Table of Content

30 August 2022, Volume 28 Issue 4

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Urban Traffic and the Environment

A review of research on the dispersion of traffic-related air pollutants in street canyons with viaduct

HE Hongdi, LU Danni, ZHAO Hongmei

2022, 28(4):  569-581.  doi:10.12066/j.issn.1007-2861.2393

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With urbanization rapidly spreading worldwide, viaduct have appeared in many cities. Although such roads materially reduce traffic congestion, they also inevitably increase traffic pollution. Hence, we aim to investigate the dispersion of traffic-related air pollutants (TRAP) in street canyons with viaduct. We will first delineate the characteristics of traffic pollution and built environments in street canyons with viaduct. Next, we will analyze the spatial and temporal distribution of TRAP in street canyons with viaduct on spatial (horizontal and vertical) and temporal (macro and micro) scales. Finally, we will summarize the influence of factors including traffic, built environment, and micro-meteorological environment on TRAP dispersion in street canyons with viaduct. We expect that these investigations will enhance our knowledge of TRAP characteristics in street canyons with viaduct, which will be of significant relevance to mitigate TRAP in streets and urban areas.

Spatiotemporal distribution of traffic particulate matter in urban non-motorized lanes

LUO Binru, CAO Ruhui, CHEN Xin, HU Xisheng, WANG Zhanyong

2022, 28(4):  582-593.  doi:10.12066/j.issn.1007-2861.2351

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To capture the high temporal and spatial resolution characteristics of air pollution in urban non-motorized lanes, a micro-sensor-based cycling measurement platform was established to collect samples of submicron particulate matter (PM_1.0 ) and black carbon (BC) in non-motorized lanes alongside an expressway in Fuzhou, China. The temporal and spatial variations of these traffic particles were then visually analyzed, and explanations were provided. Results showed that the concentrations of PM_1.0 and BC were significantly greater along the community side than on the river side and were greater in the morning and evening peak periods than in the noon. In the morning, the BC concentration showed a stable accumulation, but PM_1.0 had a greater volatility; the opposite was the case in the evening. The drop of particulate matter concentration in non-motorized lanes was positively correlated with the distance to the main road and the abundance of vegetation around. The cold spots of particles were far from the main road and near high vegetation coverage, whereas hot spots were mostly distributed in traffic environments with construction and congestion. BC hotspots were synchronized with complex road conditions, but PM_1.0 hotspots were also closely related to the surrounding environment. Therefore, focusing on the key traffic pollutants is necessary in designing show-moving traffic while considering the topographical characteristics, spatial conditions, and surrounding environment. This can improve air quality in non-motorized lanes, thereby enhancing healthy commuting.

Simulation of traffic flow on non-uniform road sections with cellular automaton model

ZHOU Wenhai, LI Shujian, DONG Liyun

2022, 28(4):  594-607.  doi:10.12066/j.issn.1007-2861.2391

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Traffic flow characteristics on non-uniform road sections under traffic light controls were investigated using a refined velocity-dependent-randomization (VDR) model, considering three traffic light strategies: in-phase, anti-phase, and self-organizing. The effects of traffic light strategies on road traffic efficiency are analyzed under the periodic boundary. The simulation results show that for uniform road sections, the green wave phenomenon occurs at low densities using in-phase and anti-phase traffic light strategies. It was found that the traffic flow under the in-phase strategy is insensitive to variation in road length. In contrast, the traffic flow under the anti-phase strategy is sensitive to variation in road length, and the green wave phenomenon is suppressed, particularly when a short road section is significantly smaller than the average road length. Under the self-organizing traffic light strategy, fundamental diagrams are insensitive to variations in road length. Moreover, the traffic efficiency on the multi-section road is significantly improved, and the green wave phenomenon is replicated within a specific density range.

Research Articles

Bionic soft-limb robot interaction model for sandy soil

YANG Yang, QI Yuyan, WANG Shun, ZHAO Yongjian, ZHONG Songyi

2022, 28(4):  608-618.  doi:10.12066/j.issn.1007-2861.2338

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Most existing sand mobile robots have rigid structures. In performing scientific activities in complex working environments, they often slip, sink, overturn, and experience other problems because of their lack of good environmental adaptability. To solve this problem, a pneumatic soft-limb robot simulating mudskipper in a sand environment is designed. Based on ground mechanics theory and soft-limb robot modeling, by considering the constraints of the robot in a sand environment and through an analysis of the mechanical interaction characteristics between the robot's soft limb and the sand, a soft-limb robot-sand interaction mechanical model is established. The relationship between the input air pressure and robot motion characteristics is also constructed. Finally, the validity and accuracy of the model are verified by experiments. The experimental results demonstrate that the soft-limb robot designed in this study has the advantages of strong environmental adaptability, simple control, and high flexibility.

Methods for two-dimensional laminar and turbulent numerical simulations

XIONG Wei, ZHANG Weiguo, DING Jue, YANG Xiaoquan, WENG Peifen

2022, 28(4):  619-631.  doi:10.12066/j.issn.1007-2861.2242

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Third-order hybrid reconstructed methods based on the combination of least-squares recovery and reconstruction were developed for solving compressible laminar and turbulent flows to improve the calculation efficiency of the discontinuous Galerkin methods and overcome the deficiency of the least-squares reconstruction in satisfying the two-exact property. Navier-Stokes equations and the modified equation of the negative Spalart-Allmaras model were coupled as the equation system and solved using the developed third-order reconstructed discontinuous Galerkin methods. The lower-upper symmetric Gauss-Seidel preconditioning generalized minimal residual method based on the semianalytical exact Jacobian matrix and the fourth-order implicit Runge-Kutta method were implemented in temporal advance. Harten-Lax-van Leer contact and second Bassi-Rebay (BR2) schemes were adopted to calculate the inviscid and viscous terms, respectively. Third-order reconstruction was applied to solve the local and global lifting operators of the BR2 scheme, improving the calculation accuracy. The benchmarks were selected to verify the accuracy and calculation efficiency of the developed rDGP₁P₂ method. The research results indicate that the developed reconstructed rDGP₁P₂ methods have high computational accuracy and efficiency.

Numerical analysis of leachate recirculation based on a normal distribution probability model

HOU Juan, BAO Shifen, LIU Lei

2022, 28(4):  632-644.  doi:10.12066/j.issn.1007-2861.2282

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Leachate recirculation can enhance landfill stability and solve the issue of excess leachate. Predicting the migration characteristics of leachate during the recirculation process is important for determining a reasonable number of recharge wells, and their separation distances. In this study, considering the heterogeneity of municipal solid waste, a probability model was developed for hydraulic conductive changes in space. Using COMSOL Multiphysics^® software, the hydraulic conductivity and head pressure of a transverse-longitudinal homogeneous model were compared with those for a normal, single porosity distribution model. The influence of the transverse-longitudinal hydraulic conductive ratio ($a$), recirculation rate ($q$), and recirculation duration ($t$) on the moisture content and horizontal radius of the two models were investigated. The results showed that after 100 d, the moisture content and horizontal influence range increased from 0.609 to 0.68, and from 4.842 to 6.79 m, respectively, under homogeneous conditions. However, in the case of the normal distribution, the moisture content and horizontal influence range increased from 0.573 to 0.610, and from 4.097 to 4.04 m, respectively. The results indicated that the influence of $a$ on leachate moisture content and horizontal migration range under conditions of a normal distribution was significantly higher than that under conditions of a homogeneous distribution. At the same $q$ and $t$, the leachate recirculation ratio under normal distribution conditions reached saturated moisture content quickly. This was only maintained for a short time, before rapidly decreasing. In contrast, with increasing $q$ and $t$, the time required to reach saturation moisture content and peak value increased gradually.

Model test on embankment reinforcement under cyclic loads using FBG sensing technology

ZHANG Mengxi, CHU Jingchen, CHEN Qiang, WANG Dong

2022, 28(4):  645-655.  doi:10.12066/j.issn.1007-2861.2261

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Fiber Bragg grating (FBG) is a new type of monitoring and sensing element with advantages of high accuracy, strong anti-interference ability, and real-time monitoring. A USTX-2000 loading device was applied using FBG sensors to evaluate the mechanical properties of a geogrid-reinforced embankment and monitor the deformation characteristics of the reinforcement under cyclic loads. A series of model tests were performed under different conditions, such as different reinforced layers and reinforced spacings. The test results showed that the geogrid strain decreased from the centre direction of the loading plate to both sides in the horizontal direction and was non-linearly distributed in the longitudinal direction of the geogrid. The geogrid strain decreased with an increase in the embankment depth in the vertical direction for the same condition under long-term dynamic loads. The reinforcement could effectively reduce the settlement of the embankment and the normal deformation of the slope, and the earth pressure in the embankment significantly increased with the reinforcement. The study demonstrated the feasibility and superiority of FBG new sensing technology in embankment slope monitoring.

Application of non-destructive testing technique for detecting surface detachment in cultural heritage buildings

HUANG Jizhong, ZHANG Yunmeng, ZHANG Yue, ZHAO Peng

2022, 28(4):  656-667.  doi:10.12066/j.issn.1007-2861.2275

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Surface detachment is one of the main defects of the Shanxi Academy walls, and it can lead to the peeling of cement mortar plaster and the weathering of interior masonry structures. Thus, it is necessary to evaluate its severity before conducting detailed conservation and restoration work. In this study, manual percussion was first performed for the preliminary detection of surface detachment defect. Next, two non-destructive testing techniques, i.e. phased-array ultrasonic imaging and infrared thermal imaging, were combined to measure the scope and area of distribution in detail. The results showed that (1) all methods could reflect the surface detachment distribution to different degrees, (2) data obtained using different non-destructive techniques were comparable to some minor errors correlated with defect types and environmental factors, (3) the detachment of cement mortar plaster from the wall surface was generally severe, and its defect rating could be divided into four specific grades. The research results are useful for detecting and evaluating surface detachment in cultural heritage buildings.

Anisotropy of tensile strength of compacted Gaomiaozi bentonite

QIN Zhenyu, SUN De'an, ZHOU Xiangyun, LIU Yuemiao

2022, 28(4):  668-677.  doi:10.12066/j.issn.1007-2861.2288

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The buffer layer in a deep geological repository used in the disposal of high-level radioactive waste (HLW) is composed of bentonite blocks that are compressed with bentonite powders, and their strength may show anisotropic characteristics. In this study, the tensile strength of compacted Gaomiaozi (Gaomiaozi, China) bentonite under different conditions was measured by direct tensile tests, and the effects of dry density and moisture content on the anisotropy of tensile strength were analyzed and discussed. The results showed that the tensile strength initially increased and then decreased with increasing water content, during which a peak value was observed. The tensile strength also increased with increasing dry density. When the direction of the tensile force was perpendicular to that of the compaction force, the tensile strength was greater than when the direction of the tensile force was parallel to that of the compaction force. In addition, under the same water content, the degree of anisotropy of tensile strength increased with increasing dry density. This could be explained by the fact that montmorillonite laminae tend to be arranged in a direction perpendicular to that of the compaction force, leading to significant anisotropy. These results can provide a reference for assessing the tensile strength characteristics of bentonite blocks in transportation and hoisting processes in the disposal of HLW in China.

Flexural performance of hybrid steel and FRP reinforced concrete beams

ZHANG Zhimei, WEI Jiuyi

2022, 28(4):  678-688.  doi:10.12066/j.issn.1007-2861.2246

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To conduct an experimental study of the flexural theory of hybrid steel and fibre reinforced plastic (FRP) reinforced beams, the finite element software ABAQUS was used to model and nonlinearly analyse existing hybrid FRP/steel reinforced test beams. The effects of FRP bar type, concrete strength, and the equivalent reinforcement ratio on the bending performance of hybrid FRP/steel reinforced beams were then studied. Finite element results revealed that the stress expression of FRP bars could be obtained and a formula for the bearing capacity of hybrid FRP reinforced beams could be derived. Finally, experimental data were used to verify the correctness of the formula. Results showed that the equivalent reinforcement ratio had the most significant effect on the bearing capacity and deformation performance of hybrid FRP bars beams, followed by FRP bar type. The strength of concrete had a certain effect on the bearing capacity but had little effect on stiffness. Based on the stress expression of FRP bars in this study, the flexural capacity of hybrid FRP reinforced beams were accurately calculated.

Decision method for preventive maintenance of asphalt pavements considering multiple damage characteristics

LI Li, GUAN Tingting

2022, 28(4):  689-701.  doi:10.12066/j.issn.1007-2861.2271

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Because of the diverse compositions of asphalt pavement damage, multiple cases of damage that are inspected using the same pavement condition index (PCI) may yield different damage combinations. When multiple types of damage coexist but the degree of damage is similar, obtaining targeted maintenance measures with PCI and determining the predominant damage (i.e., most severe road damage with the maximum deduction value) are challenging. Therefore, this study considers PCI analysis and an existing preventive maintenance decision-making method to clarify those sections in which the predominant damage was not well-targeted during inspection and proposes a supplementary approach to make more appropriate conservation decisions. Based on detection and maintenance data of urban roads in Shanghai from over the past five years, a sequential clustering method is used to classify road sections according to their PCI levels. The composition of and difference in pavement damage at different levels are analyzed. Then, for those sections with multiple cases of damage and no significant damage differences, road sections that historically reflect proper preventive maintenance are then selected based on whether effective preventive maintenance can be implemented. Finally, two back propagation (BP) neural network models for preventive maintenance decisions are established and compared based on the effective maintenance road sections. The main differences between the two models are the compositions of pavement damage. The results showed that when the PCI levels were high (84.4~93.0 points), the degrees of damage were very similar and the predominant damage was not represented. Of the two BP neural network models, Model 2,which considered multiple damage components, showed a higher decision accuracy. Specifically, its decision accuracy with the test set reached 86.20%. This was significantly better than that of Model 1 (58.50%), which considered only the predominant damage. Combining the BP neural network and traditional decision tree method can help to optimize decision-making processes related to asphalt pavement and improve the selection of maintenance measures.

Application of a meshless method based on the S-R decomposition theorem in functionally graded plates

SONG Yanqi, SHI Bokang, LI Xiangshang

2022, 28(4):  702-714.  doi:10.12066/j.issn.1007-2861.2266

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To study the nonlinear deformation problem of functionally graded plates, this study uses the S-R decomposition theorem combined with the updated comoving coordinate system method and meshless Galerkin method to derive a discrete equation for solving three-dimensional geometric nonlinear problems. The meshless method is programmed by MATLAB. The nonlinear bending problem of the functionally graded plate is first solved, and the effects of the volume fraction index and width-thickness ration on the bending of plates are studied. Results are compared with existing results, and the rationality of solving the large deformation problem of functionally graded plates using the three-dimensional S-R meshless method is verified.