Orientador: João Batista Aparecido / Banca: Jose Luiz Gasche / Banca: Paulo Gilberto de Paula Toro / Resumo: Cavitação em bombas centrífugas é a formação de bolhas de vapor do fluido bombeado na região de sucção do equipamento. As bolhas de vapor formadas em algum local do escoamento, em geral na região de sucção da bomba, entrarão posteriormente em colapso. Este fenômeno é importante cientificamente, tecnicamente e economicamente. Cientificamente é interessante, pois envolve o escoamento de um fluido em estado líquido, simultaneamente ocorre a formação de bolhas de vapor, que também escoam juntamente ao fluido líquido. O processo de vaporização e condensação de um fluido é complexo, pois envolve mudança de fase, um fenômeno térmico não linear. Tecnicamente, é importante porque quando o escoamento se dá com cavitação os parâmetros hidrodinâmicos do escoamento bem como da bomba, em geral, são fortemente alterados na direção termodinâmica de maior produção de irreversibilidades. Economicamente, é custoso porque a cavitação, em geral, leva a perda de eficiência termodinâmica dos processos e em conseqüência haverá maior custo na produção de um dado bem, diminuindo a eficiência econômica e a competitividade da empresa. O escoamento com cavitação na sucção de bombas apresenta três aspectos danosos principais: cavitação pulsante com baixa vazão; cavitação não pulsante com baixa altura útil; e erosão cavitacional. A cavitação pulsante é caracterizada por grande formação de bolhas de forma transitória com baixa freqüência e grande amplitude, gerando forças vibratórias importantes no sistema de bombeamento. A cavitação pulsante também causa colapso do fluxo de massa do fluido bombeado com valores que vão do fluxo normal da instalação até valores quase nulos, transitoriamente. Na cavitação pulsante a erosão cavitacional e a queda na altura útil são pequenas... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Cavitation in centrifugal pumps is the development of vapor bubbles from the pumped liquid into equipment suction region. Vapor bubbles developed somewhere in the flow, generally in the pump suction, will afterwards along the flow to collapse. This phenomenon is scientifically, technically and economically important. Scientifically, it is interesting because involves the flow of a fluid on liquid state, and simultaneously happens vapor bubbles development that also flow together the liquid fluid. Fluid vaporization and condensation processes are complex because involves phase change, a non-linear thermal phenomenon. Technically, it is important because when the flow happens with cavitation the flow and pump hydrodynamic parameters, generally, are strongly modified toward bigger thermodynamic irreversibility production. Economically, it is expensive because cavitation, generally, leads to thermodynamic process efficiency loss, and consequently it will have bigger costs for production of a given good, then decreasing economic efficiency and company competitiveness. Flow with cavitation in the pump suction presents three main devastating aspects: surging cavitation with low flow rate; steady cavitation with low total head; and cavitational erosion. Surging cavitation is characterized by unsteady, low frequency and high amplitude, intense bubbles development, producing strong vibration forces into the pumping system. Surging cavitation also causes the collapse of pumped fluid mass flow rate with values that goes from the normal flow to values that almost reach the zero flow, unsteadily. In surging cavitation, the cavitational erosion and the breakdown in total head are small. In steady cavitation the mass flow rate, and even the flow rate... (Complete abstract click electronic access below) / Mestre

The performance of building envelopes and roofing systems significantly depends on accurate knowledge of wind loads and the response of envelope components under realistic wind conditions. Wind tunnel testing is a well-established practice to determine wind loads on structures. For small structures much larger model scales are needed than for large structures, to maintain modeling accuracy and minimize Reynolds number effects. In these circumstances the ability to obtain a large enough turbulence integral scale is usually compromised by the limited dimensions of the wind tunnel meaning that it is not possible to simulate the low frequency end of the turbulence spectrum. Such flows are called flows with Partial Turbulence Simulation. In this dissertation, the test procedure and scaling requirements for tests in partial turbulence simulation are discussed. A theoretical method is proposed for including the effects of low-frequency turbulences in the post-test analysis. In this theory the turbulence spectrum is divided into two distinct statistical processes, one at high frequencies which can be simulated in the wind tunnel, and one at low frequencies which can be treated in a quasi-steady manner. The joint probability of load resulting from the two processes is derived from which full-scale equivalent peak pressure coefficients can be obtained. The efficacy of the method is proved by comparing predicted data derived from tests on large-scale models of the Silsoe Cube and Texas-Tech University buildings in Wall of Wind facility at Florida International University with the available full-scale data. For multi-layer building envelopes such as rain-screen walls, roof pavers, and vented energy efficient walls not only peak wind loads but also their spatial gradients are important. Wind permeable roof claddings like roof pavers are not well dealt with in many existing building codes and standards. Large-scale experiments were carried out to investigate the wind loading on concrete pavers including wind blow-off tests and pressure measurements. Simplified guidelines were developed for design of loose-laid roof pavers against wind uplift. The guidelines are formatted so that use can be made of the existing information in codes and standards such as ASCE 7-10 on pressure coefficients on components and cladding.

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Introduktion – En fråga har väckts kring hur jordtryck beräknas enligt en klassiskjordtryckteori som beskrivs i läroböcker så som (Sällfors,2009), Trafikverket krav och Eurocode av företaget Vara byggkonsult AB. För att skapa en bättre förståelse så togett praktiskt test fram för att mäta jordtrycket utifrån klassiska teorier och jämförs med dessa.Metod – Den valda forskningsmetoden är en litteraturstudie och ett experimentellkvantitativ test. Framtagandet av testet är en iterativ process där metod och utformande uppdaterats efter observationer och diskussion.Resultat – Beräknade värden för den aktiva jordtryckskoefficienten med de olika metoderna varierar mellan 0,221 - 0,278 för materialet 0–4 och mellan 0,25 - 0,334 för materialet 8-16 beroende på vilken metod som avvänds. För de uppmätta värdena så varierar dessa från 0,173 - 0,279 för materialet 0–4 och 0,227 – 0,296 för materialet 8–16 beroende på vilken last som tillförts. Att värdena varierar beror på faktorer så sominre friktionsvinkel, friktion mellan stödvägg och material, beräkningsmetod, samt vilken last som använts vid utfört test.Analys – Genom att jämföra beräkningsmetoderna med de uppmätta testvärdena går det att se likheter och skillnader mellan resultaten. För materialet 0–4 går det att se en likhet mellan de beräknade värdena och de uppmätta värdena för de beräkningsmetoder där friktionen antas vara 0. För materialet 8–16 är det uppmätta värdet konstant lägre än de beräknade för alla beräkningsmetoder. För båda materialtyperna går det att se en trend där ökningen i det uppmätta värdet minskar ju högre last som läggs på.En analys utifrån frågeställning två har gjorts där modellen och metoden för utförandet av det praktiska testet analyserats. De resultat som producerats ur modellen är trovärdiga och är upprepbara till hög grad. Modellen har konstruerats med material och verktyg tillgängliga i en vanlig bygghandel. Materiallista samt ritning på konstruktionen har dokumenterats samt att metoden för genomförande av testerna är väl dokumenterad.Utifrån en analys av fraktionsstorlekens påverkan på det uppmätta trycket observeras det att ett finkornigt material som 0–4 kan uppnå ett högre tryck än ett grövre material som 8–16. De utförda testen stödjer detta då materialet 0–4 resulterar i en högre jordtryckskoefficient än materialet 8–16. Detta är dock motsägelsefullt till hur klassiskt sett så sker det en ökning i friktionsvinkel desto större fraktionsstorleken är.Diskussion – Trafikverkets metod att beräkna jordtryckskofficienten anses vara smidigare att använda i jämförelse med Eruocdes sätt, då det inte krävs mer än ett uppskattande av materialets egenskaper.Faktorer så som mänskliga faktorn är något som också tas upp i rapporten som har haft en inverkan på det slutgiltiga resultatet samt utförandet av tester. Att rita upp en modell digitalt med perfekta linjer är en sak, men att bygga ihop den i verkligheten är en annan sak. För att motverka faktorer så som mänskliga faktorn, så har en rad olika förändringar gjort på modellen samt utförandet av testerna. Enligt de resultat som framtagits så syns det att det finns en skillnad mellan de olika materialen, men detta är inte en stor skillnad. Friktionsvinklarna för materialen skiljer ivsig inte med många grader och därför har inte heller en stor kraftskillnad kunnat uppmätas.Då grundkunskapen vid undersökningens start inte var speciellt hög så lede det tillmisstag som kunde undvikits. Den tid som lagts ner på att fixa de misstagen kunde istället lagts ner på att förbättra modellen för att få ännu bättre värden. / Introduction – A question has been raised regarding how earth pressure is being calculated regarding classical textbook theory, the Swedish Transport Administration and Eurocode by the company Vara byggkonsult AB. To create a better understanding of the subject a practical test is being derived from classical theories and compared to these.Method – The chosen research method is a litterature study and an experimental quantitative test. To produce a test an iterative process is being used that is beeing updated according to observations and discussions.Results – Calculated values for the active earth pressure coefficient with the different methods vary between 0,221 – 0,278 for the material 0-4 and between 0,25 – 0,334 for the material 8-16 depending on which method is used. For the measured values, these vary from 0,173 – 0,279 for the material 0-4 and 0,227 – 0,296 for the material 8-16, depending on the load added. The fact that the values vary depends on factors such as internal friction angle, friction between the supporting wall and material, calculation method and which load was used when the test was carries out.Analysis – By comparing the calculation methods with the measured test values, it is possible to see similarities and differences between the results. For the material 0-4, it is possible to see a similarity between the calculated values for the calculation methods where the friction is assumed to be 0. For the material 8-16, the measured value is constantly lower than the calculated values for all calculation methods. For both material types, a trend can be seen where the increase in the measured value decreases the higher the load that is applied. An analysis based on question two has been done where the model and method for preforming the practical test has been analysed. The results produced from the model are credible and are repeatable to a high degree. The model has been constructed with materials and tools available in a regular hardware store. Material list and drawing of the construction have been documented and that the method for carrying out the tests is well documented.Based on an analysis of the effect of fraction size on the measured pressure, it is observed that a fine-grained material such as 0–4 can achieve a higher pressure than a coarser material such as 8–16. The tests carried out support this as material 0–4 results in a higher earth pressure coefficient than material 8–16. However, this is contradictory to how, classically speaking, there is an increase in friction angle the larger the fraction size is.Discussion – The Swedish Transport Administration's method of calculating the earth pressure coefficient is considered easier to use in comparison to Eruocde's method, as no more than an estimation of the material's properties is required.Factors such as the human factor is something that is also addressed in the report that has had an impact on the final result as well as the execution of tests. Drawing up a model digitally with perfect lines is one thing, but building it in real life is another. To counteract factors such as the human factor, a number of different changes have been made to the model and the execution of the tests.According to the results produced, it appears that there is a difference between the different materials, but this is not a big difference. The friction angles of the materials iido not differ by many degrees and therefore a large force difference has not been measured either.As the basic knowledge at the start of the survey was not particularly high, it led to mistakes that could have been avoided. The time spent on fixing those mistakes could instead be spent on improving the model to get even better values.

Splitter plates are passive flow control devices for reducing drag and suppressing vortex shedding from bluff bodies. Most studies of splitter plates involve the flow around an “infinite” circular cylinder, however, in the present study the flow around a surface-mounted finite-height circular cylinder, with a wake-mounted splitter plate, was studied experimentally in a low-speed wind tunnel using a force balance and single-component hot-wire anemometry. Four circular cylinders of aspect ratios AR = 9, 7, 5 and 3 were tested for a Reynolds number range of Re = 1.9×10^4 to 8.2×10^4. The splitter plates had lengths, relative to the cylinder diameter, of L/D = 1, 1.5, 2, 3, 5 and 7, thicknesses ranging from T/D = 0.10 and 0.15, and were the same height as the cylinder being tested. The cylinders were partially immersed in a flat-plate turbulent boundary layer, where the range of boundary layer thickness relative to the cylinder diameter was δ/D = 1.4 to 1.5. Measurements were made of the mean drag force coefficient, the Strouhal number at the mid-height position, and the Strouhal number and power spectra along the cylinder height. For all four finite circular cylinders, the splitter plates were effective at reducing the magnitude of the Strouhal number, and weakening or even suppressing vortex shedding, depending on the specific combination of AR and L/D. Compared to the case of an infinite circular cylinder, the splitter plate is less effective at reducing the mean drag force coefficient of a finite circular cylinder. The largest drag reduction was obtained for the cylinder of AR = 9 and splitter plates of L/D = 1 to 3, while negligible drag reduction occurred for the shorter cylinders.