Effects of engine placement on flutter characteristics of a very flexible high-aspect-ratio wing are investigated using the code NATASHA (Nonlinear Aeroelastic Trim And Stability of HALE Aircraft). The analysis was validated against published results for divergence and flutter of swept wings and found to be in excellent agreement with the experimental results of the classical wing of Goland. Moreover, modal frequencies and damping obtained for the Goland wing were found in excellent agreement with published results based on a new continuum-based unsteady aerodynamic formulation. Gravity for this class of wings plays an important role in flutter characteristics. In the absence of aerodynamic and gravitational forces and without an engine, the kinetic energy of the first two modes are calculated. Maximum and minimum flutter speed locations coincide with the area of minimum and maximum kinetic energy of the second bending and torsion modes. Time-dependent dynamic behavior of a turboshaft engine (JetCat SP5) is simulated with a transient engine model and the nonlinear aeroelastic response of the wing to the engine's time-dependent thrust and dynamic excitation is presented. Below the flutter speed, at the wing tip and behind the elastic axis, the impulse engine excitation leads to a stable limit cycle oscillation; and for the ramp kind of excitation, beyond the flutter speed, at 75% span, behind the elastic axis, it produces chaotic oscillation of the wing. Both the excitations above the flutter speed are stabilized, on the inboard portion of the wing. Effects of engine placement and sweep on flutter characteristics of a backswept flying wing resembling the Horten IV are explored using NATASHA. This aircraft exhibits a non-oscillatory yawing instability, expected in aircraft with neither a vertical tail nor yaw control. More important, however, is the presence of a low frequency “body-freedom flutter” mode. The aircraft center of gravity was held fixed during the study, which allowed aircraft controls to trim similarly for each engine location, and minimized flutter speed variations along the inboard span. Maximum flutter speed occurred for engine placement just outboard of 60% span with engine center of gravity forward of the elastic axis. The body-freedom flutter mode was largely unaffected by the engine placement except for cases in which the engine is placed at the wing tip and near the elastic axis. In the absence of engines, aerodynamics, and gravity, a region of minimum kinetic energy density for the first symmetric free-free bending mode is also near the 60% span. A possible relationship between the favorable flutter characteristics obtained by placing the engines at that point and the region of minimum kinetic energy is briefly explored. Effects of multiple engine placement on a similar type of aircraft are studied. The results showed that multiple engine placement increases flutter speed particularly when the engines are placed in the outboard portion of the wing (60% to 70% span), forward of the elastic axis, while the lift to drag ratio is affected negligibly. The behavior of the sub- and supercritical eigenvalues is studied for two cases of engine placement. NATASHA captures a hump body-freedom flutter with low frequency for the clean wing case, which disappears as the engines are placed on the wings. In neither case is there any apparent coalescence between the unstable modes. NATASHA captures other non-oscillatory unstable roots with very small amplitude, apparently originating with flight dynamics. For the clean-wing case, in the absence of aerodynamic and gravitational forces, the regions of minimum kinetic energy density for the first and third bending modes are located around 60% span. For the second mode, this kinetic energy density has local minima around the 20% and 80% span. The regions of minimum kinetic energy of these modes are in agreement with calculations that show a noticeable increase in flutter speed at these regions if engines are placed forward of the elastic axis. High Altitude, Long Endurance (HALE) aircraft can achieve sustained, uninterrupted flight time if they use solar power. Wing morphing of solar powered HALE aircraft can significantly increase solar energy absorbency. An example of the kind of morphing considered in this thesis requires the wings to fold so as to orient a solar panel to be hit more directly by the sun's rays at specific times of the day. In this study solar powered HALE flying wing aircraft are modeled with three beams with lockable hinge connections. Such aircraft are shown to be capable of morphing passively, following the sun by means of aerodynamic forces and engine thrusts. The analysis underlying NATASHA was extended to include the ability to simulate morphing of the aircraft into a “Z” configuration. Because of the “long endurance” feature of HALE aircraft, such morphing needs to be done without relying on actuators and at as near zero energy cost as possible. The emphasis of this study is to substantially demonstrate the processes required to passively morph a flying wing into a Z-shaped configuration and back again.

Multi-vehicle systems offer many advantages in engineering applications such as increased efficiency and robustness. However, the disadvantage of multi-vehicle systems is that they require a high level of organization and coordination in order to successfully complete a task. Formation control is a field of engineering that addresses this issue, and provides coordination schemes to successfully implement multi-vehicle systems. Two approaches to group coordination were proposed in this work: geometric and self-organizing formations. A geometric reconfiguring formation was developed using the leader-follower method, and the self-organizing formation was developed using the velocity potential equations from fluid flow theory. Both formation controllers were first tested in simulation in MATLAB, and then implemented on the X80 mobile robot units. Various experiments were conducted to test the formations under difficult obstacle scenarios. The robots successfully navigated through the obstacles as a coordinated as a team using the self-organizing and geometric formation control approaches.

Made available in DSpace on 2014-06-11T19:35:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-09-29Bitstream added on 2014-06-13T19:05:54Z : No. of bitstreams: 1 sazima_c_dr_rcla.pdf: 3777460 bytes, checksum: 9e503b696e86d7b22cab018e597016c7 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Acompanhar animais em atividade alimentar constitui um modo comum de forragear para peixes recifais que formam associações alimentares interespecíficas. Os peixes seguidores acompanham animais nucleares para aproveitar itens alimentares expostos ou produzidos através da atividade do nuclear. Tais associações alimentares são comuns para diversos tipos de peixes e outros animais, ocorrendo em variadas áreas geográficas. Este tipo de associação alimentar foi estudado no arquipélago oceânico de Fernando de Noronha, Atlântico Sul Ocidental tropical. O presente trabalho é composto de cinco artigos científicos, dispostos em quatro capítulos. O primeiro capítulo descreve associações alimentares entre peixes recifais e tartarugas marinhas. O segundo capítulo caracteriza o comportamento alimentar versátil de uma espécie de peixe recifal ao seguir outras espécies de peixes. O terceiro capítulo é composto de dois artigos; o primeiro trata da espécie de peixe nuclear mais comum e importante no arquipélago, ao passo que o segundo artigo descreve a associação entre seguidores e uma espécie de peixe cuja família não constava como nuclear. O quarto capítulo constitui uma revisão geral sobre o tema, com informações sobre o grupo de animais, na maioria peixes recifais, que forma associações alimentares interespecíficas como nucleares e/ou seguidores. A série de artigos científicos, apresentada no presente trabalho, amplia o conhecimento sobre agrupamentos alimentares e história natural da ictiofauna recifal no Atlântico Sul Ocidental tropical, além de modificar a situação deste tipo de associação alimentar na literatura científica mundial. / Following behaviour is a foraging mode commonly recorded for reef fishes during heterospecific feeding associations. The followers escort so called nuclear foraging fishes and other animals to capitalise on food items exposed or produced by the activity of the nuclear ones. Such foraging associations are widespread and recorded for several fish and other marine animal taxa and geographic areas. This foraging mode was studied at the oceanic archipelago of Fernando de Noronha, tropical Southwest Atlantic. The present work is composed of five scientific papers, organized in four chapters. The first chapter describes foraging associations between reef fishes and marine turtles. The second chapter characterizes the variable foraging modes of a reef fish species while following other fishes. The third chapter is composed by two studies, the first dealing with the commonest and most important nuclear fish in the archipelago, while the second one describes the association between followers and a fish species in a family not previously recorded as a nuclear. The fourth chapter is an overview about this topic, with information about the assemblage of animals, mostly reef fishes, which engage in interspecific foraging associations as nuclears and/or followers. This series of articles broadens our understanding about feeding assemblages and natural history of reef fishes in the tropical Southwest Atlantic, besides modifying the knowledge on this type of foraging association.

[pt] Nesta dissertação estuda-se em detalhe o modelo de coluna submetido a carregamentos não conservativos dependentes do deslocamento. Analisa-se a influência da base elástica de Winkler e de apoios elásticos nos dois problemas clássicos de Beck e Leipholz. Apresenta-se uma metodologia para o método dinâmico de determinação da condição e carga crítica através de uma formulação matricial. A modelagem é desenvolvida para um elemento de viga esbelta através do método de Rayleigh-Ritz com o campo de deslocamentos descrito pela combinação de polinômios cúbicos e funções trigonométricas. Desenvolveu-se um programa em MATLAB de acordo com a metodologia apresentada. Os problemas clássicos foram utilizados para avaliar numericamente a eficácia desta abordagem. Apresentam-se as análises de influência de base elástica e apoios elásticos avaliados tanto separadamente como em conjunto. Isto permite mostrar que as cargas críticas e respectivos modos são afetados de forma distinta para cada tipo de apoio elástico e forma de carregamento. Finalmente, as análises são comparadas com resultados presentes na bibliografia, de modelos mais completos, considerando movimento de fluido ao longo do elemento, com o objetivo de avaliar a faixa de aplicabilidade do modelo de Beck para o caso de tubulações. / [en] In this dissertation, the model of column subjected to displacementdependent non-conservative loads is studied in detail. The influence of Winkler s elastic foundation and elastic supports is carried out for some classical problems such as Beck s and Leipholz s. A methodology based on a matrix formulation is presented for determining the critical condition and load in a dynamic approach. The model developed is based on Rayleigh-Ritz method, using a combination of cubic polynomials and trigonometric functions to describe the displacement field of slender beam elements. This methodology was implemented in a computer program developed in MATLAB. The classical problems were used as numerical tests to evaluate the accuracy of this approach. Later, the analysis of elastic foundation and elastic supports influence are presented separately and together. It was possible to show that both critical load and its respective modes are affected differently for each type of elastic support and load distribution. Finally, the influence analysis of Beck s problem is compared to results presented in in bibliography of a model which includes fluid movement within the element. This comparison has the purpose to estimate a range of applicability of the classical Beck s model to a pipe conveying fluid.

Multi-vehicle systems offer many advantages in engineering applications such as increased efficiency and robustness. However, the disadvantage of multi-vehicle systems is that they require a high level of organization and coordination in order to successfully complete a task. Formation control is a field of engineering that addresses this issue, and provides coordination schemes to successfully implement multi-vehicle systems. Two approaches to group coordination were proposed in this work: geometric and self-organizing formations. A geometric reconfiguring formation was developed using the leader-follower method, and the self-organizing formation was developed using the velocity potential equations from fluid flow theory. Both formation controllers were first tested in simulation in MATLAB, and then implemented on the X80 mobile robot units. Various experiments were conducted to test the formations under difficult obstacle scenarios. The robots successfully navigated through the obstacles as a coordinated as a team using the self-organizing and geometric formation control approaches.

This master’s thesis deals with the design of integrated voltage regulator. Topologies of linear voltage regulators and their stability are discussed. Part of the thesis deals with description and simulation of blocks of selected regulator topology. The thesis describes the difficulties of integrated circuit design in the automotive industry. The electrical scheme of the designed regulator is explained. The work also focuses on the stability of designed regulator. Then presents simulations. It discusses the layout of integrated circuits and the designed voltage regulator.

The aim of this diploma thesis is to design active frequency filters based on passive RLC prototype. Three methods of the design of active filters and active functional blocks of electronic circuits working in current or mixed mode are used to this purpose. These blocks allow to process electrical signals with frequencies up to low tens of megahertz. In addition they feature for instance with high slew rate and low supply voltage power. Active high-pass and low-pass 2nd order filters are designed using simulation of inductor by active subcircuit method. Grounded and subsequently floating synthetic inductor is made with the current conveyors in the first case and with the current operational amplifiers with single input and differential output in the second case. This method advantage is relatively simple design and disadvantage is great quantity of active functional blocks. Active filters based on passive frequency ladder 3rd order filter while only one floating inductor is connected, are designed with circuit equation method. In the first design differential input / output current followers are used and in the second case current-differencing buffered amplifiers are used. This method benefits by smaller active blocks number and disadvantage is more complex design of the active filter. Active filter based on passive prototype of low-pass 3rd order filter with two floating inductors is designed with Bruton transformation method. Final active filter uses current operational amplifiers with single input and differential output which together with other passive elements replace frequency depending negative resistor, which arise after previous Bruton transform. This method usage is advantageous if the design consists of larger quantity of inductors and less number of capacitors. High-pass 2nd order filter is simulated by tolerance and parametrical analyses. Physical realisation utilising current feedback operational amplifier which substitute commercially hardly accessible current conveyors is subsequently made. Measurements of constructed active filter show that additional modifications, which allow better amplitude frequency characteristics conformity, are necessary.

This thesis deals with design and use synthetic circuit elements with higher-order immittance with controlled current sources to implement the frequency filters. Controlled current sources which are derived from the voltage variations are presented. They are current follower, current invertor and current operational amplifier. Low-pass and high-pass filter which are used synthetic elements are simulated on computer. The influence of real properities of active elements and passive elements tolerances on filter functionality is investigated. Selected circuit of frequency filter is realized and measured the frequency characteristic.

This thesis treats of problems of nonlinear circuits. In introduction the basic possibilities of solving nonlinear circuits are described. Then the basic information on modern current active elements is mentioned, for example current follower, current operational amplifier and current conveyor. In the next part of this thesis the problem of real characteristics of semiconductor diodes is described, major attention is focused on reverse recovery time. Three various types of circuits with nonlinear elements are described in this masters thesis. The first type of circuits are diode precision rectifiers, the full-wave rectifiers containing voltage operational amplifier are most explored, current follower and other active components are described in previous chapters. Simulations in PSpice were executed for each of these circuits. Then the attention was devoted to increase of maximum working frequence. The minimum necessary amplitude of input signal was also analyzed. In the following part two designs of diode function converters are processed, function converter with voltage operational amplifier and function converter with current follower. For each of the diode function converters designed, simulations were executed to find their real properties. The variety of diode voltage limiters and diode current limiters are the third type of nonlinear circuits described, from which the upper limiter and double limiter are investigated in more detail. Simulations were executed for all limiters and their functionality and problems connected with their usage for limitation of high frequency signals were analyzed. In the last part of the thesis there is described the practical realization of precise rectifier, which showed the best ability to process high frequency signals of all investigated circuits. This circuit was realized so that it is able to operate in current and mixed mode. Measured values of real circuits were compared with values gained from the simulations.

Master’s thesis in the theoretical part deals with literature review on the topic of measurement errors and measurement uncertainties. The practical part deals with the simulation of additional capacitive and resistive load on the amplitude and phase error during shunts based measurement. For this simulation is used mathematical apparatus of cascade matrix of two-ports and their connections. For the actual simulation is used script for MATLAB. Furthermore, the work deals with the design of voltage follower to eliminate simulated errors and its practical realization. The last part deals with the design of the coaxial multiplexer for switching current shunts developed in the Czech Metrological Institute in Brno.