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The complex behavior of organoclay dispersions is influenced by the structure and the intermolecular interactions between clay platelets. The confinement of the clay particles is seen to be the main reason of this complex behavior because of the presence of surfactants with long alkyl chains on clay surfaces. The rheological properties of organo-hectorite (OHt) dispersed in gasoil were studied using a controlled stress rheometer. Commercial organoclay surfaces were modified with dimethyldialkyl quaternary ammonium cations. It was found that all the dispersions exhibit yield stress with a shear thinning behavior. Flow curves were correlated using both the Herschel-Bulkley phenomenological model and the Carreau-Yasuda structural model, in order to describe, respectively, the macroscopic and the microstructural behaviors of the dispersions (3 to 10 wt%). The parameters of the Carreau-Yasuda model showed the existence of a critical concentration of 6 wt%. Furthermore, frequency sweep tests showed that the dispersions start to have a fully developed gel behavior with a more pronounced solid-like structure at loadings greater than the critical concentration.

The rheological and flow behaviors of Pickering emulsions are studied as a function of their water concentration. The studied emulsions are water-in-gasoil inverse emulsions stabilized with organo-hectorite clay. An in-line emulsion preparation was performed and a novel emulsification system was used. The emulsification system was tested and confirmed before performing pipe-flow measurements. A stress-controlled rheometer was used to study the rheological behavior of organoclay stabilized inverse emulsions. It was found that the emulsions exhibited a shear thinning with yield stress non-Newtonian rheological behavior and that the flow curves were well correlated using the Herschel-Bulkley model. Pressure loss and axial velocity measurements were studied to investigate the pipe-flow behavior of the emulsions. Axial velocity of the fluids was measured using an Ultrasonic Pulsed Doppler Velocimeter. It was shown that, up to 50 wt% water mass concentration, an exponential increase of yield stress and viscosity values is noticed, and the phase inversion point is not reached. In the range of the applied flow rates, turbulence took place only in the case of the lowest water cut (0 wt%). The Herschel-Bulkley rheological parameters were used to simulate the pipe-flow behavior of the studied fluids, and showed a satisfactory correlation with the in-line measurements. Furthermore, wall shear stress and velocity profiles were used to study the short-, medium-, and long-term stability of the emulsions.

The last step of activated sludge wastewater treatment consists in separating the residual particulate matter from water. This separation process takes place in a clarifier: a large tank in which sludge particles settle while clear water overflows. In order to improve numerical models of clarifiers, a better understanding of activated sludge settling mechanism is required. Laboratory batch settling experiments involving acoustic Doppler velocity measurement methods have thus been developed. The raw Doppler signal was recorded over durations of up to 22hours and then post treated. At the very beginning of the sedimentation process 3D turbulence produced by the initial stirring generates a high velocity standard deviation. 3D turbulence dissipates after a few minutes. Low amplitude fluctuations of the vertical velocity remain, whereas the average velocity decreases at any vertical location. Vertical velocity profiles exhibit two areas: an area of rising velocity in the lower part of the blanket and an area in which velocity fluctuates around a uniform settling velocity in the upper part. This last area decreases constantly and disappears completely after some minutes. A change in concavity of the rising velocity profiles after three hours rest indicates a change in the physical mechanism of consolidation.

The purpose of this paper is to investigate rheology and hydrodynamic behavior of different mass concentration of bentonite suspensions in pipe flow. Bentonite suspensions exhibited shear thinning and yield stress non-Newtonian rheological behavior. Most of the data reported are for the laminar and turbulent flow, data are also included the start-up flow development. The axial velocity distribution was determined using a Ultrasonic Pulsed Doppler Velocimetry technique. The experimental results show a progressive destructuration of the suspensions in the entrance region due to the segregation of the structural elements of the fluid and tend to a steady state and a fully developed laminar pipe flow. In the majority of cases, axisymmetric flow is observed for both laminar and turbulent flow conditions. Also an asymmetry characterizes the axial velocity profiles in the laminar-turbulent transitional flow. In the laminar regime, the flow parameters were fitted by using the Herschel–Bulkley model. For the turbulent flow, the Dodge and Metzner model was applied to fit the experimental data.

The addition of an increased amount of soluble fibre pectin in foods is desired due to its proven positive health benefits to human. The aim of this research was to explore the synergies between the commonly used food additives, carboxymethyl cellulose (CMC) and two types of pectin (high or low methoxyl, HM or LM) using rheological methods. The rheological properties of the reconstituted water solutions of the food additive powder were investigated, at different mass concentrations (0.05%–3.00%) and temperatures (4 °C, 20 °C, 37 °C and 60 °C), reflecting those of food storage and food consumption, using small and large deformation rheological measurements. Dynamic tests showed that CMC alone, HM and LM pectin alone and their combinations exhibit strong viscoelastic behaviour, under the conditions used in this study. For CMC solutions, the Cox–Merz rule was found to be obeyed to a reasonable degree at temperatures lower than the cloud point temperature. However, divergence from the Cox–Metz rule is observed when phase separation takes place. The current rheological methods are feasible to examine the synergy in viscosity and elasticity of mixed gel dispersion, which was determined by the polymer interactions via hydrophobic effects and hydrogen bonds depending on variables such as polymer substitution degree, polymer proportions and applied temperature.

L’objectif de notre travail est d’apporter un supplement de connaissance quant au comportement mecanique des boues biologiques en ecoulement. Pour ce faire, des fluides modeles ont ete mis en oeuvre. Il s’agit notamment de suspensions d’argile et de melange argile-polymere. Les fluides utilises sont une suspension de bentonite de concentration massique de 5 % et un melange de 5 %/0.1 % bentonite/carboxymethyl cellulose de sodium (CMC). Il a ete etabli que le comportement rheologique de l’argile et du melange peut etre caracterise par un modele a trois parametres de type Herschel-Bulkley. Un accent est mis sur l’effet de l’ajout de polymere sur les proprietes rheologiques et en ecoulement des boues. Cette etude est motivee, d’une part, par le fait que le polymere est un constituant de la boue elle-meme et d’autre part, par son utilisation comme additif pour le controle des proprietes physiques des boues. En regime laminaire les parametres d’ecoulement sont en accord avec les resultats analytiques obtenus a partir du modele de Herschel-Bulkley. En regime turbulent, les equations de Dodge et Metzner modelisent de maniere satisfaisante le comportement de ces fluides. Il a ete montre que le polymere a des proprietes viscosifiantes en regime laminaire, par contre en regime turbulent, il est un reducteur de frottement.

La rheologie apparait comme un champ d’etude primordial pour caracteriser le comportement des boues activees. Cette etude s’attache a tester differentes equations liant la viscosite d’une suspension de boues activees a sa concentration a l’aide de simulations numeriques de sedimentation en batch. Dans un premier temps, des echantillons de boues activees ont ete preleves dans une station de traitement des eaux afin d’effectuer des mesures rheologiques de maniere a obtenir des ordres de grandeurs realistes de viscosite ainsi que le rheogramme des boues. Celui-ci peut etre decrit par un modele de Bingham avec une bonne fiabilite.Par la suite, un modele tridimensionnel utilisant les equations de la mecanique des fluides couplees a la rheologie et la vitesse de sedimentation des boues a ete utilise pour simuler la decantation en batch dans une colonne cylindrique. Differentes relations issues de la litterature liant la viscosite des boues a la concentration ont ete testees : elles se distinguent essentiellement par des croissances plus ou moins rapides de la viscosite en fonction de la concentration.Les profils verticaux et les contours de concentration obtenus avec chaque modele sont compares. L’influence du choix de la loi de comportement rheologique est particulierement sensible au niveau de la distribution des concentrations au sein du domaine de sedimentation, l’irregularite des contours de concentration augmentant avec la fluidite de la suspension. Une simulation employant un des modeles precedents modifie de maniere a generer des valeurs de viscosite tres importantes tend a confirmer ce resultat.

Beverages are an ideal food format to deliver health-promoting polyphenols (PPs) and dietary fibres (DFs) to consumers. In this study, complex beverage systems, smoothies, were formulated containing high concentrations of apple PPs (500 mg per 300 ml beverage), apple fibres of two different particle sizes (AF01, 250 μm; AF09, 300–700 μm; each containing soluble and insoluble fibres), and stabiliser carboxymethylcellulose (CMC; 0.05–2.00 %). The beverages were pasteurised at 85 °C for 15 s, and subjected to total extracted PP content (TEPC) and rheological measurements (viscosity, elastic modulus G′ and viscous modulus G″ at 4, 20, 37 and 60 °C). Scanning electron microscopy (SEM), FT-IR spectroscopy and N2 physisorption measurements on the AF01 and AF09 fibre powders showed that they differed in particle size, yet were similar in particle surface morphology, chemical composition and specific surface area. Characterisation of smoothies prepared from the AF01 and AF09 fibres showed that the particle size of the apple fibres, testing temperature and CMC concentration strongly influenced the extractability of PPs and rheological behaviour of the smoothies. The peak TEPC values of the AF01 and AF09 beverages, 327 and 351 mg catechin equivalent per 300 ml beverage, occurred at 1.50 % and 1.00 % CMC, respectively. The temperature dependence of smoothie viscosity was examined, and an Arrhenius relationship was observed for both the AF01 and AF09 smoothie systems. The stabilising effect of CMC for this type of smoothie beverage was confirmed. CMC concentrations of 1.00–1.50 % afford high extracted PP content, good phase stability and beverage flow properties. These results presented here can be used to guide the development of stable beverages containing relatively high concentrations of PPs and DFs (including both insoluble and soluble).

Dispersions of clay particles in aqueous polymer solutions generally exhibit complex rheological behaviours depending on the mechanical history of the material. In this paper, the effect of the temperature on the rheological properties of bentonite dispersions in aqueous carboxymethylcellulose solutions is examined. The bentonite concentration was fixed to 5% w/w while the polymer is 0.5 or 1% w/w. For stresses lower than a yield stress, the systems behaved as a gel and, above the yield stress, they flowed as liquids. The samples were characterized both in permanent and oscillatory shear flow. In the liquid like regime, the viscosity of the fluids decreased as the temperature increased. In the solid like regime, when the temperature increased, the experimental results displayed unusual behaviours of the viscosity and of the shear moduli. The increase of the chain mobility induced by the Brownian motion combined with a dissociation of the aggregates of particles could result in the formation of an elastic network with more crosslinks. This could explain why a dramatic increase of the solid-like character of the dispersions was observed.

L’objectif de notre travail est d’apporter un supplement de connaissance quant au comportement mecanique des boues biologiques en ecoulement. Pour ce faire, des fluides modeles ont ete mis en œuvre. Il s’agit notamment de suspensions de bentonite. A partir des mesures de profils de vitesses et des pressions, notre etude experimentale porte sur l’etude de l’evolution des parametres rheologiques des boues en ecoulement dans une conduite rectiligne. Nous etudions les profils de vitesse. Ces derniers sont caracterises par une zone bouchon au cœur de l’ecoulement et une zone cisaillee a la paroi. L’effet des singularites sur la destructuration des suspensions a ete mis en evidence. La mesure des viscosites montre le caractere rheofluidifiant des boues. L’etude des coefficients de frottement montre une evolution inversement proportionnelle au nombre de Reynolds en regime laminaire ainsi qu’une transition a la turbulence a partir de Re exp = 2050.

The rheological properties of aqueous solutions of poly(ethylene oxide) (PEO) of different molecular weights (1x10(5), 4x10(5), 1x10(6) and 4x10(6) g mol(-1)) and concentrations were investigated using shear viscosity and dynamic rheological measurements. It was found that the aqueous solutions of PEO do not exhibit a yield stress and that, above a critical shear rate, all PEO solutions exhibit shear-thinning behavior, well described by the Cross model, except for the solutions made by the lowest molecular weight (1x10(5) g mol(-1)) which were almost Newtonian. The parameters of the Cross model, namely the zero-shear rate viscosity and reciprocal of the time constant, allowed the determination of the critical concentrations c(*) and c(**) (respectively, the transition to semi-dilute network solution and concentrated solution). At concentrations higher than c(**) and below a critical shear rate, solutions made of PEO of high molecular weight exhibited a clearly shear-thickening behavior at very low shear rates. In addition, the dynamic tests showed that PEO solutions exhibit concentration-dependent viscoelastic properties, with a dominant viscous behavior at PEO concentrations lower than c(**) and a dominant elastic behavior at PEO concentrations greater than c(**).

International audience; Activated sludge settling is a complex process requiring a thorough experimental study. It is, however, difficult to obtain information on the inner behavior of the sludge blanket without disturbing it. Optical methods are inefficient due to the opacity of sludge suspensions. This paper focuses on the investigation of activated sludge batch settling using a non-invasive method based on an ultrasonic transducer. The treatment of the signal allowed obtaining data on the settling velocity and concentration profiles inside of the suspension. The different settling regimes were clearly shown by the results on the basis of the shape of the settling velocity isolines. The precision of the gathered data is adapted to the calibration and validation of numerical models. The material used in the experimental setup can be installed in actual wastewater treatment plants.

Three different experimental measurements, namely, rheology, particle sizing, and x-ray diffraction (XRD), were used to study the effect of anionic additives on the properties of bentonite suspensions. The three additives were sodium carboxymethylcellulose, xanthan gum, and sodium dodecyl sulfate. Flow curves were obtained from shear stress–shear rate measurements, and the viscoelastic properties were determined from oscillatory and transient measurements. Mineralogical data were evaluated by XRD and the particle size analysis performed by light scattering technique. The presence of the surfactant modifies the face-to-face interactions and yields changes of the mixtures rheological behavior at low deformation rates. Polymers act by coating each clay particle and prevent their agglomeration. Therefore, the additives are responsible for the mechanisms of destructuration and structure reorganization as well as the mixtures viscous and viscoelastic behavior.

Malgre les connaissances geologiques accumulees sur plus de 800 puits carottes en continu au cours des quarante dernieres annees, le forage de la phase 8''1/2 du champ petrolifere de Hassi- Messaoud (Algerie) reste a ce jour delicat en raison notamment de problemes de cavage et de pertes de boue. L'objectif de ce travail etait d'etudier les problemes de pertes de boues en utilisant une approche sedimentologique et de localiser les niveaux producteurs sous-jacents du Cambrien. Pour cela, les zones a avancement rapide et lent des forages des series sedimentaires du Trias ont ete reperees afin d'en etablir des cartes de repartition. Ainsi, il a ete mis en evidence : - que les zones a avancement rapide correspondent aux secteurs sans pertes de boue (facies argileux de la plaine d'inondation), alors que les zones a avancement lent correspondent aux secteurs a pertes importantes (facies greseux des barres fluviatiles) ; - que sous les zones a avancement rapide dans les series du Trias, se trouvent des reservoirs d'hydrocarbures potentiels.

Bentonite are extensively used materials in a wide range of applications. Creep and oscillatory shear experiments in the linear viscoelastic domain were carried out on bentonite-water suspensions at different solid fractions. It was found that bentonite dispersions exhibit important viscoelastic behavior which could be represented by the generalized Kelvin-Voigt mechanical model. It is well known that an exhaustive study of colloidal dispersions may require the determination of its viscoelastic properties over a wide frequency scale. Unfortunately, due to microstructure changes, the experiments are limited in time. In order to avoid such limitation, oscillatory data were deduced from creep curves - without actually vibrating the clay dispersions - because a periodic experiment at frequency ω is qualitatively equivalent to a creep test at time 1/ω. That is, it was possible to complete the dynamic response in the low-frequency range using data obtained from the transient response in creep.

Foams have been prepared from water added with a surfactant (Sodium-Dodecyl-Sulfate, SDS) and a polymer (Poly-Ethylene-Oxide, PEO) at different concentrations. This work was devoted to a study of the flow properties of the foams. The pressure drops were measured during flow in capillary tubes (2.5, 3.5 and 4 mm) in laminar regime. It was found a strong dependence of the flow curves on capillary diameter showing that pronounced wall slip effects exist. Two known approaches were applied to quantify the slip velocity: (a) the Mooney method, in which the key assumption is that the slip velocity depends only on the wall shear stress, was not applicable and (b) the Oldroyd-Jastrzebski method, in which the assumption is that the slip velocity depends not only on the wall shear stress but also on the flow geometry, yielded satisfactory results. The determination of the pressure drop coefficient showed that the Metzner and Reed correlation, i.e., the Reynolds analogy based on the generalised Reynolds number, could be applied if the data are corrected for slip effects.

Le but de ce travail est d’etudier l’effet du polyethylene oxyde (PEO) (polymere non ionique), utilise generalement dans la formulation des boues de forage, sur le comportement rheologique de suspensions de bentonite. Des mesures rheologiques, granulometriques et zetametriques ont ete effectuees sur une suspension de bentonite, des solutions de PEO (polyethylene oxyde de masse moleculaire de 4.106, 106, 4.105 et 105 g.mol- 1) et des melanges bentonite-PEO a differentes concentrations de polymeres. L’etude a revele une forte augmentation (d’autant plus importante que la concentration et la masse moleculaire du PEO augmentent) de la viscosite, de la contrainte seuil et des proprietes viscoelastiques de la suspension argileuse. L’origine de ce changement de comportement a ete discutee sur la base de l'etude zetametrique et granulometrique. Cette derniere a mis en evidence des liaisons pont assurees par les chaines de polymeres entre les particules de bentonite. Mots cles : Boues de forage, bentonite, polyethylene oxyde.

In this study, we investigated the way of predicting two critical concentrations of sodium carboxymethyl cellulose (CMC) solutions using simple experimental procedures with a rotational rheometer. It was found that, above a critical shear rate, all CMC solutions (0.2 to 7 wt.%) exhibit shear-thinning behavior and the flow curves could be described by the Cross model. A first critical CMC concentration c*, transition to semidilute network solution, was determined using the following methods (1) study of the flow curve shapes, (2) Cross model parameters, (3) plot of the specific viscosity vs the overlap parameter, and (4) empirical structure–properties relationships. Furthermore, both creep and frequency-sweep measurements showed that the solutions behaved as viscoelastic materials above a second critical CMC concentration c** (transition to concentrated solution). The characterization of CMC solutions was completed with a time-dependent viscosity study that showed that the CMC solutions exhibited strong thixotropic behavior, especially at the highest CMC concentrations.

In the last 2 decades, an increasing interest in emulsions, stabilized by solid particles has been observed. Also known as “Pickering”, these emulsions are stabilized through the adsorption of solid particles, with both hydrophobic and hydrophilic characteristics, on the oil/water interface. Depending on the nature, wettability, and surface modification of the used solid particles, the prepared emulsion can be direct (oil in water) or inverse (water in oil).This thesis is an experimental contribution to the study of the rheological and pipe-flow behavior of water-in-oil Pickering emulsions stabilized with organoclay particles. Two main axes were treated in this work: (i) the relationship between the interactions of the solid particles and the mechanical behavior of the emulsions, and (ii) the influence of the dispersed phase concentration on the mechanical behavior of organoclay-stabilized Pickering emulsions.; Ces dernières années, un intérêt majeur a été porté sur les émulsions stabilisées par des particules solides. Connues sous le nom de « Pickering », ces émulsions sont stabilisées par l’adsorption de particules solides, qui possèdent des propriétés à la fois lipophiles et lipophobes, à l’interface entre l’huile et l’eau. Selon la nature, l’angle de contact et le type de modification de surface des particules solides, l’émulsions préparée pourrait être directe (huile dans l’eau) ou inverse (eau dans huile). La présente thèse est une contribution expérimentale à l’étude du comportement rhéologique et en écoulement des émulsions Pickering inverses, stabilisées avec des particules d’argile modifiée (organique). Deux axes principaux ont été traités dans ce travail : (i) la relation entre les interactions des particules solides et le comportement mécanique des émulsions, et (ii) l’influence de la concentration de phase dispersée sur le comportement mécanique des émulsions Pickering stabilisées par des argiles modifiées. Un système d’émulsification a été proposé et le comportement mécanique des émulsions Pickering a été étudié en utilisant la Vélocimétrie ultrasonore, Doppler pulsée et les mesures de pression. Tout d’abord, les interactions entre les particules d’argile modifiée ont été étudiées à l’aide des mesures rhéologiques. Ensuite, les émulsions Pickering ont été préparées et étudiées en écoulement. Enfin, des phénomènes d’instabilité des émulsions, à concentrations d’eau élevées, ont été identifiés et discutés.

In the last 2 decades, an increasing interest in emulsions, stabilized by solid particles has been observed. Also known as “Pickering”, these emulsions are stabilized through the adsorption of solid particles, with both hydrophobic and hydrophilic characteristics, on the oil/water interface. Depending on the nature, wettability, and surface modification of the used solid particles, the prepared emulsion can be direct (oil in water) or inverse (water in oil).This thesis is an experimental contribution to the study of the rheological and pipe-flow behavior of water-in-oil Pickering emulsions stabilized with organoclay particles. Two main axes were treated in this work: (i) the relationship between the interactions of the solid particles and the mechanical behavior of the emulsions, and (ii) the influence of the dispersed phase concentration on the mechanical behavior of organoclay-stabilized Pickering emulsions., Ces dernières années, un intérêt majeur a été porté sur les émulsions stabilisées par des particules solides. Connues sous le nom de « Pickering », ces émulsions sont stabilisées par l’adsorption de particules solides, qui possèdent des propriétés à la fois lipophiles et lipophobes, à l’interface entre l’huile et l’eau. Selon la nature, l’angle de contact et le type de modification de surface des particules solides, l’émulsions préparée pourrait être directe (huile dans l’eau) ou inverse (eau dans huile). La présente thèse est une contribution expérimentale à l’étude du comportement rhéologique et en écoulement des émulsions Pickering inverses, stabilisées avec des particules d’argile modifiée (organique). Deux axes principaux ont été traités dans ce travail : (i) la relation entre les interactions des particules solides et le comportement mécanique des émulsions, et (ii) l’influence de la concentration de phase dispersée sur le comportement mécanique des émulsions Pickering stabilisées par des argiles modifiées. Un système d’émulsification a été proposé et le comportement mécanique des émulsions Pickering a été étudié en utilisant la Vélocimétrie ultrasonore, Doppler pulsée et les mesures de pression. Tout d’abord, les interactions entre les particules d’argile modifiée ont été étudiées à l’aide des mesures rhéologiques. Ensuite, les émulsions Pickering ont été préparées et étudiées en écoulement. Enfin, des phénomènes d’instabilité des émulsions, à concentrations d’eau élevées, ont été identifiés et discutés.

This work deals with the experimental investigation and modelling of activated sludge settling. An experimental setup combining a settling column and an ultrasonic transducer is proposed. Settling velocity and concentration profiles are obtained using this setup, allowing for a better understanding of the mechanisms of activated sludge settling. These results are applied to the development of a numerical approach. A settling model using experimental functions is built. A methodology based on the automatic differentiation of the model is developed. This methodology is used, on the one hand, to analyse the sensitivity of the results to the model parameters and, on the other hand, to identify the parameter values on the basis of experimental data. The combination of the proposed experimental and numerical methods yields an efficient process for the development of sedimentation models.; Ce travail porte sur l’étude expérimentale et la modélisation de la sédimentation des boues activées. Un pilote expérimental associant une colonne de sédimentation et un transducteur ultrasonore est proposé. Des profils de vitesse de sédimentation et de concentration en particules sont obtenus grâce à ce dispositif, ce qui permet de mieux comprendre les mécanismes de décantation des boues. Ces résultats sont utilisés afin de développer une approche numérique. Un modèle de sédimentation est construit en intégrant des fonctions expérimentales. Une méthodologie mettant en œuvre la différentiation automatique du modèle est ensuite élaborée et appliquée, d'une part, à l'analyse de sensibilité du modèle aux paramètres des fonctions utilisées et, d'autre part, à l'identification des valeurs de ces paramètres à l'aide des résultats expérimentaux. La conjonction des approches expérimentale et numérique proposées constitue un processus efficace pour le développement des modèles de sédimentation.

This work is concerned with measuring the velocity of liquids loaded with particles using pulsed ultrasonic waves. The velocity of the particles, considered as representative of the liquid velocity, is estimated from the ultrasonic signal backscattered by the moving particles. This backscattered signal is considered as a response to the excitation initially transmitted periodically through the medium. The backscattered signal during a transmission/reception cycle is range-gated to obtain a set of time-windowed signals each associated with a corresponding depth. The objective of this work consists in elaborating algorithms in order to obtain the velocity profile information. The different used methods can be divided into three main categories, coherent methods, incoherent methods and hybrid methods. The first category presents the advantage of providing velocity information with high spatial and temporal resolution. An improvement in estimating the time delay by a regularized cross-correlation method is proposed and validated on a bentonite flow. This method is based on taking into account the time and space smoothness of the velocity field. The incoherent and hybrid methods are necessary when the flows under consideration have large dimensions and flow velocities. It is shown that it is possible, either to reduce the estimate variance, or to improve the maximal unambiguous velocity without affecting the variance. An algorithm based on the localization of the inter-pulse delay is finally proposed in order to remove the phase ambiguity while minimizing the estimate variance at high velocities., Ce travail s'inscrit dans le cadre de la mesure de la vitesse d'écoulement d'un liquide chargé en particules par l'utilisation d'ondes ultrasonores pulsées. La vitesse des particules, considérée comme représentative de la vitesse de l'écoulement, est estimée à partir de l'onde ultrasonore rétrodiffusée par les particules en mouvement, en réponse à une onde d'excitation initialement émise dans le milieu de façon périodique. Le signal rétrodiffusé durant un cycle d'émission/réception est décomposé par fenêtrage temporel en un ensemble de sous-signaux où chacun correspond à une profondeur donnée. L'objectif de ce travail consiste en l'élaboration d'algorithmes pour l'accès à l'information de profil de vitesse. Les différentes méthodes employées peuvent être classifiées en trois catégories principales, à savoir les méthodes cohérentes, incohérentes et les méthodes hybrides. La première catégorie présente l'avantage de fournir une information à haute résolution spatiale et temporelle. Une amélioration de l'estimation du délai temporel par une méthode d'intercorrélation régularisée permettant de tenir compte de la douceur temporelle et spatiale du champ de vitesse est proposée et validée sur un écoulement de bentonite. les méthodes incohérentes et hybrides s'imposent dans des écoulements de grandes dimensions ainsi que des vitesses élevées. On montre qu'il est possible, soit de réduire la variance d'estimation, soit d'augmenter la vitesse maximale mesurable sans affecter cette variance. Un algorithme basé sur la localisation du délai inter-pulse est finalement proposé dans le but de lever l'ambiguïté tout en minimisant la variance pour les grandes vitesses.

This work is concerned with measuring the velocity of liquids loaded with particles using pulsed ultrasonic waves. The velocity of the particles, considered as representative of the liquid velocity, is estimated from the ultrasonic signal backscattered by the moving particles. This backscattered signal is considered as a response to the excitation initially transmitted periodically through the medium. The backscattered signal during a transmission/reception cycle is range-gated to obtain a set of time-windowed signals each associated with a corresponding depth. The objective of this work consists in elaborating algorithms in order to obtain the velocity profile information. The different used methods can be divided into three main categories, coherent methods, incoherent methods and hybrid methods. The first category presents the advantage of providing velocity information with high spatial and temporal resolution. An improvement in estimating the time delay by a regularized cross-correlation method is proposed and validated on a bentonite flow. This method is based on taking into account the time and space smoothness of the velocity field. The incoherent and hybrid methods are necessary when the flows under consideration have large dimensions and flow velocities. It is shown that it is possible, either to reduce the estimate variance, or to improve the maximal unambiguous velocity without affecting the variance. An algorithm based on the localization of the inter-pulse delay is finally proposed in order to remove the phase ambiguity while minimizing the estimate variance at high velocities.; Ce travail s'inscrit dans le cadre de la mesure de la vitesse d'écoulement d'un liquide chargé en particules par l'utilisation d'ondes ultrasonores pulsées. La vitesse des particules, considérée comme représentative de la vitesse de l'écoulement, est estimée à partir de l'onde ultrasonore rétrodiffusée par les particules en mouvement, en réponse à une onde d'excitation initialement émise dans le milieu de façon périodique. Le signal rétrodiffusé durant un cycle d'émission/réception est décomposé par fenêtrage temporel en un ensemble de sous-signaux où chacun correspond à une profondeur donnée. L'objectif de ce travail consiste en l'élaboration d'algorithmes pour l'accès à l'information de profil de vitesse. Les différentes méthodes employées peuvent être classifiées en trois catégories principales, à savoir les méthodes cohérentes, incohérentes et les méthodes hybrides. La première catégorie présente l'avantage de fournir une information à haute résolution spatiale et temporelle. Une amélioration de l'estimation du délai temporel par une méthode d'intercorrélation régularisée permettant de tenir compte de la douceur temporelle et spatiale du champ de vitesse est proposée et validée sur un écoulement de bentonite. les méthodes incohérentes et hybrides s'imposent dans des écoulements de grandes dimensions ainsi que des vitesses élevées. On montre qu'il est possible, soit de réduire la variance d'estimation, soit d'augmenter la vitesse maximale mesurable sans affecter cette variance. Un algorithme basé sur la localisation du délai inter-pulse est finalement proposé dans le but de lever l'ambiguïté tout en minimisant la variance pour les grandes vitesses.

Doppler velocimetry by pulsed ultrasounds makes it possible to obtain the velocity profile of a fluid flow. The mean velocity estimation is carried out, for each measurement volume, from a so called Doppler signal, obtained from the retrodiffused demodulated sampled signal, whose frequency is proportional to the particles velocitiy. It is shown, in the case of a plane circular transducer, for a homogeneous uniform flow in the measurement volume, that the power spectral density (PSD) of this signal can be modelled by a gaussian function. An algorithm of white noise suppression, based on parametric identification of the PSD, is proposed and validated. It consists in identifying, in real-time, the PSD components of the Doppler signal by using the Levenberg-Marquardt method with a general gaussian model. The identified white noise is withdrawn from the density in order to allow a calculation of moment unbiased by this one. The Doppler signal being sampled by nature, it is subjected to the Shannon theorem which imposes a maximum measurable velocity called Nyquist velocity. This one is inversely proportional to the pulse repetition frequency (PRF). The exploration depth is also related to the PRF. This imposes the principal limit of this method, namely the inverse relation binding the exploration depth and maximum measurable velocity. In some applications, this limit is penalizing. A method allowing velocity measurements beyond the Nyquist limit is proposed. It is based on the use of several PRF. Different folding up for each PRF allows information contribution necessary to the resolution of the velocity ambiguity. An original algorithm of spectral rebuilding is proposed. It makes it possible to recombine the folded up PSD obtained for each PRF in order to reproduce the PSD of the Doppler signal., La vélocimétrie Doppler par ultrasons pulsés permet d'obtenir, le profil de vitesses d'un écoulement de fluide. L'estimation de la vitesse est réalisée, pour chaque volume de mesure, à partir du signal Doppler, obtenu à partir du signal rétrodiffusé démodulé et échantillonné, dont la fréquence est proportionnelle à la vitesse des particules. On démontre, dans le cas d'un transducteur plan et circulaire, pour un écoulement homogène et uniforme dans le volume de mesure, que la densité spectrale de puissance (DSP) de ce signal peut être modélisée par une gaussienne. Un algorithme de suppression du bruit blanc, basée sur l'identification paramétrique de la DSP est proposée et validée. Elle consiste à identifier, en temps réel, les différentes composantes de la DSP du signal Doppler en utilisant la méthode de Levenberg-Marquardt avec un modèle général gaussien. Le bruit blanc identifié est soustrait à la densité afin de permettre un calcul de moment non-biaisé par celui-ci.Le signal Doppler étant échantillonné par nature, il est soumis au théorème de Shannon qui impose une vitesse maximale mesurable nommée vitesse de Nyquist. Celle-ci est directement proportionnelle à la fréquence de répétition des trains d'ondes (PRF pour Pulse Repetition Frequency). La profondeur d'exploration est également liée au PRF. Ceci impose la principale limite de cette méthode, à savoir la relation inverse liant la profondeur d'exploration et la vitesse maximale mesurable. Une méthode permettant des mesures de vitesses au-delà de la limite de Nyquist est proposée. Elle se base sur l'utilisation de plusieurs fréquences de répétition des trains d'ondes. Le repliement différent pour chaque PRF permet l'apport d'information nécessaire à la résolution de l'ambiguïté sur les vitesses. Un algorithme original de reconstruction spectrale est proposé. Il permet de recombiner les DSP repliés obtenus pour chaque PRF afin de reproduire la DSP du signal Doppler.