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

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

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

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

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

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

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

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

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

Inertial focusing in curved microfluidic ducts exploits the interaction of the drag force from the Dean flow with the inertial lift force to separate particles or cells laterally across the cross-section width according to their size. Experimental work has identified that using a trapezoidal cross section, as opposed to a rectangular one, can enhance the sized based separation of particles/cells over a wide range of flow rates. Using our model, derived by carefully examining the way the Dean drag and inertial lift forces interact at low flow rates, we calculate the leading order approximation of these forces for a range of trapezoidal ducts, both vertically symmetric and nonsymmetric, with an increasing amount of skew towards the outside wall. We then conduct a systematic study to examine the bifurcations in the particle equilbira that occur with respect to a shape parameter characterizing the trapezoidal cross section. We reveal how the dynamics associated with particle migration are modified by the degree of skew in the cross-section shape, and show the existence of cusp bifurcations (with the bend radius as a second parameter). Additionally, our investigation suggests an optimal amount of skew for the trapezoidal cross section for the purposes of maximizing particle separation over a wide range of bend radii. [ABSTRACT FROM AUTHOR]

In this study, the aerodynamic performance of a cambered wind turbine airfoil with a partially flexible membrane material on its suction surface was examined experimentally across various angles of attack and Reynolds numbers. It encompassed physical explanation at the pre/post-stall regions. The results of particle image velocimetry revealed that the laminar separation bubble was diminished or even suppressed when a local flexible membrane material was employed on the suction surface of the wind turbine blade close to the leading edge. The results of the deformation measurement indicated that the membrane had a range of flow modes. This showed that the distribution of aerodynamic fluctuations due to the presence of LSB-induced vortices was reduced. This also led to a narrower wake region occurring. Aerodynamic performance improved and aerodynamic vibration significantly lowered, particularly at the post-stall zone, according to the results of the aerodynamic force measurement. In addition to the lift force, the drag force was enormously reduced, corroborating and matching well with the results of PIV and deformation measurements. Consequently, significant benefits for a turbine blade were notably observed, including aerodynamic performance enhancement, increased aerodynamic power efficiency, and reduced aerodynamic vibration. [ABSTRACT FROM AUTHOR]

Water–air trans-media unmanned vehicle is a kind of aircraft, which can freely fly in the air, sail in the water and pass through free surface. For trans-media aircrafts, the development process from air–surface to air–underwater and from submarine-launched drive to autonomous drive is investigated. By analyzing the characteristic of manta ray, flying fish and existing aircraft, this paper proposes a new water–air trans-media unmanned vehicle with flat dish-airfoil-shaped main body and telescopic NACA-type wing. Then the numerical method to calculate the lift and drag forces is established and validated by the results of classic NACA cases. On this basis, the flow field around the new vehicle is numerically simulated, and its lift–drag performances in different media (air and water) and ground effect are analyzed, comparing it with a model inspired by the Blackwing Unmanned Aerial Vehicle (UAV). The findings illustrate the superior performance of the new vehicle in terms of lift and drag forces, offering an innovative design framework for water–air trans-media UAV applications. [ABSTRACT FROM AUTHOR]

Satellites in very low Earth orbits can leverage the aerodynamics forces for control purposes. Three-axis attitude control can be achieved by adjusting the orientation of aerodynamic surfaces, benefiting from both drag and lift forces. However, complete control over the orbital motion of a satellite is unattainable using aerodynamic forces alone, as positive thrust cannot be generated. Nonetheless, this limitation does not apply when focusing on the control of a satellite formation. By properly modulating the orientation of panels, positive and negative relative forces can be generated. This paper shows that even in a formation of simple microsatellites, it is possible to achieve formation and attitude simultaneous control by using no other actuators than the aerodynamics surfaces. • Very Low Earth orbits are appealing but the large atmospheric density can be a problem. • The atmospheric forces can be used for control purposes. • Formation control and attitude control can be individually realized by using aerodynamic forces. • A GNC architecture is implemented to realized both goals with the same aerodynamic actuators. • Performance in keeping or acquiring a desired state (attitude and relative position) is promising. [ABSTRACT FROM AUTHOR]

The initial flow past an impulsively started rotating and translating circular cylinder is asymptotically analysed using a Brinkman penalization method on the Navier-Stokes equation. In our previous study (J. Fluid Mech., vol. 929, 2021, A31), the asymptotic solution was obtained within the second approximation with respect to the small parameter, ϵ, that is of the order of 1/λ. Here, λ is the penalization parameter. In addition, the Reynolds number based on the cylinder radius and the translating velocity is assumed to be of the order of ϵ. The previous study asymptotically analysed the initial flow past an impulsively started translating circular cylinder and investigated the influence of the penalization parameter λ on the drag coefficient. It was concluded that the drag coefficient calculated from the integration of the penalization term exhibits a half-value of the results of Bar-Lev & Yang (J. Fluid Mech., vol. 72, 1975, pp. 625-647) as λ→∞. Furthermore, the derivative of vorticity in the normal direction was found to be discontinuous on the cylinder surface, which is caused by the tangential gradient of the pressure on the cylinder surface. The present study hence aims to investigate the variance on the drag coefficient against the result of Bar-Lev & Yang (1975). First, we investigate the problem of an impulsively started rotating circular cylinder. In this situation, the moment coefficient is independent of the pressure on the cylinder surface so that we can elucidate the role of the pressure to the hydrodynamic coefficients. Then, the problem of an impulsively started rotating and translating circular cylinder is investigated. In this situation, the pressure force induced by the unsteady flow far from the cylinder is found to play a key role on the drag force for the agreement with the result of Bar-Lev & Yang (1975), whereas the variance still exists on the lift force. To resolve the variance, an alternative formula to calculate the hydrodynamic force is derived, assuming that there is the pressure jump between the outside and inside of the cylinder surface. The pressure jump is obtained in this analysis asymptotically. Of particular interest is the fact that this pressure jump can cause the variance on the lift force calculated by the integration of the penalization term. [ABSTRACT FROM AUTHOR]

The high-speed projectile moving near the sea level will significantly suffer from the effects of waves. The water entry and exit of a high-speed projectile crossing a wave are investigated by detached-eddy simulation. Three simulations with different altitudes through the wave are conducted to analyze the altitude's influence on the cavity dynamics. To validate the numerical model, a water-entry experiment is carried out in a wave tank for comparison. The projectile crossing the wave forms a cavity channel from water entry to exit. Because the water below the cavity is more difficult to displace than the atmosphere with the water surface under the cavitation effects, the downward expansion of vapor is blocked, and the wave surface is lifted. Consequently, the cavity above the projectile expands more strongly until breaking through the water surface, while the cavity below the projectile keeps closed, and the projectile is wetted. Thus, a nose-up pitching moment is generated at water entry, while the drag force is gradually enhanced during the water exit, and a lift force acts toward the atmosphere. As the altitude increases, the upper cavity becomes more open, but the lower cavity shrinks, leading to the augmentation of the lift force. [ABSTRACT FROM AUTHOR]

Birds employ rapid pitch-up motions close to the ground for different purposes: perching birds use this motion to decelerate and come to a complete stop while hunting birds, such as bald eagles, employ it to catch prey and swiftly fly away. Motivated by these observations, our study investigates how natural flyers accomplish diverse flying objectives by rapidly pitching their wings while decelerating near ground. We conducted experimental and analytical investigations focusing on rapidly pitching plates during deceleration in close proximity to the ground to explore the impact of ground proximity on the unsteady dynamics. Initially, we executed synchronous pitch-up motion, where both pitching and deceleration have the same motion duration, at different ground heights. Experimental results demonstrate that as the pitching wing approaches the ground, the instantaneous lift increases by approximately 38% compared with a far-from-ground case, while the initial peak drag force remains relatively unchanged. Our analytical model conforms to this trend, predicting an increase in lift force as the wing approaches the ground, indicating enhanced added mass and circulatory lift force due to the ground effect. Next, we examined asynchronous pitch-up motion cases, where rapid pitching motions were initiated at different stages of deceleration. The results reveal that initiating the wing pitch early in the deceleration leads to the formation of larger counter-rotating vortices at the early stage of the manoeuvre. These vortices generate stronger dipole jets that orient backward in the later stages of the manoeuvre after impinging with the ground surface, which hunting birds utilize to accelerate after catching prey. Conversely, when the wing pitch is delayed, smaller vortices form, but their growth is postponed until late in the manoeuvre. This delayed vortex growth produces lift and drag force at the end phase of the manoeuvre that facilitates a smooth landing or perching. Thus, through strategic tuning of a rapid pitch-up motion with deceleration, natural flyers, such as birds, achieve diverse flying objectives. [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 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]

The object of this study is the process of descending illumination elements equipped with a braking device in the form of two-bladed grills rotating in different directions. The classic parachute method does not provide the necessary speed of descent, it has low illumination parameters and significant drift of illumination elements by side wind. To solve the tasks set, mathematical dependences were obtained for calculating the aerodynamic characteristics of the descent device with the illumination element and its delivery to the ejection point. The drag and lift force coefficients during the flow around the blades of a dual-rotor impeller with different Reynolds numbers were determined by the method of numerical modeling based on the ANSYS CFX software package. The optimal geometric characteristics of the profile satisfying the condition for the necessary speed of descent of the illumination element at the given weight of the descent apparatus were determined. Reasonable requirements for illumination parameters and an improved composition of the flare have been proposed. A mathematical model of the movement of a body of variable mass to the point of ejection of the illumination element was built. The new design of the descent device makes it possible to reduce the speed of descent by 10–15 % and increase the weight of the payload by 20–30 %. The proposed illumination composition provides sufficient illumination of the object for 5 minutes with a light intensity of 2–2,5 million candelas and an average diameter of the illuminated area of 2000–2500 m. The mathematical model of the movement of a variable mass body to the point of the illumination element ejection makes it possible to determine with high accuracy the gun firing settings with illumination ammunition (30–40 % more accurate) and the time of ejection of illumination elements. Results of the current research make it possible to solve the scientific problem of ensuring the maximum efficiency of illuminating the terrain at night [ABSTRACT FROM AUTHOR]

Investigation of a portable three-axis load/balance measurement system in a mini wind tunnel is the main subject of study. Firstly, a mini wind tunnel is designed, numerically analyzed and constructed. Then, measurements of lift and drag forces on a selected airfoil are carried out using data from the measurement system located in the test area. Tri-axis load/balance measurement system developed has a total of three load cells, one for drag and two for lift. Sensor data acquisition codes are written using Ardunio and force measurement experiments are performed at various angles of attack on the NACA2412 airfoil at Reynolds number of 60000, for the maximum flow rate of 5200 m3 /h through fan controller in the constructed mini wind tunnel. After completing the mesh independence test, numerical studies are conducted in ANSYS Fluent for the same range of angles of attack using three different turbulence models. Realizable k-ε turbulence model gives more realistic high stall angles of attack than other turbulence models and similar to experimental results. In addition to the current experimental study, four other literature studies in similar Reynolds number ranges are used as reference cases. A visual study of the flow around the airfoil is given as velocity contours in addition to the numerical comparisons. From the numerical and experimental results, it is concluded that the NACA2412 airfoil profile wings are more efficient for moderate to high Reynolds numbers and the constructed load/balance measurement system and mini wind tunnel are highly successful in terms of lift and drag measurements. [ABSTRACT FROM AUTHOR]

To understand passive vortex-induced vibrations (VIV) coexisting with active structure motions, this paper numerically investigates the use of pure pitch oscillation to control a square cylinder mounted with a deformable splitter plate at the Reynolds number of 333. The oscillation is enforced with an amplitude of 3° and different frequencies from 0 to 6 Hz. Direct numerical simulations using a partitioned method with a semi-implicit coupling algorithm are performed. According to the trajectories of the splitter-plate tip displacement with respect to the lift or drag force coefficient, a specific lock-in regime determined by the frequency of the enforced pitch oscillation is identified. Further spectral analyses of the tip displacement and lift force show that the lock-in frequencies are equal to the enforced frequencies. Next to the lock-in regime, semi-lock-in regimes with narrow bandwidths are distinguished, exhibiting both lock-in and non-lock-in features. In the non-lock-in regimes, the frequencies of the most predominant peaks in the spectra are found near the natural frequency of the splitter plate of 3.236 Hz, and the frequencies of the two secondary peaks are distributed along the characteristic lines following the ratios of these frequencies to the enforced frequency, which are ±1. Thus, the interaction is dependent on the combined effects of the passive VIV and the actively enforced pitch oscillations. Moreover, the intersection points of the characteristic lines are located close to the upper and lower frequency limits of the lock-in regime, inferring the conditions for the lock-in onset. [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]

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]

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]

The study of the aerodynamic properties of wings is considered one of the most prominent topics in the field of aircraft manufacturing in general and drones in particular. This research focuses on studying the aerodynamic properties of an unmanned aerial vehicle wing with a streamlined aerodynamic section that falls under the NACA 0012 classification. The wing is made of aluminium, with dimensions of 30 x 30 cm. It was tested at angles of attack (0, 5, 10, 15, 18 degrees) and at speed values of 12, 15, 18, 21, and 23 metres per second to determine the aerodynamic features of the test section. This test was done through a subsonic tunnel. These parameters are crucial in understanding how a wing behaves under different flight conditions. One of the most prominent results reached in this research is the increase in drag forces when the angle of attack and wind speed increase. The maximum value obtained is 9.6 Newtons at an angle of attack of 18 degrees and a wind speed of 23 m/s. The maximum lift factor was 0.1856 at an angle of attack of 15 degrees and an average wind speed of 21 m/s. [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]

The interaction mechanism of external flow with two inline rectangular cylinders having different aspect ratios under the impact of gap spacing (G) is the subject of this research. The gap spacing between the cylinders was varied from 0.25 to 20 times their size. Both cylinders were vertically mounted, with the first having a higher aspect ratio than the second. The results revealed five distinct flow patterns under the influence of G: single slender body, shear layer reattachment, intermittent shedding, binary vortex street, and single-row vortex street. The mean pressure on both cylinders was found to vary due to changes in flow patterns. Both cylinders bore the same shedding frequency but had different pressure variations. The second cylinder placed in the wake of first experienced negative average drag force for some spacing values, while the first cylinder had positive average drag values for all chosen G. Due to the change in flow pattern from shear layer reattachment to intermittent shedding flow, the negative drag force on the second cylinder jumped to a positive drag. It was also observed that the rms values of drag and lift force coefficients, as well as their amplitudes for the second cylinder, were mostly higher than corresponding values for the first cylinder at all selected G. This study revealed that G = 4 and 8 are the critical gap spacing values due to sudden changes in fluid force parameters. [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]

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]

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]

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]

NACA 0012 symmetric airfoil is commonly used for the aerodynamic analysis of aircraft. This research work investigates modifications in the airfoil design to improve the lift-drag ratios. The initial phase involves computational analysis on the two-dimensional airfoil and later, the obtained results were validated by comparing them to standard data obtained by calculations. The modified airfoil designs are stepped trailing edge, tubercle leading edge and combination of both. The design alterations implemented was based on insights gained from various simulations with the adjustment in angle of attack ranging from 0° to 8°. The stepped design in trailing edge generated less drag and produced less lift. Whereas, the tubercle in leading edge of airfoil exhibited more drag and lift forces. Although generation of lift is favourable for an aircraft, it is of paramount importance to reduce its drag counterpart for efficient flying. Hence, the characteristics of tubercle leading edge and stepped trailing edge airfoil was incorporated into a single airfoil and their aerodynamic performance results were explained in this paper. [ABSTRACT FROM AUTHOR]

Biomass straw fuel has the advantage of low-carbon sustainability, and therefore, it has been widely used in recent years in coupled blending combustion with coal-fired utility boilers for power generation. At present, the drag force FD, the lift force FL, and the torque T evaluation model are very limited. In this study, within a wide range of Reynolds numbers (10 ≤ Re ≤ 2000) and incident angles (0° ≤ θ ≤ 90°), the computational fluid dynamics open source code OpenFOAM-body-fitted mesh method is used to carry out the direct numerical simulation of the flow characteristics of large cylindrical biomass particles with a high aspect ratio of L/D = 9:1. The results show that (1) the projected area of the cylinder begins to decrease after reaching the maximum at θ = 15°, while the change in the incident angle causes the formation of a smaller recirculation zone on the leeward side of the structure, and the effect of the pressure difference on the drag coefficient (CD) is reduced. (2) The lift coefficient (CL) displays a parabolic symmetric distribution when θ = 45°, and then the distribution becomes asymmetrical when Re > 100. The torque coefficient (CT) exhibits a similar trend. (3) Based on the simulation data and the literature data, new models for CD, CL, and CT for cylinders with L/D = 9:1, 10 ≤ Re ≤ 2000 and 0° ≤ θ ≤ 90° are obtained, and the mean square errors are 2.4 × 10−2, 1.4 × 10−2, and 6.4 × 10−2, respectively. This new model can improve the accuracy and adaptability of the universal model of gas–solid dynamics for biomass particles. [ABSTRACT FROM AUTHOR]

The presence of particles with a small but finite size, suspended in viscous fluids with low volumetric concentrations, is observed in many applications. The present study focuses on the tridimensional and incompressible lid-driven flow of Newtonian fluids through the application of the immersed boundary method and the Euler–Lagrange approach. These methods are used to numerically predict three-dimensional particle motion by considering nearly neutrally buoyant conditions as well as all relevant elementary processes (drag and lift forces, particle rotation, particle–wall interactions, and coupling between phases). Considering the current stage of the numerical platform, two coupling approaches between phases are considered: one-way and two-way coupling. A single particle is inserted in the cavity after steady-state conditions are achieved. Its three-dimensional motion is obtained from numerical simulations and compared with research data, considering the same conditions, evidently showing that the particle trajectory follows the experimental data until the first collision with a solid surface. After this first contact, there is a deviation between the results, with the two-way coupling results better representing the experimental data than the one-way coupling results. The dimensionless forces' peaks acting on the particles are associated with the relative velocity of the particle near the wall–particle collision position. In terms of magnitude, in general, the drag force has shown greater influence on the particle's motion, followed by the rotation-induced and shear-induced lift forces. Finally, a special application is presented, in which 4225 particles are released into the domain and their dynamic is evaluated throughout dimensionless time, showing similar behavior for both couplings between phases, with variations in local concentrations observed in certain regions. The mean square displacement used to quantify the dispersion evolution of the particles showed that the particulate flow reaches an approximately homogeneous distribution from the moment of dimensionless time tU/S = 130. [ABSTRACT FROM AUTHOR]

Feedforward neural network (FNN) models with strong learning ability and prediction accuracy are crucial for optimization. This paper investigates the effects of the number of training samples and the hidden layers on the accuracy of the FNN model. Meanwhile, under the premise of a high space-fillingness degree, a sample expansion strategy based on the max--min distance criterion is proposed, which ensures that the expanded sample set completely contains the pre-expanded. The strategy can eliminate the interference of sample differences. Furthermore, the multi-objective optimization on the train nose shape is accomplished by minimizing the aerodynamic lift force of the tail car (LT), as well as the aerodynamic drag force of the head (DH) and tail car (DT) using the FNN model. The results indicate that the number of training samples has a greater impact on the prediction error of the FNN model than the number of hidden layers does. Prediction errors decrease as the number of training samples increases and then stabilise, the most accurate one is chosen for nose shape optimization. The DH, DT, and LT all have prediction errors of less than 2%. Compared with the original high-speed train, the DH, DT, and LT of the optimal model are reduced by 5.24%, 3.74%, and 2.61%, respectively. Meanwhile, the correlation analysis reveals that the height of the cab window and the horizontal profile have a significant impact on the aerodynamic characteristics of the high-speed train. [ABSTRACT FROM AUTHOR]

The aerodynamic performance of a morphing airfoil is numerically and experimentally investigated. The morphing airfoil is designed based on macro fiber composites, capable of trailing edge flapping during 10–90 Hz with a maximum amplitude of 0.55 mm. A numerical model with flexible deformation walls based on the experiment is established to precisely restore the actual dynamic morphing instead of segmental deformation to explore the transient aerodynamic performance of high-frequency flapping. The drag coefficient is reduced by 2.07% at the flapping frequency (ff) of 37.5 Hz compared with the rigid airfoil, while the drag coefficient and the lift coefficient increase by 4.8% and 5.8% for ff at 600 Hz. The vortex is broken up by flapping, and the corresponding position has been forwarded to the tail. Dynamic mode decomposition shows that the wing's flapping dominates the second mode and the high-frequency vortex has changed to low-frequency. The energy of higher modes is transferred to lower-order modes that the first mode's power has risen sharply from 49.29% of the rigid airfoil to 91.83%. In the wind tunnel experiment, the lift and drag forces are increased by 1.88% and 0.77% at the flapping frequency of 40 Hz, respectively. Furthermore, the lift force frequency is locked by flapping and changes from 124.9 Hz of the rigid airfoil to the flapping frequency, consistent with the computational fluid dynamics results. The research has provided a solution to reduce the drag force and increase the lift force of the aircraft by the trailing edge flapping. [ABSTRACT FROM AUTHOR]

In this investigation, two-dimensional flow past square cylinders with slip boundary have been studied with the lattice Boltzmann method. Three modes, which are a single cylinder, an oblique cylinder, and side-by-side cylinders, are investigated with Reynolds numbers from 25 to 200 while relative slip length ranges from 0 to 0.1. It can be concluded that both the flow state and the slip boundary have a great effect on the drag reduction rate. For a single square cylinder, drag forces decrease with larger slip length while the Strouhal number is almost constant. For an oblique cylinder, the slip length also has effects on the stability of the flow except the drag and lift forces. Vortex separation delays with a slip wall of oblique cylinder. For side-by-side cylinders, the jet between two cylinders is not conducive to the drag reduction rate of the slip boundary. Moreover, the application of slip boundary may also lead to additional drag force as vortex separation intensifies, which is extremely different from simple channel flows. Studies have shown that the slip boundary does not always reduce the drag in some complex flow fields. It can be concluded that the drag reduction effect of slip boundaries is more effective in uniform flow. [ABSTRACT FROM AUTHOR]

The forces arising on the ship's rudderat different angles of attack in an unbounded flow are investigated. The components of the resulting force on the rudder are represented in terms of the rudder lift and drag forces, as well as in terms of the normal and tangential forces on the rudder. The well-known mathematical models of hydrodynamic rudder coefficients are analyzed, and their disadvantages are found. New mathematical models of hydrodynamic coefficients have been obtained, in particular, the coefficients of rudder lift and drag, which take into account the aspect ratio of the rudder, its relative thickness and can be applied to any angle of attack of the flow on the rudder. On specific examples for rudders of the NACA series, the adequacy of the proposed models and their consistency with known experimental studies are illustrated. It is shown how the rudder lift and drag change, as well as the components of the resulting force for the maximum possible range of changes in the local drift angle and the rudder angle. [ABSTRACT FROM AUTHOR]

This paper focused on the investigation of the blades for a carousel rotor of a wind turbine with a vertical axis. Cross sections of the single coherent (SC) and the dual coherent (DC) blades were compared in terms of the aerodynamic forces and aerodynamic torque generated during rotor operation for various wind attack angles. The design of the DC blade is novelty proposed by the authors. The main objective of the study was to determine the influence of the blade cross-section on the propelling torque of a wind turbine with three blades, which is an important parameter for rotor starting. First, experimental studies were carried out in a wind tunnel for real-size blade models. A CFD analysis of the airflow around the blades was then conducted. The obtained results were used to evaluate the suitability of applying the studied blade types in the design of the carousel wind rotor. The assessment compared the drag force and the lift force as well as aerodynamic torque as a function of a wind attack angle. It was concluded that the rotor with three DC blades involved mainly the drag force in contrast to the rotor with three SC blades that also involved the lift force to a greater extent. Despite the rotor with DC blades obtained greater values of the drag forces on the blades, the rotor with SC blades obtained a greater starting torque. [ABSTRACT FROM AUTHOR]

The flow past an inclined cylinder is simulated using large eddy simulations to study the three-dimensional wake flow effects on the forces on the cylinder at Re = 3900. Four inclination angles of α = 0°, 30°, 45°, and 60° are considered. The validity of the independence principle (IP) at the four investigated angles is examined. The results suggest that IP can predict the vortex shedding frequency at 0° ≤ α ≤ 60°, while it fails to predict the drag, lift, and pressure coefficients variations because the three-dimensional effect is neglected for IP. A comprehensive analysis is performed to provide insights into the three-dimensional effects on the drag and lift forces caused by α. The flow velocities, the Reynolds stress, and the spanwise characteristic length of the flow structures are discussed in detail. It is found that the recirculation length reaches its maximum at α = 45°, which results in the smallest drag coefficient and lift force amplitudes. The spanwise characteristic lengths of the vortices are similar for all cases, while spanwise traveling patterns are observed only for α > 0°. A force partitioning analysis is performed to quantify the correlations between the forces and the spanwise and cross-spanwise vortices. It reveals that for α = 30°, the drag force becomes dominated by the cross-spanwise vorticity. With the increasing α, the dominant contribution gradually changes from the cross-spanwise to the spanwise vorticity, and the cross-spanwise vorticity contribution to the drag force further becomes negative at α = 60°. [ABSTRACT FROM AUTHOR]

Inertial microfluidics utilize hydrodynamic forces for particle manipulation and require precise trajectory estimation for efficiency. This study examines parameters affecting micro- and nanoparticle inertial focusing in microchannels by introducing a novel sunflower geometry through asymmetric serpentine segments. This design enhances inertial focusing and particle separation through the Dean effect and continuous acceleration modulation, bolstering operational efficiency. Dynamic variations in lift (FL) and drag forces (FD) within the sunflower geometry augment their ratio, improving particle separation. Asymmetric serpentine attribute enhances lift force by adapting the coefficients (G1 and G2) along the channel and amplifies the net lift force. The varying FL in different sunflower zones concentrates particles of different sizes, while the channel curvature influences FD. While the traditional spiral microchannel only provides global forces due to its radius of curvature, the sunflower microchannel gives rise to the superposition of local forces induced by the expanding and narrowing changing of the serpentine shape and the global forces caused by the spiral shape. The study also examines the differences between local and global force effects on particle focusing. Ultimately, a passive separation of 500 nm particle is achieved by collecting the nanoparticle on the inner surface, while 1 μm particle locates at the central axis and 3.3 μm particle clusters on the outer surface. The significance of the study is that the effective passive particle separation could be managed even for sub micrometer particles without any auxiliary external forces but with inertial forces thanks to the novel sunflower microchannel design. [ABSTRACT FROM AUTHOR]

A vehicle is more stable when the geometric center, center of gravity, and stagnation point are in line. However, the inflow direction and velocity magnitude of the operational environment of road vehicles are varying. This study aims to investigate the aerodynamic behavior of a water-drop-shaped vehicle under side wind conditions. Some essential aerodynamic performances of the vehicle are numerically and graphically analyzed at 0 deg, 10 deg, and 20 deg of side wind directions. The value of the coefficient of drag, drag force, coefficient of lift, and lift force exponentially increases as the yaw angle elevates. The lower part on the area of the front-wheel compartment becomes the critical location indicated by the results on pressure coefficient, friction coefficient, and total wall shear stress distribution along the vehicle surface. Increasing the side wind angle triggers more significant vortex regions generated around the wheel compartment and on the leeward side of the vehicle. [ABSTRACT FROM AUTHOR]

Wind load is one of the key factors affecting the structural safety of long-span bridges. However, the tornado-induced load on the streamlined bridge deck is rarely studied and the influence of the translation of tornado vortices has not been considered. This study develops a computational fluid dynamics (CFD) method to simulate the translating tornado-like vortex (TLV) to investigate the tornado-induced load on the streamlined bridge deck. First, the numerical method for simulating a translating TLV is introduced and the model of the streamlined bridge deck of a kilometer-level bridge is constructed and verified. The characteristics of the flow field around the bridge deck are then analyzed. Finally, the lift force, drag force, and torsional force on the bridge deck in the translating TLV are investigated and compared with those in the straight-line wind field and the stationary TLV. The non-dimensional forces obtained in the translating TLV are provided as a reference for calculating the tornado-induced load on a streamlined bridge deck. The result shows that the wind load on the bridge deck in the TLV changes along the spanwise direction, which is significantly different from that in the straight-line wind field. In the translating TLV, the bridge deck sustains the lift force induced by the updraft and the drag force induced by the translating velocity. The load on the bridge deck in the translating TLV is significantly larger than that in the straight-line wind and the stationary TLV, which indicates that the translation effects of tornadoes should not be ignored. [ABSTRACT FROM AUTHOR]

We consider a problem occurring in a magnetostatic levitation. The problem leads to a linear PDE in a strip. In engineering literature a particular solution is obtained. Such a solution enables one to compute lift and drag forces of the levitating object. It is in agreement with the experiment. We show that such a solution is unique in a class of bounded regular functions. Moreover, as a byproduct, we obtain nonstandard uniqueness results in two linear PDEs in unbounded domains. One of them is an eigenvalue problem for the Laplacian in the strip in the nonstandard class of functions. [ABSTRACT FROM AUTHOR]

Through particle‐resolved direct numerical simulations of flow past arrays of ellipsoids, the hydrodynamic force on ellipsoids depends on the particle orientation, aspect ratio, particle Reynolds number, and solid volume fraction is revealed at moderate Reynolds numbers. The results show that the mean drag force on arrays of prolate/oblate ellipsoids decreases/increases as the Hermans orientation factor increases when flows are in the reference direction defined by the average symmetric axis of particles. The individual drag force on a prolate/oblate ellipsoid increases/decreases with the increase of incidence angle, and it is also affected by the orientation of surrounding particles. The individual lift force is also significant when the aspect ratio is away from unity at large particle Reynolds numbers. Based on simulation results, correlations for the hydrodynamic force on ellipsoids at arbitrary particle Reynolds numbers, solid volume fractions, Hermans orientation factors, incidence angles, and aspect ratios are formulated. [ABSTRACT FROM AUTHOR]