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Chinese Journal of Aeronautics 2014年第5期27卷 1312-1317页

作者： bai Jiangbo Xiong Junjiang School of Transportation Science and Engineering Beihang University

This paper seeks to outline the temperature effect on the buckling properties of ultra-thin-walled lenticular collapsible composite tube（LCCT） subjected to axial *** buckling tests of the LCCT specimens subjected to axial compression were carried out on INSTRON-500 N servo-hydraulic machine in dry state and at the temperatures of 25 C, 100 C and 80 C. The load–displacement curves and buckling initiation loads were measured and the buckling initiation mechanism was discussed from experimental observations. Experiments show that the buckling initiation load, on average, is only about 2.2% greater at the low temperature of 80 C than at the room temperature of 25 C due to the material hardening, demonstrating an insignificant increase in the buckling initiation load, whereas it is about 19.5% lower at the high temperature of 100 C than at the room temperature owing to the material softening, implying a significant decrease in the buckling initiation load. The failure mode of the LCCT in axial compression tests at three different temperatures can be reckoned to be characteristic of the buckling initiation and propagation around the central region until rupture. The finite element（FE） model is presented to simulate the buckling initiation mechanism based on the eigenvalue-based methodology. Good correlation between experimental and numerical results is achieved.

关键词： Axial compression Buckling Composite Finite element analysis Lenticular collapsible tube

Numerical study of regional environmental carrying capacity for livestock and poultry farming based on planting-breeding balance

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Journal of Environmental Sciences 2013年第9期25卷 1882-1889页

作者： Lihong Peng Yu bai College of the Environment & Ecology Xiamen University

In consideration of the need to maintain planting-breeding balance, this article examines the capacity of the soil in Putian City, Fujian Province to absorb livestock and poultry excreta, and computes the environmental carrying capacity for livestock and poultry farming （ECCLPF） in each district of the city in terms of the fertility characteristics of the soil in the city, as well as its mix of crops cultivated and farming methods. On the basis of the computations, this work proceeds to classify the alarm grades of the city＇s environmental carrying capacity for livestock and poultry framing, and assess the environmental impact of the livestock and poultry farming industry. The results of our study indicate that, the city＇s ECCLPF ranges from 8.27 to 23.23 heads per ha when computed on the basis of nitrogen, and from 5.79 to 24.53 heads per ha when computed on the basis of phosphorus. A comparison between our research findings and the existing farming scale in Putian reveals that, in certain parts of the city, ECCLPF is overburdened to varying degrees. Specifically, Chengxiang District is severely overburdened, Hanjiang District and Meizhou Island have a level of overburdening between virtual overburdening and significant overburdening, Licheng District is virtually overburdened, and Xiuyu, Xianyou, and Bei＇an Districts have not exceeded their environmental carrying capacity and therefore have varying levels of potential for growth.

关键词： livestock and poultry farming planting-breeding combination nitrogen and phosphorus balance alarm classification system

Protective Properties of High Temperature Oxide Films on Ni-based Superalloys in 3.5% NaCl Solution

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Journal of Materials Science & Technology 2007年第4期23卷 541-546页

作者： Huiping bai Fuhui WANG State Key Laboratory for Corrosion and Protection Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China

The electrochemical behaviors of high temperature oxide film formed on the sputtered microcrystalline coating of M38 alloy （mc-M38） were investigated by potentiodynamic and electrochemical impedance spectroscopy （EIS） techniques in 3.5% NaCl solution. Mott-Schottky analysis was used to study the semi-conductive properties of the surface oxide. The results of the capacitance measurements showed that the oxide films on both the coating and the cast alloy were p-type semiconducting characteristics. Both the carrier density （Na）and the flat band potential （Efb） were obviously frequency-dependent, and the optimal frequency range was from 1000 to 1500 Hz. The oxidized coating exhibited higher protectivity than the oxidized cast alloy due to the lower carrier density compared with that of the oxidized cast alloy. The EIS data of the long-term immersing tests suggested that the oxide film served as an inner-barrier layer against chloride ions. The penetration of the aggressive ions into the surface oxide resulted in the decreased polarization resistance as a function of the immersion time.

关键词： High temperature oxide film Protective properties EIS Mott-Schottky analysis

Realization of the global yield mechanism of RC frame structures by redesigning the columns using column tree method

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Science China(Technological Sciences) 2015年第10期58卷 1627-1637页

作者： bai JiuLin OU JinPing School of Civil Engineering Harbin Institute of Technology Key Lab of Structures Dynamic Behavior and Control (Harbin Institute of Technology) Ministry of Education

Global failure mechanism, i.e., the strong-column weak-beam mechanism, can provide higher total energy dissipation capacity with less ductility demand on components than other failure modes, and results in a more uniform story drift distribution and higher resistance to earthquake loads at the system level. However, the current code-based elastic design method cannot guarantee the global failure mechanism of frame structures under severe earthquakes. In this paper, a simple, but practical design procedure is proposed to ensure the global failure mechanism of reinforced concrete(RC) frame structures by redesigning the columns using the column tree method(CTM). CTM considers the yield limit state of all beams and column bases. The code-based design is firstly carried out to determine the section information of all beams and base columns. Then, the internal force demands applied on the column tree can be derived. Lastly, the column moments, shear forces and axial forces are determined according to the free-body diagram of CTM to finish the column redesign. Two RC frame structures with 6 and 12 stories are illustrated to verify the design procedure. The analytical results demonstrate the proposed approach can realize the global failure mechanism.

关键词： global failure mechanism column tree method (CTM) reinforced concrete frame structures failure mode plastic hinges

Hypersonic starting flow at high angle of attack

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Chinese Journal of Aeronautics 2016年第2期29卷 297-304页

作者： bai Chenyuan Wu Ziniu Department of Engineering Mechanics Tsinghua University

Compressible starting flow at small angle of attack （AoA） involves small amplitude waves and time-dependent lift coefficient and has been extensively studied before. In this paper we consider hypersonic starting flow of a two-dimensional flat wing or airfoil at large angle of attack involving strong shock waves. The flow field in some typical regions near the wing is solved analytically. Simple expressions of time-dependent lift evolutions at the initial and final stages are given. Numerical simulations by compuational fluid dynamics are used to verify and complement the theoretical results. It is shown that below the wing there is a straight oblique shock （OSW） wave, a curved shock wave （CSW） and an unsteady horizontal shock wave （USW）, and the latter moves perpendicularlly to the wing. The length of these three parts of waves changes with time. The pres- sure above OSW is larger than that above USW, while across CSW there is a significant drop of the pressure, making the force nearly constant during the initial period of time. When, however, the Mach number is very large, the force coefficient tends to a time-independent constant, proportional to the square of the sine of the angle of attack.

关键词： Hypersonic Normal force Shock waves Starting flow Unsteady flow

Theoretical analyses on hydrodynamic instability in narrow deep river with variable curvature

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Applied Mathematics and Mechanics(English Edition) 2015年第9期36卷 1147-1168页

作者： Haijue XU Yuchuan bai State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin University Institute for Sedimentation on River and Coastal Engineering Tianjin University

Bending river is the most common river type in nature, and it is also a typical example for river evolution. The transform of the flow pattern can affect the development of the riverbed form. In return, the variation in the riverbed form can affect the hydrodynamic characteristics of the flow, thereby leading to the continuous evolution of the bending river. Based on this, a theoretical model for the bending river is established. The hydrodynamic instability characteristics of the laminar flow in the channel with a variable curvature, a typical and the variations of some parameters such wave frequency are also discussed. model as the meandering river, are studied, as the curvature, the wave number, and the

关键词： bending river hydrodynamic stability self-adaptability nonlinear riverdynamics

New Neural Network Response Surface Methods for Reliability Analysis

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Chinese Journal of Aeronautics 2011年第1期24卷 25-31页

作者： REN Yuan bai Guangchen School of Jet Propulsion Beijing University of Aeronautics and Astronautics Beijing 100191 China

This article presents two new kinds of artificial neural network （ANN） response surface methods （RSMs）： the ANN RSM based on early stopping technique （ANNRSM-1）, and the ANN RSM based on regularization theory （ANNRSM-2）. The following improvements are made to the conventional ANN RSM （ANNRSM-0）： 1） by monitoring the validation error during the training process, ANNRSM-1 determines the early stopping point and the training stopping point, and the weight vector at the early stopping point, which corresponds to the ANN model with the optimal generalization, is finally returned as the training result; 2） according to the regularization theory, ANNRSM-2 modifies the conventional training performance function by adding to it the sum of squares of the network weights, so the network weights are forced to have smaller values while the training error decreases. Tests show that the performance of ANN RSM becomes much better due to the above-mentioned improvements： first, ANNRSM-1 and ANNRSM-2 approximate to the limit state function （LSF） more accurately than ANNRSM-0; second, the estimated failure probabilities given by ANNRSM-1 and ANNRSM-2 have smaller errors than that obtained by ANNRSM-0; third, compared with ANNRSM-0, ANNRSM-1 and ANNRSM-2 require much fewer data samples to achieve stable failure probability results.

关键词： neural networks response surface reliability analysis early stopping regularization

Characteristics of organic and elemental carbon in atmospheric fine particles in Tianjin,China

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Particuology 2009年第6期7卷 432-437页

作者： Weifang Li Zhipeng bai State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control College of Environmental Science and Engineering. Nankai University Tianjin 300071 China Institute of New Energy Material Chemistry College of Chemistry Nankai University Tianjin China

PM2.5 samples were collected at urban, industrial and coastal sites in Tianjin during winter, spring and summer in 2007. Concentrations of elemental carbon （EC） and organic carbon （OC） were analyzed using the IMPROVE thermal-optical reflectance （TOR） method. Both OC and EC exhibited a clear seasonal pattern with higher concentrations observed in the winter than in the spring and summer, due to cooperative effect of changes in emission rates and seasonal meteorology. The concentrations of carbonaceous species were also influenced by the local factors at different sampling sites, ranking in the order of industrial〉 urban 〉 coastal during winter and spring. In the summer, the port emissions, enriched with EC, had a significant impact on carbonaceous aerosols at the coastal site. Total carbonaceous aerosol accounted for 40.0% in winter, 33.8% in spring and 31.4% in summer of PM2.5 mass. Good correlation （R = 0.84-0.93） between OC and EC indicated that they had common dominant sources of combustion such as coal burning and traffic emissions. The daily average OC/EC ratios ranged from 2.1 to 9.1, the elevated OC/EC ratios being found in the winter. The estimated secondary organic carbon （SOC） accounted for 46.9%, 35.3% and 40.2% of the total OC in the winter, spring and summer, respectively, indicating that SOC may be an important contributor to fine organic aerosol in Tianjin.

关键词： PM2.5 Organic carbon Elemental carbon Secondary organic carbon Tianjin

Molecular sieving through a graphene nanopore： non-equilibrium molecular dynamics simulation

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Science Bulletin 2017年第8期62卷 554-562页

作者： Chengzhen Sun Bofeng bai State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

Two-dimensional graphene nanopores have shown great promise as ultra-permeable molecular sieves based on their size-sieving effects. We design a nitrogen/hydrogen modified graphene nanopore and conduct a transient non-equilibrium molecular dynamics simulation on its molecular sieving effects. The distinct time-varying molecular crossing numbers show that this special nanopore can efficiently sieve CO_2 and H_2S molecules from CH_4 molecules with high selectivity. By analyzing the molecular structure and pore functionalization-related molecular orientation and permeable zone in the nanopore, density distribution in the molecular adsorption layer on the graphene surface, as well as other features, the molecular sieving mechanisms of graphene nanopores are revealed. Finally, several implications on the design of highly-efficient graphene nanopores, especially for determining the porosity and chemical functionalization, as gas separation membranes are summarized based on the identified phenomena and mechanisms.

关键词： Graphene nanopore Molecular sieve Molecular dynamics Gas separation membrane

ON THE CONVERGENCE OF THE RELAXATION METHODS FOR POSITIVE DEFINITE LINEAR SYSTEMS

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Journal of Computational Mathematics 1998年第6期16卷 527-538页

作者： bai, ZZ Huang, TZ Chinese Acad Sci ICMSEC Beijing 100080 Peoples R China Univ Elect Sci & Technol China Dept Appl Math Chengdu 610054 Peoples R China

We establish the convergence theories of the symmetric relaxation methods for the system of linear equations with symmetric positive definite coefficient matrix, and more generally, those of the unsymmetric relaxation... 详细信息

关键词： system of linear equations relaxation method convergence theory positive definite matrix