Static And Dynamic Response Analysis Research Of A Deepwater Jack-up Drilling Platform

As a kind of mobile platform structure,jack-up platform has several advantages which are not available in fixed platform structure such as jacket platform and it is the one of the main structures of offshore oil exploit.But because the leg flexibility of the jack-up drilling platform is large and its nature periods is longer,so with the increment of the operating water depth,it is easy to occur resonance phenomenon under the action of complex and variable wave loads,which can results in the too large overall response that influence the strength of the platform.So it is necessary to make dynamic wave response analysis for jack-up drilling platform.Moreover,considering the extreme environment occurred in the operating sea,particularly the storm environment in a hundred years,the static plastic collapse analysis must be carried out to evaluate the strength margin of jack-up unites.When the jack-up drilling platform is subjected to the periodic medium and low frequency waves for a long time,the structure of the platform is prone to fatigue damage under the action of alternating loads,which can affect the service life of the whole platform structure,so it is very important to analyze the fatigue of the platform.In order to solve the platform structure strength problem during the stage of basic design of jack-up unite,this paper uses the software SACS of ocean engineering to make static plastic collapse analysis,dynamic wave response analysis and fatigue analysis for the 350 ft jack-up unite working in the North Atlantic Ocean.Firstly,the 3D finite element model of jack-up unite is established by SACS and the main hull structure and spud can is established by equivalent simplified method.The100-year environmental load in the North Atlantic Ocean is chosen as the extreme environment loads condition and considering the 16 different environment directions,Then the paper is based on the nonlinear static plastic collapse analysis theory,using the COLLAPSE module of SACS to make collapse analysis to solve the ultimate bearing capacity of the platform and confirm the beams and nodes of the platform structure occurring damage firstly by using the progressive load method.Secondly,this paper uses SACS to make modal analysis and dynamic wave response analysis under the operating conditions and compares the base shear force and overturning moment with static state to evaluate the resonance probability and the influence of the wave dynamic response on the platform structural strength.Finally,based on the Miner linear cumulative damage theory,the Fatigue Damage module of the SACS is used to make deterministic fatigue analysis and spectral fatigue analysis for the target jack-up unite.The parameters sensitivity analysis of S-N curve,wave spectrum and wave scatter diagram are carried out,and the influence of these three parameters on the fatigue life of the platform structure are discussed.Based on the static and dynamic analysis results,the maximum bearing capacity of the target platform is 1.33 times of that of the designed load,which occurs in the direction of 112.5 ° and 247.5 ° and the leg brace beam near the spud can is the vulnerable structure of the whole platform structure.When the fatigue damage happened,the bearing capacity of chords near its surroundings also decreased obviously.Moreover,the beams whose fatigue lives are lower are concentrated in splash areas,the fatigue life of brace 0180-0232 is the lowest,the value of fatigue is 39 year,which just to meet the jack-up unite service life requirements of 25 year.