检索结果-南通市图书馆

Analysis of the forces acting on the saltating particles in the coupled wind-sand-electricity fields

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2009年第2期52卷 239-247页

作者： wu jianjun YAN GuangHu Key Laboratory of Mechanics on Western Disaster and Environment of Ministry of Education School of Civil Engineering and MechanicsLanzhou UniversityLanzhou 730000China

Based on the theoretical model describing the saltation of sand particles in the coupled wind-sand- electricity fields, the numerical simulations of the forces acting on saltating particles, such as the aerodynamic drag force, Magnus effect, Saffman force and electrostatic force, are analyzed in com- parison to the gravity force of the particles in the steady windblown sand movement. Furthermore, the laws of the above forces vary with the friction velocity, the diameter of the sand particle, the initial an- gular velocity and the lift-off velocity are discussed.

关键词： sand particles coupled wind-sand-electricity fields saltation acting force

Reduced K-best sphere decoding algorithm based on minimum route distance and noise variance

在线全文

学校读者我要写书评

暂无评论

Journal of Systems Engineering and Electronics 2014年第1期25卷 10-16页

作者： Xinyu Mao jianjun wu Haige Xiang School of Electronics Engineering and Computer Science Peking University

This paper focuses on reducing the complexity of K-best sphere decoding （SD） algorithm for the detection of uncoded multi-ple input multiple output （MIMO） systems. The proposed algorithm utilizes the threshold-pruning method to cut nodes with partial Euclidean distances （PEDs） larger than the threshold. Both the known noise value and the unknown noise value are considered to generate the threshold, which is the sum of the two values. The known noise value is the smal est PED of signals in the detected layers. The unknown noise value is generated by the noise power, the quality of service （QoS） and the signal-to-noise ratio （SNR） bound. Simulation results show that by considering both two noise values, the proposed algorithm makes an efficient reduction while the performance drops little.

关键词： chi-square distribution (CSD) K-best sphere decoding(SD) multiple input multiple output (MIMO) systems.

Optical detection method of discharge mode transition of inductively coupled plasma in an atmosphere-breathing electric propulsion system

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2024年第10期37卷 172-183页

作者： Yuxuan ZHONG Yu ZHANG jianjun wu Peng ZHENG College of Aerospace Science and Engineering National University of Defense TechnologyChangsha 410073China

Plasma discharge stability is an important problem in atmosphere-breathing electric propulsion system when maintaining long-term missions at ultra-low earth *** paper designed an inductively coupled plasma source to imitate the ionization *** effect of inflow rate and Radio Frequency(RF)power on the plasma discharge mode transition is experimentally studied.A discharge mode detection method is proposed,which determines the discharge mode by identifying the morphology of the plasma *** using the method,the discharge mode transition is quantified and a control model based on the parameter sensitivity is *** verify the method,the spectra are measured and the electron temperature spatial distribution is *** the method has been proven *** results show that the inductively coupled discharge contains capacitive components affected by the mass flow rate and the radio frequency *** plasma characteristics can be maintained stably by controlling the radio frequency power when the mass flow rate randomly changes in a certain *** is demonstrated that the application of detection method effectively identifies the discharge mode,which is a promising active control method for the plasma discharge mode.

关键词： Atmosphere-breathing electric propulsion Inductively coupled plasma Discharge mode transition Optical diagnosis Ultra-low earth orbit

Topological-based bottleneck analysis and improvement strategies for traffic networks

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2009年第10期52卷 2814-2822页

作者： jianjun wu ZiYou Gao HuiJun Sun State Key Laboratory of Rail Traffic Control and Safety (Beijing Jiaotong University) Beijing 100044 China School of Traffic and Transportation Beijing Jiaotong University Beijing 100044 China MOE Key Laboratory for Urban Transportation Complex Systems Theory and Technology Beijing Jiaotong University Beijing 100044 China

A method is proposed to find key components of traffic networks with homogenous and heterogeneous topologies, in which heavier traffic flow is transported. One component, called the skeleton, is the minimum spanning tree (MST) based on the zero flow cost (ZCMST). The other component is the infinite incipient percolation cluster (IIC) which represents the spine of the traffic network. Then, a new method to analysis the property of the bottleneck in a large scale traffic network is given from a macroscopic and statistical viewpoint. Moreover, three effective strategies are proposed to alleviate traffic congestion. The significance of the findings is that one can significantly improve the global transport by enhancing the capacity in the ZCMST with a few links, while for improving the local traffic property, improving a tiny fraction of the traffic network in the IIC is effective. The result can be used to help traffic managers prevent and alleviate traffic congestion in time, guard against the formation of congestion bottleneck, and make appropriate policies for traffic demand management. Meanwhile, the method has very important theoretical significance and practical worthiness in optimizing traffic organization, traffic control, and disposal of emergency.

关键词： traffic congestion user equilibrium assignment heterogeneous and homogenous networks

Multi-Objective Optimization for China's Power Carbon Emission Reduction by 2035

在线全文

学校读者我要写书评

暂无评论

Journal of Thermal Science 2019年第2期28卷 184-194页

作者： wu jianjun TANG Guihua WANG Run SUN Yanwei Key Lab of Urban Environment and Health Institute of Urban Environment Chinese Academy of Sciences University of Chinese Academy of Sciences MOE Key Laboratory of Thermo-Fluid Science and Engineering Xi'an Jiaotong University Hubei University Geography & Spatial Information Techniques Department of Ningbo University

Low carbon transformation plays an important role in promoting the energy production and consumption revolution. Currently, the power sector of China still faces a series of challenges, such as the overcapacity of coal-fired power, the renewable energy consumption, the new constraints of carbon-emissions, and fragmented power planning. This study develops a multi-objective optimization model to predict the future trend of China power structure by 2035. The key factors such as network, power, load and storage are taken into account. Besides, the technical feasibility, economic rationality and social acceptable constraints are also fully considered. Through planning and optimization, the premise of low carbon transformation is to ensure the continuity of existing policies for removing inefficient assets, and the core is to develop and utilize non-fossil energy on a large scale. Specifically, the capacity of coal-fired power will be attained in the peak in 2025, and the factor will also transfer from main power supplier to main power and energy supplier. Before 2025, the clean replacement of incremental power installation will be completed. In 2035, 92% of new investment comes from non-fossil energy. The economy and competitiveness of wind power and PV(Photovoltaic) power generation are continuously increasing. By 2020, the coal-fired power and the wind power in eastern of China will be parity firstly. In 2025, the cost of PV and wind power will be the same. Furthermore, the evaluation dimension of modern power system with clean, low-carbon, safety and high efficiency are innovatively constructed, and the index system target of 2035 is quantitatively analyzed and prospected.

关键词： power sector carbon emission reduction optimization energy outlook comprehensive evaluation

An atmosphere-breathing propulsion system using inductively coupled plasma source

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2023年第5期36卷 223-238页

作者： Peng ZHENG jianjun wu Yu ZHANG Bixuan CHE Yuanzheng ZHAO College of Aerospace Science and Engineering National University of Defense TechnologyChangsha 410073China

CubeSats have attracted more research interest recently due to their lower cost and shorter production time.A promising technology for CubeSat application is atmosphere-breathing electric propulsion,which can capture the atmospheric particles as propulsion propellant to maintain longterm mission at very low Earth *** paper designs an atmosphere-breathing electric propulsion system for a 3 U CubeSat,which consists of an intake device and an electric thruster based on the inductively coupled *** capture performance of intake device is optimized considering both particles capture efficiency and compression *** plasma source is also analyzed by experiment and ***,the thrust performance is also estimated when taking into account the intake *** results show that it is feasible to use atmosphere-breathing electric propulsion technology for CubeSats to compensate for aerodynamic drag at lower Earth orbit.

关键词： Atmosphere-Breathing Electric Propulsion(ABEP) CubeSat Inductively coupled plasma Intake device Very Low Earth Orbit(VLEO)

Measurement method and results of divergence angle of laser-controlled solid propellants used in space propulsion

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2023年第9期36卷 195-206页

作者： Yang OU jianjun wu Yuqiang CHENG Yu ZHANG Yuqi LI College of Aerospace Science and Engineering National University of Defense TechnologyChangsha 410073China

The plume divergence angle is an important reference index for evaluating the thrust efficiency and propellant utilization of space propulsion ***,the characteristics of the dynamic variation of plume divergence angle over time cannot be measured using current *** paper utilizes high-speed photography and image processing methods to develop a strategy that can give a quick,non-destructive and real-time detection of the divergence *** of the strategy is verified,and the characteristics of plume divergence angles of different lasercontrolled solid propellants were further analyzed and *** experimental results indicate that graphene could effectively reduce the divergence angle,while oxide-doped samples had larger divergence angles than alloy-doped and carbon-doped samples.

关键词： Ablation Image processing Laser Plume divergence angle Propellant Space application

Drought Planning Research in the United States: An Overview and Outlook

在线全文

学校读者我要写书评

暂无评论

International Journal of Disaster Risk Science 2013年第2期4卷 51-58页

作者： Xinyu Fu Zhenghong Tang jianjun wu Kevin McMillan Community and Regional Planning Program College of ArchitectureUniversity of Nebraska-LincolnLincolnNE 68588USA Academy of Disaster Reduction and Emergency Management Beijing Normal UniversityBeijing 100875China School of Natural Resources University of Nebraska-LincolnLincolnNE 68588USA

Drought is widely known as an insidious hazard due to its complex and unique characteristics. Drought disasters have brought tremendous economic losses and significant social and environmental impacts to communities across the globe. To further understand the hazard drought poses and provide insights into planning for drought preparedness, this article conducts a thorough literature review of drought hazard and drought planning frameworks within the United States. Two main approaches and three major forms of drought planning are discussed and summarized. Based on this review, a preliminary overview of drought planning status in the United States is presented. This study provides insight into major drought planning literature and establishes a link with drought mitigation and adaptation. The article concludes with discussion and implication for future drought planning and a future research outlook.

关键词： drought hazard insight

Application of Lattice Boltzmann Method to Simulate Forest Edge

在线全文

学校读者我要写书评

暂无评论

Advances in Applied Mathematics and Mechanics 2023年第2期15卷 376-401页

作者： Jie Wei jianjun wu An Jiang Kun Wan Key Laboratory of Mechanics on Disaster and Environment inWestern China Attached to the Ministry of Education of ChinaLanzhou UniversityLanzhouGansu 730000China College of Civil Engineering and Mechanics Lanzhou UniversityLanzhouGansu 730000China Shenzhen TenFong Technology Co. LtdGuangdongChina ZhongJiao TianHe Machinery Equipment Manufacturing Co.LTD SuzhouJiangsuChina

This study is focused on the forest edge flow by using numerical *** model the effects of a forest canopy on airflow,source terms are introduced into the governing *** lattice Boltzmann method in conjunction with the standard k-εmodel is applied to solve the turbulent wind *** order to perform the simulation on non-uniform grids,the Taylor series expansion and least square based lattice Boltzmann method(TLLBM)is adopted to improve the accuracy and computational *** present method and code are verified with an earlier forest edge simulation.A series of forest canopies are established to explore the impacts of canopy morphology on wind *** canopies cover 3 canopy architectures and the Leaf Area Index(LAI)ranges from 2.0 to *** further study is carried out by adjusting the canopy foliage amount and the canopy *** present study demonstrates the potential of lattice Boltzmann method to simulate the high Re number forest edge *** impacts of canopy morphology on zero plane displacement,aerodynamic roughness length,friction wind velocity,permeability coefficient,wall-shear stress are illustrated in *** results show that the canopy sub-layer wind field,especially the wind velocity profiles within and above the forest canopy,are mainly determined by canopy morphology.

关键词： Forest edge lattice Boltzmann method non-uniform grids canopy morphology