Reliability assessment of maintained ship hulls with correlated corroded elements

This paper reviews the factors that affect the corrosion rate of the ship hull girder. It is shown that corrosion rates vary as a function of the location of the element in the structure, of the ocean area and type of ballast tank and steel. However, the corrosion rate in elements that are subjected to similar conditions is highly correlated.

A time-variant formulation is proposed including the correlation between the corrosion rates in neighbouring elements in modelling the degrading effect that corrosion has on the reliability of ship hulls. The effect of corrosion is represented as a time-dependent decrease of plate thickness that affects the midship section modulus. One repair policy was considered and the example results show the effect of plate replacement when its thickness reaches 75% of the original value. The results also illustrate how the limit value of the thickness in the repair criteria influences the reliability and the decision about repair actions. This is also shown for the effect of different corrosion rates, inspection intervals, and allowable stresses.     

Eddies around Madagascar — The retroflection re-considered

The Agulhas Current with its retroflection and attendant eddy-shedding is the cause of some of the greatest mesoscale variability in the ocean. This paper considers the area to the south and east of Madagascar, which provides some of the source waters of the Agulhas Current, and examines the propagating sea surface height signals in altimetry and output from a numerical model, OCCAM. Both show bands of variability along the axis of the East Madagascar Current (EMC) and along a zonal band near 25°S. Sequences of images plus associated temperature data suggest that a number of westward-propagating eddies are present in this zonal band. The paper then focuses on the region to the south of the island, where ocean colour and infra-red imagery are evocative of an East Madagascar Retroflection. The synthesis of data analysed in this paper, however, shows that remotely observed features in this area can be explained by anticyclonic eddies moving westward through the region, and this explanation is consistent with numerical model output and the trajectories of drifting buoys.     

Regional impacts of new transport infrastructure: a multisectoral potentials approach

This is the second of two background papers sponsored for the Symposium by the Administrative Commission for the north of the Netherlands. Its purpose is to provide an indication of the effects of the proposed high speed rail line between Amsterdam, Groningen and Hamburg on employment in the corridor. The authors first review the techniques of forecasting these effects discussed in the literature. The potentials approach is adopted for their analysis, the mathematics and underlying assumptions of which are presented. Finally, this model is run to provide an estimate of the impact on regional employment of three variants of the proposed rail line.     

The design of bus route systems — An interactive location-allocation approach

An interactive modelling approach is developed to solve the practical problem of bus route network design. Possible bus routes are identified with facilities which can be located. Zones or pairs of zones in the urban area are identified with customers who will be allocated to the established facilities. It is shown that the classical Set Covering Problem is useful under the assumption of fixed demand; the Simple Plant Location Problem is effective under the assumption of demand which is sensitive to the level of bus service provided.     

Teleworking in the Netherlands: an evaluation of changes in travel behaviour

This article describes the first experiment on teleworking in the Netherlands, and presents the results of an analysis of the impact of teleworking on the travel behaviour of the participants in the experiment and their household members. It was concluded that teleworking has resulted in a significant decrease in the total number of trips by teleworkers (–17%). Peak-hour traffic by car has been reduced even more (–26%). An unexpected result was that the household members of the teleworkers also appeared to travel less than before the experiment.     

Travel behaviour and the total activity pattern

In the past years the behavioural basis of travel demand models has been considerably extended. In many cases individual behaviour is taken as the starting point of the analysis. Conventional aggregate models have been complemented by disaggregate models. However, even in most disaggregate models there is still the well-known sequence of generation, distribution, mode split, and assignment. In fact, travel behaviour is isolated from other human activities, and analyzed separately. The alternative is to take the general activity pattern of individuals as the departure point, and to consider travel as a derived demand. The basis of this study are diaries, kept during a full week on the basis of quarter hours by a sample of approximately 1100 persons.First, results with respect to travel frequency and travel time are given. Secondly, the influence of car availability and degree of urbanisation on travel behaviour is studied. Next, the population is divided into five person categories, and the travel pattern and activity pattern are studied separately per person group. Finally, links between travel and other activities are tentatively established.     

Performance Benefits in Passive Vehicle Suspensions Employing Inerters

A new ideal mechanical one-port network element named the inerter was recently introduced, and shown to be realisable, with the property that the applied force is proportional to the relative acceleration across the element. This paper makes a comparative study of several simple passive suspension struts, each containing at most one damper and inerter as a preliminary investigation into the potential performance advantages of the element. Improved performance for several different measures in a quarter-car model is demonstrated here in comparison with a conventional passive suspension strut. A study of a full-car model is also undertaken where performance improvements are also shown in comparison to conventional passive suspension struts. A prototype inerter has been built and tested. Experimental results are presented which demonstrate a characteristic phase advance property which cannot be achieved with conventional passive struts consisting of springs and dampers only.     

Spatial Dynamics of Multibody Tracked Vehicles Part II: Contact Forces and Simulation Results

In this part of the paper, three dimensional computational capabilities, that includes significant details, are developed for the nonlinear dynamic analysis of large scale spatial tracked vehicles. Three dimensional nonlinear contact force models that describe the interaction between the track links and the vehicle components such as the rollers, sprockets, and idlers as well as the interaction between the track links and the ground are developed and used to define the generalized contact forces associated with the vehicle generalized coordinates. Tangential friction and contact forces are developed in order to maintain the stability of the track motion and avoid the slippage of the track or its rotation as a rigid body. Body and surface coordinate systems are introduced in order to define the spatial contact conditions. The nonlinear equations of motion of the tracked vehicle are solved using the velocity transformation procedure developed in the first part of this paper. This procedure is used in order to obtain a minimum set of differential equations, and avoid the use of the iterative Newton-Raphson algorithm. A computer simulation of a tracked vehicle that consists of one hundred and six bodies and has one hundred and sixteen degrees of freedom is presented in order to demonstrate the use of the formulations presented in this study.     

Spatial Dynamics of Multibody Tracked Vehicles Part I: Spatial Equations of Motion

In this paper, the nonlinear dynamic equations of motion of the three dimensional multibody tracked vehicle systems are developed, taking into consideration the degrees of freedom of the track chains. To avoid the solution of a system of differential and algebraic equations, the recursive kinematic equations of the vehicle are expressed in terms of the independent joint coordinates. In order to take advantage of sparse matrix algorithms, the independent differential equations of the three dimensional tracked vehicles are obtained using the velocity transformation method. The Newton-Euler equations of the vehicle components are defined and used to obtain a sparse matrix structure for the system dynamic equations which are represented in terms of a set of redundant coordinates and the joint forces. The acceleration solution obtained by solving this system of equations is used to define the independent joint accelerations. The use of the recursive equations eliminates the need of using the iterative Newton-Raphson algorithm currently used in the augmented multibody formulations. The numerical difficulties that result from the use of such augmented formulations in the dynamic simulations of complex tracked vehicles are demonstrated. In this investigation, the tracked vehicle system is assumed to consist of three kinematically decoupled subsystems. The first subsystem consists of the chassis, the rollers, the sprockets, and the idlers, while the second and third subsystems consist of the tracks which are modeled as closed kinematic chains that consist of rigid links connected by revolute joints. The singular configurations of the closed kinematic chains of the tracks are also avoided by using a penalty function approach that defines the constraint forces at selected secondary joints of the tracks. The kinematic relationships of the rollers, idlers, and sprockets are expressed in terms of the coordinates of the chassis and the independent joint degrees of freedom, while the kinematic equations of the track links of a track chain are expressed in terms of the coordinates of a selected base link on the chain as well as the independent joint degrees of freedom. Singularities of the transformations of the base bodies are avoided by using Euler parameters. The nonlinear three dimensional contact forces that describe the interaction between the vehicle components as well as the results of the numerical simulations are presented in the second part of this paper.