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Fatigue Reliability of Tension-Leg Platform Tendon under Random Wave Load

Nazari, Negin | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50550 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Tabeshpour, Mohammad Reza
  7. Abstract:
  8. The primary objective of this research is probabilistic quantification of the fatigue life of tension-leg platforms (TLP) using reliability methods. The need for such methods stems from the significant uncertainty in the loads exerted on offshore structures. The scope of this paper is limited to the study of fatigue in TLP tendons. For this purpose, nonlinear force time history response of the TLP tendon under random wave loads is computed and the damage due to fatigue is estimated in accordance with the Palmgren-Miners rule. Assuming a Rayleigh distribution for stress variation and eight different sea states, the ultimate fatigue damage is computed by accumulating the damage over all individual sea states. This cumulative damage enters the limit-state function that is based on thePalmgren-Miners rule. Prevailing sources of uncertainty in this problem are those in the estimation of fatigue stresses, fatigue strength, and the Palmgren-Miners rule. Finally, reliability analysis is carried out for five different service livesusing the first- and second-order reliability methods (FORM and SORM) and Monte Carlo sampling. The results indicate that FORMcomputes the probability of failure sufficiently accurately and campare with second order method calculate the probability of failure is more confident. It is concluded that the probability of failure increases drastically with the service life. The importance vector from the sensitivity analysis in FORM reveals that the model error is the most influential source of uncertaintyon the probability of failure. The calculation is repeated for four different values of Pre-Tension and the effect of the Pre-tension on the failure of structure is investigated. Consequently, the probability of failure decreases with increasing the amount of Pre-Tension has been obtained
  9. Keywords:
  10. Tendon ; Tension Leg Platform ; Fatigue ; Monte Carlo Sampling ; Uncertainty ; Reliability ; First Order Reliability Method (FORM)

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