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Fatigue Analysis of Mooring Lines

Hajnoruzi, Farhad | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48026 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Tabeshpour, Mohammad Reza
  7. Abstract:
  8. Designing of giant oil platforms in deep seas is one of the most important challenges of the country’s oil industry. The valuable reservoirs of oil and gas in caspian sea, increases the need of designing platforms for drilling these regions. One of the platforms which is drilling in this region, is Amirkabir platform. In this research, at first this platform is modelled in AQWA software and analyzed. This analysis includes finding loads acting on the platform and consequently RAOs of different degrees of freedom in different directions and also the time history of motions of the platform and tensions in its mooring cables. Motions of moored floating platform consists of two types of motions. One is the WF motion due to linear wave-induced motions and the other is the LF motion whic is due to second-order wave components. These platform motions appear in tensions of mooring cables, as well. Tension analysis of mooring lines due to WF motions should be performed dynamically but for LF tensions, quasi-static analysis is adequate for obtaining the results. After performing hydrodynamic analysis of the platform and tensions arising from platform motions, tensions in different points of the lines are obtained using Finite Element Method (FEM). Of course the effects of motions of mooting on tensions can be neglected in lower parts of the line. Time history of motion of different points of the line are obtained and compared in this step. Fatigue analysis of mooring lines in time domain are obtained using available T-N curves in recommended practices like [14] and one of the counting methods. In this research, fatigue analysis of eight mooring lines of Amirkabir platform in 32 nodal points of each line are obtained in time and frequency domain. Results of frequency domain are compared with time domain ones. These results show consistency from the viewpoint of the location of maximum fatigue damage and a little different in values
  9. Keywords:
  10. Semisubmersible Platform ; Fatigue Analysis ; Finite Element Method ; Boundary Element Method ; Mooring Lines Force

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