Resurrecting Dead-water Phenomenon

We revisit experimental studies performed by Ekman on dead-water using modern techniques in order to present new insights on this peculiar phenomenon. We extend its description to more general situations such as a three-layer fluid or a linearly stratified fluid in presence of a pycnocline, showing the robustness of dead-water phenomenon. We observe large amplitude nonlinear internal waves which are coupled to the boat dynamics, and we emphasize that the modeling of the wave-induced drag requires more analysis, taking into account nonlinear effects

Dead Waters: Large amplitude interfacial waves generated by a boat in a stratified fluid

We present fluid dynamics videos of the motion of a boat on a two-layer or three-layer fluid. Under certain specific conditions, this setup generates large amplitude interfacial waves, while no surface waves are visible. The boat is slowed down leading to a peristaltic effect and sometimes even stopped: this is the so-called dead water phenomenon

A novel internal waves generator

We present a new kind of generator of internal waves which has been designed for three purposes. First, the oscillating boundary conditions force the fluid particles to travel in the preferred direction of the wave ray, hence reducing the mixing due to forcing. Secondly, only one ray tube is produced so that all of the energy is in the beam of interest. Thirdly, temporal and spatial frequency studies emphasize the high quality for temporal and spatial monochromaticity of the emitted beam. The greatest strength of this technique is therefore the ability to produce a large monochromatic and unidirectional beam

Beacon Synchronization for GTS Collision Avoidance in an IEEE 802.15.4 Meshed Network

International audienceIndustrial process control architectures are generally composed of nodes organized in a cluster-tree. Today, wired communications between nodes enable guaranteeing the constraint respect attached to determinism. Innovations in wireless technology allow using these new technologies instead of wired systems. IEEE 802.15.4 standard meet industrial local network needs, but it does not propose any mechanisms to avoid beacon and GTS (Guaranteed Time Slot ) collisions in meshed network. This communication proposes a new synchronization method for beacons and GTSs in meshed networks using IEEE 802.15.4

A simple method for guaranteed deadline of periodic messages in 802.15.4 cluster cells for automation control applications

International audienceWe propose the implementation of a wireless sensor network applied to automation control applications, when the guarantee of a delay delivery for the complete reception of messages is necessary. The 802.15.4 wireless standard network offers possibilities of management of the bandwidth. This paper presents the method to guarantee the deadline transmission of periodic messages. For external messages (crossing the network from clusters to its destination), this average latency is used as a parameter of the routing protocol decision balance between energy saving and delay transmission. In this last case, a QoS method all over the network has to be installed to maintain a bounded end to end transmission delay. This work is still in progress. A specific Matlab simulator has been developed, principles of this routing method are mentioned at the end of this paper

New (Internal) Wave Generation - Laboratory Experiments

In this fluid dynamics video, we demonstrate the experimental generation of various internal wave fields using a novel wave generator. Specifically, uni-directional internal wave beams and vertical modes 1 and 2 are generated and visualized using Particle Image Velocimetry. Further details and analysis of these experiments can be found in [1].Comment: 2 pages, no figures, article linked to a fluid dynamics video submitted to the Gallery of Fluid Motion, APS DFD 200

Représentation du niveau de croyance en lien avec la notion d’aléa

In this technical note, we develop a belief representation that generalizes the vanillapossibility theory, extending it to a bi-dimensional representation where randomness is taken intoaccount. This way, we revisit and extend the usual quantitative implementation of belief level.We state the basic requirements and discuss the difference with the vanilla possibility theorybefore investigating the compatibility with Boolean and Kleene’s three-valued logic calculus. Wethen relate this representation to the probability theory, based on the assumption that necessityand possibility provide bounds for probability values, and finally discuss how to define a relevantprojection of real values onto an admissible representation.This provides the basic ingredients to implement such extension of belief representation in existingmechanisms using the basic representation. The operational part of this development is availableas open-source code.Dans cette note technique, nous développons une représentation de la notionde niveau de croyance qui généralise la théorie des possibilités standard, en l’étendant à unereprésentation bidimensionnelle où l’aléatoire est pris en compte. De cette façon, nous revisitonset étendons l’implémentation numérique habituelle du niveau de croyance.Nous énonçons les contraintes de base et discutons de la différence avec la théorie des pos-sibilités usuelle avant d’étudier la compatibilité avec le calcul logique booléen à trois valeursde Kleene. Nous relions ensuite cette représentation à la théorie des probabilités, basée surl’hypothèse que la nécessité et la possibilité fournissent des bornes pour les valeurs de probabil-ité, et discutons enfin de la manière de définir une projection pertinente des valeurs réelles surune représentation admissible.Cela fournit les ingrédients de base pour mettre en œuvre une telle extension de la représen-tation des croyances dans les mécanismes existants utilisant la représentation de base. La partieopérationnelle de ce développement est disponible en code open-source

The Clermont radiometric reference rocks: a convenient tool for dosimetric purposes

soumis à Ancient TLBoreholes drilled in 8 different rocks situated in the vicinity of the Clermont TL laboratory have been used for testing and calibrating methods devoted to measure the natural radioactivity. The present paper gives updated data for the nuclide contents and internal dose-rates for those reference media. Two examples of application are presented. The first example shows dose-rate calibration of a scintillator gamma probe using a threshold method. The second example shows a routine technique for TL dosimetry, based on the rocks for dose-rate reference