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Modeling Effect of Soil behavior on Fatigue Life of Steel Catenary Risers in Touch Down Zone

Malekzadeh Kebria, Mahyar | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51517 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Raie, Mohammad
  7. Abstract:
  8. Purpose of this research is an investigation on the effect of soil behavior on fatigue life of steel catenary risers in touch down zone. Steel catenary risers are a part of pipeline installed between the seabed and the offshore platform on the sea level, and its application is to transfer the gas or oil from the seabed to the sea level. Steel catenary risers for their resilience against buckling, easy installation, lower cost comparing other conductors are preferred to other means of conducting oil in recent years. The most challenging issue in the design of this kind of riser is the fatigue problem. The characteristic of the wave loadings we are facing in this environment is cyclic; therefore, we are facing with fatigue issue. One of the most critical parameters affecting the fatigue damage is the behavior of the seabed soil. Investigation on this issue that what will be the response that riser receives from the soil and what will be the behavior of the soil after repeating this process will lead us to better estimation of fatigue life of steel catenary risers. Soil stiffness is of the great importance and needs to be appropriately determined for accurate modelling of soil-seabed interaction. Soils with high stiffness cause high-stress concentration resulting in higher fatigue damage and lower fatigue life and soils with low stiffness cause opposite of this scenario.
    In the present research seabed response is determined with the aid of finite element analysis of riser body with series of beam elements and modelling the interactions between seabed and riser with series of nonlinear springs. Then responses will be compared and verified with experimental tests. In further steps with the use of soil behavior models regarding remolding and reconsolidation, the effects of this phenomenon on soil response and fatigue life will be obtained
  9. Keywords:
  10. Steel Catenary Riser ; Sea Bed ; Fatigue Life ; Finite Element Method ; Nonlinear Spring ; Soil-Pipe Interaction

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