum relative error of the DA-KF variant remaining below 0.27% while providing a dynamic response comparable to or faster than period-based techniques. Since the analysis is based on an ideal encoder model, these figures should be interpreted as an upper bound on the achievable performance, which experimental validation will further refine. Full article

High-speed permanent magnet motors, due to their high speed, compact size, and light weight, are increasingly widely used in renewable energy systems, electric pump drives, fuel cell air compressors, and other fields. As a core component of high-speed permanent magnet motors, the reasonable design of the rotor system structure directly affects motor stability. To ensure the safe and reliable operation of high-speed permanent magnet motors, this paper designs the structure of a certain type of high-speed electric pump rotor. First, the actual interference amount between the rotor permanent magnet and the high-temperature alloy sleeve under high-speed and high-temperature conditions is considered, and radial and tangential stress analyses are performed on both the rotor and high-temperature alloy sleeve to determine the optimal interference amount. Second, based on rotor dynamics and fluid–structure coupling theory, the natural frequency and critical speed of rotors under wet and dry modals are studied; on this basis, harmonic response analysis and fatigue assessment were conducted; furthermore, an elastoplastic mechanical model of the rotor sleeve is introduced to analyze the effects of interference amount and rotational speed on the sleeve’s yield failure; finally, the dynamic safety of the high-speed rotor structure is verified through modal tests and overspeed operation tests. The results show that the optimal interference amount for the rotor is 0.02 mm; the first-order critical speeds in both dry and wet modals are well above the rated speed of 40,000 rpm, with no risk of resonance; the minimum cycle for fatigue life is 6.9 × 10⁵, meeting usage requirements; the equivalent force on the rotor sleeve increases with speed and interference amount; when the speed exceeds 44,000 rpm, the sleeve undergoes plastic deformation and failure; modal test error is less than 5%. This paper provides theoretical basis and experimental support for the rotor structure design and strength evaluation of high-speed permanent magnet motor drive equipment. Full article

A unified modeling framework is presented in this work to predict the free vibration and loss factor characteristics of damping sandwich rotational plates. The formulation starts from the first-order shear deformation theory, where the zigzag hypothesis and interlayer displacement continuity are combined to couple the displacement fields of the individual plies. An artificial spring scheme is adopted to enforce the layer–layer compatibility and the external boundary restraints, which leads to a Lagrangian functional composed of the kinetic energy, the strain energy, and the potential energies contributed by the boundary and coupling springs. The displacement unknowns are discretized with Chebyshev polynomials of the first kind, and the natural frequencies and damping loss factors are extracted by solving the resulting eigenvalue problem with the Rayleigh–Ritz method. Convergence tests are conducted, and the reliability of the model is validated against finite element results. Finally, a series of numerical examples is presented to systematically investigate the effects of key model parameters on the vibration characteristics of the structure. The results indicate that increasing the thicknesses of the inner and outer layers of the damping sandwich rotational plate structure can significantly raise the natural frequencies. Increasing the inner diameter helps to reduce the area of the low-frequency region, where the difference between the two sides exceeds 40 Hz, caused by the close thicknesses of the inner and outer layers. When only the outer boundary is clamped, the natural frequencies of the annular plate are more than twice those of the solid rotational plate, although the solid rotational plate yields a larger loss factor. When only the outer circular edge is fixed, increasing the total thickness of the structure can effectively raise the natural frequencies, with a maximum increase exceeding 110 Hz, while the loss factor decreases significantly. Full article

Isolated mixing regions (IMRs) commonly persist during steady laminar stirring and limit the attainable mixing degree. Planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) were combined for simultaneous measurements in this study. Experiments were conducted with pure glycerol and microbubbles as PIV tracers over $Re$ = 1.76–10.58. Relatively stable IMRs were identified by PLIF throughout the investigated Re range. As $Re$ increased, the mean specific kinetic energy in the measurement plane rose from 2.84 × 10⁻⁶ m²/s² to 1.77 × 10⁻³ m²/s², whereas the steady-state mixing degree remained near 70%. PIV results showed that the velocity components obtained from boundary and center projections agreed well in magnitude and trend. At all investigated $Re$ values, the center-radial projected velocities at the IMR boundary points remained close to zero. Increasing rotational speed primarily intensified fluid motion within each region and tangential motion near the IMR boundary, without generating persistent, coherent radial exchange. Restricted boundary-normal motion is therefore an important reason for IMR persistence and the limited improvement in steady-state mixing degree. These findings provide quantitative experimental evidence for understanding steady IMRs and enhancing laminar mixing. Full article

This paper presents an experimental investigation into the flow characteristics and volumetric efficiency (η_vol) of a fixed-displacement external gear pump (GHD 17R) operating under coupled hydraulic parameters using an eco-friendly synthetic ester-based hydraulic fluid (48 mm²·s⁻¹ at 40 °C). Measurements were performed on a laboratory single-circuit hydraulic test rig across a rotational speed range of 500–2500 min⁻¹, operating pressure range of 2–10 MPa, and fluid temperature range of 30–60 °C. To eliminate flow fluctuations caused by structural vibrations at 1250 and 1750 min⁻¹, a 15% trimmed mean statistical filter was successfully implemented. A comparative sensitivity analysis—evaluating absolute, normalized, and relative significance—was developed and compared against a three-way analysis of variance (ANOVA) effect size model (η² and partial η²). The relative sensitivity approach identified rotational speed as the dominant parameter for direct hydraulic flow, accounting for 95.80% of total variation. Conversely, when evaluating volumetric efficiency, the proportional impact of speed was removed, revealing a balanced distribution of internal losses: rotational speed contributed 54.73%, fluid temperature 26.08%, and pressure 19.19%. The three-way ANOVA confirmed that all primary parameters and their cross-interactions had a statistically significant effect (p < 0.05). The findings scientifically demonstrate that temperature-induced viscosity collapse exhibits a stronger relative dynamic sensitivity on volumetric losses than pressure fluctuations within standard operating envelopes. The constructed multi-dimensional flow and efficiency maps provide practical input for advanced diagnostic tools, real-time thermal condition monitoring, predictive maintenance, and energy-optimized control schemes in modern fluid power systems using eco-friendly lubricants. Full article

This paper presents an application and validation case for the recently obtained variational principle of a shock stationed in a duct. The streamline curvature method for the circumferentially averaged through-flow and blading design inverse problem remains fundamentally used in current axial compressor design systems and is indispensable as the generator of multi-stage blade coordinates. However, this method inherently smoothens flow discontinuities and thus, to date, cannot provide the stage stall margin, the key performance indicator most critical in the adjustment of high-loading stages, requiring instead a time-consuming CFD validation afterward. Leveraging the variational principle for shock stationarity, this paper acquires a method to show efficiently the stage stall margin by visualizing rotor passage shock rapidly. In the general coaxial rotating relative motion, by modeling the transonic streamlines as a set of layered quasi-one-dimensional duct flows, a variational principle of flow impulse potential energy for the stationary normal shock is derived. It is found that the factors governing the stationarity and location of the normal shock in relative motion include the variable cross-sectional area, the frictional and other on-way losses, and the variable rotational radius of the duct flow. In the applications to transonic rotor cascades, the frictional and other on-way losses are prescribed. First, the discontinuous entropy generation distributions along the cascades of each transonic layer are set to consider the boundary layer, oblique shock, normal passage shock, shock–boundary layer interference, and trailing edge losses. Second, with the total streamline loss fixed by the through-flow design, all shock locations possessing positional stability are determined via the variational principle for each streamline. Third, by comparing with CFD direct problem resu lts, a dimensionless rule governing the actual entropy generation distribution along the layer cascades is established. In three kinds of design cases of axial compressor stage, this method yields consistently 3D curved-surface structures of passage shock that agree well with CFD direct problem solutions, demonstrating its effectiveness and a certain applicability. Full article

The helical-channel magnetohydrodynamic (MHD) thruster is a silent underwater propulsion device free of rotating mechanical components, which fundamentally eliminates the inherent mechanical noise induced by blades and shaft systems in conventional propeller-driven thrusters. Taking a 10 T-class superconducting helical-channel MHD thruster as the research object, this work establishes a three-dimensional numerical simulation model with bidirectional electromagnetic-fluid coupling via Maxwell–Fluent, filling the research gap of systematic optimization of helical pitch angles in existing low-magnetic-field numerical investigations. A composite magnetic circuit configuration consisting of main coils and compensation coils is adopted, achieving a magnetic field uniformity of 90.13% within the effective working section and markedly alleviating magnetic field attenuation at both ends of the flow channel. Three schemes with helical pitch angles of 23.00°, 17.66°, and 14.29° are quantitatively compared to analyze the effects of helical pitch angle on current density, static pressure, total pressure, radial/axial flow velocities and three-dimensional helical streamlines. Under the rated design mass flow rate of 15.5 kg/s, the scheme with the small pitch angle of 14.29° delivers a thrust of 262.56 N and an electromagnetic efficiency of 7.23%; compared with the large pitch angle scheme of 23.00°, its thrust is improved by 28% and electromagnetic efficiency rises by 53%. Reducing the helical pitch angle extends the effective coupling distance between seawater and the electromagnetic field, optimizes the uniformity of radial current distribution, suppresses eddy currents and Joule heat loss, converts more electromagnetic energy into fluid pressure energy, and thus greatly improves the energy utilization efficiency of the propulsion system. This study provides quantitative design references for the structural optimization and engineering prototype development of low-noise superconducting underwater propulsion equipment, and supports the engineering application of helical-channel magnetohydrodynamic thrusters. Full article