Complete Modeling for Systems of a Marine Diesel Engine

This paper presents a simulator model of a marine diesel engine based on physical, semi-physical, mathematical and thermodynamic equations, which allows fast predictive simulations. The whole engine sy...     

Whitecap coverage in coastal environment for steady and unsteady wave field conditions

Breaking waves represent a “key” parameter for many applications involved with a large number of environmental phenomena. In particular, it is well recognized that the whitecap cover induced by breaking waves allows substantial enhancement of heat, momentum, gas and particle transfer at the air–sea interface. A large number of studies were conducted during the last decades on the variation of the whitecap fraction, commonly noted W. The results presented in this paper deal with the evolution of the whitecap coverage in coastal zone. In such areas, the wave field is often unsteady with an important variety of sea state developments. The present analysis is based on an extensive series of data obtained during an experimental campaign which took place on the Mediterranean coast in 2001. The results allow observation of the influence of the sea state conditions of the wave field on the whitecap coverage. In addition, this paper confirms the occurrence of a peak in the variations of the whitecap fraction with the wave age for coastal areas as suggested by Lafon et al. [Lafon, C., Piazzola, J., Forget, P., Le Calvé, O. and Despiau, S., 2004. Analysis of the variations of the whitecap fraction as measured in a coastal zone. Boundary-Layer Meteorol., 111: 339-360.]. A wave age dependent model for the whitecap fraction is then proposed, which takes into account both the wind and the wave influence, and hence, is characteristics of the different sea state conditions.     

The benefits of improving public transport: a myth or reality?

As part of a research project completed some four years ago at Imperial College, London, a number of case studies were undertaken to examine the impacts that major improvements to the public transport system have on parallel road traffic. The three studies of major improvements to the public transport systems in three U.K. and German cities were: the Victoria Line in London; the extension of the U‐Bahn system in West Berlin (at the time of the study); and the S‐Bahn extension in Stuttgart. Each scheme is reviewed, with particular reference to the degree in which they have relieved congestion on the roads in the same corridor. This was examined simply to see whether or not public transport improvements are the only answer to traffic congestion, as is sometimes suggested. In the event, every scheme was a unique example in itself. The different conditions in each situation are presented and the actual impacts of the schemes assessed, based on the available information. The findings were rather different from the expectations. Only marginal relief from road traffic was recorded, with a substantial shift from buses to the improved rapid rail system. In the case of Stuttgart, for example, traffic growth on parallel roads was actually higher than the average growth on all city roads, though for other reasons.     

Solution of the Multiple Wheel and Rail Contact Dynamic Problem

An unconventional method for calculating the forces developing in the wheel and rail contact patches of a railway vehicle has been implemented at the New Technology Laboratory of INRETS. It takes into account the elastic deformations of the materials in the Hertzian elliptical contact areas; the possibility of having simultaneously several contact patches on each wheel, is introduced in the simulation of the dynamic phenomena.

The theory is applied for a high speed bogie running on a perfectly straight track.     

Solving conformal contacts using multi-Hertzian techniques

Recently, publications aiming at wheel–rail contact surveys let readers think that multi-Hertzian methods present severe drawbacks with respect to ‘virtual penetration’ methods. These surveys criticise multi-Hertzian solutions mainly because presenting ‘larger contacts overlaps’ and ‘frequent secondary contacts near the border of the first contact’, both obvious geometric possibilities of which the practical occurrence and eventual inconvenience would remain purely theoretical unless established over definite methods demonstrating poor practical results. Recent surveys all quote Piotrowski–Chollet 2005 survey of wheel–rail contact models that attempted to illustrate defective multi-Hertzian techniques by concentrating on the method initiated by Sauvage in the 1990s and further developed by Pascal. The 2005 paper not only gives no evidence of practical inconveniences of Sauvage’s method but also confuses static geometric contact overlaps with the dynamical overlapping of forces. In reality it mixes Sauvage method up with a quite different technique. Thus a clarification is now necessary by reminding what the proper Sauvage technique really is and by showing some of its practical successful applications. The present paper, focusing on determination of normal contact forces in conformal situations, intends to explain clearly the advantages of the unequivocal localisation of secondary ellipses in that multi-Hertzian method which has been developed in INRETS VOCO codes in the 1990s and successfully used by SNCF and ALSTOM in the INRETS-SNCF code, VOCODYM, and later in Pascal’s online calculation of railway elastic contacts code. It proved its effectiveness for studying freight wagons derailments as well as rail wear and head-check, unrounded wheels wear, high-speed lines’ deformations or TGV comfort. While simulating American ACELA trainsets’ behaviour on the US North-East Corridor tracks, prior to actual tests, as part of the commercial contract. It has been also a major tool for bringing back together French and American Safety Standards.