Wake stabilization mechanism of low-drag suppression devices for vortex-induced vibration

Law, Yun Zhi; Jaiman, Rajeev K.

doi:10.1016/j.jfluidstructs.2017.02.005

Cited by 65 publications

(15 citation statements)

References 27 publications

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“…Using the modal decomposition, we have quantitatively explained the interaction dynamics of the flow features which have been conjectured by many previous studies. For example, many successful VIV suppression techniques are proposed by passive (Law & Jaiman 2017) and active (Guan et al 2017;Narendran et al 2018) methods with the experience based presumption that preventing the interaction between the shear layer, the vortex street and the near-wake will suppress the synchronized wake-body lock-in phenomena. The cycle proposed above provides a proper physical mechanism for the success of those methods: they prevent the vorticity transfer between the shear layer and the vortex shedding and/or near-wake bubble, which breaks the self-sustenance of the wake interaction cycle.…”

Section: Wake Feature Interaction and Sustenance Of Viv Lock-inmentioning

confidence: 99%

“…The phenomenon of frequency lock-in is a major concern in offshore, marine and aeronautical engineering, whereby structures are designed to avoid the large-amplitude vibrations by selecting optimal system parameters (e.g., geometric dimensions, stiffness, damping) and/or installing active and passive devices to control the intensity of fluidstructure interaction. In particular, several studies have been conducted with the purpose of controlling the wake-body interaction via passive and active devices (Law & Jaiman 2017;Guan et al 2017;Narendran et al 2018) with the physical insight based on the reliance of frequency lock-in on the large-scale features of the wake. In fact, these studies were found to be remarkably successful in suppressing large-amplitude motion of the body by avoiding the interaction between the major organized features of the wake.…”

Section: Introductionmentioning

confidence: 99%

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Decomposition of wake dynamics in fluid–structure interaction via low-dimensional models

Miyanawala

Jaiman

2019

J. Fluid Mech.

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We present a dynamic decomposition analysis of the wake flow in fluid-structure interaction (FSI) systems under both laminar and turbulent flow conditions. Of particular interest is to provide the significance of low-dimensional wake flow features and their interaction dynamics to sustain the free vibration of a square cylinder at a relatively low mass ratio. To obtain the high-dimensional data, we employ a body-conforming variational fluid-structure interaction solver based on the recently developed partitioned iterative scheme and the dynamic subgrid-scale turbulence model for a moderate Reynolds number (Re). The snapshot data from high-dimensional FSI simulations are projected to a low-dimensional subspace using the proper orthogonal decomposition (POD). We utilize each corresponding POD mode for detecting features of the organized motions namely the vortex street, the shear layer and the near-wake bubble. We find that the vortex shedding modes contribute solely to the lift force, while the near-wake and shear layer modes play a dominating role to the drag force. We further examine the fundamental mechanism of this dynamical behavior and propose a force decomposition technique via low-dimensional approximation. To elucidate the frequency lock-in, we systematically analyze the decomposed modes and their dynamical contributions to the force fluctuations for a range of reduced velocity at low Re laminar flow. We ascertain quantitatively that the shear layer feeds the vorticity flux to the wake vortices and the near-wake bubble during the wake-body synchronization. Based on the decomposition of wake dynamics, we suggest an interaction cycle for the frequency lock-in during the wake-body interaction, which provides the inter-relationship between the high amplitude motion and the dominating wake features. Through our investigation of wake-body synchronization below critical Re range, we discover that the bluff body can undergo a synchronized high-amplitude vibration due to flexibility-induced unsteadiness. Owing to the wake turbulence at a moderate Reynolds number of Re = 22, 000, a distorted set of POD modes and the broadband energy distribution are observed, while the interaction cycle for the wake-synchronization is found to be valid for the turbulent wake flow.

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Section: Wake Feature Interaction and Sustenance Of Viv Lock-inmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Decomposition of wake dynamics in fluid–structure interaction via low-dimensional models

Miyanawala

Jaiman

2019

J. Fluid Mech.

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“…On the other hand, no external energy input is required in passive control. Flow control is achieved by modification of the shape of the body or via use of additional bodies, for example, control cylinder(s) (Mittal & Raghuvanshi 2001) or splitter plate(s) (Roshko 1954, 1955; Law & Jaiman 2017).…”

Section: Introductionmentioning

confidence: 99%

Numerical study of flow-induced vibration of a circular cylinder with attached flexible splitter plate at low

2019

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Flow-induced vibration (FIV) of an elastically mounted circular cylinder with an attached splitter plate in uniform flow is studied numerically via a stabilized space–time finite element method. The Reynolds number based on the cylinder diameter $D$ and the free-stream speed is restricted to 150. The ratio of the density of the body to that of the fluid, for the major part of the study, is 10. Two different reduced speeds are defined to quantify the compliance of the elastic support and flexibility of the splitter plate, respectively: $U_{s}^{\ast }$ based on the natural frequency of the spring–mass system and $U_{p}^{\ast }$ based on the fundamental natural frequency of the plate. Flow past a stationary cylinder ($U_{s}^{\ast }=0$) with a flexible splitter plate of length $3.5D$ is studied at different values of $U_{p}^{\ast }$. The vibration response of the plate exhibits lock-in with various eigenmodes of the plate in different ranges of $U_{p}^{\ast }$. The onsets of these lock-in regions are abrupt and hysteretic. The elastically mounted cylinder, without the splitter plate, undergoes large-amplitude vortex-induced vibration (VIV) for $4<U_{s}^{\ast }<7$. These large-amplitude oscillations are a consequence of synchronization, wherein the vortex shedding frequency locks in to the cylinder oscillation frequency. A rigid splitter plate attached to the cylinder reduces significantly the peak amplitude during VIV. Increasing the length of the plate from $1.5D$ to $3.5D$ only marginally affects the peak amplitude. It, however, leads to a wider range of lock-in. Unlike the case of an isolated cylinder, the lock-in and desynchronization regimes are not well demarcated in the presence of the splitter plate. Further, galloping is observed beyond a critical value of $U_{s}^{\ast }$; the amplitude of vibration increases with an increase in $U_{s}^{\ast }$ while the vibration frequency is relatively low and remains nearly constant. Increase in plate length delays, in terms of $U_{s}^{\ast }$, the onset of galloping. It is also found that the flexibility of the plate affects the maximum oscillation amplitude in the VIV regime. It also dictates the presence/absence of galloping. The system behaves similar to an isolated cylinder for a very flexible plate. The response is devoid of galloping, but relatively large amplitude of oscillation is observed during lock-in. The behaviour of the cylinder with a stiff plate is similar to that with the rigid one. The galloping instability sets in when the flexibility of the plate is less than a certain value ($U_{p}^{\ast }<4.7$, approximately for $U_{s}^{\ast }=22$). The VIV and galloping are separated by a range of $U_{s}^{\ast }$ in which the flow is either steady, for longer plates, or exhibits very weak vortex shedding. In the VIV regime, the plate tip and cylinder vibrate in phase for low $U_{p}^{\ast }$; their motion is out of phase for larger $U_{p}^{\ast }$. The change in phase is also associated with change in the frequency of vibration. At low $U_{p}^{\ast }$, the frequency of vibration is close to the first natural frequency of the system, while at high $U_{p}^{\ast }$ it becomes closer to the second natural frequency. The vibration amplitude of the cylinder is close to maximum in the VIV regime for $U_{s}^{\ast }=6$. Computations for various $U_{p}^{\ast }$, for $U_{s}^{\ast }=6$ and $22$, are utilized to determine optimal flexibility that leads to minimal FIV. The effect of the length of the flexible splitter plate, mass ratio and damping ratio is studied. A strategy is proposed to utilize the computations from various combinations of $U_{s}^{\ast }$ and $U_{p}^{\ast }$ to choose the appropriate flexibility of the attached splitter plate to minimize FIV.

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“…Assi et al [154] Assi et al [154] Assi et al [154] Assi et al [154] Assi et al [154] Law and Jaiman [192 Stappenbelt [182] Stappenbelt [182] Yu et al [193] Xie and Yu [194] rameters ( r U , the given liter helical strakes i tail, and for spl may be taken a and / y A D…”

Section: Splitter Platesmentioning

confidence: 99%

A review on flow-induced vibration of offshore circular cylinders

2020

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As a fundamental fluid-structure interaction (FSI) phenomenon, vortex-induced vibrations (VIVs) of circular cylinders have been the center of the FSI research in the past several decades. Apart from its scientific significance in rich physics, VIVs are paid great attentions by offshore engineers, as they are encountered in many ocean engineering applications. Recently, with the development of research and application, wake-induced vibration (WIV) for multiple cylinders and galloping for VIV suppression attachments are attracting a growing research interest. All these phenomena are connected with the flow-induced vibration (FIV). In this paper, we review and give some discussions on the FIV of offshore circular cylinders, including the research progress on the basic VIV mechanism of an isolated rigid or flexible cylinder, interference of multiple cylinders concerning WIV of multiple cylinders, practical VIV suppression and unwanted galloping for cylinder of attachments. Finally, we draw concluding remarks, give some comments and propose future research prospects, especially on the major challenges as well as potentials in the offline/online modelling and prediction of real-scale offshore structures with high-fidelity CFD methods, new experimental facilities and applications of artificial intelligence tools.

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Wake stabilization mechanism of low-drag suppression devices for vortex-induced vibration

Cited by 65 publications

References 27 publications

Decomposition of wake dynamics in fluid–structure interaction via low-dimensional models

Decomposition of wake dynamics in fluid–structure interaction via low-dimensional models

Numerical study of flow-induced vibration of a circular cylinder with attached flexible splitter plate at low

A review on flow-induced vibration of offshore circular cylinders

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