Improving crosswind stability of fast rail vehicles using active secondary suspension

Rail vehicles are today increasingly equipped with active suspension systems for ride comfort purposes. In this paper, it is studied whether these often powerful systems also can be used to improve crosswind stability. A fast rail vehicle equipped with active secondary suspension for ride comfort purposes is exposed to crosswind loads during curve negotiation. For high crosswind loads, the active secondary suspension is used to reduce the impact of crosswind on the vehicle. The control input is taken from the primary vertical suspension deflection. Three different control cases are studied and compared with the only comfort-oriented active secondary suspension and a passive secondary suspension. The application of active secondary suspension resulted in significantly improved crosswind stability.     

Quasi-steady-state linearisation of the racing vehicle acceleration envelope: a limited slip differential example

In the motorsport environment, passive limited slip differentials are a well-established means of improving the traction limitation imposed by the open differential. Torque sensing types are highly adjustable, and can alter both the stability and agility of the vehicle in the various cornering phases of a typical manoeuvre. In this paper, an adjustable clutch plate or ‘Salisbury’ differential model is presented, which can significantly alter its torque bias characteristics through adjustments in the drive/coast ramp angle, the number of friction faces and preload. To allow robust evaluation of differential parameter changes on ultimate vehicle performance and handling balance, a unified acceleration or ‘GG’ diagram framework is then described. This builds on traditional GG diagram approaches, by using nonlinear constrained optimisation to define both the vehicle acceleration limits and a ‘feasibility’ region within the performance envelope. By linearising a seven degrees of freedom vehicle model at multiple operating points, eigenvalue and yaw rate response analysis is then used to establish contours of stability and agility throughout the GG envelope. This brings new insights into the way in which handling balance changes below and up to the vehicle's acceleration limits.     

Hybrid state-feedback sliding-mode controller using fuzzy logic for four-wheel-steering vehicles

This paper presents a fuzzy controller for high-speed four-wheel-steering (4WS) vehicles based on the state-feedback and the sliding-mode control methods. In the proposed fuzzy controller, the consequent part of the fuzzy IF-THEN rules consists of either a sliding-mode controller or a state-feedback controller. Also, it will be proved that, if every fuzzy rule is stable in the sense of Lyapunov for a general Lyapunov function, defined for the whole system, then the whole system is stable in the sense of Lyapunov. The effectiveness of the proposed method for handling improvement of the 4WS systems will be demonstrated by simulations using a nonlinear vehicle model. The simulation results show that the proposed control method can enhance the dynamic response of the 4WS vehicles by reducing the transient response time and improving vehicle stability as compared to the sliding-mode and the fuzzy sliding-mode control methods.     

A curving ACC system with coordination control of longitudinal car-following and lateral stability

The paper presents a curving adaptive cruise control (ACC) system that is coordinated with a direct yaw-moment control (DYC) system and gives consideration to both longitudinal car-following capability and lateral stability on curved roads. A model including vehicle longitudinal and lateral dynamics is built first, which is as discrete as the predictive model of the system controller. Then, a cost function is determined to reflect the contradictions between vehicle longitudinal and lateral dynamics. Meanwhile, some I/O constraints are formulated with a driver permissible longitudinal car-following range and the road adhesion condition. After that, desired longitudinal acceleration and desired yaw moment are obtained by a linear matrix inequality based robust constrained state feedback method. Finally, driver-in-the-loop tests on a driving simulator are conducted and the results show that the developed control system provides significant benefits in weakening the impact of DYC on ACC longitudinal car-following capability while also improving lateral stability.     

基于离散单元法的软岩隧道施工过程数值模拟与围岩变形分析

以震后重建工程S302线大马庄隧道为工程实例,采用通用离散元程序UDEC建立平面弹塑性模型,进行了隧道施工过程数值模拟,得到了某一指定横断面上各监控点的全断面开挖围岩变形量及其变化规律,并与实际现场量测数据对比,发现模型计算所得量值与实测量值能较好地吻合。同时采用UDEC程序对该断面进行了台阶法开挖模拟,模拟结果表明分部开挖可有效减小拱顶沉降量和水平位移量,抑制底拱部隆起,且围岩变形主要发生在上台阶开挖阶段,及早闭合临时仰拱可有效减少围岩变形。离散元程序可根据现场情况模拟围岩变形规律,并可结合实测数据对施工提出修改和指导意见。     

某公路大型滑坡稳定性评价及治理方案设计

以贵州境在建杭瑞高速公路某大型滑坡作为研究对象,在综合分析已有的工程地质勘探资料的基础上,对滑坡产生的原因进行了剖析。同时运用极限平衡法,分析了滑坡变形破坏的模式及滑坡稳定性,提出了强支挡、削坡减载+抗滑桩及全削坡减载等3种滑坡治理措施。在此基础上对不同整治措施的技术可行性及经济指标进行比较分析,优选削坡减载+抗滑桩方案。实践表明,削坡减载+抗滑桩方案是一种治理滑坡性价比很好的方法。     

商用车电子稳定性控制系统的标准发展及关键技术

介绍了商用车电子稳定性控制系统(ESC)的基本原理及其技术背景,阐述了系统标准的发展现状,并从系统功能定义、系统评价、系统的试验方法及仿真方法等方面,分析了标准的核心内容.简述了系统控制策略、车辆状态估计、执行器设计开发、系统评价体系、底盘综合控制等关键技术.     

软土中无筋刚性桩复合地基支承路堤的整体稳定实用计算方法

为了合理评估无筋刚性桩复合地基支承路堤的稳定性,基于已进行的软土地基上刚性桩复合地基支承路堤的破坏机理研究,提出了刚性桩复合地基的整体稳定性简化分析方法,结合3个典型算例,与基于桩身抗剪强度的传统复合地基稳定方法进行了对比分析。结果表明：基于传统的复合地基稳定计算方法,采用桩身抗剪强度将显著高估路堤稳定性,桩身等效抗剪强度法可更好地反映刚性桩复合地基的破坏机理;采用等效荷载法、等效砂桩法和等效抗剪强度法计算得到的路堤稳定安全系数很接近;采用英国BS 8006规范方法、等效荷载法、摩擦接触法计算得到的路堤稳定安全系数显著依赖于桩土应力比。建议对无筋刚性桩复合地基支承路堤采用多种简化分析方法进行分析,保证设计的冗余度。     

土工格栅加筋碎石桩复合地基稳定性计算分析

简要叙述了土工格栅加筋碎石桩的处治机理以及土工格栅加筋碎石桩复合地基稳定下计算原理,并结合实例进行了计算分析。实例计算结果表明土工格栅加筋碎石桩复合地基在进行软基处治中能提高土基的承载能力及稳定性,同时减小路基沉降。     

基于边坡稳定计算的软件分析对比

边坡稳定性分析一直是工程建设领域的常见问题也是难点,传统的分析方法主要借助于工程地质类比法、刚体极限平衡法等对边坡进行定性评价并求得安全系数。利用有限差分法软件FLAC3D,有限元法软件PLAXIS和传统的刚体极限平衡法软件理正对兴隆土质边坡进行稳定性分析和求解安全系数,数值分析法得到的滑动面比传统方法假定的圆弧滑动面更加合理,强度折减法得到的安全系数比传统方法更加准确。