Dynamic Response Characteristics of Jack-Up Drilling Unitsby David T. McDonald, Chevron Research & Technology Co, San Ramon, United States,
Robert G. Bea, Chevron Research & Technology Co, San Ramon, United States,
Abstract: The effects of five parameters on the dynamic amplification of the global base shear on a deep water jack-up drilling unit were analyzed using a time domain nonlinear model. The five parameters investigated were; foundation stiffness, foundation yield strength, environmental loading (time histories of sea states), leg spacing and system damping. The foundation conditions (stiffness, strength and yield strain) were chosen to be representative of soil conditions of the Gulf of Mexico and the North Sea. Environmental loadings on the unit were varied using recorded and synthetic time histories of wave conditions of hurricanes Camille, Elena and Juan. Wave cancellation effects were estimated by varying the leg spacing between 48.8 m and 61.0 m. The effects of hydrodynamic, structural and foundation damping were determined by varying the system damping between 1% and 8%. The analyses indicated that the maximum dynamic base shear experienced by the unit is associated with the largest wave load at which the dynamic amplification factor is approximately unity. Large values of the dynamic amplification factors are associated with low values of wave loadings and result in dynamic base shears less than those experienced under the largest wave conditions.
Subject Headings: Dynamic loads | Offshore structures | Jacking | Damping | Drilling | Dynamic response | Load factors | Shear strength | Shear waves | Foundations | Water waves | North Sea | Gulf of Mexico
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