TLP Fatigue Due to Second-Order Springing

by S. R. Winterstein, Stanford Univ, United States,
T. Marthinsen, Stanford Univ, United States,
T. C. Ude, Stanford Univ, United States,



Document Type: Proceeding Paper

Part of: Probabilistic Mechanics and Structural and Geotechnical Reliability

Abstract:

For offhsore oil production in water depths beyond 300-350 m, the tension leg platform (TLP) has become an increasingly popular design concept. The TLP is a floating structure with excess buoyancy, anchored to the sea bottom with tethers. Natural periods of the TLP are typically around 1-2 minutes for horizontal (slow-drift) motions, and about 2-4 seconds for vertical (springing) modes. These periods avoid most first-order wave energy. Nonlinear effects, however, give additional forces at sums and differences of wave frequencies. The sum-frequency terms drive resonant springing response, while difference frequencies control slow drift motions. The authors focus in the paper on tether fatigue problems due to springing.

Subject Headings: Offshore platforms | Offshore structures | Fatigue (material) | Wave forces | Wave diffraction | Wave climates | Dynamic models

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