Abstract:Reinforced concrete(RC) bridge piers and columns located in strong saline soil and salt lake area in western China are suffering from corrosion attack, so a new type of composite column is proposed,which is herein referred to as steel reinforced polyethylene plastic pipe(SRPE) confined reinforced concrete column. Eight SRPE confined reinforced concrete columns and four unconfined control columns subjected to eccentric load were tested to study their mechanical properties.The failure pattern and load-axial displacement curves of specimens were obtained. The influence of design parameters such as pressure level of SRPE pipe, eccentricity and slenderness ratio on the mechanical properties of specimens was analyzed. The calculation formula of ultimate bearing capacity of SRPE pipe confined reinforced concrete columns subjected to eccentric load is also proposed for the actual application reference. The experimental results show that the ultimate bearing capacity and ductility of the RC columns under eccentric load are significantly improved for the confinement by SRPE pipe; The bearing capacity increases with the increase of pressure level of SRPE pipe, but the ductility is improved little. The bearing capacity decreases with the increase of eccentricity and slenderness ratio. The ductility of specimens decreases with the increase of slenderness ratio; The lateral peak deflection in the middle height of column confined by SRPE pipe is much larger than that of the control specimens, which increases with the increase of eccentricity and slenderness ratio; The lateral deflection corresponding to ultimate load is close to sine half-wave curve.

Abstract:Clarifying the structural composition and mineral composition of arsenic sandstone is the basis for revealing the mechanism of soil erosion in the arsenic sandstone area and developing methods for controlling soil erosion in the arsenic sandstone area. This article analyzes the structural composition and mineral composition of arsenic sandstone in the Ordos area of Inner Mongolia by means of material analysis methods such as quantitative XRD and optical microscope analysis. The results show that：the structure of arsenic sandstone is composed of granular framework materials and clay-like cementing materials, and its cementing method is contact cementation; arsenic sandstone granular framework materials are mainly composed of quartz, calcium carbonate and feldspar, etc. Clay cementing materials are montmorillonite, chlorite, kaolinite and iron oxide, etc.; arsenic granular framework crystals (quartz and feldspar, etc.) rely on the cementing force of hydrophilic weak cementing clay materials. The solid mixture formed by friction between crystals, mechanical bite force and particle support is a ternary particle support permeable structure.

Abstract:In view of the characteristics that the settlement of pile raft foundation is in the linear elastic stage under design load, based on the vertical stiffness of single pile obtained from the static load test curve, relevant theories and empirical formulas, the calculation method of the overall vertical stiffness of pile raft foundation is established. On this basis, the practical calculation method of the average settlement of pile raft foundation under working load is proposed. Through the comprehensive analysis of the field measurement and calculation results of 8 engineering cases in 4 categories of high-rise building foundation in soft soil area and loess area, rock-socketed pile foundation and large traffic engineering, the validity of the proposed method is examined. The calculated settlement value is basically 0.8~1.5 times of the measured settlement, which verifies the reliability of the proposed settlement calculation method in practical engineering. In addition, the calculation method can provide reference for the preliminary design of settlement calculation of actual pile raft foundations.

Abstract:In order to analyze the influence of rainfall seepage on the stability of cofferdam, focusing on an navigation-powered junction project in Jiangxi Province, based on the unsaturated seepage theory, this study simulates and explores condition of the seepage and the stability of cofferdam under different rainfall conditions by using the Geo-studio numerical simulation software, and the influence of different rain patterns on the stability of cofferdam is obtained. The results show that the influence of rainfall on the cofferdam has a hysteretic quality. The influence of different rainfall types on the strength hysteresis of weir body is as follows: rear peak type, uniform type, middle peak type and front peak type, and the hysteresis are affected by rainfall intensity. The rainfall infiltration is affected by the time of the peak rainfall, and the safety factor of the cofferdam decreases sharply with the peak rainfall intensity. Compared with the initial stability conditions, the front peak type rainfall has the least impact on the stability of the cofferdam, and the rear peak rainfall has the greatest impact on the stability of the cofferdam. Under the influence of early rainfall, the permeability coefficient of soil in the slope would be at a high level. Thus, the ability of cofferdam to resist sudden heavy rainfall weakens with the increase of permeability coefficient.

Abstract:Taking residual interception height and falling rock buffer distance as the key technical indexes to evaluate the deformation performance of passive flexible protective structures, a new passive flexible rockfall barrier for intercepting and buffering the impact energy of falling rocks is proposed. Based on ANSYS/LS-DYNA, general finite element analysis and calculation software, three types of ring net models are established, and the energy consumption and deformation performance of ring net are analyzed from three aspects: maximum energy consumption, residual interception height and falling rock buffer distance. The results show that the ring net with vertical support can effectively reduce the buffer distance of falling rocks and increase the residual interception height of the ring net, but the maximum energy consumption of the ring net has decreased to some extent. Compared with unsupported and double-supported ring nets, single-supported ring nets have the following advantages: the maximum energy consumption ratio is relatively high, it has the function of rapidly attenuating the impact energy of falling rocks under the action of instantaneous impact load, the buffer distance of falling rocks is small, and the protective performance is basically not affected by the impact position of falling rocks. Therefore, the single-supported ring net should be preferentially used in rockfall protection projects such as the slope with the rockfall barrier laying position close to the road, the horizontal laying of rockfall barrier in the steep slope and the secondary protection.

Abstract:There are both important practical value and scientific research significance of monitoring the global terrestrial water storage change(TWSC)by satellite gravity technology. Based on the GRACE time-varying gravitational field model, this paper studies the TWSC of global typical river basins from 2002 to 2020, and discusses the influence of climate and human factors on the regional TWSC. The research results show that the TWSC in similar geographic regions have similar cycles and amplitudes, while the TWSC of adjacent watersheds located in the northern and southern hemispheres present opposite periodic signals. The TWSC in the Murray -Darling Basin is affected by precipitation and evaporation, while the Indus-Ganga River Basin has been declining due to excessive groundwater extraction. The correlation between GARCE and GLDAS acquired water storage changes in the Amazon basin reached 0.86. At the same time, it was found that GRACE has a unique advantage in detecting regional drought events.

Abstract:During the COVID-19 epidemic prevention and control period, the safety and limitations of the online vehicle operation model lead to difficulties in meeting the safe travel needs of residents in areas with recurring epidemics. To realize the requirement of synergistic development of the quality of net-hailing services and environmental benefits, the current problem of electric vehicle ridesharing is studied about the characteristics of the COVID-19 prevention and control. Considering the heterogeneity of passengers′ own infection risk, the characteristics of virus transmission, and vehicle charging, different riding strategies are adopted to identify the types of passengers' infection risk. From the perspective of epidemic prevention and control, vehicle route constraints, vehicle disinfection constraints, and vehicle charging constraints are established, and the total profit of the driver, consisting of driver compensation, government subsidies, and vehicle operating costs, is taken as the optimization objective to build a ridesharing optimization model with epidemic prevention and control characteristics. A small-scale example is designed and solved using a Lingo18.0 solver. The analysis of the example proves the validity of the optimization model. Meanwhile, it can provide reference for the network car operation model in the real environment.

Abstract:In order to quantitatively analyze the influence of highway dynamic congestion traffic information caused by traffic accidents and traveler heterogeneity on travel choice behavior, a large-scale SP/RP survey data covering 2 500 highway users in west Japan is used for this study. Latent class analysis(LCA) is adopted for extracting different preference features on traffic information, followed by a multilevel model which sets the results of LCA as explanatory variable. The research results show that：Through the potential category analysis of the data, travelers can be divided into three types of heterogeneous groups, namely, dynamic traffic information high dependence group, dynamic traffic information low dependence group and dynamic traffic information independent group, accounting for 38.8%, 36.1% and 25.1%. And there are significant differences in gender, age and occupation among these groups. The travel behaviors of travelers in different traffic information dependence groups are significantly different under dynamic traffic information. The travel prediction model considering data hierarchical structure is more accurate than the prediction model without data hierarchical structure.

Abstract:Transportation industry is one of the main sources of pollution emission at present. To reduce environmental pollution in freight industry, it has become an important measure to guide freight flow from road transportation to rail transportation in view of the advantages of railway transportation in environmental protection. Therefore, this paper studies the choice of freight transport mode considering environmental cost under the competition between road transportation and rail transportation, where the environmental influence on share rate is quantified. The unit environmental cost is calculated by various pollutants emissions and cost factors and the unit time value of goods is calibrated through the Logit model. Aiming at the minimization of the total social cost composed of transportation cost, time cost and environmental cost, a choice model for freight transportation is then formulated. Taking the freight data of road network and railway network in Shandong as an example, the transportation mode and route selection schemes are discussed under different values of environmental cost coefficient. It is found that considering the environmental cost, the freight market share of railway transportation will increase, and transportation cost and pollutant emission will decrease correspondingly.

Abstract:In the current research of traffic flow prediction, the time step mainly depends on the artificial selection which is easy to be disturbed, and there is a lack of methods to select the time step from the theoretical aspect. In order to adaptively select the time step, three typical algorithms of least squares support vector machine (LSSVM), random forest(RF) and long short-term memory(LSTM) in machine learning are used to predict traffic flow with multiple time step based on the autocorrelation analysis of historical time series for traffic flow and explore the feasibility of selecting the best time step by the value of autocorrelation coefficient. The experimental results show that when the autocorrelation coefficient of the time step is 0.83 ~0.91, LSSVM can obtain better prediction accuracy while the autocorrelation coefficient is 0.47~0.51, LSTM can have better prediction accuracy. However, due to the low autocorrelation degree of the time step corresponding to the lowest error of traffic flow prediction, the autocorrelation analysis method may not be applicable to RF.

Abstract:Due to physical fitness and travel time different from commuters, the elderly usually travel by bus or on foot. Using the confirmatory factor analysis and binary Logit model, studying the influences of the elderly′s personal statistical attributes and psychological factors on the travel behavior, such as their attitude towards daily travel, their feelings about taking buses at peak times, and their travel intention to avoid rush hours before and after the preferential policy of suspending public transport at morning peak hours, the latent classification model was used to classify and analyze the elderly groups. The results show that all kinds of psychological factors have significant influence on elderly′s short-distance trips. The bus preferential policy and the group′s support for off-peak travel have a significant impact on the elderly′s choice. The latent classification model shows that the survey objects have necessary travel purpose, and the proportion of elderly groups who are sensitive to bus travel and off-peak travel is low.

Abstract:The semi-solid billet of light -high entropy alloy AlMgLi_0.5Zn_0.5Cu_0.2 was prepared by isothermal heat treatment and the effects of holding temperature and holding time on the microstructure evolution of the lighthigh entropy alloy AlMgLi_0.5Zn_0.5Cu_0.2 were investigated. The results show that with the increase of holding temperature, the average grain size of semi-solid light-weight high entropy alloy AlMgLi_0.5Zn_0.5Cu_0.2 decreases first and then increases, while the roundness of the grains increases first and then decreases. With the prolongation of holding time, the average grain size and roundness of the light-weight high entropy alloy AlMgLi_0.5Zn_0.5Cu_0.2 increase. The best semi-solid microstructure of the light-weight high entropy alloy AlMgLi_0.5Zn_0.5Cu_0.2 was obtained at 460 ℃ for 60 min, whose average grain size is about 41 μm, roundness is 0.82, and coarsest coefficient K=20.95 μm³ /s.

Abstract:Aiming at the problems of electromagnetic interference and shortened service life of input source caused by inherent intermittent ripple current on the input side of switching converter, a passive ripple compensation circuit for flyback converters is proposed. The circuit is composed of transformer, diode and electrolytic capacitor. Under the designed ripple suppression condition, it works in a similar flyback state and generates compensation current, which effectively suppresses the inherent intermittent ripple current on the input side. On the basis of explaining its working principle, the parameter calculation methods of system gain, suppression conditions of ripple current and related variables are deduced by using the formula. An experimental prototype with 60~80 V input, 30 V rated output voltage and 65 W rated power is built. The experimental results verify the feasibility of the proposed passive ripple compensation circuit and the correctness of theoretical analysis.

Abstract:Traditional grinding robots are fixed on the base or installed on the guide rail, which has low mobility and limited working area. Aiming at the high mobility of indoor wall grinding robot, a four-wheel grinding robot mobile platform based on Mcnamu wheel is proposed. Firstly, the structure of a single Mcnamu wheel is analyzed to understand its motion mode. Then, the forward and inverse kinematics of the Mcnamu four-wheel mobile platform is analyzed, and the inverse kinematics formula of the four-wheel mobile platform is obtained. In addition, the inverse kinematics model is established in Simulink. Finally, the forward kinematics is verified in Vrep. The results show that the analysis of the Mcnamu wheel mobile platform is correct, and the Mcnamu wheel mobile platform can fully improve the mobility of the grinding robot and lay a good foundation for the automatic grinding of the robot.

Abstract:Cluster analysis is an important technique for data mining. In the 5G era, massive data has high dimensions and large data sets. The K-means algorithm is susceptible to outliers, and the k value and the selection of initial clustering centers affect the stability and accuracy of the clustering result. It even causes the clustering to fall into the local optimum, so the improvement of the K-means algorithm has attracted the attention of many researchers. This article mainly summarizes the current research status of K-means clustering. Firstly, it introduces the principle of K-means algorithm. Secondly, according to the selection of the initial clustering center point, the determination of the K value, and the outliers, the existing improved algorithms are classified and summarized based on density and distance, and the advantages and disadvantages of each improved algorithm are analyzed. Finally, the K-means algorithm is analyzed and prospects for possible future research directions and trends are discussed.