西南交通大学学报

Polygonal Wheel Detection Model Based on Track Irregularity of High-Speed Railways

WANG Ping, WANG Xin, WANG Yuan, ZHANG Ronghe

2020, 55(4): 681-687. doi: 10.3969/j.issn.0258-2724.20180283

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Abstract:
To detect the amplitudes of polygonal wheels of high-speed railways and better understand the track spectrum, a model based on track irregularity was established for rapidly measuring the amplitude of polygonal wheels. Firstly, the amplitude distribution of polygonal wheels was analyzed within track irregularity inspection data and intensive sampling method (ISM) was proposed. The dynamic detection model of polygonal wheels was established on the basis of the sparse sampling data of track irregularity. The results of numerical simulation show that the polygonal wheel has little influence on the amplitude of the discrete track irregularity data obtained by the inertial reference method, but it has great influence on the frequency domain of track irregularity (track spectrum density). The polygonal wheel can affect the track irregularity inspection data with its wavelength being less than or equal to wheel length and the former is more affected. It also affects the long-wave track inspection irregularity. The maximum influence wavelength is only related to wheel perimeter and sampling interval. The proposed dynamic detection model can effectively extract the amplitude of polygonal wheels from track irregularity inspection data. The measuring error can be limited to 0.02 mm.

Effect of Flakiness-Elongation Index on Shear Behavior of Railway Ballast

JING Guoqing, QIANG Weile, CHANG Jinxiu, LI Xu

2020, 55(4): 688-694. doi: 10.3969/j.issn.0258-2724.20180677

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In order to investigate the influences of flat and (or) elongated ballasts on direct shear mechanical properties considering the breakage effect, the direct shear tests with different test conditions were conducted to study the effect of the flat and/or elongated ballast content with the analysis of testing results from the ballast shear strength, deformation and breakage. The results show that: (1) With the increase of the flakiness and elongation index, the shear behavior of the ballast decreases, both the shear strength and internal friction angle (at 100 kPa, the shear strength respectively decreases by 10.9%, 16.8% when the elongation index increases from 0 to 20%, 40%; the shear strength respectively decreases by 14.7%, 22.3% when the flakiness index increases from 0 to 20%, 40%; the shear strength respectively decreases by 12.4%, 18.9% when the flakiness-elongation index increases from 0 to 20%, 40%). (2) The shear dilatation and shrinkage of samples decrease with the flat and/or elongated ballast content increasing. (3) The flat and elongated ballast particles are prone to break up during the direct shear test, and most of them are fractured with the sharp corner breakage, which significantly affects the ballast bed maintenance cycle.

Operating Environment and Pollutant Distribution in Xiang’an Undersea Tunnel

WANG Mingnian, WANG Xu, YU Li, DENG Tao

2020, 55(4): 695-703. doi: 10.3969/j.issn.0258-2724.20180714

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In order to clarify the distribution of environmental parameters and pollutants in the urban undersea road tunnel, a field test was carried out for the ventilation effect of Xiamen Xiang'an undersea tunnel. The atmosphere pressure, temperature and humidity, air speed, CO, NO₂, and PM concentration in the tunnel were tested during the peak and off-peak periods. Combined with the one-dimensional diffusion theory and the Fluent component transport model, the distribution of environmental parameters and pollutants along the traffic volume in the undersea road tunnel was studied. The results show that: (1) during the rush hours, the temperature increases gradually along the direction of traffic flow and reaches to 36℃ at the outlet. The humidity decreases gradually along the direction of traffic flow and reaches to 94% at the inlet. The CO, NO₂, and PM concentrations increase gradually with the direction of traffic flow and reach to maximum at the outlet, the maximum concentrations were 21.00 ppm, 3.73 ppm and 1.76 mg/m³, respectively. The PM concentration at the bottom of the V-shaped slope reaches to 2.03 mg/m³. According to the conversion formula of particulate matter concentration and extinction coefficient, the extinction coefficients at the outlet and the bottom of the V-shaped slope are 0.008 3 m⁻¹ and 0.009 5 m⁻¹ , respectively. The NO₂ and PM concentrations exceed the threshold value. (2) The maximum concentration of NO₂ during off-peak hours is 1.68 ppm, and the extinction coefficients at the outlet and the bottom of the V-shaped slope are 0.006 9 m⁻¹ and 0.007 7 m⁻¹ , respectively. The NO₂ concentration at the outlet and the extinction coefficient at the bottom of the slope exceed the threshold value.

Force Characteristics of Longitudinal Joints of Shield Tunnel under Seismic Action

GENG Ping, WANG Qi, GUO Xiangyu, HE Chuan, LU Shujun, XIAO Mingqing

2020, 55(4): 704-712. doi: 10.3969/j.issn.0258-2724.20180634

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The longitudinal joints of shield tunnels are the weak parts of the structure when bearing loads and deformations in practical engineering. A numerical analysis method which analyzes from the whole to the local was put forward based on the mechanical characteristics of the longitudinal joints under seismic action. According to the equivalent longitudinal stiffness beam theory, the 3D time-history analysis model of stratum-structure was established to obtain the extreme value of structural longitudinal internal force, the extreme value was then taken as the external load which was applied on the entire 3D analysis model of the whole ring to obtain the boundary force of the most unfavorable region of shield tunnels. The mechanical characteristics of the longitudinal joints were analyzed by applying the boundary force to the local refined model of the longitudinal joints. The method was discussed by an integrated corridor project specifically. The results show that the shield tunnels mainly suffer cyclic horizontal bending in the longitudinal direction when it is under the transverse seismic excitation, the cyclic vertical bending and longitudinal tension of the tunnel are notable when the seismic wave is excited longitudinally. The local area with the largest longitudinal opening is always under tension whether subjected to axial tension or longitudinal horizontal bending moment, which means that the influence of these two working conditions on the force pattern of the local area are essentially the same. When the local area with the largest longitudinal opening is under tension, the maximum tensile stress area is located at the hand hole on the inside of the segment, and the maximum compressive stress area is distributed around the bolt hole in a ring shape.

Unidirectional Vibration Waterproof Test of Ring Joint of Shield Tunnel under the Action of Earthquake

XIE Hongming, HE Chuan, FENG Kun, LIANG Minfei, LI Ce, AL-SEBAEAI Maged

2020, 55(4): 713-718. doi: 10.3969/j.issn.0258-2724.20180456

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In order to study the waterproof performance of the elastic sealing gasket of shield tunnel segment joint under seismic action, on the basis of the large section subsea shield tunnel—Su’ai Channel project in high-intensity seismic region, a unidirectional vibration waterproof test device for segment ring joint under the action of simulated earthquake was developed according to the waterproof index. The unidirectional vibration waterproof test under different ring joint openings was carried out, compared with the static waterproof test under the corresponding working conditions of opening and offset, the influence of openings on waterproofing performance of sealing gasket is obtained, and the corresponding indexes of the vibration and static waterproof of the gasket were put forward. The results show that when water leakage happens under the unidirectional vibration condition, the water spurts rather than slowly flows out through the sealing gasket, and the increase of the opening is more likely to reduce the gasket waterproof performance significantly than that of the offset. With the changes of ring joint openings, the hydraulic resistance value under unidirectional vibration is 0.2−1.4 MPa and the static hydraulic resistance value is 0.1−1.1 MPa. The waterproof performance of the sealing gasket is about 45%−78% of its static water resistance under unidirectional vibration.

Failure Characteristics and Engineering Application of Layered Rock with Two Pre-existing Non-coplanar Fissures

WANG Jun, LIN Guojin, TANG Xie, XU Guowen, TANG Rui

2020, 55(4): 719-725, 732. doi: 10.3969/j.issn.0258-2724.20180044

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In order to study the failure mechanism of layered rock with pre-existing cracks, a numerical model which is based on particle discrete element method and can reflect the anisotropic characteristics of rock is built. The initiation and propagation of micro-cracks in anisotropic rock with two pre-existing non-coplanar fissures under uniaxial compression tests are analyzed. Furthermore, the failure process of surrounding rock after tunnel excavation is also obtained. Results shows that, the compressive strength of specimens with pre-existing fissures is smaller than that of intact rock, while the curve of relationship between strength and inclination angles is still ‘U’ shaped. The failure patterns are controlled by inclination angle of bedding plane (β) and inclination angle of fissures (α). For β < α, failure is controlled by fissures; for β > α, failure is controlled by both fissures and bedding planes or bedding planes. Failure patterns of surrounding rock is also related to β and α, while the damage zone is concentrated in certain regions around the tunnel in the direction normal to layers in all cases.

Modelling of Velocity Pulse-Like Ground Motions Based on Adaptive Matching Algorithm

YANG Cheng, LIU Jiaxin, TANG Zenan, ZHAO Baihan, XIN Benjian

2020, 55(4): 726-732. doi: 10.3969/j.issn.0258-2724.20190075

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Due to the lack of a complete waveform parameter identification method aiming at the velocity pulse-like ground motions up to now, it is still difficult to identify the pulse-like records quantitatively, which hinders definitely collecting the wave shape parameters from ground motion database. In order to solve this problem, a framework for the parameters identification of pulse waveform is presented by combining the pulse quantitative identification and impulsive function analysis with an adaptive matching algorithm to realise the adaptive matching between pulse waveform and the analytic function. As the key part of the framework, the adaptive matching algorithm for parameterizing the pulse waveform is proposed by virtue of the empirical mode decomposition (EMD) in order to smooth the near-fault pulse-like earthquake records. Based on the pulse function given by Marverodis, and within the distribution range of the model parameters, a procedure for parameters adaptive matching is developed, characterized by the enumeration with several loops corresponding to the pulse frequency, pulse shape, and pulse oscillation characteristic respectively. In addition, the least square-based optimization method is applied to determine the final parameters. Using this method, the shape parameters of the main pulses existing in these pulse-like ground motions records were identified. In addition, the relationship between the peak ground velocity and the period of main pulse is drawn from the statistical results. According to the statistical and image analysis, compared with the existing method using the Dickinson model, the algorithm for identifying the main pulse period in this paper can reduce the classification mistake by about 67%. The better stability of near-fault records identification is meaningful to practical engineering applications in seismic design.

Experimental Study on Frost Heave, Thaw Settlement and Thermal Properties of Foundation Soils along China-Russia Crude Oil Pipeline

WANG Wei, ZHANG Xifa, LÜ Yan

2020, 55(4): 733-742. doi: 10.3969/j.issn.0258-2724.20180801

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The China-Russia crude oil pipeline is one of the strategic energy channels of China. The pipeline passes through the permafrost region of the Da Hinggan Mountains, where the engineering geological conditions are very complex, especially near the Yilehuli Mountains, and frost heave and thaw settlement seriously affect the normal operation of the pipeline. Experiments were therefore conducted on soils in this area to study their properties of frost heave, thaw settlement and thermal conductivity, and the test data were subjected to the regression analysis and influencing factors analysis. Results show that when the plasticity of fine-grained soils is less than 10, the frost heave ratio of soils does not necessarily increase with an increase in the initial water content. Thus, gravel and breakstone should be used as cushion and filling materials, and waterproof and drainage measures should be taken. Meanwhile, the coefficient of thaw settlement increases with water content and decreases with dry density. The silt is very sensitive to the thawing action, hence not suitable for pipe foundation, and fine gravel is the best frozen soil foundation. Besides, the thermal conductivity increases with the increase of total water content and dry density. The thermal conductivity of coarse-grained soil is higher than that of fine-grained soil, and the thermal conductivity of frozen soil is higher than that of thawed soil. However, when the water content is less than 10%, the thermal conductivity of the thawed soil is higher than that of the frozen soil. In addition, the results of thermal conductivity obtained by different test methods are significantly different. Generally, the thermal conductivity of disturbed coarse-grained soil sample should be measured by heat flow meter method, that of disturbed fine-grained soil sample should be measured by hot wire method, and that of undisturbed sample should be measured by comparison method.

Number of Earthquake Ground Motion Inputs for Time-History Analysis of Seismic Design Code in China

JI Kun, WEN Ruizhi, REN Yefei, YIN Jianhua

2020, 55(4): 743-751. doi: 10.3969/j.issn.0258-2724.20180604

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This study aims to determine a proper input number of strong motion recordings for structural time-history analysis in China seismic design code. The cumulative probability curves of structural response under different number of records were simulated using 500 times of Monte Carlo samplings based on the assumption that the seismic demand can be represented by a lognormal distribution. Consequently, significant difference was observed in cumulative probability curves between using the maximum response of three ground motions and using the average response of seven or more ground motions: in the former, the expectation of results is much higher than the theoretical mean structural response and is significantly affected by the structural response variation; while in the latter, the expectation of results is close to the theoretical mean structural response. In addition, nonlinear time-history analysis was carried out of a 10-story typical reinforced concrete (RC) frame according to Chinese seismic code. It turns out that using three records has a significantly higher mean M_IDR (maximum inter-story displacement angle) and C_OV (coefficients of variation) compared with other schemes using more records as input and controlling the record-to-record variation. Finally, on the basis of the response mean values of seven or more strong vibration records, an empirical correction formula using record number and structural response variation as parameters was proposed to calculate the 0.84 quantile value to guarantee the assurance rate of 84% required by seismic design code. The applicability of the empirical correction formula under the seismic code of China is verified by numerical simulation of the 10-story RC frame.

Comparative Analysis of Influence of Foundation on Reinforced Soil Retaining Walls

XU Peng, JIANG Guanlu, WANG Ning, HAN Yijun, WANG Zhimeng, LIU Yong

2020, 55(4): 752-757. doi: 10.3969/j.issn.0258-2724.20180765

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Two centrifuge model tests were carried out to study the influence of foundation on reinforced soil retaining wall. Firstly, the similarity scale was obtained using the similarity theory. Then, materials used in model tests were determined according to the scaling law and models with sand and clay foundations were designed. Finally, values of displacement, horizontal earth pressure on the wall, vertical earth pressure, and reinforcement strain during the construction stage and the loading stage were collected and analyzed. Results show that the maximum horizontal displacement was located at the top of the structure for the wall constructed on compacted sand foundation; the horizontal displacement of the model wall constructed on clay foundation at the end of the construction was about 3 times that constructed on sand foundation and its bottom displacement could increase to 30 cm in the loading stage; the horizontal earth pressure coefficient was nonlinear along the wall height and was smaller in the clay foundation case. Besides, the value in the loading stage was smaller than that in the construction stage in both cases. Compared with the wall constructed on sand soil foundation, the deformation of the clay could reduce the concentration of the vertical stress at the bottom of the wall facing, resulting in the ratio of the vertical stress to the self-weight stress being close to 1.0. As the displacement of the wall constructed on clay foundation increased, the strain was about 3 times that with compacted sand foundation, and the position of the maximum reinforcement strain was far away from the wall facing.

Three-Dimensional High-Precision Laser Non-contact Detection of Asphalt Pavement Surface Texture

DING Shihai, YANG Enhui, WANG Chenping, JI Yaying, LEI Kaiyun, ZHANG Xinrui

2020, 55(4): 758-764. doi: 10.3969/j.issn.0258-2724.20181056

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In order to realize the high-precision automatic detection of asphalt pavement textures and the 3D reconstruction of pavement textures with the help of 3D laser technology, a method for measuring the depth of the asphalt pavement structure by simulating the sand patch test was proposed. First, a high-precision 3D laser scanner was used to obtain the 0.1 mm-precision 3D elevation data of asphalt pavement of Ya’an–Kangding expressway, and the artificial sand patch method was used to measure the macro-structure depth value in the same area. Second, the digital image processing technology was used to reconstruct the 3D cloud image of the asphalt pavement and perform data noise processing. Finally, a four-connected multi-seed combination filling algorithm was designed to automatically pave sand on the filtered 3D road texture cloud map and obtain the macro structure depth of road texture. The results show that the average absolute error between the mean texture depth (MTD) values measured by the simulation method and the artificial method is 0.052 mm, and the correlation coefficient between them is 0.96, which verifies the feasibility of replacing the existing contact road surface friction performance test with a non-contact road surface texture test, and can lay a foundation for network-level monitoring and management of road traffic safety.

Innovative Hysteresis Model and Parameter Identification Method for Reinforced Concrete Rectangular Hollow Piers

LI Jing, SHAO Changjiang, QIAN Yongjiu, YANG Huaping

2020, 55(4): 765-771. doi: 10.3969/j.issn.0258-2724.20190058

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In order to precisely simulate the stiffness degradation of RC (reinforced concrete) rectangular hollow piers and provide the theoretical base for the research on post-earthquake resilient bridges, 14 RC rectangular hollow pier specimens with different design parameters were tested under semi-static loading. A modified Bouc-Wen-Baber-Noori (BWBN) hysteresis model was built, in which a peak-displacement coefficient was introduced to reflect the correlation between stiffness degradation and peak displacement. The hysteresis model parameters of each measured hysteresis curve were identified by combination of particle swarm optimization and gravitational search algorithm (PSOGSA). The relationship between the design parameters of hollow piers and hysteresis model parameters were regressed, and an empirical prediction method was summarized. The results show that the modified BWBN hysteresis curve is well matched with the measured hysteresis curve and the correlation coefficients are all above 0.98. The new hysteresis model can reflect how the lateral stiffness of piers degrades with peak displacement. PSOGSA is able to identify the hysteresis model parameters of the measured hysteresis curve precisely. The correlation coefficients between the measured hysteresis curve and modelling curve generated by empirical prediction method is 0.83. The method is applicable to the cases of bridge piers without the measured hysteresis curves.

Extreme Value Distribution Estimation Method for Nonlinear Seismic Response of Bridge Structures

CHEN Zhiqiang, ZHENG Shixiong, ZHOU Qiang, CHEN Zhiwei, LI Xi

2020, 55(4): 772-779, 788. doi: 10.3969/j.issn.0258-2724.20180948

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To study the extreme value distribution (EVD) of nonlinear seismic response of bridges subjected to near-fault impulse ground motion and accurately estimates the dynamic reliability of bridges at small failure probability level, an effective method is proposed and validated. Considering the nonlinearity of bridge structures and the uncertainty of ground motions, the random parameters of near-fault impulse ground motion and structure are sampled by Latin hypercube sampling (LHS). The required number of seismic samples is determined by the relative error between the mean square value of simulated high-frequency ground motion and the exact value. Using synthetic near-fault impulse ground motions as seismic excitation, the structural nonlinear dynamic equation is solved by time history analysis, and the structural nonlinear seismic response extreme value samples are obtained. Then, the improved maximum entropy principle with fraction moment is adopted to obtain the EVD of bridges. The accuracy and efficiency of the proposed method are verified by a single degree freedom system and a three-story shear frame structure in comparison with the Monte Carlo simulation. Results indicate that the proposed method can not only effectively simulate the EVD of dynamic response of bridge under the double uncertainties influence of structure and ground motion, but also accurately estimate the tail distribution of the extreme value of nonlinear seismic response of bridge structure, with a balanced between efficiency and calculation accuracy. This method provides an effective way for evaluating the non-linear dynamic reliability of bridge structures.

Separation-Reattachment Flows Characteristics of Rectangular High-Rise Buildings with Different Side Ratios

ZENG Jiadong, LI Mingshui, ZHANG Zhitian, CAO Baozhu

2020, 55(4): 780-788. doi: 10.3969/j.issn.0258-2724.20190259

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To study the influents of turbulence characteristics, side ratio, and spatial position on the separation-reattachment flows of rectangular high-rise buildings, Firstly, the measured data of surface pressure under different conditions were obtained by synchronous pressure tests of rectangular building models with different side ratios. Secondly, various factors affecting the evolution of the three-dimensional separation-reattachment flows and the mean separation length of rectangular high-rise buildings were analyzed, the intrinsic correlation between the unsteady aerodynamic forces and the separation-reattachment flows of rectangular buildings under large-scale turbulences was discussed. Finally, the mean separation lengths in the vertical direction were given quantitatively. The results show that the ratio of the turbulence integral scale to the feature size of the building affects the test accuracy of separation-reattachment flows and aerodynamic characteristics, with a maximum deviation of about 24%. The interference of incoming turbulence causes the curvature of the separated shear layers to increase, and enhances the entrainment of the uniform-shear flows in the separation zone, the stable reattachment will occur when the side ratio is 2. The mean separation length of the rectangular high-rise building gradually increases in the vertical direction, correction suggestions for predicting the lateral wind pressure of high-rise buildings are also given based on the test results.

Bending Capacity Calculation Method for Corroded Reinforced Concrete Beams

LIU Tingbin, JIA Rubo, ZHANG Chenyu, JIN Wenqiang, ZHAO Jianchang

2020, 55(4): 789-795. doi: 10.3969/j.issn.0258-2724.20190277

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The corrosion state of longitudinally stressed steel bars in corroded reinforced concrete beams is very complicated. Moreover, the form of the load applied to beams is variable. In order to obtain the bending capacity of corroded RC (reinforced concrete) beams, the corroded RC beam with simple support is taken as the object, which is regarded as a composite beam composed of steel bars and concrete with bond and slip. Based on the deformation coordination conditions between corroded steel bars and concrete, the equilibrium differential equation of corroded reinforced concrete beam is expressed by deflection. By the homogeneous solution of the differential equilibrium equation that is used as the unit shape function, the element stiffness matrix, the equivalent node load matrix, and the internal force calculation formula of the corroded reinforced concrete beam is derived under each load step. The calculation method for the bending capacity of corroded reinforced concrete beams which can reflect the corrosion condition of the steel and the load form is established. The analytical method is validated with the test data of 17 corroded reinforced concrete beams. The average ratio of test results to predicted results is 1.06 and the variance is 0.012, which shows good agreement between test and prediction results, and desirable accuracy of the calculation method.

Damage Assessment Method for Concrete-Filled Steel Tubular Columns under Impact Loading

WANG Luming, LIU Yanhui, ZHU Wenkai, HE Tingjun, KANG Xiangjie

2020, 55(4): 796-803, 819. doi: 10.3969/j.issn.0258-2724.20181037

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In order to develop a damage assessment method for concrete-filled steel tubular (CFST) columns subjected to lateral impact, the drop hammer impact tests are carried out on CFST columns near supports. By the use of numerical simulation and theoretical analysis, the effects of pre-loading axial force, impact mass and impact velocity on the damage degree of CFST columns are studied. The impact mass and velocity are selected as the main control variables of damage assessment for CFST columns. Then the calculation formula D of damage assessment based on the residual bearing capacity is established and the levels of damage assessment are defined. The damage assessment method is given by taking a typical CFST column subjected to lateral impact. The damage assessment curves are fitted by simulation and trial calculation, and then the graphic method for damage assessment is established. The results show that the impact mass and velocity have great influence on the damage degree, while the effect of pre-loading axial force on the damage degree has great variability. The damage assessment curves (D=0.3, 0.5, 0.7) divide the coordinate plane into four regions, which respectively represent the slight damage, moderate damage, severe damage and failure for CFST columns. According to the position relationship between the combination point of the impact mass and velocity and the damage assessment curves, the damage degree of CFST columns can be quickly determined.

Influence of Biologic Retention Zone Structure on Its Infiltration-Storage

YANG Qian, YANG Qinghua, TANG Xueqin, YAO Yuan, YAO Jintao

2020, 55(4): 804-810. doi: 10.3969/j.issn.0258-2724.20180627

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To investigate the influence of structural parameters and combination mode of the biologic retention zone on its infiltration-storage effect, the evaluation index for determining the infiltration-storage effect of biologic retention zone was put forward, and the 16 groups orthogonal experiments under the different conditions of the biological retention zone structural layer parameters were carried out. The composition and content of the planting soil and packing layer, the position of the geotextile, the grain gradation of the sand layer, and the thickness of structure layer on infiltration-storage effect of the biological retention zone were studied quantitatively. The results show that the degree of effect which varies from large to small is the grain gradation of sand layer, the composition and content of packing layer, the structural thickness, the position of geotextile, the composition and content of planting soil. The optimal structure of the biological retention zone from top to bottom is: 20 cm thick planting soil, 35 cm thick filler layer (the volume fraction are 10% perlite, 5% vermiculite, 10% loam, and 75% sand), 10 cm thick sand (0−0.5 mm accounting for 15%, 0.5−0.7 mm accounting for 40%, 0.7−1.0 mm accounting for 30%, and 1.0−2.0 mm accounting for 15%), 20 cm thick gravel layer, and without the geotextile.

Parallel Interaction Influence of Single-Stage Photovoltaic Grid-Connected Multi-Inverter System

CHEN Weirong, WANG Xuan, LI Qi

2020, 55(4): 811-819. doi: 10.3969/j.issn.0258-2724.20180900

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Under the condition of weak grid, the dynamic interactions between multi-inverters and between multi-inverters and the grid affect the power quality and stability of the power system, which is likely to cause harmonic resonance. In order to study the harmonic resonance characteristics of the single-stage photovoltaic grid-connected multi-inverter system, the modal analysis method is used for systematical analysis and discussion on the resonance problem while the interaction between the photovoltaic generation and the system is considered. Firstly, according to the structure and control strategy of three-phase single-stage photovoltaic grid-connected system, the Thevenin equivalent model for the multi-inverter system is established. Secondly, a modal analysis method is applied, which can determine the system resonance frequency, resonance center and the participation degree of each node by constructing node admittance matrix of the multi-inverter system. The resonance characteristics and variation laws of the system are studied from three aspects: the number of inverters, external environment and transmission distance. Finally, with the use of MATLAB/Simulink simulation platform, the correctness and effectiveness of the modal analysis method are validated by a simulation model of a three-phase single-stage photovoltaic grid-connected multi-inverter system. The results show that when the number of inverters increases, the low resonance frequency tends to decrease, which is 30th, 27th, and 25th harmonics respectively, while the high resonance frequency remains unchanged at 2 230 Hz. When the ambient temperature decreases, the low resonance frequency increases gradually, which is 22th, 23th, and 24th harmonics respectively, and the high resonance frequency is stable at about 2 225 Hz. When the transmission distance increases, the low and high resonance frequencies gradually decrease and become close to each other.

Energy Management Strategy for Trams with Novel Power System

LI Qi, HUANG Wenqiang, SHANG Weilin, ZHU Yanan, SU Bo, CHEN Weirong, LI Ming

2020, 55(4): 820-827. doi: 10.3969/j.issn.0258-2724.20180231

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In order to improve the efficiency of absorbing the braking energy for hybrid trams, an energy management strategy is proposed, which takes into account the initial and final states of charge (SOC) of an energy storage system. The strategy allocates the load power for the hybrid power system by using the minimum principle from the tram start to the braking, which achieves the effective control on the safety range of the supercapacitor SOC, and ensures sufficient remaining SOC to absorb the braking energy as the tram brakes. Furthermore, the strategy combines the tram traction control during start and traction operation with the energy recovery during the braking process, and uses an integrated device composed of the insulated gate bipolar transistor chopper and braking resistor to suppress the bus voltage rise. Finally, based on the actual tram operating conditions, a simulation test is conducted with the MATLAB/Simulink platform. The results show that at the moment of tram braking, the supercapacitor SOC can reach about 0.4 as expected, and during the entire braking process, the bus voltage can always lie below 875 V, which meets the requirements of bus voltage control.

Review on Fault Diagnosis for Flooding and Drying in Proton Exchange Membrane Fuel Cells

ZHANG Xuexia, JIANG Yu, SUN Tengfei, CHEN Weirong

2020, 55(4): 828-838, 864. doi: 10.3969/j.issn.0258-2724.20190548

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In running proton exchange membrane fuel cells (PEMFCs), the flooding and drying are the most common faults. Firstly, water generation and transfer mechanism in PEMFCs are elaborated, and the impact factors of flooding and drying faults are generalized. The diagnostic indicators for flooding and drying in terms of voltage, pressure drop, and impedance are listed with the analysis on their merits and demerits. In addition, the damages caused by flooding and drying faults are presented from the perspective of internal structure and charge transport. Next, the model-based, experimental-based, and data-driven diagnostic methods for flooding and drying faults and their application range are discussed. Moreover, popular mitigation strategies for flooding and drying are analyzed. Finally, the researches on flooding and drying are summarized and their prospects are presented. Of these researches, online diagnostic approaches based on data-driven, model establishment for fault diagnosis, flooding and drying diagnosis in large-scale stacks and multi-stacks, and the efficient and accurate diagnostic indicators need further studies.

Parameters Optimization for Hybrid Energy Storage System of Electric Vehicles Based on Cross-Entropy Algorithm

DAI Chaohua, LIU Yang, HUANG Chenxi, ZHAO Duo, GUO Ai, CHEN Weirong, LIU Nan

2020, 55(4): 839-846. doi: 10.3969/j.issn.0258-2724.20190442

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In order to improve the dynamic performance of electric vehicles and reduce costs, a parameter optimization method for vehicle-mounted hybrid power supply based on cross-entropy (CE) algorithm is explored with the intent of minimizing the hybrid power supply cost and power consumption. Firstly, a hybrid electric vehicle is used as the object, and the capacity ranges of its lithium-ion batteries and super-capacitors are determined according to the energy and power performance indexes. Secondly, the multi-objective optimization function of minimizing power supply cost and power consumption and the vehicle simulation model are established in ADVISOR. Subsequently, with CE algorithm, the mean and variance of the Gaussian probability density function are updated by the continuous iterations of populations to find out the optimal Pareto solution set. Finally, the typical solutions are selected to analyze the cost, power consumption and vehicle performance. The results show that under the basic requirements, 100 optimal solutions are found, which constitute an optimal Pareto solution set. Compared with the results of (non-dominated sorting genetic algorithm-Ⅱ) NSGA-Ⅱ, the convergence and distribution of CE algorithm are better, the cost of hybrid power supply is reduced by 9.49% and the vehicle power consumption by 22.81% on average. Furthermore, the maximum error of vehicle speed is reduced by 16.15% under UDDS cycle condition, and the vehicle dynamic performance is improved significantly with the acceleration time of 100 km reduced by 7.81% and the maximum speed increased by 1.98%.

Load Forecasting and Transformer Capacity Optimization for Newly-built Traction Substation

ZHANG Liyan, KONG Zongze, BIAN Liding

2020, 55(4): 847-855. doi: 10.3969/j.issn.0258-2724.20190429

[Abstract](691)

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Abstract:
In order to predict the load of a newly-built traction substation and optimize the traction transformer capacity, Gaussian mixture model was employed for clustering the measured data of traction loads, and then the neural network is introduced to match and assign the new traction load. According to the results of clustering and matching, the new load process for new electrified railway is evaluated by the probability density and Monte Carlo method. Then based on the theory of heat transfer and the calculation of aging rates, the difference equation models of the temperature rise and loss of life is proposed to optimize the capacity of new transformer. After analyzing large amount of measured data from traction substations, the pseudo-F value of the clustered data is 12.81, and rises to 12.90 when new load is matched and assigned, indicating that the clustering and assigning methods are effective. The capacity utilization ratio in case study rises from 60% to 96% by modeling the traction transformers. Even with safety margin, the capacity should be expanded and the capacity utilization ratio is also 75%, which achieves the goal of capacity optimization and makes the best of the temperature rise and loss of life.

Co-Phase Traction Power Supply and Energy Storage Technology for Electrified Railway

HUANG Xiaohong, ZHAO Yi, LI Qunzhan, LIAO Qinyu, TANG Sida, WANG Xijun

2020, 55(4): 856-864. doi: 10.3969/j.issn.0258-2724.20181083

[Abstract](711)

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Abstract:
In order to further optimize the economical and energy-efficient operation of electrified railway traction substations, a new scheme integrated with co-phase traction power supply and energy storage technology is proposed. Based on train diagrams and historical data, and with the intent of load peak clipping, it can achieve the real-time control on the charging or discharging of energy storage devices. As a result, the power quality problems mainly due to negative sequence can be solved. Meanwhile, the equipment capacity and operation costs are less demanded, and the regenerative braking energy can be utilized effectively. By means of the measured data of the Beijing－Shanghai high-speed railway, the proposed method shows the capability of improving negative sequence. The simulation analysis and experimental verification are performed through the flywheel energy storage device. Finally, its economic performance is also analyzed. The results show that the integration of co-phase traction power supply and energy storage can eliminate the neutral sections by 50%, and the function of eliminating negative sequence depends on the power of the energy storage device. When the energy storage device power is 10% of the large value of 95% probability for traction load power, the negative sequence limit can be reduced by 10%.

Repair Strategies for Failure of Urban Rail Transit Stations

YIN Yong, CHEN Jinqu, ZHU Man, LIU Jie

2020, 55(4): 865-872. doi: 10.3969/j.issn.0258-2724.20191133

[Abstract](726)

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Abstract:
In order to improve the ability of urban rail transit (URT) systems to respond to emergencies, the effective repair strategies for URT stations under natural disasters and human attack are discussed. Firstly, the station failure caused by natural disasters and human attack are simulated by random attack and intentional attack, respectively. Secondly, the simulation repair strategy for damaged URT network is proposed. Finally, the average repair strategy, preference repair strategy and simulation repair strategy are used to repair the damaged URT network, and the effectiveness of repair strategies is measured with two categories of resiliency loss indicators: global accessibility resiliency loss and global proportion of unaffected passengers resiliency loss, which are proposed on the basis of the global accessibility and proportion of unaffected passengers. The results show that the global accessibility and proportion of unaffected passengers decrease by 2.54% and 64.82% in case of intentional attack, which are higher than 2.34% and 55.28% of random attack. Intentional attack is more harmful to the URT network than random attack. When the damaged URT network caused by random attack is repaired, the resiliency loss indicators of the simulation repair strategy are 0.009 and 0.182, which are better than 0.012 and 0.305 for average repair strategy and 0.010 and 0.197 for preference repair strategy; when the damaged URT network caused by intentional attack is repaired, the resiliency loss indicators of the simulation repair strategy are 0.009 and 0.258, which are better than 0.012 and 0.312 for average repair strategy and 0.014 and 0.354 for preference repair strategy. It indicates that the simulation repair strategy is more suitable for repairing the damaged URT network. The average slope of the simulation repair strategy curve is 0.146, which are higher than 0.092 for average repair strategy and 0.117 for preference repair strategy. Compared with conventional repair strategies, the simulation repair strategy has higher repair efficiency. Using simulation repair strategy can achieve optimal result when the repair resources are limited.

Autonomous Operation Mode of Aircrafts in Tube Air Corridor

YE Bojia, XUE Aolin, WU Xiaoyuan, DONG Yunlong

2020, 55(4): 873-881. doi: 10.3969/j.issn.0258-2724.20180678

[Abstract](507)

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Abstract:
To improve the operational efficiency of aircrafts in tube air corridor, reduce flight delays and conflicts, three representative aircraft operation modes were analyzed including, the speed-based mode, speed-independent mode and self-separation mode. Then, an autonomous operation model was built by simulation, and the correlation between important variables in the model were analyzed in a way of combining the Monte Carlo simulation and machine learning. Finally, the upper air route between Beijing Capital Airport and Guangzhou Baiyun Airport was selected as a study case. The regression models for all metrics were established and sensitivity analysis was conducted for the typical metrics of three modes. The results show that in the self-separation mode throughput and delay time are desirable while the conflict rate is relatively high with a minimum of 0.0361. The speed-independent mode leads to moderate results, which implies a low utilization of route resource with about 61.89% throughput of the self-separation mode. The speed-based mode lacks the functions of speed and separation adjustment, which is obviously affected by the initial separation.

Collaborative Optimization for Timetable and Maintenance Window Based on Two-Stage Algorithm

XU Chang’an, NI Shaoquan, CHEN Dingjun

2020, 55(4): 882-888. doi: 10.3969/j.issn.0258-2724.20180577

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Abstract:
There is mutual coupling between train timetable generation and maintenance window setting. To achieve the purpose of optimizing the train timetable structure and reasonably configuring the railway transportation capacity. According to the dynamic analysis of train timetable generation and maintenance window setting, the minimum impact of maintenance windows setting on train timetable planning is used as the objective function, and a mixed integer programming (MIP) model is built to realize the collaborative optimization of train timetable and maintenance window. To solve this complex problem, a two-stage solving algorithm including preliminary optimization and comprehensive optimization is designed. In the preliminary optimization stage, a heuristic algorithm based on experts’ experience is used to obtain the general framework of the train timetable. In the comprehensive optimization stage, the tabu search algorithm is used to obtain the global optimal solution. Finally, a case study based on Baoji−Chengdu railway line (Yangpingguan−Chengdu section) was conducted to verify the model. The results show that compared with the timetable compiled by human-computer interaction, the proposed method can effectively reduce the total residence time of all passenger and freight trains at stations by 6.19%, a total reduction of 1 355 min, of which the passenger trains and freight trains station residence time are decreased by 3.08% and 7.40%, with the total reduction time of 189 min and 1 166 min, respectively.

Condition Monitoring of Axle Box Bearing Based on Improved Safety Region

ZHAO Congcong, BAI Yang, LIU Yumei, ZHAO Yinghui, SHI Jihong

2020, 55(4): 889-895. doi: 10.3969/j.issn.0258-2724.20180584

[Abstract](640)

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To improve the operating reliability of the axle box bearing of high-speed trains, the safety region theory was introduced into condition monitoring of the axle box bearing. The traditional assessment of the safety region was transformed into determining the boundary values, aiming to avoid the influence of complex model parameters on the evaluation process of the safety region. The normalized energies of intrinsic mode functions were used to construct the eigenvector of bearing operating state, and the correlation function was used to establish the evaluation model of the safety region boundary values, where the particle swarm optimization algorithm was adopted to get optimal solution. On the basis of estimation results of boundary values, correlation function was utilized to assess the operating state of bearing quantitatively. The effectiveness was verified by the fatigue test of rolling bearing, and the method was used for condition monitoring of the axle box bearing. The results show that the detection rate and classification rate of bearing operating state of fatigue test are 0.951 and 0.939, respectively; the classification rate of operating state of the axle box bearing is 0.935, indicating that the axle box bearing is running normally, which is consistent with its actual operating state.

Adaptive Detection Algorithm for High-Speed Railway Fasteners by Vision

FAN Hong, HOU Yun, LI Bailin, XIONG Ying

2020, 55(4): 896-902. doi: 10.3969/j.issn.0258-2724.20180496

[Abstract](908)

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Abstract:
In order to achieve accurate, rapid and automatic detection of high-speed railway defective fasteners, an adaptive vision detection algorithm for high-speed railway fastener was proposed based on image processing technology. Aiming at the particularity of high-speed railway fastener images, the improved LBP (local binary pattern) operator was used to extract the salient features of fastener. Based on the prominent feature maps of fastener, the template matching algorithm was used to obtain the precise position of fastener region in the original image, and then get the sub-map of fastener and use the position information of fastener to verify the localization result; The difference between two adjacent sub-maps was used as the judgment basis, if the difference was greater than the preset threshold, the corresponding fasteners were judged as defective fasteners. The detection algorithm was applied to the real fastener image provided by the track maintenance division. The results show that the adaptive fastener detection algorithm proposed in this paper performs worst on rainy days, with a correct detection rate of 96% and a false detection rate of 0.50%; It performs best on sunny days, with a correct detection rate of 100% and a false detection rate of 0.22%; It achieves a comprehensive correct detection rate of 99% and a comprehensive false detection rate of 0.33% under different weather, lighting and environment.

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2020 Vol. 55, No. 4