Riser modal identification in CFD and full-scale experiments

Lucor, Didier; Mukundan, Harish; Triantafyllou, Michael

doi:10.1016/j.jfluidstructs.2006.04.006

Cited by 64 publications

(56 citation statements)

References 14 publications

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“…The sectional in-line and cross-flow force coefficients are defined as C x = 2F x /ρ f DU 2 and C y = 2F y /ρ f DU 2 , where F x and F y are the in-line and cross-flow dimensional sectional fluid forces. The structural dynamics are governed by forced vibrating string equations which can be expressed as follows [23]:…”

Section: Formulation and Numerical Methodsmentioning

confidence: 99%

Vortex-induced vibrations of a flexible cylinder at large inclination angle

Bourguet

Triantafyllou

2015

Phil. Trans. R. Soc. A.

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The free vibrations of a flexible circular cylinder inclined at 80° within a uniform current are investigated by means of direct numerical simulation, at Reynolds number 500 based on the body diameter and inflow velocity. In spite of the large inclination angle, the cylinder exhibits regular in-line and cross-flow vibrations excited by the flow through the lock-in mechanism, i.e. synchronization of body motion and vortex formation. A profound reconfiguration of the wake is observed compared with the stationary body case. The vortex-induced vibrations are found to occur under parallel, but also oblique vortex shedding where the spanwise wavenumbers of the wake and structural response coincide. The shedding angle and frequency increase with the spanwise wavenumber. The cylinder vibrations and fluid forces present a persistent spanwise asymmetry which relates to the asymmetry of the local current relative to the body axis, owing to its in-line bending. In particular, the asymmetrical trend of flow–body energy transfer results in a monotonic orientation of the structural waves. Clockwise and counter-clockwise figure eight orbits of the body alternate along the span, but the latter are found to be more favourable to structure excitation. Additional simulations at normal incidence highlight a dramatic deviation from the independence principle, which states that the system behaviour is essentially driven by the normal component of the inflow velocity.

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Section: Formulation and Numerical Methodsmentioning

confidence: 99%

Vortex-induced vibrations of a flexible cylinder at large inclination angle

Bourguet

Triantafyllou

2015

Phil. Trans. R. Soc. A.

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“…The fundamentals of VIV have been well documented for a cylinder whose axis in quiescient fluid is perpendicular to the oncoming flow (normal incidence case), the body being either rigid and elastically-mounted (King et al 1973;Bearman 1984Bearman , 2011Naudascher 1987;Mittal & Tezduyar 1992;Hover et al 1998;Okajima et al 2002;Sarpkaya 2004;Williamson & Govardhan 2004;Klamo et al 2006;Leontini et al 2006;Benaroya & Gabbai 2008;Lucor & Triantafyllou 2008;Dahl et al 2010;Navrose & Mittal 2013;Cagney & Balabani 2014;Konstantinidis 2014) or flexible (Trim et al 2005;Chaplin et al 2005;Lie & Kaasen 2006;Lucor et al 2006;Huera-Huarte & Bearman 2009, 2014; Vandiver et al 2009;Modarres-Sadeghi et al 2011;Bourguet et al 2011aBourguet et al ,b, 2012Bourguet et al , 2013a. VIV naturally appear both in the cross-flow direction and in the in-line direction, i.e.…”

Section: Introductionmentioning

confidence: 99%

The onset of vortex-induced vibrations of a flexible cylinder at large inclination angle

Bourguet

Triantafyllou

2016

J. Fluid Mech.

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The onset of the vortex-induced vibration (VIV) regime of a flexible cylinder inclined at 80 • within a uniform current is studied by means of direct numerical simulations, at Reynolds number 500, based on the body diameter and inflow velocity magnitude. A range of values of the reduced velocity, defined as the inverse of the fundamental natural frequency, is examined in order to capture the emergence of the body responses and explore the concomitant reorganization of the flow and fluid forcing. Additional simulations at normal incidence confirm that the independence principle, which states that the system behavior is determined by the normal inflow component, does not apply at such large inclination angle. Contrary to the normal incidence case, the free vibrations of the inclined cylinder arise far from the Strouhal frequency, i.e. the vortex shedding frequency downstream of a fixed rigid cylinder. The trace of the stationary body wake is found to persist beyond the vibration onset: the flow may still exhibit an oblique component that relates to the slanted vortex shedding pattern observed in the absence of vibration. This flow component which occurs close to the Strouhal frequency, at a high and incommensurable frequency compared to the vibration frequency, is referred to as Strouhal component; it induces a high-frequency component in fluid forcing. The vibration onset is accompanied by the appearance of novel, low-frequency components of the flow and fluid forcing, which are synchronized with body motion. This second dominant flow component, referred to as lock-in component, is characterized by a parallel spatial pattern. The Strouhal and lock-in components of the flow coexist over a range of reduced velocities, with variable contributions, which results in a variety of mixed wake patterns. The transition from oblique to parallel vortex shedding, that occurs during the amplification of the structural responses, is driven by the opposite trends of these two component contributions: the decrease of the Strouhal component magnitude, associated with the progressive disappearance of the high-frequency force component, and simultaneously, the increase of the lock-in component magnitude, which dominates once the fully-developed VIV regime is reached and the flow dynamics is entirely governed by wake-body synchronization.

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“…Lucor et al 23) performed full-scale experiments for riser modal identification. A main feature of riser modes, as described by Lucor et al 23) , is that they are complex showing variations in amplitude and phase along the length of the riser and are mainly a mixture of traveling and standing waves.…”

Section: (1) Modal-based Damage Detection Resultsmentioning

confidence: 99%

Vibration-Based Damage Detection in Flexible Risers Using Time Series Analysis

Riveros

Utsunomiya

Maeda

et al. 2007

Structural Eng./Earthquake Eng.

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In this paper, a statistical pattern recognition method based on time series analysis is implemented in flexible risers. This method uses a combination of Auto-Regressive (AR) and Auto-Regressive with eXogenous inputs (ARX) prediction models. The flexible riser model used in this paper is experimentally validated employing a proposed numerical scheme for dynamic response of flexible risers. A modal-based damage detection approach is also implemented in the flexible riser model and its results are compared with the ones obtained from time series analysis. The numerical results show that the time series analysis presented in this paper is able to detect and locate structural deterioration related to fatigue damage in flexible risers. Finally, considering the case study results presented in this paper, the presented AR-ARX prediction model works better than the modal-based damage detection method.

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Riser modal identification in CFD and full-scale experiments

Cited by 64 publications

References 14 publications

Vortex-induced vibrations of a flexible cylinder at large inclination angle

Vortex-induced vibrations of a flexible cylinder at large inclination angle

The onset of vortex-induced vibrations of a flexible cylinder at large inclination angle

Vibration-Based Damage Detection in Flexible Risers Using Time Series Analysis

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