Search Results (832)

This study investigates the impact of eddy viscosity on equatorially trapped waves and the instability of the background shear in a simple barotropic–baroclinic model. It is the first study to include eddy viscosity in the study of tropical wave dynamics. This study also unifies the study of baroclinic and barotropic instabilities by using a coupled barotopic and baroclinic model of the tropical atmosphere. Linear wave theory is combined with a systematic Galerkin projection of the baroclinic dynamical fields onto parabolic cylinder functions. This study investigates varying shear strengths, eddy viscosities, and their combined effects. In the absence of shear, baroclinic and barotropic waves decouple. The baroclinic waves themselves separate into triads, forming the equatorially trapped wave modes known as Matsuno waves. However, when a strong eddy viscosity is included, the structure and propagation characteristics of these equatorial waves are significantly altered. Different wave types interact, leading to strong mixing in the meridional direction and coupling between meridional modes. This coupling destroys the Matsuno mode separation and offers pathways for these waves to couple and interact with one another. These results suggest that viscosity does not simply suppress growth; it may also reshape the propagation characteristics of unstable modes. In the presence of a background shear, some wave modes become unstable, and barotropic and baroclinic waves are coupled. Without eddy viscosity, instability begins with small scale and slowly propagating modes, at arbitrary small shear strengths. This instability manifests as an ultra-violet catastrophe. As the shear strength increases, the catastrophic instability at small scales expands to high-frequency waves. Meanwhile, instability peaks emerge at synoptic and planetary scales along several Rossby mode branches. When a small eddy viscosity is reintroduced, the catastrophic small-scale instabilities disappear, while the large-scale Rossby wave instabilities persist. These westward-moving modes exhibit a mixed barotropic–baroclinic structure with signature vortices straddling the equator. Some vortices are centered close to the equator, while others are far away. Some waves resemble synoptic-scale monsoon depressions and tropical easterly waves, while others operate on the planetary scale and present elongated shapes reminiscent of atmospheric-river flow patterns. Full article

High-resolution in situ field measurements capturing seasonal 3D mixing dynamics at river confluences are scarce, yet this understanding is essential for effective water-quality management and pollutant-transport prediction in river–lake systems. To address this gap, this study investigates the confluence of the North and South Han Rivers in the Paldang Reservoir. We introduce and apply a novel mixing proximity index (MPI) to quantify the degree of mixing and water-mass origin based on 3D electrical conductivity and temperature data. Seasonal field campaigns, conducted with an acoustic Doppler current profiler and multi-parameter sensors, revealed distinct hydrodynamic behaviors: strong summer stratification suppressed vertical mixing; winter momentum asymmetry induced persistent flow separation despite minimal temperature differences; and spring conditions fostered rapid mixing, barring some residual unmixed deep layers. The MPI effectively delineated shear layers and identified unmixed water zones, providing an enhanced understanding of mixing dynamics beyond the capabilities of traditional tracer- or statistics-based metrics. These findings highlight the combined influence of density differences, tributary momentum, and dam operations on confluence mixing, offering practical insights for water-resource management and improving 3D hydrodynamic model validation. Full article

This study investigates the aerodynamic characteristics of drafting cyclists during 45° cornering through numerical simulations, and under the conditions of a vehicle speed of 15 m/s and a 45° body inclination, the SST k-ω turbulence model and grid independence verification (final grid count:12 million) are used to systematically analyze the distribution of velocity, vortex, pressure, and wall shear stress fields. The effects of riding velocity (5–25 m/s) and inter-rider spacing (100–500 mm) on aerodynamic drag were analyzed to reveal the underlying flow mechanisms. The results indicate that as velocity increases, airflow acceleration and boundary-layer shear intensify, leading to enhanced vortex shedding and elevated wall shear stress. In contrast, reduced spacing significantly strengthens wake coupling between riders, effectively lowering the frontal pressure and skin-friction drag of trailing cyclists. The drag reduction rate decreases monotonically with increasing spacing, with the second rider consistently achieving higher aerodynamic benefits than the third rider. Distinct from previous studies that predominantly focus on straight-line motion, this work fills a critical knowledge gap in sports aerodynamics and competitive cycling strategy. By elucidating the unique wake coupling mechanisms induced by body inclination, this study provides scientific evidence for optimizing drafting tactics specifically during high-speed technical cornering. Full article

This study presents the effects of using pyrite aggregate in field concretes on the mechanical, surface performance, and algal growth tendency of concrete. The substitution of pyrite influences the process of hydration, as the gradual release of its iron- and sulfur-bearing components shifts the reaction mechanism, leading to differences in phase formation and some modification in the pore structure of the cement matrix. Three different concrete mixes (PB0, PB2.5%, and PB7.5%) were designed by replacing 0%, 2.5%, and 7.5% of the total weight of sand and crushed sand with ground pyrite as a fine aggregate. Prismatic specimens of 80 × 100 × 200 mm were produced from these mixtures and mechanical properties such as flexural, splitting tensile, and abrasion were investigated after 28 days of curing. Then, to determine the effect of pyrite on concrete surface properties, pyrite was substituted on the surface of three concrete specimens produced in 50 × 240 × 500 mm dimensions at rates of 0, 1, and 3 kg/m². These specimens were divided into two groups: one group was exposed to clean water drops at a constant flow rate in a closed environment, and the other group was exposed to dirty water in an open environment, and observed for 2 months. At the end of the process, sections of 50 × 80 × 200 cm³ were taken from the specimens and friction, abrasion and flexural tests were carried out. The results of the study demonstrate that a 7.5% pyrite substitution improves both flexural and shear strength by 38%. At the same time, pyrite substitution prevented algal growth on the surface of field concrete under clean water and delayed its formation in those under contaminated water. Finally, it was observed that pyrite, when used in concrete mix and surface applications, optimizes mechanical performance and environmental durability. Full article

In the field of engineering construction design, slope instability near water bodies remains a significant challenge. This issue is influenced by various factors, including fluid dynamics and external load disturbances. This study focuses on the design and stability evaluation of the slope in the Sejiang deformation area of the Baala Hydropower Station, applying three advanced techniques: PS-InSAR remote sensing for dynamic slope deformation data, FLAC3D stability simulation for numerical analysis of slope stability, and FLOW-3D wave calculation for quantifying secondary wave effects caused by potential landslides. By integrating these technologies, the study provides a multi-dimensional, quantitative evaluation of the secondary disasters triggered by landslides in this region. The findings are as follows: (1) The slope in the deformation zone exhibits a long-term “stable-creep” evolution, characteristic of a “stable-creep landslide” type; (2) Sliding failure primarily occurs along the interface between the bedrock and overburden layer due to shear deformation; (3) When the deformation body, with a volume of 2.1 million cubic meters, slides into the water at a velocity of 24 m/s, the calculated maximum water level height on the opposite bank reaches approximately 2925 m, near the top elevation of the dam, but still within the project’s preset safety threshold. The design methodologies and conclusions drawn from this study offer valuable insights for evaluating and designing the stability of near-water slopes in other hydropower stations. Full article

With the rise of the low-altitude economy, there is growing demand for performance and safety evaluation of logistics drones and urban aircraft operating in complex turbulent environments. Conventional wind tunnels, however, face challenges in simulating the non-uniform wind fields characteristic of urban low-altitude conditions, such as building wake flows, street canyon winds, and tornadoes. To address this gap, this study proposes a novel simulation device for low-altitude complex wind fields, which utilizes multi-fan coordinated control technology integrated with jet fan arrays, pressure-stabilizing chambers, and swirl fan systems to dynamically replicate horizontal flows, vertical flows, and specialized wind patterns. Numerical simulations using Ansys Icepak validate the effectiveness of the design: the optimized horizontal flow field achieves a wind speed of 83 m/s with a turbulence intensity ranging from 5% to 20%; the gust mode attains rapid response within 3 s; and high-fidelity simulations are achieved for wind shear, tornadoes (with a maximum tangential wind speed of 50 m/s), and downbursts (with a central vertical jet velocity of 40 m/s). Furthermore, for typical urban wind environments such as alley winds and intersection flows, the study elucidates the characteristics of abrupt wind speed variations and vortex dynamics induced by building obstructions. This research provides a new perspective and a potential technical pathway for testing low-altitude aircraft, assessing urban wind environments, and supporting related studies, thereby contributing to the advancement of complex wind field simulation technologies. Full article

Microfluidics is considered a revolutionary interdisciplinary technology with substantial interest in various biomedical applications. Many non-Newtonian fluids often used in microfluidics systems are notably influenced by the external active fields, such as acoustic, electric, and magnetic fields, leading to changes in rheological behavior. In this study, a numerical investigation is carried out to explore the rheological behavior of non-Newtonian fluids in a T-shaped microfluidics channel integrated with complex micropillar structures under the influence of acoustic, electric, and magnetic fields. For this purpose, COMSOL Multiphysics with laminar flow, pressure acoustic, electric current, and magnetic field physics is used to examine rheological characteristics of non-Newtonian fluids. Three polymer solutions, such as 2000 ppm xanthan gum (XG), 1000 ppm polyethylene oxide (PEO), and 1500 ppm polyacrylamide (PAM), are used as a non-Newtonian fluids with the Carreau–Yasuda fluid model to characterize the shear-thinning behavior. Moreover, numerical simulations are carried out with different input parameters, such as Reynolds numbers (0.1, 1, 10, and 50), acoustic pressure (5 Mpa, 6.5 Mpa, and 8 Mpa), electric voltage (200 V, 250 V, and 300 V), and magnetic flux (0.5 T, 0.7 T, and 0.9 T). The findings reveal that the incorporation of active fields and micropillar structures noticeably impacts fluid rheology. The acoustic field induces higher shear-thinning behavior, decreasing dynamic viscosity from 0.51 Pa·s to 0.34 Pa·s. Similarly, the electric field induces higher shear rates, reducing dynamic viscosities from 0.63 Pa·s to 0.42 Pa·s, while the magnetic field drops the dynamic viscosity from 0.44 Pa·s to 0.29 Pa·s. Additionally, as the Reynolds number increases, the shear rate also rises in the case of electric and magnetic fields, leading to more chaotic flow, while the acoustic field advances more smooth flow patterns and uniform fluid motion within the microchannel. Moreover, a proposed experimental framework is designed to study non-Newtonian fluid mixing in a T-shaped microfluidics channel under external active fields. Initially, the microchannel was fabricated using a high-resolution SLA printer with clear photopolymer resin material. Post-processing involved analyzing particle distribution, mixing quality, fluid rheology, and particle aggregation. Overall, the findings emphasize the significance of considering the fluid rheology in designing and optimizing microfluidics systems under active fields, especially when dealing with complex fluids with non-Newtonian characteristics. Full article

Local scour around pile-group foundations is a predominant cause of hydraulic instability in bridge engineering. This study employs a fully coupled three-dimensional computational fluid dynamics model to investigate local scour around a 2 × 2 inline pile group under steady flows. The model is validated against detailed laboratory measurements of flow and scour, demonstrating good agreement in both hydrodynamic and scour results, with scour depth simulations deviating by less than 15% from experimental data. Analysis of the flow fields reveal that scour evolution is accompanied by the descent of the horseshoe vortex, intensification of gap-flow, and acceleration around the side piles, while migration of bed shear stress from the pile flanks to the upstream slope dictates the equilibrium scour morphology. A systematic parametric study was conducted to evaluate the influence of the Froude number (Fr) and pile spacing (G/D) on scour depth. The results indicate that scour depth increases rapidly with Fr up to approximate 0.35, beyond which it plateaus as form-induced drag dissipates the incoming flow energy. Increasing G/D from 1 to 1.5 reduces the scour depth by about 12%, with smaller further reduction beyond G/D = 1.5, suggesting that this spacing offers a pragmatic compromise between structural footprint and scour resistance. Full article

We use deep Physics-Informed Neural Networks (PINNs) to simulate stratified forced convection in plane Couette flow. This process is critical for atmospheric boundary layers (ABLs) and oceanic thermoclines under global warming. The buoyancy-augmented energy equation is solved under two boundary conditions: Isolated-Flux (single-wall heating) and Flux–Flux (symmetric dual-wall heating). Stratification is parameterized by the Richardson number $(R_i\in [-1,1\left]\right),$ representing $\pm 2 °\mathrm{C}$ thermal perturbations. We employ a decoupled model (linear velocity profile) valid for low-Re, shear-dominated flow. Consequently, this approach does not capture the full coupled dynamics where buoyancy modifies the velocity field, limiting the results to the laminar regime. Novel contribution: This is the first deep PINN to robustly converge in stiff, buoyancy-coupled flows ($\mid R_i\mid \le 1$) using residual connections, adaptive collocation, and curriculum learning—overcoming standard PINN divergence (errors $>28\%$). The model is validated against analytical ($R_i=0$) and RK4 numerical ($R_i\ne 0$) solutions, achieving $L_2$ errors $\le 0.009\%$ and $L_{\mathrm{\infty }}$ errors $\le 0.023\%$. Results show that stable stratification $(R_i>0)$ suppresses convective transport, significantly reduces local Nusselt number ($Nu$) by up to $100\%$ (driving $Nu$ towards zero at both boundaries), and induces sign reversals and gradient inversions in thermally developing regions. Conversely, destabilizing buoyancy $(R_i<0)$ enhances vertical mixing, resulting in an asymmetric response: $Nu$ increases markedly (by up to $140\%$) at the lower wall but decreases at the upper wall compared to neutral forced convection. At $5–10\times$ lower computational cost than DNS or RK4, this mesh-free PINN framework offers a scalable and energy-efficient tool for subgrid-scale parameterization in general circulation models (GCMs), supporting SDG 13 (Climate Action). Full article

Increasingly slender bridge decks are prone to wind-induced damage, where the complex interactions between the incoming wind, deck, and adjacent wake flows play a deciding role. However, the unsteady wake dynamics at small but realistic angles of attack and their compact reduced-order representation remain insufficiently understood. The unsteady wakes subject to angle of attack from 3° to 5° are investigated via Koopman analysis with the Dynamic Mode Decomposition (DMD), aiming to construct accurate reduced-order models for largely repeated canonical cases, while preserving physical and phenomenological fidelity. Instantaneous velocity and vorticity fields reveal a clear separation-reattachment cycle: leading edge separation bubbles form and migrate upstream at drag peaks, then collapse and reattach at drag valleys. Shear layers roll up into dual vortices that pair, merge with Kelvin–Helmholtz-type shear-layer instabilities, and alternately shed from the deck’s upper and lower surfaces, driving oscillatory wake deflection and attendant drag and lift fluctuations. DMD identifies four dominant modes that together account for over 90% of the turbulent kinetic energy: time averaged base flow, the fundamental vortex shedding mode, and two higher frequency shear-layer modes. Adequate truncation reduces data dimensionality by an order of magnitude while keeping the normalized error below 6%. The results demonstrate that a DMD-based reduced-order model built on Unsteady Reynolds Averaged Navier–Stokes (URANS) data can faithfully preserve both large-scale separation topology and fine-scale vortical structures across small angles of attack, providing a compact and accurate representation of bridge-deck wakes for repeated canonical configurations. Full article

Foam is a field-proven technique to reduce CO₂ mobility and mitigate the impacts of reservoir heterogeneity in CO₂-enhanced oil recovery (CO₂-EOR). However, foams are unstable and tend to break down in the presence of oil. Screening foam generation and stability in the presence of oil, at representative reservoir pressure and temperature, at core-scale is critical for successful upscaling. This study investigates the effect of oil on foam generation and stability across a range of foam qualities (f_g = 0.30 to 1.0) and injection velocities (4 ft/day to 16 ft/day). Foam quality and rate scans using Bentheimer sandstone cores were conducted in presence/absence of oil (n-decane and Troll crude) at reservoir conditions (60 °C and 180 bar). Foam quality scans co-injected supercritical CO₂ and foaming solutions with increasing foam quality (f_g = 0.30 to 1.0) to determine the optimal foam quality (highest apparent viscosity foam). T optimal foam quality was then used in rate scans to determine the effect of injection velocity on foam strength. In addition, two separate core floods at two fixed foam qualities (f_g = 0.30 and 0.70) were performed to determine the oil recovery factor during foam injection. Strong foam was generated, in both the presence and absence of oil, but oil significantly reduced foam strength. The foam apparent viscosity was reduced by ~93% (Troll crude) and ~90% (n-decane) compared to foam in the absence of oil. Increasing the surfactant concentration from 0.10 wt.% to 1.0 wt.% significantly enhanced the foam mobility control, with the apparent viscosity in the presence of oil increasing from 7.9 cP to 25.9 cP. The optimal foam quality in the presence of both oils ranged from f_g = 0.60 to 0.70. Foam rate scans revealed shear-thinning rheology (foam viscosity decreased at higher flow rates), which is beneficial for maintaining field-scale injectivity. This study provides critical insights into how oil impacts supercritical CO₂ foam strength, stability mechanisms, and oil recovery at reservoir conditions, crucial for field-scale implementation in CO₂-EOR and CO₂ storage projects. Full article

This study proposes the insufficient prediction accuracy of load–displacement behavior for pile foundations in soft soil regions by proposing an elastoplastic load-transfer model applicable to axially loaded piles in soft clay, aiming to enhance the prediction capability of shaft resistance mobilization. The model systematically incorporates the elastoplastic shear deformation of the soil within the plastic zone adjacent to the pile shaft and the small-strain stiffness degradation of the soil in the elastic zone. The elastoplastic constitutive relationship in the plastic zone is formulated using critical state theory, plastic potential theory, and the associated flow rule, whereas the nonlinear elastic shear deformation in the elastic zone is described based on Hooke’s law combined with a small-strain stiffness degradation model. The developed load-transfer function is embedded into an iterative computational framework to obtain the load–displacement response of piles in multilayered soft soils. The model is validated using field pile test data from Louisiana and Shanghai. The results show that the proposed model can reasonably reproduce the elastoplastic $\tau -z$ evolution along the pile shaft and provides a theoretically robust and practically applicable method for predicting the settlement behavior of piles in clayey soils. This approach offers significant engineering value for optimizing pile design, evaluating bearing capacity, and developing cost-efficient foundation solutions in soft soil regions. Nevertheless, the current applicability of the model is primarily limited to short and medium-length piles in saturated normally consolidated clay. Future work will focus on incorporating strain-softening mechanisms and extending the model to a wider range of soil types. Full article

The processing of bulk amorphous alloys is typically realized through superplastic deformation in the supercooled liquid region, and current research efforts predominantly focus on enhancing formability by optimizing processing parameters such as temperature and duration. However, excessive temperatures or prolonged exposure times can induce crystallization, which severely compromises the mechanical and functional properties of the alloy. This study presents the design of an ultrasonic vibration (UV)-assisted metal hot-forming apparatus that integrates an ultrasonic vibration field into the superplastic flow deformation of amorphous alloys. High-temperature compression experiments were conducted on Zr₅₅Cu₃₀Al₁₀Ni₅ amorphous alloy, and finite element simulations were performed to model the experimental process. Results show that ultrasonic vibration reduces the flow stress of the amorphous alloy, thereby enhancing its superplastic deformation capability. Simulation analysis reveals that surface effects arise from periodic interface separation between the pressure plate and the specimen caused by ultrasonic vibration, leading to a cyclic disappearance of friction forces, which manifest macroscopically as a reduction in effective friction. On the other hand, vibration introduces additional strain rates. Since the undercooled liquid of amorphous alloys exhibits non-Newtonian fluid behavior characterized by shear-thinning, ultrasonic vibration assistance can effectively reduce the apparent viscosity, thereby improving their filling capacity. Full article

Microfluidics enables precise manipulation of scarce Traditional Chinese Medicine (TCM) samples while accelerating analysis and enhancing sensitivity. Device-level structures explain these gains: staggered herringbone and serpentine mixers overcome low-Reynolds-number constraints to shorten diffusion distances and reduce incubation time; flow-focusing or T-junction droplet generators create one-droplet–one-reaction compartments that suppress cross-talk and support high-throughput screening; “Christmas-tree” gradient generators deliver quantitative dosing landscapes for mechanism-aware assays; micropillar/weir arrays and nanostructured capture surfaces raise surface-to-volume ratios and probe density, improving capture efficiency and limits of detection; porous-membrane, perfused organ-on-a-chip architectures recreate apical–basolateral transport and physiological shear, enabling metabolism-aware pharmacology and predictive toxicology; wax-patterned paper microfluidics (µPADs) use capillary networks for instrument-free metering in field settings; and lab-on-a-disc radial channels/valves exploit centrifugal pumping for parallelised workflows. Framed by key performance indicators—sensitivity (LOD/LOQ), reliability/reproducibility, time-to-result, throughput, sample volume, and sustainability/cost—this review synthesises how such structures translate into value across TCM quality/safety control, toxicology, pharmacology, screening, and delivery. Emphasis on structure–function relationships clarifies where microfluidics most effectively closes gaps between chemical fingerprints and biological potency and indicates practical routes for standardisation and deployment. Full article

In this study, the evolution of the flow field near a Geotextile Mattress with a Floating Plate (GMFP) are numerically investigated, with a specific focus on the influence of the Froude number and the dynamic response of the floating plate. Key findings identify a critical Froude number that separates two protection regimes. Below this critical flow condition, the bottom vortex and the protective zone remain stable. Above it, the vortex contracts upstream, and the protection efficacy becomes substantial but diminished due to the competing effects of vortex development and a reduction in plate obstruction height. The bed shear stress over a considerable distance leeward of the GMFP is significantly reduced compared to unprotected conditions. Due to the blockage of the GMFP, upstream backup and downstream drawdown were observed in the water surface over the GMFP. These results provide valuable insights for the design and application of GMFPs, particularly in optimizing structural parameters to enhance protection effectiveness under varying flow conditions. Full article