Dynamic response of offshore triceratops with elliptical buoyant legs

Abstract

Oil and gas exploration in ultra-deepwaters necessitates innovative geometric forms for offshore steel structures. Offshore triceratops is one of a new steel compliant structures found suitable for ultra-deepwater applications. It consists of three buoyant legs attached to the deck by ball joints, which partially isolate the deck from the buoyant legs and constitute the novelty. The present study discusses a detailed numerical analysis of triceratops with buoyant legs of elliptical cross section. The focus is to assess the hydrodynamic diffraction characteristics of the platform caused by the change in cross section of buoyant legs from a conventional tubular one to the elliptical ones. Three elliptical sections with varying eccentricities are considered in the dynamic analyses to assess the response behavior of triceratops under regular waves. The results showed an increase in the total force in the buoyant legs in sway degree of freedom with the increase in the eccentricity of the cross section. Besides, reduced transverse vibrations and increased stability are also observed in both the deck and elliptical buoyant legs. Based on the numerical results, it is recommended that elliptical buoyant legs with eccentricity close to 2 are highly suitable for offshore triceratops in ultra-deepwaters.