Les dimensions des satellites spatiaux tendent à croître fortement alors que le volume disponible dans la coiffe des lanceurs est limité. L'utilisation de structures déployables permet de résoudre cette contradiction. Afin de développer l'offre disponible, le département Recherche de Thales Alenia Space étudie les mètres rubans comme solution innovante de déploiement. La première structure envisagée est un télescope déployé par le déroulement de six mètres rubans assurant également le positionnement du miroir secondaire. D'autres structures déployables utilisant les propriétés des mètres rubans sont également en cours d'étude : mât, panneaux solaires, etc.Il convient alors de se doter d'outils de modélisation spécifiques pour modéliser les scénarios de déploiement et multiplier les configurations envisagées. Deux précédentes thèses ont conduit à l'élaboration de modèles énergétiques de poutre à section flexible, rendant compte du comportement plan des rubans ([Guinot2011]) puis de leur comportement tridimensionnel ([Picault2014]). Cette thèse présente différentes contributions autour de ces modèles de poutre à section flexible. Les hypothèses du modèle ont été améliorées. Le re-positionnement de la ligne de référence sur le barycentre des sections conduit à des résultats plus proches des scénarios physiques (apparition et disparition des plis sur le ruban). A ce jour, les hypothèses et les équations du modèle sont définitivement formalisées. Nous avons établi les équations locales 1D (équilibre, comportement) dans le cas des comportements tridimensionnels avec le souci de la plus grande généralité. Établir ensuite les équations dans des cas dérivés simplifiés (restriction aux comportements 2D, section faiblement courbée) nous a permis d'obtenir un certain nombre de solutions analytiques et les équations à implémenter dans l'outil métier.Nous avons développé sur le logiciel de continuation ManLab les premiers éléments d'un outil métier performant dédié à la modélisation des mètres rubans. Nous avons ainsi pu réaliser deux contributions principales :- Un outil généraliste, performant en temps de calcul, permettant d'étudier les systèmes différentiels 1D (BVP, Boundary Value Problems). Les équations locales des modèles de poutre à section flexible ont été implémentées dans cet outil, avec une discrétisation par interpolation polynomiale et collocation orthogonale.- Un élément fini spécifique pour les poutres à section flexible et son implémentation dans ManLab.Ces éléments ont permis de réaliser différentes simulations numériques conduisant à une meilleure compréhension du comportement des mètres rubans grâce aux diagrammes de bifurcation associés à plusieurs essais significatifs. / Dimensions of spatial satellites tend to grow bigger and bigger, whereas the volume in launchers remains very limited. Deployable structures must be used to meet this contradiction. To expand the offer of possible solutions, the Research Department of Thales Alenia Space is currently studying tape springs as an innovative deployment solution. The first structure to be considered is a telescope that is deployed by the uncoiling of six tape springs that also ensure the positioning of the secondary mirror. Other deployable structures that use the properties of tape springs are under investigation : mast, solar panels,...Specific modeling tools then appear compulsory to model deployment scenarios and multiply the tested configurations. Two previous PhD thesis lead to the development of energetic rod models with flexible cross-sections that account for planar ([Guinot2011])and three dimensional behavior of tape springs ([Picault2014]). This PhD thesis presents several contributions on these rod models with flexible cross-sections. The hypotheses of the model were improved. Re-positioning the reference rod line so that it passes through the sections' centroids leads to results that are closer to experimental scenarios (creation and disappearance of folds in the spring). The hypotheses and equations of the model are now definitively formalized.We have derived the 1D local equations in the three-dimensional behavior case in the most generalist way. Then, the derivation of the equations in simplified cases (restriction to 2D behavior, shallow cross-section) enabled us to obtain several analytic solutions and the equations to implement in the specific modeling tool.We have developed on the continuation software ManLab the first elements towards a home made, efficient modeling tool dedicated to the modeling of tape springs. Two main contributions can be listed :- A generalist tool, efficient in calculus times, to study 1D differential problems (BVP, Boundary Value Problems). The local equations of the rod models with flexible cross sections were implemented in this tool, with a discretization based on polynomial interpolation and orthogonal collocation.- A specific finite element for rods with flexible cross sections and its implementation in ManLab.These elements enabled us to perform several numerical simulations and have a better understanding of the behavior of tape springs thanks to full bifurcation diagrams obtained for significant tests.

>Magister Scientiae - MSc / The objective of this project is to study the production of Li, Be and B isotopes emitted in the interaction of 12C with 12C at incident energies of 200 and 400 MeV.The energies of these produced fragments were measured with a detector telescope consisting of two silicon detectors at the incident energy of 200 MeV while a third silicon detector was added for the measurements at 400 MeV. / South Africa

Structural steel design standards recognize lateral torsional buckling as a failure mode governing the capacity of long span unsupported beams with wide flange cross-sections. Standard solutions start with the closed form solution of the Vlasov thin-walled beam theory for the case of a simply supported beam under uniform moments, and modify the solution to accommodate various moment distributions through moment gradient expressions. The Vlasov theory solution is based on the assumption that cross-sectional distortional effects have a negligible effect on the predicted elastic critical moment. The present study systematically examines the validity of the Vlasov assumption related to cross-section distortion through a parametric study. A series of elastic shell finite element eigen-value buckling analyses is conducted on simply supported beams subject to uniform moments, linear moments and mid span point loads as well as cantilevers subject to top flange loading acting at the tip. Cross-sectional dimensions are selected to represent structural steel cross-section geometries used in practice. Particular attention is paid to model end connection details commonly used in practice involving moment connections with two pairs of stiffeners, simply supported ends with a pair of transverse stiffeners, simply supported ends with cleat angle details, and built in fixation at cantilever roots. The critical moments obtained from the FEA are compared to those based on conventional critical moment equations in various Standards and published solutions. The effects of web slenderness, flange slenderness, web height to flange width ratio, and span to height ratios on the critical moment ratio are systematically quantified. For some combinations of section geometries and connection details, it is shown that present solutions derived from the Vlasov theory can overestimate the lateral torsional buckling resistance for beams.

Lors du traitement d'une tumeur par radiothérapie utilisant des ions comme le 12C, le faisceau peut subir des réactions nucléaires avec les noyaux des tissus menant à la création de particules secondaires plus légères. Cela a pour conséquences de délocaliser une partie de la dose dans les tissus sains et de créer un champ d'irradiation mixte. Afin d'améliorer les connaissances sur la fragmentation du projectile, une expérience a été réalisée par notre collaboration en Mars 2015 au GANIL avec un faisceau de 12C à 50 MeV/n. Cette expérience a permis de mesurer les sections efficaces doublement différentielles en angle et en énergie pour tous les isotopes créés, et ce, sur différentes cibles d'intérêt médical (C, H, O et Ca). Les distributions angulaires et les taux de production ont également été obtenus pour chaque fragment et pour chaque cible. Les résultats ont ensuite été comparés à différents modèles de réactions nucléaire disponibles dans les outils de simulation Monte Carlo GEANT4 et PHITS. Des écarts importants ont été observés avec les résultats expérimentaux, mais aussi entre les différents modèles. Ces conclusions avaient déjà poussé notre collaboration à créer un nouveau modèle, appelé SLIIPIE, spécialisé dans les réactions d'ions légers aux énergies intermédiaires. Les paramètres de ce modèle ont ainsi été ajustés de façon à reproduire au mieux les données expérimentales obtenues. / During the treatment of cancerous diseases using ions such as 12C, the beam will undergo nuclear reactions with the tissues leading to the production of lighter secondary fragments. This tends to delocate a part of the dose into healthy tissues and create a mixed radiation field. In order to improve the knowledge on the projectile fragmentation, an experiment was performed by our collaboration in March 2015 with a 50 MeV/n 12C beam at GANIL. This led to the measurement of double differential cross sections in angle and energy of every isotope created by the fragmentation of carbon on targets of medical interest (C, H, O and Ca). Energy and angular distributions, as well as production rates have also been obtained for every fragment and every target. Experimental data were then compared with nuclear reaction models included in the Monte-Carlo (MC) simulation codes, GEANT4 and PHITS. Important discrepancies were observed with our data, as well as between models. These observations had already led our collaboration in creating a new MC model called SLIIPIE, specialized in intermediate energies reactions with light ions. The parameters of this model were then adjusted in order to best fit the experimental data.

Six geomorphic study reaches were established in 2002 along a forested mountain stream (gradients range from 0.02 to 0.05) on Cal Poly's Swanton Pacific Ranch in Santa Cruz County, California. These study reaches are a component of paired and nested watershed studies in the approximately 500 hectare Little Creek watershed. The overall goal of this study was to monitor water quality and channel conditions before, during, and after a selective harvest of redwood. A selective harvest occurred in the North Fork of Little Creek in Summer 2008. In August 2009, approximately 90% of the Little Creek Watershed was burned in the Lockheed Fire. Channel change was evaluated by measuring ground profiles using traditional survey methods. Cross section and longitudinal profiles are surveyed annually every summer in the six study reaches. Change is assessed through evaluation of cross sections and longitudinal profiles, analysis of bed elevation and cross-sectional area change data, and analysis of residual pool characteristics and longitudinal profile variability. Changes in the channel during this time have been relatively small and are typically associated with movement or introduction of coarse woody debris to the stream channel. However, during the study period no large stream flow events occurred (return interval at the closest USGS gauging station does not exceed 5 years). Historically, large debris flow events have occurred in this watershed, with well documented events in 1955 and 1998. The survey data is an important tool for understanding change detection in channel characteristics before and after harvesting, and following fire disturbance.

No description available.

<p>Comprehensive sensitivity and uncertainty analysis has been performed for light-water reactor and heavy-water reactor lattices using three techniques; adjoint-based sensitivity analysis, Monte Carlo sampling, and direct numerical perturbation. The adjoint analysis was performed using a widely accepted, commercially available code, whereas the Monte Carlo sampling and direct numerical perturbation were performed using new codes that were developed as part of this work. Uncertainties associated with fundamental nuclear data accompany evaluated nuclear data libraries in the form of covariance matrices. As nuclear data are important parameters in reactor physics calculations, any associated uncertainty causes a loss of confidence in the calculation results. The quantification of output uncertainties is necessary to adequately establish safety margins of nuclear facilities. In this work, the propagation of uncertainties associated with both physics parameters (e.g. microscopic cross-sections) and lattice model parameters (e.g. material temperature) have been investigated, and the uncertainty of all relevant lattice calculation outputs, including the neutron multiplication constant and few-group, homogenized cross-sections have been quantified. Sensitivity and uncertainty effects arising from the resonance self-shielding of microscopic cross-sections were addressed using a novel set of resonance integral corrections that are derived from perturbations in their infinite-dilution counterparts. It was found that the covariance of the U238 radiative capture cross-section was the dominant contributor to the uncertainties of lattice properties. Also, the uncertainty associated with the prediction of isotope concentrations during burnup is significant, even when uncertainties of fission yields and decay rates were neglected. Such burnup related uncertainties result solely due to the uncertainty of fission and radiative capture rates that arises from physics parameter covariance. The quantified uncertainties of lattice calculation outputs that are described in this work are suitable for use as input uncertainties to subsequent reactor physics calculations, including reactor core analysis employing neutron diffusion theory.</p> / Doctor of Philosophy (PhD)

Parametric modeling has many applications. These applications include data estimation and interpolation, modern spectral estimation, and data encoding. This research applies parametric modeling to radar cross section data in an attempt to encode it as well as preserve its spectrum. Traditionally, radar data has been processed through Fourier spectral estimation techniques. These methods not only require large amounts of data, for good spectral estimates, but assume the unobserved data values are zero which leads to spectral smearing. Modern spectral estimation methods alleviate these problems by basing the spectral estimate on a parametric model fit to the data set. The spectral estimate is then derived from the parameters of the model. For models which give a good fit to the data, a good spectral estimate can be made. The most common parametric models are the autoregressive moving-average (ARMA), the moving-average (MA) and the autoregressive (AR) model. These models represent filters, which when excited by a white Gaussian noise sequence give some output sequence. If the parameters of the models and the noise sequence are selected properly, a desired output data sequence can be modeled. The variance of the white noise is often small compared to the variance of the data sequence. This means that the model parameters plus the noise can be stored with fewer bits than the original data sequence while maintaining the same amount of accuracy in the data. The model parameters and noise sequence can be used to reproduce the original data sequence. Further, if only the spectrum of the data is of interest, only the noise variance plus the parameters need to be stored. This could lead to an even greater amount of data reduction. Most high resolution radar data applications require only that the spectrum of the data be preserved which makes modern spectral estimation appealing. This research project applies parametric modeling and modern spectral estimation to high resolution radar data as a means of encoding it. Several different parametric modeling techniques are evaluated to see which would be most useful in radar data encoding. The Burg AR parametric model was chosen due to its computational efficiency and its good spectral estimates. The Burg method applied to two radar range profile data sets gave a reduction in data storage by a factor of four. Further encoding was achieved by fitting the Burg AR parameters to a set of basis functions. This produced an additional data reduction by a factor of 36, for a total compression factor of 144. The latter led to some distortion of the high resolution range profiles, yet targets were still sufficiently characterized. / Master of Science

This study focuses on a series of thrust sheets exposed in the Appalachian Valley and Ridge Province Blacksburg-Pembroke area in southwest Virginia. Structures in the hanging wall of the Saltville thrust (Saltville thrust sheet) and the footwall of the Saltville thrust (Narrows thrust sheet) are examined. The first part of this study involves the construction of a series of thrust transport-parallel 1:24,000 scale geologic cross sections to constrain the subsurface geometry of fault and fold structures within the Saltville and Narrows thrust sheets. The second part of the study involves an outcrop-scale study of geologic structures exposed along a series road cuts in the footwall of the Saltville thrust and the geometric and relative timing relationships between folding, cleavage formation and thrust faulting. The cross sections show a series of interconnected splay faults branching off of the Saltville thrust and cutting both its hanging wall and footwall. Angle of dip and magnitude of dip-slip displacement on thrust and splay faults progressively decrease from hinterland to foreland within this fault system that is referred to as the Spruce Run Mountain-Newport (SRMN) fault system. Bedding within this fault system essentially forms a structural transition zone between the Saltville and Narrows thrust sheets, defining a km-scale fractured synform-antiform fold structure that has many structural attributes usually associated with fault propagation folding. In the road cut outcrops, early meter-scale faults are folded by later foreland-(NW) vergent folds. Although cleavage defines convergent cleavage fans about these folds, subtle obliquities between folds and cleavage indicate that folding post-dates early layer-parallel shortening and associated foreland-vergent thrusting. / Master of Science

Because of the great difficulty of obtaining exact numerical values of cross-section, and because of the inherent uncertainties in interpreting and evaluating the approximate methods, accurate experimental cross-section data would be extremely useful to the radar engineer. It was with this purpose in mind that the present long-range research program in microwave scattering was undertaken. Of immediate interest were the scattering properties of the prolate spheroid, the ogive (formed by rotating the minor segment of a circle around the chord), and, for comparison, the long cylinder.