Dynamic Analysis of Semi-submersible Under the Postulated Failure of Restraining System with Buoy
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International Journal of Steel Structures https://doi.org/10.1007/s13296-020-00420-7
Dynamic Analysis of Semi‑submersible Under the Postulated Failure of Restraining System with Buoy Srinivasan Chandrasekaran1 · Syed Azeem Uddin1 · Mubarak Wahab2 Received: 26 March 2020 / Accepted: 21 September 2020 © Korean Society of Steel Construction 2020
Abstract Coupled dynamic analyses of a deep-water Semi-submersible platform, in the South China Sea region, is carried out under postulated damage of the restraining system for both 10 and 100-years return period events. Under the combined action of wind, wave, and current loads, motion responses of Semi-submersible at 1500 and 2000 m water depths are analyzed in timedomain. Dynamic tension variations in the mooring lines are investigated for a fatigue failure using the S–N curve approach. Inclusion of a submerged buoy in the mooring system resulted in a marginal increase of the response due to a reduction in the restoration force of the mooring lines; submerged buoy also resulted in additional damping. The results of numerical studies showed an increase in tension in the mooring lines, which are adjacent to the damaged ones, causing reduced fatigue life. With the inclusion of submerged buoy in the mooring system, there is a considerable decrease in tension variation in mooring lines, increasing fatigue life. Failure of a mooring line causes an increase in tension of the adjacent mooring line, but not valid under all circumstances. It is seen from the studies that despite the postulated failure induced in a mooring, the adjoining line remains unaffected due to a steady coupling motion of the platform. Keywords Coupled analysis · Fatigue analysis · Offshore platform · Postulated damage · Semi-submersible · Steel mooring
1 Introduction Floating offshore platforms are designed and constructed to withstand harsh dynamic environmental loads. Semisubmersible is one of the floating offshore platforms, predominantly preferred over other alternatives because of its advantages, namely: better stability in harsh environments, larger deck area, superior constructional and installation features, and higher mobility. Preliminary studies showed that natural frequencies of Semi-submersible inversely vary with that of the draft and length of the platform. Therefore, the effects of change in length are dominant in comparison * Srinivasan Chandrasekaran [email protected] Syed Azeem Uddin [email protected] Mubarak Wahab [email protected] 1
Department of Ocean Engineering, Indian Institute of Technology Madras, Chennai 600036, India
Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS, Seri Iskandar, Malaysia
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to their weight (Sunil and Mukhopadhyay 1995; Stansberg 2008). Researchers showed that the contribution of viscous forces in the splash zone is dominant, and affects the mean horizontal drift of the Semisubmersible (Dev and Pinkster 1995; Berthelsen et al. 2009). The Numerical studies carried out by Mavrakos et al. (1996) confirme
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