Numerical Study on the Effect of Current Profiles on Vortex-Induced Vibrations in a Top-Tension Riser

• Published in: Journal of marine science and application Vol. 16; no. 4; pp. 473 - 479
• Main Authors: Fu, Bowen, Zou, Lu, Wan, Decheng
• Format: Journal Article
• Language: English
• Published: Harbin Harbin Engineering University 01.12.2017; Springer Nature B.V; State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, China
• Subjects: computational; Computational fluid dynamics; Computer simulation; Cross flow; Current profiles; dynamics; Electrical Machines and Networks; Engineering; Finite element method; fluid; Fluid flow; fluid-structure; Forces (mechanics); Geotechnical Engineering & Applied Earth Sciences; Hydrodynamics; interaction; Machinery and Machine Elements; Mathematical models; multi-modal; Navier-Stokes equations; Offshore Engineering; Power Electronics; Profiles; Riser pipes; Risers; Shear; Shear rate; Spectral analysis; Tension; theory; Time domain analysis; Vibration; Vibration analysis; Vibration mode; vibration;strip; Viscosity; vortex-induced; Vortex-induced vibrations; Vortices; fluid-structure interaction; multi-modal vibration; computational fluid dynamics; vortex-induced vibration; strip theory; risers
• DOI: 10.1007/s11804-017-1429-3
• ISSN: 1671-9433

In this paper, numerical simulations of vortex-induced vibrations in a vertical top-tension riser with a length-to-diameter ratio of 500 using our in-house code viv-FOAM-SJTU are presented. The time-dependent hydrodynamic forces on two-dimensional strips are obtained by solving the Navier-Stokes equations, which are, in turn, integrated into a finite-element structural model to obtain the riser deflections. The riser is discretized into 80 elements with its two ends set as pinned and 20 strips are located equidistant along the risers. Flow and structure are coupled by hydrodynamic forces and structural displacements.In order to study the effects of the shear rate, of the current profiles on the vortex-induced vibrations in the riser, vibrations, with varying shear rates, in both the in-line and cross-flow directions,are simulated. In addition to the time domain analysis, spectral analysis was conducted in both the temporal and spatial domains.Multi-mode vibration characteristics were observed in the riser. The relationship between dominant vibration mode number and the shear rate of current profiles is discussed. In general, the overall vibrations in the riser pipe include contributions from several modes and each mode persists over a range of shear rates.Moreover, the results suggest that with a larger shear rate the position of the maximum in-line time-averaged displacement will move closer to the end where the largest velocity is located.