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THE WALL EFFECT ON VENTILATED CAVITATING FLOWS IN CLOSED CAVITATION TUNNELS

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Journal of Hydrodynamics 2008年第5期20卷 561-566页

作者： CHEN Xin LU chuan-jing LI Jie PAN Zhan-cheng Department of Engineering Mechanics Shanghai Jiao Tong University Shanghai 200240 China

For ventilated cavitating flows in a closed water tunnel, the wall effect may exert an important influence on cavity shape and hydrodynamics, An isotropic mixture multiphase model was established to study the wall effect based on the RANS equations, coupled with a natural cavitation model and the RNG k-ε turbulent model. The governing equations were discretized using the finite volume method and solved by the Gauss-Seidel linear equation solver on the basis of a segregation algorithm. The algebraic multigrid approach was carried through to accelerate the convergence of solution. The steady ventilated cavitating flows in water tunnels of different diameter were simulated for a conceptual underwater vehicle model which had a disk cavitator. It is found that the choked cavitation number derived is close to the approximate solution of natural cavitating flow for a 3-D disk. The critical ventilation rate falls with decreasing diameter of the water tunnel. However, the cavity size and drag coeflicient are rising with the decrease in tunnel diameter for the same ventilation rate, and the cavity size will be much different in water tunnels of different diameter even for the same ventilated cavitation number.

关键词： ventilated cavitation water tunnel choked cavitation number critical ventilation rate

Impact of meteorological condition changes on air quality and particulate chemical composition during the COVID-19 lockdown

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Journal of Environmental Sciences 2021年第11期33卷 45-56页

作者： jing Ding Qili dai Yafei Li Suqin Han Yufen Zhang Yinchang Feng Tianjin Environmental Meteorological Center Tianjin 300074China State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control College of Environmental Science and EngineeringNankai UniversityTianjin 300350China CMA-NKU Cooperative Laboratory for Atmospheric Environment-Health Research Tianjin 300074China

Stringent quarantine measures during the Coronavirus Disease 2019(COVID-19)lockdown period(January 23,2020 to March 15,2020)have resulted in a distinct decrease in anthropogenic source emissions in North China Plain compared to the paralleled period of ***,22.7%decrease in NO_(2)and 3.0%increase of O_(3)was observed in Tianjin,nonlinear relationship between O_(3)generation and NO_(2)implied that synergetic control of NOx and VOCs is *** meteorological condition during the COVID-19 lockdown obscured the actual PM2.5 *** transport in 2020 Spring Festival(SF)triggered regional haze ***2.5 during the COVID-19 lockdown only reduced by 5.6%in *** we used the dispersion coefficient to normalize the measured PM2.5(DN-PM2.5),aiming to eliminate the adverse meteorological impact and roughly estimate the actual PM2.5 reduction,which reduced by 17.7%during the COVID-19 *** terms of PM2.5 chemical composition,significant NO_(3)−increase was observed during the COVID-19 ***,as a tracer of atmospheric oxidation capacity,odd oxygen(Ox=NO_(2)+O_(3))was observed to reduce during the COVID-19 lockdown,whereas relative humidity(RH),specific humidity and aerosol liquid water content(ALWC)were observed with noticeable *** oxidation rate(NOR)was observed to increase at higher specific humidity and ALWC,especially in the haze episode occurred during 2020SF,high air humidity and obvious nitrate generation was *** enhanced air humidity may response for the nitrate increase during the COVID-19 lockdown period.

关键词： COVID-19 lockdown Air quality Meteorological condition Air humidity Aerosol chemistry

Robust Clustering with Topological Graph Partition

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Chinese Journal of Electronics 2019年第1期28卷 76-84页

作者： WANG Shuliang LI Qi YUAN Hanning GENG jing dai Tianru DENG Chenwei School of software Beijing Institute of Technology School of Information and Electronics Beijing Institute of Technology

Clustering is fundamental in many fields with big data. In this paper, a novel method based on Topological graph partition(TGP) is proposed to group objects. A topological graph is created for a data set with many objects, in which an object is connected to k nearest neighbors. By computing the weight of each object, a decision graph under probability comes into being. A cut threshold is conveniently selected where the probability of weight anomalously becomes large. With the threshold,the topological graph is cut apart into several sub-graphs after the noise edges are cut off, in which a connected subgraph is treated as a cluster. The compared experiments demonstrate that the proposed method is more robust to cluster the data sets with high dimensions, complex distribution, and hidden noises. It is not sensitive to input parameter, we need not more priori knowledge.

关键词： Clustering Topological graph partition(TGP) Decision graph under probability Noise edge

Metal-free visible-light-mediated aerobic oxidation of silanes to silanols

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Science China Chemistry 2018年第12期61卷 1594-1599页

作者： jing Wang Bin Li Li-chuan Liu Chenran Jiang Tao He Wei He School of Pharmaceutical Sciences Tsinghua University

Oxidation of silanes into silanols using water/air has attracted considerable attention. The known methods with no exception required a metal catalyst. Herein we report the first metal-free method: 2 mol% Rose Bengal as the catalyst, air(O2) as the oxidant, water as the additive and under visible light irradiation. While this method produces various silanols in a simple, costeffective, efficient(92%–99% yields) and scalable fashion, its reaction mechanism is very different than the reported ones associated with metal catalysis.

关键词： metal-free photoredox aerobic oxidation silanes

Traffic flow and safety analysis

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Theoretical & Applied Mechanics Letters 2018年第5期8卷 304-314,361页

作者： jing Gao Lili dai Xu Gan The College of Post and Telecommunication of WIT Wuhan 430073China The Engineering Quality Supervision Bureau of Hubei Transport Department Wuhan 430000China Wuhan University Wuhan 430072China

Traffic rule is a key factor affecting traffic flow and *** develop our models,including the cellular automata traffic flow model as well as the linear regression one,aiming at calculating traffic flow and evaluating safety conditions with varied traffic ***,we thoroughly investigate four types of paths in a freeway,namely two straight lanes,three straight lanes,ramps,and roundabouts as case studies and discuss the different traffic rules as *** results demonstrate that"Keep-Right-Except-To-Pass"rule is not as effective as the free rule in promoting traffic flow;however,this rule ensures safety for drivers better than the free ***,a new traffic rule,which sets different posted speed limits for adjacent lanes,is proposed to promote better traffic flow with safety requirements ***,we apply effective rules and alternatives,left driving norms as well as intelligent system as extension and obtain better ***,model’s sensitivity analysis regarding to probability of decelerating and posted speed limits proves the stability of our results.

关键词： Traffic flow Cellular automata Safety evaluation

Harvesting biomechanical energy in the walking by shoe based on liquid metal magnetohydrodynamics

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Frontiers in Energy 2012年第2期6卷 112-121页

作者： Dan dai jing LIU Yixin ZHOU Key Laboratory of Cryogenics Technical Institute of Physics and ChemistryChinese Academy of SciencesBejing 100190China Department of Biomedical Engineering School of MedicineTsinghua UniversityBeijing 100084China

A liquid metal magnetohydrodynamics generation system （LMMGS） was proposed and demonstrated in this paper for collecting parasitic power in shoe while walking. Unlike the conventional shoe-mounted human power harvesters that use solid coil and gear mechanism, the proposed system employs liquid metal （Ga62In25Sn13） as energy carrier, where no moving part is requested in magnetohydrodynamics generators （MHGs）. While walk- ing with the LMMGS, the foot alternately presses the two liquid metal pumps （LMPs） which are respectively placed in the front and rear of the sole. As a result, the liquid metal in the LMPs （LMP I and II） is extruded and flows through the MHGs （MHG I and II） in which electricity is produced. For a comparison, three types ofLMMGSs （LMMGS A, B and C） were built where all the parts are the same except for the LMPs. Furthermore, performances of these LMMGSs with different volume of injected liquid metal were tested respectively. Experimental results reveal that both the output voltage and power of the LMMGS increase with the volume of injected liquid metal and the size of the LMPs. In addition, a maximum output power of 80 mW is obtained by the LMMGS C with an efficiency of approximately 1.3%. Given its advantages of no side effect, light weight, small size and reliability, The LMMGS is well-suited for powering the wearable and implantable micro/nano device, such as wearable sensors, drug pumps and so on.

关键词： human energy harvesting liquid metal wear-able magnetohydrodynamics generator parasitic power inshoe

A Rapid Crack Detection Technique Based on Attention for Intelligent M&O of Cross-Sea Bridge

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China Ocean Engineering 2024年第5期38卷 866-876页

作者： ZHOU Yong-chuan LI Guang-jun WEI Wei WANG Ya-meng jing Qiang Hong Kong-Zhuhai-Macao Bridge Authority Zhuhai 519015China National Observation and Research Station of Material Corrosion and Structural Safety of Hong Kong-Zhuhai-Macao Bridge in Guangdong Zhuhai 519000China Wuhan Maritime Communication Research Institute Wuhan 430079China

Rapid and accurate segmentation of structural cracks is essential for ensuring the quality and safety of engineering *** practice,however,this task faces the challenge of finding a balance between detection accuracy and *** alleviate this problem,a lightweight and efficient real-time crack segmentation framework was ***,in the network model system based on an encoding-decoding structure,the encoding network is equipped with packet convolution and attention mechanisms to capture features of different visual scales in layers,and in the decoding process,we also introduce a fusion module based on spatial attention to effectively aggregate these hierarchical *** are connected by pyramid pooling model(PPM)*** results show that the crack segmentation accuracy and real-time operation capability larger than 76%and 15 fps,respectively,are validated by three publicly available *** wide-ranging results highlight the potential of the model for the intelligent O&M for cross-sea bridge.

关键词： bridge defect detection crack detection lightweight design

Relevance between abutment pressure and fractal dimension of crack network induced by mining

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International Journal of Mining Science and Technology 2013年第6期23卷 925-930页

作者： Gao Mingzhong Jin Wencheng dai Zhixu Xie jing State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University College of Hydraulic and Hydropower Engineering Sichuan University Energy&Chemical Industry Research Institute Shenma Group of Pingdingshan Coal Group College of Architecture and Environment Sichuan University

Based on the geological conditions of coal mining face No.15-14120 at No.8 mine of Pingdingshan coal mining group,the real-time evolution of coal-roof crack network with working face advancing was collected with the help of intrinsically safe borehole video *** according to the geology of this working face,a discrete element model was calculated by *** in situ experimental data with numerical results,the relationship between the fractal dimension of boreholes'wall and the distribution of advanced abutment pressure was studied under the condition of mining *** results show that the variation tendency of fractal dimension and the abutment pressure has the same characteristic *** distance between working face and the peak value of the abutment pressure has a slight increasing trend with the advancing of *** the working face is set as the original point,the trend of fractal dimension from the far place to the origin can be divided into three phases:constant,steady increasing and *** the turning points of these phases are the max-influencing distance(50 m)and peak value(15 m)of abutment pressure.

关键词： Boreholes Coal mines Cracks Finite difference method Fractal dimension

Determination of particle size distribution by multi-scale analysis of acoustic emission signals in gas-solid fluidized bed

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2011年第4期12卷 260-267页

作者： Cong-jing REN jing-dai WANG Di SONG Bin-bo JIANG Zu-wei LIAO Yong-rong YANG State Key Laboratory of Chemical Engineering Department of Chemical and Biochemical Engineering Zhejiang University Hangzhou 310027 China

Particle size distribution(PSD) is an important parameter in the process of fluidization,and it always plays a crucial role in a gas-solid fluidized system.A PSD model for on-line PSD determination based on acoustic emission(AE) measurement was developed according to the mechanism of particle collision with the inner wall of the cylinder and multi-scale wavelet decomposition *** PSD model illuminates the quantitative relationship between the energy percentage of AE signals for different scales and the PSD,which indicates the feasibility of the application of the PSD *** were undertaken both in lab and plant gas-solid fluidized setup with polyethylene particles,and the parameters of the PSD model were calibrated and *** experimental conditions and results proved that the PSD model was suitable for on-line measurement and was sufficiently sensible and *** agglomeration,the PSD model also showed exact serviceability on detecting the onset of agglomeration by abnormal PSD,and the result agreed with that from the radiation ***,AE measurement was found to be a reliable and credible means for understanding the PSD information that affects the behavior of a system,which can provide valuable guidance for practical applications.

关键词： Particle size distribution(PSD) Acoustic emission(AE) Fluidized bed Multi-scale Agglomeration