Table of Content

25 July 2021, Volume 49 Issue 7

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Contents



2021, 49(7):  0. 

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Traffic & Transportation Engineering

Energy Saving Optimization of Metro Train Working Diagram Under Regenerative Braking



ZHENG Yajing, LI Yaohui, LI Yuheng, et al

2021, 49(7):  1-7.  doi:10.12141/j.issn.1000-565X.200552

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Increasing the utilization rate of regenerative braking power can effectively improve the energy-saving effect of metro system and reduce the catenary voltage fluctuation． In this paper，by fine-tuning the departure interval and stop time，the optimization model of metro train working diagram was constructed on the basis of not changing the train operation scheme． The goal is to maximize the overlap between the“generated energy”period of train arrival and the“used energy”period of train departure under the same power section，and to ensure that the departure interval and stop time do not exceed the acceptable range of normal operation of rail transit． The model was solved by using the classical time-space local rolling optimization method and commercial optimization software and verified by an actual metro train working diagram． The results show that the average utilization rate of regenerative braking energy of metro train can be increased to more than 15% ，and the metro train operation diagram for energy saving is effectively optimized．

Impact of Soil Massively Stacked in the Bridge Side on the Safety of the Bridge



HE Zhiyong, ZHANG Haoran, YANG Cheng, et al

2021, 49(7):  8-16.  doi:10.12141/j.issn.1000-565X.200446

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Aiming at the usually reported accidents induced by soil massively stacked in the bridge side，a numerical simulation for the behavior of pile foundation of a highway ramp bridge subjected to surcharge load was carried out． A computational model of bridge，foundation soil，stacked soil was constructed through the finite element software ABAQUS，and variables such as varied structural forms of bridges and pile dimensions were selected． The effects of soil squeezing，deformation of foundation soil，pile-soil coupling relationship，overall displacement and internal force of the bridge were modeled to assess the safety status of the bridge． The influence of dimensions of the pile on the stability of bridge structure was discussed according to the deformation law of the foundation soil，and the safety status of different bridge structures under asymmetric loading were comparatively analyzed． The results show: when mass earth is heaped laterally on the bridge，the bending moment and axial force of the bridge increase by 177. 7% and 27. 3% ，respectively; the internal forces of the main pier and upper structure has no obvious change，indicating that the ramp bridge is safe; the deformation，moment change and the lateral displacement of the bridge pile foundation are consistent with the existing conclusions; the lateral displacement mainly occurs in the layer of soft soil，which may exceed the allowable value under large loading; decreasing the height of the stacked soil and increasing the space between soil piles can prevent the deformation of the foundation soil and reduce the displacements of the bridge structure; the width of the stacked soil has significant influence on the lateral displacements of the foundation soil and little influence on the sink of the foundation soil; clearing the soil near the bridge can effectively control pile foundation deformation and horizontal displacement; the bridge is prone to greater structural deformation under the influence of massively stacked soil after setting expansion joints and supports; linear curvature and load position also have an effect on expansion joint of bridge deformation．

Operating Speed Prediction Based on Dynamic Visual Field in Three-Dimensional Point Cloud Environment



LUO Dongyu, WANG Jiangfeng, CHEN Jingya, et al

2021, 49(7):  17-25.  doi:10.12141/j.issn.1000-565X.200465

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To comprehensively consider the influence of the three-dimensional road alignment on the operating speed，the research on the operating speed prediction in the three-dimensional point cloud environment was carried out based on the driver's dynamic visual field． Firstly，the point cloud data was used to calibrate the road and the terrain on both sides，and the three-dimensional point cloud road environment was established． Secondly，through the transformation and projection of point cloud coordinates，the view plane model with the driver's viewpoint as the center was constructed to obtain the driver's static visual field image． Thirdly，according to the principle of space geometry and the parameters of dynamic visual field，the projection ellipse equation was calculated and the driver's dynamic visual field image was obtained． Finally，the road-to-dynamic-visual-field-area-ratio was used as the research index of operating speed，and the operating speed prediction model was established by the vehicle dynamic performances and threshold control． The prediction model was testified by the example of dong-lu-mountain section of Ningxia-Hangzhou freeway． The results show that the average relative error between the predicted values and the measured values is 2. 726% for passenger cars and 9. 023% for trucks． The prediction result of trucks indicates that this section is a bad alignment section and the result is consistent with the measurement result． Therefore，the proposed prediction model can effectively solve the problem that the existing model cannot accurately predict the operating speed inside the section division unit of freeway

Analysis of Nonlinear Rolling Damping and Rolling Motion of Asymmetric Catamaran



ZHANG Yihan WANG Ping HU Jingfeng

2021, 49(7):  26-33.  doi:10.12141/j.issn.1000-565X.200268

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A numerical prediction method of rolling damping was established for asymmetric catamaran with computational fluid dynamics ( CFD) method and overset grid technology． Firstly，the study simulated the rolling decay curves with different rolling angles and ship speed under different transverse and longitudinal space，and analyzed the rolling damping characteristics． Then based on 3D potential flow theory and considering the correction of the nonlinear rolling damping and nonlinear restoring，the rolling motion response of asymmetric catamaran in regular waves was calculated，and the characteristics of rolling motion under different wave directions were analyzed． Finally， model tests were carried out to verify the numerical prediction methods of rolling damping and rolling motion． It is showed that the model test results are close to the numerical prediction，and the transverse wave disturbance in the side body leads to greater rolling response than that in the main body of the asymmetric catamaran．

Collaborative Optimization of Urban Conventional Bus and Customized Bus Under Epidemic Prevention and Control



SHEN Chan SUN Yao CUI Hongjun

2021, 49(7):  34-41.  doi:10.12141/j.issn.1000-565X.200467

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The public transport space is a high-risk environment for the spread of the epidemic because of the dense flow of people and the narrow and closed internal space of the vehicles． The characteristics of customized bus “one person，one seat”and “one stop direct”are just in line with the requirements of epidemic prevention and control． Therefore，considering the advantages of conventional bus and customized bus，this paper proposed a collaborative optimization method of urban conventional bus and customized bus under epidemic prevention and control． It established a total cost minimization model considering risk cost，operation cost and travel cost，and designed an improved column generation algorithm to solve the model． The results show that: the collaborative optimization scheme proposed in this paper is significantly better than the independent conventional bus scheme and customized bus scheme，and ensures the service level of passengers; with the decrease of risk level，the number of conventional bus lines increases，the number of customized bus lines decreases，and the total number of service increases with the decrease of epidemic level． The study confirms the beneficial effect of customized bus on epidemic prevention and control and provides a theoretical guidance for the optimization of public transport system under the situation prevention and control．

Adaptive Regenerative Braking Control Strategy of Range-Extended Electric Vehicle Based on Multi-Objective Optimization



LIU Hanwu, LEI Yulong, FU Yao, et al

2021, 49(7):  42-50,65.  doi:10.12141/j.issn.1000-565X.200531

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Aiming at the multi-objective optimization ( MOO) problem of the range-extended electric vehicle regenerative braking control strategy，a real-time adaptive regenerative braking control strategy was proposed based on the MOO model and optimal optimization theory． Firstly，the vehicle simulation model was established on AVL / Cruise and Matlab /Simulnk software，and a MOO model was built with the system braking performance ( BP) ， regenerative braking loss efficiency ( RBLE) and battery capacity loss rate ( BCLR) as the objective functions based on NSGA-Ⅱ algorithm． Then Parato optimal solution was obtained through off-line optimization under the comprehensive regenerative braking performance． Combined with the optimization results，a real-time adaptive fuzzy controller was designed． The controller considers the road adhesion and the state of battery，and can adjust the distribution of the regenerative braking work-point online． Simulation results on WLTP driving cyclic conditions show that the adaptive regenerative braking control strategy can effectively balance the relationship among BP，RBLE and BCLR，and it can effectively reduce BP and RBLE while maintaining a small BCLR．

Computer Science & Technology

Path Planning of Mobile Robots Based on Dual-Tree Quick-RRT* Algorithm



WEI Wu, HAN Jin, LI Yanjie, et al

2021, 49(7):  51-58.  doi:10.12141/j.issn.1000-565X.200769

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The optimal rapid expansion randomized tree ( RRT* ) is an asymptotically optimal path planning method for mobile robots． Quick-RRT* reduces the initial path length of RRT* and increases the path convergence speed． In order to further improve the convergence speed of Quick-RRT* ，this paper proposed a dual-tree Quick-RRT* ( Quick-RRT* -Connect) algorithm． Firstly，two random trees were generated at the start and end points respectively based on the Quick-RRT* algorithm． Two trees grew in turn and they were connected with greedy method． Then， the probability completeness and asymptotic optimality of the proposed algorithm were analyzed and testified． Finally，based on the Matlab platform，Quick-RRT* -Connect was compared with RRT* ，Quick-RRT* and RRT* - Connect in three environments． The results show that the improved algorithm can not only find initial path and suboptimal path in a shorter time，but also reduce the initial path length．

Coupled Collaborative Filtering Model Based on Attention Mechanism 



HUANG Min QI Haitao JIANG Chunlin

2021, 49(7):  59-65.  doi:10.12141/j.issn.1000-565X.200473

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As a common implementation of recommender system，collaborative filtering can bring personalized recommendation service experience to users． Traditional collaborative filtering models do not mine and analyze the attention level of different explicit attributes of users and items，leading to the critical level of different explicit attributes not paid attention by the model． Therefore，based on the coupled collaborative filtering model based on convolutional neural network，an attention mechanism was introduced in the paper to deeply mine the critical degree of explicit attributes and enhance the parameter learning gradient on critical attributes． And a new method of calculating the coupling degree was proposed to ensure the flushness of parameters and to improve the recommendation performance of the model． The experimental results show that the recommendation accuracy rate of the model proposed in the paper is better than that of traditional collaborative filtering methods and coupled collaborative filtering models，and the cumulative gain of topK@ 10 hit ratio and normalized discount cumulative gain reach 0. 8508 and 0. 5850，respectively．

Tightly Coupled Recommendation Algorithm Based on Heterogeneous Information Networks



LIU Huiting, LI Yinjie, GUO Lingling, et al

2021, 49(7):  66-75.  doi:10.12141/j.issn.1000-565X.200689

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In view of the problems of sparsity and underutilization of the heterogeneity of auxiliary information faced by current collaborative filtering methods and the advantages of heterogeneous information networks ( HIN) in modeling complex heterogeneous information，a HIN based tightly coupled recommendation model ( HTCRec) was proposed in this paper． It utilizes the heterogeneous information network embedding and a tightly coupled collaborative filtering framework to carry out personalized recommendation． Firstly，it aggregates meta-paths in a HIN and their corresponding path instances． Then it uses the attention mechanism to represent the auxiliary information of the target users or items in terms of the embedding of the respective aggregation meta-paths． At last，the meta-path is explicitly incorporated into the tightly coupled interaction model for personalized recommendation． The experimental results of the real data sets show that compared with the state-of-the-art recommendation models，the HTCRec model has better recommendation performance and effectively alleviates the problem of data sparsity．

Unsupervised Surface Defect Detection Method Based on Image Inpainting



HU Guanghua, WANG Ning, HE Wenliang, et al

2021, 49(7):  76-85,124.  doi:10.12141/j.issn.1000-565X.200749

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For the detection of non-uniform and non-periodic irregular texture surface defects，it is difficult to achieve conventional image reconstruction as the background texture is a non-stationary signal． It is also difficult to obtain sufficient information about the defects such as shape，gray scale and other image features in advance． And the visual features of similar defects can present great dispersion． The existing detection methods based on target features are inapplicable． Therefore，this paper proposed an unsupervised learning surface defect detection method based on image inpainting． Firstly，the method used a small number of normal texture samples as training set to train the network model． Then，the missing area was set artificially in the sample image and the network model was used to predict the content of the missing areas during the testing stage． By combining the structural similarity evaluation and residual error of the reconstructed image and the image to be tested，the defect detection and separation were realized． The experimental results show that the proposed method can not only effectively detect the defects on the regular texture surface but also detect the defects of irregular texture surfaces effectively，showing good practicability and adaptability．

Adaptive Scheduling Algorithm for Object Detection and Tracking Based on Device-Cloud Collaboration



TAN Guang LI Changhao ZHAN Zhaohuan

2021, 49(7):  86-93.  doi:10.12141/j.issn.1000-565X.200722

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As smart mobile devices become increasingly popular，mobile applications such as object detection in videos are greatly limited by the computing and storage capacity of mobile devices． Traditional cloud computing can not meet the requirements of applications for network delay，network jitter，security and other issues． For this purpose，this paper designed the quality of experience ( QoE) as a comprehensive measure of object detection accuracy and energy consumption based on end-cloud collaborative system． Regarding the quality of experience as the optimization goal，this paper then proposed an adaptive scheduling algorithm for video image detection and tracking． The algorithm schedules object detection and object tracking by predicting network bandwidth and calculating transmission delay． Experimental results on the KITTI video dataset show that the detection-tracking adaptive scheduling algorithm can achieve a higher QoE value，significantly reduce the energy loss，and achieve an detection accuracy of 78. 3% ．

Vehicle Recognition Method Based on Improved CenterNet



HUANG Yuezhen, WANG Naizhou, LIANG Tiancai, et al

2021, 49(7):  94-102.  doi:10.12141/j.issn.1000-565X.200496

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A vehicle recognition algorithm based on improved CenterNet was proposed to solve the problem of low target recognition rate in vehicle recognition system． Firstly，the algorithm used ResNet18 as the basic network to reduce network parameters． Secondly，in view of the problem that the CenterNet model has the demerits of inaccurate positioning of vehicles，it was proposed to use the distance intersection over union loss to replace offset loss and width-high loss; meanwhile，single-scale spatial feature fusion ( SASFF) method and adaptive hierarchical feature fusion ( AHFF) method were employed to fuse several feature maps of the network． The experimental results show that on the Vehicle data set，mean average precision of the improved CenterNet models increases by 1. 9% ; on the BDD100K and Pascal VOC data sets，average precision at 0. 5 of the intersection over union between the predicted boxes and the true boxes increase by 5. 2% and 2. 5% ，respectively，and the inference speed on GTX1080Ti can reach 149 f /s． The improved CenterNet proposed in this paper can significantly improve vehicle recognition accuracy．

Power & Electrical Engineering

Optimal Generation Configuration Methods for Standalone Microgrids Based on Wind and Solar Resources Characteristics



LIN Lingxue LIAO Biying GUAN Lin

2021, 49(7):  103-115.  doi:10.12141/j.issn.1000-565X.200597

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With the wide application of renewable energy and the development of distributed generation technology， more and more microgrids operate independently in island mode，and the requirements for microgrid construction are also higher and higher． As an important part of microgrid construction，Microgrid power planning needs to configure power according to the resource characteristics of different regions． Based on the background of“wind / photovoltaic /battery”standalone microgrids，this paper proposed an optimal power configuration method for standalone microgrids based on the characteristics of wind and solar resources． An optimization model with the objective of minimizing the annual generation cost and considering the constraints of power output and energy storage battery capacity was established and solved by linear programming algorithm． Considering the randomness of the wind and photovoltaic output，the wind and photovoltaic output scenario was simulated by the generative adversarial network algorithm，and the scene was reduced by the improved K-medoids clustering algorithm． In order to analyze the characteristics of wind and solar resources，an evaluation system including wind power resources，photovoltaic resources and wind solar complementary indicators was constructed，and the subjective and objective combination weight method based on“entropy weight-complex correlation coefficient-order relationship analysis”was proposed． Fuzzy evaluation and grey evaluation methods were used to comprehensively evaluate the level of wind and solar resources in 30 provinces of China． Finally，according to the evaluation results，five representative regions were selected for example analysis． The results show that there is a corresponding relationship between the evaluation level of wind power resource evaluation index and the proportion of wind turbine configuration capacity． The study can provide reference for the planning of standalone microgrids power supply．

Structure Optimization of 350 t/d Waste Incinerator



LIN Tao, LIAO Yanfen, YANG Xucong, et al

2021, 49(7):  116-124.  doi:10.12141/j.issn.1000-565X.200177

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In view of the diversity of domestic solid waste calorific value，there will be some problems such as fuel calorific value is not suitable for the incinerator introduced from abroad． In this study，the adaptability modification of a 350 t /d grate waste incinerator in Guangdong was carried out and based on the bed FLIC calculation software and computational fluid dynamics software Fluent，the combustion in garbage incinerators of different structures was simulated to predict the distribution features and fuel adaptability of the temperature field，velocity field and the gas composition of the front wall folding flame angle and arch u-shaped angle of furnace． The results show that: eliminating the front wall flame angle and the U-shaped angle of the rear arch makes the combustion area of the furnace move down; when the high temperature area is between the grate and the secondary air outlet，the furnace combustion is more sufficient，effectively reducing the output of NOx，saving the amount of out of stock reductant and resulting more suitable mixed combustion of sludge and garbage． Besides，adding 5% LD-40 sludge can effectively reduce the production of CO，CO2 and furnace temperature and slow down the high temperature corrosion phenomenon． The average error between the numerical simulation results and the measured temperature is less than 5% ．

Aerodynamic Force Characteristics and Wind-Induced Swing Response Analysis of Ellipse Iced Conductor with Ice Bridge



ZHANG Yuelong, LOU Wenjuan, CHEN Zhuofu, et al

2021, 49(7):  125-133.  doi:10.12141/j.issn.1000-565X.200535

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Under severe icing conditions，the iced sub-conductor may be connected by the ice bridge to form a connected ellipse iced conductor，resulting in the increase of windward area and aerodynamic shape deterioration of conductors． In order to study the aerodynamic force characteristics of the connected ellipse iced conductor ( with the ice bridge) and the separated ellipse iced conductor ( without the ice bridge) ，the high frequency force balance wind tunnel tests were conducted． Based on the test results，the effects of aerodynamic force characteristics of two ice accretion types on galloping stability and wind-induced swing response were analyzed． The results show that: ( 1) compared with the separated ellipse iced conductor condition，the lift force curve of the connected ellipse iced two-bundled conductor has a slower drop around peak，and the mean lift force coefficient is much larger in high wind attack angle cases; ( 2) near the wind attack angle of 170°，the mean torque coefficient of the separated ellipse iced conductor is larger than that of the connected ellipse iced two-bundled conductor; ( 3) the drag forces of conductors with the two iced types both satisfied the quasi-steady assumption; ( 4) for the vertical galloping，the separated ellipse iced conductor has worse stability，and for the torsional galloping，the connected ellipse iced conductor is more disadvantageous; ( 5 ) under the same wind velocity and transmission line condition，the wind-induced response of the connected ellipse iced conductor is larger than that of the separated ellipse iced conductor，leading to greater wind-induced swing accident risk．

Relaxation Calculation Method and Analysis of Jet-Buffer Mechanism in Water Hammer with Liquid Column Separation



FU You NIU Xuetian MIN Zheng

2021, 49(7):  134-141.  doi:10.12141/j.issn.1000-565X.200674

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A multiphase relaxation calculation method with the adaptive process was established to analyze jetbuffer mechanism in water hammer with liquid column separation． The rationality and stability of this calculation method were verified by air-water two-phase shock tube． The internal flow mechanism of water hammer with liquid column separation was analyzed． The results show that for water hammer with liquid column separation whose secondary pressure variation value is higher than the theoretical ones，it can be divided into the direct water hammer， the buffer water hammer，and the jet water hammer． In the stage of buffer water hammer，the presence of bubbles reduces the pressure impact on the boundary，causing the water hammer wave appear buffered and the change of pressure value is smaller than the theoretical ones． In the stage of jet water hammer，the jet acceleration generated during void compression and collapse does not directly affect the pressure impact on the boundary，but it causes a secondary pressure change accumulation in the initial value after back propagation，and the change value is higher than the theoretical calculation value． The occurrence of jet water hammer affects the accuracy of value calculated by direct water hammer method，so this is the most noteworthy part of water hammer with column separation calculation．

Analysis of Bolt Pretension of LNG Ultra-Low Temperature Ball Valve



LI Shuxun, YIN Huiquan, ZHAO Minjie, et al

2021, 49(7):  142-148.  doi:10.12141/j.issn.1000-565.200247

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In order to study the effect of temperature on the bolt pretension of flange structure，the bolt pretension and sealing conditions of flange in liquified natural gas ( LNG) ultra-low temperature ball valve at different temperatures were analyzed by ANSYS finite element software，and the pretension states of bolt materials with different linear expansion coefficients at room temperature and low temperature were compared． The results show that when the bolt material is B8M and XM-19，the preload force increases with the decrease of temperature，and the pretension under the low temperature conditions increases by 24. 93% and 6. 28% respectively compared with normal temperature; when the bolt material is Inconel625，the pretension decreases with the decrease of temperature，and the pretension under the low temperature condition decreases by 26. 39% compared with normal temperature． At the same time，the variation of the sealing specific pressure of the metal spiral wound gasket with temperature exhibits the same trend with the bolt pretension．