198 research outputs found
Validation of a 1D Simplified Model of Gironde Estuary Based on a Database of TELEMAC Simulations
Hydrodynamic
Trim optimisation in waves
The trim optimisation is nowadays a common practice for all ship owners.
Reduction o fuel consumption and improvement of ship energy efficiency concern all sectors of the
maritime industry. The trim optimisation consists in finding the best trim angle with
regards to the lowest power - i.e. fuel consumption - for a given operating condition (loading
condition and speed). Although the operational efficiency of trim optimisation based on calm water
resistance computations databases could be proven at sea, it is well known that added resistance
due to wave can significantly impact fuel consumption. The increase of cluster computing
power make it today possible to evaluate the added resistance in waves using state of the art free
surface RANSE solvers. This study of the optimal trim depending on the sea- states show that taking
into account the waves could have a significant impact on the optimal trim that have been identify
on still water. Although the optimal trim angle trends are the same on still water and in waves for
low sea-states, for highest sea-states the trends can be the perfect opposite. This study shows
that the optimal trim mainly depends on the draft and the sea-state. The speed seems to have an
effect on the gains / losses amplitude but not on the best trim value. The in waves databases
will enable operators to predict their ship efficiency with better accuracy, taking into
account weather predictions. The trim needs to be therefore adapted
regularly depending on the weather conditions the ship encounter during her voyage
Simulations numériques de l'évolution des fonds et effet du mélange turbulent sur le transport sédimentaire:Application au remplissage d'une fosse d'extraction
International audienceLe profil linéaire de longueur de mlange classiquement utilisé, ne permet pas d'obtenir le profil de vitesse logarithmique observ\é expérimentalement, et sa validité est limitée aux domaines de faible rugosité (conditions aux limites du type 'fond lisse'). Dans ce travail, nous proposons trois types de profils de longueur de mélange ainsi que les profiles de vitesses de mélange associés. Les résultats obtenus, sont testés sur des cas académiques et comparés aux résultats expérimentaux de remplissage d'une fosse d'extraction issus des essais présentés dans le projet Européen Sandpit
Modélisation numérique des processus de transport des sédiments et de l'évolution des fonds
International audienceWe propose a new mixing length profile, based on an extension of von Kármán similarity hypothesis, as well as the associated mixing velocity profile. This profile was compared with other profiles and was tested on three academic and experimental cases. The validation of the model was made from a set of reference examples and concerns the erosion of a bottom of sand in a uniform flow, and the filling of an extraction pit resulting from the tests presented in the European project SANDPIT.On propose un nouveau profil de longueur de mélange lm (z) , basé sur une extension de l'hypothèse de similitude de von Kármán, ainsi que le profil de vitesse de mélange associé. Ce profil a été comparé à d'autres profils et testé sur trois cas test académiques et expérimentaux. La validation du modèle a été effectuée à partir d'un ensemble d'exemples de références et concernent l'érosion d'un fond de sable érodable dans un écoulement uniforme en canal, et le remplissage d'une fosse d'extraction issus des essais présentés dans le projet Européen SANDPIT
The hydrodynamic, sea-state and infrastructures platform developed by Saint-Venant Hydraulics Laboratory and Cerema: a special focus on the TELEMAC2D surge levels numerical model of the Atlantic Ocean, the Channel and the North Sea
Water Qualit
Influences of the separation distance, ship speed and channel dimension on ship maneuverability in a confined waterway
High quality factor nitride-based optical cavities: microdisks with embedded GaN/Al(Ga)N quantum dots
We compare the quality factor values of the whispery gallery modes of
microdisks incorporating GaN quantum dots (QDs) grown on AlN and AlGaN barriers
by performing room temperature photoluminescence (PL) spectroscopy. The PL
measurements show a large number of high Q factor (Q) resonant modes on the
whole spectrum which allows us to identify the different radial mode families
and to compare them with simulations. We report a considerable improvement of
the Q factor which reflect the etching quality and the relatively low cavity
loss by inserting QDs into the cavity. GaN/AlN QDs based microdisks show very
high Q values (Q > 7000) whereas the Q factor is only up to 2000 in microdisks
embedding QDs grown on AlGaN barrier layer. We attribute this difference to the
lower absorption below bandgap for AlN barrier layers at the energies of our
experimental investigation
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