Search Results (517)

The present study investigates the statistical distribution of radar reflectivity slopes [S-Ze] in the lower troposphere along the west coast of India using a C-band radar during the pre-monsoon and monsoon seasons in 2024. The study period spans a range of meteorological conditions, from a drier atmosphere during pre-monsoon months to a moist atmosphere during the monsoon months, with varying updraughts and downdraughts. To investigate the S-Ze, we calculated the difference in Ze between 4 km and 2 km altitudes in the lower troposphere. The S-Ze could be either positive or negative, where, in a positive [negative] S-Ze, the Ze decreases [increases] towards the surface. The monthly variations in S-Ze from the pre-monsoon to monsoon months are observed in the lower troposphere and are higher in monsoon months compared to pre-monsoon months, which are too near the coast. The land–ocean contrasts of the vertical profiles contributing to +ve and −ve S-Ze are lower compared to north–south gradients and higher in monsoon months. The average S-Ze shows the highest +ve and −ve S-Ze magnitude near the coast among all the months. The highest magnitude in S-Ze is observed in March and April and is associated with the lower and higher numbers of vertical Ze profiles. The increase or decrease in hydrometeor size is less during the monsoon months (June, July, August, and September) compared to pre-monsoon months, where the March–April months have the highest increase or decrease in the hydrometeor’s size in the lower troposphere. The variations in the S-Ze are the combined effect of the atmospheric, thermodynamic (relative humidity (RH) and moisture flux), and dynamic conditions (zonal, meridional, and vertical velocity). Strong updraughts that carry RH to higher altitudes make the lower atmosphere drier and contribute to a +ve S-Ze; Ze tends to decrease in the lower troposphere. However, a weaker updraught or a moderate downdraught with sufficient RH provides sufficient time for hydrometeors to grow and contributes to −ve S-Ze, and Ze tends to increase in the lower troposphere. For example, in March and April, the atmosphere is dry, and we observe the largest decrease in hydrometeors near the coastal boundary. However, we also see significantly higher negative radar reflectivity slopes, and weak downdraughts provide enough time for hydrometeors to grow. In June and July, there are strong updraughts (downdraughts) with high (low) RH, making the atmosphere more conducive to a decreasing tendency in Ze and contributing to a higher fraction of +ve S-Ze. The results presented here would be an extension of the study from the satellite-based observations, revealing the extension of climatology for the inclusion of stratiform precipitation. Full article

Accurate prediction of nonlinear wave–structure interaction is essential for the safe design of coastal structures. In this study, a fully nonlinear high-order spectral numerical wave tank is developed to investigate nonlinear wave interaction with a vertical wall. The incident-wave boundary is introduced through an additional velocity potential, with the incident-wave kinematics prescribed from corresponding nonlinear analytical wave solutions. The model is validated against the Fourier solution, demonstrating good accuracy in predicting free-surface elevation, pressure distribution, and resultant wave force. Numerical results show that wave nonlinearity significantly modifies both the standing-wave field and the wall loading. Under strongly nonlinear conditions, negative pressure develops near the lower part of the wall during the crest phase, giving rise to a characteristic saddle-shaped force history. Water depth further modulates this nonlinear mechanism by altering both the force magnitude and the pressure distribution along the wall. For focused wave groups, the force response is strongly affected by the focusing type, wave steepness, and spectral bandwidth. A narrower bandwidth maintains stronger phase coherence over a longer portion of the wave group, leading to slightly larger focused extrema and more pronounced amplification of adjacent wave and force cycles. These findings highlight the importance of nonlinear pressure effects and spectral characteristics in predicting extreme wave loads on vertical-wall coastal structures. Full article

The global transition to a diversified renewable energy portfolio requires reliable assessment of predictable marine energy resources. This study develops a high-resolution, three-dimensional Regional Ocean Modeling System (ROMS) to quantitatively evaluate theoretical tidal current energy resources in the Bohai and Yellow Seas. The model, configured with fine-scale bathymetry and forced by harmonic tidal constituents, is validated against tide gauge and Acoustic Doppler Current Profiler (ADCP) observations. Multi-year simulations reveal pronounced spatial heterogeneity in tidal current energy distribution. Rather than treating resource assessment as a single power density mapping exercise, this study combines annual mean theoretical power density, peak theoretical power density, threshold-dependent effective flow duration, effective water depth, current directionality, and vertical velocity structure to characterize resource intensity, temporal persistence, and vertical deployability. The results identify distinct hydrodynamic resource regimes. High theoretical resource intensity is concentrated west of Laotieshan Cape and east of Chengshantou, where cumulative annual effective flow duration exceeds 5000 h and short-term instantaneous theoretical power density can reach approximately 10 kW/m² and 8 kW/m², respectively. These peak values indicate strong local tidal acceleration but should be interpreted together with annual mean power density and effective flow duration. In contrast, the northern Jiangsu coastal area exhibits lower peak intensity but relatively persistent moderate flow conditions. The results provide a hydrodynamic resource basis for preliminary site screening and for guiding subsequent turbine-performance, wake/array, environmental, grid accessibility, and techno-economic assessments. Full article

Airflow is widely used in grain cleaning and sorting processes to separate grains according to their aerodynamic properties. However, separation efficiency depends on airflow parameters and grain physical characteristics. The aim of this study was to evaluate the movement and sorting of wheat grains under different airflow conditions and to compare the effects of vertical and horizontal airflows on grain separation efficiency. A theoretical analysis was conducted to investigate grain motion in laminar and turbulent airflows by determining grain displacement and displacement differences. Theoretical calculations were used to predict the displacement behavior and separation potential of grains with different critical velocities under various airflow conditions. To evaluate these predictions, laboratory experiments were conducted in a horizontal airflow sorting chamber at grain feed rates of 1 and 2 kg min⁻¹. The experimentally observed grain distributions were then compared with the theoretical predictions, allowing comparison between predicted and experimentally observed grain movement patterns. The average critical velocity of wheat grains was found to be 10.35 m s⁻¹ at 14.2% moisture content, while the floating coefficient was approximately 0.092. The theoretical analysis showed that displacement differences between grains with different aerodynamic properties ranged from 0.103 to 0.185 m within 1 s, depending on airflow conditions. Experimental results revealed a non-uniform distribution of grains within the sorting chamber, with the majority of grains collected in the first boxes. Increasing the grain feed rate reduced separation efficiency to approximately 55%, indicating a significant influence of grain flow intensity on the separation process. The results demonstrate that efficient grain sorting requires the optimization of both airflow parameters and grain feeding conditions. The findings of this study may contribute to the design and improvement of grain cleaning and sorting equipment. Full article

This study applies the Constructal Design method to the geometric optimization of a branched symmetric concentration divider for calibrating ultrasound devices used to monitor tumor response with dynamic contrast. Accurate calibration ensures image quality and diagnostic reliability. The geometry consists of a three-dimensional, tree-shaped flow network with two inlets and three outlets, where inlet 1 carries water containing contrast particles, while inlet 2 carries only water. Laminar flow simulations are performed using Computational Fluid Dynamics (CFD) with Ansys Fluent, assuming no-slip wall conditions and zero-pressure outlets. The analysis investigates the effects of the inlet velocity ratio, the diameter ratio, and the vertical positions of the central outlet and inlet tubes, while keeping the total volume and inlet diameter constant. Additionally, velocity, pressure, particle distributions, flow partition ratio, and hydraulic resistance are evaluated. Results show nearly linear concentration responses among the outlets (100%, 50%, and 0%) when the device approaches geometric symmetry with equal inlet velocities, demonstrating efficient control of flow splitting. Although the diameter ratio imposes a trade-off with hydraulic resistance, geometric symmetry combined with Constructal Design promotes improved flow uniformity and enhanced performance, with potential applications in microfluidic mixers that require precise intermediate concentrations. Full article

This paper investigates flow resistance and heat transfer during flow boiling of HFE-649 in a vertical annular minigap formed between an outer glass tube and an inner copper tube heated by a centrally located cartridge heater. Two variants of the copper heating surface were examined: a smooth surface and an enhanced surface produced by threading. The experimental measurements included fluid temperature and pressure at the inlet and outlet of the minigap, wall temperature along the test section, and the electrical parameters of the heater. The total pressure drop was analyzed using the Lockhart–Martinelli approach, with the Fanning friction factor calculated from a correlation in the literature and from an empirical relation fitted to the present dataset. Because the available pressure drop dataset is limited, the latter relation is treated here as a preliminary, geometry-specific fitting used as an auxiliary input for the present calculations rather than as a generally validated correlation. The resulting pressure drop estimates were then used to determine an effective axial velocity profile in the minigap. The thermal analysis was based on a system of steady-state energy equations for the copper tube and the fluid. The coupled inverse problems were solved using the Trefftz method, which provided two-dimensional temperature distributions in both domains and enabled the calculation of local heat transfer coefficients at the solid–fluid interface. The wall temperature results obtained using the Trefftz method were cross-checked against the Fourier-transform-based solution, with both approaches giving similar results. For the dataset considered, the empirical friction factor relation provided lower mean relative differences in pressure drop prediction than the literature relation, particularly for the smooth surface. The reconstructed wall temperature field showed good agreement with the measurements, while validation of the fluid temperature field was limited to the inlet and outlet data. For the present operating conditions, the results indicate that the threaded surface modifies local heat transfer behaviour only moderately and does not produce a pronounced overall enhancement over the entire minigap length. Full article

The Arabian Sea is a key region for global marine biogeochemical research, yet the distribution characteristics and influencing factors of dissolved oxygen and chlorophyll a concentration in its central oxygen minimum zone still require further in-depth investigation. Based on survey data and reanalysis data from 2024, this paper analyzes the distribution characteristics and underlying causes of chlorophyll a concentration and dissolved oxygen using empirical orthogonal function (EOF) decomposition of chlorophyll a concentration and dissolved oxygen saturation along the depth direction, combined with the distribution of the barrier layer, Ekman pumping induced by wind fields, and the diagnostic vertical velocity distribution calculated from ADCP-observed flow velocities. Taking approximately 10° N as the boundary, the chlorophyll a concentration in the layer shallower than 35 m exhibits a distribution pattern of high in the northwest and low in the southeast, while the water layer between 45 m and 95 m shows a pattern of low in the northwest and high in the southeast. A thick barrier layer exists in the southeastern region, whereas the barrier layer in the northwestern region is thinner or absent, resulting in lower surface chlorophyll a concentration in the southeast. ADCP observations indicate that horizontal flow velocities are higher in the south, bringing oxygen-rich water from the south, which leads to higher dissolved oxygen saturation in the southern region compared to the northern region in water shallower than 45 m. At the 65 m water layer, the higher chlorophyll a concentration in the south may result in relatively low dissolved oxygen. The hypoxic zone (dissolved oxygen saturation less than 30%) begins to appear at depths below 105 m, with its southern boundary located between 9° N and 11° N, and this boundary gradually shifts northward as depth increases. The diagnostic vertical velocity between 9° N and 11° N is higher than that in other regions, which may hinder the northward movement of oxygen-rich water from the south. In the southern region, influenced by wind stress, the vertical water movement induced by Ekman pumping is relatively significant, which may lead to a slight increase in dissolved oxygen saturation in water layers with a depth below 125 m. Full article

The spatiotemporal evolution of seepage fields and the associated hydrodynamic risk of subsequent internal erosion pose a critical threat to the structural integrity of marine and hydraulic infrastructure. To quantify these complex fluid–solid interactions, this study develops a high-fidelity numerical model—coupling the Navier–Stokes equations with the Darcy–Forchheimer resistance model and the Volume of Fluid (VOF) method—to investigate transient hydrodynamics within porous foundations under complex geometric and geological boundary conditions. Parametric analyses reveal that spatial porosity distribution fundamentally dictates the system’s seepage capacity; notably, relocating a highly permeable stratum to the shallow sub-surface eliminates upper hydraulic bottlenecks and significantly escalates total volumetric discharge. Furthermore, the study systematically evaluates the hydrodynamic efficacy of multi-dimensional seepage control structures. Results demonstrate that while increasing the vertical depth of a cutoff wall is highly efficient in restricting bulk volumetric flux, it inadvertently induces intense localized streamline convergence and flow acceleration at the structural tip. Conversely, lateral expansion of the wall base, though yielding only a moderate reduction in total seepage, successfully diffuses this concentrated flow and substantially attenuates peak pore fluid velocities. Ultimately, a combined design paradigm is proposed for practical coastal engineering applications: prioritizing vertical penetration to optimize bulk seepage reduction, concurrently integrated with moderate lateral base expansion to redistribute concentrated hydrodynamic shear stresses, thereby minimizing the hydrodynamic potential for localized piping and ensuring long-term stability against seepage-induced degradation. Full article

Shield tunneling in urban areas can generate ground vibrations that may threaten adjacent buildings, especially in hard rock strata. However, the effect of foundation type on the vibration response of multi-story buildings is not yet fully understood. This study investigates this issue through a combined approach of field monitoring and three-dimensional numerical simulation based on the Jinan Metro Line 4 project. Five-story frame buildings with pile, raft, and isolated footing foundations were analyzed, and the numerical model was validated against measured data to ensure reliability. The results show that vibration waves attenuate in an approximately symmetric elliptical pattern and are amplified by the presence of buildings. A significant vertical amplification effect is observed, with peak particle velocity at the top floor reaching up to 2.11 times that at the ground surface. Foundation type exerts a significant influence on vibration transmission. Raft foundations exhibit a more uniform vibration distribution, whereas isolated footings demonstrate a weaker attenuation capacity, with only 23.6% attenuation and a first-floor response approximately 3.3 times greater than that of pile foundations. Although the structural safety requirements are satisfied, the vibration levels at upper floors may still exceed the human comfort limit of 75 dB, with the pile-founded building reaching 85.38 dB. These findings improve the understanding of vibration transmission mechanisms under symmetric disturbance conditions and provide a scientific basis for foundation selection and vibration mitigation in urban tunneling projects. Full article

This study utilizes computational fluid dynamics (CFD), numerical simulation of particle separation characteristics enhanced by synergistic extraction–shearing is performed, and the two-phase flow in a liquid–solid stirred tank is simulated using the Eulerian–Eulerian two-fluid model and the standard $k-\epsilon$ model. The effects of impeller speed, the hole arrangement pattern of the annular shroud, and the hole area on the multiphase fluid dynamics behavior and stirring power inside the tank are systematically studied. The results show that stirring speed is a key operating parameter affecting turbulence intensity and particle mixing uniformity. When the stirring speed increases from 2000 r/min to 4000 r/min, the overall tank turbulence increases significantly, but the stirring power increases from 4.69 kW to 36.57 kW. The annular cover at the bottom is arranged with vertical openings, which enables full energy transfer within the tank and effectively enhances the turbulence intensity in the middle and lower sections of the flow field; the horizontal opening form is more conducive to the radial diffusion of particles in the middle layer. Reducing the hole area by half increases the fluid jet velocity and local shear stress, effectively improving particle distribution uniformity, while the stirring power decreases by 43.75%, thereby achieving the collaborative optimization of mixing efficiency and energy consumption. Full article

This paper conducts numerical simulations of nozzles with different structural parameters based on fluid mechanics, computational fluid dynamics and jet theory. The structural parameters of the nozzles were optimised by analysing flow field characteristics such as the pressure distribution within the nozzle chamber, velocity distribution, curves of the outlet cross-sectional area and external axial velocity, and velocity uniformity. Combining the results of orthogonal experiments, the optimal combination of factors was determined, and the impurity removal efficiency of the optimised nozzle was tested in the field, providing a reference for subsequent optimisation design. The results indicate that adding a fillet transition to the nozzle can mitigate sudden pressure drops and suppress the generation of vortices; when the fillet transition radius is 80 mm, the flow performance approaches the optimum; the optimal combination of the three factors was determined to be a contraction angle of 13°, λ of 0.65 (corresponding to an outlet height of 27 mm and an inlet diameter of 41 mm), and a nozzle length of 15 mm; this configuration yields the best external flow field characteristics and velocity uniformity; Analysis of the orthogonal test results indicates that the contribution of each structural parameter to velocity uniformity, in descending order, is: contraction angle (77.16%), λ (outlet height/inlet diameter) (18.25%), and nozzle length (0.73%); Field tests confirmed that the removal efficiency of foreign fibres using the optimal parameter combination remained consistently above 95%, with an overall average removal rate of 96.31%. This represents an improvement of approximately 7.5 percentage points compared to the original nozzle (88.83%). The optimised nozzle reduced the number of false rejections of cotton by 57%, demonstrating excellent and highly stable overall removal performance. The influence of the nozzle’s vertical height and its angle relative to the cotton on the removal efficiency requires further investigation. Full article

To elucidate the hydraulic transport characteristics of coarse-particle slurry in deep-sea mining vertical lifting pipelines and the governing effects of key operating parameters, a bidirectionally coupled CFD-DEM model was established, in which seawater was treated as the continuous phase and ore particles were treated as the discrete phase, while particle–fluid momentum exchange and particle–particle/particle–wall collisions were explicitly accounted for. The effects of inlet velocity, feed concentration, particle size, and particle shape on local particle concentration, local particle flow rate, and particle volume fraction distribution were systematically investigated. The results show that increasing the inlet velocity markedly reduces local particle concentration, increases the local particle flow rate, and promotes a faster transition of the solid–liquid two-phase flow toward a uniformly mixed state. Increasing the feed concentration enhances the conveying capacity, but simultaneously increases the risk of particle aggregation. The effect of particle size on local concentration is non-monotonic: the local concentration is relatively high at approximately 20 mm, whereas smaller particles exhibit better flow uniformity. The effect of particle shape is mainly manifested under low-velocity and high-concentration conditions, and gradually weakens with increasing inlet velocity. The present results provide a theoretical basis for parameter optimization of deep-sea mining vertical lifting systems. Full article

Flood discharge observations in Japan are shifting from the conventional float-based methods to unmanned techniques such as radio-wave current meters. These approaches differ fundamentally in their measurement principles: the former is based on a Lagrangian framework, whereas the latter relies on a Eulerian framework. In this study, surface velocity fields obtained using particle image velocimetry (PIV) were used to track virtual tracers and derive Lagrangian surface velocities, providing a basis for examining the characteristics of Lagrangian and Eulerian measurements in an actual river under flood conditions. The uncertainties associated with the two frameworks were quantitatively compared, and the principal sources of uncertainty in Lagrangian measurements were identified. To achieve accurate discharge observation based on Eulerian measurements, the influences of measurement duration, subsection configuration, and vertical velocity distribution were investigated. The results suggest that measuring many points over a short duration is more effective than measuring a few points over a long duration. In a fixed-point measurement of subsurface velocity, a velocity dip was observed. Furthermore, the results quantitatively demonstrate the effects of bridge-pier wakes on the required averaging time and subsection configuration, highlighting the practical advantage of conducting observations on the upstream side of bridges. Full article

In sediment-laden irrigation channels, sediment deposition upstream of hydraulic measuring structures can degrade hydraulic performance, reduce measurement reliability, and increase maintenance demand. To clarify the effects of structural optimization on sediment transport and siltation resistance, physical model experiments were conducted on an airfoil weir-orifice facility under different discharges, structural angles, and sediment concentrations. The analysis focused on sediment deposition patterns, longitudinal water surface profiles, sediment concentration, suspended sediment transport rate, cross-sectional velocity distribution, vertical velocity gradient, and Froude number. The results showed that the optimized configuration produced a flatter and more uniform upstream bed morphology, and the average deposition thickness decreased from 4.83 cm to 4.31 cm, corresponding to a reduction of 10.58%. Under all tested conditions, the optimized configuration reduced upstream backwater, increased local flow velocity, and shifted the hydraulic jump closer to the facility outlet. Sediment concentration and suspended sediment transport rate were consistently higher after optimization, indicating enhanced sediment carrying capacity. In addition, the optimized configuration increased the vertical velocity gradient and Froude number, while all cases remained within the subcritical-flow regime. These findings demonstrate that structural optimization can simultaneously improve hydraulic regulation and siltation resistance, and provide an experimental basis for the application of streamlined hydraulic measuring structures in sediment-laden irrigation channels. Full article

Electromagnetic hydrodynamic (EMHD) mixed convective flow of tetra hybrid nanofluid (TeHNF) in a Darcy-Forchheimer porous medium in a vertical channel with thermal radiation is considered in the paper. The electric and magnetic fields are homogeneous, magnetic perpendicular to the walls of the channel, and electric perpendicular to the plane formed by the directions of the magnetic field and the basic current. The channel walls are impermeable, and they are at constant but different temperatures. The basic equations that describe this problem are ordinary nonlinear differential equations (ODEs), and they are transformed into dimensionless ODEs by introducing dimensionless quantities, which are analytically solved using the homotopy perturbation method (HPM). The relations for velocity and temperature distributions, Nusselt numbers and shear stresses on the channel walls were determined. These relations are functions of introduced physical parameters that characterize the observed problem. For TeHNF, where the base fluid is water and the nanoparticles are made of aluminum oxide, titanium dioxide, magnesium oxide and magnetite, a part of the obtained results is given. Velocity and temperature plots are presented in the form of graphs, and Nusselt numbers and shear stresses are presented in the form of tables. Based on the analysis of the obtained results, appropriate conclusions were drawn. It was concluded that an increase in the Hartmann number as well as an increase in the porosity factor decrease the fluid velocity and shear stress, and increase the fluid temperature and Nusselt numbers. Higher values of the Forchheimer factor and higher heat radiation correspond to lower fluid velocities, lower temperatures, lower values of shear stresses and Nusselt numbers. By increasing the value of the Grashof number, the velocity of the fluid increases, and so do the shear stresses. TeHNF shows advantages over simpler hybrid nanofluids and commercial fluids. Full article