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In this study, the round-trip motion of air-rich bubbles exhaled from a water vapor-rich bubble was investigated. The local heating of non-degassed water produced a vapor-rich bubble with a maximum diameter of 9 μ m, which intermittently exhaled air-rich bubbles with a radius of less than 1 μ m. The exhaled air-rich bubbles initially moved away from the heat source; however, as the air-rich bubbles fused and grew larger, they returned to the heat source and fused with the vapor-rich bubble. This round-trip motion of the air-rich bubbles is explained by the balance between the Marangoni and quasi-steady drag forces induced on the bubbles. As the quasi-steady drag force is approximately proportional to the bubble radius and the Marangoni force is proportional to the square of the bubble radius, a larger bubble correlates with a greater effect of the Marangoni force. To produce a quasi-steady drag force that can balance the increased Marangoni force, air-rich bubbles were attracted to the heat source against the flow created by the vapor-rich bubble. These results provide insight into the stabilization of water-vapor-rich microbubbles in non-degassed water, which can generate strong flows on the order of 1 m/s. [ABSTRACT FROM AUTHOR]

In this paper, a homogenized multiphase lattice Boltzmann (LB) model is established for parallelly simulating immiscible two-phase flow in both solid-free regions (pore scale) and porous areas (continuum scale). It combines the color-gradient multiphase model with the Darcy–Brinkman–Stokes method by adding a term that includes surface force and drag force of porous matrix to multiple-relaxation-time LB equation in moment space. Moreover, an improved algorithm is proposed to characterize and implement the apparent wettability in the locally homogenized porosity field. Validations and test cases are given to demonstrate the accuracy and robustness of this new model, as well as its applicability for trans-scale fluid simulation of transport and sorption behavior from porous (Darcy flow) area to free (Stokes flow) area. For practicality, the two-phase seepage flow in a composite rock structure with multiscale pores is simulated by this new model, and the effects of viscosity ratio and wettability on the displacement process are discussed. [ABSTRACT FROM AUTHOR]

This study investigates acoustic radiation forces on spherical objects generated by Bessel beams in a viscous fluid. Radiation forces on elastic spheres and shells of different materials are examined using viscid expression with the thermoviscous correction included, and the results are then compared with numerical simulations based on the finite element method. The Stokes drag force for zero-order Bessel waves was theoretically derived, and in turn, a practical example of negative radiation forces is proposed and investigated together with the gravity, the buoyancy, and the drag force from acoustic streaming. It is found that the negative pulling force exists even including the positive forces from the other sources; however, the parameter regions for pulling forces are reduced especially for small objects. This work helps the further study of particle manipulations by acoustic Bessel beams in viscous fluids and also guides the experimental realization of acoustic tractor beams. [ABSTRACT FROM AUTHOR]

Nanoparticles (NPs) can be highly beneficial as additives to lubricating fluids, and the tribotronic response of charged NPs tuned by external fields represents an area of great technological potential. Tribotronic response, however, is expected to be highly size dependent, which represents a significant design challenge. To explore this issue, quartz crystal microbalance and cyclic voltammetry were employed to characterize nanotribological and electrochemical behavior of platinum–nanofluid interfaces formed by aqueous suspensions of different-sized negatively charged titanium dioxide (TiO2) NPs. Suspensions of 5, 40, and 100 nm NPs were all observed to reduced interfacial frictional drag forces upon introduction into pure water in zero field conditions, with reductions for the 40 nm NPs about twice those of 5 nm particles at comparable concentrations. Suspensions of 100 nm NPs produced even greater reductions, but rapidly precipitated from the suspension when left unstirred. NPs were also driven to and from Pt electrode surfaces by applying external electric fields with varying amplitudes and modulation frequencies. For electric fields of sufficient amplitude and duration, the 40 nm TiO2 nanosuspension exhibited tribological properties consistent with a reversible electrophoretic deposition of the NPs, accompanied by changes in the electrochemical attributes and increasing interfacial drag. The 5 nm NP properties were consistent with progressive reductions in interfacial drag forces at the NP–suspension interface linked to field-induced increases in concentration. [ABSTRACT FROM AUTHOR]

Single-file transport occurs in various scientific fields, including diffusion through nanopores, nanofluidic devices, and cellular processes. We here investigate the impact of polydispersity on particle currents for single-file Brownian motion of hard spheres when they are driven through periodic potentials by a constant drag force. Through theoretical analysis and extensive Brownian dynamics simulations, we unveil the behavior of particle currents for random binary mixtures. The particle currents show a recurring pattern in dependence of the hard-sphere diameters and mixing ratio. We explain this recurrent behavior by showing that a basic unit cell exists in the space of the two hard-sphere diameters. Once the behavior of an observable inside the unit cell is determined, it can be inferred for any diameter. The overall variation of particle currents with the mixing ratio and hard-sphere diameters is reflected by their variation in the limit where the system is fully covered by hard spheres. In this limit, the currents can be predicted analytically. Our analysis explains the occurrence of pronounced maxima and minima of the currents by changes in the effective potential barrier for the center-of-mass motion. [ABSTRACT FROM AUTHOR]

This study employs a two-dimensional and incompressible flow of Herschel–Bulkley visco-plastic materials in order to investigate the hydrodynamic forces that are acting on a barrier that is located close to the inlet of a channel. As the benchmark configuration, the flow domain that has been selected is a channel that still contains the impediment. The two important parameters of the Herschel–Bulkley Model (HBM) are the yield stress τ y and power law index n. Obtaining special situations within the HBM, such as Newtonian, power-law, and Bingham fluids, can be accomplished by assigning certain values to these parameters at the appropriate times. Utilizing a numerical strategy grounded in the Finite Element Method (FEM), we tackle the nonlinearity of the governing equations as well as the viscosity models. As a result of this nonlinearity, FEM becomes an essential tool. The generation of a refined hybrid mesh is done in order to guarantee accuracy in the computations. The stable finite element pair ( ℙ 2 ∕ ℙ 1 ) has been selected for discretization purposes. The discretized nonlinear system is linearized with Newton's method and subsequently, a direct linear solver PARDISO has been employed in the inner iterations. The pressure, velocity, and viscosity profiles are plotted for various values of n and Bingham number (Bn). In addition, the velocity behavior is observed along the y-direction in a channel through line graphs. Code validation is done as a special case Bn = 0 and a good agreement is found with the results available in the literature. Finally, a correlation analysis has been performed for the drag coefficient C d and lift coefficient C l . [ABSTRACT FROM AUTHOR]

Hybrid nanofluids provide several advantages over conventional fluids, including improved thermal characteristics, increased stability, customizable features, multifunctionality, and environmental advantages. Hybrid nanofluids are an appealing alternative for a variety of applications due to these benefits. This study aims to compute the non-similar solution of single-multi wall carbon nanotubes (SWCNTs-MWCNTs)-based hybrid nanofluid flow over an inclined extending surface. Heat transmission and flow are observed under the effects of quadratic convection, Darcy-Forchheimer quadratic drag forces, viscous dissipation, and non-linear thermal radiative heat flux. The velocity and thermal slip constraints are imposed at the inclined surface. For the model-based comparison, Xue, and Modified Hamilton Crosser thermal conductivity models for carbon nanotubes (CNTs) are adopted. The irreversibility of the system is also investigated using the second law of thermodynamics for the distinct CNTs-based thermal conductivity models. Non-similarity variables are adopted to convert nonlinear partial differential equations into dimensionless PDEs. Analytical modeling of non-similar systems is done by adopting non-similarity transformations up to second-level truncation, and the bvp4c technique is then used to compute the results numerically. The research found that at 75° of plate inclination, the Modified Hamilton Crosser model for CNTs outperforms the Xue model in terms of heat transfer rate. Further, entropy generation is significantly larger for the Xue model than for the Modified Hamilton Crosser model for CNTs against higher values of viscous dissipation and porosity parameters. It is also revealed that for opposing buoyancy force GR < 0, the temperature of the fluid escalates. This study possesses multiple applications including petroleum engineering, heat exchangers, environmental remediation, and biomedical applications. [ABSTRACT FROM AUTHOR]

Recently, researchers are facing great challenges to form the homogeneous solutions of various liquids at biomedical and industrial levels. Such homogeneous solutions can be controlled through stratification phenomenon directly which is ignored by the researchers in the existing literature specifically quadratic stratification and melting heat mechanism which is valid only for higher temperature processes. Thus, to form the homogeneous and stable liquid solutions for various industrial processes, we investigate the melting heat phenomenon in quadratic stratified Jeffery Nano fluid flow deformed due to linearly stretching sheet along with stagnation point. Inclined constant magnetic field is implemented on the fluid through an arbitrary angel. Characteristics of heat and transportations are disclosed through viscous dissipation, Brownian motion and thermphoresis. Temperature and concentration of the surrounding fluids are assumed higher than the stretching surface. The resultant governing equations are reduced to ordinary differential equations through proper transformations. Convergent analytical series solutions are computed via homotopic approach. Impact of various emerging parameters on temperature, velocity and concentration fields are illustrated and discussed comprehensively. Sherwood and Nusselt numbers and drag force are scrutinized mathematically, physically and graphically. It is analyzed from the study that (i) dominant melting reduces the temperature field (ii) higher thermal and solutal stratification decay the temperature and concentration fields respectively (iii) higher thermophoresis enhances the temperature field. Further, it is concluded that stable and homogeneous solutions may be made by increasing melting and reducing stratification phenomena. This study will help us to provide actual amount of heat for heating processes in industries and biomedicine which is the basic requirement for excellent quality of products. [ABSTRACT FROM AUTHOR]

Mobilization of in situ fine particles in geothermal reservoirs is a key contributor to permeability damage and clogging of the reservoir rock, leading to a decline in well productivity during enhanced geothermal operations. This phenomenon is a result of disturbance in the mechanical equilibrium of the forces acting on a given fine particle, most significant of which are electrostatic and drag forces. These forces are affected by changes in fluid flow velocities, in situ temperatures, or ionic strength of in situ fluids. Theoretical formulation of migration of fine particles in porous media driven by non-isothermal flow remains challenging, and requires a considerable number of parameters to quantify the characteristics of a given colloidal particle-pore fluid–solid grain system. The identification of all the involved parameters often necessitates costly, intricate, and time-consuming physical experiments. Moreover, implementing the complete form of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, commonly adopted to evaluate changes in electrostatic forces, is complicated, computationally demanding, and impractical, particularly when applied to evaluate fines migration at a reservoir scale. This study presents a theoretical framework for accurate and practical prediction of fine particle migration driven by non-isothermal flow in a clay-NaCl-quartz system. The novel contributions of this study are twofold. Firstly, a new numerical model is developed based on the complete DLVO theory, which integrates for the first time the effects of both thermal and hydraulic loads on all underlying parameters including both the static dielectric constant and the refractive index of the pore fluid. Secondly, an innovative simplified DLVO-based model has been introduced, requiring notably fewer parameters compared to existing models, thus offering a practical and efficient solution. The proposed models are utilized to conduct a comprehensive assessment of the fundamental mechanisms involved in fine particle liberation. Findings are key to predict fines-migration-induced permeability damage in geothermal reservoirs to achieve a sustainable design of energy storage/production operations as well as to develop effective strategies to prevent or mitigate the decline in well productivity in time. [ABSTRACT FROM AUTHOR]

Polyploid giant cancer cells (PGCCs) contribute to the genetic heterogeneity and evolutionary dynamics of tumors. Their size, however, complicates their isolation from mainstream tumor cell populations. Standard techniques like fluorescence-activated cell sorting (FACS) rely on fluorescent labeling, introducing potential challenges in subsequent PGCC analyses. In response, we developed the Isosceles Trapezoidal Spiral Microchannel (ITSμC), a microfluidic device optimizing the Dean drag force (FD) and exploiting uniform vortices for enhanced separation. Numerical simulations highlighted ITSμC's advantage in producing robust FD compared to rectangular and standard trapezoidal channels. Empirical results confirmed its ability to segregate larger polystyrene (PS) particles (avg. diameter: 50 μm) toward the inner wall, while directing smaller ones (avg. diameter: 23 μm) outward. Utilizing ITSμC, we efficiently isolated PGCCs from doxorubicin-resistant triple-negative breast cancer (DOXR-TNBC) and patient-derived cancer (PDC) cells, achieving outstanding purity, yield, and viability rates (all greater than 90%). This precision was accomplished without fluorescent markers, and the versatility of ITSμC suggests its potential in differentiating a wide range of heterogeneous cell populations. [ABSTRACT FROM AUTHOR]

In this paper, a forced vibration caused by drag and lift forces with time‐varying mass is studied. The construction of the model is conducted by adding impact force to the previous model. The periodicity of the solution is yet known. Hence, the model is seen as a perturbation problem. Since the unperturbed problem has a periodic solution, we applied the averaging method to determine the sufficient condition such that the limit cycle exists. [ABSTRACT FROM AUTHOR]

Kelps are resilient organisms, capable of thriving in high-energy wave environments. However, when hydrodynamic drag forces exerted by the wave environment exceed the kelps’ structural limits, individuals become dislodged. Floating kelps generally follow ocean currents, traveling long distances until air-filled structures fail or the epibiont load becomes too great, causing them to sink to the seafloor. The ability of kelp to disperse over vast offshore and nearshore systems makes them important for organic subsidy and as a dispersal vector for marine organisms. Previous research on dislodged macroalgae focused on context-specific rafts, limiting insights into the broader ecological role of floating kelp. This study employed a site-specific Lagrangian trajectory model to describe the spatial distribution of floating Ecklonia maxima along the South African coastline. The model incorporated buoyancy and sinking using site-specific morphological data. Findings revealed that the distribution of floating E. maxima is influenced by oceanographic conditions, and seasonal patterns were also evident. Mesoscale features played a vital role in kelp accumulation on the surface and seafloor and acted as barriers to dispersal. This study offers essential insights into kelp’s role as an organic subsidy and provides numerical evidence for kelp’s potential as a carbon sink, contributing to a better understanding of kelp ecosystems and their ecological functions. [ABSTRACT FROM AUTHOR]

Inhabitants of rocky intertidal shores, including gastropods, require specific adaptations to cope with numerous challenges that vary across the intertidal levels. We collected Stramonita biserialis snails from upper (wave-protected and intense predation) and lower (wave-exposed and low predation) intertidal sites to compare the following traits: shell skeleton (ventral and abaxial lateral views of shell shape, thickness, and mass), foot size, energy metabolism, and attachment strength to determine whether the trait values of snails from each zone fit the environmental challenges they face. We used a Principal Component Analysis to reduce the dimensionality of the data. Multivariate Analysis of Covariance (MANCOVA) for comparing characteristics between the two intertidal zones, and Partial Least Squares (PLS) analyses for testing the integration of overall snail characteristics. The traits of the snails of the two intertidal sites matched with the adaptations expected to allow them to cope with their contrasting challenges. The snails from the lower intertidal had more streamlined shells (which reduces drag forces) and a larger aperture and foot extension (which increase the strength of their attachment to the substrate) compared to snails from the upper sites. Snails from the lower intertidal also had a high mass-specific metabolism and soft body proportion, indicating that these snails from the wave-exposed sites have an energetically active musculature that matches their strong substrate attachment. The thin shell walls of the snails of the lower intertidal match the relatively low predatory pressure there. [ABSTRACT FROM AUTHOR]

Understanding particle ejection behaviours in plume-regolith interaction is important for a safe soft-landing system and landing manoeuvre in planetary missions. In this study, a Mach 5.8 hypersonic jet at the different Reynolds numbers of 2.58 × 104 and 9.35 × 102 impinges on the deposited glass particles of 80 μm diameter in a vacuum chamber, and the particle and gas motions at the nozzle pressure ratios (NPR) of 95, 950, and 1900 are investigated using the time-resolved PIV and high-speed Schlieren techniques. A narrow hypersonic jet consisting of several shock cells forms at the lower NPR of 95 and causes a deeply narrow crater due to its jet penetration into the deposited particles. The deeply narrow crater makes a particle ejection angle increase upwardly. On the other hand, a relatively wide crater forms due to the jet impingement at the other NPR conditions which a widely long shock cell is generated. Based on the present experimental results, a dominant factor in particle ejection angle is the crater size and depth, whereas a particle diffusion velocity is dominated by surrounding pressure. The diffused particles move faster in a low surrounding pressure because of a low aerodynamic drag force acting on the diffused particles. • A dominant factor in particle ejection angle is the crater size and depth. • The diffused particles move faster in a low surrounding pressure. • The particle and gas motions at several NPRs are investigated in a vacuum chamber. [ABSTRACT FROM AUTHOR]

In mineral processing, column flotation is being used extensively for fine particle beneficiation. Although a few attempts were made to develop computational fluid dynamics (CFD) models for column flotation in the past, validation against comprehensive experimental data is yet to be demonstrated. This work employs an Eulerian-Eulerian model coupled with the standard k-ε turbulence model for modeling the hydrodynamics in the column flotation. The two-phase simulations were performed on both laboratory and industrial-scale column flotations. The two-fluid model was further modified with the appropriate interphase forces (Ishii-Zuber drag force and Tomiyama lift force) and population balance method (PBM) to accurately simulate and predict the bubble dynamics. The axial and radial gas holdup variations along with the axial liquid velocity are predicted at different air and liquid superficial velocities. The numerical predictions were then validated against the Electrical Resistance Tomography (ERT) data in a 4-inch laboratory column flotation and conductivity probe data in an industrial column flotation. The modified two-fluid model was able to predict accurate hydrodynamics close to ERT data. The gas holdup was found to increase with the superficial air velocity, liquid height, and liquid velocity. The gas holdup found uniformly dispersed radially at low superficial air velocities and heterogenous dispersed bubble flow at higher superficial velocities. A parabolic profile of liquid flow observed at higher superficial air velocities. [ABSTRACT FROM AUTHOR]

Understanding the effect of airfoil geometry on the criticality of leading-edge suction is key to modeling the leading-edge vortex (LEV) dynamics of unsteady airfoils in a simple and robust manner. The current work aimed at investigating the dependency of the leading-edge suction parameter (LESP), a nondimensional measure of the leading-edge suction, at its critical value, which is indicative of leading-edge vortex initiation, on airfoil camber. Computational data for six NACA XX12 series airfoils with varying camber magnitude and maximum camber location at Reynolds numbers 30,000 and 3 million were analyzed. Observations indicate that increasing the airfoil camber leads to delayed LEV initiation and suction breakdown due to higher leading-edge flow curvature. The rate of increase of critical LESP with camber was seen to be independent of Reynolds number. Aftward movement of the maximum camber location was seen to have a reducing effect on the airfoil's forces and LEV dynamics. Lift and drag forces were observed to be dependent on camber magnitude and location prior to LEV formation but independent during the LEV-dominated part of the motion. The findings from the current work provide insights into reducing the dependency of the LESP on airfoil geometry. [ABSTRACT FROM AUTHOR]

This article explores the trajectory of rockets and artificial satellites in the atmosphere, specifically focusing on the effects of drag forces. It discusses different types of orbits and highlights the lack of information on drag forces in high school textbooks. The article proposes a new calculation method to help students understand spiral motion caused by drag forces and also delves into the use of energy and power in analyzing these effects. The document further discusses the drag force experienced by objects in Earth's atmosphere, providing equations for different scenarios based on the Reynolds number. It also covers the motion of objects in circular paths and concludes with an equation describing the trajectory of objects experiencing drag force. The text emphasizes the study's focus on spherical objects passing through the stratosphere and troposphere, providing physical constants and presenting results of different mass values on the trajectory. The authors derived formulas for spiral trajectories based on energy loss caused by drag forces, and computational estimations showed that ideal spherical objects subjected to drag forces perform spiral motion. The study's findings can aid students and teachers in understanding the trajectory of objects experiencing drag forces. [Extracted from the article]

The article explores the issue of projectile motion with atmospheric drag, specifically focusing on vertical launch. The authors present an analytical solution for the projectile's position and maximum height over time, assuming a constant drag coefficient. They compare this solution with a numerical one that allows for a varying drag coefficient. The article emphasizes the importance of intermediate-level solutions in physics education and the need to consider drag forces in projectile motion problems. The authors also discuss the application of the analytical solution in studying volcanic eruptions and highlight its potential use in analyzing volcanic bomb trajectories. The research was supported by the European Research Council. [Extracted from the article]

Considerable parts of riparian forests around the world are covered by deciduous trees and tall shrub species with rigid trunk and flexible-broadleaf. Experiments are conducted on artificial rigid and flexible models to estimate drag coefficient and resistance to flow for deciduous trees in forest floodplains under nonsubmerged condition. The rigid and flexible models with similar size and configuration are tested in a laboratory flume to clearly determine the effects of vegetation flexibility and density, and the flow velocity and depth on the roughness coefficients. Ratios of the flexible to rigid drag forces and drag coefficients indicate considerable effects of flexibility on the roughness coefficients. In this study, the flexural rigidity of the tree leaf is used in the roughness equations to account for vegetation flexibility instead of the traditionally used tree trunk flexural rigidity. This is based on the assumption that foliage flexibility governs tree reaction to the flow for most species of deciduous trees and leafy tall shrub families. The developed roughness coefficient equations are scaled up to determine the variation of Manning's n -value with increase of flow depth for a riparian canopy of black willow. The estimated Manning's n -values are compared with the reported Manning n -values for the same black willow canopy. [ABSTRACT FROM AUTHOR]

This article presents research into the feasibility of applying a nonlinear damper of a new conceptual structure. The key component of the damper is a circular membrane with slits that can move in a cylinder filled with viscous fluid. When an external load is applied to the damper, the membrane deforms, opening the slits. The flow of viscous fluid through the slits generates a damping force. The phenomenological model of the damper is based on the notion that the slit membrane moves according to the fundamental axisymmetric vibration mode of a circular membrane. The slit membrane blocks the entire radius of the pipe in the state of equilibrium when all slits are closed. As the membrane moves, the opening area of the slits varies depending on its deformation. This gives a nonlinear damping characteristic. The damping constant depends on the input displacement and velocity, which is the reason for the nonlinearity of the damping characteristic. From the phenomenological model, the nonlinear characteristic of the drag force is obtained. The performance of the damper is simulated using a mass–spring–damper system. Two cases of harmonic excitation and impulse excitation are analyzed. The results show that, using the slit membrane damper, the suppression of dynamic loads is more effective compared to a conventional linear damper. [ABSTRACT FROM AUTHOR]

This investigation explores the interactions of different shaped debris with an array of obstacles under subcritical flow conditions, representative of a flood associated with a storm surge or tsunami. Panels, blocks and cylinders were used in a flow channel, as analogues for house panels, cars/containers and trees respectively, whilst some tests used a mix of debris. The backwater effect due to the blockage caused by the obstacles was most (least) significant for panels (cylinders). There was some evidence that smaller key log types and higher flow rates led to smaller dams. It was also evident that key logs formed at different depths depending on debris shape; debris shape also determined the vertical shape of the dam. Capture efficiency had a broadly negative (positive) correlation with the Froude number (permeability). Also, from video footage there were examples of the debris moving more quickly through partial dams. Finally, the drag force, deduced from only the water depths and the flow discharge, showed a clear relationship between drag force and Froude number, and a dependency of drag force on debris shape. There are some implications for the layout of building footprints in the inundation zones and the use of large, break‐away panels. [ABSTRACT FROM AUTHOR]

Effects of Sn on microstructure, texture and magnetic properties of 2.7%Si-0.5%Al non-oriented silicon steel in industrial production were studied by X-ray diffraction and electron backscattering diffraction. Furthermore, combining first-principles simulation with White–Coghlan model calculation, grain boundary segregation of Sn was also investigated. In Sn-0.05 steel, cold-rolled sheet showed more ingrain shear bands and intensity of textures weakened significantly. Addition of Sn obviously reduced intensity of {111}<112> and increased intensity of {114}<481>; strong {100}<120> and nearly Goss textures appeared in annealed sheet. P1.5/50 decreased by 0.05W/kg, B50 increased by 0.005 T, and stability of magnetic properties were obviously improved of Sn-0.05. In the unit grain boundary layer (1 Å−2), the excess solute concentration on the grain boundary layer of Sn corresponding to 20,000–30,000 appm was 0.16–0.22 and gradually decreased with temperature and increased with intragranular solute content. As a segregation element, during annealing process of hot-rolled band and cold-rolled sheet, Sn exerted a drag force on the grain boundaries, thus inhibiting the grain growth. {114}<481> and {100}<120> oriented grains could grow selectively and distribute evenly by virtue of their mobility and quantity advantage higher than {111}<112>, thus improving magnetic properties and stability of 2.7%Si-0.5%Al non-oriented silicon steel. [ABSTRACT FROM AUTHOR]

Recent advancements in nanofluid technology have emphasized the potential of ternary hybrid nanofluids (THNFs) to significantly enhance thermal and hydrodynamic properties. The implementation of a wavy sinusoidal cylinder is proposed as a novel approach to optimize heat transfer in a variety of engineering applications. This study focuses on analysing the flow and thermal behaviour of TiO2-Al2O3-MoS2/Kerosene oil a THNF around a circular cylinder with a sinusoidal radius, demonstrating enhanced heat conduction capabilities compared to conventional hybrid nanofluids. The governing equations, formulated as partial differential equations, are solved using the bvp4c solver. The study reveals that the shape of nanoparticles plays a crucial role in heat transfer efficiency. Specifically, when the solid volume fraction increases from 1% to 3%, brick-shaped particles exhibit the lowest heat transfer enhancement of 25.80%, while blade-shaped particles achieve the highest enhancement of 68.24%. Additionally, the heat transfer coefficient improves from 1.5% to 1.8% across different nanoparticle shapes under varying dissipation parameters. Similar trends are observed in the reduction of drag force with changes in the velocity slip parameter. These findings underscore the significant impact of nanoparticle shape and volume fraction on the thermal performance of THNFs, offering valuable insights for optimizing heat transfer systems in engineering applications. [ABSTRACT FROM AUTHOR]

In this paper, we present a refined framework for the global-in-time well-posedness theory for the pressureless Euler–Navier–Stokes system and the optimal temporal decay rates of certain norms of solutions. Here the coupling of two systems, pressureless Euler system and incompressible Navier–Stoke system, is through the drag force. We construct the global-in-time existence and uniqueness of regular solutions for the pressureless Euler–Navier–Stokes system without using a priori large time behavior estimates. Moreover, we seek for the optimal Sobolev regularity for the solutions. Concerning the temporal decay for solutions, we show that the fluid velocities exhibit the same decay rate as that of the heat equations. In particular, our result provides that the temporal decay rate of difference between two velocities, which is faster than the fluid velocities themselves, is at least the same as the second-order derivatives of fluid velocities. [ABSTRACT FROM AUTHOR]

The significant increase in thermal efficiency and the rate of energy exchange used in fuel dynamics and automobile coolants are leading to a better understanding of nanofluids. This computational analysis explores the thermal conductivity performance for radiative cross-flow of a nanofluid across an expanding/constricting sheet with a suction effect as a result of its application. To compute or calculate the magnificent point of nanofluid flow, the entropy, and asymmetrical heat source/sink effects are also elicited. The boundary layers traverse a stream-wise procedure for expanding and contracting sheets. Additionally, the study examines the features of heat transfer and cross-flow of nanofluids using numerical simulations. By employing similarity variables, the basic PDE equations of the current model are transformed into ODEs, and they are subsequently evaluated using the bvp4c method. Therefore, the effects of embedded flow variables on drag force, heat transfer rate, and entropy generation profiles have been framed using parametric research. Multiple solutions are offered for a specific range of the contracting parameter as well as the mass suction parameter. In addition, the heat transfer rate accelerates due to the heat source and decelerates due to the heat sink. The literature that is already published has been compared favorably, and it reveals many commonalities. [ABSTRACT FROM AUTHOR]

The flow structure around limited-size vegetation patches is crucial for understanding sediment transport and vegetation succession trends. While the influence of vegetation density has been extensively explored, the impact of the relative diameter of vegetation stems remains relatively unclear. After validating the reliability of the numerical model with experimental data, this study conducted 2D-URANS simulations (SST k-ω) to investigate the impact of varying relative diameters d/D under different vegetation densities λ on the hydrodynamic characteristics and drag force of vegetation patches. The results show that increasing d/D and decreasing λ are equivalent, both contributing to increased spacing between cylinder elements, allowing for the formation of element-scale Kármán vortices. Compared to vegetation density λ, the non-dimensional frontal area aD is a better predictor for the presence of array-scale Kármán vortex streets. Within the parameter range covered in this study, array-scale Kármán vortex streets appear when aD ≥ 1.4, which will significantly alter sediment transport patterns. For the same vegetation density, increasing the relative diameter d/D leads to a decrease in the array drag coefficient C ¯ D and an increase in the average element drag coefficient C ¯ d . When parameterizing vegetation resistance using aD, all data points collapse onto a single curve, following the relationships C ¯ D = 0.34 ln a D + 0.78 and C ¯ d = − 0.42 ln a D + 0.82 . [ABSTRACT FROM AUTHOR]

Small finite-size particles suspended in fluid flow through an enclosed curved duct can focus to points or periodic orbits in the two-dimensional duct cross-section. This particle focusing is due to a balance between inertial lift forces arising from axial flow and drag forces arising from cross-sectional vortices. The inertial particle focusing phenomenon has been exploited in various industrial and medical applications to passively separate particles by size using purely hydrodynamic effects. A fixed size particle in a circular duct with a uniform rectangular cross-section can have a variety of particle attractors, such as stable nodes/spirals or limit cycles, depending on the radius of curvature of the duct. Bifurcations occur at different radii of curvature, such as pitchfork, saddle-node and saddle-node infinite period (SNIPER), which result in variations in the location, number and nature of these particle attractors. By using a quasi-steady approximation, we extend the theoretical model of Harding et al. (J. Fluid Mech. , vol. 875, 2019, pp. 1–43) developed for the particle dynamics in circular ducts to spiral duct geometries with slowly varying curvature, and numerically explore the particle dynamics within. Bifurcations of particle attractors with respect to radius of curvature can be traversed within spiral ducts and give rise to a rich nonlinear particle dynamics and various types of tipping phenomena, such as bifurcation-induced tipping (B-tipping), rate-induced tipping (R-tipping) and a combination of both, which we explore in detail. We discuss implications of these unsteady dynamical behaviours for particle separation and propose novel mechanisms to separate particles by size in a non-equilibrium manner. [ABSTRACT FROM AUTHOR]

The clustering of debris floating on liquid interfaces such as water surfaces is a complex phenomenon that finds its applications in numerous examples from industrial processing and environmental systems. The recent paper by Shin & Coletti (J. Fluid Mech. , vol. 984, 2024, R7) presents an experimental campaign investigating the three effects of turbulence, particle interactions and interfacial effects, to elucidate how the three force scales drag, capillary forces and lubrication give rise to three distinct regimes of clustering in dense suspensions. The study, hence, provides a useful systematic to categorize the clustering mechanisms. As an important finding, it is shown that, depending on volume fraction and non-dimensional turbulent shear, particles either tend to cluster into aggregate sizes larger than the Kolmogorov scale or can break into pieces that are as small as the primary particle size. [ABSTRACT FROM AUTHOR]

This study presents a computational analysis of fluid flow characteristics around two staggered arranged square cylinders using the Lattice Boltzmann Method (LBM). With Reynolds number (Re) fixed at 200, numerical simulations explore the influence of varying gap ratios (G) ranging from 0 to 10 times the cylinder size. Emphasis is placed on understanding the impact of cylinders spacing on flow structure mechanisms and induced forces. Investigation of fluid flow parameters includes vorticity behavior, pressure streamlines, and variations in drag and lift coefficients alongside the Strouhal number under different values of G. From the results, four distinct flow patterns emerge: single bluff body flow, flip flopping flow, modulated synchronized flow, and synchronized flow, each exhibiting unique characteristics. This study reveals the strong dependence of fluid forces on G, with low spacing values leading to complex vortex structures and fluctuating forces influenced by jet flow effects. At higher spacing values, proximity effects between cylinders diminish, resulting in a smoother periodic flow. The Strouhal number, average drag force and the rms values of drag and lift force coefficients vary abruptly at narrow gaps and become smooth at higher gap ratios. Unlike the tandem and side-by-side arrangements the staggered cylinders arrangement is found to have significant impact on the pressure variations around both cylinders. Overall, this research could contribute to a comprehensive understanding of staggered cylinder arrangements and their implications for engineering applications. [ABSTRACT FROM AUTHOR]

This paper investigates the two-phase flow hydrodynamics of a column flotation operated from a homogeneous to a heterogeneous flow regimes using experimental and computational fluid dynamics (CFD) techniques. Experiments were conducted in a lab scale column flotation of 0.1 m internal diameter and 2.5 m length at various superficial gas velocities using a dual plane electrical resistance tomography (ERT). The mean gas holdup increased from 2 to 18% with the increase in superficial gas velocity from 0.6 to 7.2 cm/s. The gas holdup-based bubble swarm velocity method identified four distinct flow regimes, i.e. homogeneous bubbling regime, narrow discrete bubbling regime, a sustained helical flow regime and churn turbulent flow regime in the column. Further, transient simulations were conducted using a two-fluid model coupled with a population balance model to assess the flow behavior inside the column. Virtual mass, lift and drag forces were incorporated into the model to account for the interphase forces. Numerical simulations predicted mean gas holdup was matching with the experimental data at low gas velocities (<2.4 cm/s), and a marginal deviation was noted at higher gas velocities (>2.4 cm/s). The predicted radial gas holdup profiles were found to change from flatter to parabolic with the increase in gas velocities, i.e. similar to the experiments. The effect of particle size on the rate constant and recovery was estimated with Luttrell and Yoon’s performance model using the particle floatability input data and the two-phase experimental data. The developed CFD model can be useful to optimize the operating and design parameters for efficient operation of the column flotation process. [ABSTRACT FROM AUTHOR]

This investigation studied numerically the aerodynamical effects of different modifications in a model of a common sedan. Four car modifications as spoiler, wing profile spoiler, standard diffuser and curved diffuser and their combinations were reported. Using a three-dimensional sedan model created with Computer-Aided Design software, the modifications are applied and assessed their influence on aerodynamics at speeds ranging from 60 to 120 km/h. The spoiler, wing spoiler, standard diffuser and curved diffuser reducing the lift forces experienced by the vehicle. Three cases, spoiler, wing spoiler, and curved diffuser increase the drag forces Combining a curved diffuser and a spoiler significantly decreases lift forces by an average of 77.8%, albeit with a 15.3% increase in drag forces, by 120 km/h The synergy of a curved diffuser and a wing spoiler achieves a substantial 63.3% reduction of net vertical forces, with only a 7.9% increase in drag forces, by 120 km/h, offering improved control with lesser energy consumption in comparison to other combinations. Results show that modifications, greatly influence airflow interaction, with effects varying by speed. Importantly, the impact of using two modifications is not a simple sum of their individual effects; and it must be assessed thoughtfully alongside airflow alterations. [ABSTRACT FROM AUTHOR]

In this article, the test particle method is used in order to calculate the Cherenkov radiation of runaway electrons. We have applied the dielectric tensor for hot magnetized plasma to derive the wave frequency of Cherenkov radiation due to particle resonance with the warm electrostatic waves. The electric field from the Cherenkov radiation is numerically calculated to model the radiation reaction force as a correction to the Coulomb logarithm in the collisional drag force. Then, the behavior of the correction term in strongly and weakly magnetized regimes is investigated. It is shown that both magnetic field strength and the speed of runaway electrons significantly modify the correction term. [ABSTRACT FROM AUTHOR]

With continuous increase in the train speed, the aerodynamic drag forces of high-speed trains increase sharply in a square relationship. As an important source of train aerodynamic drag, pantograph regions have become the key areas to share the contribution to the train's total drag. Thus, improving the pressure distribution in pantograph regions can be a potential and effective method to reduce train aerodynamic drag. Coleoptera has smooth and hard elytra to protect the hindwings, which provides a new design concept for the pantograph deflectors. Based on the biological pattern of Coleoptera, the geometric shape of pantograph biomimetic elytra (i.e., deflector) was constructed in a three-car group mode. Therefore, four calculation cases were set up, i.e., the original unraised pantograph model, original raised pantograph model, unraised pantograph + deflector model, and raised pantograph + deflector model. A time-dependent numerical method improved delayed detached-eddy simulation (IDDES), first validated by the previous wind tunnel test, was employed to analyze the aerodynamic drag forces in different schemes, and the drag reduction mechanism of deflectors was studied. The results show that although an extra drag force is introduced from the deflector, a larger drag reduction is obtained from the pantograph itself. Thus, the aerodynamic drag of pantograph regions is significantly reduced after installing pantograph deflectors. The air flows over the pantograph region in a smoother way with less blocking effect, and the flow above the deflector is accelerated. After the deflector separately installed on three-car high-speed train models with unraised/raised pantographs, the drag reduction for the unraised/raised pantograph regions can be up to 83.88% and 35.29%, while for a three-car grouping model, it can be achieved by 10.76% and 4.49%, respectively. [ABSTRACT FROM AUTHOR]

The suspension of porous particles in fluids occurs widely in various natural and industrial processes. However, the sedimentation behavior of porous particles is not extensively understood as the solid impermeable counterparts. In this work, the drafting–kissing–tumbling (DKT) phenomenon in a narrow channel containing porous particles is investigated by the multi-relaxation-time (MRT) lattice Boltzmann method (LBM). The initial particle spacing L p * (1.5 ∼ 6) and Darcy number Da (8 × 10 − 6 ∼ 6 × 10 − 2 ) are examined on the sedimentation process of two particles under three initial arrangements, i.e., the trailing particle is porous (case 1), the leading particle is porous (case 2), and both the particles are porous (case 3). The results show that the presence of porous particles can enhance the interactions between two particles, and increasing the penetrability reduces the particle drag force to accelerate sedimentation. The drafting time is insensitive to Da at small L p * , and it decreases with Da at large L p * in cases 1 and 3 while it changes to increase with Da in case 2. A phase diagram with respect to Da and L p * is further extracted to identify three sedimentation modes of particle pairs. It is found that the transition between the one-off DKT and repeated DKT modes is not affected by L p * in cases 2 and 3, while the critical condition for the non-DKT and one-off DKT modes depends strongly on Da and L p * in case 2. [ABSTRACT FROM AUTHOR]

This study investigates the dynamic characteristics of suspended particles in a free field under the influence of a single cavitation bubble. The phenomenon of suspended particles being influenced by cavitation bubbles of comparable size reflects the dynamic characteristics of particles, a common occurrence in both hydraulic machinery and biopharmaceutical fields. A high-speed camera captures the process of a single cavitation bubble interacting with suspended particles. Combined with three-dimensional numerical simulations, the motion states of suspended particles as the cavitation bubble expands and contracts are analyzed. Observations reveal that at various initial distances between suspended particles and the cavitation bubble, suspended particle motion is consistently influenced by the expansion and contraction of the same cavitation bubble during the initial four processes. The particle motion direction is parallel to the propagation direction of the radiation force produced during the expansion and collapse of the cavitation bubble, consistent with the characteristics of motion under longitudinal wave effects. The initial distance between suspended particles and the cavitation bubble dictates the ultimate displacement direction of suspended particles, with the influence of the cavitation bubble on suspended particle velocity weakening as their distance increases. Under conditions where particle size closely matches that of the bubble, the jet produced by the cavitation bubble does not significantly accelerate particles, and the influence of the jet on suspended particle motion states could be disregarded. The investigation reveals that the suspended particles are primarily influenced by the radiation force, drag force, and virtual mass force exerted by the cavitation bubble. [ABSTRACT FROM AUTHOR]

When undergoing deformation, elastoviscoplastic fluids exhibit simultaneous viscous, elastic, and plastic characteristics. This study presents an extensive numerical investigation into how the combined elasticity and plasticity of such fluids influence the flow dynamics past a circular cylinder in the laminar vortex-shedding regime. By varying dimensionless numbers, such as the Weissenberg and Bingham numbers, this study elucidates their effects on various fluid-mechanical aspects, including streamlines, vorticity, drag and lift forces, and vortex-shedding frequency. The results show significant differences in the vortex street length, width, and shedding frequency downstream of the cylinder when both fluid elasticity and plasticity are present, compared to Newtonian fluids or fluids with only elasticity under the same flow conditions. Notably, flow field fluctuations are suppressed as fluid elasticity increases, an effect further accentuated by the introduction of fluid plasticity. These rheological behaviors also have a pronounced effect on the drag and lift forces acting on the cylinder. In particular, the drag forces increase with the Weissenberg and Bingham numbers while lift forces decrease. Furthermore, this study conducts the dynamic mode decomposition (DMD) analysis, a widely used reduced order modeling technique, to obtain insights into the coherent flow structures associated with the time-resolved vorticity fields for various fluids. This analysis uncovers hidden differences in the downstream vorticity structures of various fluid types using only a few DMD modes, differences that are not apparent from simple vorticity plots alone. Overall, the findings of this study are valuable for manipulating fluid-dynamical aspects, particularly the vortex-shedding phenomenon from bluff bodies, which is observed in many practical applications and natural processes. [ABSTRACT FROM AUTHOR]

A comprehensive study of the nature of micropolar fluid on an unsteady MHD-free convective transference through a perforated sheet is discussed considering the suction and Lorentz's force effects. The corresponding similarity equations of temperature, momentum, concentration, and angular momentum equations have been modified into the non-dimensional similarity equations of the temperature, momentum, concentration, and angular momentum equations by utilizing the similarity technique. The modified equations have been resolved by exerting the shooting technique with the help of the finite difference method (FDM) through MATLAB. The fluid flow is inversely proportional to the changes in micro rotational effect (Δ). The concentration boundary layer gets thinner as the Schmidt number (Sc) advances and hence the concentration of the fluid decreases. Micropolar fluid helps reduce drag forces and also acts as a coolant. The heat transmission rate advances by around 391%, and 110% due to growing amounts of Pr from 0.71 to 7.0, and v 0 from 0.6 to 3.0, respectively. The surface couple stress decays by about 33%, 45%, and 36% due to increasing values of M from 0.6 to 3.6, ∆ from 3.0 to 6.0, and λ from 0.1 to 1.2, respectively. [ABSTRACT FROM AUTHOR]

The electromagnetohydrodynamic (EMHD) has a vital role due to its importance in aerospace and plasma physics, including energy transformation systems in which interaction between the liquid and magnetic field is crucial. Further, micropolar fluids with microstructural slip is used in the lubrication and liquid crystals. From this observation, the current study is conducted to express an EMHD flow of liquid on a microstructural slipped surface. The effects of a uniform heat source/sink (HS/S) with homogeneous and heterogeneous chemical reactions have been incorporated in energy and mass profiles. The governing equations are converted to ordinary differential equations using proper similarity variables. The converted equations are computed by the implementation of Runge–Kutta–Fehlberg (RKF) 4th 5th order with shooting technique. A list of the essential dimensionless constraints and graphs showing how they are affected are provided. The outcome of the problem shows that the electric parameter will improve the velocity but decline the microrotation profile. Further, both heterogeneous and homogeneous reactions have a decreasing concentration. While the heat distribution rate increases with greater magnetic and electric fields, the surface drag force decreases. [ABSTRACT FROM AUTHOR]

This study focuses on the poorly known effect of polar cap patches (PCPs) on the ion‐neutral coupling in the F‐region. The PCPs were identified by total electron content measurements from the Global Navigation Satellite System (GNSS) and the ionospheric parameters from the Defense Meteorological Satellite Program spacecraft. The EISCAT incoherent scatter radars on Svalbard and at Tromsø, Norway observed that PCPs entered the nightside auroral oval from the polar cap and became plasma blobs. The ionospheric convection further transported the plasma blobs to the duskside. Simultaneously, long‐lasting strong upper thermospheric winds were detected in the duskside auroral oval by a Fabry‐Perot Interferometer (FPI) at Tromsø and in the polar cap by the Gravity Recovery and Climate Experiment satellite. Using EISCAT ion velocities and plasma parameters as well as FPI winds, the ion drag acting on neutrals and the time constant for the ion drag could be estimated. Due to the arrival of PCPs/blobs and the accompanied increase in the F‐region electron densities, the ion drag is enhanced between about 220 and 500 km altitudes. At the F peak altitudes near 300 km, the median ion drag acceleration affecting neutrals more than doubled and the associated median e‐folding time decreased from 4.4 to 2 hr. The strong neutral wind was found to be driven primarily by the ion drag force due to large‐scale ionospheric convection. Our results provide a new insight into ionosphere‐thermosphere coupling in the presence of PCPs/blobs. Plain Language Summary: This study investigates how the evolution of the polar cap patches (PCPs) affects the upper layer of the Earth's atmosphere, termed the thermosphere. PCPs are dense patches of charged particles that move from the dayside to the nightside of the high‐latitude ionosphere through the polar cap region. Using the measurements by multiple ground‐based instruments and satellites, this study found that PCPs can enhance the formation of strong upper thermospheric winds. The winds are primarily driven by the ion drag force due to the interactions between charged particles and neutral gases. The results show that because of the arrival of PCPs, which increase the F‐region electron densities in the auroral oval, the ion drag acceleration acting on the neutrals can more than double and the related time constant of the ion drag can be halved. Key Points: Transportation of polar cap patches (PCPs) and their development in the nightside auroral oval was observed by multiple instrumentsVery strong, long‐lasting westward upper thermospheric wind in the duskside oval was associated with large‐scale ionospheric convectionHigh electron density produced by PCPs increases the ion drag force that drives the upper thermospheric wind [ABSTRACT FROM AUTHOR]

The present study uses results of eddy‐resolving numerical simulations to investigate the open channel flow over large clusters of freshwater mussels (Unio elongatulus) partially buried in a rough, gravel bed. The density of the mussels forming the array varies from 26 to 500 mussels/m2. The flow structure is analyzed at large distances from the leading edge of the mussel bed, where the flow can be considered fully developed. The effects of changing the mussel bed density, the filtering discharge, the burial level and the roughness of the bed surface in which mussels are burrowed, are investigated in terms of flow field, turbulent structures, drag forces, and bed shear stresses. It is found that strong interactions occur between energetic eddies generated by the larger gravels on the exposed bed surface and by the mussel shells. Simulations results show that for a burial depth close to 50% and a ratio between the average gravel size and the mussel protruding height of 0.13, the shell induced turbulence becomes dominant for mussel bed densities around 50 mussels/m2. The influence of the bed roughness becomes less relevant with increasing mussel density, as the generation of energetic eddies is mostly controlled by mussel‐to‐mussel interactions. For fixed bed roughness, burial level and filtering velocity, the mean streamwise drag force and the associated drag coefficient for the exposed part of each mussel decrease with increasing mussel density, even if strong variations are observed for individual mussels. For constant mussel bed density and burial level, the mean streamwise drag force and the mean drag coefficient decrease slightly with increasing bed roughness. Increasing the burial level decreases not only the drag forces but also the drag coefficients because of the more streamlined shape of the top of the mussels. Strong active filtering acts toward decreasing the mean streamwise force and the mean drag coefficient. The spanwise drag forces contribute significantly to the total drag force, especially for high mussel bed densities. Based on smooth bed calculations, bed‐averaged shear stresses are reduced in highly dense clusters. Key Points: Mussel‐to‐mussel interactions are important for dense arrays and influence flow structure and turbulenceEddy resolving simulations showed that the effect of bed roughness become less significant with increasing mussel bed densityIn dense clusters of mussels, forces on the shells and bed shear stresses are reduced thus favoring mussel stability [ABSTRACT FROM AUTHOR]

Rare-earth mud and manganese nodules coexist on the seafloor around Minamitorishima Island. To investigate the feasibility of a pulp-lift system that can ensure economic efficiency by pumping manganese using rare-earth mud as the working fluid, we conducted pulp-lift experiments at a head of 5.0 m using a squeeze pump for mortar pumping. In the study, we used carboxymethylcellulose (CMC) as the working fluid, which is a pseudo-plastic fluid like deep muddy seawater. We investigated the effects of the viscosity of the working fluid and the pump pulsation characteristics on lifting. The results revealed that the drag force acting on the pumped ore increased as the fluid became more viscous and the pulsation period became higher, while the reverse flow rate increased due to the negative pulsation pressure. This suggests that there is an optimum value for the viscosity of the working fluid. [ABSTRACT FROM AUTHOR]

As part of the strategy to achieve net-zero Greenhouse Gas (GHG) emissions in international maritime shipping, there is ongoing exploration into the use of wind propulsion systems as auxiliary ship propulsion devices. When considering a rigid sail as the wind propulsion system, evaluating the performance of a single sail is relatively simple. However, assessing the performance of multiple sails is more challenging due to the interference between the sails and between the sails and the hull. In this study, the thrust characteristics of two rigid sails attached to a ship are investigated by using Computational Fluid Dynamics (CFD). This includes considering the interference effects between the sails themselves and between the sails and the hull. The research reveals the innovative optimized angle of attack for maximizing thrust under tailwind conditions. At 150° in relative wind direction, the best performance is achieved with a low angle of attack on the fore side sail and a high angle of attack on the aft side sail. At 180° in relative wind direction, a high angle of attack on the fore side sail and a low angle of attack on the aft side sail yield the best results. Here, a "low" angle of attack means that the lift force is greater than the drag force, while a "high" angle of attack means the drag force is greater than the lift force. In this study, the force in the ship's forward direction is only focused on optimizing the angles of attack of the two sails. However, the side forces caused by the sails are also significant for the ship's sailing conditions. Therefore, future work will involve optimizing the angles of attack under drifting conditions. [ABSTRACT FROM AUTHOR]

An event-triggered neural adaptive cooperative control is proposed for the towing system (TS) with model parameter uncertainties and unknown disturbances. Different from ordinary multi-vessel formation control, the tugs and unactuated offshore platform in the TS are connected together by towlines, and the resultant tension of the towlines serves as the actual drag force for the platform. Initially, based on the radial basis function neural network (RBFNN), an adaptive RBFNN is designed to compensate unknown disturbances and model parameter uncertainties of the TS, and we use minimal learning parameter (MLP) algorithm to reduce the online learning parameters of adaptive RBFNN. Combined with dynamic surface technology and event-triggered control (ETC) mechanism, an event-triggered neural adaptive virtual controller is designed to obtain the desired drag force of the platform. According to the quadratic programming algorithm, the desired drag force is allocated as the desired tensions of towlines. Subsequently, the desired towline length and the desired position information of the tugs are obtained sequentially through the towline model and the position relationship between the tugs and the platform. Then, according to the desired positions of tugs, an event-triggered neural adaptive distributed cooperative controller is designed for achieving the multi-tug towing of the offshore platform. The ETC mechanism is introduced to reduce the communication burden within the TS and the execution frequency of the tugs' thrusters. Finally, the stability of the closed-loop system is proven using the Lyapunov theory, and the ETC mechanism proves that no Zeno behavior occurs. The effectiveness of the ETC mechanism and the MLP-based adaptive RBFNN on the controllers of TS is verified through simulations and comparison analysis. [ABSTRACT FROM AUTHOR]

In automobiles, the cooling system is essential in increasing engine performance. Conventional coolants like water and ethylene glycol have low thermal conductivity. Nanotechnology allows the development of a high thermal conductivity coolant named 'nanocoolant', a colloidal suspension. This study is focused on the effect of nanocoolant size on the radiator, which is also responsible for fuel consumption. To prepare nanocoolant two-step method was used, in which nanoparticles were prepared separately and dispersed in a base fluid under ultrasonic agitation. This research was carried out for the dispersion of Al2O3 in a water-ethylene glycol mixture with volume concentrations of 0%, 0.2%, 0.4% and 0.6%. The experimentation was carried out on 180, 216, 288 and 360 mm tube-length radiators. The experiments were conducted at a coolant inlet temperature 65 °C, air velocity of 1.05 m/s, and volume rate of 4 to 9 litres per minute. The result shows that using 0.2% Al2O3 nanoparticles, the overall heat transfer coefficient was augmented by 43% more than the base fluid. It is also seen that for 0.6% volume fraction nanocoolant, approximately 65% reduction in frontal radiator area is possible, which leads to decrement in the drag force and pumping power. [ABSTRACT FROM AUTHOR]

The present paper develops a new framework to predict the mean flow through an array of cylinders in which the flow around the array (array‐scale) and the flow around individual cylinders (element‐scale) are modeled separately using actuator disc theory and empirical drag models respectively, and then coupled through the net drag force. Applying this framework only requires knowledge of the array geometry and incident flow. The framework is validated using high‐fidelity direct numerical simulations for arrays of between 7 and 109 cylinders having different arrangements (staggered, concentric, random) and bounding shapes (circular, square) in both two‐ and three‐dimensional flows. In general, the framework outperforms existing models which require calibration and are only valid for part of the practical parameter space. The demonstrated scale separation suggests different combinations of element‐scale and array‐scale models/theories may be used for other arrangements of bluff bodies. Plain Language Summary: The temporally and spatially averaged velocity, or mean flow, within an array of cylinders is important for many practical applications including, for example, estimating the rates of sediment transport and nutrient uptake within a patch of aquatic vegetation, the hydrodynamic forces on offshore structures, and the efficiency of power generation with a turbine farm. However, a general predictive tool for mean flow is currently lacking. To develop this predictive capacity, this study uses the idea of scale separation to integrate models from different research fields, including the actuator disc theory originally developed for design of turbines and propellers, and element‐scale drag models initially proposed for aquatic vegetated flows, to develop a unifying, predictive, analytical framework to estimate the mean flow. The framework is validated using high‐fidelity direct numerical simulations of arrays of cylinders with different arrangements (staggered, concentric, random) and array shapes (square, circular). With only knowledge of the array geometry and incident flow, the framework predicts the mean flow exceptionally well across a wide range of practical flow conditions. This leads to a step‐change in our ability to predict the fraction of incoming flow passing through a porous array, hydrodynamic load on offshore structures, and sediment flux within aquatic vegetation systems when combined with bed load transport models. The framework could be an important guide for coastal and riverine restoration projects using aquatic vegetation and the design of offshore structures and turbine farms. Key Points: A predictive framework based on an idea of scale separation is proposed for the mean velocity of the flow passing through an array of cylindersThe framework is versatile, being applicable for a wide range of practically meaningful cylinder arrangements, array shapes and array flow blockagesHigh‐fidelity, three‐dimensional direct numerical simulations are employed to investigate flow through the array of cylinders and validate the new predictive framework [ABSTRACT FROM AUTHOR]

This study presents a semi‐implicit MPM to adequately characterize the mechanical behavior of unsaturated soil based on Biot's mixture theory. To represent the dependency of the degree of saturation on the suction, we employ the VG model along with a soil‐water characteristic curve, which determines a functional form of permeability called the Mualem model. Hencky's hyperelastic model and the Drucker‐Prager model assuming nonassociativity are adopted for elastic and plastic deformations, respectively. The novelty of this study is the incorporation of the fractional‐step method into the MPM framework so that the pore water pressure is obtained by implicitly solving the pressure Poisson's equation, which reduces numerical instability and improves computational efficiency. Also, because the drag force between solid and liquid phases is evaluated using the intermediate velocity of pore water relative to the intermediate velocity of solid skeleton, the time increment can be chosen without considering the magnitude of water permeability. In addition, to suppress "odd‐even" oscillation, we employ a sub‐grid method in which two grids with different spatial resolutions are used for the velocities and pore water pressure. Furthermore, considering the advantages and disadvantages of two different interpolation schemes for pore water pressure, we suggest switching the schemes depending on the model conditions. Several numerical examples are presented to demonstrate the performance of the proposed method. Specifically, unidirectional consolidation and leak flow analyses are performed for verification purposes, followed by validation analysis of a model experiment of infiltration‐induced landslides. [ABSTRACT FROM AUTHOR]

Controlling microrobot locomotion in vessels and capillaries is crucial for precise drug delivery and minimally invasive surgeries. However, this is challenging due to the complex interactions with red blood cells (RBCs) and the difficulty navigating within the dense environment. Here, we construct a numerical framework to evaluate the relative resistance coefficient ( C r * ) of a microrobot propelled through RBC suspensions. Our experiments validate the numerical results. We find that C r * increases for smaller microrobots and higher hematocrit levels, while magnetic force strength weakly impacts C r * . C r * is smaller than the resistance coefficient of a macroscale robot estimated from the apparent viscosity of the RBC suspension. The aspect ratio of a prolate ellipsoidal microrobot influences C r * along its long-axis direction. Additionally, machine learning accurately predicts C r * . These insights could enhance the design and control of microrobots for medical applications. Controlling microrobot movement in blood vessels is vital for medical treatments but is challenging due to red blood cells. This study combines simulations, experiments, and machine learning to demonstrate how hematocrit levels and robot geometry affect its locomotion characteristics in blood [ABSTRACT FROM AUTHOR]

Fluidized bed reactor can enhance mass transfer and increase reaction rate. Numerical simulation helps to optimize fluidized bed reactors. The present paper models the photocatalytic oxidation of 2,4-dichlorophenoxy acetic acid in a fluidized bed reactor using the Eulerian-Eulerian model. The drag models have influences on the distribution of catalysts particles. The bed expands under the fluid flow and reaches a quasi-steady height at approximately 3s. The asymmetric distribution of catalysts with respect to the axis plane is predicted. The Gidaspow model predicts the nearly same bed expansion with the experimental data, whereas the Syamlal-O ′ Brien model overestimates it. The simulation results at two pH values are in accordance with the experimental data. The removal in the continuous stirred tank reactor decreases with the increase in flow rate. [ABSTRACT FROM AUTHOR]

When the high-speed elevator is running, the air in the hoistway is rapidly compressed and released to form the piston effect. Especially when the car and counterweight intersect, the piston effect makes the aerodynamic force of the car and counterweight change sharply, affecting the stability of elevator operation. In this study, a three-dimensional car counterweight intersection model is constructed, and a multi-region dynamic layered method is proposed to calculate the aerodynamic flow field in the whole moving process, the changes of aerodynamic drag force and aerodynamic lateral force of the car and the counterweight under different length ratio, blockage ratio and spacing are analyzed and simulated, and the influence of structural changes in the hoistway on the aerodynamic flow field is studied. Furthermore, the accuracy of the numerical results is verified by the real elevator test. Finally, the results show that when the car intersects the counterweight in the hoistway, the interaction between the car and the counterweight is enhanced, and the drag force coefficient and lateral force coefficient of the car suddenly change, and return to the normal state after the intersection, with the decrease of length ratio and spacing and the increase of blockage ratio, the sudden change degree of drag force also increases, and the sudden change of lateral force of the car is mainly affected by the car counterweight spacing, and increases with the decrease of spacing. [ABSTRACT FROM AUTHOR]

The accurate assessment of hydraulic transmissivity in rock fractures filled with particles is not only a scientific challenge but also a critical need for various industrial applications. However, the intricate dynamics of particle erosion and pore clogging that govern transmissivity evolution remain largely unexplored. In this study, we experimentally examine the fluid‐driven particle migration behavior in filled fractures and its consequent impact on fracture transmissivity under various hydraulic gradients, normal stresses, and fracture apertures. We find that escalating hydraulic gradients not only intensify particle erosion through amplified fluid drag forces and hydro‐mechanical coupling effects but also lead to an increase in the size of migrating particles, thereby augmenting pore clogging. The dynamics of erosion and clogging define four distinct migration phases within the filled fractures. Variations in normal stress and initial fracture aperture significantly alter the particle arrangement and the soil structure stability within the fractures, thereby modulating the progress of particle migration in response to hydraulic gradients. The pattern of particle migration in filled fractures dictates the development of the internal pore structure and normal deformation, ultimately affecting fracture transmissivity. We propose an empirical expression to encapsulate the comprehensive evolution of fracture transmissivity across different particle migration patterns. Our research advances the understanding of fluid‐driven particle migration within filled fractures and provides a practical tool for the precise determination of hydraulic properties of fractured rocks amidst complex geological settings. Plain Language Summary: Filled fractures in rock masses, serving as dominant flow channels and potential failure planes, are typically perceived to exhibit constant hydraulic transmissivity. However, this perspective oversimplifies the dynamic nature of filled fractures, where fluid flow can greatly change the hydraulic characteristics by either eroding or accumulating the internal particles. Understanding how these filling particles respond to water flow and affect fracture transmissivity is vital for many geological processes and human activities. Here, we experimentally uncover four distinct phases of particle migration within a filled fracture, instigated by the dynamics of erosion and clogging under elevated hydraulic gradients. Variations in normal stress and fracture aperture significantly influence the particle arrangement and the soil structure stability within fractures, thereby affecting particle migration characteristics across phases. On this basis, we delve into how the patterns of particle migration impact the geometric structure of the filled fracture and, thus, the fracture transmissivity. Finally, we quantitatively portray the evolution in fracture transmissivity across various particle migration scenarios using an empirical model. Our findings enhance the understanding of fluid‐driven particle migration in filled fractures and provide a path forward for accurately assessing the hydraulic properties of fractured rocks in complex geological environments. Key Points: Erosion and clogging dynamics, modulated by hydraulic gradients, define four particle migration phases in stressed‐filled fracturesParticle migration patterns dictate pore structure and normal deformation, impacting fracture transmissivityAn empirical model encapsulates fracture transmissivity evolution across different particle migration patterns [ABSTRACT FROM AUTHOR]