Directional performance issues in evaluation and design of articulated heavy vehicles

This review of the dynamics of heavy road-vehicle systems emphasizes directional performance. The review presents information on the following topics: why are articulated vehicles used; units, hitches, and combination vehicles; multiple axle suspensions and steering systems; important performance issues; models and simulation tools; and controlling directional performance. The concluding section summarizes the material presented and provides ideas regarding the application of vehicle system dynamics concepts in developing controllers for road trains.     

Simulation of an airbag deployment in out-of-position situations

The commonly used 'uniform pressure method' (UP) is a well-tried method to simulate an airbag deployment in accident cases. Nevertheless, this method indicates rather heavy inadequacies at the examination of the airbag deployment in the first milliseconds. A solution is the airbag deployment calculation by using computational fluid dynamics (CFD) methods, wherein the calculated gas flow pressure may be applied 'correctly' to the airbag shell elements.

This CFD simulation is integrated in LS-Dyna with the so-called Arbitrary Lagrangian Eulerian (ALE) method and in this review the result's accuracy will be discussed. According to the FMVSS 208, an OoP model will be built-on and comparisons with simulations and tests are done. Another important detail in this labour is the airbag cover examination and the tear seam modelling, as a trivial FE modelling cannot be done due to the very fine mesh. So two possible solutions for tear seam modelling are introduced and discussed. Furthermore considerations concerning the gas generator combustion will also be revealed and an analysis about the impossibility of the direct comparison between gas generator tank test and airbag deployment will be done. At least some parameters, which take effects in the simulation, are researched and evaluated, so finally an optimised simulation model can be made available for further examinations.     

高速公路路基养护评价方法研究

针对高速公路路基养护评价方法,首先从养护对象的角度建立了高速公路路基的评价指标体系,然后根据指标体系与养护对象的关系构建了模型框架,最后利用在江苏省现场采集的30个高速公路路段数据建立了主观评分值和客观评分值的主客观联系。通过线性回归的方法得到了江苏省高速公路路基评价模型,并验证了模型的合理性。     

Introducing alternative fuel vehicles in Hong Kong: views from the public light bus industry

Hong Kong was the first place in the world to implement a trial scheme to convert all public light buses (PLBs) on the road from diesel to alternative fuel vehicles (AFVs). The scheme, however, did not receive much support from PLB operators. At present, there is a rich literature on households’ demand for AFVs (especially in the USA). However, there have not been many studies about the demand for commercial AFVs in the business and public transport sectors. Since light buses running on alternative fuels are not widely available in the Hong Kong market, a stated preference (SP) survey was conducted to solicit the preferences of PLB operators on eight commercial vehicle attributes and seven forms of government support. The SP data are analyzed by multinomial logit (MNL) models. Detailed analyses on market segmentation and price elasticities follow. The results are of theoretical and practical significance.     

On the reserve capacities of priority junctions and roundabouts

The concept of reverse capacity of a whole junction has been used extensively in the design of signal-controlled junctions. This concept, however, has not been applied to priority junctions and roundabouts, probably because of the complicated demand and supply relationship. When the demands on the approaches to the junction increase, the capacities of those non-priority approaches reduce at different rates. This makes the calculation of reserve capacity of the whole junction not a straightforward task. Using the definition of reserve capacity of a whole junction in Allsop (1972; Transpn Res. 6, 245–255), explicit formulae for the estimation of reserve capacities of priority junctions and roundabouts are derived in this paper. Numerical examples are given to illustrate the usefulness of these formulae.     

Distributions of queue lengths at fixed time traffic signals

This paper presents a new model which studies probability distributions of queue lengths at fixed time traffic signals. It extends Haight's model for Poisson arrivals that the arrival distribution during the effective red period is general and the headway between two successive departures is not less than the minimum departure headway. Moreover, the probability generating function of the queue length, at the end of the effective red period, is derived. The probabilities of the queue lengths, at the ends of the effective green, actual red and amber periods, are also obtained. Comparison is made with Haight's model. Finally a case study for the proposed model is reported.     

Two alternative definitions of traffic equilibrium

The paper shows that, under reasonable conditions, if there are junction or modal interactions then a Wardrop equilibrium exists but a user—optimised flow may well not.     

Fatigue analysis for a multi-lap spot welded joint of high strength steel using quasi static tensile-shear test

The welding quality of spot weldment is an important factor that significantly affects the strength, stiffness, safety, and other performance characteristics of vehicles. Therefore, quality control and fatigue life evaluation of spot weldment are necessary processes. This paper presents a method for determining the fatigue life of multi-lap spot weldment of a high strength steel sheet. In this method, the fatigue life is estimated using the lethargy coefficient, which is the total defect coefficient according to rupture stress and time obtained by the quasi static tensile-shear test. The DC potential drop method was used to check initiation and propagation of cracks in addition to the test. Also, in this study, we modified the lethargy coefficient by using the welding current. Furthermore, we define a specific lapping constant, which is a characteristic constant of 2 or 3 lap weldments. The fatigue life obtained by the fatigue estimate equation, which contains a specific lapping constant was compared and verified with an experimental value. Finally we analyzed the relation of lap number, welding current and fatigue life. This method can save processing time and cost for predicting the life cycle of a structure.