Abstract

Mooring lines are used as station keeping systems for the deep-water floating offshore platforms. Mooring lines have considerable effect on the project overall cost. Therefore, it is necessary to economize their cost by choosing appropriate material and configuration which, in turn give the required responses for the platform by possessing good restoring capability. Hence, a numerical study has been conducted on the restoring behavior of the mooring system for different mooring line materials, line diameters and fairlead slopes. Two mooring systems consisting of mooring lines arranged unsymmetrical were considered. Assuming the drag forces on the mooring lines to be negligible and the change in the line geometry as insignificant, the mooring system has been analyzed using the quasi-static analysis. The numerical model thus developed has been validated using experimental model test data and a parametric study was conducted using the parameters mentioned. It can be concluded that the polyester mooring lines provide better restoring forces compared to the other materials and also the behavior of mooring system can be greatly affected with change in line diameter and fairlead slope.

Keywords:

Fairlead slope, mooring line properties , mooring system, quasi-static analysis,

References

1. Agarwal, A.K. and A.K. Jain, 2003. Dynamic behaviour of offshore spar platforms under regular sea waves. J. Ocean Eng., 30: 487-516.
   CrossRef    
2. Downie, M.J., J.M.R. Graham, C. Hall, A. Incecik and I. Nygaard, 2000. An experimental investigation of motion control devices for truss spars. J. Marine Struct., 13: 75-90.
   CrossRef    
3. Flory, J.F., 1982. New and used strength of large marine hawsers. Proceeding of the Offshore Technology Conference. Houston, Texas, Paper No: OTC 4304.
   CrossRef    
4. Flory, J.F., J.W.S. Hearle and M. Goksoy, 1987. Abrasion resistance of polymeric fibres in marine conditions. Proceeding of the 2nd International Conference on Polymers in a Marine Environment. IME, London.
   
5. Flory, J.F., M.R. Parsey and H.A. McKenna, 1988. The choice between nylon and polyester for large marine ropes. Proceeding of the 7th Conference on Offshore Mechanics and Arctic Engineering. ASME, New York.
   
6. Flory, J.F., S.P. Banfield and D.J. Petruska, 2004. Defining, measuring and calculating the properties of fiber rope deepwater mooring lines. Proceeding of the Offshore Technology Conference. Houston, Texas, Paper No: OTC 16151.
   CrossRef    
7. Flory, J.F., S.P. Banfield and C. Berryman, 2007a. Polyester mooring lines on platforms and MODUs in deep water. Proceeding of the Offshore Technology Conference. Houston, Texas, Paper No: OTC 18768.
   CrossRef    
8. Flory, J.F., Ahjem and S.P. Banfield, 2007b. A new method of testing for change-in-length properties of large fiber-rope deepwater mooring lines. Proceeding of the Offshore Technology Conference. Houston, Texas, Paper No: OTC 18770.
   
9. Gobat, J.I. and M.A. Grosenbaugh, 2001. A simple model for heave-induce dynamic tension in catenary moorings. J. Appl. Ocean Res., 23: 159-174.
   CrossRef    
10. Lee, M.Y. and T. Grove, 1999. Use of synthetic ropes in deepwater moorings: ABS guidance notes. Proceeding of the Riding the Crest into the 21st Century (OCEANS '99 MTS/IEEE). Seattle, WA, 1: 257-268.
    
11. Markussen, B.H., E.S. Hunt and R.E. Hobbs, 1984. Wear of nylon hawsers over rollers, pulleys and fairleads. Proceeding of the 16th Offshore Technology Conference. Houston, Texas, Paper No: OTC 4765.
    
12. Mavrakos, S.A., V.J. Papazoglou, M.S. Trintafyllou and J. Hatjigeorgiou, 1996. Deep water mooring dynamics. J. Marine Struct., 9: 181-209.
    CrossRef    
13. Nielsen, F.G. and A.U. Bindingbo, 2000. Extreme loads in taut mooring lines and mooring line induced damping: An asymptotic approach. Appl. Ocean Res., 22: 103-118.
    CrossRef    
14. Pascoal, R., S. Huang, N. Barltrop and C.G. Soares, 2005. Equivalent force mdel for the effect of mooring systems on the horizontal motions. Appl. Ocean Res., 27: 165-172.
    CrossRef    
15. Pascoal, R., S. Huang, N. Barltrop and C.G. Soares, 2006. Assessment of the effect of mooring systems on the horizontal motions with an equivalent force to model. J. Ocean Eng., 33: 1644-1668.
    CrossRef    
16. Ran, Z., 2000. Coupled dynamic analysis of floating structures in waves and currents. Ph.D. Thesis, Texas A&M University, Texas.
    
17. Rosales, B. and C.P. Filipich, 2006. Full modelling of the mooring non-linearity in a two-dimensional floating structure. Int. J. NonLin. Mech., 41: 1-17.
    
18. Smith, R.J. and C.J. MacFarlane, 2001. Statics of a three component mooring line. J. Ocean Eng., 28: 899-914.
    CrossRef    
19. Vlasblom, M.P., J. Boesten, S. Leite and P. Davies, 2012. Development of HMPE fiber for permanent deepwater offshore mooring. Proceeding of the Offshore Technology Conference. Houston, Texas, Paper No: OTC 23333.
    CrossRef    

Competing interests

The authors have no competing interests.

Open Access Policy

This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Copyright

The authors have no competing interests.