COUNTEREXAMPLES TO KAPLANSKY'S UNIT CONJECTURE

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CALCUL DE L'ECOULEMENT AUTOUR DES STRUCTURES MINCES PAR LA METHODE DES SINGULARITES. DEVELOPPEMENT DU PRINCIPE DE MINIMISATION ET APPLICATION A DIFFERENTES CONFIGURATIONS SUB- ET PARTIELLEMENT CAVITANTES.

A non-linear calculation method of a flow around thin structures using the Boundary Element Method (BEM) has been built. The minimization concept is developed and applied to sub-cavitating, partially cavitating and super-cavitating configurations. This concept relates to the numerical errors occurring on the leak-flows. The non-linear calculation of the cavity geometry is obtained by an iterative procedure. The method is validated by various comparisons of the results with the results of reference extracted from the literature. The case of the blade cascade was treated, the results compared with those obtained with the Finite Elements Method (FEM). The comparison between MEM and FEM is excellent. The method was extended to 3D configurations, in particular for a 3D span-wing under partially cavitation and super-cavitation cases, joined with the presence of a free surface. The 3D case of a rotating propeller was performed, determining the 3D geometry of the downstream wake. The results were confronted with the experimental results.Une méthode de calcul non-linéaire d'écoulement autour de structures minces par la méthode des singularités est présentée. Le concept de minimisation est développé et appliqué à des configurations sub-cavitantes, partiellement cavitantes et super-cavitantes. Ce concept est relatif aux erreurs numériques commises sur les débits de fuite. Le calcul non-linéaire de la géométrie de la poche de cavitation est obtenu par une procédure itérative. La méthode est validée par différentes comparaisons des résultats avec les résultats de référence issus de la littérature. Le cas de la grille d'aubes a été traité, les résultats comparés à ceux obtenus avec une méthode d'éléments finis. La comparaison est excellente. Le code de calcul a été étendu au calcul 3D de l'écoulement autour d'une aile partiellement cavitante et super-cavitante en présence d'une surface libre ainsi qu'au calcul 3D d'une hélice sub-cavitante, suivie de son sillage, en écoulement tournant. Les résultats sont confrontés aux résultats expérimentaux

Vorticity Dynamics of Hydrodynamic Instabilities Occurring at Material Interfaces: Application to High-Energy-Density Systems

Inertia-dominated hydrodynamic instabilities at material interfaces are ubiquitous phenomena observed in nature and man-made applications, spanning core collapse supernovae, inertial confinement fusion, supersonic combustion, and cavitation bubble collapse. When subjected to accelerations, perturbations along an interface may grow due to the Rayleigh-Taylor (RT) or Richtmyer-Meshkov (RM) instability, while in the presence of shear, they may grow due to the Kelvin-Helmholtz (KH) instability. The main focus of this thesis is the RM instability. The RM instability occurs when a perturbed interface separating two fluids of different densities is impulsively accelerated, e.g., by the passage of a shock wave. During the interaction of the shock with the interface, baroclinic vorticity is generated along the interface due to the misalignment between the density and pressure gradients, thus leading to perturbation growth. The subsequent interface evolution can be described using vorticity dynamics. Although the early stage of vorticity deposition along the interface is relatively well understood, the late-time vorticity dynamics and their effects on the interface evolution are less well known. Our objective is to understand the role of vorticity dynamics in the late-time evolution of RM-type problems. To examine the vorticity dynamics of the RM instability, we implement a vortex-sheet model allowing us to isolate the different contributions of vorticity production in the evolution of the interface. We first use the vortex-sheet model to understand the relative importance between RM and KH in the evolution of perturbations subjected to an oblique shock under high-energy-density (HED) conditions. At early times, the perturbation growth is dominated by the impulsive acceleration of the shock (RM), as evidenced by our proposed scaling accounting for the normal and tangential components of the shock. At later times, the perturbation growth is modulated by the positive and negative vorticity generated by the shear and the decompression due to the arrival of the rarefaction produced by laser turn off. As the tilt angle is increased, the onset of the shear-dominated dynamics occurs earlier and becomes more pronounced. We further demonstrate the ability of the vortex-sheet model to reproduce roll-up dynamics for non-zero Atwood numbers by comparing to past laser-driven HED experiments. We then explain the mechanisms of vorticity generation in the late-time evolution of the single-mode RM instability. In particular, we explore the generation of secondary opposite-sign vorticity occurring inside the roll-ups as the interface spirals inward. We show that, in the case of a zero Atwood number, opposite-sign vorticity never develops. In this case, the vorticity distribution along the interface is only governed by the rate of change of the sheet surface. Near the vortex core, the rate of change of the sheet surface alternates between positive and negative values, indicating that the interface near the vortex core undergoes a series of contractions and expansions, thus giving rise to oscillations in the corresponding sheet strength. In the case of small Atwood numbers, performing a vorticity budget suggests that opposite-sign vorticity is generated by the nonlinear vorticity advection along the interface. To quantify the amount of opposite-sign vorticity generated along the interface, we consider positive and negative circulations, and their dependence of the strength of the incident shock and the Atwood number. We show that opposite-sign circulation behaves according to a power law in time and that the interface evolution scales in time with respect to the shock Mach number.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/168005/1/spellone_1.pd

Directorless Shakespeare

“Directorless Shakespeare” means an ensemble staging of a Shakespeare play with no single external authority to interpret the play for the actors, where all decisions in the rehearsal room are made collaboratively by the actors, including casting, cutting, design and interpretation of characters. This thesis posits that the heteroglossia (Bakhtin) of Shakespeare’s texts, its myriad mindedness (Coleridge) and its dialogical forces have a greater chance of being released by the centrifugal force of the collective ensemble, rather than the centripetal force of the single director: the heterogeneity of the text served by the concomitant heterogeneity of a directorless, diverse acting company. It considers critically the contemporary mindset and cultural bias towards leadership to reconsider possibilities of working without a director when we stage Shakespeare’s plays, and the philosophical conundrums involved in giving actors a sense of what the existentialists termed “autonomy”. It examines the power imbalances in the rehearsal room with director-led, conceptual, contemporary Shakespeare in contrast with the distributed mindset evidenced in the actor-led historical practice of English Renaissance theatre. As well as investigating praxis at Shakespeare’s Globe and the American Shakespeare Center, this thesis conducts original practice-based research as Embodied Literary Criticism (ELC), detailing the process and reception of three directorless Shakespeare plays (five productions) – a History, a Comedy, a Tragedy – with different acting companies, different performance spaces, and in different countries. These directorless Shakespeare productions, by Anərkē Shakespeare and V.enice S.hakespeare C.ompany, revealed obscured aspects of the plays and offered alternative conclusions to currently accepted academic theories on the working process of English Renaissance theatre concerning cue scripts and rehearsals. Directorless Shakespeare as ELC has revelatory potential, supports and empowers the acting process, and can produce great and moving art

Specific Modeling Issues on an Adaptive Winglet Skeleton

Morphing aeronautical systems may be used for a number of aims, ranging from improving performance in specific flight conditions, to keeping the optimal efficiency over a certain parameters domain instead of confining it to a single point, extending the flight envelope, and so on. An almost trivial statement is that traditional skeleton architectures cannot be held as a structure modified from being rigid to deformable. That passage is not simple, as a structure that is able to be modified shall be designed and constructed to face those new requirements. What is not marginal, is that the new configurations can lead to some peculiar problems for both the morphing and the standard, supporting, elements. In their own nature, in fact, adaptive systems are designed to contain all the parts within the original geometry, without any "external adjoint", such as nacelles or others. Stress and strain distribution may vary a lot with respect to usual structures and some particular modifications are required. Sometimes, it happens that the structural behavior does not match with the common experience and some specific adjustment shall be done to overcome the problem. What is reported in this paper is a study concerning the adaptation of the structural architecture, used to host a winglet morphing system, to make it accomplish the original requirements, i.e., allow the deformation values to be under the safety threshold. When facing that problem, an uncommon behavior of the finite element (FE) solver has been met: the safety factors appear to be tremendously dependent on the mesh size, so as to raise serious questions about the actual expected value, relevant for the most severe load conditions. On the other side, such singularities are more and more confined into single points (or single lines), as the mesh refines, so to evidence somehow the numerical effect behind those results. On the other side, standard engineering local methods to reduce the abovementioned strain peaks seem to work very well in re-distributing the stress and strain excesses to the whole system domain. The work does not intend to give an answer to the presented problem, being instead focused on describing its possible causes and its evident effects. Further work is necessary to detect the original source of such inconsistencies, and propose and test operative solutions. That will be the subject of the next steps of the ongoing research

Does Stanford's induction apply to engineering sciences?

Recent works in scientific realism by Stanford (2006) and Chakravartty (2008) have generated interests in the research of a more selective and sophisticated scientific realism. Such debates advance the philosophical development of scientific realism, and arguably shape scientific realism toward a more refined description. Among many scientific theories discussed by Stanford (2006) and Chakravartty (2008), we have found their examples excluding those from engineering sciences, and this attracts our attention. In this paper, we first give an overview of Stanford's induction. Second, we analyze the arguments presented by Stanford (2006) and Chakravartty (2008) in depth to explore possible reasons why engineering sciences are seemly out of the scope of the debates. Third, we re-examine the philosophical debates by Stanford (2006) and Chakravartty (2008) in the context of an interesting case in mechanical engineering, d'Alembert's paradox, presented by Grimberg (2008). We conclude in the final section on the validity of applying Stanford's induction to engineering sciences

Acute care needs in a rural Sub-Saharan African Emergency Centre: A retrospective analysis

AbstractIntroductionIn June of 2008, Karoli Lwanga (“Nyakibale”) Hospital and Global Emergency Care Collaborative (GECC) opened the first functional Emergency Centre (EC) in rural Uganda. GECC is developing a training programme for a new cadre of midlevel Emergency Care Practitioners (ECPs), to increase access to quality emergency care. In order to determine the skills and resources needed, the unique practice demographics and the feasibility of treating patients in this setting must be understood.MethodsA descriptive cross-sectional analysis of the first 500 consecutive patient visits in the EC’s patient care log was reviewed. Data on demographics, procedures performed, laboratory testing, bedside ultrasounds (USs) performed, radiographs (XRs) ordered, diagnoses, condition upon discharge and disposition were collated. Descriptive statistics were performed.ResultsOf the first 500 patient visits, there were 275 (55%) male visits and 132 (26.4%) visits for children under five. Procedures were performed in 367 (73.4%) patients. Laboratory testing, XRs and USs were performed in 188 (37.6%), 99 (19.8%) and 45 (7%) patients, respectively. Infectious diseases were diagnosed in 217 (43.4%) patients; traumatic injuries in 140 (28%) patients. Only one patient expired in the ED, and 401 (80.2%) were in good condition after treatment. One person was transferred to another hospital. After treatment, 180 (36%) patients were discharged home. Only five (1.0%) patients went directly to the operating theatre.ConclusionsThis pilot study describes the patient population, resource and training needs of a rural Emergency Centre in SSA. It demonstrates that acute care providers will be required to evaluate a wide variety of patient complaints, effectively utilise laboratory and radiologic testing, and perform numerous focused treatments and therapies. Specialised training programmes, such as GECC’s ECP programme, are needed to create providers able to provide high quality, lifesaving care

Lâcher tourbillonnaire à l'arrière des pales d'une turbine Darrieus

Le travail présenté a pour objectif la modélisation bidimensionnelle de l'écoulement tourbillonnaire dans une turbine Darrieus bipale droite. Dans une telle configuration l'incidence de l'écoulement sur les pales varie constamment sur un tour, provoquant des décollements dynamiques importants ainsi que de fortes interactions pales / tourbillons. Les résultats expérimentaux de Lannevile et Vittecoq (1986), obtenus sur une turbine Darrieus bipale droite, mettent en évidence des structures tourbillonnaires lâchées par une pale et interagissant fortement avec celle-ci. En conséquence les courbes de traînée et de portance sur un cycle de rotation présentent une hystérésis significative. On a utilisé un code de calcul RANS-K-omega (code académique TurbFlow) utilisant un maillage structuré par blocs et des schémas numériques peu dissipatifs a été choisi. Leur capture est suffisamment précise pour retrouver une hystérésis du cycle de portance conforme à celle mesurée dans l'expérienc