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Science china(Technological Sciences) 2010年第12期53卷 3232-3240页

作者： MU YunFei & JIA HongJie key laboratory of Power System Simulation and Control of ministry of education, tianjin university, tianjin 300072, china key laboratory of Power System Simulation and Control of ministry of education Tianjin University

A new approach to determining the local boundaries of voltage stability region in power injection space (IVSR) for power system with wind farms is presented. It can be used for power system voltage stability analysis and on-line security assessment with considering the output uncertainty of the wind farms. Firstly, power flow tracing and double dispatching are used to determine the generators that are closely related to the wind farms, in order to balance the power fluctuations caused by the wind speed variation. Then, modal analysis is used to get the key generators to achieve an effective dimension reduction for IVSR. Finally, the forecasting output power (or wind speed) of wind farms is divided into several intervals. For each interval, the corresponding local IVSR boundaries can be calculated by the method based on small disturbance. Moreover, parallel process is used to accelerate the computing speed. The presented approach is validated by several power systems. It can be revealed that the approach can give the local IVSR boundaries at different wind speeds and has a good engineering application prospect.

关键词： voltage stability region power flow tracing modal analysis parallel process

In situ synthesis and phase analysis of low density O'-sialon-based multiphase ceramics

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Rare Metals 2010年第2期29卷 214-219页

作者： XU Xiongwen, LIANG Hui, LI Xiaolei, JI Huiming, LU Huixiang, and WAN Yizao key laboratory for Advanced Ceramics and Machining Technology(ministry of education), tianjin university, tianjin 300072, china key laboratory for Advanced Ceramics and Machining Technology (ministry of education) Tianjin University

In situ formed low density O＇-sialon-based multiphase ceramics were prepared by liquid-phase sintering method at 1400°C with Si3N4, SiO2 and Al2O3 as raw *** phases were identified by X-ray diffraction（XRD）.The quantitative phase analysis was finished by matrix-flushing method and the substitution parameter x value of O＇-sialon was *** effects of sintering additives on the phase composition of the material were *** results show that, when using Y2O3 alone, Al6Si2O13 phase can be formed in the material, but when using Y2O3 and MgO, MgAl2O4 phase can be preferentially formed and the Al6Si2O13 is not *** mechanical properties of the material were measured and the relationships between microstructure and mechanical properties were *** sample with Y2O3 and MgO sintering additives, using fused quartz alone as SiO2 source, displays a combination of high bending strength（163 MPa） and good fracture toughness（3.11 MPa·m1/2）.Bending strength and fracture toughness of the samples increase with the increase of the content and aspect ratio of elongated grains and decrease with the increase of the porosity.

关键词： ceramics sialon phase analysis bending strength fracture toughness

Second mode unstable disturbance measurement of hypersonic boundary layer on cone by wavelet transform

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Acta Mechanica Sinica 2011年第4期27卷 488-493页

作者： Jian Han.Nan Jiang.Yan Tian Department of Mathematics,tianjin university,300072 tianjin,china Department of Mechanics,tianjin university,300072 tianjin,china tianjin key laboratory of Modern Engineering Mechanics,300072 tianjin,china State key laboratory of Nonlinear Mechanics,Institute of Mechanics,Chinese Academy of Sciences,100190 Beijing,china Department of Mathematics Tianjin University Tianjin China Department of Mechanics Tianjin University Tianjin China tianjin key laboratory of Modern Engineering Mechanics Tianjin China State key laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences Beijing China

Experimental investigation of hypersonic boundary layer instability on a cone is performed at Mach number 6 in a hypersonic wind tunnel. Time series signals of instantaneous fluctuating surface-thermal-flux are measured by Pt-thin-film thermocouple temperature sensors mounted at 28 stations on the cone surface in the streamwise direction to investigate the development of the unstable disturbance. Wavelet transform is employed as a mathematical tool to obtain the multi-scale characteristics of fluctuating surfacethermal-flux both in the temporal and spectrum space. The conditional sampling algorithm using wavelet coefficient as an index is put forward to extract the unstable disturbance waveform from the fluctuating surface-thermal-flux *** generic waveform for the second mode unstable disturbance is obtained by a phase-averaging technique. The development of the unstable disturbance in the streamwise direction is assessed both in the temporal and spectrum space. Our study shows that the local unstable disturbance detection method based on wavelet transformation offers an alternative powerful tool in studying the hypersonic unstable mode of laminar-turbulent transition. It is demonstrated that, at hypersonic speeds, the dominant flow instability is the second mode, which governs the course of laminar-turbulent transition of sharp cone boundary layer.

关键词： Hypersonic boundary layer. Sharp cone Insta-bility Wavelet transform

The reliability of the improved e^N method for the transition prediction of boundary layers on a flat plate

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Science china(Physics,Mechanics & Astronomy) 2012年第5期55卷 837-843页

作者： SU CaiHong1,2 1 Department of Mechanics,tianjin university,tianjin 300072.china 2 tianjin key laboratory of Modern Engineering Mechanics,tianjin 300072.china tianjin university Department of Mechanics Tianjin China (GRID:grid.33763.32) (ISNI:***) tianjin key laboratory of Modern Engineering Mechanics Tianjin China (GRID:grid.33763.32)

The transition criterion in the improved eN method is that transition would occur whenever the velocity amplitude of disturbance reaches 1%-2% of the free stream velocity,while in the conventional eN method,the N factor is an empirical *** this paper the reliability of this key assumption in the improved eN method is checked by results of transition prediction by using the Parabolized Stability Equations(PSE).Transition locations of an incompressible boundary layer and a hypersonic boundary layer at Mach number 6 on a flat plate are predicted by both the improved eN method and the PSE *** from both methods agree fairly well with each other,implying that the transition criterion proposed in the improved eN method is reliable.

关键词： transition prediction boundary layer eN PSE

Integrated modeling of nitrogen oxides formation in diesel engines

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Progress in Natural Science:Materials International 2007年第12期17卷 1476-1481页

作者： Song Jinou, Yao Chunde and Wang Hongfu(State key laboratory of Engine, tianjin university, tianjin 300072, china) State key laboratory of Engine Tianjin University Tianjin 300072 China

To account for the effects of both chemistry and flow turbulence, the present study proposes an integrated NO sub-model that combines the extended Zel’dovich mechanism and engine CFD computations to simulate the NO histories in a diesel engine. NOx sub-model parameters and pollutant formation mechanisms can be more easily investigated by solving the NOx sub-model. The new NO formation model incorporating the effects of both chemical kinetics and turbulent mixing was applied to simulate a diesel engine with a quiescent combustion chamber, and one with a re-entrant combustion chamber; the premise of the model being the reaction rate is mainly determined by a kinetic timescale and a turbulent timescale. The results indicate that the predicted NO formulation from the new model agrees well with the measured data. As the utilization of fossil fuels continues to increase, the control of NOx emissions is a worldwide concern; and it is imperative to understand fully the NOx reaction processes in combustion systems. This technology has the potential to enhance the application of various combustion techniques used to reduce NOx emissions from practical combustion systems.

关键词： nitrogen oxides (NOx) combustion turbulence diesel.

HYDRODYNAMICS OF FRACTAL FLOCS DURING SETTLING

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Journal of Hydrodynamics 2009年第3期21卷 347-351页

作者： ZHANG Jin-feng ZHANG Qing-he School of Civil Engineering Key Laboratory of Harbour and Ocean Engineering Ministry of Education Tianjin University Tianjin 300072 China Department of Ocean and Resources Engineering University of Hawaii at Manoa HI 96822 USA

The settling and hydrodynamic properties of 3-D fractal flocs in quiescent water are investigated with a numerical model based on the Lattice Boltzmann Method （LBM）, with considering the settling velocity, hydrodynamic drag force and infra-floc flow. The comparisons of floc settling velocities and effective densities indicate that the numerical results present good agreements with observations in field and at laboratory. The results show that the drag force Fo increases with the floc size dr according to the relationship FD ∝ df^3. Moreover, the intra-floc flow field and movement of the pore water provide a better understanding of the intra-floc flow from the microscopic viewpoint. The results also indicate that the lattice Boltzmann method is a promising approach to reveal the mechanisms of the flocculation in aquatic environments.

关键词： Lattice Boltzmann Method (LBM) fractal floc hydrodynamic properties drag force infra-floc flow

Clustering behavior of solid particles in two-dimensional liquid-solid fluidized-beds

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Particuology 2007年第5期5卷 305-311页

作者： Xiaodong Ana, Mingyan Liua,b,, Yunguan Fua a School of Chemical Engineering and Technology, tianjin university, tianjin 300072, china b State key laboratory of Chemical Engineering, tianjin university, tianjin 300072, china School of Chemical Engineering and Technology Tianjin University Tianjin 300072 China State key laboratory of Chemical Engineering Tianjin University Tianjin 300072 China

In this paper, the clustering behavior of solid particles in a two-dimensional (2D) liquid-solid fluidized-bed was studied by using the charge coupled devices (CCD) imaging measuring and processing technique and was characterized by fractal analysis. CCD images show that the distribution of solid particles in the 2D liquid-solid fluidised-bed is not uniform and self-organization behavior of solid particles was observed under the present experimental conditions. The solid particles move up in the 2D fluidized-bed in groups or clusters whose configurations are often in the form of horizontal strands. The box fractal dimension of the cluster images in the 2D liquid-solid fluidized-bed increases with the rising of solid holdup and reduces with the increment of solid particle diameter and superficial liquid velocity. At given solid holdup and solid particle size, the lighter particles show smaller fractal dimensions.

关键词： CCD Liquid–solid ?uidized-bed Fractal dimension Cluster Self-organization structure

Surface Motion of Alluvial Valley in Layered Half-Space for Incident Plane P-Waves

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Transactions of tianjin university 2011年第3期17卷 157-165页

作者：巴振宁梁建文 School of Civil Engineering Tianjin University key laboratory of Coast Civil Structure Safety of ministry of education

The indirect boundary element method (IBEM) is used to study the surface motion of an alluvial valley in layered half-space for incident plane P-waves based on Wolf’s theory. Firstly, the free field response can be solved by the direct stiffness method, and the scattering wave response is calculated by Green’s functions of distributed loads acting on inclined lines in a layered half-space. The method is verified by comparing its results with literature and numerical analyses are performed by taking the amplification of incident plane P-waves by an alluvial valley in one soil layer resting on bedrock as an example. The results show that there exist distinct differences between the wave amplification by an alluvial valley embedded in layered half-space and that in homogeneous half-space and there is interaction between the valley and the soil layer. The amplitudes are relatively large when incident frequencies are close to the soil layer’s resonant frequencies.

关键词： layered half-space alluvial valley plane P-waves scattering one layer over bedrock indirect boundaryelement method

Piezoelectric Actuator/Sensor Wave Propagation Based Nondestructive Active Monitoring Method of Concrete Structures

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Journal of Wuhan university of Technology(Materials Science) 2011年第3期26卷 541-547页

作者：朱劲松 School of Civil Engineering Tianjin University key laboratory of Coast Civil Structure Safety(tianjin university) Ministry of Education

In order to monitor the basic mechanical properties and interior damage of concrete structures,the piezoelectric actuator/sensor based wave propagation method was investigated experimentally in the laboratory using a specifically designed test *** energy attenuation of stress waves was measured by the relative index between the output voltage of sensors and the excitation voltage at the *** on the experimental results of concrete cube and cylinder specimens,the effect of excitation frequencies,excitation amplitude,wave propagation paths and the curing age on the output signals of sensors are *** results show that the relative voltage attenuation coefficient RVAC is an effective indicator for measuring the attenuation of stress waves through the interior of concrete.

关键词： piezoceramics actuator/sensor wave propagation method non-destructive evaluation (NDE) active monitoring concrete

Dynamic security risk assessment and optimization of power transmission system

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Science china(Technological Sciences) 2008年第6期51卷 713-723页

作者： YU YiXin1 & WANG DongTao1,2 1 key laboratory of Power System Simulation and Control of ministry of education, tianjin university, tianjin 300072, china 2 School of Computer & Automation, Hebei Polytechnic university, Tangshan 063009, china key laboratory of Power System Simulation and Control of ministry of education Tianjin University School of Computer & Automation Hebei Polytechnic University

The paper presents a practical dynamic security region (PDSR) based dynamic security risk assessment and optimization model for power transmission system. The cost of comprehensive security control and the influence of uncertainties of power injections are considered in the model of dynamic security risk assessment. The transient stability constraints and uncertainties of power injections can be considered easily by PDSR in form of hyper-box. A method to define and classify contingency set is presented, and a risk control optimization model is given which takes total dynamic insecurity risk as the objective function for a dominant con-tingency set. An optimal solution of dynamic insecurity risk is obtained by opti-mizing preventive and emergency control cost and contingency set decomposition. The effectiveness of this model has been proved by test results on the New Eng-land 10-genarator 39-bus system.

关键词： power transmission system risk assessment dynamic security practical dynamic security region (PDSR) comprehensive security control optimization