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Table of Content

    28 May 2016, Volume 50 Issue 05 Previous Issue    Next Issue
    Modified Hungarian Algorithm and Fuzzy Logic ControlBased Scheduling Method for Interbay Material Handling System
    ZHANG Jie1,PAN Cong1,SUN Yinbin1,WU Lihui2,QIN Wei1
    2016, 50 (05):  647-653. 
    Abstract ( 1485 )   Save
    Abstract: In order to fulfill the multiobjective and realtime demands of the Interbay material handling system, an intelligent dispatching method based on modified Hungarian algorithm and fuzzy logic control was proposed. First, a multiobjective cost function was calculated with the weighted sum of four factors, i.e., wafer lots’ delivery time, waiting time, due date, and production factor. Then, the weights were dynamically adjusted by using fuzzy logic control, and thus wafer lots’ multiobjective cost was calculated in realtime. Finally, a modified Hungarian algorithm was proposed to get the assignment scheme between multiple wafer lots and vehicles to minimize the total cost. The simulation results show that the proposed intelligent dispatching method improves the system efficiency in terms of mean delivery time, mean waiting time and so on. Meanwhile, compared with several conventional dispatching approaches, the proposed dispatching method efficiently reduces the average delivery time and cycle time and has a better comprehensive performance.
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    Sphericity Error Estimation Method Based on Spherical Grinding Marks
    2016, 50 (05):  654-659. 
    Abstract ( 988 )   Save
    Abstract: A mathematical model was established and analysis of geometric deviation was conducted based on spherical grinder to study the influence of the grinder on sphericity error. The grain trajectory considering geometric deviation was studied and the relevant model was built. The grossed ratio of grinding marks was defined as a statistic feature to evaluate the geometric deviation. A novel vision detectionbased method was proposed to estimate the sphericity error based on the crossed ratio of grinding marks. The proposed method enables insitu evaluation of sphericity error and is meaningful for further insitu sphericity error compensation.
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    Integrating Failure and Economic Dependence for Maintenance of Electric Multiple Unit MultiComponent System
    WANG Hong,DU Weixin,LIU Zhilong,YANG Xinzhu,LI Zhongxue
    2016, 50 (05):  660-667. 
    Abstract ( 948 )   Save
    Abstract: In order to explore the effects of dependence among components on the maintenance plan of the system, based on the theory of correlation among components and relationship between components described in failure chains, components were numbered according to the failure level in the chains. Besides, the reliability model of each component in complex mechanical system was established. By dividing the maintenance costs of the components into fixed and variable costs, the economic relevance model was completed, the maintenance cost and maintenance time was treated as the optimal goals, and the group maintenance strategy was implemented with indefinite period for various components in the system. The application of genetic algorithms to optimize maintenance plan and the computational experiments demonstrate that the proposed model can get a proper maintenance schedule. The analysis of key sensitive parameters indicates that in setting reasonable lowest reliability, components with larger deterioration rate should be focused on and the flexible connection between components should be strengthened.
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    Modeling of Geometric and Thermal Complex Positioning Error of CNC Machine Tools Based on Cubic Spline Interpolation
    TUO Zhanyu,HUANG Yiqiao,SHEN Muwen,YANG Jianguo
    2016, 50 (05):  668-672. 
    Abstract ( 988 )   Save
    Abstract: Based on the analysis of the mathematical laws of machine error data up to the thermal equilibrium, the geometric error and thermal error were separated and the mathematical model for geometric and thermal error was established using the cubic spline interpolation algorithm and the residual error of the linear fitting. The experimental results show that the proposed model based on pressing boundary condition can effectively fit the positioning error curve and significantly improve the positioning accuracy of CNC machining by up to 80% at least. The method can be used for positioning error compensation in different processing times or at different temperatures. The modeling process is simple and fast and the result is applicative.
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    Thermal Error Modeling and RealTime Compensation of CNC Machine Tools Based on Time Series Method
    YAO Xiaodong1,3,HUANG Yiqiao1,MA Xiaobo2,XUE bo3,YANG Jianguo1
    2016, 50 (05):  673-679. 
    Abstract ( 973 )   Save
    Abstract: The principle and process of thermal error modeling on NC machine tools based on the time series method were presented. Comprehensive analysis software of the time series method was used to preprocess the thermal error datum, recognize the mode, estimate the parameters of the model, and distinguish and confirm the model order through a loop computing method. After that, a realtime compensation model was established which showed the changing rule of thermal error on NC machine tools. The iteration coefficients were adjusted in real time with the analysis and comparison of the variation of temperature. The thermal error compensation model established was used to realize the realtime compensation for the thermal drift error of CNC machine tools by making use of the realtime compensation system. The processing results with compensation showed that the errors of the workpieces in diametric direction were reduced from 112 μm to 7 μm, which demonstrated that the machining precision and stability of the machine tool were improved significantly.
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    Optimization of Central Angle of Transition Curve of Cam-Rotor Vane Motor
    YUAN Fan1,WANG Xuyong1,ZHANG Wenjun1,TAO Jianfeng1,MIAO Zhonghua2
    2016, 50 (05):  680-685. 
    Abstract ( 957 )   Save
    Abstract: The continuous rotary cam-rotor vane motor, a kind of hydraulic servo element to convert fluid potential energy to mechanical energy, is the appropriate actuator for the hydraulic servo system which has good performance requirements. The parameter optimization design method which focuses on the transition curve segment of the camrotor outer contour was proposed herein. The relationships between the pressure angle and the disturbing torque, the flow fluctuation rate, the leakage and the central angle of transition curve were obtained based on theoretical derivation and analyses. Theoretical basis was conducted and optimized parameter of this kind of vane motor was obtained through analytical calculation and simulation. Experimental verification indicated that the camrotor vane motor had a very good servo precision and proved the feasibility and validity of the parameter optimization design method.
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    Thermal Error Modeling of Machine Tool Spindle Based on Particle Swarm Optimization and Neural Network
    MA Chi,ZHAO Liang,MEI Xuesong,SHI Hu,YANG Jun
    2016, 50 (05):  686-695. 
    Abstract ( 911 )   Save
    Abstract: To overcome the lower accuracy, poor convergence and worse generality of the thermal error modeling method based on BP neural network, the fuzzy cluster theory was used to group temperature variables and the correlation analysis was conducted to select thermal senstive points to mine the correlation between temperature variables and thermal errors and to reduce the coupling among temperature variables. Besides, the reciprocal of the square sum of the residual errors was regarded as the individual fitness function in the PSO algorithm. Moreover, the performance code of the head of the individual was regarded as the number of the nodes in the hidden layer and the body of the individual was mapped to the weights and thresholds of the BP network. The extreme value and global extreme value of the individual were tracked to update the speed and position of the individuals. Then, the fivepoint method was utilized to measure the spindle thermal errors of a jigboring. After that, the elongation and thermal tilt angle models were established based on the BP and PSOBP models. The results show that the thermal error model based on PSOBP model can predict thermal errors of the machine tool spindle under different cutting conditions and the results validate the effectiveness of the measuring and modeling methods.
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    Unidirectional Proportional PumpControlled Asymmetric Cylinder Control Method Based on Predictive Control
    WANG Xuan,TAO Jianfeng,ZHANG Fengrong,WU Yajin,LIU Chengliang
    2016, 50 (05):  696-701. 
    Abstract ( 867 )   Save
    Abstract: To resolve the problem of nonovershooting position control of the unidirectional proportional pumpcontrolled asymmetric cylinder system, this paper proposed a threeorder state space model with constraints to describe the system of unidirectional proportional pumpcontrolled asymmetric cylinder. It also proposed a design of model predictive controller applicable to this model to guarantee its nonovershooting output. The simulation results indicate that the proposed method has successfully resolved the overshooting problem without introducing nonlinear characteristics, thus realizing the aim of highprecision position control under multiple constraints.
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    Type Synthesis of FullyIsotropic and Decoupled 3T1R Parallel Mechanism
    CAO Yi1,2a,2b,3,QIN Youlei1,3,CHEN Hai1,3,LIU Kai1,3,ZHOU Hui1,2a,2b,3
    2016, 50 (05):  702-709. 
    Abstract ( 1069 )   Save
    Abstract: In order to obtain fullyisotropic and decoupled structures of the parallel robot, a very simple yet very effective structural design was proposed based on GF set. First, the basic concept of GF set, algorithms and the type synthesis principle, requirements for rotation based on GF set were introduced. Next, the selection criterion of the input pair and type synthesis principle of decoupled branches were given, which ensured that the input of various branches were isotropic and the decoupled. According to the type synthesis theory, the specific process for structural synthesis of 3T1R four degrees of freedom fullyisotropic and decoupled parallel mechanism were accomplished. Simultaneously, a lot of new mechanisms were obtained. Finally, the screw theory was applied to analyze the kinematic characteristic of the parallel mechanism synthesized above. The expression of the Jacobian matrix was deduced which validated the fullyisotropic of the mechanism and demonstrated the effectiveness of the novel method of structural synthesis for parallel mechanisms.
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    Modeling of Thermally Induced Grating Positioning Error of Large Machine Tools Based on Temperature Integral Method
    FENG Wenlong,HUANG Yiqiao,TUO Zhanyu,LI Huimin,YANG Jianguo
    2016, 50 (05):  710-715. 
    Abstract ( 961 )   Save
    Abstract: To decrease the grating positioning error of large machine tools, a novel modeling theory based on thermal characteristic analysis with its compensation method were proposed. The case of the error was analyzed to be the thermal deformation of the grating scale, whose manifestations were discussed. By analyzing the thermal characteristic, the mathematical expression between the elongation of grating scale and the variation of temperature was established. Several temperature sensors were installed on the grating scale, with which the temperature of grating scale were recorded. The temperature of each point on the grating scale were calculated by interpolating between adjacent sensors. The thermally induced positioning error of the grating scale model was established by conducting the integral for the variations of position and temperature. By using the developed compensation system, the compensation for floor type borer TK6920 was implemented by applying the established model. The results show that the thermally induced positioning error of the grating scale has been decreased by 90% and the residual error is less than 1.5 μm/m. The positioning accuracy of the grating scale is significant improved.
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    Commutating Characteristics of Low-Friction Cylinder Based on Air Bearing
    ZHU Xiao,TAO Guoliang
    2016, 50 (05):  716-722. 
    Abstract ( 946 )   Save
    Abstract: In order to study the working condition of the bearing in the commutation process of the air bearing based lowfriction cylinder, the mathematical model of the commutation was established based on the theory of charging, releasing process of fixedvolume chamber and the leakage model of the air bearing. The characteristic values, the commutation time and the pressure fluctuation ratio were proposed in theoretical analysis and simulated base on Matlab. The simulation result shows that the inner chamber of the piston has a pressure keeping effect in the commutation process, and as the commutation process quickens, the pressure fluctuation ratio decreases. A test bench was set up to further study of the commutation characteristics. The experimental results confirmed the simulation result, and proved that with this design the cylinder could achieve a smooth commutation. The experiment data with different additional chamber can also provide reference for the best commutating time.
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    Bearing Fault Pattern Recognition Using Harmonic Wavelet Sample Entropy and Hidden Markov Model
    LI Qing1,LIANG Steven Y1,2,YANG Jianguo1
    2016, 50 (05):  723-729. 
    Abstract ( 922 )   Save
    Abstract: According to the excellent characteristics of the nonstationary vibration signals decompose with harmonic wavelet and the strong temporal pattern classification ability of hidden Markov model(HMM), a bearing fault pattern recognition based on harmonic wavelet sample entropy and HMM was proposed. First, by applying the harmonic wavelet to decompose each bearing fault signal, the frequency layer characteristics of harmonic wavelet threedimensional time frequency trellis was used to estimate the reasonable sample entropy dimension and threshold value, and the feature vector sequence was constructed by extracting sample entropy of rolling bearing each layer vibration signal. Then, the feature vector sequence of former 120 groups were input into HMM to be trained, so as to acquire various models corresponding to different faults,and the remaining 80 groups are tested and identified. Finally, the bearing fault types were identified by comparing the logarithmic likelihood probability value. The actual identify results and comparison with the BP, RBF neural network model prove that this coupling method has better identification accuracy and stability.
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    High-Precision and Fast Evaluation of Spatial Straightness Error of 3D Coordinate Point Set
    HUANG Shouguo1,CHEN Jianduan2
    2016, 50 (05):  730-735. 
    Abstract ( 1084 )   Save
    Abstract: This paper proposed a novel highprecision, robust and fast spatial straightness error evaluation algorithm called 3 points highprecision fast algorithm (3PHFA) to deal with the problem of low precision and low efficiency when evaluating spatial straightness errors. With reference to the related national standard for construction of mathematics models, the algorithm mainly includes 3DLSA fitting, space coordinate translation, coordinate projection, and determining minimum circumscribed circle (MCC), which can determinate the minimum cylindrical surface (MCS). By adding the highly effective search algorithm to the 3DLSA algorithm, it almost improves the evaluation accuracy by 20% in less than 1 second. Compared with other evaluating algorithms, the 3PHFA has the advantages of high efficiency and accuracy, and better robustness. It is applicable to the realtime processing system such as coordinate measuring machine (CMM), and has a good practical value for evaluating machine parts.
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    Preventive Maintenance for Machine Operating in Dynamic Environmental State
    HU Jiawen,JIANG Zuhua,HAN Lijie
    2016, 50 (05):  736-741. 
    Abstract ( 859 )   Save
    Abstract: This paper dealt with a single machine system operating at timevarying environmental state. Assuming that the failure time distribution of the system can be represented by the accelerated life model (ALM) at different environmental states, the evolution model of the hazard rate was built when environmental state changes. The time interval operated at different environmental states was converted to the equivalent working time at the baseline state, the imperfect maintenance model was proposed at the dynamic environmental state with the recursion decline factor and failure rate ascending factor. Considering the fact that the future environmental state was unknown, and taking the availability of current PM interval as an objective and a given reliability threshold as a constraint, the optimal PM intervals were calculated dynamically along with variable environmental state. The results of a numerical example indicate that the PM strategy is valid for a single machine at timevarying environmental state at a finite interval.
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    Multi-Dimensional DecisionMaking Analysis Based on Integrated Performance Evaluation
    WU Yizhou,MIAO Rui,GAO Zhe,GU Xiyao,WU Qi,ZHANG Jie
    2016, 50 (05):  742-749. 
    Abstract ( 890 )   Save
    Abstract: Performance evaluation of enterprises is a multicriteria decisionmaking problem. A system of N dimensions was constructed in view of the limitations of the previous research, which could be used to evaluate the corporate performance in multidimension. Four dimensions, that is, value, risk, cost and benefit were studied for their importance in the real problems. The MACBETH multicriteria method was used to quantify the elementary performances. Moreover, the 2additive Choquet integral considering the interactions between criteria was added to the model while reducing the complexity of the calculations. The system enhances the comprehensive of performance assessment and effectively helps enterprises to make multiple criteria decisions.
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    Channel Prediction Based on Grassmannian Manifold for Limited Feedback Multiple Antenna Systems
    LI Ting,LI Fei
    2016, 50 (05):  750-756. 
    Abstract ( 812 )   Save
    Abstract: Aimed at the feedback delay problem in the multipleantenna limited feedback precoding systems, and based on the full use of the time correlations of timevarying channel, the linear vector spaces spanned by the channel direction vector was modeled as points on a Grassmannian manifold, and the adjacent channel directions were assumed to move along the geodesic on a Grassmannian manifold, in order to compensate the effect of feedback delay on the performance of the system. Meanwhile, by exploiting the differential geometric properties of the Grassmannian manifold, the dynamic focused codebook with high resolution on the tangent space of Grassmannian manifold was proposed, which tracked the correlated channel and updated itself accordingly. The computer simulation results show that the system performance of the proposed Grassmannian predictive precoding is obviously superior to that of memoryless quantitation precoding which has a shortcoming of feedback delay. Moreover, compared with the channel prediction of fixed codebook, the proposed dynamic focused codebook with high resolution is equipped with the higher quality of keeping tracking with the timevarying channel.
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    Separation of Weak MultiSource Fault Acoustic Emission Signals Based on Wavelet Packet and Independent Component Analysis
    WANG Xianghong1a,1b,YIN Dong1a,HU Hongwei1a,MAO Hanling2
    2016, 50 (05):  757-763. 
    Abstract ( 847 )   Save
    Abstract: Multisource fault signals (such as crack and friction signals) produced from rotating machinery are difficult to detect and separate; therefore, an extraction method of multisource fault signals based on wavelet packet analysis (WPA) and independent component analysis (ICA) was proposed. The wavelet packet technology was used to reduce the noise outside the frequency band of the linear mixed signals. The signals were decomposed by db2 wavelet into five layers while the signals with the frequency band from 62.5 to 187.5 kHz were reserved. Then, the mixed signals were separated by using the FastICA algorithm. Finally, the shrinkage function was used to reduce the noise in the frequency band. By extracting the noisy weak signals with different input SNRs, the results show that this method can effectively extract the crack and the friction signals with the input SNR higher than -15 dB. Their output SNRs are -1.31 and -1.36 dB and the correlation coefficients are 0.62 and 0.63, respectively, which are higher than those obtained by using the method combined WPA and FastICA and only FastICA algorithm. The SNRs are (-1.74 and -2.06 dB) and (-4.57,-4.31 dB) and correlation coefficients are (0.59,0.59) and (0.17,0.19) for the combined method and FastICA method, respectively. Thus, the method is very suitable for extraction and separation of multisource weak signals.
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    Wideband Azimuth and Polarization Joint Estimation of Conformal Array
    HOU Wenlin1,2,GUO Ying2,ZHANG Kunfeng2,HU Yue1,2,ZHANG Ling2
    2016, 50 (05):  764-770. 
    Abstract ( 889 )   Save
    Abstract: Taking into account the direction of arrival (DOA) of wideband signals for conformal array antenna, a joint DOA and polarization estimation algorithm was proposed. First, the narrow subband was acquired by using the short time Fourier transformation (STFT). Then, two sets of snapshots which satisfied rotation invariance were construsted via timedelayed signal. So the array steering matrices corresponding respectively to different narrow subbands were estimated. Furthermore, making use of the frequency difference of different narrow subbands, the 2D DOA and polarization estimation were acquired jointly. The proposed method can be applied to arbitrary conformal array structure without parameter matching and searching process. The algorithm can also reduce the computational complexity considerably and can efficiently improve the practical engineering value. MonteCarlo simulation demonstrates the good performance and the effectiveness of the proposed method.
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    A Modified Generalized Least Square Registration Algorithm on WGS-84 Coordinate
    LI Jiaqiang1a,2,ZHAO Chunyan1b,2,CHEN Jinli1a,1b,ZHAO Ronghua1b,2
    2016, 50 (05):  771-775. 
    Abstract ( 977 )   Save
    Abstract: Aimed at the low convergence rate and unstable convergence performance of the generalized least squares algorithm on WGS84 coordinate, a modified generalized least square algorithm was proposed which took convergence steps as the weighting factor for measurement accuracy of the generalized least squares algorithm, making measurement accuracy vary with the changes of steps in order to achieve the decrease of the convergence steps and the advance of the stability after convergence. So this algorithm improves the performance of target tracking and positioning. Simulation results show that the modified generalized least square algorithm is superior to the generalized least square algorithm, verifying the feasibility of the proposed algorithm.
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    A Novel MU-FM-DCSK Secure Communication System
    ZHANG Gang,LI Zejin,ZHANG Tianqi
    2016, 50 (05):  776-781. 
    Abstract ( 967 )   Save
    Abstract: In view of the defects of low data rate and low security in differential chaos shift keying (DCSK), a novel multiple userfrequency modulation differential chaos shift keying (MUFMDCSK) secure communication system was proposed. In the new scheme, the information of different users was multiplied by different adjusting parameters and was modulated by the frequency modulated chaotic signal. The receiver used the correlation demodulation through which the information could be restored by detecting the different output of the correlator. Therefore, the security of the system was significantly enhanced, and the data rate was greatly raised. The analysis and simulation results show that the BER in the proposed scheme is significantly superior to that of the existing multiuser chaos shift keying communication system, especially as the SNR increases above a certain threshold.
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    Acquisition Algorithm Combining Parallel Code Phase with FractalReconstruction of TMBOC Modulation Signal
    ZHANG Tianqi,YAN Zhenhua,OU Xudong,QIAN Wenrui
    2016, 50 (05):  782-787. 
    Abstract ( 1038 )   Save
    Abstract: Aimed at the ambiguity in acquisition of the TMBOC modulation signal caused by the multipeaks of autocorrelation function, this paper proposed an acquisition algorithm combining parallel code phase with fractalreconstruction to remove ambiguity. The algorithm demodulates the received signal, and uses local PN code and BOC code to correlate with demodulated signal. Next, it takes the absolute value of the results and addition. Finally, it utilizes the fractalreconstruction algorithm to fold a new correlation function without subpeaks. Theoretical analysis and simulation results show that the algorithm can capture the signal effectively with low complexity. Moreover, its correlation peak increases by 43.7% compared to the ASPeCT algorithm, and its main peak power reaches 96% through twopath channel.
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    Channel Access Strategy Based on Dynamic MultiSpectrum Sensing in Cognitive Radio Networks
    XIAO Nan,LIANG Jun,LIU Yulei
    2016, 50 (05):  788-795. 
    Abstract ( 854 )   Save
    Abstract: Aimed at the low allocation efficiency of primary spectrum of channel access strategies based on fixed spectrumsensing, a novel channel access strategy based on dynamic multispectrum sensing was proposed for cognitive radio network. The cognitive radio base station could adjust the number of sensing channels allocated to secondary users according to their access request priority and discover the probability of idle spectrum in a single time slot. The optimized number of sensing spectrums allocated to secondary user was analyzed. As the proposed strategy is formulated as a channel selection problem coupled with a channel assignment problem, the myopic sensing policy was subsequently investigated and a Markov chainbased dynamic channel assignment algorithm was proposed. The results of simulation indicate that the proposed channel access strategy has achieved significant performance improvements in network throughput compared to the existing strategies, and the average channel access delay of secondary users has been declined while the fairness of channel access is better.
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    Hydrodynamic Speed Adjusting Control System for Marine Power
    CAI Wei1,LI Qin1,MA Wenxing1,SONG Bin2
    2016, 50 (05):  796-802. 
    Abstract ( 830 )   Save
    Abstract: Based on the analysis of the working principle of the hydrodynamic speed adjusting device, a mathematical model was established, the parameters for transmission system were determined, and the corresponding control system was designed and simulated. The simulation results show that the adjustable guide vane, which is subjected to the control system, can keep the output speed constant when the input speed varies. The traildevice was manufactured, and the test bench for the hydrodynamic speed adjusting device was accomplished. The test result verified that the hydrodynamic speed adjusting device for marine power is feasible and applicable, which lays a foundation for further study.
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    Adjacent Tunnels and Tunnel Protection
    ZHANG Hongbing,FAN Fan,HU Hao
    2016, 50 (05):  803-809. 
    Abstract ( 978 )   Save
    bstract: The influence of different distribution types of excavation adjacent to tunnels was studied systematically by classification and induction of the distribution types of excavation. The action mechanism of the effects was revealed and the corresponding protective measures was proposed to provide the theoretical support for the excavation construction and protection of the adjacent tunnels. According to the position relationship between the excavation and the adjacent tunnels, the excavation can be divided into two groups, onesideexcavation and twosideexcavation. According to the excavation depth and the sharing of retaining structure, the excavation can be divided into nearexcavation, closeexcavation and excavationinexcavation. The influence of excavation on the adjacent tunnels can be summarized as spacetime effect, earth pressure multiple unloading, soil deformation superposition effect, groundwater influence and so on. To control the influence of excavation on adjacent tunnels, some measures can be taken such as reasonable partition, reasonable arrangement of construction sequence, adjustment of structural stiffness and reinforcement. Finally, the project of Longhua Aviation Center in Shanghai was analyzed in detail by using the numerical analysis method and field monitoring method which can provide reference for other projects of excavation group construction and tunnel protection.
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    EntropyMonotone Scheme for Linear Advection Equation
    WANG Zhigang1,2,CUI Yanfen2
    2016, 50 (05):  810-813. 
    Abstract ( 939 )   Save
    Abstract: In numerical computation of conservation laws, the problem of the wear of linear discontinuity is of great concern. In order to decrease the wear of linear discontinuity, an entropymonotone scheme was designed for the linear advection equation. This scheme is a Godunov scheme, which includes reconstruction, evolution, and cellaveraging. Different from the traditional Godunov scheme, this scheme simultaneously computes the numerical solution and numerical entropy, and uses them to reconstruction the “step function” in each cell. Numerical experiments show that this scheme is very effective for the simulation of linear discontinuity.
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    Value Distribution of Difference of Transcendental Meromorphic Function in Complex Domain
    JIN Jin1,2,ZHAO Haolan3
    2016, 50 (05):  814-818. 
    Abstract ( 923 )   Save
    Abstract: Based on the Nevanlinna theory of the value distribution of meromorphic functions difference, the value distribution problem of transcendental two meromorphic function difference was discussed, two new results were obtained, and some existing results were improved and generalized.
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