Thesis (M.S.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 57-59). Also available via World Wide Web.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology, 1980. / Microfiche copy available in Archives and Science. / Bibliography: leaves 77-78. / by William Kurt Dewar. / M.S.

Wave Energy Converters (WECs) promise to be a viable alternative to current electrical generation methods. However, these WECs must become more efficient before wide-scale industrial use can become cost-effective. The efficiency of a WEC is primarily dependent upon its geometry and ballast configuration which are both difficult to evaluate, due to slow computation time and high computation cost of current models. In this thesis, we use evolutionary algorithms to optimize the ballast geometry of a wave energy generator using a two step process. First, we generate a function approximator (neural network) to predict wave energy converter power output with respect to key geometric design variables. This is a critical step as the computation time of using a full model (e.g., AQWA) to predict energy output prohibits the use of an evolutionary algorithm for design optimization. The function approximator reduced the computation time by over 99% while having an average error of only 3.5%. The evolutionary algorithm optimized the weight distribution of a WEC, resulting in an 84% improvement in power output over a ballast-free WEC. / Graduation date: 2012

[pt] O crescimento da demanda por serviços de telecomunicações em terra firme também pode ser encontrado em ambientes marítimos por usuários a bordo de embarcações, sejam elas civis ou militares. Nestes ambientes, um fenômeno conhecido como duto de evaporação influencia a propagação eletromagnética na troposfera, proporcionando a comunicação ponto-a-ponto em distâncias além do horizonte rádio. Este trabalho utiliza a técnica de traçado de raios para analisar o comportamento da onda eletromagnética nestes meios. Foi elaborado um algoritmo capaz de traçar raios e determinar amplitudes e fases do campo elétrico em meios inomogêneos bidimensionais dado um mapa de refratividade modificada M. A partir destes mapas, o algoritmo calcula os gradientes verticais de M, que podem variar ao longo do percurso, e traça os raios, a partir da antena transmissora. Como aplicação, além de cenários com dutos de evaporação, foram utilizados mapas de M estimados com base em dados meteorológicos fornecidos por radiossondas lançadas no litoral brasileiro. Os resultados obtidos foram comparados aos fornecidos pelo software Advanced Refractive Effects Prediction System (AREPS), baseado na solução numérica de equação parabólica. Este trabalho também apresenta resultados estatísticos de dutos de evaporação no litoral brasileiro, a partir de dados meteorológicos fornecidos por boias oceanográficas do Programa Nacional de Boias (PNBOIA). Para tal, é utilizado, com pequenas alterações, o algoritmo de Paulus-Jeske, que estima a altura de dutos de evaporação. / [en] The demand growth for land-based telecommunications services can also be found in maritime environments by users on board ships, whether civilian or military. In these environments, a phenomenon known as the evaporation duct influences electromagnetic propagation in the troposphere, providing point-to-point communication at distances beyond the radio horizon. This work uses the raytracing technique to analyze the behavior of electromagnetic waves in these media. An algorithm capable of tracing rays and determining electric field amplitudes and phases in two-dimensional inhomogeneous media was developed, given a map of modified refractivity M. From these maps, the algorithm calculates the vertical gradients of M, which can vary along the path, and traces rays from the transmitting antenna. As an application, in addition to scenarios with evaporation ducts, M maps were estimated based on meteorological data provided by radiosondes launched in the Brazilian coast. The results obtained were compared with those provided by the Advanced Refractive Effects Prediction System (AREPS) software, based on the numerical solution of parabolic equation. This work also presents statistical results of evaporation ducts in the Brazilian coast, based on meteorological data provided by oceanographic buoys of Programa Nacional de Boias (PNBOIA). For this, the Paulus-Jeske algorithm, which estimates the height of the evaporation ducts, is used with small changes.