Study On Typhoon Vulnerability Assessment For Offshore Jacket Platform

With the urgent need for offshore oil and gas resources,China is vigorously developing the South China Sea oil and gas fields,as the critical device for offshore oil exploration and development,the jacket platform is often subject to extreme weather conditions such as typhoons.Current research on the typhoon vulnerability is more common in civil engineering,which has not been reported for offshore jacket platform.The dissertation is supported by the National Natural Science Foundation Program of “Research on survivability and dynamic catastrophe emergency measures for fixed platforms under extreme marine environment”.The study of numerical simulation on jacket platform topside under strong typhoon,fluid-structure interaction,probability analysis of wind-resistant performance of platform,assessment process of typhoon vulnerability of offshore jacket platform are conducted.The time histories of fluctuating wind speed at various sea levels are obtained through typhoon wind power spectrum and linear filter method,combined with the secondary development of Fluent software.Flow characteristics and dynamic characteristics are studied through one-way fluid-structure interaction for jacket platform topside and two-way fluidstructure interaction for derrick structure based on ANSYS Workbench software,and further reveal the dynamic characteristics under different wind load.Structural samples are obtained by using latin hypercube sampling method which consider the uncertainty of material performance and geometrical dimension of the derrick,combined the random wind speed samples to conduct dynamic response analysis.The damage state of platform is divided into four grades,combined with the statistical characteristic of the damage state of platform to establish assessment process of typhoon vulnerability for offshore jacket platform.Results show that compared with power law,the improved wind inlet boundary conditions make better simulation of random wind load,The along-wind speed has a big influence on wind load and it should be considered in the simulation,the maximum of the along-wind speed decreases with increasing altitude.The top of the derrick structure has larger displacement with adding fluctuating wind speed at the same basic wind speed.When the wind quickly reach the surface of the derrick structure,part of the wind velocity quickly decrease with impact on the surface,part of the wind velocity quickly increase,there is vortex and fall off in the wake of derrick structure area.The probability of experiencing serious damage is 34.88% when the wind velocity reach 32m/s under 45° direction,and the probability has a obvious increase with the wind speed continued to increase,because it has a bigger wind area,thus it has a significant damage to the offshore jacket platform.