Dynamic Behaviour of a Flexible Yacht Sail Plan

• Dynamic fluid structure interaction of a sail plan is modeled in harmonic pitching • Aerodynamic forces oscillations show hysteresis phenomena • Neglecting the structural deformation underestimates the forces oscillations • Both aerodynamic and structure inertia affect loads in the rig.A numerical investigation of the dynamic Fluid Structure Interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to address both issues of aerodynamic unsteadiness and structural deformation. The FSI model | Vortex Lattice Method uid model and Finite Element structure model | has been validated with full-scale measurements. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops, suggesting that some energy is exchanged by the system. The area included in the hysteresis loop increases with the motion reduced frequency and amplitude. Comparison of rigid versus soft structures shows that FSI increases the energy exchanged by the system and that the oscillations of aerodynamic forces are underestimated when the structure deformation is not considered. Dynamic loads in the fore and aft rigging wires are dominated by structural and inertial effects. This FSI model and the obtained results may be useful firstly for yacht design, and also in the field of auxiliary wind assisted ship propulsion, or to investigate other marine soft structures.This work was supported by the French Naval Academy

Representing uncertainty by possibility distributions encoding confidence bands, tolerance and prediction intervals

For a given sample set, there are already different methods for building possibility distributions encoding the family of probability distributions that may have generated the sample set. Almost all the existing methods are based on parametric and distribution free confidence bands. In this work, we introduce some new possibility distributions which encode different kinds of uncertainties not treated before. Our possibility distributions encode statistical tolerance and prediction intervals (regions). We also propose a possibility distribution encoding the confidence band of the normal distribution which improves the existing one for all sample sizes. In this work we keep the idea of building possibility distributions based on intervals which are among the smallest intervals for small sample sizes. We also discuss the properties of the mentioned possibility distributions

Building possibility distribution based on confidence intervals of parameters of Gaussian mixtures

International audienceIn parametric methods, building a probability distribution from data requires an a priori knowledge about the shape of the distribution. Once the shape is known, we can estimate the optimal parameters value from the data set. However, there is always a gap between the estimated parameters from the sample sets and true parameters, and this gap depends on the number of observations. Even if an exact estimation of parameters values might not be performed, confidence intervals for these parameters can be built. One interpretation of the quantitative possibility theory is in terms of families of probabilities that are upper and lower bounded by the associated possibility and necessity measure. In this paper, we assume that the data follow a Gaussian distribution, or a mixture of Gaussian distributions. We propose to use confidence interval parameters (computed from a sample set of data) in order to build a possibility distribution that upper approximate the family of probability distributions whose parameters are in the confidence intervals. Starting from the case of a single Gaussian distribution, we extend our approach to the case of Gaussian mixture models

Experiencias de gestión de riesgos en Lima: actores y territorios urbanos

Risk management in Lima is made through specific actions, spatially and by sectors. This situation is partially explained due to the absence of metropolitan management, as well as public policy fragmentation. Risk management actions essentially are based on local mobilizations, specific conflicts, or support from outside institutions. This article suggests analyzing a series of actions implemented according to financing opportunities or local actors' mobilization. It proposes a non-exhaustive panorama of risk management experiences in Lima and tries to identify the actors, the territories, and the mechanisms employed. Thus it provides elements for reflection on risk management modalities and on the stakes involved in the implementation of a risk management policy in an urban agglomeration on the scale of Lima/Callao.International audienceLa gestión de riesgos en Lima se hace a través de acciones puntuales, tanto espacial como sectorialmente. Esto se explica en parte por la ausencia de gestión metropolitana de la ciudad y por la fragmentación de las políticas públicas. Por ende, las acciones de gestión de riesgos se hacen esencialmente en función de movilizaciones locales, de conflictos puntuales o de apoyos de instituciones exteriores. Este artículo propone analizar una serie de acciones realizadas según las oportunidades de financiamiento o de movilización de los actores locales. Propone un panorama no exhaustivo de experiencias de gestión de riesgos en Lima y busca identificar actores, territorios y mecanismos puestos en práctica. De este modo, nos ofrece así elementos de reflexión sobre las modalidades de gestión de riesgos y sobre los desafíos de la implementación de una política de gestión del riesgo a escala de la aglomeración urbana de Lima/Callao.La gestion des risques à Lima se fait au travers d'actions ponctuelles, spatialement et sectoriellement. Cela s'explique en partie par l'absence de gestion métropolitaine de la ville et du fait de la fragmentation des politiques publiques. Les actions de gestion des risques se font donc essentiellement en fonction de mobilisations locales, de conflits ponctuels ou d'appuis d'institutions extérieures. Cet article propose d'analyser une série d'actions réalisées au gré des opportunités de financement ou de la mobilisation des acteurs locaux. Il propose un panorama non exhaustif d'expériences de gestion des risques à Lima et cherche à identifier les acteurs, les territoires et les mécanismes à l'oeuvre. Il apporte ainsi des éléments de réflexion sur les modalités de gestion des risques et sur les enjeux de la mise en place d'une politique de gestion du risque à l'échelle de l'agglomération de Lima/Callao

Hydrothermal synthesis of nanosized BaTiO3 powders and dielectric properties of corresponding ceramics

BaTiO3 fine powders were synthesized by hydrothermal method at 150 °C or 250 °C for 7 h, starting from a mixture of TiCl3 + BaCl2 or TiO2 + BaCl2. The size of the crystallites is close to 20 nm whatever the starting mixture and the reaction temperature. These powders are well crystallized and constituted of a mixture of the metastable cubic and stable tetragonal phases. The ceramics obtained after uniaxial pressing and sintering at 1250 °C for 10 h or 20 h present high densification (up to 99.8%). The Curie temperature (Tc) and the electrical permittivity ( r) of the ceramics strongly depend on the type of titanium source that has been used for preparing the powder and on the sintering dwell time. Particularly, Tc is shifted towards lower temperature when TiCl3 is used. The permittivity value at Tc of BaTiO3 sintered at 1250 °C for 10 h reaches 7000 and 11,000 with respectively TiCl3 and TiO2 used as titanium source

Mechanically Compliant Grating Reflectors for Optomechanics

We demonstrate micromechanical reflectors with a reflectivity as large as 99.4% and a mechanical quality factor Q as large as 7.8*10^5 for optomechanical applications. The reflectors are silicon nitride membranes patterned with sub-wavelength grating structures, obviating the need for the many dielectric layers used in conventional mirrors. We have employed the reflectors in the construction of a Fabry-Perot cavity with a finesse as high as F=1200, and used the optical response to probe the mechanical properties of the membrane. By driving the cavity with light detuned to the high-frequency side of a cavity resonance, we create an optical antidamping force that causes the reflector to self-oscillate at 211 kHz

Statistical prediction of aircraft trajectory : regression methods vs point-mass model

International audienceGround-based aircraft trajectory prediction is a critical issue for air traffic management. A safe and efficient prediction is a prerequisite for the implementation of automated tools that detect and solve conflicts between trajectories. Moreover, regarding the safety constraints, it could be more reasonable to predict intervals rather than precise aircraft positions . In this paper, a standard point-mass model and statistical regression method is used to predict the altitude of climbing aircraft. In addition to the standard linear regression model, two common non-linear regression methods, neural networks and Loess are used. A dataset is extracted from two months of radar and meteorological recordings, and several potential explanatory variables are computed for every sampled climb segment. A Principal Component Analysis allows us to reduce the dimensionality of the problems, using only a subset of principal components as input to the regression methods. The prediction models are scored by performing a 10-fold cross-validation. Statistical regression results method appears promising. The experiment part shows that the proposed regression models are much more efficient than the standard point-mass model. The prediction intervals obtained by our methods have the advantage of being more reliable and narrower than those found by point-mass model