Particle Image Velocimetry (PIV) measurements in a water film, application to a tire rolling through a puddle

International audienceA measurement method based on Particle Image Velocimetry with refraction of the laser sheet at a win-dow/water interface is proposed for the measurement of the velocity field of a water flow formed by a tire moving inside a water puddle. This study focuses of the feasibility and repeatability of this optical measurement method. The characterization of the optical properties of the measurement technique defines the integration effect in height of the measurement method. The analysis of the overall features of the flow is focused on two main zones in front and around the tire. The flow inside the first zone is defined by a characteristic velocity of the water displaced in an area located in front of the tire ; in the second zone a characteristic velocity representative of the flow in the vicinity of the shoulder of the tire is also defined. Correlations of both characteristic velocities with the car speed and water film height are established. New and worn tires were tested in this work

Etude de la réfraction d'une nappe laser dans un film d'eau, application à la mesure de champ de vitesse par PIV

International audienceUne méthode de mesure de type Vélocimétrie par images de particules (PIV) adaptée aux mesures en espaces confinés et basée sur la réfraction de la nappe laser à l'interface entre le hublot transparent et l'écoulement est présentée dans ce travail. L'analyse optique de l'éclairement des particules ensemen-çant l'écoulement est effectuée par l'utilisation d'un modèle à rayon puis par la mesure de l'intensité lumineuse dans l'écoulement. Cette analyse permet ensuite l'étude critique des champs de vitesse obte-nus par cette méthode de mesure vis à vis de la structure de l'écoulement

Coupling a sugarcane crop model with the remotely sensed time series of fIPAR to optimise the yield estimation

The objective of this study was to assess the efficiency of the assimilation of the fraction of intercepted photosynthetically active radiation (fIPAR) data derived from Satellite Pour l'Observation de la Terre SPOT images into the MOSICAS sugarcane crop growth model for estimating the yield at field scale on Reunion Island. Over 3 years, time series of SPOT satellite imagery were used to estimate the daily evolution of NDVI for 60 plots located on two climatically contrasted farms. Ground measurements of the fIPAR were performed on 5 reference fields and used to calibrate a relationship with the corresponding NDVI values. Forced and not forced simulations were run and compared with respect to their ability to predict the final observed yield. Forcing MOSICAS with fIPAR values derived from SPOT images improved the accuracy of the model for the yield estimation (RMSE = 12.2 against 14.8 t ha(-1)) closer to the 1:1 line. However, underestimations of the yield by the forced model suggest that some of the model parameters were not optimal. The maximal radiation use efficiency parameter (RUEm) was optimised for each field, and an analysis of variance showed the significant effect of the ratoon number of the field, of its cultivar and of the farm where it is planted. Accordingly, the RUEm was recalibrated for each cultivar for the number of ratoons and farms. New RUEm values ranged from 3.09 to 3.77 gMJ(-1), and new computations were run using the optimised values of RUEm The results indicate that recalibrating the maximal radiation use efficiency according to the number of ratoons improved the yield estimation accuracy by as much as 10.5 t ha-1 RMSE. This study highlights the potential of time series of satellite images to enhance the estimation of the yield by a forced ecophysiological model and to obtain better knowledge about the ecophysiological processes that are involved in crop dynamics with the recalibration method

Multi-camera calibration for 3DBOS

International audienceBackgroung Oriented Schlieren (BOS) is a Schlieren-like method that can be used as a 3D quantitative method for measuring density in 3D flows. This can be done providing that there are enough points of view, at least 10, and that an accurate calibration of the multi-camera bench is available. We present here a study of multi-camera calibration for 3DBOS. We use a simple printed flat plate with a dotted regular pattern as calibration body (CB). The main issues are the workload, because there are several hundred of images, and the blurring effect. The blur affects the images of the CB when it is positioned in the common part of the fields of views of the cameras. It can not be avoided because of illumination limitation. We present practical solutions and results for both issues. A GPU implementation allows to complete the calibration of a system with 12 cameras in less than 30mn. We also propose an uncertainty analysis using the jackknife method. It is shown that the uncertainty of the estimation of the horizontal field of view (HFoV) is 0.04°. Moreover, HFoV is nearly identical for all cameras and quasi equal to the theoretical value

Particle Image Velocimetry (PIV) measurements in a water film, application to a tire rolling through a puddle

International audienceA measurement method based on Particle Image Velocimetry with refraction of the laser sheet at a win-dow/water interface is proposed for the measurement of the velocity field of a water flow formed by a tire moving inside a water puddle. This study focuses of the feasibility and repeatability of this optical measurement method. The characterization of the optical properties of the measurement technique defines the integration effect in height of the measurement method. The analysis of the overall features of the flow is focused on two main zones in front and around the tire. The flow inside the first zone is defined by a characteristic velocity of the water displaced in an area located in front of the tire ; in the second zone a characteristic velocity representative of the flow in the vicinity of the shoulder of the tire is also defined. Correlations of both characteristic velocities with the car speed and water film height are established. New and worn tires were tested in this work

Simulation cartographique au service de l'innovation collective : géoprospective territoriale à l'île de La Réunion

L'objectif de cet article est de présenter une démarche de construction d'un exercice de prospective territoriale basé sur un outil de modélisation spatiale. Cette démarche est mise en oeuvre dans le cadre du projet ANR DESCARTES dont l'objectif est de construire un outil de simulation cartographique pour analyser différents scénarios d'affectation de l'usage des sols à l'Ile de La Réunion, en termes de services environnementaux. La plateforme de simulation cartographique est composée de deux applications complémentaires (i) le langage de modélisation Ocelet et son environnement de simulation de paysages dynamiques, et (ii) la plateforme Margouill@. Le développement puis la présentation, en atelier, d'un premier démonstrateur sur la consommation des terres agricoles par l'urbanisation a permis de tester l'outil cartographique comme support d'un processus d'innovation collective entre les parties prenantes, et d'ouvrir de nouveaux champs de recherche sur l'analyse de la démarche par les apprentissages, la spatialisation et la simulation prospective des services écosystémiques, et la prise en compte du changement d'échelle