Compiègne, France
Compiègne, France

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Ji S.,CNRS Roberval Laboratory (Mechanical Research Unit) | Ouahsine A.,CNRS Roberval Laboratory (Mechanical Research Unit) | Smaoui H.,Compiègne University of Technology | Sergent P.,CETMEF
International Journal of Sediment Research | Year: 2014

Ship-generated waves and return currents are capable of re-suspending significant quantities of bottom and bank sediments. However, most of the previous studies done on the subject do not show how and where sediment is re-suspended by the wakes and the directions of net transport. In this paper, a 3D numerical model based on hydro-sedimentary coupling is presented to search the relationship between the sediment movement, and the pattern of ship-generated waves around and far away from the vessel and the return currents around the ships. The hydrodynamic model is based on 3D Navier-Stokes equations including the standard k-ε model for turbulence processes, and the sediment transport model is based on a 3D equation for the re-suspended sediment transport. The computation results show that the areas of sediment concentration and transport (whether by resuspension or by the bedload) depend mainly on the position, the speed of the ship in the waterways, the kinematics of ship-generated waves and on the return flows. Thus, a map of sediment distribution and the modes of sediment transport generated by the passage of the ship are presented. © 2014 International Research and Training Centre on Erosion and Sedimentation and the World Association for Sedimentation and Erosion Research.

Gallen R.,CETMEF | Gallen R.,UniverSud | Cord A.,UniverSud | Hautiere N.,University Paris Est Creteil | Aubert D.,University Paris Est Creteil
IEEE Intelligent Vehicles Symposium, Proceedings | Year: 2011

Compared to daytime, a larger proportion of accident happens during nighttime. The altered visibility of the road scene for the drivers may partially explain this situation. The latter becomes worse in fog presence. In this paper, two camera-based methods are proposed to detect the presence of night fog in images grabbed by in-vehicle multipurpose cameras. They rely on the visual effects of night fog. A first approach can assess the presence of fog around the vehicle thanks to the detection of the backscattered veil induced by the vehicle ego lights. It aims at detecting fog when the vehicle is alone in absence of exterior public lighting. A second approach can assess the presence of fog thanks to the detection of halos around light sources in the vehicle environment. It aims at detecting fog in presence of road traffic or public lighting. Both methods are presented and illustrated with actual images of fog. Their complementarity makes it possible to envision a complete night fog detection system. There are numerous applications for such a system: automation or adaptation of vehicle lights, contextual speed computation and reliability improvement for camera-based systems. © 2011 IEEE.

Dufour G.,Egis International | Michard B.,CETMEF | Cosquer E.,CETMEF | Fernagu E.,Egis International
Coasts, Marine Structures and Breakwaters 2013: From Sea to Shore - Meeting the Challenges of the Sea | Year: 2014

The research objectives of the French project EMACOP are to estimate the available marine energy and to study the efficiency and sustainability of systems and their morphodynamic impacts. This paper focus on the assessment of wave energy resource on existing structures along France's coastlines. Methodology through analytical calculations leading to select the most energetic sites, example case and results are described.

Dupray S.,CETMEF | Dupray S.,HR Wallingford | Gamst K.,CIRIA | Robertshaw G.,Halcrow Group Ltd. | And 2 more authors.
Coasts, Marine Structures and Breakwaters: Adapting to Change - Proceedings of the 9th International Conference | Year: 2010

The findings of the research summarised above will be available in the second half of 2009 in the form of a 'Manual on the use of concrete in the maritime environment'. The report will be published by CIRIA. It will also be translated and published in French by CETMEF.

Goutx D.,Meteo - France | Baraer F.,Meteo - France | Roche A.,Cetmef | Jan G.,Shom
Houille Blanche | Year: 2014

Risk studies of coastline flooding strive to define extreme values for sea level and the surf and then combine them to determine a threat index for the seaboard. However, these phenomenona are often generated by the same type of weather event: the storms. Meteo-France, the Cetmef and the Shom got together to study the storms threatening the coast of Brittany and to determine the extreme events the associated hydrodynamic parameters of which would allow to study the risk of coastline flooding. By combining archives and re-analysis (ERA-Intérim), each storm is documented; then a typology is implemented to establish within each cluster, which elements are the most representative. The Arpege model enables us to restore the most typical historical storms, then the Ensemble Prevision supplies data on fictitious but plausible storms that can be afterwards combined with unfavourable tide conditions. This method which enables us to study plausible extreme events not yet revealed to us, creates the problem of the likelihood of these fictitious events. It is nonetheless an innovative technique, relevant for the understanding of extreme events so that the strategies used to adapt our shorelines, as it is demanded by the 2007/60/CE European Directive in the case of extreme events, could be assessed. © 2014 Société Hydrotechnique de France.

Ji S.-C.,CNRS Roberval Laboratory (Mechanical Research Unit) | Ouahsine A.,CNRS Roberval Laboratory (Mechanical Research Unit) | Smaoui H.,CETMEF | Sergent P.,CETMEF | Jing G.-Q.,Beijing Jiaotong University
Journal of Hydrodynamics | Year: 2014

The duration of ship-generated waves (wake waves) and accelerated currents can generate significant influences on the sediment transport. A 3-D numerical model is presented to estimate these effects. The hydrodynamic model is the 3-D Reynolds averaged Navier-Stokes (RANS) equations including the standard k - ε model while the 3-D convection-diffusion model is for the resuspended sediment transport. This hydro-sedimentary model is firstly validated with the trench experimental results, and then applied to the open channel with a moving ship. The computed results demonstrate that the resuspension generation mainly depends on ship speeds, barge number, and the relative distance away from ship. The acceleration effects of ship on the sediment transport are analyzed as well. © 2014 Publishing House for Journal of Hydrodynamics.

Alderf N.,CNRS Roberval Laboratory (Mechanical Research Unit) | LefrancOis E.,CNRS Roberval Laboratory (Mechanical Research Unit) | Sergent P.,CETMEF | Debaillon P.,CETMEF
International Journal for Numerical Methods in Fluids | Year: 2011

In this paper we are interested in numerical modeling of 'dynamic' phenomenon of squat by finite elements analysis. It proposes a set of modular numerical tools; therefore, interchangeable. This model enables the study of the interaction between a two-dimensional potential flow in highly restricted waterways on irregular shaped bottom with stationary free surface in taking into account the dynamic response of a ship. The proposed model has been used to validate a stability model based on the extension of the one-dimensional theory of Schijf to the dynamic effects by pointing out stable and unstable squat positions for a ship. It is also shown that for two cases of depth change in shallow water ('step'), unstable position may be reached. © 2009 John Wiley & Sons, Ltd.

Ji S.C.,CNRS Roberval Laboratory (Mechanical Research Unit) | Ouahsine A.,CNRS Roberval Laboratory (Mechanical Research Unit) | Smaoui H.,CNRS Roberval Laboratory (Mechanical Research Unit) | Sergent P.,CETMEF
Journal of Hydrodynamics | Year: 2012

We consider waves generated by the passing of convoys in a restricted waterway. The magnitude of these waves depends mainly on the geometrical and kinematical parameters of the convoy, such as the speed and the hull geometry. The objective of this study is to predict the relationship between these geometrical and kinematical parameters and the amplitude of ship-generated waves as well as the water plane drawdown. Numerical simulations are conducted by solving the 3-D Navier-Stokes equations along with the standard k - ε model for turbulent processes. The results are compared first with the empirical model and second with experimental measurements performed by the French company Compagnie National du Rhône (CNR). © 2012 Publishing House for Journal of Hydrodynamics.

Alderf N.,CNRS Roberval Laboratory (Mechanical Research Unit) | Lefrancois E.,CNRS Roberval Laboratory (Mechanical Research Unit) | Sergent P.,CETMEF | Debaillon P.,CETMEF
Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment | Year: 2010

In this paper, a mathematical model for ship squat in highly restricted waterways is proposed. This model, which is based on the extension of Schijf's (1949) theory to dynamic effects, indicates stable and unstable squat positions for a ship. Furthermore, the transition effects are integrated into this model to simulate the behaviour of a vessel during and after an acceleration phase. This model shows that, although the vessel speed is lower than the Schijf limiting speed, grounding due to the oscillations generated at the end of the acceleration phase may occur when the unstable equilibrium position is reached. The results given by the mathematical model are validated by a numerical model based on finite element analysis.

Prevot G.,CETMEF | Boucher O.,CETMEF | Luck M.,Électricité de France | Benoit M.,Électricité de France
Proceedings of the Coastal Engineering Conference | Year: 2012

Rubble-mound breakwaters are often pre-designed with empirical formulae allowing the estimation of armour stone size or weight, taking into account the wave conditions (mainly a characteristic wave height and a characteristic period), the type and density of stone or block used, the slope of the mound, the acceptable level of damage, etc. In deep water conditions, the existing formulas are rather well established (e.g. Hudson and Van der Meer formulas among others). They use as input data wave parameters that are well defined (e.g. the significant wave height H1/3 or sometimes the height H 1/10) and easily accessible, from in situ measurements or from numerical wave models. In shallow water however, and in particular in breaking wave conditions (where most of the small breakwaters are built), a number of physical processes (refraction, shoaling and breaking) significantly modify the incoming waves. They also lead to changes in the wave height distribution (which can no longer be regarded as being of Rayleigh-type) and in the shape of the wave spectrum. This, combined with the fact that most of the models used nowadays for nearshore wave propagation are spectral wave models (e.g. SWAN, TOMAWAC, etc.) and thus provide spectral parameters as output (typically the spectral significant wave height Hm0 and the peak period T p or the mean energetic period Tm-1, 0) has raised the question of which characteristic wave parameter should be used in stability formulas for rubble-mound breakwaters in shallow water. This has led to the consideration of more representative wave parameters such as H2% or Tm-1, 0 which are sometimes less accessible from existing wave database or numerical modelling studies. The objective of the present study is to review and compare several available methods to calculate armour stone weight in shallow waters, and to provide some insight into the applicability and limitations of these methods based on a series of wave flume experiments.

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