Structure Strength And Fatigue Analysis Of90m Jack-up Platform

As the main equipment in the marine oil exploring, the Jack-up platform plays animportant role in the development of marine oil. It always works in the tough oceanenvironment and suffers from the actions of wind, wave and current, so the operation safetyof the platform will be affected inevitably at the same time. So it is very necessary toanalyze the structural strength of the platform. In addition, due to the long-term interactionbetween the leg structure of the jack-up platform and the wave, alternating stress willemerge in the leg structure, thus leading to fatigue damage of legs. So it is also important toperform fatigue analysis for the leg structures. The following researches are conducted tosolve these problems in this paper.First of all, based on the Morrison formula and stokes5th wave theory, the waveforces acting on the pile legs under the self-surviving and working conditions are calculatedusing the MATLAB program.Then, the finite element model is established for the90m Jack-up platform which isbeing constructed now. With the use of finite element analysis software Patran/Nastran, thestrength and modal analyses of the platform under the self-surviving and workingconditions are performed by considering the different combinations of wind, wave andcurrent loads. And the strength of the whole structure is checked according to the CCSRules for the Classification and Construction of Offshore Mobile Platform.Finally, the simplified model of the platform is established using the GeinE, then thehydrodynamic performance of the leg is conducted using Wajac and the fatigue analysis forthe leg under working condition is also performed using the Framework. And thecumulative damage of the leg under the circulating action of wave is calculated via thecertainty design wave method by taking the stress concentration effect into consideration,thus providing some data for the longevity estimation.It is shown that the structure of platform can meet their self-storage and drillingoperation in bad sea condition, and the platform is easily occur sympathetic vibration withlow frequency wave. In addition, fatigue analysis shows that fatigue life of tubular joints inthe bonding area of right leg and contacting area are shortest. So the tubular joints of theseareas should be paid more attention.