No description available.

No description available.

No description available.

Fundamental intuition of aerodynamics begins with understanding steady flow, a time- independent flow state. A fluid region undergoing steady flow consists of constant properties such as pressure and velocity at different positions in the flow field. This time-independent principle is crucial for beginning a foundation of understanding aerodynamics; however, analyzing this state of flow was beyond the limit at my university's Fundamentals of Aerodynamics course. There was minimal education on time-dependent unsteady flow, which created a vacuum on my understanding of how flow can be analyzed with time. The purpose of writing this thesis is to create a framework for aspiring learners of aerodynamics to better comprehend unsteady flow, including myself. The basis for developing an understanding of unsteady flow is accomplished by analyzing the aerodynamics of a simple two-dimensional zero-thickness flat plate, using a numerical method called Discrete Vortex Method under steady and unsteady conditions. Constructing a numerical method for steady and unsteady flow requires a software to compute enormous quantities of linear equations, therefore a combination of numerous arguments, functions, and loops were developed on MATLAB written in the C/C++ languages. Results from the numerical methods will be compared with the experimental and theoretical results from Katz & Plotkin (2001). The Steady Discrete Vortex Method was a basis for calculating the circulation of the flat plate at varying angles of attack and freestream velocities. The Unsteady Discrete Vortex Method derived much of the self-induced calculations in the body-fixed coordinate system. At the same time, a time-stepping method was developed to calculate the coordinates as the flat plate and shed vortices translated from the origin of an additional frame of reference called the inertial coordinate system. A wake vortex is shed from the trailing-edge of the flat plate at each time step iv to model vorticity shed from a body in motion. The flat plate undergoes sudden acceleration and plunging maneuvers to demonstrate further effects of unsteady aerodynamic conditions. The results from the flat plate undergoing sudden acceleration with a Reynolds number of 68,435.8 was an increasing proportionality between the lift and circulation of the steady and unsteady case until reaching a constant trend as time increases, demonstrating the nature of low-speed flow reaching a steady state after a given period. The results from the flat plate undergoing plunging with a Reynolds number of 106,759.8 demonstrate a sinusoidal trend in the normal force experienced as the flat plate traverses in its sinusoidal plunging translation like that observed in the theoretical results. This thesis intends to expand on the understanding of unsteady aerodynamics by developing a numerical method that can alter its dependent factors to visualize the effects of changing specific parameters on pressure and force acting on the two-dimensional body.

This thesis aims at presenting the Discrete Vortex Method (DVM) as a tool to determine the flow field and associated wind loads over structures. Two structures are considered: the first is a surface-mounted prism and is used to simulate wind loads over low-rise structures. The second is a bridge section with attached flaps that can be oriented to vary the moment coefficient. Advantages and disadvantages of using DVM for these applications are discussed. For the surface-mounted prism, the results show that the developed code correctly predicts the flow separation around the corners. As for the surface pressures, it is concluded that parallel processing, which could be easily implemented for DVM, should be used to correctly predict surface pressures and their variations. This is due to the required slow time advancement of the computations. The results on attaching flaps to bridge sections yield required orientations to minimize moments under different angles of attack. / Master of Science

O presente trabalho tem como objetivo investigar o fenômeno de vibração induzida por vórtices (VIV) em cilindros com razão de aspecto elevada. Para alcançar tal objetivo, utilizou-se o código computacional denominado ANFLEX-CFD devidamente validado através de comparações com resultados experimentais. O foco do estudo é voltado para a análise do fenômeno de VIV, causado pelo desprendimento de vórtices ao redor de cilindros, e seu efeito no comportamento estrutural desses corpos rombudos. O programa computacional utiliza o Método dos Vórtices Discretos (Discrete Vortex Method - DVM) para o cálculo das forças hidrodinâmicas, acoplado ao modelo estrutural do ANFLEX que utiliza o método dos elementos finitos para resolver a estrutura e determinar seus deslocamentos. Os ensaios que serviram para comparação dos resultados foram os realizados no tanque da IFREMER, na França. Os resultados numéricos apresentaram uma boa concordância com o experimento para as maiores velocidades de corrente, o que pode ser justificado pela menor influência da tração perante o arrasto. A partir dos resultados pode-se afirmar que o ANFLEX-CFD é uma ferramenta útil na predição do fenômeno de VIV e pode se tornar uma ferramenta fundamental na determinação da vida útil à fadiga de elementos estruturais como os risers da indústria petrolífera offshore. / This thesis aims to instigate vortex-induced vibration on circular cylinders with high aspect ratio. In order to do so, the computer code named ANFLEX-CFD is employed, and this code is validated using experimental tests results. The focus of the study is to analyze VIV phenomenon caused by the vortex shedding around circular cylinders, and its effect on the structural behavior of these bluff bodies. The computer program uses the Discrete Vortex Method (DVM) for the assessment of the hydrodynamic forces, coupled with the structural model of ANFLEX that uses the finite element method to solve the structure displacements. The tests used in the comparison were the ones carried out at IFREMER tank in France. The numerical results have shown a good agreement with the experimental results at the highest current velocity as a result of the decreasing influence of the tension on the drag. As conclusion, it can be said that the ANFLEX-CFD can become a useful tool for predicting the VIV phenomenon and therefore in a near future become a fundamental tool in determining the fatigue life of structural components such as the offshore oil industry risers.

O presente trabalho tem como objetivo investigar o fenômeno de vibração induzida por vórtices (VIV) em cilindros com razão de aspecto elevada. Para alcançar tal objetivo, utilizou-se o código computacional denominado ANFLEX-CFD devidamente validado através de comparações com resultados experimentais. O foco do estudo é voltado para a análise do fenômeno de VIV, causado pelo desprendimento de vórtices ao redor de cilindros, e seu efeito no comportamento estrutural desses corpos rombudos. O programa computacional utiliza o Método dos Vórtices Discretos (Discrete Vortex Method - DVM) para o cálculo das forças hidrodinâmicas, acoplado ao modelo estrutural do ANFLEX que utiliza o método dos elementos finitos para resolver a estrutura e determinar seus deslocamentos. Os ensaios que serviram para comparação dos resultados foram os realizados no tanque da IFREMER, na França. Os resultados numéricos apresentaram uma boa concordância com o experimento para as maiores velocidades de corrente, o que pode ser justificado pela menor influência da tração perante o arrasto. A partir dos resultados pode-se afirmar que o ANFLEX-CFD é uma ferramenta útil na predição do fenômeno de VIV e pode se tornar uma ferramenta fundamental na determinação da vida útil à fadiga de elementos estruturais como os risers da indústria petrolífera offshore. / This thesis aims to instigate vortex-induced vibration on circular cylinders with high aspect ratio. In order to do so, the computer code named ANFLEX-CFD is employed, and this code is validated using experimental tests results. The focus of the study is to analyze VIV phenomenon caused by the vortex shedding around circular cylinders, and its effect on the structural behavior of these bluff bodies. The computer program uses the Discrete Vortex Method (DVM) for the assessment of the hydrodynamic forces, coupled with the structural model of ANFLEX that uses the finite element method to solve the structure displacements. The tests used in the comparison were the ones carried out at IFREMER tank in France. The numerical results have shown a good agreement with the experimental results at the highest current velocity as a result of the decreasing influence of the tension on the drag. As conclusion, it can be said that the ANFLEX-CFD can become a useful tool for predicting the VIV phenomenon and therefore in a near future become a fundamental tool in determining the fatigue life of structural components such as the offshore oil industry risers.

In this thesis, two dimensional, incompressible, viscous flow past bluff bodies and a bridge section, in which strong vortex shedding and unsteady attribute of flow are generally found, is simulated by means of random vortex method. The algorithm and method are described in detail. The validation and applicability of the developed numerical implementation to general wind engineering problems is illustrated by solving a number of classical problems, such as flow past circular and square cylinders. An application of the numerical implementation in the area of computational wind engineering is performed by analyzing a bridge deck section. Moreover, all results are compared with experimental and numerical studies in literature.

<p>Flapping flight is one of the most widespread mean of transportation. It is a complex unsteady aerodynamic problem that has been studied extensively in the past century. Nevertheless, by its complex nature, flapping flight remains a challenging subject. With the development of micro air vehicles, researchers need new computational methods to design these aircrafts efficiently. </p><p>In this dissertation, I will present three different methods of optimization for flapping flight with an emphasis on hovering with each their advantages and drawbacks. The first method was developed by Hall et al. It is an extremely fast and powerful three-dimensional approach. However, the assumptions made to develop this theory limit its use to lightly loaded wings. In addition, it only models the motion of the trailing edge and not the actual motion of the wing. </p><p>In a second part, I will present a two-dimensional unsteady potential method. It uses a freely convected wake which removes the lightly loaded restriction. This method shows the existence of an optimal combination of plunging and pitching motion. The motion is optimal in the sense that for a required force vector, the aerodynamic power is minimal.</p><p>The last method incorporates the three-dimensional effects. These effects are especially important for low aspect ratio wings. Thus, a three-dimensional unsteady potential vortex method was developed. This method also exhibits the presence of an optimal flapping/pitching motion. In addition, it agrees really well with the two previous methods and with the actual kinematics of birds during hovering flapping flight.</p><p>To conclude, some preliminary design tools for flapping wings in forward and hovering flight are presented in this thesis.</p> / Dissertation

No description available.