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In the present study, a water transmission pipeline under steady conditions is modeled followed by examining the transient flow created by the failure of pumps in the pipeline. This pipeline is 31 km from the water transmission pipeline of Kerman, Iran. The software analysis results were compared with those of a numerical model for a laboratory test to validate transient flow modeling. While transient flows are created by pump failure, various areas of the water transmission pipelines will be affected by the transient waves produced. Long water transmission pipelines, usually large in diameter and flow rate, will pose problems in the negative pressure phase. The negative pressure causes threatening problems like water column separation and cavitation. The results indicated that using equipment like air valves when the pumps fail alone does not have the appropriate efficiency in eliminating the hazards in the water transmission pipelines. More examination showed that installing equipment like water flow feed and hydropneumatic tanks along the pipeline length in the right places prevents the negative pressure created and the pipeline risk significantly reduces.

Comparative analysis of pressure wave propagation, following laser-induced ablation of the human cornea, was performed. Evolution of the pressure field as well as temporal and spatial dependencies of the transient pressure amplitudes created at various input laser parameters, corresponding to different typical procedures of laser eye surgery, is presented comprehensively. The computations were performed with the next generation of the acoustic eye model, previously validated against existing measurements. The analysis allows the assessment of potentially problematic regions within the eye where the resultant positive and/or negative pressure may exceed values which are considered safe for the patient. Izvedena je bila primerjalna analiza širjenja tlačnega vala po laserski ablaciji človeške roženice. Izčrpno je predstavljeno širjenje tlačnega polja ter časovne in prostorske odvisnosti amplitud tlaka, ustvarjenih z različnimi vhodnimi laserskimi parametrih, ki ustrezajo različnim značilnim postopkom laserskih operacij oči. Izračuni so bili izvedeni z naslednjo generacijo akustičnega modela očesa, predhodno potrjenim z naslombo na obstoječe meritve. Analiza omogoča oceno potencialno problematičnih področij v očesu, kjer lahko pozitivni in/ali negativni tlak preseže vrednosti, ki veljajo za varne za pacienta.

The interaction of a blast wave propagating in air with different fluids like water column, aqueous foam and thermal/density inhomogeneity have been studied both experimentally and numerically. The blast waves were generated at atmospheric conditions in a newly constructed exploding wire facility. For fixed capacitance and wire size, the intensity of the shock front (measured typically at 200 mm from the wire explosion plane) was varied by controlling the charges stored in the capacitor and the size of the test section. Qualitative features of the interaction were captured using shadowgraph technique. Numerical simulations were performed to better analyze and understand the flow features observed in experiments. The main points across each fluid interactions are as follow: Water column: A new technique was implemented to create highly repeatable, properly shaped, large diameter water column. The impact of a blast wave with shock Mach number ranging from 1.75 to 2.4 on a 22 mm diameter water column resulted in a complex system of waves propagating inside the column. Due to the concave boundary of the downstream interface, the reflected expansion wave naturally focused at a point before travelling upstream resulting in the generation of large negative pressures leading to nucleation of cavitation bubbles. Through high speed photography, various aspects of the flow features were discussed qualitatively and quantitatively. With the aid of numerical simulation, the effect of size of water column and shock strength on the maximum attainable negative pressures in the absence of cavitation were quantified. Aqueous foam: The performance of various aqueous foam barrier configurations on the attenuation of externally generated blast wave peak pressure was examined. Here a blast wave with shock Mach number 4.8 was allowed to interact with an aqueous foam barrier of initial liquid fraction 0.1. The dominant process responsible for reduction of peak pressure was the `catching up' of the rarefaction wave with the wave front travelling in the foam barrier. Additional reduction was provided by the impedance mismatch factor at the foam-air interface which was further exploited to achieve greater reduction. A simple numerical model treating the foam by a pseudo-gas approach was used for re-constructing the experimental results. Density inhomogeneity: The unstable evolution of a 2D elongated, elliptically-shaped inhomogeneity embedded in ambient air and aligned both normal and at an angle to the incident plane blast wave of impact Mach number 2.15 was studied. The inhomogeneity was created on the basis of `Joule heating' wherein heat produced by a current carrying wire was used to heat its surrounding air. Two counter-rotating vortices primarily due to Richtmyer-Meshkov instability (RMI) and a train of vortices primarily due to Kelvin-Helmholtz instability (KHI) were observed for two different inclination angles. Similarly circulation, calculated from numerical simulation solving Navier-Stokes equation, was also found to vary from a linear to a quadratic function when the inhomogeneity was inclined. QC 20180518

In this work we report on experiments aimed at testing the cavitation hypothesis [Varenberg, M.; Gorb, S. J. R. Soc., Interface 2008, 5, 383–385] proposed to explain the strong underwater adhesion of mushroom-shaped adhesive microstructures (MSAMSs). For this purpose, we measured the pull-off forces of individual MSAMSs by detaching them from a glass substrate under different wetting conditions and simultaneously video recording the detachment behavior at very high temporal resolution (54,000–100,000 fps). Although microcavitation was observed during the detachment of individual MSAMSs, which was a consequence of water inclusions present at the glass–MSAMS contact interface subjected to negative pressure (tension), the pull-off forces were consistently lower, around 50%, of those measured under ambient conditions. This result supports the assumption that the recently observed strong underwater adhesion of MSAMS is due to an air layer between individual MSAMSs [Kizilkan, E.; Heepe, L.; Gorb, S. N. Underwater adhesion of mushroom-shaped adhesive microstructure: An air-entrapment effect. In Biological and biomimetic adhesives: Challenges and opportunities; Santos, R.; Aldred, N.; Gorb, S. N.; Flammang, P., Eds.; The Royal Society of Chemistry: Cambridge, U.K., 2013; pp 65–71] rather than by cavitation. These results obtained due to the high-speed visualisation of the contact behavior at nanoscale-confined interfaces allow for a microscopic understanding of the underwater adhesion of MSAMSs and may aid in further development of artificial adhesive microstructures for applications in predominantly liquid environments.

Negative pressures of liquids have been expected to contribute many kinds of technology. Nevertheless, experiments for subjecting liquids which have not too small volumes to negative pressures are difficult even now. The reason of the difficulties is because the liquids tend to generate cavities easily. In order to remove cavitation nuclei, an apparatus for enclosing water into a metal Berthelot tube under vacuum conditions was developed. By using the apparatus, negative pressures for water rose to ca. -20 MPa. This is the highest value for water in metal Berthelot tubes. Results were explained by a traditional crevice model. Keywords, {"references":["D. H. Trevena, \"Some Relevant Physics,\" in Cavitation and Tension in\nLiquids, Bristol: Adam Hilger, 1987. p. 12.","A. R. Imre, H. J. Maris, and P. R. Williams, \"Liquid-liquid phase\nequilibria in binary mixtures under negative pressure,\" in Liquids Under\nNegative Pressure, vol. 84, A. R. Imre, H. J. Maris, and P. R. Williams,\nEds. Dordrecht: Kluwer Academic Publishers, 2002. pp. 81-94.","S. J. Henderson, and R. J. Speedy, \"Temperature of maximum density in\nwater at negative pressure,\" J. Phys. Chem., vol.91, pp 3062–3068, 1987.","G. Pallares, M. A. Gonzalez, J. L. F. Abascal, C. Valeriani, and F. Caupin,\n\"Equation of state for water and its line of density maxima down to −120\nMPa,\" Phys. Chem. Chem. Phys., vol. 18, pp. 5896-5900, 2016.","A. R. Imre, and V. Hook, W. A., \"Liquid-Liquid equilibria in polymer\nsolutions at negative pressure,\" Chem. Soc. Rev., vol. 27, pp. 117-123.\n1998.","S. J. Henderson, and R. J. Speedy, \"A Berthelot-Bourdon tube method for\nstudying water under tension,\" Journal of Physics E: Scientific\nInstruments, vol. 13, pp. 778–782, 1980.","P. J. Chapman, B. E. Richards, and D. H. Trevena, \"Monitoring the\ngrowth of tension in a liquid contained in a Berthelot tube,\" Journal of\nPhysics E: Scientific Instruments, vol. 8, pp. 731-735, 1975.","Q. Zheng, D. J. Durben, G. H. Wolf, and C. A. Angel, \"Liquids at Large\nNegative Pressures; Water at the Homogeneous Nucleation Limit\",\nScience, vol. 254, pp.829-832, 1991.","K. Hiro, Y. Ohde and Y. Tanzawa, \"Stagnations of increasing trends in\nnegative pressure with repeated cavitation in water/metal Berthelot tubes\nas a result of mechanical sealing,\" J. Phys. D: Appl. Phys., vol.36, pp.\n592-597, 2003.\n[10] Y. Ohde, H. Watanabe, K. Hiro, K. Motoshita, and Y. Tanzawa, \"Raising\nof negative pressure to around -200 bar for some organic liquids in a metal\nBerthelot tube,\" J. Phys. D: Appl. Phys., vol.26, pp. 1088-1191, 1993.\n[11] Y. Ohde, M. Ikemizu, H. Okamoto, W. Hosokawa, and T. Ando, \"The\ntwo-stage increase in negative pressure with repeated cavitation for water\nin a metal Berthelot tube,\" J. Phys. D: Appl. Phys., vol. 21, pp. 1540,\n1998.\n[12] Y. Ohde, Y. Tanzawa, K. Motoshita and K. Hiro, \"Thermobarometry for\n4'-n-Octylbiphenyl-4-carbonitrile in Metal Tube Berthelot Method and\nPolymorphism in Crystalline Phase of 4'-n-Octylbiphenyl-4-carbonitrile\nFound through Cooling Paths in Negative –Pressure Range,\" Jpn. J. Appl.\nPhys, vol. 47, pp. 5591-5601, 2008.\n[13] K. Hiro, T. Wada, \"Phase Diagram of Thermotropic Liquid Crystal\nIncluding Negative Pressure Region Generated in Metal Berthelot Tube,\"\nSolid State Phenomena, vols. 181-182, pp. 22-25, 2012.\n[14] K. Hiro, T. Wada, and K. Kumagai, \"Temperatures of maximum density\nin a pressure range from 15 MPa to -15 MPa generated for water in a\nmetal Berthelot tube,\" Physics and Chemistry of Liquids, vol.52, pp.\n37-45, 2014.\n[15] D. H. Trevena, \"Historical Introduction,\" in Cavitation and Tension in\nLiquids, Bristol: Adam Hilger, 1987. p. 4."]}

Cavitation under static negative pressure is not revealed well. The Berthelot method to generate such negative pressure can be a means to study cavitation inception. In this study, metal Berthelot tubes built in observation windows are newly developed and are checked whether high static negative pressure is generated or not. Negative pressure in the tube with a pair of a corundum plate and an aluminum gasket increased with temperature cycles. The trend was similar to that as reported before., {"references":["A. R. Imre, H. J. Maris, and P. R. Williams, \"Introduction,\" in Liquids Under Negative Pressure, vol. 84, A. R. Imre, H. J. Maris, and P. R. Williams, Eds. Dordrecht: Kluwer Academic Publishers, 2002. pp. ix-xi.","H. Kato, \"Cavitation\", Tokyo: Maki-shoten, 1999. (in Japanese)","Y. Ohde, M. Ikemizu, H. Okamoto, W. Hosokawa, and T. Ando, \"The two-stage increase in negative pressure with repeated cavitation for water in a metal Berthelot tube,\" J. Phys. D: Appl. Phys., vol. 21, pp. 1540, 1998.","K. Hiro, Y. Ohde and Y. Tanzawa, \"Stagnations of increasing trends in negative pressure with repeated cavitation in water/metal Berthelot tubes as a result of mechanical sealing,\" J. Phys. D: Appl. Phys. vol.36, pp. 592-597, 2003.","Y Ohde, H Watanabe, K hiro, K Motoshita and Y Tanzawa, \"Raising of negative pressure to around -200 bar for some organic liquids in a metal Berthelot tube,\" J. Phys. D: Appl. Phys. 26, pp. 1088-1191, 1993.","H. Domininghaus, \"Appendix\", in Plastics for Engineers: Materials, Properties, Applications, Oxford u\\Univ. Press., 1993. p. 732."]}

To assure the transport from the roots to the leaves, vascular plants create strong depressions in the sap, next to -200 bars. This depression pulls the water column contained by the tree vascular system. The water cohesion keeps the sap under liquid state. This metastable state can breaks: cavitation bubbles appear. They create an air plug inside the plant hydraulic network and impede sap flow. This phenomena called embolism could lead to the plant death by preventing the sap transport.This thesis is dedicated to the air invasion into hydraulics networks under negative pressure. First, we study the leaf embolism. We developed a new technique which allows us to record the spatial propagation of embolism in leaves hydraulic network. We show that the embolism propagates by steps from biggest veins to smallest veins.Next, in order to understand the underlying physical laws, we use two model systems. We build artificial networks in a hydrogel which mimics the sap flow characteristics. After the relaxation of the negative pressure in the network by the nucleation of a bubble, we observe surface oscillations and the slow growth of the bubble. This growth is linked to the water transport through the hydrogel and can reach a stationary regime.As we are not able to reproduce all the characteristics of the leaf network with the hydrogel, we create a computer modeling based on the Ohm analogy between hydraulics networks and electrical circuits. We reproduce the specific features of the xylem which transport the sap: the conduits are linked by pits, small valves which limit the progression of the embolism. We were able to recover the distinctiveness steps in embolism.Finally, we discuss the application of the preceding results to wood and we present some results on Pinus sylvestris., Pour assurer le transport de la sève des racines vers les feuilles, les plantes vasculaires génèrent de très fortes dépressions dans le liquide, pouvant atteindre -200 bar, au niveau des feuilles. Cette dépression « tire » sur la colonne d'eau contenue dans l'appareil vasculaire de l'arbre. La cohésion de l'eau maintient la sève sous forme liquide. Cet état métastable peut se rompre : des bulles de cavitation apparaissent. Elles créent un « bouchon » d'air dans le réseau hydraulique de la plante et gênent la circulation de la sève. C'est ce que l'on appele l'embolie. Si ce phénomène se généralise, il peut provoquer la mort de la plante.Ce travail de thèse est consacré à 'invasion d'air dans des réseaux hydrauliques naturels ou artificiels initialement à pression négative. Nous avons d'abord étudié l'embolie dans les feuilles. Nous avons développé une technique novatrice permettant de relever la propagation spatiale de l'embolie dans le réseau hydraulique des feuilles. Nous montrons que l'embolie, quelque soit l'espèce, se propage par à-coups des plus grosses nervures aux plus petites.Afin de comprendre les lois physiques sous-jacentes, nous utilisons deux systèmes modèles. Nous réalisons d'abord des réseaux artificiels dans un hydrogel reproduisant les caractéristiques de la circulation de la sève ascendante. Après la relaxation de la tension dans le réseau par l'apparition de la bulle, nous observons des oscillations de surface et une croissance lente de la bulle, liée à l'évacuation de l'eau à travers l'hydrogel. Cette croissance peut atteindre un régime quasi-stationnaire. Ce systèmes ne nous permettant pas de reproduire toutes les caractéristiques géométriques du xylème, nous présentons une modélisation informatique reposant sur l'analogie entre réseaux hydrauliques et électrocinétique. Nous reproduisons les caractéristiques du xylème dans lequel circule la sève : les éléments conducteurs sont reliées par les ponctuations, des valves protégeant la plante de l'embolie. Nous retrouvons les à-coups caractéristiques de la propagation de l'embolie dans les feuilles.Enfin, nous discutons l'application des résultats précèdents dans le cas du bois et nous présentons quelques résultats obtenus sur du pin sylvestre.

Shear band dominated process in fully and partially saturated sand samples is simulated by means of dynamic strain localisation analysis together with a multiphase material model. The partially saturated medium is viewed as a multiphase continuum consisting of a solid skeleton and pores filled by water and air (vapour) which, once it appears, is presumed to remain at the constant value of cavitation pressure (isothermal monospecies approach). The governing equations are based on the general framework of averaging theories. A modified generalised plasticity constitutive model for partially saturated soils, developed from the general Pastor–Zienkiewicz sand model, has been implemented in a finite element code and used in the computational process. This model takes into account the effects of suction in the stiffness of the porous medium (solid skeleton) in partially saturated state. A case of strain localisation, which has been tested in laboratory observing cavitation of the pore water, is studied. Negative water pressures, which are of importance in localisation phenomena of initially fully saturated undrained samples of dilatant geomaterials, are obtained similarly to those observed experimentally.

Liquid water exhibits numerous anomalies, such as its expansion upon cooling below 4◦C. One of the explanations put forward involves polymorphism: two different liquid phases could exist at low temperature, in the supercooled region; this proposal has focused significant experimental and theoretical interest on the supercooled regime. We study another metastable state of water, where the liquid is at negative pressure, as explained in Section 1.2. The properties of water in this region of the phase diagram are largely unknown, although they could shed light on the debate about supercooled water, as argued in Section 1.3. Recent experiments have questioned the exact value of the limit of metastability of water at negative pressure. In Section 1.4, we present some techniques used to explore this exotic state. In Section 1.5 we discuss studies of the stability limit of water under tension based on these techniques. In Section 1.6, we consider other properties of water in this regime. Finally, we

Liquids can sustain traction forces, as solids do. In this case, they are at negative pressure (that is, under tension), in a metastable state. Nucleation of a bubble can occur, leading the system back to a stable state : this process is called cavitation. In this PhD work, we are interested in the properties of cavitation in a confined liquid, with a particular emphasis on bubble dynamics. This study is motivated by the context of water transport in plants : ascending sap is indeed under tension, in natural micro-channels. Cavitation then leads to embolism, i. e. the gas-filling of these channels. A significant part of the manuscript is devoted to the study of cavitation in a model system : spherical inclusions of water are embedded in a hydrogel, and passive evaporation of water through the gel allows the generation of negative pressures. Cavitation can then happen spontaneously or be triggered with a laser. We resolve the subsequent dynamics of the bubble, using several methods (fast or time-lapse camera, light scattering, laser strobe photography ...), showing that after a first ultra-fast inertial step, the bubble reaches a temporary equilibrium. Then, it slowly grows due to fluxes in the hydrogel, leading to full embolism of the inclusion. A theoretical chapter follows. First, the thermodynamical properties of a confined liquid under negative pressure are investigated. In a second part, we focus on the dynamics of cavitation bubbles in such systems, at short time scales. We derive a modified Rayleigh-Plesset equation which accounts for the experimentally observed ultra-fast radial oscillations of the bubbles. Liquid compressibility and confinement elasticity are key ingredients in this model. Last, the applicability of the previous results in the context of trees is discussed. A new method to directly study embolism in trees by optical means is also presented, and applied to Scots pine samples.; Les liquides sont capables, comme les solides, de supporter des forces de traction. Ils sont alors à pression négative (c'est-à-dire en tension), dans un état qui est métastable. Le retour vers un état stable à pression positive peut se faire par la nucléation d'une bulle, un processus appelé cavitation. Dans cette thèse nous nous intéressons aux propriétés de la cavitation en milieu confiné, avec un accent particulier sur la dynamique des bulles. Ce sujet est motivé par l'étude du transport de l'eau dans les arbres dont une partie (la sève montante) se fait sous tension, dans des canaux micrométriques. La cavitation entraîne alors l'embolie des éléments conducteurs de sève, c'est-à-dire leur remplissage par du gaz. Une grande partie du manuscrit est consacrée à l'étude de la cavitation dans un milieu modèle, où de l'eau est confinée dans des inclusions sphériques micrométriques au sein d'un hydrogel. L'évaporation passive de l'eau à travers le gel permet de générer des pressions négatives, et la cavitation peut se produire spontanément ou être déclenchée à l'aide d'un laser. Nous résolvons la dynamique subséquente de la bulle à l'aide de diverses méthodes (caméra time-lapse ou caméra rapide, diffusion de la lumière, strobophotographie laser ...) et montrons qu'après une séquence inertielle ultra-rapide, la bulle atteint un état d'équilibre temporaire, puis grossit de manière quasi-statique sous l'effet des flux d'eau dans l'hydrogel, provoquant "l'embolie" de l'inclusion. Une place importante est accordée à un chapitre de théorie qui explore d'une part les propriétés thermodynamiques d'un liquide confiné à pression négative, et d'autre part la dynamique aux temps courts de bulles de cavitation dans de tels systèmes. Nous proposons ainsi une équation de Rayleigh-Plesset modifiée qui rend compte de l'accélération importante des oscillations radiales des bulles que nous avons observée expérimentalement. La compressibilité du liquide et l'élasticité du confinement sont des éléments-clés de ce modèle. Enfin, nous discutons l'application des résultats précédents dans le contexte des arbres, tout en proposant une nouvelle méthode expérimentale qui permet un suivi optique du processus d'embolie. Nous présentons quelques résultats obtenus sur des échantillons de pin sylvestre.

Liquids can sustain traction forces, as solids do. In this case, they are at negative pressure (that is, under tension), in a metastable state. Nucleation of a bubble can occur, leading the system back to a stable state : this process is called cavitation. In this PhD work, we are interested in the properties of cavitation in a confined liquid, with a particular emphasis on bubble dynamics. This study is motivated by the context of water transport in plants : ascending sap is indeed under tension, in natural micro-channels. Cavitation then leads to embolism, i. e. the gas-filling of these channels. A significant part of the manuscript is devoted to the study of cavitation in a model system : spherical inclusions of water are embedded in a hydrogel, and passive evaporation of water through the gel allows the generation of negative pressures. Cavitation can then happen spontaneously or be triggered with a laser. We resolve the subsequent dynamics of the bubble, using several methods (fast or time-lapse camera, light scattering, laser strobe photography ...), showing that after a first ultra-fast inertial step, the bubble reaches a temporary equilibrium. Then, it slowly grows due to fluxes in the hydrogel, leading to full embolism of the inclusion. A theoretical chapter follows. First, the thermodynamical properties of a confined liquid under negative pressure are investigated. In a second part, we focus on the dynamics of cavitation bubbles in such systems, at short time scales. We derive a modified Rayleigh-Plesset equation which accounts for the experimentally observed ultra-fast radial oscillations of the bubbles. Liquid compressibility and confinement elasticity are key ingredients in this model. Last, the applicability of the previous results in the context of trees is discussed. A new method to directly study embolism in trees by optical means is also presented, and applied to Scots pine samples., Les liquides sont capables, comme les solides, de supporter des forces de traction. Ils sont alors à pression négative (c'est-à-dire en tension), dans un état qui est métastable. Le retour vers un état stable à pression positive peut se faire par la nucléation d'une bulle, un processus appelé cavitation. Dans cette thèse nous nous intéressons aux propriétés de la cavitation en milieu confiné, avec un accent particulier sur la dynamique des bulles. Ce sujet est motivé par l'étude du transport de l'eau dans les arbres dont une partie (la sève montante) se fait sous tension, dans des canaux micrométriques. La cavitation entraîne alors l'embolie des éléments conducteurs de sève, c'est-à-dire leur remplissage par du gaz. Une grande partie du manuscrit est consacrée à l'étude de la cavitation dans un milieu modèle, où de l'eau est confinée dans des inclusions sphériques micrométriques au sein d'un hydrogel. L'évaporation passive de l'eau à travers le gel permet de générer des pressions négatives, et la cavitation peut se produire spontanément ou être déclenchée à l'aide d'un laser. Nous résolvons la dynamique subséquente de la bulle à l'aide de diverses méthodes (caméra time-lapse ou caméra rapide, diffusion de la lumière, strobophotographie laser ...) et montrons qu'après une séquence inertielle ultra-rapide, la bulle atteint un état d'équilibre temporaire, puis grossit de manière quasi-statique sous l'effet des flux d'eau dans l'hydrogel, provoquant "l'embolie" de l'inclusion. Une place importante est accordée à un chapitre de théorie qui explore d'une part les propriétés thermodynamiques d'un liquide confiné à pression négative, et d'autre part la dynamique aux temps courts de bulles de cavitation dans de tels systèmes. Nous proposons ainsi une équation de Rayleigh-Plesset modifiée qui rend compte de l'accélération importante des oscillations radiales des bulles que nous avons observée expérimentalement. La compressibilité du liquide et l'élasticité du confinement sont des éléments-clés de ce modèle. Enfin, nous discutons l'application des résultats précédents dans le contexte des arbres, tout en proposant une nouvelle méthode expérimentale qui permet un suivi optique du processus d'embolie. Nous présentons quelques résultats obtenus sur des échantillons de pin sylvestre.

Reynolds equations and one-phase model with N-S (Navier Stocks) equations are widely used to calculate pressure distribution in the liquid film. In most cases, negative pressure exits in the obtained results. In a water-flooded single screw compressor, it is necessary to investigate the pressure of water film along the whole tooth flank. A negative pressure may not be right, because that when the pressure is lower than the saturated vapor pressure, cavitation occurs. In this paper, we investigated the pressure distribution of the water film with cavitation model. Results were compared to the pressure distribution obtained by one-phase model using N-S equations. Results show that difference of pressure distribution obtained by the two models is very similar for the positive pressure distribution. For the negative pressure distribution, the saturated vapor pressure could be applied to replace the results obtained by one-phase model with very small errors. Therefore, one-phase model will be effective to simulate pressure distribution along the tooth flank by using the vapor pressure to replace the negative pressure.

We report on experimental study of acoustic cavitation in water and some other liquids. The 1st chapter presents first order transitions in metastable regime. The 2nd presents the classical nucleation theory and the nucleation theorem of Oxtoby which enables us to evaluate the critical volume of the bubble in our experiments. Then we report some ways to investigate cavitation. Singularities of water with respect to other liquids are presented, and we show how cavitation investigation could allow understanding them. In the 3rd we describe our acoustic device, and the static pressure method which allows to to measure cavitation pressure. The fiber optic probe hydrophone built for this thesis on the model of Eisenmenger is then thoroughly described. This apparatus allows to measure density at cavitation threshold. Results and analysis are presented, for water, in the 4th, and for D2O, Ethanol, heptanes, DMSO, the 5th chapter. From the results in water, one can see that we are far from the theory. Yet a modification by a constant factor of the surface tension allows predicting our results. Nevertheless critical volume cannot be predicted with this modification. Besides the study of the other liquids shows that our method is able to reach threshold very close to the theory, all the more so the liquid surface tension is smaller.; Cette thèse porte sur l'étude expérimentale de la cavitation acoustique dans l'eau et quelques autres liquides. Le 1er chapitre est consacré à une présentation des transitions de phase du premier ordre dans le régime métastable. Le 2e chapitre présente la théorie de nucléation classique, ainsi que le théorème de nucléation d'Oxtoby qui nous permet d'évaluer le volume de la bulle critique dans nos expériences. Puis un bilan expérimental de quelques méthodes pour étudier la cavitation est dressé. Nous présentons les singularités de l'eau par rapport aux autres liquides et montrons en quoi une étude de la limite de cavitation permettrait de les comprendre. Dans le 3e, nous présentons notre dispositif acoustique ainsi que la méthode de pression statique qui permet de déterminer la pression de cavitation. Nous présentons en détail l'hydrophone à fibre optique construit pour cette thèse sur le modèle de celui d'Eisenmenger, qui permet de mesurer la densité au seuil de cavitation. Les résultats et leur analyse sont présentés, pour l'eau, dans le 4e, pour le D2O, l'éthanol, l'heptane et le DMSO, dans le 5e chapitre. De l'étude de l'eau, il ressort que l'on est très loin de la théorie, et d'un type d'expérience. En revanche une modification par un facteur constant en température, de la tension de surface de l'eau permet de prédire nos résultats en pression, mais pas les volumes critiques de nucléation. Par ailleurs, l'étude dans les autres liquides montre que nous pouvons, par notre méthode, arriver à des résultats proches de la théorie, d'autant plus que la tension de surface du liquide étudié est faible.

9 pages, 5 figures. A pure mechanical anisotropic model of a tree trunk has been developed based on the 3D finite element method. It simulates the microscopic structure of vessels in the trunk of a European beech (Fagus sylvatica) in order to study and analyse its mechanical behaviour with different configurations of pressures in the conduits of xylem and phloem. The dependence of the strains at the inner bark was studied when sap pressure changed. The comparison with previously published experimental data leads to the conclusion that a great tensile stress —or ‘negative pressure’— must exist in the water column in order to achieve the measured strains if only the mechanical point of view is taken into account. Moreover, the model can help to design experiments where qualitatively knowing the strains and the purely mechanical behaviour of the tree is required. Publicado

Any liquid can be superheated or stretched beyond its boiling curve. It will then remain in a metastable state, until a vapor bubble appears : this is the cavitation phenomenon. The study of the metastability limit gives information about the cohesion of the liquid and its equation of state. The case of water is of special interest ; indeed competiting theories predict qualitatively different temperature variations of the stability limit : either monotonic (the cavitation pressure increase with temperature), or with a minimum. We have stretched water with an ultrasonic wave, generated by a hemispherical piezoelectric ceramic, during a short time and a small volume, far from any wall, which reduces the effect of impurities. We obtain very accurate and reproducible results, allowing us to study in details the statistic of cavitation and to define a cavitation thresold. The ceramic was calibrated using two independent methods : needle hydrophones, and a method based on the variation of the static pressure. Both of them lead to the same result. We find a monotically increasing cavitation pressure, from -26 MPa at 0 Celsius C to -16 MPa at 80 Celsius C. These values are among the most negative reported, but far away from the values expected theoritically (-120 Mpa), and observed only once (Zheng etal , 1991, Science 254, 829). We discuss the possible origin of this discrepancy : it can be due either to the presence of impurities in the liquid, whose nature and concentration we discuss, or to an unexpected change in the equation of state of water at large negative pressures., Tout liquide peut être surchauffé ou détendu au delà de sa courbe d'ébullition. Il est dans un état métastable, jusqu'à ce qu'une bulle de vapeur apparaisse, c'est le phénomène de cavitation. L'étude de la limité de métastabilité renseigne sur la cohésion du liquide et sur son équation d'état. Le cas de l'eau est spécialement intéressant : des théories concurrentes prédisent des variations en température de cette limite qualitativement différentes : monotone (la pression de cavitation augmente avec la température), ou avec un minimum. Nous mettons l'eau sous tension à l'aide d'une onde ultrasonore, émise par une céramique piézo-électrique hémisphérique. L'onde est focalisée pendant une courte durée et dans un petit volume loin de toute paroi, ce qui minimise l'influence d'éventuelles impuretés. Nous obtenons des résultats très reproductibles, permettant de mesurer la statistique de cavitation et de définir précisément son seuil dans différents types d'eaux. La céramique est calibrée de deux manières : avec des hydrophones à aiguille, et avec une méthode basée sur la variation de la pression statique du liquide. Les deux méthodes sont en accord et donnent une pression de cavitation monotone de -26 MPa à 0 Celsius C à -16 MPa à 80 Celsius C. Cela fait partie des pressions les plus négatives observées dans l'eau mais reste loin de la valeur théorique attendue (environ -120 MPa) et observée dans une seule expérience (Zheng etal , 1991, Science 254, 829). Nous discutons les causes possibles de ce désaccord : il peut être du soit à la présence d'impuretés, dont nous discutons la nature et la concentration, soit à une courbure inattendue de l'équation d'état aux pressions très négatives.

An apparatus, permitting the study of the transmission of a tension (i.e. negative pressure) pulse directly applied to a column of water, is described. It is experimentally shown that, at low amplitudes, the applied and transmitted signals are proportional, and that at higher amplitudes, a characteristic deformation of the transmitted signal involves a slower rate of increase of its amplitude. This deformation, primarily described as a sharp drop of the tension during its growth, is studied. It is demonstrated that the amplitude transmitted is related not only to the amplitude applied, but to its rate of increase. To explain this behaviour, a model based on the vaporous growth of microbubbles suspended in the bulk of the liquid is proposed Description du dispositif experimental. Pour les faibles amplitudes le signal transmis est proportionnel au signal applique tandis qu'aux amplitudes eleves il subit une deformation caracteristique; l'amplitude transmise croit avec l'amplitude appliquee mais plus lentement. Etude de cette deformation qui se traduit par une chute brutale de la tension au cours de sa croissance. L'amplitude transmise depend non seulement de l'amplitude appliquee mais aussi de sa vitesse de montee