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A TVD SCHEME FOR INCOMPRESSIBLE FLOW COUPLED WITH DIFFERENT TURBULENCE MODLES ON A GROUND-MOUNTED SQUARE-RIB FLOW

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Journal of Hydrodynamics 2007年第6期19卷 743-750页

作者： WANG jia-song HUANG zhen School of Mechanical Engineering Shanghai Jiaotong University Shanghai 200240 China

A finite-difference Total Variation Diminishing （TVD） numerical simulation model for coupling the Reynolds Averaged Navier-Stokes （RANS） equations, pressure-relative continuity equation and various k-εturbulence models was developed to solve the incompressible flow based on the pseudo-compressibility method. The hyperbolicity of all these equations was studied and the discretization of the fully coupling equations with all the primal variables and source terms were made in this article. Numerical simulation for modeling the flow around a ground-mounted square rib was implemented and validated by comparing with the published wind tunnel experimental data. It is shown that such a numerical simulation method with a proper turbulence model has a very good accuracy to simulate the flow around a surface-mounted rib. It is concluded that the Renormalization Group （RNG） and Chen-Kim k-εturbulence models have much better ability to predict the characteristics of the vortex structure and flow separation than the standard k-εmodel.

关键词： Total Variation Diminishing (TVD) scheme Reynolds Averaged Navier-Stokes (RANS) turbulence models,square rib pseudo-compressibility method

ADDITIONAL PRESSURE LOSSES OF SOLID-LIQUID FLOW IN AN OSCILLATING PIPELINE

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Journal of Hydrodynamics 2002年第1期14卷 75-80页

作者： Xia, jian-Xin Huang, jia-zhen Cent. of Environ. Sci. Peking Univ. Beijing 100871 China

Manganese nodules on the ocean bed become attractive mineral resources because of its huge commercial benefits. In the last decades, a set of hydraulic lifting system with pipeline has been developed to mining these particles. It is inevitable that lifting pipe will oscillate due to its operation and the motion properties of the solid in the two-phase flow will be changed because of the oscillating of pipe-line. The pressure gradient along the lifting pipeline was investigated with a series of experiments. At the same time, a new pressure drop prediction method on the basis of Lagrange simulation technique was worked out by use of an axial momentum balance and this method provides a way to predict the pressure loss of solid-liquid mixture. The results show that compared with the fixed pipe transportation, the pressure gradient of the oscillating pipe is greater than that of the fixed pipe because of the collision and unsteady friction between particles and the pipe wall due to the oscillating motion of the pipe. Moreover, it is found that the prediction results are in good agreement with those of the experiments.

关键词： Two phase flow Underwater mineral resources

miRNAs in non-alcoholic fatty liver disease

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Frontiers of Medicine 2016年第4期10卷 389-396页

作者： zhen He Cheng Hu Weiping jia Shanghai Diabetes Institute Shanghai Key Laboratory of Diabetes Mellitus Shanghai Clinical Center for Diabetes Shanghai Jiao Tong University Affiliated Sixth People's Hospital Shanghai 200233 China

Non-alcoholic fatty liver disease （NAFLD） is a major cause of liver cirrhosis and hepatocellular carcinoma and is a considerable threat to public health, miRNAs are important post-transcriptional regulators of gene expression, and the dysregulation of miRNAs is involved in various biological processes in the liver, including lipid homeostasis, inflammation, apoptosis, and cell proliferation. Recently, a number of studies have described the association between miRNAs and NAFLD progression and have shown that circulating miRNAs reflect histological changes in the liver. Therefore, circulating miRNAs have potential use for the evaluation of NAFLD severity. In this review, we discuss the involvement of miRNAs in NAFLD pathogenesis and the key role of miRNAs in the screening, diagnosis, and staging of NAFLD.

关键词： nonalcoholic fatty liver disease nonalcoholic steatohepatitis hepatocellular carcinoma miRNA

Spatial patterns of leaf nitrogen and phosphorus stoichiometry across southeast to central Tibet

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Journal of Mountain Science 2022年第9期19卷 2651-2663页

作者： WANG Wei ZHAO jia-min XING zhen College of Resources and Environmental Sciences Tibet Agriculture&Animal Husbandry UniversityNyingchi 860000China Research institute of Tibet Plateau Ecology Tibet Agriculture&Animal Husbandry UniversityNyingchi 860000China

Leaf N and P stoichiometry in terrestrial ecosystems has been widely investigated in recent years owing to the importance of these elements in improving the predicted vegetation responses to global *** vertical distribution of leaf N and P stoichiometry has attracted increasing attention because of the dramatic changes in environmental factors at regional ***,the characteristics of leaf N and P stoichiometry in the southeast Qinghai–Tibet plateau(SET)are not clear,although this area is sensitive to global ***,we analyzed the leaf N and P concentrations in dominant plant species on natural altitudinal gradients on the Duoxiongla(DXL),Sejila(SJL),Mila(ML),and Gangbala(GBL)mountains across the SET all the way to central *** results showed that the leaf N concentrations were comparable among the regions,whereas the leaf P concentrations dramatically decreased from SET to central Tibet(CT).The leaf N concentrations were 23.6,21.3,20.8,and 22.4 g kg^(-1),and the leaf P concentrations were 2.40,2.49,1.94,and 1.59 g kg^(-1) on the SJL,DXL,ML and GBL mountains,*** leaf N/P ratios on the DXL,SJL,ML,and GBL mountains were 8.81,10.3,11.2,and 14.2,*** the increasing trend of the leaf N/P ratio from southeast Qinghai–Tibet plateau to central Tibet,N limitation might widely exist in well vegetated ecosystems in the Qinghai–Tibet plateau.

关键词： Leaf N and P concentration Southeast Tibet Stoichiometry Spatial variations

Microstructure evolution of eutectic Nb–24Ti–15Si–4Cr–2Al–2Hf alloy processed by directional solidification

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Rare Metals 2017年第6期36卷 472-477页

作者： zhen Li Sai-Nan Yuan Li-Na jia Bin Kong zhen Hong Hu Zhang School of Materials Science and Engineering Beihang Universtity Beijing 100191 China

In this work, the near-eutectic Nb-24Ti-15Si-4Cr-2Al-2Hf（at%） alloy was directionally solidified at 1900 ℃ with withdrawal rates of 6, 18, 36, 50 mm·min^-1 and then heat-treated at 1450 ℃ for 12 h. The microstructure evolution was investigated. The results show that the microstructure of the directionally solidified（DS） alloy is composed of Nbss＋Nb5Si3 eutectics within the whole withdrawal rate range, while the variation of rates makes a great difference on the solidification routes,the morphology and size of Nb_（ss）＋Nb_5Si_3 eutectic *** the increase in withdrawal rates, the petaloid Nbss＋Nb5Si3 eutectic cells transform into granular morphology. After the heat treatment, a mesh structure Nbssis formed gradually which isolates the Nb5Si3, and the phase boundaries become smoother in order to reduce the interfacial energy. Moreover, two kinds of Nb5Si3 exist in the heat-treated（HT） samples identified by crystal form and element composition, which are supposed as α-Nb5Si3 and γ-Nb5Si3, respectively. This study exhibits significant merits in guiding the optimization of Nb-Si-based alloys＇ mechanical properties.

关键词： Nb-Si-based alloy Directional solidification Heat treatment Microstructure evolution Intermetallic

Research on the steam–gas pressurizer model with Relap5 code

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Nuclear Science and Techniques 2017年第5期28卷 1-8页

作者： Xi-zhen Ma Hai-Jun jia Yang Liu Institute of Nuclear and New Energy Technology Collaborative Innovation Center of Advanced Nuclear Energy Technology Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education Tsinghua University Beijing 100084 China

Steam–gas pressurizers are self-pressurizing, and since steam and noncondensable gas are used to sustain their pressure, they experience very complicated thermal–hydraulic phenomena owing to the presence of the latter. A steam–gas pressurizer model was developed using Relap5 code to investigate such a pressurizer's thermal–hydraulic *** important thermal–hydraulic processes occurring in the pressurizer model include bulk flashing, rainout, wall condensation with noncondensable gas, and interfacial heat and mass transfer. The pressurizer model was verified using results from insurge experiments performed at the Massachusetts Institute of Technology. It was found that noncondensable gas was one of the important factors governing the pressure response, and the accuracy of the developed model would change with different mass fractions and types of noncondensable gas.

关键词： Relap5 code Noncondensable gas Heat and mass transfer Steam–gas pressurizer Condensation

Factors influencing water quality indices in a typical urban river originated with reclaimed water

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Frontiers of Environmental Science & Engineering 2017年第4期11卷 73-82页

作者： jiao Zhang zhen Wei Haifeng jia Xia Huang State Key Joint Laboratory of Environment Simulation and Pollution Control School of Environment Tsinghua University Beijing 100084 China

The water quality in a typical urban river segment originated with reclaimed water in Beijing was monitored for two years to investigate the evolution of water quality along the rivcr, and statistical analysis was applied to determine factors influencing water quality of such river recharged by reclaimed water. It was found that no significant change in pollutant concentrations （including COD, NH4＋-N, TN and TP） was observed during this time, and their average values were close to those of the original reclaimed water. However, turbidity and algal contents fluctuated temporally in the direction of river flow. Statistical analysis showed that turbidity was strongly positively correlated with algal contents for flow rate 〈 0.1 m.s-1. whereas it was strongly positively correlated with both algalcontents and TOC for flow rate 〉 0. 1m. s-1. It was observed that diatom was the absolute predominant phyla with Melosira as the major species. In terms of algal bloom control, the specific growth rate of algae was strongly correlated to temperature, and was influenced by flow rate as well. Compared with two other rivers originated with reclaimed water and one originated with natural water, the Shannon Wiener index in the objective river was the lowest, with values between 0.7 and 1.6, indicating a high risk for algal bloom. Statistics showed that Shannon Wiener index was strongly negatively correlated to nutrient salts and cations.

关键词： Reclaimed water Urban river Turbidity Algae Flow rate

An efficient formulation based on the Lagrangian method for contact–impact analysis of flexible multi-body system

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Acta Mechanica Sinica 2016年第2期32卷 326-334页

作者： Peng Chen Jin-Yang Liu jia-zhen Hong Department of Engineering Mechanics School of Naval ArchitectureOcean and Civil EngineeringShanghai Jiaotong University

In this paper,an efficien formulation based on the Lagrangian method is presented to investigate the contact–impact problems of f exible multi-body ***,the penalty method and the Hertz contact law are the most commonly used methods in engineering ***,these methods are highly dependent on various non-physical parameters,which have great effects on the simulation ***,a tremendous number of degrees of freedom in the contact–impact problems will influenc thenumericalefficien *** of these two problems,a formulation combining the component mode synthesis method and the Lagrangian method is presented to investigate the contact–impact problems in fl xible multi-body system ***,the finit element meshing laws of the contact bodies will be studied preliminarily.A numerical example with experimental verificatio will certify the reliability of the presented formulationincontact–***,aseries of numerical investigations explain how great the influenc of the finit element meshing has on the simulation *** the limitations of the element size in different regions are summarized to satisfy both the accuracy and efficien y.

关键词： Multi-body dynamics Contact–impact analysis Lagrangian method Component mode synthesis

A Marine Environment Early Warning Algorithm Based on Marine Data Sampled by Multiple Underwater Gliders

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China Ocean Engineering 2019年第2期33卷 172-184页

作者： XU zhen-zhen LI Lu YU jian-cheng XU Xiu-juan jia Ming-fei School of Software Technology Dalian University of Technology The State Key laboratory of Robotics Shenyang Institute of AutomationCAS

This study analyzes and summarizes seven main characteristics of the marine data sampled by multiple underwater gliders. These characteristics such as the big data volume and data sparseness make it extremely difficult to do some meaningful applications like early warning of marine environment. In order to make full use of the sea trial data, this paper gives the definition of two types of marine data cube which can integrate the big marine data sampled by multiple underwater gliders along saw-tooth paths, and proposes a data fitting algorithm based on time extraction and space compression(DFTS) to construct the temperature and conductivity data cubes. This research also presents an early warning algorithm based on data cube(EWDC) to realize the early warning of a new sampled data *** results show that the proposed methods are reasonable and effective. Our work is the first study to do some realistic applications on the data sampled by multiple underwater vehicles, and it provides a research framework for processing and analyzing the big marine data oriented to the applications of underwater gliders.

关键词： big marine data early warning marine environment underwater gliders