On the influence of design parameters and nonlinearities in vehicle suspensions on road deformation

Among others, two main objectives of modern vehicle design are road friendliness and ride comfort. Both aspects are strongly related since the dynamical tire forces depend on the vertical acceleration of the vehicle. In order to investigate the influence of design and operation parameters, different car models are considered which move with constant velocity on a rippled road. First, a linear half car model is examined and the influence of different design parameters is discussed. Second, nonlinear suspensions with Coulomb friction due to sealings as well as with bilinear shock absorbers are taken into account. The vertical dynamics of the vehicle model and the dynamic tire forces between vehicle and road are calculated using analytical methods. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Numerical and experimental investigation on stochastic dynamic load of a heavy duty vehicle

Numerical simulation and field test are used to investigate tire dynamic load. Based on multi-body dynamics theory, a nonlinear virtual prototype model of heavy duty vehicle (DFL1250A9) is modeled. The geometric structural parameters of the vehicle system, the nonlinear characteristics of shock absorber and leaf springs are precisely described. The dynamic model is validated by testing the data, including vertical acceleration of driver seat, front wheel, intermediate wheel and rear wheel axle head. The agreement between the response of the virtual vehicle model and the measurements on the test vehicle is satisfactory. Using the reliable model, the effects of vehicle speed, load, road surface roughness and tire stiffness on tire dynamic load and dynamic load coefficient (DLC) are discussed. The results demonstrate that the proposed model can offer efficient and realistic simulation for stochastic dynamic loads, so as to investigate vehicle road-friendliness.     

A fuzzy clustering approach to real-time demand-responsive bus dispatching control

Quick response (QR) to passenger needs is a key objective for advanced public transportation systems (APTS), and it has become increasingly important for contemporary metropolitan bus operations to gain a competitive advantage over private transportation. This paper presents a real-time control methodology for demand-responsive bus operations that respond quickly to passenger needs. The proposed method primarily involves two levels of functionality: (1) short-term forecasting of passenger demands using time-series prediction models, and (2) identification of service strategies coupled with the associated bus service segments using fuzzy clustering technologies in response to variances in passenger demand attributes and traffic conditions. The proposed bus operations method identifies the demand-responsive vehicle service strategies primarily according to the predicted up-to-date attributes of passengers’ demands, rather than deterministic passenger arrival rates, which were generally used in previous literature. In addition, the variation of traffic conditions along bus lines is considered in the proposed method. Results from numerical studies using real data of passengers’ demands, including passenger volume at each bus stop and the passenger origin-destination (O-D) patterns, are presented to demonstrate the effectiveness of the proposed method for real-world applications.     

随机激励下四自由度车辆-道路耦合系统动力分析

采用四自由度车辆模型,以 Gauss平稳随机过程模拟路面的不平整度,编制程序得到不同路面等级下的不平整度序列;并将车辆和道路看作一个相互作用的整体系统,建立了车辆 道路耦合系统的动力平衡方程.在对车辆施加随机激励时,为了简化分析过程,避开以往研究中使用随机振动理论求解动轮胎力的复杂性,将得到的路面不平整度序列,直接以向量的形式输入到所建立的动力平衡方程中.基于增量形式的Newmark-β法开发了一个MATLAB程序对该方程进行求解.并对所提出的理论模型进行了试验验证,证明了模型的可靠性.随后,通过一个实例,分析了车速变化、路面等级变化对车辆动荷载系数和车体垂向加速度的影响.最后,对不同路基刚度对车辆振动特性的影响规律进行了探讨.     

On Dynamic Aspects and Pattern Generation in Vehicle-Road Interaction

Increasing transport capacity leads to new vehicle designs and increasing axle loads. Still it has to be better understood until which extend especially heavy vehicles cause corrugation of roads. Therefore, basic investigations concerning vehicle-road interaction are helpful to augment the understanding of the basic mechanisms. Firstly, in order to investigate the oscillatory behavior of a vehicle a MDoF oscillator moving with constant velocity on a rippled road is considered. From this, general results about wear pattern generation of the road are derived from analytical considerations concerning the dynamic contact force between vehicle and road. Secondly, a simple vehicle road interaction model is presented which consists of a vehicle model and a road exhibiting viscoelastic plastic characteristics. Results of numerical simulations are compared with the findings deduced from the analytical MDoF model. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optimizing winter road maintenance operations under real-time information

This paper introduces a real-time optimization model that can be used by maintenance managers to develop and evaluate alternative resources allocation plans for winter road maintenance operations. The model takes into account a wide range of road and weather condition factors such as road network topology, road class, weather forecasts, and contractual service levels, and produces a vehicle dispatch schedule that is optimal with respect to operating costs and quality of service. The model is then used in an analysis on a realistic case to illustrate the potential impact of improved information on winter maintenance operations.     

乘客到达时间不确定的机场动态拼车策略与算法研究

网约车拼车服务作为共享经济领域重要应用,已成为国内外研究热点。针对机场在线拼车平台运营中乘客等待时间过长和车辆行驶成本较高的突出问题,本文提出前瞻式动态拼车匹配策略。该策略将未来随机到达乘客信息纳入当前已到达乘客的拼车匹配决策中,建立了乘客匹配与车辆路径联合优化两阶段随机规划模型。为了在动态环境中实时产生高质量的匹配与路径规划方案,首先基于贝叶斯估计压缩乘客随机到达情景空间,建立了问题的确定性近似最优模型。为了快速求解模型,提出基于订单目的地和乘客期望到达时间相似度的匹配规则,并以此开发改进的差分进化算法。最后,基于某拼车平台真实订单数据,通过对比测试验证了前瞻式匹配策略和改进差分进化算法的有效性与计算效率。     

Real-time moving object segmentation in H.264 compressed domain based on approximate reasoning

This paper presents a real-time segmentation algorithm to obtain moving objects from the H.264 compressed domain. The proposed segmentation works with very little information and is based on two features of the H.264 compressed video: motion vectors associated to the macroblocks and decision modes. The algorithm uses fuzzy logic and allows to describe position, velocity and size of the detected regions in a comprehensive way, so the proposed approach works with low level information but manages highly comprehensive linguistic concepts. The performance of the algorithm is improved using dynamic design of fuzzy sets that avoids merge and split problems. Experimental results for several traffic scenes demonstrate the real-time performance and the encouraging results in diverse situations.     

Minimum-Time Travel for a Vehicle with Acceleration Limits: Theoretical Analysis and Receding-Horizon Implementation

A methodology is proposed to generate minimum-time optimal velocity profiles for a vehicle with prescribed acceleration limits along a specified path. The necessary optimality conditions are explicitly derived, allowing the construction of the optimal solution semianalytically. A receding horizon implementation is also proposed for the on-line implementation of the velocity optimizer. Robustness of the receding horizon algorithm is guaranteed by the use of an adaptive scheme that determines the planning and execution horizons. Application to a real-life scenario with a comparison between the infinite and finite receding horizon schemes provides a validation of the proposed methodology. This work has been supported in part by the US Army Research Office, Awards DAAD19-00-1-0473 and W911NF-05-1-0331. The authors thank an anonymous reviewer for his insightful comments regarding the results in Sect. 5.     

Fuzzy multi-objective optimization of passive suspension parameters

The paper proposed a systematic and effective optimization process to optimize a 3-D vehicle suspension dynamic model with eight DOF, including seat vertical motion, suspension vertical, pitching and rolling motions and wheels vertical motions using fuzzy optimization, to attain the best compromise between ride comfort and vehicle-generated road damage. The results show a substantial improvement in the vertical ride quality is obtained while keeping the suspension deflections within their allowable clearance when the vehicle moves at a constant velocity v = 20m/s, and the comfort performance of a suspension seat can be considerably enhanced.     

Real-time moving object segmentation in H.264 compressed domain based on approximate reasoning

This paper presents a real-time segmentation algorithm to obtain moving objects from the H.264 compressed domain. The proposed segmentation works with very little information and is based on two features of the H.264 compressed video: motion vectors associated to the macroblocks and decision modes. The algorithm uses fuzzy logic and allows to describe position, velocity and size of the detected regions in a comprehensive way, so the proposed approach works with low level information but manages highly comprehensive linguistic concepts. The performance of the algorithm is improved using dynamic design of fuzzy sets that avoids merge and split problems. Experimental results for several traffic scenes demonstrate the real-time performance and the encouraging results in diverse situations.     

Vehicle routing and scheduling with time-varying data: A case study

A heuristic algorithm is described for vehicle routing and scheduling problems to minimise the total travel time, where the time required for a vehicle to travel along any road in the network varies according to the time of travel. The variation is caused by congestion that is typically greatest during morning and evening rush hours. The algorithm is used to schedule a fleet of delivery vehicles operating in the South West of the United Kingdom for a sample of days. The results demonstrate how conventional methods that do not take time-varying speeds into account when planning, except for an overall contingency allowance, may still lead to some routes taking too long. The results are analysed to show that in the case study using the proposed approach can lead to savings in CO₂ emissions of about 7%.     

一个关于高柔结构顺风向抗风设计中考虑地震作用组合的概率模型及求解

基于概率方法建立了高柔结构顺风向抗风设计中,考虑地震作用组合的总水平荷载的计算模型并进行了求解．在基于Turkstra准则的具体组合分析中,考虑了风和地震作用作为离散随机过程的发生概率以及风速和地面加速度的概率分布特征,并按照随机变量及相应函数的概率密度关系,得到了风和地震作用的概率密度分布．后利用卷积方法,分析探讨了结构抗风设计中地震作用的组合,并给出了实际的高柔结构算例．该研究反映对于水平荷载由风荷载起控制作用的高柔结构,最大水平荷载验算中,考虑风和地震作用后组合的总荷载可能较抗震设计中考虑了风荷载组合的结果更为不利．     

A method for determining control inputs for prescribed accelerations of the end-effector of a motion-simulator robot

Described in this paper is an approach for generating control inputs for an industrial Kuka robot such that it produces prescribed linear acceleration time histories for a given point of the end-effector. The method takes into account the workspace limits, and uses the internal interpolation cycle of the robot controller to generate the corresponding trajectories that will produce the prescribed accelerations. The PI parameters of the internal interpolation are identified from test measurements. The control scheme consists in producing time-varying values for the desired angle values of the interpolation algorithm, making the changes as the algorithm proceeds and thus generating smooth trajectories. The resulting acceleration of these trajectories is compared to the prescribed accelerations, and an optimization procedure is run such as to determine the required time-histories of the desired angles for the interpolation algorithm such that both accelerations match. The approach is demonstrated for the example of a 500kg payload Kuka robot that is aimed at producing given motions as a physical motion simulator (e. g. for cars or complex working machines). It is shown that the desired accelerations can be generated accurately and with high repeatability, making the approach suitable for example for simulating car rollover tests. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A school bus scheduling problem

This paper introduces a school bus scheduling problem wherein trips for each school are given. A trip consists of a sequence of bus stops and their designated school. Each school has its fixed time window within which trips should be completed. A school bus can serve multiple trips for multiple schools. The school bus scheduling problem seeks to optimize bus schedules to serve all the given trips considering the school time windows. We first model the problem as a vehicle routing problem with time windows (VRPTW) by treating a trip as a virtual stop. Two assignment problem based exact approaches are then proposed for special cases and a heuristic algorithm is proposed for more general cases. Benchmark problems and computational experiments are presented. Computational experiments show the effectiveness of the proposed approaches.     

Managing vehicle breakdown incidents during urban distribution of a common product

This paper addresses a case in which a vehicle, member of a fleet distributing a single product, is immobilized while executing its distribution plan. Some active vehicles of the fleet are then rerouted to serve selected clients of the immobilized vehicle. We model this re-planning problem as a variation of the Team Orienteering Problem constraining all vehicle routes to an upper time, or distance, limit, and taking into account limited vehicle capacity. We propose an efficient heuristic to provide solutions in almost real-time. The heuristic progressively constructs new routes for each active vehicle, which may load additional product by visiting the warehouse or the immobilized vehicle. If appropriate, we solve this replenishment sub-problem by a fast labelling algorithm. We test the effectiveness of the proposed heuristic by comparing its solutions with those obtained by an appropriate Genetic Algorithm (GA) that yields high quality (but computationally expensive) results.     

智能网联下无人车配送路径优化

结合智能网联无人车实时信息共享与路径选择的特点,研究其配送路径优化问题。通过引进关键点更新策略,制定路径预规划阶段和路径实时调整阶段无人车路径选择策略,提出智能网联环境下基于实时交通信息的车辆路径问题两阶段模型。其中,路径预规划阶段模型确定初始路径与每辆车服务的客户点,路径实时调整阶段模型对每辆车的路径实时调整。对于该优化模型设计遗传算法进行求解,并通过算例验证了模型与算法的可行性。研究结果表明,本文构建的无人车配送优化模型,有效的结合了无人车实时通信与路径选择的特点,节省了无人车配送时间。研究对于无人车在第三方物流配送领域的推广应用具有一定的探索意义。     

Full velocity difference and acceleration model for a car-following theory

In order to describe the car-following behavior more actually in real traffic, a full velocity difference and acceleration model (for short, FVDAM) is proposed by synthetically taking into account headway, velocity difference and acceleration of the leading car on the basis of full velocity difference model. The analytical method and numerical simulation results show that the proposed model can describe the phase transition of traffic flow and estimate the evolution of traffic congestion, that incorporating the acceleration of the leading car into car-following model can stabilize traffic flow, suppress the traffic jam and increase capacity, and that the following car in FVDAM can accelerate more quickly than in FVDM.     

Effect of the optimal velocity function on traffic phase transitions in lattice hydrodynamic models

The original lattice hydrodynamics models of traffic flow are extended to take into account the complex acceleration behavior of drivers. A new optimal velocity function which considers the stepwise acceleration effect and fits the observed data better is introduced. The stability conditions of these two models are obtained by using the linear stability theory. It is shown that the modified optimal velocity function has a remarkable influence on the neutral stability curve and the traffic phase transitions. In a certain vehicle’s density and driver’s sensitivity region, tri-stable states will occur. In addition, the properties of the multiple phases also depend on the asymmetry of the optimal velocity function and the stage number of multi-phase transitions is closely related to the turning points of the optimal velocity function. The validity and correctness of the analytical results is confirmed by numerical simulations.