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Dans le contexte de la réfrigération secondaire, les coulis de glace offrent des avantages énergétiques et environnementaux par rapport aux fluides monophasés (généralement l'eau) en raison de la présence de particules de glace dans le liquide porteur. Ces coulis sont souvent obtenus par des générateurs à surface raclée. Cependant, ces dispositifs présentent certains inconvénients, notamment une surconsommation d'énergie liée au raclage, qui dégrade le rendement énergétique de l'installation, ainsi que des coûts de maintenance liés à l'usure des lames de raclage. Ainsi, le développement de générateurs sans raclage fait l'objet de nombreuses recherches. Ici, on s'intéresse à l'utilisation d'un revêtement superhydrophobe (SH) pour la production de coulis de glace. En effet, les surfaces superhydrophobes (SH) sont connues pour leur capacité à augmenter le degré de surfusion et à retarder la congélation, ce qui présente un grand intérêt dans le domaine de la production de froid, soit pour réduire la formation de glace sur les évaporateurs des machines frigorifiques afin d'améliorer les transferts thermiques, soit pour produire de l'eau surfondue pour des applications de réfrigération secondaire. L'objectif de ce travail est de caractériser la congélation d'une goutte d'eau sur des plaques en aluminium avec revêtement superhydrophobe (SH). Un intérêt particulier est porté aux changements des propriétés superhydrophobes (SH) de ces surfaces pendant le refroidissement. Des mesures de l'évolution de l'angle de contact ont été utilisées pour caractériser l'état de mouillage des plaques revêtues et non revêtues à différentes températures et niveaux d'humidité. Les résultats montrent que le revêtement maintient la superhydrophobie des plaques à des températures supérieures à 10 $^{\circ}$C pour différents niveaux d'humidité. À basse température, le revêtement superhydrophobe (SH) entraîne un sous-refroidissement de la goutte avec un degré de surfusion d'environ 8 $^{\circ}$C. Les angles de contact diminuent significativement avec la baisse de la température et l'augmentation de l'humidité. Un modèle semi-empirique de l'évaporation d'une goutte sur une surface superhydrophobe est présenté et comparé aux résultats expérimentaux.

International audience; An acquisition campaign of the ONERA airborne synthetic aperture radar system RAMSES have been set up on the Greenland ice-shelf to assess the detectability of buried objects and subsurface feature through dry snow/ice cover. Three band were investigated UHF band, L band and X band, forecasting a better penetration at lower band, but an higher radar cross section for a given object/feature at higher band, thus a trade off for the optimal frequency band to use that was not clear prior to experiment. Three sites were imaged, one in the accumulation zone North of the polar circle (East of Kangerlussuaq airport), one in the accumulation zone in a warmer southern area (East of Narsassuaq airport) and one in the intermediate zone between accumulation and ablation zones (plus a calibration zone and a front glacier close to Kangerlussuaq). Processing of the data revealed that both UHF and X band are indeed providing complementing results (deeper bigger feature versus shallow smaller features), but intermediate L band combining both drawbacks of higher attenuation and lower features RCS did not seem to yield any further information.

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]SPEE; International audience; Ice cream crystallization processes can be modeled by some population and energy balance equations. Due to the infinite dimensional and nonlinear characteristics, such models are highly complex, especially when all the phenomena of nucleation, growth and breakage are considered. Depending on the control problem under consideration, such a complexity can be useless and the control law can be designed on the basis of an input-output reduced order model of the process. In the present paper, we first consider a reduced order model of 6 ordinary differential equations obtained by the method of moments. By means of a sensitivity analysis and a parameter identification, it is shown that, to accurately describe the input-output behavior of the system whatever the conditions are, it is sufficient to change the values of only two parameters of this model, which is really interesting from a control point of view. However, when looking at the simulated data, the complexity of this moments model appears useless, from the input-output point of view. A second model reduction is therefore performed, based on physical assumptions. We finally get a new model with 3 ordinary differential equations, which is validated first on experimental data and then by comparison with the initial moments model.

Dans une première partie, l'auteur fait une revue des définitions et des classifications existantes du pied de glace, montrant que la notion de pied de glace est imprécise, souvent ambiguë et diffère fréquemment d'un auteur à l'autre. Dans la seconde, il définit et décrit le pied de glace dans l'estuaire du Saint-Laurent en distinguant deux grands types de pied de glace : celui de haut et de bas estran. Il souligne aussi son rôle protecteur et morpho-sedimentologique., In the first part, a review of the existing definitions and classification of the icefoot is made, showing that the icefoot notion is inaccurate, often ambiguous and not the same for everyone. In the second part, a definition and a description of the icefoot in the St. Lawrence Estuary are offered. Two main types of icefoot are distinguished : the upper and the lower strand icefoot. The protective and the morpho-sedimentological role of this feature is also emphasized.

Les pôles de la Terre ont de tout temps nourri l’imaginaire. Des utopistes protestants de la fin du xviie siècle aux romanciers de la fin du xixe siècle, tous y projettent un lieu magique, féerique où il fait bon vivre. Les récits de marins ayant vu la mer libre de glace au pôle Nord sont repris et enjolivés par les plus grands scientifiques qui cherchent à justifier leurs théories ne pouvant concevoir, en effet, que la mer puisse geler. Fiction et science se mélangent et se confortent mutuellement de sorte que la mer Arctique libre de glace devient une réalité immuable jusqu’à Mary Shelley ou à Jules Verne inclus qui rendra fou son héros après la traversée du paisible océan Polaire. Ce n’est qu’à partir du xixe siècle que le spectre de l’avancée programmée des glaces inquiète et que l’imaginaire commence à voir dans ces contrées une quantité de glace capable de provoquer un déluge… The earth’s poles nourished the imagination for a long time. For the protestant utopians of the end of the XVIIth century as for the novelists of the XIXth century, the pole is a magic, enchanting place where the weather is fine. Sailor’s tales having seen the sea free of ice near the North pole are assumed to be true and are used by the most important scientists, unable to conceive that the sea may freeze. Science and fiction blend and reinforce mutually so the Arctic sea, free of ice becomes an irremovable reality, until Mary Shelley or Jules Verne. Hatteras will cross the ice barrier until the sea free of ice and will become mad. The ghost of the advance of ice, due to the climate cooling assumed by Buffon begins to be perceptible in the literature in the middle of the XIXth century.

An ice feature comprising ice blocks ranging from football size to 0.6 m cubes to 1.2 m × 3.6 m × 0.6 m slabs was observed on the surface of a frozen lake. Site investigations revealed the source of the blocks to be an ice mound that had formed along the shore of the lake. A model, supported by local meteorological, geological, and hydrological information, is proposed to explain the formation of the ice mound and its subsequent rupture.

In order to gain a quantitative comparison among the various mechanical properties of ice, a series of tests was performed on fresh water ice in which several of the mechanical properties were tested under identical experimental conditions. In particular, the tests were standardized with respect to ice growth conditions, ice type, grain size and orientation, sample size, test temperature and strain rate. The average results of the test were: flexural strength -- cantilever beam = 770 plus or minus 150 kPa; flexural strength -- simple beam (top tension) = 2200 plus or minus 320 kPa; flexural strength -- simple beam (bottom tension) = 1770 plus or minus 190 kPa; fracture toughness = 83 plus or minus 7 kPa m[1/2]; shear strength = 500 plus or minus 220 kPa; compressive strength ( horizontal loading) = 4400 plus or minus 700 kPa and strain modulus -- cantilever beam = 1.6 plus or minus 0.4 GPa. Since most of the tests were performed using a portable compression test machine, the strength values can serve as baseline values for comparison with field results.

The ice lensing phenomenon in layered soils, a condition that simulates the process of ice growth in varved soils, has been studied experimentally. Under the limited conditions of layer thicknesses, soils used, freezing rates, and moisture conditions, ice lenses formed at the face of the fine-textured (clay) layer when it was encountered by the freezing plane. Only minor heaving occurred in the coarse-textured (silt) layer when its thickness was increased. Key words: frost action, ice lensing, frost heaving, varved soils, layered soils.

Laboratory tests on piles made of different materials (polyethylene, polyvinylchloride, steel, wood, concrete, and Inerta 160-coated steel) were used to investigate their adhesion to an ice cover at high rates of loading. Steel, wood, and concrete piles had adhesive strengths from 0.4 to 0.5 MPa; failure at these stresses occurred in the ice. Polyethylene and polyvinylchloride piles had an adhesive strength in the range 0.05–0.07 MPa; failure was characterized by separation between the pile and the ice. Inerta 160-coated steel had an intermediate strength of 0.25 MPa. Measured strengths were related both to the adhesion of ice to the pile and compliance of the pile. A special test series investigated the effect on adhesion of a tensile or compressive stress state in a polyethylene pile. An adhesive strength of 0.06 MPa was recorded in tension, and 0.13 MPa in compression, because of the relative stiffness of the pile and the ice. Keywords: ice loading, piles, ice adhesion, pile material, stress states.

A critical review of the problems associated with the design of an ideal platen for uniaxial loading tests is presented. A method of design based on an analytical approach is then formulated. The method permits a liberal choice of material for constructing the platen, which consists mainly of a low modulus plug confined in a metallic ring. A finite element approach has been employed to substantiate the proposed method. Practical design aspects are also discussed.

The propensity for crack formation on basal and prismatic planes and twin nucleation on two pyramidal planes in hexagonal ice is examined on the basis of fracture theories and anisotropic elastic theories of dislocations. Calculations show that the ease of crack formation is almost the same in the basal and prismatic planes, whereas it is almost impossible to produce mechanical twinning in ice by stress alone.

The three-dimensional failure envelope for granular/discontinuous-columnar sea ice has been investigated over a range of nominal strain rates from 9 × 10−6 s−1 to 4.4 × 10−4 s−1 by using confined compression tests. Both the applied load and side-confining load were measured. The tests were performed on samples cut from a solid block of ice in the Beaufort Sea which structurally was granular with some banding of discontinuous-columnar ice to a depth of 1.2 m. The results indicate the overall shape and size of the failure envelope of this ice, and show that although the shape is independent of loading rate, the size increases with loading rate. An analytical expression is derived which mathematically describes the failure envelope in three-dimensional space.

A test program undertaken in April 1981 on the uniaxial compressive strength of freshly recovered first-year columnar-grained sea ice at a portable field laboratory floating on top of the ice cover in Eclipse Sound, Baffin Island, Canadian Arctic, is reported. Using a small battery-operated test machine, both vertical and horizontal samples were tested so that the load could be applied either parallel or perpendicular to the axis of the columns. Rate sensitivity of the observed strength is discussed in terms of measured average strain-rate and average stress-rate to upper yield or failure. Strain and time aspects of the test results are considered as well. Although vertical samples showed considerably greater strength than horizontal samples, no significant differences were detected in the failure strains. Examination of the interdependence of failure stress and failure time revealed certain anomalies in the results for vertical samples that could be linked to the performance characteristics of the test machine. As such problems could be common to any test system, methods of analysis are proposed for rational examination of the results.

The results of studies on the relation between freeze-up, break-up and weather conditions for a small fresh-water lake in the Ottawa area are reported. Techniques using air temperature records for estimating when a solid ice-cover will form on the lake are investigated. .A formula using weather records is also developed for estimating the time taken for ice to melt from the lake. The usefulness of these relationships for estimating “freeze-up” and “break-up” dates for rivers and lakes is discussed.

A comparative study of the deformation behaviour of mechanically and chemically polished ice crystals is described. For single crystals, mechanical disturbance of the surface layer greatly reduces the maximum stress for basal glide in constant strain rate tests in compression. Single crystals with sub-boundaries do not show any prominent surface effect, but exhibit quite a low maximum stress. The results indicate that mechanically disturbed surface layers and sub-boundaries do not appear to act as strong barriers to dislocation movement in ice crystals, but rather as sources of dislocations. Surface condition does not appear to affect the maximum stress for polycrystals. The influence of strain rate (range 2.1 X 10(-5) to 1.7 X 10(-4)(s-1) and temperature (range -10 to -30 degrees C) upon the maximum stress was also investigated for both single crystals and polycrystals of ice.

X-ray photography has been used to locate the position of a growing ice lens in soil under laboratory conditions in order to establish the temperature of the actively growing face by means of its position in the thermal gradient field. It can be shown that in a general way the phase change temperatures are predictable from the Clapeyron equation. The structure of the ice phase also appears to follow the predictions of the heave rate equation proposed by Penner and Ueda (1978). When heaving occurs at low overburden pressures, there is a tendency for the ice lens to be very discrete and essentially soil free; at higher pressures and under similar thermal gradients it tends to develop in a more diffuse band and over a much wider temperature range.

International audience; This contribution addresses the different approaches that are developed in our laboratory to study the chemical evolution of organic matter in stellar or interplanetary environments. In the first approach, starting from interstellar or cometary ice analogs subjected to different energy processes (thermal, photochemical), we aim to explain the mechanism of formation of key molecules (RING project: Reactivity in INterstellar ice Grains) such as HMT, POM or amino acid precursors that are or may be detected in future space missions. In a second approach, we are interested in the detection of volatile molecules sublimating from ice analogs when these latter are heated and/or irradiated (VAHIIA project: Volatile Analysis from the Heating of Interstellar Ice Analogs) through an online experimental device coupling the simulation chamber where ices are formed to a GC-MS instrument. The objective is thus to simulate the effects of the ice material warming when a young star forms or when a comet becomes active. This project provides an inventory of molecules that can be found in hot corinos or in the gaseous phase of comets. In a third approach, we analyze the organic matter contained in the refractory residues that can be considered as cometary analogs (RAHIIA Project: Residue Analysis from the Heating of Interstellar Ice Analogs) using very high resolution mass spectrometry (VHRMS). The results of these analyses show that residues present an important molecular diversity. This technique gives also the possibility to determine the elementary composition of these residues that can be compared to the meteorite composition. These residues can then be a basic material to develop, in a specific planetary environment, a prebiotic chemistry.

Le but du projet était de comprendre le comportement électrique dynamique de la montre lors d’une décharge, les instants les plus critiques étant les transitoires. L’objectif était donc de la modéliser par un circuit électrique équivalent approchant son comportement.