The aim of this master thesis is to create a 3D electroanatomical model of a heart atria, which would be able to perform atrial fibrillation. To control the model, the differential equations of the FitzHugh-Nagumo model were chosen. These equations describe the change of voltage on the cell membrane. The equations have established parameters. The modification of them leads to changes in the behavior of the model. The simulations were performed in the COMSOL Multiphysics environment. In the first step, the simulations were performed on 2D models. Simulations of healthy heart, atrial flutter and atrial fibrillation were created. The acquired knowledge served as a basis for the creation of a 3D model on which atrial fibrillation was simulated on the basis of ectopic activity and reentry mechanism. Convincing results were obtained in accordance with the used literature. The advantages of computational modeling are its availability, zero ethical burden and the ability to simulate even rarer arrhythmias. The disadvantage of the procedure is the need to compromise between accuracy and computational complexity of simulations.

Utvecklingen av mobila hybrid applikationer har ökat drastiskt under det senaste årtiondet. Med tanke på mångfalden i hur stora företag börjar investera i ramverk med support för utveckling av mobila hybrid applikationer (multiplattforms ramverk), ökar nödvändigheten av aktuella studier inom detta ämnesområde. Facebook och Google är två välkända företag som har utvecklat React-Native respektive Flutter. Dessa multiplattforms ramverk utvecklas kontinuerligt och skillnader uppstår inom teknologierna hos ramverken vilket gör nya studier mer lämpliga. Syftet med denna studie är att undersöka vilket ramverk som bidrar med bäst produktivitet för utvecklaren med tanke på bristen av studier inom ämnet. Specifikt har en fallstudie utförts där studiens frågeställningar har besvarats.   Respektive frågeställningarna blev uppdelade i tre delfrågeställningar där varje fråga fick angivna kriterier att följa i fallstudien och båda ramverken blev tilldelade poäng om tillhörande kriterium för varje fråga var uppfylld. I slutet av studien räknades ett medelvärde ut som tilldelades till båda ramverken. Resultaten visade att det finns små skillnader i form av dess bidrag med bäst produktivitet för utvecklaren. / The development of hybrid mobile applications has increased rapidly in the last decade. Considering the diversity in how big companies starts to invest in frameworks that supports hybrid application development (cross-platform framework), the necessity of contemporary studies in this subject increase. Facebook and Google are two well-known companies that have developed React-Native and Flutter, respectively. These cross-platform frameworks are continuously developing, and differences occur in their technologies which makes new studies even more appropriate. The purpose of this study is to investigate which of these two frameworks contribute the most for the developer’s productivity considering the lack of studies in this specific subject. Specifically, a case study has been conducted where the research questions were answered.     The two research questions were divided into three sub questions, respectively where each question was given criteria to follow in the case study and each framework were assigned points if the associated criterion for each question were met. In the end of the study a mean value was assigned to each framework. The results showed that there are small differences in terms of its contribution for the developer’s productivity.

Esse trabalho consiste na determinação das velocidades críticas do vento e das amplitudes das vibrações numa estrutura composta por uma viga engastada suspensa por um estai (cabo), submetida aos efeitos de vento e chuva. Foi considerada a deformação no cabo devido ao carregamento do peso próprio e o acoplamento não-linear das vibrações do cabo e da viga. Três modos de vibração são de especial interesse, chamados de primeiro modo global (flexão da viga e vibração no cabo), primeiro modo local (vibração no cabo, com flexão na viga desprezável) e primeiro modo à torção. O modelo foi reduzido a três graus de liberdade. A modelagem dos carregamentos aerodinâmicos aplicados na viga foi feita segundo procedimentos tradicionais. O carregamento aerodinâmico aplicado ao cabo sob efeito de chuva e vento também foi levado em consideração. Para a redução do modelo matemático, os coeficientes de rigidez e de amortecimento equivalente são definidos e dependem parametricamente da velocidade do vento. Os termos não-lineares são devidos ao acoplamento das vibrações do cabo e da viga à flexão (no plano do cabo) e também aos efeitos aeroelásticos no cabo. Os seguintes regimes instáveis são avaliados: o efeito de galope (galloping) no cabo, o drapejamento (flutter) unimodal na torção e o drapejamento (flutter) do modo de flexão da viga em conjunto com vibrações transversais do cabo. / This paper is concerned with determining wind critical velocities and post-critical vibration amplitudes in a cable-stayed beam, under wind-rain condition. It is considered the cable sag due to the dead load plus the non-linear coupling between the vibration of both the cable and the beam. Three modes are of special interest, namely the first global mode (beam bending & cable vibration), the first local mode (cable vibration & negligible beam bending) and the first torsion mode. A reduced mathematical model, with three degrees of freedom, is also developed. With regard to the modelling of the aerodynamic loads applied to the beam, it can be performed after extension of classical guidelines. The aerodynamic loads applied to the cable under rain are also taken into account. For the reduced mathematical model, equivalent damping and stiffness coefficients will be defined, which depend parametrically on the wind velocity. Non-linear terms appear due to the coupling between the cable and the beam bending vibrations, and also to the aero-elastic non-linear effects on the cable. Different unstable regimes are surveyed such as the cable galloping, the unimodal flutter in torsion and the unimodal flutter with beam bending and cable vibrations coupled.

Estudos sobre a instabilidade aeroelástica em estruturas de pontes suspensas têm adquirido relevante destaque no âmbito das pesquisas em engenharia do vento nos últimos anos, haja vista que as definições resultantes dessa análise apresentam informações essenciais ao projeto, cálculo e concepção desse tipo de estrutura. Considerando que os escoamentos ao redor de pontes suspensas apresentam características turbulentas, o conhecimento acerca desse fenômeno torna-se fundamental para a análise da interação vento-ponte, estabelecendo a turbulência como uma importante e complexa vertente dentro dessa pesquisa. Nesse contexto, o presente trabalho visa contribuir com o tema através da análise numérica da ação do vento na seção transversal do tabuleiro de pontes suspensas, verificando seu comportamento quando estiverem submetidas à ação dos esforços provenientes do vento na interação de um escoamento turbulento com o tabuleiro da ponte. No trabalho foi investigada a atuação dos esforços aerodinâmicos na estrutura da ponte, ensejando na obtenção dos coeficientes aerodinâmicos de arrasto, sustentação e momento. Também foi analisado o comportamento do tabuleiro para o surgimento das vibrações induzidas por vórtices, permitindo o cálculo da frequência de desprendimento de vórtices e determinação do número de Strouhal. No que tange aos esforços aeroelásticos para o estudo específico do drapejamento (flutter), foram avaliadas as amplitudes de deslocamentos torcionais para o cálculo e obtenção da velocidade crítica do vento que acarreta o fenômeno do flutter. Juntamente com as análises aerodinâmicas e aeroelásticas da seção transversal da ponte, diferentes modelos de turbulência foram aplicados nas simulações para se estabelecer uma análise comparativa entre os escoamentos. As simulações computacionais desenvolvidas e apresentadas neste trabalho foram realizadas com auxílio de um programa de CFD (Computational Fluid Dynamics). Os modelos de ponte utilizados no trabalho foram o da ponte suspensa Great Belt East, localizada na Dinamarca e da ponte estaiada Sunshine Skyway, localizada nos Estados Unidos. Para validação da técnica computacional, os resultados das simulações foram comparados com dados numéricos e experimentais disponíveis na literatura. / Researches about aeroelastic instability in long span suspension bridges have been consistently the focus in wind engineering field in recent years, therefore the definitions from that study present essential information to design and construction of this type of road structure. Considering that fluid flows around bridges show some turbulent features, the knowledge about turbulence become critical for this wind-bridge interaction analysis, establishing the turbulence modeling study as an important and complex part within that research. According to this context, the meaning of this research was to contribute with numerical analysis of wind effects on a suspension bridge deck, verifying its behavior when this model is subjected to the action of wind loads from a turbulent fluid flow. The bridge aerodynamic behaviour was investigated and aerodynamic coefficients of drag, lift and moment were calculated. Flow induced vibrations were also analyzed for the bridge deck model, allowing it to obtain the vortex shedding frequency and Strouhal number. With regard to aeroelasticity and focusing on flutter study, the amplitudes of torsional displacements were evaluated as well as the analysis of critical wind velocity that causes flutter instabilities. Along with aerodynamic and aeroelastic analysis of the bridge deck cross sectional, fluid flow features were studied and compared applying several turbulence models to simulations. The numerical approach developed and shown in this work was performed by CFD (Computational Fluid Dynamics) software. The bridge deck models used at this dissertation were the Great Belt East suspension bridge, located in Denmark and the Sunshine Skyway cable stayed bridge, located in USA. In order to validate the computational technique, simulation results from this research were compared with numerical and experimental test data available in papers and literature.

The thesis presents background on solar thermal energy and addresses the structural challenges associated with the deployment of concentrating solar power fields in urban areas. Two potential structural systems and urban locales of deployment are proposed and investigated to determine whether they have the potential to be a cost-effective renewable energy solution for urban areas. The structural issues explored in the thesis include flutter, the wind loading of open frame structures, performance-based design, and the design of flexibly mounted equipment on a building.

Aeroelastic behavior prediction is often confined to analytical or highly computational methods, so I developed a low degree of freedom computational method using structural finite elements and unsteady loading to cover a gap in the literature. Finite elements are readily suitable for determination of the free vibration characteristics of eccentric, elastic structures, and the free vibration characteristics fundamentally determine the aeroelastic behavior. I used Theodorsen’s unsteady strip loading formulation to model the aerodynamic loading on linear elastic structures assuming harmonic motion. I applied Hassig’s ‘p-k’ method to predict the flutter boundary of nonsymmetric, aeroelastic systems. I investigated the application of a quintic interpolation assumed displacement shape to accurately predict higher order characteristic effects compared to linear analytical results. I show that quintic interpolation is especially accurate over cubic interpolation when multi-modal interactions are considered in low degree of freedom flutter behavior for high aspect ratio HALE aircraft wings.

Aeroacoustic investigations regarding different types of helicopter noise have indicated that the most annoying noise is caused by impulsive blade surface pressure changes in descent or forward flight conditions. Blade Vortex Interaction (BVI) is one of the main phenomena producing significant impulsive noise by the unsteady fluctuation in blade loading due to the rapid change of induced velocity field during interaction with vortices shed from previous blades. The tip vortex core structure and the blade vortex miss distance were identified as having a primary influence on BVI. In this thesis, piezoelectrically modulated and/or vectored blowing at the rotor blade tip is theoretically investigated as an active technique for modifying the structure of the tip vortex core as well as for increasing blade vortex miss distance. The mechanisms of formation and convection of rotor blade tip vortices up to and beyond 360 degrees wake age are described based on the CFD results for the baseline cases of a hovering rotor with rounded and square tips. A methodology combining electromechanical and CFD modeling is developed and applied to the study of a piezoelectrically modulated and vectored blowing two-dimensional wing section. The thesis is focused on the CFD analysis of rotor flow with modulated tangential blowing over a rounded blade tip, and with steady mid-plane blade tip blowing, respectively. Computational results characterizing the far-wake flow indicate that for steady tangential blowing the miss distance can be doubled compared to the baseline case, which may lead to a significant reduction in BVI noise level if this trend shown in hover can be replicated in low speed forward flight. Moreover, near-wake flow analysis show that through modulated blowing a higher dissipation of vorticity can be obtained.

This study presents the theoretical analysis of an active flutter suppression methodology applied to a smart fin. The smart fin consists of a cantilever aluminum plate-like structure with surface bonded piezoelectric (PZT, Lead- Zirconate-Titanate) patches. A thermal analogy method for the purpose of modeling of piezoelectric actuators in MSC&reg / /NASTRAN based on the analogy between thermal strains and piezoelectric strains was presented. The results obtained by the thermal analogy were compared with the reference results and very good agreement was observed. The unsteady aerodynamic loads acting on the structure were calculated by using a linear two-dimensional Doublet-Lattice Method available in MSC&reg / /NASTRAN. These aerodynamic loads were approximated as rational functions of the Laplace variable by using one of the aerodynamic approximation schemes, Roger&amp / #8217 / s approximation, with least-squares method. These approximated aerodynamic loads together with the structural matrices obtained by the finite element method were used to develop the aeroelastic equations of motion of the smart fin in state-space form. The Hinf robust controllers were then designed for the state-space aeroelastic model of the smart fin by considering both SISO (Single-Input Single-Output) and MIMO (Multi-Input Multi-Output) system models. The verification studies of the controllers showed satisfactory flutter suppression performance around the flutter point and a significant improvement in the flutter speed of the smart fin was also observed.

This thesis describes the analysis, fabrication and testing of a rotor with extremely flexible blades, focusing on application to a micro-helicopter. The flexibility of the rotor blades is such that they can be rolled into a compact volume and stowed inside the rotor hub. Stiffening and stabilization of the rotor is enabled by centrifugal forces acting on a tip mass. Centrifugal effects such as bifilar and propeller moments are investigated and the torsional equation of motion for a blade with low torsional stiffness is derived. Criteria for the design of the tip mass are also derived and it is chosen that the center of gravity of each blade section must be located ahead of the aerodynamic center. This thesis presents the design of 18-inch diameter two-bladed rotors having untwisted circular arc airfoil profile with constant chord. A systematic experimental investigation of the effect of various blade parameters on the stability of the rotor is conducted in hover and forward flight. These parameters include blade flexibility in bending and torsion, blade planform and mass distribution. Accordingly, several sets of blades varying these parameters are constructed and tested. It is observed that rotational speed and collective pitch angles have a significant effect on rotor stability. In addition, forward flight velocity is found to increase the blade stability. Next, the performance of flexible rotors is measured. In particular, they are compared to the performance of a rotor with rigid blades having an identical planform and airfoil section. It is found that the flexible blades are highly twisted during operation, resulting in a decreased efficiency compared to the rigid rotor blades. This induced twist is attributed to an unfavorable combination of tip body design and the propeller moment acting on it. Consequently, the blade design is modified and three different approaches to passively tailor the spanwise twist distribution for improved efficiency are investigated. In a first approach, extension-torsion composite material coupling is analyzed and it is shown that the centrifugal force acting on the tip mass is not large enough to balance the nose-down twist due to the propeller moment. The second concept makes use of the propeller moment acting on the tip mass located at an index angle to produce an untwisted blade in hover. It is constructed and tested. The result is an untwisted 18-inch diameter rotor whose maximum Figure of Merit is equal to 0.51 at a blade loading of 0.14. Moreover, this rotor is found to be stable for any collective pitch angle greater than 11 degrees. Finally, in a third approach, addition of a trailing-edge flap at the tip of the flexible rotor blade is investigated. This design is found to have a lower maximum Figure of Merit than that of an identical flexible rotor without a flap. However, addition of this control surface resulted in a stable rotor for any value of collective pitch angle. Future plans for increasing the efficiency of the flexible rotor blades and for developing an analytical model are described. / text

In this thesis, an aeroservoelastic test appratus is designed to investigate the flutter phenomena in a low speed wind tunnel environment. Flutter is an aeroelastic instability that may occur at control surfaces of aircrafts and missiles. Aerodynamic, elastic, and inertial forces are involved in flutter. A mathematical model using aeroelastic equations of motion is derived to investigate flutter and is used as a basis to design the test setup. Simulations using this mathematical model are performed and critical flutter velocities and frequencies are found. Stiffness characteristics of the test setup are determined using the results of these simulations. The test setup is a two degrees of freedom system, with motions in pitch and plunge, and is controlled by a servomotor in the pitch degree of freedom. A NACA 0012 airfoil is used as a control surface in the test setup. Using this setup, the flutter phenomena is generated in Ankara Wind Tunnel (AWT) and experiments are conducted to validate the results of the theoretical aeroelastic mathematical model calculations.