A travel time reliability model of urban expressways with varying levels of service

Urban expressways usually experience several levels of service (LOS) because of the stop-and-go traffic flow caused by congestion. Moreover, multiple shock waves generate at different LOS interfaces. The dynamic of shock waves strongly influences the travel time reliability (TTR) of urban expressways. This study proposes a path TTR model that considers the dynamic of shock waves by using probability-based method to characterize the TTR of urban expressways with shock waves. Two model parameters are estimated, namely distribution of travel time (TT) per unit distance and travel distances in different LOS segments. Generalized extreme value distribution and generalized Pareto distribution are derived as distributions of TT per unit distance for six different LOS. Distribution parameters are estimated by using historical floating car data. Travel distances in different LOS segments are calculated based on shock wave theory. The range of TT along the path, which can help drivers arrange their trips, can be obtained from the TTR model. Finally, comparison is made among the proposed TTR model, generalized Pareto contrast model, which does not consider different LOS or existence of shock waves, and normal contrast model, which assumes TT per unit distance as normal distribution without considering shock wave. Results show that the proposed model achieves higher prediction accuracy and reduces the prediction range of TT. The conclusions can be further extended to TT prediction and assessment of measures to improve reliability of TT in a network.     

基于图形旋转系统的渐进层次细节和拓扑改变操作

针对现有的层次细节方法不能一直保持模型的二维流形性,提出2种基于图形旋转系统的拓扑改变操作Cut Tunnel和Create Tunnel。Cut Tunnel操作算法通过输入环绕待切断柄的1条封闭轨迹的顶点集合,然后删除所有与这些顶点相连的边,从而切断1个复杂的柄。Create Tunnel是Cut Tunnel的逆操作。在此基础上,提出1种渐进层次细节理论框架,框架采用基于图形旋转系统的数据结构表示模型网格,分为生成层次细节过程和使用层次细节过程2个过程。生成层次细节过程能够改变模型的拓扑,并自动生成连续变化的细节层次网格;使用层次细节过程使模型从某一层次细节的网格逐渐变形到任意层次细节的网格,并始终保持模型的二维流形性。对Stanford大学的buddhaf模型进行拓扑改变操作、生成渐进层次细节和运行层次细节的试验。结果表明:拓扑改变操作及渐进层次细节理论框架效果良好,模型始终保持了二维流形性。     

A new source number estimation method based on the beam eigenvalue

Most source number estimation methods based on the eigenvalues are decomposed by covariance matrix in MUSIC algorithm. To develop the source number estimation method which has lower signal to noise ratio and is suitable to both correlated and uncorrelated impinging signals, a new source number estimation method called beam eigenvalue method (BEM) is proposed in this paper. Through analyzing the space power spectrum and the correlation of the line array, the covariance matrix is constructed in a new way, which is decided by the line array shape when the signal frequency is given. Both of the theory analysis and the simulation results show that the BEM method can estimate the source number for correlated signals and can be more effective at lower signal to noise ratios than the normal source number estimation methods.     

缺损评分矩阵的论文排名

传统的竞赛评判由于受各种已知或者未知因素的影响,经常会导致数据缺损的情况出现。本文从分析评委的判分与选手的真实排名存在一个高度的线性相关入手,采用了线性回归的方法填补了缺损的数据,使之成为一个完整的数据集,再采用群组特征根法对数学建模竞赛的论文进行排序,最后用计算机模拟验证这种算法较缺损数据简单求和的算法优秀。     

T*=T2时算子T的谱

对自共轭算子的概念加以推广，引进了平方共轭算子的概念．应用希尔伯特空间上正规算子的概念、性质、谱映射定理和类推的方法，研究了该类算子的性质及正则值存在的充要条件．结果表明，当T^*=T^2时，该类算子T的谱是有限的特征谱。     

解读快速公交自动引导车辆系统

快速公交是一种快速、准时、安全的运输系统,具有投资小、建设周期短和发展弹性等优势,顺应我国城市发展的特点。水平登乘在快速公交中被广泛应用,能使乘客登乘方便和迅速,以达到减少巴士车辆在站台的等候时间、提高整个系统的运营能力和效率的目的。水平登乘不仅要求巴士车辆的地板高度与站台高度基本一致,还要求其车门与站台边缘之间的距离控制在一定范围,最大值不超过10 cm。如何精确靠站停车,给驾驶员及运营管理者提出了一个难题,快速公交自动引导车辆技术因此而产生。当今世界有3种成熟技术,分别是机械式、光学、磁力自动引导车辆技术,详细介绍以上3种技术,包括代表城市和工作原理及费用比较。通过此介绍,能够为解决我国快速公交运营中水平登乘存在的巴士车门与站台边缘距离过大的问题提供借鉴。     

Level and attitude control of the active suspension system with integral and derivative action

A 7-DOF full-car model with optimal active control suspension is utilized to evaluate the vehicle dynamic performances which are achieved through proposed controllers. The optimal controller, which includes the integral action for the suspension deflection, considerably improves the attitude control of a vehicle because the rolling and pitching motion in cornering and braking maneuvers are reduced, respectively. In the viewpoint of level control, the integral control acting on the suspension deflection results in the zero steady-state deflection in response to static body forces and ramp road input. The dynamic characteristics of the suspension control system are evaluated in terms of time domain and frequency domain. The simulations in the time domain demonstrate the advantages of the active suspension system obtained by penalizing the integral and derivative of suspension deflections and the derivative of roll and pitch angles in the performance index. The frequency characteristic curves obtained by simulations regarding integral action or derivative action show the increase of both ride comfort and road-holding performances by maximizing the use of suspension deflections. The potential of derivative control is shown by the performances of the car traveling over a bump and braking.     

钢筋混凝土拱桥参数化建模及特征值屈曲分析

针对某在建的150m跨径钢筋混凝土拱桥,利用开发的基于ANSYS的拱桥参数化建模模块,分别采用梁单元和实体单元创建有限元模型。在此基础上进行拱桥的特征值屈曲分析,并对拱轴线类型、桥面结构形式以及拱脚支承形式等影响因素进行了参数分析。分析结果表明:采用梁单元与实体单元进行结构离散,对于拱桥的特征值屈曲的计算结果影响不大。     

轴承刚度及间距对水下结构声振特性影响研究

为掌握轴承刚度及间距对水下结构振动声辐射的影响,本文建立了桨-轴-壳体简化模型,利用三维水弹性力学理论和三维水弹性声学分析软件,分析了不同轴承刚度及间距下壳体结构的声源级曲线。结果表明：轴承刚度越大,水下结构的辐射总声级越大;螺旋桨横向力激励下艉后轴承刚度对水下结构声辐射影响最大,艉前轴承次之,推力轴承影响最小;轴承间距变化对水下结构的声辐射影响不大,但容易改变推进轴系的振动状态。     

Competing for level of service in the provision of mobility services: Concepts, processes and measures

One of the most striking problems societies currently deal with is to assure adequate quality standards while improving accessibility within and between cities. In addition there is also a growing awareness that, to achieve a sustainable balance between private and public means of mobility, policies have to be able to send the correct signals in order to induce users adaptive behaviour, which in turn will provide the system with a reliable feedback on the needs for further investment and expansion of transport facilities. The definition and measurement of quality of service of the transport system is thus an objective aimed by both users and producers and it is often represented by the rather holistic concept of Level of Service (LoS). However, the LoS concept is not consciously used by users, on the contrary the user concentrates her comparative evaluation on what is simply known as quality. It is the planner that translates planned quality into LoS concept. So, LoS is a concept at the interface between the provider and the user. Given the interface character of the LoS concept an accounting framework for LoS should thus take into account the need to segregate the evaluation for passengers and freight transport and also distinguish between types of travellers in the case of passenger transport and types of commodities or logistic families in the case of freight transport. Moreover the bridge between the planner and the user view must be ensured. This paper reports the results of a research work dedicated to this topic.