A three-dimensional, parallel, finite volume solver which uses Roe&#039 / s upwind flux differencing scheme for spatial and Runge-Kutta explicit multistage time stepping scheme for temporal discretization on unstructured meshes is developed for the unsteady solution of external viscous flow around rotating bodies. The main aim of this study is to evaluate the aerodynamic dynamic stability derivative coefficients for rotating missile configurations. Arbitrary Lagrangian Eulerian (ALE) formulation is adapted to the solver for the simulation of the rotation of the body. Eigenvalues of the Euler equations in ALE form has been derived. Body rotation is simply performed by rotating the entire computational domain including the body of the projectile by means of rotation matrices. Spalart-Allmaras one-euqation turbulence model is implemented to the solver. The solver developed is first verified in 3-D for inviscid flow over two missile configurations. Then inviscid flow over a rotating missile is tested. Viscous flux computation algorithms and Spalarat-Allmaras turbulence model implementation are validated in 2-D by performing calculations for viscous flow over flat plate, NACA0012 airfoil and NLR 7301 airfoil with trailing edge flap. The ALE formulation is validated in 2-D on a rapidly pitching NACA0012 airfoil. Afterwards three-dimensional validation studies for viscous, laminar and turbulent flow calculations are performed on 3-D flat plate problem. At last, as a validation test case, unsteady laminar and turbulent viscous flow calculations over a spinning M910 projectile configuration are performed. Results are qualitatively in agreement with the analytical solutions, experimental measurements and previous studies for steady and unsteady flow calculations.

abstract: In this work, the hydrodynamics of Suction Stabilization is studied. Suction stabilization was found to stabilize floating platforms/floats in a much better way as compared to the conventional methods. This was achieved by an effective increment in the metacentric height due to the Inverse Slack Tank (IST) effect. The study involves the analysis of the existing designs and optimizing its performance. This research investigates the stability of such floats and the hydrodynamic forces acting on the same for offshore applications, such as wind turbines. A simple mathematical model for the condition of parametric resonance is developed and the results are verified, both analytically and experimentally. / Dissertation/Thesis / Real time working of SSF in heavy wind and rain conditions / Animation explaining working of SSF / Experiment with patio umbrella mounted on SSF / Masters Thesis Mechanical Engineering 2014

L’introduction de fuselages et de pales de plus en plus légers durant le développement des nouveaux hélicoptères, combinée à une puissance disponible augmentée peut donner lieu à des couplages rotor/structure d’un nouveau genre. Ces instabilités complexes apparaissent à des fréquences plus élevées que les couplages connus et étudiés tels que les résonances sol et air, et impliquent des modes de pale souple, des modes de structure, et des phénomènes aérodynamiques. Des codes de calcul multi-corps aéromécaniques tels que HOST sont capables de déterminer la stabilité de l’hélicoptère, mais sont difficilement modifiables et manipulables. Des modèles analytiques existent également pour les instabilités maîtrisées citées précédemment, mais n’ont pas les capacités de modélisation nécessaires à la prédiction de ces couplages haute fréquence. Ce travail de thèse se concentre sur le développement d’un modèle semi-analytique, capable de prédire la stabilité de l’hélicoptère vis-à-vis de ces phénomènes. Cette approche est différente de l’approche multi-corps et a un double avantage car elle permet des études paramétriques rapides et une analyse terme à terme des équations de la dynamique de l’hélicoptère. Ce modèle a été validé à l’aide de HOST et le mécanisme de l'instabilité a été détaillé. Enfin, l’influence des paramètres de rotor, de structure, et de vol a été évaluée et les considérations architecturales pour éviter l'apparition de tels phénomènes sont présentées. / The introduction of lightweight fuselages and blades during new developments, combined with an increased available power, may lead to the triggering of a new kind of rotor/structure coupling. These complex instabilities appear at higher frequencies than known and studied couplings, such as ground and air resonance, and involve elastic blade modes, structure modes, and aerodynamic phenomena. Comprehensive analysis codes, like HOST, are able to determine the helicopter stability but can hardly be tweaked and handled. Rotor/structure coupling analytical models also exist for ground and air resonance, but do not have the modeling capabilities required to predict these high frequency couplings. This research work focuses on the development of a semi-analytical model, able to predict the helicopter stability with respect to these phenomena. This approach has a two-fold advantage since fast parametric studies can be carried out and a term-by-term analysis of the helicopter stability equations can be performed. This model has been validated with HOST and the triggering mechanism has been detailed. Finally, the influence of rotor, structure, and flight parameters has been evaluated and architectural considerations to avoid the appearance of such couplings are presented.

A muscular co-operation change was observed at exercising intent on improvement of a scapula dynamic stability. In the study there were ten individuals participating in a specific resistance exercise for a period of seven to nine weeks. The cooperation of scapular muscles was evaluated in stand - by (tilt test) and investigation the stereotype of arm abduction, visually and by the help of a surface polyelectromyography. A distinct improvement of a scapula dynamic stability occurred at three observed objects. Powered by TCPDF (www.tcpdf.org)

The master thesis deals with the possibility of using dynamic damper in hydrodynamics. Specifically, the assessment of the impact of dynamic damper on the dynamic stability of the fluid system when the system exhibited unstable behaviour prior to damper installation due to self-excited vibration. In the thesis is presented the algorithm for the calculation of pressure and flow pulsations based on the transfer matrix method, the transition matrices for different damper designs variants are derived. Using the algorithm, the effect of a damper placed in a stable and unstable fluid system is solved. The output of this work is software for solution of pressure and flow pulsations in the system with serially arranged hydrodynamic elements created in the MATLAB program.

Over the last decades, the frequency on the Nordic electrical power grid has deteriorated. Therefore, new stricter requirements are developed for the hydropower delivering regulating active power on the Frequency Containment Reserve market (FCR). This thesis aims to investigate the possibility of modeling two double-regulated hydropower plants, referred to as Unit 1 and 2, to evaluate their compliance with the new FCR-requirements.  By modeling the hydropower plants, the first goal was to find a model structure that captures the essential dynamics of the systems. A second goal was to evaluate whether the two units currently fulfill the new FCR-requirements, and investigate how the turbine governors’ settings could be optimized to fulfill the new requirements. Data obtained from FCR-tests was used in MATLAB to evaluate the two stations’ dynamic stability and performance requirements. Through system identification in MATLAB, grey-box modeling was used to create linear and non-linear turbine and waterways models for Unit 1 and Unit 2. The non-linear turbine and waterways models were implemented in Simulink, together with corresponding turbine governors, to find optimal parameter settings to fulfill the FCR-requirements.  The evaluation of the new FCR-requirements shows that none of the two units fulfills the dynamic stability requirement. However, Unit 1 fulfills the performance requirement. The results imply that double-regulated turbines will most likely have difficulties fulfilling the new requirements, which will cause major consequences in improving the frequency regulation quality. The results from the grey-box modeling present that the linear models are not validated with the step response data, due to not capturing the system dynamics when compared with provided data from the units. On the other hand, the non-linear models are validated with step response data as the model captures the system dynamics more accurately. However, the non- linear Simulink models cannot capture the dynamics of the hydropower systems for sinusoidal signals with varying frequencies which are used in the new FCR-requirement test. Consequently, the thesis has no result of the optimal parameter setting of the turbine governors to fulfill the new FCR-requirements. In conclusion, the grey-box models, with the level of detail presented in this thesis, are inadequate in capturing the system’s dynamics to evaluate the new FCR-requirements. Thus, the thesis contributes to filling a knowledge gap within the area of modeling for frequency regulation.

Solutions of self-assembled wormlike micelles are used with ever increasing frequency in a multitude of consumer products ranging from cosmetic to industrial applications. Owing to the wide range of applications, flows of interest are often complex in nature; exhibiting both extensional and shear regions that can make modeling and prediction both challenging and valuable. Adding to the complexity, the micellar dynamics are continually changing, resulting in a number of interesting phenomena, such as shear banding and extensional flow instabilities. Presented in this thesis are the results of an investigation into the flow fields generated by both a controllable and idealized porous media, effected as a periodic array of cylinders as well as a single circular cylinder. In order to fully characterize the kinematics, two rheologically documented test fluids were used. The first test channel geometry consists of six equally spaced cylinders, arranged perpendicular to the flow, while the second consists of a single circular cylinder. By systematically varying the Deborah number, the flow kinematics, stability and pressure drop were measured. A combination of particle image velocimetry in conjunction with flush mount pressure transducers were used to characterize the flow, while flow induced birefringence measurements were used to determine micelle deformation and alignment. In the periodic geometry, the pressure drop was found to decrease initially due to the shear thinning of the test fluid, and then exhibit a dramatic upturn as other elastic effects begin to dominate in one of the test fluids. In the case of the single cylinder, no such upturn was observed. Presented is evidence of the onset of an elastic instability in one of the test fluids above a critical Deborah number, manifest in fluctuating transient pressure drop measurements and asymmetric streamlines. This instability was observed in both test geometries. It is argued that this instability can be attributed to the measurable differences in the extensional rheology of the two fluids.

No description available.

[pt] Nesse trabalho, estuda-se o desempenho de um absorsor pendular no controle de vibrações de torres altas e esbeltas, ocasionadas por carregamentos dinâmicos, tais como, por exemplo, cargas ambientais. Em virtude da possibilidade de oscilações de grande amplitude, considera- se na modelagem do problema a não-linearidade do pêndulo. O principal objetivo é estudar o comportamento do sistema torre-pêndulo, submetido a um carregamento harmônico, no regime não-linear, abordando-se aspectos gerais ligados à estabilidade dinâmica. Apresenta-se, inicialmente, a formulação necessária para obter o funcional de energia do sistema coluna-pêndulo, tanto para o caso linear quanto para o caso não-linear, do qual derivam-se as equações diferenciais parciais de movimento. A partir das equações lineares, obtêm-se as freqüências naturais e modos de vibração para alguns casos relevantes de coluna. A seguir, com base na análise modal do sistema coluna-pêndulo, deriva-se um modelo de dois graus de liberdade capaz de descrever com precisão o comportamento do sistema na vizinhança da freqüência fundamental da coluna, do qual obtêm-se as equações de movimento e as equações de estado não- lineares. Uma análise paramétrica detalhada das oscilações não-lineares do sistema coluna-pêndulo demonstra que o absorsor pendular passivo pode reduzir ou amplificar a resposta da coluna. No estudo da influência da não-linearidade geométrica do pêndulo, verifica-se a importância dessa na resposta do sistema, evidenciando que a nãolinearidade não pode ser desprezada nessa classe de problema. Por fim, com base nos resultados, propõe-se um absorsor pendular híbrido. Os estudos revelam que este controle é mais eficiente que o passivo e que não requer grande gasto de energia. / [en] In the present work the performance of a pendulum absorber in the vibration control of tall and slender towers, caused by dynamic loads, such as, environmental loads, is studied in detail. Due to the possibility of large amplitude oscillations, the non-linearity of the pendulum is considered in the modeling of the problem. The main objective of this research is to study the behavior of the tower-pendulum system, submitted to a harmonic load, in the nonlinear regimen, with emphasis on general aspects related to its dynamic stability. It is presented, initially, the formulation necessary for the derivation of the system´s energy functional, both for the linear and the nonlinear cases, from which the partial differential equations of motion are derived and the vibration frequencies and related vibration modes are obtained. Then, based on the modal analysis of the column-pendulum system, a two degrees of freedom model, capable of describing with precision the behavior of the system in the neighborhood of the fundamental frequency of the column is derived, from which the equations of motion and the nonlinear state-space equations are obtained. A detailed parametric analysis of the nonlinear oscillations of the system is carried out. It shows that the pendulum may reduce or amplify the response of the column. The results show a marked influence of the geometric not-linearity of the pendulum on the response of the system, showing that its not-linearity cannot be neglected in this class of problems. Finally, based on the results, a hybrid control approach is proposed. These studies show that this control strategy is more efficient than the passive control alone and that it does not require a large amount of energy.

[pt] Nesta tese, as vibrações não-lineares e a estabilidade de uma casca cilíndrica contendo um fluido são estudadas com base em modelos de dimensão reduzida, isto é, modelos com um número reduzido de graus de liberdade. A partir dos funcionais de energia potencial e cinética de uma casca cilíndrica, deduzem-se suas equações de movimento. O campo de deformações da casca cilíndrica segue a teoria não- linear de Donnell para cascas abatidas. O fluido é considerado interno à casca irrotacional, não-viscoso e incompressível, sendo descrito a partir de um potencial de velocidade que leva em consideração a interação entre o fluido e a estrutura. Para resolver o sistema de equações de equilíbrio da casca, desenvolve-se um procedimento analítico que permite obter os campos de deslocamento axial e circunferencial em função dos deslocamentos laterais, além de atender as condições de contorno do problema. Desta forma, reduz-se o sistema de equações de equilíbrio a uma única equação diferencial parcial que é resolvida com o método de Galerkin. A determinação dos deslocamentos laterais é feita a partir de técnicas de perturbação que ordena os modos não-lineares de acordo com sua importância na solução da casca cilíndrica. Comprova-se essa ordenação através do método de Karhunen-Loève que fornece, também, uma expansão ótima para os deslocamentos laterais. Além dessas técnicas, apresenta-se uma redução polinomial que relacionam as amplitudes dos modos não-lineares com a amplitude do modo linear, criando uma expansão modal com 1 GDL. Apresentam-se respostas no tempo, fronteiras de instabilidade e diagramas de bifurcação para uma casca cilíndrica submetida a dois tipos de carregamentos harmônicos, pressão lateral e carga axial. A seguir, são propostos alguns critérios para a análise da a integridade do sistema dinâmico tanto para um sistema com 1 GDL quanto para um sistema multidimensional através da evolução e erosão das bacias de atração. Por fim, estuda-se o comportamento de cascas cilíndricas parcialmente cheias, mostrando a influência da altura do fluido nas fronteiras de instabilidade e curvas de ressonância da casca cilíndrica. / [en] The nonlinear vibrations and stability of a fluid-filled cylindrical shell is investigated using reduced order models. First, the nonlinear equations of motion of the cylindrical shell are deduced based on the expressions for the potential and kinetic energy, which are obtained using Donnell shallow shell theory. The internal fluid is considered to be irrotational, non- viscous and incompressible. It is described by a velocity potential that takes into account the fluid-shell interaction. A procedure is proposed to obtain analytically the axial and circumferential displacements of the shell, satisfying the in-plane equations of motion and the associated boundary conditions. So, the problem is reduced to one partial differential equation of motion which is solved by the Galerkin method. The transversal displacement field is obtained by perturbation techniques. This enables one to identify the relevance of each term in the nonlinear expansion of the vibration modes. Then, the Karhunen-Loève method is employed to investigate de relative importance of each mode obtained by the perturbation analysis on the nonlinear response and to deduce optimal interpolation function to be used in the Galerkin procedure. A SDOF model is also obtained by relating the modal amplitudes of the nonlinear modes to the vibration amplitude of the linear mode. Time responses, instability boundaries and ifurcation diagrams are obtained for cylindrical shells subjected to harmonic lateral and axial loads. Different procedures for the analysis of the shell integrity are proposed based on the evolution and erosion of the basins of attraction in state-space. Finally, the influence of the fluid height on the stability boundaries and resonance curves is studied.