Thesis (M.App.Sc.) - Carleton University, 2005. / Includes bibliographical references (p. 109-120). Also available in electronic format on the Internet.

Thesis (Ph.D)--Aerospace Engineering, Georgia Institute of Technology, 2009. / Committee Co-Chair: Dr. Dimitri Mavris; Committee Co-Chair: Dr. Lakshmi N. Sankar; Committee Member: Dr. Daniel P. Schrage; Committee Member: Dr. Kenneth S. Brentner; Committee Member: Dr. Mark Costello. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The total wind power capacity installed in the world has substantially grown during the last few years, mainly due to the increasing number of horizontal axis wind turbines (HAWT). Consequently, a big effort was employed to increase HAWT\'s power capacity, which is directly associated to the size of blades. Then, novel designs of blades may lead to very fexible structures, susceptive to large deformation, not only during extreme events, but also for operational conditions. In this context, this thesis aims to compare two geometrically nonlinear structural modeling approaches that handle large deformation of blade structures: 3D geometrically-exact beam and shell finite element models. Regarding the beam model, due to geometric complexity of typical cross-sections of wind turbine blades it is adopted a theory that allows creation of arbitrary multicellular cross-sections. Two typical blade geometries are tested, and comparisons between the models are done in statics and dynamics, always inducing large deformation and exploring the accuracy limits of beam models, when compared to shells. Results showed that the beam and shell models present very similar behavior, except when violations occur on the beam formulation hypothesis, such as when shell local buckling phenomena takes place. / A capacidade total de energia eólica instalada no mundo cresceu substancialmente nos últimos anos, principalmente devido ao número crescente de turbinas eólicas de eixo horizontal. Consequentemente, um grande esforço foi empregado com o intuito de aumentar a capacidade de produção das turbinas eólicas, que está diretamente associada ao tamanho das pás. Assim, surgiram projetos inovadores quanto à concepção de pás de turbinas eólicas levando a estruturas bastante flexíveis, susceptíveis a grandes deslocamentos, não apenas em eventos extremos, mas também em condições normais de operação. Nesse contexto, a presente dissertação tem por objetivo comparar duas abordagens de modelos estruturais geometricamente não-lineares capazes de lidar com grandes deslocamentos de pás de turbinas eólicas: elementos finitos geometricamente exatos 3D de vigas e cascas. Em relação ao modelo de viga, devido à complexidade geométrica das seções transversais típicas de pás de turbinas eólicas, adota-se uma teoria que permite a criação de seções transversais arbitrárias multicelulares. Duas geometrias de pás s~ao testadas e comparações entre os modelos s~ao feitas em análises estáticas e dinâmicas, sempre induzindo grandes deslocamentos e explorando os limites de precisão do modelo de viga, quando comparado ao modelo de cascas. Os resultados indicam que os modelos de viga e casca apresentam comportamento muito similar, exceto quando ocorrem violações em hipóteses do modelo de viga, tal como quando ocorre flambagem local do modelo de casca.

In current design methods for gas turbines there are important features of the flow which are not yet within the scope of the available prediction methods for both the calculation of surface pressures and heat transfer rates. Such features include the prediction of three-dimensional viscous flowfields, the accurate location and strengths of the secondary flow regimes in a turbine passage, and allowance for time-dependent variations. It is the understanding of the time-varying phenomena which is the subject of this study. Such phenomena occur due to the periodic interaction between stages in a turbine, either that of a nozzle guide vane on a rotor downstream or vice-versa. In most contemporary designs of turbines the effects are due primarily to the wakes from the trailing-edge of the upstream airfoil, and to any associated shock structures resulting from transonic exit flow Mach numbers. The present investigation is concerned with furthering knowedge of these wake and shock interactions, using a method of simulation established in the Isentropic Light Piston Tunnel and Oxford. Measurements of heat transfer rates and pressures are presented, supported by flow visualisation methods such as surface oil-dots and schlieren photography, for two examples of high-pressure turbine rotor blades. The majority of analysis deals with the first of these (a highty-loaded transonic profile) whilst the second blade (designed for use in a large civil engine) is included for investigation of the effects of flow unsteadiness on the film cooling process The transition process is examined in detail by use of wide bandwith heat transfer measurements, and a new method derived for modelling this process. It has been possible to observe the effect of the enhanced turbulence in the simulated nozzle guide vane wake and effects due a shock-boundary layer interaction. The reaction of the blade boundary layers to these disturbances is identified, and trajectories of disturbed events tracked along the blade surfaces. The measurements which have been taken allow for some aspects of wake and shock interactions to be included in the design process for turbine blading. A better understanding has been obtained of how these types of transient flow regimes affect the boundary layers on the blade surfaces.

Due to the requirements for high blade loading, modern turbo‐machine blades operate very close to the stall regime. This can lead to flow separation with periodic shedding of vortices, which could lead to self induced oscillations or stall flutter of the blades. Previous studies on stall flutter have focused on flows at high Reynolds number (Re ~ 106). The Reynolds numbers for fans/propellers of Micro Aerial Vehicles (MAVs), high altitude turbofans and small wind turbines are substantially lower (Re < 105). Aerodynamic characteristics of flows at such low Re is significantly different from those at high Re, due in part to the early separation of the flow and possible formation of laminar separation bubbles (LSB). The present study is targeted towards study of stall flutter in a cascade of blades at low Re. We experimentally study stall flutter of a cascade of symmetric NACA 0012 blades at low Reynolds number (Re ~ 30, 000) through forced sinusoidal pitching of the blades about mean angles of incidences close to stall. The experimental arrangement permits variations of the inter‐blade phase (σ) in addition to the oscillation frequency (f) and amplitude; the inter‐blade phase angle (σ) being the phase difference between the motions of adjacent blades in the cascade. The unsteady moments on the central blade in the cascade are directly measured, and used to calculate the energy transfer from the flow to the blade. This energy transfer is used to predict the propensity of the blades to undergo self‐induced oscillations or stall flutter. Experiments are also conducted on an isolated blade in addition to the cascade. A variety of parameters can influence stall flutter in a cascade, namely the oscillation frequency (f), the mean angle of incidence, and the inter‐blade phase angle (σ). The measurements show that there exists a range of reduced frequencies, k (=πfc/U, c being the chord length of the blade and U being the free stream velocity), where the energy transfer from the flow to the blade is positive, which indicates that the flow can excite the blade. Above and below this range, the energy transfer is negative indicating that blade excitations, if any, will get damped. This range of excitation is found to depend upon the mean angle of incidence, with shifts towards higher values of k as the mean angle of incidence increases. An important parameter for cascades, which is absent in the isolated blade case is the inter‐blade phase angle (σ). An excitation regime is observed only for σ values between ‐450 and 900, with the value of excitation being maximum for σ of 900. Time traces of the measured moment were found to be non‐sinusoidal in the excitation regime, whereas they appear to be sinusoidal in the damping regime. Stall flutter in a cascade has differences when compared with an isolated blade. For the cascade, the maximum value of excitation (positive energy transfer) is found to be an order of magnitude lower compared to the isolated blade case. Further, for similar values of mean incidence angle, the range of excitation is at lower reduced frequencies for a cascade when compared with an isolated blade. A comparison with un‐stalled or classical flutter in a cascade at high Re, shows that the inter‐blade phase angle is a major factor governing flutter in both cases. Some differences are observed as well, which appear to be due to stalled flow and low Re.

In the context of the rapid development of the research in the biosystem structure materials domain, a representative direction shows the analysis of the behavior of these materials. This direction of research requires the use of various means and methods for theoretical and experimental measuring and evaluating. PhD thesis "Methods and means for analyzing the behavior of biosystems structure materials" shall be given precedence in this area of research, aimed at studying the behavior of polymeric materials and composites biosystems structure and in particular the skeletal structure biosystem. Therefore, it is developed a specific method of research based on the development of theoretical models for the prediction of the mechanical, thermal and machinability properties of these materials. There are used Moldflow, Solidworks and Ansys software types. In order to validate the theoretical research were designed and conducted experimental research on the mechanical properties and the behavior of the polymeric biomaterials represented by ABS, UHMWPE, HDPE, PA, PC, PET, PP, PP_GF-30% and composite materials with polymeric thermoplastic matrixes from the skeletal biosystem¿s structure. In order to analyze the theoretical and experimental correlations, the experimental data were processed using the statistical analysis software programs SPSS v17, v8 Origin, Palisade Decision Tools. In conclusion, the thesis represents a technic, scientific and efficient support for analyzing the behavior of the new polymeric and composite materials from the biosystem structure. / Mitu, LG. (2014). Methods and techniques for bio-system's materials behaviour analysis [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/35445 / TESIS

The master thesis deals with design and comparison of condensing steam turbine for steam-gas cycle for single-cylinder and double-cylinder body with air condenser at its end, one regulated take and ability to use additive steam. Thesis is based on the calculation of thermal scheme which is followed by a preliminary and subsequently a detailed design of steam turbine. Thermodynamic efficiency for single-cylinder turbine was calculated at 93,28 % with terminal power 136,2 MW. The design procedure was repeated for a double-cylinder body. Calculated terminal power for two-cylinder turbine was 134,4 MW with thermodynamic efficiency of 92.1%. By dividing turbine into two rotors resulting low-pressure turbine has a smaller rotor diameter, a longer blade and at the same time a larger number of stages. For double-cylinder turbine, it was necessary to consider twice the number of seals and radial bearings. Due to the increase in flow diameter of low-pressure turbine, losses related to the geometry of the stage increased. Thesis is supplemented by a section drawing of steam turbine with higher efficiency.

The aim of this diploma thesis is the structural design of continous mixer with output range 5-12 tons per hour. The work contains a brief description of mixing technology and basic parameters of similar machines. The work is devoted to the design of double-arm sand mixer with a belt conveyor. An important part of this diploma thesis is a 3D model of fundamental parts of sand mixer, as well as its composition. Based on the 3D model is elaborated strenght analysis of selected parts with finite element method. The work is accompanied by manufacturing drawings of selected components and assembly drawing of deposit of mixing blades to the shaft.

In gas turbines, the temperature behind the combustors is the highest, meaning that the blades in the first stage of the turbine require cooling air. This makes the structural blade model very detailed due to the presence of the cooling pattern. For aeromechanical design, one of the first steps is to perform a modal frequency check by using 3d Finite Element models and the Campbell diagram to establish if the design is acceptable with respect to resonance margins. If the 3d detailed geometry (including all the cooling details) is used the model becomes extremely large. In order to perform various loops between structural dynamics and aerodynamics in an early stage, the dynamic model of cooled blades should be simplified. The simplified model should be accurate enough in terms of predicting correct frequencies but much lighter in size.   The objective of this thesis is to perform parametric studies of different 3d simplified cooled turbine blade models. Various models with different geometrical features are created from the history of the CAD software (NX). Different FE meshes are produced in the Hypermesh software and the modal analyses are solved in Abaqus. The results are compared with the fully detailed model. The influence of the cooling features for each test case is summarized and this will be useful for creating reduced order models. Explanation and guidelines with respect to the mesh generation and loading conditions in Hypermesh software are also included in the appendix section.    For quick frequency checks during the intial stages of the design, the solid blade model can be used which has the modal frequencies within 10 percent range from the fully detailed model. The cooling core features that are important with respect to dynamics are cooling matrix, the ribs and the trailing edge cutback which contribute to the stiffness of the blade.

Flutter is an aeroelastic instability phenomenon that can result either in serious damage or complete destruction of a gas turbine blade structure due to high cycle fatigue. Although 90% of potential high cycle fatigue occurrences are uncovered during engine development, the remaining 10% stand for one third of the total engine development costs. Field experience has shown that during the last decades as much as 46% of fighter aircrafts were not mission-capable in certain periods due to high cycle fatigue related mishaps. To assure a reliable and safe operation, potential for blade flutter must be eliminated from the turbomachinery stages. However, even the most computationally intensive higher order models of today are not able to predict flutter accurately. Moreover, there are uncertainties in the operational environment, and gas turbine parts degrade over time due to fouling, erosion and corrosion resulting in parametric uncertainties. Therefore, it is essential to design engines that are robust with respect to the possible uncertainties. In this thesis, the robustness of an axial compressor blade design is studied with respect to parametric uncertainties through the Mu analysis. The nominal flutter model is adopted from [9]. This model was derived by matching a two dimensional incompressible flow field across the flexible rotor and the rigid stator. The aerodynamic load on the blade is derived via the control volume analysis. For use in the Mu analysis, first the model originally described by a set of partial differential equations is reduced to ordinary differential equations by the Fourier series based collocation method. After that, the nominal model is obtained by linearizing the achieved non-linear ordinary differential equations. The uncertainties coming from the modeling assumptions and imperfectly known parameters and coefficients are all modeled as parametric uncertainties through the Monte Carlo simulation. As iv compared with other robustness analysis tools, such as Hinf, the Mu analysis is less conservative and can handle both structured and unstructured perturbations. Finally, Genetic Algorithm is used as an optimization tool to find ideal parameters that will ensure best performance in terms of damping out flutter. Simulation results show that the procedure described in this thesis can be effective in studying the flutter stability margin and can be used to guide the gas turbine blade design.