| In recent years, with the high-speed railway in china being completed and opend to traffic,operating mileage growing, which makes the technology innovation theme of high-speed railway to be no longer confined to the construction and design, whilethe operation and maintenance technology guaranteeing the safe operation of high-speed railway has become a new hotspot now. Despite high standard design parameters adopted in the design of high speed railway subgrade, deterioration of service status of subgrade in local area during operation is showing more and more under the combined action of train dynamic load and complex nature forces, because of powders characteristics of soil and stone material.Whether uneven settlement of subgrade or frosting boil at subgrade bed will cause track irregularity, which become excitation source of the train-line vibration , threatening traffic safety and increasing the dynamic forces of train on ballastless subgrade. There is still a lack of in-depth theoretical research on the dynamic problem caused by track irregularity, which further caused by the damages of ballast-less track subgrade. In this paper, the vibration response characteristics of subgrade-ballastless track-vehicle system are researched, under the railway line irregularity excitation caused by the uneven settlement of subgradeand frost boilingat subgrade : (1) Recalling the development of vehicle - track -subgrade system dynamics, the discrete models of the vehicle, track, and the subgrade structure during the research of system dynamics are summarized. Based on dynamic analysis model of the traditional vehicle/track system , the integrated subgrade is included in to the vibration system, and the contact status between ballastless track and subgrade is also considered, therefore the space-time-variant calculation model of the integrated subgrade- ballastless track-vehicle system which can reveal the line irregularity and the effect feature of track-subgrade contact interface caused by the subgrade damage is developed. Aiming at the contact problems between rigid concrete base plate and flexible graded gravel subgrade surface, three contact patterns which consist of full contact, vibrate contact and full disengagement together with their assembly patterns of elements is presented, and the restrictions that satisfies mechanics and geometric boundaries is also developed, therefore it can reflect the two-node double-contact unit model caused by the nonlinear contact behavior between disengaged bedplate and roadbed surface, and also derive the contact model vibration equation. In the end, the iterative solution process of track nonlinear contact problems and the adaptive algorithm of contact unit constrained modulus coefficient is elaborated.(2) Based on interactive software development platform Visual Studio 2010 , dynamic analysis program of subgrade — ballastless track —vehicle coupling system with intellectual property was developed with the Fortran language. The one dimensional variable bandwidth method is chosen for storage of large stiffness matrix elements. Based on the correlation analysis of freedom degree, the elements of stiffness matrix are divided into three parts, which include zero element part, nonzero elements part and time-varying nonzero elements part.It's addressing formula and half-bandwidth calculation equation were deduced . The program structure of element group sets has been designed based on the partition division of stiffness matrix elements and elements time-varying effect . Using"Column Major" law of multidimensional array storage, the operating program of array was optimized, which improves the execution efficiency of the program. The problem of multidimensional array stack overflow in oversized DOF dynamic calculation was solved by increasing stack space, avoiding the definition inside subprogram and employing large array. The reason of NAN error is analyzed and the corresponding solution was raised too.(3)The article expounds identification methods of main parameters for system dynamic analysis43 of the vehicle, ballastless track and subgrade. The rational length of the model and the effective integration step size is researched by numerical experiments. The results show that the length of the calculation model should guarantee the vehicle length and irregularity, in addition, the distance between the contact point of wheel set and the head of model should not less than 6 span length. The value ranges of numerical integration step size are analyzed by newmark integral equations.The results show that the lower limit of integration step ?t is codetermined by rounding error of the computer program and higher-order equation ill-posed problem that may caused by the integration algorithm. After the trail of maximum reasonable and effective integration step by zero-speed steady-state response test, the results show that that the maximum reasonable and effective integration step associates with driving speed and irregularity wavelength. Within a certain range,the maximum effective integration step increases with the increasing of irregularity excitation wavelength,decreases with the increasing of driving speed.(4)The SBVDAS is used to study the effect of wave depth of uneven settlement ,wave velocity and the speed of the trains on vibration characteristics of the vehicle, ballastless tra ck and subgrade are studied, under the condition of the medium long wave irregularity excit ation of rail surface caused by subgrade uneven settlement. Based on this, limiting value of uneven settlement of high speed railway subgrade in operation were analyzed. The results s how that vehicle running performance deteriorated significantly when the vehicle passes sec tion of uneven settlement of subgrade. The destructive effect of vehicle on ballastless track subgrade is strengthened. Vibration strength of vehicle body system increases with increasin g, while the vibration strength parameters of ballastless track and subgrade structure increas e linearly. The effect of wave depth of uneven settlement on vehicle vibration response is gr eater than ballastless track and subgrade structure. The vibration acceleration of the vehicle is affected significantly by the "frequency domain effect" of wave length, and 17.5m is the s ensitive wavelength of the vibration acceleration of the vehicle body in the 5?20m wavelen gth range. Dynamic response of each structural layer of ballastless track subgrade decreases with the increasing wave depth of settlement, and the effect is gradually weakened. The irre gularity excitation of rail surface leads to uneven distribution of dynamic stress on the top s urface of the subgrade caused by uneven settlement of subgrade, and the dynamic stress am plitude of the subgrade surface shows the characteristic of cosine field distribution along the longitudinal direction of the line. Dynamic evaluation of limiting value of subgrade uneven settlement should be taken into account for the vehicle safety and comfort, ballastless track subgrade structure fatigue damage and long-term dynamic stability. When the train speed is 250km/h, the vertical acceleration of vehicle body is the control index of ballastless track su bgrade uneven settlement limit. Ballastless track subgrade uneven settlement should be cont rolled within 18mm/20m during operation.(5)The effect of parameters of frost-boiling region length, contact failure value, train speed on the dynamic responses of the vehicle, ballastless track, subgrade are analysed by t he subgrade-ballastless track-vehicle coupled system analytic model under the condition of subgrade frost-boiling. The result reveals that subgrade frost-boiling has a greater impact on dynamic response of the ballastless track and subgrade structure than the vehicle dynamic index. The train's vertical vibrational acceleration shows a gentle increase as the contact failure length caused by frost-boiling, while the vertical force between wheels and track hardly changes, and the dynamic displacement of the track, slab and support layer of the ballastless track increases obviously in a nonlinear way. When the frost-boiling zone reaches 8 spans, the dynamic displacement of the track exceeds the limit, which suggests that 8 spans should be the control value of the frost-boiling area length. Frost boiling also leads to significant differences of the dynamic stress distributionon on the subgrade surface.Stress on the subgrade surface of the frost boiling area decreases obviously, while there is a stress concentration emerges on the edge. The increase of the vehicle speed will exacerbate the structure vibration of the ballastless track among the frost boiling area, and the vertical force between wheels and track grows slightly, but both the train's vibrational acceleration and the dynamic displacement of the track are reduced. The critical interlayer contact failure value caused by the frost boiling is relevant to the vehicle speed and the frost boiling area length. The sensitive factor of the dynamic displacement of the slab and support layer reach the value of 5.14, and the value of dynamic displacement amplitude ratio when the subgrade is in good condition (0.92) is much higher than the value when frost boiling occurs (0.1),which could be regarded as the dynamic index to preliminary identify the frost boiling disease.(6)The subgrade frost boiling under ballastless track is a special form of high-speed railway subgrade defectsappearing in recent years. In order to study the effect of the frost boiling on dynamic characteristics of ballasted track subgrade, in-situ survey and train-induced vibration tests were carried out in Shanghai-Nanjing intercity railway defects section. The vibration characteristics of ballastless track subgrade under the condition of forst boiling are analyzed. The results show that the subgrade frost boiling mainly resulted from the high content of fine particles in graded gravel and the cracking in expansion joints and side joints of foundation plate. The frost boiling at subgrade bed reduces the support and constraint effect of subgrade on the ballastless track, and intensifies the vibration of ballasted track structure, especially to the foundation plate of ballastless track. The vibration amplification effect increases with the increase of train speed. The defect also changes vibration wave transmission between ballastless track and subgrade bed, which restricts the energy dissipation function of subgrade bed. When the train speed reaches 247km/h, the amplitude of vibration displacement at the surface of subgrade reduces by 45%. The vibration displacement transfer function from the foundation plate to subgrade bed decreases by 2/3, and the value is between 0.22-0.39 in dynamic loading mainly frequency range (0?15Hz) of the subgrade. |
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