The Study Of Dynamic Response And Fatigue Analysis For Jack-up

Jack-up is one of the major engineering structures in offshore oil development. Because of its large flexibleness and long natural cycles, it is easily resonant with low frequency wave. Meanwhile, waves will give a greater dynamic magnification effect on platform. So the dynamic analysis on jack-up is very important.Platforms in marine environment will be affected by the cycled waves, and alternating stresses will appear on the platform structure. Although the stress level is below the yield strength, long-term exposure to the alternating stresses may make the platform suffer the suddenly fatigue damage. So it has important significance to apply fatigue analysis to the jack-up platform.In this paper, we will use ANSYS for simulation analysis. We will do Modal Analysis on platform under different conditions, calculate the platform's natural frequencies under different conditions, compare them with wave frequencies, and estimate the possibility of the platform to resonate with waves. After Modal Analysis, we will apply transient dynamic analysis using modal superposition method on better platform finite element model, and we have solved the problem to apply dynamic analysis on large finite element model.In this paper, we also use the"design-wave"method and"spectrum"method to apply fatigue analysis on key components of the platform. Then we compare the calculation results from the two methods, analyze the causes for the differences, and give an advice for how to choose fatigue analysis methods.