Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 1997. / This dissertation considers the feasibility of using atmospheric drag to control constellations of micro-satellites in low Earth orbits. The constellation control requirements include an acquisition phase and a maintenance phase. Optimal strategies are designed to control the relative positions of the satellites during these two phases. It is shown that the feasibility and success of the strategies depend on many factors, including the satellite properties and orbital configuration. A nominal test constellation is presented and used as a generic example for the application of the control strategies. The dissertation also focuses on the accurate modelling and simulation of a typical low Earth orbit satellite, moving under the influence of a variety of significant orbit perturbation forces. The simulations form an integral part of the study and are used to verify the application of all the proposed control strategies.

A novel laminar flow control based on generation of spanwise mean velocity gradients (SVG) in a flat plate boundary layer is investigated where disturbances of different types are introduced in the wall-bounded shear layer. The experimental investigations are aimed at; (i) generating stable and steady streamwise streaks in the boundary layer which set up spanwise gradients in the mean flow, and (ii) attenuating disturbance energy growth in the streaky boundary layers and hence delaying the onset of turbulence transition. The streamwise streaks generated by four different methods are investigated, which are spanwise arrays of triangular/rectangular miniature vortex generators (MVGs) and roughness elements, non-linear pair of oblique waves, and spanwise-periodic finite discrete suction. For all the investigated methods the boundary layer is modulated into regions of high- and low speed streaks through formation of pairs of counter-rotating streamwise vortices. For the streaky boundary layers generated by the MVGs a parameter study on a wide range of MVG configurations is performed in order to investigate the transient growth of the streaks. A general scaling of the streak amplitudes is found based on empiricism where an integral amplitude definition is proposed for the streaks. The disturbances are introduced as single- and broad band frequency twodimensional Tollmien–Schlichting (TS) waves, and three-dimensional single and a pair of oblique waves. In an attempt to obtain a more realistic configuration compared to previous investigations the disturbances are introduced upstream of the location were streaks are generated. It is shown that the SVG method is efficient in attenuating the growth of disturbance amplitudes in the linear regime for a wide range of frequencies although the disturbances have an initial amplitude response to the generation of the streaks. The attenuation rate of the disturbance amplitude is found to be optimized for an integral streak amplitude of 30% of the free-stream velocity which takes into account the periodic wavelength of the streaky base flow. The stabilizing effect of the streamwise streaks can be extended to the nonlinear regime of disturbances which in turn results in transition to turbulence delay. This results in significant drag reduction when comparing the skin friction coefficient of a laminar- to a turbulent boundary layer. It is also shown that consecutive turbulence transition delay can be obtained by reinforcing the streaky boundary layer in the streamwise direction. For the streaky boundary layer generated by pair of oblique waves their forcing frequency sets the upper limit for the frequency of disturbances beyond which the control fails. / <p>QC 20160208</p>

Wall-bounded turbulent flows such as plane Couette flow, channel, pipe flows and boundary layer flows are fundamental problem of interest that we often meet in many scientific and engineering situations. The goal of the present thesis is to investigate the origin of large-scale streaky motions observed in the wall-bounded turbulent flows. Under a hypothesis that the large-scale streaky motions sustain with a process similar to the well-known near-wall self-sustaining cycle, the present thesis have pursued on four separate subjects: (i) non-modal amplification of streaks, (ii) the secondary instability of the finite amplitude streaks, (iii) existence of a self-sustaining process at large scale and (iv) turbulent skin friction reduction by forcing streaks. First, using a linear model with turbulent mean flow and the related eddy viscosity, it is shown that the streaks are largely amplified by harmonic and stochastic forcing. The largely amplified streaks undergo the secondary instability and it has been associated with the formation of the large-scale motions (bulge). The existence of a self-sustaining process involving the amplification and instability of streaks at large scale is proved by quenching the smaller-scale energy carrying eddies in the near-wall and logarithmic regions. Finally, it is shown that artificially forcing of large-scale streaks reduce the turbulent skin friction up to 10\% by attenuating the near-wall streamwise vortices.

Advances in numerical optimization have raised the possibility that efficient and novel aircraft configurations may be ``discovered'' by an algorithm. To begin exploring this possibility, a fast and robust set of tools for aerodynamic shape optimization is developed. Parameterization and mesh-movement are integrated to accommodate large changes in the geometry. This integrated approach uses a coarse B-spline control grid to represent the geometry and move the computational mesh; consequently, the mesh-movement algorithm is two to three orders faster than a node-based linear elasticity approach, without compromising mesh quality. Aerodynamic analysis is performed using a flow solver for the Euler equations. The governing equations are discretized using summation-by-parts finite-difference operators and simultaneous approximation terms, which permit nonsmooth mesh continuity at block interfaces. The discretization results in a set of nonlinear algebraic equations, which are solved using an efficient parallel Newton-Krylov-Schur strategy. A gradient-based optimization algorithm is adopted. The gradient is evaluated using adjoint variables for the flow and mesh equations in a sequential approach. The flow adjoint equations are solved using a novel variant of the Krylov solver GCROT. This variant of GCROT is flexible to take advantage of non-stationary preconditioners and is shown to outperform restarted flexible GMRES. The aerodynamic optimizer is applied to several studies of induced-drag minimization. An elliptical lift distribution is recovered by varying spanwise twist, thereby validating the algorithm. Planform optimization based on the Euler equations produces a nonelliptical lift distribution, in contrast with the predictions of lifting-line theory. A study of spanwise vertical shape optimization confirms that a winglet-up configuration is more efficient than a winglet-down configuration. A split-tip geometry is used to explore nonlinear wake-wing interactions: the optimized split-tip demonstrates a significant reduction in induced drag relative to a single-tip wing. Finally, the optimal spanwise loading for a box-wing configuration is investigated.

Bakgrund: Vårdmiljön inom psykiatrisk heldygnsvård har beskrivits framkalla olika känslor och präglas av en hård miljö där patienter bland annat kan vårdas mot sin vilja och vara utsatta för tvångsåtgärder och restriktioner. Aggressivitet är vanligt förekommande på dessa avdelningar och bedöms vara ett problem. En kunskapslucka finns vad gäller vilka patienter och situationer som ökar risken för aggressivitet inom kontexten psykiatrisk heldygnsvård. Syfte: Att identifiera karaktäristiska drag hos patienter med aggressivt beteende och identifiera aspekter som påverkar situationer där hot- och våldsincidenter uppstått inom psykiatrisk heldygnsvård samt syntetisera en förklaringsmodell. Metod: En integrativ litteraturöversikt beståendes av både kvalitativa och kvantitativa artiklar. Materialet analyserades med hjälp av Whittemore och Knafls (2005) arbetsprocess. Resultat: Resultatet genererade i tre huvudteman och tio underteman. Följande tre huvudteman identifierades: patienten som en trigger, vårdmiljön som en trigger och personalen som en trigger. Diskussion: Metoden diskuteras utifrån begreppen: trovärdighet, pålitlighet, bekräftelsebarhet och överförbarhet. Resultatets huvudfynd diskuteras med stöd av tidigare forskning och i relation till Phil Barkers teori tidvattenmodellen. / Background: The care environment within psychiatric inpatient care has been described to create different emotions and is characterized as a hard environment where patients sometimes are treated against their will and can be exposed to coercive measures and restrictions. Aggressiveness is common at these wards and is considered a problem. There is a knowledge gap when it comes to patients and situations that increase the risk for aggressiveness in the context of psychiatric inpatient care. Aim: To identify characteristic features of aggressive patients and to identify aspects that effects situations where threats and violence has occurred in psychiatric inpatient care and to synthesise an explanatory model. Method: An integrative literature overview containing both qualitative and quantitative articles. The data were analysed using Whittemore and Knafl’s (2005) working procedure. Results: The result generated in three main themes and ten subthemes. Following three main themes were identified: the patient as a trigger, the care environment as a trigger and the staff as a trigger. Discussion: The method is discussed in relation to these concepts: trustworthiness, dependability, confirmability and transferability. The results are discussed with support of previous research and in relation to Phil Barker's theory the Tidal model.

Approved for public release, distribution is unlimited / For over half a century the NPS Aerolabʼ Low Speed Wind Tunnel located in Halligan Hall of the Naval Postgraduate school has served to provide students and faculty with meaningful aerodynamic data for research and problem analysis. New data acquisition hardware was installed three years ago but never fully verified, and contained no integrated software program to collect data from the strain-gauge balance pedestal. Existing National Instruments based hardware for the NPS low-speed wind tunnel was reconfigured to obtain data from the strain-gauge pedestal. Additionally, a data acquisition software program was written in LabVIEW⠭ to accommodate the hardware. The Virtual Instruments (VI) program collects and plots accurate data from all four strain gauges in real-time, producing non-dimensional force and moment coefficients. A research study on the performance of an OH-6A helicopter fuselage was conducted. NPS Aerolabʼ wind tunnel tests consisted of drag, lift, and pitching moment measurements of the OH-6A along yaw and angle-of-attack sweeps. The results of the NPS wind tunnel data were compared against testing conducted on a full-scale OH-6A helicopter in NASA Ames' 40 ft. x 80ft. wind tunnel, along with the U.S. Army's Light Observation Helicopter (LOH) wind tunnel tests. Results of current testing substantiate the LabVIEW⠭ code. / Ensign, United States Navy

International aviation regulations on emissions are becoming more strict. Improvements goals on fuel efficiency demand development of technologies capable of reducing fuel consumption and gas emissions. Morphing structures capability to adapt their aerodynamic shape for optimal condition in flight brings potential for reduction of aircraft drag and operating fuel consumption, minimizing gas emissions and fuel expenses. This study presents an investigation on the impact of a camber morphing winglet on midsize business jet using numerical simulation and wind tunnel experiments. A genetic algorithm was used to optimize the winglet sections camber for different flight conditions. Optimized geometries achieved total drag reduction of up to 0.58% compared to original winglet for single condition optimization, reaching up to 7 % reduction on consumed fuel on a typical mission. This efficiency improvement allows aircraft to carry 900 kg additional load, comprising the morphing system and extra payload. There is an indication of even better results for applications on a bigger commercial jet. Presented methodology is also suitable for new winglet fixed geometry design or incorporating morphing technology. Aerodynamic balance force measurements showed that optimized winglets increased the wing effective aspect ratio (AReff), reducing the lift-induced drag, and maximum lift coefficient (CLmax). However, maximum lift to drag ratio (L/Dmax) was reduced on CL optimization region due to flow differences between optimization and wind tunnel conditions. Aerodynamic efficiency improvement was found for greater lift coefficients (CL). Reductions on wing tip vortex size and intensity due to winglet installation are seen on measured vorticity map, showing liftinduced drag reduction according to Maskells equation. Parabolic drag polar and Maskells equation methods were used for lift-induced drag calculation, using balance force and flowing mapping data for calculations. The presented concept showed considerable aircraft performance improvement, using a feasible device with greater certification ease than other morphing structures concepts, once the failure of this system would not compromise flight safety. Further investigation using computational fluid dynamics (CFD) and wind tunnel experiments is necessary to develop and test a functional camber morphing winglet device. / Regulamentações internacionais sobre emissões estão se tornando mais rigorosas. Metas de melhoria da eficiência de consumo de combustível demandam o desenvolvimento de tecnologias capazes de reduzir o consumo e emissões de gases. Estruturas capazes de adaptar sua forma aerodinâmica para condição ótima em voo trazem potencial de redução do arrasto e consumo de combustível da aeronave, minimizando as emissões de gases e gastos com combustível. Este estudo apresenta uma investigação sobre o impacto de uma winglet de camber variável em um jato executivo da categoria mid size utilizando simulação numérica e experimentos em túnel de vento. Um algoritmo genético foi usado para otimizar o camber das seções para diferentes fases de voo. As geometrias otimizadas reduziram o arrasto total em até 0.58% comparadas a winglet original na otimização de condição única, alcançando até 7% de redução no combustível consumido em missão típica. Essa melhoria de eficiência permite a aeronave carregar 900 kg de carga adicional, composta pelo sistema de adaptação e carga paga extra. Há uma indicação de resultados ainda melhores para aplicação em um jato comercial maior. A metodologia apresentada é apropriada para projeto de uma nova winglet de geometria fixa ou que incorpore a tecnologia de adaptação. Medidas de força com balança aerodinâmica mostraram que as winglets otimizadas aumentaram o alongamento efetivo da asa (AReff), reduzindo o arrasto induzido, e o coeficiente de sustentação máximo (CLmax). No entanto, a máxima razão entre sustentação e arrasto (L/Dmax) foi reduzida dentro do intervalo de CL da otimização devido as diferenças entre as condições do escoamento na otimização e no túnel de vento. Melhoria na eficiência aerodinâmica foi obtida para coeficientes de sustentação (CL) maiores. Reduções no tamanho e intensidade do vórtice de ponta de asa são vistas nos mapas de vorticidade medidos, mostrando redução do arrasto induzido segundo a equação de Maskell. Os métodos da polar de arrasto parabólica e da equação de Maskell foram usados para o cálculo do arrasto induzido, utilizando nos cálculos os dados de força da balança e o mapeamento do escoamento. O conceito apresentado mostrou melhoria considerável no desempenho da aeronave, utilizando um sistema factível e com maior facilidade para certificação que outros conceitos de estruturas adaptáveis, uma vez que a falha desse sistema não comprometeria a segurança do voo. Mais estudos são necessários para desenvolver e testar uma winglet de camber varável funcional.

Cette thèse CIFRE est le fruit d’une collaboration entre Renault Trucks et le LMFA dans la perspective d’une évaluation de la pertinence du contrôle actif pour la réduction de traînée de véhicule industriel. Les deux principaux objectifs de ces travaux expérimentaux consistent à l’analyse de l’influence de l’écoulement de soubassement sur la dynamique du sillage et l’étude d’une stratégie de contrôle d’écoulement combinant des volets déflecteurs (positionnés sur les bords supérieurs et latéraux du culot) à des actionneurs de type jets pulsés dans l’optique d’une réduction de la traînée aérodynamique d’un corps non profilé à culot droit. Le développement du sillage pour différentes vitesses de soubassement évoluant de 10% à plus de 80% de la vitesse de l’écoulement infini amont est étudié sur une maquette simplifiée de véhicule poids lourd à l’échelle 1/43e. Des mesures de pression au culot permettent d’identifier quatre classes d’écoulement associées à des structures de sillage différentes mises en évidence par des mesures PIV 2D-3C. Le sillage de la première classe d’écoulement obtenu pour les très faibles vitesses de soubassement ressemble au sillage derrière une marche 3D. Pour des vitesses de soubassement plus élevées, l’écoulement de soubassement décolle au niveau du sol et impacte soit le culot ou soit la couche de cisaillement supérieure favorisant le développement des instabilités de type Kelvin-Helmoltz dans ce dernier cas. Enfin, la dernière classe est caractérisée par un sillage comparable à celui d’un corps d’Ahmed. L’ajout de volets déflecteurs à l’arrière du culot engendre une augmentation de la pression au culot pour l’ensemble des classes d’écoulement. Cette augmentation réside principalement dans l’effet de vectorisation de l’écoulement. Un système de contrôle actif est intégré sur une maquette 1/8e géométriquement identique à celle à l’échelle 1/43e et équipée de volets déflecteurs. Deux angles de volet supérieur sont testés afin d’obtenir en moyenne (i) un écoulement naturel attaché à la paroi du volet et (ii) un écoulement naturel détaché du volet. Par rapport au cas sans contrôle actif, des gains sur la traînée sont obtenus pour une certaine gamme de fréquence d’actionnement uniquement dans le cas (ii). Ces gains sont obtenus suite au recollement de l’écoulement sur le volet. Enfin, la robustesse des gains sur la pression au culot est testée avec succès en mettant la maquette en dérapage pour simuler un vent de travers. / This PhD thesis was realized in the scope of a collaboration with Renault Trucks and the LMFA in view of an evaluation of the relevance of active flow control for the drag reduction industrial vehicle. The two main objectives of this experimental work are to analyze the impact of the underbody flow on the wake dynamics and to study a flow control strategy combining inclined flaps (located on the upper and lateral edges of the rear base) with pulsed jet actuators for reducing the aerodynamic drag of a square-back bluff body. The wake development for several underbody velocities ranging from 10% to more than 80% of the free-stream velocity is studied on a simplified truck model at scale 1 :43. Rear base pressure measurements lead to the identification of four flow classes associated with different wake structures highlighted by 2D-3C PIV measurements. The wake of the first flow class obtained for very low underbody velocities looks like that of the wake of a 3D backward facing step. For higher underbody velocities, the underbody flow is separated from the ground impaging either the rear base or the upper shear layer triggering Kelvin-Helmoltz instabilities for this last case. Finally, the fourth class is characterized by a wake comparable to that of the Ahmed body. The implementation of inclined flaps at the rear base increases the base pressure for all classes. This increase is mainly due to the vectoring effect of the flow. An active control system is integrated to a 1 :8 scale model geometrically identical to that of the 1 :43 scale model with flaps. Two upper flap angles are tested to have (i) a natural flow attached to the flap and (ii) a natural flow detached from the flap. In comparison to the case without active flow control, drag reductions are obtained only for a specific range of actuation frequencies only in case (ii). These gains are associated with the reattachment of the flow on the flap. Finally, the robustness of the pressure gains is successfully tested in crosswind conditions.

Diferentes tipos de sólitons têm sido observados em meios ópticos não-lineares, e seus comportamentos individuais descritos pela equação não-linear de Schrödinger e pela equação não-linear de Schrödinger generalizada, em diferentes dimensões e geometrias. Entretando, há situações onde muitos sólitons são gerados formando uma densa rede de sólitons. Nestes casos, é impossível desprezar as interações entre os sólitons e temos que considerar a evolução da estrutura como um todo. A teoria das ondas de choque dispersivas em meios fotorrefrativos e a teoria da difração não-linear de intensos feixes de luz propagando-se em meios fotorrefrativos com um fio refletor incorporado a esse meio foi desenvolvida, e verificamos que está em excelente acordo com nossas simulações numéricas. No caso da formação de sólitons em condensados, fizemos cálculos numéricos realísticos dentro da aproximação de campo médio usando a equação de Gross-Pitaevskii, incluindo também um potencial de confinamento, um potencial móvel e um potencial dipolar. A maioria dos resultados puderam ser comparados com experimentos recentes. / Different kinds of solitons have already been observed in various nonlinear optical media, and their behavior has been explained in the frameworks of such mathematical models as the nonlinear Schrödinger and generalized nonlinear Shrödinger equations for different dimensions and geometries. However, there are situations when many solitons are generated so that they can comprise a dense soliton train. In such situations, it is impossible to neglect interactions between solitons and one has to consider the evolution of the structure as a whole rather than to trace the evolution of each soliton separately. The theory of optical shock waves in photorefractive media and the theory of nonlinear diffraction of light beams propagating in photorefractive media with embedded reflecting wire was developed and agrees very well with our numerical simulations. In the condensate soliton formation case, we did numerical calculations in the mean field approach using the Gross-Pitaevskii equation, adding a trap potential and a moving potential and a potential of the dipole-dipole interaction. The main results were also checked by recent experiments.

Dois dos principais objetivos no estudo da aerodinâmica de veículos comerciais são a redução no consumo de combustível e o aumento na eficiência da refrigeração do motor. Esses objetivos podem ser alcançados através do desenvolvimento de dispositivos que modifiquem o escoamento do ar ao redor do veículo e também através da alteração da forma das superfícies externas. A inclinação das superfícies da parte traseira de um ônibus, por exemplo, tem grande influência sobre a esteira turbulenta que se forma atrás do veículo. O uso de ferramentas computacionais permite uma redução de custo e maior flexibilidade na análise aerodinâmica de autoveículos. Ainda é preciso, no entanto, que o resultado dessas ferramentas computacionais seja verificado com o maior número possível de casos para que se possa escolher e ajustar o modelo matemático de forma adequada. O objetivo do presente trabalho é a verificação dos resultados computacionais e experimentais no desenvolvimento de metodologias que visem à redução no consumo de combustível e aumento na eficiência da refrigeração do motor. Foram comparados resultados experimentais e computacionais do escoamento sobre um modelo de um ônibus comercial em escala 1:17,5. Para a realização do experimento foi utilizado um túnel de vento de seção aberta, onde foram analisadas as distribuições de pressão nas superfícies da carroceria e o arrasto aerodinâmico. Para o teste computacional, foi utilizado um software de dinâmica dos fluidos computacional em que as equações de Navier-Stokes com média de Reynolds são resolvidas pelo método dos volumes finitos usando um modelo de turbulência RNG 'capa' - 'épsilon' / Two main objectives in the study of commercial vehicle aerodynamics are the reduction in fuel consumption and the improvement in engine refrigeration efficiency. These objectives can be achieved through development of devices which vary the flow characteristics around the vehicle and also through modification of the shape of external surfaces. The slope of rear surfaces, for instance, has large influence over the wake turbulence which forms behind the vehicle. The use of computational tools yields cost reduction and greater flexibility in automotive aerodynamic analysis. There is still a need, however, for verification of results, generated by these computational tools, with the largest possible number of test cases so that the mathematical model is adequately chosen and adjusted. The objective of the present work is the verification of experimental and computational results in the development of methodologies aiming at reduction of fuel consumption and improvement in engine refrigeration efficiency. Experimental and computational aerodynamic results were compared for a commercial bus model with a 1:17.5 scale. The experiments were conducted in an open section wind tunnel where pressure distribution and aerodynamic drag were analyzed. The numerical analysis was conducted using computational fluid dynamics software which solves the Reynolds Averaged Navier-Stokes equations using the finite volume method with a RNG 'capa' - 'épsilon' turbulence model