A indústria aeronáutica vem promovendo avanços tecnológicos em velocidades crescentes, para sobreviver em mercados extremamente competitivos. Neste cenário, torna-se imprescindível o uso de ferramentas de projeto que agilizem o desenvolvimento de novas aeronaves. Os atuais recursos computacionais permitiram um grande aumento no número de ferramentas que auxiliam o trabalho de projetistas e engenheiros. O projeto de uma aeronave é uma tarefa multidisciplinar por essência, o que logo incentivou o desenvolvimento de ferramentas computacionais que trabalhem com várias áreas ao mesmo tempo. Entre elas se destaca a otimização multidisciplinar em projeto, que une métodos de otimização à modelos matemáticos de áreas distintas de um projeto para encontrar soluções de compromisso. O presente trabalho introduz a otimização multidisciplinar em projeto (Multidisciplinary Design Optimization - MDO) e discorre sobre algumas aplicações possíveis desta metodologia. Foi realizada a implementação de um sistema de MDO para o projeto de asas flexíveis, considerando restrições de aeroelasticidade dinâmica e massa estrutural. Como meta, deseja-se encontrar distribuições ideais de rigidezes flexional e torcional da estrutura da asa, para maximizar a velocidade crítica de flutter e minimizar a massa estrutural. Para tanto, foram utilizados um modelo dinâmico-estrutural baseado no método dos elementos finitos, um modelo aerodinâmico não-estacionário baseado na teoria das faixas e nas soluções bidimensionais de Theodorsen, um modelo de previsão de flutter que utiliza o método K e, por fim, um otimizador baseado no método de algoritmos genéticos (AGs). São apresentados os detalhes empregados em cada modelo, as restrições aplicadas e a maneira como eles interagem ao longo da otimização. É feita uma análise para a escolha dos parâmetros de otimização por AG e em seguida a avaliação de dois casos, para verificação da funcionalidade do sistema implementado. Os resultados obtidos demonstram uma metodologia eficiente, que é capaz de buscar soluções ótimas para problemas propostos, que com devidos ajustes pode ter enorme valor para acelerar o desenvolvimento de novas aeronaves. / The aeronautical industry is always trying to speed up technological advances in order to survive in extremely competitive markets. In this scenario, the use of design tools to accelerate the development of new aircraft becomes essential. Current computational resources allow greater increase in the number of design tools to assist the work of aeronautical engineers. In essence, the design of an aircraft is a multidisciplinary task, which stimulates the development of computational tools that work with different areas at the same time. Among them, the multidisciplinary design optimization (MDO) can be distinguished, which combines optimization methods to mathematical models of distinct areas of a design to find compromise solutions. The present work introduces MDO and discourses on some possible applications of this methodology. The implementation of a MDO system for the design of flexible wings, considering dynamic aeroelasticity restrictions and the structural mass, was carried out. As goal, it is desired to find ideal flexional and torsional stiffness distributions of the wing structure, that maximize the critical flutter speed and minimize the structural mass. To do so, it was employed a structural dynamics model based on the finite element method, a nonstationary aerodynamic model based on the strip theory and Theodorsen’s two-dimensional solutions, a flutter prediction model based on the K method and a genetic algorithm (GA). Details on the model, restrictions applied and the way the models interact to each other through the optimization are presented. It is made an analysis for choosing the GA optimization parameters and then, the evaluation of two cases to verify the functionality of the implemented system. The results obtained illustrate an efficient methodology, capable of searching optimal solutions for proposed problems, that with the right adjustments can be of great value to accelerate the development of new aircraft.

Modern turbomachines are designed towards thinner, lighter and highly loaded blades. This gives rise to increased sensitivity to flow induced vibrations such as flutter, which leads to structure failure in a short period of time if not sufficiently damped. Although numerical tools are more and more reliable, flutter prediction still depends on a large degree on simplified models. In addition, the critical nature of flutter, resulting in poor well-documented real cases in the open literature, and the lack of experimental database typical of engine flows make its apprehension even more challenging.  In that context, the present thesis is dedicated to study flutter in recent turbines through aerodynamic analysis of subsonic or supersonic flows in response to a prescribed vibratory mode of the structure. The objective is to highlight some mechanisms potentially responsible for flutter in order to be in better position when designing blades. The strategy consists in leading both experimental and numerical investigations.  The experimental part is based on a worldwide unique annular turbine sector cascade employed for measuring the aeroelastic response by means of the aerodynamic influence coefficient technique. The cascade comprises seven low pressure gas turbine blades one of which can oscillate in a controlled way as a rigid body. Aeroelastic responses are measured at various mechanical and aerodynamic parameters: pure and combined modeshapes, reduced frequency, Mach number, incidence angle. In addition to turbulence level measurements, the database aims at assessing the influence of these parameters on the aerodynamic damping, at validating the linear combination principle and at providing input for numerical tools. The numerical part is based on unsteady computations linearized in the frequency domain and performed in the traveling wave mode. The focus is put on two industrial space turbines: 2D computations are performed on an integrally bladed disk, also called blisk; its very low viscous material damping results in complex motions with combined modes and extremely high reduced frequency. The blisk operates at low subsonic conditions without strong non-linearities. Although the blades have been predicted aeroelastically stable, an original methodology based on elementary decompositions of the blade motion is presented to identify the destabilizing movements. The results suggest that the so-called classical flutter is surprisingly prone to occur. Moreover, the aerodynamic damping has been found extremely sensitive to the interblade phase angle and cut-on/cut-off conditions. 3D computations are then performed on a supersonic turbine, which features shock waves and boundary layer separation. In contrast, the blade motion is of elementary nature, i.e. purely axial. The blades have been predicted aeroelastically unstable for backward traveling waves and stable for forward traveling waves. The low reduced frequencies allow quasi-steady analysis, which still account for flutter mechanisms: the shock wave motion establishes the boundary between stable and unstable configurations. / <p>QC 20111209</p>

In this thesis, aeroelastic concepts for increased aircraft performance are developed and evaluated. Active aeroelastic concepts are in focus as well as robust analysis concepts aiming at efficient analysis using numerical models with uncertain or varying model parameters. The thesis presents different approaches for exploitation of fluid-structure interaction of active aeroelastic structures. First, a high aspect ratio wing in wind tunnel testing conditions is considered. The wing was developed within the European research project \textit{Active Aeroelastic Aircraft Structures} and used to demonstrate how structural flexibility can be exploited by using multiple control surfaces such that the deformed wing shape gives minimum drag for different flight conditions. Two different drag minimization studies are presented, one aiming at reduced induced drag based on numerical optimization techniques, another one aiming at reduced measured total drag using real-time optimization in the wind tunnel experiment. The same wing is also used for demonstration of an active concept for gust load alleviation using a piezoelectric tab. In all studies on the high aspect ratio wing, it is demonstrated that structural flexibility can be exploited to increase aircraft performance. Other studies in this thesis investigate the applicability of robust control tools for flutter analysis considering model uncertainty and variation. First, different techniques for taking large structural variations into account are evaluated. Next, a high-fidelity numerical model of an aircraft with a variable amount of fuel is considered, and robust analysis is applied to find the worst-case fuel configuration. Finally, a study investigating the influence of uncertain external stores aerodynamics is presented. Overall, the robust approach is shown to be capable of treating large structural variations as well as modeling uncertainties to compute worst-case configurations and flutter boundaries. / QC 20100713

O estudo do comportamento de um perfil de uma seção aerolástica típica, com Reynolds na faixa de microaeronaves, constitui o principal foco deste trabalho, tomando como objetivo a estimativa de parâmetros do fenômeno de flutter. A pesquisa analisa o escoamento de um fluido sobre um corpo (cilindro e perfil de aerofólio) em estado estacionário e oscilante, em escoamento de velocidade constante, e, especificamente, o fenômeno de flutter. As equações de Navier-Stokes, com termo de força, são resolvidas pelo método da fronteira virtual para modelagem da interface escoamento/estrutura, representada pela geometria de um corpo de geometria complexa. Na discretização das equações governantes foi utilizado o método de diferenças finitas, sobre malhas deslocadas, com avanço temporal das velocidades do escoamento por meio de um esquema de Runge-Kutta de ordem 4. Os códigos computacionais, para as simulações das diretrizes e a lógica de cálculo, foram criados no contexto deste trabalho. A verificação foi feita através do método da solução manufaturada por meio de um problema fictício, que tem uma solução analítica conhecida, e que preenche as condições de contorno implementadas no código. O modelo da fronteira virtual é testado para os casos de escoamento sobre cilindro de base quadrada, cilindro de base circular e perfil de aerofólio tipo NACA0012, com malhas regular e não regular, e para condições estacionária e sob oscilação forçada. Foi estudado o comportamento de formação de vórtices, provocados por escoamento uniforme sobre o perfil de aerofólio, através dos coeficientes de arrasto, sustentação e pressão com visualização por meio da vorticidade e linhas de corrente, para vários ângulos de ataque e oscilação forçada com elevação e rotação em torno de um pivô posicionado no centro geométrico do perfil (50% da corda). Finalmente, é apresentada uma determinação numérica das características aeroelásticas para o perfil de aerofólio NACA0012, em escoamento de número de Reynolds ultra baixo (Re = 1.000), e parâmetros de flutter para um caso de baixa frequência de oscilação. / The behavior study of a profile of a typical aerolastic section, with Reynolds in range of micro aerial vehicle, is the main focus of this work, taking as objective the estimation of parameters of flutter phenomenon. The research analyzes of the flow of a incompressible fluid on a body (cylinder and airfoil profile) at steady state and oscillating with constant speed and, specifically, the flutter phenomenon. The Navier-Stokes equations, with force term, are solved by virtual boundary method for modeling interface flow/structure, represented by the geometry of a body of complex geometry. In discretization of the governing equations, the method of finite differences on staggered grid, with temporal advancement of discharge velocity through a Runge-Kutta of order 4. The computer codes, for simulations guidelines and logic calculation, were created in the context of this work. The verification was done by method ofmanufactured solution through a fictional problem, which has a known analytical solution, and satisfies the boundary conditions implemented in code. The model of the virtual boundary is tested for cases of flow over a square cylinder, circular cylinder and profile of a NACA0012 airfoil type, with regular and non-regular meshes, over stationary and forced oscillation conditions. We studied the behavior of vortex formation, caused by uniform flow over the airfoil profile, by the drag, lift and pressure coefficients with view through the vorticity and streamlines for various attack angles and forced oscillation with plunge and pich around a pivot witch was positioned at the geometric airfoil profile (half chord). Finally, it is presented a numerical determination of aeroelastic characteristics for the NACA0012 airfoil profile, flow under ultra low Reynolds number, and flutter parameters for a case of low oscillation frequency.

A indústria aeronáutica vem promovendo avanços tecnológicos em velocidades crescentes, para sobreviver em mercados extremamente competitivos. Neste cenário, torna-se imprescindível o uso de ferramentas de projeto que agilizem o desenvolvimento de novas aeronaves. Os atuais recursos computacionais permitiram um grande aumento no número de ferramentas que auxiliam o trabalho de projetistas e engenheiros. O projeto de uma aeronave é uma tarefa multidisciplinar por essência, o que logo incentivou o desenvolvimento de ferramentas computacionais que trabalhem com várias áreas ao mesmo tempo. Entre elas se destaca a otimização multidisciplinar em projeto, que une métodos de otimização à modelos matemáticos de áreas distintas de um projeto para encontrar soluções de compromisso. O presente trabalho introduz a otimização multidisciplinar em projeto (Multidisciplinary Design Optimization - MDO) e discorre sobre algumas aplicações possíveis desta metodologia. Foi realizada a implementação de um sistema de MDO para o projeto de asas flexíveis, considerando restrições de aeroelasticidade dinâmica e massa estrutural. Como meta, deseja-se encontrar distribuições ideais de rigidezes flexional e torcional da estrutura da asa, para maximizar a velocidade crítica de flutter e minimizar a massa estrutural. Para tanto, foram utilizados um modelo dinâmico-estrutural baseado no método dos elementos finitos, um modelo aerodinâmico não-estacionário baseado na teoria das faixas e nas soluções bidimensionais de Theodorsen, um modelo de previsão de flutter que utiliza o método K e, por fim, um otimizador baseado no método de algoritmos genéticos (AGs). São apresentados os detalhes empregados em cada modelo, as restrições aplicadas e a maneira como eles interagem ao longo da otimização. É feita uma análise para a escolha dos parâmetros de otimização por AG e em seguida a avaliação de dois casos, para verificação da funcionalidade do sistema implementado. Os resultados obtidos demonstram uma metodologia eficiente, que é capaz de buscar soluções ótimas para problemas propostos, que com devidos ajustes pode ter enorme valor para acelerar o desenvolvimento de novas aeronaves. / The aeronautical industry is always trying to speed up technological advances in order to survive in extremely competitive markets. In this scenario, the use of design tools to accelerate the development of new aircraft becomes essential. Current computational resources allow greater increase in the number of design tools to assist the work of aeronautical engineers. In essence, the design of an aircraft is a multidisciplinary task, which stimulates the development of computational tools that work with different areas at the same time. Among them, the multidisciplinary design optimization (MDO) can be distinguished, which combines optimization methods to mathematical models of distinct areas of a design to find compromise solutions. The present work introduces MDO and discourses on some possible applications of this methodology. The implementation of a MDO system for the design of flexible wings, considering dynamic aeroelasticity restrictions and the structural mass, was carried out. As goal, it is desired to find ideal flexional and torsional stiffness distributions of the wing structure, that maximize the critical flutter speed and minimize the structural mass. To do so, it was employed a structural dynamics model based on the finite element method, a nonstationary aerodynamic model based on the strip theory and Theodorsen’s two-dimensional solutions, a flutter prediction model based on the K method and a genetic algorithm (GA). Details on the model, restrictions applied and the way the models interact to each other through the optimization are presented. It is made an analysis for choosing the GA optimization parameters and then, the evaluation of two cases to verify the functionality of the implemented system. The results obtained illustrate an efficient methodology, capable of searching optimal solutions for proposed problems, that with the right adjustments can be of great value to accelerate the development of new aircraft.

O cateter irrigado foi comparado com o de 8 mm para ablação com radiofrequência do istmo cavo-tricuspídeo(Ist-CT). Foram randomizados 52 pacientes portadores de flutter atrial típico para ablação com cateter irrigado(grupoI) ou com cateter de 8 mm(grupo II). O bloqueio do Ist-CT foi obtido em 51 pacientes. Não houve diferença estatística em relação aos parâmetros de aplicação de RF entre os dois grupos. A ablação do Ist-CT com cateter irrigado versus cateter de 8mm foi igualmente eficaz e segura no controle do flutter atrial típico. / A 4-mm cooled tip catheter was compared to an 8-mm tip catheter to cavotricuspid isthmus(CTI) ablation. This prospective study enrolled 52 patients with typical atrial flutter to ablation with a closed cooled-tip catheter(group1) or an 8-mm tip catheter. Radiofrequency(RF) applications were performed to achieve complete CTI block wich was achieved in 51 patients. No significant differences were found in the procedure parameters. CTI ablation with an irrigated tip catheter versus an 8-mm tip catheter was equally effective and satisfactorily safe for ablation of typical atrial flutter.

Neste trabalho, desenvolve-se um método de fronteira imersa para o estudo de escoamento compressível modelado pelas equações de Euler bidimensionais. O método de discretização de diferenças finitas é empregado, usando o método de Steger-Warming de ordem dois para discretizar as variáveis espaciais e o esquema de Runge-Kutta de ordem quatro para discretizar as variáveis temporais. O método da fronteira imersa foi empregado para o estudo de aeroelasticidade computacional em uma seção típica de aerofólio bidimensional com dois movimentos prescritos: torsional e vertical, com o objetivo de se verifcar a eficiência do método e sua aplicabilidade para problemas em aeroelasticidade computacional. Neste estudo desenvolveu-se também um programa de computador para simular escoamentos compressíveis de fluido invíscido utilizando a metodologia proposta. A verificação do código gerado foi feita utilizando o método das soluções manufaturadas e o problema de reflexão de choque oblíquo. A validação foi realizada comparando-se os resultados obtidos para o escoamento ao redor de uma seção circular e de uma seção de aerofólio NACA 0012 com os resultados experimentais, para cada caso. / In this work, an immersed boundary method is developed to study compressible flow modeled by the two-dimensional Euler equations. The finite difference method is employed, using the second order Steger-Warming method to discretizate the space variables and the fourth order Runge-Kutta method to discretizate the time variables. The immersed boundary method was employed to study computational aeroelasticity on a typical two-dimensional airfoil section with two prescribed motion: pitching and plunging, in order to verify the efficiency of the numerical method and its applicability in computational aeroelasticity problems. In this work, a computer program was developed to simulate compressible flows for inviscid fluids using the methodology proposed. The verification of the computational code was performed using the method of manufactured solutions and the oblique shock wave reflection problem. The validation was performed comparing the obtained results for flows around a circular section and a NACA 0012 airfoil section with the experimental results, for each case.

Transonic utter is an aeroelastic instability characterized by part-chord shocks over an airfoil and single mode oscillations leading to a drop in the utter boundary. We present a numerical study that examines the influence of shocks, shock-boundary layer interactions, and three-dimensional flow features on the transonic utter boundary. Using energy concepts we show that shocks and shock-boundary layer interactions have a profound influence on the stability of an aeroelastic system. Viscosity stabilizes the aeroelastic system through thickness effects up-to the bottom of the transonic dip. Beyond, shock induced separation not only stalls the aeroelastic system, but also makes it oscillate about a new equilibrium position. In this region, where viscous effects are dominant, the inviscid utter boundary shows multiple utter points. Modal contributions to the response of the aeroelastic systems |viscous and inviscid | indicate that viscosity restricts higher mode participation. Restriction of higher modes by viscosity is responsible for the elimination of multiple utter points that are present in the inviscid case. Multiple forcing frequencies are observed in those regions of the utter boundary where viscous effects are dominant. Further, the shock dynamics exhibit shock-reversal where-in the shock motion predicted by the viscous simulation is 180_ out of phase relative to that of the inviscid case. At Mach numbers beyond the shock-stall region the shock moves close to the trailing edge of the airfoil, and inviscid and viscous simulations predict almost a similar utter boundary. Three-dimensional transonic flow structures on a finite-span wing aeroelastic model de-stabilizes it relative to an equivalent two-dimensional model.

Idag ser man ett ökat intresset för applikationsutveckling. Den hybrida applikationsutvecklingen är något företag inte kan se förbi längre då dess fördelar väger tungt. Fördelarna med hybrida applikationer är bland annat det faktum att de använder en kodbas för flera plattformar. Detta i sin tur leder till en kraftig tids- och resursbesparing under utvecklingsfasen. De två hybrida ramverken som valts ut i ett jämförande syfte är Apache Cordova och Flutter, och syftet är att identifiera vilket ramverk presterar bäst ur ett prestandaperspektiv. Den frågeställning som besvaras i studien är: Vilket ramverk för att skapa en hybrid applikation av Apache Cordova och Flutter, är att rekommendera ur ett prestandaperspektiv? Studien mäter prestandarelaterade variabler, dessa är exekveringshastighet, uppstartstid, CPU-, RAM- och batterianvändning. Studien gör detta genom skapandet av två funktionellt identiska applikationer i respektive ramverk. Datainsamlingen görs genom Android Profiler, Logcat samt egen implementerad kod. Resultatet presenterar mätningar i respektive prestandarelaterad variabel. Det som redovisas i det totala resultatet visar på att Flutter är det ramverk som presterar snabbare men även är det ramverk som har en högre resursanvändning. / Today we see an increased trend around the interest in application development, and in our society there are over three billion smartphone users. Hybrid application development is something companies can no longer overlook because the benefits weigh heavily. The benefits with hybrid applications include the fact that it uses a multi-platform code base. This in turn leads to a significant saving of time and resources during the development process. The two hybrid frameworks chosen for a comparative purpose are Apache Cordova and Flutter, and the purpose is to identify which framework performs the best out of a performance perspective. The question answered in the study is: What framework for creating a hybrid application between Apache Cordova and Flutter, is recommended out of a performance perspective? The study measures performance-related variables, these are execution speed, start-up time, CPU, RAM and battery usage. The study does this by creating two functionally identical applications in each framework. Data collection takes place via Android Profiler, Logcat and own implemented code. The result shows measurements in each performance-related variable. Not only does the overall results show that Flutter is the faster performing framework but also the framework with a higher use of resources.

Syfte Syftet med detta examensarbete var att undersöka potentiella prestandaskillnader mellan React Native och Flutter för att underlätta vid val av multiplattform-ramverk. Metod För att besvara examensarbetets frågeställningar utfördes en experimentell studie för att samla empirisk data. Resultat Studiens resultat påvisar att React Native presterar bättre än Flutter vid bildbehandling genom applicering av filter. Implikationer Detta examensarbete bidrar till att minska kunskapsluckan gällande jämförelser i prestanda mellan ramverken React Native och Flutter. Begränsningar Under den experimentella studien har en iOS enhet och en Android enhet använts. Studien begränsades till applicering av tre olika filter. Nyckelord Multiplattform, React Native, Flutter, bildbehandling, prestanda, mobil apputveckling. / Purpose The purpose of this student thesis was to investigate potential differences in performance between React Native and Flutter, this to make the decision easier when choosing a cross-platform framework. Method To answer the thesis questions an experimental study was conducted to collect empirical data. Findings The findings in this student thesis shows that during image processing with filters, React Native performs better than Flutter. Implications This student thesis contributes by shrinking the gap regarding comparisons in performance between the frameworks React Native and Flutter. Limitations The experimental study was conducted on one iOS device and one Android device. The thesis was limited to applying three different image filters. Keywords Cross-platform, React Native, Flutter, image processing, performance, mobile app development.