Modal Excitation Of A Flexible Cylinder Undergoing Vortex Induced Vibrations
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Modal Excitation Of A Flexible Cylinder Undergoing Vortex Induced Vibrations
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Author : Harrison P. Zimmer
language : en
Publisher:
Release Date : 2014
Modal Excitation Of A Flexible Cylinder Undergoing Vortex Induced Vibrations written by Harrison P. Zimmer and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with Offshore structures categories.
Mapping The Hydrodynamic Properties Of Flexible And Rigid Bodies Undergoing Vortex Induced Vibrations
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Author : Dixia Fan
language : en
Publisher:
Release Date : 2019
Mapping The Hydrodynamic Properties Of Flexible And Rigid Bodies Undergoing Vortex Induced Vibrations written by Dixia Fan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019 with categories.
Long slender structures within the steady oncoming flow are subject to vibrations caused by vortical structures forming due to a distributed flow instability in their wake. The features of these vibrations are a complex function of the main parameters, and hence systematic exploration of the basic mechanisms has only recently begun. The problem has considerable theoretical interest as it constitutes a fundamental nonlinear flow-structure interaction system, while it is very important for the design of offshore industry systems, such as risers, cables, and hawsers, which are subject to large drag loads and potentially catastrophic fatigue damage as a consequence of the vortex-induced vibrations. The much simpler problem of a flexibly mounted rigid cylinder in cross-flow has become the canonical problem of bluff body flow-structure interaction and has been extensively studied and mapped both experimentally and computationally. Attempts have been made to extend and apply the properties and databases found in rigid structures to flexible structures. This requires, first of all, a strip-theory approach, but it was also found that additional concepts are needed, such as the presence of "hybrid" modes consisting of mixed traveling and standing waves, a strong interaction between in-line and cross-flow modal responses, and a response that consists of multiple frequencies. In this thesis we employ an optical tracking experimental tool that can measure the detailed vibrational response and also allows the evaluation of the distributed forces acting along the structure, together with targeted CFD calculations that provide the detailed vortical structures in the wake, to investigate some fundamental properties of the vortex-induced vibrations of flexible structures, and assess the validity of basic assumptions that are currently in use. Specifically, we assess first the validity of the strip theory approach that uses databases obtained from rigid cylinders to calculate the local forces in a flexible structure. We compare the experimentally derived forces in a flexible structure with those obtained from the rigid cylinder and we find the conditions under which they are applicable. Next, we demonstrate that a newly designed "Intelligent Towing Tank" (ITT) can derive with a minimal number of experiments databases for rigid cylinders to be used for flexible structure response prediction, covering the entire parametric space. We employ Gaussian Process Regression to guide the selection of a sequence of experiments in an automated Towing Tank to cover the parametric space within narrow uncertainty range. Our findings are as follows: 1. The strip theory assumption for uniform flexible structures in uniform flow undergoing in-line and cross-flow oscillations is applicable, but additional concepts are needed to describe the form of the extended coupling of flow and structure, which we discuss in detail. 2. For a flexible cylinder consisting of two segments of equal length but different diameter, it is shown that the strip theory approach is still valid, but the existing rigid cylinder databases do not provide accurate force estimates because they fail to account for multi-frequency response. 3. We derived a new database for rigid cylinders that accounts for a two-frequency response. This was made possible due to the substantial experimental time saving of the ITT. A major conclusion is that when the response contains two frequencies that are both within the excitation region, reduced energy is transferred from the fluid to structure.
Vortex Induced Vibration Of Flexible Cylinders In Time Varying Flows
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Author : Themistocles L. Resvanis
language : en
Publisher:
Release Date : 2014
Vortex Induced Vibration Of Flexible Cylinders In Time Varying Flows written by Themistocles L. Resvanis and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with categories.
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
Hydrodynamics Around Cylindrical Structures
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Author : Jorgen Fredsoe
language : en
Publisher: World Scientific
Release Date : 1997-03-17
Hydrodynamics Around Cylindrical Structures written by Jorgen Fredsoe and has been published by World Scientific this book supported file pdf, txt, epub, kindle and other format this book has been release on 1997-03-17 with categories.
This book discusses the subject of wave/current flow around a cylinder, the forces induced on the cylinder by the flow, and the vibration pattern of slender structures in a marine environment.The primary aim of the book is to describe the flow pattern and the resulting load which develops when waves or current meet a cylinder. Attention is paid to the special case of a circular cylinder. The development in the forces is related to the various flow patterns and is discussed in detail. Regular as well as irregular waves are considered, and special cases like wall proximities (pipelines) are also investigated.The book is intended for MSc students with some experience in basic fluid mechanics and for PhD students.
Modelling And Analysis Of Vortex Induced Vibrations Of Rigid And Flexible Cylinders
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Author : Hossein Zanganeh
language : en
Publisher:
Release Date : 2014
Modelling And Analysis Of Vortex Induced Vibrations Of Rigid And Flexible Cylinders written by Hossein Zanganeh and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with categories.
Vortex-induced vibration (VIV) is a fundamental phenomenon commonly encountered in various practical engineering. Owing to the complexities associated with this phenomenon, modelling and prediction of VIV is a challenging task. In this research, a new predictive phenomenological model is developed for VIV of an elastically mounted rigid cylinder subjected to a fluid flow and free to vibrate in both cross-flow (CF) and in-line (IL) directions. The ensuing dynamical system is based on double Duffing-van der Pol (structural-wake) oscillators with the two structural equations containing both cubic and quadratic nonlinear terms. The cubic nonlinearities capture the geometrical coupling of CF/IL displacements excited by hydrodynamic lift/drag forces whereas the quadratic nonlinearities allow the fluid-structure interactions. The model predictions are extensively compared with published and in-house experimental results. Experiments are carried out at the Department's towing tank to calibrate and validate numerical prediction results. Comparisons illustrate the qualitative resemblance between experimental and prediction results, highlighting how the new model can capture several important VIV characteristics including a two-dimensional lock-in, jump and hysteresis phenomenon, and figure-of-eight trajectory tracing the periodically coupled CF/IL oscillations. Moreover, the parametric studies reveal the important effect of geometrical nonlinearities, mass ratio, damping ratio and natural frequency ratio. Insights into hydrodynamic properties such as VIV-induced mean drag, added mass and damping are drawn based on the newly proposed model via analytical-numerical approaches and comparisons with published literature. Consequently, the new prediction model is applied to the VIV analysis of flexible circular cylinders subjected to uniform and linearly sheared currents. To capture a three-dimensional aspect of the flexible cylinder experiencing VIV, nonlinear equations of CF, IL and axial structural oscillations are considered to be coupled with the distributed van der Pol wake-oscillators. Governing equations are numerically solved via a space-time finite difference scheme, and the obtained numerical results highlight several aspects of VIV of elastic cylinders along with the axial motion effects. Apart from the validation of the numerical model with published experimental results, this study reveals how the effect of axial motion and its nonlinear coupling with the two transverse CF/IL motions can be very important. These depend on the reduced velocity, the fluid-structure parameters, the single or multi-mode lock-in condition, and the standing-wave versus travelling-wave features.
Vortex Induced Vibration Of Cylindrical Structures
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Author : Enhao Wang
language : en
Publisher:
Release Date : 2017
Vortex Induced Vibration Of Cylindrical Structures written by Enhao Wang and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with categories.
Once Sx/D is large enough for the vortices to be completely detached from the upstream cylinder, the response of the upstream cylinder is similar to the typical VIV response whereas the downstream cylinder undergoes wake-induced vibration (WIV). The characteristics of the response of the downstream cylinder in the present study are similar to those of the first two response regimes. The third response regime is not observed for the flexible downstream cylinder with both ends fixed. The two changes in the phase relation between the cross-flow displacements of the two tandem flexible cylinders are discovered to be linked with the initial-upper branch transition and the upper-lower branch transition, respectively. The correlation lengths of the two tandem flexible cylinders decrease significantly in the transition range between the upper and lower branches. Three vortex shedding modes (2S, P + S and 2P) have been identified in the present study. It is found that the upper-branch 2P mode is associated with large-amplitude vibration of the upstream cylinder and the P + S mode is related to large-amplitude vibration of the downstream cylinder for Sx/D = 3.5 and 5. On the other hand, the lower-branch 2P mode leads to small-amplitude vibration of the downstream cylinder in the post-lock-in range at Sx/D = 2.5. The relative phase shifts of the sectional lift coefficients on different spanwise cross sections can be attributed to the variation of the vortex shedding flow along the flexible cylinders and these phase shifts result in poor phasing between the forces and the displacements which is related to the decrease of the correlation lengths.
Modal Interactions And Targeted Energy Transfers In Laminar Vortex Induced Vibrations Of A Rigid Cylinder With Strongly Nonlinear Internal Attachments
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Author :
language : en
Publisher:
Release Date : 2013
Modal Interactions And Targeted Energy Transfers In Laminar Vortex Induced Vibrations Of A Rigid Cylinder With Strongly Nonlinear Internal Attachments written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.
A Critical Review Of The Intrinsic Nature Of Vortex Induced Vibrations
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Author : Turgut Sarpkaya
language : en
Publisher:
Release Date : 2003
A Critical Review Of The Intrinsic Nature Of Vortex Induced Vibrations written by Turgut Sarpkaya and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2003 with Vibration categories.
This is a concise and comprehensive review of the progress made during the past two decades on vortex induced vibration (VIV) of mostly circular cylindrical structures subjected to steady uniform flow. The critical elements of the evolution of the ideas, theoretical insights, experimental methods, and numerical models are traced systematically; the strengths and weaknesses of the current state of the understanding of the complex fluid/structure interaction are discussed in some detail. Finally, some suggestions are made for further research on VIV. The organization of the paper is given at the end of the next section.
Flow Induced Vibration
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Author : Robert D. Blevins
language : en
Publisher:
Release Date : 1977
Flow Induced Vibration written by Robert D. Blevins and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1977 with Science categories.
Flow Induced Vibration Of Circular And Square Cylinder With Low Mass And Damping
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Author : Jisheng Zhao
language : en
Publisher:
Release Date : 2012
Flow Induced Vibration Of Circular And Square Cylinder With Low Mass And Damping written by Jisheng Zhao and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.
This thesis investigates cross-flow flow-induced vibration of elastically mounted rigid circular and square cylinders with low mass and damping ratio over a range of low and vibration parameters. In particular, two typical body oscillator phenomena of flow-induced vibration, vortex-induced vibration and galloping, are studied experimentally. Thus, the study consists of two main parts. The first part, using simultaneous displacement, force and vorticity measurements, investigates the dynamic response of a circular cylinder undergoing transverse free vortex-induced vibrations and controlled trajectory-following vibrations. The second part characterises the amplitude and frequency responses of a square cylinder with angle of attack variation. Despite extensive work has been undertaken to understand the fundamental characteristics of free and forced vibrations of a circular cylinder, there are still a number of unresolved questions in the literature concerning the similarities and differences between the free and forced vibration cases. In order to directly compare these two vibration cases, a low-friction air-bearing rig and a real-time feedback control system were therefore designed and implemented in experiments. The major results obtained show that the transverse lift force and the decomposed vortex force experienced by a cylinder forced to follow the trajectory of free VIV are identical to the free vibration case, when both the total phase and the vortex phase relative to the body motion are constantly stable. However, significant differences between the two vibration cases are found at a reduced velocity located in the middle upper branch of VIV where largest-scale body vibration occur with complex switching phenomena in the total phase and the vortex phase. The results from the second part, flow-induced vibration of a square cylinder with angle of attack variation, show that the cylinder, as expected, experiences galloping at the zero angle of attack orientation (0 degree) and vortex-induced vibration at the diamond orientation (45 degree). As the angle of attack is varied from 45 degree to 0 degree, the body can undergo combinations of both vortex-induced vibration and galloping in a mixed response region. In this region, the oscillation amplitude response exhibits a new branch that exceeds the responses resulting from the two body-oscillator phenomena independently. For velocities above this resonant region, the body oscillation frequency splits into two diverging branches. Further, analysis of the amplitude reveals that the transition between galloping and vortex-induced vibrations occurs over a narrow range of angle of incidence. Despite the rich set of states found in the parameter space the vortex shedding modes remain very similar to those found previously in vortex-induced vibration.