西南交通大学学报

Seismic Response of Continuous Beam-Arch Bridge under Spatially Varying Ground Motions

LI Xiaozhen, YANG Dehai, LEI Kangning, XIAO Lin, DAI Shengyong

2021, 56(2): 221-228. doi: 10.3969/j.issn.0258-2724.20190400

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Abstract:
In order to investigate the dynamic responses of a long-span continuous beam-arch bridge subjected to multi-support and multi-dimensional ground motions, a finite element model for a concrete-filled steel tubular arch bridge with a span of 139 m in South China was built using OpenSEES software. The spatially varying ground motions were artificially simulated to investigate the effects of the coherency loss, local site conditions, and wave-passage. The results show that the spatially varying ground motions have significant influence on the dynamic responses of bridge, and considering uniform excitations only might overestimate the responses. The influence of the local site effect on the seismic responses of the bridge is the most prominent. With softer site conditions at the support points, the inner forces and displacements responses of each part of the bridge are greatly increased. Weakly correlated ground motions can lead to larger arch inner forces and smaller arch peak displacements. Although the wave-passage effect has no obvious tendency, its influence is not negligible. Only considering the wave-passage effect may seriously underestimate the seismic responses of the bridge substructure. Therefore, the spatially varying ground motions should be considered in the seismic responses analysis of long-span bridges, and the effect of each factor should be accurately measured.

Seismic Responses Analysis of Train-Track-Bridge System Considering Pile-Soil Interaction

LEI Hujun, HUANG Jiangze

2021, 56(2): 229-237. doi: 10.3969/j.issn.0258-2724.20190694

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Understanding the influence of pile-soil interaction on seismic responses of a train-bridge system is necessary for studying the safety of trains running over high-speed railway bridges under earthquake. Based on the train-track-bridge coupled vibration theory, the Winkler foundation beam is used to simulate the pile group foundation and spring parameters are calculated by m method. A complete train-track-bridge-pile group coupled vibration model with seismic excitations is established, and a simulation analysis program is developed. Taking a (88 + 168 + 88) m prestressed concrete continuous rigid frame bridge as an example, a pile group foundation model considering pile-soil interaction, a rigid foundation model and an elastic foundation model are established respectively, and the last two models are used for comparison with the first one. By inputting three typical seismic waves, the coupled vibration responses of the three models are calculated and compared, and the pile-soil interaction is studied. The results show that the influence of pile-soil interaction on the lateral dynamic responses of the bridge, track and train subsystems under earthquake is greater than that on the vertical one, and the influence on the dynamic responses of the bridge and track subsystems is greater than that of the train subsystem. For the calculation conditions of this paper, the dynamic responses of bridge, track and train subsystems will be smaller if pile-soil interaction is not considered; specifically, the derailment coefficient, wheel load reduction rate and wheel-axle lateral force of the train are 5.8%, 8.6% and 9.0% smaller, respectively. Besides, the influence of pile-soil interaction on the safety index of the train will not change with the train speed. The obtained results can provide reference for the seismic design of high-speed railway bridges in earthquake areas.

Effect Mechanism of Central Slot Width on Vortex-Induced Vibration Characteristics of Streamlined Box Girders

CHEN Xingyu, XU Xinyu, ZHENG Xiaolong, ZENG Yongping, LI Yongle

2021, 56(2): 238-245. doi: 10.3969/j.issn.0258-2724.20190505

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The streamlined box girders with central slots usually have good flutter stability, but the vortex-induced vibration (VIV) performance of such box girders at large angles of attack is not clear. For the streamlined box girder section of a long-span bridge, the flow field characteristics and VIV performances of the box girders with five different central slot widths were analyzed by numerical simulation method. Then the influence law of the central slot width on the VIV performances of box girder at large angles of attack were investigated, and the corresponding aerodynamic mechanisms were discussed systematically according to the changes of static and dynamic flow fields. The results show that the drag coefficient of the closed box girder is always the smallest for the wind attack angles in the range of −10°~10°, while the lift coefficient of the closed box girder is generally larger than that of the slotted box girder. The width of central slot has a significant effect on the VIV performance of the box girder, and the VIV amplitude of box girder decreases with an increase in slot width. When L/B changes from 0 to 0.20, the VIV amplitude varies by 40.9%. The change of the slot width will affect the movement of large vortices on the upper surface of a box girder and also affect the separation degree of incoming flow in the central region of the box girder, making VIV amplitude of streamlined box girder change.

Rapid Recognition of Rock Mass Fractures in Tunnel Faces

LENG Biao, ZHANG Yi, YANG Hui, HOU Gaopeng

2021, 56(2): 246-252, 322. doi: 10.3969/j.issn.0258-2724.20190749

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Tunnel faces contain much geological information, which, if fully extracted and analyzed, will help to evaluate the geological state of tunnel engineering and guide tunnel design and construction. In this paper, rock mass crack detection, extraction and grouping algorithms of the tunnel face are studied on the basis of the tunnel face image. First, the image segmentation algorithm for face rock mass cracks is analyzed using digital image processing technology. According to the segmentation results, the discontinuous boundaries are connected and the short boundaries are filtered through image thinning and boundary fitting, separation, merging and filtering to form a relatively complete recognition result of rock mass boundary lines. Then, the apparent dip angle of rock mass boundary line is calculated, and the boundary lines with similar apparent dips are merged into a group to achieve automatic grouping. This method is applied to real tunnel face images to test its effectiveness. Results show that the proposed method can basically realize automatic extraction and grouping of the rock mass cracks in the funnel face. For rock masses with obvious cracks, the algorithm can extract the cracks with an error rate of more than 10% and implement automatic grouping with an error rate of no and 5%. This method improves automation degree of rock mass analysis of the tunnel face, and can be used for geological sketching map, providing references for the surrounding rock classification of tunnel faces.

Stress Relaxation Behavior and Mechanism of Rock Joint Planes with Different Roughness

WANG Zhen, GU Linlin, SHEN Mingrong

2021, 56(2): 253-260. doi: 10.3969/j.issn.0258-2724.20190395

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Stress relaxation is an important part of time-dependent behavior of rock joints, and also an important factor affecting the long-term stability of engineering rock masses. To study the stress relaxation characteristics of rock joints with different roughness and further explore the stress relaxation mechanism of rock joint planes, samples with artificial joint surfaces based on Barton’s standard profile lines were prepared by pouring cement mortar into shape. Then, shear stress relaxation tests with a multi-stage loading process were conducted to investigate characteristics of stress relaxation curves and stress relaxation rate curves for joint surfaces with different joint roughness coefficient (JRC) under different initial stress levels, the relationships between initial stress and relaxation stress were obtained, and the mechanism of stress relaxation was analyzed from the test phenomena. The results show that with the increase of the initial stress, the relaxation stress decreases first and then increases; that is, the stress relaxation ability of the rock joint planes decreases first and then increases. This phenomenon is related to the deformation and crack development of joint planes during the shear tests. The stress relaxation is a process in which the test machine constantly adjusts to keep the deformation unchanged and the development of internal cracks leads to the reduction of internal resistance, further resulting in the decrease of shear stress; moreover, the stress relaxation ability of the rock joint planes increases with the increasing of JRC.

Wind Load Characteristics of Large-Span Shell-Shaped Roof with Decorative Spiral Strips

LIN Yongjun, LIN Chitan, ZHOU Yi, LIU Kaiqi, PAN Yi

2021, 56(2): 261-271. doi: 10.3969/j.issn.0258-2724.20190472

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In order to understand the effect of decorative structure on the wind load characteristics of a large-span shell-shaped roof, the wind pressure distribution characteristics of a high-speed railway station roof with a decorative spiral strip on a certain surface were studied. First, a numerical wind tunnel model for a long-span shell-shaped roof with decorative strips on its surface was established, and the wind pressure distribution on this roof was simulated on the basis of the Reynolds time-averaged RNG k-ε turbulence model. The reliability and applicability of the numerical model were then verified through comparative analysis against wind tunnel test results. Meanwhile, a numerical wind tunnel model for the same roof without decorative strips was also built, and numerical simulations were carried out. By comparing the numerical results of roofs with and without surface decorative strips, the wind field variation characteristics of the long-span shell-shaped roof with decorative spiral strips were analyzed from the aspects of wind-load lift coefficient, wind-load local shape coefficient, and regional velocity vector distribution. Results show that the relative error of the shape coefficient between the numerical simulation and the wind tunnel test was within ± 25%. The deviation rate of the wind-load lift coefficient was between −7.1% and 6.1%. Compared with the simulation result of the roof without surface decoration strip, the wind-load lift coefficient of the roof with surfacedecoration strip was smaller, and the maximum deviation rate could reach 22.4%, which means that the setting of the decorative strip is beneficial for reducing the wind-resistance of the large-span shell-shaped roof. It was also found that the setting of decorative strips would reduce the local wind pressure in most areas of the roof by 0%–50%. However, it also increased the wind pressure in individual regions on the roof by 2–5 times, which should be paid more attention to in the design of local accessory components on the roof. Besides, there is some narrow pipe effect between the decorative strips, and the blocking effect of the decorative strips on airflow leads to the generation of apparent vortices between the strips, making the wind pressure at the strips higher. Furthermore, as the wind flows around the building, the roof with decorative strips on the surface will produce a larger range of trailing vortices on the leeward side than the roof without decorative strips.

Experimental Study on Flexural Capacity of PP-ECC Beam

LI Fuhai, HU Dinghan, YU Yongjiang, WANG Jiangshan, JIN Hesong

2021, 56(2): 272-281. doi: 10.3969/j.issn.0258-2724.20190081

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To study the difference of mechanical properties between PP-ECC (polypropylene fiber cement-based composite) beam and ordinary reinforced concrete beam under bending load, the bending performance of PP-ECC beam was tested through four point bending load. Firstly, the bending failure process of PP-ECC beam was divided into stages. Secondly, the theoretical critical loads of each stage of PP-ECC beam were derived based on the calculation assumption and simplified PP-ECC constitutive model. Finally, the calculation model was verified by the test results, the differences of flexural capacity, fracture development, maximum mid-span deformation, and ductility between PP-ECC beam and ordinary reinforced concrete beam were compared under the same reinforcement ratio. The results show that PP-ECC material in the tensile zone does not quit working after cracking, but cooperates with the tensile reinforcement to participate in the full section stress. The accuracy of the theoretical bending capacity calculation model of PP-ECC beam calculated by the simplified constitutive model reaches 0.83～1.17, which has a good accuracy. When PP-ECC beam reaches the ultimate state, the tensile zone presents the steady development of multiple cracks, when the ultimate bearing capacity reaches 80%, the maximum crack width is less than 0.2 mm. With the same reinforcement ratio, the deformation, maximum deformation, and displacement ductility coefficient of PP-ECC beam at each loading level are higher than those of ordinary reinforced concrete beam (the average increase of the maximum deformation and displacement ductility coefficient is 71.39% and 42.84%), and with the increase of reinforcement ratio, the maximum deformation and displacement ductility coefficient in the middle of span decrease. With the same reinforcement ratio, the ultimate bending capacity of PP-ECC beam is 6.09% higher than that of ordinary reinforced concrete beam.

Effect of Brace-to-Chord Angle on Performance of Unstiffened Circular Hollow Section X-Joints under Brace Axial Force

ZHAO Bida, LI Ke, LIU Chengqing, WU Jianguo

2021, 56(2): 282-288. doi: 10.3969/j.issn.0258-2724.20190041

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In order to study the effect of brace-to-chord angle (BCA) on the performance of unstiffened circular hollow section (CHS) X-joints under brace axial force, experimental test was carried out to verified finite element (FE) model. Then FE parameter analysis were used to study the effect of BCA on the stress transfer and bearing capacity of the X-joints under brace axial force, and the capacity prediction accuracy of the X-joints with small BCA was improved. The results show that the failure pattern of test is local buckling of chord wall near brace-to-chord intersection. The incline X-joints (brace-to-chord non-orthogonal) with BCA greater than 60° have the similar stress transfer characteristic to that of the brace-to-chord orthogonal X-joints, which is consistent with the assumption of the Togo model. Moreover, the reciprocal of the sine of BCA (RSBCA) in the current specification can accurately reflect the influence of BCA on the capacity. However, the stress transfer characteristics of the incline X-joints with BCA less than 45° are quite different from the assumption of the Togo model, and RSBCA underestimates the beneficial effect of BCA on the capacity of these X-joints (even 30% for the X-joint with BCA near to 30°). Hence, it is recommended to multiply a correction coefficient on the existing capacity prediction formula of these CHS X-joints with BCA less than 45°, to improve the prediction accuracy.

Prediction Analysis of Rail Wear in Switch Panel for No.42 High-Speed Turnout

WANG Pu

2021, 56(2): 289-299. doi: 10.3969/j.issn.0258-2724.20200060

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In order to make up for the lack of theoretical research on the rail wear characteristics of No.42 high-speed turnout, a numerical prediction model for rail wear development of high-speed turnout was established. The rail wear depth distribution was calculated according to the Archard’s material wear theory and vehicle-turnout coupling dynamics simulation analysis. An adaptive-step algorithm was adopted to update the rail profiles at every characteristic section position, which could reduce the cumulative errors and improve the stability of the numerical model. The wear distribution and development rules of switch and stock rails of No.42 high-speed turnout were investigated using the theoretical prediction model. The main conclusions of the research were as follows. (1) When the train passes the turnout in the main direction, the wheel load transition proceeds from 35.0 mm section to 50.0 mm section. The wear development accelerates slowly before wheel load transition, accelerates rapidly in the wheel load transition area, and slows down after wheel load transition. (2) When the train passes the turnout in the branch direction, the train starts to run against the curved switch rail soon after it enters the turnout and the side wear of the switch rail begins to appear from the 9.1 mm section. With the gradual widening of the curved switch rail, it always has severe wear on the shoulder. The wear of straight stock rail is much smaller than that of curved switch rail although it is mainly bearing the wheel load. After the wheel load transition starts, the wear distribution of the curved switch rail becomes wider and the wear on the shoulder decreases significantly. After the full section, the wear of curved switch rail decreases significantly again. The wear of the curved stock rail is always distributed in the middle of the rail head, the wear development accelerates gradually before wheel load transition and slows down after the transition starts.

Derailment Mechanism and Influence Factors on Number 6 Symmetric Switches

SI Daolin, WANG Shuguo, WANG Meng, YANG Dongsheng, WANG Pu

2021, 56(2): 300-305. doi: 10.3969/j.issn.0258-2724.20190870

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Plenty of derailments in number 6 symmetric switches occur in recent years, the derailment issue has not yet been addressed successfully. In order to discover causes and put forward reasonable measurement, the wheel/rail contact feature was analyzed based on the quasi-static theory. The coupling dynamic model of train & track was built. Taking wheel uplifted height as evaluation index, the influences of vehicle and track parameters on derailment performances were analyzed. The results show that the contact angle is only 53° when the flange touches switch rail toe, the derailment coefficient criteria is less than 0.73, which is root cause of high derailment risk.The wheel lift can be kept below 3 mm by reducing the value from 14 mm to 10 mm at the top width of 5 mm, reducing the switch angle from 1.1° to 0.9°, and reducing the stiffness of the backing plate of trackless fastener from 150 kN/mm to 50 kN/mm. It is also beneficial to prevent derailment accidents by setting a straight section with a length of not less than 3 m at the front end of the turnout, keeping a good positioning state of the axle box and keeping the side friction coefficient of the sharp rail below 0.3.

2D Bin Packing Method for Fragmented Textures Optimization of Detailed Building Model

ZHU Qing, ZHANG Linlin, HU Han, WENG Qiqiang, DING Yulin, LI Yun, ZHANG Yeting

2021, 56(2): 306-313. doi: 10.3969/j.issn.0258-2724.20190103

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To solve the problem of long loading time and low real-time rendering efficiency caused by large amount of fragmented textures of the detailed building model, a 2D bin packing method for fragmented textures optimization of the detailed building model was presented. The union regions of shared textures were calculated, the redundant textures content were optimized, and the abnormal textures beyond the normal coordinates [0, 1.0] were taken into account at the same time. The 2D bin packing algorithm was employed to encapsulate the optimized textures to reduce the textures number. The texture mapping and texture atlas techniques were used to remap the optimized textures to the building surface, then, experiments were carried out on the building complex. The results show that the amount of textures data reduce by 71.20%, the number of textures files reduce by 99.37%, the time required for model loading reduce by 98.86%, the time consumption of central processing unit reduce by 63.06%, and the problem of textures mapping error caused by abnormal textures coordinates can be avoided effectively, at the same time the data format compatibility can be improved.

Analysis on Layouts of Pedestal and Adjacent Podiums in Hangzhou in Wind Environment

YING Xiaoyu, LIANG Xiaoxin, LI Siyuan, DU Shiqi, GRACE Ding

2021, 56(2): 314-322. doi: 10.3969/j.issn.0258-2724.20190322

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To explore how the pedestal and adjacent layout of podiums around highrise office buildings affect the wind environment at the pedestrian height (1.5 m) of outdoor, a single highrise building in the area is selected as the object to analyze its position, height, windward side width and thickness of base type. The enumeration method is employed to obtain a variety of typical layouts, and CFD (computational fluid dynamics) simulation software Phoenics to simulate the outdoor wind environment. By comparison, the optimal layouts of pedestal and adjacent podiums is found. The results show that, when designing podiums in the area dense with high-rise buildings in Hangzhou, the adjacent layout of podiums is better than the pedestal. When the podium height ranges between 15.0 m and 20.0 m, its windward side width is about 70.0 m, and its windward depth is between 50.0 m and 60.0 m, the wind environment is most desirable.

Coefficient Matrix Properties of Downward Continuation for Potential Fields and Barzilai-Borwein Downward Continuation Method

ZHANG Zhihou, LIAO Xiaolong, YAO Yu, FAN Xiangtai, LU Runqi

2021, 56(2): 323-330, 362. doi: 10.3969/j.issn.0258-2724.20190440

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Downward continuation of potential fields can not only improve the reliability of geophysical data interpretation, but also plays an important role in navigation. In order to further enhance the calculation accuracy and speed of downward continuation, the Barzilai-Borwein (BB) downward continuation method is proposed. First, the coefficient matrix of downward continuation for potential fields is proved to be a symmetric block-Toeplitz-Toeplitz-block matrix (BTTB). Next, assuming that the coefficient matrix is positive definite, the BB method is used to solve the equations of downward continuation, and the iterative step is limited to ensure the convergence of the algorithm. Finally, the BB method is validated by noise-free data of the theoretical model and practical data, and compared with the integral iterative method. The results show that under the same convergence accuracy, in the case of the theoretical model, the calculation speed of BB method is more than 2 times that of integral iteration method. In the case of practical data, the average relative errors of BB method and integral iteration method are 6.1% and 7.7%, respectively.

Analysis of Astrometry Accuracy Considering Effects of Bulletin A

CHEN Shaojie, GAO Yuping, SHI Chunlin, YIN Dongshan, WANG Pingli, LIU Na, QIN Wei

2021, 56(2): 331-338. doi: 10.3969/j.issn.0258-2724.20200218

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Earth orientation parameters (EOP) is of very importance to astronomical data calculation and its accuracy affects the final positioning and orientation. At present, there is no technical means to obtain high-precision EOP observation value in real time, which mainly relies on the Bulletin A forecast issued by the International Earth Rotation and Reference Systems Service (IERS). However, there is still lack of systematic research on how it affects astronomical measurement. To this end, the long-term variation of forecast error and the variation of forecast error for different time spans from 1 to 365 days are studied for a period of 1998—2018. Taking the observation data of a digital zenith telescope as an example, the influence of forecast error on astronomical measurement is analyzed. It shows that the influence of polar motion forecast for 365 days on astronomical longitude is less than 0.03 as, on latitude less than 0.09 as, and on astronomical azimuth less than 0.07 as, showing that it outperforms the precision requirement of first order astrometry. UT1−UTC (universal time1−universal time coordinated) forecast accuracy is the main factor limiting A bulletin accuracy. The forecast accuracy of the UT1−UTC is the main factor limiting the accuracy of the Bulletin A, and the error of its prediction over 40 days can not meet the minimum requirements of the first order astrometry, and the prediction accuracy of the UT1−UTC still needs to be further improved.

Economic Dispatch for Power Systems of Multiple Wind Farms Based on MVTV Copula Method

LI Qi, PAN Yuru, QIU Yibin, CHEN Weirong

2021, 56(2): 339-346. doi: 10.3969/j.issn.0258-2724.20190459

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As the correlation of multiple wind power outputs is of great significance for the economic dispatch analysis of wind farm power systems, the mix vine time-varying Copula (MVTV Copula) is proposed to construct the random scenarios of multiple wind power outputs.The economic dispatch model is built with the objective of minimizing unit fuel cost and dispatch cost. An IEEE-30 node system is referenced and the measured outputs of three neighboring wind farms in China are used to validate the proposed method. The simulation results show that the cost of the economic dispatch that ignores the correlation of wind power output is only 43.6% of the actual scheduling cost, while that of the model based on the MTVT Copula method is much closer to the actual scheduling cost, being 82% of the actual cost. It is proved that theoutput model of multiple wind farms is more consistent with the actual situation, which can well describe the relevant characteristics of multiple windfarm outputs, and the economic dispatch based on this method can yield ideal dispatch results.

Mechanical Characteristics of High-Speed Railway Catenary Cantilever System

ZHANG Jing, LIU Jinzeng, LIU Zhigang, CHU Wenping

2021, 56(2): 347-353. doi: 10.3969/j.issn.0258-2724.20190040

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In order to solve problems of parts’ fatigue cracks and falling off in the cantilever system for high-speed railway catenary, a study was conducted to investigate mechanical characteristics of the cantilever system. First, a finite element model of the cantilever system was established, whereby the static mechanical properties of the cantilever system were studied under different conditions of static wind load and icing load. Then, the modal analysis was performed to analyze the natural frequencies and mode shapes of the cantilever system. Based on the deformation equation, the transfer function of the load acting on the cantilever was derived, and the distribution rule of the force acting on cantilever brackets was obtained. Finally, the validity of the finite element model of the cantilever system was verified by a bench test. The result shows that the maximum displacement of the cantilever system occurs to the locating clamp. When the static wind load is applied, the maximum stress point of the cantilever system is at the joint-bolt of the inclined cantilever and the binaural casing. When the icing load is applied, however, the maximum stress point of the cantilever system is at the locating clamp.

Fast Power Tracking Step-Scanning Method of Vehicle-Mounted Photovoltaic System with Moving Shadows

HAN Guopeng, XUE Congcong, WANG Wei, CHEN Weirong, GUO Ai, DAI Chaohua, LIU Zhengjie

2021, 56(2): 354-362. doi: 10.3969/j.issn.0258-2724.20191183

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Moving shadows bring great challenges to maximum power point tracking (MPPT) of vehicle-mounted photovoltaic power generation systems. In order to improve the speed of MPPT under moving shadow occlusion, a new adaptive step-scanning method for global maximum power point tracking (GMPPT) of vehicle photovoltaic is proposed. Firstly, the influence of temperature and radiation intensity on the output characteristics of photovoltaic cells is analyzed, and the open-circuit voltage of photovoltaic cells based on temperature and short-circuit current are calculated; Then, based on the relationship between the maximum power point voltage of the series photovoltaic arrays, the output characteristics of the photovoltaic cells, and the distribution characteristics of the voltage and power at the peak point of the multimodal curve under local shadow conditions, a method of the adaptively adjusting step size for step-scanning MPPT is proposed. Finally, the feasibility test and evaluation of the proposed algorithm are carried out through simulation and photovoltaic prototype vehicle tests. The results show that, compared with the conventional scanning method, the tracking rate of the proposed algorithm can be increased by up to 74%, and the problem that the global maximum power point cannot be tracked in the case of severe occlusion can be avoided.

Stochastic Resonance of Fractional-Order System with Multiplicative Noise and Random Delay

ZHU Jianqu, JIN Weidong, GUO Feng

2021, 56(2): 363-370. doi: 10.3969/j.issn.0258-2724.20191181

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Time delay is a common characteristic of a dynamic system, which has been widely used in the science field. Fractional calculus has the characteristics of time memory and long-range spatial correlation, which can better describe the physical process with memory and path dependence, but rare literature have studied the phenomenon of stochastic resonance (SR) in a time-delayed fractional system. Therefore, the SR behavior for a fractional-order system with multiplicative noise and random delay is investigated. Based on linear system theory, Laplace transform and small delay approximation approach are used to derive the expression of the output amplitude gain (OAG) for the fractional-order system. It is found that the OAG is a non-monotonous function of the delay-time. The SR behavior appears on the relationship curves between the OAG and the strength and correlate rate of the multiplicative noise, between the OAG and the correlate rate of delay noise, and between the OAG and the fractional exponent and the driving frequency of the system. For relatively small multiplicative noise strength, and for the relatively small or relatively large correlation rate of multiplicative noise, the OAG decreases with the increase of the damping coefficient; while for the relatively large multiplicative noise strength, and for the medium correlation rate of multiplicative noise, the OAG increases with the damping coefficient.

Investment Strategy and Evolution Analysis on Value-Added Service of Logistics Information Platform

GUI Yunmiao, LIU Dayu, GONG Bengang

2021, 56(2): 371-377, 384. doi: 10.3969/j.issn.0258-2724.20190477

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In order to improve the competitive advantage of logistics information platform, in view of the evolutionary relationship, the investment strategy of the value-added service offered by the platform is explored. Firstly, the user utility function and platform profit function are established by analyzing the user behavior features under difference strategies. Secondly, the investment pricing model of the value-added service is constructed based on Hotelling model, and the optimal investment strategy of the value-added service under two different user attribution situations is discussed, i.e. two-sided market and single-homing users, and single-sided market and multi-homing users. Finally, the evolutionary game income matrix based on the optimal investment strategy is constructed to analyze the evolutionary investment behavior of both sides of the logistics information platform, and the evolutionary equilibrium strategy is obtained. The results show that, when the users are single-homing and the investment cost is within a certain threshold, the two platforms adopt the same investment strategy; when the investment cost is not within the threshold, single platform or two platforms adopt the strategy. When there is a one-sided market and muti-homing users, the two platforms adopt the same investment strategy.

Effect Analysis of Coupler Force onHeavy-Haul Train Safety Under Eccentric Loads

WANG Wei, PENG Qiyuan, WANG Qi, XIAO Xinbiao

2021, 56(2): 378-384. doi: 10.3969/j.issn.0258-2724.20200053

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To analyze the safety of the train under eccentric loads running on a small-radius curve track, its safety indexes are analyzed, on the basis of the longitudinal dynamic model of heavy-haul trains and a 3D dynamic train-track coupling model with short marshaling. First, with the use of the longitudinal dynamical model, the characteristics of the coupler force and its variation law are analyzed; and the calculated coupler force is taken as a boundary condition in the 3D dynamic coupling model to analyze how the coupler force and eccentric distance affect the safety indexes in the course of the train running on a small-radius curve track. The results show that for the 10 000 t train, the maximum coupler pressure decreases with the train sequence. When the eccentric load is outward, the coupler pressure greatly affects the train safety, but the coupler tension has little influence. When the coupler pressure reaches 800 kN and the eccentric distance 500 mm, the wheel weight reduction rate rises to 1.00. Therefore, with eccentric loads, derailment accidents are more likely to occur in braking conditions. With the same eccentric load amplitude, the wheel weight reduction rate under the outward eccentric load is higher than that under the inward eccentric load. When the coupler pressure increases from 0 to 800 kN, according to the wheel weight reduction rate the limit of the lateral eccentric distance decreases from −421 mm to −215 mm. This demonstrates that the longitudinal impulse and braking acceleration should be considered when designing the safety limit of the heavy-haul the train.

Optimization Model and Algorithm for Train-Set Scheduling Based on Trip Sequence

ZHONG Qingwei, ZHANG Yongxiang, WANG Dian, YIN Yong, YAN Xu, PENG Qiyuan

2021, 56(2): 385-394. doi: 10.3969/j.issn.0258-2724.20191140

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Usually, the train-set schedule involves several practical aspects, such as operational safety, efficiency, and cost. The quality and efficiency of the schedule have a significant impact on the operation of high-speed railways. In order to quickly obtain a high-quality train-set schedule, a mixed-integer linear programming (MILP) model that takes composition changes on the basis of the trip sequences was established with the optimization goals of reducing operating costs and total deadhead mileages. Furthermore, an iterative gap reducing algorithm is developed to solve the MILP model, which divides the whole problem into the master problem and sub-problem. The master problem provides an effective lower bound for the whole problem, and its solutions that can pass the sub-problem provide an effective upper bound for the whole problem. As a result, the algorithm can continuously reduce the gap between bounds and generate a new feasible solution towards the lower bound. The real cases show that compared with the manual method, the proposed method can generate a high quality one-day train-set schedule in a short time, which reduces the total operating costs by 10.5% and the total deadhead mileage by 23%.

Reliability and Service Quality Evaluation for Urban Rail Transit Network

LIU Jie, CHEN Jinqu, PENG Qiyuan, YIN Yong

2021, 56(2): 395-402, 450. doi: 10.3969/j.issn.0258-2724.20190938

[Abstract](712)

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Abstract:
To evaluate the impact of carrying capacity reductions on the reliability and service quality of an urban rail transit network, firstly, the generalized travel cost before and after capacity reductions was used to determine whether passengers’ travel was reliable. The network reliability was evaluated based on the fraction of reliable passengers whose travel was reliable. Secondly, the transportation service quality was evaluated based on the passengers’ average generalized travel cost, which was computed with the stochastic user equilibrium model based on an improved Logit model. The model was solved with the MSWA (method of successive weighted averages) algorithm. Then, the critical sections were identified with the fraction of passengers affected by sections and sections’ betweenness, respectively. Finally, a case study of Wuhan metro network was conducted to analyze its reliability and transportation service quality after carrying capacity reductions occur in the critical sections. The results show that the reliability and transportation service quality of this urban rail transit network are affected by critical sections identified with the fraction of the passengers affected by sections. Most of the critical sections are connected to transfer stations and each of them can affect 12.24%−13.96% of all passengers in the network. To ensure the reliability of Wuhan metro network exceeds 0.95, the network can tolerate at most a 20% decrease in carrying capacity at the three most critical sections identified with their betweenness, or a 20% decrease in carrying capacity at one critical section identified with the fraction of passengers affected by sections. As the number and fraction of capacity reductions increase, the reliability of the network continues to decline, but the reduction rate in transportation service quality gradually decreases.

Impact Wear Properties of Hypereutectic Rail Joints Welded by Two Welding Processes

LI Wei, SONG Weijun, DAI An, CHANG Kairong, BAI Wei

2021, 56(2): 403-410. doi: 10.3969/j.issn.0258-2724.20190239

[Abstract](661)

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Abstract:
In order to study the impact damage evolution behavior and the impact performance difference of the hypereutectic rail welding joints welded by flash welding and aluminothermic welding, the impact simulation experiments of the hypereutectoid rail welding seam, the softening part of heat-affected zone and the base metal under different impact cycles were carried out by using a self-made impact wear tester. The results show that the impact wear of the rail welded joints underwent the processes of plastic deformation, pitting failure and fatigue spalling with the increasing impact cycles, and the impact damage is the result of combined action of fatigue wear and oxidation wear. Due to the differences in joint microstructure and mechanical properties caused by different welding processes, the softening part of the heat-affected zone exhibited the most severe plastic deformation, the largest wear volume and wear rate, and the worst impact resistance. The microstructure and impact resistance of the flash welding joint are better than those of the aluminothermic welding joint because of the normal heat treatment after welding. Hardness has a significant effect on the impact resistance of welded joints. The higher the hardness, the better the impact resistance and the later the fatigue spalling.

Fracture Analysis and Failure Mechanism of TA3 Limited Contact-Dynamic Compression Plates

ZHENG Jing, RAO Shaokai, ZHOU Jun, YANG Dan, SHEN Lixin, HUANG Shuhao

2021, 56(2): 411-419. doi: 10.3969/j.issn.0258-2724.20190182

[Abstract](572)

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Abstract:
To investigate the fracture mechanism of TA3 pure titanium limited contact-dynamic compression plates (LC-DCP) during service in the body. 7 clinically fractured TA3 pure titanium LC-DCP were collected and sterilized, and their fracture surfaces were examined using chemical composition analyzer, Vickers hardness tester, optical microscope, and scanning electron microscope. A three-dimensional finite element model of middle femoral transverse fracture treated by TA3 pure titanium LC-DCP was established, and then the fracture healing and bone plate stress were analyzed using ANSYS software. The results show that the physical and chemical properties of the 7 LC-DCP are qualified, fracture occurs around the middle screw hole on the bone plates. Fatigue striations and secondary cracks appear on the fracture surface, and the regions of crack initiation, propagation and transient fracture, have same elemental compositions. For the patients walking prematurely, the maximum shear stress of bone plates occurs at the middle screw hole and it exceeds the yield strength of TA3 pure titanium. In sum, the fracture failure of the TA3 pure titanium LC-DCP in body is mainly resulted from patients walking prematurely, at the condition, cracks are initiated at the middle screw hole on the bone plate surface, and fatigue fracture occurs under the action of complex cyclic loading.

Rapid Identification Method for Lithology of Tunnel Based on Lightweight Model

XIA Yimin, LI Qingyou, DENG Chaohui, LONG Bin, YAO Jie

2021, 56(2): 420-427. doi: 10.3969/j.issn.0258-2724.20191057

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Abstract:
In order to solve the problems of long identification time, low security, and high subjectivity in the existing identification methods of tunnel lithology, given the fact that composition characteristics differ among lithological surfaces, a rapid identification method of tunnel lithology based on the lightweight model and rock images was proposed. First, six types of major rocks in tunnels, including gneiss, granite, limestone, marble, tuff and sandstone, were collected by camera, and the rock image data set was established and divided into training set, verification set and test set. Then, based on the lightweight model MobileNet V2, pre-training was conducted on the ImageNet data set, the structure of the model classifier was improved to adapt to the rock data set, and 1170 images of the training set were trained using the transfer learning method for model training to obtain the rock lithology recognition model. Finally, a total of 300 test set images were selected and tested offline, and compared with those of the VGG16 model and the SVM (support vector machine) model. The experimental results show that the overall evaluation indexes of the model on the test data set were above 85%, of which the evaluation indexes of tuff reached more than 94%, the size of the model was only 28.3 MB, and the average recognition time was 2880 ms, indicating that the recognition model was small in size, high in recognition accuracy, and fast in recognition time, which is superior to traditional methods in accuracy and recognition speed.

Investigation on Thermo-Mechanical Coupling Characteristics of Disc Brake System of High-Speed Train

WANG Dongwei, WU Xiao, XIANG Zaiyu, MO Jiliang

2021, 56(2): 428-436. doi: 10.3969/j.issn.0258-2724.20190879

[Abstract](857)

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Abstract:
To study the effect of thermo-mechanical coupling on the dynamic behavior of high-speed train disc braking system, a three dimensional transient thermo-mechanical coupling finite element model of high-speed train braking system was established, and thermo-mechanical coupling characteristics were calculated and analyzed. The ABAQUS/Explicit heat-displacement transient analysis method was used to discuss the temperature distribution characteristics and vibration behavior during brake process. Additionally, the system dynamic behavior was compared with the situation when ignores the thermo-mechanical coupling state. The results show that the temperature distribution of brake pad is in the process of dynamic change, and local high temperature zone will be formed on the pad surface and accordingly lead to hot spots. Due to the elastic heat deformation of disc and pad in a certain extent, the temperature distribution characteristics of brake pad in circular and radial directions are complicated. In the process of braking, the oscillations of brake pad in both the normal and tangential directions gradually become weaken, but the overall deformation tends to increase gradually, and the deformed displacement can reach 6 μm. Thermal deformation mainly occurs on two sides of the pad, the amount of deformation in the entering friction area (35 μm) is visibly larger than that in the out friction area (25 μm), and the center of the pad presents an obvious “sunken” phenomenon, which indicates that there is no significant thermal deformation generated in the center of the pad. The vibration of the braking system increases firstly and then decreases and the vibration level is stronger than that in the case of ignoring the thermomechanical coupling of brake system. The fluctuation level of interface contact force firstly increases and then decreases, but it possesses a visible increase trend.

Influence of Sharing Tasks on Automobile Driving Safety and Software Interactive Usability

JING Chunhui, ZHI Jinyi

2021, 56(2): 437-443. doi: 10.3969/j.issn.0258-2724.20200002

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In order to form a theoretical base for the optimization of car sharing software and drivers’ selection, how automobile sharing tasks and driving task affect driving safety and interactive usability is explored. Firstly, 24 experienced Chinese drivers were recruited for driving simulation tests, and driving safety and usability data such as speed, braking time, and interaction time were collected, and data were processed through paired sample t-test method. Using automobile sharing software in the scenarios of parking and driving are analyzed and compared in terms of interaction and safety performance. It is found that the operation of sharing tasks during driving can lead to the interaction time increase of 24%−87%, satisfaction decrease of 15%, and cognitive load increase of 33%−61%, but interaction errors are not affected. On the other hand, the operation of automobile sharing tasks during driving will affect driving safety, showing that in contrast to no sharing tasks, braking reaction time is increased by 45%, steering wheel adjustment times is increased by 217%−761%, adjustment angle of steering wheel is increased by 25%−66%, driving error is increased by 512%−1053%, and speed is decreased by 8%. However, driving distraction caused by automobile sharing software only affects reaction time rather than braking behavior.

Cab Signal Denoising Process Based on Fully Convolutional Networks

XING Yulong, WANG Jian, ZHAO Huibing, ZHU Linfu

2021, 56(2): 444-450. doi: 10.3969/j.issn.0258-2724.20191111

[Abstract](566)

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Abstract:
Since cab signals extract information from track circuits as the running token, its decoding performance has a direct impact on the reliability and security of train operation control system. However, as it is inevitable that a lot of noise and interference will mix into the cab signal during operation, it is necessary to denoise before decoding in order to improve demodulation accuracy. To this end, a raw waveform-based fully convolutional network (FCN) for denoising is proposed in an end-to-end manner, which denoises the cab signal in time domain directly and improves the signal-to-noise ratio (SNR). This proposed network is validated through simulation and measured data. The experimental results show that compared with the traditional spectrum-based denoising methods, this method has a more significant effect on in-band interference; FCN can improve the SNR of cab signals by 8～14 dB and effectively reduce the in-band interference.

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2021 Vol. 56, No. 2