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...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 1000-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.展开更多
In this technologically advancing world,the demand for more energy,oil and gas production is rapidly escalating.To accomplish this,people have inclined more towards completely floating offshore structures,deployed in ...In this technologically advancing world,the demand for more energy,oil and gas production is rapidly escalating.To accomplish this,people have inclined more towards completely floating offshore structures,deployed in deep waters.A semi-submersible is selected in the present study,due to its better response characteristics and stability under harsh environmental conditions.The semi-submersible is position restrain with spread mooring lines incorporated with submerged buoy at different locations has been studied.A detailed numerical analysis is carried out using Ansys Aqwa for dynamic response analysis of semi-submersible under the combination of wind,wave,and current forces for 0°,45°,and 90°directions.It was observed that damping ratios and natural periods had been affected based on the position and number of submerged buoys in the mooring system.Also,reduction in mooring force after incorporating buoy in the mooring lines was observed.Subsequently,a Matlab code based on the S-N curve approach was generated and employed to investigate the fatigue damage of mooring lines under dynamic variation of mooring forces.When pegged with submerged buoys,fatigue life of mooring lines is increased under intact and postulated damaged mooring conditions.Moreover,coupling of motion responses of semi-submersible is observed,and unbounded response is not seen in any degrees-offreedom,even during damaged condition of mooring lines.展开更多
文摘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 1000-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.
文摘In this technologically advancing world,the demand for more energy,oil and gas production is rapidly escalating.To accomplish this,people have inclined more towards completely floating offshore structures,deployed in deep waters.A semi-submersible is selected in the present study,due to its better response characteristics and stability under harsh environmental conditions.The semi-submersible is position restrain with spread mooring lines incorporated with submerged buoy at different locations has been studied.A detailed numerical analysis is carried out using Ansys Aqwa for dynamic response analysis of semi-submersible under the combination of wind,wave,and current forces for 0°,45°,and 90°directions.It was observed that damping ratios and natural periods had been affected based on the position and number of submerged buoys in the mooring system.Also,reduction in mooring force after incorporating buoy in the mooring lines was observed.Subsequently,a Matlab code based on the S-N curve approach was generated and employed to investigate the fatigue damage of mooring lines under dynamic variation of mooring forces.When pegged with submerged buoys,fatigue life of mooring lines is increased under intact and postulated damaged mooring conditions.Moreover,coupling of motion responses of semi-submersible is observed,and unbounded response is not seen in any degrees-offreedom,even during damaged condition of mooring lines.
