Postulated Tendon Failure of Offshore Triceratops

Abstract

Offshore triceratops is one of the successful manifestations of the form-dominant design approaches deployable in ultra-deepwater oil and gas exploration. The deck’s geometric shape and partial isolation from the legs counteract lateral loads. Legs are position-restrained to the sea bed by taut-moored tendons, while ball joints partially isolate the deck from the buoyant legs. However, compliance in the horizontal plane imposes large displacements, intuiting the necessity to examine tendon failure. Numerical analysis of triceratops under wave and wind combined action is carried out under the postulated conditions of a tendon failure. 10-yr, 100-yr, and 1 000-yr post-Katrina hurricane conditions are assumed as loading to the platform. Results confirm a marginal increase in the natural periods of stiff degrees of freedom even under postulated failure conditions, ensuring good adaptability to ultra-deep water. Under postulated failure, the tension of adjacent tendons varies significantly, causing a shift to the mean position of the platform. Fatigue life is significantly reduced under the postulated failure of tendons, making the platform free-floating without affecting its stability. Results also show that the pitch response of the deck is a clear manifestation of the postulated failure, which is otherwise absent due to the presence of ball joints. The attempted study deliberates on the fatigue life of tendons, assessing the platform’s suitability to ultra-deep waters and identifying the vulnerable legs for the chosen load combinations.

Keywords

Ball joints / Tendons / Buoyant legs / Fatigue life / Irregular waves / Postulated failure

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