Understanding the limitations of different vehicle models for roll dynamics studies

An accurate and realistic vehicle model is essential for the development of effective vehicle control systems. Many different vehicle models have been developed for use in various vehicle control systems. The complexity of these models and the assumptions made in their development depend on their application. This article looks into the development and validity of vehicle models for prediction of roll behavior and their suitability for application in roll control systems. A 14 DOF vehicle model that includes dynamics of roll center and nonlinear effects due to vehicle geometry changes is developed. The limitations, validity of simplified equations, and various modeling assumptions are discussed by analyzing their effect on the model roll responses in various vehicle maneuvers. A formulation of the popular 8 DOF vehicle model that gives good correlation with the 14 DOF model is presented. The possible limitations of the 14 DOF model compared with an actual vehicle are also discussed.     

Understanding the limitations of different vehicle models for roll dynamics studies

An accurate and realistic vehicle model is essential for the development of effective vehicle control systems. Many different vehicle models have been developed for use in various vehicle control systems. The complexity of these models and the assumptions made in their development depend on their application. This article looks into the development and validity of vehicle models for prediction of roll behavior and their suitability for application in roll control systems. A 14 DOF vehicle model that includes dynamics of roll center and nonlinear effects due to vehicle geometry changes is developed. The limitations, validity of simplified equations, and various modeling assumptions are discussed by analyzing their effect on the model roll responses in various vehicle maneuvers. A formulation of the popular 8 DOF vehicle model that gives good correlation with the 14 DOF model is presented. The possible limitations of the 14 DOF model compared with an actual vehicle are also discussed.     

OSCAR statement of methods

OSCAR (Outil de Simulation du CAptage pour la Reconnaissance des défauts) is the pantograph–catenary dynamic software developed by Société Nationale des Chemins de fer Français (SNCF) since 2004. A three-dimensional finite element (FE) mesh allows the modelling of any catenary type: alternating current (AC) or direct current (DC) designs, and conventional or high-speed lines. It is a representative of the real overhead line geometry, with contact wire (CW) irregularities, staggered alignment of the CW, dropper spacing, wire tension, etc. Nonlinearities, such as slackening of droppers and unilateral contact between the pantograph and the CW, are taken into account. Several pantograph models can be used, with a complexity level growing from the three-lumped-mass model to the multibody model. In the second case, a cosimulation between the FE method catenary and the multibody pantograph models has been developed. Industrial features for pre- and post-treatments were developed to increase robustness of results and optimise computation time. Recent developments include volume meshing of the CW for stress computation or statistical analysis and lead to new fields of studies such as fatigue failure or design optimisation. OSCAR was fully validated against in-line measurements for its different AC and DC catenary models as well as its different pantograph models (with independent strips for instance) and has continuously been certified against EN50318 since 2008.     

Improved Vehicle Performance Using Combined Suspension and Braking Forces

This work presents a preliminary investigation into the integration of particular subsystems of an automobile's chassis. The specific focus of this research is the integration of Active Suspension components with Anti-Lock braking (ABS) mechanisms. The performance objective for the integrated approach is defined as a reduction in braking distance over just anti-lock brakes. Several models, of varying degrees of complexity, are presented to determine the effect of modeling accuracy on the potential performance improvement. In the most detailed model, a four degree of freedom Half Car vehicle model is developed along with models for a hydraulic Active Suspension and an ABS system. For both subsystems, actuator dynamics are included. The tire-road interface is modeled using the Magic Formula tire model. Individual controllers are developed for the subsystems and a governing algorithm is constructed to coordinate the two controllers. Simulations of the integrated controller and an ABS system, for each system model, demonstrate a significant increase in performance.     

Quasi steady-state aerodynamic model development for race vehicle simulations

Presented in this paper is a procedure to develop a high fidelity quasi steady-state aerodynamic model for use in race car vehicle dynamic simulations. Developed to fit quasi steady-state wind tunnel data, the aerodynamic model is regressed against three independent variables: front ground clearance, rear ride height, and yaw angle. An initial dual range model is presented and then further refined to reduce the model complexity while maintaining a high level of predictive accuracy. The model complexity reduction decreases the required amount of wind tunnel data thereby reducing wind tunnel testing time and cost. The quasi steady-state aerodynamic model for the pitch moment degree of freedom is systematically developed in this paper. This same procedure can be extended to the other five aerodynamic degrees of freedom to develop a complete six degree of freedom quasi steady-state aerodynamic model for any vehicle.     

Development and Evaluation of Vehicle Simulation Models for a 4WS Application

In the scope of the European Prometheus project a passenger car with active rear wheel steering was developed by TNO in cooperation with PSA. During development and engineering of the rear wheel steering system simulation tools have been used to reduce development costs. This paper describes the evaluation of different simulation models, from simple to complex, with results of full vehicle driving tests. The optimal balance for model complexity and accuracy was achieved with a 2-dimensional model with an added roll degree of freedom. The results show that validation using time responses can give ambiguous and inaccurate results, and that frequency response functions are much more usable in validation.     

Model reduction in vehicle dynamics using importance analysis

Previous work by the authors developed a novel model reduction method, namely importance analysis, that offered a unique set of properties: concurrent dynamic and kinematic reduction, applicability to nonlinear systems, preservation of realisation, and trajectory dependence. This paper investigates the utility of importance analysis as a model reduction tool within the context of vehicle dynamics. To this end, a high-fidelity model of a High Mobility Multipurpose Wheeled Vehicle (HMMWV) is considered, and this model is reduced for three different scenarios. Reduction is achieved in both dynamics and kinematics while preserving the original definition and interpretation of state variables and parameters. Furthermore, the resulting reduced models are very different in terms of complexity, containing only what is necessary for their respective scenarios, and providing important insight and computational savings. The conclusion is that importance analysis can be an invaluable reduction tool in vehicle dynamics, offering the aforementioned unique set of properties.     

Development and Evaluation of Vehicle Simulation Models for a 4WS Application

SUMMARY

In the scope of the European Prometheus project a passenger car with active rear wheel steering was developed by TNO in cooperation with PSA. During development and engineering of the rear wheel steering system simulation tools have been used to reduce development costs. This paper describes the evaluation of different simulation models, from simple to complex, with results of full vehicle driving tests. The optimal balance for model complexity and accuracy was achieved with a 2-dimensional model with an added roll degree of freedom. The results show that validation using time responses can give ambiguous and inaccurate results, and that frequency response functions are much more usable in validation.     

基于有限混合零截尾事故预测模型的事故多发段判别方法

为了准确判别事故多发段,有针对性地提出安全应对措施以提升道路交通的安全水平,针对零值缺失交通事故数据并考虑其异质性特点,在单零截尾负二项(ZTNB)模型的基础上建立有限混合零截尾事故预测模型(FMZTNB)。应用R软件对单零截尾负二项模型中的参数进行估计,采用马尔科夫链蒙特卡洛算法(MCMC)对FMZTNB预测模型参数进行求解,并采用Gelman-Rubin收敛统计量对抽样结果进行检查。选择事故风险水平分别为低、中和高的9个路段,分别用2种模型对交通事故次数进行预测。综合观测到的事故次数和相应的事故预测模型结果,采用经验贝叶斯方法对事故相对多发段进行判别。最后采用事故次数一致性检验、判别点段一致性检验和排序一致性检验3种检验方式对判别结果对比分析。结果表明:基于事故率的事故相对多发段判别方法存在较大的不一致性,基于零截尾负二项预测模型的路段事故相对多发判别结果明显优于基于传统负二项预测模型的结果。整体上,基于有限混合零截尾事故预测模型的事故相对多发路段的判别结果高于基于单零截尾负二项分布模型的判别结果。     

New tyre-road contact model for applications at low speed

Most of the tyre models have been developed for high speed, combined forces, etc., however, in certain tests it is necessary to know tyre behaviour at very low speed in order to evaluate different systems. So, during vehicle inspection and maintenance of the steering and brake system, by means of sideslip tester and roller brake tester respectively, the forces transmitted by the tyres are measured; all of these inspections are carried out at low speeds. Furthermore, usually, automobile vehicles run at low speeds during an important part of their operating life (less than 60 km/h), mainly during urban traffic, and in steady state conditions. Therefore, it is particularly interesting to develop an accurate model of the contact patch tyrepavement for low speeds without the complexity of models that cover a wide speed range but provide less precision at very low speeds. The dynamometer plate has proved to be an appropriate test equipment to characterise the tyre-pavement contact at low speed and the steering geometry and wheel alignment. It has the feature of being able to carry out tests with the tyre installed in the vehicle as in completely real conditions. The main aim of this research is to set up a contact model between tyre and pavement at very low speed based on the measurement of longitudinal and lateral forces. A test methodology that allows carrying out the experimental tests in a systematic and controlled way with the dynamometer plate has also been developed. From this model it will be possible to estimate the forces that tyres are capable of transmitting in different situations to act in the parameters which affect these forces and maximize them.     

Models and methodology for optimal trajectory generation in safety-critical road–vehicle manoeuvres

There is currently a strongly growing interest in obtaining optimal control solutions for vehicle manoeuvres, both in order to understand optimal vehicle behaviour and, perhaps more importantly, to devise improved safety systems, either by direct deployment of the solutions or by including mimicked driving techniques of professional drivers. However, it is non-trivial to find the right combination of models, optimisation criteria, and optimisation tools to get useful results for the above purposes. Here, a platform for investigation of these aspects is developed based on a state-of-the-art optimisation tool together with adoption of existing vehicle chassis and tyre models. A minimum-time optimisation criterion is chosen for the purpose of gaining an insight into at-the-limit manoeuvres, with the overall aim of finding improved fundamental principles for future active safety systems. The proposed method to trajectory generation is evaluated in time-manoeuvres using vehicle models established in the literature. We determine the optimal control solutions for three manoeuvres using tyre and chassis models of different complexities. The results are extensively analysed and discussed. Our main conclusion is that the tyre model has a fundamental influence on the resulting control inputs. Also, for some combinations of chassis and tyre models, inherently different behaviour is obtained. However, certain variables important in vehicle safety-systems, such as the yaw moment and the body-slip angle, are similar for several of the considered model configurations in aggressive manoeuvring situations.     

Urban Traffic Flow Prediction Using a Spatio-Temporal Random Effects Model

Traffic prediction is critical for the success of intelligent transportation systems (ITS). However, most spatio-temporal models suffer from high mathematical complexity and low tune-up flexibility. This article presents a novel spatio-temporal random effects (STRE) model that has a reduced computational complexity due to mathematical dimension reduction, with additional tune-up flexibility provided by a basis function capable of taking traffic patterns into account. Bellevue, WA, was selected as the model test site due to its widespread deployment of loop detectors. Data collected during the 2 weeks of July 2007 from 105 detectors in the downtown area were used in the modeling process and traffic volumes predicted for 14 detectors for the entire month of July 2008. The results show that the STRE model not only effectively predicts traffic volume but also outperforms three well-established volume prediction models, the enhanced versions of autoregressive moving average (ARMA) and spatiotemporal ARMA, and artificial neural network. Even without further model tuning, all the experimental links produced mean absolute percentage errors between 8% and 16% except for three atypical locations. Based on lessons learned, recommendations are provided for future applications and tune-up of the proposed STRE model.     

Influence of uneven rail irregularities on the dynamic response of the railway track using a three-dimensional model of the vehicle–track system

A mathematical model of the vehicle–track interaction is developed to investigate the coupled behaviour of vehicle–track system, in the presence of uneven irregularities at left/right rails. The railway vehicle is simplified as a 3D multi-rigid-body model, and the track is treated as the two parallel beams on a layered discrete support system. Besides the car-body, the bogies and the wheel sets, the sleepers are assumed to have roll degree of freedom, in order to simulate the in-plane rotation of the components. The wheel–rail interface is treated using a nonlinear Hertzian contact model, coupling the mathematical equations of the vehicle–track systems. The dynamic interaction of the entire system is numerically studied in time domain, employing Newmark's integration method. The track irregularity spectra of both the left/right rails are taken into account, as the inputs of dynamic excitations. The dynamic responses of the track system induced by such irregularities are obtained, particularly in terms of the vertical (bounce) and roll displacements. The numerical model of the present research is validated using several benchmark models reported in the literature, for both the smooth and unsmooth track conditions. Four sample profiles of the measured rail irregularities are considered as the case studies of excitation sources, examining their influences on the dynamic behaviour of the coupled system. The results of numerical simulations demonstrate that the motion of track system is significantly influenced by the presence of uneven irregularities in left/right rails. Dynamic response of the sleepers in the roll direction becomes more sensitive to the rail irregularities, as the unevenness severity of the parallel profiles (quantitative difference between left and right rail spectra) is increased. The severe geometric deformation of the track in the bounce–pitch–roll directions is mainly related to such profile unevenness (cross-level) in left/right rails.     

Development of a new analytical model for a railway vehicle equipped with independently rotating wheels

The urban tram introduced recently has a low-floor structure for the convenience of passengers getting on and off. To adjust the low-floor level and improve performance on curves, most low-floor trams have IRWs (independently rotating wheels) with no central axle between the two wheels. Eliminating the central axle, however, creates several inherent problems, such as insufficient guiding force and excessive wear. To analyze these problems, a new analytical model is described in this paper to describe the dynamic characteristics of IRWs more precisely. This analytical model is developed to consider the effects of longitudinal creep in particular, which have been ignored in conventional analytical models of IRWs. In addition, a running stability analysis based on the newly developed analytical model is conducted to compare the critical speeds of IRW-axle vehicles and rigid-axle vehicles. The dynamic characteristics of an initial disturbance are compared to verify that the analytical model is effective in expressing the dynamic characteristics of IRWs.     

公交动态信息下通勤出发时间选择行为分析

在交通行为分析中,传统效用函数形式不能反映个人属性对信息效用感知的影响。改进效用函数形式,运用多项Logit模型理论,建立了公交动态信息下的公交通勤者出发时间选择行为初始模型。从初始模型中选择t检验显著的解释变量,并分别基于传统效用函数形式、改进的效用函数建立了2个修正模型。对比2个修正模型标定结果发现,改进的效用函数比传统的效用函数更有利于提高模型性能。研究也表明:性别、收入的t检验值分别为2.02、-2.25,说明二者对乘坐时间信息效用感知显著;教育属性的t检验值为2.03,说明其对车内拥挤程度信息效用感知影响显著;乘坐时间取均值,车内拥挤度为0.7时,二者效用比值为1.54∶1,说明乘坐时间信息是影响出发时间选择最重要的因素。      

面向运营管理的多粒度省际客运需求预测方法

客运量是表征省际客运需求,开展行业运营管理的基础指标.为增强省际客运行业运营管理水平,提高旅客出行效率和应急保障能力,建立面向省际客运运营管理的年客运量和节假日客运量的多粒度预测模型.在影响因素与省际年客运量关联度分析的基础上,构建基于BP神经网络的年客运量预测模型.考虑特殊节假日的影响特征,提出了指数平滑与季节模型相结合的节假日客运量组合预测模型,实现节假日总客运量、日客运量的预测.以北京的实际数据为例,对预测模型进行精度验证.结果表明,年客运量预测模型的平均相对误差为0.15%,春运期间每日客运量预测模型的平均相对误差为6.7%,能较好地体现客运量在不同阶段的变化趋势,具有良好的稳定性.      

层次分析法在汽车购买中的应用

近年来随着国家经济的不断发展，国民可支配收入的不断增加以及经济全球化趋势的加剧，中国的消费者往往需要在更多的消费产品中做出选择，对于汽车购买决策行为尤其如此。诸如汽车购买决策这样的大型消费决策行为往往需要用户在综合收集处理大量的相关信息以后进行。然而，普通消费者对汽车的详细参数、性能以及车型具体信息等并不熟悉，同时大量的汽车车型以及参数的存在，都使得做出明智的汽车购买决策变得非常困难。本文就如何让大多数顾客购买到合适且满意的爱车建立了利用层次分析法解决该问题的数学模型。首先本文建立了清晰的层次结构图，即：目标层为顾客购买到合适的爱车；准则层为汽车的价格、外观设计，舒适性以及油耗、售后服务；决策层为别克凯越、大众捷达、轩逸3款车型。最后本文还评价了层次分析法的优缺点。     

交叉口绿闪信号行人过街行为模型

城市信号交叉口通过设置绿闪信号,在机动车获得通行权之前清空人行横道上的过街行人.为研究行人在此信号期间的过街行为,提出一种绿闪信号时行人过街运动模型.综合分析绿闪信号、周围过街行人、人行横道边界以及右转冲突车辆对行人过街的影响机理,基于社会力模型,建立绿闪后人行横道上行人过街行为模型,并根据实际调查所获得的人行横道尺寸、行人与车辆速度等数据,标定模型参数.基于模型仿真行人运动行为,产生行人分层现象以及与周围行人、冲突车辆避碰等行为,验证模型在宏观层面的有效性;对不同断面的仿真行人与实际过街行人的过街速率变化曲线进行拟合,拟合优度指标显示模型对人行横道前/后半段过街行人模拟精度分别为83% 和95%,验证了模型在微观层面的有效性.      

Safety performance functions for low-volume rural minor collector two-lane roadways

The Fixing America's Surface Transportation Act (FAST Act) highlights a data-driven method to improve traffic safety on all public paved roads in the U.S. The first edition of the Highway Safety Manual (HSM) is a widely used tool that provides crash predictive models in the form of safety performance functions (SPFs). There are no specific SPFs for low-volume roadways in the HSM. It is important to know that low-volume roadways are the major roadway types in terms of total mileage. This study used 2015–2019 crash data from Texas, incorporating with other relevant geometric and traffic variables, to develop SPFs for a specific low-volume roadway type (rural minor collector two-lane roadways). This study proposed a rules-based SPF developed approach that makes the prediction accuracies higher compared to the full model. The R² values range from 0.18 to 0.22 for all data (without splitting) for different injury level models. The prediction accuracies are improved in the decision tree-based models. For different class specific models (based on injury levels), the R² values range from 0.25 to 0.41. Three SPF groups are developed based on crash injury types. The SPFs can provide guidance in refining the prediction accuracies of rural minor collectors.     

车内低频振动噪声的虚拟传递路径分析

传递路径分析法是诊断汽车振动噪声问题准确有效的方法。试验传递路径分析耗时耗力且需要实制样车,为在整车开发初期诊断汽车振动噪声问题,对整车虚拟传递路径分析法进行了研究。首先建立了包含底盘的整车声固耦合有限元模型,采用频率响应法预测车内声学振动响应,发现驾驶员右耳声压在38 Hz处以及驾驶员座椅导轨振动在59 Hz处存在较大峰值。在有限元模型基础上建立了整车虚拟传递路径分析模型,该模型合成的声学振动结果与频率响应法结果吻合较好,验证了模型的正确性。利用虚拟传递路径法对两处峰值作诊断分析,根据分析结果对贡献量大的路径进行优化。优化结果表明,38 Hz处驾驶员右耳声压降低2 dB,59 Hz处座椅振动改善效果明显。