The chatter of racing motorcycles

The chatter of motorcycles appears during braking and consists of a vibration of the rear and front unsprung masses at a frequency in the range of 17-22 Hz depending on the motorcycle. This vibration could be very strong and acceleration of the unsprung masses can reach 5-10 g. The chatter is an auto-excited vibration and this fact explains why it appears suddenly when the mechanism of auto-excitation is generated. This paper presents the chatter phenomenon both from an experimental and a numerical point of view. First, the chatter is defined on the basis of some experimental data from racing motorcycles and from the comments of some racing teams technicians. Then, chatter is analysed in different motion conditions and for different braking styles by means of linear and non-linear simulations of the motorcycle dynamics. A physical interpretation of the phenomenon is also proposed.     

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交通流密度是衡量道路服务水平的指标之一. 当交通流中车辆长度和速度变化较大时,占有率则可以更好地反映交通流密度状况. 占有率的测定能够考虑到车辆的长度和速度变化,但是其值受到测量区域长度的影响,并且在混合交通情况下测量值缺乏准确性. 对于没有车道行驶规则的混合交通流,应当以整条路段为单位进行交通流分析. 因此本文提出了“区域占有率”的概念,且利用仿真技术验证其有效性. 对混合交通流条件下的占有率和区域占有率进行比较分析,区域占有率可以更合理地描述混合交通流的密度. 同时,得出混合交通条件下的区域占有率和交通流速度关系,证明了混合交通流条件下区域占有率提出的合理性和准确性.     

Approximations to the magic formula

Pacejka’s tire model is widely used and well-known by the automotive engineering community. The magic formula describes the brake force, side force and self-aligning torque in terms of the longitudinal slip and slip angle, plus several corrections. This paper uses approximation theory to obtain different types of approximations to the magic formula: rational functions (RA) resulting from the Remez algorithm, expansions in a series of Chebyshev polynomials (ACh), a series of Chebyshev rational polynomials (ARChPs), a series of rational orthogonal functions (ORF) and a series of ARChPs that result from grade-1 ORFs. The last expansion shows the fastest convergence and most effective computation. Jacobi rational polynomials can also be obtained to complement this expansion and facilitate fine-tuning in specific areas of the error curve. This work is complemented by obtaining the original rational approximations to the inverse tangent function, which take advantage of the curve symmetry to reduce the computation load and provide models that include the influence of the vertical load. The convergence properties of the development in series and the error values resulting from numeric examples for the three types of stress are shown. The proposed final ARChP expressions show very low error (1%) compared to the original magic formula. They can be computed 20 times faster; they can be evaluated, derived and integrated analytically easily; and their coefficients can be obtained from tests using common least-squares algorithms.     

不同外加剂对OGFC混合料路用性能的影响

OGFC为开级配沥青混合料,主要由粗集料嵌挤组成,在世界各地越来越广泛地用于铺筑路面.OGFC混合料可以增大路表面渗透性,减少噪音,增强表面摩擦力,尤其是在潮湿条件下.该文主要研究不同外加剂对OGFC路用性能的影响,其混合料分别由再生聚乙烯改性沥青(RPEB)、橡胶粉改性沥青(CRMB)和70#基质沥青+纤维与矿料拌和而成.并分别采用析漏试验、肯塔堡飞散试验、渗水试验、劈裂试验、静态模量试验,车辙试验和抗滑试验评估OGFC混合料的路用性能.结果表明:纤维和聚合物可以有效地减小OGFC离析的可能性,混合料每面击实50次能相应地提高磨耗性和其他相关的性能.改性沥青混合料的抗拉强度比(TSR)低于纤维+基质沥青混合料的抗拉强度比.     

Environmental innovation and the role of stakeholder collaboration in West Coast port gateways

The paper explores the role of stakeholder collaboration in the adoption of innovations as part of the environmental and sustainability agenda of port gateways. We do this through a comparative assessment of the port of Vancouver, British Columbia, and the twin ports of Los Angeles and Long Beach, California. An inductive research approach is used to identify and assess the initiation and implementation process behind exemplary innovations. Innovation includes new technologies and processes for handling and moving cargo, mechanisms for planning and policy making, as well as financing, implementing, upgrading, managing and operating infrastructure systems. A relatively new arena for competition on the basis of innovation concerns environmental performance. The conceptual framework and empirical evidence suggest that while there may be intense demand for and supply of innovation in port gateways, the complex dynamics of the logistics chain are such that successful innovation requires conscious involvement and collaboration of stakeholders.     

Methodology for bus structure torsion stiffness and natural vibration frequency prediction based on a dimensional analysis approach

Engineering bus design requires testing of bus structures prototypes in order to guarantee a certain level of strength and an appropriate static and dynamic behavior of the bus superstructure when exposed to road loads. However, experimental testing of real bus structures is very expensive as it requires expensive resources and space. If testing is done on a scale bus model the previous required expenses are considerably reduced. Therefore, a novel methodology based on dimensional analysis applied to bus structure prediction to evaluate the bus structure static and dynamic performance is proposed. The static performance is evaluated attending to torsion stiffness and the dynamic in terms of the natural vibration frequencies and rollover threshold. A scale bus has been manufactured and dimensionless parameters have been defined in order to project the results obtained in the scale bus model to a larger model. Validation of the proposed methodology has been carried out under experimental and finite element analysis.     

Analysis of travel activity determinants using robust statistics

This study investigates travel behavior determinants based on a multiday travel survey conducted in the region of Ghent, Belgium. Due to the limited data reliability of the data sample and the influence of outliers exerted on classical principal component analysis, robust principal component analysis (ROBPCA) is employed in order to reveal the explanatory variables responsible for most of the variability. Interpretation of the results is eased by utilizing ROSPCA. The application of ROSPCA reveals six distinct principal components where each is determined by a few variables. Among others, our results suggest a key role of variable categories such as journey purpose-related impedance and journey inherent constraints. Surprisingly, the variables associated with journey timing turn out to be less important. Finally, our findings reveal the critical role of outliers in travel behavior analysis. This suggests that a systematic understanding of how outliers contribute to observed mobility behavior patterns, as derived from travel surveys, is needed. In this regard, the proposed methods serve for processing raw data typically used in activity-based modelling.     

Model-based control system design in a urea-SCR aftertreatment system based on NH3 sensor feedback

This paper presents preliminary control system simulation results in a urea-selective catalytic reduction (SCR) aftertreatment system based on NH₃ sensor feedback. A four-state control-oriented lumped parameter model is used to analyze the controllability and observability properties of the urea-SCR plant. A model-based estimator is designed via simulation and a control system is developed with design based on a sliding mode control framework. The control system based on NH₃ sensor feedback is analyzed via simulation by comparing it to a control system developed based on NO_x sensor feedback. Simulation results show that the NH₃ sensor-based strategy performs very similarly in comparison to a NO_x sensor-based strategy. The control system performance metrics for NO_x index, urea index, urea usage, and NH₃ slip suggest that the NO_x sensor can be a potential alternative to a NO_x sensor for urea-SCR control applications.     

The trade-off between trips and distance traveled in analyzing the emissions impacts of center-based telecommuting

Several travel indicators were compared between telecommuting (TC) days and non-telecommuting days for a sample of 72 center-based telecommuters in California. Distance traveled decreased significantly on TC days, with average reductions of 51 person-miles (58%) and 35 vehicle-miles (53%). When weighted by telecommuting frequency, average reductions of 11.9% in PMT and 11.5% in VMT were found over a five-day work week. Person-trips and vehicle-trips increased slightly (but not significantly) on TC days. This was due to statistically significant increases in commute trips by telecommuters (who more often went home for lunch on their TC days), partly counteracted by decreases in non-commute travel. The drive-alone mode share increased on TC days, both for all trips, and for commute trips in particular. Walking and biking shares also increased modestly on TC days, whereas shares of transit and ridesharing declined. Despite the increase in trip rates, TC-day reductions were found for all pollutants analyzed: 15% for total organic gas emissions, 21% for carbon monoxide, 35% for oxides of nitrogen, and 51% for particulate matter. The reduction in VMT more than compensated for the marginal increase in number of trips (and consequently, cold starts) on telecommuting days.     

Severity of injury resulting from pedestrian–vehicle crashes: What can we learn from examining the built environment?

This paper examines the impact of personal and environmental characteristics on severity of injuries sustained in pedestrian–vehicle crashes using a generalized ordered probit model. The data covers 2000–2004 of pedestrian–vehicle crashes taken from police incident reports for Baltimore City and supplemented with local land use, urban form and transportation information specific to the individual crash locations. The results on personal and behavioral variables confirm previous findings. Women pedestrians involved in crashes tend to be injured less frequently than their male counterparts; children have an increased likelihood of sustaining injuries and older persons are more likely to be fatally injured. Pedestrians who cross against the traffic signal, are not in a crosswalk and are involved in a crash after dark are associated with greater injury risk. Of the built environment policy variables of interest, transit access and greater pedestrian connectivity, such as central city areas, are significant and negatively associated with injury severity. These results suggest that the environmental conditions should be given more scrutiny and be an important consideration when evaluating and planning for pedestrian safety.