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Journal of Materials Science & Technology 2022年第24期119卷 11-24页

作者： W.L.Wang W.q.Liu X.yang R.R.Xu q.y.dai School of Metallurgical Engineering Xi’an University of Architecture and TechnologyXi’an 710055China

A model of coupling macro finite volume method(FVM) and cellular automata(CA) is proposed in this paper to explore the columnar-to-equiaxed transition(CET) during selective laser melting(SLM) of rare earth magnesium *** into account the impact of recoil pressure and Marangoni convection on the molten pool temperature field,the grain structure is *** suggested by the simulation results,with the undissolved Zr serving as heterogeneous nucleation sites,the liquid undercooled layer under the combined action of forced cooling,the temperature gradient and the liquid solute concentration gradient leads to *** considering the dissolution of Zr in magnesium matrix,the results demonstrate that the dissolution of element Zr is effective in significantly inhibiting the growth of columnar crystals and ensuring the sufficient constitutional supercooling(CS) required for *** addition,to raise the preheating temperature contributes to enhancing the outcome of nucleation and incresing the grain *** the interdependence model(IM),with the cooling rate gradually increasing in the SLM process of magnesium alloy,the nucleation-free zone(NFZ) reduces by decreasing the solute diffusion layer in the front of the solid/liquid(SL) interface and the temperature *** reduction in temperature gradient can promote undercooling for nucleation and facilitate the development of equiaxed *** simulation results are qualitatively verified as highly consistent through experimentation.

关键词： Multi-scale simulation Columnar-to-equiaxed transition Selective laser melting Rare earth magnesium alloy Constitutional supercooling

Generation of unsteady waves by concentrated disturbances in an inviscid fluid with an inertial surface

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Acta Mechanica Sinica 2008年第3期24卷 267-275页

作者： D.q.Lu S.q.dai Shanghai Institute of Applied Mathematics and Mechanics Shanghai University200072 ShanghaiChina Shanghai Key Laboratory of Mechanics in Energy and Environment Engineering 200072 ShanghaiChina

The surface waves generated by unsteady concentrated disturbances in an initially quiescent fluid of infinite depth with an inertial surface are analytically investigated for two- and three-dimensional cases. The fluid is assumed to be inviscid, incompressible and homogenous. The inertial surface represents the effect of a thin uniform distribution of non-interacting floating matter. Four types of unsteady concentrated disturbances and two kinds of initial values are considered, namely an instantaneous/oscillating mass source immersed in the fluid, an instantaneous/oscillating impulse on the surface, an initial impulse on the surface of the fluid, and an initial displacement of the surface. The linearized initial-boundary-value problem is formulated within the framework of potential flow. The solutions in integral form for the surface elevation are obtained by means of a joint Laplace-Fourier transform. The asymptotic representations of the wave motion for large time with a fixed distance- to-time ratio are derived by using the method of stationary phase. The effect of the presence of an inertial surface on the wave motion is analyzed. It is found that the wavelengths of the transient dispersive waves increase while those of the steady-state progressive waves decrease. All the wave amplitudes decrease in comparison with those of conventional free-surface waves. The explicit expressions for the freesurface gravity waves can readily be recovered by the present results as the inertial surface disappears.

关键词： Waves Inertial surface Concentrated disturbances Asymptotic representation

Rational design of AgGaS/ZnS/ZnS quantum dots with a near-unity photoluminescence quantum yield via double shelling scheme

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Journal of Materials Science & Technology 2024年第2期169卷 235-242页

作者： H.X.Lu H.Liu Z.Z.Fu y.y.Chen H.q.dai Z.Hu W.L.Zhang R.q.Guo Institute for Electric Light Sources School of Information Science and TechnologyFudan UniversityShanghai 200433China Institute of Future Lighting Academy for Engineering and TechnologyFudan UniversityShanghai 200433China yiwu Research Institute of Fudan University YiwuZhejiang 322000China Zhongshan-Fudan Joint Innovation Center Zhongshan 528437China

In this study,a two-step method was used to synthesize highly luminescent AgGaS/ZnS/ZnS quantum dots(qDs).In the first step,an inner ZnS shell was formed via a one-pot method,which resulted in a smaller lattice mismatch between the AgGaS core and the outer ZnS shell,thereby facilitating the formation of a thick outer *** the two-step shelling process,the synthesized AgGaS/ZnS/ZnS qDs showed an excellent photoluminescence quantum yield(PLqy)of 96.4%with a peak wavelength of 508 nm,repre-senting the highest PLqy reported thus far for AgGaS ***,the effect of halogen ions in Zn precursors on the shelling process was *** was proposed that the capacity of halogen ions to coordinate with the qDs influenced the balance between Zn cation diffusion and ZnS shelling ***,the ZnS shelling reaction was dominant when ZnCl_(2)was employed,while Zn cation diffusion was the dominant process under the I^(−)-rich *** work provides insights into the interfacial restructuring during the ZnS shelling and offers a clear map for the tailored synthesis of core/shell qDs.

关键词： AgGaS quantum dots Photoluminescence Core/shell Alloyed core/shell interface

Numerical Simulation of Electroosmotic Flow near Earthworm Surface

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Journal of Bionic Engineering 2006年第4期3卷 179-186页

作者： y.q. Zu y.y. yan School of the Built Environment The University of Nottingham Nottingham NG7 2RD UK

The electroosmotic flow near an earthworm surface is simulated numerically to further understand the anti soil adhesion mechanism of earthworm. A lattice Poisson method is employed to solve electric potential and charge .distributiorts in the electric double layer along the earthworm surface. The external electric field is obtained by solving a Laplace equation. The electroosmotic flow controlled by the Navier-Stokes equations with external body force is simulated by the lattice Boltzmann method. A benchmark test shows that accurate electric potential distributions can be obtained by the LPM. The simulation shows that the moving vortices, which probably contribute to anti soil adhesion, are formed near earthworm body surface by the nonuniform and variational electrical force.

关键词： electroosmotic flow earthworm anti-adhesion LBM EDL

An analysis of the chaotic motion of particles of different sizes in a gas fluidized bed

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Particuology 2008年第6期6卷 549-556页

作者： y.q. Feng A.B. yu Lab for Simulation and Modelling of Particulate Systems School of Materials Science and Engineering University of New South Wales Sydney NSW 2052 Australia

The dynamic behavior of individual particles during the mixing/segregation process of particle mixtures in a gas fluidized bed is analyzed. The analysis is based on the results generated from discrete particle simulation, with the focus on the trajectory of and forces acting on individual particles. Typical particles are selected representing three kinds of particle motion： a flotsam particle which is initially at the bottom part of the bed and finally fluidized at the top part of the bed; a jetsam particle which is initially at the top part of the bed and finally stays in the bottom de-fluidized layer of the bed; and a jetsam particle which is intermittently joining the top fluidized and bottom de-fluidized layers. The results show that the motion of a particle is chaotic at macroscopic or global scale, but can be well explained at a microscopic scale in terms of its interaction forces and contact conditions with other particles, particle-fluid interaction force, and local flow structure. They also highlight the need for establishing a suitable method to link the information generated and modeled at different time and length scales.

关键词： Fluidization Segregation Discrete particle simulation Granular dynamics

Risk management for sulfur dioxide abatement under multiple uncertainties

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Frontiers of Earth Science 2016年第1期10卷 87-107页

作者： C. dai W. SUN q. TAN y. LIU W.T. LU H.C. GUO College of Environmental Science and Engineering Peking University Beijing 100871 China Institute for Energy Environment and Sustainable Communities University of Reginal Regina Saskatchewan S4S 7H9 Canada College of Water Resources & Civil Engineering China Agricultural University Beijing 100083 China

In this study, interval-parameter programming, two-stage stochastic progranaming （TSP）, and conditional value-at-risk （CVaR） were incorporated into a general optimization framework, leading to an interval-parameter CVaR-based two-stage programming （ICTP） method. The ICTP method had several advantages：（i） its objective function simultaneously took expected cost and risk cost into consideration, and also used discrete random variables and discrete intervals to reflect uncertain properties; （ii） it quantitatively evaluated the right tail of distributions of random variables which could better calculate the risk of violated environmental standards; （iii） it was useful for helping decision makers to analyze the trade-offs between cost and risk; and （iv） it was effective to penalize the second-stage costs, as well as to capture the notion of risk in stochastic programming. The developed model was applied to sulfur dioxide abatement in an air quality management system. The results indicated that the ICTP method could be used for generating a series of air quality management schemes under different risk-aversion levels, for identifying desired air quality management strategies for decision makers, and for considering a proper balance between system economy and environmental quality.

关键词： risk management conditional value-at-risk,interval optimization two-stage programming uncertainty,air quality management

Tuning the microstructure for superb corrosion resistance in eutectic high entropy alloy

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Journal of Materials Science & Technology 2022年第14期109卷 197-208页

作者： S.Shuang q.yua X.Gao q.F.He J.y.Zhang S.q.Shi y.yang Department of Mechanical Engineering City University of Hong KongKowloon TongKowloonHong KongChina Department of Mechanical Engineering Hong Kong Polytechnic UniversityHung HomKowloonHong KongChina Department of Materials Science and Engineering City University of Hong KongKowloon TongKowloonHong KongChina

In this work,we demonstrate that the corrosion resistance of the FeCrNiCoNb_(0.5) eutectic high entropy alloy(EHEA)can be tuned by controlling the size of its eutectic *** microstructure refinement,the EHEA exhibits a superb corrosion resistance in 1 M NaCl in terms of a very low corrosion current density and an ultra-high transpassviation potential,which outperforms a variety of other HEAs and conventional metals and *** the fundamental level,the microstructure refinement results in a rapid formation of a thick and compact passive film with less Cl-adsorption on the EHEA,which results in significant enhancement in its corrosion *** outcome of our research provides important insights into the design of corrosion resistant chemically complex alloys.

关键词： Eutectic high entropy alloy Passivation Transpassivation potential Microstructure size

Strain Growth in Containment Vessels

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Transactions of Tianjin University 2006年第B9期12卷 193-198页

作者： DONG q LI q M ZHENG J y School of Mechanical Aerospace and Civil Engineering The University of Manchester PO Box 88 Manchester M60 1QD UK Institute of Chemical Machinery Zhejiang University Hangzhou 310027 China

Strain growth is a phenomenon observed in containment vessels subjected to internal blast loading. The elastic response of the vessel may become larger in a later stage compared to its response during the initial stage. The dynamic responses of infinitely long cylindrical containment vessels subjected to uniformly-distributed internal blast loading are studied using LS-DyNA. The development of bending modes and the interaction between the breathing mode and bending modes are observed. The methodology developed for dynamic elastic buckling analysis is employed to study the strain growth phenomenon in explosion containment vessels. It is shown that the dynamic instable vibration of a containment vessel is the basic mechanism of strain growth.

关键词： strain growth containment vessel dynamic response impulsive loading

Crack Initiation Mechanism of Z3CN20.09M Duplex Stainless Steel during Corrosion Fatigue in Water and Air at 290 °C

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Journal of Materials Science & Technology 2015年第11期31卷 1144-1150页

作者： H.C.Wu B.yang y.Z.Shi q.Gao y.q.Wang State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Collaborative Innovation Center of Universal Iron & Steel Technology School of Materials Science and Engineering Anhui University of Technology

The crack initiation mechanism of a Z3CN20.09M duplex stainless steel （DSS） during corrosion fatigue （CF） in water and air at 290 ℃ was investigated by using a CF cracking machine and a scanning electron microscopy （SEM）. The cracks were initiated successively at the persistent stip bands （PSBs）, phase boundaries （PBs） and pitting corrosion points （PCPs） of the specimens when they were tested in water at 290 ℃, while in airat 290 ℃ the cracks were only initiated at the PSBs and PBs. And the cracks were found mainly to initiate at the PSBs and PBs when the specimens were tested in water and air at 290 ℃, respectively. The results also reveal that the cracks were likely to be initiated at the first 20% of fatigue life of the specimens tested in water at 290 ℃. However, the cracks were not found until 50% of fatigue life when tested in air at 290 ℃. Moreover, the crack numbers of the specimens tested in water at 290 ℃ were much more than those tested in air at 290 ℃.

关键词： Duplex stainless steel Corrosion fatigue Crack initiation High temperature water

One-dimensional non-Darcy flow in a semi-infinite porous media:a multiphase implicit Stefan problem with phases divided by hydraulic gradients

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Acta Mechanica Sinica 2017年第5期33卷 855-867页

作者： G.q.Zhou y.Zhou X.y.Shi State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and Technology School of Mechanics and Civil Engineering China University of Mining and Technology JiangSu Collaborative Innovation Center for Building Energy Saving and Construct Technology

One-dimensional non-Darcy flow in a semi-infinite porous media is investigated. We indicate that the non-Darcy relation which is usually determined from experimental results can always be described by a piecewise linear function, and the problem can be equivalently transformed to a multiphase implicit Stefan problem. The novel feature of this Stefan problem is that the phases of the porous media are divided by hydraulic gradients, not the excess pore water pressures. Using the similarity transformation technique, an exact solution for the situation that the external load increases in proportion to the square root of time is developed. The study on the existence and uniqueness of the solution leads to the requirement of a group of inequalities. A similar Stefan problem considering constant surface seepage velocity is also investigated, and the solution, which we indicate to be uniquely existent under all conditions, is established. Meanwhile, the relation between our Stefan problem and the traditional multiphase Stefan problem is demonstrated. In the end, computational examples of the solution are presented and discussed. The solution provides a useful benchmark for verifying the accuracy of general approximate algorithms of Stefan problems, and it is also attractive in the context of inverse problem analysis.

关键词： Moving boundary problem Stefan problem Analytical solution Non-Darcy flow Soil consolidation