The Nonlinear Behaviour of a MacPherson Strut Wheel Suspension

Three nonlinear models of a MacPherson strut wheel suspension have been studied. The nonlinearities considered are due to the nonlinear geometrical effects in the mechanism, the amplitude limitation due to the bumpstop, the progressive stiffness of the bumpstop and the different damping coefficients for the shock absorber in bump and rebound. The models have been derived according to physical parameter values of. the MacPherson strut wheel suspension of the car SAAB 9.000. The most suitable model was further studied with special attention to nonlinear phenomena. For harmonic forcing the system had phenomena such as multiple solutions and subharmonics. For some parameter values the solution was very sensitive to changes in the integration tolerances in the numerical integration routine. No chaotic steady state solutions were found for the parameter values studied.     

A comparative analysis of the European and North-American approaches to dealing with major oil spills

Background  

The question of what should be the right level of preparedness to react to a major oil spill (i.e. the EXXON VALDEZ spill, the ERIKA spill, and the PRESTIGE spill) is highly debated, especially in the aftermath of such spills. Little research, however, has been conducted with the aim to identify and compare governments’ best practices not only to fund preparedness measures but also to assess the countries’ ability to respond effectively to catastrophic oil spills. It is the author’s belief that important lessons can be learnt from a comparative analysis of countries’ best practices.     

Why are work travel plans effective? Comparing conclusions from narrative and meta-analytical research synthesis

Reliable research synthesis is of high significance for a transport policy which tries to base its decisions on available empirical evidence. There is growing doubt whether the frequently used narrative approach provides a scientifically defensible way of synthesising a body of quantitative research results. The present paper demonstrates meta-analysis as a more objective and powerful alternative for this task. For this purpose evaluation data synthesised in two earlier narrative reviews on the effectiveness of work travel plans [Cairns et al. Making travel plans work: research report (former), Department for Transport, Local Government and the Regions (DTLR), London, 2002; Smarter choices—changing the way we travel. (Final report of the research project: The influence of soft factor interventions on travel demand. Research report for the Department for Transport.) London. Retrieved 1 December 2005, from , 2004] are meta-analytically re-analysed and compared with the conclusions drawn from the narrative synthesis of these data. Our meta-analyis provides only limited support for the conclusion that addressing parking is the hallmark of successful work travel plans. Our meta-analysis indicates that site and organisational factors as well as characteristics of the monitoring process are significant predictors of effective work travel plans, whereas Cairns et al. view little evidence for the impact of these factors.     

Guidelines for samplers: measuring a change in behaviour from before and after surveys

This paper addresses the issue of using before and after surveys to evaluate behavioural changes in response to transport policies and investments, a procedure that, we argue is done far too rarely in this profession. Further, it demonstrates very clearly that, in almost all conceivable cases, there are considerable economies to be obtained by using a panel (again, under-utilised in our profession) to undertake evaluation, rather than successive independent cross-sectional surveys. The paper also addresses the critical issue of sample size requirements for measuring changes of a relatively small magnitude in travel behaviour; i.e., to state, with 95% confidence, that if there is a ∂ percent change in behaviour for the sample, there is a ∂ percent ± e percent change in the behaviour of the population, where e is the sampling error. In this paper, we present a method for calculating such sample size requirements from first principles and demonstrate the applicability both hypothetically and then empirically using data from the Puget Sound Transportation Panel. The formulation enables designers of before and after surveys to investigate the trade-offs between the statistical accuracy of their predictions and the sample size requirements systematically, without the need to specify ∂ a priori. This latter point is crucial, we argue, because we have limited information on ∂, yet, as we explain here, it drives the sample size requirements using alternative, well-cited approaches for calculating sample sizes to assess behavioural change. The results have important ramifications both for those implementing transport policies intended to produce behavioural change, especially when a cost-benefit evaluation of the policy is desired, and for those interpreting the results reported in previous studies.     

台湾海底隧道之接头与管段变化研析及对策

台湾唯一之海底隧道系采沉埋方式施工,该隧道不仅处于具高度盐份腐蚀之不利环境,且位于软弱地盘上.于营运二十余年后,轻微异状已有显现,如管段接头锈蚀、管体渗漏及管体裂损等异状.上述异状可能为接头构件变形、管体变位/变形及结构劣化等影响隧道安全之前兆,甚至降低其耐震能力;因该隧道肩负港区及区域经济发展之运输重任,如何藉由整体性体检进行安全评估及研订适当之维护补强对策,为计划执行重点;故本文将说明隧道接头、结构体等隧道重要构件之检测调查(如地球物理、钢筋腐蚀、裂缝深度、氯离子试验、防蚀电位、接头防水等项目)、数值分析及自动化监测(接缝计、单元沉陷仪、结构倾斜仪、电位计等)等综合评估结果及维护补强对策,以提供工程界日后参考.     

Basic design of a series propeller with vibration consideration by genetic algorithm

Genetic algorithms (GAs) can powerfully search for parameters in a large multidimensional design space. Thus, the principle can be applied to preliminary series propeller design problems with multiple considerations. In the present study, B-series propeller design was conducted using a GA for both hydrodynamic efficiency and vibration consideration. The objective function was set by users who could freely weight the relative importance of efficiency and vibration. GAs were successfully shown to be able to obtain an optimal set of parameters leading to efficient performance and low vibration.     

A study of train dwelling time at the hong kong mass transit railway system

This paper investigates the relationship between the dwelling time of trains and the crowding situations at Mass Transit Railway (MTR) stations in Hong Kong. Regression models were established for the dwelling delays of trains due to congestion at stations, and a simulation model making use of the Monte-Carlo technique is developed to assess the reliability of the estimated train dwelling time. Therefore, the distribution and the confidence interval of the train dwelling time can be predicted on the basis of observed boarding and alighting distributions.     

A note on trip matrix estimation from link traffic count data

In this note, a simple network equilibrium based approach for estimating a trip matrix using link traffic count data is proposed. In essence a combined distribution and assignment model is formulated in which the link flow data serve to furnish an estimate for the sum of the integrals of the link cost functions. A comparison of this model with others proposed previously is made.     

An approximate analytic model of supertanker lightering operations

The most economical means of transporting crude oil over long distances is through the use of very large and ultra large crude containers (VLCCs and ULCCs respectively). These ships require sea lane depths of more than 55 feet to navigate. Since no major U.S. port is deeper than 45 feet, special offloading procedures must be employed. One such procedure is lightering, the process of offloading crude oil from VLCCs to smaller vessels for final delivery to the port.A linked set of queuing models is developed in an effort to understand lightering operations better and to enhance tradeoff analyses. The model assumes that port service times, lightering vessel loading times and VLCC interarrival times are exponentially distributed, allowing us to model lightering vessel operations using a cyclic queuing model. VLCC delays are modeled using an approximate M/E_k/S queue. The two models are linked through a VLCC service time model. The sensitivity of the model to changes in key inputs as well as the likely impacts of the model's assumptions and approximations are discussed. The paper concludes with recommendations for future studies.