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**Efficient fatigue analysis of helix elements in umbilicals and flexible risers: theory and applications.**
*(English)*
Zbl 1251.74037

Summary: Fatigue analysis of structural components such as helix tensile armors and steel tubes is a critical design issue for dynamic umbilicals and flexible pipes. The basis for assessment of fatigue damage of such elements is the long-term stress cycle distribution at critical locations on the helix elements caused by long-term environmental loading on the system. The long-term stress cycle distribution will hence require global dynamic time domain analysis followed by a detailed cross-sectional analysis in a large number of irregular sea states. An overall computational consistent and efficient fatigue analysis scheme is outlined with due regard of the cross-sectional analysis technique required for fatigue stress calculation with particular attention to the helix elements. The global cross-section is exposed to pure bending, tensile, torsion, and pressure loading. The state of the different cross-section elements is based on the global response. Special emphasis is placed on assessment of friction stresses caused by the stick-slip behavior of helix elements in bending that are of special importance for fatigue life assessments. The described cross-sectional analysis techniques are based on an extensive literature survey and are hence considered to represent industry consensus. The performance of the described calculation scheme is illustrated by case studies.

### MSC:

74S30 | Other numerical methods in solid mechanics (MSC2010) |

74R99 | Fracture and damage |

### Software:

RIFLEX
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\textit{G. Skeie} et al., J. Appl. Math. 2012, Article ID 246812, 22 p. (2012; Zbl 1251.74037)

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### References:

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