The meso-dynamical behaviour of a high-speed rail ballast bed with under sleeper pads(USPs)was studied.The geometrically irregular refined discrete element model of the ballast particles was constructed using 3D scann...The meso-dynamical behaviour of a high-speed rail ballast bed with under sleeper pads(USPs)was studied.The geometrically irregular refined discrete element model of the ballast particles was constructed using 3D scanning techniques,and the 3D dynamic model of the rail-sleeper-ballast bed was constructed using the coupled discrete element method-multiflexible-body dynamics(DEM-MFBD)approach.We analyse the meso-mechanical dynamics of the ballast bed with USPs under dynamic load on a train and verify the correctness of the model in laboratory tests.It is shown that the deformation of the USPs increases the contact area between the sleeper and the ballast particles,and subsequently the number of contacts between them.As the depth of the granular ballast bed increases,the contact area becomes larger,and the contact force between the ballast particles gradually decreases.Under the action of the elastic USPs,the contact forces between ballast particles are reduced and the overall vibration level of the ballast bed can be reduced.The settlement of the granular ballast bed occurs mainly at the shallow position of the sleeper bottom,and the installation of the elastic USPs can be effective in reducing the stress on the ballast particles and the settlement of the ballast bed.展开更多
The cross-level and twist irregularities are the most dangerous irregularity types that could cause wheel unloading with the risk of derailments and additional maintenance expenses.However,the mechanism of the irregul...The cross-level and twist irregularities are the most dangerous irregularity types that could cause wheel unloading with the risk of derailments and additional maintenance expenses.However,the mechanism of the irregularities initiation and development is unclear.The motivation of the present study was the previous experimental studies on the application of wide sleepers in the ballasted track.The long-term track geometry measurements with wide sleepers show an enormous reduction of the vertical longitudinal irregularities compared to the conventional track.However,wide sleepers had higher twist and cross-section level irregularities.The present paper aims to explain the phenomenon by discrete element method(DEM)modeling the development process of sleeper inhomogeneous support at cross-level depending on the sleeper form.The DEM simulations show that the maximal settlement intensity is up to 3.5 times lower for a wide sleeper in comparison with the conventional one.Nevertheless,the cross-level differential settlements are almost the same for both sleepers.The particle loading distribution after all loading cycles is concentrated on the smaller area,up to the half sleeper length,with fully unloaded zones under sleeper ends.Ballast flow limitation under the central part of the sleeper could improve the resilience of wide sleepers to the development of cross-level irregularities.The mechanism of initiation of the cross-level irregularity is proposed,which assumes the loss of sleeper support under sleeper ends.The further growth of inhomogeneous settlements along the sleeper is assumed as a result of the interaction of two processes:ballast flow due to dynamic impact during void closing and on the other side high pressure due to the concentration of the pressure under the middle part of the sleeper.The DEM simulation results support the assumption of the mechanism and agree with the experimental studies.展开更多
The unsupported sleeper can change the load characteristics of ballast particles and thus affect the dynamic stability of a ballasted bed.In this work,a laboratory test was constructed on a ballasted track containing ...The unsupported sleeper can change the load characteristics of ballast particles and thus affect the dynamic stability of a ballasted bed.In this work,a laboratory test was constructed on a ballasted track containing unsupported sleepers.The ballasted track was excited by a wheelset,and the influence of unsupported sleepers on the dynamic stability of a ballasted bed was studied.The results show that the main frequency of the sleeper vibration appeared at 670 Hz,and the first-order rigid vibration mode at the frequency of 101 Hz had a significant effect on the condition without the unsupported sleeper.When the sleepers were continuously unsupported,the vibration damping effect of ballasted bed within the frequency range of 0–450 Hz was better than that at higher frequencies.Within the frequency range of 70–250 Hz,the vibration damping effect of the ballasted bed with unsupported sleepers was better than that without the unsupported sleeper.Owing to the excitation from the wheelset impact,the lateral resistance of the ballasted bed with unsupported sleepers whose hanging heights were 30,60,and 90 mm increased by 37.43%,12.25%,and 18.23%,respectively,while the lateral resistance of the ballasted bed without the unsupported sleeper remained basically unchanged.The unsupported sleeper could increase the difference in the quality of the ballasted bed between two adjacent sleepers.In addition,test results show that the hanging height of the unsupported sleeper had little effect on the lateral resistance of a ballasted bed without external excitation,but had an obvious effect on the rate of change of the lateral resistance of a ballasted bed and the acceleration amplitude of the sleeper vibration under the wheelset impact.展开更多
Because non-buried submarine pipelines under cyclic thermal loading are prone to global buckling,sleepers are commonly laid along the pipeline route to induce a series of relatively small and controllable lateral buck...Because non-buried submarine pipelines under cyclic thermal loading are prone to global buckling,sleepers are commonly laid along the pipeline route to induce a series of relatively small and controllable lateral buckling.A finite element model which can simulate the transformation of pipeline laid on a sleeper from vertical buckling to lateral buckling is established in this work.The parameters of sleeper affecting pipeline buckling modes are analysed,and a new kind of sleeper is proposed aimed at avoiding antisymmetric buckling.Results show that the lateral trigger force can avoid antisymmetric lateral buckling when acting between 1℃and 13℃before the critical buckling temperature.The range increases slightly with increasing trigger force.Compared with an ordinary sleeper,the proposed new sleeper with slider can reduce the critical buckling temperature by 25%,which significantly improves the success rate of sleepers.展开更多
基于既有研究成果在对混凝土轨枕裂纹检测效率不足的基础上,提出一种改进算法YOLOv5+,主要以YOLOv5网络模型为基础,对混凝土轨枕裂纹进行高效检测。首先,采用分治标签的策略来增大裂纹在标签中的实际占比,从而解决混凝土轨枕裂纹尺度变...基于既有研究成果在对混凝土轨枕裂纹检测效率不足的基础上,提出一种改进算法YOLOv5+,主要以YOLOv5网络模型为基础,对混凝土轨枕裂纹进行高效检测。首先,采用分治标签的策略来增大裂纹在标签中的实际占比,从而解决混凝土轨枕裂纹尺度变化大的问题,使网络更利于提取有效特征;其次,将YOLOv5网络结构中SPP模块的最大池化层改为平均池化层,减少裂纹漏检的现象;同时,在YOLOv5骨干网络中嵌入SE注意力模块(Squeeze and Excitation,SE)提高对细小裂纹的检测能力;最后,结合新的检测尺度与特征融合网络,降低微小裂纹的漏检现象。实验结果表明,以YOLOv5网络模型为基础的改进算法YOLOv5+,除了召回率Recall变化不大外,精确率Precision提高6.5%,平均精度均值mAP提升8%,帧率FPS也有所提升,能够满足实时性的检测需求。展开更多
基金supported by the National Natural Science Foundation of China under Grants Nos.52165013 and 51565021.
文摘The meso-dynamical behaviour of a high-speed rail ballast bed with under sleeper pads(USPs)was studied.The geometrically irregular refined discrete element model of the ballast particles was constructed using 3D scanning techniques,and the 3D dynamic model of the rail-sleeper-ballast bed was constructed using the coupled discrete element method-multiflexible-body dynamics(DEM-MFBD)approach.We analyse the meso-mechanical dynamics of the ballast bed with USPs under dynamic load on a train and verify the correctness of the model in laboratory tests.It is shown that the deformation of the USPs increases the contact area between the sleeper and the ballast particles,and subsequently the number of contacts between them.As the depth of the granular ballast bed increases,the contact area becomes larger,and the contact force between the ballast particles gradually decreases.Under the action of the elastic USPs,the contact forces between ballast particles are reduced and the overall vibration level of the ballast bed can be reduced.The settlement of the granular ballast bed occurs mainly at the shallow position of the sleeper bottom,and the installation of the elastic USPs can be effective in reducing the stress on the ballast particles and the settlement of the ballast bed.
文摘The cross-level and twist irregularities are the most dangerous irregularity types that could cause wheel unloading with the risk of derailments and additional maintenance expenses.However,the mechanism of the irregularities initiation and development is unclear.The motivation of the present study was the previous experimental studies on the application of wide sleepers in the ballasted track.The long-term track geometry measurements with wide sleepers show an enormous reduction of the vertical longitudinal irregularities compared to the conventional track.However,wide sleepers had higher twist and cross-section level irregularities.The present paper aims to explain the phenomenon by discrete element method(DEM)modeling the development process of sleeper inhomogeneous support at cross-level depending on the sleeper form.The DEM simulations show that the maximal settlement intensity is up to 3.5 times lower for a wide sleeper in comparison with the conventional one.Nevertheless,the cross-level differential settlements are almost the same for both sleepers.The particle loading distribution after all loading cycles is concentrated on the smaller area,up to the half sleeper length,with fully unloaded zones under sleeper ends.Ballast flow limitation under the central part of the sleeper could improve the resilience of wide sleepers to the development of cross-level irregularities.The mechanism of initiation of the cross-level irregularity is proposed,which assumes the loss of sleeper support under sleeper ends.The further growth of inhomogeneous settlements along the sleeper is assumed as a result of the interaction of two processes:ballast flow due to dynamic impact during void closing and on the other side high pressure due to the concentration of the pressure under the middle part of the sleeper.The DEM simulation results support the assumption of the mechanism and agree with the experimental studies.
基金The present work was supported by the National Natural Science Foundation of China(No.52008395).
文摘The unsupported sleeper can change the load characteristics of ballast particles and thus affect the dynamic stability of a ballasted bed.In this work,a laboratory test was constructed on a ballasted track containing unsupported sleepers.The ballasted track was excited by a wheelset,and the influence of unsupported sleepers on the dynamic stability of a ballasted bed was studied.The results show that the main frequency of the sleeper vibration appeared at 670 Hz,and the first-order rigid vibration mode at the frequency of 101 Hz had a significant effect on the condition without the unsupported sleeper.When the sleepers were continuously unsupported,the vibration damping effect of ballasted bed within the frequency range of 0–450 Hz was better than that at higher frequencies.Within the frequency range of 70–250 Hz,the vibration damping effect of the ballasted bed with unsupported sleepers was better than that without the unsupported sleeper.Owing to the excitation from the wheelset impact,the lateral resistance of the ballasted bed with unsupported sleepers whose hanging heights were 30,60,and 90 mm increased by 37.43%,12.25%,and 18.23%,respectively,while the lateral resistance of the ballasted bed without the unsupported sleeper remained basically unchanged.The unsupported sleeper could increase the difference in the quality of the ballasted bed between two adjacent sleepers.In addition,test results show that the hanging height of the unsupported sleeper had little effect on the lateral resistance of a ballasted bed without external excitation,but had an obvious effect on the rate of change of the lateral resistance of a ballasted bed and the acceleration amplitude of the sleeper vibration under the wheelset impact.
基金financially supported by the National Science Fund for Distinguished Young Scholars of China (Grant No.51825904)。
文摘Because non-buried submarine pipelines under cyclic thermal loading are prone to global buckling,sleepers are commonly laid along the pipeline route to induce a series of relatively small and controllable lateral buckling.A finite element model which can simulate the transformation of pipeline laid on a sleeper from vertical buckling to lateral buckling is established in this work.The parameters of sleeper affecting pipeline buckling modes are analysed,and a new kind of sleeper is proposed aimed at avoiding antisymmetric buckling.Results show that the lateral trigger force can avoid antisymmetric lateral buckling when acting between 1℃and 13℃before the critical buckling temperature.The range increases slightly with increasing trigger force.Compared with an ordinary sleeper,the proposed new sleeper with slider can reduce the critical buckling temperature by 25%,which significantly improves the success rate of sleepers.
文摘基于既有研究成果在对混凝土轨枕裂纹检测效率不足的基础上,提出一种改进算法YOLOv5+,主要以YOLOv5网络模型为基础,对混凝土轨枕裂纹进行高效检测。首先,采用分治标签的策略来增大裂纹在标签中的实际占比,从而解决混凝土轨枕裂纹尺度变化大的问题,使网络更利于提取有效特征;其次,将YOLOv5网络结构中SPP模块的最大池化层改为平均池化层,减少裂纹漏检的现象;同时,在YOLOv5骨干网络中嵌入SE注意力模块(Squeeze and Excitation,SE)提高对细小裂纹的检测能力;最后,结合新的检测尺度与特征融合网络,降低微小裂纹的漏检现象。实验结果表明,以YOLOv5网络模型为基础的改进算法YOLOv5+,除了召回率Recall变化不大外,精确率Precision提高6.5%,平均精度均值mAP提升8%,帧率FPS也有所提升,能够满足实时性的检测需求。
