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Some open problems in granular matter mechanics

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Progress in Natural Science:Materials International 2009年第5期19卷 523-529页

作者： Qicheng Sun a, Guangqian Wanga, Kaiheng Hub a department of Hydraulic Engineering, State Key Laboratory for Hydroscience and Engineering, Tsinghua University, beijing 100084, china b Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, china [a]department of Hydraulic Engineering State Key Laboratory for Hydroscience and Engineering Tsinghua University Beijing 100084 China [b]Institute of Mountain Hazards and Environment Chinese Academy of Sciences Chengdu 610041 China

Granular matter is a large assemblage of solid particles, which is fundamentally different from any other type of matters, such as solid and liquid. Most models presented for granular matter are phenomenological and are only suitable for solving engineering problems. Many fundamental mechanical problems remain open. by analyzing characteristics of internal state structure, we propose that granular matter is intrinsically multiscale, i.e. microscale of particle size, mesoscale of force chain, and macroscale of the bulk of granular matter. The correlations among difference scales would be crucial. The mesoscale force chain network is determined by both particle properties and macroscopic boundary conditions. The evolution of the force the chain network contributes to macroscopic mechanical properties of granular matter. In addition, we discuss the drawbacks in simplifying contact forces in the current models, and the difficulties in analyzing the interaction of interstitial fluid in wet granular matter. As an appropriate application of granular matter, debris flow can be studied with granular matter mechanics; meanwhile, debris flow brings more challenges which certainly motivate future studies on granular matter.

关键词： Granular matter Multiscale mechanics Force chain Contact mechanics Debris flow

A NUMERICAL STUDY OF THE TRAIN-INDUCED UNSTEADY AIRFLOW IN A SUbWAY TUNNEL WITH NATURAL VENTILATION DUCTS USING THE DYNAMIC LAYERING METHOD

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Journal of Hydrodynamics 2010年第2期22卷 164-172页

作者： HUANG Yuan-dong GAO Wei KIM Chang-Nyung department of Environmental Engineering University of Shanghai for Science and Technology Shanghai 200093China department of mechanical Engineering Kyung Hee University Yongin 449-701 Korea Industrial Liaison Research Institute Kyung Hee University Yongin 449-701 Korea

The objective of this study is to investigate numerically the characteristics of train-induced unsteady airflow in a subway tunnel with natural ventilation ducts.A three-dimensional numerical model using the dynamic layering method for the moving boundary of a train is first developed,and then it is validated against the model tunnel experimental *** the tunnel and subway train geometries in the numerical model exactly the same as those in the model tunnel experimental test,but with the ventilation ducts being connected to the tunnel ceiling and a barrier placed at the tunnel outlet,the three-dimensional train-induced unsteady tunnel flows are numerically *** computed distributions of the pressure and the air velocity in the tunnel as well as the time series of the mass flow rate at the ventilation ducts reveal the impact of the train motion on the exhaust and suction of the air through ventilation ducts and the effects of a barrier placed at the tunnel outlet on the duct ventilation *** the train approaches a ventilation duct,the air is pushed out of the tunnel through the *** the train passes the ventilation duct,the exhaust flow in the duct is changed rapidly to the suction *** the train passes the duct,the suction mass flow rate at the duct decreases with time since the air pressure at the opening of the duct is gradually recovered with time.A drastic change in the mass flow rate at a ventilation duct while a train passes the corresponding ventilation duct,causes a change in the exhaust mass flow rate at other ventilation ***,when a barrier is placed at the tunnel outlet,the air volume discharge rate at each ventilation duct is greatly increased,i.e.,the barrier placed at the tunnel outlet can improve remarkably the ventilation performance through each duct.

关键词： train-induced flow subway tunnel natural ventilation duct ventilation performance dynamic layering method

NUMERICAL AND EXPERIMENTAL INVESTIGATION OF bEVELED TRAILING EDGE FLOW FIELDS

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Journal of Hydrodynamics 2008年第3期20卷 273-279页

作者： MOSALLEM M.M. department of mechanical Power Engineering and Energy Faculty of EngineeringMinia University

The characteristics of flow past beveled trailing edges attached to flat plates have been investigated numerically and experimentally. The test models used in the present study were two 2D blunt-faced flat plates having asymmetric beveled trailing edges of angles 27° and 60°. The numerical simulation results display an asymmetric wake behind the 27° beveled trailing edge and von karmen street vortices behind the 60° beveled trailing edge. The flow visualization using cavitation technique showed the same observations of the numerical simulation. Therefore, it is obvious that the trailing edge geometry has a pronounced effect on the wake development and vortex shedding. Also, it is concluded that the cavitation phenomenon can be used as a visualization technique at high flow velocities.

关键词： cavitation technique visualization beveled trailing edge vortex shedding

Periodic Motion Planning and Control for Double Rotary Pendulum via Virtual Holonomic Constraints

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IEEE/CAA Journal of Automatica Sinica 2019年第1期6卷 291-298页

作者： Zeguo Wang Leonid b.Freidovich Honghua Zhang beijing Institute of Control Engineering IEEE the Robotics and Control Laboratory (www.control.tfe.umu.se) Department of Applied Physics and ElectronicsUmea University

Periodic motion planning for an under-actuated system is rather difficult due to differential dynamic constraints imposed by passive dynamics, and it becomes more difficult for a system with higher underactuation degree, that is with a higher difference between the number of degrees of freedom and the number of independent control inputs. However, from another point of view, these constraints also mean some relation between state variables and could be used in the motion *** consider a double rotary pendulum, which has an underactuation degree 2. A novel periodic motion planning is presented based on an optimization search. A necessary condition for existence of the whole periodic trajectory is given because of the higher underactuation degree of the system. Moreover this condition is given to make virtual holonomic constraint(VHC) based control design feasible. Therefore, an initial guess for the optimization of planning a feasible periodic motion is based on this necessary condition. Then, VHCs are used for the system transformation and transverse linearization is used to design a static state feedback controller with periodic matrix function gain. The controller gain is found through another optimization procedure. The effectiveness of initial guess and performance of the closed-loop system are illustrated through numerical simulations.

关键词： Double rotary pendulum periodic motion planning under-actuated mechanical systems virtual holonomic constraint (VHC)

Design and Application for Environmental Air Quality Automatic Monitoring System

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Design and Application for Environmental Air Quality Automat...

A　CONSTITUTIVE　THEORY　FOR　THE　REYNOLDS－STRESS　CLOSURES　IN　TURbULENCE　MODELLING

2009 9th International Conference on Electronic Measurement & Instruments（ICEMI’2009）

作者： Haiming Zheng department of mechanical Engineering North china Electric Power University baoding Hebei Province china

Air Quality Monitoring System（AQMS） is a real time system for environmental monitoring that has been developed in accordance with china EPA rules relevant to emission monitoring and control of pollutants from large combustion *** is designed to provide collection,evaluation and storage of environmental data for the sake of air quality and environment safeguard and health protection inside and outside the factory or *** can be used in all kind of plants that may produce emissions to the atmosphere（*** fired boilers,combustion turbines,kilns,etc.） by means of definition of specific limit and guideline values for all air pollutants with various sampling *** paper designs a set of AQMS for Industrial district.

关键词： Air Quality Monitoring System SO2/NOx/CO continuous monitoring beta ray Attenuation method weather parameter monitoring

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Journal of Hydrodynamics 1996年第1期8卷 103-109页

作者： L. Y. Tao,(department of mechanical Engineering, University of Pittsburgh, PA15261,USA)G. Q. Chen(Centre for Environmental Sciences, Peking University, beijing 100871,P. R. china)K. R. Rajagopal(department of mechanical Engineering, University of Pittsbur

For the Reynolds-stress closures in turbulence modelling, a constitutive theory is developed based on the principle of frame indifference and the theory of invariants. The present study sheds light on existing closure... 详细信息

关键词： turbulence modelling Reynolds-Stress constitutive theory

Influences of Ti substitution on the structure and electrochemical properties of Mg_(1-x)Ti_xNi(x=0,0.1, 0.2, and 0.3) hydrogen storage alloys

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Rare Metals 2009年第5期28卷 504-510页

作者： HUANG Hongxia HUANG Kelong LIU Suqin CHEN Dongyang College of Chemistry and Chemical Engineering Central South University Changsha 410083 China department of Materials and Chemical Engineering Guilin University of Technology Guilin 541004 China

MgNi-based hydrogen storage alloys Mg1–xTixNi （x = 0, 0.1, 0.2, and 0.3） were prepared by means of mechanical alloying. Mg in the alloy was partially substituted by Ti to improve the cycle stability of the alloys. The effects of the substitution of Ti for Mg on the microstructure and electrochemical performances of the alloys were investigated in detail. The results indicate that the substitution of Ti for Mg obviously decreases the discharge capacity, but it significantly improves their cycle stabilities. The microstructure of the alloys analyzed by X-ray diffraction （XRD） and scanning electron microscopy （SEM） shows that the alloys have a dominatingly amorphous structure. The substitution of Ti for Mg helps to improve the anti-oxidation/corrosion ability of the MgNi alloy but demolishes the electrochemical kinetics of hydrogenation/dehydrogenation. The Mg0.9Ti0.1Ni alloy electrode milled for 80 h exhibits the best integrative capability, which has the maximal discharge capacity of 331.66 mAh/g and the C30/Cmax of 63.65%.

关键词： hydrogen storage alloys Ti substitution structural characteristic electrochemical properties

Ultrasonic focusing and scanning with multiple waves

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Chinese Physics b 2013年第1期22卷 312-317页

作者：张碧星刘冬冬师芳芳 Hefeng Dong State Key Laboratory of Acoustics Institute of Acoustics Chinese Academy of Sciences department of electronics and Telecommunications Norwegian University of Science and Technology

This paper presents a new focusing and scanning method which focuses multiple waves on a target. The key of the method is to control excitation pulses for each element of the transducer array. The excitation pulse on each array element is obtained by time reversing the signal received by the same element, which is generated by an imaginary source at the target. The excitation pulses from all array elements are transmitted and arrive at the target simultaneously, and focusing is achieved. The performance of the two methods is compared in numerical examples, and it is demonstrated that the proposed method achieves a satisfactory focusing and a good signal-to-noise ratio no matter where the target location is.

关键词： ultrasonic focusing and scanning multiple waves transducer array

CERAMIC MATRIX COMPOSITE SYNTHESIZED bY THE PURE Al+NaOH SELF-OXIDATION

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Acta Metallurgica Sinica(English Letters) 2001年第4期14卷 296-302页

作者： S.X. He1), S. Yuan2), J. Wang1) and b.D. Sun1) 1) department of Marterials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200030, china 2) department of Marterials Science and Engineerin Dept. of Mat. Sci. Shanghai Jiaotong Univ. Shanghai 200030 China

An Al2O3 ceramic matrix composite was fabricated by self-oxidation of pure Al+NaOH, and its microstructure, mechanical properties and growth mechanism were analyzed. Experimental results show that the composite possesses better mechanical properties, higher density and faster growth velocity than that made of Al-Mg-Si alloy. The composite grows primarily along the crucible wall and its microstructure is characterized by a periodic wavy like structure.

关键词： Aluminum Caustic soda Oxidation Synthesis (chemical)