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• Numerically investigate folding pattern and rigid-flexible coupled dynamics of satellite-sphere system. • Achieve a larger volume folding rate by pattern of inflatable sphere with orderly deployment. • Inflating process has great influence on satellite based on rigid-flexible coupled dynamic model. • Reduce influence by heavier satellite, small inflation rate and appropriate control torque. Inflatable spheres can be applied to the aerodynamic drag deorbiting device for satellites. It may bring about a complicated dynamic problem under the disturbance from the lightweight large-volume inflatable sphere to the satellite. In order to explore this problem, rigid-flexible coupled dynamics behaviors of satellite-sphere system during inflating process are numerically studied in this paper. The folding pattern of inflatable sphere is designed to obtain the parametric model in the folded state. The dynamic analysis model of this system is established to analyze dynamic behaviors, including the dynamics of the satellite-sphere system, the gas state of the airbag and the disturbance to the satellite, during the inflating process. Parameter effects on the attitude disturbance are studied. The results show that the satellite mass, inflating mass rate and control torque have a great impact on the attitude disturbance. These works provide theoretical bases and technical supports for the engineering development of inflatable sphere deorbiting devices. [ABSTRACT FROM AUTHOR]

Refractive and diffractive solar sails have been cited to yield benefits in both performance and utility over reflective sails, but their range of viable flight regimes and future applications have not been fully explored. In this paper, a flight model is developed to test and compare these transmissive sail designs under realistic conditions. Raw performance is translated into tangible flight characteristics within a range of flight regimes, such as rate change of orbital energy and minimum operational altitude, and used to make comparison with reflective sails and contemporary thrusters. Additionally, the sensitivity of these flight characteristics to certain orbital parameters is explored when operating under either a locally optimal or simplified Sun-pointing steering law. The developed flight model focuses on solar radiation pressure, atmospheric drag and the effects of eclipse and orbital precession; locally optimal steering laws are numerically generated for every flight regime using a ray tracing-derived performance sensitivity profile. Relative to an idealised reflective sail, the sensitivity of transmissive sail performance is found to be lower for altitude, but higher for orbital inclination. High performance transmissive sail designs are found to outperform idealised reflective ones in every flight regime nonetheless. Meanwhile, only certain lower performance designs demonstrate this trait; others retain advantage only within high inclination, low altitude orbits. 36 m 2 transmissive sails performing an orbit-raising manoeuvre from low Earth orbit are shown to generate transit times comparable to mid-range electric thrusters. In light of these findings, potential applications for transmissive sails are discussed, as well as several practical considerations and potential limitations. • Solar sail performance and operational flexibility improved by transmissive membranes. • Non-meta transmissive sails find advantage at low altitude and/or high inclination. • Transmissive metasails find advantage in every flight regime. • Transmissive sails may fulfil contemporary thruster roles in low Earth orbit. • Transmissive sails may provide feasible space debris mitigation strategy. [ABSTRACT FROM AUTHOR]

In order to meet the demanding drag reduction requirements of high-speed aircraft, the drag reduction mechanism of array microslit-opposed jets in the passivation leading edge is studied using a numerical method based on the shear stress transfer (SST) k-ω two-path turbulence model. The computations are performed with the commercial CFD solver FLUENT 13.0 code. The interference characteristics of the array jets are analyzed, the influence laws of the microslit array mode and the angle of attack on drag reduction performance are explored, and a prediction method of passivation leading edge drag characteristics based on radial basis function (RBF) neural network is constructed. The research conditions are as follows: the incoming Mach number is 2.0, the angle of attack ranges from 0° to 30°, and the number of microslits is 0 to 5. The results show that when there is interference between microslit jets, the interaction between adjacent reverse reflux regions will change the shape of the reflux regions. When there is a microslit jet in the center line, the position of the detached shock wave is more affected by the angle of attack. The drag characteristics of the leading edge are determined by the location of the detached shock wave and the characteristics of the reflux regions. The mode of microslits determines the drag reduction efficiency and sensitivity to the angle of attack. There may be contradictions in the design of array microslit-opposed jet schemes regarding the overall drag reduction efficiency, local load, and drag reduction stability. The drag prediction model based on the RBF neural network has an accuracy of 5%, which can provide support for the design of array microslit-opposed jets. Practical Applications: The array microslit-opposed jets provide a new technical approach for reducing drag on the passivation leading edge. The paper studies its flow characteristics and laws and provides relevant conclusions. It can serve as a theoretical reference during design. The number of microslits is not the more the better. When designing microslit patterns, many factors need to be considered. [ABSTRACT FROM AUTHOR]

In this paper, a novel Model Predictive Control (MPC) technique for multi-satellite formation flying geometry acquisition and maintenance in high-drag environment is presented. The proposed MPC relies on a linearized and convexified quasi-nonsingular Relative Orbital Elements (ROE) model based on state transition matrices propagation, allowing to include the effect of perturbations in the prediction to optimize fuel efficiency and tracking accuracy. The formation is controlled with respect to a non-decaying orbiting point to perform absolute and relative station keeping simultaneously. For this purpose, a new dedicated plant matrix to include drag effects on ROE in the propagation is derived and validated with respect to numerical results. In all simulations, the satellites are assumed to be equipped with a single low-thrust propulsion unit, therefore, specific constraints are included in the controller to obtain a feasible solution in a real operational scenario. Moreover, a collision avoidance constraint is added in case of close proximity operations exploiting a linear mapping between the set of ROE and cartesian coordinates expressed in the Local-Vertical-Local-Horizontal (LVLH) reference frame. The controller response is simulated in several realistic mission contexts with a high-fidelity orbital propagator and the results are validated for fuel efficiency by comparing them to similar approaches available in literature and to optimal solutions obtained respectively with a direct single shooting algorithm and with a closed-form impulsive formulation. [ABSTRACT FROM AUTHOR]

Buildings increase the urban surface roughness and reduce near‐surface wind speeds in the urban canopy due to the drag effect. Urban heat storage and other effects cause urban warming as well, which decreases the urban boundary layer stability and enhances the turbulence exchange between upper and lower layer. As upper momentum is transported downward, the wind speed of urban canopy increases. Quantitative descriptions of these mechanisms are still lacking currently. This paper presents high‐resolution numerical simulation results of a mega city, Shanghai, China from 2016 to 2020 using the building effect parameterization in WRF (WRF‐BEP) with urban morphological parameters. The dynamic and thermal effects of building morphology on urban canopy wind speed were separated and their quantitative expression functions were given. The results indicate that the influence of building morphology on urban canopy wind speed is mainly dynamic resulting in a wind speed attenuation of approximately 50% and nearly constant. The thermal effect of building morphology on urban canopy wind speed increases with the urban heat island intensity, and the thermal effect could increase urban canopy wind speed by about 30% under the condition of strong urban heat island. The relative contributions of the dynamic and thermal effects of building morphology to urban canopy wind speed change with the wind speed. As wind speed increases, the contribution of the thermal effect of building morphology to urban canopy wind speed gradually decreases. This paper provides a quantitative relationship between the urban canopy wind speed variation and urban morphology, as well as urban heat island intensity. Plain Language Summary: Urbanization changes the dynamic and thermal properties of urban and creates new dynamic and thermal processes in urban areas. Buildings increase the urban surface roughness and reduce urban canopy wind speed due to the drag effect. At the same time, urban warming causes the downward transportation of momentum, which increases the wind speed. Quantitative descriptions of these mechanisms are lacking currently. This study investigated the impact of building morphology on urban canopy wind speed using WRF‐BEP model with high‐resolution urban morphological parameters. The dynamic and thermal effects of building morphology on urban canopy wind speed were separated and their quantitative expression functions were given. Key Points: The dynamic and thermal effects of building morphology on urban canopy wind speed are separatedThe quantitative expression functions of the dynamic and thermal effects of building morphology on wind speed are givenThe relative contributions of the dynamic and thermal effects on urban canopy wind speed are investigated [ABSTRACT FROM AUTHOR]

This work investigated the influence of crosswinds and leg positions on the aerodynamics of an articulated cycling mannequin on a track bicycle. Force, wake total pressure and wake velocity measurements were made in a low-speed sports wind tunnel of closed-circuit type. The freestream velocity and wheel speeds were kept at 15 m/s . The crank angle of the mannequin was varied across a pedal cycle. Yaw angles from 0 ∘ to 20 ∘ were examined. The experimental results reveal that the leg position significantly affects the aerodynamic performance of a cyclist. At high yaw angles, the aerodynamic drag on the cyclist showed noticeable deviations between most leg positions and their 180 ∘ -apart pairs. A wake analysis technique effectively captured the influence of leg positions on drag. The total pressure deficit contributes dominantly to the overall drag. The wake pressure contours demonstrate how leg-wheel interaction affects the total pressure distribution and drag under crosswinds. This study offers valuable insights into the flow behavior and drag generation around a cyclist with varying leg positions under crosswinds. [ABSTRACT FROM AUTHOR]

The significant impact of Nb on ferrite transformation, both in terms of solute drag effect (SDE) and interphase precipitation, was investigated quantitatively. Ferrite transformation kinetics were characterized using thermal expansion experiments and theoretical calculations. The microstructures were characterized using high−temperature confocal laser scanning microscopy (CLSM), a field−emission scanning electron microscope (FESEM), and a transmission electron microscope (TEM). Under a higher driving force, interphase precipitations were observed in the sample with a higher Nb content. A three−dimensional (3D) reconstruction method was used to convert the two−dimensional (2D) image of interphase precipitation into a three−dimensional model for a more typical view. The SDE and interphase precipitation had opposite effects on the kinetics of ferrite transformation. A lower Nb content showed a strong contribution to the SDE, which delayed ferrite transformation. A higher concentration of Nb was expected to enhance the SDE, but the inhibition effect was eliminated by the interphase precipitation of NbC during interfacial migration. Both the experimental results and theoretical calculations confirmed this phenomenon. [ABSTRACT FROM AUTHOR]

The wheels of a passenger vehicle contribute to a significant part of the vehicle's aerodynamic drag. The previous research has shown that the flow is sensitive to small geometrical variations of the tyre, such as its shoulder profile and tread pattern. This work investigates the effect of altering the tyre profile in the transition region between the tyre and the rim by adding a so-called rim protector. Full-scale wind tunnel tests capturing forces, flow fields and surface pressures were conducted for three tyre variants in combination with two rim configurations on a crossover SUV. With a low rim protector, the forces and flow fields were similar to the reference tyre without a rim protector for both rims. With a wide, protruding, rim protector on the open rim, a larger and more outwashed front wheel wake was obtained with differences in the vortex structures, resulting in a drag penalty of 0.017 C D . The altered front wheel wake reduced the shielding of the rear wheel, resulting in differences in the rear wheel wake and base pressure. With a closed rim, the differences with the wide rim protector were much smaller with only a slight drag increase compared to the reference, demonstrating that there can be a strong interaction between the tyre and rim design. [ABSTRACT FROM AUTHOR]

In the practical application of hydraulic rotating machinery, it is essential to thoroughly explore drag reduction and rheological characteristics of drag-reducing additives to optimize machinery efficiency and reduce equipment consumption. This paper combines simulation and experimental approaches to investigate the drag-reduction performance and rheological properties of drag-reducing additives. Numerical simulations are initially conducted to investigate the shear-thinning properties of drag-reducing fluid and explore variations in drag-reduction rate. Turbulent phenomena characteristics are described by analyzing turbulent statistical quantities. Subsequently, the rheological behaviors of polyethylene oxide (PEO), cetyltrimethyl ammonium chloride (CTAC), and their mixed solutions under different conditions are scrutinized using a rotational rheometer. The findings indicate that the drag reduction effect amplifies as the rheological index n and characteristic time λ decrease. The numerical simulations show a maximum drag reduction rate of 20.18%. In rheological experiments, a three-stage viscosity variation is observed in single drag-reducing additives: shear thickening, shear thinning, and eventual stabilization. Composite drag-reducing additives significantly reduce the apparent viscosity at low shear rates, thereby strengthening the shear resistance of the system. [ABSTRACT FROM AUTHOR]

Reactive air brazing of 3YSZ ceramic and aluminized Crofer22H stainless steel was conducted using Pd-modified Ag-2CuO fillers in this study. The influence of Pd content on the interfacial microstructure and the mechanical properties of the joints at room (25 °C) and high temperatures (600 °C) was thoroughly investigated. The results revealed that an increase in Pd content resulted in a decrease in the solubility of O element in the filler system, thereby altering the form of CuO at high temperatures and significantly enhancing its reactivity with aluminized Crofer22H stainless steel. Additionally, there was a significant deterioration observed in the wettability of the fillers on ceramics. Well-joined joints were only achieved with the use of Ag2CuO-3 wt.% Pd filler, resulting in a 27.9% increase in room temperature shear strength due to enhanced interface reaction. At 600 °C, plastic deformation caused Ag-based filler to soften through dynamic recrystallization, but the addition of Pd dissolved in the matrix produced a solute drag effect that inhibited this process and increased joint shear strength by 41.1%. [ABSTRACT FROM AUTHOR]

Soil adhesion is one of the important factors affecting the working stability and quality of agricultural machinery. The application of bionic non-smooth surfaces provides a novel idea for soil anti-adhesion. The parameters of sandy loam with 21% moisture content were calibrated by the Engineering Discrete Element Method (EDEM). The final simulated soil repose angle was highly consistent with the measured soil repose angle, and the obtained regression equation of the soil repose angle provides a numerical reference for the parameter calibration of different soils. By simulating the sinusoidal swing of a sandfish, it was found that the contact interface shows the phenomenon of stress concentration and periodic change, which reflects the effectiveness of flexible desorption and soil anti-adhesion. The moving resistance of the wedge with different wedge angles and different serrated structures was simulated. Finally, it was found that a 40° wedge with a high-tail sparse staggered serrated structure on the surface has the best drag reduction effect, and the drag reduction is about 10.73%. [ABSTRACT FROM AUTHOR]

The streaming instability, a promising mechanism to drive planetesimal formation in dusty protoplanetary discs, relies on aerodynamic drag naturally induced by the background radial pressure gradient. This gradient should vary in discs, but its effect on the streaming instability has not been sufficiently explored. For this purpose, we use numerical simulations of an unstratified disc to study the non-linear saturation of the streaming instability with mono-disperse dust particles and survey a wide range of gradients for two distinct combinations of the particle stopping time and the dust-to-gas mass ratio. As the gradient increases, we find most kinematic and morphological properties increase but not always in linear proportion. The density distributions of tightly coupled particles are insensitive to the gradient whereas marginally coupled particles tend to concentrate by more than an order of magnitude as the gradient decreases. Moreover, dust–gas vortices for tightly coupled particles shrink as the gradient decreases, and we note higher resolutions are required to trigger the instability in this case. In addition, we find various properties at saturation that depend on the gradient may be observable and may help reconstruct models of observed discs dominated by streaming turbulence. In general, increased dust diffusion from stronger gradients can lower the concentration of dust filaments and can explain the higher solid abundances needed to trigger strong particle clumping and the reduced planetesimal formation efficiency previously found in vertically stratified simulations. [ABSTRACT FROM AUTHOR]

The Casimir–Lifshitz force of friction between neutral bodies in relative motion, along with the drag effect, causes their heating. This paper considers this frictional heating in a system of two metal plates within the framework of fluctuation electromagnetic theory. Analytical expressions for the friction force in the limiting cases of low (zero) temperature and low and high speeds, as well as general expressions describing the kinetics of heating, have been obtained. It is shown that the combination of low temperatures (T < 10 K) and velocities of 10–103 m/s provides the most favorable conditions when measuring the Casimir–Lifshitz friction force from heat measurements. In particular, the friction force of two coaxial disks of gold 10 cm in diameter and 500 nm in thickness, one of which rotates at a frequency of 10–103 rps (revolutions per second), can be measured using the heating effect of 1–2 K in less than 1 min. A possible experimental layout is discussed. [ABSTRACT FROM AUTHOR]

Computational rhinology is a specialized branch of biomechanics leveraging engineering techniques for mathematical modelling and simulation to complement the medical field of rhinology. Computational rhinology has already contributed significantly to advancing our understanding of the nasal function, including airflow patterns, mucosal cooling, particle deposition, and drug delivery, and is foreseen as a crucial element in, e.g., the development of virtual surgery as a clinical, patient-specific decision support tool. The current paper delves into the field of computational rhinology from a nasal airflow perspective, highlighting the use of computational fluid dynamics to enhance diagnostics and treatment of breathing disorders. This paper consists of three distinct parts—an introduction to and review of the field of computational rhinology, a review of the published literature on in vitro and in silico studies of nasal airflow, and the presentation and analysis of previously unpublished high-fidelity CFD simulation data of in silico rhinomanometry. While the two first parts of this paper summarize the current status and challenges in the application of computational tools in rhinology, the last part addresses the gross disagreement commonly observed when comparing in silico and in vivo rhinomanometry results. It is concluded that this discrepancy cannot readily be explained by CFD model deficiencies caused by poor choice of turbulence model, insufficient spatial or temporal resolution, or neglecting transient effects. Hence, alternative explanations such as nasal cavity compliance or drag effects due to nasal hair should be investigated. [ABSTRACT FROM AUTHOR]

In order to mitigate the impact of particulate pollutants in Nanjing Sample Industrial Park, it is imperative to simulate the wind field and pollutant dispersion inside the park. Therefore, a CFD-DPM study was employed to simulate the wind field and pollutant dispersion with an accurate landform model. A large eddy simulation was utilized for calculating wind flow distribution inside the park, which is more suitable than Reynolds-Averaged Navier–Stokes Equations (RANS). The physical model of the plant canopy was incorporated to assess its influence on the wind field and particulate pollutants through drag, buoyancy, and deposition effects. Using this method, the distributions of the wind field, and contaminant and the sensitivity tests were obtained by means of calculating a number of research cases under different meteorological conditions. In the numerical results, the wind field was obstructed by the plant canopy, resulting in near-ground uniformity under unstable weather conditions. The distribution of particulate pollutants was influenced not only by the drag and buoyancy effects but also by deposition, which caused an accumulation of particulate pollutants on the windward side of the canopy under unstable weather conditions. The sensitivity tests were performed by comparing the concentrations of particulate pollutants under various conditional settings. The canopy regions can remove the particulate pollutant by 50% under stable weather conditions. The deposition effect is enhanced by larger particle density and diameter and is also influenced by leaf area density. [ABSTRACT FROM AUTHOR]

We present a 3D ideal MHD simulation of magnetospheric accretion on to a non-rotating star. The accretion process unfolds with intricate 3D structures driven by various mechanisms. First, the disc develops filaments at the magnetospheric truncation radius (RT) due to magnetic interchange instability. These filaments penetrate deep into the magnetosphere, form multiple accretion columns, and eventually impact the star at ∼30o from the poles at nearly the free-fall speed. Over 50 per cent (90 per cent) of accretion occurs on just 5 per cent (20 per cent) of the stellar surface. Secondly, the disc region outside RT develops large-scale magnetically dominated bubbles, again due to magnetic interchange instability. These bubbles orbit at a sub-Keplerian speed, persisting for a few orbits while leading to asymmetric mass ejection. The disc outflow is overall weak because of mostly closed field lines. Thirdly, magnetically supported surface accretion regions appear above the disc, resembling a magnetized disc threaded by net vertical fields, a departure from traditional magnetospheric accretion models. Stellar fields are efficiently transported into the disc region due to above instabilities, contrasting with the 'X-wind' model. The accretion rate on to the star remains relatively steady with a 23 per cent standard deviation. The periodogram reveals variability occurring at around 0.2 times the Keplerian frequency at RT , linked to the large-scale magnetic bubbles. The ratio of the spin-up torque to |$\dot{M}(GM_*R_T)^{1/2}$| is around 0.8. Finally, after scaling the simulation, we investigate planet migration in the inner protoplanetary disc. The disc driven migration is slow in the MHD turbulent disc beyond RT , while aerodynamic drag plays a significant role in migration within RT. [ABSTRACT FROM AUTHOR]

Underwater bionic-legged robots encounter significant challenges in attitude, velocity, and positional control due to lift and drag in water current environments, making it difficult to balance operational efficiency with motion stability. This study delves into the hydrodynamic properties of a bionic crab robot's shell, drawing inspiration from the sea crab's motion postures. It further refines the robot's underwater locomotion strategy based on these insights. Initially, the research involved collecting attitude data from crabs during underwater movement through biological observation. Subsequently, hydrodynamic simulations and experimental validations of the bionic shell were conducted, examining the impact of attitude parameters on hydrodynamic performance. The findings reveal that the transverse angle predominantly influences lift and drag. Experiments in a test pool with a crab-like robot, altering transverse angles, demonstrated that increased transverse angles enhance the robot's underwater walking efficiency, stability, and overall performance. [ABSTRACT FROM AUTHOR]

This paper deals with the problem of controlled atmospheric re-entry, which has recently gained growing interest from the aerospace scientific and industrial communities for the economic and environmental benefits related to the development of reusable space vehicles. In this context, an original technique based on the incremental formulation of the Model Predictive Control methodology is proposed to tackle the trajectory tracking problem of a small satellite equipped with a deployable heat shield in the de-orbiting phase, focusing on a range of altitude from 300 km to 130 km, i.e., before the atmosphere is dense enough to begin a terminal re-entry phase. The proposed control logic allows following a given pre-determined guidance law, limiting position offsets due to unmodelled disturbances or uncertainties in the knowledge of spacecraft parameters (e.g., drag coefficient). An extensive numerical simulation campaign to assess the control performances in different perturbing conditions has demonstrated its ability to reach a km-error level in the position error at the final altitude of 130 km. • Controlled deorbiting based on aerodynamic drag modulation is addressed. • An Incremental formulation of the MPC controller is proposed for trajectory-tracking. • Performance assessment is carried out in a realistic simulation environment. • The achieved tracking error is kept below 1 km at re-entry interface (130 km). [ABSTRACT FROM AUTHOR]

Salt marshes provide valuable ecosystem services, which are influenced by their interaction with currents and waves. On the one hand, currents and waves exert hydrodynamic forces on salt marsh plants, which shapes the distribution of species within the marsh. On the other hand, the resistance produced by the plants can shape the flow structure, turbulence intensity, and wave dissipation over the canopy. Because marsh plants are flexible structures, their reconfiguration modifies the drag felt by the plants and the flow. While several previous studies have considered the flexibility of the stem, few studies have considered the leaf component, which has been shown to contribute the majority of plant resistance. This paper reports a unique dataset that includes laboratory measurements of both the force on an individual plant and the flow structure and wave energy dissipation over a meadow of plants. In the individual plant experiment, the motion of the plant and plant drag, free-surface displacement, and velocity profile were measured. The individual plant experiments considered both a live marsh plant (Spartina alterniflora) and a mimic consisting of 10 leaves attached to a central stem. For the meadow experiment, velocity profiles were measured both upstream and within the meadow, and free-surface displacement was measured along the model marsh plant meadow with high spatial and temporal resolution. These experiments used five water depths (covering both submerged and emergent conditions), three wave periods (from long wave to short waves), seven wave heights (from linear to nonlinear waves), and six current conditions (including pure current, pure wave, and combined current and wave). In summary, there are 102 individual plant tests and 58 meadow tests. The drag, free-surface displacement, and velocity are reported in the SMCW.mat and SMCW.nc files including the raw data, the phase averages, and the statistical values. A link to the plant motion videos is also provided. This dataset provides high-quality measurements that can be used to develop and validate models of plant motion, hydrodynamic drag on individual plants, vegetation-generated turbulence, the evolution of flow structure through a meadow, and the transformation and dissipation of waves over natural salt marshes. The dataset is available from Figshare with detailed instructions for reuse (10.6084/m9.figshare.24117144; Zhang and Nepf, 2023a). [ABSTRACT FROM AUTHOR]

Based on the analysis of typical operating modes of modern high-speed trains and transport aircraft, the influence of various schemes of surface relief modification and blowing through it on aerodynamic drag has been thoroughly investigated. A set of several schemes of the combined effect of these two factors is proposed to create an easy-to-use, cheap-to-produce streamlined surface of the desired structure with a reliable and controllable effect of active influence on aerodynamic drag reduction. The potential effect of reducing aerodynamic drag has been verified by numerical and Particle Image Velocimetry experimental modeling. The proposed technological innovations are encouraging and relevant; by reducing energy costs, they increase the commercial and environmental attractiveness of their implementation. [ABSTRACT FROM AUTHOR]

This paper presents a new control surface, which we have named auxiron, that helps a solar-powered aircraft to orient itself according to the position of the sun in the sky to collect more solar power. The auxiron also enables an aircraft to land in crosswind conditions with no or reduced sideslip angle depending on the auxiron control power. The auxiron serves to produce the necessary side aerodynamic force for counterbalancing the horizontal component of the lift force. Its primary purpose is to eliminate the sideslip angle during flight with a nonzero bank angle. This results in a reduction in aerodynamic drag and power consumption required to maintain a straight-line flight with nonzero bank angles. By implementing this innovative control surface, an aircraft can now cruise straight without experiencing any sideslip angle, even with nonzero bank angles. The modified stability and control derivatives for the aircraft configuration with the auxiron are established, and these derivatives are incorporated into the aircraft dynamics. The 6-DoF simulation is carried out for the solar UAV, Maraal, which demonstrates the effectiveness of the auxiron. [ABSTRACT FROM AUTHOR]

• AEMFC model includes GDL anisotropy for accuracy. • Enhances multi-physical field coupling for completeness. • Anode GDL porosity gradient boosts AEMFC efficiency. • Higher anode GDL contact angle optimizes cell performance. • Improved AEMFC performance with anode GDL wettability gradient. Alkaline anion-exchange membrane fuel cells (AEMFCs) have been regarded as a promising alternative of proton exchange membrane fuel cells (PEMFCs) due to their high oxygen reduction reaction activity in the cathode side, which allow the usage of non-noble metal catalyst. Unlike PEMFCs, water is generated on the anode side of AEMFCs, and the electro-osmotic drag effect exacerbates the flooding phenomenon on the anode side and the dry-out on the cathode side. Therefore, water management plays a crucial role in the performance of AEMFC. In this study, we develop a multiphase flow multi-physics AEMFC model considering the anisotropy of gas diffusion layer (GDL). The study examines the impact of varying porosity gradients in GDLs, as well as changes in wettability, on cell performance. We find that in GDLs with varying porosity gradients, reducing porosity near the interface between the anode GDL and the catalyst layer (CL) promotes even distribution of reactive gases, enhancing cell performance. Under the operating conditions of this paper, the maximum power density can be increased by 1.27 %. Regarding wettability changes, optimal cell performance was observed with a higher contact angle on the anode GDL and a lower contact angle on the cathode GDL. The maximum power density can be increased by 1.59 %. Moreover, a higher contact angle near the anode GDL/CL interface maintained high membrane hydration levels, resulting in improved cell performance. The maximum power density can be increased by 2.68 %. [ABSTRACT FROM AUTHOR]

Accurate prediction of the dynamics and deformation of freely moving drops is crucial for numerous droplet applications. When the Weber number is finite but below a critical value, the drop deviates from its spherical shape and deforms as it is accelerated by the gas stream. Since aerodynamic drag on the drop depends on its shape oscillation, accurately modeling the drop shape evolution is essential for predicting the drop's velocity and position. In this study, 2D axisymmetric interface-resolved simulations were performed to provide a comprehensive dataset for developing a data-driven model. Parametric simulations were conducted by systematically varying the drop diameter and free-stream velocity, achieving wide ranges of Weber and Reynolds numbers. The instantaneous drop shapes obtained in simulations are characterized by spherical harmonics. Temporal data of the drag and modal coefficients are collected from the simulation data to train a Nonlinear Auto-Regressive models with eXogenous inputs (NARX) neural network model. The overall model consists of two multi-layer perceptron networks, which predict the modal coefficients and the drop drag, respectively. The drop shape can be reconstructed with the predicted modal coefficients. The model predictions are validated against the simulation data in the testing set, showing excellent agreement for the evolutions of both the drop shape and drag. [Display omitted] • Parametric interface-resolved simulations were performed for a comprehensive dataset. • Drop shape evolution is characterized by temporal variation of spherical harmonics. • NARX neural networks are used to predict the time-dependent drop shape and drag. • Model predictions for drop shape and drag agree very well with the testing data. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel sBF method for scalable, cost-effective slippery surface was developed. • Nonzero interfacial slip was confirmed by direct velocity field measurements. • Significant drag reduction was observed under turbulent flow condition. • Remarkable anti-biofouling was shown in real-sea tests over 50 days. The maritime industry has been seeking efficient solutions to combat hydrodynamic friction and biofouling, which increase operational costs and environmental issues. To address these concerns, we developed a novel sprayable breath figure (sBF) method to create a scalable and cost-effective lubricant-infused surface (LIS) for reducing frictional drag forces on marine vehicles. The proposed sBF method facilitated the rapid production of multilayered porous polymer films with micron-scale spherical cavities. It can be applied to large and curved surfaces, thus overcoming the limitations of traditional breath figure methods. Further surface treatment of oxygen plasma etching followed by polydimethylsiloxane (PDMS) brush grafting was employed to optimize the interfacial slip and lubricant retention of the slippery surface coating. The PDMS brush-grafted slippery surfaces demonstrated significant drag reduction under turbulent flow conditions. This was confirmed by direct velocity field measurements, showing nonzero slip velocity unlike conventional no-slip surfaces. The same surfaces also exhibited remarkable anti-biofouling performance, severely resisting marine biofouling in real-sea field tests over 50 days. The proposed sBF method was successfully applied to large-area and curved submerged bodies, and achieved a noticeable drag reduction under high-speed turbulent flows. This study is a critical step toward the practical implementation of this technology in the marine industry. [ABSTRACT FROM AUTHOR]

• The coupling between the elastic spike and hypersonic flow is solved by a new FSI algorithm. • The drag reduction by spike is affected by the spike geometry sizes and materials. • The spike deformation, pressure distribution, aerodynamic drag and lift forces are revealed. • Larger spike diameters, shorter spikes, and spikes with larger elastic moduli and lower densities are preferred for drag reduction. In this study, a new fluid structure interaction (FSI) algorithm is developed for the aerodynamic-elasticity problem, aiming to address the coupling problem between compressible fluids and deformable solid structures. To verify the feasibility of the proposed model, a two-dimensional cantilever panel case under shock waves was conducted. Our numerical results present good consistency with the data from literatures. Furthermore, the validated FSI algorithm is applied on an elastic spike under compressible hypersonic flow. The complicated interaction between the fluid and solid structure under various spike geometry sizes and materials were revealed in respect of the spike deformation, pressure, temperature, and flow fields distribution. The main findings show that the spike deformation largely affects pressure and temperature on the blunt, the aerodynamic drag and lift force, indicating the necessity of FSI. For the spike diameters and lengths, it is found that larger spike diameters and shorter spikes benefits for deformation reduction, thereby minimizing fluctuations in aerodynamic drag force. For spike materials, spikes with larger elastic moduli and lower densities are preferred for the drag reduction. Thus, the proposed FSI model can accurately predict flow fields around and deformations for elastic spikes and offer guidance for drag reduction design in aerospace engineering. [Display omitted] [ABSTRACT FROM AUTHOR]

Water Droplet Machining (WDM) is a new manufacturing process, which uses a series of high-velocity, pure-water droplets to impact and erode solid workpieces, for the purpose of through-cutting, milling and surface profiling. The process is conducted within a vacuum environment to suppress aerodynamic drag and atomization of the waterjet and droplet train. This preserves droplet momentum and allows for a more efficient transfer of energy between the water and workpiece, than in standard atmospheric pressure. As a new manufacturing technique, parameter-specific details and characteristics of this process are absent from the scientific literature. Therefore, this study aims to elucidate the capabilities of WDM, and uncover its erosion characteristics. Experiments are performed using a custom-fabricated machine, where a range of waterjet-types (and droplet trains) are produced. The experiments are performed on two industrial-relevant metals: stainless steel SS 316 L and aluminum AA 6022-T4. The target shape is a partial-cut through the material, i.e., a trench. A parametric study investigates the effects of stand-off distance, orifice diameter, and feed-rate on the trench shape, material-removal-rate, and reveals the conditions which render WDM an effective machining process. It was found that, for orifice diameters of 100 μ m, an effective stand-off distance is between 457 and 686 mm; below that, no material removal is observed. In this configuration, accurate through-cuts are produced and can be used for manufacturing purposes. For large orifice diameters, e.g., 250 μ m, an atomized spray is produced, which features a comparatively large material removal rate, and can be used for surface profiling and milling. [Display omitted] • A new pure waterjet cutting technology is proposed, which utilizes a series of droplet impacts for material removal. • The workpiece and waterjet are immersed in a vacuum environment to suppress aerodynamic drag and droplet atomization. • Parameter-specific details of the process are provided, which facilitate high material removal rates. • The technique can be used for precise through-cutting or for rough milling and surface profiling. [ABSTRACT FROM AUTHOR]

• The PMP has an advantage in simultaneous control of flow drag and noise. • The PMP reduces the pressure drag coefficient more than 20%. • The PMP suppresses both the tonal and broadband noise components. • The PPI is an important parameter affecting pressure drag and noise level. Pressure drag and noise level are two key parameters related to flow past a bluff body, thus various active and passive methods have been developed to reduce the drag and noise. The paper presents a passive method of simultaneously reducing the pressure drag and aerodynamic noise associated with flow past a smooth circular cylinder by placing a porous material plate (PMP) downstream the cylinder. Multi-points instantaneous wall pressure and far-field acoustic pressure have been measured in an anechoic wind-tunnel facility. The experimental results confirm that the PMP is effective to reduce both the pressure drag and the noise level, showing an attractive advantage compared with the impermeable splitter plate and porous coating. Parametric studies reveal effects of the pores per inch (PPI) of PMP, PMP-cylinder spacing and incoming flow velocity on the pressure drag and noise level. [ABSTRACT FROM AUTHOR]

The solute drag effect of phosphorus (P) in the single-phase austenite (γ-Fe) region was studied under isothermal annealing conditions at temperatures of 1050 °C, 1150 °C, 1250 °C and 1350 °C. High-temperature laser scanning confocal microscopy (HT-LSCM) was used to observe and quantify in situ grain growth on the surface of three different samples containing 0.026 wt.-% P, 0.044 wt.-% P and 0.102 wt.-% P. The dependence of the arithmetic mean grain sizes on time and temperature were modeled mathematically using a simple ordinary differential equation (ODE) according to normal grain growth (NGG) theory. As no other major effects, i.e., Zener-pinning by precipitates, occurred under the selected experimental conditions, grain growth interference was only considered by grain boundary (GB) segregation of P. Thus, the total grain boundary mobility (M) was directly determined depending on the P content and isothermal annealing temperature. The fitted GB mobility values enabled the determination of an average binding energy value between impurity P atoms and grain boundaries (E 0 = -1.1 - -0.6 eV) in the system. Finally, the GB segregation of P in γ-Fe was derived from the observed grain growth kinetics. The results showed reasonable agreement with calculations using segregation enthalpies from the literature. [Display omitted] [ABSTRACT FROM AUTHOR]

The amount of energy delivered to a solid-fueled rocket motor is its most crucial performance indicator. Metallic fuels, such as aluminum, is commonly added to propellants for obtaining high energy densities. In this study, the agglomeration of four distinct types of composite solid propellants, comprising different adhesives, oxidants, and Al particles, during gradual heating was experimentally investigated using a microscopic heating device. Thermogravimetry, quenching analysis, microscopic observations, and the collection of condensed combustion products were used to examine the microscale processes of agglomeration in the propellants during their combustion. Melting of the binder was found to enable the aluminum particles to travel and relative motion between the particles and the melting layer will act liquid drag forces on the particles, while oxidiser recession in the binder led to unbalanced surface tension forces acting on the aluminum particles, both these two forces pulling them closer together. Some particles were ejected into the gas under the action of aerodynamic drag. The addition of 10% RDX to the HTPB propellant increased the agglomerate size from 200 to 224 μm. Reducing the diameter of the aluminum particles in the NEPE propellant from 29 to 13 μm increased the agglomerate size from 200 to 632 μm. Moreover, RDX reacted exothermically at low temperatures in the HTPB propellant, enhancing the capillary forces and increasing the agglomerate size. The agglomeration process was dominated by a balance between the aerodynamic, adhesive, and capillary forces. [ABSTRACT FROM AUTHOR]

Semi-oval hollow section is an innovative cross-section profile, including one semi-circular flange, one flat flange and two flat webs. While the semi-circular flange (exposed to fluid or wind) offers a low level of hydrodynamic or aerodynamic drag, the flat elements facilitate connections with other members. This paper presents experimental and numerical investigations into the local buckling behaviour and resistances of austenitic stainless steel semi-oval hollow sections under combined compression and bending. A testing programme was firstly conducted and included initial local geometric imperfection measurements and ten eccentric compression tests. In conjunction with the testing programme, a numerical modelling programme was performed, where finite element models were developed to validate against the test results and conduct parametric studies for expanding the test data pool over a wider range of cross-section dimensions and loading combinations. The obtained test and numerical data were used to evaluate the applicability of the relevant design interaction curves for austenitic stainless steel rectangular hollow sections, as prescribed in the European code and American specification, to austenitic stainless steel semi-oval hollow sections. On the basis of the evaluation results, the codified design interaction curves were found to provide conservative resistance predictions. Finally, an improved design interaction curve, with more accurate end points and suitable shape, was developed and led to more accurate and consistent resistance predictions for austenitic stainless steel semi-oval hollow sections under combined compression and bending. • The local buckling of austenitic stainless steel semi-oval hollow sections under combined loading was studied. • Ten eccentric compression tests were conducted. • FE models were developed to simulate the test results and then used to perform parametric studies. • The applicability of relevant codified design interaction curves was assessed, showing conservatism. • A new design interaction curve was proposed and provided improved design accuracy and consistency. [ABSTRACT FROM AUTHOR]

A stacking-based ensemble prediction method is proposed in order to improve the efficiency and accuracy of aerodynamic shape optimization. This can be divided into a two-level model. The first-level model uses various base learners to predict the training dataset and obtain various combinations of predictions. In the second-level model, the meta-learner is trained using various combinations of predictions as inputs and the true response values as outputs. The RMSE and R-Square metrics results show that the performance metrics of the stacked models are significantly better than those of the original surrogate models, except for the stacked RBFNN model. The stacked Kriging model and LSSVR model achieved the best results with RMSE and R-Square index values of 0.0039 and 0.8418 for aerodynamic drag coefficient, respectively. The stacked Kriging model, RBFNN model, and LSSVR model achieved the best results with RMSE and R-Square index values of 0.0024 and 0.76 for aerodynamic lift coefficient, respectively. Four state-of-the-art multiobjective optimization algorithms are used to perform the optimization process. The results of hypervolume and Pareto fronts demonstrate the effectiveness of the selected FDV-NSGAII algorithm. After optimization, the drag and lift coefficients before and after optimization are reduced by 1.9% and 12.7%, respectively. • A stacking-based prediction framework is proposed to improve prediction accuracy. • The effects of different stacking combinations on prediction accuracy are analyzed. • The effectiveness of the selected FDV-NSGAII algorithm is demonstrated. • The efficiency and accuracy of aerodynamic optimization can be improved. [ABSTRACT FROM AUTHOR]

The carbon partitioning and lengthening rate of bainitic ferrite (α b) are excellent experimental parameters to estimate our level of understanding of the mechanism of bainitic transformation from a continuum perspective and our ability to capture it in analytical expressions. For Fe-C alloys and relatively simple steels the classical Zener-Hillert theory captures the bainitic transformation rather well but mispredicts the level of carbon in solution in the bainite and overestimates the lengthening rates for transformations at lower temperatures. To address this issue, this paper presents a new thermo-kinetic model based on the Zener-Hillert theory and the Gibbs energy balance concept to simulate the lengthening behavior of α b in the Fe-C and low alloyed steels. The model incorporates the effect of the temperature dependent carbon diffusion within the migrating interface via a temperature dependent ferrite/austenite interfacial energy and a temperature dependent diffusion coefficient but does not impose local equilibrium across the interface. The good agreement between the model predictions and nine sets of published experiments indicates that both the carbon supersaturation in α b and the slower lengthening rate are caused by carbon diffusion within the migrating interface. It is found that the degree of carbon supersaturation in α b increases significantly with decreasing temperature. Consequently, the enhanced carbon solute drag effect, resulting from carbon diffusion within the interface, strongly retards the lengthening rates of α b at lower temperatures. Transformation strain is shown to have a modest effect on the lengthening rates but to lower the degree of carbon supersaturation. [Display omitted] [ABSTRACT FROM AUTHOR]

Water and land (W-L) resources become even more important in the context of urban-rural integration in China's arid northwest region in order to achieve sustainable development goals (SDGs). Our study used Gini coefficients to examine the relationship between natural resources and economic development in China's Xinjiang Uygur Autonomous Region. Cobb-Douglas (C-D) production functions were used to determine the economic impacts of W-L resources on rural-urban economic development. We also examined the spatiotemporal interaction characteristics of the growth drag effect of W-L resources. As a result of the decline in Gini coefficients between 2000 and 2020, Xinjiang experienced a decrease in water resources, land resources, and urban-rural GDP (gross domestic product). The output elasticities of urban-rural land and water resources were 0.3544 and 0.4790, respectively, whereas the output elasticities of urban-rural land resources were 0.1501 and 0.2185, respectively. As a result, water resources contribute to the growth of urban-rural GDP more than land resources, and W-L resources contribute to the economic development of rural areas more than it does to that of urban areas. Land resources were found to have a drag effect on urban and rural economies, respectively, in 7 and 56 counties, respectively, and water resources were found to have a drag effect on urban and rural economies, respectively, in 67 and 58 counties. In Xinjiang, water resources contributed more to economic growth than land resources. Even though W-L resources still have a drag effect on urban-rural economic growth, we can gain greater driving force by optimizing and improving resource use. However, this requires an optimal allocation and efficient use of water resources. • The drag model can analyze the drag effects of natural resource use on the urban-rural economy. • Water resources are more compatible with the urban-rural economy than land resources. • Water constraints affect Xinjiang's economic growth more than land constraints. • Water scarcity reduced Xinjiang's urban economic growth by 0.68%–1.57% from 2000 to 2020. [ABSTRACT FROM AUTHOR]

• We developed an impression-based approach combining impact and indentation to isolate dislocation drag. • We developed a constitutive framework to fully quantify the dislocation-phonon drag regime. • We measured a fourfold increase in plastic work per unit volume during impact compared to indentation. • Dislocation drag emerged as the dominant deformation mechanism during impact. A substantial contribution from thermal activation was also identified. • It takes ∼2 orders of magnitude increase in rate for the contribution of the dislocation drag to increase from 10 % to 90 %. As deformation rate increases, the thermally activated dislocation glide gives way to a continuous glide of dislocations governed by their interactions with phonons. Understanding the dislocation-phonon drag regime is critical for designing metallic materials for extreme deformations rates. However, it has proven challenging to study empirically, partly due to the resource intensive nature of the experimental approaches targeting this regime. Here, we develop an impression-based experimental approach combining laser-induced microprojectile impact (Hassani et al., 2020a) and spherical nanoindentation to characterize the dislocation-phonon drag regime. We also develop a physically based constitutive framework that, when integrated with our experimental measurements, can quantify the dislocation-phonon drag regime. We isolate the effect of dislocation-phonon drag by leveraging the similar deformation geometries and length scales but different operative mechanisms during spherical nanoindentation and microprojectile impact. We discuss mechanistic contributions to the plastic work for microprojectile impacts in a range of impact velocities producing strain rates up to 109 s−1. We also develop a deformation mechanism map focused on the transition from thermal activation to dislocation drag for a model FCC metal, copper. [Display omitted] [ABSTRACT FROM AUTHOR]

The Direct Simulation Monte Carlo method (DSMC) is utilized in this study to investigate the flowfield surrounding the spike-aerodisk without and with an opposing jet under rarefied hypersonic conditions within near space (altitudes of 60∼90 km and Mach numbers 7∼20). As the flight altitude increases, the incoming flow gradually becomes rarefied, weakening the drag reduction effect of the spike-aerodisk model. At altitudes reaching 90 km, the spike-aerodisk loses its drag reduction effect due to the increasing proportion of the viscous drag coefficient. At a flight altitude of 70 km, as flight Mach numbers increase, the drag reduction and thermal protection performance of the spike-aerodisk remains unchanged, mainly demonstrating the excellent performance of the spike-aerodisk model at high Mach numbers. However, the peak wall heat flux coefficient on the aerodisk can be 4.8 times higher than on the blunt body. Therefore, an opposing jet is introduced to protect the spike-aerodisk from overheating and further improve the spike-aerodisk's drag and heat reduction efficiency. Within the investigated parameter range, when the opposing-jet pressure ratio is 0.02, the peak wall heat flux coefficient of the aerodisk can decrease from 0.58 to a level similar to that of the blunt body, approximately 0.12. To make the aerodisk more certain from overheating, choosing the opposing-jet pressure ratio of 0.08 can improve drag reduction and heat prevention on the blunt body by 60.9 % and 59.7 %, respectively, compared to the spike-aerodisk model without an opposing jet. [ABSTRACT FROM AUTHOR]

[Display omitted] • The hydroxy-containing cationic surfactant exhibits excellent hydrophobicity through simple synthesis. • Effectively reduce the thickness of the interface water film. • The thinning of the water film results in a high drag reduction effect during water injection into the core. • Promising candidate for water injection development in low-permeability oilfields. In water injection development of low-permeability reservoirs, the elevated flow resistance between the rock surface and the injected water results in enhanced injection pressure. Reducing the thickness of interfacial water film to expand flow radius is a new thought to achieve a decrease in injection pressure. In this work, a hydroxyl-containing cationic surfactant tetradecyl methyl dihydroxy-ethyl ammonium bromide (HTTAB) was designed and synthesized. The introduction of hydroxyl groups enhances the binding to the negatively-charged rock surface. HTTAB can modify the strong hydrophilic rock surface to a hydrophobic state, with the water contact angle increasing from 20.2° to 110.3°. HTTAB shows excellent drag-reducing effect, maintaining a drag reduction rate of over 30 % even after 30 PV of flushing. Particle Image Velocimetry (PIV) experiments show that after HTTAB adsorption, the interfacial slip velocity and centerline velocity can increase by 1.67 times and 33.66 % respectively, and the flow radius expands significantly. In addition, the thickness of the interfacial water film is obtained using Atomic Force Microscope (AFM). The results show that the thickness of the interfacial water film is reduced significantly from 79.42 nm to 8.85 nm. This study provides important guidance for the design of drag-reducing agents and the understanding of interfacial drag-reduction behavior. [ABSTRACT FROM AUTHOR]

This study evaluated the individual drag force model (iDFM), a subgrid-scale model for simulating tsunami inundation in coastal urban areas. The iDFM was then applied to characterize Typhoon Haiyan-induced storm surge inundations in 2013. Using a post-typhoon survey dataset containing inundation depths at different survey points with inundation limits, the performance of iDFM was validated, and the results confirmed that iDFM accurately estimates the storm surge inundation depths but overestimates the limit of inundation. In addition, the results revealed that the iDFM flow velocity was a dominant factor, and the inclusion of buildings in the simulated affected the arrival of the leading edge of inundation. Furthermore, the reduction in flow velocity was sensitive to the subgrid-scale parameters, and the spatial distribution pattern of buildings located in the inundated area affected the relative difference in the maximum flow velocity with the regional roughness model. The inundation characteristics of the Typhoon Haiyan storm surge models were compared with a historical tsunami event. The inundation characteristics were similar and model differences were observed mainly in the fluid velocity and momentum flux rather than the inundation depth. However, the magnitudes of relative differences observed in Tacloban were larger for fluid velocity and momentum flux, respectively, than in the tsunami event. The effect of building drag on advection was also substantial in Tacloban due to the differences in the inflow mass and momentum fluxes. • This study applys a subgrid-scale model of the tsunami inundation in a coastal urban area, called the individual drag force model (iDFM), to Typhoon Haiyan-induced storm surge inundations in 2013. The accuracy of iDFM is validated in comparison with the post-survey dataset, measuring inundation depths at survey points and the limit of inundation. In addition, the characteristics of the modeled inundation flow by the iDFM are examined by comparing them with the characteristics of the regional roughness model corresponding to the land use category. Moreover, the similarities and differences in the inundation characteristics are compared with a historical tsunami event in the authors' previous publication. [ABSTRACT FROM AUTHOR]

• Grain boundary (GB) triple junction (TJ) can migrate as an aggregate of TJ grooving and GB migration. • Accumulation of dislocations at the TJ compensates the misfit in shear coupling factors of constituent GBs. • Dislocation accumulation-initiated GB migration model explains the TJ drag effect. • TJ migration and its competition with other TJ deformation mechanisms depend on GB misorientation. The evolution of grain boundary (GB) networks in polycrystalline metals depends not only on the movement of the constituent GBs but also on the migration of GB triple junctions (TJs), the latter would have strong influence on the mechanical properties of polycrystals. We investigate the migration mechanism of TJs in face-centered cubic metals using molecular dynamics simulations. The TJ migration is revealed to follow a typical stick-slip behaviour that involves TJ grooving and coordinated GB migration. Upon external shear loading, the TJ experiences a quick migration process, resulting in a grooved TJ configuration with curved GBs at the TJ. The accumulation of dislocations at the TJ facilitates the TJ grooving process, since it compensates the angle gap caused by the inconsistent shear-migration coupling factors between the GBs. After reaching a critical grooving depth, the TJ migration is stagnated, while the connecting GBs begin to migrate via disconnections emitted from the TJ. Based on the mechanism of accumulated dislocation-initiated TJ migration, we propose an energetic model that considers the extra energy barrier for the accumulation of dislocations, to quantify the effect of GB misorientation on TJ migration. These findings deepen our understanding of the physical origin of TJ migration and point out the importance of dislocation accumulation on coordinated GB motion in nanocrystalline metals. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermodynamic coupling studied in bio-refining of butanol from ABE feed. • Butanol activity coefficients and volume fractions inhibited by ethanol and acetone. • Second order interaction effects dominant in flux coupling. • Sorption isotherms indicate penetrant-polymer interactions are negligible. • Flux isotherms reveal origin of flux coupling in thermodynamic coupling. A comprehensive investigation of sorption characteristics and the influence of thermodynamic coupling on targeted organophilic pervaporation of bio-butanol from multicomponent Acetone-Butanol-Ethanol (ABE) fermentation solutions is presented, emphasizing the effect of penetrant-penetrant and penetrant-membrane interactions on sorption and permeation. In addition to initial screening of thermodynamic models and simulation of activity coefficients and volume fractions, pervaporation experiments were also analogously conducted for multicomponent ABE feed mixtures. Statistically validated second order models were then derived to forecast the influence of solvent concentrations, feed temperature and mutual interaction terms on butanol volume fractions and partial fluxes. Negative first order coupling effects due to ethanol and acetone are observed to be more significant for both activity coefficients and volume fractions, with sorption being most inhibited when acetone and ethanol are at their highest concentrations in feed. In contrast, contribution of non-linear and second order coupling effects is dominant in flux coupling, with positive "drag effects" due to additional plasticization being less pronounced at higher solvent concentrations. For instance, at 313.15 K, increasing ethanol and acetone concentrations by 3 wt% and 6 wt%, respectively, predicts reduction in volume fractions by approximately 29 % and 43 % compared to 3 wt% butanol-water binary systems. Conversely, the corresponding flux values exhibit initial increase of approximately 17 %, followed by subsequent decrease of around 14 %. However, sorption isotherms indicate that the penetrant-polymer interactions have a negligible influence on butanol volume fractions in the PDMS membrane irrespective of feed composition. Similarly, analysis of flux isotherms also suggests that flux coupling effects may ultimately be traced to thermodynamic coupling phenomena. Consequently, prudent membrane selection for pervaporation becomes crucial to overcome the inherently detrimental thermodynamic coupling effects and improve butanol recovery. [ABSTRACT FROM AUTHOR]

• Using ammonia combustion to reduce drag for the first time. • Ammonia demonstrates superior local drag reduction. • The self-ignition point decides overall anti-drag effects. • The inlet decomposition ratio is not the higher the better. Boundary layer combustion is an effective method to reduce friction in scramjet combustors. In existing research on drag-reducing fuels, hydrocarbons pose challenges related to carbon deposition and emissions. Meanwhile, hydrogen presents significant difficulties in storage and transportation. For the first time, this paper explores ammonia as a drag-reducing alternative. We employed the Reynolds-averaged Navier-Stokes (RANS) method to investigate the characteristics of drag reduction by ammonia combustion in supersonic flow. Numerical results indicate that the local drag reduction by ammonia combustion is better than hydrocarbon and worse than hydrogen compared to existing research. Ammonia exhibits superior potential for drag reduction. However, the overall drag reduction at room ammonia injection temperature is limited due to the significant distance between the ammonia self-ignition point and the injection port. To address this challenge, we proposed two optimization strategies: increasing the ammonia injection temperature and increasing the inlet ammonia decomposition ratio. As the ammonia injection temperature increases, the self-ignition position moves towards the inlet, and the combustion drag reduction region expands upstream. Interestingly, a higher ammonia inlet decomposition ratio does not necessarily lead to a better drag reduction effect. In fact, an excessively high decomposition ratio can inhibit the combustion drag reduction effect. The most effective drag reduction occurs when the ammonia inlet mass fraction is 50%, resulting in a 42.8% reduction in integrated drag compared to the case without NH 3 injection. Overall, this paper offers critical insights into the utilization of ammonia combustion in scramjets to reduce drag. [Display omitted] [ABSTRACT FROM AUTHOR]

The foldable unmanned aerial vehicle can reduce the storage space and improve the platform adaptability. However, the conventional foldable wing aircraft is configured with a low aspect ratio, which leads to a high aerodynamic drag and limited flight endurance. In this study, a foldable wing unmanned aircraft that can increase its wingspan to improve aerodynamic performance and flight endurance is proposed. The aerodynamic characteristics and flight performance of the aircraft is evaluated using the computational fluid dynamic method. The numerical results show that the increased wingspan can effectively decrease the wingtip vorticity and aerodynamic drag. The fully-extended wing configuration achieves a lift-to-drag ratio of 16.72, which results in an increase of 36.94% than that of the non-extended wing. The flight endurance and range of the fully-extended wing configuration are 3.81 hour and 249.89 km, respectively, which creates 86.22% more endurance and 36.88% more range than the non-extended wing. To validate the feasibility of the proposed concept, a flight test was carried out and the flight performance was obtained from flight control system. The flight data corrects well with the numerical results, which proves the effectiveness and feasibility of the variable span-morphing wing in improving flight performance for unmanned aircraft. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phase field model for solute drag effect in multicomponent system is developed. • Effect of solute–solute interaction on solute drag is evaluated for two Mg alloys. • It was found that interaction of solutes can either strengthen or weaken solute drag. • New index for describing co-segregation tendency at grain boundaries is introduced. • Insights into texture weakening of Mg alloys are gained from the results obtained. The application of Mg alloy sheets is currently limited owing to their poor room-temperature formability. The solute-drag effect is a potential mechanism via which the texture intensity of Mg alloys can be lowered to improve their formability. However, detailed analyses of the effects of solute–solute interactions on the solute drag in multicomponent systems are lacking. Herein, a CALPHAD-linked phase-field model was developed to evaluate the grain boundary segregation and solute-drag effects in a multicomponent system. The model was used to calculate the grain boundary segregation and solute drag in several Mg alloys, and the effect of solute–solute interactions on these phenomena was evaluated. The results showed that Zn and Ca mutually enhanced the grain boundary segregation in Mg alloys, leading to greater solute drag. However, the combination of Al and Zn mutually suppressed the grain boundary segregation and consequently, reduced the solute drag. These results support a previously proposed theory that Mg-Zn-Ca alloys exhibit strong solute drag owing to the co-addition of Zn and Ca, which reduces the texture intensity and improves the room-temperature formability. Furthermore, a new index for describing co-segregation and competitive segregation at grain boundaries, based on Hillert's grain boundary phase model, was introduced. The value of the index was calculated for various combinations of alloying elements in Mg alloys. The results showed that many ternary Mg alloys with a low texture intensity tended to co-segregate alloying elements. [ABSTRACT FROM AUTHOR]

Obtaining ultra-high strength in commercial ZK60 wrought alloys is rather difficult by conventional processes due to their limited precipitation hardening. In this work, we proposed a novel strategy to enhance the strength of ZK60 alloy by constructing a high density of multi-scale particles in the matrix. As expected, the ultra-high tensile strength, such as ultimate tensile strength of 436 MPa and yield strength of 400 MPa, is achieved in the co-addition of minor Ca and Er in ZK60 extrusion alloys, outperforming most of Mg-Zn-based alloys reported previously. The co-addition of Ca and Er induces more multi-scale particles, including submicron-broken particles and fine dynamic precipitates formed in the matrix during extrusion. Note that fine precipitates at sub-grain boundaries stabilize their misorientations due to the pinning role and thus retard the dynamic recrystallization process, which intensifies the deformation texture of the bimodal structures. Solute segregation of Ca and Zn to grain boundaries was also observed, which favors refining recrystallized grains by solute drag effect. Compared to ZK60 alloy, the enhanced tensile strength in co-modified ZK60 alloy with Ca and Er is mainly attributed to the Orowan strengthening of multiscale particles. These results are expected to provide an important reference for fabricating high-strength Mg-Zn-based alloys. [ABSTRACT FROM AUTHOR]

The near-rapid solidification conditions during additive manufacturing can lead to selection of non-equilibrium phases. Sharp interface models via interface response functions have been used earlier to explain the microstructure selection under such solidification conditions. However, most of the sharp interface models assume linear superposition of contributions of alloying elements without considering the non-linearity associated with the phase diagram. In this report, both planar and dendritic Calphad coupled sharp interface models have been implemented and used to explain the growth-controlled phase selection observed at high solidification velocities relevant to additive manufacturing. The implemented model predicted the growth-controlled phase selection in multicomponent alloys, which the other models with linear phase diagram could not. These models are calculated for different steels and the results are compared with experimental observations. [Display omitted] • Linear and Calphad coupled sharp interface solidification models were implemented. • Calphad coupled models predicted the phase selection which linear models could not. • Incorporating the effect of solute drag improved the predictions. [ABSTRACT FROM AUTHOR]

• Acoustic cavitation and impact effects generated by the ultrasonic field promote the detachment of hydrogen bubbles from the surface of the catalytic layer. • The evolutionary stages of hydrogen bubbles include nucleation, adherent growth, detachment and even polymerization. • Energy and mechanical analyses were used to reveal the mechanism and evolution of hydrogen bubbles. • The influence of working temperature on hydrogen bubble parameters (nucleation frequency, bubble radius, growth rate, etc) was studied. To improve the hydrogen precipitation performance on the surface of the catalytic layer of the proton exchange membrane (PEM) hydrogen cathode, ultrasonic vibration was employed to accelerate the detachment of hydrogen bubbles on the surface of the catalytic layer. Based on the energy and mechanical analyses of nano and microbubbles, the hydrogen bubble generation mechanism and the effect of temperature on bubble parameters during the evolution process when the ultrasonic field is coupled with the electric field are investigated. The nucleation frequency of the hydrogen bubbles, the relationship between the pressure and temperature and the operating temperature during the generation and detachment of bubbles as well as the detachment radius of bubbles under the action of the ultrasonic field are obtained. The effects of ultrasound and temperature on hydrogen production were verified by visual experiments. The results show that the operating temperature affects the nucleation, growth, and detachment processes of hydrogen bubbles. The effect of temperature on the nucleation frequency of bubbles mainly comes from the Gibbs free energy required for the electrolysis reaction. The bubble radius and growth rate are both related to the temperature to the power of one-third. Ultrasonic waves enhance the separation of hydrogen bubbles from the catalyst surface by acoustic cavitation and impact effects. An increase in the working temperature reduces the activation energy barriers to be overcome for the electrolysis reaction of water, which together with a decrease in the Gibbs free energy and the surface tension coefficient, leads to an increase in the nucleation frequency of the catalytic layer and a decrease in the radius of bubble detachment, and thus improves the hydrogen precipitation performance. Visualization experiments show that in actual PEM hydrogen production, ultrasonic intensification can promote the formation of nucleation sites. The ultrasonic induced fine bubble flow not only has a drag effect on the bubble, but also intensifies the polymerization growth of the bubble due to the impact of the fine bubble flow, thus speeding up the detachment of the bubble, shortening the covering time of the hydrogen bubble on the surface of the catalytic electrode, reducing the activation voltage loss and improve the hydrogen production efficiency of PEM. The experimental results show that when the electrolyte is 60°C, the maximum hydrogen production efficiency of ultrasound is increased by 7.34%, and the average hydrogen production efficiency is increased by 5.83%. [ABSTRACT FROM AUTHOR]

This work innovatively proposed a micro-controlled carbon fiber (CF) energy to achieve the rapid curing of carbon fiber reinforced composites (CFRC). Compared with the traditional curing process, this process controlled the thin layer coated with CF bundles, explored the influence law of cross-linking curing of the CFRC with different power (current, voltage) and drag speed, and regulated the optimal process parameters. The results showed that the micro-controlled energy in the CF had an obvious effect on the curing of the CFRC. The curing degree first increased and then decreased with increasing power. Meanwhile, the effect of increasing drag speed on different viscous state was studied, which resulted in the different effects on the mechanical properties of the CFRC. In addition, the energy in the CF was micro-differentiated to construct the energy space, and the energy model in the curing process of the CFRC was proposed. Finally, it was proved that the CF spline curing process using this technology saved 95% time compared to traditional curing process, and it opened up a new idea for the large-scale preparation of the CFRC. [ABSTRACT FROM AUTHOR]

When flexible structures deflect under unidirectional flow or sway under oscillatory flow, their hydrodynamic drag forces are reduced. The flow-induced motion of a structure is governed by the balance between hydrodynamic forces and restoring forces due to stiffness (a ratio known as the Cauchy number, C a). Movement of and drag on structures under unidirectional (current) and oscillatory (wave) flow have often been studied separately, but such flows frequently coexist. In this study, a simple numerical model of a slender flexible plate, which can represent a seagrass blade, was used to investigate how the posture of and drag on the plate in oscillatory flow was impacted by collinear currents moving in the same (following) and opposite (opposing) directions, relative to the wave propagation. The rate of work done against hydrodynamic drag forces defines the rate of wave energy dissipation, E D , w. The velocity acting on the blade was modeled as if the blade existed in a canopy of blades. For conditions in which blade motion was observed, added currents influenced E D , w in two ways. When the ratio of the time-averaged velocity within the canopy, U 1 , to the wave velocity amplitude, U w , was less than 0.33 ± 0.05 , E D , w was reduced relative to the pure wave condition, which was attributed to current-induced deflection. However, when U 1 / U w exceeded 0.33 ± 0.05 , E D , w increased. While the blade increasingly deflected with increasing current, higher currents also limited unsteady wave-induced reconfiguration, increasing the relative motion between the blade and fluid and therefore increasing drag. While C a can predict the drag reduction associated with weak current, it cannot predict the increase in drag for U 1 / U w > 0.33. Finally, the model was used to explore the influence of current on wave amplitude evolution across a seagrass meadow. Relative to pure wave conditions, opposing currents enhanced wave damping, but following currents had little impact on wave damping. [ABSTRACT FROM AUTHOR]

The evolution of wake structures behind thin pitching panels at Reynolds number 1000 is studied numerically for a wide range of aspect ratios (0. 54 ≤ A R ≤ 16). At the maximum pitching angle (θ max) of 5 ° and 15 ° , simulations are performed for pitching frequency S t = 0. 5 , 1. The higher pitching angle and frequency promote thrust generation for all the A R. Although the propulsive power grows with AR in the thrust cases, the propulsion efficiency remains insensitive to the A R. Higher A R imparts stabilizing effect on the flow in the drag regime, though it triggers instabilities with asymmetric vortex pairing in the thrust cases. Wake topology for the drag cases reveals the emergence of horseshoe vortices and bridgelets-type vortex structures within the range of A R studied. The wake consists of entangled vortices undergoing subsequent reconnections in the thrust cases. A smaller θ max and S t induces organized 3D structures for A R ≤ 4 , although the end instabilities diffuse for increasing A R , resulting in a 2D wake signature at larger A R. The spanwise circulation data show the dominant influence of primary instability in rendering a high horizontal velocity-compressed separated region in the drag regime. [Display omitted] • The evolution of wake structures behind thin pitching panels. • The higher pitching angle and frequency promote thrust generation. • An increase in aspect ratio yields wake transition. • The thrust cases render more complex wake structures. • The wake grows from the trailing edge following a parabolic profile. [ABSTRACT FROM AUTHOR]