广州地铁柔性接触网检测问题分析

接触网动态检测是确保地铁正常运行的一项重要技术措施,使用检测车对地铁柔性接触网进行预防性检测,对地铁列车正常取流和预防断电事故有着非常重要的作用。对地铁柔性接触网检测车工作过程中存在的问题进行理论分析,并提出具体解决办法。     

考虑车轮谐波磨耗的动车组车轴疲劳寿命

以CRH380BL型高速动车组为研究对象,基于车轮谐波磨耗的实测结果,建立刚性轮轨、刚性轮柔性轨、柔性轮刚性轨以及柔性轮轨4种不同轮轨关系下的车辆-轨道耦合动力学模型,通过对比分析4种模型的轮轨振动特性,得到最能反映真实情况的轮轨耦合动力学模型;基于车轴受力分析,采用有限元软件ANSYS进行车轴静强度计算;采用多体动力学软件计算考虑车轮谐波磨耗的车轴载荷时间历程;根据疲劳累积损伤理论,采用FE-SAFE软件分析考虑车轮谐波磨耗的车轴疲劳寿命。结果表明:柔性轮轨关系更能反映轮轨的真实接触状态;车轴轮座内侧圆弧过渡处的应力最大,为114.4 MPa;考虑车轮谐波磨耗的车轴疲劳寿命约为19.2 a;车轮谐波磨耗导致轮轨振动加剧,对车轴疲劳寿命产生明显不利的影响。     

Bottleneck model revisited: An activity-based perspective

The timing of commuting trips made during morning and evening peaks has typically been investigated using Vickrey’s bottleneck model. However, in the conventional trip-based approach, the decisions that commuters make during the day about their activity schedules and time use are not explicitly considered. This study extends the bottleneck model to address the scheduling problem of commuters’ morning home-to-work and evening work-to-home journeys by using an activity-based approach. A day-long activity-travel scheduling model is proposed for the simultaneous determination of departure times for morning and evening commutes, together with allocations of time during the day among travel and activities undertaken at home or at the workplace. The proposed model maximizes the total net utility of the home-based tour, which is the difference between the benefits derived from participating in activities and the disutility incurred by travel between activity locations. The properties of the model solution are analytically explored and compared with the conventional bottleneck model for a special case with constant marginal-activity utility. For the case with linear marginal-activity utility, we develop a heuristic procedure to seek the equilibrium scheduling solution. We also explore the effects of marginal-work utility (or the employees’ average wage level) and of flexible work-hour schemes on the scheduling problem in relation to the morning and evening commuting tours.     

Maximizing net benefits for conventional and flexible bus services

Transit ridership is usually sensitive to fares, travel times, waiting times, and access times, among other factors. Therefore, the elasticities of demand with respect to such factors should be considered in modeling bus transit services and must be considered when maximizing net benefits (i.e. “system welfare” = consumer surplus + producer surplus) rather just minimizing costs. In this paper welfare is maximized with elastic demand relations for both conventional (fixed route) and flexible-route services in systems with multiple dissimilar regions and periods. As maximum welfare formulations are usually too complex for exact solutions, they have only been used in a few studies focused on conventional transit services. This limitation is overcome here for both conventional and flexible transit services by using a Real Coded Genetic Algorithm to solve such mixed integer nonlinear welfare maximization problems with constraints on capacities and subsidies. The optimized variables include service type, zone sizes, headways and fares. We also determine the maximum welfare threshold between optimized conventional and flexible services) and explore the effects of subsidies. The proposed planning models should be useful in selecting the service type and optimizing other service characteristics based on local geographic characteristics and financial constraints.     

Time-domain structural analysis during block turnover and lifting using 2D flexible multibody dynamics

Ship construction involves the assembly of several blocks on a dock. When a block is lifted using a crane, it undergoes deformation. Until now, structural analysis has been applied in a few cases to evaluate the stress on such blocks. Therefore, this study proposes an evaluation method for time-domain stress using 2D flexible multibody dynamics. We adopt the discrete Euler-Lagrange equation to achieve robustness during the numerical integration of problems that involve high stiffness. We formulate the equations of motion of 2D shell elements based on the absolute nodal coordinate formulation, which is an efficient analysis technique for nonlinear and large deformation cases. We also derive the two types of kinematic constraints (ball and fixed joints) between the rigid and shell element, which can be attached to an arbitrary point. Based on the theories, we develop the program to build models, including 2D flexible multibody dynamics and several joints, and to solve the equations of motion efficiently. As a result, it is successfully applied to the dynamic analysis of the block turnover by a gantry crane and the block lifting by a floating crane. The von-Mises stresses that change over time are compared to the maximum yield stress and analyzed according to the wave direction.     

Local structural analysis of flexible pipes subjected to traction,torsion and pressure loads

Helically armored cables or pipes find a wide range of applications as structural members in engineering. An example of this is the increasing use of flexible pipes in the oil offshore production. Although keeping a geometrical similarity with other helically armored structures such as wire ropes and ACSR conductors, and borrowing from them a useful methodology for the structural analysis, some care must be taken in order not to indiscriminately use an approach which was not thought for a flexible pipe: internal and external pressures, for instance, are a great concern in the analysis of flexible pipes, but obviously not for wire ropes. This work aims at giving some additional contribution to the structural response of flexible pipes when subjected to axisymmetric loads, including the effect of both internal and external pressure in pipe displacements. Derivation of linear operators, relating the stress-resultants to their related displacements or deformations in each of the layers of the pipe, as well as the process of deriving an analogous linear operator to represent the behavior of the pipe as a whole, are clearly presented, highlighting interesting mathematical aspects and their associated physical meaning. A numerical case study of a 2.5″ flexible pipe subjected to traction and internal pressure is also presented and discussed.     

非粘结柔性立管静态分析

海洋柔性立管因材料和结构上的复杂性在设计分析中存在许多技术难题。本文在变形能原理和能量守恒的基础上,推导出了柔性立管各层的刚度矩阵。将各层刚度矩阵进行叠加,得到柔性立管总体刚度矩阵,并用总体刚度矩阵求解静载荷作用下立管变形响应。同时基于ABAQUS软件建立八层非粘结柔性立管有限元模型,并将有限元计算结果和刚度矩阵计算结果进行比较。结果分析表明：运用推导得到的刚度矩阵求解静态载荷下立管的变形是一种简便且准确的方法。     

A finite element model for flexible pipe armor wire instability

The constructive disposition of metallic and plastic layers confers flexible pipes with high and low axial stiffness respectively when tensile and compressive loads are applied. Under certain conditions typically found during deepwater installation or operation, flexible pipes may be subjected to high axial compression, sometimes accompanied by bending. If not properly designed, the structure may not be able to withstand this loading and fails. From practical experience observed offshore and in laboratory tests two principal mechanisms, which will be discussed in this paper, have been identified regarding the configuration of the armor wires. When the pipe fails by compression the armor wires may exhibit localized lateral or radial deflections, consequently permanent damage is observed in the armor wires with a sudden reduction of the structure’s axial stiffness. The pressure armor may also unlock, thus causing potential fluid leakage.In this work a finite element model is developed to estimate the critical instability load and failure modes. An axi-symmetric model is constructed employing a complex combination of beam and spring elements. For each armor layer only one wire needs to be modeled, hence the computational cost is minimized without compromising the phenomenon characterization. A parametric case study is performed for a typical flexible pipe structure, where the friction coefficient between the wire armors and the external pressure are varied, and the critical instability loads and failure modes are obtained and results are discussed.     

ABAQUS二次开发在海洋柔性立管设计分析中的应用

基于ABAQUS软件利用Python脚本语言和GUI功能开发了针对柔性立管的建模界面和求解模块.借此设计分析人员可以快速地建立柔性立管的有限元模型并进行计算分析,有效地解决了柔性立管在研制阶段的设计-分析-校核的重复繁琐问题,缩短了研发周期.