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非光滑表面离心泵叶轮的流动减阻特性

上海交通大学学报 2016年第2期50卷 306-312页

作者：牟介刚代东顺谷云庆刘剑郑水华 wang evan 浙江工业大学机械工程学院杭州310014 约瑟夫傅立叶大学格勒诺布尔国立综合理工学院法国格勒诺布尔38031

为了分析非光滑表面对离心泵性能的影响,基于仿生凹坑表面的减阻特性,将凹坑型非光滑单元体排布于离心泵叶片的工作面,建立具有非光滑表面的叶轮离心泵的流动减阻特性分析模型,通过RNGk-ε湍流模型对离心泵内部流场进行数值模拟,分析具... 详细信息

为了分析非光滑表面对离心泵性能的影响,基于仿生凹坑表面的减阻特性,将凹坑型非光滑单元体排布于离心泵叶片的工作面,建立具有非光滑表面的叶轮离心泵的流动减阻特性分析模型,通过RNGk-ε湍流模型对离心泵内部流场进行数值模拟,分析具有非光滑表面叶轮的流动减阻特性,研究不同流量下非光滑表面对叶片近壁面的速度分布、剪应力和离心泵内部流场的影响.结果表明:凹坑型非光滑表面能够降低因黏性阻力产生的叶轮扭矩,其扭矩的最大降幅为5.8%;非光滑表面能够有效控制叶片近壁面边界层的流体流动,减小叶片的壁面剪应力;凹坑型非光滑表面能够降低离心泵叶轮内部流体的湍动程度,减小湍动产生的能量耗散,使叶轮内部的流体流动更加稳定并提高离心泵的效率.

关键词：离心泵非光滑表面减阻边界层

Characteristics and mechanism investigation on drag reduction of oblique riblets

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Journal of Central South University 2017年第6期24卷 1379-1386页

作者： GU Yun-qing FAN Tian-xing MOU Jie-gang WU Deng-hao ZHENG Shui-hua College of Mechanical and Engineering Zhejiang University of TechnologyHangzhou 310014China Zhijiang College Zhejiang University of TechnologyHangzhou 310024China Institute National Polytechnique of Grenoble Joseph Fourier UniversityGrenoble 38031France

This work primarily focuses on the drag reduction characteristics and mechanism investigation of oblique riblets. First, a calculation model of the oblique riblets surface is established, and Reynolds stress model(RSM) turbulence model is used for numerical simulation of the oblique riblets flow field. Subsequently, the influence of inclination angle between flow direction and arrangement direction of riblets on friction resistance and drag reduction rate is further analyzed. Through the investigation of the distribution of shear stress, pressure stress and velocity in oblique riblets boundary layer, the oblique riblets drag reduction mechanism is finally revealed. Results show that, with increase of velocity and inclination angle, the pressure resistance increases obviously, along with the decreasing of the viscous resistance distinctly. The maximum drag reduction rate of the oblique riblets is 7.33%. Moreover, when the inclination angle increases, the wall shear stress reduces on oblique riblets surface; while differential pressure increases at both sides of oblique riblets tips. In addition, when inclination angle is small, the secondary vortex at oblique riblets tips will disappear soon. New vortices will be formed inside the oblique riblets and cause the decrease of viscosity resistance. Thus, oblique riblets show a better drag reduction effect and have an effective control on boundary layer.

关键词： oblique riblets drag reduction Reynolds stress model (RSM) secondary vortex numerical simulation

Predicting the synthesizability of crystalline inorganic materials from the data of known material compositions

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npj Computational Materials 2023年第1期9卷 733-743页

作者： evan R.Antoniuk Gowoon Cheon George wang Daniel Bernstein William Cai evan J.Reed Materials Science Division Physical and Life Sciences DirectorateLawrence Livermore National LaboratoryLivermoreCAUSA Department of Chemistry Stanford UniversityStanfordCAUSA Department of Applied Physics Stanford UniversityStanfordCAUSA Google Research Mountain ViewCAUSA Department of Physics Stanford UniversityStanfordCAUSA Department of Mathematics Stanford UniversityStanfordCAUSA Department of Computer Science Stanford UniversityStanfordCAUSA Department of Materials Science and Engineering Stanford UniversityStanfordCAUSA

Reliably identifying synthesizable inorganic crystalline materials is an unsolved challenge required for realizing autonomous materials *** this work,we develop a deep learning synthesizability model(SynthNN)that leverages the entire space of synthesized inorganic chemical *** reformulating material discovery as a synthesizability classification task,SynthNN identifies synthesizable materials with 7×higher precision than with DFT-calculated formation *** a head-to-head material discovery comparison against 20 expert material scientists,SynthNN outperforms all experts,achieves 1.5×higher precision and completes the task five orders of magnitude faster than the best human ***,without any prior chemical knowledge,our experiments indicate that SynthNN learns the chemical principles of charge-balancing,chemical family relationships and ionicity,and utilizes these principles to generate synthesizability *** development of SynthNN will allow for synthesizability constraints to be seamlessly integrated into computational material screening workflows to increase their reliability for identifying synthetically accessible materials.

关键词： inorganic crystalline utilize

An index for deformation controllability of small-volume materials

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Science China(Technological Sciences) 2014年第4期57卷 663-670页

作者： wang ZhangJie SHAN ZhiWei LI Ju SUN Jun MA evan Center for Advancing Materials Performance from the Nanoscale CAMP-Nano) & Hysitron Applied Research Center in China (HARCC) State Key Laboratory for Mechanical Behavior of Materials Xi'an Jiaotong University Department of Nuclear Science and Engineering and Department of Materials Science and Engineering Massachusetts Institute of Technology Department of Materials Science and Engineering Johns Hopkins University

Mechanical tests on small-volume materials show that in addition to the usual attributes of strength and ductility, the controlla- bility of deformation would be crucial for the purpose of precise plastic shaping. In our present work, a ＂mechanical controlla- bility index＂（MCI） has been proposed to assess the controllability of mechanical deformation quantitatively. The index allows quantitative evaluation of the relative fraction of the controllable plastic strain out of the total strain. MCI=0 means completely uncontrollable plastic deformation, MCI=∞ means perfectly controllable plastic shaping. The application of the index is demonstrated here by comparing two example cases： 0.273 to 0.429 for single crystal A1 nanopillars that exhibit obvious strain bursts, versus 3.17 to 4.2 for polycrystalline A1 nanopillars of similar size for which the stress-strain curve is smoother.

关键词： mechanical controllability index plastic deformation strain bursts nanomechanics

In-situ surface transformation of magnesium to protect against oxidation at elevated temperatures

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Journal of Materials Science & Technology 2020年第9期44卷 48-53页

作者： Yuecun wang Meng Li Yueqing Yang Xin’ai Zhao evan Ma Zhiwei Shan Center for Advancing Materials Performance from the Nanoscale(CAMP-Nano)&Hysitron Applied Research Center in China(HARCC) State Key Laboratory for Mechanical Behavior of MaterialsXi’an Jiaotong UniversityXi’an710049China Department of Materials Science and Engineering Johns Hopkins UniversityBaltimore21218MDUSA

The native oxide thin scale on magnesium(Mg)surface appears continuous and crack-free,but cannot protect the Mg matrix from further oxidation,especially at elevated *** thermal oxidation process is witnessed in its entirety using a home-made in-situ heating device inside an environmental electron transmission *** proposed,and verified with real-time experimental evidence,that transforming the native oxide scale into a thin continuous surface layer with high vacancy formation energy(low vacancy concentration),for example MgCO3,can effectively protect Mg from high-temperature oxidation and raise the threshold oxidation temperature by at least two hundred degrees.

关键词： Magnesium Thermal oxidation In-situ E-TEM Carbonation Oxidation inhibition

Predicting the propensity for thermally activated β events in metallic glasses via interpretable machine learning

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npj Computational Materials 2020年第1期6卷 46-57页

作者： Qi wang Jun Ding Longfei Zhang Evgeny Podryabinkin Alexander Shapeev evan Ma Department of Materials Science and Engineering Johns Hopkins UniversityBaltimoreMD 21218USA Center for Advancing Materials Performance from the Nanoscale(CAMP-Nano) State Key Laboratory for Mechanical Behavior of MaterialsXi’an Jiaotong UniversityXi’an 710049China Department of Computer Science Johns Hopkins UniversityBaltimoreMD 21218USA Center for Energy Science and Technology Skolkovo Institute of Science and Technology3 Nobel StreetMoscow 143026Russia

The elementary excitations in metallic glasses(MGs),i.e.,β processes that involve hopping between nearby sub-basins,underlie many unusual properties of the amorphous alloys.A high-efficacy prediction of the propensity for those activated processes from solely the atomic positions,however,has remained a daunting ***,employing well-designed site environment descriptors and machine learning(ML),notable progress has been made in predicting the propensity for stress-activated β processes(i.e.,shear transformations)from the static structure.

关键词： structure glasses metallic

The effects of elevated ozone and CO_(2) on growth and defense of native,exotic and invader trees

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Journal of Plant Ecology 2018年第2期11卷 266-272页

作者： Hong wang Ling Zhang Xiaochi Ma Jianwen Zou evan Siemann College of Resource and Environment Anhui Science and Technology University168 Shungeng RoadChuzhou 233100China College of Resources and Environmental Sciences Nanjing Agricultural UniversityNo.1 WeigangNanjing 210095China College of Forestry Jiangxi Agricultural University1225 Zhimin AvenueNanchang 330045China Department of Biosciences Rice University6100 Main StreetHoustonTX 77005USA

Aims Elevated ozone and CO_(2) can differentially affect the performance of plant *** among native,exotic and invader spe-cies in their growth and defense responses to CO_(2) and ozone may shape CO_(2) and ozone effects on invasions,perhaps in part also due to variation between native and invasive populations of *** We manipulated ozone(control or 100 ppb)and CO_(2)(ambient or 800 ppm)in a factorial greenhouse experiment in replicated *** investigated growth and defense(tannins)of seedlings of Triadica sebifera from invasive(USA)and native(China)populations and pairs of US and China tree species within three genera(Celtis,Liquidambar and Platanus).Important Findings Overall,ozone reduced growth in ambient CO_(2) but elevated CO_(2) limited this *** plants from invasive populations had higher growth than those from native populations in control con-ditions or the combination of elevated CO_(2) and ozone in which invasive populations had greater increases in *** perfor-mances were similar in elevated CO_(2) because native populations were more responsive and their performances were similar with elevated ozone because invasive populations were more *** to other species,*** had high growth rates but low levels of tannin production that were insensitive to vari-ation in CO_(2) or *** China and US Platanus plants reduced tannins with increased CO_(2) and/or ozone and US Liquidambar plants increased tannins with the combination of elevated CO_(2) and *** growth results suggest that intraspecific variation in *** will reduce the effects of CO_(2) or ozone alone on inva-sions but increase their combined *** tannin results suggest that defense responses to CO_(2) and ozone will be variable across native and exotic *** effects of CO_(2) and ozone on growth and defense of native and exotic species indicate that the benefit or harm to species from these global

关键词： global change intraspecific variation invasions tannins Triadica sebifera

Soil Respiration and Litter Decomposition Increased Following Perennial Forb Invasion into an Annual Grassland

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Pedosphere 2016年第4期26卷 567-576页

作者： ZHANG Ling MA Xiaochi wang Hong LIU Shuwei evan SIEMANN ZOU Jianwen College of Forestry Jiangxi Agricultural University College of Resources and Environmental Sciences Nanjing Agricultural University Department of Ecology and Evolutionary Biology Rice University

Exotic plant invasions may alter ecosystem carbon processes, especially when native plants are displaced by plants of a different functional group. Forb invasions into grasslands are common, yet little is known about how they impact carbon cycling. We conducted a field study over 2 years from April 2010 to March 2012 in China to examine changes in soil respiration （Rsoil） following invasion of exotic perennial forb species （Alternanthera philoxeroides or Solidago canadensis） into an annual grassland dominated by a native annual graminoid （Eragrostis pilosa）. Measurements of Rsoil were taken once a week in stands of the native annual graminoid or one of the forb species using static chamber-gas chromatograph method. Aboveground litterfall of each of the three focal species was collected biweekly and litter decomposition rates were measured in a 6-month litterbag experiment. The monthly average and annual cumulative Rsoil increased following invasion by either forb species. The increases in cumulative Rsoil were smaller with invasion of Solidago （36%） than Alternanthera （65%）. Both invasive forbs were associated with higher litter quantity and quality （e.g., C：N ratio） than the native annum graminoid. Compared to the native annual graminoid, the invasive forbs Altevnanthera （155%） and Solidago （361%） produced larger amounts of more rapidly decomposing litter, with the litter decay constant k being 3.8, 2.0 and 1.0 for Alternanthera, Solidago and Eragrostis, respectively. Functional groups of the invasive plants and the native plants they replaced appear to be useful predictors of directions of changes in Rsoil, but the magnitude of changes in Rsoil seems to be sensitive to variations in invader functional traits.

关键词： carbon cycling exotic plant functional group functional traits invasive plants litterfall native plants

UV-B has larger negative impacts on invasive populations of Triadica sebifera but ozone impacts do not vary

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Journal of Plant Ecology 2016年第1期9卷 61-68页

作者： Hong wang Xiaochi Ma Ling Zhang evan Siemann Jianwen Zou College of Resources and Environmental Sciences Nanjing Agricultural UniversityNanjing 210095China Department of Biosciences Rice UniversityHoustonTX 77005USA College of Forestry Jiangxi Agricultural UniversityNanchang 330045China

Aims Abiotic stresses may interact with each other to determine impacts on plants so that their combined impact is less than or more than *** UV-B radiation and surface ozone(O3)are two major components of global change that may have such interactive ***,invasive and native populations of plants may respond differently to stresses as they can vary in primary and secondary *** Here,we conducted a factorial field experiment with open-top chambers assigned to an ozone treatment(ambient,100 ppb,or 150 ppb)and UV-B treatment(ambient or increased 20%).We grew seedlings of native and invasive populations of Triadica sebifera in these chambers for one growing *** Findings Invasive plants grew faster than native plants in ambient UV-B but they did not differ significantly in elevated *** production of invasive plants was especially sensitive to UV-B in a way that increased with UV-B for native plants but decreased for invasive plants which may be important for nutrient *** ambient UV-B,total mass decreased as ozone *** mass was lower with elevated UV-B but there was no additional impact of increasing *** area did not decrease with UV-B so SLA and LAR were lowest at ambient ozone *** results suggest that the effects of ozone will depend on UV-B conditions perhaps due to changes in foliar *** traits that allow invasive populations of plants to be successful invaders may make them especially sensitive to UV-B which may reduce their success in future climatic conditions.

关键词： invasive UV-B O3 cross-tolerance litter