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15 October 2016, Volume 56 Issue 10
    

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  • Three-dimensional object recognition and posture calculations based on the whitening transformation and curvature characteristics
    ZHENG Jun, WEI Haiyong
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1025-1030. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.033
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The whitening transformation and a U chord curvature are used to improve three-dimensional object recognition and posture calculation. The algorithm first extracts the shape characteristics of the object and then matches the contours of the target image with templates using the whitening transformation so that there is only a rotational relationship between the contour point sets. Then, the U chord curvature is improved to match the contours. Tests show that this method is affine invariant with a fast recognition speed which can reach 58 ms/frame (CPU: 2.3 GHz, RAM: 4 GB), a high recognition rate of 100% without shelter and a high detection accuracy of the posture calculation of 1.5°.
  • Motion planning method for complex three dimensional path welding
    ZENG Jinle, DU Dong, CHANG Baohua, HONG Yuxiang, CHANG Shuhe, PAN Jiluan
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1031-1036. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.034
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    Good forming and metallurgical quality in complex three dimensional welds requires accurate motion planning. Existing planning methods do not provide uniform welding speeds and stable positioning and pose between the torch and the workpiece. This paper presents a motion planning method for complex three dimensional path welding that first uses a B-spline curve to connect selected points along the seam. Then, a kinematic model is used to calculate the displacements and velocities of each joint at each time using an inverse kinematic method. Simulations show that this method keeps the welding region horizontal during the entire welding process and keeps the welding speed, inclination angle and distance between the welding region and the end of the welding torch equal to the predetermined values. This welding path planning method can be applied to complex three dimensional path planning for arc welding, laser welding and friction stir welding.
  • Numerical simulations of welding residual stresses in VPTIG-welded joints of the 2219 aluminum alloy
    LI Yanjun, WU Aiping, LIU Debo, ZHAO Haiyan, ZHAO Yue, WANG Guoqing
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1037-1041,1046. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.035
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    2219 aluminum alloy welded joints have significantly reduced strength because of the softening during welding. The influence of joint softening on the welding residual stress was studied using the thermal elastic plastic finite element method (T-E-P FEM) to predict the welding temperature and residual stresses in a variable polarity tungsten inert gas (VPTIG) welded 2219 aluminum alloy joint. The influences of work hardening and the annealing were also examined. The simulations show that joint softening significantly influences the longitudinal residual stress and that the longitudinal residual stresses in the weld zone and nearby regions are overestimated when the joint softening is not taken into account. Comparison of the simulated results with measured data shows that when work hardening, annealing and joint softening are considered, the residual stresses predicted by the T-E-P FEM agree well with the measured data, which indicates that this approach can accurately predict residual welding stresses in 2219 aluminum alloy.
  • Training gloves for inducing brain damagedchildren to actively participate in rehabilitation training
    LIU Yali, GUAN Xinyu, JI Linhong, DONG Jie
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1042-1046. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.036
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    The hand motor functions of brain damaged children are limited because of high muscle tension. These children cannot easily extend or flex their fingers because of the muscle tension. There is currently little equipment developed for young patients. The aim of this study is to design gloves based on child's psychology to attract the children to actively participate in rehabilitation training. The gloves attract the children's attention by a series of LEDs that turn on or off as well as music playing or stopping. The gloves have been used by brain damaged children in the China Rehabilitation Research Center with results showing that the median frequencies of affected thenar and extensor proprius longus increase, which indicates that the muscle endurance is improved. The root-mean-square and average amplitude of the thenar and extensor proprius longus decrease, suggesting that the muscle tension decreases and the ability to control their fingers motion improves. The results verify the effectiveness of these gloves with brain damaged children.
  • Measurement trajectory evaluation and error compensation for kinematic calibration of a 5-axis hybrid machine tool
    LIU Yuzhe, WU Jun, WANG Liping, WANG Jinsong
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1047-1054. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.037
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    This paper described the kinematic calibration of the measurement trajectory and error compensation of a 5-axis hybrid machine tool. The kinematics model was based on the closed loop vector kinematic equations while the error model was based on the linear perturbation method. An index to evaluate the measurement trajectory was developed from a non-orthogonal index of the trajectory vectors. Two calibration tests were performed using different trajectories. Two error compensation schemes were based on the forward and inverse kinematics. The calibration tests show that the error compensation scheme based on the inverse kinematics has higher compensation accuracy. Finally, a test of machining an "S"-shape test specimen shows that 94% of the detected points are acceptable. The results verify the effectiveness of the index and the error compensation scheme.
  • Quality factor estimates of resonant beams with nonlinear vibrations
    YAN Bin, LIU Yunfeng, DONG Jingxin
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1055-1060. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.038
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    Vacuum resonant accelerometers have nonlinear sweeping frequency response, so the regular method cannot be used to measure the quality factor. A nonlinear model of the resonant beam is used here to monitor the effect of the vacuum package. The system calculates the quality factor through fitting the sweeping frequency data for the nonlinear vibrations. Tests on a resonant accelerometer verify the consistency and accuracy of the method. The measured quality factors of the accelerometers are all above 2×105. In addition, this method is also used to measure the relationship between the pressure and the quality factor, which indicates that the pressure inside the vacuum package is about 0.1 Pa. The temperature tests and long-term monitoring tests show the reliability of the vacuum packaging.
  • AlN/α-SiC based surface acoustic wave resonator and its strain response
    CHEN Shuo, YOU Zheng
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1061-1065. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.039
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    The need to monitor the health of gas turbines, geothermal wells and other equipment in harsh environments requires micro and nano sensors for harsh environments. This paper introduces an AlN/α-SiC based surface acoustic wave resonator. The strain coefficient factor (SCF) of the resonator is analyzed and calculated theoretically based on the strain field and a proposed strain-velocity relationship. The resonator is micro-fabricated and characterized to determine the SCF of the fabricated resonator. An AlN/α-SiC resonator with a 1.5 μm thick AlN layer, has an SCF of 0.515×10-6/με at 298 K, which matches well with the calculated results.
  • Two-position alignment for SINS based on north gyroscope bias self-observations
    PENG Zhuo, GUO Meifeng, ZHANG Rong, LUO Shouhong
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1066-1071,1078. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.040
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    The traditional one-position initial alignment system for the strap-down inertial navigation system (SINS) is not completely observable because the unobservable east gyroscope bias creates a large heading error. The two-position method can improve the observability but always needs an additional precise rotator which is impractical. This paper describes a two-position method based on a north gyroscope bias self-observation, which only needs two arbitrary approximate horizontal positions. The north gyroscope bias is extracted from one position and transmitted to the other position as an observation to make the east gyroscope bias observable and reduce the heading error. The rotation angle is optimized using a comprehensive degree of observability which includes a relative degree of observability and an order of observability. The relative degree of observability indicates the observability of the same state for different conditions while the order of observability indicates the convergence rate. The relative degree of observability shows that the optimal rotation angle is ±90°, which is verified by numerical simulations. Tests show that this two-position method reduces the heading error from 0.268° to 0.041° and estimates the horizontal gyroscope bias.
  • Effect of acid systems for determination of trace elements in coal combustion byproductsusing microwave digestion method
    ZHU Zhenwu, ZHUO Yuqun
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1072-1078. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.041
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    Microwave digestion is the most common method for pretreating coal fly ash and flue gas desulfurization (FGD) gypsum before determination of the trace elements in the flow streams. This study analyzes previous microwave digestion methods. Then, the standard microwave digestion method 3052 from the US Environment Protection Agency is used to design three acid systems using HNO3, HNO3-HCl and HNO3-HF-H3BO3 for digesting certified reference gypsum material (FGD-2). After digestion, the As, Be, Cd, Co, Cr, Mn, Pb and Se contents are determined using inductively coupled plasma mass spectrometry (ICP-MS). The results show that HNO3-HF-H3BO3 gives the best digestion. The Cr, Mn and Se recoveries are 93.5%, 88.0% and 97.7%. Tests using a fly ash (GBW 08401) reference material also show good results with the As, Co, Cr, Mn, Pb and Se recoveries between 90.6% and 101.8%, but the Be and Cd recoveries are not good enough. This method can be used to determine the trace elements in coal fly ash and FGD gypsum by microwave digestion with HNO3-HF-H3BO3 followed by ICP-MS analysis.
  • Advanced characterization of three-dimensional pores in coking sand by micro-CT
    SHI Lin, XU Ran, XU Qianghui, XU Ying, ZHENG Licai
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1079-1084. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.042
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    Coke formation is very important for in-situ oil combustion. Previous studies of the coke distribution and coke content for in-situ combustion have used two-dimensional surface observations and macro parameter measurements that cannot accurately describe the mechanisms for the burning of heavy oil which limits the accuracy of numerical simulations. X-ray microtomography (micro-CT) has been used as a non-destructive technique to characterize the material's microstructure for petroleum geology. This paper describes micro-CT measurements of coking sand samples in a laboratory to reconstruct three dimensional pore scale images. These measurements give relatively high contrast gray scale images with the watershed segmentation method and the Chen-Vese model algorithm used to construct the three dimensional images of the pores coke or in sand. The images are verified against data from TGA and densitometer measurements with good agreement. This method provides excellent models for analyzing the coke content, the relationship between the porosity and the coking content, and even for porous media fluid flow simulations of in-situ combustion.
  • Numerical investigation of an aerospace thruster with ADN-based liquid propellant
    JING Liyue, HUO Jialong, YAO Zhaopu, YOU Xiaoqing, ZHU Min
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1085-1090. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.043
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    The ammonium dinitramide (ADN) based liquid propellant is an environmentally friendly propellant that can be used in small rockets. Combustion of an ADN-based liquid propellant in an aerospace thruster is investigated numerically with the droplets described by the Euler-Lagrange approach and with the heat transfer in the porous media using the non-equilibrium model. The interactions among the gas, liquid droplets and porous media are all included. An 18 species and 40 reactions reduced chemical mechanism is used to model the reactions between ADN and CH3OH in the gaseous phase to estimate the thruster performance. The results show that the heat release from the combustion is transferred upstream to enhance the evaporation of the liquid propellant by the porous media. In the thruster, the ADN decomposition and the CH3OH oxidization do not happen at the same time. The ADN decomposition occurs near the inlet while the CH3OH is oxidized downstream of the porous media and in the combustor.
  • Congruent duplex redundant central coordinators in automotive electric and electronic networks
    MIAO Feng, LIAN Xiaomin
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1091-1096. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.044
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    The central coordinators in automotive electric and electronic networks control all the electrical devices in the vehicle, so they need to be very reliable. This paper describes a congruent duplex redundant central coordinating system for automobiles. The two central coordinators are congruent in both their hardware and software. They communicate through the controller area network (CAN) bus, vote by sending and receiving arbitration frames, and monitor each other by sending and receiving status frames. They work as the master and assistant coordinators. When one of them fails, the other takes over the task and sends a warning message to the driver. Tests validate that the congruent duplex redundant central coordinating system can work well in vehicles. The congruent duplex redundant method improves the system reliability and mean life without design and manufacturing cost increases.
  • Braking intention classification and identification considering braking comfort for electric vehicles
    PAN Ning, YU Liangyao, SONG Jian
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1097-1103. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.045
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    Hydraulic control units (HCUs) are widely used as precise pressure regulators for the composite brakes in electric vehicles. The braking comfort can be improved by appropriate braking intention classification and identification. A braking intention classification method is developed to improve braking comfort that classifies the braking intention as normal deceleration, emergency braking and a pressure following pattern. The pressure control method is then based on the classification results. The on-line braking intention identification method uses multiple sensors and a neural network. Simulations and tests show that the braking comfort and safety are improved by this method.
  • Finite element model refinement for elastic-plastic dynamic buckling of a belt bar during impact
    LIU Sai, LÜ Zhenhua
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1104-1108. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.046
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    The dynamic buckling experiment of a belt bar subjected to axial impact was previously studied experimentally. The tests show that previous simulation methods are not very accurate. The finite element analysis accuracy is improved by improving the fidelity of the boundary conditions and properly selecting the finite element type and size. The boundary conditions for the joint clearance and friction are determined by comparing the numerical results with the test data, and shell elements and solid elements are found to give better results than beam elements. Simulations with thin or thick shell elements or solid elements with the new boundary conditions are more accurate than previous results with beam elements and simple boundary conditions. The refined finite element model predicts the 3-D reverse buckling of the belt bar.
  • Design and tests of a combustion chamber for an electrically controlled, single-cylinder diesel engine
    LAN Xudong, PAN Chunyu, ZHOU Ming
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1109-1113. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.047
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    The design of a combustion chamber must match the intake air and fuel injection systems to improve the power, specific fuel consumption (SFC) and emissions of diesel engines. Numerical simulations and experimental validations are used to optimize the combustion chamber of an electrically controlled, single-cylinder diesel engine. The power and torque of a single-cylinder diesel engine are predicted using a hybrid Euler-Lagrange method with comparisons to test measurements. A parameterized design is then used to design the combustion chamber. Three key parameters for the re-entrance ratio, depth and inner diameter of the combustion chamber relate to the engine performance (power, torque, SFC and emission). The results show that the hybrid Euler-Lagrange method can be used to design the combustion chamber. The three key parameters strongly affect the engine performance for the given intake air and fuel injection systems.
  • Assessment of heavy fuel aircraft piston engine types
    FENG Guangshuo, ZHOU Ming
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1114-1121. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.048
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    The objective of this study is to assess spark ignition (Otto cycle) and compression ignition (Diesel cycle) engines as heavy fuel aircraft piston engines. Spark ignition aircraft engines give a higher power to weight ratio, but have higher specific fuel consumption (SFC), knocking, poor starting, higher electro magnetic interference (EMI), lower reliability and narrower power regions. Spark ignition systems use direct injection, pneumatic atomizers and high energy ignition systems. Compression ignition aircraft engines have lower SFC, improved range, lower EMI, higher reliability and wider power regions, but have worse power to weight ratios and more vibration. Compression ignition engines have advanced electronic controls, fuel injection systems and variable high-pressure ratio superchargers. The assessments show that both approaches are feasible with some technical challenges, with compression ignition engines as the more promising approach.
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  • Spatial correlation analysis of Suomi-NPP nighttime light data and GDP data
    GUO Yongde, GAO Jinhuan, MA Hongbing
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1122-1130. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.049
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    Nighttime light imagery removes most natural disturbances, so nighttime images can be used to reflect human activity, especially for research on spatialization of socio-economic development. This study utilized night-light data collected by the Suomi-NPP satellite in a spatial correlation model with GDP data to analyze both the spatial distribution and factors influencing development. The model extracted the lighting information and calculated night-light indexes to select the best night-light index for each Chinese mainland province. Tests show that the normalized total radiance index relates well to the GDP, so this index is related to the GDP using linear and nonlinear spatial models to develop a model to predict the GDP. The fitting results for the linear, power law and logistic models are all greater than 0.8. The power law model predicts the GDP of each mainland provincial-level region in 2014 with an average relative error of only 26.0%.
  • ERP research on the emotional voice for different languages and non-speech utterances
    CHANG Jiang, ZHANG Xueying, ZHANG Qiping, CHEN Hongtao, SUN Ying, HU Fengyun
    Journal of Tsinghua University(Science and Technology). 2016, 56(10): 1131-1136. https://doi.org/10.16511/j.cnki.qhdxxb.2016.22.050
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    The event-related potential (ERP) is an effective method to study the brain mechanism of voice processing. This investigation studies how semantic understanding affects the emotional voice during speech and how speech influences the emotional voice for speech and non-speech utterances. In the tests, the audio signals are preprocessed using the endpoint detection technique to synchronize the ERP starting position with its corresponding signal content to enable superposition of the ERP waveforms. The ERP tests show that the negative waveform at around 200 ms in the temporal region may be associated with the prosody perception and the semantic understanding. In addition, the latency and amplitude results suggest that the brain is more sensitive to native emotional language than foreign emotional language and that the brain more quickly processes emotional non-speech utterances than emotional speech.
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