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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 Laboratory 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.

Experimental study on bed-load sediment transport under irregular wave and current combined flow

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Acta Oceanologica Sinica 2001年第2期20卷 271-280页

作者： Wu Yongsheng,Qin Chongren (1. department of Hydraulic engineering, Tsinghua {2., beijing 100084, china 2. School of Civil engineering, Tianjin {2., Tianjin 300072. china) department of Hydraulic engineering Tsinghua University Beijing 100084 China

Using an irregularly oscillating tray and flume, a series of experiments are completed to evaluate bed-load sediment transport rate under irregular wave -current coexistent field. Testing conditions include three interaction angles 0', 45', 90' and two kinds of median sizes (0.38 and 1.10 mm). The results of transport rate show that the net sediment transport rate can be expressed approximately as the function of the maximum bottom shear stress of waves, mean shear stress of current and the grain size.

关键词： Irregular wave-current bed-load transport rate

On three-dimensional geological modeling and visualization

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Science china Earth Sciences 2004年第8期47卷 739-748页

作者： WU Qiang1 & XU Hua2.1. department of Resource Exploitation engineering, {2. university of Mining and Technology, beijing 100083, {2. 2. beijing Institute of Petrochemical Technology, beijing 102.17, {2. 1. department of Resource Exploitation engineering China University of Mining and Technology 100083 Beijing China 2. beijing Institute of Petrochemical Technology 102617 Beijing China

The technology of 3D geological modeling will bring about great changes in the methods of geological data acquiring, storing, processing and displaying. However, no perfect or convenient software systems have been developed up to now since the geologic data which re-flect geological entities bear the feature of diversity, uncertainty and complexity. Some supervoxel models, mathematical models of fault and geometrical models of fold have been contrived so as to show the space geometric configuration of the complicated geologic structures. The application-oriented system architecture for 3D geological modeling is established; and a novel design concept based on spatial data processing is also proposed with the technology of solid modeling as its core and the application of models as its objective. Theories and methods for 3D geological modeling will hopefully be enriched and developed. In the light of these theories and methods, a feature-based navigation visualization technique is also put forward in the paper. By integrating geo-database, graphics libraries and KBS with 3D dynamic simulation systems, geologists will be able to capture the partial characteristics and whole structure embodied in the geological data in a direct-viewing, figurative and accurate manner.

关键词： 3D geological modeling,geometrical model,system architecture,visualization

Mechanism and control of convective heat transfer——Coordination of velocity and heat flow fields

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Chinese Science Bulletin 2001年第7期46卷 596-599页

作者： QUO Zengyuandepartment of engineering {2., Tsinghua university, beijing 100084, china department of engineering {2. Tsinghua University Beijing 100084 China

A second look has been given at the mechanism of convective heat transfer based on the analogy between convection and conduction with heat sources. The strength of convective heat transfer depends not only on the fluid velocity and fluid properties, but also on the coordination of fluid velocity and heat flow fields. Hence, based on the included angle of velocity and temperature gradient vectors, the presence of fluid motion may enhance or reduce heat transfer. With this concept, the known heat transfer phenomena may be understood in a deeper way. More important is that some novel approaches of heat transfer control can be developed.

关键词： convective heat transfer coordination heat transfer enhancement.

Study on near-wall turbulence structures with local Reynolds stress

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Communications in Nonlinear Science and Numerical Simulation 2000年第3期5卷 105-117页

作者： Li LI Chunxiao XU Guixiang CUI and Zhaoshun ZHANG(department of engineering {2., Tsinghua university, beijing 100084, china) department of engineering {2. Tsinghua University Beijing 100084 China

The direct- numerical- simulated ch annel turbulence is analyzed with two-dimensional wavelet transform. Considering the relation between turbulence coherent structure and Reynolds stress in near wall region, the local Reynolds stress (LRS) is defined.A new method for extracting coherent signals from turbulence based on the LRS is developed. Velocity fiuctuations are decomposed to coherent signals and background signals. It is found that the scaling exponents of coherent signals have a considerable deviation from the Kolmogorov scaling law q/3 (K41 theory), while that of background signals is very close to q/3. It is confirmed that coherent signals are mainly responsible for the anomalous *** characterized by the positive peaks of LRS, the typical structures in near wall region are obtained by conditional statistical averaging. It is shown that the local character of near-wall turbulence structures can be effectively described with LRS.

关键词： wavelet channel turbulence the local Reynolds stress

Droplet creator based on electrowetting-on-dielectric for lab on a chip

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Science china(Technological Sciences) 2006年第2期49卷 248-256页

作者： ZENG Xuefeng1, YUE Ruifeng1, WU Jiangang1, HU Huan1, DONG Liang1, WANG Zheyao1, HE Feng2.& LIU Litian1 1. Institute of Microelectronics, Tsinghua university, beijing 100084, {2. 2. department of engineering mechanics, Tsinghua university, beijing 100084, {2. 1. Institute of Microelectronics Tsinghua University Beijing 100084 China 2. department of engineering {2. Tsinghua University Beijing 100084 China

Electrowetting-on-dielectric (EWOD) is to directly control the wettability of liquids on the solid surface by applying the electric potential to the microelectrode array under the dielectric layer. The prototype of the EWOD droplet creator with the sandwiched structure is used: the droplet is sandwiched between the top and bottom plates; the bot- tom plate consists of silicon used as the substrate of the microelectrode array, nitride sili- con film deposited by low pressure chemical vapor deposition as the dielectric layer and the fluorocarbon polymer film deposited by inductively coupled plasma chemical vapor deposition as the hydrophobic layer; and the top plate is the transparent electrode covered with the hydrophobic layer. To obtain the required minimum voltage, the process and the criterion of creating droplets are analyzed. At the voltage of 35 V the deionized water droplet surrounded in silicone oil is successfully created.

关键词： micro total analysis system, electrowetting-on-dielectric, creation and control of droplets, inductively coupled plasma chemical vapor deposition.

Feature combination for classifying single-trial ECoG during motor imagery of different sessions

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Progress in Natural Science:Materials International 2007年第7期17卷 851-858页

作者： Wei Qingguo~(1,2. Meng Fei~1 Wang Yijun~1 Gao Xiaorong~1 Gao Shangkai~(1**) (1.department of Biomedical engineering,School of Medicine,Tsinghua {2.,beijing 100084,china 2.department of Electronic engineering,School of Information,Nanchang {2.,Nanchang 33002.,china) [a]department of Biomedical engineering School of Medicine TsinghuaUniversity Beijing China [b]department of Electronic engineering School of Information Nanchang University Nanchang China

The input signals of brain-computer interfaces(BCIs)may be either scalp electroencephalogram(EEG)or electrocor- ticogram(ECoG)recorded from subdural *** make BCIs practical,the classifiers for discriminating different brain states must have the ability of session-to-session *** paper proposes an algorithm for classifying single-trial ECoG during motor imagery of different *** features,derived from two physiological phenomena,movement-related potentials(MRP)and event-related desynchronization(ERD),and extracted by common spatial subspace decomposition(CSSD)and waveform mean,are combined to per- form classification *** specific signal processing methods utilized are described in *** algorithm was successfully applied to Data SetⅠof BCI CompetitionⅢ,and achieved a classification accuracy of 91% on test set.

关键词： brain-computer interface(BCI) electrocorticogram(ECoG) session-to-session transfer feature combination movement-related potentials(MRP) event-related desynchronization(ERD)

ELASTO-PLASTICITY ANALYSIS BASED ON COLLOCATION WITH THE MOVING LEAST SQUARE METHOD

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Acta Mechanica Solida Sinica 2003年第2期16卷 162-170页

作者： Song Kangzu Zhang Xiong Lu Mingwan (department of engineering {2.,Tsinghua university,beijing 100084,china) departmentofengineering{2. TsinghuaUniversityBeijing100084China

A meshless approach based on the moving least square method is developed for elasto-plasticity analysis,in which the incremental formulation is *** this approach,the dis- placement shape functions are constructed by using the moving least square approximation,and the discrete governing equations for elasto-plastic material are constructed with the direct collo- cation *** boundary conditions are also imposed by *** method established is a truly meshless one,as it does not need any mesh,either for the purpose of interpolation of the solution variables,or for the purpose of construction of the discrete *** is simply formu- lated and very efficient,and no post-processing procedure is required to compute the derivatives of the unknown variables,since the solution from this method based on the moving least square approximation is already smooth *** examples are given to verify the accuracy of the meshless method proposed for elasto-plasticity analysis.

关键词： meshless method elasto-plasticity collocation method moving least square incremental formulation

A SOLUTION PROCEDURE FOR LOWER BOUND LIMIT AND SHAKEDOWN ANALYSIS BY SGBEM

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Acta Mechanica Solida Sinica 2001年第2期14卷 118-129页

作者： Zhang Xiaofeng Liu Yinghua Cen Zhangzhi (department of engineering {2.,Tsinghua university,beijing 100084,china) ***

The symmetric Galerkin boundary element method (SGBEM) instead ofthe finite element method is used t perform lower bound limit andshakedown analysis of structures. The self-equilibrium stress fieldsare constructed by a linear combination of several basicself-equilibrium stress fields with parameters to be *** basic self-equilibrium stress fields are expressed as elasticresponses of the body to im- posed permanent strains and obtainedthrough elastic-plastic incremental analysis.

关键词： limit and shakedown analysis SGBEM self-equilibrium stress