Coupled dynamics of deepwater structures – issues and challenges

Abstract

Offshore systems consisting of floaters linked to line structures such as risers and mooring lines are favoured for deepwater applications. The dynamic coupling analysis of a floater together with the line structures has been the subject of several studies in recent years. Powerful numerical tools have been developed implementing full-fledged time-domain approaches as well as more efficient frequency-domain approaches for the analysis of deepwater systems. The present article provides a brief overview of coupled analysis techniques employing both time-domain and frequency-domain approaches, focusing on the basic modelling issues and challenges. It is worth formulating compact but sufficiently accurate dynamic models of line structures. The consequence of truncation errors of numerical integration schemes in long-term time-domain simulations needs to be studied. There is a need to standardise the statistical linearisation approach applied to dynamic response which spreads over a very wide frequency range. Verification of the nonlinear drag force model in the Morison equation through basic computational fluid dynamics studies may be undertaken.

Numerical Modelling for Synthetic Fibre Mooring Lines Taking Elongation and Contraction into Account

“…The third member is the drag force that is related to the relative velocity of the segment and the seawater flow. The third member is used for the formulation of the damping within the motion equation [29,30]. Thus, the drag force is the damping in considerations of the mooring line dynamics.…”

“…Only one finite element was used for the segment with an assumption that the value of the axial deformation was constant over the element length. On the basis of the presented assumptions, we formulated the nodal displacements and the nodal tensions as per Equations ( 28) and (29), respectively:…”

“…The assumption of the nonlinear drag model as a quadratic function of relative velocity between the water particle and structure as well as the drag force coefficient used are both empirically defined. Forces on moorings (and risers) that oscillate/vibrate are generally evaluated using the well-known generalised Morison equation [29,30].…”

Two-phase flow induced vibrations in a marine riser conveying a fluid with rectangular pulse train mass

“…Results showed that the lateral vibrations are negligible, and hence, the idea of using planar motion models seems to be a plausible approximation. Furthermore, a number of useful contributions to the analysis and design of marine risers or pipelines are available in the literature published in recent years (Ai et al, 2018;Lou et al, 2017;Park et al, 2015;Yuan et al, 2018;Khan and Ahmad, 2017;Li and Low, 2012;Guo et al, 2013;Gao et al, 2014;Gao et al, 2016;Xu et al, 2017;Bai et al, 2017;Zhang et al, 2015;Ye et al, 2014;Dong et al, 2013;Katifeoglou and Chatjigeorgiou, 2016;Park et al, 2018;Vendhan, 2014;Gu et al, 2017).…”