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Rozprawy doktorskie na temat "Rétrodiffusion Rayleigh"
Royer, Philippe. "Lidars à rétrodiffusion Rayleigh-Mie et Raman mobiles pour l’étude des cycles couplés des aérosols et de la vapeur d’eau". Paris 6, 2011. http://www.theses.fr/2011PA066576.
Pełny tekst źródłaMaraval, Damien. "Mesure dynamique de déformation par rétrodiffusion Brillouin spontanée B-OTDR". Thesis, Paris, ENST, 2017. http://www.theses.fr/2017ENST0023/document.
Pełny tekst źródłaToday, three distinct and complementary technologies are available for distributed temperature, strain or vibration measurements with the analysis of Raman, Brillouin and Rayleigh backscattered light. Current industrial needs are distributed strain measurements for linear infrastructures, such as pipelines, for which linear and real-time strain distribution is required. The research work aims to design a new distributed and dynamic strain measurement system based on the analysis of spontaneous Brillouin backscatter by reflectometry. Slope assisted technique is used to accelerate the measurement acquisition, currently limited to static events because of their actual principle of sweep frequency acquisition of the Brillouin backscattering spectrum. The experimental results are characterized and validated by the simulation of the measurements of the deformation and displacement of a pipe supported between two simple supports. A mechanical model, adapted to this configuration and transposable on real projects, is developed. Through Cementys industrial partner, this model is then used for two monitoring project of pipelines with different installation facilities and purpose
Maraval, Damien. "Mesure dynamique de déformation par rétrodiffusion Brillouin spontanée B-OTDR". Electronic Thesis or Diss., Paris, ENST, 2017. http://www.theses.fr/2017ENST0023.
Pełny tekst źródłaToday, three distinct and complementary technologies are available for distributed temperature, strain or vibration measurements with the analysis of Raman, Brillouin and Rayleigh backscattered light. Current industrial needs are distributed strain measurements for linear infrastructures, such as pipelines, for which linear and real-time strain distribution is required. The research work aims to design a new distributed and dynamic strain measurement system based on the analysis of spontaneous Brillouin backscatter by reflectometry. Slope assisted technique is used to accelerate the measurement acquisition, currently limited to static events because of their actual principle of sweep frequency acquisition of the Brillouin backscattering spectrum. The experimental results are characterized and validated by the simulation of the measurements of the deformation and displacement of a pipe supported between two simple supports. A mechanical model, adapted to this configuration and transposable on real projects, is developed. Through Cementys industrial partner, this model is then used for two monitoring project of pipelines with different installation facilities and purpose
Guerrier, Sterenn. "High bandwidth detection of mechanical stress in optical fibre using coherent detection of Rayleigh scattering". Electronic Thesis or Diss., Institut polytechnique de Paris, 2022. http://www.theses.fr/2022IPPAT004.
Pełny tekst źródłaTelecommunication fibres are being deployed all over the world, connecting distant people, institutions, companies with an outstanding quality of service in terms of data rate and latency. Their strategic value in terms of global economy and daily life is now undeniable. Monitoring such an infrastructure has become mandatory, and that far beyond the standard case of breaks localization. From a broader standpoint, optical fibres are an alternative to electro-dynamic point sensors, with a strong asset: the capability to detect and localize multiple independent phenomena all along a fibre. Thus, the millions of kilometers of currently deployed optical fibre around the world constitute a huge potential base of sensors. Distributed vibration sensors have a huge potential regarding sensing of dynamic events, detecting of multiple acoustic signatures up to speech signals. In this thesis, we show how distributed optical fibre sensors can be designed on top of telecommunication fibres, namely standard single mode fibres, and we explore their potential in terms of reach, detection threshold, and sensing bandwidth. We present the interrogator systems for distributed fibre sensing and build a dual-polarization numerical model of such an interrogation system and fibre sensor. Secondly, we tackle the coherent fading issue by means of frequency diversity in the digital domain, i.e. directly applicable at the modulation of the interrogation sequences, before entering the optical domain. We developed MIMO-OFDM which retrieves independent channel estimations from a single fibre segment; the estimations are further combined, and the obtained estimations are assessed with regards to the reliability metric. Throughout this thesis, many experimental measurements were conducted, assessing the capabilities of the Coherent-MIMO interrogator on single-mode-fibre sensors in terms of reach, bandwidth, and detection threshold. We also demonstrate the co-propagation of a sensing signal along with high data rate channels, without any impact on the transmitted data, paving the way to the enhanced monitoring and telemetry in deployed telecommunication networks
Saidi, Mohamed. "Mesure et analyse de l'état de déformation et d'endommagement interne dans les composites à matrice cimentaire utilisés pour le renforcement des structures de génie civil". Thesis, Lyon, 2020. http://www.theses.fr/2020LYSE1092.
Pełny tekst źródłaDue to their mechanical, environmental and aesthetic compatibility, textile reinforced cementitious matrix composites are used on a large scale for rehabilitation and reinforcement of the built heritage and civil engineering structures. Under the effect of mechanical or environmental loads, the phenomena of interaction and damage between the textile reinforcement and the cementitious matrix are more complex than in the case of polymer matrix composites. These are mainly related to the cracking behaviour of the composite, the fragile nature of the matrix and the behaviour of the reinforcement/matrix bond. In particular, knowledge and understanding of the load transfer mechanisms at the reinforcement/matrix interface and crack initiation remain a major scientific challenge.Conventional measurement techniques used to characterise the mechanical behaviour of cementitious matrix composites (mechanical extensometers, digital image correlation, etc.) are able to provide information on the strain and stress state at the surface of a tested specimen. The different mechanisms of internal forces and degradation of the components (reinforcement, matrix, interface) are deduced using approaches of continuum and fracture mechanics.In this context, this work aims at implementing and adapting a measurement system that can be integrated into the core of composites: distributed optical fibre sensors. In order to check its reliability, this measurement technique is coupled with classical extensometer technics such as strain gauges implemented on the surface of the composites and digital image correlation. The main objective is to analyse more precisely the mechanical parameters at the micro scale and the load transfer mechanisms, crack initiation and propagation as well as damage mechanisms. On the basis of uni-axial tensile tests, coupled with the chosen instrumentation, a methodology for identifying local laws of reinforcement/matrix interaction is implemented. The aim of the thesis work is, using these local laws, to determine the micro-mechanical parameters of the composite (load transfer length, shear stress at the reinforcement/matrix interface, etc.) and to establish parameters characteristic of the local and global behaviour (cracking pattern and crack opening, damage indicators, constitutive equations, etc.). Nine configurations are tested and analysed in this work: two types of matrix, two types of textile reinforcement and three reinforcement ratios. The adaptation of the experimental protocol and the reliability of the results obtained are validated. The global and local behaviour of the composite, matrix, textile and their interface are measured and analysed. Load transfer length, shear stress at the textile/matrix interface, interface damage and crack opening are quantified and discussed. The effects of reinforcement ratio, matrix and textile type, mechanical and geometrical parameters of the composite on its mechanical tensile response are identified and evaluated. These results are used for the refinement and/or development of mechanical models of the stiffness and fracture behaviour of textile and cement-matrix reinforced composites
Yu, Francois T. H. "Paramétrisation de la rétrodiffusion ultrasonore érythrocytaire haute fréquence et pertinence comme facteur de risque de la thrombose veineuse". Thèse, 2009. http://hdl.handle.net/1866/3600.
Pełny tekst źródłaThe aggregation of erythrocytes is the main determinant of blood non Newtonian behaviour under low shearing flow conditions. When red blood cells (RBCs) aggregate, they form « rouleaux » and complex tridimensional structures that increase blood viscosity from a few mPa.s to a hundred mPa.s. The reversible RBC aggregation phenomenon is attributed to weak adhesive links between erythrocytes that are readily broken by increasing flow shearing. Blood bulk rheological properties have been comprehensively studied. However, the in vivo physiological impacts of abnormal clustering of RBCs are more difficult to assess. Clinical studies have identified altered hemorheology as a risk factor for thrombosis, but a clear etiological relationship between abnormal aggregation and thrombosis has not yet been established, in part because clinical conclusions were derived from correlative findings. It is to note that cardiovascular diseases such as deep venous thrombosis generally occur at specific locations within the vascular bed, suggesting a hemodynamic contribution to the development of this disease. Consequently, it is postulated that in vivo hemorheological characterization may help shed some light on the role of RBC hyper-aggregation on cardiovascular disorders. Ultrasound imaging, a non-invasive method relying on the propagation of mechanical waves within biological tissues, is sensitive to RBC aggregation. Indeed, the study of backscattered waves allows characterizing blood microstructure in vivo and in situ under physiological flow conditions. The work described in this thesis is based on prior simulation studies, performed at the Laboratory of Biorheology and Medical Ultrasonics of the University of Montreal Hospital Research Center, in which the backscattering of ultrasound from aggregating RBCs was modeled by considering a particle scattering strategy. In this approach, each RBC is a weak ultrasound scatterer (Born assumption) and the backscattering coefficient is modeled as the product of the RBC number density, the RBC backscattering cross section and a structure factor. This model relates variations in the backscattering coefficient to the RBC spatial organisation through the structure factor, which is the only parameter that changes during the aggregation process. A second order expansion in frequency of the structure factor was used to describe blood microstructure in terms of a packing factor W and an ensemble averaged aggregate diameter D. The model was first presented and validated by considering a homogenous shear flow condition using three broadband mono-element transducers. It was then extended in 2D to allow computation of parametric images in tube flow. An extrapolation based on the assumption that viscosity is related to the level of aggregation was used to compute local viscosity maps. Finally, a last contribution was the demonstration that a sudden increase in aggregation tendency directly promoted the formation of venous thrombosis in an experimental animal model. In that study, RBC aggregation, thrombus formation and flow variations were monitored longitudinally for two weeks using ultrasound. The results reported in this thesis suggest that rheological parameters on RBC clustering, ideally assessed in vivo and in situ, should be included in thrombosis risk profiling.