Estudo da implantação offshore de turbina eólica sobre torre treliçada em betão pré-esforçado

Dissertação para obtenção do Grau de Mestre em Energias Renováveis Conversão Elétrica e Utilização Sustentável

Limitações dos sistemas de transmissão AC quando aplicados a parques eólicos offshore

De modo a garantir as metas propostas pela União Europeia de diminuição de emissão de gases poluentes, alguns países membros apostaram na tecnologia eólica offshore. Com a evolução tecnológica, estes países pretendem aumentar as potências instaladas nos parques eólicos offshore, garantindo a sua otimização ao estarem em águas profundas, tendo assim um maior aproveitamento do potencial eólico. Com esta dissertação, realizou-se um estudo para analisar, sob o ponto de vista de modelos, as limitações dos sistemas de transmissão em HVAC (High Voltage Alternating Current) quando estabelecidos em cabos submarinos. Os mecanismos dos sistemas de alimentação em HVAC, na forma tradicional (linhas aérea), são confrontados com condicionalismos. Este tipo de infraestrutura submarina impõe restrições, pelo simples facto dos parâmetros de capacidade e indutância serem bastante significativos, que para uma situação de trânsito de energia, inviabilizam o transporte de energia, devido ao elevado consumo de potência reativa, bem como os seus custos extremamente elevados. Assim, os sistemas de alimentação em HVAC quando aplicados a parques eólicos offshore apresentam limitações. O recurso à tecnologia HVDC (High Voltage Direct Current), poderá ser a solução que se revela mais adequada para os sistemas de transmissão de energia associados aos parques eólicos offshore. Para além dos fatores técnicos é fundamental considerar os custos associados à construção e exploração do parque eólico, sendo fundamental analisar todos os dados relacionados com o projeto.

A method to correct the flow distortion of offshore wind data using CFD simulation and experimental wind tunnel tests

The assessment of wind energy resource for the development of deep offshore wind plants requires the use of every possible source of data and, in many cases, includes data gathered at meteorological stations installed at islands, islets or even oil platforms—all structures that interfere with, and change, the flow characteristics. This work aims to contribute to the evaluation of such changes in the flow by developing a correction methodology and applying it to the case of Berlenga island, Portugal. The study is performed using computational fluid dynamic simulations (CFD) validated by wind tunnel tests. In order to simulate the incoming offshore flow with CFD models a wind profile, unknown a priori, was established using observations from two coastal wind stations and a power law wind profile was fitted to the existing data (a=0.165). The results show that the resulting horizontal wind speed at 80 m above sea level is 16% lower than the wind speed at 80 m above the island for the dominant wind direction sector.

Valuing an offshore exploration project through real options analysis

This thesis applied real options analysis to the valuation of an offshore oil exploration project, taking into consideration the several options typically faced by the management team of these projects. The real options process is developed under technical and price uncertainties, where it is considered that the mean reversion stochastic process is more adequate to describe the movement of oil price throught time. The valuation is realized to two case scenarios, being the first a simplified approach to develop the intuition of the used concepts, and the later a more complete cases that is resolved using both the binomial and trinomial processes to describe oil price movement. Real options methodology demonstrated to be capable of assessing and valuing the projects options, and of overcoming common capital budgeting methodologies flexibility limitation. The added value of the application of real options is evident, but so is the method's increased complexity, which adversely influence its widespread implementation.

Simulation of humidity fields in concrete: experimental validation and parameter estimation

The moisture content in concrete structures has an important influence in their behavior and performance. Several vali-dated numerical approaches adopt the governing equation for relative humidity fields proposed in Model Code 1990/2010. Nevertheless there is no integrative study which addresses the choice of parameters for the simulation of the humidity diffusion phenomenon, particularly in concern to the range of parameters forwarded by Model Code 1990/2010. A software based on a Finite Difference Method Algorithm (1D and axisymmetric cases) is used to perform sensitivity analyses on the main parameters in a normal strength concrete. Then, based on the conclusions of the sensi-tivity analyses, experimental results from nine different concrete compositions are analyzed. The software is used to identify the main material parameters that better fit the experimental data. In general, the model was able to satisfactory fit the experimental results and new correlations were proposed, particularly focusing on the boundary transfer coeffi-cient.

Electromagnetic fields and environmental noise: human health impacts in Serzedelo, Guimarães (Portugal)

The present paper investigates the risks that arise from exposure to noise from powerpoles and powerlines in Serzedelo, in the municipality of Guimarães, in Portugal. This research focused on four guiding questions: Can powerlines cause noise? Do powerlines cause discomfort? Do powerlines cause discomfort due to noise? And can powerlines effect human health? Two groups were the basis of the study: people that were exposed to electromagnetic waves and people that were not. the research pointed to the harmful influence of the presence of powerlines and high-voltage masts in residential areas and the damage to the cells in the human body. This type of environmental noise, which has the spectral content of a low frequency, typically tonal noise and a very high speed of propagation, is a complex source to explain in terms of the health profiles of the human population living in Serzedelo, located in an area that is densely occupied by high voltage powerlines and powerpole.

Simulation of a rectifier malfunction on a offshore wind system with HVDC transmission

A new integrated mathematical model for the simulation of an offshore wind system having a rectifier input voltage malfunction at one phase is presented in this paper. The mathematical model considers an offshore variable-speed wind turbine on a floating platform, equipped with a permanent magnet synchronous generator using full-power three-level converter to inject energy into the electric network, through a high voltage direct current transmission submarine cable. The model for the drive train is a discrete three mass, incorporating the dynamic of the moving surface. A case study is presented to access conclusion about the malfunction.

Chemical and physical attributes and calcium, magnesium, potassium, and phosphorus in the soil of murundu fields in Brazil

Fields of murundus (FM) are wetlands that provide numerous ecosystem services. The objectives of this study were to evaluate the chemical [organic carbon (OC), P, K+, Ca2+, Mg2+, Al3+ and H+Al] and physical [texture and bulk density (Bd)] soil attributes and calculate the organic matter (OM) and nutrient stock (P, Ca, Mg, and K) in soils of FM located in the Guapore River basin in Mato Grosso. Thirty-six sampling points were selected, and soil samples were collected from two environments: the murundu and plain area surrounding (PAS). At each sampling point, mini trenches of 0.5 × 0.5 × 0.4 m were opened and disturbed and undisturbed soil samples were collected at depths of 0-0.1, 0.1-0.2, and 0.2-0.4 m. In the Principal Component Analysis the variables H+Al (49%) and OM (4%) were associated with the F1 component and sand content (47%) with the F2 component. The FM had lower pH values and higher concentrations of K+, P, and H+Al than PAS at all depths (p < 0.05). Additionally, FM stocked up to 433, 360, 205, and 11 kg ha-1 of Ca, Mg, K, and P, respectively, for up to a depth of 0.2 m. The murundu stored two times more K and three times more P than that in the PAS. Our results show that the FM has high sand content and Bd greater than 1.5 Mg m-3, high acidity, low OC content, and low nutrient concentrations. Thus, special care must be taken to preserve FM such that human intervention does not trigger environmental imbalances.

Dynamic potential fields for guided exploration in virtual environments

Dynamic potential fields, guided exploration, virtual environments, navigation

Instability of excitation waves induced by electrical fields

Pyrogallol, uncatalyzed bromate oscillator, electric field, pulse wave, Belousov-Zhabotinsky reaction, reversal

Extraction of topological structures in 2D and 3D vector fields

feature extraction, feature tracking, vector field visualization

Extraction of vortex structures in 3D flow fields

Magdeburg, Univ., Fak. für Informatik, Diss., 2009

Lagrangian methods for visualization and analysis of time-dependent vector fields

Magdeburg, Univ., Fak. für Informatik, Diss., 2013

Shapes in vector fields : methods for continuous deformations and surface-based flow visualizations

Magdeburg, Univ., Fak. für Informatik, Diss., 2013