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Exploration of the coupled lattice Boltzmann model based on a multiphase field model:A study of the solid-liquid-gas interaction mechanism in the solidification process

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Chinese Physics B 2024年第3期33卷 638-648页

作者：朱昶胜王利军高梓豪刘硕李广召 College of Computer and Communication Lanzhou University of TechnologyLanzhou 730050China State Key Laboratory of Gansu Advanced Processing and Recycling of Non-Ferrous Metal Lanzhou University of TechnologyLanzhou 730050China Institute of Modern Physics Chinese Academy of SciencesLanzhou 730000China

A multiphase field model coupled with a lattice Boltzmann(PF-LBM)model is proposed to simulate the distribution mechanism of bubbles and solutes at the solid-liquid interface,the interaction between dendrites and bubbles,and the effects of different temperatures,anisotropic strengths and tilting angles on the solidified organization of the SCN-0.24wt.%butanedinitrile alloy during the solidification *** model adopts a multiphase field model to simulate the growth of dendrites,calculates the growth motions of dendrites based on the interfacial solute equilibrium;and adopts a lattice Boltzmann model(LBM)based on the Shan-Chen multiphase flow to simulate the growth and motions of bubbles in the liquid phase,which includes the interaction between solid-liquid-gas *** simulation results show that during the directional growth of columnar dendrites,bubbles first precipitate out slowly at the very bottom of the dendrites,and then rise up due to the different solid-liquid densities and pressure *** bubbles will interact with the dendrite in the process of flow migration,such as extrusion,overflow,fusion and *** the case of wide gaps in the dendrite channels,bubbles will fuse to form larger irregular bubbles,and in the case of dense channels,bubbles will deform due to the extrusion of *** the simulated region,as the dendrites converge and diverge,the bubbles precipitate out of the dendrites by compression and diffusion,which also causes physical phenomena such as fusion and spillage of the *** results reveal the physical mechanisms of bubble nucleation,growth and kinematic evolution during solidification and interaction with dendrite growth.

关键词： multiphase field model lattice Boltzmann model(LBM) Shan-Chen multiphase flow solidification organization

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A Distributed Cooperative Dynamic Task Planning Algorithm for Multiple Satellites Based on Multi-agent Hybrid Learning

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Chinese Journal of Aeronautics 2011年第4期24卷 493-505页

作者： wang Chong li jun JING Ning wang jun CHEN Hao College of Electronic Science and Engineering National University of Defense Technology Changsha 410073 China

Traditionally, heuristic re-planning algorithms are used to tackle the problem of dynamic task planning for multiple satellites. However, the traditional heuristic strategies depend on the concrete tasks, which often affect the result’s optimality. Noticing that the historical information of cooperative task planning will impact the latter planning results, we propose a hybrid learning algorithm for dynamic multi-satellite task planning, which is based on the multi-agent reinforcement learning of policy iteration and the transfer learning. The reinforcement learning strategy of each satellite is described with neural networks. The policy neural network individuals with the best topological structure and weights are found by applying co-evolutionary search iteratively. To avoid the failure of the historical learning caused by the randomly occurring observation requests, a novel approach is proposed to balance the quality and efficiency of the task planning, which converts the historical learning strategy to the current initial learning strategy by applying the transfer learning algorithm. The simulations and analysis show the feasibility and adaptability of the proposed approach especially for the situation with randomly occurring observation requests.

关键词： multiple satellites dynamic task planning problem multi-agent systems reinforcement learning neuroevolution of augmenting topologies transfer learning

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Microstructural characterization of titanium matrix composite coatings reinforced by in situ synthesized TiB + TiC fabricated on Ti6Al4V by laser cladding

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Rare Metals 2010年第5期29卷 465-472页

作者： li jun YU Zhishui wang Huiping li Manping School of Materials Engineering Shanghai University of Engineering Science Shanghai 201620 China

Titanium-based composite coatings reinforced by in situ synthesized TiB and TiC particles between titanium and B4C were successfully fabricated on Ti6Al4V by laser cladding. Phase constituents of the coatings were predicted by thermodynamic calculations in the Ti-BnC-Al and Ti-B-C-Al systems, respectively, and were validated well by X-ray diffraction （XRD） analysis results. Microstructural and metallographic analyses were made by scanning electron microscopy （SEM） and electron probe micro-analysis （EPMA）. The results show that the coatings are mainly composed of α-Ti cellular dendrites and the eutecticum in which a large number of needle-shaped TiB and a few equiaxial TiC particles are embedded. C is enriched in α-Ti cellular dendrites and far exceeds the theoretical maximum dissolubility, owing to the extension of saturation during laser cladding. The coatings have a good metallurgical bond with the substrate due to the existence of the dilution zone, in which a great amount of lamella β-Ti grains consisting of a thin needle-shaped martensitic microstructure are present and grow parallel to the heat flux direction; a few TiB and TiC reinforcements are observed at the boundaries of initial β-Ti grains.

关键词： composite coatings laser cladding in situ synthesis microstructure thermodynamic calculation

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NUMERICAL INVESTIGATION OF PERFORMANCE OF AN AXIAL-FLOW PUMP WITH INDUCER

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Journal of Hydrodynamics 2007年第6期19卷 705-711页

作者： li Yao-jun wang Fu-jun College of Water Conservancy and Civil Engineering China Agricultural University Beijing 100083 China

The interaction of flow through the inducer and impeller of an axial-flow pump equipped with an inducer has significant effect on its performance. This article presents a recent numerical investigation on this topic. The studied pump has an inducer with 3 blades mounted on a conical hub and a 6-blade impeller. The blade angle of the impeller is adjustable to generate different relative circumferential angles between the inducer blade trailing edge and the impeller blade leading edge. A computational fluid dynamics code was used to investigate the flow characteristics and performance of the axial-flow pump. For turbulence closure, the RNG k-ε model was applied with an unstructured grid system. The rotor-stator interaction was treated with a Multiple Reference Frame （MRF） strategy. Computations were performed in different cases： 7 different relative circumferential angles （ Δθ ） between the inducer blade trailing edge and the impeller blade leading edge, and 3 different axial gaps （G） between the inducer and the impeller. The variation of the hydraulic loss in the rotator was obtained by changing Δθ . The numerical results show that the pressure generated is minimum in the case of （ G = 3%D）, which indicates that the interference between inducer and impeller is strong if the axial gap is small. The pump performances were predicted and compared to the experimental measurements. Recommendations for future modifications and improvements to the pump design were also given.

关键词： axial-flow pump inducer CFD numerical simulation of flow

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Multi-wavelength study of two possible cloud-cloud collision regions: IRAS 02459+6029 and IRAS 22528+5936

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Research in Astronomy and Astrophysics 2012年第9期12卷 1269-1279页

作者： Nan li jun-Jie wang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China linan @ bao. ac. cn

Based on observations of 12CO (J=2–1), we select targets from archived Infrared Astronomical Satellite (IRAS) data of IRAS 02459+6029 and IRAS 22528+5936 as samples of cloud-cloud collision, according to the criteria given by Vallee. Then we use the Midcourse Space Experiment (MSX) A band (8.28 μm) images and the NRAO VLA Sky Survey (NVSS) (1.4 GHz) continuum images to investigate the association between molecular clouds traced by the CO contour maps. The distribution of dust and ionized hydrogen shows an obvious association with the CO contour maps toward IRAS 02459+6029. However, in the possible collision region of IRAS 22528+5936, NVSS continuum radiation is not detected and the MSX sources are merely associated with the central star. The velocity fields of the two regions indicate the direction of the pressure and interaction. In addition, we have identified candidates of young stellar objects (YSOs) by using data from the Two Micron All Sky Survey (2MASS) in JHK bands expressed in a color-color diagram. The distribution of YSOs shows that the possible collision region is denser than other regions. All the evidence suggests that IRAS 02459+6029 could be an example of cloud-cloud collision, and that IRAS 22528+5936 could be two separate non-colliding clouds.

关键词： ISM: molecules — stars: formation — stars: individual (IRAS 02459+6029 IRAS 22528+5936) — ISM: clouds

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Free Boundary Value Problem for the Cylindrically Symmetric Compressible Navier-Stokes Equations with a Constant Exterior Pressure

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Acta Mathematicae Applicatae Sinica 2018年第4期34卷 761-774页

作者： Ru-xu liAN jun-li wang Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China Guanghua School of Management Peking University Beijing 100871 China

This paper is concerned with the free boundary value problem（FBVP） for the cylindrically symmetric barotropic compressible Navier-Stokes equations（CNS） with density-dependent viscosity coefficients in the case that across the free surface stress tensor is balanced by a constant exterior pressure. Under certain assumptions imposed on the initial data, the unique cylindrically symmetric strong solution is shown to exist globally in time and tend to a non-vacuum equilibrium state exponentially as time tends to infinity.

关键词： Navier-Stokes equations cylindrically symmetric density-dependent viscosity coefficients con-stant exterior pressure strong solution

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Non-dispersive solvent extraction ofp-toluic acid from purifiedterephthalic acid plant wastewater with p-xylene as extractant

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2016年第10期17卷 828-840页

作者： Qing-ran KONG You-wei CHENG li-jun wang Xi li College of Chemieal and Biological Engineering Zhejiang University Hangzhou 310027 China

Non-dispersive solvent extraction （NDSE） with p-xylene as extractant was employed as a novel separation methodto recover both ρ-toluic （PT） acid and water from purified terephthalic acid （PTA） wastewater. The mass transport behavior ofPT acid from aqueous solution to ρ-xylene was investigated by experiments and numerical simulation. Experiments showed thatNDSE is feasible and effective. Residual PT acid in the raffinate can be reduced to lower than the permitted limit of wastewaterre-use （100 g/m^3） with extraction time longer than 60 s in industrial conditions. A mathematical model of PT acid mass transportwas developed to optimize the membrane module performance. The model was validated with the experimental results withrelative errors of less than 6%. Numerical analysis for mass transfer through the lumen side, the porous membrane layer, and theshell side showed that PT acid transport in the aqueous solution is the rate determining step. The effects of the membrane andoperating parameters on membrane module performance were investigated by means of computational simulations. The keyparameters suggested for industrial NDSE design are： fiber inner radius r1=200-250 μm, extraction time tc=50-60 s, aqueous/organic volumetric ratio a/o=9.0, and temperature T-318 K.

关键词： Non-dispersive solvent extraction (NDSE), Purified terephthalie acid (PTA) wastewater, p-toluic (PT) acid,ρ-xylene (PX), Mass transfer

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Morphology and distribution of precipitates and their effects on compression cracks in Fe-6.5Si-0.02B electrical steel

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Journal of Iron and Steel Research International 2018年第1期25卷 99-107页

作者： Zhi-hao Zhang jun-li wang Hua-dong Fu Institute for Advanced Materials and Technology Universityof Science and Technology Beijing Beijing 100083 China Beijing Amorphous Energy Conservation Materials IndustryAlliance Beijing 100081 China

Morphology and distribution of precipitates in the Fe-6.5Si-0.02B alloy were characterized, and these effects on room- temperature compression cracks were investigated. The results showed that the precipitate in the Fe-6.5Si-0.02B alloy is FezB with body-centered tetragonal structure, and its nano-hardness is 15.0 GPa which is higher than that of the matrix （- 8.5 GPa）. In the as-cast alloys, most of the intragranular precipitates are coarse lath-like with the length of 5-15 μm and width of 2-5 μm, and the precipitates formed at the grain boundaries are of about 2-3 μm in width. After oil quenching followed by heat treatment at 1100 ℃ for more than 30 min, the precipitates inside grains are refined with a size of several hundred nanometers and the precipitates at the grain boundaries are refined with a size of 〈 1 μm. After compression test, transgranular and intergranular cracks occur in the as-cast alloys with coarse precipitates. For the quenched alloys with fine precipitates, the number of cracks decreases significantly, and no transgranular cracks happen because some cracks are blocked or the propagation direction is changed by grain boundary.

关键词： Fe-6.5 wt% Si alloy Precipitates Nano-hardness Room-temperature compression

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Validity of Diagnostic Evidence for Deceased Cases in Hospitals

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Biomedical and Environmental Sciences 2008年第3期21卷 247-252页

作者： XIA WAN li-jun wang jun-FANG wang AI-PING CHEN GONG-HUAN YANG Institute of Basic Medical Sciences Chinese Academy of Medical Sciences Peking Union Medical University Beijing 100005 China Chinese Center for Disease Control and Prevention Beijing 100050 China

Objective To determine the validity of the diagnostic evidence for deceased cases in hospitals. Methods All information collected from medical records of the deceased cases in tertiary care health facilities was input into ottr database. Four diagnosis levels were determined based on level of diagnostic evidence： level Ⅰ was based on autopsy, pathology or operative exploration, level Ⅱ on physical and laboratory tests plus expert clinical judgment, level Ⅲ on expert clinical judgment, level Ⅳ on postmortem assumptions. After the diagnostic evidence of each deceased case was reviewed by a panel of three experts, the diagnostic level of each diagnosis was determined. Results Among the 2102 medical cases for verbal autopsy study, only 26 （1.24%） afforded diagnostic evidence for level Ⅲ Among the level Ⅲ evidence-based cases of death, the major causes of death were cardiovascular diseases, respiratory diseases, and gastroenterological diseases. According to some special symptoms and medical histories, these cases could be diagnosed by comprehensive clinical judgment. Only one case met the criteria for level Ⅳ. Conclusion Level Ⅰ diagnostic evidence is hard to attain in China because of the traditional concept and economic restriction. The causes for 2101 deaths can be validated by level Ⅱ or Ⅲ diagnostic evidence.

关键词： Validity Diagnosis criteria Diagnostic evidence Laboratory examination

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Two universal runoff yield models： SCS vs. LCM

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Journal of Geographical Sciences 2015年第3期25卷 311-318页

作者： li jun liU Changming wang Zhonggen liANG Kang Key Laboratory of Water Cycle & Related Land Surface Processes Institute of Geographic Sciences andNatural Resources Research CAS Beijing 100101 China

Runoff calculation is one of the key components in the hydrological modeling. For a certain spatial scale, runoff is a very complex nonlinear process. Currently, the runoff yield model in different hydrological models is not unique. The Chinese LCM model and the American SCS model describe runoff at the macroscopic scale, taking into account the rela- tionship between total actual retention and total rainfall and having a certain similarity. In this study, by comparing the two runoff yield models using theoretical analyses and numerical simulations, we have found that：（1） the SCS model is a simple linear representation of the LCM model, and the LCM model reflects more significantly the nonlinearity of catchment runoff. （2） There are strict mathematical relationships between parameters （R, r） of the LCM model and between parameters （S） of the SCS model, respectively. Parameters （R, r） of the LCM can be determined using the research results of the SCS model parameters. （3） LCM model parameters （R, r） can be easily obtained by field experiments, while SCS parameters （S） are difficult to measure. Therefore, parameters （R, r） of the LCM model also can provide the foundation for the SCS model. （4） The SCS model has a linear relationship between the reciprocal of total actual retention and the reciprocal of total rainfall during runoff period. The one-order terms of a Taylor series expansion of the LCM model describe the same relation- ship, which is worth further study.

关键词： rainfall infiltration runoff calculation nonlinearity the SCS model the LCM model

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