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Numerical anatomy of lock-release gravity current

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Communications in Nonlinear science and Numerical Simulation 2001年第4期6卷 183-192页

作者： Lizhu ZHANG, Yiran AN, Zhi LI, G. Q. CHEN and Joseph H. W. LEE department of mechanics and {2. science / state key laboratory for Studies of turbulence and complex systems, peking university, beijing 100871,{12. e-mail: zhlzh@*** De Dept. of mechanics and Eng. science State Key Lab. Studs. T./C.S. Peking University Beijing 100871 China department of Civil engineering University of Hong Kong Hong Kong Hong Kong

Gravity currents created by releasing a fixed fluid into a less dense fluid are simulated numerically by using the renormalization group (RNG) k-ε. model for Reynolds-stress closure and a two-layer function as near wall treatment. A numerical anatomy of the gravity currents is made to characterize the concentration contour, velocity vector diagram, velocity profile, distribution of turbulent kinetic energy. streaklines and entrainment. Computed velocity structure of the current head explains why the front velocity decreases after the current advances about twelve lock lengths.

关键词： gravity current numerical simulation. environmental hydraulics

A method for exploring some new solutions of complex lamellar flow

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Communications in Nonlinear science and Numerical Simulation 2000年第1期5卷 17-20页

作者： Xin HU Yongnian HUANG and Yi ZENG department of mechanics and {2. science, state key laboratory for turbulence Research, peking university, beijing 100871, china Basic department, Jiaotong {12. of Eastern china, Nanchang 330013, china Dept. of mechanics and Eng. science State Key Lab. for Turbulence Res. Peking University Beijing 100871 China Basic department Jiaotong University of Eastern China Nanchang 330013 China

complex lamellar flow is a typical flow in fluid mechanics. Its research has high theoretical value. Generally speaking, there are only two typical flows in nature: one is Beltrami flow, the other is complex lamellar flow. We have known much about the former. But the solutions of the latter are hard to obtain because it is difficult to solve the N-S equation or Euler equation. From the incompressible condition, if we let the form of the velocity satisfy some special conditions, we would obtain some new solutions of this flow.

关键词： Beltrami flow complex lamellar flow exact solution incompressible condition

Stabilization of the systems with Quadratic Constraint Uncertainties

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Stabilization of the Systems with Quadratic Constraint Uncer...

第二十四届中国控制会议

作者： Zhiyong Geng state key {2. for turbulence and complex systems and department of mechanics and engineering science, peking university, beijing, {12., china

＜正＞ In this paper, a convex parameterization methodology is presented for the problem of robust stabilization of the systems with quadratic constraint uncertainties. By this approach, the robust stabilization problem is converted to a convexly parameterized robust SPR synthesis problem. To solve this convexly parameterized robust SPR synthesis problem, the S-procedure is used to convert the problem to finding the feasible solutions of frequency dependent LMIs which can be solved by combining the techniques of griding the frequency range to get a limited number of LMIs and using KYP lemma to check the feasibility of the solutions.

关键词： Robust stabilization Convex parameterization Structured uncertainties LMIs

ROBUSTNESS ANALYSIS OF LEADER-FOLLOWER CONSENSUS

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Journal of systems science & {2.ity 2009年第2期22卷 186-206页

作者： Jinzhi WANG Ying TAN · Iven MAREELS state key {2. for turbulence and complex System and department of mechanics and Aerospace Engi-neering College of Engineering Peking University Beijing 100871 China. Departmen~ of Electrical and Electronic engineering University of Melbourne Melbourne VIC. 3010 Aus-tralia.

In this paper,robustness properties of the leader-follower consensus are *** of presentation,the attention is focused on a group of continuous-time first-order dynamicagents with a time-invariant communication topology in the presence of communication *** orderto evaluate the robustness of leader-follower consensus,two robustness measures are proposed:the L_2.ain of the error vector to the state of the network and the worst case L_2.gain at a *** L_2.gain of the error vector to the state of the network is widely used in robust control design andanalysis,the worst case L_2.gain at a node is less conservative with respect to the number of nodes inthe *** is thus suggested that the worst case L_2.gain at a node is used when the robustnessof consensus is *** analysis and simulation results show that these two measuresare sensitive to the communication *** general,the 'optimal' communication topology thatcan achieve most robust performance with respect to either of the proposed robustness measures isdifficult to characterize and/or *** the in-degree of each follower is one,it is shown thatboth measures reach a minimum when the leader can communicate to each node in the network.

关键词： Communication errors leader-follower consensus robustness.

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Numerical simulation of air-water two-phase flow over stepped spillways

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science china(Technological sciences) 2006年第6期49卷 674-684页

作者： CHENG Xiangju1, CHEN Yongcan1 & LUO Lin2.1. department of Hydraulic engineering, Tsinghua {2., beijing 100084, china 2. state key laboratory of Hydraulics and Mountain River engineering, Sichuan {2., Chengdu 610065, china department of Hydraulic engineering Tsinghua University Beijing 100084 China state key {2. of Hydraulics Mountain River engineering Sichuan University Chengdu 610065 China

Stepped spillways for significant energy dissipation along the chute have gained interest; popularity among researchers; dam engineers. Due to the complexity of air-water two-phase flow over stepped spillways, the finite volume computational fluid dynamics module of the FLUENT software was used to simulate the main characteristics of the flow. Adopting the RNG k- turbulence model, the mixture flow model for air-water two-phase flow was used to simulate the flow field over stepped spillway with the PISO arithmetic technique. The numerical result successfully reproduced the complex flow over a stepped spillway of an experiment case, including the interaction between entrained air bubbles; cavity recirculation in the skimming flow regime, velocity distribution; the pressure profiles on the step surface as well. The result is helpful for understanding the detailed information about energy dissipation over stepped spillways.

关键词： stepped spillway, mixture model, RNG k-εmodel, air-water two-phase flow.

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A new numerical method on unstructured grids

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science china(Physics,{2. & Astronomy) 2009年第12期52卷 2016-2026页

作者： WU WangYi & XIE WenJun state key {2. for turbulence and complex System,department of mechanics and Aerospace engineering,College of En-gineering,peking university,beijing 100871,{12.

A new numerical method-basic function method is proposed. This method can directly discrete differential operators on unstructured grids. By using the expansion of basic function to approach the exact function,the central and upwind schemes of derivative are constructed. By using the polynomial as basic function,applying the technique of flux splitting method and the combination of central and upwind schemes,the non-physical fluctuation near the shock wave is suppressed. The first-order basic function scheme of polynomial type for solving inviscid compressible flow numerically is constructed in this paper. Several numerical results of many typical examples for one-,two-and three-dimensional inviscid compressible steady flow illustrate that it is a new scheme with high accuracy and high resolution for shock wave. Especially,combining with the adaptive remeshing technique,the satisfactory results can be obtained by these schemes.

关键词： basic function scheme new numerical method unstructured grids

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Robust dichotomy for nonlinear uncertain systems

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Robust dichotomy for nonlinear uncertain systems

第2.届中国控制会议

作者： Wang Jinzhi, Duan Zhisheng, Huang Lin The state key {2. for turbulence and complex systems and department of mechanics and engineering science, peking university, beijing 100871

＜正＞In this paper, properties of dichotomy for nonlinear systems with norm-bounded uncertainty are considered. By using some results of H∞, theory and method of linear matrix inequality （LMI） some criterions of testing robust dichotomy of uncertain nonlinear systems are given. A approach of designing {2. feedback controller guaranteeing dichotomy of closed loop systems with norm-bounded uncertainty is proposed. The given results are applied to Chua’s circuit. A numerical algorithm of designing a controller guaranteeing dichotomy of the closed-loop system is presented which enlarges the range of some parameters.

关键词： Uncertain nonlinear systems Robust dichotomy H∞ norm Linear matrix inequality.

An Approach to Formation Maneuvers of Multiple Nonholonomic Agents using Passivity Techniques

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An Approach to Formation Maneuvers of Multiple Nonholonomic ...

2.09中国控制与决策会议

作者： Wu Fan,Geng Zhiyong The state key {2. for turbulence and complex systems, department of mechanics and Aerospace engineering,peking university,beijing {12.

＜正＞This paper studies the problem of formation maneuver of multiple nonholonomic agents.A dynamic feedback linearization method is used to transform each agent’s dynamic model into two chains of 3rd order *** a decentralized discontinuous formation control law with inter-agent damping injection is *** stability of the overall system is proved by using Lyapunov *** proposed algorithm is applied to a nonholonomic multi-vehicles formation maneuver simulation,which shows the effectiveness of our strategy.

关键词： Multiple nonholonomic agents Formation Full-state linearization Passivity

Special Decentralized Control Problems in Discrete-time Interconnected systems Composed of Two Subsystems

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Special Decentralized Control Problems in Discrete-time Inte...

第2.届中国控制会议

作者： Duan Zhisheng, Wang Jinzhi, Huang Lin state key {2. for turbulence and complex systems and department of mechanics and engineering science peking university, beijing 100871

＜正＞In this paper, some special decentralized control problems are addressed for discrete-time interconnected systems. First it is pointed out that some subsystems must be unstable to ensure stability of the overall system in some special cases. Then a special kind of decentralized control problem is studied. This kind of problem can be viewed as harmonic control among independent subsystems. Research results show that two unstable systems can generate a stable system through some effective cooperations. In addition, linear matrix inequality based based decentralized controller design method is also given by using parameter-dependent Lyapunov function method developed for the study of robust stability. Two examples are given to illustrate the results.

关键词： Interconnected systems Decentralized control Parameter-dependent Lyapunov function (PDLF) Linear matrix inequality (LMI)