The Fatigue Life Prediction And Structure Optimization Reseach Of Jack-up Drilling Platform Wedge

Jack-up drilling platform is widely used in oil and gas exploration and development in the continental shelf waters as the result of good fixing and reliable working.Wedge as important assistant components of jack-up drilling platform elevating gear has played an important role in fixing pile leg during the operation of the platform.When the platform works in standing state,it not only bears its own gravity and variable load,but also suffers from bad sea conditions such as wind,wave and current for a long time.The wedge is easily damaged and needs to be replaced frequently.In order to reduce costs and improve the safety of the platform,the structure forms of long-service-life wedge need to be researched urgently.In this paper,BH7 jack-up platform is taken as the research object.By using the direct finite element calculation method,the static strength of the wedge under typical working conditions is studied.The stress distribution of platform wedge under storm self-storage,normal operation and ascending and descending conditions is compared and analyzed.Discussing the evaluation method of fatigue life of the wedge,fatigue damage and fatigue life of the hotspot of the wedge were estimated,and the influences of the wedge hole number,web thickness and stiffeners on fatigue damage and fatigue life of the wedge were investigated.It was pointed that the anti-fatigue wedge with stiffener was the reasonable structural form.The main results of this paper are included below:(1)Under the storm environments,the normal operation and rise and fall conditions,the stress peak values of jack-up platform module changes with the wave-to-course angle.Under the storm environments,when the course angle close to 46 degrees,the stress peak value appears in the opening zone of the bottom half the web plate.(2)According to the state of the working region,the load conditions of fatigue analysis were selected,and the fatigue lifespan assessment method of the platform wedge was established by the material matched asymmetric cycle index S-N curve(r=-0.5)and palmgren-miner damage summation.The fatigue life evaluation method of platform wedge is established,and the fatigue life of platform wedge hot spot is estimated by using this method.Then the results are basically consistent with the wedge life provided by the application,which verifies the rationality of the evaluation method in this paper.(3)Using the upper fatigue lifespan assessment method,influences of structural geometrical factors on fatigue life of the platform wedge were studied,then the effect laws of the number of opening holes,thickness of web plates,reinforcement of the wedge on the fatigue damage and the fatigue life of the platform wedge were obtained.Through comparison and analysis,the conclusion that the reinforced wedge is a reasonable structural type of the anti-fatigue wedge is obtained.