检索结果-南通市图书馆

Science china Mathematics 2005年第Z1期48卷 392-399页

作者： ZHOU Zehua & CHE renyu Department of Mathematics, tianjin university, tianjin 300072, china LiuHui Center for Applied Mathematics, nankai university & tianjin university,tianjin 300072, china Department of Mathematics Tianjin University Tianjin China LiuHui Center for Applied Mathematics Nankai University & Tianjin University Tianjin China

In this paper we first look upon some known results on the composition operator as bounded or compact on the Bloch-type space in polydisk and ball, and then give a sufficient and necessary condition for the compositio... 详细信息

关键词： Bloch space, bounded symmetric domains, composition operator, bergman metric.

Inflow conditions for spatial direct numerical simulation of turbulent boundary layers

在线全文

学校读者我要写书评

暂无评论

Science china(physics,Mechanics & Astronomy) 2008年第8期51卷 1106-1115页

作者： HUANG ZhangFeng & ZHOU Heng Department of Mechanics,tianjin university,tianjin 300072,china Liu-Hui Center of Applied Mathematics,nankai university and tianjin university,tianjin 300072,china Department of Mechanics Tianjin University Tianjin China Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University Tianjin China

The inflow conditions for spatial direct numerical simulation(SDNS) of turbulent boundary layers should reflect the characteristics of upstream turbulence,which is a puzzle. In this paper a new method is suggested,in which the flow field obtained by using temporal direct numerical simulation(TDNS) for fully developed turbulent flow(only flow field for a single moment is sufficient) can be used as the inflow of SDNS with a proper transformation. The calculation results confirm that this method is feasible and effective. It is also found that,under a proper time-space transformation,all statistics of the fully developed turbulence obtained by both temporal mode and spatial mode DNS are in excellent agreement with each other,not only qualitatively,but also quantitatively. The normal-wise distributions of mean flow profile,turbulent Mach number and the root mean square(rMS) of the fluctuations of various variables,as well as the reynolds stresses of the fully developed turbulence obtained by using SDNS,bear similarity in nature.

关键词： inflow conditions spatial direct numerical simulation turbulent boundary layer similarity

Stochastic DEA model with undesirable outputs: An application to the prediction of anti-HIV therapy efficiency

在线全文

学校读者我要写书评

暂无评论

progress in Natural Science:Materials International 2006年第7期16卷 753-759页

作者： BIAN Fuping and TANG Xiaoqin ( Department of Mathematics, School of Science, tianjin university, tianjin 300072, china Liuhui institute of Applied Mathematics, nankai university and tianjin university, tianjin 300072, china) tianjin Univ Sch Sci Dept Math Tianjin 300072 Peoples R China nankai Univ Liuhui Inst Appl Math Tianjin 300072 Peoples R China

This paper proposes a stochastic prediction DEA model with undesirable outputs and simplifies the process using chance-constrained techniques in order to obtain an equivalent linear programming formulation. The existence and stability of the optimal solutions have been proved. And the model is used to describe and predict the efficiency of anti-HIV therapy in AIDS patients.

关键词： data envelopment analysis (DEA) decision making units (DMU) undesirable outputs stochastic DEA model anti-HIV therapy.

Transition prediction for supersonic and hypersonic boundary layers on a cone with angle of attack

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Science china(physics,Mechanics & Astronomy) 2009年第8期52卷 1223-1232页

作者： SU CaiHong1 & ZHOU Heng1,2 1 Department of Mechanics,tianjin university,tianjin 300072,china 2 Liu-Hui Center of Applied Mathematics,nankai university and tianjin university,tianjin 300072,china Department of Mechanics Tianjin University Tianjin China Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University Tianjin China

Transition prediction for boundary layers has always been one of the urgent problems waiting for a solution for the development of aero-space technology,yet there is no reliable and effective method due to the complexity of the *** eN method has been regarded as an effective method for the transition prediction of boundary ***,it heavily relies on experiment or *** in cases with three-dimensional base flow,for instance,the boundary layer on a cone with angle of attack,the result of its application is not *** authors have found its cause and proposed the method for its improvement,which did yield the fairly satisfactory result for a given test case,and also did not rely so much on experiment or ***,before people can really apply this method to practical problems,more test cases have to be *** this paper,more test cases for the application of the improved eN method to problems of transition prediction of supersonic and hypersonic boundary layers on cones with angle of attack will be *** results are compared with those obtained by experiments and/or direct numerical simulations,confirming that the improved eN method is effective and *** also find that there may be more than one ZArF for each meridian plane,and which one should be chosen for the eN method has been clarified.

关键词： angle of attack cone boundary layer transition eN method

Transition prediction of a hypersonic boundary layer over a cone at small angle of attack——with the improvement of e^N method

在线全文

学校读者我要写书评

暂无评论

Science china(physics,Mechanics & Astronomy) 2009年第1期52卷 115-123页

作者： SU CaiHong1 & ZHOU Heng1,2 1 Department of Mechanics, tianjin university, tianjin 300072, china 2 Liu-Hui Center of Applied Mathematics, nankai university and tianjin university, tianjin 300072, china Department of Mechanics Tianjin University Tianjin China Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University Tianjin China

The problem of transition prediction for hypersonic boundary layers over a sharp cone has been studied in this work. The Mach number of the oncoming flow is 6, the cone half-angle is 5°, and the angle of attack is 1°. The conventional e N method is used, but the transition location so obtained is obviously incorrect. The reason is that in the conventional method, only the amplifying waves are taken into account, while in fact, for different meridians the decay processes of the disturbances before they begin to grow are different. Based on our own previous work, new interpretation and essential improvement for the e N method are proposed. Not only the amplification process but also the decay process is considered. The location, where by linear stability theory, the amplitude of disturbance wave is amplified from its initial small value to 1%, is considered to be the transition location. The new result for transition prediction thus obtained is found to be fairly satisfactory. It is also indicated that for the calculation of base flow, boundary layer equations can be used for a small angle of attack. Its computational cost is much smaller than those for DNS.

关键词： angle of attack cone transition eN method

Search for B_c (ns) via the B_c (ns) → B_c (ms) π^+ π^- transition at LHCb and Z^0 factory

在线全文

学校读者我要写书评

暂无评论

Science china(physics,Mechanics & Astronomy) 2010年第11期53卷 2019-2024页

作者： KE HongWei 1 & LI XueQian 2 1 School of Science,tianjin university,tianjin 300072,china 2 School of physics,nankai university,tianjin 300071,china School of Science Tianjin University Tianjin China School of physics Nankai University Tianjin China

It is interesting to study the characteristics of the whole family of B c which contains two different heavy *** and the proposed Z 0 factory provide an opportunity because a large database of the B c family will be achieved.B c and its excited states can be identified via their decay *** suggested by experimentalists,B-c (ns) → B c +γ is not easy to be clearly measured,instead,the trajectories of π + and π- occurring in the decay of B c (ns) → B c (ms) + π + π( n > m ) can be unambiguously identified,thus the measurement seems easier and more reliable;therefore this mode is more favorable at the early running stage of LHCb and the proposed Z 0 *** this work,we calculate the rate of B c (ns) → B c (ms) + π + π-in terms of the QCD multipole-expansion and the numerical results indicate that the experimental measurements with the luminosity of LHC and Z 0 factory are feasible.

关键词： meson hadronic decay QCD multipole-expansion

The mechanism of breakdown in laminar-turbulent transition of a supersonic boundary layer on a flat plate-temporal mode

在线全文

学校读者我要写书评

暂无评论

Science china(physics,Mechanics & Astronomy) 2005年第5期48卷 614-625页

作者： HUANG Zhangfeng 1, CAO Wei 1,2 & ZHOU Heng 1,2 1. Department of Mechanics, tianjin university, tianjin 300072, china 2. Liu-Hui Center of Applied Mathematics, nankai university and tianjin university, tianjin 300072, china Department of Mechanics Tianjin University Tianjin China Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University Tianjin China

Temporal mode direction numerical simulation has been done for the transition of a supersonic boundary layer on a flat plate with Mach number 4.5. Analysis of the result showed that during the breakdown process in laminar-turbulent transition, the mechanism causing the mean flow profile to evolve swiftly from laminar to turbulent was that the modification of mean flow profile by the disturbances,when they became larger,led to a remarkable change of its stability characteristics. Though the most unstable T-S wave was of second mode for laminar flow, the first mode waves played the key role in the breakdown process in laminar-turbulent transition.

关键词： supersonic boundary layer, transition, breakdown.

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

在线全文

学校读者我要写书评

暂无评论

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

Direct numerical simulation of a supersonic turbulent boundary layer on a flat plate and its analysis

在线全文

学校读者我要写书评

暂无评论

Science china(physics,Mechanics & Astronomy) 2005年第5期48卷 626-640页

作者： HUANG Zhangfeng1, ZHOU Heng1,2 & LUO Jisheng1,2 1. Department of Mechanics, tianjin university, tianjin 300072, china 2. Liu-Hui Center of Applied Mathematics, nankai university and tianjin university, tianjin 300072, china Department of Mechanics Tianjin University Tianjin China Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University Tianjin China

Temporal mode direct numerical simulation (DNS) has been done for a supersonic turbulent boundary layer on a flat plate with Mach number 4.5. It was found that the mean flow profile, the normal-wise distribution of turbulent Mach number and the root mean square (rMS) of the fluctuations of various variables, as well as the reynolds stresses, bore similarity in nature, when the turbulence reached a fully developed state. But the compressibility effect was strong and must be considered. The strong reynolds analogy (SrA) and the Morkovin hypothesis were no longer valid. From the end of transition to the fully developed state of turbulence, it was in the transient period, for which the similarity did not hold.

关键词： turbulence, similarity, compressibility effect, supersonic boundary layer, direct numerical simulation.