Numerical Study On Vortex Induced Vibration Responses Of A Circular Cylinder Attached By A Free To Rotate Dartlike Overlay
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Numerical Study On Vortex Induced Vibration Responses Of A Circular Cylinder Attached By A Free To Rotate Dartlike Overlay
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Author :
language : en
Publisher:
Release Date : 2016
Numerical Study On Vortex Induced Vibration Responses Of A Circular Cylinder Attached By A Free To Rotate Dartlike Overlay written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.
Two Dimensional Numerical Study With Les Modeling Of Vortex Induced Vibration Of A Circular Cylinder Subjected To A Uniform Flow At A Moderate Reynolds Number
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Author : Helmi Nazmi Al-Jamal
language : en
Publisher:
Release Date : 2002
Two Dimensional Numerical Study With Les Modeling Of Vortex Induced Vibration Of A Circular Cylinder Subjected To A Uniform Flow At A Moderate Reynolds Number written by Helmi Nazmi Al-Jamal and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2002 with Vibration categories.
Vortex Induced Vibration And Forced Oscillation Motion Of A Circular Cylinder Fitted With A Single Spanwise Tripwire
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Author : Ehsan Vaziri
language : en
Publisher:
Release Date : 2021
Vortex Induced Vibration And Forced Oscillation Motion Of A Circular Cylinder Fitted With A Single Spanwise Tripwire written by Ehsan Vaziri and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021 with categories.
This experimental study consisted of two main parts. The first part investigated the control induced by a spanwise tripwire on a circular cylinder undergoing one-degree-of-freedom vortex-induced vibration (VIV). The cylinder vibrates in the cross-stream direction as a result of the fluid forcing in a recirculating water tunnel. Changing mass and damping ratios in the test rig allowed the investigation at different VIV response branches. The tripwire diameter was 6.25% of the cylinder diameter. Experimental research was conducted by attaching the large-scale tripwire along the span of the cylinder at various angular positions ranging from 0° to 180° (with respect to the most upstream point of the cylinder). Along with measuring the trajectory of the cylinder motion, the instantaneous velocity field in the near wake of the cylinder was obtained simultaneously at a fixed Reynolds number of 10,000 (based on the cylinder diameter) using a Particle Image Velocimetry (PIV) system. Various vortex-formation modes induced by the tripwire were observed. It was shown that the oscillation pattern, frequency, and amplitude of the cylinder can be altered significantly depending on the angular position of the tripwire and the VIV response branch. For specific tripwire positions, increases of up to 52 times and decreases of up to 98% were identified in the oscillation amplitude of the tripped cylinder compared to the amplitude of the clean cylinder.The second part of the study investigated the effects of the tripwire on the flow structure behind a circular cylinder forced to oscillate harmonically at prescribed amplitudes and frequencies in the cross-stream direction. Oscillation amplitudes are 0.05, 0.3 and 0.6 times the cylinder diameter, and oscillation frequencies are 0.61, 0.8, and 1 times the vortex shedding frequency of the stationary clean cylinder counterpart. For a fixed oscillation amplitude and frequency, the tripwire can either induce intermittent switching between various vortex shedding modes or cause a wake mode to be dominant during the entire observed oscillation motion by altering the vortex shedding mechanism. The wake of the tripped cylinder undergoing the lowest amplitude forced oscillation motion showed resemblance to the wake of the stationary tripped cylinder.
Investigating Phenomena In Vortex Induced Vibration Of A Cylinder Using Controlled Vibration
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Author : Timothy Lester Morse
language : en
Publisher:
Release Date : 2009
Investigating Phenomena In Vortex Induced Vibration Of A Cylinder Using Controlled Vibration written by Timothy Lester Morse and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
In this study, we use controlled vibration, where we oscillate a rigid cylinder with a prescribed motion, in a fluid flow, in order to provide insight into aspects of vortex-induced vibration. We make extensive measurements of the fluid forces on a cylinder that oscillates sinusoidally, transverse to a free stream, at both Re = 4,000 and Re = 12,000, and generate high resolution contour plots of various fluid forcing quantities in the plane of normalized amplitude and wavelength. With such resolution, we are able to discover discontinuities in the force and phase contours, which enable us to clearly identify boundaries separating different fluid forcing regimes. These boundaries appear remarkably similar to boundaries separating different vortex formation modes in the Williamson & Roshko (1988) map of regimes. Wake vorticity measurements (using DPIV) exhibit the 2S, 2P, and P+S modes, as well as a regime where the vortex formation is not synchronized with the cylinder oscillation. A further new discovery is the existence of a region where two vortex formation regimes overlap. Associated with this overlap region, we identify a distinct mode of vortex formation where two pairs of vortices are shed per cycle of oscillation (similar to the 2P mode) but the secondary vortex is much weaker, which we have termed '2POVERLAP ', or simply the '2PO ' mode. This '2PO ' mode is of particular importance, as it is responsible for generating the peak resonant response of the body. By examining the energy transfer from fluid to body motion we predict the response of an elastically mounted cylinder that agrees remarkably well with measured free vibration responses. We introduce the concept of an "energy portrait", which allows us to identify stable and unstable amplitude response solutions and thus to predict clearly the hysteretic and intermittent switching mode transitions, both of which correspond with such phenomena measured from free vibration. In addition to predicting steady state (sinusoidal) behavior, we develop a quasi-steady model which allows us to predict the dynamics of a freely oscillating cylinder having transient or unsteady behavior. Using this model, we find a regime of normalized flow velocity where steady state vortex-induced vibrations cannot occur, and the cylinder can only oscillate with unsteady motion. Further studies include the effect of Reynolds number on the critical mass for an oscillating body, below which a structure will vibrate up to infinite normalized velocity. Finally, we measure the effect of spanwise end conditions on a free vibration response.
Experimental Investigation Of Vortex Induced Vibration Of A Circular Cylinder
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Author : Asif Khalak
language : en
Publisher:
Release Date : 1996
Experimental Investigation Of Vortex Induced Vibration Of A Circular Cylinder written by Asif Khalak and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1996 with categories.
Vortex Induced Vibrations Of A Tethered Circular Cylinder In A Free Stream
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Author : Patrick Browne
language : en
Publisher:
Release Date : 2006
Vortex Induced Vibrations Of A Tethered Circular Cylinder In A Free Stream written by Patrick Browne and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with Cylinders categories.
Enhancement Of Vortex Induced Vibrations Using Roughness Strips
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Author : Ashwin Vinod
language : en
Publisher:
Release Date : 2013
Enhancement Of Vortex Induced Vibrations Using Roughness Strips written by Ashwin Vinod and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with Surface roughness categories.
"The current experimental work focuses on studying the effects of surface roughness on vortex induced vibration (VIV) of an elastically mounted circular cylinder which is free to vibrate in a direction transverse to the flow. Flow separation in known to occur due to viscous effects when a fluid flows over a bluff body. The separation of fluid causes shedding of alternating vortices in the downstream region, which in turn impart an alternating force on the bluff body. The vibrations incurred due to such forces are called as Vortex Induced Vibrations (VIV) and have been traditionally known to be harmful to civil, aerospace, marine and offshore structures. VIV has thus been extensively studied by many researchers in the past, in order to mitigate this harmful phenomenon. The focus of this thesis work is enhancing VIV, mostly for the purpose of energy harvesting. This effort aims in understanding the dynamics of vortex shedding and its enhancement when complex boundaries are coupled to the problem. Our main objective is to identify cylinder configurations which would lead to high amplitudes of vibrations and a greater range of synchronization. Sandpaper strips of ISO/FEPA designations ranging from very fine to extra course macro grits were used in order to study the effect of roughness on VIV of a circular cylinder. Increased amplitudes of vibration and range of synchronization were observed for the configurations with the roughness. The response also showed a dependence on the grit size. In order to study the effect of position of the strip, experiments were performed with zero roughness strips (strips with only thickness and no roughness) placed at different angular positions from the stagnation point. A change in the response profile compared to the case of the smooth cylinder was observed. The response profiles of the configurations with the sandpaper strips and the zero roughness strips were compared in an attempt to decouple the effect of roughness and thickness. The profile showed different response characteristics within different ranges of reduced velocities. Experiments were repeated with springs of different stiffness to investigate the effect of stiffness and a variation in the range of synchronization and the amplitudes of vibration was observed. Configurations that could lead to increased amplitudes of vibration and range of synchronization were found"--Abstract, leaf iii.
Vortex Induced Vibration Of A Circular Cylinder
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Author : 朱執均
language : en
Publisher:
Release Date : 2011
Vortex Induced Vibration Of A Circular Cylinder written by 朱執均 and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
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 On A Two Dimensional Circular Cylinder With Low Reynolds Number And Low Mass Damping Parameter
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Author :
language : en
Publisher:
Release Date : 2015
Vortex Induced Vibration On A Two Dimensional Circular Cylinder With Low Reynolds Number And Low Mass Damping Parameter written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.