Dynamic characteristics and VIV of deepwater riser with axially varying structural properties

Abstract

a b s t r a c tA time-domain approach for predicting dynamic characteristics and vortex-induced vibration (VIV) response of deepwater risers is proposed based on finite element simulation combined with a hydrodynamic model. Effects of axially varying structural parameters, i.e. the effective tension and bending stiffness, on the dynamic characteristics and VIV of slender riser are examined using the presented approach. Our numerical results indicate that axially varying structural parameters can efficiently change the modal wave length as well as the modal displacement. The vibration amplitude of riser VIV response is influenced by the complex effect of factors involving the axial tension, bending stiffness and modal wave length. Generally speaking, for lower modes the response amplitude is larger at the axial position where the tension is smaller, whereas for higher modes the response amplitude is larger at the axial position where the bending stiffness is lower. Moreover, vibration wave velocity increases with increasing modal wave length along the riser length.

Dynamic analysis of coupling between floating top-end heave and riser's vortex-induced vibration by using finite element simulations

“…New approaches of lift force during lock-in were proposed, which are more accurate and reasonable because coupling between structural and fluid dynamics were taken into accounts [2,30,33]. Sarpkaya [1] experimentally measured the Fourier average of hydrodynamic force over many cycles of vibration.…”

Impacts of top-end vessel sway on vortex-induced vibration of the submarine riser for a floating platform in deep water

“…D is the riser outer diameter. C D and C a are the coefficients of added mass and drag forces respectively, of which the values are C a ¼ 1:0 and C D ¼ 1:1 for a flexible riser with large aspect ratio (Sarpkaya, 2004;Chen et al, 2012). When it comes to the vortex-induced lift force F L , its expression is more complicated because VIV has always been a challenging issue concerning the interaction between fluid and structural dynamics.…”

“…With recently increasing experimental observations, along with plenty of CFD simulations, it is noted that it would be more reasonable and accurate if the coupling between structural and fluid dynamics is included in hydrodynamic force model (Gopalkrishnan, 1993;Vandiver, 2002;Sarpkaya, 2004;Chen et al, 2012). Sarpkaya(2004) experimentally measured the Fourier average of hydrodynamic force over many cycles of vibration.…”

“…2, we can get the values of coefficients C L0 , C 1 , C 2 and C 3 in Eq. (4) by solving an equation group (Chen et al, 2012). Observing Eq.…”

“…1) by using FEM code (Chen et al, 2012). In order to explore the impacts of top-end vessel sway on riser's VIV, we present the riser response displacements and vibration wave propagations along riser length while the sway amplitudes or frequencies change.…”