Search Results (1,868)

This study investigates the tribological performance of three commercial PTFE-based Xylan^® coatings—Xylan^® 1425, Xylan^® 1052, and Xylan^® 1010—applied to 18CrNiMo7-6 steel under dry sliding conditions. Ball-on-Disk tests were conducted at normal loads of 5, 7.5, and 10 N, wear-track radii of 12, 16, and 20 mm, and corresponding sliding velocities of 0.31–0.52 m·s⁻¹. The tribological evaluation was complemented by measurements of coating thickness, surface roughness, nanoindentation, wear-track profilometry, scanning electron microscopy, EDS mapping, and post-test cross-sectional microscopy. All coatings reduced the coefficient of friction from approximately 0.49–0.64 for the uncoated steel to 0.09–0.13, corresponding to an average reduction of 78–80%. Xylan^® 1425 exhibited the highest nanohardness of 57.02 MPa, the highest reduced elastic modulus of 3.33 GPa, and the most favorable elastoplastic indices. It also achieved the lowest wear, with a volumetric loss of approximately 0.03 mm³ under the most severe conditions, representing a reduction of more than 99% compared with the substrate. Xylan^® 1010 provided the lowest friction but showed pronounced plastic deformation, whereas Xylan^® 1052 exhibited fragmentation and increased wear. Post-test cross-sectional microscopy confirmed local exposure of the steel substrate in both coatings. Overall, Xylan^® 1425 provided the best balance of low friction, mechanical stability, coating continuity, and wear resistance. 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

Water-mist curtains act as thermal barriers to longitudinal smoke propagation in confined-space fires, but their downstream cooling remains difficult to predict with reduced-order models. This study develops a calibrated semi-analytical model that uses the incident temperature at the curtain’s upstream face and combines a one-dimensional droplet residence-time solution with a Stefan-flow heat-transfer reduction. A lumped closure coefficient, k = Aeq/A0, collectively accounts for the simplified initial velocity and trajectory, spray nonuniformity, ensemble shielding, representative properties, and boundary inputs. The coefficient is inferred from 5 MW FDS cases with D₃₂ = 400–700 μm and is not interpreted as breakup or coalescence, which were absent from the monodisperse simulations. Cases at 2, 4, and 6 MW provide within-domain blind tests, whereas 1, 3, and 7 MW provide supplementary assessment; the maximum reconstructed relative deviation in exit temperature is 13.4%. A 1:5 experiment supplies a cross-scale trend comparison, but its geometry differs from the full-scale FDS domain, and only the 3 MW-equivalent fire has an archived mass-loss calibration. The model is therefore limited to the present calibration domain and should not be transferred directly across geometries, nozzles, or ventilation conditions. Full article

The formation of oil–water emulsions following reservoir-water breakthrough is widely observed during oil production. The viscosity of these polydisperse systems may increase sharply with increasing water cut, creating substantial operational difficulties in well-gathering systems and increasing hydraulic pressure losses. The rheological behaviour of oil emulsions is influenced by the phase ratio, flow velocity, degree of dispersion, temperature and several other parameters. However, no generally applicable model is currently available for describing the rheological behaviour and predicting the properties of oil emulsions, which are anomalous and rheologically complex systems. Therefore, developing a reliable method for estimating the viscosity of stable emulsions while accounting for increasing water content is of considerable practical importance. This study evaluates existing empirical correlations used to characterise the rheological properties of oil emulsions. The analysis shows that their application under oilfield conditions is associated with several limitations and that, in many cases, they are unsuitable for solving practical engineering problems. Accordingly, a mathematical model was developed and validated for estimating and predicting the viscosity of structurally stable oil emulsions as a function of water cut. The proposed model demonstrated good agreement with the experimental data and may be used for engineering calculations related to the production and transportation of water-cut oil. Full article

Pumping stations serve as critical hydraulic infrastructure for water conveyance and irrigation. Sediment deposition in forebays can deteriorate intake flow conditions, increase hydraulic losses, reduce pumping efficiency, and consequently impair the long-term operational performance of pumping systems. To accurately predict sediment deposition in complex three-dimensional flow fields, we developed a dynamics-driven boundary-responsive numerical model that integrates sediment particle dynamics with real-time bed evolution. This model adopts the near-bed vertical velocity of sediment particles as the deposition discrimination criterion and dynamically updates bed topography via a mass-conservation-based boundary response strategy. The proposed method was validated against open-channel experimental data. The simulated flow structures, deposition patterns, and temporal variations in deposition thickness agreed well with the measurements, with average deviations below 4%. Compared with conventional static-boundary numerical methods, the proposed model reproduces the coupled evolution of sediment transport, flow redistribution, and bed deformation with higher fidelity. The developed framework provides an effective numerical tool for sediment deposition prediction and offers practical support for hydraulic structure optimization, maintenance scheduling, and energy-efficient operation of pumping stations with sediment-laden flow. Full article

The accurate prediction of anchor penetration depth is critical for assessing the potential risk of emergency anchoring to subsea infrastructure. In this study, a three-dimensional coupled Eulerian–Lagrangian (CEL) model was developed to investigate the dynamic penetration behavior of a Hall anchor in homogeneous clay and soft-over-stiff layered clay. The model was validated against published experimental results and showed good agreement with measured penetration depths. For homogeneous clay, an energy-based prediction model was proposed by introducing a resistance modification coefficient, and the relationships between this coefficient and soil strength parameters were established from CEL simulations. The proposed model accurately predicted the penetration process and final penetration depth, with errors generally within ±5%. For layered clay, the evolution of the resistance coefficient revealed three penetration stages: initial impact energy dissipation, penetration through the upper soft layer with increasing resistance, and penetration of the lower hard layer with approximately constant resistance. An energy loss coefficient and layer-dependent resistance formulations were subsequently introduced to develop a simplified prediction model. Comparisons with CEL results demonstrated that the proposed model effectively predicts anchor penetration behavior under various soil strength conditions and impact velocities, with most errors within 10%. The proposed approach provides a computationally efficient tool, reducing the computational cost from hours of CEL simulation to seconds of engineering calculation, for the rapid assessment of penetration depth for Hall anchors with similar geometric characteristics under soft-over-stiff layered clay seabed conditions. Full article

Roman artillery represents a key element of ancient military technology, reflecting the advanced level of technical knowledge achieved in the late Republican and early Imperial periods. However, the operational capabilities and the design methodology of these weapons are not adequately described in historical references. This study investigates the launch performance of Roman Scorpio catapult by integrating archeological evidence from impact craters on Pompeii’s northern walls with analytical modeling of torsion-spring behavior. The present study determines the required release velocity of an arrow capable of creating impact craters reported by applying ballistic and aerodynamic analytical models. Historically cited rope materials for torsion springs are evaluated using experimentally reported mechanical properties and geometric constraints. The integrated analysis highlights how material selection and drag-related energy losses influence projectile velocity, supporting the plausibility of the proposed catapult configuration and offering highlights into ancient artillery design. Full article

Pump-as-Turbine (PaT) systems represent a cost-effective solution for hydraulic energy recovery in existing water networks and industrial processes. However, the prediction of their performance in turbine mode remains challenging, especially under off-design conditions where unsteady flow structures and internal losses strongly affect the machine efficiency. In this work, transient CFD simulations of a real industrial centrifugal pump operating as a turbine are performed using OpenFOAM and ANSYS CFX and compared with available experimental data. The investigated operating range extends from $0.7Q_{\mathrm{BEP}}$ to $1.3Q_{\mathrm{BEP}}$. A mesh independence analysis is first carried out using the Grid Convergence Index method, leading to the selection of a mid-size computational mesh as a compromise between accuracy and computational cost. The transient OpenFOAM results show close agreement with the ANSYS CFX predictions over the complete operating range. Both numerical frameworks reproduce the experimental hydraulic-efficiency trend and the location of the BEP, while systematic deviations in hydraulic head and mechanical power are mainly attributed to the geometrical and physical simplifications adopted in the common computational model. The local pressure coefficient monitored at the tongue region shows that both the mean pressure level and the fluctuation amplitude increase with flow rate, indicating stronger transient behavior under high-flow conditions. Beyond the global performance comparison, the flow field is analyzed using $Q_{crit}$ iso-surfaces, mean circumferential velocity, the swirl-intensity parameter $S_{\mathrm{int}}$, relative velocity fields at the PaT operational leading edge, and volute head-loss evaluation. The results show that part-load operation is characterized by strong outlet vortical structures and high residual swirl intensity, while the BEP region corresponds to reduced outlet rotational content. Under overload conditions, the outlet swirl remains limited, but the volute head loss increases significantly, becoming a dominant contributor to the efficiency drop. The study demonstrates that PaT performance cannot be interpreted from outlet swirl alone, but results from the combined effect of residual rotational structures, tongue-region unsteadiness, impeller incidence conditions, and volute dissipation. Full article

Three-dimensional wind vector retrieval from Coherent Doppler Wind Lidar (CDWL) in Velocity–Azimuth Display (VAD) mode is susceptible to anomalous radial velocity observations induced by low signal-to-noise ratios, clutter echoes, and spectral estimation errors, which degrade inversion accuracy. To address this issue, a robust retrieval method, termed KSR-Huber, is proposed by integrating K-nearest-neighbor (KNN)-based local statistical priors with Huber iterative reweighted least squares (IRLS). The method employs KNN-based local consistency and adaptive Sigmoid weighting, together with Huber residual reweighting within the IRLS framework, to suppress anomalous observations while preserving valid data. Simulations across diverse scenarios, conducted under controlled numerical experiments with varying observation redundancies and outlier contamination levels, show that the proposed method consistently outperforms existing approaches, including DSWF, KNN-COOKS, and airSWF, particularly in terms of robustness under controlled noise and outlier conditions. Real lidar observations further demonstrate the practical applicability of the method, while comprehensive validation against independent reference measurements is left for future work. Full article

To clarify the origin of asymmetric arc ablation in hydroelectric generator slip rings, a Steel 45/carbon current-carrying friction pair was selected to investigate the influence of current polarity on arc behaviour and interfacial damage. Static gap discharge tests (10 A) and dynamic tests (current density of 10 A/cm², sliding velocity of 0.419 m/s) were performed to characterize polarity-dependent erosion behaviour. The results indicate that, under the steel(+)–carbon(−) condition, the arc exhibits unstable burst-like discharge accompanied by intense spark spattering. The carbon cathode experiences severe material loss due to the combined effects of cathode-spot heating, positive-ion bombardment, and molten metal droplet impact. The steel surface is characterized by nested erosion pits and spherical resolidified spatter particles, while the apparent ablation-affected area shows an overall increase with accumulated arc duration, with a more pronounced expansion observed at longer durations. Pronounced bidirectional material migration and interfacial elemental enrichment are observed under the steel(+)–carbon(−) configuration, resulting in an apparent net mass loss rate approximately 2.5 times higher than that under the steel(-)–carbon(+) configuration. The reversed steel(−)–carbon(+) configuration produces a spatially constrained and stable arc discharge, accompanied by a continuous remelted layer and network-like thermal-stress cracks on the steel surface. Polarity reversal changes the direction of the interfacial electric field and charged-particle migration, thereby regulating cathode electron emission, arc discharge behaviour, energy distribution in the near-electrode region, and bidirectional material migration across the interface. These results provide a theoretical basis for elucidating the polarity-dependent arc ablation mechanism of steel/carbon friction pairs and for optimizing polarity configuration and differentiated protection strategies for hydroelectric generator slip rings. Full article

Pressure losses in heating, ventilation, and air-conditioning (HVAC) duct elbows significantly increase fan power requirements and reduce overall system efficiency. This study presents a comprehensive computational fluid dynamics (CFD) investigation aimed at identifying effective strategies for reducing pressure losses in 90° HVAC duct elbows. The numerical methodology was first validated against published experimental measurements, demonstrating excellent agreement and providing confidence in the predictive capability of the CFD model. The validated model was then employed to evaluate the influence of duct geometry, inlet velocity, guide vane configuration, inter-vane spacing, perforated guide vanes, and duct material roughness on aerodynamic performance using the SST k–ω turbulence model. The results show that round elbows reduce pressure losses by approximately 50% compared with hydraulically equivalent rectangular elbows, highlighting the strong influence of duct geometry on flow separation. Among the flow-control strategies investigated, curved guide vanes produced the greatest improvement, with an optimized three-vane arrangement and a non-dimensional spacing of $\mathrm{s}/{\mathrm{D}}_{\mathrm{h}}\approx 0.15$ (corresponding to 150 mm for the specific geometry tested) reducing pressure losses by approximately 31% relative to the baseline elbow without guide vanes. In contrast, the investigated perforated guide vane provided only marginal improvement, indicating that its geometry requires further optimization to minimize blockage and mixing losses. The material roughness study showed that smooth, rigid duct materials produced only minor differences in pressure loss, whereas flexible ducts generated noticeably higher losses because of their increased surface roughness. These findings demonstrate that optimizing elbow geometry and guide vane design is considerably more effective than modifying duct material or using the investigated perforated vane configuration. The study provides practical design recommendations for improving the aerodynamic performance and energy efficiency of HVAC duct systems. Full article

The rapid paradigm shift from traditional keyword-matching algorithms to AI-driven answer engines has fundamentally disrupted Search Engine Optimization (SEO). As Large Language Models (LLMs) power modern Search Generative Experiences (SGEs), organizations must transition from legacy web analytics to sophisticated Business Intelligence (BI) frameworks to capture visibility. Despite the immense strategic implications of this shift, academic literature remains fragmented across computer science, information systems, and digital marketing management. To bridge this gap, this paper adopts an integrative literature review methodology, synthesizing 70 high-value studies selected from an initial corpus of 11,382 papers filtered to 2962 on-topic studies. Rather than utilizing restrictive systematic protocols (e.g., PRISMA) that isolate empirical data within narrow boundaries, the integrative approach enables a holistic synthesis of emerging, multi-disciplinary concepts necessary to decode a rapidly evolving phenomenon. Through this methodological lens, this study introduces the Signal–Structure–Surface–Score (4S) lifecycle framework, illustrating how AI-BI systems capture conversational search intents (Signal), architect machine-readable, entity-based data (Structure), optimize content for LLM retrieval and Generative Engine Optimization (Surface), and define novel attribution metrics for zero-click environments (Score). Furthermore, the paper maps the critical technical and strategic landscape, systematically evaluating prevailing trends (e.g., zero-click searches, AI-generated content velocity), core organizational challenges (e.g., search data attribution loss, algorithmic opacity), and emerging strategic opportunities (e.g., real-time intent mapping, competitor LLM audit trails). Ultimately, this paper bridges the gap between AI search mechanics and strategic BI measurement, providing a robust future research agenda designed to guide scholars and practitioners in navigating data-driven visibility in the age of generative search. Full article

Special orthogonal lateral-intake pumping stations on coastal plains face severe lateral deflection and recirculation in the approach channel and forebay. Their underlying evolutionary mechanisms remain unclear, and conventional rectification methods cause substantial hydraulic losses. Using numerical simulations and hydraulic model experiments, this study investigates these unfavorable flow patterns and proposes an original Combined Arc-Frame Flow Straightening Structure (CAFS). This newly proposed CAFS differs from existing structures, achieving effective flow pattern improvement with reduced hydraulic loss. Results reveal three typical flow regimes—S-shaped mainstream, branching flow, and recirculation—and the flow field is partitioned into four hydrodynamic zones: the Mainstream Incident Zone, Mainstream Impact Zone, Mainstream Reflection Zone, and Low-Velocity Recirculation Zone. Axial velocity uniformity and flow angle are strongly influenced by lateral velocity, while turbulent kinetic energy exhibits intrinsic correlations with vertical vorticity. Lateral velocity, recirculation intensity, and hydraulic losses all increase positively with the Froude number. The CAFS effectively suppresses the low-velocity recirculation zone. Quantitative data show an improvement of 46.40 percentage points in uniformity of axial velocity distribution, a reduction of 0.157 rad (9°) in velocity-weighted average angle, 60.98% less turbulent dissipation, and 38.85% less total hydraulic loss. This study clarifies lateral-intake defect mechanisms and provides a valuable engineering reference. Full article

Identifying parameters of dynamical systems from sparse measurements is a core task in structural health monitoring and vibration engineering. For second-order oscillators, standard physics-informed neural networks (PINNs) struggle because different parameter values can produce nearly identical displacement records, making the inverse problem ill-posed. We propose the derivative-observation-augmented PINN (D-PINN), which incorporates velocity measurements into the training loss to resolve this degeneracy. Three theoretical results support the method: a Sobolev-type inequality proves that constraining the velocity error automatically bounds the displacement error; a Fisher information analysis shows that velocity observations increase the information available for parameter estimation; and a residual-based estimate bounds the parameter error in terms of the solution accuracy and its derivatives. Experiments on linear, forced near-resonance, and Duffing oscillators (10 random seeds, 20,000 epochs) show that D-PINN reduces the damping coefficient relative error from 40% to 11.7% without any parameter prior. With a weak prior (${\mu }_0=3.2$, a 20% deviation from the true value 4.0), the error drops further to 2.1%, a 19-fold improvement over standard PINN. We also analyze sensitivity to prior quality, derivative observation source, and measurement noise, and identify scenarios where derivative observations do not improve displacement fitting. Full article

Objective: This article reports the prespecified boxing-specific component of a randomized controlled trial comparing velocity-based resistance training (VBT) with percentage-based training (PBT) in collegiate boxers. Boxing-specific performance was specified as a parallel primary outcome domain in the original ethics-approved protocol, although no single boxing-specific measure was designated as the sole primary endpoint; the five measures are therefore reported as prespecified exploratory outcomes. Methods: The trial was designed before participant recruitment to address two parallel research objectives: changes in general lower-limb performance and changes in boxing-specific performance. Twenty-eight male collegiate boxers were randomly allocated to VBT (n = 14) or PBT (n = 14). Results for lower-limb strength, jumping, and sprinting from the same trial have been reported previously. The present report focuses on lead and rear straight-punch (LSP and RSP) force and continuous-punch (CP) frequency over 10 s, 30 s, and 1 min. Both groups were prescribed the back squat, Bulgarian split-squat, and deadlift twice weekly for eight weeks. PBT participants completed four sets of five repetitions at 70% of one-repetition maximum (1RM), whereas VBT participants were prescribed four sets using the velocity associated with 70% 1RM and ended each set at 10% velocity loss. Results: The between-group differences in mean change, calculated as VBT minus PBT, were 6.97 kg for lead straight-punch force (95% CI: 0.40 to 13.54), 7.21 kg for rear straight-punch force (95% CI: 3.56 to 10.86), 4.47 punches·10 s⁻¹ for 10 s continuous-punch frequency (95% CI: 0.33 to 8.62), 5.05 punches·30 s⁻¹ for 30 s continuous-punch frequency (95% CI: 0.14 to 9.96), and −2.65 punches·min⁻¹ for 1 min continuous-punch frequency (95% CI: −13.97 to 8.67). Conclusions: Greater mean improvements in straight-punch force and short-duration continuous-punch performance were observed in the VBT group, although the precision of several estimates was limited and the findings should be interpreted cautiously because multiple exploratory outcomes were analyzed without formal multiplicity adjustment. For the 1 min test, there was no statistically conclusive evidence of a between-group difference. Registration: The trial was retrospectively registered with the Chinese Clinical Trial Registry (ChiCTR2500111377), and the study materials were subsequently registered on the Open Science Framework (OSF; DOI: 10.17605/OSF.IO/VY6TS). Full article