On the existence of stationary states in general road networks

Our daily driving experience and empirical observations suggest that traffic patterns in a road network are relatively stationary during peak periods. In numerous transportation network studies, there has been an implicit conjecture that stationary states exist in a network when origin demands, route choice proportions, and destination supplies are constant. In this study, we first rigorously formulate the conjecture within the framework of a network kinematic wave theory with an invariant junction model. After defining stationary states, we derive a system of algebraic equations in 3-tuples of stationary link flow-rates, demands, and supplies. We then introduce a new definition of junction critical demand levels based on effective demands and supplies. With a map in critical demand levels, we show that its fixed points and, therefore, stationary states exist with the help of Brouwer’s fixed point theorem. For two simple road networks, we show that the map is well-defined and can be used to solve stationary states with a brute-force method. Finally we summarize the study and present some future extensions and applications.     

润滑油对发动机曲轴摩擦功影响的仿真与试验研究

以某直列3缸汽油机为研究对象,利用 AVL EXCITE 软件建立了曲轴多体动力学仿真模型,通过台架试验,验证了该仿真模型的正确性,在此模型基础上分析了润滑油温度、供油压力以及润滑油种类对发动机曲轴摩擦功的影响规律。研究表明：指定条件下的曲轴摩擦损失功率仿真结果为106．6 W ,台架试验结果为102 W ,误差在5％以内,表明仿真模型具有相当的精度;当润滑油供油温度从40℃升高到110℃时,曲轴摩擦损失功率减小到最低,约为104 W ,当温度超过110℃后,摩擦损失增加,当温度上升到150℃时,摩擦损失功率达到140 W ,润滑条件急剧恶化;当轴承主油道入口压力从0．31 MPa 增加到0．4 MPa 时,曲轴摩擦功率减小约10 W ,且供油温度较低时润滑油供油压力对曲轴摩擦功率影响较大;曲轴摩擦功率随黏度的提高而增加,供油温度较低时,润滑油黏度对曲轴摩擦功率的影响较大。     

Slip-based terrain estimation with a skid-steer vehicle

In this paper, a novel approach for online terrain characterisation is presented using a skid-steer vehicle. In the context of this research, terrain characterisation refers to the estimation of physical parameters that affects the terrain ability to support vehicular motion. These parameters are inferred from the modelling of the kinematic and dynamic behaviour of a skid-steer vehicle that reveals the underlying relationships governing the vehicle-terrain interaction. The concept of slip track is introduced as a measure of the slippage experienced by the vehicle during turning motion. The proposed terrain estimation system includes common onboard sensors, that is, wheel encoders, electrical current sensors and yaw rate gyroscope. Using these components, the system can characterise terrain online during normal vehicle operations. Experimental results obtained from different surfaces are presented to validate the system in the field showing its effectiveness and potential benefits to implement adaptive driving assistance systems or to automatically update the parameters of onboard control and planning algorithms.     

轮毂电机驱动电动汽车双横臂前悬架运动学优化

基于传统汽车底盘平台进行电动轮驱动改型时,轮毂电机的布置将导致悬架硬点坐标的改变,从而严重影响悬架运动学特性,为此须对电动轮驱动改型车悬架系统进行优化设计.以某传统车底盘平台的双横臂前悬架运动学特性为优化目标,根据参数灵敏度分析结果,提出两步优化方案,即首先进行主销定位参数的优化,而后再进行前轮外倾角和前轮前束角的优化...     

车辆排队间距对交叉口通行能力的影响

对交叉口车辆队列的启动离去过程建立运动学方程,研究交叉口等待车辆的车间距与通过时间的相互关系,进一步分析影响交叉口通行能力的其他因素.分析发现:车辆队列的间距过小或过大均可导致交叉口通行能力下降.最后,通过理论分析和仿真试验表明,当问距在4～8 m之间时,可有效降低等待队列长度及车辆通过交叉口的启动延时时间,从而最大可能提高交叉口通行能力.     

纵向耦合独立车轮转向架建模方法研究

根据多体系系统动力学理论,在建立动力学模型时,可将车轮间的动力学矢量设计成树形结构,这种处理使车轮间仅生成动力学约束而不是运动学约束。另一种方式将车轮间的纵向耦合方式视为无质量的运动约束,即车轮在连接点处具有相同的运动,运动矢量形成闭环。目前,在建立纵向耦合独立车轮转向架动力学模型时,都采用运动学约束来处理一侧前后车轮的耦合关系。以某COMBINO型纵向耦合独立车轮转向架为例,分别采用运动学约束和动力学约束的方法,对比曲线通过能力,以评价动力学约束方法的合理性。     

基于Adams的调距螺旋桨滑块式调距机构运动学分析

本文主要进行调距桨滑块式变距机构的运动学分析,在设计工况下,通过运动学分析软件Adams对调距桨的变距机构进行仿真,得出相应工况下变距机构各个部件的运动参数,并将运动参数与设计理论参数对比,为此种螺旋桨调距机构的设计和生产提供理论依据。     

GPS在移动机器人导航定位系统中的应用

为了获得移动机器人定位数据的真实性，减少各种随机误差对定位精度的影响，通过运动载体当前统计模型，取位置作为观测量建立移动机器人动态定位模型，同时针对传统卡尔曼滤波的不足进行了分析，提出自适应卡尔曼滤波算法，该算法始终保持噪声模型接近于真实模型，从而较好地解决了GPS动态定位中状态噪声与观测噪声建模不准确和时变问题，在此基础上，通过模拟噪声和轨迹曲线，进行了仿真，结果显示效果显著。     

连山大桥泥石流沟灾害特征分析

2013年7月10日和7月12日在强降雨的作用下,连山大桥泥石流沟连续两次发生泥石流,造成都汶高速公路和G213线200 m长度范围内堆积泥石流约8万m3,汶川至都江堰的交通中断。以连山大桥泥石流沟为研究对象,分别从流域因素、物源和水源这三个方面分析泥石流的形成原因,并分析泥石流的成灾过程机制,以及计算泥石流的运动参数和泥石流发展趋势及影响范围,提出防治工程措施。     

Robust hierarchical controller with conditional integrator based on small gain theorem for reference trajectory tracking of autonomous vehicles

ABSTRACT

A robust trajectory tracking controller is designed for autonomous vehicles based on a hierarchical architecture to make the autonomous vehicle track a given reference trajectory. The controller consists of two sub controllers: kinematic controller and dynamic controller. Based on the kinematics of tracking reference trajectory, a desired yaw rate is calculated by kinematic controller to make the lateral deviation global asymptotic stable. Then, steering wheel angle is calculated by a vehicle dynamic controller to make the vehicle yaw rate converge to the desired value and make the vehicle dynamic stable. Conditional integration method is used in the sub controllers. This method guarantees global asymptotic stability of tracking reference values and considers the uncertainty of parameters and constraints of desired yaw rate and actuators. Then based on small-gain theorem, the condition of the finite-gain L stability is given to the hierarchical controller to ensure the interconnected sub systems stable and prevent the amplification of system disturbance. Finally, the effectiveness and robustness of the controller are validated by real vehicle experiments.