Browsing by Author "Duarte, Pedro"
Now showing 1 - 10 of 36
Results Per Page
Sort Options
- Um algoritmo para dimensionamento de ciclonesPublication . Maurício, Pedro; Silva, Pedro; Fonseca, Ana; Duarte, PedroOs ciclones são instrumentos de separação gás-sólido, largamente utilizados na indústria. O seu dimensionamento resulta da conjugação de diversas variáveis que afectam a performance deste equipamento, muitas vezes através de um processo iterativo baseado na experiência do executante, com alguma subjectividade associada. Neste estudo desenvolveu-se um algoritmo de dimensionamento automático de ciclones que permite obter resultados fiáveis, optimizando as dimensões e o número de ciclones e respectivas dimensões a partir de duas restrições – eficiência mínima de captura das partículas e perda de carga máxima do gás. Cyclones are gas-solid separation devices, largely used in industry. The cyclone design process is based on the combination of several variables that influence its performance. This is an iterative process dependent, most of the times, on individual experience. In this study, an algorithm was developed for automatic cyclone designing, which has produced reproducible results, optimizing the dimensions and the number of cyclones given two limiting conditions – minimum particle capture efficiency and maximum head loss.
- Análise e verificação de um modelo ecológico para a Albufeira de Crestuma-LeverPublication . Azevedo, Bruno; Duarte, Pedro; Bordalo, AdrianoA Directiva Quadro da Água coloca uma série de desafios novos à gestão dos recursos hídricos. Estes desafi os poderão implicar a utilização de modelos matemáticos que permitam antecipar os efeitos das acções antropogénicas sobre as águas superfi ciais. Este trabalho tem como principal objectivo apresentar um modelo ecológico da barragem de Crestuma- Lever e os resultados dos primeiros testes efectuados com o mesmo. O modelo foi desenvolvido no âmbito de um dos projectos em que participa o CIIMAR e a Universidade Fernando Pessoa e espera-se que possa vir a ser utilizado como uma ferramenta útil na gestão da barragem de Crestuma-Lever.
- Análise e verificação de um modelo ecológico para a albufeira de Crestuma-LeverPublication . Azevedo, Bruno; Duarte, Pedro; Bordalo, Adriano A.A Directiva Quadro da Água coloca uma série de desafi os novos à gestão dos recursos hídricos. Estes desafios poderão implicar a utilização de modelos matemáticos que permitam antecipar os efeitos das acções antropogénicas sobre as águas superfi ciais. Este trabalho tem como principal objectivo apresentar um modelo ecológico da barragem de Crestuma-Lever e os resultados dos primeiros testes efectuados com o mesmo. O modelo foi desenvolvido no âmbito de um dos projectos em que participa o CIIMAR e a Universidade Fernando Pessoa e espera-se que possa vir a ser utilizado como uma ferramenta útil na gestão da barragem de Crestuma-Lever.
- Analysis of coastal lagoon metabolism as a basis for managementPublication . Duarte, Pedro; Bernardo, João; Costa, Ana; Macedo, M.F.; Calado, Gonçalo; Cancela da Fonseca, LuísThis work was carried out in a shallow eutrophic coastal lagoon (St. André lagoon, SW Portugal) which is artificially opened to the sea each year in early spring. Macrophytes, mainly Ruppia cirrhosa, are keystone species in this ecosystem covering up to 60% of its total area with peak biomasses over 500 g DWm−2. The main objectives were to study ecosystem metabolism, to evaluate the metabolic contribution to the community of the macrophyte stands and their influence in the development of thermal stratification and bottom oxygen depletion. The work combined an experimental and a modelling methodology. The experimental approach included open water, mesocosm and microcosm seasonal experiments. During these experiments several physical, chemical and biological parameters were monitored in the lagoon and in plastic enclosures (mesocosms) for periods of 24 hours. The microcosm experiments followed the light-dark bottle technique. The simultaneous use of these different methodologies allowed the analysis of the contribution of the planktonic and benthic compartments to the ecosystem’s oxygen budget. The modelling work was based on the mathematical simulation of heat and gas exchanges in a vertically resolved water column, under different macrophyte densities. Several simulations were carried out, in order to investigate the importance of the macrophytes in the development of water column stratification and anoxia. The simulation results suggest that macrophytes may greatly influence thermocline and oxycline development. This influence is proportional to their biomass and canopy height. It is suggested that controlled macrophyte biomass removal of up to 25% of available biomass in summer, may be useful in preventing bottom anoxia without compromising benthic net primary production.
- Analysis of the deep chlorophyll maximum across the Azores FrontPublication . Macedo, M.F.; Duarte, Pedro; Ferreira, João; Alves, M.; Costa, V.Physical, chemical and biological observations made in late July and August 1997 across the Azores Front (37ºN, 32ºW to 32ºN, 29ºW) are presented. The objectives of the study were: (1) to analyse horizontal and vertical profiles of temperature, salinity, density, nutrients and chlorophyll-a (Chl a) of the top 350 m; (2) to identify the main differences in the deep Chl a Maximum (DCM) and hydrographic structure between the water masses that pass north and south of the Azores Front; and (3) to estimate phytoplankton primary production in these water masses. Horizontal and vertical profiles of salinity, temperature, density, nutrients and phytoplankton pigments in the top 350 m were analysed. The Front separates two distinct water types: the 18 ºC ModeWater (18MW) of subtropical origin, and the 15 ºC ModeWater (15MW) of sub-polar origin. Differences in the DCM and hydrographic structure between 18 MW and 15 MW were observed in the contour plots of each section. The average Chl a concentration between 5 and 200 m depth decreased significantly from 15 MW to 18 MW. The same pattern was observed for the Chl a concentration at the DCM depth. A vertical one-dimensional model was used to estimate the phytoplankton primary production in the 15 MW and 18 MW and led to an estimated water column average gross primary productivity (GPP) between 1.08 and 2.71 mg C m
- Assessment and comparison of the Marennes-Oléron Bay (France) and Carlingford Lough (Ireland) carrying capacity with ecosystem modelsPublication . Bacher, C.; Duarte, Pedro; Ferreira, João; Héral, M.; Raillard, O.Based on the individual growth, food limitation, population renewal through seeding, and individual marketable size, a theoretical model of the cultured species population dynamics was used to assess the carrying capacity of an ecosystem. It gave a domeshape curve relating the annual production and the standing stock under the assumption of individual growth limited by the available food in an ecosystem. It also showed the influence of mortality rate and marketable size on this curve and was introduced as a means to explore the global properties resulting from the interactions between the ecophysiology of the reared species and the environment at the ecosystem level. In a second step, an ecosystem model was built to assess the carrying capacity of MarennesOl ´eron bay, the most important shellfish culture site in France, with a standing stock of Crassostrea gigas around 100 000 tonnes fresh weight (FW) and an annual production of 30 000 tonnes FW. The ecosystem model focused on the oyster growth rate and considered the interaction between food availability, residence time of the water, oyster ecophysiology and number of individuals. It included a spatial discretization of the bay (box design) based on a hydrodynamicmodel, and the nitrogen or carbon cycling between phytoplankton, cultured oysters, and detritus. From simulations of the oyster growth with different seeding values, a curve relating the total annual production and the standing stock was obtained. This curve exhibited a dome shape with a maximum production corresponding to an optimum standing stock. The model predicted amaximum annual production of 45 000 tonnes FWfor a standing stock around 115 000 tonnes FW. The prediction confirmed some results obtained empirically in the case of MarennesOl ´eron bay and the results of the theoretical model. Results were compared with those obtained in Carlingford Lough (Ireland) using a similar ecosystem model. Carlingford Lough is a small intertidal bay where the same species is cultured at a reduced scale, with current biomass less than 500 tonnes FW. The model showed that the standing stock can be increased from 200 tonnes FW to approximately 1500 tonnes FW before any decrease of the production.
- Avaliação da Capacidade de Carga no âmbito da Gestão Integrada da Zona CosteiraPublication . Duarte, PedroA gestão integrada da zona costeira (GIZC) é um processo de gestão que utiliza uma abordagem integrada, em todos os aspectos da zona costeira, numa tentativa de alcançar a sustentabilidade. A GIZC implica a integração e a coordenação de diversas actividades sendo que algumas podem gerar externalidades para outras. Assim, o processo de tomada de decisão no âmbito de um programa de GIZC é complexo e requer o recurso a bases de dados, sistemas de informação geográfica (SIG), modelos matemáticos, sistemas de apoio à decisão (SAD), etc. A ideia de sustentabilidade está ligada ao conceito de capacidade de carga (CC). Na verdade, a CC será talvez a forma adequada de definir quantitativamente os níveis de sustentabilidade de diferentes actividades e modelos de gestão dos recursos naturais. Em função do exposto, os objectivos desta apresentação são: (i) discutir o conceito de CC ambiental (CCA) e a sua utilização; (ii) apresentar diversos métodos de quantificação da CCA; (iii) apresentar ferramentas de apoio à decisão que permitem integrar o referido conceito e ser um instrumento útil no âmbito da GIZC. Grande parte da discussão vai ser organizada em torno de um estudo de caso concreto relacionado com o problema da CCA – o cultivo de bivalves suspensívoros – em função da importância económica desta actividade em muitas zonas costeiras, da abundância de estudos já efectuados, da familiaridade do autor com o tema e da facilidade de extrapolar diversos conceitos para outras dimensões da CCA.
- Avaliação da capacidade de carga para o cultivo de bivalves filtradoresPublication . Baltazar, João; Lamas, José; Vale, Nuno; Bandeira, Rui; Duarte, PedroA aquicultura de bivalves é uma actividade com uma grande importância económica em diversas regiões, pelo que deve ser dimensionada de modo correcto, para garantir a sua sustentabilidade. Nesse sentido, a determinação da capacidade de carga (CC ) dos ecossistemas costeiros para o cultivo de bivalves é um tema importante. A CC determina-se, geralmente, com recurso a modelos matemáticos. O objectivo deste trabalho é avaliar empiricamente a importância da resolução espacial desses modelos na determinação da CC . Os resultados obtidos põem em causa o desempenho de modelos com uma resolução espacial reduzida, tendentes a estimar por excesso a CC .
- Biogeochemical Modelling of Ria Formosa (South Coast of Portugal) with EcoDynamo - Model descriptionPublication . Duarte, Pedro; Pereira, António; Falcão, Manuela; Serpa, Dalila; Ribeiro, Catarina; Bandeira, Rui; Azevedo, Bruno
- Biogeochemical Modelling of Ria Formosa (South Portugal)Publication . Duarte, Pedro; Azevedo, Bruno; Guerreiro, Maria; Ribeiro, Catarina; Bandeira, Rui; Pereira, António; Falcão, Manuela; Serpa, Dalila; Reia, João; yesRia Formosa is a large (c.a. 100 km2) mesotidal lagunary system with intertidal areas with conflicting uses such as fisheries, aquaculture, tourism and nature conservation. Its watersheds cover an area of approximately 864 km2, with a perimeter of 166 km and a maximum altitude of 522 m. Land use may be classified into six major groups: 1) urban, 2) agricultural, 3) forest, 4) rangeland and pastures, 5) wetlands and 6) water bodies. The main objectives of this work are to: (i) Evaluate the relative importance of land drainage, waste water treatment plants (WTP) and water exchanges across the lagoon inlets, for nutrient dynamics; (ii) Analyse management scenarios related to changes in lagoon bathymetry and their potential effects on system dynamics. The Soil and Water Assessment Tool (SWAT model) has been applied to the catchment areas in order to simulate water discharges into Ria Formosa providing forcing to a twodimensional vertically integrated coupled physical-biogeochemical model, implemented with EcoDynamo – an object oriented modelling software. This model includes water column and sediment processes as well as their interactions and several biological sub-models (e.g. phytoplankton dynamics and bivalve growth). Obtained results suggest that the river network may have a significant effect on lagoon concentrations, in spite of the relatively low river flows, due to the high ammonium and nitrate loads. Scenarios reflecting increases in lagoon bathymetry through dredging operations suggest an increase in lagoon water washout time with potential impacts on water quality and impacts at a scale of tens of km. The obtained results are being used by the Ria Formosa Natural Park authority for management purposes and may be useful to feedback future updates of the watershed management plans, within the scope of the European Union Water Framework Directive. The use of a lagoon scale models is therefore justified in this work