Mooring line tension observed through a maximum entropy spectrum

A method for measuring mooring line tension is proposed based on observation of the natural frequencies of the mooring line segment between the winch and the fairlead. The anchor line tension is observed through the string equation where an analytical expression for the line's eigen-frequencies is obtained. The tension is observed on line by utilizing a nonparametric system identification approach in which the peaks of a maximum entropy spectrum of the transverse acceleration measures of the vibrating string are automatically identified. The method is verified against full-scale data from the Troll B floating concrete oil production platform operating in the North Sea. Received for publication on Feb. 24, 1999; accepted on July 26, 1999     

Participating mass in colliding risers

One of the main challenges in estimating impact energy in collisions between marine risers is the assessment of the riser mass involved in the collision. Evidently the entire riser mass does not contribute to the collision. Hence, the question is: What is the equivalent riser mass which contributes to the impact energy? This article presents three different ways of estimating the riser mass participating in the collision energy. The first method is strictly experimental. The second method uses a numerical experiment together with system identification techniques. The third method is a strictly analytical method, which results in an asymptotically upper bounded estimate of the participating mass. Two risers are examined as case studies. The first riser is a 1 : 100 model scale riser used in collision experiments carried out at Marintek's towing tank in Trondheim, Norway. The second case uses a real world riser in use on the Troll B oil production platform operating in the North Sea. The proposed methods yield consistent and comparable results. Received for publication on Feb. 1, 1999; accepted on July 8, 1999     

湍流边界层脉动压力对声强测量的影响研究

实际声强测量时常常存在风流或水流,如在飞机或船舶上进行测量,声强探头将受到湍流边界层脉动压力的影响。如何评估该影响以及如何修正测量结果是人们十分关心的工程实用问题。该文首先简要介绍了建立的由湍流边界层脉动压力诱发声强的理论模型。接着利用现有的湍流边界层脉动压力频率-波数谱模型,对湍流边界层脉动压力及其诱发的声强进行了数值分析。为了验证理论模型及数值结果,设计制作了一套实验装置,对湍流边界层脉动压力及其产生的声强进行了具体测量分析。结果表明,湍流边界层脉动压力的测量结果与数值结果吻合良好,测量得到的边界层脉动压力诱发的声强特性与计算结果也十分一致,但必须注意对测量传感器的空间响应进行修正。     

Car drivers' willingness to pay for not losing their driving licence

The aim of this article is to discuss theoretically and to study empirically how Norwegian drivers' willingness to pay (WP) for not losing their driving licence vary with their personal characteristics. The theoretical discussion and empirical results are based on standard microeconomic theory and contingent valuation, respectively. The WP values increase concavely with the length of the suspension period of the driving licence and differ greatly between drivers. They increase significantly with a driver's income, dependence on the car at work and driving experience. Moreover, male drivers, young drivers and drivers living in rural areas have higher WP values than their counterparts. Consequently, driving licence suspension will deter drivers to different extents. The relative impacts of the above explanatory variables on the WPs are, broadly speaking, independent of the length of the suspension period.     

Workshop report - Public transport markets in development

Developing countries and countries in transition represent between 85% and 90% of the world’s population and face unique public transport challenges that are not necessarily present in developed countries. Issues such as the affordability and accessibility of public transport, funding support and capacity to implement are some of the challenges these countries face. Barriers to strategy implementation in these countries could be a failure to understand the broader business and social environment, poor leadership, a lack of inter-disciplinary and inter-implementer collaboration, and weak monitoring and feedback loops. Weak institutional frameworks are evidenced in inappropriate structures often resulting in institutional inertia and conflict. Over-promising of potential impacts and benefits together with a failure to develop sustainable funding mechanisms often lead to a lack of implementation. The workshop argued that different competition and ownership solutions are needed for a range of factors. This poses a challenge to the THREDBO community as it could mean that the traditional concepts are either not relevant or not usable in the majority of the world’s developing countries, or that the traditional approaches are relevant in many respects but need to be substantially extended and adapted to be applicable and usable in the rest of the world.     

Determinants affecting ferry users’ waiting time at ferry terminals

Transportation - The paper develops a model to examine how different factors influence ferry users’ waiting time at the terminals. The estimations are based on interviews of 10,952 Norwegian...     

Estimating the inefficiency in the Norwegian bus industry from stochastic cost frontier models

A stochastic cost frontier function based on data from 170 of the 175 Norwegian subsidized bus companies is estimated under two alternative presumptions regarding the distribution of the inefficency among the bus operators. When the inefficiency is assumed to be half-normally distributed, the average inefficiency in the industry is estimated to be 13.7 per cent. This calculated value is nearly halved (7.2 per cent) when the exponential distribution is applied, while the ranking of the companies according to inefficiency is unchanged. By regressing the estimated inefficiency values for each company on some exogenous variables describing its ownership structure and the subsidy policy which it faces, it is seen that inefficiency of the companies which negotiate with the public authorities over the subsidy amounts is slightly higher than the inefficiency of the companies which face a subsidy policy based on cost norms. Our analysis gives, however, no significant differences in the efficiency between privately owned bus companies and publicly owned bus operators, and shows only minor economies of scale.     

Market role and regulation of extensive urban minibus services as large bus service capacity is restored - Case studies from Ghana, Georgia and Kazakhstan

In some cities, the degeneration and collapse of formal bus services has allowed large-scale minibus operations to become established but, over time, city authorities and municipal bus operators regain at least part of their operating capacity and seek to regain their market share. This paper examines and compares three case studies: Accra, Tbilisi, and cities of Kazakhstan. It examines the development of the urban minibus services market as conventional bus services went into decline, the gradual re-emergence of large buses, how the authorities have viewed the minibuses as circumstances change, and market and regulatory strategies followed by city authorities.     

A two-stage-training support vector machine approach to predicting unintentional vehicle lane departure

Advanced driver assistance systems, such as unintentional lane departure warning systems, have recently drawn much attention and efforts. In this study, we explored utilizing the nonlinear binary support vector machine (SVM) technique to predict unintentional lane departure, which is innovative, as the SVM methodology has not previously been attempted for this purpose in the literature. Furthermore, we developed a two-stage training scheme to improve SVM's prediction performance in terms of minimization of the number of false positive prediction errors. Experiment data generated by VIRTTEX, a hydraulically powered, 6-degrees-of-freedom moving base driving simulator at Ford Motor Company, were used. All the vehicle variables were sampled at 50 Hz and there were 16 drowsy drivers (about 3 hours of driving per subject) and six control drivers (approximately 20 minutes f driving each). In total, 3,508 unintentional lane departures occurred for the drowsy drivers and 23 for the control drivers. Our study involving these 22 drivers with a total of more than 7.5 million prediction decisions demonstrates that (a) excellent SVM prediction performance, measured by numbers of false positives (i.e., falsely predicted lane departures) and false negatives (i.e., lane departures failed to be predicted), was achieved when the prediction horizon was 0.6 seconds or less, (b) lateral position and lateral velocity worked the best as SVM input variables among the nine variable sets that we explored, and (c) the radial basis function performed the best as the SVM kernel function.     

湍流对流动管道中声强测量的影响

实际声强测量大多是在流动环境条件下进行,因此湍流对声强测量的影响是人们十分关心的工程实用问题.文章结合声强和湍流边界层等相关领域的技术,对流动条件下的声强技术进行了研究分析,导出了由湍流边界层引起的声强的具体表达式.应用Corcos建立的湍流边界层脉动压力模型,对湍流边界层脉动压力诱导的声强进行了数值计算分析,分析了测量传感器间距、马赫数等对声强测量的影响.