Este trabalho tem por objetivo estudar através de simulações numéricas a interação fluido-estrutura de um escoamento ao redor de um cilindro livre para vibrar na direção transversal do escoamento, com o objetivo de compreender melhor o fenômeno muito recorrente em estruturas oceânicas, principalmente os dutos de extração de petróleo, chamados risers. A condição a ser estudada é a de escoamento com número de Reynolds igual a 10000, em um cilindro com parâmetro de massa igual a 3,3 e de amortecimento igual a 0,0026. Nestas condições, diversos modelos serão criados para representar toda a faixa de velocidades reduzidas em que ocorre o fenômeno de sincronização. Estes parâmetros foram escolhidos devido à presença de dados experimentais para o comparativo entre as simulações e os dados experimentais, que será apresentado ao final do trabalho. Resultados como a média do coeficiente de arrasto e o RMS do coeficiente de sustentação também serão comparados com dados experimentais disponíveis na literatura e uma análise dos perfis de escoamento na região da esteira é feita para a identificação de padrões recorrentes nestes tipos de caso. / The objective of this work is to study through numerical simulations the fluid-structure interaction in a cylinder, which is free to oscillate in the cross flow direction, aiming to better comprehend the phenomena that frequently appears in offshore structures, mainly in pipelines for oil extraction, called risers, The studied condition is a flow with Reynolds 10000 around a cylinder with mass ratio of 3.3 and damping factor of 0.0026. Under these conditions, multiples models are created to represent the reduced velocities range where the synchronization phenomena happen. Those parameters were chosen due to the availability of experimental data in the literature, which allows the comparison between the simulations and experiments that is presented in the end of the work. Results such as the drag coefficient mean and the lift coefficient RMS are also compared with the experimental data available in the literature and an analysis of the flow in the wake region is done with the intention of identifying the patterns found in this type of case.

Uma parte significativa das perdas por atrito num motor automotivo resulta da ação de partículas abrasivas. Dentre as fontes possíveis, podem ser citados o próprio meio ambiente - partículas que passam pelo filtro de ar - o desgaste de partes metálicas do motor ou mesmo resíduos de combustão. Essas partículas podem ficar encrustadas em anéis do pistão, ou ficar na interface entre pistão e bloco ou camisa, e são responsáveis por sulcos axiais, na direção do movimento do pistão, observáveis em motores usados. O objetivo deste trabalho foi obter um melhor entendimento dos mecanismos de desgaste relacionados com o sulcamento de camisa/bloco e identificar conjuntos de testes laboratoriais capazes de reproduzi-los sob condições controladas. Amostras de ferro fundido cinzento (FoFo) e de aço AISI 1070 com dureza de matriz próxima daquela encontrada em FoFo (?200HV30) foram submetidas a ensaios de riscamento em tribômetros. Verificou-se que riscos executados com um endentador cônico submetido a cargas na faixa de 20 a 50 mN eram similares aos sulcos observados em camisas ou blocos. Ensaios com outros materiais, como alumínio e latão e mesmo aço de diferentes durezas contribuíram para melhorar o entendimento dos resultados. Não foi observada transição brusca entre mecanismos de abrasão. O cálculo do fator de remoção de material, fab, a partir de perfilometria óptica resultou em valores com dispersão elevada; não foi possível associa-los aos diferentes mecanismos de abrasão observados. Valores obtidos para o coeficiente de atrito no riscamento permitiram fazer uma estimativa inicial de energia gasta nos processos abrasivos do motor. / A significant part of the friction losses in an automotive engine results from the abrasive action of particles. Among possible sources of such particles one can mention the environment - particles that were not retained by the filters - metallic residues from worn parts or even combustion residues. They may be picked up by piston rings and become part of their surfaces or stay loose in the piston/liner interface. Those particles are responsible for axial grooves that are observed in the liners of used engines. The objective of this work was to get a better understanding of the wear mechanisms related to liner/bore grooving and to identify a laboratory testing setup that might reproduce them under controlled conditions. Specimens of Gray Cast Iron (GCI) and of AISI 1070 steel with matrix hardness close to that found in GCI (?200HV30) were submitted to scratch tests in a tribometer. It was found that scratches performed under 20-50 mN indenter load (conical tip) were similar to grooves observed in cylinder liners. Tests with other materials such as aluminum, brass and even steel with different hardness values contributed to a better understanding of the results. No sharp transition between abrasion mechanisms was observed. Calculation of material removal factor fab from optical profilometry resulted in values with a large dispersion; they could not be associated with different abrasion mechanisms. Friction coefficient values obtained from the tests were used to make preliminary estimates of energy consumption due to abrasive processes in the engine.

The transportation sector continues to be a primary source of greenhouse gas (GHG) emissions, contributing more than any other sector in the United States in 2017. Medium-duty and heavy-duty trucks trail only passenger cars as the largest GHG contributor in this sector [1]. The intense operating requirements of these vehicles create a reliance on the diesel engine that is projected to last for many decades. Therefore, it is vital that the efficiency and environmental sustainability of diesel engines continue to be advanced.<br><br>Cylinder deactivation (CDA) is a promising technology to improve diesel engine fuel efficiency and aftertreatment thermal management for emissions reduction. This work presents original experimental results demonstrating fuel efficiency improvements of CDA implemented on a modern engine at idle operating conditions through testing of various CDA configurations. Idle calibration optimizations result in up to 28% fuel consumption reduction at steady-state unloaded idle operation and 0.7% fuel consumption reduction over HD-FTP drive cycles at equivalent emissions levels. The low-load thermal management performance of CDA is also investigated through creep and extended idle transient cycles, during which CDA is shown to reduce fuel consumption by up to 40% with similar thermal management performance and reduced NOx and soot emissions. <br><br>Variants of CDA implementation are explored through an experimental comparison of deactivation strategies. The effort described here compares charge trapping strategies through examination of in-cylinder pressures following deactivation because: (1) choice of trapping strategy dictates the in-cylinder pressure characteristics of the deactivated cylinders, and (2) deactivated cylinders can affect torque, oil consumption, and emissions upon reactivation. Results discussed here suggest no significant differences between the strategies. As an example, the in-cylinder pressures of both trapping strategies are shown to converge as quickly as 0.8 seconds after deactivation.<br><br>Finally, the NVH effects of CDA are characterized through studies of torsional vibration, linear vibration, and acoustics. CDA causes frequency content at reduced frequencies compared to conventional operation, which has effects on all aspects of NVH. This creates possible constraints on achievable fuel efficiency and thermal management performance by restricting CDA usage. An alternate form of CDA, dynamic cylinder activation (DCA), is explored as a possible option of avoiding undesirable frequency output while maintaining the desired engine performance. <br>

A previsão e entendimento da formação de tensões residuais oriundas da têmpera plena ou superficial nos aços tem sido objeto de estudo por um número considerável de pesquisadores, devido ao seu grande interesse tecnológico. Neste trabalho o objetivo principal consistiu no desenvolvimento de um modelo numérico para a previsão das tensões residuais em peças cilíndricas temperadas por indução. A têmpera por indução executada num componente previamente \"beneficiado\", isto é, temperado e revenido, é capaz de produzir uma camada superficial de alta dureza e tensões compressivas num núcleo resistente e tenaz. É esperado, entretanto, que o aumento da camada endurecida possa gerar tensões trativas indesejáveis abaixo da superfície, comprometendo a integridade estrutural do componente e levando as falhas prematuras. Portanto, neste trabalho ênfase foi dada no estudo da influência da profundidade de camada induzida no perfil e magnitude das tensões residuais em corpos de prova cilíndricos (c.ps.) de aço. O método de elementos finitos foi adotado para a solução do problema térmico (distribuição de temperatura) e estrutural (cálculo das tensões) com o emprego do programa ANSYS 5.3. Os efeitos metalúrgicos da mudança de fase Austenita - Martensita, responsável pelas altas tensões compressivas residuais na superfície, como resultado da expansão volumétrica inerente a esta transformação, foi modelado através de uma rotina FORTRAN especialmente desenvolvida neste trabalho e acoplada ao programa ANSYS 5.3. A criação da geometria do modelo e passos da solução foram automatizados através do uso da linguagem paramétrica APDL (ANSYS Parametric Design Language) do programa ANSYS 5.3. Trata-se de um problema termo-elasto-plástico onde as propriedades termo-físicas e mecânicas necessárias para o cálculo foram consideradas dependente da temperatura. Verificação e calibração do modelo computacional foi efetuada através da medição das ) tensões residuais em c.ps. cilíndricos de aço com o emprego da técnica de difração de raios X. Finalmente, são discutidos aspectos de precisão e principais fontes de erro, como também proposta de melhorias e futuras aplicações deste modelo. / Large efforts have been made to predict and understand the residual stresses formation in through hardening and case hardening of steel. In the present work the objective was to develop a model to predict the residual stresses in induction hardening of cylindrical steel bars. Induction hardening, i.e. electromagnetic heating and subsequent quenching, is a surface treatment of great use in industry because it is suitable to improve locally mechanical properties of the high stressed regions of the part. A hard surface layer with high compressive residual stress is normally obtained, while retaining ductility and toughness in the core. Applied to components that undergo severe duty cycles, such as gears, shafts axles and bearings, it is also clean, fast and suitable for on-line applications. It is expected however, that increasing the hardening depth leads to undesirable high subsurface tensile stress, which can cause premature failure of the component. Emphasis has been on investigating the influence of case depth on the residual stress distribution of the cylindrical steel specimens. A finite element model was developed to compute the temperature history, phase transformation and residual stress for the induction hardening process. The Austenite to Martensite phase transformation during quenching, responsible for the high surface compressive stress, as result of volume expansion, was evaluated by a custom FORTRAN routine linked to the ANSYS5.3 FEA code. The model geometry and solution process were automated by the use of ANSYS Parametric Design Language (APDL). The thermoelastoplastic behavior of the material was studied, considering material properties temperature dependent. The results of the calculations have been compared to experimental measurements of the residual stresses at the surface, using X Ray diffraction technique. Finally, accuracy and main source of erros are discussed. Future improvements and applications of this model are proposed.

Esta tese apresenta o desenvolvimento e aplicação de modelos de turbulência, transição laminar-turbulenta e de interações fluido-estrutura ao escoamento externo em cilindro rígido estacionário e em vibrações induzidas por vórtices. Tais desenvolvimentos foram realizados no código ReFRESCO, baseado em técnicas de dinâmica de fluidos computacional (CFD). Realizou-se um estudo quanto ao desempenho do modelo k- SST em extensa faixa de números de Reynolds, segundo o qual se identificaram as deficiências de modelagem para este escoamento. A modelagem adaptativa das escalas (SAS) e o modelo de transição por correlações locais (LCTM), ambos combinados ao SST, melhoraram a aderência aos resultados experimentais para este escoamento, em uma contribuição original deste trabalho. A aplicação de técnicas de verificação e validação possibilitou a estimação de incertezas e erros para os modelos e números de Reynolds e também de identificada como outra contribuição deste trabalho. A combinação da modelagem em SST, SAS e LCTM com movimentos impostos de realizada para números de Reynolds moderados, diferentes frequências e amplitudes de vibração, algo que poucas publicações abordam em detalhes. Com relação aos movimentos livres, este trabalho traz contribuições com a aplicação dos modelos SST e SAS ao estudo de vibrações induzidas por vórtices em dois graus de liberdade, baixa razão de massa e números de Reynolds moderados, mais altos do que normalmente observados na literatura. Por fim, a investigação da importância relativa de efeitos da turbulência aos casos de movimentos livres e impostos, com relação ao caso de cilindro estacionário, comprovou a conjetura formulada na parte inicial deste trabalho, no que tange à escolha do modelo de turbulência em determinadas aplicações. Tal escolha mostrou-se menos decisiva no caso do cilindro em movimento imposto e ainda menos nos movimentos livres, em comparação ao caso estacionário, uma vez que a resposta em movimentos do corpo filtra grande parte dos efeitos turbulentos de ordem superior. Esta observação mostra-se relevante, uma vez que pode permitir simplificações na modelagem e aplicação de ferramentas de CFD em uma classe importante de projetos de engenharia. / This thesis presents the development, implementation and application of turbulence and laminar-turbulent transition models and fuid-structure capabilities to address the vortexshedding and vortex-induced vibrations of a rigid cylinder. These numerical developments have been carried out in the computational fuid dynamics (CFD) code ReFRESCO. In the current work, an investigation of the performance of the turbulence modeling with k- SST in a broad range of Reynolds numbers is carried out identifying its modeling deficiencies for this fow. The implementation and systematic application of the scale adaptive simulations (SAS) and the local correlation transition model (LCTM), both combined with the SST, have improved the agreement with experimental results for the cylinder ow, in a novel contribution of this work. The application of verification and validation technique has allowed the estimation of numerical errors and uncertainties for the diferent models. That is also identified as a contribution of this thesis. The combination of SST modeling with imposed motions is carried out as well as with the SAS and LCTM for moderate Reynolds numbers, diferent vibration frequencies and amplitudes, which is considered novel, as few publications address this issue in extent. Regarding the free-moving cylinder capabilities, the present work brings contributions with the application of SST and SASSST with free-moving cylinder for the study of VIV of two degrees of-freedom, low mass ratio and moderate Reynolds numbers, higher than commonly seen in the literature. Finally, the investigation of the relative importance of turbulence effects on the freemoving cylinder and the imposed-motions case, with respect to the fixed case is carried out. A natural conjecture that has been raised early on this work and proved correct is that, for engineering applications, the choice of turbulence modeling strategy is less decisive when the cylinder is moving with prescribed motion and even less stringent, for free motions as the body response filters most of the higher order turbulence effects. That is a relevant observation as it might allow modeling simplifications and the application of CFD tools to a range of engineering problems.

Les phénomènes d’interaction fluide-structure jouent un rôle important dans le calcul de tenue au séisme des assemblages combustibles. Afin de quantifier les marges de dimensionnement, le modèle de forces fluides utilisé doit être validé et affiné. Pour cela, des campagnes d’essais à l’échelle industrielle ont été réalisées en amont de la thèse. L’objectif ici est de contribuer à l’interprétation des essais industriels pour le cas stationnaire, et de valider les méthodes numériques permettant de simuler ce type d’écoulement. La problématique industrielle s'inscrit dans la tradition de l'étude des structures élancées sous écoulement axial. Le modèle de force fluide locale généralement utilisé, que nous appelons modèle de Taylor-Lighthill-Païdoussis (TLP), consiste en stationnaire à combiner un terme de force fluide potentielle, proportionnel à la courbure, et un terme de force fluide visqueuse, proportionnel à la pente. Des versions dynamiques de ce modèle ont été employées avec succès pour prédire le comportement vibratoire de cylindres flexibles en écoulement axial. Néanmoins, la littérature propose très peu de données de validation directe de cette représentation des forces fluides. Afin d’acquérir de telles données, pour le cas particulier d’un cylindre confiné dans un réseau de cylindres, un nouveau banc d’essai a été conçu et mis en place au laboratoire. Il s’agit d’un faisceau de 3x3 cylindres disposé dans une veine de soufflerie. Le cylindre central possède trois degrés de liberté : rotation, translation, flexion. Les efforts fluides résultants sont mesurés à l’aide d’une balance. Un modèle numérique similaire à la maquette est aussi réalisé et donne accès aux forces fluides locales. Les forces globales obtenues numériquement et expérimentalement sont comparables. Les forces locales obtenues dans les simulations numériques s’expliquent bien à l’aide du modèle TLP, en ignorant les effets de bord à l’entrée et à la sortie du faisceau. La transposition au cas industriel, de géométrie plus complexe, est réalisable par recalage des coefficients du modèle. / Fluid-structure interaction phenomena play a major role in the seismic design of fuel assemblies. In order to evaluate the design margins, the implemented model of fluid forces needs to be carefully assessed. Industrial-scale tests have been carried out with that purpose. Our goal is to contribute to their interpretation in the steady case, and to validate CFD methods usually applied to the type of flow at stake here. This fits in the tradition of the study of slender structures in axial flow. The local steady fluid forces decompose in a potential term, which is proportional to the curvature of the structure, and a viscous term, proportional to the angle of incidence. Adapted versions of this representation, which we call Taylor-Lighthill-Païdoussis (TLP) model, have proved successful in predicting the dynamic behaviour of flexible cylinders in axial flow. However, there is a lack in the literature of sound validation data for the fluid forces themselves. In order to gather such data, a new test rig has been designed and built. It consists in a 3x3 cylinder bundle confined in a wind tunnel. The central cylinder can be rotated, translated or bent. Resultant fluid forces are measured using a load cell. CFD calculations give access to the local fluid forces. CFD and experiments give similar results on the global fluid forces. The TLP model performs well at predicting the local fluid forces, except in the inlet and outlet regions. It can be fitted to the industrial case by adapting its coefficients.

<p>This paper explores the statistical properties of microfragment recovery techniques used on NTFS filesystems in the use of digital forensics. A microfragment is the remnant file-data existing in the cluster slack after this file has been overwritten. The total amount of cluster slack is related to the size distribution of the overwriting files as well as to the size of cluster. Experiments have been performed by varying the size distributions of the overwriting files as well as the cluster sizes of the partition. These results are then compared with existing analytical models.</p> / FIVES

Sootblowing is a process in which supersonic steam jets are used to periodically blast deposits off heat transfer tubes in kraft recovery boilers. However, sootblowing significantly consumes the valuable high pressure steam generated by the boiler, hence it should be optimized. A recovery boiler consists of three convective sections - superheater, generating bank and economizer. The tube arrangement in these sections, particularly the tube spacing is different from each other. Moreover, tubes in an economizer are finned. A sootblower jet will interact differently with these tube arrangements, potentially affecting its strength, and hence deposit removal capability. The objective of this work was to characterize jet/tube interaction in the three sections of a recovery boiler. Lab-scale experiments were conducted in which these interactions were visualized using the schlieren technique coupled with high-speed video, and were quantified by pitot pressure measurements. This work is the first to visualize the interactions. The offset between the jet and tube centrelines, the nozzle exit diameter relative to the tube diameter, and the distance between the nozzle and tube were varied to examine their effects on jet/tube interaction. Results showed that due to the very low spreading rate of a supersonic jet, a jet (primary jet) stops interacting with a superheater platen when the jet is only a small distance away from it. When the jet impinges on a tube, the jet deflects at an angle, giving rise to a weaker ‘secondary’ jet. Due to the large inter-platen spacing, a secondary jet has an insignificant impact in a superheater. In a generating bank, the primary jet weakens between the closely spaced tubes due to increased mixing. However, a secondary jet impinges on the adjacent tubes exerting a high impact pressure on those tubes. The primary jet also weakens between finned economizer tubes, but remains stronger for a greater distance than in a generating bank. As in the case inside a generating bank, a secondary jet also impinges on adjacent rows of tubes in an economizer. The results imply that in a superheater, a sootblower jet must be directed close to the platens to yield useful jet/deposit interactions, and to avoid wasting steam by blowing between the platens. In a generating bank, deposits beyond the first few tubes of a row experience a weaker sootblower jet, and thus may not be removed effectively. However, secondary jets may contribute to removing deposits from the first few adjacent tubes. They may also induce erosion-corrosion of those tubes. Secondary jets may also help remove deposits from adjacent rows in a finned tube economizer. In an economizer, the strength and hence, the deposit removal capability of a sootblower jet diminish only slightly beyond the supersonic portion of the jet. A mathematical model was also developed to determine the feasibility of using inclined sootblower nozzles in recovery boiler superheaters, and suggests that it may be possible to clean superheater platens more effectively with slightly inclined nozzles.

Sootblowing is a process in which supersonic steam jets are used to periodically blast deposits off heat transfer tubes in kraft recovery boilers. However, sootblowing significantly consumes the valuable high pressure steam generated by the boiler, hence it should be optimized. A recovery boiler consists of three convective sections - superheater, generating bank and economizer. The tube arrangement in these sections, particularly the tube spacing is different from each other. Moreover, tubes in an economizer are finned. A sootblower jet will interact differently with these tube arrangements, potentially affecting its strength, and hence deposit removal capability. The objective of this work was to characterize jet/tube interaction in the three sections of a recovery boiler. Lab-scale experiments were conducted in which these interactions were visualized using the schlieren technique coupled with high-speed video, and were quantified by pitot pressure measurements. This work is the first to visualize the interactions. The offset between the jet and tube centrelines, the nozzle exit diameter relative to the tube diameter, and the distance between the nozzle and tube were varied to examine their effects on jet/tube interaction. Results showed that due to the very low spreading rate of a supersonic jet, a jet (primary jet) stops interacting with a superheater platen when the jet is only a small distance away from it. When the jet impinges on a tube, the jet deflects at an angle, giving rise to a weaker ‘secondary’ jet. Due to the large inter-platen spacing, a secondary jet has an insignificant impact in a superheater. In a generating bank, the primary jet weakens between the closely spaced tubes due to increased mixing. However, a secondary jet impinges on the adjacent tubes exerting a high impact pressure on those tubes. The primary jet also weakens between finned economizer tubes, but remains stronger for a greater distance than in a generating bank. As in the case inside a generating bank, a secondary jet also impinges on adjacent rows of tubes in an economizer. The results imply that in a superheater, a sootblower jet must be directed close to the platens to yield useful jet/deposit interactions, and to avoid wasting steam by blowing between the platens. In a generating bank, deposits beyond the first few tubes of a row experience a weaker sootblower jet, and thus may not be removed effectively. However, secondary jets may contribute to removing deposits from the first few adjacent tubes. They may also induce erosion-corrosion of those tubes. Secondary jets may also help remove deposits from adjacent rows in a finned tube economizer. In an economizer, the strength and hence, the deposit removal capability of a sootblower jet diminish only slightly beyond the supersonic portion of the jet. A mathematical model was also developed to determine the feasibility of using inclined sootblower nozzles in recovery boiler superheaters, and suggests that it may be possible to clean superheater platens more effectively with slightly inclined nozzles.

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