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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]

Transport of particles in flows is often modeled in a combined Eulerian–Lagrangian framework. The flow is evaluated on an Eulerian grid, while particles are modeled as Lagrangian points whose positions and velocities are evolved in time, resulting in particle trajectories embedded in the time-dependent flow field. The method essentially resolves the flow field in complex geometries in detail but uses a closure model for the particle dynamics aimed at including the essential particle–fluid interactions at the cost of detailed small-scale physics. Rarefaction effects are usually included through the phenomenological Cunningham correction on the drag force experienced by the particles. In this Lagrangian point-particle approach, any explicit reference to the finite size and the shape of the particles, and their local orientation in the flow field, is typically ignored. In this work we aim to address this gap by deriving, from fully-resolved Direct Simulation Monte Carlo (DSMC) studies, heuristic or closure models for the drag force acting on prolate and oblate spheroidal particles with different aspect ratios, and a fixed orientation, in uniform ambient rarefied flows covering the transition regime between the continuum and free-molecular limits. These closure models predict the drag in the transition regime for all considered parameter settings (validated with DSMC data). The continuum limit is enforced a priori and we retrieve the free-molecular limit with reasonable accuracy (based on comparisons with literature data). We also include in the models the capability to predict effects related to basic gas-surface interactions via the tangential momentum accommodation coefficient. We furthermore assess the validity of the proposed closure model for particle dynamics in proximity to solid walls. This investigation extends our previous work, which focused on small aspect ratio spheroids with exclusively diffusive gas-surface interactions [see Livi et al. (2022)]. The derived models are obtained for isothermal, subsonic flows relevant for particle contamination control in semiconductor manufacturing. • DSMC-enhanced drag force closures for particle tracking under rarefied gas conditions. • The drag force on finite-size spheroids in the transition regime of rarefied flows. • Towards algorithms for particle contamination control in semiconductor manufacturing. • Covering the device-to-nanoparticle scale separation in high-tech equipment. [ABSTRACT FROM AUTHOR]

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

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

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

Understanding the dynamic response of trees to a strong wind is crucial to alleviating the damages and losses of tree forests caused by windstorms. Previous studies have elucidated small deformations of a broad range of tree species, yet mathematical models that can accurately pinpoint the location and severity of wind-induced damages are still lacking. To bridge this gap, the present work puts forward the first geometrically accurate, physics-based model to capture large deformation of trees induced by a strong wind. The proposed model incorporates a branched tree architecture to represent the topology of a realistic tree. The large, dynamic deformation of the trunk and branches of the tree is described by a system of nonlinear partial differential equations derived from structural theories rooted in classical mechanics. The aerodynamic loading is quantified based on the instantaneous relative velocity between the wind and the tree. The proposed model could successfully reproduce the effects of aerodynamic damping by capturing the nonlinear interplays between the wind and the tree, in contrast to prior analytical models that relied on empirical assumptions of the damping coefficients. The model further reveals a reduction in the drag force due to wind-induced shape reconfiguration, which is enhanced exponentially as a function of the wind speed. The proposed modeling framework could aid in the development of novel forest management strategies to mitigate wind-induced economic and environmental losses. • Quantifying the large dynamic deformation of trees in a strong wind is essential to mitigating wind-induced damages. • This work puts forward the first geometrically accurate, physics-based model to capture the large deformation of trees. • The model incorporates branched tree architectures and structural theories rooted in classical mechanics. • The model accurately captures the effects of aerodynamic damping without empirical assumptions on the damping coefficients. • The analysis reveals that drag reduction enhances exponentially with respect to the wind speed due to shape reconfiguration. [ABSTRACT FROM AUTHOR]

• The measurement of total flow resistance with a novel drag plate system. • Analysis of the effect of emergent or submerged canopies on the total flow resistance. • Accurate estimation of the total flow resistance parameters with simple relations. In canopy flows, flow resistance mainly originates from vegetation drag and depends on vegetation characteristics and flow conditions. In the present study, a series of experiments were performed in various hydraulic scenarios with high stem Reynolds numbers (2641 ≤ Re d ≤ 17333) using relatively sparse rigid canopies, represented with four different dimensionless vegetation densities (0.0044, 0.0098, 0.0174 and 0.0392), on a smooth bed. A novel drag plate mechanism was developed to measure the total flow resistance due to the emergent and submerged vegetation arrays in a staggered pattern under subcritical flow conditions. Manning's roughness coefficient and Darcy–Weisbach friction factor were adopted to represent the total flow resistance in the analyses. Simple empirical relationships based on roughness concentration and submergence ratio were derived to determine the total flow resistance parameters within a broad range of stem Reynolds numbers. Although relationships were proposed in a simple form to be used for direct practical applications, they show similar or better performance in the prediction of total flow resistance parameters than the existing equations in the literature, which require considerable computational effort. Additionally, analyses demonstrated that the results of the present study and those of similar studies regarding canopy flow resistance are in good agreement. Accordingly, the novel drag plate looks promising for measuring flow resistance due to vegetation and bed conditions similar to those in nature. [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]

• Operando observation system is developed to make in-situ test on lab-on-a-chip. • Actual evolution process of charged submicron particles is recorded intuitively. • This work demonstrates direct influence of drag force on particle chain fracture. • It is first-time visualization of mechanism elucidation of particle re-entrainment. Inhalable particle is a harmful air pollutant that causes a significant threat to people's health and ecological environments, which should be removed to purify air, but there exists limited removal efficiency due to particle re-entrainment. Here, Operando observation system based on microscopic visualization method is developed to make in situ test of particle migration, deposition and re-entrainment characteristics on a lab-on-a-chip to achieve the investigation in micro-level scale. The deposition evolution of charged particles is recorded in electric field region intuitively, which confirms the fracture of particle chain occurs during the growth process of deposited particles. It captures the instantaneous process that a larger particle with micron size due to the coagulation of submicron particles fractures from main body of the particle chain for the first time. The analysis of migration behavior of a single submicron particle near electrode surface demonstrates the direct influence of drag force on the fracture of particle chain. This work is the first-time visualization of dynamic process and mechanism elucidation of particle re-entrainment at the micron level, and the findings will provide the theory support for the particle re-entrainment mechanism and bring inspires of enhancing capture efficiency of inhalable particle. [Display omitted] [ABSTRACT FROM AUTHOR]

In recent years, magnetoactive soft continuum robots (MSCRs) with multimodal locomotion capabilities have emerged for various biomedical applications. Developments in nonlinear dynamic models and effective control methods for MSCRs are deemed vital not only to gain a better understanding of their coupled magneto-mechanical behavior but also to accurately steer the MSCRs inside the human body. This study presents a novel dynamic model and model-based AI-driven control method to guide an MSCR in a fluidic environment. The MSCR is fully exposed to fluid flows at different rates to simulate the biofluidic environment within the body. A novel nonlinear dynamic model considering the effect of damping and drag force attributed to fluidic flows is first developed to accurately and efficiently predict the response of the MSCR under varying magnetic and mechanical loading. Fairly accurate correlations were observed between the theoretical responses based on the developed magneto-viscoelastic model and the experimental data for various scenarios. A novel model-based control algorithm based on a fractional-order sliding surface and deep reinforcement learning algorithm (DRL-FOSMC) is subsequently developed to accurately steer the magnetoactive soft robot on predefined trajectories considering varying fluid flow rates. A fractional-order sliding surface and a compensator, trained using the deep deterministic policy gradient algorithm, are designed to mitigate the amount of chattering and enhance the tracking performance of the closed-loop system. The stability proof of the developed control algorithm is also presented. A hardware-in-the-loop experimental framework has been designed to assess the effectiveness of the proposed control algorithm through various case studies. The performance of the proposed DRL-FOSMC algorithm is rigorously assessed and found to be superior when compared with other control methods. • Developing a computationally efficient model for magnetoactive soft continuum robots, accounting for damping and drag force. • Formulating an AI-driven fractional-order sliding mode algorithm to guide the robot on trajectories amid fluid flow rates. • Introducing a deep reinforcement learning-based compensator to cope with unmodeled dynamics and uncertainties of the robot. • Designing an optimal fractional-order sliding surface for control performance improvement. • Fabricating the magnetoactive soft robot and conducting a HIL experimental study to control it under varied fluid flow rates. [ABSTRACT FROM AUTHOR]

Objects in Low-Earth Orbit (LEO) experience a range of environmental conditions that influence their trajectories. Aside from gravitational effects and solar radiation pressure, drag due to the residual background atmosphere is conventionally viewed as the primary perturbing factor. The ionosphere is an additional background environment composed of charged particles that is well-known to result in spacecraft charging, and in the worst case, cause arcing or unwanted electrostatic discharges. While the ionospheric plasma density is typically an order of magnitude (or more) lower than the atmospheric neutral gas density, electrostatic charging can lead to the formation of plasma sheath and wake structures around an object that artificially increase its effective collecting area. Direct charged particle collection and indirect charged particle deflection gives rise to a drag force that can exceed that due to atmospheric neutral gas alone at some altitudes and charging potentials. Here, we present a model accounting for charged particle flow effects (i.e. charged aerodynamics) around objects in LEO, and validate this model with previous particle-in-cell simulations and experiments. Using atmospheric properties from the Mass Spectrometer and Incoherent Scatter radar (MSIS) model and ionospheric properties from the International Reference Ionosphere (IRI), we show that plasma-induced drag in LEO can be significant and may have important orbit prediction implications for space domain awareness and space traffic management. Through differential spacecraft biasing, ionospheric plasma drag can also be used as a propellantless and "solid-state" mechanism to achieve in-orbit mobility for precision maneuvers, formation flying, deorbiting, and even partial attitude control. [Display omitted] • Charging in the ionosphere generates electrostatic fields around spacecraft. • Collection/deflection of charged particles produces a drag force. • Sheath expansion increases the effective collecting area, amplifying plasma drag. • Plasma drag is an additional environmental disturbance affecting spacecraft motion. • Plasma drag can be exploited as a propellantless propulsion mechanism. [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]

Present work is concerned with hydromagnetic bioconvective chemically reactive flow of Reiner-Rivlin nanoliquid. Analysis is constructed for entropy generation. Thermal relation consists of Joule heating, radiation and dissipation. Soret effect for chemically reactive flow is examined. Nonlinear governing systems after adequate transformations are solved by ND-solve technique. Graphical analysis for velocity, microorganism field, entropy rate, thermal field and concentration is analyzed. Graphical description for coefficient of skin friction, microorganism density number, heat transport rate and concentration gradient are studied. Entropy rate increase is detected for higher magnetic parameter while reverse trend holds for velocity. Clearly temperature augments against thermophoresis and radiation. Radiation intensifies entropy rate and heat transport rate. Similar impact of drag force and temperature for magnetic parameter is noticed. Concentration and mass transport rate rise against higher Soret number. Brownian motion variation results in concentration decays. Large Peclet number leads to decrease of microorganism field whereas it intensifies the microorganism density number. [ABSTRACT FROM AUTHOR]

• A novel model of using nSFEM and DPM to solve particle-laden flows. • The super robustness in handling extremely distorted polygonal meshes of the present method. • The unified implementation of mean value coordinates interpolation as shape function and fluid drag interpolation with high-fidelity. • The polygon mesh in this paper shows a great adaptation to complex geometry. In this work, an n-sided polygonal smoothed finite element method (nSFEM) using mean value shape function for concave polygonal element coupled with the discrete phase model (DPM) is developed to solve particle-laden flows. The fluid phase is solved using nSFEM stabilized by the well-developed characteristic-based split (CBS) algorithm. The concave polygonal element is successfully constructed via the intrinsic characteristic of mean value shape function and a new smoothing domain (SD) construction with more physical meaning; thus, addressing the severely distorted local mesh, as well as retaining good geometric adaptability. In the meantime, the modeling of the coupling between the fluid and the particle is achieved by reusing the mean value interpolation to obtain the fluid drag force acting on the particle. The accurate capture of fluid velocities at particle positions within arbitrary polygonal elements via mean value interpolation ensures fluid drag with high-fidelity. Several classical numerical examples, including particle-laden flow around a circular cylinder, are presented to demonstrate the high accuracy and good robustness, and the capability of the proposed method for predicting particle motion in the analysis of complex particle-laden flows. [ABSTRACT FROM AUTHOR]

With the continuous increase of train speeds, the aerodynamic drag force provided by aerodynamic braking plates can effectively solve problems of insufficient emergency braking force. The newly proposed aerodynamic braking plates installed in the inter-car gap (ICG) avoid the destruction of the carbody's strength. In this study, a numerical simulation model of a four-car marshalling train with a speed of 300 km/h is established to study the effect of installation position and opening height of the braking plates mounted in the ICG on the aerodynamic characteristics. The aerodynamic characteristics of the braking plate installed upstream and downstream of the ICG were investigated separately. The downstream plate, which showed better braking performance, was further studied at plate heights of 200 mm, 400 mm, 500 mm, 600 mm, and 800 mm. Results indicate that compared to upstream plates, the aerodynamic drag force coefficient generated by the downstream plates increased by 13.2%. The aerodynamic resistance of the train and the aerodynamic lift of each car increased gradually as the height of the downstream plates increased. Additionally, the braking plate in the ICG had limited anti-crosswind capabilities, with its braking effect significantly weakened in a crosswind of 10 m/s or higher. These results will serve as a guide for the design of aerodynamic braking plates for high-speed trains. [ABSTRACT FROM AUTHOR]

The magnetic field condition has a great influence on the magnetic control drag of reentry vehicle, so it is an important research topic to select appropriate magnetic field condition to control the drag force of vehicle. This paper analyzes the magnetic control drag by solving the hypersonic magnetohydrodynamic equations and combining the magnetic field working conditions, studies the influence of the axisymmetric magnetic field direction on the drag, supplements the mechanism of Lorentz force, pressure and conductivity on the axisymmetric magnetic control drag, and compares the drag value and drag composition ratio under different magnetic field directions. The problem is solved numerically for a particular model of a dipole magnetic field. Under different dipole magnetic fields, the magnitude and distribution shape of Lorentz force are different. There are several dividing lines where the Lorentz force is 0, and the Lorentz force directions on both sides are opposite, and this line divides the Lorentz force field into multiple parts. In addition, it is found that the change of the angle between the axis of the aircraft and the direction of the magnetic field will cause the change of the aircraft resistance, which will reduce or increase it. • The deflected magnetic field can produce greater resistance. • The mechanism of aircraft magnetic resistance is supplemented. • The magnetic resistance and its composition in different magnetic field directions are calculated. [ABSTRACT FROM AUTHOR]

Motion of a solar sail or a spacecraft equipped with a solar sail is one of the interesting problem of celestial mechanics. This paper deals with stationary solution of solar sail problem with radiating first primary and triaxial second primary under the frame of circular restricted three body problem (RTBP). First, equations of motion is derived with triaxiality and sail lightness number and then artificial equilibrium points (AEPs) are determined. It is noticed that impact of triaxiality parameters (σ 1 and σ 2) of second primary is less than that of sail lightness number (β) due to which a considerable deviations in the positions of AEPs are occurred. Further, linear stability test is performed for all AEPs and it is found that similar to equilibrium points in classical RTBP, collinear AEPs are unstable for all mass parameter μ ∈ (0 , 1 / 2 ] and triangular AEPs are stable in the range 0 < μ < μ c = 0.03758902. Moreover, stability range decreases with the values of β and σ 1 but increases with σ 2 . After this we analyze the periodic orbits of the solar sail in the vicinity of AEPs and it is noticed that nature of motion is unaffected but time period is influenced from the sail number β and triaxiality parameters σ 1 and σ 2 . The findings are useful to describe the more generalized solar sail problem with other perturbations such as oblateness, albedo, drag forces etc. [ABSTRACT FROM AUTHOR]

• The original design of the plow-subsoiler-fertilizer. • Deep loosener combined with a reversible plow. • Soil fertilization is combined with the process of its cultivation. • Vibratory subsoiler reduces drag force. • Calculated optimal design parameters. The use of intensive technologies for the cultivation of agricultural crops provides for the application of fertilizers in the process of tillage. This reduces the compaction of the soil, increases its fertility and the quality of the crop. The purpose of these studies is to develop a universal working tool that allows you to combine several technological operations in one pass of the unit. The authors have developed an original design of a plow-subsoiler-fertilizer. This combined working body includes a reversible plow and a vibratory subsoiler with fertilizer ducts. This solution allows you to combine the application of fertilizers when plowing the field, loosening the subsoil layer and mixing the soil. As a result of the work, the dependences of the geometric dimensions of the structure on the traction resistance to movement in the soil were obtained. To implement the developed idea into a real design, the main parameters of the plow-subsoiler-fertilizer are determined. Particular attention is paid to the calculation of the spring mechanism that ensures the vibration of the subsoiler. The optimal number and location of belleville springs in the block and shock absorber were selected, at which the subsoiler will perform self-oscillations with a given amplitude. [ABSTRACT FROM AUTHOR]

The impact of converging steady blowing on the global drag past a square back Ahmed bluff body is investigated experimentally. The dynamics of the recirculation bubble are studied for a width to height aspect ratio, w / h of 1.346, with a ground clearance of g / w = 0. 154 , and for a nominal Reynolds number of R e h = 2. 86 × 1 0 5 . When unforced, the bistable wake alternates between a left and right skewed states. Adaptable Coanda devices are used in combination with side air-knife blowers to deflect steady blowing jets into a converging (boat-tail) configuration. Two jet injection angles are investigated: 45 ° and 90 °. Planar PIV and time-history force and pressure measurements indicate that inwards steady blowing reshapes the recirculation bubbles and induces significant variations of the pressure drag. On one hand, bilateral steady blowing leads to the interruption of bistability associated with a removal of the vertical pressure gradient for velocity ratios V R ≈ 0. 35 − 0. 4. This has a favourable impact on the total drag with a reduction up to 3%. On the other hand, the boat-tailing effect shortens the recirculation length which tends to increase drag. This counter-productive effect limits and then outweighs drag reduction for higher velocity ratios. Another symmetry breaking is brought to light for intense highly deflected forcing. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of viscous effects on the added mass and damping forces during free heave decay of a cylinder with a hemispherical bottom. Results from unsteady Reynolds-averaged Navier–Stokes (URANS) simulations and linear potential-flow solutions are compared. Expressions for the cycle-averaged viscous added mass and damping coefficients are derived based on first-order Fourier analysis of the URANS results. Viscous effects are extracted by comparing the URANS results and linear potential-flow solutions, as nonlinear potential-flow effects in this case are demonstrated to be negligible. It is observed that viscous effects on the added mass coefficient are minor during heave decay, such that the linear potential-flow model can predict the value of the added mass coefficient to within 5% deviations. In contrast, the viscous damping coefficient exhibits strong cycle-dependent variations. A parametric study of the effects of initial displacement, cylinder diameter and draft shows that viscous damping forces can play an important role when the cylinder has a relatively small diameter and large draft. Further, the damping coefficient is transformed to the nondimensional drag force coefficient, and its dependence on the Reynolds number R e is investigated, for Keulegan–Carpenter numbers in the range K C = 1.5–2.5. It is found that the drag force coefficient is likely to be unrelated to R e and K C during the first cycle. From the second cycle to the fourth cycle, the drag force coefficient rapidly decreases with increasing R e , up to R e ≈ 3 × 1 0 5 . [ABSTRACT FROM AUTHOR]

• Empirical measurements of vehicle snow-plow force match closely to proposed physics-based model. • Proposed physics-based model for snow plowing forces developed zones of snow compression, shear, and turbulence as the vehicle travels through snowpack. • At low vehicle speeds, the force of compressing snow dominates inertial forces of accelerating snow in front of the vehicle. Determining trafficability of winter surfaces is a critical capability for Army operations in cold regions. Over the years, a substantial amount of research has been conducted to characterize different winter surfaces (and different vehicles, tires, and tracks on these surfaces) for this purpose. Trafficability model for snow and ice have been implemented in numerous tools currently in use by the Army including the NATO Reference Mobility Model (NRMM), GeoWATCH, and other stand-alone implementations. However, these models are generally based on empirical testing of vehicles driving through snow of shallow to moderate depth and do not adequately capture additional compressive and inertial plowing forces as well as friction drag forces resulting from deep snow being pushed forward by the vehicle bumper, nose, compression caused by the undercarriage, or undercarriage components catching the snow (e.g. suspension arms). In this paper we propose a generalizable snow plowing model for estimating the force required for a vehicle to travel through deep snow. The results of the model compare well to empirical measurements of the force required for a mid-weight all-terrain tactical vehicle to move through different depths of deep snow (over the bumper) and at different ride height settings. [ABSTRACT FROM AUTHOR]

The utilisation of the Very Low Earth Orbit (VLEO) region offers significant application specific, technological, operational, and cost benefits. However, attaining sustained and economically viable VLEO flight is challenging, primarily due to the significant, barely predictable and dynamically changing drag caused by the residual atmosphere, which leads to a rapid deterioration of any spacecraft's orbit unless mitigated by a combination of active and passive techniques. This article addresses one passive method by optimising satellite shapes in order to achieve a minimisation of the atmospheric drag force and thus extension of operational lifetime. Contrary to previous investigations in the field, a constant internal volume is maintained to account for the placement of satellite instruments and payload inside the structure. Moreover, the satellite geometry is not varied heuristically but optimised, via a numerical 2D profile optimisation specifically developed for this purpose. From the resulting optimal satellite profiles, 3D satellite bodies are derived, which are then verified via the Direct Simulation Monte Carlo method within the open-source particle code PICLas. In addition, rather unconventional designs, i.e. ring geometries, which are based on the assumption of fully specular particle reflections, are proposed and assessed. The optimised satellite geometries offer pure passive lifetime extensions of up to 46 % compared to a slender reference body, while the above-mentioned ring geometries achieve passive lifetime extensions of more than 3000 %. Finally, the article presents design recommendations for VLEO satellites in dependence of different surface properties. • Optimisation of constant-volume VLEO satellite geometries for lifetime extension. • Optimisation of front and tail geometry designs. • Full 3D simulations with the open-source particle code PICLas. • Evaluation of satellites with a ring structure. • Different satellite designs are recommended depending on the surface properties. [ABSTRACT FROM AUTHOR]

The study of a chemically reacting fluid in a vertical micro-channel limited to an applied transverse magnetic field that has fully developed steady natural convection flow under the impact of internal heat generation or absorption effects is the focus of this research. The governing equations are solved in dimensionless form using the homotopy perturbation method, HPM. Temperature, velocity, volume flow rate, and frictional drag force fundamental flow attributes are investigated as a function of controlling parameters such as heat generating or absorbing parameters, chemical reaction parameter, rarefaction parameter, fluid-wall interaction parameter and wall-ambient temperature difference ratio. The results are thoroughly analyzed and graphically depicted in a variety of plots. It is worth noting that raising the chemical reaction and rarefaction parameters increases fluid flow and volume flow rate, respectively. Furthermore, the action of heat absorption is observed to suppress fluid flow whereas heat generation establishes the opposite condition. Additionally, numerical data was generated and tabulated to compare the findings of this study to those of Jha et al. (2014) when the chemical reactant and heat generating/absorbing parameters were neglected, and an excellent agreement was discovered. [ABSTRACT FROM AUTHOR]

Heat transfer improvement using electro-magneto hydrodynamics is a technique that can result in significant heat exchanger reduction as well as "on-demand" heat transfer. Electrohydrodynamic (EHD) is a multidisciplinary science that studies how fluids interact with electric fields or charges. It has been found applications in many areas such as EHD pump, EHD enhanced heat transfer, microelectromechanical systems (MEMS) and other industrial processes. MHD offers a broad array of applications for researchers in astrophysics, planetary magnetic fields, generators, flow meters, metallurgy, metal dispersion (granulation), ship propulsion, crystal development, magnetic filtration, and fusion reactors. Investigation of the mass and heat transfer properties of hybrid nanofluid Transformer o i l + T i O 2 + F e 3 O 4 in three dimensions is considered. In this research, cumulative effects of magnetic and electric hydrodynamic are examined between two rotating plates in viscous hybrid nanofluid. To generate the hybrid nanofluid, transformer oil is utilized as a base fluid in the nanoparticles Ti O 2 and F e 3 O 4. Using a similarity approach, the flow model in the form of PDEs is reduced to a system of dimensionless ODEs. The obtained equations are solved by using a shooting (bvp4c) method to attain a numeric solution. Reynolds number, rotational factors and effects of magnetic and electric properties in hydrodynamics have all been researched and argued about thermal efficiency, drag force, and mass flux. Numerical data of Nusselt number, Sherwood number, and drag forces are calculated. By minimizing the influence of physical constraints, the hybrid nanofluid enhances heat transfer rate and mass transport. [ABSTRACT FROM AUTHOR]

• The aerodynamics of a half-span delta wing are studied using wind tunnel experiments at subsonic flow regime. • The lift on the delta wing is generated close to the leading edge for the focus range of the incidence angles. • Locations of the additional lift and the drag forces of the delta wing is identified based on the experimental results. Low-speed wind tunnel experiments are conducted to study the aerodynamic performance of a half-span delta wing with 45° leading-edge sweep at subsonic flow regime. The experiments are carried out at a Reynolds number of 8.37 × 105, a free-stream Mach number of 0.1 and angles of attack up to 25°, in steps of 5°. The test model was designed with thirty-two pressure taps fixed on its surfaces (sixteen on each side). Multi-tube manometers were connected to these taps using long tubes to enable recording the pressure readings. Surface pressure distributions and aerodynamic characteristics were calculated at different span-wise locations along the non-dimensional chord-wise distance. Results exhibited that most lift on the studied wing is generated in the region close to the leading edge for all the studied incidence angles. Additional lift is created in the region close to the root chord rather than the tip chord, whereas drag forces increases from tip to root. This can be attributed to the formation of trailing edge vortexes due to the flow separation at the wing leading edge that produces more drag, hence suppressing lift. The study showed also that angle of attack increases the drag coefficient from tip to root, especially at high angle of attack, indicating unfavourable behaviour for manoeuvring. Moreover, the angle of attack increased the pitching moment coefficient up to 10° before it drops sharply until it reaches the tip of the wing model. [ABSTRACT FROM AUTHOR]

The present study aims at simultaneously optimizing the nose and tail of two distinct Autonomous Underwater Vehicles (AUVs) using a full turbulent continuous adjoint solver. The entire procedure is carried out utilizing two open-source software: Salome (CAD and mesh generator) and OpenFOAM v2206 (CFD solver and optimizer). Reynolds-Averaged Navier–Stokes (RANS) equations closed by the k- ω SST model are employed to simulate the turbulent flow around AUV hulls. Besides, adjointOptimisationFoam solver is used to perform the shape optimization. Two different unconstrained and constrained optimizations of AUV hulls are conducted at an angle of attack (α) equal to 0 °. In the unconstrained optimization, the drag force is chosen as an objective function to be minimized while a partial volume is considered as a geometric constraint in the constrained optimization. The predicted drag force is validated against experimental results from the literature, indicating a mere 0.58% discrepancy. In the unconstrained optimizations, the first and second AUV hulls reveal a 4.17% and 3.66% reduction in the drag force, respectively. In the constrained optimizations of the first and second AUV hulls, drag force is reduced by 3.25% and 2.63%, respectively. • Optimization of the noses and tails of two AUV hulls for drag minimization. • Optimization was done using a VEV continuous adjoint solver in OpenFOAM v2206. • Two optimization scenarios were considered: unconstrained and constrained. • In unconstrained optimization, the first AUV hull reduced drag by 4.17% and the second by 3.66%. • In constrained optimization, the first AUV hull reduced drag by 3.25% and the second by 2.63%. [ABSTRACT FROM AUTHOR]

In this study, geometrical parameters such as twist, section thickness, and angle of attack are numerically investigated for their influence on lift and drag coefficients, as well as cavitation development. The Delft 11 Hydrofoil, a twisted version of the NACA0009 foil with a −2° angle of attack, is used as the benchmark geometry for validation studies under both non-cavitating and cavitating flow conditions. After the validation studies, the geometries of the NACA0009 and NACA0015 hydrofoils were redesigned as half-twisted and twisted. These redesigned hydrofoils, along with the original no-twist versions, were analyzed under cavitating flow conditions within an angle of attack range of −2

A fully nonlinear Navier-Stokes/VOF numerical water tank is developed for barge-type floaters with coupling to the dynamic mooring line model. Wave excitation forces, free decay responses, and dynamic responses in regular waves predicted by numerical water tank show good agreement with experimental results. Then, hydrodynamic force models used in engineering models are improved by applying the numerical water tank results. It is clarified that the cause of the overestimation of normalized wave excitation force at water tank test relative to that predicted by potential theory is the underestimation of the input wave height due to the interference of the reflected wave from the floater. The new drag coefficient model is proposed based on numerical forced oscillation simulations at the surge natural period. The wave drift QTF is evaluated using the numerical water tank and the prediction accuracy of the mean floater displacement in the surge direction is improved, compared to the conventional Newman's approximation model. The surge-pitch coupling terms of drag force and its mechanism are investigated by forced oscillation simulations. The correction method of surge-pitch coupling terms of drag force is proposed and the prediction accuracy of the floater displacement in the surge direction is improved. • A numerical water tank provides accurate predictions of the dynamic responses of barge-type floaters. • Hydrodynamic forces are evaluated by using a numerical water tank, which are difficult to evaluate by experiments. • Surge-pitch coupling term of drag force play an important role for accurate prediction of surge response. [ABSTRACT FROM AUTHOR]

This study focuses on wave diffraction loads influenced by heave plates at deep and shallow submerged depths. An extensive experimental campaign is conducted on a fixed vertical and free-surface piercing circular cylinder with five different circular plates, including a perforated plate. The horizontal and vertical wave forces are studied in monochromatic and bichromatic waves. The results show that the heave plate significantly influences the forces varying in time and representative harmonics, including sum- and difference-frequency components. The study found that wave steepness and submerged depth of the plate contribute to the nonlinearity of the loads and that the porous plate reduces the loads compared to the solid plate. Corresponding results from a boundary element method (BEM) solver, HydroStar, provide a reasonable prediction of the harmonics. However, the first harmonic of the vertical force is underpredicted at low frequencies, specifically where the BEM results indicate the cancellation of the forces. Dedicated computational fluid dynamics (CFD) simulations are carried out to investigate the discrepancy, and it is observed that flow separation occurs around the edge of the plate. A simplified approach based on Morison's equation is employed to model the flow separation effects using a quadratic drag force calculated with a constant drag coefficient. The approach shows that viscous drag is the dominant contributor to vertical wave forces on the heave plate in the low-frequency regime. • Wave diffraction loads affected by heave plates are experimentally investigated. • The model is designed as a fixed vertical circular cylinder with a circular plate. • Boundary element method solver is used as a support for the experimental campaign. • Dedicated CFD simulations are conducted to visualize the flow around heave plates. • A simplified method based on Morison's equation is used to model the flow separation. [ABSTRACT FROM AUTHOR]

• An innovative magnetic microrobot driven by an external rotating magnetic field is proposed. • Environmental interactions such as fluid, viscoelastic, and magnetic interactions are modeled. • Magnetic microrobot dynamics are modeled and simulated. • The kinematic characteristics of the microrobot will depend on the frequency and amplitude of the electric current input to the magnetic field generator. This paper investigates design, modeling, simulation, and dynamic issues related to self-propelled endoscopic capsule navigated inside the human body through external magnetic fields. A novel magnetic propulsion system is proposed and fabricated, which has great potential of being used in the field of noninvasive gastrointestinal endoscopy. The endoscopic capsule dynamic is studied on a medical silicone plate as the closest available material for the stomach tissue. First, the mechanical characteristics of the medical silicone plate is measured. Next, the forces acted on the endoscopic capsule which are friction, hydrodynamic and magnetic forces are determined by means of test and numerical techniques such as finite element method. Having known the magnitude of forces and torques on the endoscopic capsule, the dynamics of capsule are calculated under different initial conditions and external magnetic fields. [ABSTRACT FROM AUTHOR]

• Digital image processing techniques were used to reveal the dynamics of bubbles in MEA solutions. • Drag coefficients at different constraints are revealed. • The effects of chemical reactions and contaminants on mass transfer during bubble rise are revealed. The dynamic behavior of CO 2 bubbles in MEA solutions at different constraint limits was investigated using a high-speed camera. We measured the morphological characteristics, velocity, and mass transfer coefficient of the bubbles as they ascended. The findings indicate that: The limitation of the bubble's movement influences its fluctuation during the ascent, with more confinement resulting in a more pronounced zigzag motion. In a confined area, the resistance encountered by a rising bubble is mostly due to drag force and wall shear force. When the confinement is less, the drag force becomes the dominant factor, but in larger confinements, the shear force takes precedence. Increased confinement of bubbles hinders the process of bubble surface renewal, as it leads to the accumulation of a substantial quantity of generating materials on the surface. When the bubble is not limited, its capacity to renew the surface increases, resulting in a bigger mass transfer coefficient. [ABSTRACT FROM AUTHOR]

• A method for modeling the lateral distributions of depth-averaged velocity behind an emergent vegetation patch is provided. • The model incorporates bed friction, vegetation-induced resistance, secondary flow effects, and lateral momentum exchange. • The influence of secondary flow term on the lateral distributions of depth-averaged velocity is evaluated. • Some modeling insights for those with limited experience are offered. Aquatic vegetation provides ecological, hydrological, and aesthetic functions for rivers, and measuring velocity in vegetated channels is essential for river management. The paper presents a method for modeling the lateral distributions of depth-averaged velocities behind an emergent vegetation patch. Based on SKM, this approach divides the channel behind an emergent vegetation patch into pseudo-vegetation and free-flow regions, offering analytical solutions for the depth-averaged velocities in these two regions. The model incorporates several critical parameters, including the Darcy–Weisbach coefficient, lateral dimensionless eddy viscosity, drag force coefficient, and secondary flow coefficients. These coefficients are associated with bed friction, vegetation-induced resistance, secondary flow effects, and lateral momentum exchange, respectively, affecting the depth-averaged velocities. A comparison with published experimental data validates that the proposed model can predict the lateral distributions of depth-averaged velocities behind an emergent vegetation patch. A steady wake section exists behind an emergent vegetation patch for low-flow blockage. In the steady wake section, the secondary flow coefficients in pseudo-vegetation and free-flow regions remain relatively constant. Upon exiting the stable wake section, the secondary flow coefficient in the pseudo-vegetation region decreases with increasing distance from an emergent vegetation patch, and it in the free-flow region increases with increasing distance from an emergent vegetation patch. A sensitivity analysis of drag coefficient and secondary flow coefficients suggests that secondary flow coefficient in the free-flow region has a more significant effect on the lateral distributions of depth-averaged velocities compared to drag coefficient and secondary flow coefficient in the pseudo-vegetation region. [ABSTRACT FROM AUTHOR]

In the present study, a new disturbing rotary centrifugal classifier was designed and a method was proposed to characterize its pressure signals. The models for evaluating the classification effects were established based on multi-zones. It was found that the flow field, processing parameters, and material properties significantly affected on the particle force and classification performance. The pressure with high amplitude and energy analyzed using Hilbert-Huang Transform (HHT) concentrated within 200–400 Hz, and the screening cage facilitated energy transfer to lower frequency bands. Correlation analysis demonstrated the correlation coefficients (A5 and A6) between adjacent measurement points increased with frequency, further enhanced by the screening cage. The flow field of simulation was characterized by a low-pressure, high-velocity gradient at the center and a high-pressure, low-velocity gradient at the sidewalls and the gas velocity and flow for experiment achieved the maximum at z = 0.50 m, while the magnitude of pressure change was significant at the inlet end and discharge end, where the velocity gradient and pressure drop had the same trend and small errors for experiments and simulation. The flow field affected the competing relationship between centrifugal and drag forces on the particles with different kinematic behavior during the classification process. The errors between the predicted values of the theoretical, simulated, and experimental cut particle size models and the true values were all within 10 %, based on which the multi-zone classification efficiency model applicable to the disturbing centrifugal classifier was established, and it was found that the models all had high prediction accuracy and suitability. The article delves into the correlation between pressure signals, flow field characteristics and particle behavior, aiming to provide an important reference for the internal flow field and classification performance of air classifiers. [Display omitted] • Analyzed the time-frequency characteristic of pressure signals by HHT. • Measured the correlation degree of neighboring signals using correlation analysis. • Studied the spatial flow field characteristics for simulation and experiments. • Theoretical, simulate and experimental models of cut particle size were established. • Predicted and compared the multi-zone classification efficiency model. [ABSTRACT FROM AUTHOR]

Polydisperse particle feed into centrifugal slurry complicates hydraulic performance and wall erosion but is poorly understood. This paper presents a numerical study of a centrifugal slurry pump, focusing on the effect of particle size distribution (PSD) using the combined computational fluid dynamics and discrete element method (CFD-DEM). It incorporates rigid impeller rotation and wall erosion. On this basis, the hydraulic and erosion model validity is verified by clear water performance and jet erosion test, respectively. Additionally, this CFD-DEM model is compared with the dense discrete phase model (DDPM), demonstrating more precise erosion prediction as its fully resolved particle-particle interactions. Generally, total pump erosion severity intensifies when the PSD is broadened. Compartment-wise, it indicates the necessity of tailoring flow structure to enlarge drag force, therefore, mitigate particle aggregation in the impeller. This in-house CFD-DEM model is promising for addressing particle-fluid flow problems in centrifugal pumps or coupling with data driven method. [Display omitted] • Erosion characteristics to particle-fluid interaction force is elaborated. • Particles accumulate at the trailing side of blade in rotation of impeller. • Increment in particle size distribution (PSD) intensifies the total pump erosion. • Compartment-wise erosion is greatly influenced by the equivalent particle size. [ABSTRACT FROM AUTHOR]

In order to enhance the ecological security of the coastal ecosystem, the Chinese government has initiated a comprehensive program for the removal of Spartina alterniflora. Upon completion of the removal project, the area underwent a notable transformation, transitioning from its original vegetated state to a predominantly bare salt marsh landscape. This transformation has the potential to give rise to new ecological security issues and facilitate the re-invasion of Spartina alterniflora. At the time of writing, restoration work is underway in the restoration area, with the aim of reinstating native vegetation, specifically Suaeda salsa. Nevertheless, the survival strategies that the target species, Suaeda salsa , may employ to adapt to the challenging wave environment remain unknown, potentially introducing unforeseen challenges to the revegetation efforts. To address this issue, we conducted a study to examine the impact of water-imposed drag forces on the physiological and biomechanical properties of Suaeda salsa , with the aim of defining its survival strategies in wave environments. Our research findings indicate that Suaeda salsa exhibits limited sensitivity to wave disturbance. Suaeda salsa is relatively rigid and thus finds it difficult to adjust its shape flexibly in order to withstand the mechanical force caused by wave motion. As the intensity of the wave increases, Suaeda salsa exhibits a tolerance strategy. In the optimal wave environment (before the failure of plant tissue under extreme wave drag force), enhanced waves can stimulate the growth of Suaeda salsa , thus potentially contributing positively to the restoration efforts of the Yellow River Delta. [ABSTRACT FROM AUTHOR]

Vertical tubes are proposed to connect the collar and bottom ring to address the significant deformation of gravity cage nets caused by currents and waves. The goal is to minimize the volume loss of the cages, which reduces the habitat available for fish. This study analyses the effect of vertical tubes on drag forces using numerical and experimental methods. Tests are conducted in a towing tank to measure drag forces and validate a numerical model that employs beam and link elements to simulate the gravity cage behaviour. The differences between numerical simulations and experiments are discussed. Cages with thin tubes show larger differences than those with thick tubes due to initial bending. Comparing the results with those of gravity cages without reinforcement, it is found that the vertical tubes increase the drag force and thicker tubes exacerbate this effect. At 0.5 m/s, the cages with reinforcement tilt, leading to a different trend in drag force with wavelength compared to the cages without reinforcement. • Vertical tubes are proposed to connect the collar and bottom ring to address the significant deformation of gravity cage nets • The goal is to minimize the volume loss of the cages, which reduces the habitat available for fish. • This study analyses the effect of vertical tubes on drag forces using numerical and experimental methods. • Tests are conducted in a towing tank to measure drag forces and validate a numerical model that simulates the cage behaviour. • The tests showed that the vertical tubes increase the drag force and thicker tubes exacerbate this effect [ABSTRACT FROM AUTHOR]

Physics simulations like computational fluid dynamics (CFD) are a computational bottleneck in computer-aided design (CAD) optimization processes. To overcome this bottleneck, one requires either an optimization framework that is highly sample-efficient, or a fast data-driven proxy (surrogate model) for long-running simulations. Both approaches have benefits and limitations. Bayesian optimization is often used for sample efficiency, but it solves one specific problem and struggles with transferability; alternatively, surrogate models can offer fast and often more generalizable solutions for CFD problems, but gathering data for and training such models can be computationally demanding. In this work, we leverage recent advances in optimization and artificial intelligence (AI) to explore both of these potential approaches, in the context of designing an optimal unmanned underwater vehicle (UUV) hull. For first approach, we investigate and compare the sample efficiency and convergence behavior of different optimization techniques with a standard CFD solver in the optimization loop. For the second approach, we develop a deep neural network (DNN) based surrogate model to approximate drag forces that would otherwise be computed via the CFD solver. The surrogate model is in turn used in the optimization loop of the hull design. Our study finds that the Bayesian Optimization—Lower Condition Bound (BO-LCB) algorithm is the most sample-efficient optimization framework and has the best convergence behavior of those considered. Subsequently, we show that our DNN-based surrogate model predicts drag force on test data in tight agreement with CFD simulations, with a mean absolute percentage error (MAPE) of 1.85%. Combining these results, we demonstrate a two-orders-of-magnitude speedup (with comparable accuracy) for the design optimization process when the surrogate model is used. To our knowledge, this is the first study applying Bayesian optimization and DNN-based surrogate modeling to the problem of UUV design optimization, and we share our developments as open-source software. • We evaluate various optimization algorithms on the task of optimal UUV hull design. • An AI surrogate model approach eschews a CFD solver in the design optimization loop. • We provide a ready-to-use software package for drag-based design optimization. [ABSTRACT FROM AUTHOR]

Superhydrophobic surfaces are expected to reduce drag on bluff bodies moving in water due to the introduction of a thin air layer around the solid and the resulting partial slip boundary condition. The use of Leidenfrost vapor layers, sustained on the surface of a heated metal body is a reliable method to estimate the maximum drag reduction possible due to such air layers. In the past such an approach was used to estimate the drag reduction on a free-falling heated sphere, in which case the form drag is the lead component of the drag force. Here, we extend this approach to evaluate the effect of the thin gas layers on the hydrodynamic drag of free-falling streamlined projectiles and towed model boats, where the form drag is minimal, and the skin friction drag is the lead component of the drag force. By comparing the drag for streamlined bodies with and without sustained air-layers, we see only incremental drag reductions, for the sub-critical Reynolds number tested herein. The same is true for towed model boats. These results hold both for superhydrophobic surface treatments and Leidenfrost vapor layers. Thus, we concluded that for the investigated range of sub-critical Reynolds numbers, the skin friction drag is less sensitive to the effect of the thin gas layers compared to the form drag. These novel findings have important implications for the practical potential of energy savings using gas layers sustained on superhydrophobic surfaces. [Display omitted] • Drag reduction by Leidenfrost vapor layers predict the limit for superhydrophobic surfaces drag reduction. • For spheres there is a dramatic effect due to early drag crises. • For streamlined projectile and model boats the drag reduction is moderate. • For sub-critical Reynolds numbers skin friction is less sensitive than form drag to the gas layer effects. [ABSTRACT FROM AUTHOR]

Deep-towed multi-channel seismic arrays play vital role in marine geological exploration. However, these arrays often assume a "W" shape due to the weight of digital transmission units, adversely affecting hydrophone positioning and strata imaging. Floaters and a cone-shaped drogue are designed to correct the array shape, and numerical simulations are employed to validate the corrective effect in this paper. Additional drag forces induced by the floaters and drogue are identified using computational fluid dynamics, then they are integrated into the array model compiled to express the nonuniform mass distribution and concentrated loads based on absolute nodal coordinate formulation. Moreover, bending characteristics of arrays is fine-tuned through physical tests. Finally, simulation results indicate the floater has obvious effect than the drogue in the array shape correction, and the array shape becomes a simple convex curve with the presence of floaters and drogues under various towing conditions, facilitating hydrophone positioning. Furthermore, the array shape from the travel time positioning in sea trials also exhibit similar convex curves, and the signal-to-noise ratio of the seabed profile is much improved compare to previous one. This study also underscores the efficiency of numerical simulation in developing stabilization equipment for deep-towed multi-channel seismic arrays. • Floaters and drogue are designed to correct "W" shape in deep-towed seismic arrays. • ANCF-based model simulates array corrections, enhancing understanding and design efficiency. • Correction results in a streamlined array shape, aiding data processing and positioning accuracy. • Travel time positioning confirms correction effectiveness. • Drogue enhances array stability, mitigating effects of seawater density variations. [ABSTRACT FROM AUTHOR]

Under the influence of ocean currents, multiple inverted-droplet shaped gas storage devices positioned on the seafloor may interact, potentially leading to structural damage. In this study, hydrodynamic experiments were conducted, and the resulting data were employed to validate the Computational Fluid Dynamics (CFD) model. Based on the validated CFD model, simulations were performed to explore the hydrodynamic characteristics of full-scale inverted-droplet shaped gas storage devices. The results indicate that the drag coefficient and lift coefficient of the device are 0.7813 and 0.4332, respectively, at a flow velocity of 0.1 m/s. A study examining the effects of incident current angle and device spacing on the force characteristics was conducted, revealing that the device's resistance increases with a greater incident angle, and that both drag and lift forces are minimized when the device spacing is 2.5D. These findings offer valuable insights for optimizing the design and arrangement of future underwater gas storage systems. • A balloon-shaped underwater gas storage device as a research object. • Underwater downsizing experiments were conducted. • The CFD model was validated based on experimental data. • Study of force characteristics and flow field characteristics of gas storage devices. • Influence of current incidence angle and arrangement spacing on forces. [ABSTRACT FROM AUTHOR]

This study investigates the effects of drawdown flushing in hydraulic structures on sediment transport and morphological changes within and around reservoirs. Utilizing the Smoothed Particle Hydrodynamics (SPH) method, the research focuses on local erosion induced by drawdown flushing and examines the interaction between water and sediment. To validate sediment behavior, we analyzed a granular dam-break model using three rheological models: Herschel-Bulkley (H–B), Bingham, and μ(I). Two drawdown flushing scenarios are explored, considering mobile bed conditions at the reservoir's inlet and outlet. The study area is categorized into three zones: water, sediment, and the interface between water and sediment, with the μ(I) rheological model applied to the sediment portion. Within the interaction zone of sediment and water, the Shields parameter is defined based on Julien's relations to determine the yield stress of sediments. This value is then incorporated into the H–B model for sediment in this specific zone. Additionally, the drag force is introduced into the momentum equation within this zone. The study's findings are rigorously validated against existing numerical and experimental studies, affirming the credibility of the modeling approach. This research provides valuable insights into the complex dynamics of sediment transport during drawdown flushing in hydraulic structures. • Rheological models used to evaluate sediment behavior: Herschel-Bulkley (H-B), Bingham, and μ(I) models. • The study area in the drawdown flush is divided into three zones: water, sediment, and the water-sediment interface. • The μ(I) model is used in the sediment phase, and the H-B model is used at the water-sediment interface. • The study area is divided into segments, and backpressure is calculated in each segment for the sediment phase. • The Shields parameter, based on Julien's relations, and the drag force are applied at the water-sediment interface. [ABSTRACT FROM AUTHOR]

The objective of this research is to analyze vortex structures, lift, and drag coefficients, generated by a variety of obstacles in the context of a 2D laminar flow, comparing the results between the different cases. To that aim, numerical simulations using the Smoothed Particle Hydrodynamics (SPH) method have been carried out. The resulting data presented herein constitute a comprehensive study of the flow around obstacle problem in 2D using SPH. The influence of the geometry on vortex formation has been studied at the Reynolds number Re = 100. The results show a strong agreement with the values in the literature for cylinders and squares. This is a crucial stage for the validation of the methodology before expansion to various geometries, e.g. square-cylinder combinations, piggybacks, and horizontal spoiler configurations. Notably, this study introduces a novel horizontal spoiler configuration, as opposed to the conventional vertical orientation found in the literature. To the best of the authors' knowledge, this configuration is presented here for the first time. Among single shapes, the cylinder with a spoiler exhibits the highest value for the drag coefficient, being 34% greater when compared to the single cylinder configuration. In addition, regarding configurations with a pair of side-by-side obstacles, the results indicate a notable increase in the drag coefficient for the case of a larger cylinder coupled with a smaller cylinder at the smallest gap amongst the ones tested. Having a look at the lift coefficient, the results for the different shapes oscillate considerably compared to the case of a single cylinder used as a reference. The maximum increase is obtained for the cylinder with spoiler (122%) and the piggyback at the minimum distance tested (135%), suggesting that objects in close proximity (or joined together) highly influence lift inception. Conversely, the greatest reduction in lift oscillations is found for the both the piggyback (58%) and the cylinder with a square (52%) when the gap between the two objects increases. In terms of the Strouhal number, the highest value is observed for the case of a single cylinder. For the other shapes tested, the Strouhal number is reduced from 11% to 63%. Therefore, the study allows to analyze the influence of different shapes on lift and drag forces, vortex shedding frequencies, and the relation amongst them, helping to understanding interference effects and shape influence, thus offering relevant insights to various engineering applications. The SPH method is validated using two of the geometries considered. In addition, a verification analysis is carried out in the case of the single cylinder considering lift and drag coefficients as well as Strouhal number. These studies (validation and verification) constitute a comprehensive convergence analysis – customary in CFD applications – for the proposed numerical scheme, confirming the accuracy of the SPH results for this particular problem. The simulations were carried out using the AQUAgpuSPH software, developed at Universidad Politécnica de Madrid (UPM). • Vortex formation and forces from various obstacle shapes are studied with SPH. • Verification and validation studies are done for cylinder and square single shapes. • A novel spoiler with the highest drag coefficient among tested shapes is introduced. [ABSTRACT FROM AUTHOR]

• Gas-liquid–solid flow fields in mini-fluidized bed were studied by Fluorescence PIV. • Bubbles rise as straight line and S-shaped spiral trajectory in mini-fluidized bed. • Superficial gas velocity has a greater influence on bubble radial movement. • Divergence and vorticity of the liquid flow field were analyzed. • Particle's radial motion is caused by entraining of bubble vortex and surface force. The fluorescence-based tracer particle image velocimetry (fluorescence PIV) was used to obtain the flow regimes transition, bubble size and velocity, liquid and particle flow field characteristics of the 1 ∼ 3 mm GLSMFBs and 93 ∼ 195 μm glass beads. When the bed-to-particle diameter ratio increased, the bubble size and velocity distribution tended to be more concentrated. Bubble rose as straight line and S-shaped spiral trajectory. The divergence and vorticity of the flow field were preliminarily quantified. There showed a close relationship between the macroscopic hydromechanical behaviors such as bubble size and velocity and the mesoscopic behaviors such as the movement and development of vortices. The upward drag force of liquid and bubble on particles mainly affected the particle axial velocity, while the particle radial motion was mainly caused by bubble wake and surface force among particles. The results provide theoretical reference for the design and optimization of GLSMFB reactors. [ABSTRACT FROM AUTHOR]

A constant-depth ichthyoplankton sampler (CDIS) is widely employed for quantitative sampling surveys, yet challenges related to sampling distortion due to unstable tows of the CDIS persist. The drag force of the square-frame sampling net is pivotal in maintaining the dynamic stability of the CDIS during horizontal towing. This study delves into the hydrodynamics and filtration performance of square-frame sampling nets through flume-tank experiments and numerical simulations. The results show that the drag coefficient for the square-frame ichthyoplankton sampling net initially decreases and then increases as the solidity ratio rises from 0.3 to 0.7. It becomes greater as the net length becomes shorter and the net mouth area becomes larger. A response model for the drag force for the square-frame sampling net is proposed that is capable of accurate predictions. The results also reveal that the flow decelerates at the net mouth and gradually accelerates in the posterior section of the net, and the filtration efficiency increases as the net length and mouth area increase but decreases slightly as the solidity ratio increases. Our study provides vital scientific data for reference and methodologies for designing or modifying a square-frame CDIS, fostering enhanced stability and accuracy in ichthyoplankton surveys. • The drag coefficient for the square-frame ichthyoplankton sampling net initially decreases and then increases as the solidity ratio rises from 0.3 to 0.7. • The drag coefficient for the square-frame ichthyoplankton sampling net becomes greater as the net length becomes shorter and the net mouth area becomes larger. • A response model for the drag force for the square-frame sampling net is proposed that is capable of accurate predictions. • The flow decelerates at the net mouth and gradually accelerates in the posterior section of the net. • The filtration efficiency increases as the net length and mouth area increase but decreases slightly as the solidity ratio increases. [ABSTRACT FROM AUTHOR]

• Firstly, for the drag force of granules, a porous and permeable drag force model is chosen. • Secondly, the complicated flow characteristics of gas–liquid-solid three-phase in the first reaction chamber of IC reactor was studied. • By introducing correction factors, the drag force model is adjusted. • For this previously unstudied system, CFD is carried out to analyze and predict the flow behavior in the first reaction chamber. • Additionally, regression equations for the critical relationship of superficial liquid and gas velocity for complete expansion of granules were suggested. This study aims to investigate the characteristics of gas–liquid-solid three-phase flow in an Internal Circulation (IC) anaerobic reactor during the treatment of wastewater. Through computational fluid dynamics (CFD) simulations of the gas–liquid-solid three-phase in the first reaction chamber and based on the anaerobic granule swarms drag coefficient model, the study investigates the effects of superficial liquid velocity and superficial gas velocity on granules distribution, uniformity index, gas holdup, flow velocities of each phase, and the dimensionless variance of residence time distribution. In addition, the relationship between the fully mixed superficial velocities of gas and liquid in the first reaction chamber is also determined. [ABSTRACT FROM AUTHOR]

The number of blades and their angle in a turbine gas meter directly affect its performance and the amount of lift force, pressure drop and flow rate passing through the blades. In this research, the combination of software simulation and optimization method has been used as an effective research tool to investigate the effect of these geometric parameters on the amount of pressure drop, volume flow rate and lift force. First, the flow in a turbine gas meter is simulated using computational fluid dynamics. The set of governing equations including continuity, linear momentum and angular momentum have been solved by Fluent software. To simulate the turbulent flow, the standard k-ε model is used. In the next step, with the help of TOPSIS model, it has been optimized to check the effect of each of the parameters and determine their optimal values. The results of this research showed that by increasing the number of blades and increasing the blade angle, the lift force increases. Among the two parameters, the number of blades and the angle value, changing the number of blades has a significant effect. Reducing the number of blades and decreasing the blade angle can be effective strategies to minimize pressure drop. Also, the effect of changing the number of blades plays an important role in pressure drop. The pressure drop in the number of 20 blades is the highest and this's due to its large number of blades. In this article, 21 cases have been investigated with the help of TOPSIS and it can be seen that the angle of 30 ° with 12 blades is an optimal model. The ratio of lift force to drag force is observed at an angle of 30°, the number of 20 blades is the highest and its dimensionless value is 78.23. For an angle of 37.5°, the ratio of lift force to drag force for 20 blades has the highest value and its dimensionless value is 915.9. Also, for an angle of 45°, the ratio of lift force to drag force and the number of 20 blades has the highest value, and its dimensionless value is 1190.94. [Display omitted] • Software simulation and optimization for turbine gas meter research. • Optimal model: 12 blades with 30° angle (TOPSIS analysis). • 45° blade angle maximizes lift-to-drag ratio, generating more lift. • Increasing the blade and angle increases the lift force. • Changing the number of blades affects pressure drop. [ABSTRACT FROM AUTHOR]

CNTs have been shown to exhibit exceptional electrical and thermal conductivities, chemical and mechanical stability and physiochemical reliability in wide-ranging applications covering biomedicine, energy and aerospace. Motivated by emerging applications in nano-drug delivery in medicine and radiative ablation therapy, a steady-state mathematical model is established for magnetohydrodynamic boundary-layer transport of chemically reactive carbon nanotubes (CNTs)-doped electrically conducting blood along a porous stretching wall of a blood vessel. Multiple and single walls CNTs are considered using the model developed by Xue (2005). Heat generation, radiative flux, wall mass (concentration) slip, viscous heating and Joule magnetic dissipation are incorporated. Chemical reaction effects are addressed utilizing homogenous first-order model. The Darcy-Forchheimer drag force model is utilized for bulk matrix and inertial drag effects in the porous medium. Radiative heat-transport is studied considering Rosseland's diffusion model. The governing partial differential conservation equations for mass, momentum, energy and species are formulated in a two-dimensional Cartesian coordinate system with allied wall and free-stream boundary conditions. Via scaling transformations, a nonlinear boundary value problem is derived. Numerical computations are achieved through bvp4c scheme. The impact of selected parameters on dimensionless quantities (velocity, temperature, concentration, skin friction, local Nusselt and Sherwood numbers) are computed and elaborated through tables and graphs. A good correlation of the numerical solutions with earlier simpler models from the literature is included. The simulations show that with augmentation in Hartmann magnetic number and Forchheimer inertial drag number, significant damping in the nano-doped blood flow is produced for both SWCNTs and MWCNTs. Temperature is elevated with increment in dissipation effect i. e. Eckert number. Higher values of mass (solutal) slip parameter induce a depletion in the concentration. Nusselt number i. e. heat transfer rate to the blood vessel wall is improved with greater values of solid volume fraction for both CNTs. The present model is relevant to radiative ablation therapy combined with nano-medical treatments in blood vessels wherein constant mechanical loading via blood pressure and flow can elevate internal stresses (circumferential wall stress and endothelial shear stress) and induce morphological alterations in blood vessel wall (stretching) and endothelium in conjunction with biochemical reactions. [Display omitted] [ABSTRACT FROM AUTHOR]

We unravel the nonmodal stability of a three-dimensional nonstratified Poiseuille flow in a saturated hyperporous medium constrained by impermeable rigid parallel plates. The primary objective is to broaden the scope of previous studies that conducted modal stability analysis for two-dimensional disturbances. Here, we explore both temporal and spatial transient disturbance energy growths for three-dimensional disturbances when the Reynolds number and porosity of the material are high, based on evolution equations with respect to time and space, respectively. Modal stability analysis reveals that the critical Reynolds number for the onset of shear mode instability increases as porosity increases. Moreover, the Darcy viscous drag term stabilizes shear mode instability, resulting in a delay in the transition from laminar flow to turbulence. In addition, it demonstrates the suppression of three-dimensional shear mode instability as the spanwise wavenumber increases, thereby confirming the statement of Squire's theorem. By contrast, nonmodal stability analysis discloses that both temporal and spatial transient disturbance energy growths curtail as the effect of the Darcy viscous drag force intensifies. But their maximum values behave like O (R e 2) for a fixed porous material, where R e is the Reynolds number. However, for different porous materials, the scalings for both temporal and spatial transient disturbance energy growths are different. Furthermore, increasing porosity also suppresses both temporal and spatial disturbance energy growths. Finally, we observe that temporal transient disturbance energy growth becomes larger for a spanwise perturbation, while spatial transient disturbance energy growth becomes larger for a steady perturbation when angular frequency vanishes. The initial disturbance that excites the largest temporal energy amplification generates two sets of alternating high-speed and low-speed elongated streaks in the streamwise direction. • Nonmodal stability of a Poiseuille flow through a hyperporous medium. • Viscous drag force stabilizes shear mode instability. • Spanwise wavenumber suppresses shear mode instability, confirming Squire's theorem. • Temporal and spatial transient energy growths curtail as viscous drag force intensifies. • Maximum transient energy growths behave like O (R e 2) for a fixed porous material. • Temporal transient energy growth becomes larger for a spanwise perturbation. [ABSTRACT FROM AUTHOR]

Understanding the seasonal variations of vegetation drag coefficients is crucial for improving wave attenuation predictions and adapting to climate impacts. This study explores the seasonal changes in drag coefficients within salt marsh vegetation, using data from a year-long series of field measurements at the Chongming Dongtan Wetland. It uncovers the complex seasonal variations of drag coefficients. Results demonstrate that incorporating a nonlinear equation for characteristic flow velocity and effective vegetation length significantly improves the precision of drag coefficient predictions, ensuring a closer match with field observations. Furthermore, it introduces a refined drag coefficient formula that incorporates adjustments for vegetation stiffness and relative submergence, offering a more accurate representation of the seasonal variability in drag forces exerted by salt marsh vegetation. This enhanced formula is crucial for accurately assessing vegetation's role in wave attenuation, providing critical insights for the design and implementation of coastal defense and wetland conservation initiatives. • Significant seasonal fluctuations are evident in the drag coefficient, vegetation stiffness, and relative submergence. • Nonlinear characteristic velocity within the stem Reynolds number is influenced by seasonal variations in vegetation stiffness and relative submergence. • Development of a new formula that adjusts for the seasonal changes in drag coefficient within salt marsh vegetation. [ABSTRACT FROM AUTHOR]