基于时空等待特征系数的大型活动出行规划研究

高效、合理的综合交通路径规划是成功举办大型活动的前提之一。本文针对观众群体参 与大型活动的出行路径规划问题，引入乘客出行偏好，转换为时空等待优化问题，再根据大型活 动中乘客通过多模式公共交通出行特点，构建多维时间-空间-交通方式网络，以乘客出行时间总 成本最小为目标建立整数线性规划模型。为提高模型的求解效率与质量，提出一种基于拉格朗 日松弛和次梯度优化的算法进行求解，并在求解中提出基于逆向推断的搜索空间约减方法，提高 了算法求解速度。本文以观众从北京市城区前往延庆区高山滑雪中心观赛为案例验证模型与算 法。结果表明，引入时空等待特征系数后，提升了大型活动综合交通出行路径规划方案的合理 性，改善了乘客的出行体验，并有效缓解举办大型活动时的道路拥堵状况。     

Modelling shared space users via rule-based social force model

The promotion of space sharing in order to raise the quality of community living and safety of street surroundings is increasingly accepted feature of modern urban design. In this context, the development of a shared space simulation tool is essential in helping determine whether particular shared space schemes are suitable alternatives to traditional street layouts. A simulation tool that enables urban designers to visualise pedestrians and cars trajectories, extract flow and density relation in a new shared space design, achieve solutions for optimal design features before implementation, and help getting the design closer to the system optimal. This paper presents a three-layered microscopic mathematical model which is capable of representing the behaviour of pedestrians and vehicles in shared space layouts and it is implemented in a traffic simulation tool. The top layer calculates route maps based on static obstacles in the environment. It plans the shortest path towards agents’ respective destinations by generating one or more intermediate targets. In the second layer, the Social Force Model (SFM) is modified and extended for mixed traffic to produce feasible trajectories. Since car movements are not as flexible as pedestrian movements, velocity angle constraints are included for cars. The conflicts described in the third layer are resolved by rule-based constraints for shared space users. An optimisation algorithm is applied to determine the interaction parameters of the force-based model for shared space users using empirical data. This new three-layer microscopic model can be used to simulate shared space environments and assess, for example, new street designs.     

Airline competition and market frequency: A comparison of the s-curve and schedule delay models

We compare two common ways of incorporating service frequency into models of airline competition. One is based on the so called s-curve, in which, all else equal, market shares are determined by frequency shares. The other is based on schedule delay—the time difference between when travelers wish to travel and when flights are available. We develop competition models that differ only with regard to which of the above approaches is used to capture the effect of frequency. The demand side of both models is an approximation of a nested logit model which yields endogenous travel demand by including not traveling in the choice set. We find symmetric competitive equilibrium for both models analytically, and compare their predictions concerning market frequency with empirical evidence. In contrast to the s-curve model, the schedule delay model depicts a more plausible relationship between market share and frequency share and accurately predicts observed patterns of supply side behavior. Moreover, the predictions from both models are largely the same if we employ numerical versions of the model that capture real-world aspects of competition. We also find that, for either model, the relationship between airline frequency and market traffic is the same whether frequency is determined by competitive equilibrium, social optimality, or social optimality with a break-even constraint.     

A real-time approach to robust identification of tyre–road friction characteristics on mixed-μ roads

ABSTRACT

The interaction between the tyre and the road is crucial for understanding the dynamic behaviour of a vehicle. The road–tyre friction characteristics play a key role in the design of braking, traction and stability control systems. Thus, in order to have a good performance of vehicle dynamic stability control, real-time estimation of the tyre–road friction coefficient is required. This paper presents a new development of an on-line tyre–road friction parameters estimation methodology and its implementation using both LuGre and Burckhardt tyre–road friction models. The proposed method provides the capability to observe the tyre–road friction coefficient directly using measurable signals in real-time. In the first step of our approach, the recursive least squares is employed to identify the linear parameterisation form of the Burckhardt model. The identified parameters provide, through a T–S fuzzy system, the initial values for the LuGre model. Then, a new LuGre model-based nonlinear least squares parameter estimation algorithm using the proposed static form of the LuGre to obtain the parameters of LuGre model based on recursive nonlinear optimisation of the curve fitting errors is presented. The effectiveness and performance of the algorithm are demonstrated through the real-time model simulations with different longitudinal speeds and different kinds of tyres on various road surface conditions in both Matlab/Carsim environments as well as collected data from real experiments on a commercial trailer.     

Biodynamic responses of seated pregnant subjects exposed to vertical vibrations in driving conditions

A pregnant woman's body is a very sophisticated dynamic system that is sensitive to whole-body vibrations in a sitting posture. While much effort has been devoted to vibration effects on non-pregnant seated persons, little research has been devoted to the biodynamic responses of seated pregnant women exposed to vertical vibrations, especially in driving conditions. In this study a thorough survey of lumped-parameter models for non-pregnant seated persons is implemented. According to the literature the mathematical models adequate for representing the increase in mass due to pregnancy are proposed and evaluated systematically. On the basis of an analytical study and experimental validation, the six-degree-of-freedom model modified from the non-linear model proposed by Muksian and Nash is recommended. In addition, the recommended pregnant model is further integrated with two-dimensional half-car and three-dimensional full-car models to assess the responses of pregnant drivers or passengers exposed to vertical vibrations due to road unevenness. It is believed that the study presented in this report provides a profound understanding of biodynamic responses of seated pregnant women and that it may offer vehicle engineers a good reference in the design of vehicle suspension systems.     

A control strategy for parallel hybrid electric vehicles based on extremum seeking

An energy management control strategy for a parallel hybrid electric vehicle based on the extremum-seeking method for splitting torque between the internal combustion engine and electric motor is proposed in this paper. The control strategy has two levels of operation: the upper and lower levels. The upper level decision-making controller chooses the vehicle operation mode such as the simultaneous use of the internal combustion engine and electric motor, use of only the electric motor, use of only the internal combustion engine, or regenerative braking. In the simultaneous use of the internal combustion engine and electric motor, the optimum energy distribution between these two sources of energy is determined via the extremum-seeking algorithm that searches for maximum drivetrain efficiency. A dynamic programming solution is also obtained and used to form a benchmark for performance evaluation of the proposed method based on extremum seeking. Detailed simulations using a realistic model are presented to illustrate the effectiveness of the methodology.     

船用螺旋桨加工工艺及数控编程技术研究

结合不同类型船用螺旋桨的加工工艺特点和企业加工技术现状,在进行螺旋桨数控加工工艺研究的基础上,针对企业如何在最短的时间内编制出可靠、高效的数控程序这一问题,以UG的CAM模块为平台,以UG OPEN/API和高级编程语言VC++为主要开发工具,在模块化软件开发思想的指导下,将CAM系统所包含的各类参数设置、刀轨计算和后处理等功能集成起来,实现了船用螺旋桨数控编程的集成化、自动化和智能化。     

新建船队的船队优化模型建立和比较

船队规划问题通常是通过建立连续变量线性规划模型或混合整数线性规划模型来解决,但往往会得到要求一艘船营运于多条航线的结果。而企业出于安全因素和便于管理的角度考虑,希望船队单船个体的航线能固定,这就需要采用整数规划模型来解决此类问题。针对新建船队的整体配置规划问题,在建立连续变量线性规划模型和混合整数线性规划模型的基础上,探索并建立线性整数规划模型和非线性整数规划模型并进行优化。通过对计算实例的分析比较,论述了4种优化数学模型的特点与适用范围。     

美国公路桥梁设计规范中关于设计汽车荷载的研究

美国公路桥梁设计规范(AASHTO LRFD)中设计汽车荷载种类多样且复杂,介绍该规范中关于HL-93设计汽车荷载的相关规定,以及荷载影响线的动态规划法分析原理,进而研究变轴距、变车距等形式的HL-93设计汽车荷载在MIDAS Civil通用有限元软件中的快速实现方法。对国外某实桥进行HL-93设计汽车荷载效应分析,并与中国规范做对比分析。结果表明:对该多跨等截面连续梁,随着轴距的增加,主梁支点负弯矩、跨中正弯矩逐渐减小;而随着车距的增加,跨中正弯矩基本不变,支点负弯矩呈现先增大而后逐渐减小的规律。中国公路Ⅰ级与美国HL-93设计汽车荷载效应相比,主梁剪力与跨中正弯矩前者比后者大,支点负弯矩前者比后者小15%左右。