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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 paper focuses on the hydrodynamic interaction between a semipermeable spherical particle and a laminar flow of couple stress fluid. The framework of the flow is divided into two regions, in which the non‐Newtonian characteristics of the couple stress fluid are governed by classical Stokes equations and the permeable region is governed by Darcy's law. The asymptotic series expansion involves the stream functions in terms of modified Bessel's function and Gagenbauer's polynomials for the inner and outer regions. The graphical analysis demonstrating the superior outcomes of numerous parameters such as the couple stress parameter, the permeability parameter, and the couple stress viscosity ratio on the drag coefficient is conducted, and the outcomes are discussed comprehensively. The present study discovered that the drag of a semipermeable sphere is greater than that of a couple stress fluid sphere. A continuous reduction in the pressure distribution is observed with the rising value of the couple stress parameter. However, an increasing value of the couple stress parameter in the semipermeable medium contributes to increasing the tangential stress with respect to the distance from the surface. The current study's findings could be useful in analyzing significant clinical and industrial applications such as the filtration process for wastewater treatment, the design of the digestive system, fluid–solid disperse systems, and the petroleum industry. However, experimental verification is required for the proposed work. [ABSTRACT FROM AUTHOR]

The objective of this paper is to analyze the unsteady incompressible flow of the viscous nanofluid on a contracting surface with viscous dissipation effects. Presented and contrasted are analyses of both multi-wall carbon nanotubes (MWNTs) and single-wall carbon nanotubes (SWNTs). As the common (or base) fluids, kerosene oil and water are utilized. In the existence of first-order thermal and velocity slip conditions, mathematical modeling and analysis are performed. Using the MATLAB software's bvp4c solver tool, numerical solutions to the governing nonlinear modeled problems were obtained. This technique is particularly effective for developing many solutions to highly nonlinear differential equations. In addition, a comparison is done between this study and previously published works. The temperature, velocity, skin friction coefficient and heat-transfer rate have been explored for various significant factors included in the problem statements. In the unsteadiness parameter regime, dual solutions can be found. As the velocity slip parameter is increased, the flow slows down. In comparison to SWCNTs kerosene, MWCNTs kerosene oil has a greater velocity curve for the nanoparticles volume fraction. Increases in volume fraction decrease skin friction, whereas increases in the unsteadiness parameter speed up the drag force. Furthermore, as the Eckert number intensity increases, so do the temperature profiles in both solutions. Finally, the stability study revealed that the initial solution is robust, whereas the breakage in the second solution in the Nusselt number shows singularity, and thus the second solution is considered unstable. [ABSTRACT FROM AUTHOR]

Accurate assessment of rolling resistance is important for wheelchair propulsion analyses. However, the commonly used drag and deceleration tests are reported to underestimate rolling resistance up to 6% due to the (neglected) influence of trunk motion. The first aim of this study was to investigate the accuracy of using trunk and wheelchair kinematics to predict the intra-cyclical load distribution, more particularly front wheel loading, during hand-rim wheelchair propulsion. Secondly, the study compared the accuracy of rolling resistance determined from the predicted load distribution with the accuracy of drag test-based rolling resistance. Twenty-five able-bodied participants performed hand-rim wheelchair propulsion on a large motor-driven treadmill. During the treadmill sessions, front wheel load was assessed with load pins to determine the load distribution between the front and rear wheels. Accordingly, a machine learning model was trained to predict front wheel load from kinematic data. Based on two inertial sensors (attached to the trunk and wheelchair) and the machine learning model, front wheel load was predicted with a mean absolute error (MAE) of 3.8% (or 1.8 kg). Rolling resistance determined from the predicted load distribution (MAE: 0.9%, mean error (ME): 0.1%) was more accurate than drag test-based rolling resistance (MAE: 2.5%, ME: −1.3%). [ABSTRACT FROM AUTHOR]

Magneto-thermomechanical applications range from magnetic resonance imaging to electric diodes and the design of dielectric grease. To contribute significantly to the biomedical industry for proper prediction and treatment of diseases such as cancer, stenosis, and technological advancement in the design of electronic tools. This study presents the significance of magneto-thermomechanical modeling of Reiner–Philippoff fluid flow subject to thermal radiation influence. The Reiner–Philippoff fluid encapsulates the properties of shear-thinning, shear-thickening, and Newtonian fluids in different viscosity regimes. The main-stream velocity ue is considered in its generalized form as well as taking into account the influence of thermal radiation and thermal conductivity. To obtain the computational model analysis, a numerical tool via the bivariate spectral collocation method is deployed on the resulting transformed PDEs. Upon validation of the method, the profile distributions of respective boundary layers with respect to the Bingham number, magneto-thermomechanical parameter, and Reiner–Philippoff fluid parameter are analyzed and discussed. The results of the engineering quantities of skin friction and Nusselt number are presented in graphical and tabular form. Among the findings of this study is that the Newtonian fluid is a turning point for skin drag force and heat transfer rate. Besides, the ferrohydrodynamic parameter recedes the velocity of shear-thinning fluid the most, although, boosts its (shear-thinning fluid) heat transfer coefficient. [ABSTRACT FROM AUTHOR]

In this study, models for the wake capture lift and drag force coefficients of a hovering flapping wing were presented using numerical fluid dynamics simulation to improve the blade element theory. The investigated wing is inspired by the fruit fly and has combined flapping and pitching movements. The effect of changing the wing acceleration time at the start (Δ τ A ) and end of the half cycle (Δ τ D ), as well as the Reynolds numbers in the range of 136–6800, on wake capture using the Taguchi orthogonal array test design, is investigated using the numerical fluid dynamics method, and the values of average lift and drag coefficients due to wake capture are obtained. These force coefficients were applied to linear and nonlinear regression methods to obtain the mathematical model, and a model for its changes was extracted. Finally, to obtain the instantaneous coefficients, the extracted models were placed in the normal distribution function, and the final instantaneous model was obtained. Examining the verification cases of the application of these wake capture relationships with the blade element theory, as well as the effects of translational force, rotational force and added mass force, revealed that this developed theory is capable of correctly predicting the wake capture force's initial peak. The force coefficient trend in the final quasi-steady model with wake capture is similar to the computational fluid dynamics (CFD) results, according to a qualitative examination of the lift and drag force coefficients in a half cycle. This demonstrates a significant result: this theory, which is divided into four parts: transnational, rotational, added mass and wake capture, adequately covers the general physics of these complex movements. [ABSTRACT FROM AUTHOR]

The influence of bitumen coating on the development of unit shaft resistance along driven steel and precast concrete piles resulting from subsiding surrounding soft soil (gyttja) induced by fill placement at terrain was investigated. All piles were instrumented with conventional discrete-point vibrating wire strain gauges and distributed fibre optic sensors to achieve high-resolution strain measurements. The magnitude of the mobilised unit shaft resistance along uncoated piles was observed to be primarily related to an increase in effective stress resulting from the dissipation of excess pore water pressures. The unit shaft resistance along bitumen-coated piles was found to be primarily related to the rate of relative movement between pile and soil, which highlights the effectiveness of bitumen coating in reducing shaft resistance. [ABSTRACT FROM AUTHOR]

The drag force experienced by astronomical objects moving through gaseous media (gas dynamical friction) plays a crucial role in their orbital evolution. Ostriker derived a formula for gas dynamical friction by linear analysis, and its validity has been confirmed through subsequent numerical simulations. However, the effect of gas accretion onto the objects on the dynamical friction is yet to be understood. In this study, we investigate the Mach number dependence of dynamical friction considering gas accretion through three-dimensional nested-grid simulations. We find that the net frictional force, determined by the sum of the gravitational force exerted by surrounding gas and momentum flux transferred by accreting gas, is independent of the resolution of simulations. Only the gas outside the Bondi–Hoyle–Lyttleton radius contributes to dynamical friction, because the gas inside this radius is eventually absorbed by the central object and returns the momentum obtained through the gravitational interaction with it. In the subsonic case, the front–back asymmetry induced by gas accretion leads to larger dynamical friction than predicted by the linear theory. Conversely, in the slightly supersonic case with a Mach number between 1 and 1.5, the nonlinear effect leads to a modification of the density distribution in a way that reduces the dynamical friction, compared with the linear theory. At a higher Mach number, the modification becomes insignificant and the dynamical friction can be estimated with the linear theory. We also provide a fitting formula for dynamical friction based on our simulations, which can be used in a variety of applications. [ABSTRACT FROM AUTHOR]

Coastal wetlands act as natural buffers against wave energy and storm surges. In the course of energy dissipation, vegetation stems are exposed to wave action, which may lead to stem breakage. An integral component of wave attenuation modeling involves quantifying the extent of damaged vegetation, which relies on determining the maximum drag force (FDmax) and maximum moment of drag (MDmax) experienced by vegetation stems. Existing closed-form theoretical equations for MDmax and FDmax are only valid for linear and weakly nonlinear deep water waves. To address this limitation, this study first establishes an extensive synthetic dataset encompassing 256,450 wave and vegetation scenarios. Their corresponding wave crests, wave troughs, MDmax , and FDmax , which compose the dataset, are numerically computed through an efficient algorithm capable of fast computing fully nonlinear surface gravity waves in arbitrary depth. Seven dominant wave and vegetation related dimensionless parameters that impact MDmax and FDmax are discerned and incorporated as input feature parameters into an innovative sparse regression algorithm to reveal the underlying nonlinear relationships between MDmax , FDmax and the input features. Sparse regression is a subfield of machine learning that primarily focuses on identifying a subset of relevant feature functions from a feature function library. Leveraging this synthetic dataset and the power of sparse regression, concise yet accurate closed-form equations for MDmax and FDmax are developed. The discovered equations exhibit good accuracy compared with the ground truth in the synthetic dataset, with a maximum relative error below 6.6% and a mean relative error below 1.4%. Practical applications of these equations involve assessment of the extent of damaged vegetation under wave impact and estimation of MDmax and FDmax on cylindrical structures. [ABSTRACT FROM AUTHOR]

The purpose of the current study is to evaluate the mass and energy transmission of a blood-based Casson Ferrofluid flow across a stretching cylinder. The consequences of the Casson parameter, cylinder curvature, thermal radiation, chemical reaction, and non-Newtonian viscous dissipation are also considered. The nanofluid flow phenomena are mathematically designed in the form of a system of nonlinear PDEs which are degraded and non-dimensionalized to the set of ODEs by using suitable similarity transformations. The homotopy analysis method has been applied to find out a semi-analytical solution for the nonlinear set of ODEs. The significance and physical behavior of flow parameters are graphically characterized versus the velocity, energy, and mass profiles. The numerical outcomes for Sherwood number, drag force and Nusselt number are also presented through Tables. A comparative evaluation has been done for validation purposes to authorize and justify the present results. From the tabular and graphical results, it has been noticed that the velocity profile lowers while the energy profile develops versus the variation of magnetic factor. The impact of curvature factor boosts the velocity and mass transfer rate of the Casson nanofluid while reducing the temperature curve. Furthermore, the consequences of the thermophoresis effect raise the temperature profile of the Casson Ferrofluid flow. [ABSTRACT FROM AUTHOR]

How far can a person sink downwards in quicksand? Experience would seem to suggest that there is low risk of submerging completely, but it is not easy to demonstrate this because of the complex rheology of granular suspensions. We study several mathematical models for the sinking of a vertical cylinder downwards into quicksand, finding that an approach with a buoyancy equation modified by drag force gives an unphysical answer. We instead argue that our proposed conclusion is supported by considering the dynamics of vibration-induced compactification of liquid-saturated granular suspensions. We compare quicksand with other non-Newtonian fluids, emphasising that in this case the same model does not apply and that the risk of drowning could be much more significant. We finish by suggesting some relevant experiments that can be performed in a classroom setting. [ABSTRACT FROM AUTHOR]

[Display omitted] Interactions between nanoparticles and the mucus layer are crucial to understand the behaviours in biological environments and design drug delivery systems. In this study, we developed a kinetic deposition model for the dynamic mucin-nanoparticle interactions using quartz crystal microbalance with dissipation (QCM-D). We investigated the effects of the physiochemical properties of several nanoparticles (including size, charge, and shape) and the physiological conditions on the mucin-nanoparticle interaction. Interestingly, layered double hydroxide (LDH) nanoparticles showed stronger interactions with the mucus layer compared to other types of nanoparticles due to their unique plate-like morphology. In specific for sheet-like LDH nanoparticles, our model found that their equilibrium adsorption capacity (Q e) followed the Langmuir adsorption isotherm, and the adsorption rate (k 1) increased proportionally with the nanoparticle concentration. In addition, the particle size and thickness affected Q e and the surface coverage. Furthermore, bovine serum albumin (BSA) coating dramatically increased k 1 of LDH nanoparticles. We proposed a novel mechanism to elucidate mucin-nanoparticle interactions, shedding light on the synergistic roles of drag force (F d), repulsive force (F r), and adsorptive force (F a). These findings offer valuable insights into the complex mucin-nanoparticle interactions and provide guidance for the design of drug delivery systems. [ABSTRACT FROM AUTHOR]

The characteristics of iron minerals in cyanidation tailings with a low iron grade were determined via chemical composition analysis, iron phase analysis, and mineral liberation analysis (MLA). The results showed that the cyanidation tailings contained 15.68% iron, mainly occurring in the form of magnetite (19.66%) and limonite (79.91%), in which 16.52% magnetite and 65.90% limonite particles were fully liberated. Most ultra-fine magnetite grains were adjacent and wrapped with limonite to form complex intergrowths, which resulted in low-efficiency magnetite recovery in low-intensity magnetic separation (LIMS) and adversely affected the downstream high-gradient magnetic separation (HGMS) process. Thus, in this work, the optimization of the flow field was proposed to enhance the separation of ultra-fine magnetite from the cyanidation tailings using pilot-scale LIMS separation, and the controllable parameters (including feed flow, separation gap, drum rotating speed, and solid weight) affecting ultra-fine magnetite capture were investigated. Under optimized conditions, a high-grade magnetite concentrate assaying 63.31% Fe with 86.46% magnetite recovery was produced, which, respectively, increased by 0.76% and 15.22%, compared with those obtained from industrial production. In addition, from the flow dynamics simulation, it was found that the magnetite particles in the −6 µm ultra-fine fraction were lost much more easily than those of coarser fractions due to the relatively enhanced hydrodynamic drag force acting on the particles compared with the magnetic force. However, this loss would be effectively reduced with the regulation and control of the flow field. The iron recoveries in the −16~+6 µm and −6 µm fractions of magnetite concentrate increased by 3.66% and 4.42%, respectively, under optimized hydrodynamic conditions. This research outcome provides a valuable reference for the economic and effective utilization of iron resources from such solid wastes. [ABSTRACT FROM AUTHOR]

This review examines studies aimed at the organization of energy (non-mechanical) control of high-speed flow/flight using spatially multi-component plasma structures and combined energy deposition. The review covers selected works on the experimental acquisition and numerical modeling of multi-component plasma structures and the use of sets of actuators based on plasma of such a spatial type for the purposes of control of shock wave/bow shock wave–energy source interaction, as well as control of shock wave–boundary layer interaction. A series of works on repetitive multiple laser pulse plasma structures is also analyzed from the point of view of examining shock wave/bow shock wave–boundary layer interaction. Self-sustained theoretical models for laser dual-pulse, multi-mode laser pulses, and self-sustained glow discharge are also considered. Separate sections are devoted to high-speed flow control using combined physical phenomena and numerical prediction of flow control possibilities using thermal longitudinally layered plasma structures. The wide possibilities for organization and applying spatially multi-component structured plasma for the purposes of high-speed flow control are demonstrated. [ABSTRACT FROM AUTHOR]

The effect of particle shape on the suffusion of gap-graded soils is an essential although poorly understood subject in geotechnical engineering that requires further investigation. This work presents a macroscale and microscale numerical investigation into the effect of particle shape on the suffusion of gap-graded granular materials. Rounded, elliptical, and convex particles with the same volume-equivalent diameter and varying shape coefficients were generated and used to produce samples. Next, a series of resolved coupled computational fluid dynamics (CFD) and discrete-element method (DEM) simulations were performed to provide evidence of the effect of particle shape on the suffusion susceptibility of gap-graded soils. The evolution of particle orientation, moment, and drag force coefficient were analyzed to determine the mechanisms by which particle shape exerts influence. The fine angular particles under seepage flow were found to adjust their orientation, reducing the projected area of the particle perpendicular to the fluid flow direction. Fine particles in high-flow-velocity regions had a smaller projected area and drag force coefficient. The continuous rotation of the irregularly shaped particles during suffusion implies that their migration should counteract the moments exerted by the surrounding particles. In the sample containing various irregularly shaped particles, the initial position of the most irregularly shaped particle was closer to the outlet, implying that irregularly shaped particles are less susceptible to suffusion. [ABSTRACT FROM AUTHOR]

A comprehensive 2D numerical model was conscientiously developed to investigate the vortex-induced vibration phenomena in a cylindrical structure with rounded corners. The Navier-Stokes equation was adeptly solved under the specific condition of a Reynolds number (Re) of 150. The investigation reveals intricate details of the phenomena. The study aimed to systematically analyze the interaction between drag and lift force coefficients, cylinder vibration amplitude, and the patterns of vortex shedding modes under various conditions. This study systematically altered the radius of the cylinder's rounded corners to evaluate their effects on both structural and hydrodynamic responses. This variation was crucial in comprehending how slight alterations in the cylinder's geometry impact significant changes in the flow dynamics and correlated vibration behavior. The model's numerical results revealed the significant impact of the curved edge ratio on both the hydrodynamic forces acting on the cylinder and its vibration response. The variation in edge curvature resulted in changes in drag and lift coefficients, leading to a significant impact on the amplitude of vibration. This elucidates the crucial role of geometric design in controlling and optimizing the structural behavior of cylindrical structures under fluid flow conditions. [ABSTRACT FROM AUTHOR]

Stressed soft materials commonly present viscoelastic signatures in the form of power-law or exponential decay. Although exponential responses are the most common, power-law time dependencies arise peculiarly in complex soft materials such as living cells. Understanding the microscale mechanisms that drive rheologic behaviors at the macroscale shall be transformative in fields such as material design and bioengineering. Using an elastic network model of macromolecules immersed in a viscous fluid, we numerically reproduce those characteristic viscoelastic relaxations and show how the microscopic interactions determine the rheologic response. The macromolecules, represented by particles in the network, interact with neighbors through a spring constant k and with fluid through a non-linear drag regime. The dissipative force is given by γvα, where v is the particle's velocity, and γ and α are mesoscopic parameters. Physically, the sublinear regime of the drag forces is related to micro-deformations of the macromolecules, while α ≥ 1 represents rigid cases. We obtain exponential or power-law relaxations or a transitional behavior between them by changing k, γ, and α. We find that exponential decays are indeed the most common behavior. However, power laws may arise when forces between the macromolecules and the fluid are sublinear. Our findings show that in materials not too soft not too elastic, the rheological responses are entirely controlled by α in the sublinear regime. More specifically, power-law responses arise for 0.3 ⪅ α ⪅ 0.45, while exponential responses for small and large values of α, namely, 0.0 ⪅ α ⪅ 0.2 and 0.55 ⪅ α ⪅ 1.0. [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]

This paper investigates the force and heat transfer characteristics of deformable alumina droplets in compressible flow. The numerical scheme couples the Navier–Stokes equations with the volume-of-fluid method, fuzzy theory, and a proportional–derivative controller. The effects of the Reynolds number, Weber number, and relative Mach number on the droplet deformation and the drag and heat transfer characteristics are studied. The results show that the fuzzy theory coupled with the proportional–derivative controller allow the droplet to reach the quasi-steady state more efficiently and robustly. The drag coefficient and Nusselt number of the droplet increase with the degree of deformation and the relative Mach number between the flow field and the droplet. The relative Mach number and the Weber number are weakly coupled with the drag coefficient and the Nusselt number. Finally, the inner two-phase flow fields of a solid rocket motor are calculated. The mechanisms whereby particle deformation influence the inner flow field of the solid rocket motor are analyzed. [ABSTRACT FROM AUTHOR]

For models with large numerical simulation costs, such as high-speed trains, using as few samples as possible to construct a high-precision surrogate model during aerodynamic multi-objective optimization is critical to improving optimization efficiency. This study proposes a sequential infill criterion (SIC) appropriate for the Kriging surrogate model to address this issue. Three multi-objective functions are employed to test the feasibility of constructing a surrogate model based on SIC, and the SIC surrogate model then performs multi-objective aerodynamic optimizations on the high-speed train. The findings indicate that the expected improvement infill criterion (EIC) in the first stage can enhance the global prediction accuracy of the SIC. An infill criterion based on EIC that fuses gradient information (PGEIC) in the second stage is proposed to seek samples in the Pareto front. The PGEIC surrogate model achieves the lowest generational distance and prediction error. The performance of EIC for global search, EIC for Pareto front search, and infill criterion for Pareto front search using only gradient information is poor. The final PGEIC–SIC surrogate model of train aerodynamics has less than 1% prediction error for the three optimization objectives. The optimal solution reduces the aerodynamic drag force of the head car and the aerodynamic drag and lift force of the tail car by 4.15%, 3.21%, and 3.56%, respectively, compared with the original model. Furthermore, sensitivity analysis of key parameters revealed that the nose height v1, cab window height v3, and lower contour line have a greater impact on aerodynamic forces. Moreover, the nose and cab window heights of the optimal model have been reduced, and the lower contour line is concave. Correspondingly, the streamlined shape appears more rounded and slender. [ABSTRACT FROM AUTHOR]

This study investigated the weakly nonlinear propagation of pressure waves in compressible, flowing water with spherical microbubbles, considering various forces. Previous theoretical studies on nonlinear pressure waves in bubbly flows did not consider the forces acting on the bubbles, although the validity of ignoring these forces has not been demonstrated. We focused on every possible force such as drag, gravity, buoyancy, and Bjerknes (acoustic radiation) forces acting on bubbles and studied their effects on pressure waves in a one-dimensional setting. Using a singular perturbation method, the Korteweg–de Vries–Burgers equation describing wave propagation was derived. The following results were obtained: (i) Bjerknes force on the bubbles enhanced the nonlinearity, dissipation, and dispersion of the waves; (ii) Drag, gravity, and buoyancy forces acting on the bubbles increased wave dissipation; (iii) Thermal conduction had the most substantial dissipation effect, followed by acoustic radiation, drag, buoyancy, and gravity. We confirmed that the dissipation due to forces on gas bubbles was quantitatively minor. [ABSTRACT FROM AUTHOR]

Drag reduction technology has a promising application in marine fields and has drawn much interest in scientific fields. Superhydrophobic surface has been proven to be effective in drag reduction due to thin film of gas adsorbed on surface because of its low friction drag and large slip length. Here, macroscopic and stable gas film was observed when water flowed over superhydrophobic surface with step without additional gas injection under laminar flow and turbulent flow. Superhydrophobic surface was prepared with contact angle more than 150° and roll-off angle nearly 0°. Macroscopic gas film could maintain under laminar flow and turbulent flow and keep up to 80% after 1 h water flowing with optimized parameters of step, showing different morphological deformations under different velocities and Reynolds numbers. Compared with untreated hydrophilic surface, superhydrophobic surface with step exhibited good drag reduction performance with maximum drag reduction rate 20% under laminar flow and turbulent flow, after optimizing of height of step and distance between steps. Mechanisms of gas film drag reduction were the ultra-low skin friction drag force between liquid–gas interface, large slip length on liquid–gas interface, and flexible gas film surface acted like compliant wall. Gas film of millimeter scale was much larger than thickness of boundary layer and reduced turbulence intensity near wall. This work provides a new way to obtain macroscopic gas film and analyze liquid–gas interface. [ABSTRACT FROM AUTHOR]

Numerical simulation is vital for evaluating urban ventilation. However, accurate urban-scale ventilation modeling requires extensive building surface simulation for computational demand. The distributed drag force approach simplifies the urban canopy by modeling buildings as a porous volume that accounts for momentum and turbulence. This method is a practical solution for simulating urban airflow. The drag force coefficient (Cd) is a crucial aerodynamic parameter in this approach. This study examines how Cd varies with urban design parameters such as plan area density (λp), average building height (H), frontal area density (λf), floor aspect ratio (AR), and sky view factor (SVF). Employing extensive numerical simulations conducted under neutral atmospheric conditions, we explore ranges of λp = 0.04–0.07 and λf = 0.1–1.2. The numerical model has been validated against existing wind tunnel data. The results show that Cd is insensitive to the model scale and background wind speed. We discover a nonlinear relationship between Cd and the parameters λp, λf, and SVF. For urban layouts with cubic-shaped buildings, Cd peaks at different λp within the range of 0.2~0.8. When λp and H are constant, Cd has a linear relationship with AR and λf. It is recommended to use λp, SVF, and AR as predictors for Cd across various urban configurations. [ABSTRACT FROM AUTHOR]

This study investigated the momentum and thermal characteristics of a blunt‐headed cylinder immersed in a stream of generalized Newtonian fluids (i.e., power‐law fluids) under various planar confinements. The flow and heat transfer characteristics were obtained by solving the constitutive equations with a finite‐element‐based solver for varying ranges of governing parameters. Reynolds number (Re = 1–40), Prandtl number (Pr = 5–100), power‐law index (n = 0.3–1.8), and blockage ratios (β = 2–40) were considered as the governing parameters for the study. Streamlines, drag coefficients, isotherm contours, and average Nusselt numbers were obtained as output parameters of the study. The local distribution of the pressure coefficient and Nusselt number are also presented to gain deep insight into the vicinity of the blunt‐headed cylinder. Shear‐thickening and shear‐thinning fluids exhibited an inverse trend for flow separation under planar confinements. The average Nusselt number exhibits a positive correlation with the Reynolds and Prandtl numbers while showing negative dependence on the power‐law index and blockage ratio. Overall, momentum and heat transfer show complex relationships with the governing parameters. The functional relationships are shown as correlations for flow‐separation Reynolds number, total drag force, and average Nusselt number on relevant dimensionless parameters for general applications. [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]

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]

Deep reinforcement learning (DRL) is gaining attention as a machine learning tool for effective active control strategy development. This study focuses on employing DRL to develop an efficient active control strategy for flow around three circular cylinders arranged in an equilateral-triangular configuration in a two-dimensional channel. The analysis of control outcomes reveals that DRL induces vortices of varying sizes between the cylinders, resulting in large elliptical vortices at the rear. This enhancement in flow stability leads to a significant 40.40% reduction in cylinder drag force and an approximate 8.23% decrease in overall drag oscillations. Our research represents a pioneering application of DRL for stabilizing complex flow around multiple cylinders, yielding remarkable control effectiveness. The noteworthy outcomes in controlling the stability of complex flows highlight the capability of DRL to grasp intricate nonlinear flow dynamics, showcasing its potential for investigating active control strategies within complex nonlinear systems. [Display omitted] • Demonstrating deep reinforcement learning in non-linear, complex flow problems. • Remarkable 40.40% drag reduction, 8.23% less overall drag fluctuations. • Efficient implementation of real-time, multi-point active control for complex flow. [ABSTRACT FROM AUTHOR]

The current study emphasizes bioconvective viscous fluid flow between two horizontal deformable cylinders. At the cylindrical walls, the Newtonian heat and mass condition with velocity slip is examined. The thermal and solutal transfer is optimized by amalgamating Soret–Dufour effects with variable heat source/sink. The equations that regulate the flow are simplified via appropriate transformations. The bvp4c algorithm is employed to obtain the numerical solution. The ramifications of the emerging parameters are portrayed graphically. Numerical values for drag force coefficient, heat flux, mass flux, and local motile density numbers are enumerated in tabulated form. Axial velocity accelerates on varying the unsteadiness parameter. The thermal field elevates by augmenting the Dufour number and thermal conjugate parameter. The drag force coefficient exhibits a decreasing behavior on enhancing the unsteadiness and velocity slip parameters. An opposite behavior is exhibited by heat and mass flux on amplifying the Soret and Dufour number. Motile density deteriorates on elevating the Lewis number and unsteadiness parameter. A substantial correlation has been noticed by graphically comparing the results of this study with the previous literature. [ABSTRACT FROM AUTHOR]

Flow and heat transfer in a bidisperse gas–solid system with freely moving spheres are simulated by particle‐resolved direct numerical simulation (PR‐DNS). Gas–solid coupling is enforced by the direct‐forcing immersed boundary method. Compard with the DNS database, it is found that the existing polydisperse drag correction model developed from static systems combined with various monodisperse drag models underestimates the drag force on dynamic arrays of particles. The existing Nusselt number correction model developed from static systems combined with various monodisperse models overestimates the Nusselt number of dynamic arrays of particles. Sensitivity analysis indicates that the effects of the granular temperature on the drag force and Nusselt number are negligible. Novel polydisperse drag and Nusselt number models are derived based on the database. The advantages of the derived polydisperse drag and Nusselt number models are demonstrated and confirmed by comparing the results of the computational fluid dynamics–discrete element method using various drag and Nusselt number models with experimental or additional PR‐DNS data. [ABSTRACT FROM AUTHOR]

The bullet shape is critical in efficient bullet design because it affects the lift and drag forces. This paper proposes a new bullet shape with a logarithmic curve and analyzes the lift and drag coefficients of bullets with different curves under different angles of attack. The results are compared with a bullet whose shape is described by the power law curve. Fluent simulations demonstrate that the optimal power exponent values are 0.65, 0.6, and 0.65 for the bullet with the power law curve and 1.3, 1, and 1 for the bullet with the logarithmic curve at 0°, 30°, and 40° angles of attack, respectively. At a 0° angle of attack, the lift coefficient of the logarithmic curve is the largest. The lift force of the bullet with the logarithmic curve is 129.4% higher than that with the von Karman curve. The drag coefficient is the largest for the bullet with the rectilinear curve; it is 1.30% larger than that of the bullet with the logarithmic curve. At 30° and 40° angles of attack, the lift coefficient of the bullet with the power law curve is larger. The difference in the lift coefficients between the two angles of attack is 18.47%. The bullet's drag coefficient is the largest for the logarithmic curve, and the difference in the drag coefficients between the two angles of attack is 18.59%. [ABSTRACT FROM AUTHOR]

For the first time, this paper examines the aerodynamic forces that arise in a platoon of Heavy Goods Vehicle lorries travelling in close proximity during an overtaking manoeuvre. Through an in-depth programme of wind tunnel experiments it is demonstrated that there is a complex relationship between the drag and side force coefficients, with a possible hysteresis-like behaviour shown. The influence of the overtaken lorry on the overtaking lorry is shown to be key in terms of the aerodynamic-induced forces experienced by the latter. Furthermore, the overtaking lorry is shown to benefit aerodynamically from the overtaken lorry, and this is attributed to the elliptical nature of the Navier-Stokes equations. In addition to examining the forces that arise during overtaking, the variation of the wind-induced forces with respect to yaw on a single lorry is compared to those on a middle lorry in a 3-lorry platoon. The aerodynamic benefits arising from platooning/vehicles travelling in close proximity are again demonstrated, although it is shown that these benefits may only exist over a limited range of yaw angles, raising questions about the real-world application of this approach. This has important implications for platooning in crosswinds and the drag force reduction that is assumed due to platooning. [ABSTRACT FROM AUTHOR]

The presence of a dispersed phase can significantly modulate the drag in turbulent systems. We derived a conserved quantity that characterizes the radial transport of azimuthal momentum in the fluid–fluid two-phase Taylor–Couette turbulence. This quantity consists of contributions from advection, diffusion and two-phase interface, which are closely related to density, viscosity and interfacial tension, respectively. We found from interface-resolved direct numerical simulations that the presence of the two-phase interface consistently produces a positive contribution to the momentum transport and leads to drag enhancement, while decreasing the density and viscosity ratios of the dispersed phase to the continuous phase reduces the contribution of local advection and diffusion terms to the momentum transport, respectively, resulting in drag reduction. Therefore, we concluded that the decreased density ratio and the decreased viscosity ratio work together to compete with the presence of a two-phase interface for achieving drag modulation in fluid–fluid two-phase turbulence. [ABSTRACT FROM AUTHOR]

An experimental investigation identifying the effects of surface roughness on the drag coefficient ($C_{D}$) of freely rolling spheres is reported. Although lubrication theory predicts an infinite drag force for an ideally smooth sphere in contact with a smooth wall, finite drag coefficients are obtained in experiments. It is proposed that surface roughness provides a finite effective gap ($G$) between the sphere and panel, resulting in a finite drag force while also allowing physical contact between the sphere and plane. The measured surface roughnesses of both the sphere and panel are combined to give a total relative roughness ($\xi$). The measured $C_{D}$ increases with decreasing $\xi$ , in agreement with analytical predictions. Furthermore, the measured $C_{D}$ is also in good agreement with the combined analytical and numerical predictions for a smooth sphere and wall, with a gap approximately equal to the root-mean-square roughness ($R_q$). The accuracy of these predictions decreases for low mean Reynolds numbers ($\overline {Re}$), due to the existence of multiple scales of surface roughness that are not effectively captured by $R_{q}$. Experimental flow visualisations have been used to identify critical flow transitions that have been previously predicted numerically. Path tracking of spheres rolling on two panels with different surface roughnesses indicates that surface roughness does not significantly affect the sphere path or oscillations. Analysis of sphere Strouhal number ($St$) highlights that wake shedding and sphere oscillations are coupled at low $\overline {Re}$ but with increasing $\overline {Re}$ , the influence of wake shedding on the sphere path diminishes. [ABSTRACT FROM AUTHOR]

This study aims to provide insights into the intricate interactions between gas and liquid phases within flow components, which are pivotal in various industrial sectors such as nuclear reactors, oil and gas pipelines, and thermal management systems. Employing the Eulerian–Eulerian approach, our computational model incorporates interphase relations, including drag and non-drag forces, to analyze phase distribution and velocities within a complex U-bend system. Comprising two horizontal-to-vertical bends and one vertical 180-degree elbow, the U-bend system's behavior concerning bend geometry and airflow rates is scrutinized, highlighting their significant impact on multiphase flow dynamics. The study not only presents a detailed exposition of the numerical modeling techniques tailored for this complex geometry but also discusses the results obtained. Detailed analyses of local void fraction and phase velocities for each phase are provided. Furthermore, experimental validation enhances the reliability of our computational findings, with close agreement observed between computational and experimental results. Overall, the study underscores the efficacy of the Eulerian approach with interphase relations in capturing the complex behavior of the multiphase flow in U-bend systems, offering valuable insights for hydraulic system design and optimization in industrial applications. [ABSTRACT FROM AUTHOR]

Unlike uniform motion, when an object moves underwater with variable speed, it experiences additional resistance from the water, commonly referred to as added mass force. At present, several methods exist to solve this force, including theoretical, experimental, and simulation approaches. This paper addresses the challenge of determining the added mass force for irregularly shaped small objects undergoing variable speed motion underwater, proposing a method to obtain the added mass force through numerical simulation. It employs regression analysis and parameter separation analysis to solve the added mass force, added mass, viscous drag coefficient, and pressure drag coefficient. The results indicate that an added mass force exists during both the acceleration and deceleration of the object, with little difference between them. Under the same velocity conditions, significant differences exist in pressure drag forces, while differences in viscous drag forces are not significant. This suggests that the primary source of added mass force is pressure drag, with viscous drag having little effect on it. During acceleration, the surrounding fluid accelerates with the object, increasing the pressure drag with a high-pressure area concentrating at the object's front, forming an added mass force that is directed backward. By contrast, during deceleration, the fluid at the object's front tends to detach, and the fluid at the rear rushes forward, leading to a smaller high-pressure area at the front and a larger one at the rear, reducing the pressure drag and forming an added mass force that is directed forward. By comparing the added mass of a standard ellipsoid obtained from numerical simulation with theoretical values, the regression analysis method is proven to be highly accurate and entirely applicable for solving the added mass of underwater vehicles. [ABSTRACT FROM AUTHOR]

Reducing space debris is a critical challenge in current space exploration. This study focuses on designing a drag sail for CubeSat models and examining their aerodynamic properties using the direct simulation Monte Carlo (DSMC) method. The analysis encompasses the aerodynamic performance of intricate three-dimensional shapes with varying sail dimensions at orbital altitudes of 125 km, 185 km, 300 km, and 450 km. Additionally, free molecular flow (FMF) theory is applied and compared with the DSMC findings for both a flat-plate model and the CubeSat. The results reveal that FMF accurately predicts the drag coefficient at altitudes of 185 km and above, while significant discrepancies occur at lower altitudes due to increased inter-molecular collisions. This study also suggests that the drag sail substantially enhances the CubeSat's drag force, which effectively reduces its deorbiting time. [ABSTRACT FROM AUTHOR]

The results of a numerical study of the flow around a circular rotating cylinder under the subcritical regime of the Reynolds number are presented. A numerical flow simulation was carried out using the Realisable k-ε turbulence model, which effectively visualizes the fallout of vortices. At Reynolds numbers 16,000, 30000, and 50,000 and revolutions 300,500 and 700, the velocity field around the cylinder with the plate and the static pressure distribution field around the cylinder with the plate are obtained. It is determined that with an increase in the rotation frequency of the cylinder with the plate, the vortex formation increases. In the future, there will be an increase in lifting force and drag force due to an increase in flow velocity and, consequently, a decrease in pressure. Due to the rotational motion, there is a change in the pressure field at the ends of the cylinder with the plate. [ABSTRACT FROM AUTHOR]

Imitating Dolphin fish-like movement is productive method for enhancing their hydrodynamic capabilities. This work aims to analyze and understand the oscillations of tail fluke of Dolphin, which can be used as a propulsive mechanism for underwater fish robots and vehicles. The objective of the work is to achieve the desired oscillating amplitude by simulating the NACA 0012 profile using computational models and Set up the swimming movement of the dolphin, imitating a fish like model. Computational techniques were employed to examine the propulsive capabilities of the oscillating hydrofoil, inspired by the dolphin's biological propulsion. The evolutionary of fluid pattern in the field surrounding both Dolphin fish model and the NACA0012 hydrofoil, from initial motion to cruising, was established, and the hydrodynamic impact was subsequently studied. An user-defined function (UDF) was developed to create a dynamic mesh interface with CFD code ANSYS FLUENT for establishing the oscillations of Dolphin tail across the flow field. Influencing hydrodynamic coefficients such as lift and drag coefficients at different frequencies were also obtained. The findings shown that when the acceleration of the Dolphin fish model increases, the time averaged drag force coefficient drops because The wake field's vortex disperses to have some beneficial effects and pressure of water surrounding the fish head intensifies to produce a large resistance force. Simulation results show a 98% agreement at lower frequency and speed levels but a 5% deviation at higher frequency and speed due to turbulence effects in both models. It was established that the vortex superposition enhances the Dolphin fish like model rather than lowering its positive impacts. The Strouhal number, which is obtained by the fluid field's evolution rule, can be linked to the Kármán vortex street span with reverse. [ABSTRACT FROM AUTHOR]

The force exerted on a cylindrical intruder as it penetrates a granular medium was analyzed utilizing both experiments and the discrete element method (DEM). In this work, a series of penetration experiments were performed, considering cylindrical intruders with different nose shapes. We found that the drag force of the intruder with a hemispherical nose is close to that of those with conical noses with apex angles of 53° and 90°. The drag force of the blunt-nosed intruder is bigger; the drag force of the conical-nosed intruder with an apex angle of 37° is the smallest. We studied the interplay between the drag force on an intruder with a hemispherical nose and key variables—the penetration velocity (V), penetrator's diameter ( d i ), and friction coefficient (μ). From this analysis, two piecewise functions were derived: one for the average drag force versus the penetration velocity, and the other for the scaled drag force versus the friction coefficient. Furthermore, the average drag force per contact point, Fa/P, can be succinctly represented by two linear relationships: Fa/P = 0.232 μ + 0.015(N) for μ < 0.9 , and Fa/P = 0.225(N) for μ ≥ 0.9 . [ABSTRACT FROM AUTHOR]

Solution to the high pressure drop in the dry gas desulfurization tower of a certain company' s liquid phase diesel hydrogenation unit was introduced. The main measures to control the pressure drop of dry gas desulfurization tower are determined through the combination of Storks law theory analysis and experiments, including reducing the flow rate of sulfur-containing dry gas and solving the problem of packing layer blockage. The results show that if the sulfur-containing dry gas flow rate was reduced from 7,600 m³/h to 6,500 m³/h, the pressure drop of the dry gas desulfurization tower was decreased by 6. 5 kPa, and the effect was poor. The blockage of the filling layer is mainly due to the large amount of high carbon solid particles in the upstream lean amine solution, which suspend and settle in the lean amine solution. According to Storks law and utilizing this drag force characteristic, the settling speed of solid black particles is 0. 012 m/s. Therefore, through the full tower operation, the lean amine solution inside the packing tower was quickly sent out, and the high-speed flow generated drag force opposite to settlement, which was enough to suspend it and remove a large number of high carbon solid particles from the packing. The pressure drop of the dry gas desulfurization tower was quickly decreased from 53 kPa to 1 kPa. The problem of high pressure drop caused by blockage of high carbon solid particles in the packing layer was solved, with strong operability and significant effects. [ABSTRACT FROM AUTHOR]

Wall-based spanwise forcing has been experimentally used with success by Auteri et al. (Phys. Fluids, vol. 22, 2010, 115103) to obtain large reductions of turbulent skin-friction drag and considerable energy savings in a pipe flow. The spatial distribution of the azimuthal wall velocity used in the experiment was not continuous, but piecewise constant. The present study is a numerical replica of the experiment, based on a set of direct numerical simulations (DNS); its goal is the identification of the effects of spatially discrete forcing, as opposed to the idealized sinusoidal forcing considered in the majority of numerical studies. Regardless of the discretization, with DNS the maximum drag reduction is found to be larger: the flow easily reaches complete relaminarization, whereas the experiment was capped at 33% drag reduction. However, the key result stems from the observation that, for the piecewise-constant forcing, the apparent irregularities of the experimental data appear in the simulation data too. They derive from the rich harmonic content of the discontinuous travelling wave, which alters the drag reduction of the sinusoidal forcing. A detailed understanding of the contribution of each harmonic reveals that, whenever for example technological limitations constrain one to work far from the optimal forcing parameters, a discrete forcing may perform very differently from the corresponding ideal sinusoid, and in principle can outperform it. However, care should be exercised in comparison, as discrete and continuous forcing have different energy requirements. [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]

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Space weather indices are used to drive forecasts of thermosphere density, which directly affects objects in low‐Earth orbit (LEO) through atmospheric drag force. A set of proxies and indices (drivers), F10.7, S10.7, M10.7, and Y10.7 are used as inputs by the JB2008, (https://doi.org/10.2514/6.2008‐6438) thermosphere density model. The United States Air Force (USAF) operational High Accuracy Satellite Drag Model (HASDM), relies on JB2008, (https://doi.org/10.2514/6.2008‐6438), and forecasts of solar drivers from a linear algorithm. We introduce methods using long short‐term memory (LSTM) model ensembles to improve over the current prediction method as well as a previous univariate approach. We investigate the usage of principal component analysis (PCA) to enhance multivariate forecasting. A novel method, referred to as striped sampling, is created to produce statistically consistent machine learning data sets. We also investigate forecasting performance and uncertainty estimation by varying the training loss function and by investigating novel weighting methods. Results show that stacked neural network model ensembles make multivariate driver forecasts which outperform the operational linear method. When using MV‐MLE (multivariate multi‐lookback ensemble), we see an improvement of RMSE for F10.7, S10.7, M10.7, and Y10.7 of 17.7%, 12.3%, 13.8%, 13.7% respectively, over the operational method. We provide the first probabilistic forecasting method for S10.7, M10.7, and Y10.7. Ensemble approaches are leveraged to provide a distribution of predicted values, allowing an investigation into robustness and reliability (R&R) of uncertainty estimates. Uncertainty was also investigated through the use of calibration error score (CES), with the MV‐MLE providing an average CES of 5.63%, across all drivers. Plain Language Summary: Objects in low‐Earth orbit, are affected by atmospheric drag, which depends on density. A currently used thermosphere density model, JB2008, (https://doi.org/10.2514/6.2008‐6438), relies on a collection of space weather solar drivers as inputs. Currently, these drivers rely on a linear forecasting algorithm, which supplies single point forecasts for 6 days. No current methods exist for providing probabilistic forecasts and uncertainty estimates for three of the drivers. In this work, we introduce a machine learning approach which provides a probabilistic forecast of all solar drivers used by JB2008, (https://doi.org/10.2514/6.2008‐6438). The new approach uses a combination of individual predictions, which can be combined to produce less error than the current operational method. This new approach provides improvement over single point forecasting made by the operational method and provides a measure of confidence in the forecasted values. Key Points: A new striped sampling approach is developed to achieve improved performance on limited dataEnsemble methods show promise for short term forecasting of JB2008 solar drivers and provide robust and reliable uncertainty estimatesStacked neural network ensemble methods provide the best short‐term solar driver forecasts [ABSTRACT FROM AUTHOR]

A numerical simulation of the Herschel–Bulkley laminar steady state shear flow around a stationary particle located on a sedimentation layer was carried out. The surface of the sedimentation layer was formed by hemispheres of the same radius as the particle. The drag force, lift force, and torque values were obtained in the following ranges: shear Reynolds numbers for a particle  R e S H = 2 – 200 , corresponding to laminar flow; power law index  n = 0.6 – 1.0 ; and Bingham number  B n = 0 – 10 . A significant difference in the forces and torque acting on a particle in shear flow in comparison to the case of a smooth wall is shown. It is shown that the drag coefficient is on average 6% higher compared to a smooth wall for a Newtonian fluid but decreases with the increase in non-Newtonian properties. At the edge values of  n = 0.6  and  B n = 10 , the drag is on average 25% lower compared to the smooth wall. For a Newtonian fluid, the lift coefficient is on average 30% higher compared to a smooth wall. It also decreases with the increase in non-Newtonian properties of the fluid, but at the edge values of  n = 0.6  and  B n = 10 , it is on average only 3% lower compared to the smooth wall. Approximation functions for the drag, lift force, and torque coefficient are constructed. A reduction in the drag force and lifting force leads to an increase in critical stresses (Shields number) on the wall on average by 10% for incipient motion (rolling) and by 12% for particle detachment from the sedimentation bed. [ABSTRACT FROM AUTHOR]