Un des enjeux importants de l’écologie est de comprendre comment les pratiques anthropiques affectent la biodiversité et quelles en sont les conséquences sur le fonctionnement des écosystèmes. L’objectif de cette thèse est d’améliorer la compréhension des mécanismes régissant les communautés végétales aquatiques, et plus particulièrement ceux liés aux perturbations anthropiques et aux phénomènes d’eutrophisation. Les méta-écosystèmes constitués de réseaux d’étangs agro-piscicoles sont des modèles d’étude adaptés à notre problématique car ils sont sous forte pression anthropique et présentent une forte variabilité environnementale. Dans un premier temps, nous avons étudié l’impact des modes de gestion des bassins versants sur l’eutrophisation des étangs. Dans un second temps, nous avons mesuré l’effet de l’eutrophisation sur la productivité et la diversité des communautés phytoplanctoniques. Enfin, nous avons relié 3 types de contraintes générées par les pratiques anthropiques (l’eutrophisation, l’assèchement et la connectivité entre les étangs) sur les communautés de plantes aquatiques en termes de diversité spécifique et fonctionnelle. L’effet de l’eutrophisation, le recrutement et l'établissement des communautés des plantes aquatiques a été abordé au travers de la relation entre la banque de graines et la végétation établie. L’eutrophisation est le facteur majeur responsable de la diminution de la biodiversité végétale dans les étangs. Cependant les perturbations récurrentes constituées par les assecs, engendrent une succession cyclique qui contribue à maintenir une forte biodiversité dans les étangs. / One important issue of research in Ecology is to understand how anthropogenic activities are influencing biodiversity and what are the consequences on ecosystem functioning. The aim of the study is to improve the knowledge of the mechanisms governing aquatic plant communities, particularly those related to human disturbance and eutrophication. Meta-ecosystems constituted by networks of fish-farming shallow lakes are study models adapted to our problematic because they are submitted to a strong anthropogenic pressure and because they show a high environmental variability. First, we studied the impact of watershed management practices on shallow lakes eutrophication. In a second step, we measured eutrophication effect on productivity and on diversity of phytoplankton communities. Finally, we were able to link 3 types of constraints generated by human practices (eutrophication, drying and connectivity between shallow lakes) to aquatic plant communities in terms of specific and functional diversity. The impact of eutrophication, recruitment and establishment of aquatic plant communities has been approached through the relationship between the seed bank and established vegetation. Eutrophication is the major factor responsible for the loss of plant biodiversity in shallow lakes. However frequent disturbances due to drying events induce a cyclic succession that helps maintain a high biodiversity.

In this paper, a new algorithm for utilizing energy storage is proposed and applied on floating wind turbine economics. The proposed algorithm’s decision making on storing energy or selling electricity onto the grid is based on the electricity price, which makes it unique and different from similar algorithms. From the literature review, it was concluded Ocean Renewable Energy Storage to be most suitable with the Spar-Type and Semi-Submersible floating wind turbine to which the paper is based upon. The objective of this paper is to find the suitable ratio of energy storage versus wind farm, find the product of increase in wholesale, and evaluate whether the proposed method makes the hybrid economically sound. The algorithm was applied on spot-price data from Denmark due to its large share of wind energy with wind data from off the coast of Morro Bay in California, USA. Additionally, a sensitivity analysis is applied to evaluate to energy storage cost impact as well as evaluate the algorithm by lowering the required energy storage size.   Using the algorithm, the wind farm must account for nine days’ worth of energy production with a product of energy storage versus wind farm ratio of 1.42. The wholesale price increased with 11.9-21.5% for the four years studied, however, all financial results favored not utilizing energy storage. By the results derived from the sensitivity analysis, it was concluded that with future cost reductions, the algorithm will still favor no energy storage. However, by fine tuning the algorithm to reduce the need for storage, positive financial result might be achievable. The key to achieve a profitable result seems to rely on minimizing the need for energy storage, to which the proposed algorithm fail to achieve. Conclusively, spot-price decision-based energy storing is not economically sound.

This thesis focused on investigating flow, coherent structures, and mechanisms leading to scour around a series of three submerged groynes in a high curvature (radius of curvature (R)/channel width (B)=1.5) channel bend using a Large Eddy Simulation Numerical (LES) model. Flow was investigated during both an initial and a later stage of scour. The results showed that the groynes appeared effective in keeping the main core of high streamwise velocity away from the outer bank wall in the region where they were installed, although high potential still existed for local scour around the groynes. During the initial stage of scour, horseshoe vortices (HVs) showed the greatest propensity to induce scour immediately upstream of the groyne tips. During the later stage of scour, the HV in front of the first upstream groyne (G1) induced very high mean pressure fluctuations on the outer bank wall. Scour was also of very great concern around the tip of G1 due to severe mean bed pressure fluctuations. Downstream of the groyne field, the presence of a counter-rotating outer bank cell was capable of endangering the stability of the outer bank. The second focus of this thesis was to investigate flow in a 135° channel bend using both Reynolds Averaged Navier Stokes (RANS) and LES numerical models. The RANS study examined the effects of curvature ratio (R/B), and aspect ratio (B/H, where H is the inlet flow depth), on secondary circulation strength, and bed shear stresses. The study revealed that a decrease in R/B was associated with an increase in secondary circulation strength and peak bed shear stress. A change in B/H also substantially affected cross stream circulation strength. The LES study was conducted in a 135° (R/B = 1.5) bend flume with a fixed bed corresponding to near equilibrium scour conditions, and the results were compared to a similar high curvature 193° bend numerical study. Inner bank vortices and shear layers were present in both cases although their characteristics were substantially different. Distributions of boundary friction velocities, and turbulence were also quite different for each case.

In the continuous casting of steel, the Submerged Entry Nozzle (SEN), in particular the SEN geometry, has a primary influence on the flow pattern: the SEN controls the speed, direction and other characteristics of the jet entering the mould. The SEN is however relatively inexpensive to change (in comparison with other continuous casting equipment). Thus; there is a feasible incentive to exactly understand and predict the flow of molten steel through the SEN and into the mould, in order to maximise the quality of the steel by altering the design of the SEN. By changing the SEN geometry and SEN design, the flow pattern in the mould will also change: it is thus possible to obtain an optimum SEN design if (or when) the desired flow patterns and/or certain predetermined temperature distributions are achieved. Expensive and risky plant trials were traditionally utilised to “perfect” continuous casting processes. As opposed to the plant trials, this dissertation is concerned with the Computational Fluid Dynamics (CFD) modelling of the SEN and mould, which, when used in conjunction with the Mathematical Optimiser LS-OPT, will enable the optimisation of the SEN design to achieve desired results. The CFD models are experimentally verified and validated using 40%-scaled (designed and built in-house) and full-scale water model tests. This dissertation proves that the CFD modelling of the SEN and mould can be quite useful for optimisation and parametric studies, especially when automated model generation (geometry, mesh and solution procedures) is utilised. The importance of obtaining reliable and physically correct CFD results is also emphasised; hence the need for CFD model verification using water modelling. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2007. / Mechanical and Aeronautical Engineering / unrestricted

Made available in DSpace on 2017-06-01T18:20:30Z (GMT). No. of bitstreams: 1 dissertaca-_marcelo_silva.pdf: 974611 bytes, checksum: 8bf2b65106d8d1d7d04ec3c0dd5827f6 (MD5) Previous issue date: 2011-03-17 / The production of protease and biosurfactant by Bacillus licheniformis UCP-1014 was investigated in this work. The experiments were performed in Erlenmeyer flasks, in triplicate, and inoculum 10% v/v, 150 rpm and 37ºC. A factorial design was conducted to investigate the concentrations of the medium. Metabolic fluid samples were collected, centrifuged and the supernatant used to determine pH, proteolytic activity and surface tension. The liquid was concentrated by ultrafiltration metabolic the stability and proteolytic activity in the retentate was determined for pH and temperature. In making the retentate was used a factorial design, and protease stability was determined during 10, 20 and 30 days at 28ºC. The determination of protease was performed in the presence of azo-casein. The culture of B.licheniformis UCP-1014 produced 112 U/mL protease in the presence of 1% molasses and urea 0,5%, pH 7,5 at 24h of culture. The reduction in surface tension was not significant in these metabolic conditions. The concentration of proteases produced by B. licheniformis UCP-1014 had the highest stability of enzyme activity in the absence of substrate at pH 7 during 60 min of incubation and maximum thermal stability between 40 90ºC for 90 min. The liquid concentrate and formulated metabolic retained about 50% of proteolytic activity whose value decreased during storage at 28ºC. Proteases produced by B. licheniformis UCP-1014 in the presence of nutrients of low cost can be competitive in the market / A produção de proteases e biossurfactantes por Bacillus licheniformis UCP-1014 foi investigada neste trabalho. Os experimentos foram realizados em frascos de Erlenmeyer de 125 mL, em triplicata, inóculo 10% v/v, a 150 rpm e 37ºC. Um planejamento fatorial foi realizado para investigar as concentrações dos componentes do meio de cultivo. Amostras de líquido metabólico foram coletadas, centrifugadas e os sobrenadantes utilizados para determinar pH, atividade proteolítica e tensão superficial. O líquido metabólico foi concentrado por ultrafiltração e a estabilidade da atividade proteolítica no retentado foi determinada quanto ao pH e à temperatura. A estabilidade do retentado foi investigada por planejamento fatorial e a atividade proteolítica determinada com 10, 20 e 30 dias de armazenamento a 28 ºC. A determinação de proteases foi realizada na presença de azo-caseína. A cultura de B. licheniformis UCP-1014 produziu 112 U/mL de proteases na presença de melaço 1% e uréia 0,5%, a pH 7,5 com 24 h de cultivo. A redução da tensão superficial do líquido metabólico não foi significativa nessas condições de trabalho. O líquido metabólico concentrado reteve cerca de 50% da atividade proteolítica inicial. O concentrado de proteases apresentou a maior atividade enzimática em pH 8 durante 30 min de incubação, retendo 97 % da atividade; a estabilidade térmica máxima foi a 50ºC durante 30 min, retendo 98 % da atividade enzimática. O retentado do líquido metabólico após formulado manteve 54 % da atividade com 30 dias de armazenamento a 28ºC. Proteases produzidas por B. licheniformis UCP-1014 na presença de nutrientes de baixo custo podem ser competitivas no mercado

A utilização do eletrodo tubular no processo de soldagem a arco submerso leva a um aumento na produtividade com um custo relativamente baixo, pois não requer investimentos complementares em equipamentos. A mudança do eletrodo sólido para o tubular acarreta variações microestruturais no metal de solda que influenciam as propriedades mecânicas, tais como dureza, tração e tenacidade ao impacto. Este trabalho tem como objetivo principal estudar a tenacidade à fratura dinâmica do metal de solda, mostrando que o uso do eletrodo tubular diminui a propagação de trincas ao impacto, além de melhorar as propriedades de dureza e tração. Para a confecção da junta soldada foi utilizado o aço ASTM-A516 com espessura de 37,5 mm; para o metal de solda, o eletrodo sólido AWS EM12K, com diâmetro de 4,0 mm, e fluxo AWS F6A4 e o eletrodo tubular AWS E71T-5, com diâmetro de 4,0 mm, fabricado em caráter experimental, untamente com os fluxos AWS F6A4 e AWS F7A8 (Fluxo Neutro). Os ensaios de impacto, dureza e tração foram realizados em corpos de prova com e sem alívio de tensão, e o ensaio Charpy instrumentado em corpos de prova entalhados e em corpos de prova entalhados e com trinca por fadiga, nas temperaturas de 25, 200, 400 e 600OC. O metal de solda utilizando eletrodo sólido foi o que mostrou menor percentual de ferrita acicular (54%), enquanto que o utilizando eletrodo tubular e fluxo AWS F6A4 foi o que mostrou maior percentual de ferrita acicular (89%). Os ensaios de dureza mostraram uma influência do microconstituinte ferrita acicular: maior dureza para o maior percentual de ferrita acicular. Os limites de resistência e de escoamento também sofreram o efeito deste microconstituinte, apresentando maiores valores quando os percentuais de ferrita acicular foram maiores. Para a análise da tenacidade para o início de propagação da trinca foram utilizados os métodos da variação da taxa da flexibilidade elástica, o método da energia da carga máxima revisada e o método da energia da carga máxima. Foram calculados os valores de JId e de KJd (K derivado de J). Os únicos valores validados, de acordo com a norma, foram os de JId calculados pelo método da variação da taxa da flexibilidade elástica. Os resultados encontrados, utilizando este método, mostraram, à 600OC, a influência da ferrita acicular, sendo que o metal de solda com maior percentual deste microconstituinte forneceu maior valor de tenacidade. Os valores de JId utilizando o método da variação da taxa da flexibilidade elástica para os corpos de prova com trinca por fadiga ficaram próximos aos resultados encontrados quando o ensaio foi realizado em corpos de prova somente entalhados. Os resultados mostraram que a substituição do eletrodo sólido pelo tubular levou à maior tenacidade e a propriedades mecânicas superiores. / The cored wire application in the submerged arc welding process leads to a increase productivity with relative low cost, because it doesn’t require complementary investments in equipments. Changing from solid to cored wire promotes microstructural modification in the weld metal that enhances mechanical properties, such as hardness, stretching and impact toughness. The principal aim of this work is to study the dynamic fracture toughness of the weld metal. The use of cored wire reduces the impact crack propagation, as well as hardness and strength properties. The welded plate was composed of ASTM-A516 steel with 37.5 mm thickness and for making the weld metal was utilized AWS EM12K wire, with 4.0 mm diameter, and AWS F6A4 flux, and AWS E71T-5 cored wire, with 4.0 mm diameter, making in experimental mode, with AWS F6A4 and AWS F7A8 (Neutral Flux) fluxes. Impact, hardness and tensile tests were carried out in specimens with and without stress relief. The instrumented Charpy tests were carried out at notch and notch plus fatigue crack specimens, at 25, 200, 400 and 600OC temperatures. The solid wire weld metal produced 53.9% of acicular ferrite, while the cored wire weld metal and AWS F6A4 flux produced 88.8% of acicular ferrite. The hardness values were influenced by acicular ferrite and showed higher hardness for acicular ferrite higher values. Tensile strength and yield stress data suffered the same effect of this micro constituent also, they had bigger amount when the acicular ferrite percentiles were bigger. For toughness analysis to crack propagation start were utilized the compliance changing rate method, the energy revised method, and the maximum load energy method. JId and KJd (K derived of J) values were calculated according to the standards. The results met for this method had acicular ferrite influence at 600OC, where the weld metal with the biggest micro constituent had bigger toughness value. The JId values utilized the compliance changing rate method for the precracked specimen got values near to the notched specimen. The change solid wire by the cored wire had better toughness, and it gets better the other mechanical properties.

This diploma thesis deals with submergence of low rectangular sharp-edged broad-crested weirs. From measurement of water levels in front of and behind of weir at different discharges and different weir heights, were determined values of submergence coefficient depending on relative height of submergence. From these values were determined the equation of submergence coefficient. Measured values were compared which results measurements, which are given in professional literature.

Wood is a widely used construction material that has many advantageous properties, and some drawbacks. These drawbacks are mainly associated with the porous vascular structure of wood that makes it a high water-absorbent material. In addition, wood’s properties alter substantially with respect to the moisture content. Amongst the treatment techniques that limit the water uptake capacity of wood, vacuum-aided impregnation has exhibited promising results. However, little research has explored the effect of key parameters (such as the vacuum pressure) on the effectiveness of the impregnation. This study aims to optimize the performance of SiO2 impregnation of spruce wood under vacuum pressures. The main objective of this research is to overcome wood’s weakness by reducing its water uptake capacity through a vacuum-aided impregnation technique and study its effect on the physico-mechanical properties of wood under dry and saturated conditions. The study was conducted in two parts. In the first part, wood samples underwent impregnation under atmospheric and three vacuum pressures. Density measurements, water uptake tests, microscopy examination, thermogravimetric analysis, and dynamic mechanical analysis were conducted on non-treated and SiO2-treated samples. Quantitative and qualitative analyses demonstrated that SiO2 impregnation performed under -90 kPa was able to effectively enhance the wood’s properties compared to the other conditions. The SiO2 impregnation under high vacuum pressure demonstrated an effective increase in the density of the wood and achieved a significant reduction in the water uptake capacity. The analysis of the wood’s viscoelastic properties revealed that SiO2 impregnation under atmospheric and vacuum conditions triggered two different reinforcing mechanisms: a solid film, causing stick-slip oscillation, and particle diffusion, causing particle-particle and particle-lumen wall friction, respectively. For the second part, characterization methods such as Impact test, DMA, SEM, EDS, Porosity, and SAXS tests were conducted on non-treated and -90 kPa treated spruce wood samples in dry, saturated, and submerged states in order to reveal the synergistic effect of the SiO2 impregnation pressure and water uptake on the wood’s properties. The results showed that high vacuum impregnation pressure has a significant positive reinforcing effect on the wood’s properties. It increased the impact resistance of wood in dry and saturated conditions. A high vacuum impregnation was able to overcome the softening effect of water and caused a significant increase in the Storage modulus by strengthening the wood’s vascular structure, which accordingly increased the wood’s capacity to absorb energy. High vacuum impregnation was also able to counteract the plasticizing effect of water and significantly increased the Loss modulus by increasing the internal friction in the wood with the diffusion of the nanoparticles in the wood’s cell walls and vascular structure. This phenomenon increased the wood's capacity to absorb and dissipate energy under dry and submerged conditions.

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