The loss of a jack-up under tow

The events leading up to the capsize and total loss of a jack-up under tow are briefly summarised. The investigation of the causes of this are described in some detail. It involved model tests, finite element analysis, stability calculations, a determination of motions by analysis of newsreel videos taken at the time and close examination of an underwater film taken of the wreckage.

The likely sequence of structural failures leading up to the capsize is established. These are summarised and the lessons learnt from the enquiry highlighted.     

The Application of Linear Optimal Control Theory to the Design of Active Automotive Suspensions

Some linear stochastic control theory relevant to the design of active suspension systems subject to integrated or filtered white noise excitation is reviewed, and application of the theory to a particular problem is considered. The problem considered is the well known quarter car problem in which a control law which minimises a performance function representing passenger discomfort, suspension working space, and tyre load fluctuations is required. With full state feedback, the requirement for a formulation of the problem which leads to the system under consideration being observable and controllable is referred to, and it is shown how a well known coordinate transformation enables this requirement to be satisfied. With limited state (or output) feedback, problem formulations which will avoid potential numerical problems in deriving the optimal control are described. Example solutions are included in order to illustrate the methods.     

Urban transportation and decision making — A comparison of three case studies in Britain

In spite of the impacts that new transportation facilities have upon the economic, social and political structures of established urban areas, the decision process leading to policy formation and plan implementation has received little, if any, attention. Case studies of three County Boroughs in Britain having different urban transport policies suggest that the decision making process is dominated by groups and individuals who attempt to implement policies which benefit the sectional interests which they represent. Within a changing relevant environment, local technicians, politicians and community groups compete and form coalitions in order to acquire authority and implement their own notions of justice and equity in the adaptation of the built environment.     

On the practicality of the UNCTAD 40-40-20 Code for liner conferences

The potential effects of a rigid adherence to the UNCTAD Code are analysed for 26 developing countries. A brief commentary is given on the advantages of a more liberal application of the Code, including reciprocal sharing of liner tonnages by regions of developing countries with regions of developed market-economy countries.     

Off-Road Vehicle Dynamics

Recent developments in off-road vehicle dynamics are reviewed. Progress on this topic and the application of new techniques to the particular problemsassociated with off-road operation tend to lag behind practices established for road vehicles.

The factor which limits further progress is the lack ofappropriate off-road tyre data, in particular, on vibrational and lateral force generation characteristics. Also, a long term study should be aimed at understanding the dynamic behaviour of tyres on yielding surfaces.     

Dynamic and Vibration Analysis of a Vehicle Rear Axle System

A detailed finite element model for the rear axle system of a sport utility vehicle is developed in this investigation. The axle system is treated as a multibody system that consists of nine bodies that include the input shaft, two output shafts, the carrier and tube system, four control arms and a track bar. The rotating input and output shafts are mounted on the carrier and tube system using six bearings. The four control arms and the track bar are connected to the carrier system and the frame of the vehicle using rubber bushings. In the model developed in this investigation, three dimensional beam elements are used to develop the finite element model for the input and output axle shafts, the control arms, and the track bar. A non-conventional finite element formulation is used to develop the equations of motion of the rotating input and output shafts in order to account for the effect of their angular velocities. These equations are expressed in terms of inertia shape integrals that depend on the assumed displacement field. The inertia shape integrals are first evaluated for each finite element. The inertia shape integrals of the rotating shafts are obtained by assembling the inertia shape integrals of its finite elements using a standard finite element assembly procedure. A conventional finite element formulation is used for the control arms and the track bar. The model developed in this investigation includes the effect of the bearing stiffness, the effect of the stiffness of the helical springs of the suspension system, and the effect of the stiffness of the tires. Using the Lagrangian dynamics and the finite element method, the equations of motion of the axle system are developed and expressed in terms of the nodal coordinates of the shafts, the control arms and the track bar as well as the degrees of freedom of the carrier. This finite dimensional model is used to determine the mode shapes and the natural frequencies of the axle system. The discrepancies between several of the natural frequencies predicted using the dynamic model developed in this investigation and natural frequencies determined experimentally are found to be less than 2%. A parametric study is performed in order to investigate the effect of the axle system parameters on the natural frequencies and mode shapes. Using the modal transformation, a set of differential equations of motion of the axle system is developed and used to examine the system dynamics under given loading conditions. The solutions of the resulting equations of motion are obtained using numerical methods.     

Accessibility: an evaluation using consumer welfare

This study explores the worth consumers place on mode-destination accessibility for the AM journey to work trip. To accomplish this, a multinomial mode-destination choice model is estimated and the denominator of the specified logit model is used as an estimate of mode-destination accessibility. To improve the interpretability of this measure, compensating variation is then applied to convert the mode-destination accessibility to units of dollars per AM journey to work trip. The model is estimated using travel survey data from the Puget Sound Region in Washington state. It is reasonable to assume, for example, that the worth placed on mode-destination accessibility varies by mode, by destination, and by market segment (e.g., low income, high income). Less intuitive, however, are the magnitude and direction of these variations. This paper presents a methodological approach, followed by an empirical evaluation, for examining the worth of journey to work mode- destination accessibility. The results have important policy implications and also provide a mechanism for incorporating a monetary value for accessibility in future cost-benefit analyses.     

Effect of Frame Compliance on the Lateral Dynamics of Motorcycles

The lateral dynamics of an uncontrolled motorcycle, running on a straight, level road surface, is investigated in this paper. The structural compliances in the front and the rear frames of the motorcycle are taken into account by introducing additional degrees of freedom in the analysis. The kinematics of the tires is represented by linear differential equations which are based on the taut-string model of pneumatic tires. The linear differential equations of motion are solved to yield the eigensolutions of the system. Numerical results, obtained for parameters corresponding to a Honda CB750 motorcycle, are presented and discussed.     

Distributed work and travel behaviour: The dynamics of interactive agency choices between employers and employees

This paper develops a framework within which multiple agents make discrete choices in respect of a common objective – the determination of participation in distributed work, especially the opportunities and constraints associated with telecommuting. Ideas in discrete choice theory and game theory are combined to define a set of choice experiments in which employees and employers interact in arriving at a choice path in a distributed work context. A state choice experiment with offers and feedback, known as an interactive agency choice experiment (IACE), is empirically investigated in the context of telecommuting options with an exploratory sample of employees and employers in Sydney, Australia. The approach highlights the role of information and negotiation in breaking down the barriers to more flexible work activity, to deliver potential benefits to the transport system such as reduced traffic congestion and environmental sustainability. The paper identifies the types of incentives that an employee/er has to offer the employer/employee in securing effective telecommuting. This revised version was published online in June 2006 with corrections to the Cover Date.