西南交通大学学报

Standardisation and Evolution of Next Generation Railway Mobile Communication Systems in China

XIONG Jie

2018, 53(5): 879-885. doi: 10.3969/j.issn.0258-2724.2018.05.001

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Abstract:
At present, the industrial chain of second-generation mobile communication systems in China is in a state of atrophy. Hence, application-oriented research of next generation railway mobile communication systems (NGRMSs) is of great significance to the development of railway mobile communication systems in China. The urgency of developing NGRMSs in China is presented. The state-of-the-art popular mobile communication systems were reviewed. The adaptability of fourth generation (4G) and fifth generation (5G) communication systems for railway applications were analysed taking the requirements of future railway systems in China into consideration. Based on the analyses, the following developments were proposed. A practical and dedicated spectrum should be applied for NGRMS based on the trial line verification results. Third generation partnership project (3GPP), long-term evolution (LTE), and 3GPP group communication schemes should be used in NGRMSs for realising trunking communications in railway intervals. Furthermore, multiple wireless communication standards, including 5G communication systems, should be made functional in railway yards and terminals. Technological and equipment research should be carried out with field trial at high-speed line. Technical standards for NGRMSs should be established. Finally, research should be performed on the applications of 5G and other new technologies in railway engineering.

Standardisation and Evolution of Next Generation Railway Mobile Communication Systems in China

XIONG Jie

2018, 53(5): 879-885. doi: 10.3969/j.issn.0258-2724.2018.05.001

[Abstract](92)

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Abstract:
At present,the industrial chain of second-generation mobile communication systems in China is in a state of atrophy. Hence,application-oriented research of next generation railway mobile communication systems (NGRMSs) is of great significance to the development of railway mobile communication systems in China. The urgency of developing NGRMSs in China is presented. The state-of-the-art popular mobile communication systems were reviewed. The adaptability of fourth generation (4G) and fifth generation (5G) communication systems for railway applications were analysed taking the requirements of future railway systems in China into consideration. Based on the analyses,the following developments were proposed. A practical and dedicated spectrum should be applied for NGRMS based on the trial line verification results. Third generation partnership project (3GPP),long-term evolution (LTE),and 3GPP group communication schemes should be used in NGRMSs for realising trunking communications in railway intervals. Furthermore,multiple wireless communication standards,including 5G communication systems,should be made functional in railway yards and terminals. Technological and equipment research should be carried out with field trial at high-speed line. Technical standards for NGRMSs should be established. Finally,research should be performed on the applications of 5G and other new technologies in railway engineering.

Video Error Concealment Algorithm Based on Visual Saliency

WANG Bing, PENG Qiang

2018, 53(5): 886-892. doi: 10.3969/j.issn.0258-2724.2018.05.002

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Abstract:
In order to avoid new noticeable distortions owing to replacement information selected improperly during error concealment, this paper combines visual saliency with video processing and proposes a novel video error concealment algorithm based on visual saliency. Firstly, each video frame is divided into two parts: a region of interest (ROI) and non-ROI, by a suitable saliency detection method. The saliency information serves as an important reference to guide error concealment in the decoder, and limits the range of the replacement block to the region with similar saliency as the original image. Secondly, a saliency reduction operator is designed and applied iteratively in a loop to decrease the intensity and colour contrast of the replacement block of the non-ROI; then, the candidate replacement blocks will have good match and low saliency value. Finally, a low-complexity non-local means denoising method is used to reduce the imperfections of error concealment. The experimental results indicate that when the packet loss rate is 3%, 5%, and 10%, the proposed algorithm has increased 0.79–1.66 dB relative to the boundary matching algorithm, and 0.39–1.55 dB relative to decoder motion vector estimation. In addition, the performance of the algorithm combined with non-local means denoising improved by 0.05–0.51 dB compared to using the proposed algorithm alone.

An Improved LBP Feature for Rail Fastener Identification

WANG Qiang, LI Bailin, HOU Yun, FAN Hong

2018, 53(5): 893-899. doi: 10.3969/j.issn.0258-2724.2018.05.003

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Abstract:
An improved LBP (local binary pattern) algorithm is proposed to raise the auto-detection accuracy on fasteners. The original LBP is sensitive to noise. To solve this problem, the pixel means value and deviation are calculated, according to the different noise in different neighborhood and the measuring error is following the Gaussian distribution. Then the threshold is set to realize adaptive noise suppression, according to the deviation values. The original LBP cannot completely express the neighboring difference relationship. To avoid this defect, the proposed method gets the sampled point pairs by random sampling in neighborhood. Then LBP coding is generated through comparing the difference relationship of random point pairs. Tests are carried on fasteners images on clear, cloudy and rainy days with original and other improved LBP algorithms. The comparing results show the proposed method owns more detection accuracy. The detection accuracies increase by 3.32%, 3.27% and 4.10% independently on clear, cloudy and rainy days, which shows the proposed method can meet auto-detection on railway fasteners.

Simulation of Electromagnetic Response Characteristics and Three-Dimensional Imaging of Inverted Arch Diseases

JIANG Wujun, YIN Xiaobo, DAI Qianwei, ZHANG Bin

2018, 53(5): 900-905. doi: 10.3969/j.issn.0258-2724.2018.05.004

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A new wave field analytical approach, based on forward simulation and migration imaging theory using rotated staggered grid (RSG) algorithm, is proposed for enhancing the imaging efficiency and detection precision of inverted arch diseases in tunnelling using three-dimensional electromagnetic (EM) waves technique. The RSG algorithm was employed to establish an inverted arch numerical model with typical diseases. The complex propagation simulation process of EM waves was performed in the inverted arch and bottom structures, and the gathers and electromagnetic response phenomenon of the EM waves were analysed, taking their attenuation, diffraction, and dispersion into consideration. Next, based on the RSG imaging theory, the three-dimensional migration imaging of the simulated data of inverted arch diseases was performed, using the local depicted image processing and three-dimensional slicing technique. The results reveal an electric field of amplitude greater than 6.5 × 10⁴ V/m at the steel bars and steel bracing concrete medium, which within inverted arch. However, the amplitude of electric field at the diseases underneath the inverted arch is approximately 6.0 × 10⁴ V/m. Comparing the two values, it was concluded that the proposed approach provides higher imaging resolutions in both the lateral as well as vertical directions. Moreover, the extent of incompactness and undulation of the weak interlayer is well depicted, which will result in a great improvement of the imaging accuracy of EM waves while detecting inverted arch diseases.

Theoretical Study on Fatigue Stress Spectrum of Longitudinal Connected Slab Track on Bridge

XU Qingyuan, LIN Qingteng, FANG Ziyun, LOU Ping, YANG Rongshan, CHEN Wei, ZHANG Ze

2018, 53(5): 906-912. doi: 10.3969/j.issn.0258-2724.2018.05.005

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Abstract:
To obtain the fatigue stress spectrum, the calculation theory is proposed for longitudinally connected slab tracks on a bridge during service life. The temperature field calculation model of longitudinally connected slab tracks, the multi-scale high speed train-longitudinal connected slab track-bridge three-dimensional finite element coupling dynamic model, and the longitudinal connected slab track-bridge-piers and abutments longitudinal interaction model, which considers the interaction between steel bars and concrete in ballastless tracks, the crack and closure effects of concrete in the ballastless track, as well as the combined effects and time-varying characteristics of loads of the ballastless track, were established and verified. On the basis of these verifications, the calculation theory of the fatigue stress spectrum of longitudinally connected slab tracks on a bridge was proposed. The following conclusions were obtained: firstly, the stress time history and fatigue stress spectrum of steel bars and concrete in a ballastless track during service life can be obtained using the proposed calculation theory; secondly, the calculation theory can consider various loads and investigate the fatigue failure mechanism and its influence on depth; and lastly, the calculation theory can provide an important basis for enriching and perfecting the design theory of ballastless tracks in China.

Influence of Interface Crack on Impact Dynamic Properties of CRTS III Slab Track-Subgrade System

SONG Xiaolin, LÜ Tianhang, PEI Chengjie

2018, 53(5): 913-920. doi: 10.3969/j.issn.0258-2724.2018.05.006

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Abstract:
To investigate the influence of the interface crack on the dynamic characteristics of high-speed railway infrastructure, a wheel-drop test was performed using the full-scale experimental platform of CRTS III ballastless track-subgrade system. The distribution of the one-sided interface crack between the slab and self-compacting concrete layer was measured and summarised. The 3D dynamic finite element model of the CRTS III track-subgrade system with a one-sided interface crack was established using the ANSYS/LS-DYNA software. The influence of the interface crack subjected to the wheel-drop load was investigated on the basis of comparisons between the experimental data and numerical results. The results indicate that the average width and height of the interface are 28.18 cm and 2.15 mm, respectively. The crack width has a stronger effect than the crack height on the infrastructure dynamic reaction. When the crack width increases within a range of 0 to 800 mm, all the displacements of the infrastructure and the accelerations of the rail and slab increase proportionally with the increase of the crack width. When the crack width approaches the distance between the rail and slab edges in the lateral direction, the accelerations of the filling layer, concrete basement, and subgrade reach their respective maxima. The maximum icrements of the displacement and the acceleration for the track and the subgrade are both occurred in the slab, which are respectively 56.8% and 143.3%. All the displacements and accelerations of the track and subgrade slightly increase with the increase of the crack height from 0 to 3 mm, and the maximum increments are 8% and 12%, respectly. The influence of the crack is more remarkable on the dynamic properties with the decrease of the distance between the infrastructure level and the crack locsation.

Vertical Stability of Longitudinal Continuous Ballastless Track Under Temperature Variation

LIU Xiaokai, LIU Xueyi, XIAO Jieling, DI Yinqiao, YANG Rongshan

2018, 53(5): 921-927, 944. doi: 10.3969/j.issn.0258-2724.2018.05.007

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To study the vertical instability form and process of a longitudinal continuous ballastless track, the arch curve of the slab that is influenced by temperature can be deduced based on the deflection differential equation of the Euler beam. The equation of the arch camber and wavelength of the slab was obtained from the arch curve. The equilibrium path of the slab with the initial arch was analysed based on stationary potential energy. Compared with the method of assuming a deformation, the method of solving differential equations is more accurate, and the error is reduced by nearly 30%. The course can be divided into three stages: steady, expansion, and destabilization. The limit of the steady and expansion stages decreases along with the increase of the initial arch camber. The effect of the release of slab temperature on the equilibrium path shows that the path appears as a stiffening stage, and the larger the friction coefficient, the earlier the stage occurs, whereas it has little effect when the deformation is small. The larger the initial camber, the greater the allowed wavelength is. When the initial arch is smaller than 50 mm, the vertical instability of the slab does not occur.

Effects of Fastener Stiffness of Monolithic Bed Track on Vertical Rail Sound Power Characteristics

SHENG Xi, ZHAO Caiyou, WANG Ping, CHEN Junhao, WEI Xiao

2018, 53(5): 928-936, 1094. doi: 10.3969/j.issn.0258-2724.2018.05.008

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To study the effects of fastener stiffness of the monolithic bed track on vertical rail sound power characteristics, the plane half-track model was built and the spectral element method was utilised to obtain rail mobility. A periodic track-substructure model was also built, and the spectral transfer matrix method was utilised to obtain the track decay rate. Combining the results of both rail mobility and track decay rate, the power level of rail sound under unit harmonic point excitation was calculated, and the effects of fastener stiffness on the relative rail sound power level were investigated. The results show that the power level of rail sound increases with the increase in the frequency in the low-medium frequency range. The power level of rail sound has a peak at the centre frequency of 800 Hz in the one third octave band. With the decrease in fastener stiffness, the power level of rail sound increases, which is more obvious in frequency range under 400 Hz. The level is increased more significantly when the stiffness gets a larger decrease. The rail sound power level mostly increases at the rail bending resonance frequency because the rail mobility amplitude increases and the track decay rate decreases deeply.

Study on Fatigue Strength of Welds in Bogie Frame Based on Structural Stresses

ZHOU Zhangyi, HUANG Yunhua, YANG Yang, DING Junjun

2018, 53(5): 937-944. doi: 10.3969/j.issn.0258-2724.2018.05.009

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In order to solve problems in application of the permissible fatigue strength data for welds in bogie frames, comparisons of different structural stress approaches and data were carried out. The relations and differences in the measurement methods of weld structural stress, permissible stress amplitude, survival probability of design value, mean stress modification, fatigue strength improvement of weld improvement and determination of limit permissible stress were compared. And the fatigue diagrams and S-N curves based on measured structural stress for Q345 steel welds were established. From the research conclusions, the fatigue diagrams and S-N curves based on measured structural stress for Q345 steel welds were established. The results show that the measuring method of weld structural stress provided by B12/RP17, the end of stress gauge, length of 6 mm, should be against the weld toe, can be continually used. It is recommended that the basic two data sets of IIW (International Institute of Welding) FAT100 and FAT90 can be used as reference to establish the more reasonable permissible fatigue strength data based on structural stress along with its mean stress and fatigue strength improvement of welds modification methods. For a fatigue diagram with 2 × 10⁶ stress cycles, the limit permissible stress can be determined by reducing the yield strength of the base material by the corresponding safety factor according to DVS 1612.

Wear and Damage Mechanism of Wheel-Rail Materials Based on Contact Zone Energy Dissipation

GUO Lichang, YANG Bin, HE Chenggang, ZHU Wentao, WANG Wenjian, LIU Qiyue

2018, 53(5): 945-950. doi: 10.3969/j.issn.0258-2724.2018.05.010

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In order to establish a uniform standard for wheel-rail wear and damage experiments, an analytic technique for wheel-rail wear and damage is put forward on the wear and damage mechanisms. As there is currently no wheel-rail wear and damage experiment standard, the wear and damage results from various current experimental methods are comparatively analyzed. Using the results of this comparative analysis, an analysis method for wheel-rail wear and damage mechanisms based on contact spot energy dissipation is proposed. Furthermore, the change rule of the relationship between contact spot energy dissipation unit area and wear rate is discussed for different wheel-rail materials and experimental methods. The results show that, on the basis of the relationship between contact spot energy dissipation unit area and wear rate and the damage characteristics of wheel-rail materials, wheel-rail wear can be divided into three types: mild wear, severe wear, and disastrous wear. Furthermore, the curve between contact spot energy dissipation unit area and wear rate can be used to predict wheel-rail wear in practical application. The wear rate and type of damage of wheel-rail material are analyzed accurately by the wheel-rail contact spot dissipation energy, which as be used to the data comparative analysis of wheel-rail wear and damage.

Analysis of Guided Wave Behaviour in Rails Using Numerical or Analytical Models

DAI Feng, LIU Xueyi, ZHU Ying, THOMPSON David, YANG Jizhong

2018, 53(5): 951-957, 1016. doi: 10.3969/j.issn.0258-2724.2018.05.011

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The vibration of rails is a major contributor to railway rolling noise, and consists of different guided waves that propagate along the rail. To study the dynamic behaviour of a railway track, models based on the Timoshenko beam theory and the waveguide finite-element method were established. The solution procedures to obtain the free wave response and the forced response for each model were determined. The characteristics of guided waves in rails, such as wavenumber, group velocity, mobility, and decay rate, were analysed based on two different models. The waveguide finite-element model, which includes all the features of rail cross-section deformation, makes it possible to identify eight kinds of guided waves in rails within a frequency range of as much as 6 kHz. Moreover, the phenomena of wave mode exchange and group velocity exchange between waves are discussed, as well as the peak in the mobility caused by the excitation of the higher-order wave mode. The Timoshenko beam model can identify five of these wave modes, including those for bending, torsion, and extensional waves, but it cannot identify the ones associated with cross-section deformations that cut on at frequencies of more than 1.5 kHz. The Timoshenko beam model provides acceptable results for point mobilities of as much as 2 kHz.

Dynamic Influence of Gap Height of CA Mortar on Track Structure Under Mixed Traffic Conditions

LI Xiao, REN Juanjuan, LIU Xueyi, DENG Shijie, WANG Ji, WANG Zeping

2018, 53(5): 958-965. doi: 10.3969/j.issn.0258-2724.2018.05.012

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For CRTS I prefabricated slab tracks used in mixed passenger-freight railway, the gap between the CA mortar and the track slab is a common disease. In order to analyse the influence of the gap height of CA mortar on the dynamic response of the track structure, a vertical coupling model of CRTS I slab track with gaps between CA mortar and track slab is established based on the vehicle-track coupling dynamics and the substructure modal superposition method. Firstly, the self-vibration characteristics data of the track component sub-structure, which was calculated by ANSYS, was inputted into SIMPACK, and the track components were connected through a force element to form the track system. Then, the train and rail subsystems were coupled via data transmission of the displacement and force between the nodes of the wheel-rail contact surface and flexible rail. The results show that with the increase in gap height, there is a significant increase in the dynamic displacement of the rail, vibration response of the track slab, and the dynamic stress of the CA mortar. For CRH380, when the gap height was increased to 1.0 mm and 2.0 mm, the rail displacement increased by 0.24 mm and 0.27 mm, respectively. At the same time, the vibration levels of the slab increased by 21.0 dB and 21.7 dB at a frequency of 25 Hz, and the maximum dynamic stress of the CA mortar at both ends of the gap reached 0.2 MPa. Thus, when the height of the gap exceeds 1.0 mm, the influence of the gap on the dynamic response of the track structure tends to be gentle. However, for SS7E, when the gap height was increased to 1.0 mm and 2.0 mm, the displacement of the rail increased by 0.48 mm and 0.66 mm, respectively. Simultaneously, the vibration level of the slab increased by 15.5 dB and 19.4 dB at a frequency of 8 Hz, and the maximum dynamic stress of the CA mortar at the ends of the gap reached 0.24 MPa and 0.36 MPa, respectively. Thus, when the height of the gap exceeds 1.0 mm, there is still a considerable increase in the influence of the gap on the dynamic response of the track structure.

Failure Analysis on Surrounding Rock of Soft-Layered Rock Tunnel Using Coupled Continuum-Discrete Model

XU Guowen, HE Chuan, WANG Yao, CHEN Ziquan

2018, 53(5): 966-973. doi: 10.3969/j.issn.0258-2724.2018.05.013

[Abstract](465)

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In order to study the failure mechanism of layered surrounding rock after tunnel excavation, taking the Zhegu mountain tunnel of Wenma highway as an example, a new numerical approach is put forward based on continuum-discrete coupling method. The failure patterns of surrounding rock under different geo-stress fields and bedding spacing are obtained through this method. The results show that: slipping and opening failure occurs on joint surface because of its low strength after stress redistribution during tunnel excavation. Then, stress field is disturbed furtherly and this disturbance leads to tensile failure of rock matrix; Micro-cracks in rock mass increases with the decrease of lateral pressure coefficient for the same stress level. When the lateral pressure coefficient is 1.00, 0.80, 0.67, 0.57, and 0.50, the total number of micro-cracks is 304, 391, 602, 999, and 1240, respectively. When the bedding spacing is 0.6 m, bedding has a controlling influence on the failure mode of surrounding rock, while this influence is weakened and the failure mode is similar to that of homogeneous surrounding rock with the increase of bedding spacing from 0.6 m to 1.2 m.

Approximate Analytical Method for Skin Friction of Tunnel-Type Anchorage Used in Suspension Bridge Engineering

XIAO Shiguo, ZHAO Linzhi

2018, 53(5): 974-981. doi: 10.3969/j.issn.0258-2724.2018.05.014

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Based on the theory of elasticity, the calculation formulas for the skin friction stress of tunnel-type anchorages used in suspension bridge engineering is provided, taking into account the boundary conditions on the two ends of the anchorage. Firstly, an analysis model is established in light of the practical loading conditions on the anchorage. Then, considering the conditions that the shear stresses on the two ends of the anchorage are individually equal to zero and that the entire anchorage is in a static equilibrium state, a calibrated computation formula for the skin friction stress of the anchorage is proposed based on the shear stress expression of Mindlin solution. Finally, a test model is cited to verify the acceptability of the proposed method, and the distribution characteristics of the skin friction stress are further revealed by using a practical example of tunnel-type anchorage. The analysis results show that the distribution of the skin friction stress along the axial direction of the anchorage is unimodal. The skin friction stress computed using the proposed method agrees well with that obtained using three-dimensional numerical simulation method. The average error between the maximum skin friction stresses of the two methods is about 8.5%. The calculation results also show that the skin friction stress is very small owing to the effect of self-weight load of the anchorage if the actual tension force on the main cable is close to the design value; however, the effect decreases with increase in tension force （e.g. 3.5 times the design value）. In particular, the local interface between the anchorage and the surrounding rock is likely to be in a failure state with increase in the tension force. This causes a corresponding adjustment of the skin friction stress to keep the entire anchorage in balance.

Numerical Analysis on Seismic Performance of Load Bearing 3D Walls

HUANG Qunyi, LIANG Dong, HUANG Yanxia, RUI Yi

2018, 53(5): 982-988. doi: 10.3969/j.issn.0258-2724.2018.05.015

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To investigate the seismic performance of load bearing 3D walls under low cyclic reversed loads, numerical analysis for load-displacement curves of load bearing 3D walls under low cyclic reversed loads are performed by using the solid model based on ABAQUS software. The simulation results agree well with the test results in literature. The influences of the height-width ratio, concrete thickness and concrete strength on the seismic performance of load bearing 3D walls under low cyclic reversed loads are analyzed. The analytical results indicate that height-width ratio is the major influence factors on the seismic performance of the walls. The flexural failure is more likely to observe in the wall with large aspect ratios, which increases the ductility and energy dissipation capacity of structure. When concrete layer thickness increased from 30 mm to 40 mm and 50 mm, the wall’s ultimate load-bearing capacity increased from 208 kN to 253 kN and 279 kN. Similarly, when the concrete layer strength increased from C25 to C30 and C35, the ultimate strength of the element accordingly increased from 236 kN to 253 kN and 260 kN.

Shaking Table Test of Model Structure with Viscous Dampers Subjected to Random Earthquake Ground Motions

MEI Zhen, GUO Zixiong, HOU Wei, LI Haifeng, WANG Haifeng

2018, 53(5): 989-999. doi: 10.3969/j.issn.0258-2724.2018.05.016

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To investigate the control efficiency of structures installed with viscous dampers subjected to random excitations, shaking table tests on vibration control of a randomly base-driven structure with and without dampers, were conducted. In the experiments, the base excitation was represented by a physical stochastic ground motion model. By comparing the probabilistic characteristics of the responses of the controlled and uncontrolled structures, such as the mean, standard deviation, and the probability density function, the seismic mitigation effect of viscous dampers was systematically analysed. The results show that the interstory drifts of the controlled structure are obviously smaller than those in the uncontrolled cases, and interstory shear forces are reduced to some extent in the root-mean-square sense, while absolute accelerations of most floors increase to different degrees. It was also found that the variability of dynamic responses of the model structure subjected to random earthquake ground motions is very significant, and the control efficiency is different when various representative time histories of ground accelerations are adopted as seismic inputs. Moreover, the working viscous damper-steel support system can provide additional stiffness and damping to the controlled structure, and thus make the structural dynamic characteristics change, which leads to a change in the structural seismic response. Finally, the mean and standard deviation of the bottom floor displacements of the controlled structure are considerably mitigated throughout the whole duration of ground motions, and the distribution width and shape of the probability density function of the displacements at each moment of time, change significantly compared with those in the uncontrolled cases.

Numerical Simulation on Stability Development of Geogrid Reinforced Widening Embankment with Rigid Retaining Wall

JIANG Xin, CHEN Tao, WU Yu, ZHU Qijiong, GENG Jianyu, QIU Yanjun

2018, 53(5): 1000-1008. doi: 10.3969/j.issn.0258-2724.2018.05.017

[Abstract](446)

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Rigid retaining walls are widely used in highway widening embankments in mountainous regions. To interpret the dynamic development law and mechanics of geogrid reinforced widening embankment with the rigid retaining wall in mountainous region, combined with the particularity of the rigid retaining wall, the finite element software Phase² and strength reduction method were employed to analyse the stability of geogrid reinforced highway widening embankment in such regions. The interactions between soil and structure were introduced in the established numerical model. The dynamic development law of the mechanical response of the filling, geogrid and filling-geogrid interface, and their influences upon the embankment stability were also discussed. The findings regarding the reinforcement effect obtained from the numerical simulation were verified macroscopically using the geotechnical centrifuge model test results. The results showed that the embankment surface differential settlement was reduced by 47.1%, the maximum wall extraversion was reduced by 65.4%, and the embankment stability factor was increased by 12.8% with the geogrid reinforcement. With the increase in the shear reduction factor, the joint elements between the filling and the geogrid failed (slipped), but this slip was not responsible for the failure of the subgrade. Thus, the axial tension decreased suddenly owing to the failure of the geogrid in the upper layer, which was located outside the edge of the balancing platform. The tensile failure of the geogrid induced the instability and failure of widening embankment.

Wind Tunnel Test of Tension Effects on Vibration Responses of Catenary System

XIE Qiang, ZHI Xi

2018, 53(5): 1009-1016. doi: 10.3969/j.issn.0258-2724.2018.05.018

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The tensions of contact wire and messenger wire are important to the wind-induced vibration responses of a catenary system. Based on the design of an actual railway project, a five-post and four-span aero-elastic catenary system model for a wind tunnel test was designed according to the similarity theory. A wind tunnel test on the aero-elastic catenary system model with four different types of contact wire and messenger wire tension combinations was carried out. The characteristics of the wind-induced vibration responses were studied by the measured acceleration and displacement responses in the test. The results demonstrated that the natural frequency of the contact wire increased, and its wind deflection decreased with the increase in the tensions on the contact wire. The cantilever and the mast were hardly influenced by the tensions on the wires. The catenary system is a wind-sensitive structure. It is an effective method for decreasing the wind deflection on the contact wire by increasing the tensions on the contact wire and the messenger wire.

Shear Rheological Characteristics and Nonlinear Constitutive Model of Serrate Structure Surface

TIAN Guanghui, SHEN Mingrong, YANG Ruifang, ZHANG Qingzhao, WANG Zhen

2018, 53(5): 1017-1025. doi: 10.3969/j.issn.0258-2724.2018.05.019

[Abstract](462)

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In order to investigate the creep and stress relaxation characteristics of rock mass discontinuity with different slope ratios, the creep and stress relaxation tests of dentate discontinuity poured by cement mortar on the condition of shear stress are carried out by using a biaxial creep machine. First, the comparison of creep and relaxation was made. Secondly, the establishment and solution of nonlinear rheological constitutive model were discussed. Final, nonlinear rheological equation was used to fit the test curve. According to the test results, both creep curves and relaxation curves can be divided into three stages: the instantaneous stage, attenuation stage, and stable stage. From the energy perspective, creep is the process of energy accumulation and dissipation, and stress relaxation is the process of energy dissipation. The constitutive equation of nonlinear rheological model should be deduced by using rheological theory. The initial condition of creep is different to that of relaxation when the finite integration method and Laplace transformation is used to solve equations. The creep equation and relaxation equation of the nonlinear-parameters Maxwell model are obtained by determining the relation between the viscosity coefficient and time, and the equation curves agree with the test results. The parameter values of the creep equation is different to that of relaxation equation, which reveal that the creep properties are not equivalent to the relaxation properties and creep and relaxation cannot be mutual conversion.

Soil Compaction Effect of Bagged Grouting Piles in Saturated Soft Clay Subgrade

LI Qiyue, WU Zhengyu, ZHANG Dianji

2018, 53(5): 1026-1032, 1047. doi: 10.3969/j.issn.0258-2724.2018.05.020

[Abstract](433)

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To study the soil compaction effect of bagged grouting piles in saturated soft clay roadbeds, field tests were conducted on roadbeds reinforced with bagged grouting piles to analyse the displacement of the soil and the applied super-static pore pressure occurring during pile formation. First, the horizontal displacement of the soil was monitored by using the inclined pipe, and the distribution characteristics of soil displacement and variation in soil displacement with grouting pressure and time were obtained. Second, the super-static pore pressure in the soil was monitored by using a sensor to measure the hole pressure, and the distribution and trend of the super-static pore pressure were obtained. The test results indicate that the horizontal displacement of the soil around the pile has a saddle-shaped distribution, and the soil exhibits maximum displacement at a distance of 0.1–0.3 times and 0.8–1.0 times the pile length. The range of influence of the horizontal displacement caused by soil compaction is approximately six times the pile diameter. After the pile has been cured, the grouting pressure has little influence on the compaction effect. Furthermore, after curing, the horizontal displacement of the soil around the pile shows a significant rebound, which amounts to approximately 40%–60% of the displacement on the day of grouting. The super-static pore pressure dissipates rapidly during the first 10 days and decreases linearly with increasing distance from the centre of the pile. The range of influence of the super-static pore pressure is approximately 10 times the pile diameter.

Correlation Analysis between Clay Mineral Composition and Shear Strength

WANG Jinshu, WANG Shiming, HONG Meiling, LI Yongzhi, WU Guang, LI Lin, ZHANG Jilong

2018, 53(5): 1033-1038. doi: 10.3969/j.issn.0258-2724.2018.05.021

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Abstract:
The influence of mineral composition on soil shear strength was investigated in this study. Using scanning electron microscopy and X-ray diffraction measurements, the composition and microstructure of pure clay minerals was obtained. Single-component clay samples were manually prepared with different initial water contents, and direct shear tests were performed to analyse the influence of moisture content on the cohesive force and internal friction angle of single mineral viscous soil. The results show that the cohesion and friction angle of kaolinite decrease monotonically with an increase in water content. Illite and montmorillonite exhibit peak cohesion when the water content is 18% and 25%, respectively. When the moisture content is approximately 20%, the maximum internal friction angle for montmorillonite appears.

Probabilistic Risk Analysis of Multi-Climatic Coupling Sections of Expressway in Fog Area

LI Xiaolei, TANG Boming, SONG Qianghui

2018, 53(5): 1039-1047. doi: 10.3969/j.issn.0258-2724.2018.05.022

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Abstract:
The fog sections of an expressway often experience fog accompanied by rain, ice, or snow, as well as other complex climatic conditions. Therefore, evaluating and researching the accident risk of an expressway with consideration of the coupling of complex factors such as fog, rain, snow, and ice has great significance. On the basis of field theory, a risk field model of an expressway in a fog area was established, and the parameters and risk classification of coupling sections in fog and multi-climate areas of the expressway were studied based on the model. First, rasterization of the typical fog sections of the expressway was performed to construct the risk field. Then, the method of probabilistic risk analysis （PRA） was used to analyse the risk field in the fog area and the chain risk, and the numerical model of the risk field in the fog area was constructed. Finally, the model was validated for the G5 Ya-an to Shi-mian expressway. The results show that field theory is more suitable for risk analysis of multi-climate-coupled fog areas of the expressway. The risk field in the fog area of the expressway is a number field as well as an unstable field, and its instability mainly manifests as the time variability of each climatic parameter in the fog area. Based on field theory, the risk classification index of the multi-climatic coupling section of the expressway in the fog area was provided, the index was matched with the current domestic meteorological warning classification, and the risk of the fog section was classified into four levels, with the traffic risk level being the highest.

Time Variant Characteristics of Piston Wind for Billboards Affiliated with Subway Tunnels

ZHU Fu, YU Zhixiang, CAO Ruizhou, LIU Zhixiang

2018, 53(5): 1048-1057. doi: 10.3969/j.issn.0258-2724.2018.05.023

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Abstract:
In order to predict the time-variant characteristics of a piston wind for billboards in subway tunnels, a simulation based on computational fluid dynamics was employed to solve the three-dimensional unsteady flow problem. User-defined functions were used to define the movement manipulating the train and the dynamic mesh, thereby leading to the establishment of a more accurate simulation method for the piston wind. The rationality of the method was verified according to previously conducted experiments and simulations by Kim. A full-scale tunnel model was then set up based on a real tunnel cross-section. Different train speeds were taken into account to analyse the flow field changes caused by train movements, thus focusing on the changes of the static pressure on the billboard surfaces in subway tunnels. The results show that speed increases cause the static pressure on the billboards to increase significantly, thus changing from positive to negative when the train passes by. The static pressure amplitudes exceed 500 Pa for train speeds of 80 km/h and 1 kPa for some subways at an operating speed of 120 km/h.

Investigation of Traffic-Information Quantity Measurement Based on Information Theory

LUO Chen, LIU Lan, ZHANG Ling

2018, 53(5): 1058-1064. doi: 10.3969/j.issn.0258-2724.2018.05.024

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Abstract:
In view of the lack of voice-information quantification and that road-sign information measures have no effect on the road network size under actual travel conditions, information theory was introduced to construct a voice-information volume measurement model and an image-information volume measurement model. An experimental road network, including 23 sets of different amounts of information, was designed to measure the driver reaction time under different information volumes. The results of the study demonstrate that when the total amount of traffic information is 52.22 bits and 57.90 bits, there is a regional response-time peak. When the total amount of information is in the 50.74 bit to 57.38 bit interval, it can help drivers recognize traffic information without generating information overload. When the information volume is 45.10 bits and 49.70 bits, the voice-information volume should be in the range of 5.12 bits to 10.24 bits to reduce the driver reaction time. When the voice-information volume is 5.12 bits, the mark information is in the range of 49.70 bits to 54.30 bits, and it can improve the driver awareness of traffic conditions.

Study of Aerodynamic Characteristics in Detached Cooling Module Based on Cluster Analysis

FU Jiahong, ZUO Qiang, ZHANG Xufang, XIAO Baolan, SUN Shuli, LU Qianqian, ZHANG Yu

2018, 53(5): 1065-1071. doi: 10.3969/j.issn.0258-2724.2018.05.025

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Abstract:
Numerical and experimental studies were conducted to investigate the cluster effect of aerodynamic characteristics in detached cooling modules with multiple types of heat exchangers, considering the typical dual heat exchangers in construction machinery cooling modules as examples. The porous media model was used to simulate the heat exchanger, and the multiple reference frame method was used to simulate fan performance. Numerical analyses and further experimental research of the cooling modules were conducted under four different heat exchanger arrangements. Using numerical methods, the control method for the aerodynamic characteristics of an independent cooling module was studied by adjusting the area and thickness ratios of the heat exchanger. The experimental and numerical simulation results show that the aerodynamic characteristics of the independent cooling module is unique: when the two heat exchangers are arranged in opposing positions, the aerodynamic drag is equal regardless of the inclination angles of the exchangers. Numerical simulations of the active control method for aerodynamic characteristics show the following: Compared to modifying the area ratio of the heat exchanger, thickness ratio modification is a active control strategy because the flow rate ratio changes more gently and is less affected by the fan speed. Based on these findings, the experimental correlations among cooling air volume, aerodynamic drag, and structural parameters of the two heat exchangers are obtained.

Algorithm Based on Cooperative Vehicle Infrastructure Systems

LUO Wenhui, DONG Baotian, WANG Zesheng

2018, 53(5): 1072-1077, 1086. doi: 10.3969/j.issn.0258-2724.2018.05.026

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Abstract:
In order to determine the problem of vehicle positioning deviation caused by a lack and delay of the positioning signal, a cooperative map-matching（CMM）algorithm, based on the cooperative vehicle infrastructure system, is proposed in this paper. First, the information obtained by GPS and that obtained by vehicular dead reckoning（DR）were fused to obtain the initial position of cooperative map-matching using an extended Kalman filter（EKF）. Then, vehicle information was exchanged and shared based on dedicated short-range communication （DSRC）. On the basis of an electronic map, the further positioning of vehicles was accomplished using road constraints. In order to verify the effectiveness of the proposed algorithm, an environment to simulate real scenes was set up to conduct the experiments. The experimental results demonstrate that the average positioning deviation of vehicles at intersections using EKF, which fuses data obtained from GPS and DR, is 9.90 m. The positioning deviation decreased by 30.87%, when compared with the average deviation of GPS, which is 14.31 m. The proposed CMM algorithm has an average position deviation of 4.5 m when the number of vehicles involved is 7, and 2.75 m when the number of vehicles involved is 10. The positioning deviation decreased by 69.74%.

Optimized Design of New Coupling Mechanism for Electric Vehicles

SUN Yue, TAN Ruoxi, TANG Chunsen, WANG Zhihui, DAI Lin

2018, 53(5): 1078-1086. doi: 10.3969/j.issn.0258-2724.2018.05.027

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Abstract:
Aimed at the application of wireless charging in electric vehicles, a type of concave-convex magnetic coupling mechanism is proposed, which realizes better coupling characteristics and improves the system power transmission capacity. Based on the finite element theory and the COMSOL simulation software, a model of the concave-convex coupling mechanism was developed. According to the height of the convex magnetic core at both ends of the coil, the length ratio of the convex magnetic core at both ends of the coil, and the core length, the relationship between the length and the width of the core and the main structural parameters such as the thickness of the core was analysed and optimised from the perspective of mutual inductance and coupling coefficient, respectively. The magnetic saturation after thinning is also discussed. The feasibility of the coupled mechanism and the advantages of the magnetic field distribution and coupling characteristics were verified by the simulation and experimental results. The output power and efficiency of the system improved by 37% and 10%, respectively, compared with those of the original strip core structure.

Operation Mode of Solar and Untreated Sewage Source Heat Pump System for Heating Biogas Digesters

GUO Pei, MA Rongjiang, YU Nanyang

2018, 53(5): 1087-1094. doi: 10.3969/j.issn.0258-2724.2018.05.028

[Abstract](361)

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Abstract:
A solar and untreated sewage source heat pump system (SUSSHPS) for heating biogas digesters was designed because of the high investment and difficult operation of current heating systems. To determine the optimal operation mode, three operation modes were designed: annual middle-temperature fermentation mode (mode 1), annual high-temperature fermentation mode (mode 2), and summer high-temperature fermentation and winter middle-temperature fermentation mode (mode 3). The three modes were evaluated from four perspectives: energy consumption, environmental protection, economy, and gas production. Finally, a comprehensive evaluation system of SUSSHPS operation mode was built based on comprehensiveness and independence. The evaluation index was a comprehensive weight calculated via an improved entropic coefficient method. The results indicate that model 3 (0.379 5) > model 2 (0.327 5) > model 1 (0.293 0), thus model 3 is the optimal operation mode.

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2018 Vol. 31, No. 5