The Analyse Of The Static And Dynamic Strength For The Jack-up Platform's Legs In The Transition Condition

Jack-up platform is one of movable offshore drilling equipment, which is the most popular drilling equipment in offshore petroleum exploration in China, and it is composed of main hall, legs, jacking system and a pack of drilling equipment. The displacement from the top of the leg to the main deck is more than 100 meters in the transition condition. The legs have environment force and many kinds of force due to the movement of the platform. And the platform will have serious accident. Therefore the analysis of the static and dynamic strength for the jack-up platform has important engineering meaning to the safety of the hull and legs in the transition conditionThe dynamical force on the leg is caculated using the method of the simulative static under the requirement of《The classification and construction regulations of movable platform》. The transition condition contains sea transit and oil field transit. Due to the requirement of the platform's period is different under the two condition, we should calculate the two different force, and then checkout the leg stress. We mostly checkouts the leg stress near the jack tower.As an example, a calculation of platform is introduced to this thesis. The force on the leg is caculated in the transition condition. And then the leg stress is calculated using equivalent girder method.According to the requirement of《The classification and construction regulations of movable platform》,free vibration analysis is necessary. The leg's free period should disagree with wave period to avoid sympathetic vibration., 3D FEM model of the structure is established, and make model analysis, then obtain the leg's free frequency. At last , as leg is excited by period sway, study the leg's deformation and stress by harmonic analyse .The results show that the legs have inertia force, gravity, wind force under wind and wave, and inertia force is important to the leg stress. The jack-up platform which is caculated as an example will not occur sympatheic vibration. The legs will sway seriously in the sea transition condition. An feasible scheme will be advanced according to the result of the static and dynamic caculationg,and be used for prepareing a transition scheme.