40 research outputs found
Application de la méthode LSPIV pour la mesure de champs de vitesse et de débits de crue sur modÚle réduit et en riviÚre
International audienceLSPIV technique enables the measurement of surface flow velocities using image sequence analysis. EDF and Irstea partnership made possible the development of FudaaâLSPIV freeware by DeltaCAD Company. Two software applications at flume and field scales are detailed: (i) bed shear stresses were calculated owing to LSPIV velocities, water depth and bathymetry for a physical model of the Old Rhine; (ii) the software was used to optimize the calculation parameters of LSPIV flood discharge measurement stations in Mediterranean rivers.La technique LSPIV (Large Scale Particle Image Velocimetry) permet de mesurer les vitesses de surface d'un Ă©coulement par analyse de sĂ©quence d'images. Pour faciliter l'application opĂ©rationnelle de la mĂ©thode, un logiciel, Fudaa-LSPIV, a Ă©tĂ© dĂ©veloppĂ© par la sociĂ©tĂ© DeltaCAD dans le cadre d'une collaboration entre EDF et Irstea. Deux applications en laboratoire et en riviĂšre sont prĂ©sentĂ©es : (i) couplĂ©e avec des mesures de hauteur d'eau et de bathymĂ©tries, la LSPIV a permis d'estimer des paramĂštres de Shields sur le modĂšle physique Ă fond mobile du Vieux-Rhin ; (ii) le logiciel a Ă©tĂ© utilisĂ© pour procĂ©der Ă des analyses de sensibilitĂ© pour paramĂ©trer ainsi au mieux les stations LSPIV de mesure de dĂ©bit en crue de riviĂšres cĂ©venoles
Crowdsourcing Methods for Data Collection in Geophysics: State of the Art, Issues, and Future Directions
Data are essential in all areas of geophysics. They are used to better understand and manage systems, either directly or via models. Given the complexity and spatiotemporal variability of geophysical systems (e.g., precipitation), a lack of sufficient data is a perennial problem, which is exacerbated by various drivers, such as climate change and urbanization. In recent years, crowdsourcing has become increasingly prominent as a means of supplementing data obtained from more traditional sources, particularly due to its relatively low implementation cost and ability to increase the spatial and/or temporal resolution of data significantly. Given the proliferation of different crowdsourcing methods in geophysics and the promise they have shown, it is timely to assess the stateâofâtheâart in this field, to identify potential issues and map out a way forward. In this paper, crowdsourcingâbased data acquisition methods that have been used in seven domains of geophysics, including weather, precipitation, air pollution, geography, ecology, surface water and natural hazard management are discussed based on a review of 162 papers. In addition, a novel framework for categorizing these methods is introduced and applied to the methods used in the seven domains of geophysics considered in this review. This paper also features a review of 93 papers dealing with issues that are common to data acquisition methods in different domains of geophysics, including the management of crowdsourcing projects, data quality, data processing and data privacy. In each of these areas, the current status is discussed and challenges and future directions are outlined
Nouvelles utilisations des mesures de bassins de dĂ©flexion pour caractĂ©riser lâĂ©tat structurel des chaussĂ©es
The evaluation of the structural characteristics of pavements is involved in their maintenance. The measurement of deflection is a key indicator of this evaluation. Currently, only the maximum deflection and the radius of curvature are analyzed. However, the curviameter and the deflectograph are able to record the whole deflection bowl and the parameters deduced from thismeasurement could help to better characterized damages on pavements. The interpretation of the measurements is only qualitative and back calculation of pavement layer moduli gives unsatisfactory results. The thesis aims to improve the interpretation of deflection measurements. The working principle of these apparatus and the measurement assumptions introduce several measurement biases.To overcome these issues, a correction process has been developed. The comparison with theoretical basins has given satisfactory results on bituminous or flexible pavements. Then, a numerical study has been conducted to determine the influence of pavements damages on the deflection measurement. By this study, it has been showed that the usual indicators of the deflection measurement are notable to detect all damages. So, a methodology hasbeen developed in order to create an optimized indicator specified to a special defect. A study on numerical results has been conducted to validate the implementation of these indicators. Then, the correction method and these new indicators have been tested on experimental sites with and without damages. At last, the research works have been studied at network level.LâĂ©valuation des caractĂ©ristiques structurelles des chaussĂ©es permet lâoptimisation de leur maintenance. La mesure de dĂ©flexion est une mesure de base de cette Ă©valuation. Aujourdâhui,seuls la dĂ©flexion maximale et le rayon de courbures ont analysĂ©s. Pourtant, le curviamĂštre et le dĂ©flectographe relĂšvent le bassin de dĂ©flexion complet dont lâanalyse permettrait dâextraire des paramĂštres plus sensibles Ă lâendommagement des chaussĂ©es. Actuellement, lâinterprĂ©tation des mesures est seulement qualitative et aucun calcul inverse de lâĂ©tat de dommage de la structure nâest rĂ©alisĂ©. La thĂšse vise Ă amĂ©liorer lâinterprĂ©tation des mesures de dĂ©flexion. Le fonctionnement des appareils a montrĂ© que leurs hypothĂšses de mesure conduisent Ă des biais de mesure. Pour pallier ce problĂšme, une procĂ©dure de correction des mesures a Ă©tĂ© mise en place. La comparaison avec des bassins thĂ©oriques a montrĂ© que la mĂ©thode de correction Ă©tait satisfaisante. Ensuite, une Ă©tude numĂ©rique visant Ă dĂ©terminer la sensibilitĂ© du bassin de dĂ©flexion Ă la prĂ©sence de diffĂ©rents dĂ©fauts a Ă©tĂ© conduite. Celle ci a montrĂ© que les indicateurs classiques de la mesure de dĂ©flexion Ă©taient peu sensibles Ă un endommagement dans la chaussĂ©e. Une mĂ©thodologie a donc Ă©tĂ© dĂ©veloppĂ©e pour la crĂ©ation dâindicateurs optimisĂ©s Ă un type de dĂ©fauts spĂ©cifiques. LâĂ©tude sur cas thĂ©oriques a conduit Ă lâobtention de rĂ©sultats concluants. Lâensemble de ces travaux a ensuite Ă©tĂ© validĂ© sur sites expĂ©rimentaux pour des mesures de rĂ©pĂ©tabilitĂ©, mais Ă©galement sur site avec la prĂ©sence avĂ©rĂ©e de dĂ©fauts. Finalement, la thĂšse a envisagĂ© lâutilisation des travaux prĂ©cĂ©dents sur des mesures rĂ©elles recueillies sur itinĂ©raire
New uses of deflection bowls measurements to characterize the structural conditions of pavements
LâĂ©valuation des caractĂ©ristiques structurelles des chaussĂ©es permet lâoptimisation de leur maintenance. La mesure de dĂ©flexion est une mesure de base de cette Ă©valuation. Aujourdâhui,seuls la dĂ©flexion maximale et le rayon de courbures ont analysĂ©s. Pourtant, le curviamĂštre et le dĂ©flectographe relĂšvent le bassin de dĂ©flexion complet dont lâanalyse permettrait dâextraire des paramĂštres plus sensibles Ă lâendommagement des chaussĂ©es. Actuellement, lâinterprĂ©tation des mesures est seulement qualitative et aucun calcul inverse de lâĂ©tat de dommage de la structure nâest rĂ©alisĂ©. La thĂšse vise Ă amĂ©liorer lâinterprĂ©tation des mesures de dĂ©flexion. Le fonctionnement des appareils a montrĂ© que leurs hypothĂšses de mesure conduisent Ă des biais de mesure. Pour pallier ce problĂšme, une procĂ©dure de correction des mesures a Ă©tĂ© mise en place. La comparaison avec des bassins thĂ©oriques a montrĂ© que la mĂ©thode de correction Ă©tait satisfaisante. Ensuite, une Ă©tude numĂ©rique visant Ă dĂ©terminer la sensibilitĂ© du bassin de dĂ©flexion Ă la prĂ©sence de diffĂ©rents dĂ©fauts a Ă©tĂ© conduite. Celle ci a montrĂ© que les indicateurs classiques de la mesure de dĂ©flexion Ă©taient peu sensibles Ă un endommagement dans la chaussĂ©e. Une mĂ©thodologie a donc Ă©tĂ© dĂ©veloppĂ©e pour la crĂ©ation dâindicateurs optimisĂ©s Ă un type de dĂ©fauts spĂ©cifiques. LâĂ©tude sur cas thĂ©oriques a conduit Ă lâobtention de rĂ©sultats concluants. Lâensemble de ces travaux a ensuite Ă©tĂ© validĂ© sur sites expĂ©rimentaux pour des mesures de rĂ©pĂ©tabilitĂ©, mais Ă©galement sur site avec la prĂ©sence avĂ©rĂ©e de dĂ©fauts. Finalement, la thĂšse a envisagĂ© lâutilisation des travaux prĂ©cĂ©dents sur des mesures rĂ©elles recueillies sur itinĂ©raire.The evaluation of the structural characteristics of pavements is involved in their maintenance. The measurement of deflection is a key indicator of this evaluation. Currently, only the maximum deflection and the radius of curvature are analyzed. However, the curviameter and the deflectograph are able to record the whole deflection bowl and the parameters deduced from thismeasurement could help to better characterized damages on pavements. The interpretation of the measurements is only qualitative and back calculation of pavement layer moduli gives unsatisfactory results. The thesis aims to improve the interpretation of deflection measurements. The working principle of these apparatus and the measurement assumptions introduce several measurement biases.To overcome these issues, a correction process has been developed. The comparison with theoretical basins has given satisfactory results on bituminous or flexible pavements. Then, a numerical study has been conducted to determine the influence of pavements damages on the deflection measurement. By this study, it has been showed that the usual indicators of the deflection measurement are notable to detect all damages. So, a methodology hasbeen developed in order to create an optimized indicator specified to a special defect. A study on numerical results has been conducted to validate the implementation of these indicators. Then, the correction method and these new indicators have been tested on experimental sites with and without damages. At last, the research works have been studied at network level
Estimation de débit de crue par utilisation de films amateurs
Flood discharge estimation using non professional movies.
Knowing the discharge of a river during flood events is essential for hydrological studies. Unfortunately, measurements using traditional gauging devices are too difficult or unsafe to conduct during extreme events. As a result, high flow discharges are often very imprecise or, sometimes, donât even exist. With the aim of improving the possibilities of discharge measurements during extreme floods, an image based method using non professional movies is being developed from the already well known LSPIV method. Those movies, made by non professional and quickly released on internet, are more and more numerous at each new extreme events, providing a source of information which we propose a new form of valuation.La connaissance du dĂ©bit en crue est essentielle pour la comprĂ©hension des Ă©pisodes hydrologiques extrĂȘmes et la mise en place de gestion des risques. Or en raison des difficultĂ©s techniques que prĂ©sentent les jaugeages par mĂ©thode traditionnelle en cas de forte crue, ces donnĂ©es sont souvent manquantes ou trĂšs imprĂ©cises. En se basant sur les mĂ©thodes maintenant maĂźtrisĂ©es de mesure de dĂ©bit par analyse de sĂ©quence dâimages telles que la LSPIV, une mĂ©thode est en dĂ©veloppement afin dâexploiter les films amateurs de crue et de pouvoir rĂ©aliser des estimations de dĂ©bit dans des gammes souvent peu ou pas jaugĂ©es. Ces films, gĂ©nĂ©ralement rĂ©alisĂ©s par des particuliers et dont le nombre augmente Ă chaque nouvel Ă©vĂ©nement hydrologique intense, reprĂ©sentent une source de donnĂ©es dont il est proposĂ© ici une nouvelle forme de valorisation.Le Boursicaud RaphaĂ«l, Penard Lionel, Le Coz JĂ©rĂŽme. Estimation de dĂ©bit de crue par utilisation de films amateurs. In: 35es journĂ©es de lâhydraulique de la SociĂ©tĂ© Hydrotechnique de France. HydromĂ©trie 2013. Paris, 15-16 mai 2013. 2013
Guide mĂ©thodologique : Collecte et prĂ©paration de film amateur en vue dâune exploitation par analyse dâimage
[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAUIn the context of flash floods, or in ungauged basin, we propose to use the acquired video and posted online by witnesses. The preliminary work carried out since 2012 on this issue were used to develop and validate an image sequence processing methodology to overcome the difficulties related to the amateur nature of video capture : camera movements , known optical sensor . This methodology is now stabilized and requires free software tools freely available , including Fudaa - LSPIV ( Irstea / EDF ) . This procedure explain the processing of witness films for the analysis of velocities and flow rates.Dans le contexte de crues rapides, ou dans des bassins non instrumentĂ©s, ou bien encore dâinondations urbaines sans jaugeages, nous proposons dâutiliser des vidĂ©os acquises puis mises en ligne par des tĂ©moins. Les travaux prĂ©alables menĂ©s depuis 2012 sur ce sujet ont permis de dĂ©velopper et valider une mĂ©thodologie de traitement des sĂ©quences dâimages pour pallier les difficultĂ©s liĂ©es au caractĂšre amateur de lâacquisition vidĂ©o : mouvements de la camĂ©ra, optique inconnue du capteur. Cette mĂ©thodologie est maintenant stabilisĂ©e et ne requiert que des outils logiciels gratuits et disponibles librement, dont Fudaa-LSPIV (Irstea/EDF). Afin de rendre son application possible par d'autres utilisateurs, voilĂ un mode opĂ©ratoire pour le traitement des films amateur en vue de l'analyse des vitesses et dĂ©bits
Jaugeage par radar mobile, protocole et résultats
La technique de mesure des vitesses de surface par radar mobile sĂ©duit les Ă©quipes d'hydromĂ©trie du fait de sa rapiditĂ© et de la simplicitĂ© de sa mise en Ćuvre pour des jaugeages en crue. Les radars mobiles viennent ainsi complĂ©ter la flotte d'instruments dĂ©jĂ disponible dans les Ă©quipes. L'intĂ©rĂȘt de ces radars et de cette technique est de pouvoir explorer le champ de vitesse de surface sans contact avec la riviĂšre. Le calcul du dĂ©bit Ă partir de ces mesures partielles nĂ©cessite des mesures complĂ©mentaires, notamment de bathymĂ©trie et de hauteur d'eau. L'Ă©valuation du coefficient de vitesse est aussi un point important. Cette technique est particuliĂšrement bien adaptĂ©e aux mesures en crue. Cette Ă©tude prĂ©sente le protocole de mesure proposĂ© par Irstea pour le jaugeage par radar mobile, qui propose notamment une solution de dĂ©ploiement pour les cas oĂč la hauteur d'eau varie trĂšs rapidement dans le cours d'eau. Des cas d'application sur des sites variĂ©s sont prĂ©sentĂ©s notamment lorsque la technique par radar a Ă©tĂ© testĂ©e et comparĂ©e avec d'autres mĂ©thodes. Les rĂ©sultats sont trĂšs encourageants
Jaugeage par radar mobile. Protocole et résultats
Mobile radar gauging, field procedure and results.
The non-contact surface velocity measurement using SVR (Surface Velocity Radar) can be used to measure river discharge during floods. This method convinces hydrometry services because it is quick and simple to apply. The SVR is a complimentary instrument to add to the field panoply, especially for flood measurements. For computing discharge from surface velocities, additional measurements (bathymetry, velocity profiles, water level) are needed, and a velocity coefficient has to be estimated for each site. Mean velocity and surface velocity are linked through this coefficient. This study explains the field procedure suggested by Irstea (National Research Institute of Science and Technology for Environment and Agriculture) for gauging streams with a SVR system, with a two-way procedure to improve the discharge measurement accuracy during fast flood with fast water level variations. Some application results are presented in different rivers, with a comparison between the radar method and other conventional discharge measurements. The quality of the results is very encouraging.La technique de mesure des vitesses de surface par radar mobile sĂ©duit les Ă©quipes d'hydromĂ©trie du fait de sa rapiditĂ© et de la simplicitĂ© de sa mise en oeuvre pour des jaugeages en crue. Les radars mobiles viennent ainsi complĂ©ter la flotte d'instruments dĂ©jĂ disponible dans les Ă©quipes. L'intĂ©rĂȘt de ces radars et de cette technique est de pouvoir explorer le champ de vitesse de surface sans contact avec la riviĂšre. Le calcul du dĂ©bit Ă partir de ces mesures partielles nĂ©cessite des mesures complĂ©mentaires, notamment de bathymĂ©trie et de hauteur d'eau. L'Ă©valuation du coefficient de vitesse est aussi un point important. Cette technique est particuliĂšrement bien adaptĂ©e aux mesures en crue. Cette Ă©tude prĂ©sente le protocole de mesure proposĂ© par Irstea pour le jaugeage par radar mobile, qui propose notamment une solution de dĂ©ploiement pour les cas oĂč la hauteur dâeau varie trĂšs rapidement dans le cours dâeau. Des cas d'application sur des sites variĂ©s sont prĂ©sentĂ©s notamment lorsque la technique par radar a Ă©tĂ© testĂ©e et comparĂ©e avec d'autres mĂ©thodes. Les rĂ©sultats sont trĂšs encourageants.Dramais Guillaume, Le Coz JĂ©rĂŽme, Le Boursicaud RaphaĂ«l, Hauet Alexandre, Lagouy MickaĂ«l. Jaugeage par radar mobile. Protocole et rĂ©sultats. In: 35es journĂ©es de lâhydraulique de la SociĂ©tĂ© Hydrotechnique de France. HydromĂ©trie 2013. Paris, 15-16 mai 2013. 2013
An improved passive scalar model for hydrogen hazardous ignition prediction
International audienceWith an increasing interest in hydrogen as an alternative fuel for transportation, there is a need to develop tools for the prediction of ignition events. A cost-effective passive scalar formulation has been recently developed to predict hydrogen auto-ignition. A single scalar advection-diffusion-reaction equation is used to reproduce the chain-branched ignition process, where the scalar represents the radical pool responsible of ignition (H, O, OH, HO2 , H2O2). The scalar reaction rate is analytically deduced from the Jacobian matrix associated to hydrogen ignition chemistry. This method was found to reproduce with good accuracy the ignition delays obtained by detailed chemistry for temperature where the branching is the leading process. For temperature close or below the crossover temperature, where other phenomenon such as the thermal runaway are important, the scalar approach fails to predict correctly ignition events. Thus, an extension of the scalar source term formulation is proposed to extend its validity over the entire temperature range. In addition, a simple way to approximate the diffusion properties of the scalar is introduced: the radical pool composition may vary drastically, with molecules having very different diffusion properties (e.g. H and HO2). The complete modified framework is presented and its capability is assessed in canonical scenarios and more complex simulations relevant to hydrogen safety