Tubes légers à haute résistance pour des applications pétrolières marines Light High Strength Tubes for Offshore Petroeleum Applications

Les besoins nouveaux en tubes à haute résistance, créés par le développement actuel des gisements pétroliers marins, nous ont conduits à étudier des tubes composites particuliers, élaborés par enrouiement hélicoïdal de rubans d'acier minces à haute résistance enrobés d'une résine époxy polymérisable. Un mode de recouvrement adapté des rubans d'acier confère au composite une bonne étanchéité et des caractéristiques mécaniques élevées. Les propriétés physiques et chimiques de la matrice de résine permettent également d'obtenir une faible densité et une résistance convenable à la corrosion par les fluides pétroliers, l'eau de mer ou les boues de forage. Cette étude préliminaire comporte une analyse théorique simplifiée de ce type de structure composite, puis une partie expérimentale destinée a sélectionner les caractéristiques optimales de l'acier et de la résine et à vérifier les propriétés mécaniques et physico-chimiques obtenues sur ces tubes. Enfin, des exemples d'application en mer profonde destinés à comparer ces tubes composites aux tubes en acier sont présentés. Les premières conclusions de cette étude semblent confirmer l'intérêt de ce type de matériau pour ces applications. <br> The new requirements for high-strength tubes created by thé current development of offshore oilfields led thé authors ta study thé development ot spécial composite tubes formed by thé spiral winding of high-strength thin steel strips coated with a polymerïzable epoxy resin. A particular method of overlapping thé steel strips makes the composite leakproof and leads to good mechanical properties: The physical and chemical properties of thé resin matrix also make for a low specific gravity and suitable résistance to corrosion coused by petroleum fluids, seawater or drilling mud. This preliminary article presents a simplified theoretical analysis of this type of composite structure, followed by an expérimental study of thé choice of thé optimum steel and resin properties and thé controls of thé mechanical and physico-chemical properties of these tubes. Finally, deep offshore applications are described in an effort to compare thé composite tubes with steel tubes. The initial conclusions of this study appear to comfirm the interest of this type of material for such applications

Quantum modeling, beyond secularity, of the collisional dissipation of molecular alignment using the energy-corrected sudden approximation

International audienceWe propose a Markovian quantum model for the time dependence of the pressure-induced decoherence of rotational wave packets of gas-phase molecules beyond the secular approximation. It is based on a collisional relaxation matrix constructed using the energy-corrected sudden approximation, which improves the previously proposed infinite order sudden one by taking the molecule rotation during collisions into account. The model is tested by comparisons with time-domain measurements of the pressure-induced decays of molecular-axis alignment features (revivals and echoes) for HCl and CO2 gases, pure and diluted in He. For the Markovian systems HCl-He and CO2-He, the comparisons between computed and measured data demonstrate the robustness of our approach, even when the secular approximation largely breaks down. In contrast, significant differences are obtained in the cases of pure HCl and CO2, for which the model underestimates the decay rate of the alignment at short times. This result is attributed to the non-Markovianity of HCl-HCl and CO2-CO2 interactions and the important contribution of those collisions that are ongoing at the time when the system is excited by the aligning laser pulse

Non-Markovian collisional dynamics probed with laser-aligned molecules

International audienceThe Markov, as well as the secular approximations, are key assumptions that have been widely used to model decoherence in a large variety of open quantum systems, but, as far as intermolecular collisions are considered, very little has been done in the time domain. In order to probe the limits of both approximations, we here study the influence of pressure on the alignment revivals (echoes) created in properly chosen gas mixtures (HCl and CO2, pure and diluted in He) by one (two) intense and short laser pulse(s). Experiments and direct predictions using molecular dynamics simulations consistently demonstrate, through analyses at very short times (< 15 ps) after the laser kick(s), the breakdown of these approximations in some of the selected systems. We show that the nonadiabatic laser-induced molecular alignment technique and model used in this study directly provide detailed information on the physical mechanisms involved in the collisional dissipation. Besides this "fundamental" interest, our findings also have potential practical applications for radiative heat transfer in planetary atmospheres and climate studies. Indeed, short time delays in the dipole autocorrelation function monitoring the light absorption spectrum correspond to large detunings from the optical resonances in the frequency domain, thus influencing the atmospheric transparency windows. Furthermore, the fact that the approach tested here for linear rotors can potentially be applied to almost any gas mixture (including, for instance, nonlinear and/or reacting molecules) further strengthens and broadens the perspectives that it opens

Echo-assisted impulsive alignment of room-temperature acetone molecules

International audienceWe experimentally and theoretically investigate the field-free alignment of the asymmetric-top acetone molecule. Our study shows that the production of postpulse aligned molecules in a dense sample (0.05-0.2 bar) of room-temperature acetone using a single-pulse excitation can be significantly improved by rotational alignment echoes induced in a two-pulse excitation scheme. We report the observation of fractional echoes that can be used to reveal the nonlinearity of the molecular system. In a proof-of-principle experiment, a pre-aligned sample of acetone is also used for third-harmonic generation. The analysis of the experimental data with numerical simulations based on quantum and classical models enables the determination of the collisional decay rate of acetone alignment, as well as a test of the static, second-order, electric hyperpolarizabilities of the molecule derived from ab initio calculations presented in this work

Echo-assisted impulsive alignment of room-temperature acetone molecules

International audienceWe experimentally and theoretically investigate the field-free alignment of the asymmetric-top acetone molecule. Our study shows that the production of postpulse aligned molecules in a dense sample (0.05-0.2 bar) of room-temperature acetone using a single-pulse excitation can be significantly improved by rotational alignment echoes induced in a two-pulse excitation scheme. We report the observation of fractional echoes that can be used to reveal the nonlinearity of the molecular system. In a proof-of-principle experiment, a pre-aligned sample of acetone is also used for third-harmonic generation. The analysis of the experimental data with numerical simulations based on quantum and classical models enables the determination of the collisional decay rate of acetone alignment, as well as a test of the static, second-order, electric hyperpolarizabilities of the molecule derived from ab initio calculations presented in this work