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Turbulence and mixing in a freshwater-influenced tidal bay: Observations and numerical modeling

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Science China Earth Sciences 2015年第7期58卷 2049-2058页

作者： LIAN Qiang liu Zhiyu Department of Physical Oceanography College of Ocean & Earth Sciences Xiamen University State Key Laboratory of Marine Environmental Science Xiamen University

In situ observations and numerical simulations of turbulence are essential to understanding vertical mixing processes and their dynamical controls on both physical and biogeochemical processes in coastal embayments. Using in situ data collected by bottom-mounted acoustic Doppler current profilers(ADCPs) and a free-falling microstructure profiler, as well as numerical simulations with a second-moment turbulence closure model, we studied turbulence and mixing in the Xiamen Bay, a freshwater-influenced tidal bay located at the west coast of the Taiwan Strait. Dynamically, the bay is driven predominantly by the M2 tide, and it is under a significant influence of the freshwater discharged from the Jiulong River. It is found that turbulence quantities such as the production and dissipation rates of the turbulent kinetic energy(TKE) were all subject to significant tidal variations, with a pronounced ebb-flood asymmetry. Turbulence was stronger during flood than ebb. During the flooding period, the whole water column was nearly well mixed with the depth-averaged TKE production rate and vertical eddy viscosity being up to 5?10?6 W kg?1 and 2?10?2 m2 s?1, respectively. In contrast, during the ebb strong turbulence was confined only to a 5?8 m thick bottom boundary layer, where turbulence intensity generally decreases with distance from the seafloor. Diagnosis of the potential energy anomaly showed that the ebb-flood asymmetry in turbulent dissipation and mixing was due mainly to tidal straining process as a result of the interaction between vertically shared tidal currents and horizontal density gradients. The role of vertical mixing in generating the asymmetry was secondary. A direct comparison of the modeled and observed turbulence quantities confirmed the applicability of the second-moment turbulence closure scheme in modeling turbulent processes in this weakly stratified tidally energetic environment, but also pointed out the necessity of further refinements of the model.

关键词： tidal bay turbulent mixing second-moment turbulence closure model turbulent kinetic energy dissipation rate vertical eddy viscosity

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NUMERICAL SIMULATION OF MOLTEN POOL AND CONTROL STRATEGy OF KISS POINT IN A TWIN-ROLL STRIP CASTING PROCESS

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Acta Metallurgica Sinica(English Letters) 2008年第6期21卷 459-468页

作者： G.M. Cao C.G. Li Z. y. liu D. Wu G.D. Wang X.H. liu State Key Laboratory of Rolling ＆ Automation Northeastern University Shenyang 110004 China

Coupled turbulent flow, temperature fields of the twin-roll casting strip process were simulated by three-dimensional finite element method. Based on the heat balance calculation and using inverse methods between the simulations and real experiments, the relational models among casting speed, location, and coefficient of heat transfer between molten metal and rolls in different regions are given. In the simulation, the calculated surface temperatures are in good agreement with the measured values. An on-line model of kiss point is derived by simulations and the geometry of molten pool, corresponding control strategy is also proposed.

关键词： Twin-roll strip casting Coupled temperature and flow field Numerical simulation Kiss point Control strategy

ON THE BURN RESISTANCE OF Ti-35V-15Cr-0.05C TITANIUM ALLOy

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Acta Metallurgica Sinica(English Letters) 1998年第3期11卷 202-206页

作者： G.P.Li D.Li y.y.liu Q.J.Wang S.X.Guan Q.C.Li Inst of Metal Research The Chinese Acad of Sciences Shenyang China

The Ti-35V-15Cr-0.05C (wt% is a new nonburning titanium alloy. The test for alloy combustibility was carried out by using CO2 laser. A 430 watt and 6mm diameter laser spot impinges directly on the sample within normal atmospheric pressure and temperature. The results show that the ignition time of the nonburning titanium alloy is the longest in the eight examined titanium alloys, and is 3.5 times that of TC4 alloy. The ignition tempeerature of the nonburning alloy is 2991° C, and is higher than that of TC4 alloy by 1976°C. On the condition of high tempeerature and rich oxygen,the surface of alloy forms a melting layer which plays roles of oxygen insulation, heat insulation and burning products insulation. This is the mechanism of combustion resistance.

关键词： Ti-35V-15Cr-0.05C (wt%) nonburning titanium alloy combustion resistance

Microscopic stresses in carbon nanotube reinforced aluminum matrix composites determined by in-situ neutron diffraction

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Journal of Materials Science & Technology 2020年第19期54卷 58-68页

作者： X.X.Zhang J.F.Zhang Z.y.liu W.M.Gan M.Hofmann H.Andrä B.L.Xiao Z.y.Ma Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China German Engineering Materials Science Centre at MLZ Helmholtz-Zentrum GeesthachtD-85747 GarchingGermany Heinz Maier-Leibnitz Zentrum(MLZ) Technische Universität MünchenD-85747 GarchingGermany Fraunhofer Institute for Industrial Mathematics Fraunhofer-Platz 1Kaiserslautern 67663Germany

One of the most desired strengthening mechanisms in the carbon nanotube reinforced aluminum matrix composites(CNT/Al)composites is the load transfer strengthening mechanism(LTSM).However,a fundamental issue concerning the LTSM is that quantitative measurements of load partitioning in these composites during loading are very *** this study,in-situ neutron diffraction study on the tensile deformation of the 3 vol.%CNT/2009 Al composite and the unreinforced 2009 Al alloy was ***{311}and{220}diffraction elastic constants(DECs)of the 2009 Al alloy were *** those DECs the average stress in the 2009 Al matrix of the composite was *** the average stress in the CNTs was separated by using the stress equilibrium *** homogenization models were also applied to explain the stress evolution in each *** results agree with experimental *** the present case,the average stress in the CNTs reaches 1630 MPa at the yield strength of the composite based on linear regression of the measured data,which leads to an increment of yield strength by about 37 *** the result of this work,an approach to quantify load partitioning in the CNTs is developed for the CNT/Al composites,which can be applied to optimize the mechanical properties of the composites.

关键词： Carbon nanotubes Aluminum matrix composites In-situ neutron diffraction Load partitioning

Single crystal growth, structural and transport properties of bad metal RhSb2

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Chinese Physics B 2020年第3期29卷 1-6页

作者： D S Wu y T Qian Z y liu W Wu y J Li S H Na y T Shao P Zheng G Li J G Cheng H M Weng J L Luo Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100190China Songshan Lake Materials Laboratory Dongguan 523808China

We have successfully grown an arsenopyrite marcasite type RhSb2 single crystal, and systematically investigated its crystal structure, electrical transport, magnetic susceptibility, heat capacity, and thermodynamic properties. We found that the temperature-dependent resistivity exhibits a bad metal behavior with a board peak around 200 K. The magnetic susceptibility of RhSb2 shows diamagnetism from 300 K to 2 K. The low-temperature specific heat shows a metallic behavior with a quite small electronic specific-heat coefficient. No phase transition is observed in both specific heat and magnetic susceptibility data. The Hall resistivity measurements show that the conduction carriers are dominated by electrons with ne = 8.62 × 10^(18) cm^(-3) at 2 K, and the electron carrier density increases rapidly above 200 K without change sign. Combining with ab-initio band structure calculations, we showed that the unusual peak around 200 K in resistivity is related to the distinct electronic structure of RhSb_2. In addition, a large thermopower S(T) about -140 μV/K is observed around 200 K, which might be useful for future thermoelectric applications.

关键词： single crystal growth ab-initio band calculations susceptibility heat capacity thermodynamic transport properties

Adaptive partitioning-based discrete unified gas kinetic scheme for flows in all flow regimes

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Advances in Aerodynamics 2023年第1期5卷 282-311页

作者： L.M.yang L.C.Han H.Ding Z.H.Li C.Shu y.y.liu Department of Aerodynamics College of Aerospace EngineeringNanjing University of Aeronautics and AstronauticsNanjing 210016China State Key Laboratory of Mechanics and Control of Mechanical Structures Nanjing University of Aeronautics and AstronauticsNanjing 210016China Key Laboratory of Unsteady Aerodynamics and Flow Control Ministry of Industry and Information TechnologyNanjing University of Aeronautics and AstronauticsNanjing 210016China Department of Modern Mechanics University of Science and Technology of ChinaHefei 230027China National Laboratory for Computational Fluid Dynamics Beihang UniversityBeijing 100191China Department of Mechanical Engineering National University of SingaporeSingapore 117576Singapore

To improve the efficiency of the discrete unified gas kinetic scheme(DUGKS)in capturing cross-scale flow physics,an adaptive partitioning-based discrete unified gas kinetic scheme(ADUGKS)is developed in this *** ADUGKS is designed from the discrete characteristic solution to the Boltzmann-BGK equation,which contains the initial distribution function and the local equilibrium *** initial distribution function contributes to the calculation of free streaming fluxes and the local equilibrium state contributes to the calculation of equilibrium *** the contribution of the initial distribution function is negative,the local flow field can be regarded as the continuous flow and the Navier-Stokes(N-S)equations can be used to obtain the solution ***,the discrete distribution functions should be updated by the Boltzmann equation to capture the rarefaction *** this,in the ADUGKS,the computational domain is divided into the DUGKS cell and the N-S cell based on the contribu-tion of the initial distribution function to the calculation of free streaming *** the N-S cell,the local flow field is evolved by solving the N-S equations,while in the DUGKS cell,both the discrete velocity Boltzmann equation and the correspond-ing macroscopic governing equations are solved by a modified *** more and more cells turn into the N-S cell with the decrease of the Knudsen number,a significant acceleration can be achieved for the ADUGKS in the continuum flow regime as compared with the DUGKS.

关键词： Boltzmann-BGK equation Discrete unified gas kinetic scheme Adaptive partitioning Discrete characteristic solution All flow regimes

NUCLEATION OF RARE EARTH-RICH PHASE PARTICLES IN Ti-5Al-4Sn-2Zr-1Mo-0.25Si-1Nd ALLOy

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Acta Metallurgica Sinica(English Letters) 1998年第4期11卷 265-269页

作者： G.P.Li D.Li and y. y. liu (Department of Titanium Alloys, Institute of Metal Research, The Chinese Academy of Sciences, Shenyang 110015, China) Inst of Metal Research The Chinese Acad of Sciences Shenyang China

High resolution electron microscopy studies of rure earth-rich phase particles in a melt-quenched Ti-5Al-4Sn-2Zr-1MO-0.25Si-1Nd alloy indicate that the α-Ti matrix crystallizes prior to the rare earth-rich phase particles. According to a new nucleation model, the heteropeneous nucleation of the rare earth-rich phase particles at the matrix interface is easier than the homogeneous nucleation off the interface matrix, which is consistent with the results of the HREM obseroations.

关键词： Ti alloy rure earth rich phase nucleation

Assessment of COVID-19 aerosol transmission in a university campus food environment using a numerical method

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Geoscience Frontiers 2022年第6期13卷 265-278页

作者： M.Zhao C.Zhou T.Chan C.Tu y.liu M.yu Laboratory of Aerosol Science and Technology China Jiliang UniversityHangzhouChina Department of Mechanical Engineering The Hong Kong Polytechnic UniversityKowloonHong KongChina College of Modern Science China Jiliang UniversityHangzhouChina

With the prevalence of COVID-19,the phenomenon of viruses spreading through aerosols has become a focus of *** in university dining halls have a high risk of exposure to respiratory droplets from others without the protection of face masks,which greatly increases the risk of COVID-19 ***,the transmission mechanism of respiratory droplets in extremely crowded dining environments should be *** this study,a numerical simulation of coughing at dining tables under two conditions was performed,namely the presence and absence of protective partitions,and the evaporation and condensation of aerosol droplets in the air were *** using the numerical method,we analyzed and verified the isolation effect of dining table partitions in the propagation of aerosol *** effect of changes in room temperature on the diffusion of coughed aerosols when partitions were present was *** demonstrated how respiratory droplets spread through coughing and how these droplets affect ***,we proposed a design for a dining table partition that minimizes the transmission of COVID-19.

关键词： COVID-19 transmission University dining hall Cough Table partition Computational fluid dynamics

Identifying the shortfalls of crude protein-reduced,wheat-based broiler diets

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Animal Nutrition 2022年第4期11卷 181-189页

作者： Peter H.Selle Shemil P.Macelline Shiva Greenhalgh Peter V.Chrystal Sonia y.liu Poultry Research Foundation Within the University of Sydney Camden 2570NSWAustralia Sydney School of Veterinary Science The University of SydneyCamden 2570NSWAustralia School of Life and Environmental Sciences Faculty of ScienceThe University of SydneyCamperdown 2006NSWAustralia Complete Feed Solutions Pakurangao2140 AucklandNew Zealand

The objective of this review is to identify the shortfalls of wheat-based,crude protein(CP)-reduced diets for broiler chickens as wheat is inferior to maize in this context but to inconsistent *** factors in wheat may be compromising gut integrity;these include soluble non-starch polysaccharides(NSP),amylase trypsin inhibitors(ATI)and *** NSP in wheat induce increased gut viscosities,which can lead to compromised gut integrity,which is not entirely ameliorated by NSP-degrading feed *** ATI probably compromise gut integrity and may also have the capacity to increase endogenous amino acid flows and decrease apparent starch and protein *** inclusions of 20 g/kg in a maize-soy diet depressed weight gain and feed intake and higher gluten inclusions have been shown to activate inflammatory cytokine-related genes in broiler *** research is required,perhaps particularly in relation to wheat *** protein content of wheat is typically higher than maize;importantly,this results in higher inclusions of non-bound amino acids in CP-reduced broiler *** higher inclusions could trigger post-enteral amino acid imbalances,leading to the deamination of surplus amino acids and the generation of ammonia(NH3)which,if not adequately detoxified,results in compromised growth performance from ***,alternatives to nonbound amino acids to meet amino acid requirements in birds offered CP-reduced,wheat-based diets merit *** digestion of wheat starch is more rapid than that of maize starch which may be a disadvantage as the provision of some slowly digestible starch in broiler diets may enhance ***,slowly digestible starch may result in more de novo ***,it may prove instructive to evaluate CP-reduced diets based on maize-wheat and/or sorghum-wheat blends rather than entirely *** would reduce non-bound amino acid inclusions by lowering dietary CP derived

关键词： Biomarkers Broiler chickens Reduced-crude protein diets Wheat