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3D Rigid-Plastic Finite Element Analysis for Skew Rolling Process of the Stepped Part

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Journal of Materials Science & Technology 2003年第Z1期19卷 38-40页

作者： gang FANG Pan zeng Department of Mechanical Engineering Tsinghua University Beijing 100084 China Department of Mechanical Engineering Tsinghua University Beijing 100084 China

Based on rigid-plastic finite element method, a skew rolling process of stepped part is simulated. Considering nodesaving and effective remeshing, the tetrahedron solid elements are used to discrete workpiece. The workpiece material adopts rigid-plastic model, where the flow stress is function of effective strain, effective strain rate and *** thermomechanical coupling is considered in the simulation. To model the spinning workpiece undergoing plastic deformation, a novel solution is presented and applied in this paper. The stress state in the workpiece and forming characteristic of skew rolling are analyzed. The forming load, including roller torque and forces in three directions are predicted. The above analyses are helpful to understanding of forming mechanisms and improving of process and die design.

关键词： FEM, Skew rolling, Stepped part, Spinning part, Fracture

Effects of Network Closure on Cooperative Innovation: Evidence from Dongying's Petroleum Equipment Industry in China

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Chinese Geographical Science 2019年第3期29卷 517-527页

作者： MA Shuang zeng gang Institute of Information Shanghai Academy of Social Sciences School of Urban and Regional Science East China Normal University

There are two opposing viewpoints on which kind of network configuration provides a more competitive advantage, namely,network closure or structural holes, with the latter occupying the dominant position in the literature. Using social network analysis and negative binomial regression methods, we graph the co-patent network of Dongying's petroleum equipment industry in China and explore its impact on enterprise innovation. The analysis is based on 17 face-to-face interviews, 31 enterprise questionnaires, and 354 co-patent records from the China State Intellectual Property Office identifying cooperative innovation for the years 1988–2013. We find that this network is closed, controlled by state-owned enterprises, and its closure has positive effects on enterprise innovation performance. This may be related to China's unique industrial development history, state system and policies, regional culture and circumstances, and enterprise characteristics. Therefore, for some industries in specific regions, the advantages usually attributed to structural holes and open innovation may not necessarily apply.

关键词： network closure structural holes enterprise innovation petroleum equipment industry Dongying

Regional Characteristics of Cloud Radiative Effects before and after the South China Sea Summer Monsoon Onset

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Journal of Meteorological Research 2020年第6期34卷 1167-1182页

作者： Man HUANG Jiandong LI gang zeng Yongkun XIE Key Laboratory of Meteorological Disaster of Ministry of Education(KLME) Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters(CIC-FEMD)Nanjing University of Information Science&TechnologyNanjing 210044 State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029 Collaborative Innovation Center for Western Ecological Safety Lanzhou UniversityLanzhou 730000

The South China Sea summer monsoon(SCSSM)onset is characterized by rapid thermodynamical changes in the atmosphere that are critical to regional weather and climate *** far,few studies have focused on the changes in the associated cloud and radiative *** study investigates spatiotemporal characteristics of topof-atmosphere(TOA)cloud radiative effects(CREs)before and after the SCSSM onset over the South China Sea(SCS)and South China(SC),based on the 2001–2016 Clouds and the Earth’s Radiant Energy System(CERES)Energy Balanced and Filled(EBAF)satellite data and ERA-Interim reanalysis *** the SCSSM onset,strong net CRE(NCRE)dominated by its cooling shortwave component occurs over SC,while descending motion and weak NCRE prevail over the *** the SCSSM onset pentad,convection,high clouds,and longwave and shortwave CREs(LWCRE and SWCRE)abruptly increase over the southern and central SCS,and their high-value centers subsequently move northeastward and are strongly affected by the western Pacific subtropical *** strong offset between LWCRE and SWCRE enables the NCRE intensity(TOA radiation budget)to be quite small(large)between the SCS and the western North Pacific after the SCSSM *** contrast,low–middle-level clouds and strong cooling SWCRE remain over SC after the SCSSM onset,but the increasing high clouds and LWCRE weaken(intensify)the regional NCRE(TOA radiation budget)*** marked latitudinal differences in CREs between the SCS and SC primarily arise from their respective dominant cloud types and circulation conditions,which manifest the differences between the tropical SCSSM and subtropical East Asian monsoon *** results indicate that regional cloud fractions and CREs before and after the SCSSM onset are strongly modulated by quickly changed largescale circulation over the East Asian monsoon regions,and the spatiotemporal variation of CREs is a response to the monsoonal circulation adjustment to a large extent

关键词： cloud radiative effects(CREs) top-of-atmosphere(TOA)radiation budget South China Sea summer monsoon(SCSSM) South China(SC)

Future Changes in Extreme High Temperature over China at 1.5℃-5℃ Global Warming Based on CMIP6 Simulations

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Advances in Atmospheric Sciences 2021年第2期38卷 253-267页

作者： Guwei ZHANG gang zeng Xiaoye YANG Zhihong JIANG Key Laboratory of Meteorological Disaster of Ministry of Education(KLME) Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters(CIC-FEMD)Nanjing University of Information Science and TechnologyNanjing 210044China

Extreme high temperature(EHT)events are among the most impact-related consequences related to climate change,especially for China,a nation with a large population that is vulnerable to the climate *** on the latest Coupled Model Intercomparison Project Phase 6(CMIP6),this study assesses future EHT changes across China at five specific global warming thresholds(1.5℃-5℃).The results indicate that global mean temperature will increase by 1.5℃/2℃ before 2030/2050 relative to pre-industrial levels(1861-1900)under three future scenarios(SSP1-2.6,SSP2-4.5,and SSP5-8.5),and warming will occur faster under SSP5-8.5 compared to SSP1-2.6 and *** SSP5-8.5,global warming will eventually exceed 5℃ by 2100,while under SSP1-2.6,it will stabilize around 2℃ after *** China,most of the areas where warming exceeds global average levels will be located in Tibet and northern China(Northwest China,North China and Northeast China),covering 50%-70%of the ***,about 0.19-0.44 billion people(accounting for 16%-41%of the national population)will experience warming above the global *** to present-day(1995-2014),the warmest day(TXx)will increase most notably in northern China,while the number of warm days(TX90p)and warm spell duration indicator(WSDI)will increase most profoundly in southern *** example,relative to the present-day,TXx will increase by 1℃-5℃ in northern China,and TX90p(WSDI)will increase by 25-150(10-80)days in southern China at 1.5℃-5℃ global *** to 2℃-5℃,limiting global warming to 1.5℃ will help avoid about 36%-87%of the EHT increases in China.

关键词： extreme high temperature China CMIP6 1.5℃-5℃global warming

Essential Norms of Weighted Composition Operators from Weighted Bergman Space to Mixed-norm Space on the Unit Ball

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Acta Mathematica Sinica,English Series 2013年第3期29卷 547-556页

作者： Ze Hua ZHOU Yu Xia LIANG Hong gang zeng Department of Mathematics Tianjin University

In this paper, we characterize the boundedness and compactness of the weighted composi- tion operators from the weighted Bergman space to the standard mixed-norm space or the mixed-norm space with normal weight on the... 详细信息

关键词： Weighted composition operator weighted Bergman space mixed-norm space essentialnorm compact

Remnants and fragments of the subducted paleo-Pacific plate:Constraints from geochemistry and geophysics

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Science China Earth Sciences 2024年第10期67卷 3041-3061页

作者： Xisheng XU Zhouchuan HUANG Dingsheng JIANG gang zeng Li-Qun DAI State Key Laboratory for Mineral Deposits Research School of Earth Sciences and EngineeringNanjing UniversityNanjing 210023China School of Earth and Space Sciences University of Science and Technology of ChinaHefei 230026China

The subduction and rollback of the paleo-Pacific plate during Mesozoic time was the key engine for the evolution of the continental margin in eastern China. It led to lateral accretion of continental crust in Northeast China, lithospheric destruction beneath the North China Craton, and the generation of huge volumes of felsic magmatic rocks in South China. This had a profound influence on deep material cycles and the evolution of epigenetic environmental systems along the continental margin of East Asia. To fully understand the transformation of the dynamic mechanism during the subduction and rollback of the paleoPacific plate, we have attempted to trace the remnants and fragments of the subducted paleo-Pacific plate at great depths. Such remnants in both temporal and spatial dimensions can be tracked by using geochemical and geophysical approaches. Studies of the trace elements, Mg-Zn isotopes and Os-Nd-Hf-Pb-O isotopes in continental basalts from eastern China reveal a significant number of the remnants of subduction of the paleo-Pacific plate, and the initial subduction can be traced back to the Early Jurassic. Large-scale geophysical imaging unveils a multitude of high-velocity anomalies in the lower mantle of East ***, many high-velocity bodies, aptly referred to as “slab graveyards”, are nestled at the base of the lower mantle. Numerous isolated high-velocity anomalies are also present in the upper part of the lower mantle, creating conduits for the descent of the subducted slabs into the lower mantle. However, a resolution of the remnants for the subducted slabs within the lower mantle are quite low. Consequently, their impact on the lower mantle's dynamics is yet to be thoroughly investigated. Finally, the presently observed big mantle wedge(BMW) in East Asia has developed through subduction of the Pacific plate in the ***, following the rollback of the paleo-Pacific plate(began at ~145 Ma), a Cretaceous BMW system would also form above

关键词： Paleo-Pacific plate Big mantle wedge Late Mesozoic Remnants and fragments Geochemistry Geophysics

Regional changes in extreme heat events in China under stabilized 1.5℃ and 2.0℃ global warming

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Advances in Climate Change Research 2020年第3期11卷 198-209页

作者： ZHANG Gu-Wei zeng gang Vedaste IYAKAREMYE YOU Qing-Long Key Laboratory of Meteorological Disaster of Ministry of Education(KLME) Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters(CIC-FEMD)Nanjing University of Information Science and TechnologyNanjing210044China Department of Atmospheric and Oceanic Sciences Institute of Atmospheric SciencesFudan UniversityShanghai200433China

Extreme heat events(EHEs)have a significant impact on the social economy and human *** is a country with a large population and diverse terrain,and it is necessary to project future extreme heat changes in the *** study used a specially designed dataset,the Community Earth System Model(CESM)simulations,namely CESM low-warming,to investigate the EHEs in China under 1.5℃ and 2.0℃ global *** results indicate that the regional mean warming over China will exceed the global average,about 1.63℃ and 2.24℃ in 1.5℃ and 2.0℃ warmer *** to the present-day(1976–2005),the frequency and duration of the EHEs in South China are projected to increase the most among the *** example,the frequency of EHEs in South China at 1.5℃ and 2.0℃ warming will exceed 3 and 3.5 times the present-day ***,when global warming rises from 1.5℃ to 2.0℃,the increased impacts relative to the 1.5℃ warming level will be the lowest in South China(less than 40%),and the highest increased impacts are projected to appear in Northeast China(53%-84%)and Northwest China(53%–107%).The main reason for this situation is that compared with the 1.5℃ scenario,the upper zonal westerly in northern China weakens and the continental high pressure enhances under the 2.0℃ ***,limiting global warming at 1.5℃ instead of 2.0℃ is beneficial for eliminating extreme heat events,especially for Northeast China and Northwest China.

关键词： China Regional changes Extreme heat events 1.5℃and 2.0℃global warming CESM low-warming

Enhanced Grain Refining Effect of Mg–Zr Master Alloy on Magnesium Alloys via a Synergistic Strategy Involving Heterogeneous Nucleation and Solute‑Driven Growth Restriction

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Acta Metallurgica Sinica(English Letters) 2024年第8期37卷 1354-1366页

作者： gang zeng Hong Liu Jing‑Peng Xiong Jian‑Long Li Yong Liu Key Laboratory of Lightweight and High Strength Structural Materials of Jiangxi Province School of Advanced ManufacturingNanchang UniversityNanchang 330031China

Zirconium(Zr)emerges as the most effective grain refiner for magnesium(Mg)alloys incorporating ***,Zr is introduced in the form of an Mg–Zr master ***,within Mg–Zr master alloys,Zr predominantly exists in a particle form,which tends to aggregate due to attractive van der Waals *** clustered Zr is prone to settling,thereby reducing its refining impact on Mg *** this work,a combined pretreatment process for Mg–Zr master alloys was proposed,encompassing the introduction of a physical field to intervene the agglomeration of particle Zr and the employ of high-temperature dissolution and peritectic reactions to promote the solid solution of *** results demonstrate that the particle Zr within the pretreated Mg–Zr master alloy is effectively dispersed and refined,and greater solute Zr levels can be *** subsequent grain refinement ability was studied on a typical Mg–6Zn–0.6Zr(wt%)*** outcome highlights that an improvement in the grain refinement efficacy(32.4%)of Mg–Zr master alloys was obtained with a holding time of 60 *** pretreated Mg–Zr master alloy significantly augments the efficiency of grain refinement for Mg alloys through a synergistic strategy involving heterogeneous nucleation and solute-driven growth *** crucial factor in achieving effective grain refinement of Zr in Mg alloys lies in regulating the presence and morphology of Zr in the Mg–Zr master alloy,distinguishing between particle Zr and solute *** study introduces a novel method for developing more efficient Mg–Zr refiners.

关键词： Magnesium alloy Mg-Zr master alloy Grain refinement Heterogeneous nucleation Solute-driven growth restriction Synergistic strategy

Numerical study on the turbulent mixing of planar shock-accelerated triangular heavy gases interface

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Acta Mechanica Sinica 2018年第5期34卷 855-870页

作者： Wei-gang zeng Jian-Hua Pan Yu-Xin Ren Yu-Tao Sun Department of Engineering Mechanics School of AerospaceTsinghua UniversityBeijing 100084China Institute of Applied Physics and Computational Mathematics Beijing 100094China

The interaction of a planar shock wave with a triangle-shaped sulfur hexafluoride (SF6) cylinder surrounded by air is numerically studied using a high resolution finite volume method with minimum dispersion and controllable dissipation *** vortex dynamics of the Richtmyer-Meshkov instability and the turbulent mixing induced by the KelvinHelmholtz instability are discussed.A modified reconstruction model is proposed to predict the circulation for the shock triangular gas-cylinder interaction *** typical stages leading the shock-driven inhomogeneity flow to turbulent mixing transition are *** the decoupled length scales and the broadened inertial range of the turbulent kinetic energy spectrum in late time manifest the turbulent mixing transition for the present *** analysis of variable-density energy transfer indicates that the flow structures with high wavenumbers inside the Kelvin-Helmholtz vortices can gain energy from the mean flow in ***,small scale flow structures are generated therein by means of nonlinear ***,the occasional 'pairing' between a vortex and its neighboring vortex will trigger the merging process of vortices and,finally,create a large turbulent mixing zone.

关键词： Richtmyer-Meshkov instability Kelvin-Helmholtz instability Length scale Turbulent mixing