交通运输工程学报

Interlaminar interface shear slip characteristics of composite pavement

CAO Ming-ming, LU Yang, HUANG Wan-qing, LI Yi-ming, WU Zhi-yong

Abstract: Based on the composite pavement test section of Nandaliang Expressway, the exposed bone ratios and texture depths of different roughened interfaces were tested, and 45°shear tests were carried out with core samples drilling in the field test section. Combined with 45°shear test results and the mechanical properties in the interlaminar shear process, the interlaminar shear and deformation curve was divided into four stages: elastic stage, failure stage, shear strength reduction phase, and residual phase. The interlaminar shear and deformation behavior was evaluated by using the texture depth, peak shear strength, relative interlaminar slip displacement corresponding to the peak shear strength, and residual shear strength. The effects of interface roughness mode, types and amounts of waterproof cohesive materials, temperature, and loading rates on the interlaminar shear and deformation characteristics of composite pavement wereanalyzed. Test result shows that the texture depth of the chiseling interface (1.17 mm) is greater than that of the sand-blasting interface (0.37 mm). Combined with the interlaminar mechanical property differences of different roughened interfaces in the shearing process, the composite specimen formed at the chiseling interface has better shear resistance performance than that formed at the sand-blasting interface. The relative interlaminar sliding displacement corresponding to the peak shear strength of the chiseling interface (0.19-0.79 mm) is larger than that of the sandblasting interface (0.16-0.33 mm) with the same waterproof cohesive materials. Moreover, the effect of waterproof cohesive materials on the peak shear strength and residual shear strength is greater than that of the interlaminar relative slip displacement corresponding to the peak shear strength. As a whole, the effect of temperature on interlaminar shear and deformation characteristics is remarkable, and the peak shear strength at 5℃is 7.0-10.0 times of the value at40℃. The test conditions have a great influence on the interlaminar shear strength, and the interlaminar peak shear strength measured at 50 mm·min^-1 loading rate is 1.9-3.5 times of the value measured at 5 mm·min^-1 loading rate. Thus, the chiseling roughened method is more helpful to improve the interlaminar shear strength of the composite pavement, and the multiindex should be used to evaluate the interlaminar shear and deformation characteristics of the composite pavement.More>

2018, 18(4): 1-11. doi: 10.19818/j.cnki.1671-1637.2018.04.001

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Environmental impact of asphalt pavement construction based on discrete event simulation

YU Bin, SUN Yue

Abstract: To lower energy consumption, greenhouse gases (GHGs) production, and pollutant emission in the asphalt pavement construction process, a calculation model of the environmental impact of asphalt pavement construction, based on discrete event simulation (DES), was established. The construction steps were abstracted by using the probability distribution function and a logical statement. The discrete event model of asphalt pavement construction was built by using agraphical DES software. The Nonroad calculation model was implemented to perform the dynamic calculation of the amount of different GHGs and pollutants, and the simulation emission results of different construction conditions were compared. Analysis result shows that the transportation of asphalt mixture to the paving site by trucks is the main energy consumption source in the asphalt pavement construction process, accounting for 44% of the total energy consumption. The energy consumption of the paving and truck-returning processes respectively account for 32%and 12% of the total energy consumption. The primary construction steps that lead to the emission of GHGs and pollutants are the transportation and paving processes, accounting for more than 50% of the total emissions. NO_x and CO₂ are the main emissions in the paving and compaction processes, and the transportation process, respectively. To optimize construction technology, the application of continuous paving construction can remarkably reduce the emissions of NO_x by approximately 15%. Considering construction equipment, an appropriate increase in the capacity of paving equipment can reduce the emissions of CO₂ and HC by approximately 25%and 17%, respectively. This shows that the developed environmental impact calculation model of asphalt pavement construction based on DES can quantify the energy consumptions and emissions of GHGs and air pollutants of asphalt pavement construction, and optimize the construction scheme.More>

2018, 18(4): 12-21. doi: 10.19818/j.cnki.1671-1637.2018.04.002

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Effect of replacing-filling and dewatering-draining measures on frozen characteristics of weak subgrade in cold valley region

WU Li-bo, NIU Fu-jun, LIN Zhan-ju, QI Wei, FENG Wen-jie

Abstract: Based on the Tanchang-Diebu Secondary Highway in South Gansu, two typical soft soilsubgrade test sections in the cold valley region were selected, the subgrade's temperature, moisture content, deformation and the groundwater level were monitored, and the influences of the muck gravel soil's replacing-filling depth and dewatering-draining measure on the frozen characteristics of the subgrade were analyzed. Analysis result indicates that in the two monitored frozen periods, the maximum frozen depths at the test section K18+180 with 2.0 m-replacingfilling thickness is 0.12-0.16 m deeper than those at the test section K18+330 with 1.0 mreplacing-filling thickness, so the bigger the replacing-filling thickness is, the bigger the frozen depth is. For the test section K18+330, the initial groundwater level is 3.4 m. When the surface drains were only adopted, the groundwater level in the frozen periods is about 3.4 m, and the smallest distance to the frozen surface is 1.7 m, which shows that the surface drains scarcely affect the groundwater level in the frozen periods. For the test section K18+180, the initial groundwater level is 1.3 m. When the seepage ditches are adopted, the groundwater level in the frozen periods is about 2.0 mand reduces by 0.7 m, and the smallest distance to the frozen surface is 0.2 m, therefore, the seepage ditches can reduce the groundwater level and prevent the frost heave of the subgrade. The maximum frost heaves of the center of the test section K18+330 are 3.4 and 4.2 mm in the frozen periods, respectively, and the values of the test section K18+180 at the relevant position are 10.7 and 14.0 mm that are more than three times as much as the formers, respectively, therefore, the bigger the replacing-filling thickness is, the smaller the frost heave of the subgrade is. The maximum frost heaves of the test sections K18+180 and K18+330 are 4.2 and 1.4 mm, respectively, the maximum settlements are 1.5 and 1.8 mm, respectively, and they are much less than the admissible frost heave of 50 mm and the admissible settlement of weak subgrade of 500 mm for the secondary road in the Specifications for Design of Highway Subgrades (JTG D30—2015), therefore, the stability of the subgrade at the test section is good, and the replacing-filling and dewatering-draining measures can effectively control the frost heave of the subgrade.More>

2018, 18(4): 22-33. doi: 10.19818/j.cnki.1671-1637.2018.04.003

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Effect of colluvial soil slope fracture’s anisotropy characteristics on rainwater infiltration process

ZENG Ling, LIU Jie, SHI Zhen-ning

Abstract: The SEEP/W module of the finite element software Geo-Slope was used to analyze the effects of fracture depth, permeability coefficient ratio, fracture angle and fracture number on the rainwater infiltration process. The effect of fracture seepage anisotropy on slope stability was studied along with the unsaturated seepage theory. Analysis result shows that when the rainfall duration is 1 and 7 d, respectively, the maximum pore water pressure in a 1 m fissure is 9.69 and 9.70 kPa, respectively, and the rainwater infiltration depth along the bottom of the fracture is 0.5 and 1.5 m, respectively. The pore water pressure in a fracture increases rapidly with the rainfall until it changes from a negative pressure to a positive pressure. The greater the fracture depth, the greater the pore water pressure in the fracture, and the greater the infiltration depth is when rainfall stops. The size of the saturated area is positively correlated with the fracture depth. When the permeability coefficient ratio is 1, the maximum permeability coefficient in the fracture range is 1.51×10^-7 m・s^-1. At this moment, the permeability coefficient along the fracture direction is less than the rainfall intensity, and the infiltration process is controlled by the soil permeability coefficient. When the fracture permeability coefficient along the fracture direction is larger than the rainfall intensity, the infiltration process is controlled by the rainfall intensity. The smaller the fracture angle, the greater the maximum pore water pressure in the fracture depth range, the greater the depth of the positive pore water pressure, and the smaller the range of surface saturation zone is. When there is no fracture, the slope still maintains a negative pressure state after rainfall, and there is no saturation zone. When there is a fracture, the rainwater infiltrates along the fracture and forms a saturated positive pressure zone inside the slope. The areas of the saturated zones formed by 1-5 fractures are16.4, 34.7, 60.9, 75.6 and 110.7 m², respectively. A power relation exists between the saturation area and fracture number. The influence range and degree of rainwater on the seepage field increase with the increase of fracture number. The concentration distribution of long fractures directly forms a large connected saturated zone and raises groundwater. 1 tab, 14 figs, 33 refs.More>

2018, 18(4): 34-43.

Instability characterization coefficient of key block and evaluation of rock slope stability

WANG Fei-li, WANG Shu-hong, GAO Hong-yan, XIU Zhan-guo

Abstract: A key block determination method was established to realize the quasi-quantitative evaluation of rock slope stability. The concept of instability characterization coefficient of key block was defined by comprehensively considering the geometric characteristics and mechanical properties of key blocks. The program GeoSMA-3 Ddeveloped by the authors'team was used to develop the search module for key blocks based on the instability characterization coefficient. The entire instability process of key blocks, including the search for blocks, judgment of moveable blocks, determination of key blocks, slide and instability of blocks was visualized. Using the instability characterization coefficient of key blocks, the weight of each key block was calculated through the introduction of the analytic hierarchy process. The characterization safety factor ofrock slope stability was determined through the combination of the safety factors and weights of key blocks. Key block information was used to characterize rock slope stability, and a method for evaluating the rock slope stability was proposed by considering rock structural planes and key blocks. Taking the Jianchang Rock Slope in Liaoning Province as an example, the determination and visualization of key blocks were carried out by using the proposed method to examine the rock slope stability. The results were compared with those of the numerical manifold method (NMM) and the on-site monitoring data to verify the applicability and feasibility of the proposed method. Research result shows that there are six controlling key blocks for the rock slope stability. The characterization safety factor of rock slope stability calculated through the proposed method is0.566 9 (an unstable rock slope). The relative difference between the calculated results and those from on-site monitoring is 7.066%. In the simulation results from NNM, the slippage of the most unfavorable key block determined by the safety factor method does not cause the instability of the rock slope, while the most unfavorable key block determined by the proposed method contributes to the overall instability of the rock slope. Therefore, the evaluation of rock slope stability by simultaneously considering the volumes and safety factors of key blocks is more reasonable. The rock slope stability characterized by key block information agrees well with the engineering practice.More>

2018, 18(4): 44-52. doi: 10.19818/j.cnki.1671-1637.2018.04.005

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Dynamic response of rock-socketed pile foundation for extra-large bridge under earthquake action

LIU Chuang, FENG Zhong-ju, ZHANG Fu-qiang, WU Jing-wu, DONG Yun-xiu, YIN Hong-hua, YUAN Feng-bin, LI Xiao-xiong, WEN Jun-qiang

Abstract: Combined with the Puqian Bridge project and based on the interaction mechanism of artificial mass model and pile-soil inertia, the vibration response of free field under seismic actionwas simulated by the vibration table model test and the laminated shear model box. The response characteristics of acceleration, relative displacement and bending moment, as well as the damage of large diameter bridge rock-socketed piles under the ground vibration intensity of 0.15 g-0.60 g (gis gravity acceleration) were analyzed. Research result shows that the acceleration peak value of pile foundation increases from the pile bottom to the pile top. The acceleration amplification coefficient decreases with the increase of ground vibration intensity. When the ground vibration intensity is 0.55 g, the acceleration amplification coefficient of pile top tends to a stable value of1.34. The acceleration time-history response frequency of pile top is lower than that of pile bottom. The upper cover layer has obvious effect on seismic wave amplification and filtering effect. With the increase of the ground vibration intensity, the relative displacement peak value of pile top approximately increases linearly. Under the ground vibration intensity of 0.15 g-0.60 g, the peak value variation range of relative displacement of pile top is 1.97-6.73 mm. The bending moment of pile foundation changes in a"3"shape along the length of the pile, and it reaches the peak value at the upper boundary between soft and hard soil layer and near the bedrock surface. The peak value of bending moment increases with the ground vibration intensity. When the ground vibration intensity is 0.50 g, the peak value of bending moment reaches 190.9 kN·m. The bending moment exceeds the bending capacity of the pile. With the increase of ground vibration intensity, the fundamental frequency of pile foundation decreases as a whole. Under the ground vibration intensity of 0.50 g, the frequency of pile foundation decreases by 50.1%, compring with that under the action of 0.35 gground vibration intensity, and the pile foundation is damaged. Cracks easily occur at near the junction of pile top and cap, the soft-hard soil interface and bedrock surface under seismic action, and the seismic design of the bridge pile foundation should be considered.More>

2018, 18(4): 53-62. doi: 10.19818/j.cnki.1671-1637.2018.04.006

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Settlement control standard of existing metro line undercrossed by new metro tunnel in loess area

LAI Hong-peng, ZHAO Xin, KANG Zuo

Abstract: Based on the actual condition of metro line 5 undercrossing metro line 2 at close range in Xi'an, China, the safety judgment criteria, normal-use requirement and service status of existing metro line undercrossed by new metro tunnel in the loess area were analyzed, the bending moment, radius of curvature, allowable stress, allowable shear strain and track deformation were taken as the control factors of the settlement of existing metro line, the mechanical model of existing metro line was constructed, the settlement computation formula was deduced, and thesettlement control standard was determined. Analysis result shows the corresponding allowable settlements of the existing metro line are 22.40, 20.85, 48.14, 20.23 and 21.06 mm under the control factors of bending moment, radius of curvature, allowable stress, allowable shear strain and track deformation, respectively, and the empirical allowable settlements of other regional undercrossing projects and the standard allowable settlements of relevant domestic regulations are20 mm. The most unfavorable control factor is the track deformation, and the corresponding allowable settlement is close to the existing relevant allowable settlements, so, it is suggested that the settlement control standard is 20 mm for the existing metro line undercrossed by new metro tunnel in the loess area. The level-to-level administration of settlement control standard of existing metro line is performed, the 100%, 80%and 60%of the settlement control standard are taken as the control value (20 mm), alarm value (16 mm) and warning value (12 mm), respectively, and an early warning system of undercrossed existing metro line is proposed. The safety level of existing metro line undercrossed by new metro line is evaluated, and the corresponding treatment measures are given. When the safety level is ClassⅠand the corresponding settlement is no more than 12 mm, the new metro tunnel should be normally constructed and monitored. When the safety level is Class Ⅱ and the corresponding settlement is (12, 16]mm, strengthening monitoring and real-time feedback should be carried out. When the safety level is Class Ⅲ and the corresponding settlement is (16, 20]mm, the construction should be stopped and the emergency plan should be started. The safety level is Class Ⅳ and the corresponding settlement is more than20 mm, the damage level has reached and the construction is never allowed.More>

2018, 18(4): 63-71. doi: 10.19818/j.cnki.1671-1637.2018.04.007

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Seismic response of metro tunnel oriented parallel to ground fissures

LIU Ni-na, ZHU Yong-feng, LI Jun, FENG Xiao-yang, MA Yu-jie, BULUT Rifat

Abstract: Under the different magnitudes' synthetic earthquake waves, the acceleration, displacement and internal force were studied by the numerical simulation method for the metro tunnel oriented parallel to ground fissures in short distance, and the influence area of the ground fissures, dynamic earth pressure variation law of the surrounding rock and contacting dynamicearth pressure variation law between the tunnel and surrounding rock were calculated. Analysis result shows that there is an additional magnification area of the acceleration response within a horizontal distance of 25-50 mfrom the ground surface to the tunnel. When the magnitude of the synthetic earthquake wave is smaller (the 50-year exceedance probability is 63%), the relatively horizontal displacements at the top and bottom of the tunnel are smaller (about 0.39 mm), but increase with the increasing earthquake magnitude. The largest displacement is 1.53 mm when the 50-year exceedance probability is 2%. Under the earthquake, the axial forces at the right and left shoulders and foot are larger, and the largest force is 1 926 kN at the right arch foot. The moments and shear forces are larger at the right and left arch waists, and the largest moment and shear force are at the right arch waist and 78.54 kN·m and 1 830 kN, respectively. The internal force increases with the increasing earthquake magnitude. The dynamic earth pressure near the fissure is large and gradually decreases to both sides. Under the earthquake, at the top of the tunnel, the influenced widths of the hanging wall and foot wall are 25 and 20 m, respectively. At the bottom of the tunnel, the influenced widths of the hanging wall and foot wall are 26 and 22 m, respectively. The influence widths of the hanging wall and foot wall of ground fissure increase by about 35% under the large earthquake compared with the moderate earthquake. The dynamic earth pressure variation laws at the top and bottom of the tunnel are similar with and without the fissures, the pressures close to the tunnel are larger, and the largest pressure is 138 kPa. The contacting dynamic earth pressure increment is larger at the arch waist of the tunnel under the earthquake, the maximum increment is 45.27% at the right arch waist (close to the ground fissure), the second increment is 13.41% at the top, and the minimum increment is 6.86% at the bottom.More>

2018, 18(4): 72-81. doi: 10.19818/j.cnki.1671-1637.2018.04.008

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Analysis on rail wear and crack initiation and recommendation on rail selection in urban rail transit

ZHOU Yu, MU Dong-sheng, KUANG Di-feng, ZHENG Xiao-feng, HAN Yan-bin

Abstract: The theory of rolling contact fatigue (RCF) crack prediction based on the energy density method and critical plane method, and wear prediction theory based on the Archard method were analyzed, aprediction model of the coexistence of RCF crack initiation and wear growth in rails of urban rail transit (URT) was presented. The RCF crack initiation life, corresponding rail profile evolution and wear growth rate were predicted for three kinds of the rails with different hardnesses, named U71 Mn as-rolled, U75 Vas-rolled, and U75 Vheat-treated rails that were commonly used in URT. The development characteristics of the fatigue crack initiation and wear growth were analyzed. Based on the shakedown limit theory, according to the common gradients and type ER9 wheel, the rail selection suggestion for URT was proposed considering the hardness match between the wheel and rail. Analysis result shows that the RCFcrack initiation lifes of the rails prolong and the wear growth rates reduce with the increase of the rail hardness. Compared with those of U71 Mn as-rolled rail, the wear growth rates of the U75 V as-rolled and heat-treated rails reduce by 3.2% and 12.1%, respectively, and their crack initiation lifes prolong by 14.8% and 31.1% respectively. The materials of three kinds of rails with different hardnesses are all within the elastic shakedown limit under the common gradients condition in URT, but they will tend to the plastic shakedown limit with the increase of the gradient. Given the hardness match of the ER9 wheel, it is recommended that the hardness of the rail surface should be higher than that of the wheel tread. The wheel-rail hardness ratios are 0.87-1.04 for U75 Vas-rolled rail and ER9 wheel, and 0.71-0.84 for U75 Vheat-treated rail and ER9 wheel, respectively. Both U75 Vrails can be adapted to the URT system in China.More>

2018, 18(4): 82-89. doi: 10.19818/j.cnki.1671-1637.2018.04.009

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Stability region estimation of lane change on highway for tractor-semitrailer

PENG Tao, GUAN Zhi-wei, ZHANG Rong-hui, DU Feng, ZONG Zhang-fu, LI Ke-ning

Abstract: To improve the deficiency of the traditional vehicle stability region for evaluating the unsteady steering stability of articulated train, a stability region estimation method for lane change on a highway for tractor-semitrailer was proposed. A four-degree-of-freedom nonlinear dynamics model of tractor-semitrailer with Pacejka's magic formula was established and verified by comparing the tractor-semitrailer lane change simulation and test on a highway. Though establishing the vehicle system Jacobian matrix, the vehicle stabilities in high-speed step steeringand sinusoidal steering were analyzed by using an eigenvalue method. Based on the Lyapunov stability theorem, the Lyapunov energy function was derived. The energy and energy change thresholds of the vehicle system in critical situations were analyzed, and the vehicle stability region for lane change on a highway was obtained. The stability region was verified by tractorsemitrailer lane change test at 30 m·s^-1. Analysis result shows that the eigenvalues of the vehicle system Jacobian matrix are greater than 0 during lane change on a highway, but the values finally converge to less than 0, so the system can remain stable. The vehicle stability region for lane change on a highway is an approximate concave surface, so the closer to the low point in the central area, the more stable the vehicle system is, and the vehicle system will approach instability or become unstable once approaching or even exceeding the energy threshold. A vehicle lane change test at 30 m·s^-1 indicates that the vehicle system is in critical instability when the Lyapunov energy is close to the threshold of 3.863 6 J. Therefore, the determined stability region for lane change on a highway for a tractor-semitrailer can better characterize the stability of vehicle system in the condition of high-speed transient continuous steering, and offer a valuable reference for tractor-semitrailer handling stability evaluation and control.More>

2018, 18(4): 90-102. doi: 10.19818/j.cnki.1671-1637.2018.04.010

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Relationship among internal pressure, body air tightness and external pressure of rail vehicle

WANG Qian-xuan, HU Zhe-long, LIANG Xi-feng, HUANG Zun-di

Abstract: The evaluation index system of the air tightness of a rail vehicle body was researched by using the theoretical analysis, numerical calculation, and model test. The air tightness of a vehicle body was expressed by the pressure relief time or equivalent pressure relief hole area. The law of external transient pressure transferring to the inside of the vehicle body was given, and the theoretical relation between the internal pressure and the air flow in and out of the vehicle body was obtained. Based on the large-stiffness vehicle body model, the relationships among the internal pressure, air tightness, and external pressure of vehicle body were researched. A largestiffness vehicle body model with a pressure relief hole was designed, and the relationalexpression between the pressure relief hole radius and pressure relief time was obtained. The five kinds of large-stiffness vehicle body models with five different pressure relief times were used for a test in the closed chamber of the alternating-pressure simulation test bench, and the test data were analyzed. Analysis result shows that the internal pressure of the vehicle body changes linearly with time when the volumetric flow rates of the air inlet and outlet are constant. When the flow rates of the air inlet and outlet are the function of time, the change of internal pressure is the integral of the flows of air inlet and outlet about time. The absolute errors of tested and calculated pressure relief times of the vehicle body models with different pressure relief hole radii are less than 6.5%, which shows that the relationship between the pressure relief time and the pressure relief hole radius obtained by the numerical calculation is basically correct. The relationship between the vehicle body air tightness and internal pressure change rate is a power function, and the internal pressure change rate and external pressure amplitude are linear. The relationship among the internal pressure, vehicle body air tightness, and external pressure of the large-stiffness body model is obtained, and it can provide theoretical support for the formulation of a scientific and reasonable air tightness index of the vehicle body.More>

2018, 18(4): 103-111. doi: 10.19818/j.cnki.1671-1637.2018.04.011

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Simulation of fluctuating wind velocity at given position on moving high-speed train

LI Tian, QIN Deng, CAI Hua-min, ZHANG Ji-ye

Abstract: The modified Karman wind spectrum was employed as the target spectrum. The order of the autoregressive model for the linear filtering method (LFM) was determined by using the Akaike information criterion (AIC), and the reliability of the simulation results was verified. The LFM and the harmonic superposition method (HSM) were used to simulate the fluctuating wind velocity at a given position on a moving high-speed train. The characteristic variables of fluctuating wind velocity, such as mean values, variances, amplitudes, phase frequencies and distributions calculated by the two methods were compared. The computational efficiencies of these two methods were analyzed. Analysis result shows that the power spectrum densities of fluctuating wind velocity obtained from the two methods fluctuate around the target power spectrum. The mean value of fluctuating wind velocity is approximately 0. Due to the existence of random number, there is a difference in the peak values of fluctuating wind velocity at certaintime, and the differences in the simulated power spectrums within low frequency area may exceed 50%. Under different yaw angles, the difference in the mean values of fluctuating wind velocity between the two methods is less than 2%, and the distribution rules are quite similar. When the train speed is 80 m·s^-1 and the average wind velocity at the height of 10 mabove ground level is 25 m·s^-1, the difference in the average peak values of fluctuating wind velocity between HSM and LFM is less than 1%. Both the two methods are suitable for simulating the fluctuating wind velocity at a given position on a moving high-speed train. With the increase of the frequency of fluctuating wind velocity, the amplitude of fluctuating wind velocity decreases and the phase fluctuates in the range of-πtoπ. The difference in the fluctuating wind velocity distributions in the range of-3 to 3 m·s^-1 is 0.48%. The point numbers of fluctuating wind velocity obtained by the two methods both correspond to the Gaussian distribution, and the maximum difference in the Gaussian distribution fitting coefficients is 3.15%. The variance of the fluctuating wind velocity obtained from LFM is 7.89% larger than that obtained from HSM, therefore, LFM is less stable than HSM. The running time of LFM is approximately 1/9 that of HSM, therefore, its calculation efficiency is much higher than that of HSM.More>

2018, 18(4): 112-119. doi: 10.19818/j.cnki.1671-1637.2018.04.012

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Effect of blade tip clearance on waterjet propulsion hydrodynamic performance

PENG Yun-long, WANG Yong-sheng, YI Wen-bin, LIU Cheng-jiang

Abstract: Mixed-flow and axial-flow waterjet pumps with the same design parameters were selected as objects respectively. The hydrodynamic performances of mixed-flow and axial-flow waterjet pumps with four blade tip clearances were numerically simulated based on the shear stress transport turbulence model, implicit multi grid coupling algorithm and all structured grids. The effect of blade tip clearance on the hydrodynamic performance of waterjet propulsion was analyzed, and the relationship between the influence degrees of blade tip clearance and waterjet type was researched. Analysis result indicates that the head and efficiency of two types of pumps both decrease with the increase of blade tip clearance. The power consumption of mixed-flow waterjet pump first increases and then decreases with the increase of blade tip clearance. When the blade tip clearance is 1.3 mm, the power consumption is maximum. But the consumption of axial-flow waterjet pump monotonously decreases. The pump efficiency change due to the change of blade tip clearance of mixed-flow waterjet pump is not affected by mass flow, while that of axial-flow pump increases with the increase of mass flow. When the larger blade tip clearance isused as the reference, the same variation of blade tip clearance makes the efficiency of mixed-flow pump change larger, while the efficiency of axial-flow pump is opposite. The main reason resulting in the hydrodynamic difference between mixed-flow and axial-flow waterjet pumps is the different tip vortex effects on tip clearance leakage flow caused by the structure geometry. When the blade tip clearance increases from 0.7 mm to 1.6 mm, the thrust efficiencies of two types of waterjet propulsions change within 1%. When the blade tip clearance increases, the power consumptions of two types of waterjets show the same trend with waterjet pumps. The total thrust and power of axial-flow waterjet change larger than the values of mixed-flow waterjet, which means the mixed-flow waterjet is more adaptable to the change of blade tip clearance than axial-flow waterjet.More>

2018, 18(4): 120-131. doi: 10.19818/j.cnki.1671-1637.2018.04.013

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Evaluation method and influence factors of network travel time reliability

CHEN Xi-qun, LIU Jiao-kun, HU Hao-qiang, CUI Er-jia, ZHANG Shuai-chao

Abstract: The probability distribution of network travel time rate was studied based on the regional division approach, and the travel time reliability indexes based on OD pairs were proposed to appraise the reliability of urban traffic. The multivariate linear regression model was established by choosing the relevant factors that influenced the travel time reliability indexes. The model was solved by the stepwise regression method, and the significance test was conducted to verify the estimated model parameters. The network travel time reliability indexes were calculated by Hangzhou and Beijing ride-hailing data and compared with the peak congestion delay indexes, then the temporal and spatial distributions of network travel time reliability indexes were analyzed. Research result shows that in multivariate linear regression models, the fitting determination coefficient between the planning travel time rate and five independent variables, including the waiting time, cost, distance, travel time, and number of trips for OD pairs is 0.772, and the fitting determination coefficient between the average travel time rate and fiveindependent variables is 0.857, so both models have better fitting degrees and statistical significance. In the regression model of planning travel time rate, the regression coefficients of waiting time, travel time, and travel distance are 0.386, 0.399, and-1.286, respectively. In the regression model of average travel time rate, the regression coefficients of waiting time, travel time, and travel distance are 0.162, 0.177, and-0.676, respectively. The two traffic reliability indexes are positively correlated for the waiting time and travel time, and negatively correlated for the actual travel distance. The proposed network travel time reliability indexes are consistent with the peak congestion delay index and reflect the traffic reliability characteristics from various perspectives. They provide decision support for transportation planning and help residents choose propitious routes.More>

2018, 18(4): 132-142. doi: 10.19818/j.cnki.1671-1637.2018.04.014

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Depot locations for emergency bridging buses in urban rail transit

DENG Ya-juan, RU Xiao-lei, LIANG Guo-hua, ZHOU Ming-ni

Abstract: In order to reasonably set up the emergency bridging bus depots for urban rail transit under sudden incident, the bridging starting point was taken as the center of the circle, the operation recovery time of rail transit was taken as the radius, the bridging demand point reversely covered the emergency bridging bus supply point, and a cover structure was constructed. According to whether the bridging bus arrived at the bridging point before the scheduled departure time, the calculation methods of bridging demand and passenger waiting time delay were put forward. The reverse set coverage location model with an objective function of the minimum passenger total waiting time delay was established and solved. Taking a specific depot location for emergency bridging bus in rail transit as an example, the depot location schemes under differentnumbers of preset depots were analyzed and compared. Research result shows that the passenger total waiting time delay decreases with the increase of the number of preset depots. The objective function reaches the minimum when the number of preset depots is five. The depot location distribution is affected by the location of bridging starting point and bridging demand. When the number of preset depots is two, the depot location tends to gather at the center of the city. The depot locations tend to cover the suburb when the number of preset depots is five. After considering the impact of sudden incident weight, the depot location is close to the bridging point with high sudden incident frequency. Then, a balanced bus depot configuration inside and outside the center of the city can be formed. The reverse set coverage location model can minimize the passenger total waiting time delay of emergency bridging bus by active seeking supply, and can reflect the influences of the number of preset depots, passenger flow distribution of bridging starting point and sudden incident weight at the depot location for emergency bridging bus.More>

2018, 18(4): 143-150. doi: 10.19818/j.cnki.1671-1637.2018.04.015

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Distributed preset reserve for multiple points with stochastic demands

YANG Ting-hong, JIANG Da-li, FANG Hai-yang, FANG Ling, LI Bin

Abstract: Considering the correlations of emergencies (possibility of chain reaction) among the important pass, passageway, and sensitive zone, and the randomness of demands in the key directions or areas, the optimization problems of preset reserve scale and reserve distribution about the reserve network supporting the demand network were studied. The reserve network consisted of multiple preset reserve warehouses, and the service demand network consisted of multiple stochastic demand points. The distribution characteristics of the total demand in the demand network were analyzed under the conditions that the emergency at each point and the demand quantity were random. Ensuring the effectiveness and economy of the preset reserve scale and the rationality of the reserve distribution, the reserve scale model under the given securityprobability and the distributed reserve model under the process response criterion (collectively called reserve model) were established. According to the characteristics of the model, the distributed reserve model was decomposed into a bi-level model. The sample processing method was used to resolve the random demand problem. On this basis, agenetic-simulated annealing algorithm was constructed to solve this model. Based on the concept of variation coefficient, a robustness index for reserve scheme with random emergency and random demand was proposed to analyze the robustness of the reserve model and its algorithm. The validities of the reserve model and its algorithm were verified by a case application. Research result shows that in comparison with the nearby partition principle, the reserve scale model and its algorithm can reduce the reserve scale by approximately 1/3 under the premise of ensuring the security probability. In comparison with the maximin criterion, the distributed reserve scheme under the process response criterion can reduce the response time of the first batch of materials by 11%, and the response time of 90% of materials reduces by 21%. When facing the stochastic fluctuation of emergency and demand in the demand network, the amplitude of fluctuation for the distributed reserve scheme is no more than 80% of the demand fluctuation, which suggests better robustness.More>

2018, 18(4): 151-159. doi: 10.19818/j.cnki.1671-1637.2018.04.016

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Analysis of relavent factors for highway freight volume and freight turnover based on grey entropy method

ZHAO Huai-xin, SUN Xing-xing, XU Qian-qian, HU Yuan-jiao, SUN Chao-yun, LI Wei

Abstract: The interaction effects between the national macro-economic factors and highway freight volume and freight turnover were analyzed. A grey entropy relational degree algorithm based on the grey relational degree algorithm and the entropy weight method was proposed. According to the economic data and highway freight volume and freight turnover data of Shaanxi Statistical Yearbookin the past 14 years, the relevant coefficients between the national macroeconomic factors and highway freight volume and freight turnover were studied, and the influencedegree of each economic indicator on highway freight volume and freight turnover was obtained. By removing the dimensional effect between the data, the relevant coefficients between the economic indicators and highway freight volume and freight turnover were calculated by the grey relational degree algorithm, and the weights of the economic indicators were calculated using the entropy weight method. The relevant degrees between the economic indicators and highway freight volume and freight turnover were calculated based on the relevant coefficients of the economic indicators and their weights. Moreover, the influencing factors of the highway freight volumes in Beijing and Tianjin were analyzed. Analysis result shows that for the economic indicators, the highway freight volume and freight turnover show similar relevant trends. In Shaanxi Province, the relational degrees between the highway freight volume and output value of the primary industry, added value of the industry and output value of the secondary industry are relatively higher, and are 0.944 7, 0.941 7, and 0.940 2, respectively. The relational degrees between the freight turnover and output value of the primary industry, average salary of the onjob employees in the urban units, and per capita GDP are higher, and are 0.920 7, 0.915 9, and 0.915 3, respectively. In Beijing, the relational degrees between the highway freight volume and tertiary industry index, secondary industry index, and per capita GDP index are higher, and are 0.716 2, 0.714 8, and 0.710 9, respectively. In Tianjin, the relational degrees between the highway freight volume and average salary of on-job employees in urban units, GDP, tertiary industry output value, secondary industry output value, industrial added value, and per capita GDP are higher, and are 0.862 0, 0.855 6, 0.853 4, 0.851 4, 0.851 4, and 0.851 3, respectively. In conclusion, the analysis results of the relevant factors of the highway freight volumes in Beijing and Tianjin are generally consistent with those in Shaanxi Province, and the main relevant factors are the output values of the three major industries in these regions.More>

2018, 18(4): 160-170. doi: 10.19818/j.cnki.1671-1637.2018.04.017

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Ship safe navigation depth reference map based on AIS data

HE Zheng-wei, YANG Fan, LIU Li-rong

Abstract: A new method of obtaining channel depth information was proposed by mining massive AIS data, which was used to construct ship safe navigation depth reference map. The historical and online AIS data were cleaned and mended by data preprocessing method, and ship motion trajectories were generated. The time, longitudes and latitudes of ship navigation areas were selected, and K-means clustering algorithm was used to cluster and analyze the draft data during ship navigation process, then the ship classifications in different safe navigation areas were obtained. The BP neural network model was applied to predict and complete the missing maximum ship draft information from the AIS data. The historical trajectory of the ship wassegmented, and when the time interval of the sub-trajectory was 10-20 min, the spline interpolation method was used to interpolate the missing data in the ship trajectories. The safe navigation depth area maps for similar types of ships were constructed by using convex hulls, and the maps with different draft types were combined to obtain a combined safe navigation depth map. The combined safe navigation depth map was superimposed on the channel chart to obtain a safe navigation depth reference map. Experimental result shows that when the clustering algorithm parameter is 4, four ship types are obtained by clustering. The corresponding maximum draft ranges of the ships are 0.1-4.8, 4.8-6.6, 6.6-10.0, and 10.0-13.0 m, and the corresponding least navigable ship drafts are 1.8, 2.4, 3.3, and 5.0 m, respectively. Thus, the maximum drafts of the ships are positively correlated with the least navigable drafts. The constructed ship safe navigation depth reference map covers 86% of the target channels in the electronic channel chart, and the overlap rate with the deep-water areas in the channel chart is 80%. Therefore, the constructed ship safe navigation depth reference map can reflect the true conditions of the channel depths, and meet the navigation needs of different types of ships.More>

2018, 18(4): 171-181. doi: 10.19818/j.cnki.1671-1637.2018.04.018

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Fast computation of vessel time-domain motion based on identification theory

ZAN Ying-fei, MA Yue-sheng, HAN Duan-feng, WU Chao-hui

Abstract: To meet the demand of fast computation of time-domain motion equations, four methods suitable for the fast computation of a retardation function were proposed based on the identification theory. Applying these methods, a state-space model was established by replacing the convolution term, to satisfy the property of the retardation function and fitting quality. Considering the HYSY286 vessel as the research object, the time-domain and frequency-domain identification methods were used to compare the fitting results of retardation function. Calculation result shows that when the confidence coefficient is 0.99, the fitting results of the frequency-domain regression method and the frequency-domain iteration method are consistent with the expected value. The fitting curve reaches to peak when the frequency value is 0.92-1.05 rad·s^-1, then gradually decreases to 0. When the frequency is 0.05-0.50 rad·s^-1, the deviation of the fitting result from the expected value is approximately 20%, and the accuracy is obviously lower than the frequency-domain iterative method. When the confidence coefficient is 0.99, the fitting results of the impulse response curve fitting method and the realization theory method are consistent with the expected value of retardation function. The fitting curves reach to peak initially and decrease to the minimum value at approximately 3.5 s, then increase again until they tend toward 0 at approximately 15 s. The fitting precision of the realization theory method is better than that of the impulse response curve fitting method during 7-11 s. Considering the effect of heaving direction on pitching direction, the realization theory method requires the least order of the state-space model, to be 4, 3, and 3 for swaying, heaving and pitching, respectively. Without such consideration, the frequency-domain iteration method requires the least order of the state-space model, to be 3, 2, and 2 for swaying, heaving and pitching, respectively. When the impulse response curve fitting method considers the influence of heaving direction on pitching direction to fit the state-space model, the order of the model required to fit pitching is twice as much as that without considering heaving direction, whereas the realization theory method requires the same order.More>

2018, 18(4): 182-190. doi: 10.19818/j.cnki.1671-1637.2018.04.019

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