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ISSN 1000-0585
CN 11-1848/P
Started in 1982
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  • Table of Content
      , Volume 55 Issue 7 Previous Issue    Next Issue
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    MECHANICAL ENGINEERING
    Real-time motion planning algorithm for dynamic flight simulators
    GUAN Liwen, LIU Hui, FU Meng
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 709-715.  
    Abstract   PDF (1415KB) ( 839 )
    Dynamic flight simulators (DFS) use a centrifuge to simulate sustained G-loads. The motion planning for the DFS directly affects the accuracy of the G-load simulations. This paper describes a real-time motion planning algorithm for a flight simulator. The G-load simulation model is given but is difficult to solve when the G-loads are negative. A real-time motion planning algorithm with two-dimensional interpolation is used to generate both a trapezoidal G-load curve and three-axis G-load commands. The simulation results show that the simulated G-loads precisely track the commands. The algorithm is accurate and practical.
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    Design of beam pose automatic alignment system for an interference lithography scanner
    ZHU Yu, WANG Leijie, ZHANG Ming, QI Lishan
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 716-721,733.  
    Abstract   PDF (2009KB) ( 761 )
    An accurate automatic beam alignment system is designed for beam alignment in an interference lithography scanner. The iterative alignment system uses the previously measured value in the next iteration step for the iterative alignment procedure that iterates the beam alignment in two orthogonal planes. The alignment procedure then compensates for the error accumulation and pico-motor coupling in the two orthogonal plane. Tests demonstrate that the position and angle accuracy of this automatic beam alignment system with four degrees of freedom are better than 5 μm and 3 μrad, which satisfies the alignment requirements for an interference lithography scanner.
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    Design of phase locking system for an interference lithography scanner
    WANG Leijie, ZHANG Ming, ZHU Yu, LU Sen, YANG Kaiming
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 722-727.  
    Abstract   PDF (1380KB) ( 899 )
    An interference image phase locking system is built for an interference lithography scanner. This system has a feedback control system and uses the homodyne interference method for fast, accurate phase drift measurement and an acousto-optic modulator to accurately shift the phase of the interference image. Tests show that the system has ±1/25 interference image period accuracy when the system uses closed-loop control, which illustrates that this phase locking system has good locking performance. In addition, the system has a short optical path, is easy to assemble and adjust, and has a high laser utilization ratio, so the system is suitable for high-speed interference lithography scanners.
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    Circuit compensation for efficient contactless power transmission in ultrasonic vibration systems
    SHEN Hao, FENG Pingfa, ZHANG Jianfu, YU Dingwen, WU Zhijun
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 728-733.  
    Abstract   PDF (2064KB) ( 1231 )
    Circuit compensation was used to improve the contactless power transmission efficiency in ultrasonic vibration systems. The circuit compensation model was based on an equivalent circuit model of the piezoelectric vibrator and a mutual inductance model of the loosely coupled system. The primary and secondary circuits were independently compensated to eliminate the effects of the mutual inductance. A system was built with test showing that the amplitudes were significantly improved by the compensation, especially for large air gaps and large power loads. This study indicates that circuit compensation effectively reduces the reactive power losses and improves the power transmission efficiency of the contactless power transmission in ultrasonic vibration systems.
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    Influence of low atmospheric pressures on the arc characteristics of self-shielded flux-core wire
    ZHU Zhiming, FAN Kaiguo, LIU Han, WANG Yongdong
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 734-738.  
    Abstract   PDF (1142KB) ( 890 )
    The welding characteristics of self-shielded flux-core wire were studied experimentally and theoretically for various atmospheric pressures to study the influence of low atmospheric pressures on the arc characteristics.The results show that the static arc of self-shielded flux-cored wire tends downward but moves upward with increasing welding torch height (arc length). At low atmospheric pressures, the gas density and temperature decrease in the arc region, which reduces the conducting particle density and the welding current. The arc expansion increases the arc column diameter and decreases the electric field intensity. With the increase of the voltage drops in the cathode and anode, the total arc voltage increases. The decrease in the electric field intensity within the arc column at low atmospheric pressures reduces the self-adjustment ability of the arc, the arc stability and the arc column stiffness, which influences the weld formation and joint quality. The welding process parameters for arc welding with self-shielded flux-cored wire at low atmospheric pressures have to be strictly controlled and the arc voltage need to be as low as possible.
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    Experimental research on real-time ultrasonic detection of pure metal creep
    YUAN Keyi, HAN Zandong, ZHONG Yuexian, CHEN Yifang
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 739-743.  
    Abstract   PDF (1932KB) ( 680 )
    Stress-free, room temperature creep specimens are used in almost all ultrasonic creep testing experimental research. However, the ultrasonic testing parameters for this condition (stress-free and room temperature) will differ from those for realistic conditions with the creep stress and higher temperatures. These differences will influence the creep detection accuracy. Tests in more realistic conditions are conducted using pure lead for continuous creep experiments with real-time ultrasonic detection used during the creep process and then during the relaxation process. The real-time parameter variations are plotted versus creep time for some parameters such as the attenuation, acoustic velocity, and time attenuation. The results show that the detection sensitivities of the creep ultrasonic testing parameters for realistic conditions are higher than for stress-free conditions. Thus, if stress-free ultrasonic testing parameter measurements are used to assess the creep, the actual measured parameter values must be corrected to accurately assess the creep. In addition, the experiments show that the time-attenuation parameter has the same type of variations as the attenuation parameter with the increased creep time so the objective dimensions do not need to measure to calculate the time-attenuation parameter, which is much easier, especially in practical ultrasonic testing. This result shows that the time-attenuation parameter can be used in place of the attenuation parameter in metal creep ultrasonic testing.
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    Average vector method for determining isocenter of rotated radiotherapy equipment
    ZHANG Xiang, FAN Wengang, SHI Shaohua, YE Peiqing, ZHANG Hui
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 744-749.  
    Abstract   PDF (1511KB) ( 595 )
    The isocentric accuracy of rotated radiotherapy equipment significantly influences the treatment accuracy. The average vector method is used to find the optimal isocenter considering the mechanical deformation of the rotated radiotherapy equipment. The maximum distance between the isocenter which is treated as the optimization variable and the ray vectors is considered as a constraint. An objective function is then designed to calculate the average distance between the isocenter that meets the constraint and the ray vectors. Finally, the location of the optimal isocenter and the isocentric envelop are obtained. A test with this method gives the radius of the isocentric envelop as 0.311 mm which is equal to that given by the vector-end-effector method, and about 15.5% less than that given by the point-end-effector method. The results also show that the average distance between the optimal isocenter and the ray vectors is 0.206 mm, about 11.2% less than that by the vector-end-effector method and 28% less than that by the point-end-effector method.
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    Quantitative decoupling cooperative control of CMP multi-zone pressure systems
    MEN Yanwu, ZHANG Hui, JIANG Wenxue, ZHOU Kai, YE Peiqing
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 750-755.  
    Abstract   PDF (2705KB) ( 882 )
    Chemical mechanical polishing (CMP) has a flexible elastic diaphragm that couples the mechanical deformations of the parts and complicates the pressure control. The coupling problem is solved here using offline identification based on working point linearization + quantitative coupling analysis + quantitative decoupled cooperative control. The working point linearization gives a multi-zones model. The relative gain array (RGA) method gives the degree of coupling. The feed-forward compensation decoupling controller provides the quantitative decoupling. Simulations and experiments show that this method decouples the pressure system in the multiple zones in engineering practice, so the system has less overshoot and faster response with the same control method.
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    Factors influcing rarefied gas heat transfer between a wafer and an electrostatic chuck
    SUN Yuchun, CHENG Jia, LU Yijia, HOU Yuemin, JI Linhong
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 756-760.  
    Abstract   PDF (1155KB) ( 1352 )
    Wafer cooling/heating by gas flow along the backside of the wafer is a key part of the plasma-etching process. The rarefied gas heat transfer across the gap between the wafer and the electrostatic chuck is modeled in this article with an analytical equation developed for the entire pressure range whose predictions are verified by direct simulation Monte Carlo results. The model is then used to investigate the effects of the gas pressure, gap size, accommodation coefficient and gas temperature on the heat transfer coefficient. The gap size and gas temperature have little influence, so the etching temperature and the surface profiles like the height have little effect on the heat transfer between the wafer and the electrostatic chuck. However, the gas pressure and the accommodation coefficient significantly impact the heat transfer coefficient. Therefore, changes in the gas pressure during the etching process will significantly affect the heat transfer between the wafer and the electrostatic chuck.
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    AUTOMOTIVE ENGINEERING
    Collaborative design of a motion control system for intelligent vehicles
    GUO Jinghua, LUO Yugong, LI Keqiang
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 761-768.  
    Abstract   PDF (1624KB) ( 959 )
    A dynamic control model is developed for intelligent vehicles which accurately describes the lateral and longitudinal motion characteristics. The strongly coupled, nonlinear problem with very uncertain parameter values for intelligent vehicles is modelled as a multi-layer coordinated control system of the lateral and longitudinal vehicle dynamics. Simulations are used to verify the control system with the simulation results showing that the control system has excellent tracking ability and enhanced stability, comfort and safety of intelligent vehicles.
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    Driver lane change decision analysis and intention recognition algorithm
    DING Jieyun, DANG Ruina, WANG Jianqiang, LI Keqiang
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 769-774.  
    Abstract   PDF (1174KB) ( 1799 )
    An accurate lane change intention recognition algorithm is developed to improve real-time performance. The algorithm analyzes the drivers' lane change decisions to develop a new symbol and a comprehensive decision index (CDI) based on fuzzy theory to assess the probability that the driver will change lanes. Then, the driver intention recognition algorithm is designed based on a hidden Markov model. Using the new symbol as well as representative lateral motion parameters as observed signals, and the driver's intention as the hidden state, a hidden Markov model is built and trained. The driver's intention is recognized by the HMM decoding method. Lane change data collected on a driving simulator are used to verify the overall algorithm performance. The results show that the algorithm with the CDI as one of the observation signals both guarantees the accuracy of the recognition results and improves the real-time performance.
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    Automobile style evaluation based on eye tracking
    LU Zhaolin, LI Shengbo, XU Shaobing, CHENG Bo
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 775-781.  
    Abstract   PDF (3507KB) ( 991 )
    Traditional subjective evaluation methods have limited success for automotive designs. An automobile style evaluation method based on eye tracking is developed to more accurately recognize the users' objective assessment of the automotive form design. An index system is structured based on a heat map including striping the background, extracting the color characteristics using a hue-saturation-value (HSV) model and calculating the statistics of the grey level histogram. The automobile form evaluation is defined as a binary classification model with the function model built from a Fisher discriminate. The reliability and practicality of this method are validated using a test case. The results show that this method is accurate and a feasible technical approach for rapid evaluation of automotive styling.
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    Laminate optimization of a composite stiffened panel based on surrogate model
    LIU Zhe, JIN Dafeng, FAN Zhirui
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 782-789.  
    Abstract   PDF (1386KB) ( 618 )
    This study optimized the stacking sequence of stiffeners in a composite stiffened panel to maximize the buckling load of the panel assuming a constant mass panel. The number of finite element models was reduced by using a radial basis function neural network (RBF) as the surragate model with the lamination parameters as inputs to estimate the buckling load. The lamination input parameters reduced the nonlinearities of the objective function. Due to the irregular shape of the design space, the D-optimal method was used to determine the sample points for training the RBF. The model errors were reduced by constructing a zoomed RBF to enhance the RBF accuracy near the provisional optimal laminate. A numerical example shows the accuracy and efficiency of the RBF with the lamination parameters as inputs and how the model accuracy is increased by the zoomed RBF near the optimal region.
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    Simulation on power loss of engine front end accessory belt drive systems
    TAO Run, HOU Zhichao
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 790-796.  
    Abstract   PDF (2584KB) ( 971 )
    The effects of a power loss to the engine front end accessory belt drive systems were studied using a multi-body dynamic simulation. The mechanical parameters of the belt were found in tests with the system dynamic model then built in the commercial software Adams. The effects of the system power loss were found through a series of simulations for the key design parameters, such as the belt pre-tension, accessory loads, rotating speed belt and pulley acceleration, and fuel consumption, for typical vehicle driving cycles. The results show that the power loss increases monotonically with pre-tension, load and rotating speed and changes little with acceleration. The fuel consumption agrees well with bench tests of a drive system without any accessory loads.
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    THERMAL ENGINEERING
    Regularization fast multipole boundary element method for solving potential flow problems
    ZHAI Jie, ZHU Baoshan, CAO Shuliang
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 797-802.  
    Abstract   PDF (1395KB) ( 760 )
    The fast multipole method and the regularization algorithm are combined to process the strong singular integral in the conventional boundary element method for potential flow problems. This method reduces the number of calculations and the storage which increases sharply with the number of elements in the conventional boundary element method. This method can also handle strongly singular integrals for calculating the velocities and the velocity gradient for potential flow by directly differentiating the boundary integral equation. The method is applied to simulate potential flow over a sphere. The results show that this method is accurate and efficient. This model is used to analyze the influence of the calculation parameters for other complicated boundary condition problems.
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    ENGINEERING PHYSICS
    Structure destruction based earthquake casualty estimates
    LI Yuanyuan, CHEN Jianguo, ZHANG Xiaole, YUAN Hongyong
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 803-807,814.  
    Abstract   PDF (1740KB) ( 820 )
    Post-earthquake casualty estimates are of great importance for emergency planning and rescues. The USA earthquake software HAZUS estimates casualties based on building vulnerability, but the model is mainly developed for building structures in California. A simplified rapid casualty assessment model is developed for emergency response and verified against data from the Wenchuan earthquake for Chinese building structures. The estimated number of injuries is close to the actual number, but the estimated number of deaths is lower, because the model seriously underestimates fatalities in the epicenter area. The predicted results are consistent with the actual situation and reflect the severity of the earthquake casualties. The simplified model is suitable for rapid casualty assessments to direct post-earthquake emergency response.
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    Development and application of a serious nuclear accident scenario library
    ZHAO Quanlai, SU Guofeng, CHEN Jianguo, YUAN Hongyong, ZHANG Xiaole, CHEN Peng, NI Shunjiang
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 808-814.  
    Abstract   PDF (1494KB) ( 810 )
    Approaches for dealing with emergency events can be divided into two categories. One is the traditional “forecast-response” type, while the other is the emerging “scenario-response” type. However, in recent years, the “forecast-response” type has been unable to predict the emergency needs of complex, modern scenarios because of the complexity, unpredictability and seriousness of unconventional events. Thus, the “scenario-response” type has become more widely accepted by scholars and emergency command staff. This study considers rare nuclear accidents that can have severe consequences. A serious nuclear accident scenario library is developed using consequence assessments with simple and complex wind fields. The size of the scenario library is then reduced based on analyses of the wind fields with a library developed for the source term inversion. This efficient method can save valuable time during nuclear accident emergency responses.
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    NUCLEAR AND NEW ENERGY TECHNOLOGY
    Numerical investigation of boiling model parameters for nanofluids
    YUAN Yang, LI Xiangdong, TU Jiyuan
    Journal of Tsinghua University(Science and Technology). 2015, 55 (7): 815-820.  
    Abstract   PDF (1249KB) ( 596 )
    The lack of accurate boiling heat transfer models for nanofluids limits their applications in industrial systems. This study describes the mechanisms for nucleate pool boiling of nanofluids based on experimental results in the literature. New closure correlations are given for the nucleate boiling parameters to improve the classical heat flux partitioning model. The numerical results agree well with available experimental data. The most important task when modeling nucleate boiling of nanofluids is to accurately predict the effects of the surface wettability and surface morphology caused by the nano-coating on the bubble nucleation, growth and departure from the heater surface.
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