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.     

A Review of Modelling Methods for Railway Vehicle Suspension Components

The dynamic behaviour of railway vehicles has been the subject of study for over a century but the advances in computing technology in the last few years have led to a very rapid development in the use of numerical techniques for solving railway vehicle dynamics problems. As these techniques have developed, and have been applied to ever more complex problems, the modelling of the vehicle components has increased in importance. Mathematical models of railway vehicles may now include components such as swing links, air-springs, trailing arm suspensions, load sensitive friction dampers, rubber bushes with hysteresis etc, all of which require sophisticated modelling techniques to produce accurate results. This paper looks at the developments that have taken place in this area, the background to the need for sophisticated models, the improvements in accuracy that can result and some of the difficulties in applying these techniques to the modelling of real situations.     

Motivating ship managers to use management support technology

Ship managers have been slow in their response to using information technology (IT) in spite of the dynamic environment encouraging technological support for a number of critical tasks. The reason is in part the conservatism of the shipping industry, but the main reason seems to be the poor quality of systems provided, creating a credibility gap and usage reluctance. This paper suggests five principles for the development of 'user seductive' systems and illustrates their successful use in a number of case histories of management support systems development.     

CO2 partial pressure in Northeast Atlantic and adjacent shelf waters: Processes and seasonal variability

CO₂ partial pressure in surface water was measured in the Northeast Atlantic and in the Hebride Shelf/North Sea area during a cruise with R.V. Poseidon in June 1991. A mean p_CO2 of 303 μatm was found in the Atlantic between 50°N and 60°N. For an atmospheric CO₂ content of 357.5 ppm(v) this corresponds to a partial pressure difference of −55 μatm. This supports the view that the subarctic Atlantic is a significant sink within the CO₂ cycle between the ocean and the atmosphere. A comparison of our measurements with other data reveals that the p_CO2 distribution changes significantly during May/June. This explained by seasonal warming, CO₂ exchange with the atmosphere and biomass production. The contribution by each of these processes to the seasonal variations is calculated. It was found that during a plankton bloom the production of biomass is the dominating factor and may lower seawater p_CO2 by almost 100 μatm. The shelf areas are charactrized by strong p_CO2 gradients which are explained by water exchange with the Atlantic, temperature effects and biomass production.     

Forecasting downtime event durations for the Morgantown people mover

A model was developed to forecast the duration of emergency shut downs of the Morgantown People Mover. An extensive data base of downtime events for a 2 1/2 year period were analyzed. Analysis of Variance (ANOVA) methods were applied to determine the significance of five variables which were hypothesized to influence downtime duration, including physical sub-system, restartablity, location of failure, number of vehicles in the system, and level of demand. Results of the analysis enable MPM system operators to provide improved information to system users during downtime events. The forecasting methodology also enables operators to evaluate alternative user management strategies during downtimes.     

The Influence of In-Plane Tyre Dynamics on ABS Braking of a Quarter Vehicle Model

For efficient analysis it is important to choose the proper model that fits the problem that needs to be solved. This paper discusses three pragmatic simulation models for longitudinal behaviour of a passenger car tyre (Steady State, Transient and Rigid Ring) that may be used in e.g. an ABS simulation. The characteristics of the simulation models are evaluated using some simple simulations. Simulations with a quarter vehicle model that includes load transfer effects are carried out to determine the deviation in results between the mentioned tyre models for an ABS application. The results show that the Steady State model may only be used below 10 Hz and that the Transient model is valid up to about 30 Hz. The results from the ABS simulation with the Rigid Ring model are most reliable and are clearly different from the Steady State and Transient model, which indicates that ABS simulations should be carried out with the Rigid Ring model. Additionally it is demonstrated that for tyre behaviour on uneven roads the influence of the tyre belt cannot be neglected.     

Analysis of Metropolitan Highway Capacity and the growth in vehicle miles of travel

A number of recent studies have examined the hypothesis of induced travel in an attempt to quantify the phenomenon (Hansen & Huang 1997; Noland, forthcoming). No study has yet attempted to adjust for potential simultaneity bias in the results. This study addresses this issue by the use of an instrumental variable (two stage least squares) approach. Metropolitan level data compiled by the Texas Transportation Institute for their annual congestion report is used in the analysis and urbanized land area is used as an instrument for lane miles of capacity. While this is not an ideal instrument, results still suggest a strong causal relationship but probably that most previous work has had an upward bias in the coefficient estimates. The effect of lane mile additions on VMT growth is forecast and found to account for about 15% of annual VMT growth with substantial variation between metropolitan areas. This effect appears to be closely correlated with percent growth in lane miles, suggesting that rapidly growing areas can attribute a greater share of their VMT growth to growth in lane miles.