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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

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

Convection and correlation of coherent structure in turbulent boundary layer using tomographic particle image velocimetry

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Chinese Physics B 2014年第10期23卷 323-333页

作者：王维管新蕾姜楠 Department of mechanics Tianjin University tianjin key laboratory of modern engineering mechanics The State key laboratory of Nonlinear mechanics Institute of Mechanics Chinese Academy of Sciences

The present experimental work focuses on a new model for space-time correlation and the scale-dependencies of convection velocity and sweep velocity in turbulent boundary layer over a flat wail. A turbulent boundary layer flow at Reo = 2460 is measured by tomographic particle image velocimetry （tomographic PIV）. It is demonstrated that arch, cane, and hairpin vortices are dominant in the logarithmic layer. Hairpins and hairpin packets are responsible for the elongated low-momentum zones observed in the instantaneous flow field. The conditionally-averaged coherent structures systemically illustrate the key roles of hairpin vortice in the turbulence dynamic events, such as ejection and sweep events and energy transport. The space-time correlations of instantaneous streamwise fluctuation velocity are calculated and confirm the new elliptic model for the space-time correlation instead of Taylor hypothesis. The convection velocities derived from the space-time correlation and conditionally-averaged method both suggest the scaling with the local mean velocity in the logarithmic layer. Convection velocity result based on Fourier decomposition （FD） shows stronger scale- dependency in the spanwise direction than in streamwise direction. Compared with FD, the proper orthogonal decomposition （POD） has a distinct distribution of convection velocity for the large- and small-scales which are separated in light of their contributions of turbulent kinetic energy.

关键词： turbulent boundary layer tomographic particle image velocimetry space-time correlation ellipticmodel

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

Corrosion science general-purpose data model and interface (I): Meanings and issues of design and implementation

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Science china(Technological Sciences) 2008年第9期51卷 1394-1401页

作者： TANG ZiLong School of Materials Science and engineering, tianjin University, tianjin 300072, china School of Materials Science and engineering Tianjin University Tianjin China

A brand new design of integrated corrosion information system is introduced to meet the constantly increasing demands of material corrosion information. Two concepts, "general-purpose corrosion data model" and "public corrosion data ex-changing interface", are suggested to integrate a wide variety of corrosion data sources based on detailed analysis on characteristics of each source in order to promote the information sharing and data mining. The architecture of integrated corrosion information environment is blueprinted. The insight analysis is focused on 1) architecture of the system; 2) data flow and information sharing; 3) roles of system players and their interactions; 4) approaches to data integration. Several key issues are addressed in detail including coverage of data model, data source integration and mitigation, and data granularity from system performance and model acceptance points of view. At the end, the design and implementation ap-proach of general corrosion data model is presented based on cutting edge IT techniques.

关键词： corrosion multi-source data modeling integrated information system

An approach to determining the local boundaries of voltage stability region with wind farms in power injection space

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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 Tianjin China

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

Diffraction of plane SV waves by a cavity in poroelastic half-space

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Earthquake engineering and engineering Vibration 2009年第1期8卷 29-46页

作者： Liang Jianwen and Liu Zhongxian Department of Civil engineering, tianjin University, tianjin 300072, china Professor PhD Candidate Department of Civil engineering Tianjin University Tianjin China

This paper presents an indirect boundary integration equation method for diffraction of plane SV waves by a 2-D cavity in a poroelastic *** Green＇s functions of compressive and shear wave sources are derived based on Biot＇s theory. The scattered waves are constructed using fictitious wave sources close to the boundary of the cavity, and their magnitudes are determined by the boundary conditions. Verification of the accuracy is performed by：（1） checking the satisfaction extent of the boundary conditions, （2） comparing the degenerated solutions of a single-phased case with well- known solutions, and （3） examining the numerical stability of the solutions. The nature of diffraction of plane SV waves around a cavity in a poroelastic half-space is investigated by numerical examples.

关键词： poroelastic half-space cavity diffraction plane SV waves compressive wave source shear wave source Green's function pore pressure

Influence of moisture content and time on the mechanical behavior of polymer material

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Science china(Technological Sciences) 2004年第5期47卷 595-607页

作者： ZHENG Gaofei1, 2, KANG Yilan1, SHENG Jing3, QIN Qinghua1, WANG Huaiwen1 & FU Donghui1 1. Department of mechanics, tianjin University, tianjin 300072, china 2. Department of mechanics, tianjin Polytechnic University, tianjin 300160, china 3. Department of Material engineering, tianjin University, tianjin 300072, china Correspondence should be addressed to Kang Yilan Department of mechanics Tianjin University Tianjin China Department of mechanics Tianjin Polytechnic University Tianjin China Department of Material engineering Tianjin University Tianjin China

The effects of moisture content and time on mechanical behavior of polymer materials are investigated both theoretically and experimentally in this paper. An equivalence relationship between time intervals and the moisture content for polymer nylon-6 has been established by way of experimental observation and measured results. The relationship shows that there exists equivalence between moisture and service time in affecting mechanical properties. In other words, an increase in moisture can be replaced by prolonging acting time in producing the same effect on material properties. Consequently, a moisture-time superposition principle is presented based on the experimental results and the analogy of temperature-time superposition principle. Numerical results such as stress-strain curves with different moisture contents are presented to verify the applicability and correctness. The proposed method appears very promising in study on the effect of moisture content on mechanical behavior of polymer materials.

关键词： equivalence relationship of moisture-time, moisture content, mechanical properties, shift function.

Progress of synthesizing methods and properties of fluorinated carbon nanotubes

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Science china(Technological Sciences) 2010年第5期53卷 1225-1233页

作者： LI Yu1,2,CHEN YanFang1,2,FENG YiYu1,2,ZHAO ShengLing1,2,Lü Peng1,2,YUAN XiaoYan1,2 & FENG Wei1,2 1School of Materials Science and engineering,tianjin University,tianjin 300072,china 2tianjin key laboratory of Composite and Functional Materials,tianjin 30072,china School of Materials Science and engineering Tianjin University Tianjin China tianjin key laboratory of Composite and Functional Materials Tianjin China

In this paper,the recent development of fluorinated carbon nanotubes(F-CNTs) was *** synthesizing methods of F-CNTs,including direct fluorination and plasma treatment,were discussed in detail,and the effects of factors,such as the temperature and pressure in fluorination as well as the kind of fluorine source and carbon nanotubes,on the structures and properties of F-CNTs were also *** the mean time,the special physical and chemical properties of F-CNTs and the relevant applied fields were described briefly,the exisiting problems of F-CNTs were summed up,and the direction of future development was also discussed in the end.

关键词： carbon nanotubes fluorination plasma treatment fluorinated carbon nanotubes substitution reaction