Perspectives of a visible instrument on the VLTI     

Florentin Millour  Denis Mourard  Julien Woillez  Philippe Berio  Andrea Chiavassa  Orlagh Creevey  Eric Lagadec  Marc-Antoine Martinod  Anthony Meilland  Nicolas Nardetto  Karine Perraut  Philippe Stee 《Experimental Astronomy》2018,46(3):497-509

In this paper we present the most promising science cases for a new generation visible instrument on the VLTI and the conceptual idea for the instrumental configuration. We also present a statistical study of the potential targets that may be accessible for the different classes of objects and for the required spectral resolutions.  相似文献   

Modelling of drainage dynamics influence on sediment routing system in a fold‐and‐thrust belt     

Marc Viaplana‐Muzas  Julien Babault  Stphane Dominguez  Jean Van Den Driessche  Xavier Legrand 《Basin Research》2019,31(2):290-310

Drainage networks link erosional landscapes and sedimentary basins in a source‐to‐sink system, controlling the spatial and temporal distribution of sediment flux at the outlets. Variations of accumulation rates in a sedimentary basin have been classically interpreted as changes in erosion rates driven by tectonics and/or climate. We studied the interactions between deformation, rainfall rate and the intrinsic dynamics of drainage basins in an experimental fold‐and‐thrust belt subjected to erosion and sedimentation under constant rainfall and shortening rates. The emergence of thrust sheets at the front of a prism may divert antecedent transverse channels (perpendicular to the structural grain) leading to the formation of longitudinal reaches, later uplifted and incorporated in the prism by the ongoing deformation. In the experiments, transverse incisions appear in the external slopes of the emerging thrust sheets. Headward erosion in these transverse channels results in divide migration and capture of the uplifted longitudinal channels located in the inner parts of the prism, leading to drainage network reorganization and modification of the sediment routing system. We show that the rate of drainage reorganization increases with the rainfall rate. It also increases in a nonlinear way with the rate of uplift. We explain this behaviour by an exponent > 1 on the slope variable in the framework of the stream power erosion model. Our results confirm the view that early longitudinal‐dominated networks are progressively replaced by transverse‐dominated rivers during mountain building. We show that drainage network dynamics modulate the distribution of sedimentary fluxes at the outlets of experimental wedges. We propose that under constant shortening and rainfall rates the drainage network reorganization can also modulate the composition and the spatial distribution of clastic fluxes in foreland basins.  相似文献   

Numerical implementation and sensitivity analysis of a wave energy converter in a time-dependent mild-slope equation model     

Charlotte Beels  Peter Troch  Griet De Backer  Marc Vantorre  Julien De Rouck 《Coastal Engineering》2010

Several Wave Energy Converters (abbreviated as WECs) have intensively been studied and developed during the last decade and currently small farms of WECs are getting installed. WECs in a farm are partly absorbing, partly redistributing the incident wave power. Consequently, the power absorption of each individual WEC in a farm is affected by its neighbouring WECs. The knowledge of the wave climate around the WEC is needed to predict its performance in the farm. In this paper a technique is developed to implement a single and multiple WECs based on the overtopping principle in a time-dependent mild-slope equation model. So far, the mild-slope equations have been widely used to study wave transformations around coastal and offshore structures, such as breakwaters, piles of windmills and offshore platforms. First the limitations of the WEC implementation are discussed through a sensitivity analysis. Next the developed approach is applied to study the wave height reduction behind a single WEC and a farm. The wake behind an isolated WEC is investigated for uni- and multidirectional waves; it is observed that an increase of the directional spread leads to a faster wave redistribution behind the WEC. Further the wake in the lee of multiple WECs is calculated for two different farm lay-outs, i.e. an aligned grid and a staggered grid, by adapting the performance of each WEC to its incident wave power. The evolved technique is a fast tool to find the optimal lay-out of WECs in a farm and to study the possible influence on surrounding activities in the sea.  相似文献   

An active wave generating–absorbing boundary condition for VOF type numerical model     

Peter Troch  Julien De Rouck 《Coastal Engineering》1999,38(4):2145

The objective of the present work is to discuss the implementation of an active wave generating–absorbing boundary condition for a numerical model based on the Volume Of Fluid (VOF) method for tracking free surfaces. First an overview of the development of VOF type models with special emphasis in the field of coastal engineering is given. A new type of numerical boundary condition for combined wave generation and absorption in the numerical model VOFbreak² is presented. The numerical boundary condition is based on an active wave absorption system that was first developed in the context of physical wave flume experiments, using a wave paddle. The method applies to regular and irregular waves. Velocities are measured at one location inside the computational domain. The reflected wave train is separated from the incident wave field in front of a structure by means of digital filtering and subsequent superposition of the measured velocity signals. The incident wave signal is corrected, so that the reflected wave is effectively absorbed at the boundary. The digital filters are derived theoretically and their practical design is discussed. The practical use of this numerical boundary condition is compared to the use of the absorption system in a physical wave flume. The effectiveness of the active wave generating–absorbing boundary condition finally is proved using analytical tests and numerical simulations with VOFbreak².  相似文献   

The Integration of Scene Understanding within a Geographic Information System: A Prototype Approach for Agricultural Applications     

Mark Gahegan  & Julien Flack 《Transactions in GIS》1999,3(1):31-49

This paper describes progress towards engineering a combined GIS and image understanding system, designed to analyse remotely-sensed imagery in a task-oriented manner, with the task and contextual parameters being supplied by the GIS. The overall aim is to evaluate some of the more recent developments in the field of computer vision and to show how they may be integrated (along with more traditional methods of image interpretation) to improve system performance in terms of object recognition and extraction. Three aspects are reported: (1) Development of a formal notation as the basis of describing the process of transforming data from low level image representations to high level object representations; (2) Design of collaborating low and high level image processes used in this abstraction process and their control via Process Networks encapsulated into frames ; and (3) Use of Dempster-Shafer Decision Theory as the basis for combining different types of evidence to improve the recognition of objects in the scene. Some sample results are presented to illustrate the issues raised and mechanisms for the co-operative processing of data are suggested.  相似文献   

On predicting upland erosion losses from rainfall depth     

A. M. Dawod  P. Y. Julien 《Stochastic Environmental Research and Risk Assessment (SERRA)》1987,1(2):127-134

Point rainfall triggers the complex processes of overland flow and surface erosion. The probability density functions of rainfall duration and intensity are coupled with a physically based dynamic formulation of rainfall-runoff-sediment transport relationships for upland areas. When considering a single storm, rainfall depth alone is a poor predictor of sediment transport because of the dispersion introduced by the effect of rainfall intensity. On a long terms basis, however, the total amount of rainfall can be used to predict total erosion losses.  相似文献   

Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy-permitting resolution   总被引：4，自引：6，他引：4  

Barnier Bernard  Gurvan Madec  Thierry Penduff  Jean-Marc Molines  Anne-Marie Treguier  Julien Le Sommer  Aike Beckmann  Arne Biastoch  Claus Böning  Joachim Dengg  Corine Derval  Edmée Durand  Sergei Gulev  Elizabeth Remy  Claude Talandier  Sébastien Theetten  Mathew Maltrud  Julie McClean  Beverly De Cuevas 《Ocean Dynamics》2006,56(5-6):543-567

Series of sensitivity tests were performed with a z-coordinate, global eddy-permitting (1/4°) ocean/sea-ice model (the ORCA-R025 model configuration developed for the DRAKKAR project) to carefully evaluate the impact of recent state-of-the-art numerical schemes on model solutions. The combination of an energy–enstrophy conserving (EEN) scheme for momentum advection with a partial step (PS) representation of the bottom topography yields significant improvements in the mean circulation. Well known biases in the representation of western boundary currents, such as in the Atlantic the detachment of the Gulf Stream, the path of the North Atlantic Current, the location of the Confluence, and the strength of the Zapiola Eddy in the south Atlantic, are partly corrected. Similar improvements are found in the Pacific, Indian, and Southern Oceans, and characteristics of the mean flow are generally much closer to observations. Comparisons with other state-of-the-art models show that the ORCA-R025 configuration generally performs better at similar resolution. In addition, the model solution is often comparable to solutions obtained at 1/6 or 1/10° resolution in some aspects concerning mean flow patterns and distribution of eddy kinetic energy. Although the reasons for these improvements are not analyzed in detail in this paper, evidence is shown that the combination of EEN with PS reduces numerical noise near the bottom, which is likely to affect current–topography interactions in a systematic way. We conclude that significant corrections of the mean biases presently seen in general circulation model solutions at eddy-permitting resolution can still be expected from the development of numerical methods, which represent an alternative to increasing resolution.  相似文献   

The Belledonne Border Fault: identification of an active seismic strike-slip fault in the western Alps   总被引：1，自引：0，他引：1  

François Thouvenot  Julien Fréchet  Liliane Jenatton  Jean-François Gamond 《Geophysical Journal International》2003,155(1):174-192

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Contribution à l'étude de la vitesse critique d'érosion des sols cohésifs     

Julien Gargani 《Comptes Rendus Geoscience》2004,336(6):561-566

The phenomena of erosion and sedimentation in rivers are treated qualitatively and quantitatively. An analytical solution of the bedload critical velocity for erosion and sedimentation is proposed, depending on material property, geometry and on flow characteristics. The critical velocity of erosion of the river bed, as defined by Hjulström in 1935, can be explained by a cohesive behaviour of the grains. Whereas the cohesive force is dominated by an 1/r² (r is the radius of grains) force when grains are small, it can be modelled by the cohesion C and the friction angle φ for larger grains. To cite this article: J. Gargani, C. R. Geoscience 336 (2004).  相似文献   

What is really undermining hydrologic science today?     

Vazken Andréassian  Julien Lerat  Cécile Loumagne  Thibault Mathevet  Claude Michel  Ludovic Oudin  Charles Perrin 《水文研究》2007,21(20):2819-2822

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