Dissertations / Theses on the topic 'Flow; cylinders; induced vibration'
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Thekkoodan, Dilip Joy. "Interaction of cylinders In proximity under flow-induced vibration." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92126.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 57-59).
This study examines the influence of a stationary cylinder that is placed in proximity to a flexibly mounted cylinder in the side-by-side arrangement. The problem is investigated with an immersed-boundary formulation of a spectral/hp element based (Nektar-SPM) fluid solver. The numerical method and its implementation is validated with benchmark test cases of the flow past an isolated cylinder in both the stationary and flexibly mounted configurations. The study examines a parametric space spanning 6 center-to-center spacing configurations in the range 1.5D-4D and 13 equispaced reduced velocities in the range 3.0-9.0. The simulations are performed in two-dimensional space and the Reynolds number is held at 100. The response characteristics of the moving cylinder are classified into regimes based on the shape of the response curve and the variation of the r.m.s. lift coefficient. It is shown that the moving cylinder influences the lift and drag force characteristics on the stationary cylinder and the frequency composition in the wake. A detailed look at the frequencies and the relative strengths of the frequencies indicates a diminishing influence of the moving cylinder on the stationary cylinder, both with increasing separation and smaller amplitudes. By examining the wake patterns and monitoring the frequencies in the wake of each cylinder, the interference level is qualified and explained to be the basis of the different families of response.
by Dilip Joy Thekkoodan.
S.M.
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Elbanhawy, Amr Yehia Hussein. "On numerical investigations of flow-induced vibration and heat transfer for flow around cylinders." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/on-numerical-investigations-of-flowinduced-vibration-and-heat-transfer-for-flow-around-cylinders(6722ba6d-80de-47f4-a14d-191d4e9ed7fb).html.
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Vortex shedding is an important mechanism, by which the flow around bluff bodies create forces that excite vibratory motion. Vortex-induced vibration (VIV) is studied for a single circular cylinder by means of Computational Fluid Dynamics (CFD) simulations. An arbitrary Lagrangian Eulerian (ALE) formulation is used to achieve the grid deformation needed for VIV. In this thesis, a multifaceted approach is undertaken by which response dynamics and wake interaction are addressed. Four major aspects are considered in the study: the Reynolds number (Re); the mass and damping; the degree-of-freedom for VIV; and the mutual effect between VIV and heat transfer.As attention is paid towards high pre-critical Re flow, the turbulent flow around the cylinder is treated by two turbulence modelling approaches: unsteady Reynolds Averaged Navier Stokes (uRANS), and Large Eddy Simulation (LES). The wake-VIV interaction is analyzed by looking at mean velocities and Reynolds stresses, where decomposition of flow scales is undertaken to explore the evolution of coherent eddy structures, downstream of the cylinder. Conversely, the VIV response is analyzed by considering oscillation amplitude and frequency, in addition to the excitation and inertial dynamics.High turbulence in the separated shear layers disorders the cylinder's VIV response and induces higher amplitudes. The sensitivity for Re is found more pronounced in cylinders with low mass and damping. Meanwhile, VIV is found to enhance wake mixing, and to significantly change the near wake Reynolds stresses. It is suggested that the increase in Re brings a change to the wake patterns, which are known in VIV at lower Re. The kinetic energy production, of near wake eddy structures, is qualitatively altered with the presence of VIV. Furthermore, the surface heat flux is found to cause a noticeable increase in VIV amplitude, as long as it does not disorder the wake correlation. The cylinder's oscillation increases the average value of the Nusselt number (Nu), while the local variance of Nu rises markedly post-separation.
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Rao, Zhibiao. "The flow of power in the vortex-induced vibration of flexible cylinders." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100141.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 255-259).
In this thesis techniques are developed which permit the identification of power-in and power-out regions of long cylinders exposed to flow-induced vibration. The data used to illustrate the techniques come from a set of vortex-induced vibration model tests conducted by Shell Oil Co in 2011 at the Marintek facility in Trondheim, Norway. The identification of power-in regions allows one to address the practical problem of determining the primary source of vibration energy when the long cylinder has components of various shapes, such as when buoyancy modules are used in staggered configurations. The identification of power-out regions has a direct practical connection to the estimation of damping magnitude and location on cylinders with varying cross-sections in non-uniform flows. The vibration intensity technique is used in this thesis to locate the power-in and power-out regions of a long flexible cylinder in a steady flow. This method also allows the exploration of the occurrence of secondary power-in regions after suppressing the primary power-in zones. Results may provide useful guidance for the installation and repair of suppression devices such as helical strakes. Three methods are presented to address a practical problem: "When buoyancy modules are applied in a staggered pattern on an otherwise bare cylinder, which distribution patterns result in VIV response dominated by buoyant or bare regions?" Based on the data analysis of five staggered buoyancy pipes, the three methods yielded the same results in identifying the winner. A dimensionless parameter, the "predictor", is proposed. The predictor relies only on the diameters and lengths of bare and buoyant segment. The predictor is verified with an independent set of VIV tests. An equivalent damping parameter is proposed for the purpose of classifying all flexible cylinder VIV response cases onto a single plot of response versus the equivalent damping parameter. After taking Reynolds number into account, results show that the amplitude for pipes with and without helical strakes at different Reynolds numbers can be collapsed onto a single curve as a function of the newly defined equivalent damping parameter.
by Zhibiao Rao.
Ph. D.
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Yang, Wenchao. "Two-dimensional Wakes and Fluid-structure Interaction of Circular Cylinders in Cross-flow." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/97563.
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The wake of a bluff body is a representative issue in vortex dynamics that plays a central role in civil engineering, ocean engineering and thermal engineering. In this work, a flowing soap film was used to investigate the wakes of multiple stationary circular cylinders and of a single oscillating cylinder. Corresponding computer simulations were also conducted. Vortex formation of a stationary circular cylinder was analyzed by proper orthogonal decomposition (POD). The POD analysis was used to define an unsteady vortex formation length, which suggests a relationship between the vortex formation length of a single cylinder and the critical spacing of two cylinders in a tandem arrangement. A systematic parametric study of the wake structure was conducted for a controlled transversely oscillating cylinder. Neural network and support vector machine codes assisted the wake classification procedure and the identification of boundaries between different wake regimes. The phase map of the vortex shedding regimes for the (quasi) two-dimensional experiment qualitatively agrees with previous three-dimensional experiments. The critical spacings of two identical tandem circular cylinders in a flowing soap film system were determined using visual inspections of the wake patterns and calculations of the Strouhal frequencies. The dimensionless spacing was both increased and decreased quasi-statically. Hysteresis was observed in the flow patterns and Strouhal numbers. This study appears to provide the first experimental evidence of critical spacing values that agree with published computational results. The wake interaction between a stationary upstream circular disk and a free downstream circular disk was also investigated. With the ability to tie together the wake structure and the object motion, the relationship between energy generation and flow structure in the simplified reduced order model system was studied. The research results find the optimal efficiency of the energy harvesting system by a parametric study.PHD
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Chung, Tae-Young. "Vortex-induced vibration of flexible cylinders in sheared flows." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14729.
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Humphries, J. A. "Vortex induced vibrations of slender cylinders in sheared flow." Thesis, Cranfield University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383657.
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Ortega, Mariana Silva. "Suppression of vortex-induced vibration of a circular cylinder with fixed and rotating control cylinders." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/3/3135/tde-15072016-152949/.
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The offshore oil industry is engaged in the development of new floating platforms, such as Spar, semi-submersible, tension-leg, FPSO and monocolumn for the exploration of deep and ultra-deep waters. Some of these floating systems have circular cross sections (or cross sections of other bluff geometries) being susceptible to vortex-induced vibrations (VIV). Vortex shedding behind a bluff body can be altered, suppressed or controlled over a limited range of Reynolds numbers. Various flow-control techniques, which result in the reduction of drag and unsteady forces, have been suggested and tested in simple geometries. One such method is the moving-surface boundary layer control (MSBC), in which smaller control rotating cylinders are placed close to the bluff body. This method is considered as an inspiration for the present experimental investigation of VIV suppression for omni-directional flows. In this context, three different configurations have been assembled to compare the effect of suppression on a plain cylinder surrounded by two, four and eight control cylinders distributed symmetrically around it. Experiments were carried out with static models and models free to oscillate in one-degree-of-freedom with fixed and rotating control cylinders. Experiments with a plain cylinder were performed to serve as reference. Displacements, drag and lift forces were measured. The position of the control cylinders proved to be an important parameter to VIV suppression. Configurations with two control cylinders increased lift and drag forces. In contrast, configurations of four and eight control cylinders showed to be more effective to suppress VIV. Furthermore the results for all the cases of the configuration of eight fixed control cylinders presented a reduction of displacement amplitude, lift and drag forces when compared to a plain cylinder. However, when the control cylinders were actuated, the two cases with rotating control cylinders increased drag force when compared to fixed control cylinders.A indústria offshore está envolvida no desenvolvimento de novas plataformas flutuantes como Spar, semi-submersível, TLP, FPSO e monocoluna para a exploração de águas profundas e ultra-profundas. Alguns destes sistemas flutuantes têm seções transversais circulares (ou de outras seções rombudas) sendo susceptíveis à vibrações induzidas por vórtices (VIV). A esteira de vórtices desprendida de um corpo rombudo pode ser alterada ou suprimida ao longo de uma faixa de número de Reynolds. Várias técnicas de controle do escoamento foram sugeridas e testadas em geometrias simples, resultando na redução de forças de sustentação e arrasto. Um desses métodos é o controle de camada limite por superfícies móveis (CCLSM), no qual cilindrinhos rotativos de controle são colocados próximos ao corpo rombudo. Neste trabalho, este método foi abordado através de uma investigação experimental como um supressor de VIV para o escoamento omnidirecional. Neste escopo três diferentes configurações foram montadas para comparar o efeito de supressão sobre um cilindro liso rodeado por dois, quatro e oito cilindros de controle, distribuídos simetricamente em torno dele. Foram realizados ensaios com o modelo estático, ensaios de VIV em um grau de liberdade com cilindros de controle fixos e rotativos. Foram medidos deslocamento e forças de sustentação e arrasto. Os resultados mostraram que a posição dos cilindros de controle é um parâmetro importante para a supressão de VIV. A configuração com dois cilindros de controle aumentou as forças de sustentação e arrasto. Diferentemente, as configurações de quatro e oito cilindros de controle mostraram-se mais eficazes para suprimir VIV. Além disso, todos os casos da configuração de oito cilindros de controle fixos apresentaram redução nas amplitudes de vibração e nas forças de sustentação e arrasto, quando comparados com um cilindro liso. No entanto, quando os cilindros de controle foram acionados para rotacionar, mostrou-se um aumento na força de arrasto em relação aos cilindros de controle fixos.
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杜平 and Ping To. "Interference effects on the flow-induced vibration of a flexible circular cylinder due to a larger-sized cylinder in the vicinity." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31237769.
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To, Ping. "Interference effects on the flow-induced vibration of a flexible circular cylinder due to a larger-sized cylinder in the vicinity /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19712121.
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Resvanis, Themistocles L. "Vortex-induced vibration of flexible cylinders in time-varying flows." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/93782.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 221-226).
This thesis investigates two aspects of Vortex-Induced Vibrations (VIV) on long flexible cylinders. The work is split into a minor and major part. The minor part addresses the effect of Reynolds number on flexible cylinder VIV. The major contribution addresses the prediction of VIV under unsteady current excitation or time-varying flows. The study on the effect of Reynolds number makes extensive use of a recent set of experiments performed by MARINTEK on behalf of SHELL Exploration and Production Co. Three 38[gamma] long cylinders of different diameters were towed through the ocean basin over a wide range of Reynolds numbers in both uniform and sheared flows. The experimental data showed that the response amplitudes and dimensionless response frequency are strongly influenced by the Reynolds number. Both of these Reynolds effects should be of interest to riser designers that traditionally rely on experimental data obtained at much lower Reynolds numbers. In this thesis, I propose a dimensionless parameter, [gamma], that governs whether lock-in under unsteady flow conditions is possible and show that it is useful for determining a priori whether the response under unsteady conditions will be similar to the response under steady flows. The unsteady flow parameter, [gamma], describes the change in flow speed per cycle of cylinder vibration and is defined as: ... The experimental data necessary to support this work is taken from a set of experiments performed at the State Key Laboratory of Ocean Engineering at Shanghai Jiao Tong University (SJTU), where a 4[gamma] long flexible cylinder was towed through an ocean basin under carefully selected amounts of acceleration/deceleration. Analysis of the experimental data showed that the response can typically be divided into three regimes based on the [gamma] value: For very quickly accelerating flows ([gamma] > 0.1) the cylinder cannot react quickly enough and at most a couple of cycles of small amplitude vibration will be observed. For moderately accelerating flows (0.02 < [gamma] < 0.1), the cylinder will typically start vibrating and can build up a significant response. However, most of the time, the flow will have exited the required synchronization region before the cylinder manages to reach the large amplitudes observed in steady flows. For very slowly accelerating flows ([gamma] < 0.02), the flow is changing considerably slower than the cylinder's reaction time and thus, the cylinder has more than enough time to build up its response. Under these conditions, the observed response is qualitatively similar to the response of flexible cylinders in steady flows. The [gamma] dependence that was identified in the SJTU data is not limited to that specific situation but instead, is a general property of low mass ratio cylinders vibrating in unsteady flows. This is shown by demonstrating how the unsteady flow parameter, [gamma], can be used to analyze unsteady response data from the aforementioned SHELL tests where the riser models were considerably longer than the SJTU model. This thesis shows how a single ramp test -- where the towing speed is continuously varied in a control manner -- may be used to obtain the same information as 10 constant speed tests covering the range of speeds. This can and will significantly reduce the number of runs necessary to completely characterize the VIV response of flexible cylinders and will translate into large cost savings in the future. The thesis closes by describing the differences observed in the VIV response at high mode numbers depending on whether the time-varying flow was accelerating or decelerating. In both situations a 'hysteresis' effect is noted, where the cylinder is found to 'lag behind' preferring to vibrate in the previously excited mode as a result of cylinder lock-in. In accelerating flows, this means that the cylinder will typically be responding one mode lower than it would have in a steady flow. In decelerating flows, the same 'lag' or 'hysteresis' will cause the cylinder to respond one (or more) mode number(s) higher than it would have in a steady flow.
by Themistocles L. Resvanis.
Ph. D.
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Hobbs, William Bradford. "Piezoelectric energy harvesting: vortex induced vibrations in plants, soap films, and arrays of cylinders." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33811.
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The goal of this project was to develop a wind generator that utilizes the collective oscillating motion of multiple piezoelectric devices. These devices would be an alternative to rotating turbine designs for low power generation, for use in applications such as remote power generation. A series of inexpensive devices were developed that harvested energy from vortex shedding, both as independent and cooperative devices. The behavior of single devices was studied, but more interestingly, the way that multiple devices arranged together can increase power output was studied. It was shown that individual devices could harvest more energy if they were placed as specific positions relative to the vortices shed by devices upstream. Through investigating the behavior of these devices, fundamental principles of the phenomenon of vortex induced vibrations were explored. Methods were developed to measure the amplitude and frequency of these vibrations in a wind tunnel, through high speed video and correlations that were found between oscillation and power output from the piezoelectric transducers. Similarly, vortex induced vibrations were explored in an approximation of a two dimensional system in a flowing soap film.
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Carmo, Bruno Souza. "On wake interference in the flow around two circular cylinders : direct stability analysis and flow-induced vibrations." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/4697.
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The flow around two identical circular cylinders, arranged in configurations where one of the cylinders is immersed in the wake of the other, is studied using numerical simulations. Two aspects of such flows were considered. The first is the stability of nominally two-dimensional time-periodic wakes to three-dimensional perturbations. We investigated flows around tandem and staggered arrangements with diverse centre-to-centre distances. Direct stability analysis and numerical simulations were employed, and the results are compared to those obtained for the flow around an isolated cylinder. The onsets of the three-dimensional instabilities were calculated and the unstable modes are fully described. In addition, we assess the nonlinear character of the bifurcations and physical mechanisms are proposed to explain the instabilities. The second aspect considered in this thesis is the flowinduced vibration experienced by a rigid cylinder when it is mounted on an elastic base and immersed in the wake of a fixed identical cylinder. Tandem arrangements with centre-to-centre distances varying from 1.5 to 8 cylinder diameters were tested. The flow was simulated using an Arbitrary Lagrangian-Eulerian approach that coupled the solution of the structure equations with that of the flow. Two- and three- dimensional simulations were performed to assess the mutual influence between the three-dimensional flow structures in the wake and the motion of the cylinder. The response of the downstream cylinder is compared to that of an elastically-mounted rigid isolated cylinder. Based on the simulation results we propose physical mechanisms to explain the origin of the excitation.
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Zahn, Michael L. "Flow-induced vibration of a single flexible cylinder in a normal triangular array." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=55656.
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Dahl, Jason (Jason Michael). "Vortex-induced vibration of a circular cylinder with combined in-line and cross-flow motion." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44747.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 249-256).
Deep water, string-like, marine risers subject to strong ocean currents, suffer from vortex-induced vibrations (VIV), where vortex shedding interacts with the structural properties of the riser, resulting in large amplitude vibrations in both in-line and cross-flow directions. This thesis presents an experimental approach to model and quantify the motions and hydrodynamic forces associated with the excitation of a deep water marine riser by considering the combined cross-flow and in-line excitation of a rigid cylinder. For deep water risers, the excitation of the structure through vortex shedding can lead to a condition of dual resonance, where the vortex shedding frequency locks in to the effective natural frequency (adjusted for added mass effects) in both in-line and cross-flow directions. Large motion amplitudes are observed in this condition along with large magnitude third harmonic forces in lift. Flow visualization of the wake behind the cylinder in combined in-line and cross-flow motion, shows that third harmonic forces are caused by the relative motion of the cylinder with respect to a '2P' (two pairs of vortices) or '2T' (two triplets of vortices) shedding pattern, since vortices shed in these modes remain in close proximity to the cylinder over one cycle of motion. Forced motions of a cylinder with combined in-line and cross-flow motions are performed, generating a database of force coefficients to be used in riser VIV prediction. The assumption of dual resonance is used to predict the motions of an elastically mounted rigid cylinder using measurements from forced cylinder motions. Two passive vortex suppression methods are studied for eliminating combined cross-flow and in-line cylinder motions and suppressing large third harmonic forces.
by Jason Dahl.
Ph.D.
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Luk, K. F. "Experiment on flow-induced vibration of an airfoil due to vortex shedding generated from upstream circular cylinder /." View Abstract or Full-Text, 2002. http://library.ust.hk/cgi/db/thesis.pl?MECH%202002%20LUK.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002.Includes bibliographical references (leaves 54-57). Also available in electronic version. Access restricted to campus users.
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Cicolin, Murilo Marangon. "Supressão da vibração induzida por vórtices de cilindros com malha permeável." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/3/3135/tde-07032016-102934/.
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O fenômeno de vibração induzida por vórtices (VIV) é particularmente danoso para estruturas submarinas como risers de exploração de petróleo. A maneira mais usual de se atenuarem os efeitos de VIV é instalar um supressor, como por exemplo strakes ou fairings. Dentre esses, foi desenvolvido por All Brow Universal Components um supressor chamado Ventilated Trousers (VT), que consiste em uma malha permeável feita de uma rede flexível e dezenas de bobbins. Através de um estudo experimental, procurou-se investigar os mecanismos hidrodinâmicos pelos quais o supressor V T funciona. Foram construídos três modelos diferentes de supressores: um modelo idêntico ao V T e duas malhas dele derivadas, alterando-se a geometria dos bobbins e a distribuição destes ao redor da malha. Foram realizados ensaios com o modelo xo e ensaios de VIV em um grau de liberdade alterando-se o amortecimento estrutural. Foram medidos deslocamento e forças de sustentação e arrasto. Os resultados mostraram que o supressor do tipo V T reduz as amplitudes de vibração, força de sustentação e arrasto quando comparados com um cilindro oscilando. No entanto, aumenta a força de arrasto quando comparado com o cilindro xo. A geometria da malha mostrou-se de grande importância para a supressão de VIV. Modelos que possuem o disco externo no bobbin impedem o surgimento de folga entre o modelo e o cilindro, além de aumentar o amortecimento hidrodinâmico. Três hipóteses foram levantadas para explicar o funcionamento do supressor V T. A primeira diz que a supressão é provocada pelo aumento do amortecimento hidrodinâmico. Os ensaios mostraram que, de fato, o supressor V T aumenta o amortecimento e, consequentemente, diminui as VIV. No entanto, somente esse efeito não explica toda a supressão obtida. As outras hipóteses, relacionadas à alterações bi e tridimensionais da esteira, foram avaliadas, porém não se pode afirmar que alguma delas seja isoladamente responsável por produzir o mecanismo hidrodinâmico de supressão.The phenomenon of vortex-induced vibration (VIV) is particularly harmful to submarine structures such as risers used for oil extraction. The most usual way to attenuate the effects of VIV is the installation of suppressors, like strakes or fairings. Among them, All Brow Universal Components developed a VIV suppressor called Ventilated Trousers (VT), which consist of a permeable mesh made of a flexible net and tens of bobbins. Three different models of suppressors based on permeable meshes have been assembled with the objective to understand the hydrodynamic mechanism behind the suppression: one model identical to the VT and two meshes with different bobbin geometries and distribution. Tests were carried out with xed models and models free to oscillate in one degree of freedom varying the structural damping. Displacements, drag and lift forces were measured. Results showed that the VT suppressor reduced vibration amplitudes, lift and drag forces when compared to an oscillating circular cylinder. However, it increased drag force when compared to a fixed circular cylinder. The mesh geometry proved to be important to VIV suppression. Models that had an external disc on the bobbins avoided the appearance of a gap between the model and the cylinder. Three hypotheses were formulated to explain how the VT suppressor works. The first one says that the increase on hydrodynamic damping is responsible for suppression. In fact, tests showed that the VT increased hydrodynamic damping and, consequently, reduced the VIV response. However, this effect alone does not explain the suppression as a whole. The other two hypotheses related to two-dimensional and three-dimensional wake changes were evaluated, but it cannot be stated that any of them, on its own, is responsible for the whole of the suppression mechanism.
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Franzini, Guilherme Rosa. "Investigação experimental do escoamento ao redor de cilindros inclinados, sujeitos a condições de contorno assimétricas nas extremidades." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/3/3135/tde-26072013-165702/.
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O escoamento ao redor de cilindros inclinados, ou escoamento oblíquo, é um problema bastante comum em diversas áreas da engenharia. Embora o escoamento ao redor de um cilindro não inclinado consista em um tópico clássico e bastante estudado no contexto da mecânica dos fluídos, os estudos investigativos do escoamento oblíquo existem em menor número. O procedimento mais adotado para o estudo do escoamento ao redor de um cilindro inclinado é o Princípio da Independência, que atesta que todas as características da esteira dependem unicamente da componente da correnteza incidente que é ortogonal ao eixo do cilindro. Visando um melhor entendimento do escoamento ao redor de cilindros rígidos e inclinados, três grupos de experimentos foram conduzidos com cilindros inclinados tanto à montante como à jusante. Cinco ângulos de inclinação, definidos entre o eixo do cilindro e a direção ortogonal à da correnteza foram ensaiados, a saber: teta = 0°, 10°, 20°, 30° e 45°. No primeiro grupo de experimentos, os resultados obtidos com os cilindros estacionários inclinados à montante mostraram que o coeficiente de arrasto médio concorda com os resultados da configuração de referência, desde que a componente da correnteza incidente ortogonal ao eixo do cilindro seja utilizada na normalização da força. No tocante aos experimentos dos cilindros sujeitos ao fenômeno de vibrações induzidas pela emissão de vórtices com um ou dois graus de liberdade, existe um decréscimo da amplitude de oscilação dos cilindros com o aumento do ângulo de inclinação. Em todas as campanhas experimentais, foram verificadas diferenças entre os resultados obtidos com os cilindros inclinados à montante ou à jusante. Essa diferença é tão maior quanto maior for o ângulo de inclinação, e está associada à assimetria nas condições de extremidade do cilindro.The flow around yawed cylinders, or oblique flow, is a common subject in several engineering applications. Despite the flow around a non-yawed cylinder consists on a classical and extensively investigated problem, there is a considerable lower number of investigation concerning the oblique flow. The most employed approach aiming at investigating the oblique flow is the so called Independence Principle, which states that the flow characteristics depend only on the component of the free-stream that is normal to the cylinder axis. Three groups of experiments were carried out aiming at a better understanding of the flow around yawed cylinders. Five yaw angles defined between the cylinder axis and the direction orthogonal to the free-steam were tested, namely: theta = 0°, 10°, 20°, 30° e 45°. From the first group of experiments, the results obtained with stationary cylinders yawed in the upstream orientation shown that the mean drag coeficient matches the classical results from the non-yawed cylinder, if the component of the free-stream that is orthogonal to the cylinder axis is employed in the normalization of the hydrodynamic force. Concerning vortex-induced vibrations experiments with one and two degrees-of-freedom, a decrease was observed in the maximum oscillation amplitude. For all the experiments, it was observed that the results obtained from the upstream orientation tests can be different from those obtained for the downstream orientation ones. The larger the yaw angle, the larger are the differences, which are associated to the asymmetric end conditions.
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Junior, Leonidio Buk. "Estudo numérico do escoamento ao redor de um cilindro fixo." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/3/3150/tde-12072007-160644/.
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Neste trabalho, o escoamento incompressível ao redor de um cilindro fixo é estudado numericamente através do método de elementos finitos. Foram realizadas simulações bidimensionais no domínio do tempo, com números de Reynolds variando entre 100 e 600, utilizando-se, para tanto, malhas não-estruturadas com elementos triangulares. Pretende-se aqui analisar a eficácia da solução das equações de Navier-Stokes utilizando o método das penalidades, meio pelo qual o acoplamento pressão-velocidade foi tratado. Avalia-se a convergência da solução para diferentes valores do fator de penalidade e sugere-se um método para estimá-lo. Analisa-se, ainda, a sensibilidade da resposta à utilização da matriz de inércia nos formatos consistente e concentrada. Por fim, é realizada a comparação dos coeficientes de arrasto médio, flutuação do coeficiente de sustentação e número de Strouhal obtidos neste trabalho com resultados de outras publicações.In this work, the incompressible flow around a stationary cylinder is investigated by using the Finite Element Method. Two-dimensional simulations in time domain have been carried out, with Reynolds number varying from 100 to 600, using non-structured meshes with triangular elements. The aim of this work is to analyze the efficiency of Penalty Methods, which is the way that the velocity-pressure coupling problem is treated here, in Navier-Stokes equations solution. The solution convergence from different values of penalty parameter is evaluated and it is suggested a method to estimate it. In addition, it is studied the sensibilty of response when using the mass matrix in consistent or lumped format. At last, a comparison between average drag coefficient, fluctuating lift and Strouhal number obtained here and those found in other publications is shown.
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Assi, Gustavo Roque da Silva. "Estudo experimental do efeito de interferência no escoamento ao redor de cilindros alinhados." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/3/3150/tde-11012006-154457/.
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Esta Dissertação de Mestrado apresenta um estudo experimental sobre os efeitos de interferência das vibrações induzidas pelo escoamento ao redor de cilindros rígidos livres para oscilar transversalmente ao escoamento fluido. Primeiramente, justifica a necessidade de pesquisas experimentais dentro do contexto prático da engenharia offshore, que motiva este trabalho. Apresenta uma revisão bibliográfica sobre escoamentos ao redor de corpos rombudos seguida de uma síntese sobre vibrações induzidas pelo escoamento. Destacam-se as oscilações causadas por VIV Vibrações Induzidas por Vórtices e galloping como os fenômenos até o momento atribuídos às excitações de um cilindro isolado e um par de cilindros alinhados com o escoamento. Apresenta a metodologia experimental empregada, descrevendo a aplicação de bases elásticas fletoras com um grau de liberdade. Introduz as técnicas experimentais e de tratamento de sinais utilizadas e faz rápidas considerações sobre a realização de ensaios nos dois canais de água circulante onde os experimentos foram conduzidos. Os resultados apresentados, discutidos e comparados envolvem: medições da resposta dinâmica em amplitude e freqüência dominante de oscilação; medição instantânea do ângulo de fase entre a força fluida e o deslocamento do cilindro e do ângulo de fase entre as oscilações de dois cilindros; e medições da dinâmica da esteira com PIV. Os arranjos de cilindros estudados são: cilindro isolado; par alinhado com cilindro à montante oscilando; par alinhado com cilindro à jusante oscilando; e par alinhado com ambos os cilindro oscilando. Todas as configurações analisadas em detalhes possuem baixo parâmetro de massa e baixíssimo parâmetro de amortecimento . Os espaçamentos entre os centros dos cilindros alinhados variam entre . A faixa de velocidade reduzida analisada está entre. Um cilindro isolado apresentou resposta típica de VIV com os três ramos de resposta (inicial, superior e inferior) identificados. O fenômeno de intermitência do ângulo de fase instantâneo foi verificado nas regiões de transição. Os modos 2S e 2P de emissão de vórtices foram identificados com PIV. Estes dados mostraram boa concordância com outros experimentos da literatura e serviram de referência para as demais comparações deste texto. A resposta de um cilindro oscilando à montante de outro fixo também apresentou comportamento típico de VIV. Conclui-se que o primeiro cilindro não sofre efeito de interferência do cilindro à jusante para os espaçamento e velocidades analisados. Os principais efeitos de interferência ocorrem para um cilindro oscilando à jusante de outro fixo. Este arranjo, foco deste estudo, não apresenta resposta típica de VIV, uma vez que a amplitude apresenta um ramo crescente após a faixa típica de sincronização. Também não apresenta resposta típica de excitação pura por galloping, já que a força fluida não está em fase com a velocidade do cilindro. Assim, denomina-se um novo fenômeno responsável por estas excitações que combina: captura da freqüência de emissão e faixa de sincronização de VIV; e amplitude assintoticamente crescente típica da resposta de galloping. Trata-se das WIV Vibrações por Interferência da Esteira. Quando ambos os cilindros estão livres para oscilar, o cilindro à montante continua apresentando resposta típica de VIV, enquanto o segundo cilindro responde com ramos descontínuos também excitados por WIV. Por fim, conclui-se que não é conveniente chamar de excitações por galloping os ramos crescentes nas configurações de interferência. Entende-se que esta resposta esteja sendo excitada pelos efeitos de interferência das esteiras formada entre os cilindros e desprendida no cilindro à jusante. Sugere-se que a nomenclatura Vibrações por Interferência da Esteira seja mais adequada à natureza dos fenômenos. As visualizações de PIV foram importantes para a verificação da redução do comprimento de formação de vórtices com o aumento do número de Reynolds, mostrando a necessidade de experimentos de interferência com Reynolds constante. Encerra-se o texto apresentando propostas para trabalhos futuros que continuem nesta linha de pesquisa.This MSc Thesis presents an experimental study on flow-induced vibrations and interference effects around rigid circular cylinders free to oscillate transversally to the flow. Firstly, it justifies the real needs of an experimental approach within the context of offshore engineering, which motivates this project. After that, presents a review over bluff-bodies flows followed by some consideration concerning flow-induced vibrations. Special attention is found over the oscillations caused by VIV Vortex-Induced Vibrations and galloping phenomena, which are attributed to excite either a single isolated cylinder or a pair of tandem interfering cylinders. The experimental methodology is shown, describing the applications of elastic bases with one degree of freedom. Experimental techniques and signal analysis procedures are discussed considering the executions of these experiments in two water channel facilities. Presented, discussed and compared results involve: dynamic responses in amplitude and dominant oscillation frequency; instantaneous phase angle between fluid forces and cylinder displacement and phase angle betweens the two cylinders oscillations; and wake dynamics measurements and visualizations employing PIV technique. Cylinders are arranged as follow: single isolated cylinder; tandem pair with upstream one free to oscillate; tandem pair with downstream one free to oscillate; tandem pair with both cylinders free to oscillate. All carefully analyzed arrangements present low-mass parameter and very low damping . Gaps between cylinder centers vary through . Reduced velocity range is comprised in. The isolated cylinder case presented a typical VIV response, with three identified branches (initial, upper and lower). The instantaneous phase angle intermittency phenomenon was observed in transition regions. The 2S and 2P vortex modes were verified by PIV technique. These data showed to be in accordance to other literature measurements and are employed as reference results for comparisons throughout this text. The dynamic response of a cylinder oscillating upstream a fixed one showed a typical VIV behavior. From this can be concluded that the downstream cylinder does not imply any interference phenomenon for analyzed gaps and velocities. On the other hand, major interference effects occur when a downstream cylinder is oscillating in the wake of another fixed one. This configuration, which is the focus of this study, does not show a typical VIV response, since amplitude curves present a crescent branch after the typical synchronization regime. It does not either present a typical galloping excitation response, since the fluid forces are not in phase with the cylinder velocity. Thus, a new suggested name, WIV Wake-Interference Vibrations, describes the phenomenon responsible for these excitations, which combines: lock-in of shedding frequency from VIV; and asymptotically crescent response from galloping-like excitations. When both cylinders are free to oscillate, the upstream one presents the typical VIV response, while the downstream one passes through three branches with discontinuities, excited by WIV. Finally, it can be concluded that is not convenient to call galloping excitation these crescent branches for interference arrangements. It can be understood that the dynamic response is being excited by the interference effects from upstream wake and downstream cylinder vortices. The nomenclature Wake-Interference Vibrations is suggested to be more adequate to the nature of this phenomenon. In addition, PIV visualizations showed to be very important to certify that the formation length decreases while increasing Reynolds number, requiring interference experiments with constant Reynolds numbers. To conclude, some suggestions for future work in this research field are presented.
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Gsell, Simon. "Vortex-induced vibrations of a rigid circular cylinder." Phd thesis, Toulouse, INPT, 2016. http://oatao.univ-toulouse.fr/17430/1/gsell.pdf.
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When a flexible body with bluff cross-section is immersed in a flow, the unsteady fluid forces accompanying the vortex-shedding phenomenon may lead to structural vibrations. These vortexinduced vibrations (VIV) occur through a mechanism of synchronization between flow unsteadiness and body displacement, referred to as lock-in. VIV are detrimental to many industrial systems, but may also be used as mechanical energy converter in the context of flow energy harvesting. In the present work, the VIV of a rigid circular cylinder mounted on a elastic support are investigated in various configurations on the basis of direct numerical simulations. Four aspects are studied. (i) The interaction mechanisms are first examined in the early turbulent regime, where VIV have been rarely studied numerically. The Reynolds number, based on the cylinder diameter and oncoming flow velocity, is set to 3900. A combined analysis of the structural responses and fluid forcing in the case where the cylinder is free to oscillate in the in-line and cross-flow directions, i.e. the directions parallel and perpendicular to the oncoming flow, is performed over a range of the reduced velocity (inverse of the oscillator natural frequency). (ii) The system behavior when the body is free to oscillate in a single direction only is also explored, shedding some light on the possible interactions between in-line and cross-flow motions in the two-degree-of-freedom (2-dof) case; the analysis shows for instance how large-amplitude in-line oscillations may be induced by cross-flow motion. (iii) The three-dimensional wake developing downstream of the oscillating body is analyzed in the 2-dof case as well as in the fixed body case. The spanwise flow patterns, which are analyzed quantitatively in terms of wavelength and amplitude of vorticity fluctuations, are differently altered in the shear-layer and wake regions, when the body oscillates. (iv) The last physical configuration involves a cylinder immersed in a flow linearly sheared in the cross-flow direction. The impact of the symmetry breaking induced by the shear, on the flow-structure system behavior, is explored. Different interaction regimes are uncovered in the shear rate - reduced velocity domain. Some of them are associated with a profound reconfiguration of the wake and a major alteration of the fluid forces.
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Hayder, Mir Mohammad Abu 1976. "Cross-flow past oscillating circular cylinders." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115685.
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The cross-flow past a pair of equal-diameter circular cylinders, arranged in a staggered configuration, was investigated experimentally in a closed-circuit water tunnel at Reynolds numbers, based on the mean-flow velocity and the cylinder diameter, within the lower subcritical range. The wake formation process was studied employing dye-injection flow visualization and hot-film measurements. The main emphasis was placed on acquiring a physical understanding of the mechanisms leading to vortex shedding, and particularly on the effect of a forced oscillation transverse to the flow direction of either of the two cylinders. For comparison purposes, investigations were also carried out with both cylinders stationary.Experimental results showed that, for a reasonably large angle of incidence, the flow in the wake of a stationary cylinder pair could be characterized by two distinct periodicities, each of which was dominant on one side of the wake. Furthermore, for lower Reynolds numbers (Re < 1.0x10 4), there was an integral relationship between the two Strouhal numbers, but this integral relationship was no longer maintained for Re > 1.0x10 4. On the other hand, the flow around stationary cylinders for a small angle of incidence was characterized by a single Strouhal number, which remained approximately constant over the entire Reynolds number range.
For all the cylinder configurations investigated the wake flow patterns remained essentially the same as those of the corresponding static cases, when either of the two cylinders was forced to oscillate with a nondimensional forcing frequency less than approximately 0.10. However, beyond this value, the wake underwent considerable modification vis-a-vis when the cylinders were stationary, and the flow pattern within the wake was strongly dependent on the value of the forcing frequency. In particular, there were distinct regions of synchronization between the dominant wake periodicities and the cylinder oscillation; these synchronization regions involved sub- and superharmonics as well as fundamental synchronizations. With either upstream or downstream cylinder oscillation, the wake on the mean-flow side of the downstream cylinder synchronized with the shear layers separated from its outer surface, whereas synchronizations on the mean-flow side of the upstream cylinder were caused by the periodicities formed from the interaction of the other three shear layers.
The flow phenomena associated with the synchronizations were described in detail via flow visualization. The organization of the wake was strongly dependent on whether it was the upstream or downstream cylinder which was oscillating. The synchronized wake on the mean-flow side of the downstream cylinder at both lower and higher oscillation frequencies for upstream cylinder oscillation was observed to form either by the shedding of independent vortices or by the coalescence of two or more vortices. However, for downstream cylinder oscillation, although the synchronizations on this side of the wake at lower oscillation frequencies were caused by the shedding of independent vortices or by the coalescence of vortices, those at higher oscillation frequencies were the consequence of the coalescence of vortices only. For large incidence angles, the number of shear layers separated from the downstream cylinder which interacted with those separated from the upstream cylinder was critical in causing the synchronizations on the mean-flow side of the upstream cylinder.
In most cases, the flow for all the cylinder configurations traversed between the same patterns as those obtained when the cylinders were placed stationary at their minimum and maximum transverse spacings; but there were also some situations where the oscillation of either cylinder pushed the flow outside the regimes associated with the stationary configurations. The synchronization ranges obtained when the upstream or downstream cylinder was oscillating were different from each other, and these ranges were much wider than the corresponding synchronization ranges for a single oscillating cylinder. For two cylinders, an analysis of the fundamental synchronization showed that the frequency range over which this occurred was much broader for upstream cylinder oscillation than for downstream cylinder oscillation. Also, the fundamental synchronization ranges for downstream cylinder oscillation were closer to those for single cylinder oscillation in comparison to those for upstream cylinder oscillation.
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Korkischko, Ivan. "Investigação experimental e analítica do escoamento ao redor de cilindro circular com supressores de VIV." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/3/3150/tde-08122011-150201/.
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O escoamento de um fluido ao redor de corpos rombudos configura-se em um dos principais problemas da mecânica dos fluidos. As investigações deste fenômeno são baseadas em técnicas analíticas, numéricas e experimentais. Cada abordagem apresenta suas vantagens e desvantagens, sendo impossível a plena caracterização do escoamento através de uma única técnica para a maioria das geometrias de corpo e condições de escoamento. É neste contexto que se insere esta tese, que compreende um estudo fundamental sobre a dinâmica de formação e desprendimento de vórtices baseado em técnicas experimentais. Primeiramente, realiza-se um estudo de estabilidade hidrodinâmica do escoamento em torno de cilindro circular via modelo de Ginzburg-Landau. Os resultados experimentais deste estudo serviram para validar simulações numéricas e a principal técnica experimental utilizada foi a Velocimetria por Imagem de Partículas (PIV). A decomposição de campos de velocidade em série de Fourier permite verificar a hierarquia sugerida pela solução assintótica da bifurcação de Hopf. Além disso, os resultados também indicam quando a tridimensionalidade passa a ser importante no escoamento. A tridimensionalidade do escoamento está intimamente ligada ao fenômeno de vibração induzida por vórtices (VIV), que exerce efeitos danosos em uma grande quantidade de estruturas sujeitas a escoamentos fluidos. Com o objetivo de suprimir as VIV, realizou-se um estudo paramétrico do supressor do tipo strakes helicoidal, que é bastante empregado na indústria offshore. Verificou-se que os strakes modificam as características tridimensionais da esteira de um cilindro. Apesar da eficiência dos strakes na supressão de VIV, eles possuem algumas limitações inerentes às características hidrodinâmicas do escoamento. Sendo assim, apresenta-se uma técnica que reduz as tridimensionalidades de modo a tornar o escoamento bidimensional, com a possibilidade de controle ativo de malha fechada. O método de controle de camada limite por superfícies móveis (CCLSM) suprime VIV e diminui o arrasto atrasando a separação da camada limite do cilindro através da injeção de quantidade de movimento angular pelos cilindros de controle rotativos.The fluid flow around bluff bodies is one of the main problems in fluid mechanics. The investigations of this phenomenon are based on analytical, numerical and experimental techniques. Each technique presents advantages and disadvantages, being impossible the comprehensive characterization of the flow though only one technique for the majority of body geometries and flow conditions. Within this context, the present thesis is proposed, which comprehends a fundamental study about the vortex shedding dynamics based on experimental techniques. Firstly, a hydrodynamic stability study of the flow around a circular cylinder is performed using the Ginzburg-Landau model. The experimental results of this study allowed the validation of numerical simulations and the main experimental technique employed was the Particle Image Velocimetry (PIV). The Fourier series decomposition of velocity fields permits to verify the hierarch suggested by the asymptotic solution of the Hopf bifurcation. Additionally, the results also indicate when the three-dimensionalities become important in the flow. The flow three-dimensionality is closely associated to the vortex-induced vibration (VIV) phenomenon, which exerts damaging effects on a great quantity of structures subjected to fluid flows. In order to suppress VIV, it was realized a parametric investigation of the helical strakes, that are commonly employed in the offshore industry. One verifies that the strakes modify the three-dimensional characteristics of the cylinder wake. Despite of the strake efficiency regarding the VIV suppression, the strakes have some limitations that are inherent to the flow hydrodynamic features. Consequently, it is presented a technique that reduces the three-dimensionalities in order to create a two-dimensional flow, with the possibility of closed-loop active control. The moving surface boundary-layer control (MSBC) suppresses VIV and reduces the drag delaying the cylinder boundary-layer separation through the injection of angular momentum by the rotational control cylinders.
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Slisik, Jeffrey A. "FLOW-INDUCED VIBRATION OF CARBON NANOTUBES." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1145032790.
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Marcollo, Hayden 1972. "Multimodal vortex-induced vibration." Monash University, Dept. of Mechanical Engineering, 2002. http://arrow.monash.edu.au/hdl/1959.1/7674.
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Branković, Maša. "Vortex-induced vibration attenuation of circular cylinders with low mass and damping." Online version, 2004. http://ethos.bl.uk/OrderDetails.do?did=1&uin=uk.bl.ethos.409354.
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Brankovič, Maša. "Vortex-induced vibration attenuation of circular cylinders with low mass and damping." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409354.
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Jaiswal, Vivek Ph D. Massachusetts Institute of Technology. "Effect of traveling waves on Vortex-Induced Vibration of long flexible cylinders." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/49763.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Includes bibliographical references (p. 155-160).
Offshore marine risers and pipelines, exposed to ocean currents, are susceptible to Vortex-Induced Vibration (VIV). Accurate prediction of VIV is necessary for estimating the fatigue life as well as for taking corrective measures to prevent the vibrations. State of the art response prediction methods work reasonably well for short flexible cylinders vibrating at frequencies corresponding to low mode numbers (below the tenth mode). However, for long structures, which respond above the tenth mode, lack of experimental data has until recently impeded progress. Results will be presented from recent field experiments conducted in the Gulf Stream and Lake Seneca, NY. These experiments have provided an opportunity for new insights about the VIV of long flexible cylinders, responding at high mode numbers. The experimental results also include insights on the use of VIV suppression devices such as helical strakes. The experiments reveal that the dominant response of long flexible cylinders is often in the form of traveling waves. High spatial density fiber optic strain gauge measurements are used to obtain estimates of the phase speed of the waves, the response amplitude and the added mass coefficient. The mean added mass coefficient for the bare cylinder is shown to be approximately one and the maximum response amplitude is found to be approximately one diameter. A Green's function, response prediction method, is introduced which is able to emulate both the standing and traveling wave properties observed in the experimental data.
(cont.) A novel approach to modeling the excitation force as a combination of standing and traveling wave components is shown to predict the measured response very well. The method is also able to account for high localized damping that result from the use of response suppression devices, such as helical strakes. Many marine risers are composed of nested concentric steel pipes. The relative motion of these concentric pipes in the presence of confined liquids introduces unusual dynamic properties, including the potential for beneficial effects as dynamic absorbers. Numerical and theoretical models are developed as a preliminary step in the design of dynamic absorbers for deep water risers.
by Vivek Jaiswal.
Ph.D.
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徐善強 and Sin-keung Chui. "Stability and bifurcation in flow induced vibration." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31235724.
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Chui, Sin-keung. "Stability and bifurcation in flow induced vibration /." Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B1904155X.
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Thompson, Andrew S. "Experimental charactarization of flow induced vibration in turbulent pipe flow /." Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd3162.pdf.
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Thompson, Andrew S. "Experimental Characterization of Flow Induced Vibration in Turbulent Pipe Flow." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/1906.
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This thesis presents results of an experimental investigation that characterizes the wall vibration of a pipe with turbulent flow passing through it. Specifically, experiments were conducted using a water flow loop to address three general phenomena. The topics of investigation were: 1) How does the pipe wall vibration depend on the average flow speed, pipe diameter, and pipe thickness for an unsupported pipe? 2) How does the behavior change if the pipe is clamp supported at various clamping lengths? 3) What influence does turbulence generation caused by holed baffle plates exert on the pipe response? A single pipe material (PVC) was used with a range of internal diameters from 5.08 cm to 10.16 cm and diameter to thickness ratios ranging from 8.90 to 16.94. The average flow speed that the experiments were conducted at ranged from 0 to 11.5 m/s. Pipe vibrations were characterized by accelerometers mounted on the pipe wall at several locations along the pipe length. Rms values of the pipe wall acceleration and velocity time series were measured at various flow speeds. Power spectral densities of the accelerometer data were computed and analyzed. Concurrent wall pressure fluctuation measurements were also obtained. The results show that for a fully developed turbulent flow, the rms of the wall pressure fluctuations is proportional to the rms of the wall acceleration and each scale nominally as the square of the average fluid velocity. Also, the rms of the pipe wall acceleration increases with decreasing pipe wall thickness. When changes were made in the pipe support length, it was observed that, in general, pipe support length exercises little influence on the pipe wall acceleration. The influence of pipe support length on the pipe wall velocity is much more pronounced. A non-dimensional parameter describing the pipe wall acceleration is defined and its dependence on relevant independent non-dimensional parameters is presented. Turbulence was induced using baffle plates with various sizes (2.54 cm to 0.159 cm) and numbers of holes drilled through them to provide a constant through area of 35.48 cm2 for each plate. Cavitation exists at high speeds for the largest holed baffle plates and this significantly increases the rms of the pipe wall acceleration. As the baffle plate hole size decreases, vibration levels were observed to return to levels that were observed when no baffle plate was employed. Power spectral densities of the accelerometer data from each baffle plate scenario were also computed and analyzed.
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Mark, Bill. "An experimental study of the vibration response of a single flexibly-mounted cylinder within a rigid array subjected to air cross flow /." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65431.
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Kota, Siva Kumar k. "Analysis of Heat Transfer Enhancement in Channel Flow through Flow-Induced Vibration." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1062854/.
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In this research, an elastic cylinder that utilized vortex-induced vibration (VIV) was applied to improve convective heat transfer rates by disrupting the thermal boundary layer. Rigid and elastic cylinders were placed across a fluid channel. Vortex shedding around the cylinder led to the periodic vibration of the cylinder. As a result, the flow-structure interaction (FSI) increased the disruption of the thermal boundary layer, and therefore, improved the mixing process at the boundary. This study aims to improve convective heat transfer rate by increasing the perturbation in the fluid flow. A three-dimensional numerical model was constructed to simulate the effects of different flow channel geometries, including a channel with a stationary rigid cylinder, a channel with a elastic cylinder, a channel with two elastic cylinders of the same diameter, and a channel with two elastic cylinders of different diameters. Through the numerical simulations, the channel maximum wall temperature was found to be reduced by approximately 10% with a stationary cylinder and by around 17% when introducing an elastic cylinder in the channel compared with the channel without the cylinder. Channels with two-cylinder conditions were also studied in the current research. The additional cylinder with the same diameter in the fluid channel only reduced the surface wall temperature by 3% compared to the channel without any cylinders because the volume of the second cylinder could occupy some space, and therefore, reduce the effect of the convective heat transfer. By reducing the diameter of the second cylinder by 25% increased the effect of the convection heat transfer and reduced the maximum wall temperature by around 15%. Compared to the channel with no cylinder, the introduction of cylinders into the channel flow was found to increase the average Nusselt number by 55% with the insertion of a stationary rigid cylinder, by 85% with the insertion of an elastic cylinder, by 58% with the insertion of two cylinders of the same diameter, and by approximately 70% with the insertion of two cylinders of different diameters (the second cylinder having the smaller diameter). Furthermore, it was also found that the maximum local Nusselt number could be enhanced by around 200%-400% at the entrance of the fluid channel by using the elastic cylinders compared to the channel without cylinders.
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Liao, Jung-Chi 1971. "Vortex-induced vibration of slender structures in unsteady flow." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8331.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2002.Includes bibliographical references (p. 164-165).
Vortex-induced vibration (VIV) results in fatigue damage of offshore oil exploration and production structures. In recent years, the offshore industry has begun to employ curved slender structures such as steel catenary risers in deep-water offshore oil systems. The top-end vessel motion causes the slender riser to oscillate, creating an unsteady and nonuniform flow profile along the riser. The purpose of this research is to develop a VIV prediction model for slender structures under top-end periodic motions. The key approach to this problem requires identifying the dimensionless parameters important to the unsteady VIV. A set of data from a large-scale model test for highly compliant risers conducted by industry is available. The spectral analysis of the data showed a periodic pattern of the response frequencies. A constant Strouhal (St) number model was proposed such that shedding frequencies change with local inline velocities. The Keulegan-Carpenter number (KC) controls the number of vortex pairs shed per cycle. A KC threshold larger than 40 was found to have significant response for a long structure with finite length excitation region. An approximate solution to the response of an infinite beam with a finite excitation length was obtained; this solution provided an explanation for the high KC threshold. A model for an equivalent reduced damping Sg under a non-uniform, unsteady flow was proposed. This equivalent reduced damping Sg was used to establish a prediction model for the VIV under top-end periodic motions. A time domain simulation of unsteady VIV was demonstrated by using Green's functions.
(cont.) The turning point problem wave propagation was solved for a pipe resting on a linearly varying stiffness foundation. Simple rules were established for conservative estimation of TDP fatigue damage with soil interactions. Guidelines for model test experiment design were provided based on dimensional analysis and scaling rules.
by Jung-Chi Liao.
Ph.D.
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Assi, Gustavo R. S. "Mechanisms for flow-induced vibration of interfering bluff bodies." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508992.
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Medeiros, E. B. "An experimental study of the aeroelastic behaviour of two parallel interfering circular cylinders." Thesis, University of Salford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384128.
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Capozucca, Peter. "Flow-induced vibration of a non-constant tension cable in a sheared flow." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14389.
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Pittard, Matthew Thurlow. "Large Eddy Simulation Based Turbulent Flow-induced Vibration of Fully Developed Pipe Flow." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd295.pdf.
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Pittard, Matthew T. "Large eddy simulation based turbulent flow-induced vibration of fully developed pipe flow /." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd295.pdf.
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Allison, Anne-Marie E. "Analytical investigation of a semi-empirical flow-induced vibration model." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0014/NQ31170.pdf.
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Mekanik, Abolghasem. "General solution for unsteady annular flows between concentric cylinders and annular flow-induced instabilities." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28844.
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The aim of this Thesis is to obtain time-accurate solutions of the Navier-Stokes equations for laminar incompressible unsteady flows generated by oscillating boundaries in an annular region made from two concentric cylinders. For this, a time-dependent coordinate transformation is first used to obtain a fixed computational domain. The resulting governing equations in the fixed domain are discretized in real time based on a three-time-level implicit scheme. A pseudo-time integration with artificial compressibility is then used to reduce the resulting coupled discretized equations in delta form to set a decoupled scalar tridiagonal systems.The method of solution has been applied to various 3-D unsteady flows in annular geometries, as well as to 2-D annular flows. The numerical results obtained are compared with those based on a mean position analysis, without transformation, for small-amplitude oscillation. This comparison shows that the time-dependent coordinate transformation is necessary to obtain accurate solutions for larger-amplitude oscillations.
The mean-position approach has also been applied to the analysis of axially variable annular configurations. The results obtained show more pressure recovery after a diffuser section with 6$ sp circ$ half-angle than in the case of 20$ sp circ$ half-angle.
A comprehensive experimental study was conducted to validate the theoretical results in the range of laminar flow. The results obtained were in good agreement with the numerical results, specially with those obtained by the time-dependent coordinate transformation. Experiments were also conducted for turbulent flow.
Based on the theoretical models developed, a computational method has been used to study fluid-structure interaction phenomena. It was applied to several cylindrical annular configurations in which one side of the annulus, the outer cylinder, is assumed to be flexibly supported, and thus to be susceptible to flow-induced instabilities. The structural and N-S equations were solved simultaneously by employing the numerical method developed for the unsteady flow and a fourth-order Runge-Kutta scheme for the structural motion. The numerical results thus obtained have predicted the stability of the structure for different annular geometries. The structure having a uniform annular geometry was shown to be more damped, while the annular geometry with a backward facing step is less damped. The study of the structure for a uniform annular geometry in the case of the rocking motion of the outer cylinder predicts an instability in the form of flutter of the outer cylinder.
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Thornhill, Lindsey Dorough. "Fatigue behavior of flexhoses and bellows due to flow-induced vibrations." Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/17624.
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Van, Zyl Marilize. "Prediction of flow-induced vibration in shell-and-tube heat exchangers." Diss., University of Pretoria, 2004. http://hdl.handle.net/2263/28055.
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Please read the abstract (Summary) in the 00front part of this documentDissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2006.
Mechanical and Aeronautical Engineering
unrestricted
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Kim, Chan Mun. "Vortex induced noise and vibration in flow past several flat plates /." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487673114116149.
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Alnujaie, Ali H. "Flow-induced Vibration of Double Wall Carbon Nanotubes Conveying Pulsating Fluid." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1555409894074253.
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Grant, Ivan. "Flow induced vibrations in pipes a finite element approach /." Cleveland, Ohio : Cleveland State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=csu1274384202.
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Thesis (M.S.)--Cleveland State University, 2010.Abstract. Title from PDF t.p. (viewed on June 3, 2010). Includes bibliographical references (p. 51-52). Available online via the OhioLINK ETD Center and also available in print.
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Gonzalez, Enrique C. (Enrique Casaprima) 1961. "High frequency dynamic response of marine risers with application to flow-induced vibration." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/107860.
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Peoples, W. Wesley (William Wesley) 1977. "The effects of staggered buoyancy modules on flow-induced vibration of marine risers." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/89915.
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Scott, Karen Mary Louise. "Practical Analysis Tools for Structures Subjected to Flow-Induced and Non-Stationary Random Loads." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/38686.
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There is a need to investigate and improve upon existing methods to predict response of sensors due to flow-induced vibrations in a pipe flow. The aim was to develop a tool which would enable an engineer to quickly evaluate the suitability of a particular design for a certain pipe flow application, without sacrificing fidelity. The primary methods, found in guides published by the American Society of Mechanical Engineers (ASME), of simple response prediction of sensors were found to be lacking in several key areas, which prompted development of the tool described herein. A particular limitation of the existing guidelines deals with complex stochastic stationary and non-stationary modeling and required much further study, therefore providing direction for the second portion of this body of work.
A tool for response prediction of fluid-induced vibrations of sensors was developed which allowed for analysis of low aspect ratio sensors. Results from the tool were compared to experimental lift and drag data, recorded for a range of flow velocities. The model was found to perform well over the majority of the velocity range showing superiority in prediction of response as compared to ASME guidelines. The tool was then applied to a design problem given by an industrial partner, showing several of their designs to be inadequate for the proposed flow regime. This immediate identification of unsuitable designs no doubt saved significant time in the product development process.
Work to investigate stochastic modeling in structural dynamics was undertaken to understand the reasons for the limitations found in fluid-structure interaction models. A particular weakness, non-stationary forcing, was found to be the most lacking in terms of use in the design stage of structures. A method was developed using the Karhunen Loeve expansion as its base to close the gap between prohibitively simple (stationary only) models and those which require too much computation time. Models were developed from SDOF through continuous systems and shown to perform well at each stage. Further work is needed in this area to bring this work full circle such that the lessons learned can improve design level turbulent response calculations.Ph. D.
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Yin, Decao. "Experimental and Numerical Analysis of Combined In-line and Cross-flow Vortex Induced Vibration." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Centre for Ships and Ocean Structures, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-20014.
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This thesis presents results from experimental and numerical investigations of the hydrodynamic forces on a rigid cylinder moving with prescribed orbits in uniform flow. The hydrodynamic forces are measured in both in-line (IL) and cross- ow (CF) directions. The measurements are processed to nd excitation and added mass coeffcients at discrete frequencies. The numerical simulations are used to illustrate the vortex shedding modes and are compared with the experimental results. The hydrodynamic coeffcients obtained from the harmonic forced motion experiments of a rigid cylinder do not always represent forces on a cross section of a exible beam. The orbits used in the forced motion experiments are therefore extracted from the measured motions of cross sections of a exible pipe under uniform and shear flows. Both periodic and observed orbits within a time window are applied as prescribed motions. Higher order displacement components are present in such orbits. IL response amplitudes from combined IL and CF response are larger than pure IL response amplitudes. The hydrodynamic coefficients obtained from the periodic experiments are often larger than those obtained from the pure IL tests. Higher order displacement components are more common in the IL direction than in the CF direction, and higher order IL displacement components will cause larger hydrodynamic forces in both directions. The hydrodynamic coefficients obtained from periodic motion tests are adequate for representing quasi-periodic observed motions. For chaotic observed motions, periodic orbits will yield hydrodynamic coefficients with larger uncertainties. Results from numerical analyses using large eddy simulation (LES) indicate that this method can be used to identify vortex shedding patterns and predict hydrodynamic forces under certain Re numbers and orbits.