35 research outputs found
Characterization of process-oriented hydrologic model behavior with temporal sensitivity analysis for flash floods in Mediterranean catchments
No full textThis paper presents a detailed analysis of 10 flash flood events in the Mediterranean region using the distributed hydrological model MARINE. Characterizing catchment response during flash flood events may provide new and valuable insight into the dynamics involved for extreme catchment response and their dependency on physiographic properties and flood severity. The main objective of this study is to analyze flash-flood-dedicated hydrologic model sensitivity with a new approach in hydrology, allowing model outputs variance decomposition for temporal patterns of parameter sensitivity analysis. Such approaches enable ranking of uncertainty sources for nonlinear and nonmonotonic mappings with a low computational cost. Hydrologic model and sensitivity analysis are used as learning tools on a large flash flood dataset. With Nash performances above 0.73 on average for this extended set of 10 validation events, the five sensitive parameters of MARINE process-oriented distributed model are analyzed. This contribution shows that soil depth explains more than 80% of model output variance when most hydrographs are peaking. Moreover, the lateral subsurface transfer is responsible for 80% of model variance for some catchment-flood events’ hydrographs during slow-declining limbs. The unexplained variance of model output representing interactions between parameters reveals to be very low during modeled flood peaks and informs that model parsimonious parameterization is appropriate to tackle the problem of flash floods. Interactions observed after model initialization or rainfall intensity peaks incite to improve water partition representation between flow components and initialization itself. This paper gives a practical framework for application of this method to other models, landscapes and climatic conditions, potentially helping to improve processes understanding and representation
Mesh refinement strategies for solving singularly perturbed reaction-diffusion problems
No full textAbstractWe consider the numerical approximation of a singularly perturbed reaction-diffusion problem over a square. Two different approaches are compared namely: adaptive isotropic mesh refinement and anisotropic mesh refinement. Thus, we compare the h-refinement and the Shishkin mesh approaches numerically with PLTMG software [1]. It is shown how isotropic elements lead to over-refinement and how anisotropic mesh refinement is much more efficient in thin boundary layers
Sampling plans for the estimation of moment-independent importance measures
No full textAbstractThe numerical and computational aspects underlying the approximation of moment independent sensitivity measures are discussed. Sampling plans based on column substitution and column permutations are evaluated and compared for both analytical test cases and a practical application. The influence of the sampling strategy (simple random, latin hypercube or quasi-random sequences) is investigated
Moment Independent Importance Measures: New Results and Analytical Test Cases
No full textInternational audienceMoment independent methods for the sensitivity analysis of model output are attracting growing attention among both academics and practitioners. However, the lack of benchmarks against which to compare numerical strategies forces one to rely on ad hoc experiments in estimating the sensitivity measures. This article introduces a methodology that allows one to obtain moment independent sensitivity measures analytically. We illustrate the procedure by implementing four test cases with different model structures and model input distributions. Numerical experiments are performed at increasing sample size to check convergence of the sensitivity estimates to the analytical values
Contribution to the sample mean plot for graphical and numerical sensitivity analysis
No full texta b s t r a c t The contribution to the sample mean plot, originally proposed by Sinclair, is revived and further developed as practical tool for global sensitivity analysis. The potentials of this simple and versatile graphical tool are discussed. Beyond the qualitative assessment provided by this approach, a statistical test is proposed for sensitivity analysis. A case study that simulates the transport of radionuclides through the geosphere from an underground disposal vault containing nuclear waste is considered as a benchmark. The new approach is tested against a very efficient sensitivity analysis method based on state dependent parameter meta-modelling
Model emulation and moment-independent sensitivity analysis : An application to environmental modelling
No full textInternational audienceMoment-independent sensitivity methods are attracting increasing attention among practitioners, since they provide a thorough way of investigating the sensitivity of model output under uncertainty. However, their estimation is challenging, especially in the presence of computationally intensive models. We argue that replacement of the original model by a metamodel can contribute in lowering the computation burden. A numerical estimation procedure is set forth. The procedure is first tested on analytical cases with increased structural complexity. We utilize the emulator proposed in Ratto and Pagano (2010). Results show that the emulator allows an accurate estimation of density-based sensitivity measures, when the main structural features of the original model are captured. However, performance deteriorates for a model with interactions of order higher than 2. For this test case, also a kriging emulator is investigated, but no gain in performance is registered. However, an accurate estimation is obtained by applying a logarithmic transformation of the model output for both the kriging and Ratto and Pagano (2010) emulators. These findings are then applied to the investigation of a benchmark environmental case study, the LevelE model. Results show that use of the metamodel allows an efficient estimation of moment-independent sensitivity measures while leading to a notable reduction in computational burden
Power Hardware-In-the-Loop simulation for testing multi-sources vehicles
No full text20th IFAC World Congress, TOULOUSE, FRANCE, 09-/07/2017 - 14/07/2017Energy management of multi-sources vehicles is a complex task. The higher the number of sources becomes, the higher the complexity is. Moreover, the energy management methods have to face real-time issues. As a consequence, it is important to find some testing procedures to assess the developed methods, in real-time conditions before implementation on the vehicle. In this paper, a Power Hardware-In-The-Loop simulation is implemented for a Fuel Cell - battery - Supercapacitors vehicle. The platform enables to test some Energy Management Strategies in real-time conditions
Different control schemes of a battery/supercapacitor system in Electric Vehicle
No full textIEEE Vehicle Power and Propulsion Conference 2014 , COIMBRA, PORTUGAL, 27-/10/2014 - 30/10/2014International audienceThis paper deals with energy management for electric vehicle using SuperCapacitors (SCs) and battery. SCs are connected to the DC bus through a converter whereas battery is directly connected to the DC bus. Using the inversion-based rules of Energetic Macroscopic Representation (EMR), a systematic control structure can be deduced. Some differences can be shown in comparison with classical control schemes. This paper aims to compare a control scheme deduced from EMR and another control structure designed thanks to a more classical way. It can be noticed that some differences appear. As far as the structure is concerned, the number of sensor can be reduced in the EMR case. In terms of performances, some control errors appear in the classical scheme case
Simulation 3D de la génération et de la réception d'ondes guidées : application à la détection de défauts dans des structures composites
No full textLe Contrôle Non Destructif (CND) de matériaux est en forte expansion dans les domaines de l’aéronautique, de l’aérospatial, des transports et bien d’autres. Les ondes ultrasonores guidées constituent un moyen puissant pour la mise en œuvre du CND, car elles se propagent sur de grandes distances tout en interrogeant les structures à cœur. L’emploi de transducteur à couplage par air, disposés d’un même coté, permet de faire du CND sans contact et sans démontage des pièces testées. Cette thèse a consisté à modéliser, en 3 dimensions et par éléments finis, un système de CND ultrasonore à ondes guidées. Le modèle prend en compte la taille finie des transducteurs, l’ouverture angulaire des faisceaux, la diffraction dans toutes les directions, l’anisotropie, la viscoélasticité et l’hétérogénéité des matériaux. Les prédictions numériques sont systématiquement comparées à des mesures expérimentales. Trois structures ont été étudiées avec succès : une plaque en aluminium avec un trou, une plaque en verre-époxyde avec un dommage causé par impact, un réservoir haute pression ASTRIUM pourvu d’un décollement entre son liner en Titane et son bobinage en carbone-époxyde.The Non Destructive Testing (NDT) of materials is rapidly expanding in the fields of aeronautics aerospace, transportation, and so on. Guided ultrasonic waves are a powerful means for the implementation o the NDT because they can spread over large distances while interviewing through structures. The use of air coupled transducer allows both non-contact NDT and non-disassembly of tested parts. This thesis is mainly about three-dimensional finite element modelling, and an ultrasonic NDT system based on guided waves. The model takes into account the finite size transducers, the angle of beam diffraction in all directions, anisotropy viscoelasticity and heterogeneity of materials. The numerical predictions are systematically compared with experimental measurements. Three specimens have been studied with success: an aluminium plate with a hole glass-fibre plate with an impact damage, a high pressure tank provided by ASTRIUM with a disbonding defec between the liner titanium layer and wound carbon - fibre
