Multi-mode interactions in vortex-induced vibrations of flexible curved/straight structures with geometric nonlinearities

Srinil, Narakorn

doi:10.1016/j.jfluidstructs.2010.08.005

Cited by 81 publications

(54 citation statements)

References 45 publications

(89 reference statements)

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“…The case of long and flexible structures in VIV, most relevant to offshore applications, has been extensively studied using numerical computations [5,6], experiments [7,8] and reduced-order models [9,10]. When a long flexible structure is placed perpendicular to the oncoming flow, higher vibration modes can be excited as the flow velocity is increased, through the successive synchronizations of its structural modes with the local shedding frequency [11].…”

Section: Introductionmentioning

confidence: 99%

Self-similar vortex-induced vibrations of a hanging string

et al. 2013

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An experimental analysis of the vortex-induced vibrations of a hanging string with variable tension along its length is presented in this paper. It is shown that standing waves develop along the hanging string. The evolution of the Strouhal number St with the Reynolds number Re first follows a trend similar to what is observed for a circular cylinder in a flow for relatively low Reynolds numbers (32 < Re < 700). Second, the extracted mode shapes are self-similar : a rescaling of the spanwise coordinate by a self-similarity coefficient allows all of them to collapse on a unique function. The self-similar behaviour of the spatial distribution of the vibrations along the hanging string is then explained theoretically by performing a linear stability analysis of an adapted wake-oscillator model. This linear stability analysis finally provides an accurate description of the mode shapes and of the evolution of the self-similarity coefficient with the flow speed.

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Section: Introductionmentioning

confidence: 99%

Self-similar vortex-induced vibrations of a hanging string

et al. 2013

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“…(5). The Re dependence of wake coefficients has been demonstrated by Srinil [35] for the cross-flow VIV prediction of long flexible cylinders.…”

Section: Nonlinear Fluid-structure Dynamic Modelmentioning

confidence: 93%

“…4.1. They can also be functions of system properties such as the mass ratio (m * = m/(ρπ D 2 /4)) [35,38] and Re [36]. The form in Eq.…”

Section: Nonlinear Fluid-structure Dynamic Modelmentioning

confidence: 99%

Two-dimensional vortex-induced vibration suppression through the cylinder transverse linear/nonlinear velocity feedback

Srinil

2017

Acta Mech

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Suppressing vortex-induced vibration (VIV) has recently attracted numerous researchers due to its practical significance in many engineering applications. Most of the previous studies have focused on a passive or active flow control. A structurally active control approach to mitigate a two-dimensional, nonlinear coupled, cross-flow/in-line VIV has not been well studied. This paper presents a reduced-order fluid-structure dynamic model and combined analytical-numerical solutions for the efficient suppression of two-dimensional VIV of a flexibly mounted circular cylinder in uniform flows. The theoretical model is based on the use of coupled Duffing-Rayleigh oscillators with three variables describing the cylinder cross-flow/in-line displacements and the strength of the fluid vortex circulation in the cylinder wake. These equations of fluid-structure motions contain geometric and hydrodynamic nonlinearities. Closed-loop linear and nonlinear velocity feedback controllers are implemented in the transverse direction governing the larger cross-flow response than the associated in-line counterpart. Approximated analytical expressions are derived by using the harmonic balance to explicitly capture the system nonlinear dynamic features and the effects of key dimensionless parameters. Parametric investigations are carried out to evaluate the linear versus nonlinear controller performance in terms of the maximum response suppression capability and the power requirement in a wide range of reduced flow velocities, mass ratios, and control gains. Over the main lock-in resonance region with coupled cross-flow/inline responses, the linear controller is found to be more efficient in suppressing the two-dimensional VIV by also modifying the system frequencies and phase relationships. Nevertheless, based on the power comparison, the nonlinear control is superior to the linear control for very small targeted controlled amplitudes of a very low-mass cylinder. These active control strategies may be further applied to the multimode VIV suppression of a long flexible cylinder with multi degrees of freedom.

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“…It has been observed by several experimental tests that, regardless of the specified f*, most of the x-y trajectories exhibit the figure-eight orbits (Dahl et al 2006;2010), depending on the corresponding in-line/cross-flow amplitudes, initial conditions, relative phases and the nearness of 2:1 resonant frequencies. These dual resonance characteristics result in the two-dimensional lock-in conditions.…”

Section: Extraction Of Hydrodynamic Coefficientsmentioning

confidence: 99%

“…Due to combined lift/drag forces associated with the shedding vortices and the fact that actual underwater structures possess multiple natural frequencies in different directions, a condition of coupled cross-flow/in-line VIV is certainly achievable in most practical situations which can be responsible for dangerouslyamplified dynamics. Nevertheless, most of the numerical tools currently used in the engineering industry are limited to the analysis of cross-flow-only VIV (Chaplin et al, 2005;Srinil, 2010Srinil, , 2011Srinil et al, 2009). Therefore, an advanced predictive model accounting for the coupled cross-flow/in-line, two-dimensional (2-D) or 2-DOF VIV would be worthwhile from a practical and industrial viewpoint.…”

Section: Introductionmentioning

confidence: 99%

Two-Dimensional Coupled Vortex-Induced Vibration of Circular Cylinder: Prediction and Extraction of Hydrodynamics Properties

Zanganeh

Srinil

2013

Volume 7: CFD and VIV

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An advanced model for predicting a two-dimensional coupled cross-flow and in-line vortex-induced vibration (VIV) of a flexibly-mounted circular cylinder in a uniform flow is proposed and investigated. Attention is placed on a systematic extraction of variable hydrodynamics properties associated with a bi-directional fluid-structure interaction system. The governing equations of motion are based on double Duffing-van der Pol (structural-wake) oscillators with the two structural equations containing cubic and quadratic nonlinear terms. The cubic nonlinearities capture the geometrical coupling of crossflow/in-line displacements excited by hydrodynamic lift/drag forces whereas the quadratic nonlinearities allow fluid-structure interactions. The combined analytical and numerical solutions of the proposed model are established. By varying flow velocities in numerical simulations, the derived low-order model qualitatively captures several key VIV characteristics of coupled in-line/cross-flow oscillations. By making use of a newly-derived empirical formula, the predicted maximum crossflow/in-line VIV amplitudes and associated lock-in ranges compare well with several experimental results for cylinders with low/high mass or damping ratios. Moreover, such important hydrodynamic properties as VIV-induced mean drag, added mass, excitation and damping terms can be systematically determined via the proposed model and compared well with some experimental results in the literature.

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Multi-mode interactions in vortex-induced vibrations of flexible curved/straight structures with geometric nonlinearities

Cited by 81 publications

References 45 publications

Self-similar vortex-induced vibrations of a hanging string

Self-similar vortex-induced vibrations of a hanging string

Two-dimensional vortex-induced vibration suppression through the cylinder transverse linear/nonlinear velocity feedback

Two-Dimensional Coupled Vortex-Induced Vibration of Circular Cylinder: Prediction and Extraction of Hydrodynamics Properties

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