Table of Content

    01 February 2021, Volume 55 Issue 2 Previous Issue    Next Issue
    Self-Reconfiguration Sequence of Lattice Modular Soft Robots
    LIU Jiapeng, WANG Jiangbei, DING Ye, FEI Yanqiong
    2021, 55 (2):  111-116.  doi: 10.16183/j.cnki.jsjtu.2020.005
    Abstract ( 951 )   HTML ( 390 )   PDF (7523KB) ( 612 )   Save

    A lattice self-reconfigurable modular soft robot based on the expansion-contraction motion rule is designed, which is composed of several soft modules, each of which is composed of a silica gel main body with positive hexahedron configuration and a master-slave docking surface. The internal bulged design makes it have a good expansion performance. The master-slave docking surface is composed of an iron disk and a suction disk type electromagnet connected with the silica gel main body by thread composition. Based on the relationship between the volume change of the soft module and the internal pressure, the expansion of the soft module is analyzed. The mapping relationship between the inflation pressure and the expansion of soft module is established. Besides, the inflation pressure required for the connection of adjacent two soft modules is obtained. Each soft module can expand 1.5 times under the working pressure of 30 kPa, and the docking and separation of two adjacent soft modules are realized by using the electromagnet connection and the expansion-contraction motion rules of soft modules. The self-reconfiguration of the modular soft robot can be realized by the sequential docking and separation of multiple adjacent modules. The feasibility of self-reconfiguration of soft robot is verified by the self-reconfiguration experiment.

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    Named Entity Recognition of Enterprise Annual Report Integrated with BERT
    ZHANG Jingyi, HE Guanghui, DAI Zhou, LIU Yadong
    2021, 55 (2):  117-123.  doi: 10.16183/j.cnki.jsjtu.2020.009
    Abstract ( 1113 )   HTML ( 15 )   PDF (876KB) ( 553 )   Save

    Automatically extracting key data from annual reports is an important means of business assessments. Aimed at the characteristics of complex entities, strong contextual semantics, and small scale of key entities in the field of corporate annual reports, a BERT-BiGRU-Attention-CRF model was proposed to automatically identify and extract entities in the annual reports of enterprises. Based on the BiGRU-CRF model, the BERT pre-trained language model was used to enhance the generalization ability of the word vector model to capture long-range contextual information. Furthermore, the attention mechanism was used to fully mine the global and local features of the text. The experiment was performed on a self-constructed corporate annual report corpus, and the model was compared with multiple sets of models. The results show that the value of F1 (harmonic mean of precision and recall) of the BERT-BiGRU-Attention-CRF model is 93.69%. The model has a better performance than other traditional models in annual reports, and is expected to provide an automatic means for enterprise assessments.

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    A Traffic Congestion Prediction Model Based on Dilated-Dense Network
    SHI Min, CAI Shaowei, YI Qingming
    2021, 55 (2):  124-130.  doi: 10.16183/j.cnki.jsjtu.2020.99.009
    Abstract ( 811 )   HTML ( 13 )   PDF (987KB) ( 388 )   Save

    When using the convolutional neural network (CNN) model to predict short-term traffic congestion, due to the convolution pooling operation of the model, part of the data for the information of the target position will be lost, resulting in the decline of the resolution of the output features and the decrease in the predictive ability of the model. To solve this problem, this paper proposes a dilated-dense neural network model. First, it uses dilated convolution to obtain the characteristics of a larger receptive field with fewer network parameters, and fully extracts complex and variable data spatio-temporal characteristics. Then, through down-sampling and equivalent mapping of dense network, it solves the problem of parameter degradation in the process of increasing layers of neural network. Finally, it uses the actual urban road average speed data blocks to verify the validity of the model. The results show that compared with the convolutional neural network model, the average absolute error of the network structure prediction is reduced by 3% to 23%.

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    Data Splitting Method of Distance Metric Learning Based on Gaussian Mixed Model
    ZHENG Dezhong, YANG Yuanyuan, XIE Zhe, NI Yangfan, LI Wentao
    2021, 55 (2):  131-140.  doi: 10.16183/j.cnki.jsjtu.2020.082
    Abstract ( 816 )   HTML ( 10 )   PDF (2548KB) ( 479 )   Save

    Aimed at the problem of instability and deviation of multiple training model in limited samples, this paper proposes a method of distance metric learning based on the Gaussian mixture model, which can solve this problem more reasonably by dividing the dataset. Distance metric learning relies on the excellent feature extraction capabilities of deep neural networks to embed the original data into the new metric space. Then, based on the deep features, the Gaussian mixture model is used to cluster the analyzer and estimate the sample distribution in this new metric space. Finally, according to the characteristics of sample distribution, stratified sampling is used to reasonably divide the data. The research shows that the method proposed can better understand the characteristics of data distribution and obtain a more reasonable data division, thereby improving the accuracy and generalization of the model.

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    Aerodynamic Performance of Counter-Rotating Vertical Axis Wind Turbine
    CAO Yu, HAN Zhaolong, ZHOU Dai, LEI Hang
    2021, 55 (2):  141-148.  doi: 10.16183/j.cnki.jsjtu.2019.360
    Abstract ( 856 )   HTML ( 4 )   PDF (6151KB) ( 416 )   Save

    In order to improve the aerodynamic performance and stability of the floating platform of an isolated vertical axis wind turbine, a novel structure design concept of the wind turbine with a coaxial counter-rotating vertical axis was proposed. Based on the computational fluid dynamics theory, a numerical simulation was conducted with the application of the Reynolds-averaged Navier-Stokes (RANS) shear stress transfer (SST) k-ω turbulence model, and combined with the eddy current theory, the aerodynamic performance and stability with different tip speed ratios (TSR) were further compared. The results show that in the same flow field, the floating platform of the counter-rotating wind turbine is more stable. When TSR<1.3, the long-time stall makes the de-vortex of the counter-rotating wind turbine more serious, and the wind energy utilization efficiency is lower. When TSR>1.3, the wind energy in outflow field is more absorbed by the rotor of the counter-rotating wind turbine. In addition, the length of remote vortex is shorter and the intensity is lower. Therefore, the wind energy utilization efficiency is higher. Coaxial counter-rotating has a certain reference value for the performance optimization of the vertical axis wind turbine.

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    Modeling and Simulation of an Inchworm-Like Soft Robot
    ZHANG Liwen, XU Qiping, LIU Jinyang
    2021, 55 (2):  149-160.  doi: 10.16183/j.cnki.jsjtu.2020.047
    Abstract ( 1162 )   HTML ( 25 )   PDF (7945KB) ( 614 )   Save

    It is a challenging problem to efficiently calculate and systematically analyze the motion laws and working gait of the inchworm-like soft robot. A simple mechanical model consisting of a rigid slider and a curved beam is established under quasi-static conditions, in order to realize quasi-static modeling and simulation analysis of the inchworm-like soft robot. First, based on the Euler-Bernoulli beam theory, the total potential energy expression of the beam is obtained. Next, combining the boundary conditions and the governing equation derived from the total potential energy based on the variational principle, a set of ordinary differential equations are established. Then, through discretization and dimensionlessness of those equations, a class of nonlinear algebraic equations for numerical solution is proposed. Finally, in the light of the contact situation between curved beam and ground as well as the viscous and slip condition of the system, the motion of the robot is divided into three stages. Through numerical calculations, the different configurations of the curved beam in different stages with the change of the initial curvature amplitude are obtained, which makes it possible to describe the law, the gait, and the net displacement of the soft robot in a motion cycle and solve the problem of movement connection of soft robots at different stages. The quasi-static method is characterized by high computational efficiency, which is more suitable for analyzing the motion configuration of soft robots.

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    Numerical Studies on Violent Sloshing and Resonance Frequencies in a Three-Dimensional Prismatic Tank
    XIN Jianjian, FANG Tian, SHI Fulong
    2021, 55 (2):  161-169.  doi: 10.16183/j.cnki.jsjtu.2020.066
    Abstract ( 804 )   HTML ( 3 )   PDF (2926KB) ( 310 )   Save

    To predict the resonance frequency of the real liquefied natural gas (LNG) tank, a Cartesian grid based three-dimensional (3D) multiphase flow model is used to simulate violent sloshing in a prismatic tank at different filling levels and excitation frequencies. In this model, a semi-implicit finite difference method is adopted to solve the incompressible two-phase flow Navier-Stokes (N-S) equations on a staggered Cartesian grid. Besides, a radial basis function ghost cell method (RBFGCM) is used to treat the irregular tank walls and a 3D gradient-augmented level set (GALS) method is used to capture highly nonlinear free surfaces. Based on the present model, the violent sloshing induced by rolling excitations in the 3D prismatic tank is simulated. Satisfactory convergences of grid sizes and time steps demonstrate the high accuracy and reliability of the present method. Moreover, the present results of the impulsive pressure and wave elevation agree well with the experimental data for different filling water depths. In addition, violent sloshing phenomena are captured such as wave rolling. Furthermore, the relationship between the pressure amplitude on the tank wall and the excitation frequency at four filling levels are investigated to identify the resonance frequency of the prismatic tank, to provide theorical guides for structrual design of the tanks.

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    Design and Simulation of a Titanium Alloy Lattice Bone Plate for 3D Printing
    ZHANG Cong, JIA Dejun, LI Fanchun, XU Yitong, ZHANG Yuan
    2021, 55 (2):  170-178.  doi: 10.16183/j.cnki.jsjtu.2019.196
    Abstract ( 1037 )   HTML ( 7 )   PDF (6477KB) ( 640 )   Save

    In order to improve the stress shielding effect caused by excessive elastic modulus of metal plates during fracture healing, a kind of 3D printing oriented lattice structure plate is designed based on topology optimization and the finite element modeling technology. A simplified finite element model of the titanium alloy tibial plate is established by using the finite element method. Combined with the finite element method and the data sampling method, the solid plate system and the lattice plate system are simulated, and the similarities and differences between their performances are compared. Based on the analysis of mechanical properties of lattice plate system, the lightweight design of the plate is realized and the stress shielding effect of the bone is improved. The results show that the weight of the lattice plate can be reduced by about 40% under the condition of guaranteed strength. The lattice plate is sensitive to the thickness. By reducing the thickness of the plate in a small range, the stiffness of the plate can be significantly reduced. The application of the lattice plate can effectively increase the average stress of the skeleton by about 4% and reduce the stress shielding effect of the skeleton. The simulated analysis results can provide references for the optimization design of low stress shielded plates.

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    Application of an Air Source Heat Pump System with a Three-Cylinder Two-Stage Variable Volumn Ratio Rotary Compressor
    XIAO Biao, YAN Yan, ZHAO Shunan, HUANG Tongyi, LI Xiang
    2021, 55 (2):  188-195.  doi: 10.16183/j.cnki.jsjtu.2019.269
    Abstract ( 897 )   HTML ( 6 )   PDF (1782KB) ( 711 )   Save

    Aimed at the problem of the compressors of the low temperature air source heat pump system, this paper analyzes the impact of volume ratio on performance and proposes a novel three-cylinder two-stage variable volume ratio rotary compressor. The performance of the proposed compression system is compared with that of the traditional two-stage compression system of the same terminal in the experiments. The results show that the three-cylinder two-stage system operates in a stable manner with a coefficient of performance (COP) of 1.52 at a ambient temperature of -30 ℃,while the traditional two-stage system does not work. The COP of the three-cylinder two-stage system is always 1.25% to 12.41% higher than that of the traditional two-stage systems at any ambient temperature. When the ambient temperature is stable and the water supply temperature increases, the amount of dissipated heat at the terminal increases. At the same time, the maximum heat of external machine decreases, as well as the COP. When the ambient temperature is 7 ℃ and -25 ℃ respectively, and the water supply temperature changes from 40 ℃ to 55 ℃,the COP of the three-cylinder two-stage system is 1.15% to 8.86% and 4.32% to 7.33% higher than that of the traditional two-stage system, respectively. The power consumption of the three-cylinder two-stage system is always 3.78% to 16.67% lower than that of the traditional two-stage system.

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    A Wireless Transcutaneous Energy Transfer System
    XIE Yue, SHEN Pengfei, JIANG Xiaoli
    2021, 55 (2):  196-205.  doi: 10.16183/j.cnki.jsjtu.2019.303
    Abstract ( 717 )   HTML ( 3 )   PDF (6039KB) ( 338 )   Save

    A wireless transcutaneous energy transfer (TET) system is researched. The characteristic functions of system voltage gain and transmission efficiency are obtained by circuit analysis. Meanwhile, according to the typical technical parameters of the TET system, a characteristic analysis is conducted. Therefore, based on the energy injection technique, a variable frequency constant voltage control method is proposed which enables the TET system to operate at a high efficiency all time when both the load and the transfer distance change. The experimental set of the TET system is arranged. The experimental results have verified the correctness of the theoretical analysis and design scheme. When the transfer distance is fixed, the overall efficiency remains constant in the whole load variation range. The overall efficiency of the TET system is above 83% within typical transfer distances. The multi-physics simulation software is used to simulate the human tissue safety. The simulation results show that the maximum electric field strength, the specific absorption rate, and the maximum temperature are lower than their corresponding limitations.

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    Control Strategy for Electric Vehicle Range-Extender Based on Hybrid Excitation Generator
    HOU Jue, YAO Dongwei, WU Feng, LÜ Chenglei, WANG Han, SHEN Junhao
    2021, 55 (2):  206-212.  doi: 10.16183/j.cnki.jsjtu.2019.203
    Abstract ( 930 )   HTML ( 7 )   PDF (2119KB) ( 663 )   Save

    Based on a hybrid excitation generator, a novel electric vehicle range-extender was proposed and the control system structure and the working principle were described. The multi-speed point working area was determined, according to the overall efficiency characteristics of the hybrid excitation range-extender. Based on the flexible adjustable characteristics of the air-gap magnetic field of the hybrid excitation generator, a double-closed-loop generation control algorithm was designed by decoupling the speed-power around the working area of the range-extender. The control strategy model was built by using MATLAB/Simulink and verified based on the prototype of the self-developed hybrid excitation range-extender. The test results show that the hybrid excitation range-extender has fast-dynamic response of output power and small steady-state error of speed and power control. Further, the steady-state and transient operating conditions are both located in the set working area. Therefore the power generation control strategy is feasible.

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    Expert Forum
    Flexible Coating Reduces Drag
    TIAN Xinliang
    2021, 55 (2):  213-214.  doi: 10.16183/j.cnki.jsjtu.2020.393
    Abstract ( 1081 )   HTML ( 14 )   PDF (1455KB) ( 686 )   Save

    Tian Xinliang’s group proposed a novel flow control method called "Flexible coating reduces drag" (FCRD) with a flexible enclosure constructed behind the bluff body to adjust the fluid forces received and the flow pattern around it. Compared with the traditional flow control methods, FCRD does not change the structure of the control object and thus has a positive engineering application prospect. Besides, FCRD brings out a new "fluid-structure-fluid" interaction problem, which needs further investigation.

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    Innovation and Design
    Development of a Hybrid Solar and Wind-Powered Long-Range Unmanned Ocean Stereo Exploration Vessel
    YAO Tiancheng, ZHAO Yongsheng, WANG Hongyu, HE Yanping, DING Zilong, CHI Zheying, CAI Weikai
    2021, 55 (2):  215-220.  doi: 10.16183/j.cnki.jsjtu.2020.352
    Abstract ( 1133 )   HTML ( 11 )   PDF (10222KB) ( 668 )   Save

    Aimed at the problems of unmanned marine exploration vessels, such as the short voyage time and the limited sensing ability caused by sensor failure under complex marine environments, a long-range unmanned ocean-air stereo exploration vessel driven by wind and solar energy is developed. An elevating ducted wind turbine is designed for high efficiency and low starting wind speed, and a deployable solar photovoltaic power generation system is developed. Therefore, wind power and solar energy can be utilized to realize a hybrid system, which overcomes the instability of single energy power supply, and effectively ensures the endurance of unmanned exploration vessel. Then, a ship-borne tethered ummanned aerial vehicle (UAV) system is developed with an autonomous takeoff and landing control section. Finally, the information fusion technology of ship borne and airborne sensors is adopted to greatly improve the perception ability of the unmanned ship to the surrounding environment and the function of three-dimension detection of sea and air. The unmanned surface vessel (USV) proposed in this paper is permitted to perform the assigned task with different types of loading equipment according to the scenarios.

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    Experimental Study of a Trans-Critical CO2 Mobile Air Conditioning System with an Ejector
    LI Hao, ZHANG Zhenyu, SONG Xia, CHEN Jiangping
    2021, 55 (2):  179-187.  doi: 10.16183/j.cnki.jsjtu.2020.061
    Abstract ( 834 )   HTML ( 2 )   PDF (5948KB) ( 508 )   Save

    A carbon dioxide(CO2) ejector expansion air conditioning system for vehicles is developed in a calorimeter laboratory. In experimental tests on a standard mobile air conditioning bench, the effects of different operating parameters on the performance of the CO2 refrigeration system for vehicles are studied, and the performance advantages of the CO2 ejector expansion refrigeration system are comparatively analyzed. The research results show that the cooling capacity of the CO2 ejector expansion refrigeration system for vehicles is almost equal to that of the CO2 conventional cooling system. Both increasing the indoor air flow rate and increasing the compressor speed can effectively increase the cooling capacity of the CO2 ejector expansion refrigeration system, and the ejector can increase the coefficient of performance (COP) of the system by 1.65% to 12.60% under different working conditions. The outdoor temperature has a great impact on the CO2 ejector expansion refrigeration system performance, and the performance of CO2 ejector expansion refrigeration system for vehicles decays obviously at a high ambient temperature.

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