Vortex-induced vibration of catenary riser: reduced-order modeling and lock-in analysis using wake oscillator

A new reduced-order model capable of analyzing the vortex-induced vibration of catenary riser in the ocean current has been developed. This semi analytical-numerical approach is versatile and allows for a significant reduction in computational effort for the analysis of fluid-riser interactions. The incoming current flow is assumed to be steady, uniform, unidirectional and perpendicular to the riser plane of initial equilibrium curvatures

Bifurcation and dynamic response analysis of rotating blade excited by upstream vortices

Acknowledgements The authors acknowledge the projects supported by the National Basic Research Program of China (973 Project)(No. 2015CB057405) and the National Natural Science Foundation of China (No. 11372082) and the State Scholarship Fund of CSC. DW thanks for the hospitality of the University of Aberdeen.Peer reviewedPostprin

Reduced-order modelling of vortex-induced vibration of catenary riser

A new reduced-order model capable of analyzing the vortex-induced vibration of catenary riser in the ocean current has been developed. This semi analytical-numerical approach is versatile and allows for a significant reduction in computational effort for the analysis of fluid-riser interactions. The incoming current flow is assumed to be steady, uniform, unidirectional and perpendicular to the riser plane of initial equilibrium curvatures. The equations of riser 3-D motion are based on a pinned-pinned, tensioned-beam or flexural cable, modelling which accounts for overall effects of riser bending, extensibility, sag, inclination and structural nonlinearities. The unsteady hydrodynamic forces associated with cross-flow and in-line vibrations are modelled as distributed van der Pol wake oscillators. This hydrodynamic model has been modified in order to capture the effect of varying initial curvatures of the inclined flexible cylinder and to describe the space-time fluctuation of lift and drag forces. Depending on the vortex-excited in-plane/out-of-plane modes and system fluid-structure parameters, the parametric studies are carried out to determine the maximum response amplitudes of catenary risers, along with the occurrence of uni-modal lock-in phenomenon. The obtained results highlight the effect of initial curvatures and geometric nonlinearities on the nonlinear dynamics of riser undergoing vortex-induced vibration

New model for vortex-induced vibration of catenary riser

This paper presents a new theoretical model capable of predicting the vortex-induced vibration response of a steel catenary riser subject to a steady uniform current. The equations governing riser in-plane/out-ofplane (cross-flow/in-line) motion are based on a pinned beam-cable model accounting for overall effects of bending, extensibility, sag, inclination and structural nonlinearities. The empirically hydrodynamic model is based on nonlinear wake oscillators describing the fluctuating lift/drag forces. Depending on the potentially vortex-induced modes and system parameters, a reduced-order fluid-structure interaction model is derived which entails a significantly reduced computational time effort. Parametric results reveal maximum response amplitudes of risers, along with the occurrence of uni-modal lock-in phenomenon

Vortex-Induced Vibration of a Marine Riser: Numerical Simulation and Mechanism Understanding

Marine riser is a key equipment connecting a floating platform and a seabed wellhead. Vortex-induced vibration (VIV) is the main cause of the fatigue damage of the riser. The prediction of marine riser VIV is very difficult because of its strong non-linearity, instability and uncertainty. In recent years, many numerical models of VIV of marine riser have been developed to explore the mechanism of marine riser VIV, providing scientific theoretical basis and practical engineering methods for vibration control and engineering design of marine riser. Combined with the authors’ own recent research, this chapter discusses the research progress on marine riser VIV in the ocean engineering, including phenomenon mechanism analysis and different numerical research methods

Numerical and experimental comparisons of vortex-induced vibrations of marine risers in uniform/sheared currents

This paper presents a general theoretical reduced-order model capable of evaluating the multi-mode nonlinear dynamics of marine risers subject to uniform and sheared currents. The main objectives are to predict the vortex-induced vibration responses and parametrically compare between numerical and experimental results. The emphasis is placed on the analysis of cross-flow vibrations due to unsteady lift forces. The nonlinear equations governing riser axial/transversal motions are derived based on a top-tensioned beam model with typical pinned-pinned boundary conditions. The riser geometric nonlinearities owing to possible large dynamic displacements and multi-mode interactions are accounted for. To approximate the space-time varying lift force, the empirical hydrodynamic model, based on a nonlinear van der Pol wake oscillator with a distributed diffusive term, is used. A low-dimensional dynamic model and computationally-robust time-domain tool are then developed to evaluate the multi-mode fluid-riser interactions. These are very useful in dealing with large parametric studies involving varying system parameters

Multi-modes approach to modelling of vortex-induced vibration

Acknowledgements A.P. would like to acknowledge the support of the National Subsea Research Institute (NSRI) UK. E.P. and M.W. are grateful for partial support provided by the Italian Ministry of Education, University and Research (MIUR) by the PRIN funded program 2010/11 N.2010MBJK5BPeer reviewedPostprin

Analysis and prediction of vortex-induced vibrations of variable-tension vertical risers in linearly sheared currents

Many studies have tackled the problem of previous termvortex-induced vibrationsnext term (VIV) of a vertical riser with a constant tension and placed in uniform currents. In this study, attention is focused on the cross-flow VIV modelling, time-domain previous termanalysis and predictionnext term of variable-tension vertical risers in linearly sheared currents. The partial-differential equation governing the riser transverse motion is based on a flexural tensioned-beam model with typical pinned–pinned supports. The hydrodynamic excitation model describing the modulation of lift force is based on a distributed van der Pol wake oscillator whose nonlinear equation is also partial-differential due to the implementation of a diffusion term. The variation of empirical wake coefficients with system parameters and the water depth-dependent Reynolds number is introduced. Based on the assumed Fourier mode shape functions obtained by accounting for the effect of non-uniform tension, the Galerkin technique is utilized to construct a low-dimensional multi-mode model governing the coupled fluid-riser interaction system due to VIV. Numerical simulations in the case of varying sheared flow profiles are carried out to systematically evaluate riser nonlinear dynamics and highlight the influence of fluid–structure parameters along with associated VIV aspects. In particular, the effects of shear and tensioned-beam (tension versus bending) parameters are underlined. Some comparisons with published experimental results and observations are qualitatively and quantitatively discussed. Overall parametric previous termanalysis and predictionnext term results may be worthwhile for being a new benchmark against future experimental testing and/or numerical results predicted by an alternative model and methodology

Nonlinear multi-mode interactions in subsea risers undergoing vortex-induced vibrations

This paper investigates nonlinear multi-mode interactions in subsea risers undergoing vortex-induced vibrations based on a computationally efficient reduced-order fluid-structure interaction model. Cross-flow responses as a result of a steady uniform current are considered. The geometrically nonlinear equations of riser motion are coupled with nonlinear wake oscillators which have been modified to capture the effect of initial curvatures of curved cylinder and to approximate the space-time varying hydrodynamic lift forces. The main objectives are to provide new insights into the vortex-induced vibration characteristics of risers under external and internal resonances and to distinguish nonlinear dynamic behaviors between curved catenary and straight toptensioned risers. The analyses of multi-mode contributions, lock-in regimes, response amplitudes, resonant nonlinear modes and curvatures are carried out and several interesting aspects are highlighted

6th International congress of the Serbian society of mechanics: Review

Ovaj rad prikazuje najvažnije informacije o 6. kongresu Srpskog društva za mehaniku, koji je održan na Tari od 19. do 21. juna 2017. Kongres je organizovan od strane Srpskog društva za mehaniku. Dat je kratak prikaz najznačajnijih radova predstavljenih na ovom kongresu, a koji se bave teorijskom i primenjenom mehanikom.This paper presents the most important information and describes the activities of the 6th Congress of the Serbian Society of Mechanics which was held on mountain Tara, on 19- 21 June, 2017. The Congress was organized by the Serbian Society of Mechanics. Brief summaries of the plenary lectures and some of 99 accepted papers, which admittedly attracted the most interest were shown as well