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Delayed response model for bankfull discharge predictions in the Yellow River

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International Journal of Sediment Research 2011年第4期26卷 445-459页

作者： Baosheng WU and Lingyun LI 1 Prof.,state key laboratory of hydroscience and engineering,tsinghua university,beijing 100084,china, 2 Ph.D.and Research Hydraulic Engineer,Changjing River Scientific Research Institute,Wuhan 430010,china Prof. State Key Laboratory of Hydroscience and Engineering Tsinghua University Beijing 100084 China Ph.D. and Research Hydraulic Engineer Changjing River Scientific Research Institute Wuhan 430010 China

Delayed response means that channels cannot achieve a new equilibrium state immediately following disruption;the channel requires a response time or relaxation time to reach *** follows that the morphological state of fluvial system represents the cumulative effects of all previous disturbances and environmental conditions.A unique feature of the delayed response model for bankfull discharge is that the model is capable of representing the cumulative effects of all previous flow conditions when applied to predict the path/trajectories of bankfull discharge in response to altered flow *** this paper,the delayed response model was modified by readjusting the weight for the initial boundary conditions and introducing a variableβwith respect to *** modified model was then applied to the bankfull discharge calculations for three selected river reaches of the Yellow River,with each reach having different geomorphic settings and constraints. Results indicated that the modified model can predict accurately the bankfull discharge variation in response to changes in flow discharge and sediment load conditions that have been dramatically altered in the *** also demonstrated the strong dependence of current bankfull discharge on the previous years’ flow conditions,with the relaxation time varied from 2 to 14 years,meaning that the bankfull discharge was not only affected by the flow discharge and sediment load in the current year,but also by those in previous 1 to 13 ***,the relaxation time of bankfull discharge adjustment was inversely proportional to the long-term average suspended sediment concentrations,and this may be explained by fact that high sediment concentrations may have a high potential to perform geomorphic work and there is more sediment readily available to shape the channel boundary and geometry.

关键词： Yellow River Bankfull discharge Delayed response Flow discharge Sediment load Relaxation time

NUMERICAL INVESTIGATION OF THE VENTILATED CAVITATING FLOW AROUND AN UNDER-WATER VEHICLE BASED ON A THREE-COMPONENT CAVITATION MODEL

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Journal of Hydrodynamics 2010年第6期22卷 753-759页

作者： JI Bin LUO Xian-wu PENG Xiao-xing ZHANG Yao WU Yu-lin XU Hong-yuan state key laboratory of hydroscience and engineering Tsinghua University Beijing 100084 China china Ship Scientific Research Center Wuxi 214082 China state key laboratory of hydroscience and engineering Tsinghua University Beijing 100084 China

Based on the Reynolds-Averaged Navier-Stokes equations and mass transfer model, an approach, where a three-component cavitation model is proposed, is presented to simulate ventilated cavitating flow as well as natural cavitation. In the proposed cavitation model, the initial content of nucleus in the local flow field is updated instantaneously, and is coupled with the Rayleigh-Plesset equation to capture the cavity development. The proposed model is applied to simulate the cavitating flow around an under-water vehicle in different cavitation conditions. The results indicate that for the natural and ventilated cavitation simulation, the predicted cavitation characteristics including the cavity length, cavity diameter and cavity shape agree satisfactorily with the analytic and experimental results, for the ventilated cavitation, the proposed methods reproduce the special behavior that the axial line of the cavity bends and rises at the tail part. The study concludes that the ventilated flow rate of the non-condensate gas influences the development of natural cavitation as well as ventilated cavitation, and the vapor cavity is suppressed remarkably by the gas cavity with the increase of the gas ventilation.

关键词： under-water vehicle natural cavitation ventilated cavitation three-component model

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 Department of Hydraulic engineering State Key Laboratory for Hydroscience and Engineering Tsinghua University Beijing 100084 China 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

Molecular dynamics simulations of non-Fourier heat conduction

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Progress in Natural Science:Materials International 2008年第8期18卷 999-1007页

作者： Qixin Liu, Peixue Jiang *, Heng Xiang key laboratory for Thermal Science and Power engineering of Ministry of Education, Department of Thermal engineering, tsinghua university, beijing 100084, china key laboratory for Thermal Science and Power engineering of Ministry of Education Department of Thermal Engineering Tsinghua University Beijing 100084 China

Unsteady heat conduction is known to deviate significantly from Fourier’s law when the system time and length scales are within certain temporal and spatial windows of relaxation. Classical molecular dynamics simulations were used to investigate unsteady heat conduction in argon thin films with a sudden temperature increase or heat flux at one surface to study the non-Fourier heat conduction effects in argon thin films. The studies were conducted with both pure argon films and films with vacancy defects. The temperature profiles in the argon films showed the existence of mechanical waves when the thin film was suddenly heated and the wave nature of the heat propagation. The flux phase relaxation time, sq, and the temperature phase relaxation time, st, were calculated from the temporal variations of the energy flux and temperature distribution in the film. Comparisons of the MD temperature profiles with temperature profiles predicted by Fourier’s law show that Fourier’s law is not able to predict the temperature variations with time. Different film thicknesses were also studied to illustrate the variation of the time needed for the films to reach steady-state temperature profiles after a sudden temperature rise at one surface and to illustrate the finite speed of the energy waves.

关键词： Molecular dynamics simulation Non-Fourier heat conduction Argon thin film

New method for computing unstable equilibrium points of power systems with induction motors

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Science china(Technological Sciences) 2010年第4期53卷 881-885页

作者： CHEN Lei,XU Fei & MIN Yong state key Lab of Power Systems,Department of Electrical engineering,tsinghua university,beijing 100084,china state key Lab of Power Systems Department of Electrical Engineering Tsinghua University Beijing China

The computation of the unstable equilibrium point(UEP) is a key step involved in stability region estimation of nonlinear dynamic systems.A new continuation-based method to compute the UEPs of a power system with induction motors is *** mechanical torques of motors are changed to form a parameterized equation *** the solution curve of the equation set is traced by the continuation method from the stable equilibrium point to a *** direction of mechanical torque change is varied to get multiple *** obtained UEPs are mostly *** fast assessment of induction motor stability is studied by approximating the stable manifolds of the *** method is tested in several systems and satisfactory results are obtained.

关键词： power system stability transient voltage stability unstable equilibrium point(UEP) stability boundary induction motor

Spatially discontinuous ionization phenomenon in inhomogeneous soil

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Science china(Technological Sciences) 2010年第4期53卷 918-921页

作者： ZHANG BaoPing,HE JinLiang & ZENG Rong state key Lab of Power Systems,Department of Electrical engineering,tsinghua university,beijing 100084,china state key Lab of Power Systems Department of Electrical Engineering Tsinghua University Beijing China

By using X-ray film imaging technology,a phenomenon of discontinuous ionization was observed in the inhomogeneous soil around the grounding electrode on which a surge voltage was applied.A simplified two-phase solid-gas model was built to study the electric field distribution in the soil to explain the discontinuous ionization *** showed the differences of the dielectric properties,the shapes and sizes of soil particles can cause discontinuous ionization in the soil.

关键词： discontinuous ionization inhomogeneous soil X-ray film porous medium electric field distribution

Anomalous magnetotransport in LaMn_(1-x)Te_xO_3

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Science china(Physics,Mechanics & Astronomy) 2009年第7期52卷 987-992页

作者： TAN GuoTai1,2, CHEN ZhengHao3 & ZHANG XiaoZhong4,5 1 key laboratory of Beam Technology & Materials Modification of the Ministry of Education, Institute of Low Energy Nuclear Physics, beijing Normal university, beijing 100875, china 2 beijing Radiation Center, beijing 100875, china 3 laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, beijing 100080, china 4 key laboratory of Advanced Materials of the Ministry of Education, Department of Materials Science and engineering, tsinghua university, beijing 100084, china 5 beijing National Center for Electron Microscopy, tsinghua university, beijing 100084, china key laboratory of Beam Technology & Materials Modification of the Ministry of Education Institute of Low Energy Nuclear Physics Beijing Normal University Beijing China beijing Radiation Center Beijing China laboratory of Optical Physics Institute of Physics Chinese Academy of Sciences Beijing China key laboratory of Advanced Materials of the Ministry of Education Department of Materials Science and Engineering Tsinghua University Beijing China beijing National Center for Electron Microscopy Tsinghua University Beijing China

The LaMn1-xTexO3+δ (x=0.1, 0.2, 0.3) were synthesized using solid-state reaction method for the first time. X-ray photoemission spectrum (XPS) shows that in the samples the Te ions have a valence of Te4+, and Mn3+ ions are partly converted into Mn2+ and Mn4+ due to the excess oxygen and Te doping. The magnetotransport associated with Mn2+, Mn3+ and Mn4+ was investigated. The experimental results show that the samples are insulator at 0 T when the amount of Mn3+ is much larger or less than the sum of Mn2+ and Mn4+; by contrast, the samples display metal to insulator transition with increasing temperature when the amount of Mn3+ is close to the sum of Mn2+ and Mn4+. These anomalous magnetotransport behaviors were analyzed in the frame of the double-exchange (DE) mechanism.

关键词： colossal magnetoresistance La-Te-Mn-O magnetotransport

Orthogonal linear polarized lasers (Ⅲ)——Applications in self-sensing

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Progress in Natural Science:Materials International 2005年第11期15卷 961-971页

作者： ZHANG Shulian, DU Wenhua and LIU Gang (The state key laboratory of Precision Measurement Technology and Instruments, Department of Precision Instruments, tsinghua university, beijing 100084, china) The state key laboratory of Precision Measurement Technology and Instruments Department of Precision Instruments Tsinghua University Beijing 100084 China

In this paper, the applications of orthogonal linear polarized lasers in self-sensing are reviewed. The properties for such a laser include the production of a new frequency in one longitudinal mode spacing, the tuning of frequency difference, the change of polarization states as cavity tuning, the control of mode competition intensity, the optical feedback, and so on. The orthogonal polarized lasers have been used as a laser nanometer ruler based on competition between two polarized lights in a HeNe laser and as a displacement measurement tool based on the optical feedback in the orthogonal polarized lasers. They are also used in the phase retardation measurement of a waveplate, the angle measurement, the vibration measurement, the pressure/force measurement, the weak magnetic field measurement, and so on. The structures of these new devices are simple and compact with the great advantages of high resolution and high accuracy. Some of these devices can trace to the source of the laser wavelength. The nanometer laser ruler is an example whose measurement range is 12 mm, resolution is 79 nm and linearity is less than 5×10-5. The repeatability of the phase retardation measuring system of waveplate can reach 3’.

关键词： orthogonal polarized laser frequency splitting optical feedback vibration measurement displacement measurement waveplate measurement angle measurement.

Dense coding scheme using superpositions of Bell-states and its NMR implementation

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Science china(Physics,Mechanics & Astronomy) 2005年第1期48卷 57-67页

作者： ZHANG Jingfu, XIE Jingyi, DENG Zhiwei & LU Zhiheng key laboratory for Quantum Information and Measurements, Department of Physics, tsinghua university, beijing 100084, china Center for Quantum Information, tsinghua university, beijing 100084, china Department of Materials Science and engineering, beijing Normal university, beijing 100875, china Testing and Analytical Center, beijing Normal university, beijing 100875, china Department of Physics, beijing Normal university, beijing 100875, china key laboratory for Quantum Information and Measurements Department of Physics Tsinghua University Beijing 100084 China Center for Quantum Information Tsinghua University Beijing 100084 China Department of Materials Science and engineering Beijing 100875 China Testing and Analytical Center Beijing Normal University Beijing 100875 China Department of Physics Beijing Normal University Beijing 100875 China

Dense coding using superpositions of Bell-states is proposed. The generalized Grover's algorithm is used to prepare the initial entangled states, and the reverse process of the quantum algorithm is used to determine the entangled state in the decoding measurement. Compared with the previous schemes, the superpositions of two Bell-states are exploited. Our scheme is demonstrated using a nuclear magnetic resonance (NMR)quantum computer. The corresponding manipulations are obtained. Experimental results show a good agreement between theory and experiment. We also generalize the scheme to transmit eight messages by introducing an additional two-state system.

关键词： dense coding, superpositions of Bell-states, generalized Grover's algorithm, nuclear magnetic res-onance, quantum computer.