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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]

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]

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]

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]

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]

Understanding the agglomeration behavior between inclusions during steelmaking is crucial to control steel quality and cleanliness. This work reviews the state-of-the-art lateral capillary interaction between inclusions attached to the gas/steel or slag/steel interfaces, which is an essential aspect of inclusion agglomeration. The origin of the lateral capillary force, the methodologies to measure the force, and the development of the capillary theory are discussed. High-temperature confocal scanning laser microscopy (CSLM) has been intensively used for the in situ observation of inclusion agglomeration at the gas/steel or slag/steel interfaces. To calculate the lateral capillary force between inclusions from a series of 2D CSLM images, the particle mass, the inter-particle distance, and the drag force on the inclusions are the main input parameters. We compared the capillary force between two ellipsoidal particles obtained from different particle radius approximations (long and short radii, arithmetic mean, equivalent and effective radius, and equivalent volume), separation distances (inter-center and inter-surface), and capillary models (Yin's, Chan's, Mu's, K–P, and sub-particle models). The results highlight the importance of consistency in the parameters used in the force calculation from CSLM images and capillary models. [ABSTRACT FROM AUTHOR]

Feeding strip significantly enhances continuous cast slab quality. To clarify its impact on inclusion distribution, a mathematical model coupling flow, solidification and inclusion motion have been developed. The upper recirculation, lower recirculation, and unformed recirculation flow occur during continuous casting. Under the resultant forces of drag, virtual mass, pressure gradient, Saffman, gravity, buoyancy, etc., the inclusion motion can be divided into two stages: Injection and Split flow. Feeding strip mainly affects inclusion motion by altering the drag, virtual mass, pressure gradient, and Saffman forces, which are closely related to the molten steel flow. After feeding strip, the lower recirculation on the strip feeding side is compressed, while it on the no-feeding side is expanded. The unformed recirculation flow on strip feeding side squeezes the flow below lower recirculation on no-feeding side. A higher strip feeding speed promotes downward inclusion motion, increasing the chance of being captured between the slab edge and strip. Unformed recirculation flow guides inclusions on the no-feeding side toward the slab edge, while expanded flow directs them toward the center. Consequently, inclusions on strip feeding side gradually gather between slab edge and quarter, while inclusions on no-feeding side first gather toward center and then toward edge of slab with increased strip feeding speed. [ABSTRACT FROM AUTHOR]

Coronaviruses being capable of spreading through droplet contamination have raised significant concerns regarding high-capacity public rail transport, such as the metro. Within a rapidly moving railcar cabin, the internal airflow lags behind the bulkhead, generating internally induced airflow that accelerates droplet dispersion within a non-inertial reference system. This study investigates the impact of acceleration on the diffusion of cough droplets of varying sizes using computational fluid dynamics. The modified k–ε equation in ANSYS® Fluent was utilized to simulate droplet diffusion under different body orientations by adjusting the inertial force correction source term. Results indicate that droplets in the middle size range (50–175 μm) are primarily influenced by inertial forces, whereas smaller droplets (3.5–20 μm) are predominantly controlled by air drag forces. Regardless of facial orientation, the outlet of high-capacity public rail transport poses the highest risk of infection. [ABSTRACT FROM AUTHOR]

A novel volume of fluid method is presented for mineral precipitation coupled with fluid flow and reactive transport. The approach describes the fluid-solid interface as a smooth transitional region, which is designed to provide the same precipitation rate and viscous drag force as a sharp interface. Specifically, the governing equation of mineral precipitation is discretized by an upwind scheme, and a rigorous effective viscosity model is derived around the interface. The model is validated against analytical solutions for mineral precipitation in channel and ring-shaped structures. It also compares well with interface tracking simulations of advection-diffusion-reaction problems. The methodology is finally employed to model mineral precipitation in fracture networks, which is challenging due to the low porosity and complex geometry. Compared to other approaches, the proposed model has a concise algorithm and contains no free parameters. In the modeling, only the pore space requires meshing, which improves the computational efficiency especially for low-porosity media. [ABSTRACT FROM AUTHOR]

The present-day lithospheric stress state of the Qinghai-Tibetan Plateau and neighboring areas is controlled by both the lithosphere itself and the underlying mantle. In other words, the stress is affected by the gravitational potential energy (GPE) difference caused by the change in the density distribution within the lithosphere and the drag force on the base of the lithosphere caused by mantle convection. The study of the lithospheric stress state plays an important role in further understanding the dynamic background and mechanism for the evolution of the Qinghai-Tibetan Plateau. In this study, the Crust1.0 crustal density model combined with the S40RTS mantle shear wave velocity variation model was used to calculate the GPE. The EGM2008 gravity field model was used to calculate the drag force from mantle convection at the base of the lithosphere. The lithospheric and joint stress fields of the two sources were obtained by solving the force balance under the thin sheet approximation. This way, we could comprehensively analyze the characteristics of the stress state within the Plateau. Six regions were classified according to the GPE stress field, mantle drag force stress field, the relative magnitude of the two stress fields, and correlation between the two stress fields and surface deformation. The lithospheric stress fields of the Tarim Basin and other stable blocks are mainly controlled by the GPE difference. The lithospheric stress field in the collision zone between the Indian Plate and the Qinghai-Tibetan Plateau is predominantly controlled by the deep mantle drag force. The lithospheric stress field in the interior of the Plateau is controlled by both GPE and mantle drag. The correlation between the lithospheric stress field and surface deformation at the southeast margin of the Qinghai-Tibetan Plateau is poor. It is hypothesized that the presence of lower crustal flow with lower effective viscosity leads to crust-mantle decoupling, and the mantle drag force has a weaker influence on the shallow crust, resulting in the inconsistency between the average lithospheric stress field and surface deformation. [ABSTRACT FROM AUTHOR]

We present an experimental realisation of spatial spanwise forcing in a turbulent boundary layer flow, aimed at reducing the frictional drag. The forcing is achieved by a series of spanwise running belts, running in alternating spanwise direction, thereby generating a steady spatial square-wave forcing. Stereoscopic particle image velocimetry in the streamwise–wall-normal plane is used to investigate the impact of actuation on the flow in terms of turbulence statistics, drag performance characteristics, and spanwise velocity profiles, for a non-dimensional wavelength of λ x + = 397 . In line with reported numerical studies, we confirm that a significant flow control effect can be realised with this type of forcing. The scalar fields of the higher-order turbulence statistics show a strong attenuation of stresses and production of turbulence kinetic energy over the first belt already, followed by a more gradual decrease to a steady-state energy response over the second belt. The streamwise velocity in the near-wall region is reduced, indicative of a drag-reduced flow state. The profiles of the higher-order turbulence statistics are attenuated up to a wall-normal height of y + ≈ 100 , with a maximum streamwise stress reduction of 45% and a reduction of integral turbulence kinetic energy production of 39%, for a non-dimensional actuation amplitude of A + = 12.7 . An extension of the classical laminar Stokes layer theory is introduced, based on the linear superposition of Fourier modes, to describe the non-sinusoidal boundary condition that corresponds to the current case. The experimentally obtained spanwise velocity profiles show good agreement with this extended theoretical model. The drag reduction was estimated from a linear fit in the viscous sublayer in the range 2 ≤ y + ≤ 5 . The results are found to be in good qualitative agreement with the numerical implementations of Viotti et al. (Phys Fluids 21, 2009), matching the drag reduction trend with A + , and reaching a maximum of 20%. [ABSTRACT FROM AUTHOR]

Fully resolved direct numerical simulations are used to quantify the effect of evolving heat, due to idealized smoldering processes, on the aerodynamic forces of a spherical particle, representing an idealized fixed-shape firebrand particle. Firebrand particles are small glowing particles that are generated in fires and can be transferred long distances by the wind and create new spot fires. Understanding the transport of firebrands is of great importance in fire science. The simulations are performed at a Reynolds number of 500, relevant for a wide range of firebrand size and wind velocity combinations. The spatiotemporal variation of temperature over the surface of the particle is obtained using a detailed surface energy balance analysis. The firebrand particle is assumed to have the thermal and material properties of pine needles and has a Biot number larger than unity, which means that the particle undergoes notable internal temperature gradients. The results indicate that the buoyancy-induced flow around the particle significantly modifies the trailing vortices and produces two non-interacting tunnel-shaped plumes in the wake of the sphere as the particle's Richardson number increases. As a result, the particle's drag and lift coefficients show large deviations from those of a non-heated particle and an isothermal particle. The increased surface temperatures result in an increase in the drag force while inducing a negative lift. The significant variations seen in the aerodynamic forces as a function of the particle's instantaneous temperature indicate that the influence of the transient thermal conditions of firebrands should be considered in the prediction of the particles' trajectory and landing spots. [ABSTRACT FROM AUTHOR]

In this paper, we employ the gauge/gravity duality to study some features of the quark–gluon plasma. For this purpose, we implement a holographic QCD model constructed from an Einstein–Maxwell-dilaton gravity at finite temperature and finite chemical potential. The model captures both the confinement and deconfinement phases of QCD and we use it to study the effect of temperature and chemical potential on a heavy quark moving through the plasma. We calculate the drag force, Langevin diffusion coefficients and also the jet quenching parameter, and our results align with other holographic QCD models and the experimental data. [ABSTRACT FROM AUTHOR]

Under extreme climate conditions, such as heavy precipitation, glacial lake outbursts, and ice and snow melting, the long runout flow-like landslide with mixed solid–liquid two-phase has become one of the most disastrous types in the world. Numerical simulation is one of the most important means in disaster prevention and mitigation work for this type of landslide. In this study, a new full three-dimensional landslide post-failure numerical platform (LPF3D) was proposed. This method serves as a bridge between continuum-medium algorithms and discrete-medium algorithms based on the same theoretical numerical framework of smoothed particle hydrodynamics (SPH). This computational model employs an elastic-viscoplastic constitutive law and basal resistance of frictional model for the solid grain phase, and the fluid phase is treated as a Newtonian fluid. A drag law describes the interaction stress between fluid and grain. The boundary normal forces were applied using the penalty function method to ensure the stability of the algorithm. Comparison analyses of small-scale flume experiments and realistic-scale landslide cases and different numerical methods were performed to show that this numerical modeling is capable of simulating mixed two-phase flow. This new method realizes the actual physical and mechanical action process of mixed two-phase flow with higher computational efficiency, and is an appropriate benchmark for the post-failure risk forecasting and assessment of long runout flow-like landslide. [ABSTRACT FROM AUTHOR]

We explored the gravity dual of a rotating quark-gluon plasma by transforming the boundary coordinates of the large black hole limit of Schwarchild-AdS5 metric. The Euler-Lagrange equation of the Nambu-Goto action and its solution become more complex than those without rotation. For small angular velocity, we obtained an analytical form of the drag force acting on a quark moving in the direction of the rotation axis and found it stronger than that without rotation. We also calculated the heavy quark potential under the same approximation. For the quarkonium symmetric with respect to the rotation axis, the depth of the potential is reduced by the rotation. For the quarkonium oriented in parallel to the rotation axis, the binding force is weakened and the force range becomes longer. We also compared our holographic formulation with others in the literature. [ABSTRACT FROM AUTHOR]

Sills and baffles are appurtenances used to stabilize hydraulic jump in a stilling basin. The force acting on these appurtenances are characterized by the drag coefficient (CD). This paper describes experimental methods carried out in a rectangular channel to analyze the drag characteristics of sill and baffles in free (unsubmerged) and submerged hydraulic jumps. The sills and baffles were designed as per the USBR type III stilling basin guidelines. A calibrated loadcell connected to an Arduino board was used to measure the drag force. Errors in measurements are limited to 1%. The drag co-efficient was obtained for different Froude numbers (F1=U1/√gy1) pertaining to strong jump (4.5–9) for different relative position of sills (xS/y2) and baffles (xb/y2) from the nozzle of the sluice gate. Both forced (unsubmerged) and submerged jumps were investigated. It is seen that the drag coefficient of appurtenances in submerged jumps were lower than those in free jumps. This may be attributed to the reduction in wake size in submerged jumps. Comparisons of the experimental results of the sill with the previous theoretical studies are reasonable. [ABSTRACT FROM AUTHOR]

Appropriate interaction between pantograph and catenary is imperative for smooth operation of electric trains. Changing heights of overhead lines to accommodate level crossings, overbridges, and tunnels pose significant challenges in maintaining consistent current collection performance as the pantograph aerodynamic profile, and thus aerodynamic load changes significantly with operational height. This research aims to analyse the global flow characteristics and aerodynamic forces acting on individual components of an HSX pantograph operating in different configurations and orientations, such that the results can be combined with multibody simulations to obtain accurate dynamic insight into contact forces. Specifically, computational fluid dynamics simulations are used to investigate the pantograph component loads in a representative setting, such as that of the recessed cavity on a Class 800 train. From an aerodynamic perspective, this study indicates that the total drag force acting on non-fixed components of the pantograph is larger for the knuckle-leading orientation rather than the knuckle-trailing, although the difference between the two is found to reduce with increasing pantograph extension. Combining the aerodynamic loads acting on individual components with multibody tools allows for realistic dynamic insight into the pantograph behaviour. The results obtained show how considering aerodynamic forces enhance the realism of the models, leading to behaviour of the pantograph–catenary contact forces closely matching that seen in experimental tests. [ABSTRACT FROM AUTHOR]

Vertically-aligned carbon nanotube (VaCNT) membranes allow water to conduct rapidly at low pressures and open up the possibility for water purification and desalination, although the ultralow viscous stress in hydrophobic and low-tortuosity nanopores prevents surface interactions with contaminants. In this experimental investigation, steroid hormone micropollutant adsorption by VaCNT membranes is quantified and explained via the interplay of the hydrodynamic drag and friction forces acting on the hormone, and the adhesive and repulsive forces between the hormone and the inner carbon nanotube wall. It is concluded that a drag force above 2.2 × 10−3 pN overcomes the friction force resulting in insignificant adsorption, whereas lowering the drag force from 2.2 × 10−3 to 4.3 × 10−4 pN increases the adsorbed mass of hormones from zero to 0.4 ng cm−2. At a low drag force of 1.6 × 10−3 pN, the adsorbed mass of four hormones is correlated with the hormone−wall adhesive (van der Waals) force. These findings explain micropollutant adsorption in nanopores via the forces acting on the micropollutant along and perpendicular to the flow, which can be exploited for selectivity. Micropollutant removal in polymeric nanofiltration membranes is difficult to characterise due to pore heterogeneity. A force interplay framework was developed to describe adsorption in VaCNT membranes with defined nanopores, providing insight for the design of membranes with improved selectivity. [ABSTRACT FROM AUTHOR]

Current parameterizations of the hydrodynamic forces on irregular particles consider some shape dependencies, but lack an explicit dependence on the orientation with respect to the flow. In this paper, we propose a new parameterization of the drag and lift forces acting on whole Limpet shells at arbitrary orientations with respect to the direction of flow through the linear regression of fluid forces against the velocity components in an object frame of reference. The fluid forces were estimated using boundary layer-resolving Reynolds-averaged Navier-Stokes (RANS) simulations. We verified the accuracy of the shear stress transport (SST) k - ω turbulence model on flat plates with varying angles of attack, and we achieved coefficients of determination versus existing data of approximately 0.95 for both the drag and lift coefficients. From the linear regression of our simulated force data, we developed a model as a function of 3-dimensional orientations to predict the hydrodynamic forces acting on a Limpet shell with coefficients of determination of 0.80 for normal forces and 0.51 for longitudinal forces. [ABSTRACT FROM AUTHOR]

Overtopping failure of earthfill dams is a complex process that involves strong soil–water coupling and structural failure. Physically based numerical models are essential for characterizing the breach mechanism and the failure process. In this study, a dam-break model that considers the combined effects of seepage and overflow is proposed. This model simultaneously solves the governing equations for solid and fluid phases in two different sets of Lagrangian particles. The coupling between water and soil are, respectively, modelled with SPH and DEM particles by considering their interactions, including drag force, buoyancy and particle adhesion. The capillary force caused by the meniscus between soil particles is incorporated to characterize the saturation degree of the soil. The dam-break model is validated by simulating seepage through an earth dam, a small-scale dam-break test, and dam erosion progress. Finally, the proposed model is employed to simulate the overtopping failure of an earthfill dam. Numerical simulations show that the proposed numerical model is capable for capturing the salient features of dam breach. Moreover, some other soil–water coupling processes, such as reservoir water infiltration, dam slope erosion and collapse, breach development, and dam failure, can be predicted by this model as well. [ABSTRACT FROM AUTHOR]

One challenge of current biosensors is to remove non-specifically bound (NSB). Surface acoustic wave (SAW) technology, because of its non-contact and non-marker characteristics, becomes one of the hot research fields and shows great prospects. In this paper, SAW is used to remove NSB. Firstly, the effect of the cut of the piezoelectric material on the removal force is determined based on the dispersion equation of the acoustic wave and the properties of the piezoelectric material. Secondly, the effects of channel height, excitation voltage and fluid medium temperature on the removal process are verified through theoretical calculations. The results show that the SAW force, lift force and drag force induce by the SAW can effectively remove the NSB, among which, SAW force mainly removes the nonspecifically bound from sensor surface, while the lift force and drag force mainly prevent the re-deposition of the removed NSB. Finally, the optimal region where NSB can be removed effectively by SAW is determined by comparing the SAW force and van der Waals force. When the sensing region is located in the optimal region, not only can the NSB be effectively removed, but also the performance of the sensor is guaranteed. [ABSTRACT FROM AUTHOR]

One of the beach protection techniques is using natural methods based on the coastal ecosystem. Studies show the reducing effect of forest covers on wave destruction intensity in different areas. However, it is not yet well understood how various densities of terrestrial coastal forest (TCF) affect the wave attenuation and reduce their strength. Studying the impact of various forest parameters, such as density, distance, and arrangement type on the wave force attenuation, this research measures the wave forces directly. TCF model was installed in a knife edge flume, which equipped with a load cell and an acoustic Doppler velocimeter. The experiments were performed in two staggered and parallel arrangements consisting of different densities from 12 to 273 stems per unit area. Based on obtained results, TCF had significant effects on the wave force absorption. An increase in the number of trees (density) increased TCF resistance force and the absorbed wave force. In its best, the TCF could absorb the wave force 3.76 times more than the no-TCF case. It could reduce the wave height by up to 81% at the highest density and maximum wave height. The absorbed wave force and drag coefficient rose as the number of rows of trees opposing the flow decreased and the intervals between trees were shortened. Increasing tree density from 12 to 273 stems per unit area increased the drag coefficient by the average of 61.82% for parallel and staggered arrangements, which means an average increase of 9.7% for each TCF row. [ABSTRACT FROM AUTHOR]

The development of 3D spiral microfluidics has opened new avenues for leveraging inertial focusing to analyze small fluid volumes, thereby advancing research across chemical, physical, and biological disciplines. While traditional straight microchannels rely solely on inertial lift forces, the novel spiral geometry generates Dean drag forces, eliminating the necessity for external fields in fluid manipulation. Nevertheless, fabricating 3D spiral microfluidics remains a labor-intensive and costly endeavor, hindering its widespread adoption. Moreover, conventional lithographic methods primarily yield 2D planar devices, thereby limiting the selection of materials and geometrical configurations. To address these challenges, this work introduces a streamlined fabrication method for 3D spiral microfluidic devices, employing rotational force within a miniaturized thermal drawing process, termed as mini-rTDP. This innovation allows for rapid prototyping of twisted fiber-based microfluidics featuring versatility in material selection and heightened geometric intricacy. To validate the performance of these devices, we combined computational modeling with microtomographic particle image velocimetry (μTPIV) to comprehensively characterize the 3D flow dynamics. Our results corroborate the presence of a steady secondary flow, underscoring the effectiveness of our approach. Our 3D spiral microfluidics platform paves the way for exploring intricate microflow dynamics, with promising applications in areas such as drug delivery, diagnostics, and lab-on-a-chip systems. [ABSTRACT FROM AUTHOR]

Marine mammals host a great variety of parasites, which usually co-evolved in evolutionary arms races. However, little is known about the biology of marine mammal insect parasites, and even less about physical aspects of their life in such a challenging environment. One of 13 insect species that manage to endure long diving periods in the open sea is the seal louse, Echinophthirius horridus, parasitising true seals. Its survival depends on its specialised adaptations for enduring extreme conditions such as hypoxia, temperature changes, hydrostatic pressure, and strong drag forces during host dives. To maintain a grip on the seal fur, the louse's leg morphology is equipped with modified snap hook claws and soft pad-like structures that enhance friction. Through techniques including CLSM, SEM, and histological staining, we have examined the attachment system's detailed structure. Remarkably, the seal louse achieves exceptional attachment forces on seal fur, with safety factors (force per body weight) reaching 4500 in average measurements and up to 18000 in peak values, indicating superior attachment performance compared to other insect attachment systems. These findings underscore the louse's remarkable adaptations for life in a challenging marine environment, shedding light on the relationship between structure and function in extreme ecological niches. A biomechanical study on the attachment performance of seal lice suggests that the lice use modified snap hook claws and soft pad-like structures to generate exceptionally high attachment forces on the surface of their hosts. [ABSTRACT FROM AUTHOR]

Horizontal penetration in granular media is ubiquitous, from tunneling and geotechnical site investigation, to root growth and the locomotion of burrowing animals in nature. This contribution couples the discrete element method (DEM) with ant colony optimisation, a heuristic optimisation algorithm, to find the optimal tip shapes to minimise drag and lift forces during horizontal penetration. The tip which minimizes drag has a slender profile with a low tip curvature, to give a drag force that is 15.6 % lower compared to a conventional CPT intruder, however this shape induces a downwards force that increases with intruder depth. Conversely, the tip that minimizes lift is blunt, with a high tip curvature and short width, and reduces the drag and lift forces by 4.5 % and 30.8 % (respectively) compared to the CPT. The lift and drag forces are competing optimisation objectives, thus the tip shape with the optimal trade-off between drag and lift forces can be established using Pareto optimality. The Pareto optimal tip shape reduces the drag and lift forces by 10.7 % and 19.4 % respectively, and is strikingly similar to the profile of a sandfish. This contribution shows that when a common goal exists, bio-inspired solutions can offer an optimal solution to engineering applications. We also show the potential to integrate DEM simulations within an optimization framework to develop innovative design solutions. [ABSTRACT FROM AUTHOR]

For a power-law elliptical body, the drag force in a high-speed rarefied gas flow is calculated based on several local models. By solving the variational problem, the exponent in the generatrix for a minimum drag body of various aspect ratio is determined depending on the ellipticity coefficient. [ABSTRACT FROM AUTHOR]

To adhere their silk threads for the construction of webs and to fix the dragline, spiders produce attachment discs of piriform silk. Uniquely, the aquatic spider Argyroneta aquatica spends its entire life cycle underwater. Therefore, it has to glue its attachment discs to substrates underwater. Here we show that Argyroneta aquatica applies its thread anchors within an air layer around the spinnerets maintained by superhydrophobic setae. During spinning, symmetric movements of the spinnerets ensure retaining air in the contact area. The flat structure of the attachment discs is thought to facilitate fast curing of the piriform adhesive cement and improves the resistance against drag forces. Pull-off tests on draglines connected with attachment discs on different hydrophilic substrates point to dragline rupture as the failure mode. The Young´s modulus of the dragline (8.3 GPa) is within the range as in terrestrial spiders. The shown structural and behavioral adaptations can be the model for new artificial underwater gluing devices. Multiple behavioral and functional adaptations enable the unique water living spider Argyroneta aquatica to apply its silk attachment discs for anchoring its dragline within an air layer around its spinnerets under water. [ABSTRACT FROM AUTHOR]

In this study, a new approach based on dielectric barrier discharge (DBD) plasma was used to fabricate super-buoyant dielectric materials for drag-reduction. We used a glass slide as a high-density substrate for buoyancy tests and a model boat made from Polymethyl methacrylate (PMMA) for drag-reduction experiments. In the first step, an atmospheric pressure DBD plasma was used for the deposition of the hydrogenated amorphous carbon (a-C:H) film using argon working gas and toluene precursors. The layer characterizations were performed versus the plasma deposition time by FE-SEM, AFM, FTIR, and Raman analysis. The morphological characterizations showed the formation of some micro and nanostructures on the surface followed by an increase in surface roughness. Moreover, the chemical characterizations suggested the successful formation of a-C:H film. In the next step, the effect of the deposited layer was assessed on the buoyance and drag reduction. Based on the results, the plasma coating produced a super-buoyant glass slide with remarkable load-bearing capacity, high durability, and robustness. In addition, the drag force was reduced noticeably after the plasma treatment. The results of this study promise the use of atmospheric pressure plasma for the fabrication of super-buoyant surfaces for buoyancy applications. [ABSTRACT FROM AUTHOR]

This study utilized 3D Large-eddy simulation to investigate the crosswind drag force on a square cylinder subjected to transverse wind fluctuation. Two distinct methods were employed to generate the fluctuation: a prescribed sine function at the inlet boundary and an upwind barrier. The frequency was normalized in the same Strouhal number form. The transverse wind fluctuation with a normalized frequency above 0.05 tends to excite the square cylinder transversely with the same frequency band. The frequency effect also exists on the square cylinder located downwind an obstacle half the square cylinder's size. However, an obstacle 2.5 times the size of the square cylinder generates a cross-wind fluctuation with the normalized frequency of 0.04, which cannot excite the square cylinder transversely. The frequency effect from the upwind barrier significantly dampens with the distance and disappears at 8–10 times the square cylinder size. [ABSTRACT FROM AUTHOR]

This contribution aims to optimize nonlinear thermal flow for Darcy-Forchheimer Maxwell fuzzy Al 2 O 3 + Cu + TiO 2 /EO tri-hybrid nanofluid flow across a Riga wedge in the context of boundary slip. Three types of nanomaterials, Al 2 O 3 , Cu and TiO 2 have been mixed into the basic fluid known as engine oil. Thermal properties with the effects of porous surface and nonlinear convection have been established for the particular combination Al 2 O 3 + Cu + TiO 2 /EO. Applying a set of appropriate variables, the set of equations that evaluated the energy and flow equations was transferred to the dimensionless form. For numerical computing, the MATLAB software's bvp4c function is used. The graphical display is used to demonstrate the influence of several influential parameters. It has been observed that flow rate decay with expansion in porosity parameter and nanoparticles volumetric fractions. In contrast, it rises with wedge angle, Grashof numbers, Darcy-Forchheimer, nonlinear Grashof numbers, and Maxwell fluid parameter. Thermal profiles increase with progress in the heat source, nanoparticles volumetric fractions, viscous dissipation, and nonlinear thermal radiation. The percentage increases in drag force for ternary hybrid nanofluid are 13.2 and 8.44 when the Modified Hartmann number takes input in the range 0.1 ≤ Mh ≤ 0.3 and wedge angle parameters 0.1 ≤ m ≤ 0.3 . For fuzzy analysis, dimensionless ODEs transformed into fuzzy differential equations and employed symmetrical triangular fuzzy numbers (TFNs). The TFN makes a triangular membership function (M.F.) that describes the fuzziness and comparison. This study compared nanofluids, hybrid nanofluids, and ternary nanofluids through triangular M.F. The boundary layer flow caused by a wedge surface plays a crucial role in heat exchanger systems and geothermal. [ABSTRACT FROM AUTHOR]

This article addresses two questions, why certain animals (frogs, breaststroke swimmers, hovering fliers, jellyfish) push rapidly against the surrounding fluid and then reach forward slowly, and whether this rhythm of propulsion is a manifestation of the universal phenomenon of design evolution in nature. Emphasis is on the distribution of time periods of locomotion in which, during the driving phase of cyclic movement (the motive stroke, phases 1 and 2, in alternating sequence with the dissipative stroke, phase 3), the work is generated (phase 1) and dissipated (phase 2). The relative lengths of the characteristic times t1 and t2 of the phases 1 and 2, are predicted. The relative duration of the proposed three phases of a cycle is the 'rhythm'. The analysis is based on a model of how the effective cross-sections of the stroking body parts impact the surrounding medium, water, or air, and the total power required to account for the kinetic energy losses during phases 2 and 3, which are due to drag forces posed by the surrounding medium. The body configuration (limbs' cross-sections) determines the limbs' velocities that maximize mean power, and the times t1 and t2 within the motive stroke. Emphasis is placed on the freedom to change the evolving design. Freedom is represented in two ways: the number of degrees of freedom in changing the dimensions of the model and its deformation in time, and the effect that evolutionary changes have on the access that the body has to its available space. Freedom to change the locomotion design leads to greater power and speed. [ABSTRACT FROM AUTHOR]

The present work investigates Reiner–Rivlin fluid's movement on a stretching surface with an inclined magnetic field, thermal radiation, and slip impacts. The governing equations are modeled with suitable assumptions. The governing equations are transformed into ordinary differential equations with suitable similarity terms. The numerical results are computed with the help of Runge-Kutta-Fehlberg 4th 5th order (RKF-45) and the shooting technique. The results are discussed in detail with the help of tables and graphs. The analysis mainly focuses on the different inclined angle impact over velocity and thermal profiles. The outcome reveals that the maximum thermal distribution and minimum velocity are seen with an inclined angle ξ = 90 ∘ . The cross-viscosity parameter directly impacts the velocity profile but shows a reverse trend on the thermal profile. The surface drag force is found to be minimum ξ = 90 ∘ followed by ξ = 45 ∘ and ξ = 0 ∘ . The thermal distribution rate is observed maximum at ξ = 90 ∘ than ξ = 45 ∘ and ξ = 0 ∘ . [ABSTRACT FROM AUTHOR]

In a wide variety of mechanical and industrial applications, e.g., space cooling, nuclear reactor cooling, medicinal utilizations (magnetic drug targeting), energy generation, and heat conduction in tissues, the heat transfer phenomenon is involved. Fourier's law of heat conduction has been used as the foundation for predicting the heat transfer behavior in a variety of real-world contexts. This model's production of a parabolic energy expression, which means that an initial disturbance would immediately affect the system under investigation, is one of its main drawbacks. Therefore, numerous researchers worked on such problem to resolve this issue. At last, this problem was resolved by Cattaneo by adding relaxation time for heat flux in Fourier's law, which was defined as the time required to establish steady heat conduction once a temperature gradient is imposed. Christov offered a material invariant version of Cattaneo's model by taking into account the upper-connected derivative of the Oldroyd model. Nowadays, both models are combinedly known as the Cattaneo-Christov (CC) model. In this attempt, the mixed convective MHD Falkner-Skan Sutterby nanofluid flow is addressed towards a wedge surface in the presence of the variable external magnetic field. The CC model is incorporated instead of Fourier's law for the examination of heat transfer features in the energy expression. A two-phase nanofluid model is utilized for the implementation of nano-concept. The nonlinear system of equations is tackled through the bvp4c technique in the MATLAB software 2016. The influence of pertinent flow parameters is discussed and displayed through different sketches. Major and important results are summarized in the conclusion section. Furthermore, in both cases of wall-through flow (i.e., suction and injection effects), the porosity parameters increase the flow speed, and decrease the heat transport and the influence of drag forces. [ABSTRACT FROM AUTHOR]

Projectile penetration into an immersed granular bed is a common phenomenon in both geophysics and engineering, encompassing various scenarios such as immersed crater formation and offshore soil-structure interaction. It involves the complex physical interaction between the fluid and granular materials. In this study, we investigate the dynamics of projectile penetration into a granular bed immersed in a fluid using a coupled computational fluid dynamics and discrete element method (CFD-DEM). The granular bed is composed of polydisperse particles, and the projectile is modeled as a rigid sphere. The morphology of crater formation, the dynamics of the projectile, and the drag force characteristics in immersed cases were studied in detail and compared to the dry scenario. The numerical results show that the final penetration depth of the projectile follows an empirical relation derived from experimental observations, where the falling height and the drag force during penetration obey a power-law function and a modified generalized Poncelet law, respectively. The interstitial fluid not only provides direct drag force, but also enhances the effective drag force of the granular bed by improving its generalized friction and effective viscosity in different configurations. Micro-analyses of the velocity evolution and contact force network in different stages of the fluid–solid interaction were performed to clarify the penetration dynamics. This research provides insights into the mechanisms of projectile penetration and the effects of interstitial fluid on granular media, which are crucial in engineering applications such as offshore anchoring, ball penetration tests in soft sediments, and soil-structure interactions. [ABSTRACT FROM AUTHOR]

Hydraulically fractured well productivity greatly depends on fracture conductivity, which itself is dictated by proppant transport and placement. To guide engineering design and evaluate performance of proppant placement, a full understanding of the underlying physics and robust numerical models are needed. This paper introduces a continuum approach for simulating the transport of multiple fluids and proppant particles within hydraulic fractures. To achieve computational efficiency, this proppant model is developed based on the assumption of multi-component single phase flow and captures proppant settling, hindering effects, proppant-bed erosion and transport. Inter-particle stresses and collisions are not numerically calculated but represented through empirical correlations to include the effects of particle clustering and hindered settling. This model couples the fluid phase and particle phase through the slip velocity, which is governed by particle settling, particle–particle interaction and fluid-particle drag forces. The presented proppant model is validated by comparing numerical results with experimental data. With the calibrated simulation, the modeling capabilities on fracturing treatment design are demonstrated through sensitivity analysis and field-scale applications. Moreover, based on proppant placement and deformation, a generic model is applied to forecast fracture conductivity in different scenarios. As illustrated in this study, this coupled three-dimensional model is capable of simulating proppant placement and fracture conductivity under various operational conditions. This model can be broadly applied to improve fracturing design in various formations, including tight sandstone, shale, coal bed methane and carbonate reservoirs. Highlights: To achieve computational efficiency, we introduce a continuum approach for simulating the transport of multiple fluids and proppant particles. In this new model, several underlying mechanisms are considered to highlight the coupling between proppant transport and fluid flow. The modelling predictions on proppant transport and distribution show a good agreement with the reported experimental data. Using the model calibrated to lab tests, the modeling capability is demonstrated and controlling parameters on proppant transport are identified. This model works for field-scale hydraulic fracturing simulations to model proppant transport and fracture conductivity evolution. [ABSTRACT FROM AUTHOR]

Three-dimensional plasma-dust formations consisting of calibrated dust particles differing in sizes and material densities are studied. The characteristic features of the structures formation in stratified glow discharge were studied, as well as their shapes and dynamics in the external magnetic fields. From several types of powders, the spatially separated double structures were obtained, which filled the dust trap, being located in different stratum phases. For each part of the structure, the average rotational velocities were obtained as functions of the magnetic field. In the range, in which the rotation mechanism depends on the particle size and the ion drag force is dominant, the rotational velocity was numerically estimated with allowance for the parameters variation along the stratum. [ABSTRACT FROM AUTHOR]

Today's world is moving towards the clean and green energy. Vibro Cleaner is developed based on ultrasonic technique to remove contaminations like rust, dirt, dust, oil etc. particles from the object surface. The process is eco-friendly towards the nature and completely safe for human. Vibro Cleaner has got notable impact in cleaning industries. The main goal of investigation is to examine behaviour acoustophoretic effect for finding erosion rate by introducing pressure acoustic transient model and validate by experimental investigation. Acoustic and Computational Fluid Dynamics (CFD) modules have been integrated to investigate sound pressure level, acoustic pressure, cavitation effect, particle trajectory and erosion rate in acoustophoretic environment. Piezoelectric transducer (PZT-4) of 40 kHz, which contains Lead zirconium titanate, has been sticked at bottom of steel tank which converts electrical signals into mechanical vibration and finally into pressure droplets by transience effect of tank wall in fluid. Pressure difference generates small tiny cavitation bubbles which strikes over the surface of object for cleaning. The particle sweep and erosive reaction have been scrutinised by applying particle tracing and fluid flow wear erosion modules. Experimental investigation also has been accomplished to validate the computational outcomes. The placement of object in steel tank is also one of the important factors to check the efficacy of cleaning process which has been checked at various height. The practical result erosion rate has been compared with simulation results. The experimental investigated result validates the computational simulation by achieving satisfactory out comes. [ABSTRACT FROM AUTHOR]

As we all know, the alumina inclusions on the surface of aluminum-killed molten steel are quickly attracted to form large clusters, but the alumina-magnesia complex inclusions disperse, where the interface characteristics between inclusions and molten steel play a crucial role in the agglomeration behavior on the surface of molten steel. In the present work, the effect of titanium and aluminum concentrations on the interface characteristics between molten steel and alumina inclusions is studied by using an improved sessile drop method. Then, the agglomeration behavior of alumina inclusions on the surface of molten steel is investigated by using a high-temperature laser microscope, and the attractive forces are discussed in detail from both the capillary force and viscous drag forces based on the interface characteristics between the inclusion and molten steel. The results show that the in situ observed attractive forces between the alumina inclusions on the surface of the molten steel are from 9.69 × 10−21 to 3.54 × 10−15 N, which reduce and increase, respectively, with the increase of titanium and aluminum concentration. It is agreeable to the calculated attractive force combining interface characteristics between inclusions and molten steel based on the concept of capillary force, which ranges from 1.94 × 10−21 to 3.76 × 10−16 N. Additionally, the attractive force decreases due to the viscous drag forces, which are approximately 2.43 × 10−21 to 3.11 × 10−18 N as the inclusion particles are close to each other. [ABSTRACT FROM AUTHOR]

Three-dimensional unsteady turbulent flow around Faiveley CX pantograph was described by large-eddy simulations. The aerodynamic force distributions on the structures of the pantograph were explored comparing non-cover and cover cases against the incoming flow velocity of 200, 300, 400 km/h. The averaged drag and lift forces exerted on each component of the pantograph followed the second-order polynomial relations against the incoming flow velocity. The pantograph cover reduced the overall drag forces on the pantograph because the large recirculating zone with the strong negative pressure affected to the lower parts of the pantograph. In addition, when the pantograph cover was employed, the wall-normal direction of the lift force was changed from positive (uplift force) to negative (down force). By using the force and momentum balance considering all components of the pantograph, its aerodynamic uplift force was estimated, which was improved by including the specific forces around the knee joints, where the strong flow directly impinged. The pantograph cover reduced the mean and standard deviation values of the aerodynamic uplift forces as 40∼48 % and 5∼17 % compared to those for non-cover cases. Although more power was necessary to raise up the panhead to contact the catenary wire, it would help to improve the controller design to maintain the current collection performance by decreasing the uplift force fluctuations. [ABSTRACT FROM AUTHOR]

Evolution from fines migration to deposition and clogging is critical for many geotechnical and environmental engineering practices. In this study, the coupling of computational fluid dynamic and discrete element method was adopted to tackle fines migration. The surface energy density term γ was used to represent the combination of Coulomb forces and van der Waals interactions. A particle-scale mechanical analysis method was adopted to identify three criteria of particle deposition conditions. (1) The drag force on the fines should be less than the electrical forces between particles, (2) the drag force and electrical force torques should be on the same order of magnitude, and (3) the contact angle between particles should be greater than 5.5°. The deposition efficiency increases from 8.5 to 37.8% as surface density energy increases from 0.001 to 0.01 J/m2 at a Reynolds number of 10. As the electrical force is more than 10 times the drag force, clogging occurred. Due to the inertial and Dean forces and the filtration effect of micropillars, a band of lacking particles appears in the symmetrical center of the pore throat. [ABSTRACT FROM AUTHOR]

The quasiclassical one-dimensional motion of a particle in a medium, where the drag force is proportional to the square of the particle velocity, is considered using the Caldirola–Kanai approach. The coherent state of the particle in the presence of a constant conservative force in addition to the drag force is studied. It has been shown that the wave packet undergoes quantum extension to a certain limit, forming a steady propagating profile. Thus, the drag force suppresses the quantum properties of the particle, and the classical features become more pronounced in its motion with time. This property allows one to consider such a medium as a classical instrument continuously measuring the state of the particle. For this reason, the restriction of the spatial extension of the wavefunction can be interpreted as one of the manifestations of the quantum Zeno effect. [ABSTRACT FROM AUTHOR]

Full-ceramic ball bearings are widely used in aerospace, gas engines, and extreme working conditions. The research on vibration characteristics of full-ceramic ball bearings under different pre-tightening forces and oil supply rates is relatively rare. In this paper, silicon nitride 6206 full-ceramic deep groove ball bearing is taken as the research object, the experiment of lubrication vibration characteristics of full-ceramic bearings is carried out on a bearing vibrometer by changing different pre-tightening forces and lubricating oil supply rates with the control variable method, the dynamic model of full-ceramic deep groove ball bearing under lubrication condition is established, and the influence of factors such as lubricating oil drag force, lubricating oil film thickness, rolling friction force, and pre-tightening force on bearing vibration are analyzed in essence. The experimental results show that the large vibration ratio of the bearing in the state of lack of oil is caused by insufficient oil supply, and when the oil supply rate is too high, the rolling body is dragged by too much drag force, which leads to an obvious increase in bearing vibration. The similarity between the solution signal and the measured signal of the dynamic model of full-ceramic bearing considering the drag force of the rolling body under different lubrication conditions is over 95%, which proves the reliability and accuracy of the dynamic model. [ABSTRACT FROM AUTHOR]

Maglevs are typically accelerated using electromagnetic propulsion and levitation. High-temperature superconducting (HTS) magnets along with electrodynamic suspension (EDS) and linear synchronous motors are one of the best options for Hyperloop. However, the strong magnetic fields generated by HTS magnets on the pods inevitably interact with the magnetic and conductive structures in the vacuum tubes, along with the tube itself, while the pods move through the tubes. This interaction is observed as a drag force on the pods, significantly reducing the propulsion efficiency. This study comprehensively analyzes the electromagnetic drag force (EDF) generated by HTS magnets on pods, which accounts for most of the drag forces faced by Hyperloop. Theoretical analysis and 3D FEA simulations are performed to analyze the propulsion forces with HTS magnets and all the drag forces on the pods. The EDF generated by AISI 1010 steel rebars in concrete guideways is even greater than the designed propulsion forces of 40 kN. Consequently, high-manganese (Hi-Mn) steel and insulated steel rebars are adopted and analyzed using 3D FEA simulations. The EDFs generated by the AISI 1010 steel and Hi-Mn steel vacuum tubes are determined by varying the distance between the HTS magnets and tubes at 50 and 1200 km/h, respectively; a minimum distance of 0.75 m is determined by a drag force below 8 kN within their operating velocities. Lastly, the total EDFs of the AISI 1010 steel and Hi-Mn steel tubes with EDS rails are obtained through the optimal design of rebars and tubes. The simulation results show that the total EDFs can be significantly reduced to below 10 kN (approximately 25% of the designed propulsion force after the levitation of pods). [ABSTRACT FROM AUTHOR]

The results of modeling the adhesion of droplets of different sizes to vegetation elements are presented. This study deals with issues related to extinguishing a forest fire using dispersed water. A key factor in the effectiveness of fire extinguishing is to ensure the delivery of water to the point of fire outbreak and the absorption of energy due to the vaporization process. It is assumed that the droplets do not affect the velocity field of the gas phase. Their motion is due to inertia and the effect of the force of aerodynamic drag. It is shown that the logit of the fraction of adhered droplets is described by a function close to the linear function of the logarithm of their size, which makes it possible to estimate the permeability of the forest for dispersed-water particles. It is shown that smaller droplets better flow around obstacles. [ABSTRACT FROM AUTHOR]

A novel method aimed at evaluating the active drag profile during front-crawl swimming is proposed. Fourteen full trials were conducted with each trial using a stationary load cell set-up and a commercial resistance trainer to record the tension force in a rope, caused by an athlete swimming. Seven different stroke cycles in each experiment were identified for resampling time dependent data into position dependent data. Active drag was then calculated by subtracting resistance trainer force data away from the stationary load cell force data. Mean active drag values across the stroke cycle were calculated for comparison with existing methods, with mean active drag values calculated between 76 and 140 N depending on the trial. Comparing results with established active drag methods, such as the Velocity Perturbation Method (VPM), shows agreement in the magnitude of the mean active drag forces. Repeatability was investigated using one athlete, repeating the load cell set-up experiment, indicating results collected could range by 88 N depending on stroke cycle position. Variation in results is likely due to inconsistencies in swimmer technique and power output, although further investigation is required. The method outlined is proposed as a representation of the active drag profile over a full stroke cycle. [ABSTRACT FROM AUTHOR]

In order to advance our understanding of the dynamic interactions between coronal mass ejections (CMEs) and the magnetized solar wind, we investigate the impact of magnetic erosion on the well-known aerodynamic drag force acting on CMEs traveling faster than the ambient solar wind. In particular, we start by generating empirical relationships for the basic physical parameters of CMEs that conserve their mass and magnetic flux. Furthermore, we examine the impact of the virtual mass on the equation of motion by studying a variable-mass system. We next implement magnetic reconnection into CME propagation, which erodes part of the CME magnetic flux and outer-shell mass, on the drag acting on CMEs, and we determine its impact on their time and speed of arrival at 1 AU. Depending on the strength of the magnetic erosion, the leading edge of the magnetic structure can reach near-Earth space up to ≈ three hours later, compared to the non-eroded case. Therefore, magnetic erosion may have a significant impact on the propagation of fast CMEs and on predictions of their arrivals at 1 AU. Finally, the modeling indicates that eroded CMEs may experience a significant mass decrease. Since such a decrease is not observed in the corona, the initiation distance of erosion may lie beyond the field-of-view of coronagraphs (i.e. 30 R ⊙ ). [ABSTRACT FROM AUTHOR]

A modified drag force model combining drag coefficients of four-segment functions is used to simulate the flow profile of an industrial-scale fluidized bed roaster (FBR) by computational fluid dynamics. Gas–solid flow model for industrial-scale roaster is established and used to simulate the fluid behaviour by using the modified drag coefficient model. The expansion ratio of FBR is in reasonable agreement with commercial data. Calculation results predict the dense and dilute phase in the roaster well. Volume fraction, velocity vector and averaged particle velocity of three kinds of copper concentrate are investigated and calculated. The influence on particle properties and operating conditions on flow characteristics in the roaster are analysed. Copper concentrate with smaller diameter and larger density is more difficult to fluidize. With the increase of superficial gas velocity, the solid holdup decreases, the average particle velocity increases, the side wall effect weakens, and the fluidization quality improves. [ABSTRACT FROM AUTHOR]

The problem of a slow Stokes flow past a sphere with modified slip condition on its surface is solved. The new boundary condition on the surface of a sphere establishes the linear relationship between the tangential velocity component and the vorticity of the flow. An analytical solution of the boundary value problem for the flow stream function is obtained. The expressions for drag force of the sphere and the tangential velocity are found as a function of the Knudsen number. The resulting expression for the drag force is consistent with the linear Cunningham correction factor. The developed model is compared against the results obtained within the molecular kinetic theory and the continuum mechanics model with the Basset–Maxwell slip condition. The proposed model shows the best agreement with the experimental data for the dependence of the aerodynamic drag force on Knudsen number. It is shown that in the limiting case of an infinite Knudsen number, the proposed model leads to a model of potential flow. [ABSTRACT FROM AUTHOR]

Friction velocity is one of the important scaling parameters in atmospheric boundary layer studies. However, several definitions of friction velocity exist in the literature: e.g. estimated from the total drag force or used only pressure drag, etc. In this study, a series of large-eddy simulation (LES) calculations were carried out to evaluate the impact of various definitions on the friction velocity for idealized urban geometries, i.e. staggered array of cubes with different packing densities and wind directions. We first compared the normalized velocity fields with the literature data for the case with a packing density of 25 % . The results show that the LES data normalized by the friction velocity derived from the Reynolds stress using the extrinsic spatial average is more consistent with the direct numerical simulation data. Furthermore, when varying the wind direction, the distribution of Reynolds stress and pressure drag show significant change in streamwise and spanwise directions. We further found that for packing density of 44.44 % , the frictional drag accounts for more than a quarter of the total drag, and even higher than the pressure drag in parallel wind direction. This leads to the deviation of friction velocity estimated from the pressure drag and that calculated from the total drag force up to 33%. Such characteristic of viscous effect challenges the assumption widely used in wind tunnel experiments and urban canopy parameterizations that the contribution of viscous force is negligible, especially for ultra-dense arrays. [ABSTRACT FROM AUTHOR]