SAR calculation using FDTD simulations

The main intend of this work, is to determinate the Specific Absorption Rate (SAR) on human head tissues exposed to radiation caused by sources of 900 and 1800MHz, since those are the typical frequencies for mobile communications systems nowadays. In order to determinate the SAR, has been used the FDTD (Finite Difference Time Domain), which is a numeric method in time domain, obtained from the Maxwell equations in differential mode. In order to do this, a computational model from the human head in two dimensions made with cells of the smallest possible size was implemented, respecting the limits from computational processing. It was possible to verify the very good efficiency of the FDTD method in the resolution of those types of problems

Estudo do comportamento de um navio amarrado no Posto "A" do Terminal Petroleiro do Porto de Leixões: construção e calibração do modelo físico (Physical model study of the behavior of a moored ship at the berth "A" Leixões Oil Terminal: Construction and calibration of the physical model)

O comportamento de navios amarrados, e por conseguinte, as condições de operacionalidade e de segurança num dado terminal portuário, não apresenta uma relação simples e directa com as condições ambientais locais. Dada a diversidade e a complexidade dos fenómenos hidrodinâmicos envolvidos, a modelação física e uma ferramenta fundamental para o estudo deste tipo de problemas. Após a caracterização do Terminal Petroleiro do Porto de Leixões e efectuada uma descrição sumaria dos principais problemas que afectam as condições de operacionalidade e de segurança no Posto "A". Com a componente experimental do estudo na sua fase inicial, será dado especial destaque a construção do modelo físico (incluindo os dispositivos de acostagem e amarração, o modelo do navio petroleiro, e a estrutura de acostagem) e aos ensaios de calibração do mesmo. Será também feita referencia as técnicas de experimentação e aos objectivos das fases que compõem o estudo em modelo físico.Moored ship behavior inside harbors, and therefore the operational and security conditions at a port terminal, does not have a straightforward relationship with the local environmental conditions. Due to the diversity and complexity of the involved phenomena, physical modeling is an essential tool to deal with this kind of issues. After the presentation of the Leixoes Oil Terminal, a brief description of the main problems affecting operational and security conditions at the berth "A" is carried out. Being the experimental component of the study in its initial phase, special attention is given to the construction of the physical model (including the berthing and mooring devices, the tanker model and the berthing structure) and its calibration tests. Reference is also made to experimental techniques and to the phases that compose the physical model study

Sensitivity of OWC performance to air compressibility

Air compressibility is often neglected in experimental work due to practical difficulties, even though it is known to affect the performance of OWC wave energy converters. The key question, of course, is to what extent. In this work the impact of air compressibility on the capture width ratio is thoroughly quantified by means of a comprehensive experimental campaign, with no fewer than 330 tests encompassing a wide range of wave conditions and levels of turbine-induced damping, and two experimental set-ups: one designed to account for air compressibility, the other to neglect it. This approach is complemented with the use of the RANS-based CFD model OpenFOAM® to calibrate the pressure-vs-flowrate curves, which enables the flowrate to be determined based on the pressure drop measurements from the physical model. We find that the errors that derive from disregarding air compressibility may lead to either under- or over-predictions of power output, and are highly dependent on the operating conditions, more specifically the wave conditions (sea state) and turbine-induced damping

Analysis of the Portuguese west coast morphology and morphodynamics, based on aerial images and GIS tools

Several areas of the western coast of Portugal are undergoing severe erosion. Accurateknowledge of coastal morphology and morphodynamic characteristics as well as their correlationthrough time is of great importance, not only to identify coastal erosion hazards, but also tounderstand more in-depth the movement of sediments and the action of currents, which are themain coastal processes responsible for erosion.The main goal of this work is to develop a tool capable of performing aerial image analysis,visual and computed, of coastal forms and wave breaking zones The results of this analysis will beintegrated and made available through a GIS database. With this approach, it will be possible totypify, classify and analyse coastal physiography, and the coastline evolution, in a medium to longterm period, as well as the hydromorphologies and coastal forms resulting from the wave action.The first step of this work was to store the available data into a GIS database, namely the imagesfrom the 1996 and 2001 surveys. All the surveys that dont have coordinate systems were georeferencedusing AutoCAD Map 2002 and ArcInfo 7.2.1. In parallel, a tool made with Matlab 7.0 namely itstoolbox image processing is being developed to analyse the stored images. Also, another toolusing Geographical Information Technology (GIT) is being used to perform some more aerialimage analysis.The preliminary results of this work indicate that this approach is satisfactory. The analysissystem is performing well but some improvements can be introduced to the Matlab tool in order tomake it able of processing imagery analysis disregarding its resolution. So far it is still unable toprocess high resolution images which are currently under development

A novel 2-D point absorber numerical modelling method

Despite several wave energy converters (WECs) having been developed to present, no particular concept has emerged yet. The existing inventions vary significantly in terms of the operation principle and complexity of WECs. The tethered point absorbers (PAs) are among the most known devices that, thanks to their simplicity, appear to be cost-effective and reliable for offshore installation. These devices need to be advanced further and, therefore, new tailored modelling methods are required. Numerical modelling of this type of WEC has been done mainly in one degree of freedom. Existing methods for multi-degrees of freedom analysis lack pragmatism and accuracy. Nevertheless, modelling of multiple degrees of freedom is necessary for correct analysis of the device dynamic response, wave loads and device performance. Therefore, an innovative numerical method for two degrees of freedom analysis of PA WECs, which permits precisely modelling the dynamics of PA for surge and heave motions, is introduced in this paper. The new method allows assessing, in the time-domain, the dynamic response of tethered PAs using regular and irregular sea states. The novel numerical model is explained, proved and empirically validated

Análise das marés meteorológicas em Leixões

O efeito das marés meteorológicas no projecto de obras marítimas é muitas vezes subavaliado.Com este trabalho pretende-se, a partir dos registos do marégrafo do Porto de Leixões,quantificar a sua grandeza, utilizando uma aplicação de previsão de marés, de forma a obtervalores dos níveis de água, que foram comparados com os valores reais registados no portoem estudo, para o período compreendido entre 2002 e 2006.O valor máximo obtido para a uma maré meteorológica positiva foi de 1,103m, no dia 20 deOutubro de 2004 e para uma maré meteorológica negativa foi de -0,654m, no dia 2 de Julho de2004. Deve ter-se em conta que na previsão das marés, o número de constantes harmónicasintroduzidos na aplicação foi inferior ao número de constantes necessárias para modelar ofenómeno de forma precisa, resultando em algumas diferenças sistemáticas nos valores finais.Os resultados obtidos foram afectados por alguns factores importantes, como, por exemplo, ofacto de o marégrafo do Porto de Leixões se localizar no interior da zona portuária, numamassa de água confinada pelos quebramares e pelos cais. Os efeitos da maré meteorológicapoderão, portanto, ser influenciados pela própria hidrodinâmica do porto. Como ao longo dosanos a envolvente de infra-estruturas do Porto de Leixões tem vindo a ser significativamentealterada, também os registos das marés meteorológicas locais poderão ter sofrido alterações.PALAVRAS-CHAVE: Maré Meteorológica, Maré Astronómica, Previsão de Marés, Registo deMarés, Dados Meteorológicos

The Conundrum of Specifying very low Wave Overtopping Discharges

The design of certain seawalls / breakwaters has often been required to achieve very low targetovertopping discharges when these structures protect vulnerable infrastructure or activities. Thebalance between economically viable protection and performance requirements is often difficult toachieve without good knowledge on low overtopping. The paucity of data in this space and the highuncertainties associated with existing methods, increase the challenge. The occurrence of a lownumber of overtopping waves has the consequence that any test results are substantially moreaffected by the inherent variation of random waves, therefore more uncertain. The physical model testresults presented hereafter were successful in obtaining low to very low overtopping discharge data.For low / very low overtopping, these test data present considerable scatter relative to the latestempirical prediction. A number of repetitions was performed for conditions giving very low overtoppingdischarges, which illustrated the inherent uncertainty associated with low overtopping

Análise preliminar dos efeitos da alteração da cabeça do quebramar Norte de Leixões no comportamento de um navio amarrado no Posto 'A'

As condições operacionais dos terminais portuários construídos no intradorso de quebramaresexteriores são influenciadas pela agitação marítima que, por difracção, contorna essas obras deabrigo. O artigo apresenta uma análise comparativa preliminar de duas possíveis intervençõesna cabeça do quebramar norte de Leixões, que procuram melhorar as condições operacionais ede segurança de um posto de acostagem próximo. As intervenções estudadas em modelo físicoconsistem no prolongamento de um muro-cortina, na direcção perpendicular ao alinhamento doquebramar norte, e na construção de um "maciço" com uma forma aproximadamente circular(em planta), utilizando blocos de betão dispostos de uma forma irregular. As duas intervençõestêm um efeito positivo no comportamento do navio, pois permitem a redução da amplitude dosseus movimentos. No entanto, a construção do maciço circular mostrou-se mais eficaz do que oprolongamento do muro-cortina. A redução da amplitude significativa dos movimentos do navionão ultrapassa, em geral, os 25%. A eventual optimização dessas intervenções poderá contribuirpara o aumento da sua eficácia