Application de la méthode semi-Hertzienne pour la simulation du passage d'un TGV sur un appareil de voie

Dans la plupart des simulations en dynamique ferroviaire, le profil de rail est supposé constant le long de la voie. Cette hypothèse ne peut plus être retenue si l'on considère des appareils de voie. Les cœurs à pointes mobiles sont des composants d'appareils de voie conçus pour éviter le franchissement d'une lacune (présente dans les appareils classiques) permettant ainsi un roulement le plus continu possible, recherché dans le cas des grandes vitesses. L'objet des simulations est le calcul des contraintes à l'interface roue-rail lors du franchissement d'une pointe mobile par un TGV. Le problème du contact roue-rail est résolu par la méthode dite "semi-Hertzienne" qui autorise des formes d'empreintes plus réalistes que les ellipses de Hertz. Le principe de la méthode est brièvement présenté. Le cas traité permet de montrer l'avantage de la méthode lorsque l'on s'intéresse aux contraintes de contact

Design S-N curves for old Portuguese and French riveted bridges connection based on statistical analyses

Maintenance of ancient road and railway metallic bridges has become a major concern for governmental agencies in the past few decades. Indeed, since the construction of these structures, between the end of the 19th century and the beginning of the 20th century, traffic conditions have evolved, both in weight and frequency. In the purpose to assess the remaining life of old metallic bridges, some critical structural details have been identified and associated to S-N curves in order to be used in damage estimation (using Palmgren-Miner’s rule for cumulative damage, for example). These constructional details are described by design rules of several European and North American standards, such as the Eurocode 3, BS 5400 and AASHTO standards. The particularity of ancient bridges is that hot riveted assemblies, commonly used for their construction, are not represented in most construction standards. Further experiences on the matter by numerous research teams have suggested detail category C71 from the Eurocode 3 as appropriate. In this paper, experimental data from double shear assemblies manufactures from three different metallic ancient bridges is used to identify, through a statistical analysis, the S-N curves that best fit this constructional detail. Portuguese and French puddled iron bridges were considered.The authors of this paper thank the National Society of French Railways and the SciTech - Science and Technology for Competitive and Sustainable Industries, R&D project NORTE-01-0145-FEDER-000022 cofinanced by Programa Operacional Regional do Norte ("NORTE2020"), through Fundo Europeu de Desenvolvimento Regional (FEDER) for their collaboration and support during this research works. The authors also acknowledge the Portuguese Science Foundation (FCT) for the financial support through the post-doctoral grant SFRH/BPD/107825/2015

A tailored multi-model ensemble for air traffic management: Demonstration and evaluation for the Eyjafjallajökull eruption in May 2010

High quality volcanic ash forecasts are crucial to minimize the economic impact of volcanic hazards on air traffic. Decision-making is usually based on numerical dispersion modeling with only one model realization. Given the inherent uncertainty of such approach, a multi-model multi-source term ensemble has been designed and evaluated for the Eyjafjallaj&ouml;kull eruption in May 2010. Its use for air traffic management is discussed. Two multi-model ensembles were built: the first is based on the output of four dispersion models and their own implementation of ash ejection. All a priori model source terms were constrained by observational evidence of the volcanic ash cloud top as a function of time. The second ensemble is based on the same four dispersion models, which were run with three additional source terms: (i) a source term obtained with background modeling constrained with satellite data (a posteriori source term), (ii) its lower bound estimate, and (iii) its upper bound estimate. The a priori ensemble gives valuable information about the probability of ash dispersion during the early phase of the eruption, when observational evidence is limited. However, its evaluation with observational data reveals lower quality compared to the second ensemble. While the second ensemble ash column load and ash horizontal location compare well to satellite observations, 3D ash concentrations are negatively biased. This might be caused by the vertical distribution of ash, which is too much diluted in all model runs, probably due to defaults in the a posteriori source term and vertical transport and/or diffusion processes in all models. Relevant products for the air traffic management are horizontal maps of ash concentration quantiles (median, 75 %, 99 %) at a fine-resolved flight level grid. These maps can be used for route optimization in the areas where ash does not pose a direct and urgent threat to aviation. Cost-optimized consideration of such hazards will result in much less impact on flight cancellations, reroutings, and traffic flow congestions.</p

An ensemble of state-of-the-art ash dispersion models: towards probabilistic forecasts to increase the resilience of air traffic against volcanic eruptions

High-quality volcanic ash forecasts are crucial to minimize the economic impact of volcanic hazards on air traffic. Decision-making is usually based on numerical dispersion modelling with only one model realization. Given the inherent uncertainty of such an approach, a multi-model multi-source term ensemble has been designed and evaluated for the Eyjafjallajökull eruption in May 2010. Its use for flight planning is discussed. Two multi-model ensembles were built: the first is based on the output of four dispersion models and their own implementation of ash ejection

Contraception : Recommandations pour la Pratique Clinique du CNGOF (texte court)

International audienceThe French College of Obstetrics and Gynecology (CNGOF) releases its first global recommendations for clinical practice in contraception, to provide physicians with an updated synthesis of available data as a basis for their practice. The French Health Authority (HAS) methodology was used. Twelve practical issues were selected by the organizing committee and the task force members. The available literature was screened until December 2017, and allowed the release of evidence-based, graded recommendations. This synthesis is issued from 12 developed texts, previously reviewed by experts and physicians from public and private practices, with an experience in the contraceptive field. Male and female sterilization, as well as the use of hormonal treatments without contraceptive label were excluded from the field of this analysis. Specific practical recommendations on the management of contraception prescription, patient information including efficacy, risks, and benefits of the different contraception methods, follow up, intrauterine contraception, emergency contraception, local and natural methods, contraception in teenagers and after 40, contraception in vascular high-risk situations, and in case of cancer risk are provided. The short/mid-term future of contraception mostly relies on improving the use of currently available methods. This includes reinforced information for users and increased access to contraception for women, whatever the social and clinical context. That is the goal of these recommendations