Table of Content

25 October 2021, Volume 49 Issue 10

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Contents



2021, 49(10):  0. 

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Traffic & Transportation Engineering

Extended Co-evolutionary Algorithm for Path Planning Based on the Urban Traffic Environment Evolution



WEN Huiying, LIN Yifeng, WU Haoshu, et al

2021, 49(10):  1-10.  doi:10.12141/j.issn.1000-565X.200279

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Ｒeasonable path planning can shorten the travelling time to ensure that rescue forces can arrive at the scene in time and improve the efficiency of emergency rescue． Based on the urban road traffic characteristics and the dynamic evolution of traffic environments，this paper proposed an extended co-evolutionary algorithm ( ECEA) to calculate the optimal rescue path． The ECEA establishes a co-evolutionary optimization mechanism，which means that the path planning process co-evolves with the evolution of traffic environments． Meanwhile，ECEA can flexibly select the search scope to improve the number and quality of alternative solutions． Experimental results show that ECEA outperforms timing co-evolutionary algorithm ( TCEPO) and Online re-optimization ( OLRO) both in the travelling time and robustness under the condition of limited data，thereby improving emergency rescue efficiency．

DifferentNet: Neural Network for Foreign Objects Foreground Detection in Metro



LIU Weiming, WEN Junrui, ZHENG Zhongxing, et al

2021, 49(10):  11-21,40.  doi:10.12141/j.issn.1000-565X.200671

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A foreground detection method based on semantic segmentation and background reference was proposed to solve the problem of foreign objects detection in the space between platform screen doors and train doors in metro stations． This method used a depth neural network—DifferentNet to detect foreign objects region in images． Firstly， the background image and the image to be detected were obtained during a metro stop at the platform． The feature pyramid was obtained by extracting the feature information of the images through the encoding part of the network， and feature maps of the two images were merged by concatenation． Then the foreground heat map of the image to be detected was obtained by calculating the feature difference in the decoding part． Finally，the heat map was thresholded and filtered to get detection results． The results show that this method can achieve a high foreground IoU of 81. 2% and F1-score of 89. 5% ． Furthermore，it reached 30 fps in speed． The proposed method performed better than traditional methods and other image segmentation networks without background reference．

Analysis of Urban Landscape and Traffic Safety Based on Street View Images



LU Yue FU Xinsha

2021, 49(10):  22-30.  doi:10.12141/j.issn.1000-565X.200733

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The visual environment has long been regarded as an important factor affecting traffic safety． However， limited by image analysis methods，existing studies on the relationship between environmental visual factors and traffic safety are mainly qualitative and it is difficult to conduct large-scale quantitative analysis of the visual environment． This study used rich，easy-to-extract and growing streetscape images as the data source of environmental factors，and extracts the image feature information，location information and sensory information of streetscape through methods such as expanded residual network ( DＲN) ． And Pearson correlation coefficients and ridge regression were used to screen quantitative indicators to construct a quantitative analysis framework for the association between visual environment and traffic safety based on deep learning，providing a new quantitative means to study urban landscapes． In addition，statistical analysis methods were used to identify the influencing factors that lead to changes in road traffic safety conditions． On the one hand，the variability in the contribution of influencing factors associated with the urban landscape to accident rates in different urban areas was explored． For example，an increase in the proportion of ″vegetation″ in commercial and older urban areas has a positive impact on traffic safety， but the opposite is true in suburban areas． On the other hand，patterns that may advance urban planning theory are also discovered． For example，the closer the road unit is to the city center，the safer the traffic conditions． This paper offered a new way of thinking about the link between urban landscape and traffic safety in quantitative terms， and offered the possibility for assessing urban traffic safety conditions efficiently and on a large scale． 

Distribution Path Optimization of Electric Vehicles Considering Charging and Discharging Strategy in Smart Grid



LI Jiale LIU Zhenbo WANG Xuefei

2021, 49(10):  31-40.  doi:10.12141/j.issn.1000-565X.200612

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In view of the phenomenon that more and more companies use electric vehicles ( EVs) to distribute cargo in urban areas，this paper presented an optimized EV distribution method with the time window by considering the intelligent charging strategy in the smart grid． The EVs can either charge or discharge when connecting to the smart grid through the vehicle to grid ( V2G) system． The V2G mode provides a more flexible way for EVs to operate． It can help EVs to increase efficiency and lower the cost at the same time． Based on the recharge and vehicle routing problem，this paper proposed a nonlinear integer programming model，considered the charging and discharging decisions of EVs，and proposed an improved genetic algorithm． Finally，25 cases were designed to verify the feasibility of the algorithm． The simulation result shows that the iterative efficiency of the improved genetic algorithm ( GA) is higher than other algorithms and the quality of the optimal solution is improved by 47% ．

Protection Performance of New Fabricated Guardrail Based on Collision Simulation



SONG Xuming, PAN Pengyu, RONG Yawei, et al

2021, 49(10):  41-49.  doi:10.12141/j.issn.1000-565X.200710

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In view of the existing problems such as poor energy absorption and buffering capacity of concrete rigid guardrail and the danger to driving safety，a new type of prefabricated anti-collision guardrail was proposed． In order to verify its feasibility，the LS-DYNA finite element software was used to establish a guardrail-bridge deck cooperative force model to simulate the collision process of a small car and a 40 t large truck with the guardrail at different speeds． Numerical results show that the vehicle doesn＇t climb over the guardrail in collision process，the climb height and exit angle are small，and the guardrail improves guidance effects of large trucks better than that of small cars． The peak value of lateral acceleration at the driver＇s position is significantly reduced up to 60. 8% ． The peak values of the Longitudinal and lateral collision force received by the new guardrail are reduced and the longitudinal force component is reduced by up to 49. 2% ． So the new guardrail has great guiding functions and better energy absorption effects，which can effectively improve driving safety． The guardrail design can provide reference for the actual car crash test．

Image Analysis Method of Construction Waste Filler Material Components Based on Machine Vision



XIE Kang, CHEN Xiaobin, YAO Junka, et al

2021, 49(10):  50-58,69.  doi:10.12141/j.issn.1000-565X.200764

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Construction waste recycling filler is obtained from construction waste by crushing． Due to its diversified composition，It can be used for subgrade filling only after sorting． At present，manual screening method is timeconsuming． In this paper，convolution neural network was used for image analysis and the composition of regenerated packing can be obtained automatically． Firstly，a labeled dataset composed of 36000 granular images is created to train different CNN models． Among them，the user-defined resnet34 model with 40% Dropout rate performs the best，and its verification accuracy can reach 97% ． Secondly，the mass of particles was estimated based on the particle type and shape． Finally，the method proposed in this paper was compared with the manual screening method． For most recycled fillers，the quality difference is less than 2% ． This paper aims to improve the utilization of construction waste and it is of great significance to the popularization and application of construction waste backfill subgrade engineering．

Architecture & Civil Engineering

Seismic Damage Assessment Method for Spatial Grid Structures Considering Multi-modal Contribution



ZHANG Yujian, LUO Yongfeng, GUO Xiaonong, et al

2021, 49(10):  59-69.  doi:10.12141/j.issn.1000-565X.200590

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In order to avoid the adverse effects of modal transition and unreasonable mode selection on the accuracy of damage assessment results，a seismic damage assessment method for spatial grid structures considering the contribution of multiple modes was proposed． Firstly，based on the idea of modal pushover analysis and the structural dynamic theory，the equivalent static displacement expression corresponding to the multi-modal contribution under unit seismic force was obtained． Then，according to the difference between the equivalent static displacement of original structure and damaged structure，the structural characterization parameter of the earthquake damage degree， namely，the overall damage parameter，was generated． Finally，the state of structural damage and performance degradation was assessed based on the magnitude and change of the overall damage parameters of the structure． The numerical analysis results of single-layer reticulated shell model show that the overall damage parameter of the structure calculated according to the method in this paper can more accurately assess the seismic damage degree of the space grid structure based on considering the multi-mode modal contributions． The obtained results are in good agreement with the comparison of structural characteristic response． In addition，the accuracy of the assessment results can be guaranteed in the case of severe damages．

Numerical Analysis of Fatigue Performance of Prestressed CFＲP Ｒeinforced ＲC Beams in Hygrothermal Environments



LUO Yi ZHANG Xiang GUO Xinyan

2021, 49(10):  70-77.  doi:10.12141/j.issn.1000-565X.210049

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Most parts of south China are located in subtropical region，where hygrothermal environment will reduce the performance of prestressed CFＲP reinforced ＲC structure． In order to explore the influence of hygrothermal environment on the fatigue performance of prestressed CFＲP reinforced ＲC structure，the failure criterions were established in the paper based on the two failure modes of main reinforcement fracture and debonding failure of CFＲPconcrete interface under the combined action of hygrothermal environment and fatigue load and the fatigue performance of prestressed CFＲP reinforced ＲC beams in hygrothermal environment was analyzed by numerical analysis． The results show that the fatigue performance of the reinforced beams will be reduced in hygrothermal environment， and the effect of increasing the prestress degree of CFＲP on the predicted life of the beams presents two circumstances． When the ＲC beams are damaged due to the failure of the main reinforcement，the increase of prestress degree can significantly increase the predicted life of the ＲC beams． However，when the beam is damaged due to the interface debonding，excessive prestress will reduce the life expectancy of ＲC beams．

Biaxial Tearing Behaviors and Mechanisms of Warp-Knitted Fabric Membranes Under Combined Shear and Tensile Stresses



CHEN Jianwen, GUAN Xiaoyu, ZHANG Ｒuonan, et al

2021, 49(10):  78-86.  doi:10.12141/j.issn.1000-565X.200511

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In order to explore the in-plane tearing behaviors and strength characters of fabric membranes under combined shear and tensile stresses，experimental and mesoscale numerical studies were conducted on a typical warp-knitted fabric membrane． Its specific tearing behaviors and strength characters under a series of stress ratios and stress levels，reinforced film types and coupled stresses were obtained，and the tearing mechanisms and failure behaviors of the material affected by shear-tension coupling stresses were analyzed． Ｒesults show that the fabric membranes could produce three kinds of appearance in terms of the orientation of the tear: line-shaped，crossshaped，and Z-shaped opening，which is depended on the crack orientation and stress states imposed on them，and the corresponding damage directions of yarns could belong to either warp or weft mode，instead of mixed modes． The stress states in warp and weft directions show the synergistic effect to offer the resistance to tear propagation， which affects the tearing strength obviously and leads to significant differences of tearing strength curves for different crack parameters in the stress space，resulting in the occurrence of stress strengthening at the stress ratio 1∶ 1． The stress state combined with reinforced film can obviously interfere with the tearing damage modes and crack position of membrane material，and the reinforcing effect varies depending on the stress ratios． In addition，during the tearing process，there is a coupling relationship between the tensile and shear stresses，and the tensile stress effect is the main one，while the shear stress has no obvious effect on the crack propagation and evolution． The research findings could provide references for the localized crack arresting of fabric membrane materials and safety assessment of membrane structures．

Parameterized Level Set Structural Topology Optimization Method by Introducing Level Set Band 



WEI Peng JIANG Zirun

2021, 49(10):  87-94,122.  doi:10.12141/j.issn.1000-565X.200776

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The traditional level set method overcomes the defect that it cannot automatically create holes by arranging a certain number of holes in the initial design，but the distribution form of holes causes a strong dependency on the initial design． The improved parameterized level set method could automatically create holes，but the initial design still affected the optimization results． The level set band method can combine the level set method with the variable density method and introduce a level set band region near the zero level set，and the material density in this region was interpolated by the level set function． The intermediate density materials were gradually removed through gradually reducing the width of the level set band in the iterative process，so that the structure finally converged to a 0-1 solution． Introducing level set band can improve the continuity of objective function and constraint function in topology change by combining variable density method，so as to reduce the influence of initial design on optimization results． The compliance minimization problem proves that this method can effectively reduce the initial design dependency of the optimization results and get a better objective function value． Furthermore，the influence of the reduction speed of the width of the level set band on the optimization results was studied，and this method was extended to the optimization problem with irregular design domain and reasonable optimization results were obtained

Points Selection in High-Dimensional Ｒandom-Variate Space for Simulating Stationary Stochastic Wind Field



XU Jun, LI Zhefan, Zhang Yang, et al

2021, 49(10):  95-103.  doi:10.12141/j.issn.1000-565X.210015

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To perform wind-resistant reliability analysis of structures，it is necessary to simulate the stationary stochastic fluctuating wind field． Simulating the stochastic fluctuating wind fields through spectral representation method ( SＲM) often involves thousands of random variables，leading to the“curse of dimensionality”． On this basis， this paper proposes a new method for points selection in high-dimensional random-variate space to ensure the accuracy and efficiency of SＲM． The new method mainly consists of three steps: the decomposition of high-dimensional random-variate space，the points selection in the orthogonal subspaces，and the random pairing to obtain the representative points and assigned probabilities in high-dimensional random-variate space． The proposed method is used to investigate the horizontal wind field acting along the height of a 30-story frame-shear wall structure． The results show that the proposed method is of high accuracy and efficiency for the simulation in the second-order statistical sense and a complete probability set can be constructed by only using a small number of representative sample processes． Besides，the proposed method can be further combined with the probability density evolution method to elaborately evaluate the probabilistic response of wind-induced vibration of structures．

Energy, Power & Electrical Engineering

Comprehensive Performance Analysis of Thermoelectric Coolers Based on Heat Pipe Heat Dissipation



MENG Fankai, CHEN Zhaojun, XU Chenxin, et al

2021, 49(10):  104-113.  doi:10.12141/j.issn.1000-565X.210079

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The heat pipe has the advantages of high thermal conductivity，lightness and miniaturization． This study proposed a finite-time thermodynamic model of thermoelectric coolers based on heat pipe heat dissipation and the specific calculation methods for the thermal resistance of the cold and hot junctions． In order to reflect the cooling capacity per unit area of the thermoelectric module，the refrigeration rate density analysis method and the converted area thermal resistance method were used to analyze the influence of key operating parameters and design parameters with numerical examples． In order to compare the refrigeration performance under different working conditions， the thermodynamic perfectibility was introduced and the refrigeration performance of the thermoelectric refrigerator was comprehensively analyzed． The paper also revealed the optimum current working range and temperature difference range of thermoelectric coolers and analyzed the influence of the refrigeration module filling factor，cooling temperature difference，heat pipe parameters ( evaporation section length and tube wall thickness) on the refrigeration density，coefficient of performance ( COP) and thermodynamic perfectibility of the refrigerator． Its performance was compared with that of air cooling and the results can provide theoretical guidance for the design and operation of refrigerators based on heat pipe heat dissipation．

Experimental Study on Enhanced Heat Transfer Characteristics of Plate Condenser with Liquid-Vapor Separation



YAO Yuan, CHEN Ying, CHEN Jianyong, et al

2021, 49(10):  114-122.  doi:10.12141/j.issn.1000-565X.200709

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A new type of plate condenser which can discharge condensate in the middle was designed． The drain port was set in the middle of the condenser，which can speed up the drainage，reduce the thickness of the condensate film attached to the plate，reduce the thermal resistance of the liquid film between the vapor and the plate，and increase the phase change heat transfer coefficient of the plate condenser． The performance of the liquid-vapor separation plate condenser ( LVSPC) was compared with that of the conventional plate condenser ( CPC) ． The experimental results of 10 different test conditions show that，under the same initial conditions，compared with the CPC， the condensation heat transfer coefficient of the LVSPC is increased by 8. 3% ～51. 6%，the total heat transfer coefficient is increased by 7. 6% ～ 38. 3% ，and the total pressure drop is reduced by 2. 6% ～ 11. 4% ． The experimental results proved that the LVSPC can achieve the purpose of enhancing heat transfer and reducing pressure drop． However，due to the decrease of working fluid flow in the second condensing area，the total heat transfer of the LVSPC is approximately equal to that of CPC，and there is no obvious increase．

Ｒesearch on the Characteristics of Conduction-Based Model of Partially Flattened Heat Pipe



GAN Yunhua, HUANG Zhaohui, LIANG Jialin, et al

2021, 49(10):  123-132.  doi:10.12141/j.issn.1000-565X.200746

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Accurate thermal conduction-based model is the key to the heat pipe-based thermal management simulation research． Based on the existing thermal conduction-based models，two conduction-based model for partially flattened heat pipes，the segmented anisotropic model and the layered segmentation model，were put forward in the present study． The results show that the segmented anisotropy model has higher accuracy in the case of low heat pipe operating temperature ( 28 ～ 38 ℃ ) ． The maximum relative error of heat pipe surface temperature is 5. 90% ． The layered and segmented model has higher accuracy in the heat pipe operating temperature range of 28 ～ 50 ℃ ． The maximum relative error of heat pipe surface temperature is 6. 51% ． And the effect of the effective thermal conductivity of the wick on the accuracy of the thermal conduction-based model was also investigated．

Simulation Optimization for Performance of Wave-Plate Demister Based on Re-entrainment



LIU Dingping ZHANG Yujun

2021, 49(10):  133-140,150.  doi:10.12141/j.issn.1000-565X.210048

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Aiming at the problem that the Euler-Lagrangian method can not predict the influence of the re-entrainment phenomenon on the demister performance in the numerical study，the study established a demister model based on re-entrainment phenomenon by taking wave-plate demister as the research object and coupling Euler Wall Film model on the basis of Euler-Lagrange method． Through the experimental data comparison，the model prediction curve is consistent with the experimental results． The effects of plate spacing and turning angle on the demisting performance were studied in different flow rates by the improved model． The results show that the liquid film separation at the corner is the main reason for the reduction of droplets removal efficiency at high flow rates; increasing the plate spacing and turning angle will aggravate the re-entrainment and decrease the critical velocity; below the critical velocity，the droplets removal efficiency decreases with the increase of the plate spacing，and increases with the increase of the turning angle; above the critical velocity，the droplets removal efficiency decreases with the increase of the plate spacing and the turning angle． The optimal value of the plate spacing and the turning angle is 20mm and 40°． In this situation，the droplets removal efficiency can be increased by 16. 38% ，and the pressure drop can be reduced by 9. 74% ． This result can be used to prevent the demister from re-entrainment phenomenon and improve the demister performance．

Optimization of Tunnel Multi-Loop Cable Based on Memetic Algorithm



NIU Haiqing, CHEN Zeming, YAN Tianyou, et al

2021, 49(10):  141-150.  doi:10.12141/j.issn.1000-565X.200775

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Tunnel laying is widely used in urban transmission network because of its large transmission current， easy management，maintenance and inspection． Optimizing the layout of multi-loop cables can make full use of its load capacity． In this paper，considering the electromagnetic field，thermal field，fluid field and the cross-bonding grounding mode，a simulation model of magnetic thermal flow and circuit coupling for a seven-circuit high voltage cables in a tunnel was established． The model was verified by infrared temperature measurement． Taking the induced voltage of metal sheath not exceeding the standard value as constraints and the minimizing the highest core temperature of cables as objective function，The phase sequence and position of the cable are optimized jointly based on memetic algorithm． After optimization，the maximum core temperature，sheath circulation loss，average circulation value and induced voltage of the cable decreased by 8. 18% ，21. 39% ，30. 62% and 8. 20% ，respectively． The result shows that the adoption of memetic algorithm，by properly increasing the horizontal distance of the tunnel cable loop and selecting the appropriate phase sequence layout，is conducive to weakening the mutual heat effect between the loop cables，reducing the circulating heat loss of the metal sheath，and improving the layout of the tunnel cable．