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In the research herein presented, mode III and mode I fatigue loading tests were carried out on standard compact tension (CT) specimens using a bi-axial servo-hydraulic Instron 8874 machine. Thin sheet CT specimens were made of two types of austenitic stainless steels, namely an AISI 316L stainless steel and a high-strength Cr-Mn stainless steel. Specimens were pre-cracked in mode I, at room temperature, and crack growth paths were experimentally determined. Fracture surfaces of rectangular sections were observed using optical devices and crack growth revealed to be higher at the external surfaces than at the mid plane of the specimens tested under mode III fatigue loading; in addition, smooth slant crack growth occurred, as well as crack branching. Fracture surfaces obtained under mode I loading revealed that crack grew flat, coplanar and normal to the tensile axis, as expected. Additionally, stress intensity factors present at tip of each branch crack loaded under mode III were calculated through finite element analyses (FEA). Hence, although an out-of-plane torsional loading was remotely applied, a mixture of modes was foreseen to be applied locally at crack tip during crack growth, namely mode I, mode III and mode II loading, in that order of relevance, and equivalent stress intensity factor values at the crack tip were calculated using Pook, Richard or Schollmann et al. criterion.

The main purpose of the research presented herein was to study the fatigue crack propagation under loading modes I, II or III, either for plane strain or plain stress state. Therefore, several finite element analyses (FEA) were carried out and some experimental tests were performed in a bi-axial servo-hydraulic machine. J-integral values were determined through numerical simulations and stress intensity factors, K I , K II and K III were inferred at the crack tip of both thick and thin C(T) specimens, assuming several crack’s lengths, and either for plane strain or plane stress state. Load opening-mode I shown to be the predominant mode of crack propagation under plane-strain state, leading to the highest J-integral values calculated, followed by Mode III. In addition, shearing load (mode II) induced the lowest stress intensity factor values at the crack tip both for plane stress state and for plane strain state. Finally, some fatigue crack growth rates (FCG) were determined under loading modes I or III, for thin specimens, at room temperature. C(T) specimens used in the experimental tests were made of two austenitic stainless steels, namely the AISI 316L and the Cr-Mn stainless steel, which are commonly used in several specific engineering applications. Results were compared and some conclusions could be drawn.

Ocean circulation models are frequently used in maritime Search and Rescue operations due to their skill in simulating the effects of local currents on the transport of people or objects. They are also occasionally used in forensic contexts. Frequently, positively or neutrally buoyant passive particles are used in these simulations, as a proxy for the ‘objects’ in the study. In this paper, the adequacy of passive particle model simulations is tested in an attempt to reproduce the drift of a real case situation. The case study consists of a drowning accident in which the drift was ~2 km for a post-mortem submersion interval (PMSI) of 8.6 days. The simulation results highlighted the limitation of the methodology to predict the correct drift. However, we discuss the shortcomings of the modelling approach, and suggest ways to improve the skill of such numerical tools in predicting body drift after drowning accidents.

Fatigue crack growth (FCG) could be encountered in many mechanical components, which can be made from either thin or thick steel plates (or shells) and, therefore, be subjected to a plane-stress or a plane-strain condition, respectively. The loads applied in a solid body containing a narrow notch or a sharp crack will induce a yield zone near its tip with a dimension that will depend on the mechanical properties of the material, as well as on the thickness of the body, the crack length and the magnitude of the loads applied. Crack propagation can then occur under mode I, II, III or mixed-mode for general loading. The paper presents JI, JII and JIII integral functions, which were correlated with the elastic stress intensity factors KI, KII and KIII, for thin and thick CT specimens. The evaluation of J-Integral values was carried out for different crack lengths, along the crack front, and using the Finite Element Method (FEM), with collapsed nodes and midside nodes dislocated to ¼ of the edge's length, in order to simulate the crack tip singularity. Interaction between in-plane, in-plane sliding and out-of-plane modes are also discussed in the paper. In addition, FCG rates under mode I, mode III and a mixed-mode (mode I+III) were experimentally determined, at room temperature, for a high-strength Cr-Mn austenitic stainless steel.

This paper presents the structure and application of a regional scale operational modelling tool for the West Iberian coast, and discusses its potential for products and services for both scientific and coastal management activities. The forecasting suite includes nested hydrodynamic models forced with up-to-date meteorological forecast data and large-scale model results. The present status of the system and its recent upgrades are reviewed, offering a general description of the main components of the system: the forcing data, the circulation model, the model outputs and the validation methodology of model results. Seasonal differences in temperature, salinity and current velocity fields are illustrated and show satisfactory reproduction of the top and deep layer thermodynamics. The system provides boundary forcing for a number of local-scale model applications via downscaling of the solution and enables potential products and services from which civil society will benefit.

High-resolution hydrodynamic models are a common tool to simulate water dynamics in estuaries. Results from these models are, however, difficult to interpret without the aid of additional parameters to integrate the information. In this paper a methodology to understand the transport patterns in the Tagus Estuary is proposed. It is based on the computation of two renewal time scales: residence time and integrated water fraction. This last parameter is used to build a dependency matrix that gives the integrated influence of each region of the estuary at a selected point. The parameters are computed using a Lagrangian transport model coupled to the hydrodynamic model. Results show that Tagus Estuary has two different types of regions: the central part of the estuary, with low renewal efficiency, and three regions with higher renewal efficiency. Renewal mechanisms are, however, different for each region as shown by the dependency matrix. Comparison of renewal time scales with results from a water-quality model revealed that residence time is not a limiting parameter for primary production in the Tagus Estuary.

Las trayectorias de las gotas simuladas con el modelo 3-D de dispersión de petróleo en la plataforma del mar Caribe colombiano mostraron que las gotas con diámetro de 50 μ m , forman una pluma subsuperficial, la cual es transportada horizontalmente y puede permanecer debajo de la superficie por largo tiempo. Esta pluma podría tener un impacto muy restringido, porque la dispersión es controlada solamente por las corrientes oceánicas, las cuales a 1000 metros de profundidad, tienen baja intensidad y son poco turbulentas. En este caso, la pluma formada permanece atrapada a 1000 metros de profundidad, no poniendo en riesgo la costa Caribe. En contraste, las gotas con diámetros de 250 μ m , 1mm y 10 mm, se elevaron rápidamente a la superficie, aun con diferentes velocidades (6, 10, 20 ms-1).

Mixing between estuarine and coastal waters is strongly dependent on the processes that occur in the vertical direction. This applies both for stratified and homogeneous estuaries. In homogeneous estuaries important recirculation flows in the vertical plane can arise, in regions with strong batimetry gradients, produced by the combined action of inertia and friction. On the Platform close to the inlet this structures can trap estuarine water during the ebb period, releasing it to the interior again during the flood.

Forecasting estuarine circulation is in high demand, especially in regions of high population density like Santos region. Present work intends to optimize the performance of the water level forecast for Santos Estuary, particularly, the physical forcing determining the residual tide. In extreme cases, predicted and observed water level can significantly differ, increasing significantly the predicting errors, which highlights the need to understand the factors that affect the residual tide to propose corrective measures. Furthermore, the extreme events have potentially hazardous consequences not only for navigation purposes, as also to the population that live nearby the channels. This dissertation analyzes the water level and significant wave height dataset covering the period of 2016 to 2017. Datasets comprehend 5 tide gauge stations in Santos channel and were obtained from the Pilotos da Barra and Praticagem. MOHID 2D hydrodynamic model (www.mohid.com) was used, implemented with a nested downscaling approach, being linked to AQUASAFE software that provides high-resolution forecast to give support to navigation in real-time. The model was validated for the period of 2016-2017, being minimum RMSE found of 12.5 cm and practically all stations present an excellent SKILL. The most recent astronomical global solution (FES2014) was implemented as oceanic boundary condition. Additionally, the meteorological boundary condition (CMEMS) was altered from daily to hourly data. It was also researched the possible influence of wave height on the forecast of water level (particularly the residual tide). Due to the great correlation found among these parameters, a linear regression method was developed to correct in post-processing stage the residual tide under specific wave height conditions. The appliance of distinct boundary conditions on forecasting models (meteorological and astronomical) decreased errors when compared to observations, evidencing the improvement of forecast capacity. On the other hand, the use of FES2014 shows improvements at the bay entrance, however, results get worst in the inner stations. This portrays the need of reliable bathymetric data due to increasing errors on the astronomical tidal components towards the end of the estuary. Residual tide errors remain practically constant along the estuary, however, they increase under extreme conditions. The results evidence that model modifications improve the accuracy in reproducing the water level evolution, comparing to the previous version, particularly under extreme events Atualmente, a previsão da circulação estuarina é um tópico de grande importância, especialmente em regiões com elevada densidade populacional, como é o caso da região de Santos. O presente trabalho pretende optimizar a qualidade da previsão do nível de água no estuário de Santos, particularmente os forçamentos físicos que determinam as marés residuais. Em casos extremos, os níveis de água observados e previstos podem diferir significativamente, aumentando os erros de previsão, revelando a importância da compreensão destes fenómenos, para proposta de medidas corretivas. Estes eventos têm consequências tanto para as atividades de navegação portuária, como para as populações que habitam nas zonas marginais ao estuário. A presente dissertação analisa dados observados do nível de água e altura significativa da onda, para o período de 2016 a 2017. Os dados utilizados foram registados em 5 estações e foram cedidos pelos Pilotos da Barra e Praticagem. Foi utilizado o modelo hidrodinâmico MOHID 2D (www.mohid.com), usando um método de "downscaling", conectado ao software AQUASAFE que fornece previsões de alta resolução para auxílio em tempo-real à navegação. O modelo foi validado para o período de 2016-2017, sendo que os valores mínimos RMSE foram de 12.5 cm e praticamente todas as estações apresentaram um SKILL excelente. Foi implementada a mais recente solução global astronómica (FES2014) como condição de fronteira oceânica. Adicionalmente, foi alterada a implementação da condição fronteira oceânica meteorológica (CMEMS) de dados diários para horários. Foi ainda estudada a possível influência da altura significativa da onda na previsão do nível de água (particularmente na maré residual). Devido à grande correlação encontrada entre ambos os parâmetros, foi desenvolvida uma metodologia de regressão linear para correção em pós-processamento da maré residual para determinadas condições de agitação marítima. A aplicação de diferentes condições fronteira nos modelos preditivos (meteorológico e astronómico) diminuíu os erros das previsões numéricas, o que claramente melhorou a capacidade preditiva dos modelos. No entanto, a aplicação da solução FES2014 apesar de reduzir os erros na embocadura do estuário, conduz ao seu aumento nas zonas interiores. Este resultado indica a necessidade da obtenção de novos dados batimétricos, considerando que os erros na componente astronómica de maré aumentam em direção à cabeceira do estuário. Os erros da maré residual mantêm-se praticamente inalteráveis ao longo das estações, sendo superiores em situações de tempestade. Os resultados evidenciam que as modificações do modelo melhoram a precisão na reprodução do nível de água, comparando com a versão anterior, particularmente no caso de ocorrência de eventos extremos Mestrado em Ciências do Mar e da Atmosfera

Submitted by Cristina Santos (cmaria@ua.pt) on 2019-12-03T10:11:08Z No. of bitstreams: 1 Documento.pdf: 8901963 bytes, checksum: a32ad21b0299566bd2917b67db121853 (MD5) Made available in DSpace on 2019-12-03T10:11:08Z (GMT). No. of bitstreams: 1 Documento.pdf: 8901963 bytes, checksum: a32ad21b0299566bd2917b67db121853 (MD5) Previous issue date: 2018-12-21 Mestrado em Ciências do Mar e da Atmosfera

Doutoramento em Física O principal objectivo deste trabalho consistiu no estudo da dinâmica termohalina do Canal do Espinheiro em função de dois forçamentos principais: maré e caudal fluvial, usando duas abordagens distintas: trabalho experimental e modelação numérica. A propagação da maré e o caudal fluvial do Rio Vouga são determinantes no estabelecimento da estrutura horizontal da salinidade ao longo do canal. A estrutura térmica horizontal ao longo do canal é, em grande parte, determinada pela variação sazonal da temperatura da água do Rio Vouga, bem como, pela variação sazonal das condições meteorológicas devido à reduzida profundidade. Foi observada a formação de fortes gradientes de salinidade (relacionados com a formação de frentes estuarinas) numa região a cerca de 7-8 km da embocadura do canal, observando-se a sua migração numa região de aproximadamente 1 km, dependendo do regime de maré. O balanço entre o transporte de sal de natureza advectiva e difusiva foi calculado, revelando que junto à embocadura os processos físicos que mais contribuem para o transporte de sal são a circulação residual e o aprisionamento da água em canais secundários. Junto à foz do Rio Vouga os termos devidos à descarga fluvial e à circulação gravitacional dominam o transporte de sal. Foi calibrado e validado um modelo numérico (Mohid, em modo 2D e 3D), sendo posteriormente utilizado para estudar a hidrologia do canal. Foi concedida particular atenção ao estudo da hidrologia em condições extremas de caudal fluvial e de maré. Os resultados da modelação numérica permitiram numa primeira fase avaliar o bom desempenho do Mohid na reprodução dos escoamentos barotrópicos na Ria de Aveiro, bem como na evolução temporal das propriedades termohalinas da água. Sob condições de caudal fluvial reduzido, a dinâmica do canal é essencialmente dominada pela maré. Com o aumento do caudal fluvial, a influência da água doce estende-se para jusante, estratificando a coluna de água. As simulações 3D do Canal do Espinheiro foram efectuadas para períodos marcadamente diferentes de caudal fluvial e de maré. O modelo reproduziu qualitativamente/quantitativamente as observações de alturas de água, velocidade e distribuições longitudinais de salinidade e temperatura sob um regime fraco a médio de caudal fluvial. Sob condições de caudal fluvial elevado, os resultados mostram que o modelo subestima a estratificação. Este estudo contribuiu para o aumento do conhecimento da dinâmica do Canal do Espinheiro, bem como para o desenvolvimento de um sistema numérico capaz de reproduzir e prever os processos de transporte de sal e calor. The main objective of this work was to study the Espinheiro channel’s thermohaline dynamics as a function of two major forcings: tides and river inflow using field experiments and numerical modelling simulations. The salinity distribution along the channel was found closely related to the incoming river flow and tidal propagation. The water temperature distribution is related to the freshwater temperature seasonal variation and, due to the shallowness of the study area, it is also related to the seasonal variation of meteorological conditions. The formation of strong salinity gradients (commonly related to estuarine fronts) has been found in a region between 7 and 8 km from the lagoon’s mouth. These gradients migrate within a region of about 1 km, depending on the tidal regime (spring or neap). The balance between the advective and diffusive salt transport was assessed. Near the channel’s mouth, the main contributions to the salt transport are due to the residual circulation (or freshwater discharge) and tidal correlation. Near the channel’s head, this last term is not as important as the gravitational circulation. The Mohid numerical model was calibrated and validated (both in 2D depth integrated and 3D modes), and then used to study the channel’s hydrography. The channel’s hydrography was studied under extreme conditions of tides and river inflow. The model results allow the evaluation of Mohid in reproducing the barotropic flows and the time evolution of salinity and water temperature within Ria de Aveiro. Under low river inflow regimes, the channel’s dynamics is tidally dominated. Under high river inflow, the freshwater from Vouga extends its influence downstream until the channel’s mouth, increasing the water column stratification. The three-dimensional simulations of the Espinheiro Channel were performed under markedly different tides and river runoff. Under low-to-medium river inflow, the model reproduces qualitatively/quantitatively sea level height, current velocity and longitudinal distributions of salinity and water temperature, underestimating salinity stratification when the river inflow is high. The residual circulation was calculated revealing an ebb-dominated channel. When the river inflow is high, the channel is nearly laterally homogeneous in terms of salinity and current residual velocity, presenting a two-layer structure with flood currents close to the bottom and ebb currents close to the surface. This study has contributed for the characterization and understanding of the dynamical behaviour of the Espinheiro Channel, as well as to develop a numerical system of 2D and 3D numerical models able to reproduce and predict transport processes there occurring.