Strength and Fatigue Life Analysis of the Risers for Mobile Jack-up Wellhead Platform
Considering the integrated environment of wave,ocean current,soil characteristics,attached marine organisms,temperature and corrosion,the structural strength of two types of WZ12-8E/W risers during the movement of a self-elevating off-shore platform under different design water level conditions was calculated and analyzed,and the vortex-induced vibration was checked for occurrence and the fatigue life of the two risers under alternating loads was predicted.The ORCAFLEX software was used to calculate the dynamic response of the two risers at each sea conditions,and the bending moment and tension were conver-ted into stress values.The fatigue life was predicted using S-N curve,rain-flow counting method,and Miner cumulative damage criterion.The accumulate fatigue damage for 37 conditions in each direction at 0°,45° and 90° was calculated respectively.The results showed that the two types of risers will not undergo vortex induced vibration under operating and extreme conditions,and their strength meets the design requirements.It was also found that the structural areas with significant fatigue damage does not meet the design life requirements;an improved method to increase the fatigue life was put forward.
platform riserdynamic responsestructural strengthvortex induced vibrationfatigue life
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