Electrospinning is a method of using high voltage electric fields to transform polymer solutions into nano-scale fibres. The field has seen significant work on processing different polymers and their resulting fibres but less work has focused the electrospinning process itself. The aim of this thesis is to present experimental observations of charge behaviour in the electrospinning process in the context of the underlying physics typically used to describe electrospinning. This thesis presents a review of existing methods of measuring aspects of the electrospinning process, and reviews published mathematical models of the process as representative examples of the current understanding of the underlying physics that drive the electrospinning phenomena. A novel measurement technique is introduced - high frequency data capture of the electric current flow simultaneously at the high voltage and collector electrode. This is used in three ways: to examine bulk charge density, to measure fibre flight time, and to quantify charge lost from the fibre in flight. Charge density is studied by comparing current and mass flow at the Taylor cone under a wide range of conditions. For 8% PVOH in water a constant bulk charge density was found of 7.7 C/kg. Flight time is studied by determining the time from the application of high voltage to the charged fibre first arriving at the collector electrode. It was found that for 8% PVOH the flight time depended strongly on applied voltage while electrode distance had a negligible effect. Charge loss was studied by comparing the magnitude of the simultaneous current flows in the quasi-steady state to determine if the charge flowing into the Taylor cone arrives with the fibre at the collector. For 8% PVOH, 8% PVOH with ionic salt, 9% PVOH in water and 18% PVB in ethanol, it was found that charge is always lost.

Violent crimes involving bloodshed may result in the formation of a number of blood drops that move through air and impact onto a surface producing a bloodstain pattern. Bloodstain Pattern Analysis (BPA), the analysis of the position, distribution, size and morphology of the stains within the pattern present at a crime scene, may provide information about the events that gave rise to the bloodshed. The location of blood origin, i.e. victim’s position at the moment of wounding and (or) wound location, determination is of major interest to BPA. This study investigated the dynamics of formation and flight of blood drops commonly found at a crime scene (so-called passive, cast-off, impact and gunshot drops) with the aim to facilitate blood origin determination. Features of blood drop formation at passive dripping with correlation to dripping surface characteristics were studied experimentally. A numerical scheme for accurate blood drop flight characteristics modelling, including oscillations, deformation and disintegration, was developed and validated against a number of analytical and experimental cases with special attention to the passive blood drop oscillations and ultimate deformation at terminal velocity, cast-off and impact blood drop deformation and breakup features. This provided an efficient and accurate method for typical blood drop flight reconstruction from the blood origin to impact as well as from the bloodstain location to the possible blood origin. Factors affecting blood drop trajectory and blood origin estimation were studied using the developed scheme.

IEEE has recently finished its ratification of the IEEE Standard 802.3ba in June 2010 which set the target Ethernet speed as 100 Gbps. The studies on the future trends of the ever-increasing demands for higher speed optical fiber communications show that there is no sign of decline in the demand. Constantly increasing internet traffic and the bandwidth-hungry multimedia services like HDTV, YouTube, voice-over-IP, etc. can be shown as the main driving forces. Indeed, the discussions over the future upgrades on the Ethernet speeds have already been initiated. It is predicted that the next upgrade will enable 400 Gbps Ethernet and the one after will be toward enabling the astounding 1 Tbps Ethernet.Although such high and ultra high transmission speeds are unprecedented over any transmission medium, the bottlenecks for achieving them over the optical fiber remains to be fundamental. At such high operating symbol rates, the signal impairments due to inter- and intra-channel fiber nonlinearities and polarization mode dispersion get exacerbated to the levels that cripple the high-fidelity communication over optical fibers. Therefore, efforts should be exerted to provide solutions that not only answer the need for high-speed transmission but also maintain low operating symbol rates.In this dissertation, we contribute to these efforts by proposing nonbinary-LDPC-coded modulation (NB-LDPC-CM) schemes as enabling technologies that can meet both the aforementioned goals. We show that our proposed NB-LDPC-CM schemes can outperform their prior-art, binary counterparts called bit-interleaved coded modulation (BI-LDPC-CM) schemes while attaining the same aggregate bit rates at a lower complexity and latency. We provide comprehensive analysis on the computational complexity of both schemes to justify our claims with solid evidence. We also compare the performances of both schemes by using amplified spontaneous emission (ASE) noise dominated optical fiber transmission and short to medium haul optical fiber transmission scenarios. Both applications show outstanding performances of NB-LDPC-CM schemes over the prior-art BI-LDPC-CM schemes with increasing gaps in coding gain as the transmission speeds increase. Furthermore, we present how a rate-adaptive NB-LDPC-CM can be employed to fully utilize the resources of a long haul optical transport network throughout its service time.

Direct Numerical Simulations (DNS) are performed to investigate laminar-turbulent transition in a boundary layer on a sharp cone at Mach 6. The main objective of this dissertation research is to explore which nonlinear breakdown mechanisms may be dominant in a broad--band "natural" disturbance environment and then use this knowledge to perform controlled transition simulations to investigate these mechanisms in great detail. Towards this end, a "natural" transition scenario was modeled and investigated by generating wave packet disturbances. The evolution of a three-dimensional wave packet in a boundary layer has typically been used as an idealized model for "natural" transition to turbulence, since it represents the impulse response of the boundary layer and, thus, includes the interactions between all frequencies and wave numbers. These wave packet simulations provided strong evidence for a possible presence of fundamental and subharmonic resonance mechanisms in the nonlinear transition regime. However, the fundamental resonance was much stronger than the subharmonic. In addition to these two resonance mechanisms, the wave packet simulations also indicated the possible presence of oblique breakdown mechanism. To gain more insight into the nonlinear mechanisms, controlled transition simulations were performed of these mechanisms. Several small and medium scale simulations were performed to scan the parameter space for fundamental and subharmonic resonance. These simulations confirmed the findings of the wave packet simulations, namely that, fundamental resonance is much stronger compared to the subharmonic resonance. Subsequently a set of highly resolved fundamental and oblique breakdown simulations were performed. In these DNS, remarkable streamwise arranged "hot'' streaks were observed for both fundamental and oblique breakdown. The streaks were a consequence of the large amplitude steady longitudinal vortex modes in the nonlinear régime. These simulations demonstrated that both second--mode fundamental breakdown and oblique breakdown may indeed be viable paths to complete breakdown to turbulence in hypersonic boundary layers at Mach 6.

A computationally efficient, discrete model is presented for transmission line analysis and passive model order reduction of high-speed interconnect systems. The development of this model was motivated by the on-going efforts in chip/package co-design to route a major portion of the on-chip clock and high-speed data buses through the package in order to overcome the bandwidth reduction and delay caused by the high ohmic loss of on-chip wiring. The geometric complexity of the resulting interconnections is such that model order reduction is essential for rapid and accurate signal integrity assessment to support pre-layout design iteration and optimization. The modal network theory of the skin effect in conjunction with the theory of compact differences is used for the development of discrete models for dispersive, multi-conductor interconnects compatible with passive model order reduction algorithms. The passive reduced-order interconnect modeling algorithm, PRIMA, is then used on the resulting discrete model to generate a low-order, multi-port macromodel for interconnect networks. Numerical examples are used to demonstrate the validity and efficiency of the proposed model.

Reliable and efficient data transfer on the Internet is an important issue. Since late 70's the protocol responsible for that has been the de facto standard TCP, which has proven to be successful through out the years, its self-managed congestion control algorithms have retained the stability of the Internet for decades. However, the variety of existing new technologies such as high-speed networks (e.g. fibre optics) with high-speed long-delay set-up (e.g. cross-Atlantic links) and wireless technologies have posed lots of challenges to TCP congestion control algorithms. The congestion control research community proposed solutions to most of these challenges. This dissertation adds to the existing work by: firstly tackling the highspeed long-delay problem of TCP, we propose enhancements to one of the existing TCP variants (part of Linux kernel stack). We then propose our own variant: TCP-Gentle. Secondly, tackling the challenge of differentiating the wireless loss from congestive loss in a passive way and we propose a novel loss differentiation algorithm which quantifies the noise in packet inter arrival times and use this information together with the span (ratio of maximum to minimum packet inter arrival times) to adapt the multiplicative decrease factor according to a predefined logical formula. Finally, extending the well-known drift model of TCP to account for wireless loss and some hypothetical cases (e.g. variable multiplicative decrease), we have undertaken stability analysis for the new version of the model.

High-speed craft are in high demand in the maritime industry, for example, in maintenance operations for offshore structures, for search and rescue, for patrolling operations, or as leisure craft to deliver speed and excitement. Design and operation of high-speed craft are often governed by the hydrodynamic phenomena of slamming, which occur when the craft impact the wave surface. Slamming loads affect the high-speed craft system; the crew, the structure and various sub-systems and limit the operation. To meet the ever-increasing demands on safety, economy and reduced environmental impact, there is a need to develop more efficient high-speed craft. This progression is however limited by the prevailing semi-empirical design methods for high-speed planing craft structures. These methods provide only a basic description of the involved physics, and their validity has been questioned. This thesis contributes to improving the conditions for designing efficient highspeed craft by focusing on two key topics: evaluation and development of the prevailing design methods for high-speed craft structures, and development towards structural design based on first principles modeling of the slamming process. In particular a methodological framework that enables detailed studies of the slamming phenomena using numerical simulations and experimental measurements is synthesized and evaluated. The methodological framework involves modeling of the wave environment, the craft hydromechanics and structural mechanics, and statistical characterization of the response processes. The framework forms the foundation for an extensive evaluation and development of the prevailing semi-empirical design methods for high-speed planing craft. Through the work presented in this thesis the framework is also shown to be a viable approach in the introduction of simulation-based design methods based on first principles modeling of the involved physics. Summarizing, the presented methods and results provide important steppingstones towards designing more efficient high-speed planing craft. / <p>QC 20160907</p>

Le besoin de prédire le comportement mécanique des structures industrielles en béton armé et d’évaluer leur niveau d’endommagement en conditions extrêmes sous l’action de chargements dynamiques violents nécessite de faire appel à la simulation numérique utilisant des modèles de matériaux fiables et robustes. Dans cette thèse, le modèle d’endommagement anisotrope induit utilisant une variable tensorielle d’ordre 2 est étendu aux cas de chargements peu confinés à l’aide d’un nouveau critère modulaire formulé en contraintes. Grâce au mécanisme de visco-endommagement, le modèle traite toute la gamme de vitesses de sollicitation envisagée pour des structures en béton armé. Le comportement cyclique avec refermeture des fissures est pris en compte et l’endommagement peut atteindre 1 exactement dans une ou plusieurs directions grâce à une nouvelle gestion de la rupture. Le calcul d’un tirant a montré que cette procédure est indispensable pour plastifier l’acier et éviter un endommagement généralisé du béton. Lors du volet expérimental de la thèse, des essais de caractérisation du béton et des essais d’arrachement ont été réalisés en coopération avec le Département Génie Civil de l’ENS Cachan, suivis des essais d’impact sur poutres sur la tour de chute Orion au laboratoire DYN du CEA à Saclay. Avec une prise en compte pragmatique de l'interface acier-béton, la comparaison des calculs et des essais a montré qu'il était nécessaire de disposer d’un modèle de liaison acier-béton pour éviter un endommagement trop important du béton au voisinage des armatures, de réduire les temps de calcul, d’améliorer la méthode de régularisation et de prendre en compte les déformations permanentes. / The need to predict the mechanical behavior of reinforced concrete industrial structures and assess their level of damage in extreme conditions under the action of dynamic loads requires the use of numerical simulations and develop reliable and robust material models. In this thesis, the model of induced anisotropic damage using a tensor variable of order 2 is extended to the case of low-level confined loads using a new modular criterion written with stresses. Through the mechanism of visco-damage, the model treats the entire solicitation rate range considered for reinforced concrete structures. The cyclic behavior with reclosing of cracks is taken into account and the damage can reach 1 exactly in one or more directions due to a new rupture management. The calculation of a tie-beam showed that this procedure is necessary to plasticize steel and prevent widespread damage concrete. During the experimental part of the thesis, characterization tests for concrete and pullout tests were conducted in cooperation with the Civil Engineering Department at ENS Cachan, followed by impact tests on beams on the Orion drop tower of DYN CEA Saclay laboratory. With a pragmatic consideration of steel-concrete interface, the comparison of calculations and tests showed that it was necessary to have a model of steel-concrete connection to avoid excessive concrete damage in the vicinity of reinforcements, as well as to reduce computing time, improve the regularization method, and take into account permanent deformations.

En décembre 2010, l'Espagne est devenue le pays avec le réseau à grande vitesse (GV) le plus étendu en Europe. Et au cours des années suivantes, les réalisations en cours augurent une mise en service progressive de nouvelles lignes. La question qui se pose est donc de savoir comment cette situation a été atteinte. Nous faisons l'hypothèse selon laquelle l'évolution de la GV espagnole est la conséquence directe de la façon dont cette politique publique a existé au niveau politique. En nous intéressant aux dynamiques de politisation d'une politique publique et en mobilisant deux traditions sociologiques différentes (la sociologie des champs et la sociologie des régimes d'énonciations), nous analysons la façon dont la GV est présente dans les différents lieux du politique (arènes) et est énoncée politiquement. L'analyse de ces dynamiques de politisation a été effectuée en trois temps. La première partie de notre recherche montre la façon dont le mythe politique de la GV s'est construit en Espagne à partir de la fin des années 1980 à la suite de la réalisation du premier projet de ligne à GV entre Madrid et Séville. Dans une deuxième partie, nous identifions trois cycles de politique publique au cours des années 1990 et 2000 qui ont abouti, à travers la production d'un consensus politique, à un fort développement de la GV. La dernière partie de notre thèse s'intéresse à l'émergence d'une controverse autour de la GV à travers le renforcement des forums de politiques publiques alternatifs et le déclenchement d'une dynamique de politisation divergente / In December 2010, Spain became the country with the largest high-speed rail (HSR) network in Europe. New lines under construction will be put into operation in the short term. In these circumstances the question is: how has this situation been reached? Our hypothesis is that the evolution of the HSR in Spain is a direct consequence of how this policy exists at the political level. By focusing on the politics of policy-making and bringing together two different sociological traditions (sociology of fields and sociology of enunciation regimes), we analyse how HSR issue exists within political arenas and how HSR is politically enounced. Our study is conducted in three stages. Firstly, we show how a political myth was constructed from the late of 1980s around the first Spanish HSR line project between Madrid and Sevilla. Secondly, we identify three public policy cycles between 1990 and 2010 producing a large political consensus and a strong development of the HSR. In the last part of our thesis, we analyse the emergency of a controversy about HSR policy through the strengthening of alternative policy forums and the generation of a divergent political dynamic

Les hélices sont connues pour leur avantage significatif en termes de rendement propulsif. Ces avantages se traduisent directement par une réduction de la consommation de carburant de sorte qu’elles connaissent aujourd’hui un regain d’intérêt. Actuellement, les avancées récentes en simulations numériques rendent possible d’appliquer l’optimisation multidisciplinaire au cas exigeant du design de pales d’hélice transsonique. Pour ces raisons, une méthode d’optimisation est développée, dans laquelle les objectifs de performance aérodynamique, aéroacoustique et aéroélastique sont en concurrence. Cette méthode est appliquée au design de pales d’hélice à haute vitesse et à simple rotation. L’optimisation s’appuie sur l’Evolution Différentielle Multi-Objectifs (Multi-Objective Differential Evolution - MODE). Cette technique est une des formes d’algorithme évolutionnaire qui mimique l’évolution naturelle des populations par le concours de la sélection, de la recombinaison et de l’éventuelle mutation de formes de pales, chacune d’elles étant représentée par un vecteur de variables (corde, angle de flèche, etc. . .). MODE offre l’avantage de considérer tous les objectifs en concurrence lors de la sélection des designs prometteurs au sein d’une population. Afin de garder le coût computationnel dans des limites acceptables, l’évaluation des performances des designs proposés est faite par une approche à deux niveaux. Un meta-modèle fournit les estimations de performance pour chaque design à un coût computationnel extrêmement faible alors que des codes d’analyse à haute fidélité calculent les performances précises à un coût nettement plus élevé. Pour préserver la précision des estimations, le meta-modèle est initialement entraîné sur une population composée à cet effet. L’entraînement est ensuite répété de temps à autres avec les performances haute fidélité de designs prometteurs. Différents outils à haute fidélité ont été développés et utilisés dans ce cadre. L’outil CFD exécute la simulation RANS stationnaire d’un seul passage d’entrepales pour une hélice isolée sans angle d’attaque dans un écoulement libre. Ces simulations délivrent les valeurs de performance aérodynamique. L’hélice complète est modélisée grâce à des conditions aux limites cycliques. Le modèle de turbulence k - ε est utilisé en combinaison avec un traitement adapté près des murs. Des conditions adiabatiques et sans glissement sont imposées sur le carénage et la surface de la pale tandis que la limite radiale de la section d’essais reproduit les effets d’un champ de pression lointain. Cette approche a prouvé sa robustesse et, par-dessus tout, sa précision puisque une correspondance acceptable avec des résultats expérimentaux est obtenue pour différentes conditions d’utilisation et un large éventail de formes de pales. De plus, l’indépendance par rapport au maillage est satisfaisante. Lors de l’analyse a posteriori des résultats aérodynamiques, le Sound Pressure Level (SPL) est calculé par l’outil aéroacoustique (CHA) pour le bruit tonal en différentes positions. La formulation 1A de Farassat est utilisée à cette fin. Cette formulation découle de l’équation non-homogène d’onde dérivée de l’analogie acoustique de Lighthill par Ffowcs Williams et Hawkings (FW-H). Elle bénéficie du découplage partiel des aspects aérodynamiques et aéroacoustiques en plus d’être particulièrement adaptée pour le calcul du bruit d’hélice. Le bruit d’épaisseur et le bruit de charge sont exprimés par des termes séparés dans le domaine temporel tandis que les quadripôles de l’équation de FW-H sont négligés. La surface de la pale est utilisée comme surface d’intégration et une nouvelle technique de troncation a été développée et appliquée pour circonvenir la singularité mathématique qui apparaît lorsque des parties de la pale ont des conditions soniques en termes de cinématique par rapport à l’observateur. Cette approche délivre des résultats fiables à un coût acceptable. [...] / Open rotors are known to have significant advantages in terms of propulsive efficiency. These advantages translate directly in reduced fuel burn so that they nowadays benefit from a surge of interest. At the same time, recent advances in numerical simulations make the application of multidisciplinary optimization for the demanding design of transonic propeller blades, an affordable option. Therefore, an optimization method in which the performance objectives of aerodynamics, aeroacoustics and aeroelasticity compete against each other, is developed and applied for the design of high-speed single-rotation propellers. The optimization is based on Multi-Objective Differential Evolution (MODE).This technique is a particular kind of evolutionary algorithm that mimics the natural evolution of populations by relying on the selection, recombination and eventually mutation of blade designs, each of them being represented by a vector of design variables (e.g. chord width, tip sweep, etc). MODE has the advantage of dealing concurrently with all the objectives in the selection of potentially promising designs among a population. In order to keep the computational cost within reasonable margins, the assessment of the performance of proposed designs is done in a two-level approach. A metamodel provides performance estimates for each proposed design at extremely low computational effort while high-fidelity analysis codes provide accurate performance values on some promising designs at much higher cost. To safeguard the accuracy of the estimates, the metamodel is initially trained on a population that is specifically assembled for that purpose. The training is repeated from time to time with the high-fidelity performance values of promising designs. Different high-fidelity tools have been developed and used for the assessment of performance.The CFD-tool performs steady RANS simulations of a single blade passage of the isolated propeller in free air under zero angle of attack. These simulations provide the aerodynamic performance values. The full propeller is modelled thanks to cyclic boundary conditions. The k - ε turbulence model is used in combination with wall treatment. Adiabatic no-slip wall conditions are imposed on the spinner and blade surfaces whereas the test-section radial boundary is reproducing the effects of a pressure far-field. This approach has proven its robustness and, above all, its accuracy as satisfactory agreement with experimental results has been found for different operating conditions over a wide range of blade shapes, as well as sufficient grid independency. In the post-processing of the aerodynamic results, the Sound Pressure Level (SPL)is computed for tonal noise at various observer locations by the aeroacoustic solver(CHA). Formulation 1A from Farassat is used for this purpose. This formulation is related to the inhomogeneous wave equation derived from Lighthill’s acoustic analogy by Ffowcs Williams and Hawkings (FW-H). It benefits from the partial decoupling of the acoustic and aerodynamic aspects and is particularly suited to compute the noise from propellers. The thickness noise and loading noise are expressed by separate equations in the time-domain whereas the quadrupole source term is dropped from the original FW-H equation. The blade surface is chosen as integration surface and a newly developed truncation technique is applied to circumvent the mathematical singularity arising when parts of the blade reach sonic conditions in terms of kinematics with respect to the observer. This approach delivers accurate values at acceptable computational cost. Besides, CSM-computations make use of a finite elements solver to compute the total mass of the blade as well as the stresses resulting from the centrifugal and aerodynamic forces. Considering the numerous possibilities to tailor the blade structure so that it properly takes on the stresses, only a simplified blade model is implemented. [...]