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ISSN 1000-0585
CN 11-1848/P
Started in 1982
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  • Table of Content
      , Volume 62 Issue 3 Previous Issue    Next Issue
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    MECHANICAL ENGINEERING
    Cavitation characterization simulation in connecting-rod bearings based on AVL-EXCITE
    LI Xinxin, DU Xiangning, LI Yuanzhe, CAO Hengchao, TIAN Yu
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 385-390,399.   DOI: 10.16511/j.cnki.qhdxxb.2021.21.022
    Abstract   HTML   PDF (8087KB) ( 191 )
    Cavitation is common and important in hydrodynamic lubrication that generally causes the rupture of lubrication film and affects the performance of the lubrication, which even leads to cavitation erosion in some situations. This is especially important in connecting-rod bearings in diesel engines. Thus, accurately characterizing cavitation is of great significance. Herein, a multi-body dynamic model of an engine considering elastohydrodynamic lubrication (EHL) was established based on the AVL-EXCITE software platform. According to the EHL results, a finger-like cavitation region in the big-end bearing of the connecting rod was distributed in the lubrication outlet during the work stroke. Meanwhile, the cavitation bubbles in the cavitation region might collapse and result in cavitation erosion when the oil supply bore passed through. This provides a potential method to predict the occurrence of cavitation erosion. Furthermore, the influences of lubricating-oil viscosity and oil-supply pressure on cavitation characteristics were investigated. An appropriate increase in these two parameters can slow down the cavitation effect.
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    Data-driven method for 6D robot pose estimation
    LIU Zhi, CHEN Ken, XU Jing
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 391-399.   DOI: 10.16511/j.cnki.qhdxxb.2022.25.008
    Abstract   HTML   PDF (4738KB) ( 223 )
    Accurate kinematics are fundamental to precise robot manipulations. This paper presents a motion compensation algorithm to correct for robot end-effector deformation caused by heavy loads. The data-driven method for 6D pose estimation of robot end-effector motion estimates the kinematic error based on a Gaussian process regression to predict the position of the offline target points. Then, a pose correction method based on the adjustment model is used to modify the measured and predicted values of the target points to improve the estimation accuracy of the 6D pose. Tests show that the structural deformation caused by heavy loads is well compensated for by this pose estimation method.
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    Thermofluid modeling for concurrent size-topology optimization of heat sinks for planar motors
    ZHAO Jiaqi, ZHANG Ming, ZHU Yu, CHENG Rong, LI Xin, WANG Leijie, HU Chuxiong
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 400-407.   DOI: 10.16511/j.cnki.qhdxxb.2022.25.007
    Abstract   HTML   PDF (3884KB) ( 176 )
    The thermal-hydraulics of water-cooled heat sinks for planar motors were analyzed using a thermofluid model of a heat sink to concurrently optimize the heat sink size and topology. The three-layer thermofluid model of the heat sink included the coupled flow and heat transfer effects between the cover plates and the fluid-solid mixing channel including the influence of the flow channel thickness on the thermal-hydraulics. The model used a porosity model to describe the channel topology and a continuous-adjoint structural optimization model for the geometric variables related to the channel topology and thickness in a concurrent size-topology optimization scheme. Various numerical examples show the accuracy and efficiency of the three-layer thermofluid model and the size-topology optimization scheme. The three-layer model uses 10% less calculational time than full 3D models while still accurately predicting the temperature distribution. The optimized heat sinks have unique topologies with up to 30.82% better heat transfer than baseline designs. This concurrent approach is efficient and obtains designs that are competitive with discrete optimization approach results.
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    Obstacle avoidance algorithm for redundant robots based on collision feedback
    LI Yaxin, WANG Guolei, ZHANG Jianhui, TIAN Xinliang, AN Jing, CHEN Ken
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 408-415.   DOI: 10.16511/j.cnki.qhdxxb.2021.25.022
    Abstract   HTML   PDF (8153KB) ( 120 )
    Robots for spraying in complex enclosed pipeline parts need effective obstacle avoidance capabilities. An obstacle avoidance algorithm was developed based on collision detection feedback for a redundant manipulator. The projection intersection method was used to detect a collision with the collision types divided into avoidable and unavoidable collisions. A dynamic adjustment algorithm using joint-weights was developed for avoidable collisions to restrict the collision joints while relaxing the restrictions on the other joints to optimize the motion for obstacle avoidance. For unavoidable collisions, the "lever principle" was used to adjust the obstacle avoidance by adjusting the normal direction to the target point. Finally, the joint acceleration was optimized to modify the trajectory and reduce the inertial impact of the robot. Simulations verify the feasibility of this algorithm.
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    Design of a high-speed and high-load parallel robot
    MENG Qizhi, XIE Fugui, LIU Xinjun, YUAN Xin, XUE Long
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 416-426.   DOI: 10.16511/j.cnki.qhdxxb.2022.25.005
    Abstract   HTML   PDF (13109KB) ( 197 )
    The food and retail chemical industries have many pick-and-place operations handling heavy loads with two translational degrees of freedom (DOFs), which reduce the mobility requirements but require robots that can handle heavy loads. Such processes need high-performance and high-speed parallel robots. This paper describes the advantages of closed-loop subchains of high-speed parallel robots and the coupling strategy between the subchains. The coupling strategy is then used to develop a line geometry mapping based synthesis method to design high-speed parallel robots with closed-loop subchains. A type selection index (TSI) based on the power coefficient in screw theory is used to guide the type selection between robot candidates with the same function and similar structures. A high-speed and high-load capability parallel robot TH-UR2 is then developed and tested. This robot can perform one standard travel cycle in 1.76 s with a 50 kg load, which meets the application requirements.
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    Comparison of evaluation methods for domestic and international commercial demonstrations of fuel cell electric vehicles
    QIU Bin, LIANG Hongyi, DONG Guohua, YING Zihao, LIU Yahui
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 427-437.   DOI: 10.16511/j.cnki.qhdxxb.2021.22.014
    Abstract   HTML   PDF (1573KB) ( 462 )
    The evaluation methods used in fuel cell electric vehicle (FCEV) commercial demonstration projects in China, the European Union, the USA and Japan are compared to identify several shortcomings in the evaluation methods used in domestic projects. The results are then used to develop suggestions for the statistical evaluation methods used for upcoming national FCEV demonstration projects.
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    Robust LPV/H control for automatic path tracking of heavy commercial vehicles
    DONG Qing, JI Xuewu, LIU Yulong, TAO Shuxin, LIU Yahui
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 438-446.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.011
    Abstract   HTML   PDF (5882KB) ( 173 )
    The uncertainties of external disturbances and the nonlinearity of system states usually reduce path tracking accuracy for automatic path tracking of heavy commercial vehicles which then complicates the controller design. This paper presents a robust LPV (linear parameter varying)/H lateral motion controller which provides good path tracking accuracy regardless of uncertainties in the road curvature and variations of the longitudinal speed. A weighted performance index and the robust H controller were designed for heavy commercial vehicles using a generalized 4-DOF dynamic model and an automatic path tracking model. An improved trapezoidal polytope LPV controller was designed to account for the vehicle speed variations. Simulations and a hardware-in-loop (HIL) implementation show the effectiveness and real-time response of the control algorithm. The results show that this LPV/H control algorithm improves the conservativeness of the original control algorithm and significantly improves the trajectory tracking accuracy while ensuring automatic tracking stability of heavy commercial vehicles.
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    Extended driving risk field model for i-VICS and its application
    TIAN Ye, PEI Huaxin, YAN Song, ZHANG Yi
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 447-457.   DOI: 10.16511/j.cnki.qhdxxb.2021.22.034
    Abstract   HTML   PDF (12402KB) ( 313 )
    In intelligent vehicle-infrastructure cooperation systems (i-VICS), the driving risk field is an effective method for evaluating the driving safety of connected and automated vehicles (CAVs). However, existing driving risk field models do not consider the geometric characteristics and heading angles of vehicles and ignore the influences of the ego vehicle, which limits the accuracy of these existing models for vehicle safety assessments. This paper describes an extended driving risk field model. This driving risk field model includes the time to collision (TTC) and adds the physical attributes and movement information of the ego vehicle, including the vehicle size and heading, into the driving risk field model which improves the safety assessment. Application of this driving risk field model to typical traffic scenarios shows that this extended model overcomes the limitations of existing models. Simulations using this model for trajectory planning demonstrate the promising performance of the extended model.
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    Coordination model for human lower limb motion
    ZHANG Yuzhong, LIU Shiqiang, ZHANG Junchang, ZHU Rong
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 458-462.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.027
    Abstract   HTML   PDF (5039KB) ( 183 )
    When a human is walking or running, the coordinated relationship between the movements of the thigh and shank are controlled by the motor nerve system. This relationship between the parts of the lower limb is the result of evolution and experience, which makes human movement more flexible and efficient. Research on the coordination of the lower limbs for healthy people facilitates rehabilitation of stroke patients, robot gait planning, and human-machine collaboration of assistive equipment such as exoskeletons. At present, the research on the coordination of human lower limb motion is still relatively basic, mostly focusing on observations and theoretical analyses, with few practical models. This study used a wearable motion capture system to measure and model the motion relationships of the lower limbs for human walking and running. A neural network model was then developed to characterize the coordination of the thigh and shank. This model accurately predicts the motion of the thigh and the knee joint from the shank movement information. This motion model can be used for rehabilitation, robot gait planning, intelligent assisting equipment and other related fields.
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    Numerical and experimental research on an adaptive labyrinth seal
    ZHAO Juying, XU Yiren, ZHU Tianyi, QI Zhihao, LI Yongjian
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 463-469.   DOI: 10.16511/j.cnki.qhdxxb.2021.21.035
    Abstract   HTML   PDF (3930KB) ( 165 )
    An adaptive labyrinth seal was developed to improve traditional labyrinth seal wear-resistant capabilities in harsh conditions. A numerical model shows that the floating force is mainly generated by the uneven pressure distribution in the radial clearances of the seal. For gas seals, the hydrostatic effect caused by the pressure difference is the dominant factor for the conditions used in this study, rather than the hydrodynamic effect. The model was also used to analyze the effects of the eccentricity, the groove width and the inlet throttle length on the floating force and leakage rate. Experimental results then show that the sealing capability of this adaptive labyrinth seal is 2.3-3.1 times better than that of a traditional labyrinth seal. In addition, the sealing ring of the adaptive labyrinth seal can float for pressure differences of 0.05-0.30 MPa and responds quickly to changes in the surrounding conditions.
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    Experimental study and mechanism analysis on the effect of crystallographic orientation on triboluminescence
    LI Na, XU Xuefeng
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 470-475.   DOI: 10.16511/j.cnki.qhdxxb.2021.25.019
    Abstract   HTML   PDF (5181KB) ( 133 )
    Triboluminescence has been investigated by many researchers due to its many applications in various fields related to industry and life. However, the triboluminescence mechanism is still unclear. The triboluminescence mechanisms are further investigated here by experimentally studying the triboluminescence properties of SiO2 crystals with various crystal orientations. The experimental results show that the crystal orientation significantly affects the triboluminescence. Measurements of the triboluminescence spectra showed that the triboluminescence comes from the gas discharge caused by triboelectrification. The different triboluminescence intensities in different crystal orientations are then shown to be based on the differences in the work functions for different orientations.
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    Tribological properties of overlap and non-overlap zones in laser-clad iron-based coatings
    WU Ying, LIU Yan, CHEN Wenjing, CHEN Hui
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 476-481.   DOI: 10.16511/j.cnki.qhdxxb.2021.25.021
    Abstract   HTML   PDF (7884KB) ( 137 )
    The microstructures of multi-pass laser cladding coatings exhibit periodic changes that are generally divided into overlap and non-overlap zones. The tribological properties of these two zones were studied using linear reciprocating friction tests with forces of 5 and 25 N and friction times of 150 and 300 s. This study analyzed the tribological characteristics with analyses of the microstructures and phases in the two zones. The results show the relationship between the tribological effects and the microstructure and the evolution of the microstructure during the friction process. The results show that at low pressures, the anti-wear characteristics are greatly affected by the microstructure. The overlap zone has poor wear resistance due to the coarse microstructure and less α-Fe content while the non-overlap zone with a finer microstructure and high α-Fe content has better wear resistance. At high pressures, the wear characteristics are less affected by the microstructure with the anti-wear characteristics of the overlap zone being similar to those of the non-overlap zone. The subsurface below the wear scar had a shear deformation layer after the friction test whose thickness, hardness and equivalent strain increased with increasing pressure and friction time. The overlap zone hardness increases faster than that of the non-overlap zone.
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    Thermal characteristics of grease lubricated high-speed angular contact ball bearings with thermal deformation
    ZHANG Chang, TIAN Jiyin, GUO Dan, NIU Qingbo
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 482-492.   DOI: 10.16511/j.cnki.qhdxxb.2021.25.015
    Abstract   HTML   PDF (9123KB) ( 229 )
    Grease lubricated angular contact ball bearings are usually used in spindle bearings of high-speed machine tools. The large temperature increases during high-speed operation seriously affect the bearing precision, resulting in a loss of operating precision and reduced service lives. This study predicts the bearing loads with the influence of thermal deformation on the force equilibrium of angular contact ball bearings. The local heat generation rates are predicted with grease lubrication using a multi-node thermal network to model the angular contact ball bearings that predicts each node temperature. The results show the influence of the thermal deformation on the bearing temperature rise and the forces on the bearing with the simulation results verified through experiments. The predicted bearing outer ring temperatures based on the force balance calculation with the thermal deformation are in good agreement with experimental data with errors of less than 10% which verifies the reliability of this method for predicting the temperature rise of grease lubricated high-speed bearings.
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    SPECIAL SECTION: INTELLIGENT TRANSPORTATION
    Survey of intelligent and connected vehicle technologies: Architectures, functions and applications
    CUI Mingyang, HUANG Heye, XU Qing, WANG Jianqiang, Takaaki SEKIGUCHI, GENG Lu, LI Keqiang
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 493-508.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.026
    Abstract   HTML   PDF (10523KB) ( 963 )
    The rapid development of intelligent and connected vehicles (ICV) in recent years promotes theoretical research in related fields from driving assistance to automated driving, from single-vehicle intelligent driving to multi-vehicle cooperative driving.ICV systems are expected to improve traffic safety and efficiency, but they face complex challenges in real traffic environment. This paper presents a survey of ICV technologies relating to 3 aspects:system architecture design, functional technology and application. This survey first introduces typical architectures of ICV, and then the development and challenges of three key functional technologies:perception, decision making and control, in consideration of driver-vehicle-road interactions in real traffic environment. Finally, this paper analyzes ICV applications in typical scenarios and the future development of related technologies.
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    Development of advanced traffic management systems
    LI Ruimin, WANG Changjun
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 509-515.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.023
    Abstract   HTML   PDF (3077KB) ( 275 )
    Advanced traffic management systems (ATMS) still need significant development. This study analyzed the socio-technical characteristics of urban transportation systems to predict future development directions for advanced traffic management systems. Future ATMS will be based on cyber-physical-social systems (CPSS) and have improved capabilities using big data in integrated systems. An ATMS framework was developed based on the relationships between the cyber domain, physical domain, and social domain. This study describes key implications of the three trends with suggestions for future developments of modern ATMS.
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    Adaptive modeling method based on the Fast-MCD to analyze railway track irregularity deterioration
    YANG Yaqin, XU Peng, WU Xishui
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 516-522.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.044
    Abstract   HTML   PDF (2641KB) ( 200 )
    Railway track predictive maintenance needs to identify the track irregularity deterioration mode. For this, the track irregularity deterioration process is split into maintenance periods according to the maintenance records to analyze the deterioration mode. A rail track irregularity deterioration adaptive piecewise modeling framework was developed. In order to improve the efficiency and accuracy of the framework, a two-level fast minimum covariance determinant (Fast-MCD) was developed based on the Mahalanobis distance. The critical values for each level were determined for a specific case by measurements along the Nanchang-Fuzhou railway from 2013 to 2020. Analysis of the data showed that the efficiency is improved by nearly 50% and the identification accuracy of the maintenance dates is improved by nearly 45.3% through use of the two-level Fast-MCD. The track irregularity deterioration mode was further studied by using this framework to analyze the track longitudinal deterioration of each track unit for each maintenance period with a total of nearly 6 000 maintenance periods. The goodness-of-fit and prediction capabilities of linear, exponential, and logarithmic functions were compared for each maintenance period. The results show that the linear function best describes the track longitudinal irregularity deterioration.
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    Vehicle body panel thickness optimization by a genetic algorithm
    ZHOU Wei, LI Min, QIU Mingjun, ZHANG Xilong, LIU Jiang, ZHANG Hongbo
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 523-532.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.045
    Abstract   HTML   PDF (8937KB) ( 106 )
    The interior noise in a vehicle can be reduced by optimizing the body panel thickness. A genetic algorithm was used to optimize the vehicle body panel thickness based on a coupled acoustic structure model of the vehicle body in HyperMesh. The Hammersley experimental design method was used to determine the response surfaces of the first-order global modal of the body-in-white, the body mass and the maximum sound pressure of a target point inside the vehicle. The maximum sound pressure at the target point was then used as the performance index in a genetic algorithm to optimize the vehicle body panel thickness. The optimum thickness reduced the maximum peak sound pressure at the target point by 4.0 dB. This algorithm gave 2.2% lower sound levels than a standard genetic algorithm, 2.2% lower than the global response search method, 2.3% lower than the adaptive response surface method and 2.5% lower than the feasible direction method, respectively. The results show that this genetic algorithm improves the stability and optimization ability of the genetic algorithm and this algorithm can efficiently optimize the vehicle body panel thickness.
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    Adaptability analysis of priority strategy for the novel guideway transit system
    HUAN Ning, YAO Enjian, SHEN Hao
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 533-539.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.012
    Abstract   HTML   PDF (9966KB) ( 78 )
    Guideway transit system is a novel kind of trackless mass public transit. To give priority to guideway transit vehicles in the mixed traffic flow, a front-end non-invasive-based priority strategy is proposed to improve the overall operational efficiency of the system, along with a supporting strategy for implementing dynamic signal priority control (DSPC). A series of simulation experiments are conducted to compare the adaptability of four priority strategies (i.e., non-priority, full time or intermittent dedicated lane and the proposed front-end non-invasive strategies) in a wide range of traffic conditions. The results show that the proposed strategy fits into the non-intensive operation condition where the departure interval of the guideway transit vehicle is greater than 300 s. The length of the front-end non-invasive section ought to be determined by the traffic volume. Under the integrated strategy of front-end non-invasive strategy and DSPC, the mean travel time of guideway transit vehicle decreases by 13.24%, and the per person travel cost decreases by 6.29%.
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    SPECIAL SECTION: AIR-BREATHING ENGINE AND AEROSPACE POWER TECHNOLOGY
    Fault analyses of liquid rocket engine turbopumps based on Hilbert-Huang transforms
    YANG Yi, CHEN Wenli, WANG Yongpeng, TANG Zuanjian, ZHAO Jing, GUO Huanlin, GUO Yanan
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 540-548.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.033
    Abstract   HTML   PDF (2308KB) ( 157 )
    Turbopumps are important in liquid rocket engine (LRE) propulsion systems. Turbopump failures are also the main cause of LRE failures. The Hilbert-Huang transform (HHT) has been used to adaptively and accurately analyze non-stationary data. An analysis of real LRE test data showed that the end flying wing problem in empirical mode decomposition (EMD) can be effectively solved using the signal envelope non closed image extension method. The Hilbert transform of the intrinsic mode function (IMF) using the HHT analysis gives the Hilbert energy distribution spectrum in the time and frequency domains and the time amplitude spectrum after the IMF function reconstruction. These can be used to analyze vibration data from a liquid oxygen turbopump in the time and frequency domains to diagnose turbopump faults. This method is very useful for test data analyses and fault location in rocket engines and other complex assemblies.
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    Turboshaft engine compressor design using ANSYS
    YAN Huihui, ZHOU Bohao, LI Hao, ZHANG Yuzhou, LAN Xudong
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 549-554,580.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.037
    Abstract   HTML   PDF (5438KB) ( 172 )
    Turboshaft engines are smaller, lighter and have shorter shafts than large turbofan and turbojet engines. Due to their good high altitude performance and wide power range, turboshaft engines have gradually replaced piston engines in unmanned helicopters. However, piston engines are less expensive, so they still have the absolute advantage in small unmanned helicopters. Further research is needed to develop economical low power turboshaft engines. This study analyzed the design of a 300 kW turboshaft engine using Gas Turb, a thermodynamic turbine analysis software, with the blade modeling module of ANSYS used to design the impeller and blades of the centrifugal compressor. Three-dimensional simulations of the centrifugal compressor verify the feasibility of this design.
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    Inward-turning TBCC intake design
    ZUO Fengyuan
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 555-561.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.029
    Abstract   HTML   PDF (9200KB) ( 185 )
    The increasing demand for air-breathing propulsion systems in hypersonic aircraft that can operate over a wide Mach number range has led to development of the turbine based combined cycle (TBCC). The high-performance compressed air intake system is a key component of these systems. This study analyzed the requirements for air intake systems of hypersonic aircraft operating over a wide Mach number range. This paper reviews research on the TBCC intake design, especially the internal rotating TBCC air intake system presented by TriJet. This review then summarizes the main challenges facing the development of the TBCC intake and the unique conical shock wave/boundary layer interactions in this intake to provide references for subsequent research work.
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    Skin friction reduction for boundary layer combustion in a scramjet engine
    HE Xin, XUE Rui, ZHENG Xing, ZHANG Qian, GONG Jianliang
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 562-572.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.009
    Abstract   HTML   PDF (9574KB) ( 96 )
    The skin friction characteristics for boundary layer combustion in a scramjet engine were studied numerically by analyzing the effect of adding a boundary layer combustion device and for changes in the scramjet exhaust nozzle lower wall inclination angle. The combustion was modeled using a hydrogen-air kinetics model consisting of 9 species and 27 reaction steps with the flow modeled. The turbulence was modeled using the four-equation Transition SST (shear stress transport) turbulence model which takes account the boundary layer transition to accurately predict the hydrogen combustion in the boundary layer with the hydrogen injected from the boundary layer combustion device. The investigation of the effects of various exhaust nozzle lower wall inclination angles shows that the flow expansion inhibits boundary layer combustion in the combustion chamber while dramatically reducing the skin friction in the exhaust nozzle. In contrast, a contracting exhaust nozzle enhances the boundary layer combustion in the combustion chamber while increasing the flow resistance. However, the boundary layer flame is extinguished before it propagates into the nozzle section, which further increases the skin friction. Thus, if the boundary layer combustion flame can be spread into and stabilized in the nozzle section, the scramjet with a contraction profile will exhibit superior skin friction reductions.
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    Semi-analytical algorithm for computing satellite-area target visibility
    ZHANG Zhong, E Zhibo, HUANG Lixia, LI Junfeng
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 573-580.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.020
    Abstract   HTML   PDF (5608KB) ( 159 )
    Computing the visibility of remote sensing satellites on an area target is an important basic satellite observation mission. The calculational accuracy and efficiency are then very important for satellite imaging scheduling. This paper presents a fast, semi-analytical algorithm for predicting satellite-area target visibility. First, geometric relations are used to define the boundaries of all the area targets described by ordinary arcs with the algorithm then determining the intersections. Then, the cone characteristics and the rectangular field of view of the satellite are used with a fast judgement condition for the visibility. The visibility at each discrete time step is determined analytically with a binary search which is then used to quickly predict the time for the visible window. Numerical examples show that this method is accurate and efficient. The relative error in the visibility duration is 0.1% relative to the predictions of the commercial software STK while the calculational speed is 105 times faster than the brute force method and almost 1 000 times faster than the average speed of the existing fast calculation algorithms.
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    HYDRAULIC ENGINEERING
    Factors affecting evapotranspiration analyzed based on a structural equation model
    YANG Wenjing, ZHAO Jianshi, ZHAO Yong, WANG Qingming
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 581-588.   DOI: 10.16511/j.cnki.qhdxxb.2021.22.031
    Abstract   HTML   PDF (10126KB) ( 268 )
    Surface evapotranspiration is a key process for measuring the effect of climate change on the regional hydrothermal cycle. However, the quantitative impact of vegetation on evapotranspiration is difficult to measure due to the effects of climate change and human activities. This study used time series analyses to describe the vegetation changes from 2001 to 2019. A structural equation model (SEM) for the Haihe River basin was then developed using remote sensing data and meteorological forcing data. The purpose was to separate the impact of climate change from the impact of vegetation change on the evapotranspiration. The results show that the vegetation leaf area index (LAI) increases significantly during the study period (0.014 (m2/m2)/a) and that the vegetation has a significantly greater influence on evapotranspiration than climate change. Climate factors indirectly exert a strong influence on evapotranspiration through vegetation. This study provides a basis for the assessment and integrated management of water resources in this area.
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    Literature review of conflicts and cooperation over transboundary freshwater resources
    GUO Liying, TIAN Fuqiang, WEI Jing, LU You, NI Guangheng
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 589-600.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.025
    Abstract   HTML   PDF (1497KB) ( 184 )
    The scarcity of water resources and the variety of water demands lead to conflicts between water users, especially in transboundary freshwater systems passing through several countries or regions. In the absence of a whole-basin management approach, the management of transboundary freshwater resources tends to degrade into a Tragedy of the Commons. However, the conflict and cooperation are closely related to the sustainable development of the river basin, the security and stability of the region, and the diplomacy between the water users in various countries. Therefore, research on conflict and cooperation over transboundary freshwater resources has great practical significance. This review presents an analytical research framework for conflict and cooperation in managing transboundary water resources and categorizes previous research into deduction and induction research paradigms. Three major research directions are how to define and quantify the status of water conflicts and cooperation, what are the drivers of water conflicts and cooperation and how do water conflicts and cooperation evolve. The literature review reveals knowledge gaps and potential future research directions. In future research, deduction will be used with induction to integrate the advantages of the two research paradigms. The review also shows the global dynamics and driving mechanisms of water conflicts and cooperation. The inner relationships between transboundary and domestic water resources need further exploration. In addition, new transboundary freshwater resource management strategies are needed to cope with the opportunities and challenges brought by economic development and climate change.
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    ECONOMIC AND PUBLIC MANAGEMENT
    Stabilizing land price, local government land supply, and land transaction prices and volumes
    WU Shuping, ZHANG Li, YANG Zan
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 601-613.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.032
    Abstract   HTML   PDF (2653KB) ( 107 )
    Prefecture-level panel data of successful and unsuccessful residential land auctions from 2007 to 2017 was analyzed to examine the influences of "stabilizing land price" regulations on the residential land supply volume, land transaction rate, land price premium rate, and land sale prices. Regulatory pressures have caused local governments to significantly increase the planned residential land supply, especially in low-administrative level cities or cities that have just experienced a change in mayor. However, the regulatory policies did not lower the price expectations of land use companies for residential land and, therefore, did not significantly reduce the residential land transaction rate, premium rate, or transaction price. In the end, the "stabilizing land price" regulations increased the number of residential land transactions and the land transfer income received by the local government but failed to achieve the goal of regulating land prices.
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    Panel data regression model for identifying the spatiotemporal characteristics and key factors influencing household water-energy consumption
    WANG Chunyan, ZHANG Jingxiang, LONG Jie, LIU Yi
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 614-626.   DOI: 10.16511/j.cnki.qhdxxb.2021.26.021
    Abstract   HTML   PDF (3527KB) ( 95 )
    The China family panel studies (CFPS) tracked the monthly household water and electricity consumption of 4 269 households from 2014 to 2018. The present study analyzed the household water and energy consumption characteristics to identify key factors influencing their water and energy use using descriptive analyses, correlation analyses and a random effect model based on a panel data regression. The results show that the household water and electricity consumption gradually increased with time with the monthly electricity in 2018 being 21% higher than in 2014 while the water consumption increased by 12%. The water and electricity consumption rates differed in different regions of China with southern China having the highest consumption rates, northwest China having the lowest consumption rates and northern China having the lowest water consumption rate. The household water and electricity consumption rates are positively correlated with a correlation coefficient of 0.49. The correlation was strongest in southern China and weakest in central China. The household economic and dwelling attributes significantly influence the water and electricity consumption. The household water and electricity consumption also correlate with the household size and house price with each increase in family size increasing the electricity consumption by 7.5% and the water consumption by 7.1%. Doubling the house price increases the electricity consumption by 1.3% and the water consumption by 1.2%. Price has a negative impact on water consumption with the water consumption decreasing by 13.9% for each 1.0 yuan increase in price.
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    PHYSICS AND ENGINEERING PHYSICS
    Analysis of colloidal system structures using spin-echo small-angle neutron scattering
    SONG Jing, SUN Guang'ai
    Journal of Tsinghua University(Science and Technology). 2022, 62 (3): 627-632.   DOI: 10.16511/j.cnki.qhdxxb.2021.22.033
    Abstract   HTML   PDF (2336KB) ( 217 )
    This work summarizes the theory for analyzing spin-echo small-angle neutron scattering (SESANS) data, especially for colloids. The SESANS spatial correlation function is calculated by taking the Abel transform of the density fluctuation correlation function in real space. This study also analyzes the spherical particle polydispersity effect on the SESANS spatial auto-correlation function. Thermodynamic self-consistent closure is used to solve the Ornstein-Zernike function to calculate the SESANS spatial structural correlation function. The SESANS theory for colloids with both short-range attraction and long-range repulsion shows that, unlike with traditional small angle scattering, SESANS can conveniently study the phase transition from the dispersed state to the percolation state as the colloid volume fraction increases. SESANS can characterize materials in real space to effectively reveal the structure and phase transition of colloidal systems.
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