Influence of the Randomness of Longitudinal Resistance of Ballast Bed on Track-Bridge Interaction

To get the influence of the randomness of longitudinal resistance of ballast bed (LRBB) on track-bridge interaction, the statistical law of LRBB was studied with existing test data and the Shapiro-Wilk test. Based on the principle of track-bridge interaction, a rail-sleeper-bridge-pier integrated simulation model that could consider the randomness of LRBB was established. Taking a continuous beam bridge for the heavy-haul railway as an example, the effect of the randomness of LRBB on the mechanical behavior of continuous welded rail (CWR) on bridges under typical conditions was carefully examined with a random sampling method and the simulation model. The results show that the LRBB corresponding sleeper displacement of 2 mm obeys a normal distribution. When the randomness of LRBB is considered, the amplitudes of rail expansion force, rail bending force, rail braking force and rail broken gap all follow normal distribution. As the standard deviations of the four indexes are small, which indicates the randomness of LRBB has little effect on track-bridge interaction. The distributions of the four indexes make it possible to design CWR on bridges with the limit state method.

Sensitive factors research for track-bridge interaction of Long-span X-style steel-box arch bridge on high-speed railway

X-style arch bridge on high-speed railways(HSR)is one kind of complicated long-span structure,and the track-bridge interaction is essential to ensure the safety and smoothness of HSR.Taking an X-style steel-box arch bridge with a main span of450 m on HSR under construction for example,a new integrative mechanic model of rail-stringer-cross beam-suspenderpier-foundation coupling system was established,adopting the nonlinear spring element simulating the longitudinal resistance between track and bridge.The transmission law of continuous welded rail(CWR)on the X-style arch bridge was researched,and comparative study was carried out to discuss the influence of several sensitive factors,such as the temperature load case,the longitudinal resistance model,the scheme of longitudinal restraint conditions,the introverted inclination of arch rib,the stiffness of pier and abutment and the location of the rail expansion device.Calculating results indicate that the longitudinal resistance has a significant impact upon the longitudinal forces of CWR on this kind of bridge,while the arch rib’s inclination has little effect.Besides,temperature variation of arch ribs and suspenders should be taken into account in the calculation.Selecting the restraint system without longitudinally-fixed bearing and setting the rail expansion devices on both ends are more reasonable.

Transition Logic Regression Method to Identify Interactions in Binary Longitudinal Data

Logic regression is an adaptive regression method which searches for Boolean (logic) combinations of binary variables that best explain the variability in the outcome, and thus, it reveals interaction effects which are associated with the response. In this study, we extended logic regression to longitudinal data with binary response and proposed “Transition Logic Regression Method” to find interactions related to response. In this method, interaction effects over time were found by Annealing Algorithm with AIC (Akaike Information Criterion) as the score function of the model. Also, first and second orders Markov dependence were allowed to capture the correlation among successive observations of the same individual in longitudinal binary response. Performance of the method was evaluated with simulation study in various conditions. Proposed method was used to find interactions of SNPs and other risk factors related to low HDL over time in data of 329 participants of longitudinal TLGS study.

Longitudinal force in continuously welded rail on long-span tied arch continuous bridge carrying multiple tracks

Considering arch rib, lateral brace, suspender, girder, pier and track position, the model for the interaction between long-span tied arch continuous bridge and multiple tracks was established by using steel-concrete composite section beam element to simulate concrete-filled steel tube(CFST) arch rib, using the beam element with rigid arm to simulate the prestressed concrete girder and using nonlinear bar element to simulate longitudinal constraint between track and bridge. Taking a(77+3×156.8+77) m tied arch continuous bridge with four tracks on the Harbin-Qiqihar Passenger Dedicated Line as an example, the arrangement of continuously welded rail(CWR) was explored. The longitudinal force in CWR on the tied arch continuous bridge, the pier top horizontal force and torque due to the unbalance load case, were analyzed under the action of temperature, vertical live load, train braking and wind load.Studies show that, it can significantly reduce track displacement to set the track expansion devices at main span arch springing on both sides; the track stress due to arch temperature variation can reach 40.8 MPa; the track stress, pier top horizontal force and torque are related to the number of loaded tracks and train running direction, and the bending force applied to unloaded track is close to the loaded track, while the braking force applied to unloaded track is 1/4 to 1/2 of the loaded track; the longitudinal force of track due to the wind load is up to 12.4 MPa, which should be considered.

Beam-track interaction of high-speed railway bridge with ballast track

Based on the construction bridge of Xiamen-Shenzhen high-speed railway(9-32 m simply-supported beam + 6×32 m continuous beam),the pier-beam-track finite element model,where the continuous beam of the ballast track and simply-supported beam are combined with each other,was established.The laws of the track stress,the pier longitudinal stress and the beam-track relative displacement were analyzed.The results show that reducing the longitudinal resistance can effectively reduce the track stress and the pier stress of the continuous beam,and increase the beam-track relative displacement.Increasing the rigid pier stiffness of continuous beam can reduce the track braking stress,increase the pier longitudinal stress and reduce the beam-track relative displacement,Increasing the rigid pier stiffness of simply-supported beam can reduce the track braking stress,the rigid pier longitudinal stress and the beam-track relative displacement.

Longitudinal dynamic response of pile in layered soil based on virtual soil pile model

Taking the effect of finite soil layers below pile end into account,the longitudinal dynamic response of pile undergoing dynamic loading in layered soil was theoretically investigated.Firstly,finite soil layers below pile end are modeled as virtual soil pile whose cross-section area is the same as that of the pile and the soil layers surrounding the pile are described by the plane strain model.Then,by virtue of Laplace transform and impedance function transfer method,the analytical solution of longitudinal dynamic response at the pile head in frequency domain is yielded.Also,the semi-analytical solution in time domain undergoing half-cycle sine pulse at the pile head is obtained by means of inverse Laplace transform.Based on these solutions,a parametric study is conducted to analyze emphatically the effects of parameters of soil below pile end on velocity admittance and reflected wave signals at the pile head.Additionally,a comparison with other models with different supporting conditions from soil below pile end is performed to verify the model presented.

An Integrated Dynamic Model of Ocean Mining System and Fast Simulation of Its Longitudinal Reciprocating Motion

An integrated dynamic model of China＇s deep ocean mining system is developed and the fast simulation analysis of its longitudinal reciprocating motion operation processes is achieved. The seafloor tracked miner is built as a three-dimensional single-body model with six-degree-of-freedom. The track-terrain interaction is modeled by partitioning the track-terrain interface into a certain number of mesh elements with three mutually perpendicular forces, including the normal force, the longitudinal shear force and the lateral shear force, acting on the center point of each mesh element. The hydrodynamic force of the miner is considered and applied. By considering the operational safety and collection efficiency, two new mining paths for the miner on the seafloor are proposed, which can be simulated with the established single-body dynamic model of the miner. The pipeline subsystem is built as a three-dimensional multi-body discrete element model, which is divided into rigid elements linked by flexible connectors. The flexible connector without mass is represented by six spring-damper elements. The external hydrodynamic forces of the ocean current from the longitudinal and lateral directions are both considered and modeled based on the Morison formula and applied to the mass center of each corresponding discrete rigid element. The mining ship is simplified and represented by a general kinematic point, whose heave motion induced by the ocean waves and the longitudinal and lateral towing motions are considered and applied. By integrating the single-body dynamic model of the miner and the multi-body discrete element dynamic model of the pipeline, and defining the kinematic equations of the mining ship, the integrated dynamic model of the total deep ocean mining system is formed. The longitudinal reciprocating motion operation modes of the total mining system, which combine the active straight-line and turning motions of the miner and the ship, and the passive towed motions of the pipeline, are proposed and simulated with the developed 3D dynamic model. Some critical simulation results are obtained and analyzed, such as the motion trajectories of key subsystems, the velocities of the buoyancy modules and the interaction forces between subsystems, which in a way can provide important theoretical basis and useful technical reference for the practical deep ocean mining system analysis, operation and control.

Analytical analysis for vibration of longitudinally moving plate submerged in infinite liquid domain

The vibration of a longitudinally moving rectangular plate submersed in an infinite liquid domain is studied analytically with the Rayleigh-Ritz method. The liquid is assumed to be incompressible, inviscid, and irrotational, and the velocity potential is used to describe the fluid velocity in the whole liquid field. The classical thin plate theory is used to derive mechanical energies of the traveling plate. As derivative of transverse displacement with respect to time in the compatibility condition equation exists, an exponential function is introduced to depict the dynamic deformation of the moving plate. It is shown that this exponential function works well with the Rayleigh- Ritz method. A convergence study shows a quick convergence speed for the immersed moving plate. Furthermore, the parametric study is carried out to demonstrate the effect of system parameters including the moving speed, the plate location, the liquid depth, the plate-liquid ratio, and the boundary condition. Results show that the above system parameters have significant influence on the vibration characteristics of the immersed moving plate. To extend the study, the method of added virtual mass incremental （AVMI） factor is used. The results show good agreement with those from the Rayleigh-Ritz method.

Physical model simulation of rock-support interaction for the tunnel in squeezing ground

The existence of squeezing ground conditions can lead to significant challenges in designing an adequate support system for tunnels.Numerous empirical,observational and analytical methods have been suggested over the years to design support systems in squeezing ground conditions,but all of them have some limitations.In this study,a novel experimental setup having physical model for simulating the tunnel boring machine(TBM)excavation and support installation process in squeezing clay-rich rocks is developed.The observations are made to understand better the interaction between the support and the squeezing ground.The physical model included a large true-triaxial cell,a miniature TBM,laboratoryprepared synthetic test specimen with properties similar to natural mudstone,and an instrumented cylindrical aluminum support system.Experiments were conducted at realistic in situ stress levels to study the time-dependent three-dimensional tunnel support convergence.The tunnel was excavated using the miniature TBM in the cubical rock specimen loaded in the true-triaxial cell,after which the support was installed.The confining stress was then increased in stages to values greater than the rock’s unconfined compressive strength.A model for the time-dependent longitudinal displacement profile(LDP)for the supported tunnel was proposed using the tunnel convergence measurements at different times and stress levels.The LDP formulation was then compared with the unsupported model to calculate the squeezing amount carried by the support.The increase in thrust in the support was backcalculated from an analytical solution with the assumption of linear elastic support.Based on the test results and case studies,a recommendation to optimize the support requirement for tunnels in squeezing ground is proposed.

Investigation of stimulated Raman scattering in longitudinal magnetized plasma by theory and kinetic simulation

Stimulated Raman scattering(SRS)in a longitudinal magnetized plasma is studied by theoretical analysis and kinetic simulation.The linear growth rate derived via one-dimensional fluid theory shows the dependence on the plasma density,electron temperature,and magnetic field intensity.One-dimensional particle-in-cell simulations are carried out to examine the kinetic evolution of SRS under low magnetic intensity of w_c/w_0<0.01.There are two density regions distinguished in which the absolute growth of enveloped electrostatic waves and spectrum present quite different characteristics.In a relatively low-density plasma(ne~0.20 nc),the plasma wave presents typical absolute growth and the magnetic field alleviates linear SRS.While in the plasma whose density is near the cut-off point(ne~0.23 nc),the magnetic field induces a spectral splitting of the backscattering and forward-scattering waves.It has been observed in simulations and verified by theoretical analysis.Due to this effect,the onset of reflectivity delays,and the plasma waves form high-frequency oscillation and periodic envelope structure.The split wavenumber Dk/k0 is proportional to the magnetic field intensity and plasma density.These studies provide novel insight into the kinetic behavior of SRS in magnetized plasmas.

直升机双层平尾构型气动特性分析

为分析双层平尾气动特性,采用CFD方法建立了直升机平尾计算模型,获得了低速前飞和机身大迎角状态不同构型平尾的气动特性,分析了单层和双层平尾构型的气动特性和流场特点,研究了双层平尾对低速前飞状态和大迎角状态的纵向静稳定性改善作用机理。结果表明:双层平尾构型通过抑制旋翼/平尾干扰改善低速前飞状态下的直升机俯仰力矩突增问题,前进比为0.05时,双层平尾俯仰力矩比单层平尾减小56.8%;双层平尾的失速迎角和最大俯仰力矩增大,从而增强直升机大迎角状态的纵向静稳定性,迎角20°时,双层平尾俯仰力矩比单层平尾增大60.1%。

执行功能与师生关系的变化轨迹对小学中高年级儿童学业自我效能感的独特效应和交互效应

为揭示儿童执行功能和师生关系的变化轨迹对学业自我效能感的独特效应和交互效应,对523名小学三至五年级儿童进行了6个月的追踪测量。结果表明:(1) 6个月内,儿童的执行功能有所增长,而师生关系质量有所下降;(2)执行功能和师生关系的初始水平和发展速度均能正向预测学业自我效能感;(3)师生关系初始水平和变化速度与执行功能初始水平而非发展速度之间存在交互效应。研究结果有助于揭示个体与环境因素随时间交互影响学业自我效能感的复杂机制,对提升学龄儿童学业自我效能感具有实践指导意义。

Parametric investigation of railway fastenings into the formation and mitigation of short pitch corrugation

Short pitch corrugation has been a problem for railways worldwide over one century.In this paper,a parametric investigation of fastenings is conducted to understand the corrugation formation mechanism and gain insights into corrugation mitigation.A three-dimensional finite element vehicle-track dynamic interaction model is employed,which considers the coupling between the structural dynamics and the contact mechanics,while the damage mechanism is assumed to be differential wear.Various fastening models with different configurations,boundary conditions,and parameters of stiffness and damping are built up and analysed.These models may represent different service stages of fastenings in the field.Besides,the effect of train speeds on corrugation features is studied.The results indicate:(1)Fastening parameters and modelling play an important role in corrugation formation.(2)The fastening longitudinal constraint to the rail is the major factor that determines the corrugation formation.The fastening vertical and lateral constraints influence corrugation features in terms of spatial distribution and wavelength components.(3)The strengthening of fastening constraints in the longitudinal dimension helps to mitigate corrugation.Meanwhile,the inner fastening constraint in the lateral direction is necessary for corrugation alleviation.(4)The increase in fastening longitudinal stiffness and damping can reduce the vibration amplitudes of longitudinal compression modes and thus reduce the track corrugation propensity.The simulation in this work can well explain the field corrugation in terms of the occurrence possibility and major wavelength components.It can also explain the field data with respect to the small variation between the corrugation wavelength and train speed,which is caused by frequency selection and jump between rail longitudinal compression modes.

小曲线半径条件下铁路桥梁线-梁-墩受力规律

建立朔黄铁路恢河特大桥三维有限元模型,分析不同荷载作用下恢河特大桥线-梁-墩的受力规律,并对比二维与三维计算模型的差异。结果表明:挠曲、制动作用下横向墩顶作用力均小于纵向墩顶作用力,而伸缩作用下3#—24#桥墩的横向墩顶作用力大于纵向墩顶作用力。制动力从轨面传递至墩顶纵向、横向的占比为86%、3%,离心力从轨面传递至墩顶纵向、横向的占比分别为12%、86%。

重载列车系统动力学研究进展

重载列车是现代轨道交通运输中的重要运载工具,是煤炭、化石等矿产资源运输的主干力量。随着列车编组长度不断增加和轴重不断提升,其动力学与行车安全性问题日益凸显,制约了重载铁路运输能力与技术的发展。为了提升重载列车系统的动态服役性能,保障列车运行安全性,本综述阐明了重载铁路运输面临的动力学与行车安全性问题,系统梳理了重载列车系统动力学的研究现状,研究了列车纵向动力学、三维列车动力学和列车与轨道耦合动力学的分析理论与研究方法,分析了现有研究的不足及面临的挑战,探讨了其未来研究重点和方向,以期为重载列车技术的发展提供参考。

支座摩阻力对高速铁路大跨度悬索桥梁轨相互作用的影响

运用ANSYS软件,建立某高速铁路大跨径悬索桥桥梁-轨道-塔墩空间有限元分析模型,采用组合弹簧模拟滑动支座,通过计入滑动支座摩阻力前后悬索桥桥梁-轨道系统的纵向附加力对比分析,研究支座摩阻力对梁轨相互作用的影响。结果表明:滑动支座摩阻力对大跨度悬索桥的制动附加力、偏载下的挠曲附加力和断轨附加力的影响比较显著,对伸缩附加力和对称加载下的挠曲附加力的影响较小;当摩阻系数分别为0.03,0.05和0.1时,偏载下钢轨最大挠曲附加应力分别是不计摩阻力时的58.65%,54.67%和53.39%,对称加载下钢轨最大制动附加应力分别是不计摩阻力时的72.85%,71.87%和71.01%,偏载下钢轨最大制动附加应力分别是不计摩阻力时的42.28%,39.80%和37.67%;随着摩阻系数的增大,钢轨的制动附加应力、偏载下的挠曲附加应力和断轨后钢轨断缝宽度均呈不断减小趋势,而主塔和活动墩的墩顶水平力则呈不断增大趋势。

整体桥上无缝线路钢轨非线性附加力算法研究

在计算桥上无缝线路的纵向阻力时,阻力模型通常采用无缝线路设计规范中建议的双折线纵向阻力模型,即有载与无载分别考虑后再线性叠加,未考虑钢轨的非线性行为。在计算方法上,工程中常采用有限元模型进行计算,有限元法建模效率较低、不便于对各设计参数的更改。为准确快速求得高速铁路整体式桥上梁轨相互作用下的钢轨附加力、钢轨位移、钢轨弹塑性分界点及整体桥墩顶位移等参数值的大小,提出更贴近于桥上钢轨实际受力的多折线纵向阻力模型,并采用建立微分方程组的数值解法,通过建立具有变化规律的平衡矩阵式来求解桥上无缝线路钢轨纵向阻力值的相关参数。研究分别给出了有载、无载工况下求解整体式桥上钢轨附加应力值的规律性矩阵式,经有限元法验证,得到该方法下的温度、制动力附加应力值的误差均较小,分别为1.6%和0.5%。并结合规律矩阵式得到同时考虑有载与无载下的非线性附加力的计算方法,非线性叠加与线性叠加两方法下的总附加应力计算差值随着制动/牵引力下的梁轨相对位移值的增大而增大,当梁轨相对位移小于1.8 mm时,2种方法误差少于5%,可忽略不计,但随着梁轨相对位移的进一步增加,非线性阻力模型计算的结果则更贴近于实际。

弱纵连下CRTS Ⅱ型板式无砟轨道解锁温度研究

在弱纵连施工过程中,为了避免轨道板凿除宽窄接缝后在解锁位置发生较大的位移变形,有必要明确不同解锁条件、不同解锁温度下轨道结构的受力变形特征,指导现场施工。基于梁轨相互作用原理和有限元法,建立无砟轨道-多跨简支梁桥精细化模型,利用有限元软件中“生死单元”的功能分步骤解锁轨道板,研究桥上CRTS Ⅱ型板式无砟轨道在不同解锁工况下轨道结构受力变形规律,据此分析得出合理解锁条件及解锁温度,并对应仿真计算中板端植筋工况,在预加固植筋地段进行了现场解锁实验。研究结果表明:不松开钢轨扣件,解锁板温在初始施工锁定板温±5℃范围内,可以直接解锁宽窄接缝;解锁板温在初始锁定板温±5℃之外,轨道板纵向位移不满足规范限值要求,需严格控制解锁温度;松开扣件解锁轨道板,轨道结构整体受力变形增大,轨道板纵向位移超过规范允许限值,建议解锁时不松开钢轨扣件;板端植筋有利于减小解锁后结构的受力变形,但轨道板纵向应力除外,板端植筋可作为解锁时的预防性手段。现场试验表明,解锁时轨道板板端植筋,宽窄接缝位置处轨道板间相对位移几乎不发生变化。研究成果对于CRTS Ⅱ型板式无砟轨道高温胀板病害提出了一种新的解决思路—弱纵连CRTS Ⅱ型板式无砟轨道。

东北黑土区长缓坡耕地横坡垄作与地形对土壤可蚀性的交互作用

【目的】东北黑土区坡耕地土壤侵蚀日益加重,研究横坡垄作与地形对土壤可蚀性K值的交互作用,为东北黑土区坡耕地水土流失的精准防控提供科学依据。【方法】选取黑龙江省北安市红星农场内典型坡耕地为研究对象,在横坡垄作方向与顺坡水线方向共布设25个采样点,并计算相应样点的土壤可蚀性K值,采用单因素方差分析(One-wayANOVA)检验土壤可蚀性K值的差异性,并使用地理探测器模型探讨土壤可蚀性K值的影响因子及其交互作用。【结果】横坡垄作方向,土壤可蚀性K值在垄台呈现从坡顶到坡足逐渐减小的变化趋势,坡足比坡顶减小幅度为6.2%;在垄沟呈现从坡肩到坡足逐渐减小的变化趋势,坡足比坡肩减小幅度为5.8%。顺坡水线方向,由于垄台对地表径流的阻挡作用,垄台和垄沟土壤可蚀性K值沿着坡面并没有明显的变化趋势。地理探测器分析表明,横坡垄作对土壤可蚀性K值的影响最大,其垄台和垄沟的解释率分别达51%和18%以上;横坡垄作与其他因子的交互作用增强了对土壤可蚀性K值的解释能力,特别是横坡垄作与地形的交互作用尤为明显。【结论】黑土区坡耕地土壤可蚀性K值具有明显的空间变异性,横坡垄作与地形对土壤可蚀性的影响存在明显的交互作用,横坡垄作可以显著拦蓄径流,减少土壤侵蚀,但因黑土区坡耕地横坡垄作的坡缓而长,在坡足处易于汇集径流,依然有“断垄”潜在风险。

Influence of differential longitudinal cyclic pitch on flight dynamics of coaxial compound helicopter

The Differential Longitudinal Cyclic Pitch(DLCP)in coaxial compound helicopter is found to be useful in mitigating low-speed rotor interactions and improving flight performance.The complex mutual interaction is simulated by a revised rotor aerodynamics model,where an improved Blade Element Momentum Theory(BEMT)is proposed.Comparisons with the rotor inflow distributions and aircraft trim results from literature validate the accuracy of the model.Then,the influence of the DLCP on the flight dynamics of the aircraft is analysed.The trim characteristics indicate that a negative DLCP can reduce collective and differential collective inputs in low speed forward flight,and the negative longitudinal gradient is alleviated.Moreover,a moderate DLCP can reduce the rotor and total power consumption by 4.68%and 2.9%,respectively.As DLCP further increases,the increased propeller power and unbalanced thrust allocation offset the improvement.In high-speed flight,DLCP does not improve the performance except for extra lateral and heading stick displacements.In addition,the tip clearance is degraded throughout the speed envelope due to the differential pitching moment and the higher thrust from the lower rotor.Meanwhile,the changed rotor efficiency and induced velocity alter low-speed dynamic stability and controllability.The pitch and roll subsidences are slightly degraded with the DLCP,while the heave subsidence,dutch roll and phugoid modes are improved.Lastly,the on-axis controllability,including collective,differential collective pitch,longitudinal and lateral cyclic pitches,varies with DLCP due to its effect on rotor efficiency and inflow distribution.In conclusion,a reasonable DLCP is recommended to adjust the rotor interaction and improve aircraft performance,and further to alter the flight dynamics and aerodynamics of aircraft.