检索结果-南通市图书馆

Analysis of shock wave unsteadiness using space and time correlations applied to shadowgraph flow visualization data

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Advances in Aerodynamics 2019年第1期1卷 14-38页

作者： S.Marko P.M.Ligrani Propulsion Research Center Department of Mechanical and Aerospace EngineeringUniversity of Alabama in Huntsville5000 Technology DriveOlin B.King Technology Hall S236HuntsvilleAL 35899USA

Unsteady flow characteristics of a normal shock wave,a lambda foot,and a separated turbulent boundary layer are investigated within a unique test section with supersonic inlet *** supersonic wind tunnel facility,containing this test section,provides a Mach number of approximately 1.54 at the test section *** shadowgraph flow visualization data are employed to visualize shock wave structure within the test *** data are analyzed to determine shock wave unsteadiness characteristics,including grayscale spectral energy variations with frequency,as well as time and space correlations,which give coherence and time lag properties associated with perturbations associated with different flow *** illustrate the complexity and unsteadiness of shock-wave-boundary-layerinteractions,including event frequencies from grayscale spectral energy distributions determined using a Lagrangian approach applied to shock wave location,and by grayscale spectral energy distributions determined using ensemble-averaging applied to multiple closely-located stationary pixel ***-correlation function results and two-point correlation functions(in the form of magnitude squared coherence)quantify the time-scales of periodic events,as well as the coherence of flow perturbations associated with different locations,over a range of *** time lag data provide information on the originating location of perturbation events,as well as the propagation direction and event sequence associated with different flow *** insight into spatial variations of time lag and flow coherence is provided by application of magnitude squared coherence analysis to multiple locations,relative to a single location associated with the normal shock wave.

关键词： Shock wave Supersonic flow time correlation Spatial correlation Autocorrelation Two-point correlation Frequency spectra Magnitude squared coherence time lag Lagrangian flow analysis Unsteady flow analysis

Mixing MC events in a reactor neutrino experiment

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Physics C 2013年第1期37卷 86-90页

作者：张一纯陈晓苏何苗黄性涛王萌李卫东张子平 University of Science and Technology of China Institute of High Energy Physics Chinese Academy of Sciences Shandong University

In reactor neutrino experiments, the analysis of time correlations between different physical events is an important task. Such analysis can help to understand the physical mechanisms of the signal and background events as well as the details of event selection and background estimation. This study investigates a ＂sampling and mixing＂ method used for producing large MC data samples for the Daya Bay reactor neutrino experiment. We designed a simple, generic mixing algorithm and generated large MC data samples for physics analysis from several samples according to their respective event rates. Basic plots based on the mixed data are shown.

关键词： reactor physics experiments time correlation sampling and mixing event rates

Two Methods to Solve the Ionospheric Electron Concentration Horizontal Gradient at Chongqing

在线全文

学校读者我要写书评

暂无评论

Wuhan University Journal of Natural Sciences 2000年第3期5卷 320-322页

作者： Chong Yan-wen, Huang Tian-xi, Zhao Zheng-yu, Xie Shu-guo, Yao Yong-gang College of Electronic Information, Wuhan University, Wuhan 430072, China Wuhan University College of Electronic Information Wuhan China (GRID:grid.49470.3e) (ISNI:***)

The electron concentration horizontal gradient vector of the ionosphere and its south-north and east-west components over Chongqing station are analyzed and calculated, using the first approximation, time correlation and space correlation and another approach introduced. And then, the validity of the two methods is analyzed and compared.

关键词： horizontal gradient of ionospheric electron concentration horizontal gradient vector space correlation time correlation

Several Kinematic Data Processing Methods for time-Correlated Observations

在线全文

学校读者我要写书评

暂无评论

Journal of Geodesy and Geoinformation Science 2019年第4期2卷 1-9页

作者： Bofeng LI Zhetao ZHANG College of Surveying and GeoInformatics Tongji UniversityShanghai 200092China School of Earth Sciences and Engineering Hohai UniversityNanjing 211100China

time correlations always exist in modern geodetic data,and ignoring these time correlations will affect the precision and reliability of *** this paper,several methods for processing kinematic time-correlated observations are ***,the method for processing the time-correlated observations is expanded and *** on the theory of maximum a posteriori estimation,the third idea is proposed after the decorrelation transformation and differential *** types of situations with and without common parameters are both investigated by using the decorrelation transformation,differential transformation and maximum a posteriori estimation ***,the characteristics and equivalence of above three methods are ***,in order to balance the computational efficiency in real applications and meantime effectively capture the time correlations,the corresponding reduced forms based on the autocorrelation function are ***,with GPS real data,the correctness and practicability of derived formulae are evaluated.

关键词： time correlation kinematic solution decorrelation transformation differential transformation maximum a posteriori estimation

Stochastic modeling of BeiDou double-difference observation and impact analysis

在线全文

学校读者我要写书评

暂无评论

Stochastic modeling of BeiDou double-difference observation ...

BeiDou Reliable Integer Ambiguity Resolution in the Presence of time-Correlated Obversion Errors

第十一届中国卫星导航年会

作者： Zhongzhi Wang Weikai Miao Yunzhong Shen College of Surveying and Geo-Informatics Tongji University

Double-difference integer ambiguity resolution(IAR) is playing the vital part in the high precision GNSS positioning and navigation. The IAR success rate depends on three factors: the functional model

关键词： BDS Stochastic model Cross correlation time correlation Baseline precision Integer ambiguity resolution success rate

来源： cnki会议 cnki会议 cnki会议评论

在线全文

学校读者我要写书评

暂无评论

BeiDou Reliable Integer Ambiguity Resolution in the Presence...

Stochastic model of GPS Doppler:evaluation,modeling and performance

第九届中国卫星导航学术年会

作者： Zeyu Xin Liang Li Chun Jia Hui Li Lin Zhao College of Automation Harbin Engineering University

time to first fix of ambiguity is always finished by using multiple sequential epochs in real‐time kinematic(RTK). Among different epochs, the residual observation errors exist the time correlation each other, which increases with the increase of distance of baseline. However, the characteristics of time correlation is always neglected by traditional RTK stochastic model to limit the performance of ambiguity resolution. In this paper, the characteristics of time correction among different epochs with BeiD ou observations are analyzed. The magnitudes of the time correction from GEO satellites of BeiD ou show larger than the MEO and IGSO satellites of BeiD ou and all MEO satellites of GPS. Therefore, in this paper, the characteristics of time correction are modeled by using first‐order Gaussian Markov processing to further adjust the RTK stochastic model. The proposed method is tested by a Monte‐Carlo simulation and actual Bei Dou observations. The simulated test shows that the proposed method can get more real probability of correct fix, compared with the model neglecting the characteristics of time correction. The actual test show that the proposed method deceases the probability of false alarm and missed detection by 50% and 15%, respectively, compared with the model neglecting the characteristics of time correction. As a result, the proposed method achieves the optimal ambiguity resolution performance taking the probability of success, false alarm and missed detection into account, simultaneously.

关键词： BeiDou satellite navigation system time correlation stochastic model multiple epochs Monte Carlo

来源： cnki会议评论

在线全文

cnki会议

学校读者我要写书评

暂无评论

Stochastic model of GPS Doppler:evaluation,modeling and perf...

Dynamic obstacles detection of tram based on laser radar

第三届中国卫星导航学术年会

作者： Zebo Zhou 1 Yunzhong Shen 2 Bofeng Li 31 Inst.of Astronautics and Aeronautics,University of Electronic Science Technology of China,No.2006,Xiyuan Ave,West Hi-Tech.Zone,611731,Chengdu,P.R.China2 Dept.of Surveying and Geo-informatics Engineering,Tongji University,1239 Siping Rd,200092 Shanghai,P.R.China3 GNSS Research Centre,Department of Spatial Sciences,Curtin University of Technology,GPO Box U1987,Perth WA 6845,Australia

Doppler measurement is popularly applied to estimate the vehicle’s velocity in GPS navigation and its stochastic characteristics attach a great importance to the quality of velocity *** this contribution,firstly a single differenced （SD） Doppler observation is established with the known ***,the precision of un-differenced Doppler measurement is derived from SD observation *** on the model above,the stochastic characteristics of Doppler measurements are evaluated,including elevation-dependent standard deviation,cross correlation between-frequency as well as the time correlation of each *** real Doppler data collected on ultra-short baselines using six types of receivers for a few hours are carried out to evaluate and analyze the Doppler stochastic *** results show that the precision of Doppler measurement is obviously dependent on satellite elevation *** measurements between dual-frequency are evidently cross-correlated and time correlation is proven nonexistent for all GPS *** on these experiment results,an elevation angle dependent Doppler stochastic model is proposed and fitted with curve fitting tool of *** last,both static and kinematic tests are carried out to demonstrate the efficiency of our proposed stochastic *** results indicate that the proposed Doppler stochastic model significantly improves the velocity accuracy and indirectly contributes to GPS positioning solutions.

关键词： GPS Doppler stochastic model cross correlation time correlation elevation angle model

来源： cnki会议评论

在线全文

cnki会议

学校读者我要写书评

暂无评论

Journal of Measurement Science and Instrumentation 2018年第4期9卷 316-320页

作者： KUANG Wen-zhen WU Meng-luo XU Li School of Automation & Electrical Engineering Lanzhou Jiaotong University Lanzhou 730070 China

The detection of obstacles in a dynamic environment is a hot and difficult problem.A method of autonomously detecting obstacles based on laser radar is proposed as a safety auxiliary structure of *** nearest neighbor method is used for spatial obstacles clustering from laser radar *** analyzing the characteristics of obstacles,the types of obstacles are determined by time *** were carried out on the developed unmanned aerial vehicle(UAV),and the experimental results verify the effectiveness of the proposed method.

关键词： laser radar tram dynamic obstacle detection spatial obstacle clustering time correlation nearest neigbor method