Carrier selection in a RO/RO ferry trade Part 1. Decision factors and attitudes

The choices faced by shippers are generally complex. Typically, the shipper is presented with a range of alternative carriers, each of which has its individual strengths and weaknesses. A survey of companies purchasing shipping services in an overnight RO/RO ferry trade was conducted to identify their priorities and to help understand and the decision-making process. The shippers were found to be conservative decision makers with a strong emphasis on quality of service.     

Modeling and Dynamics of Friction Wedge Dampers in Railroad Freight Trucks

A mechanical model for the vertical response of the bolster and friction-wedge suspension elements in a railroad freight truck is developed. The model incorporates linear stiffnesses and dry friction contact between rigid elements. Numerical bifurcation diagrams for sticking events, obtained for parameterizations of the amplitude and frequency of a harmonic track excitation, and for various friction laws, reveal distinct parameter-dependent dynamic responses: strongly nonlinear stick-slip oscillations, observed away from period-1 resonance; and weakly nonlinear, nearly harmonic responses, observed near the period-one resonance. The analytical method of harmonic balance is applied to develop a first order approximation for the period-1 response, and, as should be expected, is found to correspond well with the numerical results in the large amplitude limit and near the resonance location. Given that such weakly nonlinear, large amplitude, period-1 responses are not common for the speeds and system parameters of most freight vehicles, we conclude that friction-wedge models based on some form of equivalent linearization may be inadequate for simulating freight car dynamics in many cases of practical importance.     

Determining the Characteristics of Helical Springs: A Simplification for Application in Railway Suspensions

In a preceding article [1], we had presented the exact methods of calculation for the characteristics of rectilinear and helical springs. As we announced there, an important simplification can be made by replacing the helical spring with an equivalent rectilinear model. This point will be developed in the following article.     

Pedestrianisation: London's Oxford Street experiment

Oxford Street in London, is the capital's principal shopping street and famous throughout the Western World; it is also the most obvious route from the city of London to the West, the Midlands and the North of England.The conflict between its twin roles of shopping centre and major traffic route was demonstrated in its accident record which put Oxford Street top of the list of accident blackspots in London, whilst its location in the most fashionable area of London make the costs of new road construction prohibitive.A comprehensive accident analysis defined the pedestrian/vehicle conflict by time and place and facilitated the detail design of a limited traffic ban with associated rerouting.Considerable uncertainties in prediction of the resulting traffic conditions, in the absence of data on demand elasticity, dominated the design of the experiment and led to the inclusion of an avert chaos policy. Traffic predictions which included details of the probable manner in which congestion would spread were assisted by a new network simulation model developed by one of the authors and described here.The report outlines the history of the experiment from conception to implementation (in record time) and reports some early and generally encouraging results. On the strength of which the Greater London Council has confirmed the scheme (August 1973) and has announced plans for its extension to the remaining half of Oxford Street — from Oxford Circus to St. Giles' Circus — which still carries the full weight of traffic.Previously undertaking doctoral research at Imperial College, London.     

The Random Vibration of a Nonuniform Cantilever Beam with Concentrated Mass

The random vibration of a nonuniform cantilever beam with a concentrated mass at its end, is studied as a simple model of the suspension spring of a motor vehicle. The spectral response of the displacement of the concentrated mass is obtained when the beam is subjected to the random motion of the support. The conditions for the validity of the single degree approximation is also discussed.     

A model and algorithm for multicriteria route-mode choice

Using an idea proposed independently by Quandt and Schneider, the paper declares mode choice to be a special instance of route choice. It describes a (non-logit) model which includes in its route-choice mechanism the decision variables traditionally associated with mode choice. With the assumption that each traveller selects the route which minimizes his own personal linear choice function, it is clear that the routes with a nonzero chance of being picked are only those not dominated by any other path (e.g. are not both costlier and longer than any other path). The precise probability of a route being chosen is just the integral over the appropriate portion of the probability density of the coefficients of the choice function. The integration limits are implied by the amount of each disutility on each of the undominated routes. An algorithm is given which is quite efficient in finding these paths in a large and complex multimodal network.     

Comparative tests of multimodal traffic equilibrium methods

In this study we proceeded to test the relative efficiencies of the two main computational techniques now available for calculating the traffic equilibrium in multimodal networks, namely, the relaxation and projection methods. Since both of these methods solve at each step a mathematical programming problem, we first set out to test the Frank-Wolfe algorithm and the Dafermos-Sparrow algorithm and found the latter to be the more efficient algorithm. As expected, this was also the case when these algorithms were used to solve the mathematical programming problem at each step of the relaxation method. We then investigated how different versions of the projection method enhance its performance. Subsequently, we proceeded to our main goal to compare the best projection method with the relaxation method. We tested multimodal networks with three different classes of monotone travel cost functions and found that the form of the travel cost functions affects the performance of the two basic techniques available for computing the multimodal equilibrium.     

Residual stresses at a longitudinal stiffener — Web frame intersection and their effects on crack growth

Stress coining at geometrical discontinuities may introduce compressive residual stresses which will lower the propagation of surface cracks and thus increase the fatigue life. In a non-linear finite element analysis, the residual stresses after welding of a transverse web-frame to a ship hull plating is first estimated. Stress coining of one corner of a longitudinal cut-out in a transverse web-frame is then simulated in detail. The calculated residual compressive tangential stresses in the corner of the cut-out is seen to lower the propagation of edge cracks. Experiments performed on web-frames taken from a shipyard after manufacturing show indeed that large tensile residual stresses exist in the web-frame after welding. Stress coining is therefore believed to have a beneficial effect on the fatigue life.