Calibration and improved prediction of computer models by universal Kriging

This paper addresses the use of experimental data for calibrating a computer model and improving its predictions of the underlying physical system. A global statistical approach is proposed in which the bias between the computer model and the physical system is modeled as a realization of a Gaussian process. The application of classical statistical inference to this statistical model yields a rigorous method for calibrating the computer model and for adding to its predictions a statistical correction based on experimental data. This statistical correction can substantially improve the calibrated computer model for predicting the physical system on new experimental conditions. Furthermore, a quantification of the uncertainty of this prediction is provided. Physical expertise on the calibration parameters can also be taken into account in a Bayesian framework. Finally, the method is applied to the thermal-hydraulic code FLICA 4, in a single phase friction model framework. It allows to improve the predictions of the thermal-hydraulic code FLICA 4 significantly

Pinel-Hauterive – Hauterive

Identifiant de l'opération archéologique : 025435 Date de l'opération : 2008 (SU) Dans le cadre de l’agrandissement de l’usine de traitement des eaux du Lot, il a été mis au jour un certain nombre de structures romaines, dont un four ayant produit des pièces liées à la construction romaine. Le site se trouve sur la berge alluvionnaire récente dominant la rive droite du Lot en pied de falaise. Il y a une vingtaine d’années, lors de travaux d’agrandissement précédents, le site avait livré l’ext..

Formage électromagnétique et coulée directe des métaux

The use of alternating magnetic fields is studied in order to substitute, in metallurgical casting processes, the action of the lips of the supply nozzles by the electromagnetic forces. Are exposed, theoretical and experimental studies to obtain, without physical contact, a large sheet from liquid metal jets of initial circular section. The used inductor is described and its optimization presented. Experiments using mercury, tin and steel are presented. A new similitude parameter, taking into account the inertia of the jets is introduced and validated. An optimum operating frequency is found. A numerical model of solidification in the direct casting processes of thin products complete the study.On étudie l’emploi de champs magnétiques alternatifs afin de remplacer, dans les procédés de coulée métallurgique, l’action des lèvres des busettes d’alimentation par celle des forces électromagnétiques. Sont exposées, des études théoriques et expérimentales visant à obtenir, sans contact matériel, une lame de grande largeur à partir de jets de métal liquide de section circulaire. L’inducteur réalisé est décrit et son optimisation présentée. Des expériences réalisées avec du mercure, de l’étain et de l’acier sont présentées. Un nouveau paramètre de similitude, prenant en compte l’inertie des jets, est introduit et est validé. Une fréquence de travail optimum est trouvée. Un modèle numérique de solidification dans les procédés de coulées directes de produits minces complète l’étude

Human response to a frontal sled deceleration

IRCOBI Conference on the Biomechanics of Impact, MUNICH, ALLEMAGNE, 18-/09/2002 - 20/09/2002Sled tests were conducted with cadavers to obtain data on the behaviour of the human body under frontal deceleration. Two series of three tests were conducted corresponding to two levels of severity and types of restraint systems. The restraint systems used for the tests included a 4kN force-limited shoulder belt and a static lap belt. A driver airbag was mounted for the series at highest severity. The results show that the restraint systems and the test conditions modify the behaviour of the cadaver. The restrained conditions are not reflected in the same way for different segment of the body. The influence of the airbag is well observed for the chest spine behaviour, and not for the first thoracic vertebra. This study suggests that the chest acceleration (T8) could be a better predicting parameter than the Tl resultant in a combined parameters injury criterion

Ondes hydrothermales non-linéaires dans un disque et un anneau

URL: http://www-spht.cea.fr/articles/S98/109Nous nous intéressons à la convection thermocapillaire, produite par l'imposition d'un gradient {\it horizontal} de température sur une mince couche de fluide avec surface libre. En géométrie bidimensionnelle nous observons deux modes différents en compétition, tandis qu'en géométrie bidimensionnelle avec conditions limites périodiques, nous étudions la transition à la turbulence d'une onde propagative homogène

Nonlinear dynamics of waves and modulated waves in 1D thermocapillary flows. II: Convective/absolute transitions

We present experimental results on hydrothermal waves in long and narrow 1D channels. In a bounded channel, we describe the primary and secondary instabilities leading to waves and modulated waves in terms of convective/absolute transitions. Because of on the combined effect of finite group velocity and of the presence of boundaries, the wave-patterns are non-uniform in space. We also investigate non-uniform wave-patterns observed in an annular channel in the presence of sources and sinks of hydrothermal waves. We connect our observations with the complex Ginzburg-Landau model equation in the very same way as in the first part of the paper (nlin.PS/0208029).Comment: 37 pages, 23 figures (elsart.cls + AMS extensions). Accepted in Physica D. See also companion paper "Nonlinear dynamics of waves and modulated waves in 1D thermocapillary flows. I: General presentation and periodic solutions" (nlin.PS/0208029). A version with high resolution figures is available on N.G. webpag

An experimental evaluation of two effective medium theories for ultrasonic wave propagation in concrete

9 pagesInternational audienceThis study compares ultrasonic wave propagation modeling and experimental data in concrete. As a consequence of its composition and manufacturing process, this material has a high elastic scattering (sand and aggregates) and air (microcracks and porosities) content. The behavior of the "Waterman-Truell" and "Generalized Self Consistent Method" dynamic homogenization models are analyzed in the context of an application for strong heterogeneous solid materials, in which the scatterers are of various concentrations and types. The experimental validations of results predicted by the models are carried out by making use of the phase velocity and the attenuation of longitudinal waves, as measured by an immersed transmission setup. The test specimen material has a cement-like matrix containing spherical inclusions of air or glass, with radius close to the ultrasonic wavelength. The models are adapted to the case of materials presenting several types of scattering particle, and allow the propagation of longitudinal waves to be described at the scale of materials such as concrete. The validity limits for frequency and for particle volume ratio can be approached through a comparison with experimental data. The potential of these homogenization models for the prediction of phase velocity and attenuation in strongly heterogeneous solids is demonstrated

The spatio-temporal dynamics of neutral genetic diversity

International audienceThe notions of pulled and pushed solutions of reaction-dispersal equations introduced by Garnier et al. (2012) and Roques et al. (2012) are based on a decomposition of the solutions into several components. In the framework of population dynamics, this decomposition is related to the spatio-temporal evolution of the genetic structure of a population. The pulled solutions describe a rapid erosion of neutral genetic diversity, while the pushed solutions are associated with a maintenance of diversity. This paper is a survey of the most recent applications of these notions to several standard models of population dynamics, including reaction-diffusion equations and systems and integro-differential equations. We describe several counterintuitive results, where unfavorable factors for the persistence and spreading of a population tend to promote diversity in this population. In particular, we show that the Allee effect, the existence of a competitor species, as well as the presence of climate constraints are factors which can promote diversity during a colonization. We also show that long distance dispersal events lead to a higher diversity, whereas the existence of a nonreproductive juvenile stage does not affect the neutral diversity in a range-expanding population