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EXPERIMENTAL STUDY ON THE VORTEX FORMATION AND ENTRAINMENT CHARACTERISTICS FOR A ROUND TRANSVERSE JET IN SHALLOW WATER

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Journal of Hydrodynamics 2009年第3期21卷 386-393页

作者： FAN Jing-yu ZHANG Yan WANG Dao-zeng shanghai Institute of applied Mathematics and mechanics Shanghai University Shanghai 200072 China Key Laboratory of Advanced Display and System Applications Ministry of Education and SMIT Center School of Mechatronics Engineering and Automation Shanghai University Shanghai 200072 China

The vortex formation and entrainment characteristics for a round transverse jet in shallow water were experimentally investigated by means of a combination of LIF flow visualization and PIV measurement. A scarf vortex wrapped around the main body of the jet is formed in the near-wall region due to the interaction between the resulting wall jet and sufficiently shallow crossflow, with some more or less unsteady flow properties and with spreading ranges as functions of both the velocity ratio and the water depth within the near field. The entrainment of the ambient crossflow fluid into the jet main body is closely associated with the time-evolving features of the shear layer between the jet and surrounding fluid as well as the induced vortical structures near the wall. In the case of slight impingement upon the wall, the interaction between the jet shear layer and the weak, unstable scarf vortex gives rise to an appreciable local entrainment enhancement, confined in the near-wall region in the vicinity of the stagnation point. While in the case of intense impingement upon the wall, the well-organized and stable scarf vortex gives rise to a greatly enhanced entrainment and a greatly increased lateral spreading rate nearly throughout the overall near field as compared to the conventional wall jet. In addition, the entrainment of the ambient crossflow fluid by the scarf vortex in this case occurs largely on the surface of the unique spiral roller structure by itself due to the presence of smaller and unorganized eddies, and accordingly the scarf vortex is likely to keep its spiral roller structure steadily to a relatively great downstream distance within the near field.

关键词： transverse jet shallow water vortex formation entrainment PIV measurement

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Simulation of electrically driven jet using Chebyshev collocation method

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Theoretical & applied mechanics Letters 2011年第3期1卷 18-22页

作者： Yan Liu,~(a)) and Ruojing Zhang~(b)) school of aerospace engineering and applied mechanics,tongji university,shanghai 2.0092.china school of aerospace engineering and applied mechanics Tongji University Shanghai 200092 China

The model of electrically driven jet is governed by a series of quasi 1D dimensionless partial differential equations(PDEs).Following the method of lines,the Chebyshev collocation method is employed to discretize the PDEs and obtain a system of differential-algebraic equations(DAEs).By differentiating constrains in DAEs twice,the system is transformed into a set of ordinary differential equations(ODEs) with *** the implicit differential equations solver 'ddaskr' is used to solve the ODEs and post-stabilization is executed at the end of each *** show the distributions of radius,linear charge density,stretching ratio and also the horizontal velocity at a time ***,the spiral and expanding projections to X-Y plane of the jet centerline suggest the occurring of bending instability.

关键词： electrically driven jet method of lines Chebyshev collocation method differential-algebraic equation bending instability

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NUMERICAL SIMULATION OF TWO-DIMENSIONAL DAM-BREAK FLOWS IN CURVED CHANNELS

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Journal of Hydrodynamics 2007年第6期19卷 726-735页

作者： BAI Yu-chuan XU Dong LU Dong-qiang Institute for Sediment on River and Coast 300072 China shanghai Institute of applied Mathematics engineering School of Civil Engineering Tianjin University Tianjin and Mechanics Shanghai University Shanghai 200072 China

Two-dimensional transient dam-break flows in a river with bends were theoretically studied. The river was modeled as a curved channel with a constant width and a flat bottom. The water was assumed to be an incompressible and homogeneous fluid. A channel-fitted orthogonal curvilinear coordinate system was established and the corresponding two-dimensional shallow-water equations were derived for this system. The governing equations with well-posed initial and boundary conditions were numerically solved in a rectangular domain by use of the Godunov-type finite-difference scheme, which can capture the hydraulic jump of dam-break flows. The comparison between the obtained numerical results and the experimental data of Miller and Chaudry in a semicircle channel shows the validity of the present numerical scheme. The mathematical model and the numerical method were applied to the dam-break flows in channels with various curvatures. Based on the numerical results, the influence of river curvatures on the dam-break flows was analyzed in details.

关键词： dam-break flow shallow-water equations,channel bend curvilinear coordinate Godunov-type finite-difference scheme

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超混沌时滞神经网络的同步及其仿真

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系统仿真学报 2010年第3期22卷 626-629,633页

作者：张栋徐鉴同济大学航空航天与力学学院上海200092

时滞神经网络是解空间为无穷维的非线性动力系统,这样的系统可产生具有多个正的Lyapunov指数的超混沌行为。复杂的时间序列使得这类系统特别适用于保密通信中。针对一类时滞超混沌神经网络系统,利用单向耦合同步概念,设计了一个非线性... 详细信息

时滞神经网络是解空间为无穷维的非线性动力系统,这样的系统可产生具有多个正的Lyapunov指数的超混沌行为。复杂的时间序列使得这类系统特别适用于保密通信中。针对一类时滞超混沌神经网络系统,利用单向耦合同步概念,设计了一个非线性控制器,并通过Lyapunov-Krasovskii方法和Halanay不等式引理分别给出了系统渐进同步和指数同步的与时滞无关的充分条件。通过引入控制矩阵正定的条件,避免了繁复的LMI计算,简化了控制过程。数值仿真验证了该方法的有效性,数值计算给出了指数同步率和控制参数的关系。

关键词：超混沌同步时滞神经网络 L-K方法 Halanay不等式引理保密通信

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SIMULATION OF LAGRANGIAN DISPERSION USING A LAGRANGIAN STOCHASTIC MODEL AND DNS IN A TURBULENT CHANNEL FLOW

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Journal of Hydrodynamics 2009年第6期21卷 767-773页

作者： LUO Jian-ping LU Zhi-ming LIU Yu-lu school of Mechanical and Automation engineering Shanghai Institute of Technology Shanghai 200235 China shanghai Institute of applied Mathematics and mechanics Shanghai University Shanghai 200072 China

The mean square displacements of fluid particles in a turbulent channel flow at Reτ = 100 are investigated using a modified Langevin equation, and are compared with DNS results. Both the Lagrangian integral time scales directly obtained from DNS and the predicted values using an empirical relation between the Eulerian and the Lagrangian integral time scales are used in the modified Langevin equation to test the effects of integral time scales on the dispersion of particles. The results show that the slight variation of the Lagrangian integral time scale has little influence on the dispersion. The agreement between results of the model equation and those of DNS is satisfactory except the streamwise dispersion for intermediate times （ 20 〈 t^＋〈 300 ）, where the results of the model equation are slightly overestimated compared to those of DNS. The cause of such discrepancy is discussed.

关键词： turbulent channel flow Lagrangian dispersion Lagrangian stochastic model

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