The Static And Dynamic Analysis Of The Jack-up Platform's Legs In Survival Condition

With the development of the oil engineering,as an important equipment of oil exploitation,movable offshore drilling platform has been used broadly in the ocean oil engineer.Jack-up Rig is one of the movable offshore drilling equipment,which is the most popular drilling equipment in offshore petroleum exploration in China.It is composed of main hall,leg,jacking system and a pack of drilling equipment.Because of its special structural complexity and tough environment,it is very important to analyze the whole structural strength and to describe the mechanical details of the marine platform which is one of the typical ocean engineering structures.during this procedure,the key course is how to build a 3D FEM model of the whole structure.As a example,a calculation of a marine self-elevation platform is introduced to this thesis.The technique of building a 3D model is investigated for the static and dynamic analyses.Different operation water depths are taken into account,A plane-girder 3D FEM model of the structure is established.then according to survial conditional load cases,the deformation result of the plant and stress and the check of the leg are obtained. The calculation and the check are according to the regulation of CCS. Then the hull-leg model is simplified for the modal and dynamic response analysis.The frist five orders free frequencies are calculated.The effect of the connection between hull and leg is investigated and different soil elastic ratios are taken in to account for the model analysis and a more accurate 5-order STOKES wave is used to calculate and the wave load and the corresponding dynamic response of the Jack-up Rig in this pape.The results and analysis show that the strength of the chord is the fatal factor of the legs, and the soil elastic ratio plays a very important part in the natural vibration characteristics, of the platform.Because Jack-up Rig has only three or four legs which insert into the sea floor.With the increasing of the working depth,the rigidity of the whole rig becomes smaller,the frequency of its self-vibration becomes lower and it becomes more sensitive to the vibration caused by wave and wind,so the sympatheftically dynamical vibration may be large even not under the resonance conditions.