An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion pr...An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion process over aircraft wing surfaces.The multiphase flow simulation results of the wind-driven water runback(WDWR)flow are compared quantitatively with the experimental results in terms of the time-dependent variations of the water film thickness profiles and evolution of the front contact point of the runback water film flow.The underlying mechanism of the intermittent water runback behavior is elucidated by analyzing the time evolution of the airflow velocity and vorticity fields above the runback water film flow over the solid surface.To the best knowledge of the authors,the work presented here is the first successful attempt to numerically examine the transient runback characteristics of WDWR flows.It serves as an excellent benchmark case for the development of best practices to model the important micro-physical processes responsible for the transient water transport over aircraft wing surfaces.展开更多
Web-like obstacles,such as safety nets,represent a unique hazard for drones,and especially UAVs(Unmanned Aerial Vehicles).Fencing and netting are particularly difficult to distinguish from the background using either ...Web-like obstacles,such as safety nets,represent a unique hazard for drones,and especially UAVs(Unmanned Aerial Vehicles).Fencing and netting are particularly difficult to distinguish from the background using either computer vision,lidar and sonar.In contrast,animals such as flying insects may detect these web-like obstacles using Optic Flow(OF),and more precisely motion parallax.A netting-avoidance solution was proposed using a OF-based detection method.The netting detection method was based on a signature defined by the shape of the OF magnitude across the visual field.We established that the OF shape depends on the orientation of the netting in relation to the hexarotor’s movement.This paper demonstrates netting detection in real-world experiments,according to any direction flight made by the UAV along the net.The proposed NOWA method(which stands for Netting Optical floW-based distinction Algorithm)separates the OF signatures belonging to these different surfaces-netting or background-whatever their orientations.By extracting the OF signatures of these different surfaces and separating them,the proposed visual method can estimate their relative locations and orientations.In a robotic simulations,the multirotor explores and navigates automatically using this netting detection method,using saccades to avoid obstacles.In the simulations,these saccades are also used to simplify netting detection by orienting itself systematically parallel to these planes,a behavior reminiscent of flying insects.展开更多
The icing of areo-engine inlet components during flight can affect engine operational safety.Conventional hot-air anti-icing systems require a large amount of bleed air,which compromises engine performance.Consequentl...The icing of areo-engine inlet components during flight can affect engine operational safety.Conventional hot-air anti-icing systems require a large amount of bleed air,which compromises engine performance.Consequently,low-energy anti/de-icing methods based on superhydrophobic surfaces have attracted widespread attention.Previous studies have demonstrated that for stationary components,superhydrophobic surfaces can significantly reduce anti-icing energy consumption by altering the flow behavior of runback water.However,for rotating inlet components of aero-engines,the effectiveness of superhydrophobic surfaces and the influence of surface wettability on the evolution of runback water flow remain unclear due to the effects of centrifugal and Coriolis forces.This study establishes a 3D liquid water flow simulation model using the volume of fluid(VOF)method to investigate the effects of rotational speed,airflow velocity,and surface wettability on the runback water flow behavior over the rotating spinner under dynamic rotation conditions.The results show that the rotational effects and surface wettability mutually reinforce one another.Specifically,increasing the rotational speed and contact angle can both enhance the flow velocity of liquid water and accelerate the breakup and rupture of liquid film,leading to the formation of rivulets,droplets,and subsequent detachment from the surface.A theoretical model based on force balance is proposed to describe the evolution of runback water flow,and the analysis reveals that as the rotational speed and contact angle increase,the water film is more likely to break up to form rivulets and beads,and the critical radius for droplet detachment from the surface decreases,making it easier removal from the surface.展开更多
To investigate the influence of Al-Zn-Mg-Cu alloy with as-homogenized and as-rolled initial microstructures on the tensile flow behavior,isothermal tensile tests were conducted on a GLEEBLE-3500 isothermal simulator a...To investigate the influence of Al-Zn-Mg-Cu alloy with as-homogenized and as-rolled initial microstructures on the tensile flow behavior,isothermal tensile tests were conducted on a GLEEBLE-3500 isothermal simulator at temperatures of 380-440℃and strain rates of 0.05-1 s^(−1).The Johnson-Cook model,Hensel-Spittel model,strain-compensated Arrhenius model,and critical fracture strain model were established.Results show that through the evaluation of the models using the correlation coefficient(R)and the average absolute relative error,the strain-compensated Arrhenius model can represent the flow behavior of the alloy more accurately.Shear bands are more pronounced in the as-homogenized specimens,whereas dynamic recrystallization is predominantly observed in as-rolled specimens.Fracture morphology analysis reveals that a mixed fracture mechanism is prevalent in the as-homogenized specimen,whereas a ductile fracture mechanism is predominant in the as-rolled specimen.The processing maps indicate that the unstable region is reduced in the as-rolled specimens compared with that in the as-homogenized specimens.The optimal hot working windows for the as-homogenized and as-rolled specimens are determined as 410-440℃/0.14-1 s^(−1)and 380-400℃/0.05-0.29 s^(−1),respectively.展开更多
Vanadium redox flow batteries(VRFBs)are a means of large-scale energy storage due to their excellent scalability,safety,long cycling life,and decoupled power and energy capacities.However,the slow redox kinetics of va...Vanadium redox flow batteries(VRFBs)are a means of large-scale energy storage due to their excellent scalability,safety,long cycling life,and decoupled power and energy capacities.However,the slow redox kinetics of vanadium species on conventional carbon electrodes remains a major limitation to their performance.We investigated the deposition of carbon black,carbon nanotubes,and electrochemically exfoliated graphene(Exf-Gr)onto thermally-activated carbon paper(ACP)by spray coating to increase the electrode electrocatalytic activity.The modified electrodes were characterized using scanning electron microscopy,X-ray diffraction,Raman spectroscopy,X-ray photoelectron microscopy,and surface area analysis,while their electrochemical properties were evaluated by cyclic voltammetry,electrochemical impedance spectroscopy,and singlecell VRFB testing.Among the modified electrodes,Exf-Gr/ACP had the best performance,achieving a 2.9-fold reduction in charge transfer resistance compared to pristine ACP and delivering 2.5 times the discharge capacity in single-cell tests.This improvement is attributed to Exf-Gr’s high surface area,favorable catalytic activity,and excellent dispersion on the ACP substrate.Surface modification with electrochemically exfoliated graphene is a highly effective strategy for improving the electrode performance in VRFB systems,with significant implications for large-scale energy storage.展开更多
Investigating the wind-sand flow response regularity in the longitudinal slope sections of desert highways provides a scientific basis for selecting the slope of desert roads.This study uses the Tengger Desert section...Investigating the wind-sand flow response regularity in the longitudinal slope sections of desert highways provides a scientific basis for selecting the slope of desert roads.This study uses the Tengger Desert section of the Wuhai-Maqin Expressway as a case study,employing CFD numerical simulation methods to calculate and analyze the wind-sand flow field distribution characteristics in different longitudinal slope sections.The results show that:(1)Along with the direction of the incoming flow,the windward and leeward slope toes of the embankment are low-wind-speed zones,with the wind speed at the leeward slope toe being even lower.The higher the embankment,the larger the low-wind-speed zone at the windward and leeward slope toes.As the longitudinal slope increases,the extent of the lowwind-speed zone at the same location along the route also increases.(2)Along the route direction,the wind speed at the windward and leeward slope toes decreases as embankment height increases.At the embankment toe,sand particles are transported from the top to the bottom of the longitudinal slope,and the greater the longitudinal slope,the stronger the transport effect.(3)Along the route direction,the sand accumulation around the embankment gradually gathers toward the bottom of the longitudinal slope as the slope increases.When the longitudinal slope is 3%and 4%,the trend of sand accumulation moving from the windward side at the end of the route to the leeward side at the start of the route is more significant.When the longitudinal slope is less than or equal to 3%,severe sand accumulation within the embankment range is reduced by 86.4%or more compared to when the slope is 4%.(4)Under the same longitudinal slope,the higher the embankment height,the smaller its transport rate.When the embankment height is the same,the greater the longitudinal slope,the greater the embankment transport rate.展开更多
Particle-and droplet-laden flows are central to many problems in mechanics and transport.They occur in sedimentladen boundary layers,gas-solid and gas-liquid dispersions,and surface-water films driven by external forc...Particle-and droplet-laden flows are central to many problems in mechanics and transport.They occur in sedimentladen boundary layers,gas-solid and gas-liquid dispersions,and surface-water films driven by external forcing.They also underpin practical applications ranging from environmental transport to high-speed and aerothermal systems.Despite decades of progress,prediction remains difficult.The physics spans a wide range of scales and often couples turbulence,interphase momentum exchange,collisions,and interfacial transport.Reliable computation therefore requires both robust numerical methodology and careful physical interpretation.展开更多
To clarify fluid flow mechanisms and establish effective development conditions in continental shale oil reservoirs,a high-temperature,high-pressure steady-state flow system integrated with nuclear magnetic resonance(...To clarify fluid flow mechanisms and establish effective development conditions in continental shale oil reservoirs,a high-temperature,high-pressure steady-state flow system integrated with nuclear magnetic resonance(NMR)technology has been developed.The apparatus combines sample evacuation,rapid pressurization and saturation,and controlled displacement,enabling systematic investigation of single-phase shale oil flow under representative reservoir conditions.Related experiments allow proper quantification of the activation thresholds and relative contributions of different pore types to flow.A movable fluid index(MFI),defined using dual T_(2) cutoff values,is introduced accordingly and linked to key flow parameters.The results reveal distinct multi-scale characteristics of single-phase shale oil transport,namely micro-scale graded displacement and macro-scale segmented nonlinear behavior.As the injection-production pressure difference increases,flow pathways are activated progressively,beginning with fractures,followed by large and then smaller macropores,leading to a pronounced enhancement in apparent permeability.Although mesopores and micropores contribute little to direct flow,their indirect influence becomes increasingly important,and apparent permeability gradually approaches a stable limit at higher pressure difference.It is also shown that the MFI exhibits a strong negative correlation with the starting pressure gradient and a positive correlation with apparent permeability,providing a rapid and reliable indicator of shale oil flow capacity.Samples containing through-going fractures display consistently higher MFI values and superior flowability compared with those dominated by laminated fractures,highlighting the pivotal role of well-connected fracture networks generated by large-scale hydraulic fracturing in improving shale oil production.展开更多
Large-eddy simulation(LES)is conducted to study the statistical properties of mixed-phase turbulence induced by the breaking of bow waves in flow past a partially submerged plate.The simulation is performed using a fi...Large-eddy simulation(LES)is conducted to study the statistical properties of mixed-phase turbulence induced by the breaking of bow waves in flow past a partially submerged plate.The simulation is performed using a finite difference method,with the air-water interface captured by a coupled level-set and volume-of-fluid method.Four cases are conducted to investigate the effects of Froude number on turbulent statistics,including the mean velocity,turbulence kinetic energy,and turbulence mass flux(TMF),which is an additional unclosed term in the Reynolds-averaged momentum equation.The TMF,especially its vertical component,shows a complex behaviour with respect to the Froude number.This property of the TMF imposes high demands on the robustness of the closure model of TMF.The present LES data is further used to examine a closure model of the TMF production term,which shows a high correlation with the data obtained from LES.展开更多
The newly formulated non-Newtonian rivulet flows streaming down an inclined planar surface,with additional periodic perturbations arising from the application of the 2nd Stokes problem to the investigation of rivulet ...The newly formulated non-Newtonian rivulet flows streaming down an inclined planar surface,with additional periodic perturbations arising from the application of the 2nd Stokes problem to the investigation of rivulet dynamics,are demonstrated in the current research.Hereby,the 2nd Stokes problem assumes that the surface,with a thin shared layer of the fluid on it,oscillates in a harmonic manner along the x-axis of the rivulet flow,which coincides with the main flow direction streaming down the underlying surface.We obtain the exact extension of the rivulet flow family,clarifying the structure of the pressure field,which fully absorbs the arising perturbation.The profile of the velocity field is assumed to be Gaussian-type with a non-zero level of plasticity.Hence,the absolutely non-Newtonian case of the viscoplastic flow solution,which satisfies the motion and continuity equations,is considered(with particular cases of exact solutions for pressure).The perturbed governing equations of motion for rivulet flows then result in the Riccati-type ordinary differential equation(ODE),describing the dynamics of the coordinate x(t).The approximated schematic dynamics are presented in graphical plots.展开更多
Background There is still limited data on predictive value of coronary computed tomography angiography(CCTA)–derived fractional flow reserve(CT-FFR) for long term outcomes. We examined the long-term prognostic value ...Background There is still limited data on predictive value of coronary computed tomography angiography(CCTA)–derived fractional flow reserve(CT-FFR) for long term outcomes. We examined the long-term prognostic value of CT-FFR combined with CCTA–defined atherosclerotic extent in diabetic patients with coronary artery disease(CAD).Methods A retrospective pooled analysis of individual patient data was performed. Deep-learning-based vessel-specific CTFFR was calculated. All patients enrolled were followed-up for at least 5 years. Predictive abilities for major adverse cardiac events(MACE) were compared among three models(model 1), constructed using clinical variables;model 2, model 1+CCTA–derived atherosclerotic extent(Leiden risk score);and model 3, model 2+CT-FFR.Results A total of 480 diabetic patients [median age, 61(55–66) years;52.9% men] were included. During a median follow-up time of 2197(2126–2355) days, 55 patients(11.5%) experienced MACE. In multivariate-adjusted Cox models, Leiden risk score(HR: 1.06;95% CI: 1.01–1.11;P = 0.013) and CT-FFR ≤ 0.80(HR: 6.54;95% CI: 3.18–13.45;P < 0.001) were the independent predictors. The discriminant ability was higher in model 2 than in model 1(C-index, 0.75 vs. 0.63;P < 0.001) and was further promoted by adding CT-FFR to model 3(C-index, 0.81 vs. 0.75;P = 0.002). Net reclassification improvement(NRI) was 0.19(P = 0.009) for model 2 beyond model 1. Of note, adding CT-FFR to model 3 also exhibited significantly improved reclassification compared with model 2(NRI = 0.14;P = 0.011).Conclusion In diabetic patients with CAD, CT-FFR provides robust and incremental prognostic information for predicting longterm outcomes. The combined model exhibits improved prediction abilities, which is beneficial for risk stratification.展开更多
The Cooling-Storage-Ring External-target Experiment(CEE)at the Heavy Ion Research Facility in Lanzhou(HIRFL)is designed to study the properties of nuclear matter created in heavy-ion collisions at beam energies from a...The Cooling-Storage-Ring External-target Experiment(CEE)at the Heavy Ion Research Facility in Lanzhou(HIRFL)is designed to study the properties of nuclear matter created in heavy-ion collisions at beam energies from a few hundred MeV/u up to 1 GeV/u.It aims to facilitate research on the quantum chromodynamics(QCD)phase structure in the high-baryondensity region.Collective flow is a fundamental observable in heavy-ion collision experiments,providing information on the bulk properties of the produced matter.Although the standard event plane method has been widely used to measure collective flow,it is still important to validate and optimize this method for the CEE spectrometer.In this paper,we study the experimental procedures for measuring directed flow in^(238)U+^(238)U collisions at 500 MeV/u,using event planes reconstructed by Multi-Wire Drift Chamber and Zero Degree Calorimeter,respectively.Jet AA Microscopic(JAM)transport generator is used to generate events,and the detector response is simulated by the CEE Fast Simulation(CFS)package.Finally,the optimal kinematic region for proton directed flow measurements is discussed for the future CEE experiment.展开更多
This study investigates the enhancement of convective heat transfer in a serpentine pipe using ferrofluid flow influenced by dual non-uniform magnetic sources.The primary objective is to improve thermal performance in...This study investigates the enhancement of convective heat transfer in a serpentine pipe using ferrofluid flow influenced by dual non-uniform magnetic sources.The primary objective is to improve thermal performance in compact cooling systems,such as those used in heat exchangers.A two-dimensional,steady-state Computational Fluid Dynamic(CFD)model is developed in ANSYS Fluent to simulate the behavior of an incompressible ferrofluid under applied constant heat flux and magnetic fields.The magnetic force is modeled using the Kelvin force,which acts on magnetized nanoparticles in response to spatially varying electromagnetic fields generated by two strategically positioned current-carrying wires.The effects of magnetic field strength,quantified by the magnetic number(Mn),on flow behavior and temperature distribution are thoroughly analyzed.The results indicate that increasing Mn leads to higher Nusselt numbers,demonstrating enhanced convective heat transfer.Secondary vortices induced by magnetic forcing improve fluid mixing,particularly in curved regions of the pipe.A mesh-independence study and model validation with benchmark data support the reliability of the numerical framework.This work highlights the potential of magnetic-field-assisted thermal control in energy-efficient cooling applications and provides a foundation for the further development of advanced ferrofluid-based heat transfer systems.展开更多
Debris flow events are frequent in Tajikistan,yet comprehensive investigations at the regional scale are limited.This study integrates remote sensing,Geographic Information System,and machine learning techniques to ev...Debris flow events are frequent in Tajikistan,yet comprehensive investigations at the regional scale are limited.This study integrates remote sensing,Geographic Information System,and machine learning techniques to evaluate debris flow susceptibility and associated hazards across Tajikistan.A dataset comprising 405 documented debris flow points and 14 influencing factors,encompassing geological,climatic-hydrological,and anthropogenic variables,was established.Three machine learning algorithms—Random Forest,Support Vector Machine(SVM),and Multi-layer Perceptron—were applied to generate susceptibility maps and delineate debris flow risk zones.The results indicate that the areas of higher and high susceptibility accounted for 20.43%and 4.41%of the national area,respectively,and were predominantly concentrated along the Zeravshan and Vakhsh river basins.Among the evaluated models,SVM model demonstrated the highest predictive performance.Beyond conventional topographic and environmental controls,drought conditions were identified as a critical factor influencing debris flow occurrence within the arid and semi-arid mountainous regions of Tajikistan.These findings provide a scientific basis for regional debris flow risk management and disaster mitigation planning,and offer practical guidance for selecting conditioning factors in machine-learning-based susceptibility assessments in other dry mountainous environments.展开更多
The Reynolds-averaged Navier-Stokes(RANS)technique enables critical engineering predictions and is widely adopted.However,since this iterative computation relies on the fixed-point iteration,it may converge to unexpec...The Reynolds-averaged Navier-Stokes(RANS)technique enables critical engineering predictions and is widely adopted.However,since this iterative computation relies on the fixed-point iteration,it may converge to unexpected non-physical phase points in practice.We conduct an analysis on the phase-space characteristics and the fixed-point theory underlying the k-ε turbulence model,and employ the classical Kolmogorov flow as a framework,leveraging its direct numerical simulation(DNS)data to construct a one-dimensional(1D)system under periodic/fixed boundary conditions.The RANS results demonstrate that under periodic boundary conditions,the k-ε model exhibits only a unique trivial fixed point,with asymptotes capturing the phase portraits.The stability of this trivial fixed point is determined by a mathematically derived stability phase diagram,indicating the fact that the k-ε model will never converge to correct values under periodic conditions.In contrast,under fixed boundary conditions,the model can yield a stable non-trivial fixed point.The evolutionary mechanisms and their relationship with boundary condition settings systematically explain the inherent limitations of the k-ε model,i.e.,its deficiency in computing the flow field under periodic boundary conditions and sensitivity to boundary-value specifications under fixed boundary conditions.These conclusions are finally validated with the open-source code OpenFOAM.展开更多
We report an immobilized enzyme-catalyzed batch and continuous-flow synthesis of optically pure ethyl(R)-pantothenate((R)-PaOEt),the direct precursor of d-pantothenic acid.Firstly,a ketoreductase mutant designated as ...We report an immobilized enzyme-catalyzed batch and continuous-flow synthesis of optically pure ethyl(R)-pantothenate((R)-PaOEt),the direct precursor of d-pantothenic acid.Firstly,a ketoreductase mutant designated as M2,carrying two-point mutations of F97L and M242F relative to the wild-type SSCR,was constructed by site-directed mutagenesis,exhibited simultaneously improved activity toward ethyl 2′-ketopantothenate(K-PaOEt)and isopropanol,and could effectively catalyze the stereoselective reduction of K-PaOEt to(R)-PaOEt by using isopropanol as the sacrificial co-substrate to regenerate NADPH.After screening six commercially available carriers,an amino resin LXTE-700 was identified as the best solid support for the immobilization of M2 via the glutaraldehyde activation method.Upon optimization of the immobilization process and reaction conditions,the fabricated immobilized enzyme M2@amino resin demonstrated excellent recyclability and reusability,with the complete conversion of K-PaOEt to(R)-PaOEt being still realized after 12 cycles of reuse.Finally,M2@amino resin-catalyzed synthesis of(R)-PaOEt was successfully implemented in continuous-flow,accomplishing a 6.3 times higher space-time yield than that with the batch synthesis(529.2 versus 84 g L^(-1) d^(-1)).Our developed flow biocatalysis system also features an outstanding operational stability,as evidenced by the 100%conversion rate achieved after 15 consecutive days of operation.展开更多
The Rukwa Rift section of the East Africa Rift System presents a type setting for radiogenic helium accumulation in a petroleum free basin.As a prerequisite for accumulation,a considerable high heat flow anomaly is re...The Rukwa Rift section of the East Africa Rift System presents a type setting for radiogenic helium accumulation in a petroleum free basin.As a prerequisite for accumulation,a considerable high heat flow anomaly is required from tectonothermal events to drive the release and circulation of radiogenic helium in the continental crust.Here we apply statistical analysis on geochemical data observed in thermal springs and recorded heat flow to account for crustal helium mass balance for each tectonothermal event in the region.Our results demonstrate anomalously high heat flow~64-99 mW/m^(2) with a consistent trend of helium isotopic ratio and fluid chemistry in the Rukwa Rift.Mass balance calculation show that the whole crustal volume underlying the East Africa Helium Pool(EAHP)has a capability of producing radiogenic helium of about 9.9×10^(6) mol/yr(22×10^(-6) mol 4He/m^(2) yr)while the total radiogenic helium flux ranges between~2.39×10^(6) mol/yr and~2.68×10^(9) mol/yr.The Tanzania Craton contributes largely to radiogenic helium releasing up to 50% of the total capacity in the region.The total ^(4)He emission in the Rukwa Rift Basin is about 4.45×10^(5)-5.01×10^(8) mol/yr which is thus equivalent to 19%-21% of the total production capacity in the region.These results imply that the helium accumulation in the EAHP would have started as early as Paleoproterozoic(2.349 Ga).These results provide a qualitative and quantitative insight to assess both helium and geothermal potentiality in the region.展开更多
Vortex-induced vibration(VIV)of an underwater manipulator in pulsating flow presents a notable engineering problem in precise control due to the velocity variation in the flow.This study investigates the VIV response ...Vortex-induced vibration(VIV)of an underwater manipulator in pulsating flow presents a notable engineering problem in precise control due to the velocity variation in the flow.This study investigates the VIV response of an underwater manipulator subjected to pulsating flow,focusing on how different postures affect the behavior of the system.The effects of pulsating parameters and manipulator arrangement on the hydrodynamic coefficient,vibration response,motion trajectory,and vortex shedding behaviors were analyzed.Results indicated that the cross flow vibration displacement in pulsating flow increased by 32.14%compared to uniform flow,inducing a shift in the motion trajectory from a crescent shape to a sideward vase shape.In the absence of interference between the upper and lower arms,the lift coefficient of the manipulator substantially increased with rising pulsating frequency,reaching a maximum increment of 67.0%.This increase in the lift coefficient led to a 67.05%rise in the vibration frequency of the manipulator in the in-line direction.As the pulsating amplitude increased,the drag coefficient of the underwater manipulator rose by 36.79%,but the vibration frequency in the cross-flow direction decreased by 56.26%.Additionally,when the upper and lower arms remained in a state of mutual interference,the cross-flow vibration amplitudes of the upper and lower arms were approximately 1.84 and 4.82 times higher in a circular-elliptical arrangement compared to an elliptical-circular arrangement,respectively.Consequently,the flow field shifted from a P+S pattern to a disordered pattern,disrupting the regularity of the motion trajectory.展开更多
A debris flow descending through an erodible convex colluvial bed,originating from a landslide dam and its upstream deposits,can entrain massive amounts of sediment,dramatically increasing the debris flow volume.Most ...A debris flow descending through an erodible convex colluvial bed,originating from a landslide dam and its upstream deposits,can entrain massive amounts of sediment,dramatically increasing the debris flow volume.Most existing erosion models assume that bed sediments are fully saturated,although this condition is rarely observed in nature.Therefore,a thorough understanding of debris flow overtopping erosion on a convex unsaturated bed is crucial for quantifying disaster risk.In this study,we experimentally investigated the effects of sediment composition,specifically coarse-grain size distribution and fine particle content,on the pore pressure evolution and entrainment of debris flows overriding a convex unsaturated colluvial bed.The average entrainment rate at convex sites for continuously graded bed sediment was higher than its discontinuous counterpart.The measured pore pressures within the unsaturated bed sediments were primarily generated by the passing debris flows.Furthermore,it was found that these pressures decreased as the fine particle content increased and the coarse-grain size of the erodible substrates decreased.When the coarse-grain size of the debris flow was smaller than that of the bed sediment,only a portion of the eroded material was entrained by the moving debris flow.In contrast,when the coarse-grain size of the debris flow was equal to or greater than that of the bed sediment,nearly all of the eroded material was entrained.The findings of this study could contribute to the assessment of hazard amplification and inform the design of mitigation and prevention strategies.展开更多
In this paper,we study the asymptotic behavior of the micropolar fluid flow through a thin domain,assuming zero Dirichlet boundary condition on the top boundary,which is rapidly oscillating,and non-standard boundary c...In this paper,we study the asymptotic behavior of the micropolar fluid flow through a thin domain,assuming zero Dirichlet boundary condition on the top boundary,which is rapidly oscillating,and non-standard boundary conditions on the flat bottom.Assuming“Reynolds roughness regime”,in which the thickness of the domain is very small compared to the wavelength of the roughness(i.e.a very slight roughness),we rigorously derive a generalized Reynolds equation for pressure,clearly showing the roughness-induced effects.Moreover,we give expressions for the average velocity and microrotation.展开更多
基金supported by the National Science Foundation(NSF)of the USA(Grant Nos.TIP-2140489,CBET-2313310,and CBET-2415347).
文摘An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion process over aircraft wing surfaces.The multiphase flow simulation results of the wind-driven water runback(WDWR)flow are compared quantitatively with the experimental results in terms of the time-dependent variations of the water film thickness profiles and evolution of the front contact point of the runback water film flow.The underlying mechanism of the intermittent water runback behavior is elucidated by analyzing the time evolution of the airflow velocity and vorticity fields above the runback water film flow over the solid surface.To the best knowledge of the authors,the work presented here is the first successful attempt to numerically examine the transient runback characteristics of WDWR flows.It serves as an excellent benchmark case for the development of best practices to model the important micro-physical processes responsible for the transient water transport over aircraft wing surfaces.
基金The participation of X.D.in this research was made possible by the joint PhD grant from the Agence Innovation Défense(AID)and Aix-Marseille UniversityFinancial support for the running costs was provided via a ProxiLearn project grant(ANR-19-ASTR-0009)to F.R.+2 种基金via SpotReturn project grant(ANR-21-ASRO-0001-02)to T.R.and F.R.from the ANR(Astrid Program)X.D.and F.R.were also supported by Aix Marseille University and the CNRS(Life Science,Information Science,and Engineering and Science&technology Institutes)The facilities for the experimental tests has been mainly provided by ROBOTEX 2.0(Grants ROBOTEX ANR-10-EQPX-44-01 and TIRREX ANR-21-ESRE-0015).
文摘Web-like obstacles,such as safety nets,represent a unique hazard for drones,and especially UAVs(Unmanned Aerial Vehicles).Fencing and netting are particularly difficult to distinguish from the background using either computer vision,lidar and sonar.In contrast,animals such as flying insects may detect these web-like obstacles using Optic Flow(OF),and more precisely motion parallax.A netting-avoidance solution was proposed using a OF-based detection method.The netting detection method was based on a signature defined by the shape of the OF magnitude across the visual field.We established that the OF shape depends on the orientation of the netting in relation to the hexarotor’s movement.This paper demonstrates netting detection in real-world experiments,according to any direction flight made by the UAV along the net.The proposed NOWA method(which stands for Netting Optical floW-based distinction Algorithm)separates the OF signatures belonging to these different surfaces-netting or background-whatever their orientations.By extracting the OF signatures of these different surfaces and separating them,the proposed visual method can estimate their relative locations and orientations.In a robotic simulations,the multirotor explores and navigates automatically using this netting detection method,using saccades to avoid obstacles.In the simulations,these saccades are also used to simplify netting detection by orienting itself systematically parallel to these planes,a behavior reminiscent of flying insects.
基金supported by the National Natural Science Foundation of China(No.12172029)the open Resarch Project of Key Laboratory of Icing and Anti/De-icing of CARDC(No.IADL 20230101)。
文摘The icing of areo-engine inlet components during flight can affect engine operational safety.Conventional hot-air anti-icing systems require a large amount of bleed air,which compromises engine performance.Consequently,low-energy anti/de-icing methods based on superhydrophobic surfaces have attracted widespread attention.Previous studies have demonstrated that for stationary components,superhydrophobic surfaces can significantly reduce anti-icing energy consumption by altering the flow behavior of runback water.However,for rotating inlet components of aero-engines,the effectiveness of superhydrophobic surfaces and the influence of surface wettability on the evolution of runback water flow remain unclear due to the effects of centrifugal and Coriolis forces.This study establishes a 3D liquid water flow simulation model using the volume of fluid(VOF)method to investigate the effects of rotational speed,airflow velocity,and surface wettability on the runback water flow behavior over the rotating spinner under dynamic rotation conditions.The results show that the rotational effects and surface wettability mutually reinforce one another.Specifically,increasing the rotational speed and contact angle can both enhance the flow velocity of liquid water and accelerate the breakup and rupture of liquid film,leading to the formation of rivulets,droplets,and subsequent detachment from the surface.A theoretical model based on force balance is proposed to describe the evolution of runback water flow,and the analysis reveals that as the rotational speed and contact angle increase,the water film is more likely to break up to form rivulets and beads,and the critical radius for droplet detachment from the surface decreases,making it easier removal from the surface.
文摘To investigate the influence of Al-Zn-Mg-Cu alloy with as-homogenized and as-rolled initial microstructures on the tensile flow behavior,isothermal tensile tests were conducted on a GLEEBLE-3500 isothermal simulator at temperatures of 380-440℃and strain rates of 0.05-1 s^(−1).The Johnson-Cook model,Hensel-Spittel model,strain-compensated Arrhenius model,and critical fracture strain model were established.Results show that through the evaluation of the models using the correlation coefficient(R)and the average absolute relative error,the strain-compensated Arrhenius model can represent the flow behavior of the alloy more accurately.Shear bands are more pronounced in the as-homogenized specimens,whereas dynamic recrystallization is predominantly observed in as-rolled specimens.Fracture morphology analysis reveals that a mixed fracture mechanism is prevalent in the as-homogenized specimen,whereas a ductile fracture mechanism is predominant in the as-rolled specimen.The processing maps indicate that the unstable region is reduced in the as-rolled specimens compared with that in the as-homogenized specimens.The optimal hot working windows for the as-homogenized and as-rolled specimens are determined as 410-440℃/0.14-1 s^(−1)and 380-400℃/0.05-0.29 s^(−1),respectively.
基金supported by the University of Seoul’s 2025 Research Fund.
文摘Vanadium redox flow batteries(VRFBs)are a means of large-scale energy storage due to their excellent scalability,safety,long cycling life,and decoupled power and energy capacities.However,the slow redox kinetics of vanadium species on conventional carbon electrodes remains a major limitation to their performance.We investigated the deposition of carbon black,carbon nanotubes,and electrochemically exfoliated graphene(Exf-Gr)onto thermally-activated carbon paper(ACP)by spray coating to increase the electrode electrocatalytic activity.The modified electrodes were characterized using scanning electron microscopy,X-ray diffraction,Raman spectroscopy,X-ray photoelectron microscopy,and surface area analysis,while their electrochemical properties were evaluated by cyclic voltammetry,electrochemical impedance spectroscopy,and singlecell VRFB testing.Among the modified electrodes,Exf-Gr/ACP had the best performance,achieving a 2.9-fold reduction in charge transfer resistance compared to pristine ACP and delivering 2.5 times the discharge capacity in single-cell tests.This improvement is attributed to Exf-Gr’s high surface area,favorable catalytic activity,and excellent dispersion on the ACP substrate.Surface modification with electrochemically exfoliated graphene is a highly effective strategy for improving the electrode performance in VRFB systems,with significant implications for large-scale energy storage.
基金financially supported by Youth Science“Research on Failure Mechanism and Evaluation Method of Sand Control Measures for Railway Machinery in Sandy Area”(12302511)Ningxia Transportation Department Science and Technology Project(20200173)The Central Guidance on Local Science and Technology Development Funds(22ZY1QA005)。
文摘Investigating the wind-sand flow response regularity in the longitudinal slope sections of desert highways provides a scientific basis for selecting the slope of desert roads.This study uses the Tengger Desert section of the Wuhai-Maqin Expressway as a case study,employing CFD numerical simulation methods to calculate and analyze the wind-sand flow field distribution characteristics in different longitudinal slope sections.The results show that:(1)Along with the direction of the incoming flow,the windward and leeward slope toes of the embankment are low-wind-speed zones,with the wind speed at the leeward slope toe being even lower.The higher the embankment,the larger the low-wind-speed zone at the windward and leeward slope toes.As the longitudinal slope increases,the extent of the lowwind-speed zone at the same location along the route also increases.(2)Along the route direction,the wind speed at the windward and leeward slope toes decreases as embankment height increases.At the embankment toe,sand particles are transported from the top to the bottom of the longitudinal slope,and the greater the longitudinal slope,the stronger the transport effect.(3)Along the route direction,the sand accumulation around the embankment gradually gathers toward the bottom of the longitudinal slope as the slope increases.When the longitudinal slope is 3%and 4%,the trend of sand accumulation moving from the windward side at the end of the route to the leeward side at the start of the route is more significant.When the longitudinal slope is less than or equal to 3%,severe sand accumulation within the embankment range is reduced by 86.4%or more compared to when the slope is 4%.(4)Under the same longitudinal slope,the higher the embankment height,the smaller its transport rate.When the embankment height is the same,the greater the longitudinal slope,the greater the embankment transport rate.
文摘Particle-and droplet-laden flows are central to many problems in mechanics and transport.They occur in sedimentladen boundary layers,gas-solid and gas-liquid dispersions,and surface-water films driven by external forcing.They also underpin practical applications ranging from environmental transport to high-speed and aerothermal systems.Despite decades of progress,prediction remains difficult.The physics spans a wide range of scales and often couples turbulence,interphase momentum exchange,collisions,and interfacial transport.Reliable computation therefore requires both robust numerical methodology and careful physical interpretation.
基金supported by the National Science and Technology Major Project of China(Grant No.2024ZD 1004302)the Key Scientific and Technological Research project of SINOPEC(Grant No.P25186).
文摘To clarify fluid flow mechanisms and establish effective development conditions in continental shale oil reservoirs,a high-temperature,high-pressure steady-state flow system integrated with nuclear magnetic resonance(NMR)technology has been developed.The apparatus combines sample evacuation,rapid pressurization and saturation,and controlled displacement,enabling systematic investigation of single-phase shale oil flow under representative reservoir conditions.Related experiments allow proper quantification of the activation thresholds and relative contributions of different pore types to flow.A movable fluid index(MFI),defined using dual T_(2) cutoff values,is introduced accordingly and linked to key flow parameters.The results reveal distinct multi-scale characteristics of single-phase shale oil transport,namely micro-scale graded displacement and macro-scale segmented nonlinear behavior.As the injection-production pressure difference increases,flow pathways are activated progressively,beginning with fractures,followed by large and then smaller macropores,leading to a pronounced enhancement in apparent permeability.Although mesopores and micropores contribute little to direct flow,their indirect influence becomes increasingly important,and apparent permeability gradually approaches a stable limit at higher pressure difference.It is also shown that the MFI exhibits a strong negative correlation with the starting pressure gradient and a positive correlation with apparent permeability,providing a rapid and reliable indicator of shale oil flow capacity.Samples containing through-going fractures display consistently higher MFI values and superior flowability compared with those dominated by laminated fractures,highlighting the pivotal role of well-connected fracture networks generated by large-scale hydraulic fracturing in improving shale oil production.
基金supported by the National Natural Science Foundation of China(NSFC)Basic Science Center Program for‘Multiscale Problems in Nonlinear Mechanics’(Grant No.11988102)NSFC project(Grant No.11972038)Chinese Academy of Sciences Project for Young Scientists in Basic Research(Grant No.YSBR-087).
文摘Large-eddy simulation(LES)is conducted to study the statistical properties of mixed-phase turbulence induced by the breaking of bow waves in flow past a partially submerged plate.The simulation is performed using a finite difference method,with the air-water interface captured by a coupled level-set and volume-of-fluid method.Four cases are conducted to investigate the effects of Froude number on turbulent statistics,including the mean velocity,turbulence kinetic energy,and turbulence mass flux(TMF),which is an additional unclosed term in the Reynolds-averaged momentum equation.The TMF,especially its vertical component,shows a complex behaviour with respect to the Froude number.This property of the TMF imposes high demands on the robustness of the closure model of TMF.The present LES data is further used to examine a closure model of the TMF production term,which shows a high correlation with the data obtained from LES.
文摘The newly formulated non-Newtonian rivulet flows streaming down an inclined planar surface,with additional periodic perturbations arising from the application of the 2nd Stokes problem to the investigation of rivulet dynamics,are demonstrated in the current research.Hereby,the 2nd Stokes problem assumes that the surface,with a thin shared layer of the fluid on it,oscillates in a harmonic manner along the x-axis of the rivulet flow,which coincides with the main flow direction streaming down the underlying surface.We obtain the exact extension of the rivulet flow family,clarifying the structure of the pressure field,which fully absorbs the arising perturbation.The profile of the velocity field is assumed to be Gaussian-type with a non-zero level of plasticity.Hence,the absolutely non-Newtonian case of the viscoplastic flow solution,which satisfies the motion and continuity equations,is considered(with particular cases of exact solutions for pressure).The perturbed governing equations of motion for rivulet flows then result in the Riccati-type ordinary differential equation(ODE),describing the dynamics of the coordinate x(t).The approximated schematic dynamics are presented in graphical plots.
文摘Background There is still limited data on predictive value of coronary computed tomography angiography(CCTA)–derived fractional flow reserve(CT-FFR) for long term outcomes. We examined the long-term prognostic value of CT-FFR combined with CCTA–defined atherosclerotic extent in diabetic patients with coronary artery disease(CAD).Methods A retrospective pooled analysis of individual patient data was performed. Deep-learning-based vessel-specific CTFFR was calculated. All patients enrolled were followed-up for at least 5 years. Predictive abilities for major adverse cardiac events(MACE) were compared among three models(model 1), constructed using clinical variables;model 2, model 1+CCTA–derived atherosclerotic extent(Leiden risk score);and model 3, model 2+CT-FFR.Results A total of 480 diabetic patients [median age, 61(55–66) years;52.9% men] were included. During a median follow-up time of 2197(2126–2355) days, 55 patients(11.5%) experienced MACE. In multivariate-adjusted Cox models, Leiden risk score(HR: 1.06;95% CI: 1.01–1.11;P = 0.013) and CT-FFR ≤ 0.80(HR: 6.54;95% CI: 3.18–13.45;P < 0.001) were the independent predictors. The discriminant ability was higher in model 2 than in model 1(C-index, 0.75 vs. 0.63;P < 0.001) and was further promoted by adding CT-FFR to model 3(C-index, 0.81 vs. 0.75;P = 0.002). Net reclassification improvement(NRI) was 0.19(P = 0.009) for model 2 beyond model 1. Of note, adding CT-FFR to model 3 also exhibited significantly improved reclassification compared with model 2(NRI = 0.14;P = 0.011).Conclusion In diabetic patients with CAD, CT-FFR provides robust and incremental prognostic information for predicting longterm outcomes. The combined model exhibits improved prediction abilities, which is beneficial for risk stratification.
基金supported in part by the National Key R&D Program of China(No.2024YFA1610700)the National Natural Science Foundation of China(No.12475147)。
文摘The Cooling-Storage-Ring External-target Experiment(CEE)at the Heavy Ion Research Facility in Lanzhou(HIRFL)is designed to study the properties of nuclear matter created in heavy-ion collisions at beam energies from a few hundred MeV/u up to 1 GeV/u.It aims to facilitate research on the quantum chromodynamics(QCD)phase structure in the high-baryondensity region.Collective flow is a fundamental observable in heavy-ion collision experiments,providing information on the bulk properties of the produced matter.Although the standard event plane method has been widely used to measure collective flow,it is still important to validate and optimize this method for the CEE spectrometer.In this paper,we study the experimental procedures for measuring directed flow in^(238)U+^(238)U collisions at 500 MeV/u,using event planes reconstructed by Multi-Wire Drift Chamber and Zero Degree Calorimeter,respectively.Jet AA Microscopic(JAM)transport generator is used to generate events,and the detector response is simulated by the CEE Fast Simulation(CFS)package.Finally,the optimal kinematic region for proton directed flow measurements is discussed for the future CEE experiment.
文摘This study investigates the enhancement of convective heat transfer in a serpentine pipe using ferrofluid flow influenced by dual non-uniform magnetic sources.The primary objective is to improve thermal performance in compact cooling systems,such as those used in heat exchangers.A two-dimensional,steady-state Computational Fluid Dynamic(CFD)model is developed in ANSYS Fluent to simulate the behavior of an incompressible ferrofluid under applied constant heat flux and magnetic fields.The magnetic force is modeled using the Kelvin force,which acts on magnetized nanoparticles in response to spatially varying electromagnetic fields generated by two strategically positioned current-carrying wires.The effects of magnetic field strength,quantified by the magnetic number(Mn),on flow behavior and temperature distribution are thoroughly analyzed.The results indicate that increasing Mn leads to higher Nusselt numbers,demonstrating enhanced convective heat transfer.Secondary vortices induced by magnetic forcing improve fluid mixing,particularly in curved regions of the pipe.A mesh-independence study and model validation with benchmark data support the reliability of the numerical framework.This work highlights the potential of magnetic-field-assisted thermal control in energy-efficient cooling applications and provides a foundation for the further development of advanced ferrofluid-based heat transfer systems.
基金supported by the National Natural Science Foundation of China(42361144880)the Science and Technology Program of Xizang Autonomous Region,China(XZ202402ZD0001)the Qinghai Province Basic Research Program Project,China(2024-ZJ-904).
文摘Debris flow events are frequent in Tajikistan,yet comprehensive investigations at the regional scale are limited.This study integrates remote sensing,Geographic Information System,and machine learning techniques to evaluate debris flow susceptibility and associated hazards across Tajikistan.A dataset comprising 405 documented debris flow points and 14 influencing factors,encompassing geological,climatic-hydrological,and anthropogenic variables,was established.Three machine learning algorithms—Random Forest,Support Vector Machine(SVM),and Multi-layer Perceptron—were applied to generate susceptibility maps and delineate debris flow risk zones.The results indicate that the areas of higher and high susceptibility accounted for 20.43%and 4.41%of the national area,respectively,and were predominantly concentrated along the Zeravshan and Vakhsh river basins.Among the evaluated models,SVM model demonstrated the highest predictive performance.Beyond conventional topographic and environmental controls,drought conditions were identified as a critical factor influencing debris flow occurrence within the arid and semi-arid mountainous regions of Tajikistan.These findings provide a scientific basis for regional debris flow risk management and disaster mitigation planning,and offer practical guidance for selecting conditioning factors in machine-learning-based susceptibility assessments in other dry mountainous environments.
基金Project supported by the National Natural Science Foundation of China(Nos.12372214 and U2341231)。
文摘The Reynolds-averaged Navier-Stokes(RANS)technique enables critical engineering predictions and is widely adopted.However,since this iterative computation relies on the fixed-point iteration,it may converge to unexpected non-physical phase points in practice.We conduct an analysis on the phase-space characteristics and the fixed-point theory underlying the k-ε turbulence model,and employ the classical Kolmogorov flow as a framework,leveraging its direct numerical simulation(DNS)data to construct a one-dimensional(1D)system under periodic/fixed boundary conditions.The RANS results demonstrate that under periodic boundary conditions,the k-ε model exhibits only a unique trivial fixed point,with asymptotes capturing the phase portraits.The stability of this trivial fixed point is determined by a mathematically derived stability phase diagram,indicating the fact that the k-ε model will never converge to correct values under periodic conditions.In contrast,under fixed boundary conditions,the model can yield a stable non-trivial fixed point.The evolutionary mechanisms and their relationship with boundary condition settings systematically explain the inherent limitations of the k-ε model,i.e.,its deficiency in computing the flow field under periodic boundary conditions and sensitivity to boundary-value specifications under fixed boundary conditions.These conclusions are finally validated with the open-source code OpenFOAM.
基金the Science and Technology R&D Major Project of Jiangxi Province(No.20244AFI92001)the National Natural Science Foundation of China(Nos.22071033 and 21801047)for the financial supports.
文摘We report an immobilized enzyme-catalyzed batch and continuous-flow synthesis of optically pure ethyl(R)-pantothenate((R)-PaOEt),the direct precursor of d-pantothenic acid.Firstly,a ketoreductase mutant designated as M2,carrying two-point mutations of F97L and M242F relative to the wild-type SSCR,was constructed by site-directed mutagenesis,exhibited simultaneously improved activity toward ethyl 2′-ketopantothenate(K-PaOEt)and isopropanol,and could effectively catalyze the stereoselective reduction of K-PaOEt to(R)-PaOEt by using isopropanol as the sacrificial co-substrate to regenerate NADPH.After screening six commercially available carriers,an amino resin LXTE-700 was identified as the best solid support for the immobilization of M2 via the glutaraldehyde activation method.Upon optimization of the immobilization process and reaction conditions,the fabricated immobilized enzyme M2@amino resin demonstrated excellent recyclability and reusability,with the complete conversion of K-PaOEt to(R)-PaOEt being still realized after 12 cycles of reuse.Finally,M2@amino resin-catalyzed synthesis of(R)-PaOEt was successfully implemented in continuous-flow,accomplishing a 6.3 times higher space-time yield than that with the batch synthesis(529.2 versus 84 g L^(-1) d^(-1)).Our developed flow biocatalysis system also features an outstanding operational stability,as evidenced by the 100%conversion rate achieved after 15 consecutive days of operation.
基金funded by United Kingdom Commonwealth Scholarship Commission。
文摘The Rukwa Rift section of the East Africa Rift System presents a type setting for radiogenic helium accumulation in a petroleum free basin.As a prerequisite for accumulation,a considerable high heat flow anomaly is required from tectonothermal events to drive the release and circulation of radiogenic helium in the continental crust.Here we apply statistical analysis on geochemical data observed in thermal springs and recorded heat flow to account for crustal helium mass balance for each tectonothermal event in the region.Our results demonstrate anomalously high heat flow~64-99 mW/m^(2) with a consistent trend of helium isotopic ratio and fluid chemistry in the Rukwa Rift.Mass balance calculation show that the whole crustal volume underlying the East Africa Helium Pool(EAHP)has a capability of producing radiogenic helium of about 9.9×10^(6) mol/yr(22×10^(-6) mol 4He/m^(2) yr)while the total radiogenic helium flux ranges between~2.39×10^(6) mol/yr and~2.68×10^(9) mol/yr.The Tanzania Craton contributes largely to radiogenic helium releasing up to 50% of the total capacity in the region.The total ^(4)He emission in the Rukwa Rift Basin is about 4.45×10^(5)-5.01×10^(8) mol/yr which is thus equivalent to 19%-21% of the total production capacity in the region.These results imply that the helium accumulation in the EAHP would have started as early as Paleoproterozoic(2.349 Ga).These results provide a qualitative and quantitative insight to assess both helium and geothermal potentiality in the region.
基金Supported by the National Natural Science Foundation of China(No.51905211)A Project of the“20 Regulations for New Universities”Funding Program of Jinan(No.202228116).
文摘Vortex-induced vibration(VIV)of an underwater manipulator in pulsating flow presents a notable engineering problem in precise control due to the velocity variation in the flow.This study investigates the VIV response of an underwater manipulator subjected to pulsating flow,focusing on how different postures affect the behavior of the system.The effects of pulsating parameters and manipulator arrangement on the hydrodynamic coefficient,vibration response,motion trajectory,and vortex shedding behaviors were analyzed.Results indicated that the cross flow vibration displacement in pulsating flow increased by 32.14%compared to uniform flow,inducing a shift in the motion trajectory from a crescent shape to a sideward vase shape.In the absence of interference between the upper and lower arms,the lift coefficient of the manipulator substantially increased with rising pulsating frequency,reaching a maximum increment of 67.0%.This increase in the lift coefficient led to a 67.05%rise in the vibration frequency of the manipulator in the in-line direction.As the pulsating amplitude increased,the drag coefficient of the underwater manipulator rose by 36.79%,but the vibration frequency in the cross-flow direction decreased by 56.26%.Additionally,when the upper and lower arms remained in a state of mutual interference,the cross-flow vibration amplitudes of the upper and lower arms were approximately 1.84 and 4.82 times higher in a circular-elliptical arrangement compared to an elliptical-circular arrangement,respectively.Consequently,the flow field shifted from a P+S pattern to a disordered pattern,disrupting the regularity of the motion trajectory.
基金supported by the National Key R&D Program of China(Grant No.2018YFC1505205)the Science and Technology Research Program of the Institute of Mountain Hazards and Environment,Chinese Academy of Sciences(Grant No.IMHE-ZDRW-01)Sichuan Science and Technology Program(Grant No.2024NSFSC0781).
文摘A debris flow descending through an erodible convex colluvial bed,originating from a landslide dam and its upstream deposits,can entrain massive amounts of sediment,dramatically increasing the debris flow volume.Most existing erosion models assume that bed sediments are fully saturated,although this condition is rarely observed in nature.Therefore,a thorough understanding of debris flow overtopping erosion on a convex unsaturated bed is crucial for quantifying disaster risk.In this study,we experimentally investigated the effects of sediment composition,specifically coarse-grain size distribution and fine particle content,on the pore pressure evolution and entrainment of debris flows overriding a convex unsaturated colluvial bed.The average entrainment rate at convex sites for continuously graded bed sediment was higher than its discontinuous counterpart.The measured pore pressures within the unsaturated bed sediments were primarily generated by the passing debris flows.Furthermore,it was found that these pressures decreased as the fine particle content increased and the coarse-grain size of the erodible substrates decreased.When the coarse-grain size of the debris flow was smaller than that of the bed sediment,only a portion of the eroded material was entrained by the moving debris flow.In contrast,when the coarse-grain size of the debris flow was equal to or greater than that of the bed sediment,nearly all of the eroded material was entrained.The findings of this study could contribute to the assessment of hazard amplification and inform the design of mitigation and prevention strategies.
文摘In this paper,we study the asymptotic behavior of the micropolar fluid flow through a thin domain,assuming zero Dirichlet boundary condition on the top boundary,which is rapidly oscillating,and non-standard boundary conditions on the flat bottom.Assuming“Reynolds roughness regime”,in which the thickness of the domain is very small compared to the wavelength of the roughness(i.e.a very slight roughness),we rigorously derive a generalized Reynolds equation for pressure,clearly showing the roughness-induced effects.Moreover,we give expressions for the average velocity and microrotation.
