Effect of Top Tension on Vortex-Induced Vibration of Deep-Sea Risers

Abstract

With the increase of water depth, the design and use of the top-tensioned risers (TTR) are facing more and more challenges. This research presents the effect of top tension on dynamic behavior of deep-sea risers by means of numerical simulations and experiments. First, the governing equation of vortex-induced vibration (VIV) of TTR based on Euler-Bernoulli theory and Van der Pol wake-oscillator model was established, and the effect of top tension on natural vibration of TTR was discussed. Then, the dynamic response of TTR in shear current was calculated numerically by finite difference method. The displacement, bending stress and vibration frequency of TTR with the variation of top tension were investigated. Finally, a VIV experiment of a 5 m long flexible top-tensioned model was carried out at the towing tank of Tianjin University. The results show that the vibration displacement of TTR increases and the bending stress decreases as the top tension increases. The dominant frequency of VIV of TTR is controlled by the current velocity and is barely influenced by the top tension. With the increase of top tension, the natural frequency of TTR increases, the lower order modes are excited in the same current.

Bifurcation analysis of vortex-induced vibration of low-dimensional models of marine risers

“…According to previous studies [39][40][41], a parametric resonance often occurs at the low-order frequency of the structure. Therefore, in order to analyse the dynamics of the coupled system, the vibration of the first order modes for the riser and wake oscillator are investigated as follows.…”

“…With the development of technologies, impacts of the parametric excitation on the vibration of risers attract more and more attention as shown by the conducted experimental and numerical studies. The effect of top tension on dynamic behaviour of deep-sea risers was investigated numerically and experimentally by Zhang et al [41], and results showed that the vibration displacement for TTR increases and the bending stress decreases as the top tension increases. The experiment of VIV for a vertical variable-tension riser was conducted by Li et al [42], and it was shown that the dominant frequencies of risers in IL and CF directions, decrease gradually as the top tension is increased for a fixed flow velocity.…”

Numerical and Experimental Research on the Effect of Platform Heave Motion on Vortex-Induced Vibration of Deep Sea Top-Tensioned Riser

“…e design of the current velocity and the platform heave frequency in experiment is referred to the natural frequency of the TTR model (T �100 N). After the comparison between numerical simulations and experiments, it is proved that the calculating program is reliable [23].…”

“…e static component of the tension comes from the pretension imposed by the heave e dynamic component of the tension is caused by the heaving platform, and (Ω,a) is generally referred to as parametric excitations for the transverse vibration of TTR [21,22]. erefore, equation ( 1) is a partial differential equation with periodic variable coefficient, and this is different from the partial differential equation with constant variable coefficient in [23].…”

“…Recently, we studied the effect of top tension on VIV of deep sea top-tensioned riser (TTR) and presented a VIV prediction model of TTR in linearly sheared current by numerical simulation and experiment [23]. For an advanced research, this paper is to investigate the dynamic behavior of TTR under VIV and platform heave motion.…”