21 results on '"flow-induced oscillations"'
Search Results
2. Bio-Inspired adaptive damping in hydrokinetic energy harnessing using flow-induced oscillations.
- Author
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Sun, Hai and Bernitsas, Michael M.
- Subjects
- *
NONLINEAR oscillators , *OSCILLATIONS , *FLOW velocity , *ENERGY harvesting , *REYNOLDS number , *HARMONIC oscillators - Abstract
A hydrokinetic energy converter using Flow Induced Oscillations (FIOs) of a one-degree-of-freedom cylinder-oscillator, with nonlinear adaptive damping and linear spring stiffness, is introduced and studied experimentally. Comparison to a linear-oscillator in FIO shows that this new converter, with velocity-proportional damping coefficient, is more effective in galloping, where both flow and cylinder speeds are higher. It also impacts VIV, since the converter is no longer restricted by fixed damping, which results either in ceasing motion due to excessive damping, or in low harnessed energy due to insufficient damping. The impact is most profound in the VIV to galloping transition where adaptive damping prevents shutting down of hydrokinetic energy conversion. Damping-to-velocity rate, linear spring-stiffness, and flow-velocity are the experimental parameters with Reynolds number 30,000 ≤ Re ≤ 120,000. Experimental results for amplitude response, frequency response, energy harvesting, efficiency and instantaneous energy of the converter are presented and discussed. The main conclusions are: (1) The nonlinear, adaptive, velocity-proportional damping coefficient increases the harnessed power. (2) The operational range of flow velocities increases. (3) At lower flow speeds, the adaptive damping stabilizes the unstable oscillations typically occurring in this region. (4) At higher flow speeds, adaptive damping results in higher harnessed power than constant damping, thus, better emulating passively a corresponding, natural, active motion by fish. (5) Increase of 51%–95% in converted power by the nonlinear oscillator compared to linear oscillator has been measured. (6) The adaptive damping converter reaches a plateau in harnessed efficiency at high flow velocity (fully developed galloping). [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
3. Regenerative semi-active vortex-induced vibration control of elastic circular cylinder considering the effects of capacitance value and control parameters.
- Author
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Rabiee, Amir H.
- Subjects
- *
VIBRATION (Mechanics) , *ELECTRIC capacity , *COMPUTATIONAL fluid dynamics , *ELECTROMAGNETISM , *FUZZY logic - Abstract
A regenerative semi-active control system based on self-tuning Fuzzy proportional-derivative (PD) control strategy is applied to suppress the vortex-induced vibrations (VIV) of an elastically supported circular cylinder at low Reynolds numbers. Of particular interest was the effect of control parameter and capacitance on the VIV reduction and energy regeneration capabilities of adopted semi-active control system. A collaborative simulation which couples a Fuzzy PD controller along with the adjustable electromagnetic (EM) damper and corresponding energy harvesting circuit (implemented in MATLAB/Simulink) to the computational fluid dynamic (CFD) plant model (implemented in Fluent) is employed. It appears that the cylinder displacement amplitude, capacitor charging speed, and maximum stored electrical energy vary with the controller parameters and capacitance value. It is shown that the selected regenerative semiactive control system can store maximum energy in a capacitor in prescribed limiting time, along with the highest level of cylinder oscillation reduction which is the primary goal of current work. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
4. Assessment of a Hydrokinetic Energy Converter Based on Vortex-Induced Angular Oscillations of a Cylinder
- Author
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Iro Malefaki and Efstathios Konstantinidis
- Subjects
energy harnessing ,energy converter ,flow-induced oscillations ,vortex-induced vibration ,flow–structure interaction ,hydrodynamics ,vortex shedding ,cylinder wake ,Technology - Abstract
Vortex-induced oscillations offer a potential means to harness hydrokinetic energy even at low current speeds. In this study, we consider a novel converter where a cylinder undergoes angular oscillations with respect to a pivot point, in contrast to most previous configurations, where the cylinder undergoes flow-induced oscillations transversely to the incident free stream. We formulate a theoretical model to deal with the coupling of the hydrodynamics and the structural dynamics, and we numerically solve the resulting nonlinear equation of cylinder motion in order to assess the performance of the energy converter. The hydrodynamical model utilizes a novel approach where the fluid forces acting on the oscillating cylinder are split into components acting along and normal to the instantaneous relative velocity between the moving cylinder and the free stream. Contour plots illustrate the effects of the main design parameters (in dimensionless form) on the angular response of the cylinder and the energy efficiency of the converter. Peak efficiencies of approximately 20% can be attained by optimal selection of the main design parameters. Guidelines on the sizing of actual converters are discussed.
- Published
- 2020
- Full Text
- View/download PDF
5. Assessment and Nonlinear Modeling of Wave, Tidal and Wind Energy Converters and Turbines.
- Author
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Karimirad, Madjid, Collu, Maurizio, and Karimirad, Madjid
- Subjects
History of engineering & technology ,10 MW wind turbines ,AFWT ,ANSYS CFX ,Extreme Learning Machine (ELM) ,FOWT ,Kirsten-Boeing ,OWC ,Tensorflow ,air compressibility ,air turbine ,blade back twist ,blade flapwise moment ,caisson breakwater application ,cylinder wake ,dynamic analysis ,energy converter ,energy harnessing ,fatigue life assessment ,flexible power cables ,floating offshore wind turbine ,floating offshore wind turbine (FOWT) ,floating offshore wind turbines ,flow-induced oscillations ,flow-structure interaction ,flower pollination algorithm (FPA) ,frequency domain model ,hill-climbing method ,hydrodynamics ,inclined columns ,integral length scales ,large floating platform ,large-eddy simulation (LES) ,maximum power point tracking (MPPT) ,metamodeling ,multi-segmented mooring line ,negative damping ,neural nets ,off-shore wind farms (OSWFs) ,optimization ,oscillating water column ,parametric study ,pitch-to-stall ,platform optimization ,point-absorbing ,power take-off (PTO) ,semi-submersible ,semisubmersible platform ,site assessment ,tank testing ,tidal energy ,tower axial fatigue life ,tower fore-aft moments ,turbulence ,valves ,vertical axis turbine ,vortex shedding ,vortex-induced vibration ,wake model ,wave energy ,wave energy converter (WEC) ,wave power converting system ,wave-current interaction ,wave-to-wire model ,wave-turbulence decomposition ,wind energy ,wind power (WP) ,wind turbine (WT) - Abstract
Summary: The Special Issue "Assessment and Nonlinear Modeling of Wave, Tidal, and Wind Energy Converters and Turbines" contributes original research to stimulate the continuing progress of the offshore renewable energy (ORE) field, with a focus on state-of-the-art numerical approaches developed for the design and analysis of ORE devices. Particularly, this collection provides new methodologies, analytical/numerical tools, and theoretical methods that deal with engineering problems in the ORE field of wave, wind, and current structures. This Special Issue covers a wide range of multidisciplinary aspects, such as the 1) study of generalized interaction wake model systems with elm variation for offshore wind farms; 2) a flower pollination method based on global maximum power point tracking strategy for point-absorbing type wave energy converters; 3) performance optimization of a Kirsten-Boeing turbine using a metamodel based on neural networks coupled with CFD; 4) proposal of a novel semi-submersible floating wind turbine platform composed of inclined columns and multi-segmented mooring lines; 5) reduction of tower fatigue through blade back twist and active pitch-to-stall control strategy for a semi-submersible floating offshore wind turbine; 6) assessment of primary energy conversion of a closed-circuit OWC wave energy converter; 7) development and validation of a wave-to-wire model for two types of OWC wave energy converters; 8) assessment of a hydrokinetic energy converter based on vortex-induced angular oscillations of a cylinder; 9) application of wave-turbulence decomposition methods on a tidal energy site assessment; 10) parametric study for an oscillating water column wave energy conversion system installed on a breakwater; 11) optimal dimensions of a semisubmersible floating platform for a 10 MW wind turbine; 12) fatigue life assessment for power cables floating in offshore wind turbines.
6. Dual-Functional Electromagnetic Energy Harvesting and Vortex-Induced Vibration Control of an Elastically Mounted Circular Cylinder.
- Author
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Hasheminejad, Seyyed M., Rabiee, Amir H., and Markazi, A. H. D.
- Subjects
- *
ENERGY harvesting , *ELECTROMAGNETIC waves , *FORCE & energy , *CROSS-flow (Aerodynamics) , *REYNOLDS number , *ELECTRICAL energy - Abstract
A self-powered active support system, which produces a control force using the energy regenerated by a transversely mounted linear electromagnetic (EM) damper, is applied for two-dimensional (2D) (streamwise/cross-flow) vortex-induced vibration (VIV) suppression of an oscillating circular cylinder in low Reynolds number flow (R=90). In addition, a passive energy generating system is devised that achieves a proper trade-off between VIV suppression and energy harvesting actions with the EM damper acting in either the regeneration or the dissipation mode. A multifield cosimulation scheme, which links an active proportional-integral-derivative (PID) controller along with the switch-based energy harvesting circuit of the EM damper (implemented in MATLAB/Simulink) to the plant model (constructed via a user-defined function in a commercial finite volume solver), is designed and implemented. Numerical simulations compare the effects of the passive and active EM-generating systems on 2D VIV suppression of the elastic cylinder as well as on the time evolution of cylinder force coefficients. They demonstrate that the adopted self-powered (tuned) active energy harvesting system, which does not require an external power supply and makes intelligent use of the stored electrical energy for producing the required transverse control force, efficiently balances the regenerated and consumed energies by proper switching between three distinct (regeneration, drive, and brake) modes of EM device operation. It can particularly provide improved cylinder VIV suppression with lower power consumption via enhanced collaborative action between different modes of the EM device. Moreover, the selected system is also found to be effective for other Reynolds numbers in the lock-in region. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
7. Experimental and numerical study of the shielding effect of two tandem rough cylinders in flow-induce oscillation.
- Author
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Sun, Hai, Li, Huaijun, Yang, Niankai, Hou, Gangling, and Bernitsas, Michael M.
- Subjects
- *
OSCILLATIONS , *VORTEX shedding , *REYNOLDS number , *SURFACE roughness , *VORTEX motion , *TURBULENCE - Abstract
The shielding effect of the downstream cylinder in flow induced oscillation (FIO) of two cylinders arranged in tandem is studied experimentally and numerically at Reynolds number 30,000 to 120,000. Both cylinders are in one degree-of-freedom, transverse-oscillations, and have turbulence stimulation in the form of selective surface roughness to expand FIO beyond vortex-induced vibration (VIV) into galloping. Shielding of the downstream cylinder has a negative effect on harnessing hydrokinetic energy. To study its effect and mechanics, selective cases are studied both numerically and experimentally and discussed to demonstrate the shielding effect on the downstream cylinder and understand its cause. The main conclusions are: (1) The shielding effect for the downstream cylinder shows a strong relation to the damping ratio. As the damping ratio increases, the shielding effect is mitigated. Additionally, the oscillation of the rear cylinder becomes stable and shows stable frequency. (2) In the VIV region, as the stiffness and natural frequency increase, the shielding effect decreases substantially. (3) In the VIV region, the vorticity of the vortices shedding from both the upper and the lower sides of the downstream cylinder does not accumulate enough due to the attraction by the vortices shed from the upstream cylinder, thus resulting in partial suppression of the oscillation on the downstream cylinder. (4) In the galloping region, the shielding effect for the downstream cylinder depends on whether the vorticity near the downstream cylinder is strengthened by the vortices generated by the shear layers of the upstream cylinder or weakened. • Shielding effect in FIO of two cylinders in tandem is studied experimentally and numerically. • Impingement of the vortices from the upstream on the downstream cylinder are studied in details. • In the high-velocity range of galloping, the shielding effect is decided by the relative oscillation pattern. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
8. Numerical study of flow-induced oscillations of two rigid plates elastically hinged at the two ends of a stationary plate in a cross-flow.
- Author
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Darbandi, Masoud and Fouladi, Nematollah
- Subjects
- *
FLOW-induced vibration (Mechanics) , *CROSS-flow (Aerodynamics) , *FLUID-structure interaction , *FINITE element method , *DRAG coefficient , *LIFT (Aerodynamics) - Abstract
The flow-induced oscillation (FIO) of bluff bodies is commonly encountered in the fluid structure interaction (FSI) problems. In this study, we use an unstructured moving grid strategy and simulate the FIO of two rigid plates, which are elastically hinged at the two ends of a fixed flat plate in a cross-flow. We use a hybrid finite-element-volume (FEV) method in an arbitrary Lagrangian–Eulerian (ALE) framework to study FIO of the two hinged plates. The current simulations are carried out for wide ranges of flow Reynolds number (50–175), spring stiffness coefficient, and the two hinged plates' moment of inertia magnitudes. The influences of these parameters are investigated on the magnitudes of maximum deflection angle, the amplitude of oscillation, the total lift and drag coefficients, and so on. The study is also carried out in the transition period to describe the in-phase and out-of-phase angular oscillations occurring for the two elastically hinged plates with respect to each other. After the transition period, the two hinged plates eventually arrive to a similar periodic oscillation; however, with some phase lags. We find that the achieved phase lag is equal to the phase lag between the two pairs of flow vortices, which are alternatively shed into the flow from the upper and lower hinged plates. Similar to past FIO problems, the current model also exhibits two important lock-in and phase-switch FSI phenomena; however, in angular directions. There is a phase jump of approximately 170° between the aerodynamic lift coefficient and angular oscillations of hinged plates, which nearly occurs in the middle of lock-in region. Indeed, our literature review shows that this is the first time to report the phase-switch phenomenon in angular oscillations of three-element bluff bodies in a FSI problem. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
9. Active vortex-induced vibration control of a circular cylinder at low Reynolds numbers using an adaptive fuzzy sliding mode controller.
- Author
-
Hasheminejad, Seyyed M., Rabiee, Amir H., Jarrahi, Miad, and Markazi, A.H.D.
- Subjects
- *
VIBRATION (Mechanics) , *REYNOLDS number , *ADAPTIVE fuzzy control , *SLIDING mode control , *LAMINAR flow , *FLUID-structure interaction - Abstract
An adaptive fuzzy sliding mode control (AFSMC) scheme is applied to actively suppress the two-dimensional vortex-induced vibrations (VIV) of an elastically mounted circular cylinder, free to move in in-line and cross-flow directions. Laminar flow regime at Re=90, low non-dimensional mass with equal natural frequencies in both directions, and zero structural damping coefficients, are considered. The natural oscillator frequency is matched with the vortex shedding frequency of a stationary cylinder at Re=100. The strongly coupled unsteady fluid/cylinder interactions are captured by implementing the moving mesh technology through integration of an in-house developed User Define Function (UDF) into the main code of the commercial CFD solver Fluent. The AFSMC approach comprises of a fuzzy system designed to mimic an ideal sliding-mode controller, and a robust controller intended to compensate for the difference between the fuzzy controller and the ideal one. The fuzzy system parameters as well as the uncertainty bound of the robust controller are adaptively tuned online. A collaborative simulation scheme is realized by coupling the control model implemented in Matlab/Simulink to the plant model constructed in Fluent, aiming at determination of the transverse control force required for complete suppression of the cylinder streamwise and cross-flow oscillations. The simulation results demonstrate the high performance and effectiveness of the adopted control algorithm in attenuating the 2D-VIV of the elastic cylinder over a certain flow velocity range. Also, the enhanced transient performance of the AFSM control strategy in comparison with a conventional PID control law is demonstrated. Furthermore, the effect of control action on the time evolution of vortex shedding from the cylinder is discussed. In particular, it is observed that the coalesced vortices in the far wake region of the uncontrolled cylinder, featuring the C(2S)-type vortex shedding characteristic mode, are ultimately forced to switch to the classical von Kármán vortex street of 2S-type mode, displaying wake vortices of moderately weaker strengths very similar to those of the stationary cylinder. Lastly, robustness of AFSMC is verified against relatively large structural uncertainties as well as with respect to a moderate deviation in the uniform inlet flow velocity. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
10. Assessment of a Hydrokinetic Energy Converter Based on Vortex-Induced Angular Oscillations of a Cylinder
- Author
-
Efstathios Konstantinidis and Iro Malefaki
- Subjects
Control and Optimization ,020209 energy ,Energy Engineering and Power Technology ,energy harnessing ,energy converter ,flow-induced oscillations ,vortex-induced vibration ,flow–structure interaction ,hydrodynamics ,vortex shedding ,cylinder wake ,02 engineering and technology ,lcsh:Technology ,01 natural sciences ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,Cylinder ,Electrical and Electronic Engineering ,Engineering (miscellaneous) ,Physics ,Coupling ,lcsh:T ,Renewable Energy, Sustainability and the Environment ,Relative velocity ,Mechanics ,Vortex shedding ,Pivot point ,Vortex ,Nonlinear system ,Vortex-induced vibration ,Energy (miscellaneous) - Abstract
Vortex-induced oscillations offer a potential means to harness hydrokinetic energy even at low current speeds. In this study, we consider a novel converter where a cylinder undergoes angular oscillations with respect to a pivot point, in contrast to most previous configurations, where the cylinder undergoes flow-induced oscillations transversely to the incident free stream. We formulate a theoretical model to deal with the coupling of the hydrodynamics and the structural dynamics, and we numerically solve the resulting nonlinear equation of cylinder motion in order to assess the performance of the energy converter. The hydrodynamical model utilizes a novel approach where the fluid forces acting on the oscillating cylinder are split into components acting along and normal to the instantaneous relative velocity between the moving cylinder and the free stream. Contour plots illustrate the effects of the main design parameters (in dimensionless form) on the angular response of the cylinder and the energy efficiency of the converter. Peak efficiencies of approximately 20% can be attained by optimal selection of the main design parameters. Guidelines on the sizing of actual converters are discussed.
- Published
- 2020
- Full Text
- View/download PDF
11. Numerical investigation of flow-induced oscillations and noise from a rectangular cavity.
- Author
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WAN Zhen-hua, ZHOU Lin, and SUN De-jun
- Subjects
- *
COMPUTER simulation , *FLOW-induced vibration (Mechanics) , *OSCILLATIONS , *NOISE , *REYNOLDS number - Abstract
Direct numerical simulation is used to investigate flow-induced oscillations and noise for a low-Reynolds-number subsonic flow over a rectangular cavity with a constant configuration L/D=2. The results indicate that oscillations are dominated by Rossiter II mode in the range of present computational parameters. A low frequency component appears as the decreasing of the thickness of inflow boundary layer, which is directly caused by pattern switching of vortex-edge impingement. The inherent reason is unstable interaction between the recirculation zone and the shear layer. The proper-orthogonal-decomposition (POD) method is employed to analyze the influence of different oscillation pattern on the corresponding vortex structures of the intrinsic mode and its relation with vortex-edge interaction. Moreover, the process of noise generation and propagation is computed and analyzed, and the results are agreed well with available experiments and analytical model. [ABSTRACT FROM AUTHOR]
- Published
- 2012
12. Isothermal Modeling of Meniscus Oscillation in the Continuous Strip Casting Process.
- Author
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Wilcox, Kevin W., Holloway, A. Gordon L., and Gerber, Andrew G.
- Subjects
CONVEYING machinery ,SURFACE defects ,METAL castings ,MENISCUS (Liquids) ,WETTING - Abstract
In the continuous strip casting process a meniscus forms a compliant boundary between the casting nozzle and transporting conveyor. Movement of this meniscus during casting has been shown to create surface defects, which require extensive cold work to remove and limit the minimum thickness for which sections may be cast. This paper discusses experimental work conducted to test an analytical model of the meniscus oscillation. A high frame rate shadowgraph technique was used on an isothermal water model of the casting process to observe meniscus motion, and thus allow the calculation of meniscus frequency, amplitude, contact points and contact angles. Both natural frequency and flow excited tests were conducted. Natural frequency tests were also conducted using mercury which has a nonwetting contact angle typical of molten metals. The experimental results were found to be in good agreement with the predictions of theory for both wetting and nonwetting conditions. The experimentally verified analytical model for meniscus motion is valuable to the design of a continuous casting process because it describes the effect of geometrical parameters on meniscus motion and thus provides an opportunity to mitigate the effects of boundary motion on surface quality. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
13. Active control of flow-induced cavity oscillations
- Author
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Cattafesta, Louis N., Song, Qi, Williams, David R., Rowley, Clarence W., and Alvi, Farrukh S.
- Subjects
- *
AERODYNAMICS , *OSCILLATIONS , *FEEDBACK control systems , *ACTUATORS , *FLUCTUATIONS (Physics) , *AEROSPACE engineering - Abstract
Abstract: A review of active control of flow-induced cavity oscillations is motivated by two factors. First, the search for solutions to the practical problem of suppressing oscillations caused by flow over open cavities has generated significant interest in this area. Second, cavity oscillation control serves as a model problem in the growing multidisciplinary field of flow control. As such, we attempt to summarize recent activities in this area, with emphasis on experimental implementation of open- and closed-loop control approaches. In addition to describing successes, failures, and outstanding issues relevant to cavity oscillations, we highlight the characteristics of the various actuators, flow sensing and measurement, and control methodologies employed to date in order to emphasize the choices, challenges, and potential of flow control in this and other applications, such as impact on store trajectory. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
- View/download PDF
14. An experimental study of the aeroelastic behaviour of two parallel interfering circular cylinders
- Author
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Medeiros, E. B.
- Subjects
532 ,Flow-induced oscillations - Published
- 1988
15. The effects of damping on the amplitude and frequency response of a freely vibrating cylinder in cross-flow
- Author
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Klamo, J.T., Leonard, A., and Roshko, A.
- Subjects
- *
FREQUENCY response , *CROSS-flow (Aerodynamics) , *EDDY currents (Electric) - Abstract
Abstract: We have studied the effects of controlled damping on the amplitude and frequency response profiles of an elastically mounted cylinder in cross-flow. The dimensionless damping parameter, , which is closely related to the traditional “mass-damping” parameter, , was varied over a wide range of values through the use of a variable magnetic eddy current damping system. For low damping and sufficiently high Reynolds number we observe the previously described large-amplitude, three-branch (initial, upper, lower) response profile, and for high damping or low Reynolds number we observe the small-amplitude, two-branch (initial and lower) response profile. However we find that, because of the influence of Reynolds number, the traditional labels of “high mass-damping” and “low mass-damping” are incomplete with regard to predicting a large or small-amplitude response profile. In our experiments, as damping is systematically increased, we observe a transition between these two profiles characterized by a gradual “erosion” and eventual disappearance of the large-amplitude section (upper branch) and the scaling down of the lower branch region. We find that jumps from the upper to the initial branch originate on the 2S/2P boundary in the Williamson–Roshko plane. Another new finding is a hysteresis between the lower branch and the desynchronized region, which only appears at low Reynolds numbers. We also explore changes in the frequency response profile, which are connected with the changes in the amplitude profile, for our upper branch cases. We observe that analogous to the three amplitude branches, there are three distinct branches for the frequency response. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
- View/download PDF
16. On the maximum amplitude for a freely vibrating cylinder in cross-flow
- Author
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Klamo, J.T., Leonard, A., and Roshko, A.
- Subjects
- *
ENGINE cylinders , *VIBRATION (Mechanics) , *EDDY currents (Electric) , *ELASTICITY - Abstract
Abstract: The response of a freely oscillating circular cylinder (“free vibration”) in cross-flow has been studied experimentally using controlled magnetic eddy current to provide variable damping. In general, the nondimensional response amplitude, A*, and dominant frequency, ω*, depend on the Reynolds number, Re, and the nondimensional mass, m*, damping, b*, and elasticity, k*, of the system. The main objective of this study is to characterize the maximum amplitude that is achieved for a given system as cross-flow velocity is varied. We find that this maximum amplitude, , occurs within a small range of values of . For values of Reynolds number in the range 525
- Published
- 2005
- Full Text
- View/download PDF
17. Assessment of a Hydrokinetic Energy Converter Based on Vortex-Induced Angular Oscillations of a Cylinder.
- Author
-
Malefaki, Iro and Konstantinidis, Efstathios
- Subjects
- *
EQUATIONS of motion , *RELATIVE velocity , *VORTEX motion , *NONLINEAR equations , *ENERGY consumption , *VORTEX shedding , *OSCILLATIONS , *STRUCTURAL dynamics - Abstract
Vortex-induced oscillations offer a potential means to harness hydrokinetic energy even at low current speeds. In this study, we consider a novel converter where a cylinder undergoes angular oscillations with respect to a pivot point, in contrast to most previous configurations, where the cylinder undergoes flow-induced oscillations transversely to the incident free stream. We formulate a theoretical model to deal with the coupling of the hydrodynamics and the structural dynamics, and we numerically solve the resulting nonlinear equation of cylinder motion in order to assess the performance of the energy converter. The hydrodynamical model utilizes a novel approach where the fluid forces acting on the oscillating cylinder are split into components acting along and normal to the instantaneous relative velocity between the moving cylinder and the free stream. Contour plots illustrate the effects of the main design parameters (in dimensionless form) on the angular response of the cylinder and the energy efficiency of the converter. Peak efficiencies of approximately 20% can be attained by optimal selection of the main design parameters. Guidelines on the sizing of actual converters are discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
18. Flow-induced oscillations of three tandem circular cylinders in a two-dimensional flow.
- Author
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Behara, Suresh, Chandra, Venu, and Ravikanth, B.
- Subjects
- *
OSCILLATIONS , *REYNOLDS number , *VORTEX shedding , *PHASE transitions - Abstract
Flow-induced oscillations of three identical circular cylinders, arranged in tandem configuration, are studied via two-dimensional finite element computations. Cylinders are mounted on elastic supports in the streamwise and transverse directions. Each downstream cylinder is placed at a distance of 5 diameters (5 D) from its immediate upstream neighbor. Nondimensional mass ( m ∗) of 2, and zero damping (ξ) are considered. Simulations are performed with the objective of understanding dynamic response of cylinders, as they are subject to wake interference, at constant Reynolds number, R e = 150 , and for varying reduced velocity (U ∗) in the range of U ∗ = 2 − 14. Similar to the behavior of an isolated cylinder at low R e , oscillation response of the upstream body exhibits initial excitation and lower lock-in regimes. However, for both the downstream cylinders, depending on their amplitude and frequency responses, the synchronization regime of U ∗ can be categorized into three distinct regions: initial excitation, upper and lower lock-in regions. First downstream cylinder undergoes gradual transition between initial excitation and upper region, whereas the second downstream body exhibits this transition in two phases, which are separated by a periodic oscillation response regime. Upper lock-in region is characterized by periodic oscillations, while amplitude is modulated in the lower region. Only 2S shedding mode is observed for all the U ∗ considered. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
19. Analysis of the vibration of pipes conveying fluid
- Author
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Jason M. Reese, Daniel G. Gorman, and Y.L. Zhang
- Subjects
DYNAMICS ,Piping ,Plug flow ,business.industry ,FLOW-INDUCED OSCILLATIONS ,Mechanical Engineering ,Numerical analysis ,finite element method ,fluid-structure interaction ,02 engineering and technology ,Structural engineering ,Finite element method ,Ritz method ,Physics::Fluid Dynamics ,Vibration ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Fluid–structure interaction ,Coupling (piping) ,pipes conveying fluid ,TJ ,vibration ,business ,Mathematics - Abstract
The dynamic equilibrium matrix equation for a discretized pipe element containing flowing fluid is derived from the Lagrange principle, the Ritz method and consideration of the coupling between the pipe and fluid. The Eulerian approach and the concept of fictitious loads for kinematic correction are adopted for the analysis of geometrically non-linear vibration. The model is then deployed to investigate the vibratory behaviour of the pipe conveying fluid. The results for a long, simply supported, fluid-conveying pipe subjected to initial axial tensions are compared with experimentally obtained results and those from a linear vibration model.
- Published
- 1999
20. Effects of Damping and Reynolds Number on Vortex-Induced Vibrations
- Author
-
Klamo, Joseph Thomas
- Subjects
Physics::Fluid Dynamics ,Mechanical Engineering ,FOS: Mechanical engineering ,flow-induced oscillations ,VIV ,lock-in - Abstract
Vortex-induced vibrations have been studied experimentally with emphasis on damping and Reynolds number effects. Our system was an elastically-mounted rigid circular cylinder, free to oscillate only transverse to the flow direction, with very low inherent damping. We were able to prescribe the mass, damping, and elasticity of the system over a wide range of values, with the damping controlled by a custom-made variable magnetic eddy-current damping system. Special emphasis is put on a nontraditional parameter formulation. The advantages of this formulation are explained, and an important new parameter, effective stiffness, is introduced. Using this new formulation, the amplitude and frequency responses are only a function of damping, Reynolds number, and effective stiffness. We show the effects that damping and Reynolds number each have on the amplitude and frequency response profiles and make the interesting observation that changes in damping or Reynolds number have similar effects. The maximum amplitudes of our systems are studied in detail. We theoretically show that they should be functions of both damping and Reynolds number. This allows us to create constant-Reynolds-number curves of maximum amplitude over a large range of damping values, which we call a "generalized" Griffin plot. We also define maximum amplitudes in the case of zero damping as limiting amplitudes, and show that they are only a function of Reynolds number. We experimentally determine our limiting amplitude dependence on Reynolds number over the range 200 < Reynolds number < 5050. Discontinuities in the amplitude response profile are also investigated. The discontinuity between the initial branch and the large-amplitude, upper branch is studied in two ways. First, the time-averaged behavior is examined to understand what controls the discontinuity and look for damping and Reynolds number effects. Second, we track the cycle-by-cycle transient response through this discontinuous amplitude change, induced either by changes in the tunnel velocity or system damping. Finally, we also find a new discontinuity hysteresis region between the lower branch and the desynchronized region, which appears to be a low Reynolds number effect and is only seen in systems with Reynolds number < 1000.
- Published
- 2007
- Full Text
- View/download PDF
21. Flow-induced oscillations of a square cylinder due to interference effects
- Author
-
V. Sreedharan and B. H. Lakshmana Gowda
- Subjects
Flow visualization ,Oscillatory amplitudes ,Oscillations ,Acoustics and Ultrasonics ,Flow-induced oscillations ,Interference effects ,Mechanical Engineering ,Flow (psychology) ,Square cylinder ,Geometry ,Mechanics ,Condensed Matter Physics ,Interference (wave propagation) ,Wave interference ,Flow of fluids ,Physics::Fluid Dynamics ,Vibration ,Amplitude ,Mechanics of Materials ,Position (vector) ,Cylinders (shapes) ,Induced oscillations ,Cylinder ,Mathematics - Abstract
Measurements of the flow-induced oscillations of a spring-mounted square cylinder (test cylinder, side dimension B) due to the presence of a rigid square cylinder (interfering cylinder, side dimension b) are presented. Ratios of b / B = 0.5, 1.0, 1.5 and 2.0 have been used. Various relative positions of the test cylinder and the interfering cylinder, in tandem, side-by-side and staggered arrangements are considered (in all of the positions considered, the interfering cylinder was never upstream of the test cylinder). The results show that under certain combinations of the b/B ratio and the relative position, the test cylinder can experience oscillatory amplitudes almost three times those observed for the no-interfering case. Under certain other conditions, the vibrations are completely suppressed. The observed features are discussed with reference to earlier related studies. Flow visualisation results are obtained by using (a) stationary test cylinder and (b) oscillated test cylinder, to provide an explanation for the observed features. � 2006 Elsevier Ltd. All rights reserved.
- Published
- 2006
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