Study On Optimum Design And Fatigue Analysis Based On Reliability Of An Offshore Platform

As the basic equipment of the exploitation of offshore oil, gas resources and the base of the work and living at the sea, an offshore platform is playing an increasingly important role in petroleum industries. Practically, dynamic loadings such as wind, wave, current etc. may cause a platform to vibrate excessively, which affect its security and working reliability. Therefore, it is very necessary to research on and develop new design theories and methods in pursuit of economic efficiency.Practical application and engineering requirements taken into account, the development of a reliability-based optimization and fatigue analysis method for structural design and life prediction of a jacket type offshore platform that is effective and accurate is presented in this thesis. In accordance with the actual Offshore Platform CII of Bohai Oil Field in China, a finite element model is properly established, of which the natural frequencies, modal parameters of vibration and response under irregular wave loadings are calculated. Firstly, the reliability analysis of Monte Carlo Method is carried out on the structure. Secondly, the size optimization of components is made on the basis of meeting constraints such as stiffness, strength and stability. Thirdly, based on spectrum method, the fatigue analysis is stepped further and the life of the platform is estimated.The numerical studies show that the optimum total weight of the platform is 5.11% less than the original (the pipes'outer diameters being the input variables) and the platform's approximate life is 28.2 years, which meets its need fully. The results prove that the methods and technical solutions presented in this thesis are practicable and significative. Based on the obtained simulation results, it appears that this new method can provide an advantageous reference for users engaged in structural design and security evaluation of an offshore platform.