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Simulation of mass and heat transfer in liquid hydrogen tanks during pressurizing

Chinese Journal of Aeronautics 2019年第9期32卷 2068-2084页

作者： Jiachao li Guozhu liANG School of Astronautics Beihang University

In order to accurately predict the heat and mass transfer behaviors and analyze key factors affecting pressurization process in the hydrogen tank, a comprehensive 2 D axial symmetry Volume-Of-Fluid(VOF) model is established by Computational Fluid Dynamics(CFD) *** effects of phase change, turbulence and mass diffusion are included in the model and relationships between physical properties and temperature are also comprehensively considered. The phase change model is based on Hertz-Knudsen equation and the mass transfer time relaxation factor is determined by the NASA’s experimental data. The mass diffusion model is included in gaseous helium pressurizing. The key factors including the inlet temperature, inlet mass flow rate, injector types and pressurizing gas kinds are quantitatively analyzed. Compared with the experiment, the simulation results show that the deviation of pressurizing gas mass consumption, condensing mass and ullage temperature are 3.0%, 7.5% and 4.0% respectively. The temperature stratification is existed along the axial direction in the surface liquid region and the ullage region, and the bulk liquid is in subcooled state during pressurizing. The location of phase change mainly appears near the vapor–liquid interface, and the mass transfer expressing as condensation or vaporization is mainly determined by the heat convection and molecular concentration near the vapor–liquid *** key factors show that increasing the inlet temperature and inlet mass flow rate could shorten the pressurizing time interval and save the pressurizing gas mass. The proportion of the total energy addition of the tank absorbed by the ullage region, the liquid region and the tank wall respectively is greatly influenced by the injector types and more heat transferred into the ullage would result in a faster pressure rising rate. Gaseous hydrogen pressurization has a higher efficiency than gaseous helium pressurization. The simulation results presented in this

关键词： CFD Condensation Cryogenics Evaporation Phase change Pressurization

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Transversal effects of high order numerical schemes for compressible fluid flows

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Applied Mathematics and Mechanics(English Edition) 2019年第3期40卷 343-354页

作者： Xin LEI Jiequan li School of Mathematical Sciences Beijing Normal University Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Center for Applied Physics and Technology Peking University

Finite volume schemes for the two-dimensional(2D) wave system are taken to demonstrate the role of the genuine dimensionality of Lax-Wendroff flow solvers for compressible fluid flows. When the finite volume schemes are applied, the transversal variation relative to the computational cell interfaces is neglected, and only the normal numerical flux is used, thanks to the Gauss-Green formula. In order to offset such defects, the Lax-Wendroff flow solvers or the generalized Riemann problem(GRP) solvers are adopted by substituting the time evolution of flows into the spatial variation. The numerical results show that even with the same convergence rate, the error by the GRP2D solver is almost one ninth of that by the multistage Runge-Kutta(RK) method.

关键词： transversal effect generalized Riemann problem(GRP)solver Lax-Wendroff flow solver wave system

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Low-Temperature and Surfactant-Free Synthesis of Mesoporous TiO_2 Sub-Micron Spheres for Efficient Dye-Sensitized Solar Cells

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Journal of Materials Science & Technology 2016年第1期32卷 17-23页

作者： Kaimo Deng liang li College of Physics Optoelectronics and Energy & Collaborative Innovation Center of Suzhou Nano Science and TechnologySoochow University

Dye-sensitized solar cells （DSSCs） are one of the most promising next-generation solar cells due to their advantages over other counterparts. The photoanode of DSSCs has a great effect on the photovoltaic per- formance. Traditional photoanode includes a bottom nanoparticle layer and an upper scattering layer for better light capture in longer wavelength. Mesoporous nanostructures with size comparable to the wavelength of visible light are considered to be excellent light scattering centers by providing extra places for dye loading. Developing a green synthetic method is of great importance. Herein we report a facile and surfactant-free synthesis of mesoporous futile TiO2 submicrometer-sized spheres at temperature as low as 70 ℃. DSSCs based on photoanodes with an upper scattering layer composed of as-obtained mesoporous spheres on nanoparticle dense layer demonstrate an 18.0% improvement of power conver- sion efficiency. This simple approach may offer an energy-efficient and environmentally friendly alternative for DSSCs fabrication.

关键词： Titanium dioxide Mesoporous Sub-micron light scattering Dye-sensitized solar cells Energy harvesting

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Microstructure Evolutions during the Hot Extrusion Process of AZ 31B Magnesium Alloy

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Chinese Journal of Mechanical Engineering 2009年第3期22卷 369-375页

作者： li Luoxing LOU Yan State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body Hunan University Changsha 410082 China College of Materials Science and Engineering Hunan University Changsha 410082 China College of Mechantronics and Control Engineering Shenzhen University Shenzhen 518060 China

The hot bulk deformation processes （such as extrusion, forging and rolling） are efficient ways to produce fine microstructure. The effects of extrusion parameters on the evolved microstructure of directly extruded AZ 31B magnesium alloy were investigated. Extrusion processes were carried out at five different combinations with ram speed ranging from 2 to 8 mm·s^-1 and billet temperature ranging from 350 to 450 ℃. The experimental results show that the peak extrusion force decreases with increase in billet temperature and decreases in ram speed. During all the extrusion the profile temperature and die temperature rise continuously. Small particles of secondary phase （β-Mg17Al12） are uniformly distributed near the edge of the extruded profiles whereas their distribution is nonuniform in the centre of the extrudates. The size of secondary phase particles present in the central region of the specimens was found to increase with billet temperature and extrusion speed. All the specimens showed mixed microstructure--In the central region of the specimen, low volume fraction of dynamically recrystallized fine grains presented at the grain boundaries of original coarse grains; but near the edge region, the microstructure consisted nearly equiaxed fine recrystallized grains.

关键词： magnesium alloy extrusion microstructure

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Influence of Hot Deformation and Subsequent Austempering on the Mechanical Properties of Hot Rolled Multiphase Steel

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Journal of Materials Science & Technology 2006年第6期22卷 763-768页

作者： Zhuang li Di WU Shenyang Institute of Aeronautical Engineering Shenyang 110034 China State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110004 China

Influence of hot deformation and subsequent austempering on the mechanical properties of hot rolled multiphase steel was investigated. Thermo-mechanical control processing （TMCP） was conducted by using a laboratory hot rolling mill, where three different kinds of finishing rolling reduction, and austemperings with various isothermal holding duration were applied. The results have shown that a multiphase microstructure consisting of polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes. Mechanical properties increase with increasing the amount of deformation because of the stabilization of retained austenite. Ultimate tensile strength （σb）, total elongation （σ） and the product of ultimate tensile strength and total elongation （σb-σ） reach the maximum values （791 MPa, 36% and 28476 MPa%, respectively） at optimal processes.

关键词： Hot deformation Austempering Hot rolled multiphase steels Mechanical properties

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Deterministic bound for avionics switched networks according to networking features using network calculus

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Chinese Journal of Aeronautics 2017年第6期30卷 1941-1957页

作者： Feng HE Ershuai li School of Electronic and Information Engineering Beihang University

The state of the art avionics system adopts switched networks for airborne communications. A major concern in the design of the networks is the end-to-end guarantee ability. Analytic methods have been developed to compute the worst-case delays according to the detailed configurations of flows and networks within avionics context, such as network calculus and trajectory approach. It still lacks a relevant method to make a rapid performance estimation according to some typically switched networking features, such as networking scale, bandwidth utilization and average flow rate. The goal of this paper is to establish a deterministic upper bound analysis method by using these networking features instead of the complete network configurations. Two deterministic upper bounds are proposed from network calculus perspective: one is for a basic estimation,and another just shows the benefits from grouping strategy. Besides, a mathematic expression for grouping ability is established based on the concept of network connecting degree, which illustrates the possibly minimal grouping benefit. For a fully connected network with 4 switches and 12 end systems, the grouping ability coming from grouping strategy is 15–20%, which just coincides with the statistical data(18–22%) from the actual grouping advantage. Compared with the complete network calculus analysis method for individual flows, the effectiveness of the two deterministic upper bounds is no less than 38% even with remarkably varied packet lengths. Finally, the paper illustrates the design process for an industrial Avionics Full Duple X switched Ethernet(AFDX) networking case according to the two deterministic upper bounds and shows that a better control for network connecting, when designing a switched network, can improve the worst-case delays dramatically.

关键词： Deterministic bound Grouping ability Network calculus Networking features Switched networks

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Development of a Novel Parallel-spool Pilot Operated High-pressure Solenoid Valve with High Flow Rate and High Speed

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Chinese Journal of Mechanical Engineering 2015年第2期28卷 369-378页

作者： DONG Dai li Xiaoning School of Mechanical Engineering Nanjing University of Science and Technology

High-pressure solenoid valve with high flow rate and high speed is a key component in an underwater driving ***,traditional single spool pilot operated valve cannot meet the demands of both high flow rate and high speed simultaneously.A new structure for a high pressure solenoid valve is needed to meet the demand of the underwater driving system.A novel parallel-spool pilot operated high-pressure solenoid valve is proposed to overcome the drawback of the current single spool *** models of the opening process and flow rate of the valve are *** response time of the valve is subdivided into 4 parts to analyze the properties of the opening *** formulas to solve 4 parts of the response time are *** factors that influence the opening response time are *** to the mathematical model of the valve,a simulation of the opening process is carried out by *** are chosen based on theoretical analysis to design the test prototype of the new type of *** response time of the designed valve is tested by verifying response of the current in the coil and displacement of the main valve *** experimental results are in agreement with the simulated results,therefore the validity of the theoretical analysis is *** opening response time of the valve is 48.3 ms at working pressure of 10 *** flow capacity test shows that the largest effective area is 126 mm2 and the largest air flow rate is 2320 L/*** to the result of the load driving test,the valve can meet the demands of the driving *** proposed valve with parallel spools provides a new method for the design of a high-pressure valve with fast response and large flow rate.

关键词： high-pressure pneumatic solenoid valve parallel-spool high flow rate high speed opening response time

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On-line Scheduling on Parallel Machines to Minimize the Makespan

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Journal of Systems Science & Complexity 2016年第2期29卷 472-477页

作者： li Songsong ZHANG Yuzhong School of Management Qufu Normal University

This paper considers two parallel machine scheduling problems, where the objectives of both problems are to minimize the makespan, and the jobs arrive over time, on two uniform machines with speeds 1 and s （s 〉 1）, and on m identical machines, respectively. For the first problem, the authors show that the on-line LPT algorithm has a competitive ratio of （1 ＋ √5）/2 ≈ 1.6180 and the bound is tight. Furthermore, the authors prove that the on-line LPT algorithm has the best possible competitive ratio if s ≥ 1.8020. For the second problem, the authors present a lower bound of （15 - √17）/8 ≈ 1.3596 on the competitive ratio of any deterministic on-line algorithm. This improves a previous result of 1.3473.

关键词： Lower bound on-line algorithm scheduling.

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Inhibition of tumor angiogenesis by TTF1 from extract of herbal medicine

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World Journal of Gastroenterology 2011年第44期17卷 4875-4882页

作者： Chao liu Xiao-Wan li li-Min Cui liang-Chang li li-Yan Chen Xue-Wu Zhang Basic Medical College Yanbian University Yanji133002 Jilin Province China Clinical Medical College Yanbian University Yanji 133002 Jilin Province China

AIM:To study the inhibition of tumor angiogenesis by 5,2,4'-trihydroxy-6,7,5'-trimethoxyflavone(TTF1) isolated from an extract of herbal medicine Sorbaria ***:Angiogenic activity was assayed using the chick embryo chorioallantoic membrane(CAM) *** density(MVD) was determined by staining tissue sections immunohistochemically for CD34 using the Weidner capillary counting *** mRNA and protein levels of vascular endothelial growth factor(VEGF),vascular endothelialgrowth factor receptor 2(VEGFR2,Flk-1/KDR),basic fibroblast growth factor(bFGF),cyclo-oxygenase(COX)-2 and hypoxia-inducible factor(HIF)-1α were detected by quantitative real-time polymerase chain reaction and Western blotting ***:The TTF1 inhibition rates for CAM were 30.8%,38.2% and 47.5% with treatment concentrations of 25,50 and 100 μg/embryo × 5 d,*** inhibitory rates for tumor size were 43.8%,49.4% and 59.6% at TTF1 treatment concentrations of 5,10,and 20 μmol/kg,*** average MVD was 14.2,11.2 and 8.5 at treatment concentrations of 5 μmol/kg,10 μmol/kg and 20 μmol/kg TTF1,*** mRNA and protein levels of VEGF,KDR,bFGF,COX-2 and HIF-1α in mice treated with TTF1 were significantly ***:TTF1 can inhibit tumor angiogenesis,and the mechanism may be associated with the down-regulation of VEGF,KDR,bFGF,HIF-1α and COX-2.

关键词： Chinese herbal medicine Sorbaria sorbifolia TTF1 Inhibition Tumor angiogenesis

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OPTIMAL DECISIONS WHEN BALANCING EXPECTED PROFIT AND CONDITIONAL VALUE-AT-RISK IN NEWSVENDOR MODELS

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Journal of Systems Science & Complexity 2010年第6期23卷 1054-1070页

作者： Minghui XU Jianbin li School of Economics and Management Wuhan University Wuhan 430072 China. School of Management Huazhong University of Science and Technology Wuhan 430072 China.

This paper investigates a risk-averse inventory model by balancing the expected profit and conditional value-at-risk （CVaR） in a newsvendor model setting. We find out that： i） The optimal order quantity is increasing in the shortage cost for both the CVaR only criterion and the tradeoff objective, ii） For the case of zero shortage cost, the optimal order quantity to the CVaR criterion or tradeoff objective is increasing in the selling price, respectively. However, it may not be monotonic in the selling price when incorporating a substantial shortage cost. Moreover, it may be larger or less than the risk-neutral solution, iii） Under the tradeoff objective function, although the optimal order quantity for the model without shortage cost is increasing in the weight put on the expected profit, this property may not be true in general for the model with a substantial shortage cost. Some numerical examples are conducted to verify our results and observations.

关键词： Conditional value-at-risk newsvendor model risk aversion shortage cost.

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