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Rajeev K Jaiman - One of the best experts on this subject based on the ideXlab platform.
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coupled dynamics of Vortex Induced Vibration and stationary wall at low reynolds number
Physics of Fluids, 2017Co-Authors: Rajeev K Jaiman, Boo Cheong KhooAbstract:The flow past an elastically mounted circular cylinder placed in proximity to a plane wall is numerically studied in both two dimensions (2D) and three dimensions (3D). This paper aims to explain the mechanism of the cylinder bottom shear layer roll-up suppression in the context of laminar Vortex-Induced Vibration (VIV) of a cylinder placed in the vicinity of a plane stationary wall. In 2D simulations, VIV of a near-wall cylinder with structure-to-displaced fluid mass ratios of m* = 2 and 10 is investigated at the Reynolds number of Re = 100 at a representative gap ratio of e/D = 0.90, where e denotes the gap distance between the cylinder surface and the plane wall. First, the cylinder is placed at five different upstream distances, LU, to study the effects of the normalized wall boundary layer thickness, δ/D, on the hydrodynamic quantities involved in the VIV of a near-wall cylinder. It is found that the lock-in range shifts towards the direction of the higher reduced velocity Ur as δ/D increases and that the lock-in range widens as m* reduces. Second, via visualization of the Vortex shedding patterns, four different modes are classified and the regime maps are provided for both m* = 2 and 10. Third, the proper orthogonal decomposition analysis is employed to assess the cylinder bottom shear layer roll-up suppression mechanism. For 3D simulations at Re = 200, the circular cylinder of a mass ratio of m* = 10 with a spanwise length of 4D is placed at a gap ratio of e/D = 0.90 and an upstream distance of LU = 10D. The 3D Vortex patterns are investigated to re-affirm the Vortex shedding suppression mechanism. The pressure distributions around the cylinder are identified within one oscillation cycle of VIV. The pressure and the shear stress distributions on the bottom wall are examined to demonstrate the effects of near-wall VIV on the force distributions along the plane wall. It is found that both the suction pressure and the shear stress right below the cylinder peak when the cylinder is located at its negative maximum transverse displacement. This study represents a step towards an improved understanding of the hydrodynamics involved in the subsea pipelines subject to ocean currents with different boundary layer flows.The flow past an elastically mounted circular cylinder placed in proximity to a plane wall is numerically studied in both two dimensions (2D) and three dimensions (3D). This paper aims to explain the mechanism of the cylinder bottom shear layer roll-up suppression in the context of laminar Vortex-Induced Vibration (VIV) of a cylinder placed in the vicinity of a plane stationary wall. In 2D simulations, VIV of a near-wall cylinder with structure-to-displaced fluid mass ratios of m* = 2 and 10 is investigated at the Reynolds number of Re = 100 at a representative gap ratio of e/D = 0.90, where e denotes the gap distance between the cylinder surface and the plane wall. First, the cylinder is placed at five different upstream distances, LU, to study the effects of the normalized wall boundary layer thickness, δ/D, on the hydrodynamic quantities involved in the VIV of a near-wall cylinder. It is found that the lock-in range shifts towards the direction of the higher reduced velocity Ur as δ/D increases and tha...
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wake stabilization mechanism of low drag suppression devices for Vortex Induced Vibration
Journal of Fluids and Structures, 2017Co-Authors: Rajeev K JaimanAbstract:Abstract Inspired by the drag reduction mechanism in a tandem cylinder arrangement, the objective of this study is to numerically investigate the characteristic response of shear layer reattachment for the suppression of Vortex-Induced Vibration (VIV). A new device termed as connected-C is introduced, whereby its geometry can be constructed by attaching a C-shaped foil at the end of a splitter plate behind a circular cylinder. We investigate the significance of each part of the connected-C device and compare the proposed device with conventional fairings, the splitter plate, and one of its variant disconnected-C device without the connector plate between the main cylinder and the C-shaped foil. To simplify the numerical study and to concentrate on the wake stabilization mechanism, the cylinder-device systems are only allowed to move in the transverse direction. There is no relative rotation between the cylinder and the attached devices. Two- and three-dimensional studies are carried out at low Reynolds number Re =100 and subcritical Reynolds numbers Re ∈ [ 6150 , 7400 ] . We observe the counter-rotating pair of recirculations and the shear layer reattachment for the vibrating connected-C device. These flow characteristics of the connected-C device result into a similar VIV performance as the fairing with respect to the suppression of VIV. Similar to fairings, there is a net reduction in the total drag force exerted over the combined cylinder-device system. Based on the results from the low Reynolds number study, while the presence of C-shaped device is essential to prevent the occurrence of galloping at high reduced velocity, the presence of connector plate is not necessary to suppress VIV.
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interaction dynamics of gap flow with Vortex Induced Vibration in side by side cylinder arrangement
Physics of Fluids, 2016Co-Authors: Bin Liu, Rajeev K JaimanAbstract:A numerical investigation of the Vortex-Induced Vibration (VIV) in a side-by-side circular cylinder arrangement has been performed in a two-dimensional laminar flow environment. One of the cylinders is elastically mounted and only vibrates in the transverse direction, while its counterpart remains stationary in a uniform flow stream. When the gap ratio is sufficiently small, the flip-flopping phenomenon of the gap flow can be an additional time-dependent interference to the flow field. This phenomenon was reported in the experimental work of Bearman and Wadcock [“The interaction between a pair of circular cylinders normal to a stream,” J. Fluid Mech. 61(3), 499–511 (1973)] in a side-by-side circular cylinder arrangement, in which the gap flow deflects toward one of the cylinders and switched its sides intermittently. Albeit one of the two cylinders is free to vibrate, the flip-flop of a gap flow during VIV dynamics can still be observed outside the lock-in region. The exact moments of the flip-flop phenom...
Yoshiki Nishi - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of a drag assisted Vortex Induced Vibration energy converter
Journal of Fluids and Structures, 2017Co-Authors: Hamid Arionfard, Yoshiki NishiAbstract:Abstract In this study, the Vortex-Induced Vibration (VIV) of a pivoted cylinder is experimentally investigated as a potential source of energy harvesting. The design of a physical model and a theoretical analysis presented and experimental measurements on the laboratory prototype are reported. In particular, we investigate the effect of the pivot point placement, arm length ratio ( L * = l / D ) and natural frequency ( f N ) on the VIV performance over a Reynolds number range, 2880 ≤ Re ≤ 22300 . Classical studies show that the synchronization phenomenon (lock-in) occurs when the Vortex formation frequency ( f v ) is close enough to the body's natural frequency ( f N ) . Due to the configuration of the cylinder in this research, fN is also a function of flow velocity as well as the physical specifications of the system. The tests were conducted for the arm length ratio between 0.47 and 3.16 and three different spring stiffnesses were used to change the natural frequency. Results show that maximum output power is principally influenced by the arm length ration L * when the pivot point is located at the downstream, but reduced velocity is the controlling parameter when the pivot point is at the upstream. However, there is an optimum value of L * in both cases depending on the location of the pivot point and the stiffness of the spring. Based on observations, the optimum arm length ratio is relatively lower when the pivot point is at the downstream. The maximum efficiency of 31.4% has been observed for downstream placement of the pivot point by taking advantage of drag force and 2% for the upstream placement. Although the range of Reynolds numbers with high efficiency is wider when the pivot is located at the downstream, the performance of the system doesn't necessarily improve with increasing the Reynolds number in both cases.
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modeling of fluid structure interaction for simulating Vortex Induced Vibration of flexible riser finite difference method combined with wake oscillator model
Journal of Marine Science and Technology, 2015Co-Authors: Viet-phan Doan, Yoshiki NishiAbstract:This paper proposes a numerical simulation method for the dynamic motion of a flexible riser pipe undergoing Vortex-Induced Vibration (VIV). The method is based on a finite difference scheme for solving nonlinear structural dynamics of the pipe and wake oscillator model for quantifying Vortex-Induced forces acting on the pipe, the combination of which can offer a very efficient and stable computation. To investigate the accuracy of the method, we performed simulations of the VIV of riser pipes under uniform flow and sheared flow conditions; and then compared obtained results with experiments of preceding works. We consequently confirmed that the present method can simulate a couple of important aspects of the VIV of the pipes: frequency, mode shape, and amplitude of displacement of cross-flow displacement.
Ahsan Kareem - One of the best experts on this subject based on the ideXlab platform.
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Vortex Induced Vibration of bridge decks volterra series based model
Journal of Engineering Mechanics-asce, 2013Co-Authors: Ahsan KareemAbstract:AbstractA brief overview of Vortex-Induced Vibration (VIV) of bridge decks is presented, highlighting special VIV features concerning bridge decks. A popular VIV model (Van der Pol–type model) for bridge decks is examined in detail. Alternatively, a truncated Volterra series–based nonlinear oscillator is introduced to model the VIV system. Typical features of VIV such as the limit cycle oscillation (LCO), frequency shift, hysteresis, and beat phenomenon are parsimoniously and accurately captured in the proposed nonlinear model. As a functional expansion of a nonlinear system, the Volterra series is convenient for estimating the linear and nonlinear contributions to VIV. It is demonstrated that the relative contribution of nonlinear effects in VIV is around 50% of the total response for a range of bridge cross sections. The efficacy of the Volterra series as a reduced-order model (ROM) in capturing aerodynamic nonlinearities eliminates the need for reliance on conventional phenomenological models as it pro...
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An overview of Vortex-Induced Vibration (VIV) of bridge decks
Frontiers of Structural and Civil Engineering, 2012Co-Authors: Ahsan KareemAbstract:A brief overview of Vortex-Induced Vibration (VIV) of circular cylinders is first given as most of VIV studies have been focused on this particular bluff cross-section. A critical literature review of VIV of bridge decks that highlights physical mechanisms central to VIV from a renewed perspective is provided. The discussion focuses on VIV of bridge decks from wind-tunnel experiments, full-scale observations, semi-empirical models and computational fluids dynamics (CFD) perspectives. Finally, a recently developed reduced order model (ROM) based on truncated Volterra series is introduced to model VIV of long-span bridges. This model captures successfully salient features of VIVat “lockin” and unlike most phenomenological models offers physical significance of the model kernels.
Julio Romano Meneghini - One of the best experts on this subject based on the ideXlab platform.
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Vortex Induced Vibration of floating circular cylinders with very low aspect ratio
Ocean Engineering, 2018Co-Authors: Rodolfo T Goncalves, Julio Romano Meneghini, Andre Luis Condino FujarraAbstract:Abstract Experiments regarding Vortex-Induced Vibration (VIV) on floating circular cylinders with low aspect ratio were carried out in a recirculation water channel. The floating circular cylinders were elastically supported by a set of linear springs. Eight different aspect ratios were tested, namely L / D = 0.2, 0.3, 0.4, 0.5, 0.75, 1.0, 1.5 and 2.0. These aspect ratios were selected to cover the aspect ratio range of the main offshore circular platforms, such as spar and monocolumn. The aim was to understand the Vortex-Induced motions (VIM) of such platforms; due to this, the cylinders were floating, or m ∗ = 1 . The range of Reynolds number covered 2800 L / D ≤ 0.5 ; in these cases, the cylinder free-end effects were predominant. The resonant behavior was no longer observed for L / D ≤ 0.2 . The decrease in Strouhal number with decreasing aspect ratio is also verified, as well as for drag and lift forces. The added mass results help to identify the end of resonance for both directions, in-line and transverse. The amplitude results for the vertical direction, roll, pitch and yaw did not affect the VIV behavior.
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two degree of freedom Vortex Induced Vibration of circular cylinders with very low aspect ratio and small mass ratio
Journal of Fluids and Structures, 2013Co-Authors: Rodolfo T Goncalves, Julio Romano Meneghini, Guilherme F Rosetti, Guilherme Rosa Franzini, Andre Luis Condino FujarraAbstract:Abstract The investigation of Vortex-Induced Vibration on very short cylinders with two degrees of freedom has drawn the attention of a large number of researchers. Some investigations on such a problem are carried out in order to have a better understanding of the physics involved in Vortex-Induced motions of floating bodies such as offshore platforms. In this paper, experiments were carried out in a recirculating water channel over the range of Reynolds number 6000
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suppression of Vortex Induced Vibration using moving surface boundary layer control
Journal of Fluids and Structures, 2012Co-Authors: Ivan Korkischko, Julio Romano MeneghiniAbstract:Abstract Experimental results of flow around a circular cylinder with moving surface boundary-layer control (MSBC) are presented. Two small rotating cylinders strategically located inject momentum in the boundary layer of the cylinder, which delays the separation of the boundary layer. As a consequence, the wake becomes narrower and the fluctuating transverse velocity is reduced, resulting in a recirculation free region that prevents the Vortex formation. The control parameter is the ratio between the tangential velocity of the moving surface and the flow velocity ( U c / U ). The main advantage of the MSBC is the possibility of combining the suppression of Vortex-Induced Vibration (VIV) and drag reduction. The experimental tests are preformed at a circulating water channel facility and the circular cylinders are mounted on a low-damping air bearing base with one degree-of-freedom in the transverse direction of the channel flow. The mass ratio is 1.8. The Reynolds number ranges from 1600 to 7500, the reduced velocity varies up to 17, and the control parameter interval is U c / U = 5 – 10 . A significant decreasing in the maximum amplitude of oscillation for the cylinder with MSBC is observed. Drag measurements are obtained for statically mounted cylinders with and without MSBC. The use of the flow control results in a mean drag reduction at U c / U = 5 of almost 60% compared to the plain cylinder. PIV velocity fields of the wake of static cylinders are measured at Re = 3000 . The results show that the wake is highly organized and narrower compared to the one observed in cylinders without control. The calculation of the total variance of the fluctuating transverse velocity in the wake region allows the introduction of an active closed-loop control. The experimental results are in good agreement with the numerical simulation studies conducted by other researchers for cylinders with MSBC.
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experimental investigation of Vortex Induced Vibration on rigid smooth and inclined cylinders
Journal of Fluids and Structures, 2009Co-Authors: Guilherme Rosa Franzini, Ivan Korkischko, Julio Romano Meneghini, Andre Luis Condino Fujarra, Ricardo FrancissAbstract:Abstract This paper presents new experimental results of Vortex-Induced Vibration (VIV) on inclined cylinders. Models are mounted on a low damping air-bearing elastic base with one degree-of-freedom, constrained to oscillate only in the transverse direction to a free stream. The Reynolds number varied in the range 2000 ≲ Re ≲ 8000 . New measurements on the dynamic response oscillations of inclined cylinders, due to VIV, are compared with previous experiments of a vertical cylinder. Models with circular and elliptical cross sections have been tested. The purpose of this work is to check the validity of the normal velocity correction of VIV studies of inclined structures. The results show that the reduced velocity range, in which the upper and lower branches of VIV occurs, is similar to the vertical cylinder case if the proper projected velocity is considered. Tests have been conducted to support this observation with inclinations up to 45 ∘ . We have also observed that the amplitudes of oscillation of the inclined circular cylinder are comparable, but slightly lower than, to the amplitudes observed in the vertical cylinder experiments. Measured forces and added mass also show similar behaviour. However, for cases with an elliptical cylinder, the amplitudes of oscillation are considerably lower than those observed for a circular cylinder. This difference is explained by the higher added mass of the elliptical cylinder.
Liu Xiaochun - One of the best experts on this subject based on the ideXlab platform.
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performance comparisons of Vortex Induced Vibration suppression devices for top tensioned riser
Journal of Ship Mechanics, 2011Co-Authors: Liu XiaochunAbstract:In order to reduce and even eliminate the Vibrations caused by Vortex shedding and increase the fatigue life of the top tensioned risers(TTR),five types of Vortex-Induced Vibration(VIV) suppression devices were designed and the model experiments of risers equipped with suppression devices were carried out in the Physical Oceanography Laboratory of Ocean University of China.Time domain strain curves of in-line and transverse response of the model risers under the excitation of different current velocities were obtained and the corresponding model risers without suppression devices were also tested for comparison.Then the effects of the suppression devices at three different current velocities on the riser are analyzed and compared with each other.It is found that both the in-line and transverse oscillation amplitudes and frequencies of the riser with suppression devices are reduced at different degrees while their effect and efficiency on the suppression of the riser Vibrations are different from each other.
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model tests for Vortex Induced Vibration of a top tension riser based on wavelet transformation
Journal of Vibration and Shock, 2011Co-Authors: Liu XiaochunAbstract:In order to study Vortex-Induced Vibration(VIV) characteristics of a top tension riser subjected to marine current,model tests of VIV were conducted in a large wave-current flume.The riser model with changing top tension was attached vertically to the supporting structure and external current with different velocities acted on the model.The cylindrical model was equipped with six measured stations distributing averagely along the riser and each of them had two strain gauges to measure the oscillation responses both in-line direction and cross-flow one.Through wavelet transformation analysis,VIV frequencies and amplitudes as well as the coupled Vibration law between X and Y directions were obtained.The effect of varying top tensions on the natural frequencies and VIV response of the riser were also investigated.
