As expectativas dinâmicas de um mundo de inovações tecnológicas, consubstanciados por explorações menos agressivas ao meio ambiente, dirigidas a um mercado consumista emergente, representam desafios para soluções de problemas de engenharia dirigidos para diversos segmentos da sociedade. Com o desenvolvimento do concreto compactado com rolo (CCR), a partir dos anos 70, o emprego de vertedouros em degraus em barragens de gravidade tornou-se uma solução atrativa, visto que, proporciona, simultaneamente, o aumento da dissipação da energia do escoamento e a redução do tempo e dos custos de implantação dessas obras. Atualmente, têm-se usado como restrições ao seu emprego de vertedouros em degraus valores máximos de vazões específicas que, sem um limite consensual, vêm tolhendo suas potencialidades. A macrorugosidade da calha acelera o processo de aeração do escoamento, se comparado com um vertedouro de soleira lisa, protegendo, para a zona aerada, os degraus contra erosão por cavitação. Entretanto, para o trecho não aerado do escoamento, existem riscos desse processo se estabelecer. As descontinuidades da fronteira sólida propiciam a sucessiva separação da camada limite nos cantos externos dos degraus. Nessa região são geradas pressões muito baixas. O presente estudo, realizado no Instituto de Pesquisas Hidráulicas, objetivou, através de medições experimentais, descrever, caracterizar e modelar pressões hidrodinâmicas nas soleiras dos degraus, estabelecendo limites para incipiência à cavitação no trecho não-aerado do escoamento. Três calhas escalonadas com declividade 1V:0,75H e alturas de degraus iguais a 0,03 m; 0,06 m e 0,09 m foram projetadas e construídas para a investigação. As amostras de pressões registradas com transmissores de pressão a 50 Hz e duração de 3minutos e 12 horas possibilitaram caracterizar o campo de pressão identificando zonas críticas, bem como, avaliando o comportamento estatístico dessas solicitações. As maiores flutuações de pressões foram registradas nas extremidades externas dos degraus e na seção de afloramento da camada limite, chegando a valores negativos de 0,69 vezes a distância vertical entre a crista e a seção analisada. Determinaram-se freqüências dominantes compreendidas entre 7-18 Hz, com valores máximos situados nos patamares dosdegraus. Os números adimensionais de Strouhal, calculados com as freqüências predominantes e as profundidades equivalente do escoamento, diminuíram de 0,40 a 0,04 no sentido do fluxo. Quanto aos limites de incipiência à cavitação, as vazões especificas mais restritivas ao emprego de vertedouros em degraus ficaram na faixa entre 11,3 e 15,6 m²/s com velocidades médias da ordem de 17 m/s, obtidas para a seção de afloramento da camada limite. / Hydraulic researchers have to accomplish the technological and construction materials innovations to new security design project criteria compatible to low costs requirement. At 70’s years, with the development of the Roller Compact Concrete (RCC), the use of stepped spillways has become an attractive solution for gravity dams. In steeply sloping stepped spillways, the large step macro-roughness promotes the occurrence of negative pressures on the step cavity, particularly near the external edge of the vertical step face. Consequently one may expect the occurrence of sub-atmospheric pressure conditions capable to induce cavitation for velocities lower than those observed in smooth chute spillways. Predicting cavitation damage is more complex than predicting cavitation inception. Flow conditions leading to the onset of cavitation are generally conservative in predicting damage. The severity of damage that may be expected is related both to intensity of cavitation and time of exposure. There is still no consensus on the maximum unit discharge or flow velocity which assures cavitation safe design of stepped spillways.The study carried through in the Institute of Hydraulic Research (UFRGS - Brazil), had the main goal: described, characterized and modeled experimental measurements of hydrodynamic pressures on the faces of the steps and established limits of incipient cavitation. Three stepped chutes with declivity 1V:0.75H and 0.03 m; 0.06 m and 0.09 m steps heights were projected. The samples of pressures were registered with pressure transmitters with 50 Hz and 3 minutes duration. Long-duration test were also conducted (12 hours sample size) that permitted characterize the pressure field, identifying critical zones, as well as, evaluating its statistical behaviour. The largest fluctuating pressures had been registered in the outer corner on the steps and at the inception point of air entrainment. At this last position can be expected negative pressure values close to 0.69 times the vertical distance between the crest and the analyzed section. The dominant frequencies found varied between 7-18 Hz. The dimensionless number of Strouhal calculated with the predominant frequencies and the clear equivalent depth, had diminished of 0.40 the 0.04 in the direction of the flow. The pressure measurements indicated specific discharge between 11.3-15.6 m²/s and average velocity in order of 17 m/s to inception cavitation process near the inception point.

Incipient motion criterion in sediment transport is very important, as it defines the flow condition that initiates sediment motion, and is also frequently employed in models to predict the sediment transport at higher flow conditions as well. In turbulent flows, even a reasonably accurate definition of incipient motion condition becomes very difficult due to the random nature of the turbulent process, which is responsible for sediment motion under incipient conditions. This work investigates two aspects, both of which apply to incipient sediment transport conditions. The first one deals with the role of turbulence in initiating sediment motion. The second part deals with the nature of sediment-fluid interaction for more general and complex flows where the number of sediment particles that form the rough surface is varied. The first part of this work that investigates the role of turbulence in initiating sediment motion, uses a video camera to simultaneously monitor and record the sediment (glass ball) motion and corresponding fluid velocity events measured by a three-component laser Doppler Velocimeter (LDV). The results of the single ball experiment revealed that the number of LDV flow measurements increase dramatically (more than four folds) just prior to the ball motion. The fluid mean velocity and its root-mean-square (rms) values also are significantly higher than the values that correspond to the flow conditions that yield no ball motion. The second part of the work, investigation of the fluid-sediment interaction, includes five tests with varying number of sediment particles. In order to understand the nature and extent of fluid-solid interaction, velocity profile measurements using the 3-D laser system were carried out at three locations for each of these five cases. Plots of mean velocities, rms quantities located the universal layer at about 1.5 ball diameters above the porous bed. However, at higher sediment particle concentrations, this distance reduced and the beginning of the universal layer approached the top of the porous bed. / Ph. D.

<p> An experimental study of stratified fluid flow phenomena for two equal depth, different density stratified liquids in a rectangular channel is presented. Two two fluid combinations were used, a sugar water and fresh water, and fresh water and varsol. The critical value of the determined densimetric Froude number at which the upper fluid began to participate in the flow was obtained and found to be 0.28 as against Huber's (1) predicted value of 2.76. It was concluded that the interfacial mixing and viscous effects are largely responsible for this difference. </p> <p> An attempt to extend Harleman's (7) work was made. The results obtained in present work were in good agreement with Harleman's (7) experimental work. </p> / Thesis / Master of Engineering (ME)

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No description available.

This thesis generalizes and interprets Kesten\'s Incipient Infinite Cluster (IIC) measure in two ways. Firstly we generalize Járai\'s result which states that for planar lattices the local configurations around a typical point taken from crossing collection is described by IIC measure. We prove in Chapter 2 that for backbone, lowest crossing and set of pivotals, the same hold true with multiple armed IIC measures. We develop certain tools, namely Russo Seymour Welsh theorem and a strong variant of quasi-multiplicativity for critical percolation on 2-dimensional slabs in Chapters 3 and 4 respectively. This enables us to first show existence of IIC in Kesten\'s sense on slabs in Chapter 4 and prove that this measure can be interpreted as the local picture around a point of crossing collection in Chapter 5.

This thesis generalizes and interprets Kesten\''s Incipient Infinite Cluster (IIC) measure in two ways. Firstly we generalize Járai\''s result which states that for planar lattices the local configurations around a typical point taken from crossing collection is described by IIC measure. We prove in Chapter 2 that for backbone, lowest crossing and set of pivotals, the same hold true with multiple armed IIC measures. We develop certain tools, namely Russo Seymour Welsh theorem and a strong variant of quasi-multiplicativity for critical percolation on 2-dimensional slabs in Chapters 3 and 4 respectively. This enables us to first show existence of IIC in Kesten\''s sense on slabs in Chapter 4 and prove that this measure can be interpreted as the local picture around a point of crossing collection in Chapter 5.

Thesis (MEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Riprap is commonly used as an erosion protection measure around the world. In some cases, for example when constructing bed arrestors, riprap has to be designed to be stable on steep slopes. The literature shows that the problem of incipient motion is reasonably well understood, but existing hydraulic design methods are found to be largely unreliable. The main objective of this study is to improve the understanding of the different factors affecting incipient motion in order to furnish the prospective design engineer with a reliable method for sizing riprap on steep slopes adequately. Eight existing theories dealing with the threshold of incipient motion are reviewed, of which Liu’s work (1957) seems most promising. Naturally, the required median rock diameter of the riprap is reasonably large (due to the steep slopes), with high particle Reynolds numbers. However, little data is available for these flow conditions. Data collected from 12 large scale laboratory tests carried out for this research indicate that the dimensionless Movability Number is in fact constant for large particle Reynolds numbers. For design purposes, the recommended Movability Number which emerged from this study is 0.18, provided that the steep bed slope is taken into account, and that the theoretical settling velocity is calculated using an accurate drag coefficient and the d90 sieve size. A comparison of the laboratory data with design equations showed that a large variety of results are obtained, which supports the need for this study. Finally, it was shown that a calibrated one dimensional hydrodynamic model can be used by the practicing engineer to extract the hydraulic properties needed for applying Liu’s theory. It was found that the ratio ks/d90 = 0.81 may be applied to estimate the bed roughness for the grading used in this study. / AFRIKAANSE OPSOMMING: Stortklip is ‘n metode wat wêreldwyd gebruik word om erosie te voorkom. In sommige gevalle, byvoorbeeld vir die konstruksie van erosietrappe, moet stortklip teen steil hellings spesifiek ontwerp word om stabiliteit te verseker. Die literatuur beskryf die probleem van aanvanklike beweging redelik goed, maar dit is bevind dat die bestaande ontwerpmetodes grotendeels onbetroubaar is. Die hoofdoelwit van hierdie ondersoek was om die faktore wat beweging van stortklip veroorsaak, beter te verstaan en ‘n betroubare metode te ontwikkel wat ’n ingenieur kan aanwend om stortklipbeskerming wat op steil hellings geplaas word te ontwerp. Agt verskillende metodes wat die begin van beweging beskryf is bestudeer, en dit wil voorkom asof die Liu teorie van 1957 die grootste potensiaal het. As gevolg van die steil hellings wat ondersoek word, is die benodigde klipgroote redelik groot wat weereens die oorsaak is vir ‘n hoë deeltjie Reynolds getal is. In die literatuur kon geen data gevind word vir so ‘n vloeitoestand nie. Daarom is 12 laboratoriumtoetse gedoen en daar is gevind dat die Mobiliteitsgetal redelik konstant is vir groot deeltjie Reynoldsgetalle. Vir onwerpdoeleindes word ‘n Mobiliteitsgetal van 0.18 aanbeveel, met die voorwaarde dat die bodemhelling in ag geneem word, en dat die teoretiese valsnelheid bereken word met die d90 klipgroote en ‘n akkurate sleurkoëffisiënt. Verder is gevind dat die labaratorium data die voorspellings van die bestaande ontwerpvergelykings nie bevredigend pas nie. Dit ondersteun die behoefte vir hierdie studie. Om die bogenoemde bevindings vir praktiese probleme bruikbaar te maak, is daar gewys dat ‘n gekalibreerde een dimensionale hydrodinamiese rekenaarmodel gebruik kan word om die nodige hidrouliese eienskappe te verkry om die Liu teorie toe te pas. Dit is bevind dat die verhouding ks/d90 = 0.81 ‘n goeie benadering vir die hidrouliese ruheid kan voorsien.

In this study, we synthesized amphiphilic block copolymer Poly(ethylene glycol)-b-Poly(£`-caprolactone) (PEO-b-PCL), and the mesoporous silica and phenolic were synthesized by using EISA (evaporation induced self-assembly) strategy. The mesoporous carbon also obtained after carbonization. After incorporating the precursors into the mesoporous channels through incipient wetness impregnation and further hydrogen reduction, 3D body-centered cubic (BCC) metal network/silica, metal nanowires/silica, metal/phenolic, and metal/carbon nanocomposites could be obtained. Moreover, metal replica was obtained through HF etching. Transmission electron microscope (TEM) and the small angle X-ray scattering (SAXS) patterns indicate that the parent ordered mesoporous structure was well-maintained during the synthesis process. The X-ray diffraction (XRD) and selected-area electron diffraction (SAED) demonstrate that Pd and Ag were reduced within the channels of mesoporous materials. The pore size distribution and BET surface area of mesoporous materials and metal/mesoporous materials composite were recorded by N2 isotherm adsorption-desorption experiment. In the future, we expect that the mesoporous metal and mesoporous nanocomposite with specific morphologies behave excellent performance in various applications, such as catalysis, gas sensors, nano electronic/optical devices and medical diagnosis.

In this study the incipient motion of coarse solitary particles on channel beds having different roughness heights was experimentally investigated. The experiments were conducted in a tilting flume of a rectangular cross-section having a working length of 12 m and a rough bed composed of at least 2 layers of coarse gravel of almost constant size. The roughness material of the channel bed was changed three times. The slope of the channel bed and the discharge are two main parameters that determine the initiation of motion of a given particle. The artificial particles tested in the experiments were obtained by mixing cement and iron dust at certain ratios. Dimensionless hydraulic parameters determined from theoretical analysis were related to each other. Flow depths, velocity profiles were measured and flow conditions that represent the critical conditions of initiation of motion were expressed in terms of critical velocities and shear velocities. The results were compared with the previous studies&rsquo / results.