An Analysis on the Spread Mooring of the Belida FSO Induced by Squall Loads

M Murdjito  -  Departement of Ocean Engineering, Faculty of Marine Technology, Institut Teknologi Sepuluh Nopember, Indonesia
Inneke Yulistanty Pravitasari  -  Departement of Ocean Engineering, Faculty of Marine Technology, Institut Teknologi Sepuluh Nopember, Indonesia
*Eko Budi Djatmiko orcid scopus  -  Departement of Ocean Engineering, Faculty of Marine Technology, Institut Teknologi Sepuluh Nopember, Indonesia
Received: 25 Dec 2019; Revised: 31 Jan 2020; Accepted: 31 Jan 2020; Published: 29 Feb 2020; Available online: 29 Feb 2020.
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Squall is the occurrence of a sudden sharp increase in wind speed, thus amplifies sea environmental loads. In the South of Natuna Sea, squall can reach an intensity of up to 50 m/s or close to 100 knots. In this water, the Belida FSO operates at a water depth of 77.0 m, tethered to the seabed by a spread mooring system. Squall’s impacts on the FSO mooring system has been examined by implementing time-domain simulations accommodated in a numerical model based on the 3-D wave diffraction theory. The simulations were performed by varying the squall duration of escalation, i.e. 2.5, 5.0, and 10.0 minutes, for the load cases of 1-year extreme operational and 100-year extreme survival conditions propagating at 0°, 45°, 90°, 135°, 180°. The three squall durations of escalation substantially increase the significant wave height Hs by averagely 60%, 50% and 34%, respectively. The largest of the maximum mooring tension due to the sea load directions is found to be brought about the 45° load when magnified by the squall with a 2.5-minute duration of escalation. In this respect, the largest intensities of the operational and survival tension loads may reach some 2,027 kN and 3,318 kN, respectively, which are eventually far below the MBL of 7,685 kN. The largest x-axis offsets in operational and survival conditions are 3.94 m and 10.21 m, respectively. Whereas the largest y-axis offsets for operational and survival loads are found to be 13.31 m and 15.48 m. These y-axis offset intensities are larger than the limiting criteria, i.e. 15% of the water depth or 11.55 m.
Keywords: Squall; FSO; Spread Mooring; Mooring Tension; Offset
Funding: Medco E&P Natuna Ltd; PT Zee Indonesia

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  1. API, Design and Analysis of Stationkeeping Systems for Floating Structures, API RP 2SK, Washington, D.C. USA: American Petroleum Institute, 2005
  2. DNV, Classification Notes: Environmental Conditions and Environmental Loads, DNV-CN30-5, Oslo: Det Norske Veritas, Mar. 2000
  3. A. Duggal, C. Heyl, A.H. Izadparast, and J. Minnebo, “Response of FPSO Systems to Squalls”, Proc. of OMAE2011 30th Int. Conf. on Offshore Mechanics and Arctic Engineering, Rotterdam, The Netherlands, 2011
  4. L. Liu, W. Zhuang, P. Zhang, and R. Mu., “Convective Scale Structure and Evolution of a Squall Line Observed by C-band Dual Doppler Radar in an Arid Region of Northwestern China”, Advances in Atmospheric Sciences, Vol. 27, No. 5, pp. 1099-1109, Sep. 2010 DOI: 10.1007/s00376-009-8217-1
  5. R. Oberlies, A. Guha, and S. Slocum, “Mooring Analysis of a Turret Moored FPSO in a Squall Environment”, Proc. of OMAE2015 34th Int. Conf. on Offshore Mechanics and Arctic Engineering Paper No. OMAE2015-41390, St. John’s, Canada, 2015
  6. G. Jeans, G. Cooper, C. Yetsko, and G. Bryan, “Squall Characterization in the Gulf of Mexico”, 2014 Offshore Technology Conference; May 5–8; Houston, TX, 2014
  7. ABS, Rules for Building and Classing Mobile Offshore Drilling Units, Houston: American Bureau of Shipping, 2018
  8. L. Liu, L. Ran, and X. Sun, “Analysis of the Structure and Propagation of a Simulated Squall Line on 14 June 2009”, Advances in Atmospheric Sciences, Vol. 32 No. 8, pp. 1049–1062, 2015 DOI: 10.1007/s00376-014-4100-9
  9. F. Legerstee, M. François, C. Morandini, and S. Le-Guennec, “Squall: Nightmare for Designers of Deepwater West African Mooring Systems”, Proc. of OMAE2006 25th Int. Conf. on Offshore Mechanics and Arctic Engineering, Paper No. OMAE2006-92328, Hamburg, Germany, June 4-9, 2006
  10. D. Stanisic, M. Efthymiou, D.J. White, and M. Kimiaei, “Mooring System Reliability in Tropical Cyclone and North Sea Winter Storm Environments”, Applied Ocean Research, Vol. 88, pp. 306-316, Jul. 2019
  11. J. Minnebo, A. Duggal, A. Izadpaarast, and R. Huijsmans, “Response-Based Analysis of FPSO Systems for Squall Loadings”, Proc. of OMAE2012 31st Int. Conf. on Offshore Mechanics and Arctic Engineering, Rio de Janeiro, Brazil, Jul. 2012
  12. E.B. Djatmiko, Perilaku dan Operabilitas Bangunan Laut Di Atas Gelombang Acak. Surabaya: ITS Press, 2012
  13. DNV, Offshore Standard: Position Mooring, DNV-OS-E301, Oslo: Det Norske Veritas, Oct. 2010
  14. X.B. Chen, “Offshore Hydrodynamics and Applications”, The IES Journal Part A: Civil & Structural Engineering, Vol. 4, No. 3, pp. 124–142, Aug. 2011 DOI: 10.1080/19373260.2011.595903
  15. F. van Walree and H.J.J. van den Boom, “Wind, Wave, and Current Loads on Semisubmersibles”, Proc. 23rd Annual Offshore Technology Conference, Paper No. OTC-6521, Houston, TX, USA, May 6-9, 1991
  16. X. Yu, and L. Huang, “An Internal Turret Mooring System Design under Squalls in West of Africa”, Proc. of World Maritime Technology Conference, Rhode Island, USA, Nov. 2015
  17. Z.B. Zhong, Y. Luo, and D. Curic, “F(P)SO Global Responses in the West of Africa Squall Environment”, Proc. of OMAE2005 24th Int. Conf. on Offshore Mechanics and Arctic Engineering, Halkidiki, Greece, Jun. 2005
  18. N.D.P. Barltrop, Floating Structures : a Guide for Design Vol 1, Houston: CMPT, 1998
  19. S.K. Chakrabarti, Handbook of Offshore Engineering, Boston USA: Computational Mechanics Publications Documents, 2005
  20. Arda, E.B. Djatmiko, Murdjito, “A Study on the Effect of Semi-Submersible Drilling Rig Motions with Variation in Mooring Line Pre-Tension to the Safety of Drilling Riser”, Proc. 8th Int. Conf. on Marine Technology, MARTEC 2012, Paper MTP-6, Kuala Terengganu, Malaysia, 20-22 Oct. 2012
  21. Murdjito, M.P. Rosari, E.B. Djatmiko, “Analysis on the Critical Conditions of Side-by-Side Offloading Operation between SSP Type-FPSO and Shuttle Tanker”, Applied Mechanics and Materials, Vol. 874, pp. 53-63, 2018 DOI: 10.4028/
  22. OCIMF, Effective Mooring, 4th ed., London: Oil Companies International Marine Forum, 2019

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