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ISSN 1000-0585
CN 11-1848/P
Started in 1982
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  • Table of Content
      , Volume 58 Issue 7 Previous Issue    Next Issue
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    COMPUTER SCIENCE AND TECHNOLOGY
    Orientation estimate of indoor mobile robot using laser scans
    LIU Huaping, ZHENG Xiangmei, SUN Fuchun
    Journal of Tsinghua University(Science and Technology). 2018, 58 (7): 609-613.   DOI: 10.16511/j.cnki.qhdxxb.2018.25.031
    Abstract   PDF (1843KB) ( 453 )
    The positioning of mobile robots indoors is very important with the controller needed to know both the location and the orientation. This paper presents a robot orientation regression model based on a support vector machine (SVM) to estimate the robot orientation. A laser radar signal is used as the model input with the orientation as the output. Tests show that the mean square error using an extreme learning machine model is 0.320 rad with a training time of 0.936 s while the mean square error based on the current support vector regression model is 0.113 rad with a training time of 9 273 s. Thus, the regression models can provide accurate robot position estimates.
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    Cubic causality modeling and uncertain inference method for dynamic fault diagnosis
    DONG Chunling, ZHAO Yue, ZHANG Qin
    Journal of Tsinghua University(Science and Technology). 2018, 58 (7): 614-622.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.029
    Abstract   PDF (4056KB) ( 389 )
    Complex systems need dynamic, real-time, reliable fault diagnostics but current methods have some shortcomings. This paper expands the dynamic uncertain causality graph method (DUCG) for temporal causality modeling and reasoning theory to correct the limits of the DUCG method and other probabilistic graphical models. A Cubic DUCG is developed that is characterized by a true dynamic model of dynamic problems. The cubic causality graph abandons the restriction of the Markov assumption usually used in temporal models with the fault formation, evolution, and development in dynamic systems represented by allowing causal connections to penetrate among any number of time-slices. The negative feedback dynamics is modelled intuitively combined with a reliable dynamic inference algorithm. Fault tests on the secondary loop of Ningde Nuclear Power Plant Unit 1 (CPR1000) simulator show that Cubic DUCG is accurate, efficient, and capable of dealing with the complex dynamics including negative feedback.
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    Power transformer fault diagnosis based on a support vector machine and a genetic algorithm
    KARI·Tusongjiang, GAO Wensheng, ZHANG Ziwei, MO Wenxiong, WANG Hongbing, CUI Yiping
    Journal of Tsinghua University(Science and Technology). 2018, 58 (7): 623-629.   DOI: 10.16511/j.cnki.qhdxxb.2018.25.032
    Abstract   PDF (2828KB) ( 572 )
    A fault diagnosis method was developed based on a support vector machine (SVM) and a genetic algorithm (GA) to improve the accuracy of power transformer fault diagnoses. The system receives 20 different inputs from 5 common dissolved gas analysis (DGA) approaches to create the original feature set. Then, the penalty parameters, the SVM kernel function parameters and feature subsets are randomly encoded into the GA chromosome using a binary code technique with the 5-fold cross validation accuracy of the training set used as the fitness function. The SVM parameters and the feature subsets are then simultaneously optimized by the genetic algorithm. Finally, DGA samples from the testing set are examined by the model trained with the optimal parameters and the selected feature subsets. The results demonstrate that this method is able to accurately distinguish power transformer faults. This method has fault diagnosis accuracy than GA-SVM models with a non-optimal feature subset, the IEC method, the back propagation neuro network (BPNN) and the Naïve Bayes method.
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    Incremental analysis of open source repositories
    XU Fu, YANG Zhanyu, CHEN Zhibo, SUN Yu, ZHANG Haiyan
    Journal of Tsinghua University(Science and Technology). 2018, 58 (7): 630-638.   DOI: 10.16511/j.cnki.qhdxxb.2018.25.029
    Abstract   PDF (2128KB) ( 463 )
    Code traceability is a common practice for reusing open source software which relies heavily on efficient code analysis methods. Existing methods mainly identify complete grammatical structures with the analysis time depending on the total code size, so they lack the ability to do incremental analyses and cannot be used to analyze large open source code repositories. An incremental analysis method was developed here to analyze only the changed parts in code repositories based on the similarity between adjacent snapshots to effectively reduce the analysis scale. The method first parses snapshots to retrieve the modified content between snapshots and then maps these modifications into complete, analyzable functions. These functions are then converted to fingerprints for comparisons. This method significantly reduces the scale of the open source code repositories compared with traditional analysis methods to speed up function comparisons for better traces of the origin of open source codes.
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    HYDRAULIC ENGINEERING
    Integrated risk evaluation of large river-crossingbuildings in the Middle of the South-to-North Water Diversion Project
    HAN Xun, AN Xuehui, LIU Chunna
    Journal of Tsinghua University(Science and Technology). 2018, 58 (7): 639-649.   DOI: 10.16511/j.cnki.qhdxxb.2018.25.030
    Abstract   PDF (1647KB) ( 431 )
    An integrated static and dynamic risk evaluation system was developed to classify the potential risks of large river-crossing buildings over the South-to-North Water Diversion Project. The system constructs an index based on design and construction quality information, the characteristics of different types of buildings and external conditions including the hydrology and geology. The static risk is given by a neural network model while the dynamic risk is related to flood, freezing, flushing and tensile stress conditions. The integrated risk index compares well with results in the literature with good results given in a case study.
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    Analysis on the relationship between fish diversity and watershed features in the Yangtze River Basin
    SHI Ruijie, TANG Lihua, GAO Guangdong, YANG Dawen, XU Xiangyu
    Journal of Tsinghua University(Science and Technology). 2018, 58 (7): 650-657.   DOI: 10.16511/j.cnki.qhdxxb.2018.22.033
    Abstract   PDF (2882KB) ( 599 )
    Fish diversity is a key indicator of the quality of a river water ecosystem. This study used the fish diversity to analyze the main factors influencing the Yangtze River water ecosystem. A correlation analysis and a gray correlation analysis were used to identify the main factors influencing the fish diversity. A quantitative relationship between the fish diversity and the watershed features was developed using a multiple variable regression. The results show that the main factors influencing the fish diversity in the mainstream and its tributaries in the upper reaches of the Yangtze River are natural factors such as elevation and basin area. Runoff is the main factor influencing the mainstream and its tributaries in the upper reaches except Tongtian, the upper part of Jinsha River and the Yalong River with altitude exceeding 3 500 m. The main factor influencing the fish diversity in the middle and lower reaches is land use types. The transition of the key factors from natural factors to land use types reflects the increasing influence of human activities on the river water ecosystem.
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    NUCLEAR ENERGY AND NEW ENERGY
    Modeling and verification of computerized procedures in high temperature gas-cooled reactor nuclear power plants
    XU Xiaona, HUANG Xiaojin
    Journal of Tsinghua University(Science and Technology). 2018, 58 (7): 658-663.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.033
    Abstract   PDF (1222KB) ( 255 )
    The computerized procedures in high temperature gas-cooled reactor(HTGR)nuclear power plants need to be carefully monitored to efficiently control the operating characteristics of multiple nuclear steam supply system modules with one steam turbine. A normal execution process model and an interrupted variant execution process model were developed for HTGR power plants using the improved colored Petri net modeling method. The models were shown to accurately monior the execution of the computerized procedures. An analysis of a typical abnormal operating procedure for an HTGR plant shows that the modeling and verification based on the colored Petri net is effective and provides a theoretical foundation for the development of HTGR control systems.
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    Prestress measurement during glass-metal sealing based on a fiber sensor
    LI Mingze, YAN He, DIAO Xingzhong, ZHANG Yong
    Journal of Tsinghua University(Science and Technology). 2018, 58 (7): 664-670.   DOI: 10.16511/j.cnki.qhdxxb.2018.21.017
    Abstract   PDF (1836KB) ( 356 )
    An optical fiber sensing method was developed for prestress measurements of glass-metal seals. A fiber Bragg grating sensor was embedded in a hole in the sealing glass. The glass was then heated to melting, cooled and solidified so that the optical fiber sensor, the glass and the metal shell were sealed together. The fiber sensor gave real-time measurements of the sealing temperature during the sealing. The changes of the Bragg wavelength were used to measure the axial strain along the measurement path in the glass seal. The global stress distribution in the glass was then calculated by a finite element analysis. Tests show that the fiber sensor can monitor the temperature and stress during the sealing process and an optimized sealing process can be achieved by using prestress measurements in the glass as an indicator.
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    MECHANICAL ENGINEERING
    Vibration transmission mechanical model between the shaft and housing of a high speed motor spindle
    LIU Chengying, ZHENG Feng, WANG Liping
    Journal of Tsinghua University(Science and Technology). 2018, 58 (7): 671-676.   DOI: 10.16511/j.cnki.qhdxxb.2018.21.015
    Abstract   PDF (4810KB) ( 366 )
    Spindle vibration is an important factor affecting the machining accuracy of machine tools with the vibrations reflecting a large amount of working condition information about the machine tool. A vibration transmission mechanics model was developed to model the coupling between the shaft and the chassis to improve machining accuracy when measuring the acceleration of the main shaft outside the shell. Hertz theory was used to calculate the bearing stiffness because of unknown parameters in the mechanical model. The base stiffness was calculated using Ansys and Hooke's theory. The vibrations of a 170XDS20Z11 motorized spindle were analyzed with the results showing that the spindle vibrations can be efficiently and accurately measured by measuring the shell vibrations. This theory can be applied to indirect measurements of spindle vibrations to improve measurement accuracy.
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    Cyclic loading behavior and microstructure characterization of ultra-high strength steel Q&P980
    HAN Fei, ZHOU ZiHao, WANG Yun
    Journal of Tsinghua University(Science and Technology). 2018, 58 (7): 677-683.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.030
    Abstract   PDF (4173KB) ( 435 )
    The true stress-strain curve for ultra-high strength steel Q&P980 is obtained through cyclic loading of the ultra-high strength steel in terms of the number of cycles, cyclic position and anisotropy of the cyclic tensile test. The properties of the unloading ring were also analyzed to accurately characterize the mechanical properties. A metallographic microscope using X-ray diffraction (XRD) was then used to study the microstructural changes. The results show that increasing the deformation reduced the slope of the unloading and reloading curves. In addition, reducing the austenite content increased the springback strain, elongation and strength, which is called the transformation induced plasticity (TRIP) effect. For similar amounts of deformation, increasing the number of cycles did not increase the springback strain but reduce it when the cycle number increased to 10. The cyclic loading weakens the sheet anisotropy, but has little effect on the elastic modulus and springback.
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    AUTOMOTIVEENGINEERING
    Fuel-saving driving strategy for connected vehicles in multiple signalized intersections
    XIN Zhe, YU Zhou, GUO Qiangqiang, LIN Qingfeng, LI Shengbo, XU Chenxiang
    Journal of Tsinghua University(Science and Technology). 2018, 58 (7): 684-692.   DOI: 10.16511/j.cnki.qhdxxb.2018.22.036
    Abstract   PDF (2219KB) ( 379 )
    This paper describes a fuel-saving driving strategy for multiple intersections with known signal times. The fuel-saving strategy with two signals is constructed as a constrained optimal control problem with the vehicle longitudinal dynamics model as the state equations and with the vehicle physical performance and environmental conditions as constraints. A reverse recursive calculational method based on dynamic programming is used to solve the problem with an accelerate-cruise-decelerate fuel-saving driving strategy. The fuel-saving modes for two intersections are then extended to multiple intersections as a shortest path problem solved by the Floyd-Warshall algorithm. A fuel-saving driving strategy is then developed for multiple intersections with the same or different speed limits.
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