Download or read book Response of Vortex induced Vibration of Circular Structures Using Experimentally Derived Model Parameters written by Khandaker Z. Rahman and published by . This book was released on 2005 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Vortex induced Vibration of Circular Cylindrical Structure with Different Aspect Ratios written by Mohd Asamudin A Rahman and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: [Truncated] The purpose of this thesis is to study the Vortex-Induced Vibration (VIV) response of cylindrical offshore structures. The present study deals with the forces on the structure and amplitude of the structural vibration. For a bluff body exposed to the fluid flow, a VIV response can arise which leads to undesirable forces acting along the body causing fatigue and serious harm to the structure. This work focuses on VIV generation from an elastically mounted cylindrical structure with varying aspect ratio. Studies in offshore engineering have shown that the VIV of a longer structure such as riser and spar structure can be fundamentally different from a low aspect ratio structure such as circular Floating Production Storage Offloading (i.e., Sevan FPSO). Complementary approaches have been employed to study the VIV phenomenon. A series of experiments were done in an enclosed towing tank to investigate the response amplitudes, hydrodynamic forces, lock-in region, Strouhal number and frequency response while varying the aspect ratio (L/D) of the cylinder from L/D = 0.5 to 13. The experiments were conducted in a uniform current flow and limited to a single degree of freedom movement in the transverse direction. Comparisons were made between Computational Fluid Dynamics (CFD) simulations and experimental results of the same configurations. Three-dimensional forced vibration simulations were performed to capture the forces on the structure for varying structure aspect ratio. The correlation length of the vortex cells was observed to be affected by vortex shedding and the proportions of the tested structures. Aside from experimental and CFD approach, a semi-empirical model was shown to be successful in fundamentally modelling the wake development and vortex shedding. In order to capture the analytical solution of the VIV phenomenon, a wake oscillator model (WOM) was studied and compared with the experimental and numerical simulation results. An existing published WOM was modified to include the influence of the aspect ratio using present experimental data obtained from free vibrating cylinders in water. The capability of the modified model was illustrated through comparisons between the model predictions and results obtained previously from experiments and CFD simulations.
Download or read book A Critical Review of the Intrinsic Nature of Vortex Induced Vibrations written by Turgut Sarpkaya and published by . This book was released on 2003 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Flow induced Vibration of Circular and Square Cylinder with Low Mass and Damping written by Jisheng Zhao and published by . This book was released on 2012 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Wind Tunnels and Experimental Fluid Dynamics Research written by Jorge Colman Lerner and published by BoD – Books on Demand. This book was released on 2011-07-27 with total page 728 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book "Wind Tunnels and Experimental Fluid Dynamics Research" is comprised of 33 chapters divided in five sections. The first 12 chapters discuss wind tunnel facilities and experiments in incompressible flow, while the next seven chapters deal with building dynamics, flow control and fluid mechanics. Third section of the book is dedicated to chapters discussing aerodynamic field measurements and real full scale analysis (chapters 20-22). Chapters in the last two sections deal with turbulent structure analysis (chapters 23-25) and wind tunnels in compressible flow (chapters 26-33). Contributions from a large number of international experts make this publication a highly valuable resource in wind tunnels and fluid dynamics field of research.
Download or read book Modelling and Analysis of Vortex induced Vibrations of Rigid and Flexible Cylinders written by Hossein Zanganeh and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Understanding Flow induced Vibration Via a Physics constrained Data driven Approach written by Leixin Ma and published by . This book was released on 2021 with total page 206 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vortex-induced vibration (VIV) of long flexible cylinders involves a large number of physical variables, such as Strouhal number, Reynolds number, and damping. Due to the nonlinearity and high-dimensionality of the problem, current VIV prediction models have large error bounds, and require selection of input parameters without knowing which ones are most important. In this thesis, a prior-knowledge-based, trend-constrained, machine learning technique is developed for the purpose of identifying those physical parameters which are most useful in the prediction of the VIV of flexible cylinders, such as drilling risers and umbilical cables. The results show that from four to six input parameters are usually sufficient to provide acceptable predictions without overfitting the data. In the course of the research three new parameters were found to be particularly useful. The first is the dimensionless damping parameter, c*, which is derived from the requirement that vibration power flowing into the structure from the flow equals the power lost to damping. The second is the mode dominance factor, K, which reveals the extent to which the observed vibration is dominated by a single mode. The third, denoted by the character, [alpha], expresses the dominance of travelling or standing waves in the response. In a neural network model these new features are put in competition with fourteen previously known VIV parameters to see which of all these candidate features are most important. For cross-flow amplitude prediction, a trend-constrained neural network balances the usual goal of minimizing the model prediction error with the error associated with a departure from experimentally observed dependence on Reynolds number and damping. The resulting model is able to reveal important additional insights, including the role of mode number, mode dominance and travelling waves in the regulation of VIV response amplitude. Compared to unconstrained machine learning models, the trend-constrained models are more consistent with extensive experimental observations. For the prediction of higher harmonics, prior knowledge of the influence of bending stiffness and damping are embedded in the machine learning model. This model reveals the importance of mode dominance and travelling waves in the regulation of higher harmonics response. The previously postulated importance of damping parameter and bending stiffness is verified. The overall results point towards promising directions for improving existing engineering design software, that is currently used to predict the fatigue life of structures exposed to VIV.
Download or read book VORTEX INDUCED VIBRATION OF STRUCTURES WITH BROKEN SYMMETRY written by Banafsheh Seyedaghazadeh and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A bluff body, i.e., an object with a blunt cross-section immersed in cross-flow forms an unstable wake, resulting in the formation of large-scale vortical structures, which induce unsteady forces on the body. If the body is flexible or flexibly mounted, vortex-induced vibration (VIV) results, which can have significant implications for a number of physical systems, from aeolian harps to power transmission lines, towing cables, undersea pipelines, drilling risers and mooring lines used to stabilize offshore floating platforms. VIV has been a major subject of research in recent years. The majority of these studies have focused on symmetric systems in which the structure, its geometry, its boundary conditions and the incoming flow are symmetric. However, in many real-world applications, VIV occurs in asymmetric systems. A flexibly-mounted vertical uniform circular cylinder which is placed in a uniform current is an example of a system with symmetric geometry, boundary conditions and wake. This geometry is usually considered as a canonical configuration in modeling structures undergoing VIV. However, many other configurations can exist in which the geometrical symmetry of the system is broken, such as an inclined cylinder in which the cylinder is placed with an angle with respect to the incoming flow direction, or a tapered cylinder in which the diameter of the circular cylinder varies along its length, or when the geometry of the cross-section changes from circular to other shapes such as square or triangle. Also, in some other cases, such as a circular cylinder which is forced to rotate about its long axis, the symmetry of the surrounding wake is broken by the rotation imposed on the cylinder. These cases among many examples are systems with broken symmetry, and are widely used in the offshore industry. The main objective of this thesis is to study VIV of systems with broken symmetry. For this purpose, experiments are conducted and the VIV response of the systems are studied in terms of amplitude and frequency of oscillations as well as the wake of the cylinder. It is shown that higher harmonics contributions of flow forces play an important role in VIV of structures. Also, various taper ratios in VIV of tapered cylinders are found to be the major parameters influencing the VIV response of tapered cylinders. Different rotation rates in VIV of a rotating cylinder, various angles of attack in VIV of a triangular cylinder and different angles of inclination in VIV of flexible inclined cylinder are found to be the influencing parameters in studying the VIV of structures with broken symmetry.
Download or read book Flow induced Vibration of Elastically Supported Rectangular Cylinders written by Jeffrey L. Garrett and published by . This book was released on 2003 with total page 564 pages. Available in PDF, EPUB and Kindle. Book excerpt: Eight rectangular cylinders with aspect ratios that varied from 2 to 7 tested in the wind tunnel at zero degree incidence in a nearly turbulence-free flow field. The models were elastically suspended in the wind tunnel and constrained to a single degree of freedom, vertical motion transverse to the wind flow direction. Five tests were conducted for every aspect ratio, each with a different system mass. Side plates were utilized to minimize three-dimensional flow effects at the ends of the models and to maximum the two-dimensional flow field. Prior to testing each model, the following dynamic parameters were determined: natural frequency, mass, stiffness, damping, and Scruton number. Each test began with the model motionless. The wind speed was incrementally increased until vortex-induced transverse vibrations were observed. At each increment of wind speed where transverse vibrations were observed, the maximum amplitude of vibration and the wind speed were recorded. All models exhibited vortex-induced vibration lock-in during at least one wind regime. Five models exhibited vortex-induced vibration lock-in during two wind regimes. All models exhibited vortex-induced vibration lock-in at the critical reduced velocity predicted by the modified Strouhal number. Experimental results for each of the forty test cases include the reduced amplitudes and reduced velocities during lock-in, confirmation that lock-in can occur during more than one wind regime, and confirmation that the modified Strouhal number accurately predicts the reduced velocity when lock-in commences. The relation between the reduced amplitude and the mass/damping parameter was studied. As a result, a parameter for rectangular cylinders was derived as a function of the mass, damping, and geometry of the system. This parameter is analogous to the mass/damping parameter for circular cylinders, the Scruton number. Finally, a single response equation was developed that predicts the amplitude of vortex-induced vibration for a rectangular cylinders with aspect ratios from 2 to 7 utilizing the mass/damping/geometry parameter derived as part of this study.
Download or read book Flow induced Vibration written by Robert D. Blevins and published by . This book was released on 2001-01-01 with total page 477 pages. Available in PDF, EPUB and Kindle. Book excerpt: Focuses on applications for offshore platforms and piping; and, wind-induced vibration of buildings, bridges, and towers. This title also focuses on acoustic and mechanical vibration of heat exchangers, power lines, and process ducting.
Download or read book Flow Induced Vibration of Circular Cylindrical Structures written by Shoei-Sheng Chen and published by Springer. This book was released on 1987-07-21 with total page 504 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the vibration of circular cylinders in quiescent fluid, axial flow, and crossflow, and applications of the analytical methods and experimental data in design evaluation of various system components consisting of circular cylinders. It emphasizes analytical tools to predict structural vibration and experimental data for fluid forces and will help solve many important flow induced vibration problems in different industries. The techniques and results presented in this book will be useful not only to designers but also to researchers in this field. A comprehensive treatment of different situations is given in this book. For example, a thorough review of the analytical models and most recent development of fluidelastic instability of an array of cylinders in crossflow are presented in Chapter 10.
Download or read book Experimental Investigation of Vortex induced Vibration of a Circular Cylinder written by Asif Khalak and published by . This book was released on 1996 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Flow Induced Vibrations written by Eduard Naudascher and published by Courier Corporation. This book was released on 2012-03-27 with total page 434 pages. Available in PDF, EPUB and Kindle. Book excerpt: Despite their variety, the vibration phenomena from many different engineering fields can be classified into a relatively few basic excitation mechanisms. The classification enables engineers to identify all possible sources of excitation in a given system and to assess potential dangers. This graduate-level text presents a synthesis of research results and practical experience from disparate fields in the form of engineering guidelines. It is particularly geared toward assessing the possible sources of excitation in a flow system, in identifying the actual danger spots, and in finding appropriate remedial measures or cures. Flow-induced vibrations are presented in terms of their basic elements: body oscillators, fluid oscillators, and sources of excitation. By stressing these basic elements, the authors provide a basis for the transfer of knowledge from one system to another, as well as from one engineering field to another. In this manner, well-known theories on cylinders in cross-flow or well-executed solutions from the field of wind engineering--to name just two examples--may be useful in other systems or fields on which information is scarce. The unified approach is broad enough to permit treatment of the major excitation mechanism, yet simple enough to be of practical use.
Download or read book Flow induced Vibration written by Robert D. Blevins and published by . This book was released on 1977 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Hydrodynamics Around Cylindrical Structures written by Jorgen Fredsoe and published by World Scientific. This book was released on 1997-03-17 with total page 550 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Enhancement of Vortex Induced Vibrations Using Roughness Strips written by Ashwin Vinod and published by . This book was released on 2013 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: "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.
Download or read book Vortex Induced Vibration of Circular Cylindrical Structures written by Robert Blevins and published by . This book was released on 1972 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt:
