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     

A risk model for the operation of container vessels

Commercial shipping of containerized goods involves certain risks for human safety and environment. In order to actively manage these risks, they must be identified, analyzed, modeled, and quantified. This requires a systematical analysis of design and operation of container vessels. Within the EU-funded research project SAFEDOR, a Formal Safety Assessment has been applied to establish the current safety level of generic container ships and to identify potential cost-effective risk control options. This paper describes a structured approach to develop the underlying high-level risk model. It is structured as risk contribution tree consisting of a series of fault trees and event trees for the major accident categories. Statistical analysis of casualty data is used to estimate the probability of occurrence. Finally, the summation overall individual risk contributions yields the current risk pro file for the operation of container vessels is presented as FN-curve.     

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     

Behavioral adjustments and equity effects of congestion pricing: Analysis of morning commutes during the Stockholm Trial

This paper assesses the horizontal and vertical equity effects of the Stockholm Trial with Congestion Pricing for morning commuters, in terms of both travel behavioral adjustments and welfare effects, as a result of the toll’s direct effects and the behavioral adjustments. We consider specifically two behavioral adjustments: mode choice and departure time choice. Initial car drivers crossing the toll cordon had a 15 percentage-points higher rate of switching to public transit as compared with those not crossing the cordon. We also find some evidence of peak spreading, in particular toward a later departure time, as a result of the charging scheme, but most people choose a departure time within 15 min both before and during the trial. In the welfare analysis, we found no clear pattern of increasing burden by either increasing income or decreasing income, and the increase in the Gini Coefficient was insignificant. We also found no significant difference in either the mode-switching behavior or the average welfare effect for women versus for men.     

Book review

Abstract

In April 1983, the “Fourth World Conference on Transport Research” was held in Hamburg. For a period of four days, experts from all parts of the world discussed transport research and planning problems. The discussions were divided into eight so‐called ‘sub‐topics’. Fortunately, one of the sub‐topics, ‘Man and his Transport Behaviour’ (chaired by Moshe Ben‐Akiva, U.S.A. and Werner Brog, Federal Republic of Germany) dealt with the individual and his behaviour. This complemented the traditionally supply‐oriented thinking of the transport planners by introducing the demand component which had frequently been neglected in the past. Since the view has become increasingly widespread that transport is meant to serve people and thus that research should emphasize the (potential) users of the transport system, the number of papers submitted and presented on this sub‐topic was especially large.

However, the number of papers which could be included in the ‘Conference Proceedings’ was limited and this would have meant that a number of interesting documents could not be published. Therefore, papers on four special areas within this sub‐topic are to be published in four consecutive issues of Transport Reviews. The areas which will be dealt with are ‘Telecommunications’, ‘Non‐Motorised Transport’, ‘Special Problems in Third World Countries’ and ‘Fare Structures in Public Transport’. The papers were selected strictly according to their contents. A brief commentary in each issue explains in turn the reasons for choosing each of the four subject areas.     

Does habitual car use not lead to more resistance to change of travel mode?

An experiment examined the effects of an intervention (combination of information and a free public transport ticket) in a changed decision context (moving to a new residence) on travel mode choice by car users. If past frequency of car use has resulted in an automatic response to goal-related cues, one should expect resistant to change of travel mode. However, the results failed to show this. Neither past behavior or a direct habit measure predicted future travel behavior. Instead, the intervention influenced attitude, subjective norm, and perceived behavioral control, and consistent with Ajzen's theory of planned behavior, these were the main causes of the change of travel mode.     

Vehicle response-based track geometry assessment using multi-body simulation

The assessment of the geometry of railway tracks is an indispensable requirement for safe rail traffic. Defects which represent a risk for the safety of the train have to be identified and the necessary measures taken. According to current standards, amplitude thresholds are applied to the track geometry parameters measured by recording cars. This geometry-based assessment has proved its value but suffers from the low correlation between the geometry parameters and the vehicle reactions. Experience shows that some defects leading to critical vehicle reactions are underestimated by this approach. The use of vehicle responses in the track geometry assessment process allows identifying critical defects and improving the maintenance operations. This work presents a vehicle response-based assessment method using multi-body simulation. The choice of the relevant operation conditions and the estimation of the simulation uncertainty are outlined. The defects are identified from exceedances of track geometry and vehicle response parameters. They are then classified using clustering methods and the correlation with vehicle response is analysed. The use of vehicle responses allows the detection of critical defects which are not identified from geometry parameters.     

The importance of Öresund and the Drogden Sill for Baltic inflow

Based on high resolution current and salinity measurements from the Flinten and Drogden Channels, this paper assesses the relative importance of major Baltic inflows on ‘everyday' flow conditions of highly saline water (S>17 PSU) through the Öresund for a period of 43 months. During years with no major Baltic inflows, 1994–1996, it is found that the Öresund on average supplies 1.2 Peta-grams (Pg) of salt net/year to the Baltic, while inflow above 17 PSU is in the order of 2.3 to 4.0 Pg/year. Sixty percent of this inflow is in the salinity range 17–23 PSU; the remainder has a higher salinity. It is, thus, concluded that normal and regularly occurring flow in the Öresund plays a much larger role in supplying salt to the Baltic than is usually assumed.     

Shipper's councils: role and responsibility—a western view

Traditionally, liner markets have been seen as dominated by conferences on the seller side, facing small, unorganized shippers onn the buyers' side. This perceived asymmetry has greatly influenced conference legislation in North America (and more recently in the E.U.) and it has been deemed essential that government should regulate conference activities in order to curb any abuse of 'conference power'. In this view, shipowners and shippers are adversaries engaged in a zero-sum battle over transport costs rather than potential or actual partners in global distribution systems. This paper suggests that in today's global markets much can be achieved by cooperationn in the development of logistics systems and that shipowners and shippers may have much to gain from such cooperative alliances. A survey of shippers' councils in 1991-1992 demonstrates the diversity and increasing sophistication of many national shippers' councils, which devote themselves to the task of improving markets through education and the legislative process. The situation in the U.S.A. is different: for legal reasons, conventional shippers' councils do not exist. Instead, 'shippers' associations' play a commercial role in liner markets. It is suggested that European style shippers' councils can and should play an important role in the development and formulation of policies for internatinal liner markets. Such participation requires a cooperative industry environment quite different from the traditional adversarial approach, which is ill suited to global trade and logistics alliances.     

Modelling sequential ticket booking choices during Chinese New Year

Transportation - Transport systems in China face extreme capacity shortages during the Spring Festival travel season. This study therefore explores traveler’s decision making behavior when...