Search Results (159)

This paper presents a comprehensive review of forced convective heat-transfer phenomena in fluids, emphasizing the influence of fluid properties, tube geometries, and flow orientations under varying Prandtl numbers. Key governing parameters—including velocity, viscosity, thermal conductivity, density, specific heat, surface area, and flow regime (laminar or turbulent)—are expressed through dimensionless groups such as the Nusselt (Nu), Reynolds (Re), and Prandtl (Pr) numbers. The review encompasses heat-transfer characteristics of low-, medium-, and high-Prandtl-number fluids flowing through circular, square, triangular, and elliptical tubes in both horizontal and vertical orientations, aiming to critically evaluate the effectiveness and trends reported in previous studies. Where applicable, symmetry correlations—based on equivalent thermal and hydrodynamic behaviour along geometrically symmetric boundaries—were considered to interpret flow uniformity and heat-transfer distribution across cross-sectional profiles. Analysis reveals that over 84% of the reviewed studies emphasize on horizontal configurations and 55% on circular geometries, with medium-Prandtl-number fluids dominating experimental investigations. While these studies provide valuable insights, significant research gaps remain. Limited attention has been given to vertical orientations, where buoyancy effects may alter flow behaviour due to temperature and pressure gradients arising from variations in fluid density and viscosity, to non-circular geometries that enhance boundary-layer disruption, and to extreme-Prandtl-number fluids such as liquid metals and heavy oils, which are vital in advanced industrial applications. Bridging these gaps presents opportunities to design and optimize diverse engineering systems requiring efficient convective heat transfer. Practical examples include coolant flow in nuclear reactors, heat dissipation in high-performance CPUs, and high-speed airflow over automotive radiators. This review therefore underscores the need for future research extending forced-convection studies beyond conventional configurations, with particular emphasis on vertical orientations, complex geometries, and underexplored Prandtl-number regimes. Full article

Accurate estimation of branch-level traffic flows at urban Y-intersections from limited mainline measurements remains a critical challenge in intelligent transportation systems. Y-intersections, with their symmetric geometric configuration where multiple branches converge, pose unique challenges from flow coupling, signal-induced periodicity, and merging delays. This study develops a hybrid mathematical modeling framework that integrates piecewise linear segments with periodic components for each branch flow. The model enforces physical constraints including flow conservation, non-negativity, and segment continuity, while incorporating operational features such as signal timing and merging delays. Parameter estimation employs a two-stage optimization approach combining least-squares fitting with constrained nonlinear programming, utilizing sparse mainline detector data and minimal historical priors. Experimental validation across five progressive problem formulations demonstrates robust performance, achieving RMSE values of 3.3432 and 5.4467 for complex multi-branch scenarios while accurately capturing 10-min green/8-min red signal cycles and 2-min merging delays. The method successfully reconstructs branch flow profiles at required time points (07:30 and 08:30), reducing observation requirements by 60–80% while maintaining estimation accuracy. The proposed framework provides a practical and interpretable solution for branch flow estimation under sparse sensing conditions, bridging physics-based modeling with data-driven techniques and offering transportation agencies a deployable tool for intersection monitoring without extensive instrumentation. Full article

In coastal pumping stations, the intake sump geometry strongly affects flow uniformity, hydraulic loss, and vortex formation. This study establishes an Isight-based automated simulation and optimization framework for an axial-flow pump with a closed-type intake to clarify the influence of bellmouth diameter and clearance height on sump hydraulics. A Radial Basis Function surrogate model combined with the NonLinear Programming by Quadratic Lagrangian (NLPQL) was employed to minimize hydraulic loss and improve flow uniformity. The results show that hydraulic loss first decreases and then increases with bellmouth diameter, whereas velocity uniformity and the mean inflow angle exhibit nonlinear variations with clearance height. The optimal configuration increases efficiency by 3.82% and the velocity uniformity by 1.62% compared with the baseline. Helicity density and the Ω-criterion were used to identify vortex structures, revealing that small clearances intensify bottom and wall-attached vortices, whereas larger clearances promote symmetric inflow. An improved tangential-velocity method based on iso-vorticity contours effectively captured near-wall vortex dynamics. These findings provide theoretical support for achieving low head loss, stable inflow, and controlled vortex behavior in axial-flow pump intake systems. Full article

This study investigated the influence of spatial orientation on bead morphology and molten pool dynamics during cold metal transfer wire arc additive manufacturing (CMT-WAAM). Experiments in horizontal, transverse, vertical-down, and vertical-up orientations under varying wire feed speeds revealed that increasing the feed rate improved bead uniformity and reduced defects in horizontal deposition, while gravity-induced asymmetry dominated non-horizontal orientations. Transverse cladding produced tilted, uneven beads with reduced penetration; vertical-down enhanced lateral spreading but resulted in the shallowest weld depth; vertical-up limited spreading, yielding narrow beads with higher reinforcement. Optimal cladding quality was achieved at a wire feed speed of 6.7 m/min for the first layer, with a reduced heat input applied for subsequent layers to minimize residual stress and deformation. Numerical simulations further elucidated transient temperature and flow fields. Heat accumulation and dissipation varied with orientation and layer sequence: horizontal deposition formed deep, symmetric pools; transverse deposition generated asymmetric vortices and uneven solidification; vertical-up deposition caused upward counterflow with restricted spreading; vertical-down promoted rapid spreading and faster solidification. A detailed comparison between simulated and experimental temperature distributions and cross-sectional profiles demonstrated excellent agreement, thereby validating the accuracy and predictive capability of the developed model. This integrated experimental-numerical approach provided a comprehensive understanding of orientation-dependent molten pool behavior and offered a robust framework for optimizing process parameters, enhancing dimensional accuracy, and controlling defects in CMT additive manufacturing. Full article

Reliable estimation of low-flow statistics is essential for water quality regulation, ecological protection, and drought management. This study evaluates traditional univariate and two-component Mixture Probability Distributions for modeling 7-day annual minimum flows (7Q) using records from 293 gauging stations across Mexico’s 37 hydrological planning regions, each with at least 20 years of data. Candidate models include Lognormal-3, Gamma-3, Gumbel, Weibull-3, and mixtures (Gumbel–Gumbel, Gumbel–Weibull-3, Weibull-3–Gumbel, Weibull-3–Weibull-3). Parameters are estimated by maximum likelihood, goodness-of-fit is assessed with Kolmogorov–Smirnov and Anderson–Darling tests. Sampling uncertainty is quantified via nonparametric bootstrap, providing 95% confidence intervals for design return levels, including 7Q10. Mixture models are selected as the best fit at 253 of 293 stations (86.3%), with Weibull-3–Weibull-3 dominating (45.1% of all stations) followed by Gumbel–Weibull-3 and Weibull-3–Gumbel; univariate models account for only 13.7% of cases, mainly Lognormal-3, and Gumbel alone is never preferred. Gumbel-only and symmetric G–G mixtures yield negative low-flow return levels at some sites and are therefore considered physically implausible. In contrast, mixtures containing Weibull-3 components ensure non-negative support, provide superior fit to the lower tail, and generally produce narrower bootstrap confidence intervals than the best univariate alternatives, indicating more stable and defensible 7Q10 estimates and providing an additional criterion to distinguish between models with similar goodness-of-fit statistics. These findings have direct implications for Environmental Impact Assessment, effluent permitting, ecological flow setting, drought planning, and regional water policy. The results support integrating Weibull-based mixtures—especially Weibull-3–Weibull-3 and Gumbel–Weibull-3—into Mexico’s national framework for low-flow frequency analysis and regulatory design. Full article

This study presents numerical results on 2D local scour around subsea pipelines positioned on sand wave seabeds under steady flow conditions, utilizing Flow-3D (v11.2) software. In the computational model, the flow dynamics surrounding the pipeline are resolved using the time-averaged 2D Navier–Stokes equations in conjunction with the Renormalization Group (RNG) k-ε turbulence model. The bed morphology is governed by the bedload transport rate, suspended load transport rate, and sediment mass balance equation. The research explores the influence of pipeline diameter and water depth on scour patterns over flat beds and investigates how the pipeline’s relative position to symmetrical sand waves affects the severity and morphology of scour. It is demonstrated that the non-dimensional scour depth decreases with an increase in pipeline diameter, whereas in shallower waters, the intensity of scour is greater for a given diameter. In the study of sand wave bed conditions, it was determined that the scour strength exhibits a hierarchical order from strongest to weakest as follows: pipeline located at the crest, downstream slope of the sand waves, pipeline situated on the upstream slope, and at the trough. It is noteworthy that the scour effect is marginally more pronounced at the crest compared to a flat seabed. Conversely, scour intensity diminishes at the other positions, particularly at the trough, where it often results in backfilling and the self-burial of the pipeline. Finally, the distributions of velocity and bed shear stress around the pipeline and seabed are presented to elucidate the flow mechanisms underlying the scour process. Full article

In this study, numerical simulations were performed, and leaks in viscoelastic pipelines were detected. Based on the transient flow equations derived from the continuity and momentum equations, the Kelvin–Voigt model was used to describe the viscoelastic constitutive relationship and derive the strain equation, further establishing a one-dimensional transient flow model for viscoelastic pipelines. A frequency-domain analysis of the transient flow was performed by deriving the Fourier transform and transfer matrix. An inverse problem analysis method for transient flow leak detection was proposed to identify the leak location and rate by minimizing the objective function. To verify the effectiveness of the proposed model, an experimental platform was built, and the pressure head frequency-domain data under working conditions of no leak, experimental leak, and simulated leak were compared. The results showed that the experimental data were consistent with the simulated data under leakage conditions, thus proving that the model was accurate and reliable. Under leak-free conditions, the frequency-domain characteristics of transient pressure waves exhibit significant symmetrical features, whereas when a leak exists in the pipeline, the leak point acts as a localized non-uniform disturbance source, disrupting the symmetry of the frequency-domain characteristics. Moreover, the leak point can be determined by the difference in the peak heights between the no-leak and leak conditions, and the leak parameters can be accurately identified using the inverse problem method. Full article

High-pressure, high-volume fracturing in unconventional reservoirs often induces perforation erosion damage, endangering operational safety. This paper employs fluid–solid coupling theory to analyze the flow characteristics of fracturing fluid inside the casing during fracturing. Combined with strength theory, the stress distribution and variation law are investigated, revealing the mechanical mechanism of casing perforation erosion damage. The results indicate that the structural discontinuity at the entrance of the perforation tunnel causes an increase in fracturing-fluid velocity, and this is where the most severe erosion happens. The stress around the perforation is symmetrically distributed along the perforation axis. The casing inner wall experiences a combined tensile–compressive stress state, while non-perforated regions are under pure tensile stress, with the maximum amplitudes occurring in the 90° and 270° directions. Although the tensile and compressive stress do not exceed the material’s allowable stress, the shear stress exceeds the allowable shear stress, indicating that shear stress failure is likely to initiate at the perforation, inducing erosion. Moreover, under the impact of fracturing fluid, the contact forces at the first and second interfaces of the casing are unevenly distributed, reducing cement bonding capability and compromising casing integrity. The findings provide a theoretical basis for optimizing casing selection. Full article

This study presents a novel framework for uncertainty propagation in power-law, Bingham, and Casson fluids through rectangular ducts under stochastic viscosity (Case I) and pressure gradient conditions (Case II). Using the computationally efficient Stochastic Finite Difference Method with Homogeneous Chaos (SFDHC), validated via comparison with quasi-Monte Carlo simulations, we demonstrate significantly lower computational costs across varying Coefficients of Variation (COVs). For viscosity uncertainty (Case I), results show a 0.54–2.8% increase in mean maximum velocity with standard deviations reaching 75.3–82.5% of the COV, where the power-law model exhibits the greatest sensitivity (velocity variations spanning 71.2–177.3% of the mean at COV = 20%). Pressure gradient uncertainty (Case II) preserves mean velocities but produces narrower and symmetric distributions. We systematically evaluate the effects of aspect ratio, yield stress, and flow behavior index on the stochastic velocity response of each fluid. Moreover, our analysis pioneers a performance hierarchy: Herschel–Bulkley fluids show the highest mean and standard deviation of maximum velocity, followed by power-law, Robertson–Stiff, Bingham, and Casson models. A key finding is the extreme fluctuation of the Robertson–Stiff model, which exhibits the most drastic deviations, reaching up to 177% of the average velocity. The significance of fluid-specific stochastic analysis in duct system design is underscored by these results. This is especially critical for non-Newtonian flows, where system performance and reliability are greatly impacted by uncertainties in viscosity and pressure gradient, which reflect actual operational variations. Full article

Concussion, or mild traumatic brain injury, is a significant public health challenge, with females experiencing high rates and prolonged symptoms. Reliable and objective tools for early diagnosis are critically needed, particularly in pediatric populations, where subjective symptom reporting can be inconsistent and neurodevelopmental factors may influence presentation. Five minutes of resting-state (RS) EEG data were collected from non-concussed and concussed females between 15 and 24 years of age. We first applied a deep learning approach to classify concussion directly from raw, RS electroencephalography (EEG) data. A long short-term memory (LSTM) recurrent neural network trained on the raw data achieved 84.2% accuracy and an ensemble median area under the receiver operating characteristic curve (AUC) of 0.904. To complement these results, we examined causal connectivity at the source level using information flow rate to explore potential network-level changes associated with concussion. Effective connectivity in the non-concussed cohort was characterized by a symmetric pattern along the central–parietal midline; in contrast, the concussed group showed a more posterior and left-lateralized pattern. These spatial distribution changes were accompanied by significantly higher connection magnitudes in the concussed group (p < 0.001). While these connectivity changes may not directly drive classification, they provide evidence of large-scale brain reorganization following concussion. Together, our results suggest that deep learning models can detect concussion with high accuracy, while connectivity analyses may offer complementary mechanistic insights. Future work with larger datasets is necessary to refine the model specificity, explore subgroup differences related to hormone cycle changes and symptoms, and incorporate data across different sports. Full article

This study presents a high-fidelity CFD-based optimization of a combined sacrificial-pile and collar (SPC) system designed to suppress local scour at circular bridge piers. Following rigorous validation against benchmark flume experiments (scour depth error < 3%), a systematic parametric study was conducted to quantify the influence of pile-to-pier spacing (d_p/D = 4–6) and collar elevation (h_c/D = 0–0.3). The optimal layout is found to be a sacrificial pile at d_p/D = 5 and a collar at h_c/D, which yields a 51.2% scour reduction relative to the unprotected case. Flow field analysis reveals that the pile wake deflects the lower approach flow, while the collar vertically displaces the horseshoe vortex; together, these mechanisms redistribute bed shear stress and prevent secondary undermining. Consequently, the upstream conical pit is virtually eliminated, lateral scour is broadened but markedly shallower, and the downstream dune tail bifurcates into two symmetrical ridges. To the best of the authors’ knowledge, this study presents the first high-fidelity CFD-based optimization of a combined sacrificial-pile and collar (SPC) system with a fully coupled hydrodynamic-morphodynamic model. The optimized layout yields a 51.2% scour reduction relative to the unprotected case and, more importantly, demonstrates a positive non-linear synergy that exceeds the linear sum of individual device efficiencies by 7.5%. The findings offer practical design guidance for enhancing bridge foundation resilience against scour-induced hydraulic failure. Full article

This paper presents a comprehensive review and theoretical analysis of integrating Cyclic Solvent Injection (CSI) with multilateral well (MLW) technologies to enhance heavy oil recovery. Given that many MLW configurations inherently exhibit symmetrical geometries, CSI–MLW integration offers structural advantages for fluid distribution. CSI offers a non-thermal mechanism for oil production through viscosity reduction, oil swelling, and foamy oil behaviour, but its application is often limited by poor sweep efficiency and non-uniform solvent distribution in conventional single-well configurations. In contrast, MLW configurations are effective in increasing reservoir contact and improving flow control but lack solvent-based enhancement mechanisms. In particular, symmetrical MLW configurations, such as dual-opposing laterals and evenly spaced fishbone laterals, can facilitate balanced solvent distribution and pressure profiles, thereby improving sweep efficiency and mitigating early breakthrough. By synthesizing experimental findings and theoretical insights from the existing literature, laboratory studies have reported that post-CHOPS CSI using a 28% C₃H₈–72% CO₂ mixture can recover about 50% of the original oil in place after six cycles, while continuous-propagation CSI (CPCSI) has achieved up to ~85% OOIP in 1D physical models. These representative values illustrate the performance spectrum observed across different CSI operational modes, underscoring the importance of operational parameters in governing recovery outcomes. Building on this foundation, this paper synthesizes key operational parameters, including solvent composition, pressure decline rate, and well configuration, that influence CSI performance. While previous studies have extensively reviewed CSI and MLW as separate technologies, systematic analyses of their integration remain limited. This review addresses that gap by providing a structured synthesis of CSI–MLW interactions, supported by representative quantitative evidence from the literature. The potential synergy between CSI and MLW is highlighted as a promising direction to overcome current limitations. By leveraging geometric symmetry in well architecture, the integrated CSI–MLW approach offers unique opportunities for optimizing solvent utilization, enhancing recovery efficiency, and guiding future experimental and field-scale developments. Such symmetry-oriented designs are also central to the experimental framework proposed in this study, in which potential methods, such as the microfluidic visualization of different MLW configurations, spanning small-scale visualization studies, bench-scale experiments on fluid and chemical interactions, and mock field setups with pipe networks, are proposed as future avenues to further explore and validate this integrated strategy. Full article

Span-wise homogeneous supersonic cavity flows display complicated structures due to shear layer breakdown, flow acoustic resonance, and even non-linear hydrodynamic-acoustic interactions. In practical applications, such as aircraft bays, the cavity is of finite width and has doors, both of which introduce distinctive phenomena that couple with the shear layer at the cavity lip, further modulating shear layer bifurcations and tonal mechanisms. In particular, asymmetric states manifest as ‘tornado’ vortices with significant practical consequences on the design and operation. Both inward- and outward-facing leading-wedge doors, resulting in leading edge shocks directed into and away from the cavity, are examined at select opening angles ranging from $22.5°$ to $90°$ (fully open) at Mach 1.6. The computational approach utilizes the Reynolds-Averaged Navier–Stokes equations with a one-equation model and is augmented by experimental observations of cavity floor pressure and surface oil-flow patterns. For the no-doors configuration, the asymmetric results are consistent with a long-time series DDES simulation, previously validated with two experimental databases. When fully open, outer wedge doors (OWD) yield an asymmetric flow, while inner wedge doors (IWD) display only mildly asymmetric behavior. At lower door angles (partially closed cavity), both types of doors display a successive bifurcation of the shear layer, ultimately resulting in a symmetric flow. IWD tend to promote symmetry for all angles observed, with the shear layer experiencing a pitchfork bifurcation at the ‘critical angle’ ($67.5°$). This is also true for the OWD at the ‘critical angle’ ($45°$), though an entirely different symmetric flow field is established. The first observation of pitchfork bifurcations (‘critical angle’) for the IWD is at $67.5°$ and for the OWD, $45°$, complementing experimental observations. The back wall signature of the bifurcated shear layer (impingement preference) was found to be indicative of the 3D cavity dynamics and may be used to establish a correspondence between 3D cavity dynamics and the shear layer. Below the critical angle, the symmetric flow field is comprised of counter-rotating vortex pairs at the front and back wall corners. The existence of a critical angle and the process of door opening versus closing indicate the possibility of hysteresis, a preliminary discussion of which is presented. Full article

Abnormal operations, such as faults occurring in an electrical power system (EPS), disrupt its balanced operation, posing potential hazards to human lives and the system’s equipment. Effective monitoring, control, protection, and coordination are essential to mitigate these risks. The complexity of these processes is further compounded by the presence of intermittent distributed energy resources (DERs) in active distribution networks (ADNs) with bidirectional power flow, which introduces a fast-changing dynamic aspect to the system. The deployment of phasor measurement units (PMUs) within the EPS as highly responsive equipment can play a pivotal role in addressing these challenges, enhancing the system’s resilience and reliability. However, synchrophasor measurement-based studies and analyses of power system phenomena may be hindered by the absence of PMU blocks in certain simulation tools, such as PSCAD, or by the existing PMU block in Matlab/Simulink R2021b, which exhibit technical limitations. These limitations include providing only the positive sequence component of the measurements and lacking information about individual phases, rendering them unsuitable for certain measurements, including unbalanced and non-symmetrical fault operations. This study proposes a new reliable PMU model in Matlab and tests it under normal and abnormal conditions, applying real-time simulation and controller-hardware-in-the-loop (CHIL) techniques. Full article

CO₂ displacement is a key technique that was examined through numerical methods in a 3D Hele–Shaw cell, with CO₂ as the displacing phase and shear-thinning fluids as the displaced phase. Without interfacial tension effects, the displacement shows branching patterns forming two vertically symmetric fingers, regardless of whether the displacing fluid is air or CO₂. Under CO₂ displacement, viscous fingering propagates farther and achieves higher displacement efficiency than air. Compared with air displacement, the finger advancing distance increases by 0.0035 m, and the displacement efficiency is 15.2% higher than that of air displacement. Shear-thinning behavior significantly influences the process; stronger shear thinning enhances interfacial stability and suppresses fingering. As the power-law index n increases (reducing shear thinning), the fingering length extends. Variations in interfacial tension reveal it notably affects fingering initiation and velocity in CO₂ displacement of non-Newtonian fluids, but has a weaker impact on fingering formation. Interfacial tension suppresses short-wavelength perturbations, critical to interface stability, jet breakup, and flows, informing applications like foam-assisted oil recovery and microfluidics. Full article