Study On Fatigue Life Of A Closed Shell In Seawater Environment

With the progress of science and technology and the development of society,people's demand for energy is also increasing,and the development of marine energy is more and more important in the growing pressure of survival.In the rapid development of science and technology today,in order to safeguard territorial integrity and national land and energy exploitation requirement,development of deepwater equipment becomes very necessary.In this paper,the fatigue life of a closed box-shaped shell is taken as the object of study,and the fatigue life of the box-shaped shell is calculated by finite element software ANSYS.First of all,the working environment of the box-shaped shell was studied deeply and the sea flow force and wave force have been calculated.After that,the theory and the influencing factors of the fatigue life of the part were evaluated,so as to get the appropriate fatigue life criterion.Then,the welding part of the box-shaped shell are modeled with ANSYS APDL design language and the welding residual stress is calculated and analyzed to provide a basis of the influence of fatigue life.The static strength analysis,modal analysis and fatigue life evaluation of the box-shaped shell was carried out under the condition of known force analysis.At last,the fatigue life of the box-shaped shell is simulated and the corrosion mechanism of the seawater is researched simply in the end of this paper.Finally,the following simulation results are obtained:(1)Residual stress at the welded part of the shell is about 1800 Pa.(2)The first six natural frequency values of the shell are zero,the seventh,eighth and ninth order natural frequency values are 9291,12278,12514 respectively.(3)The fatigue life of the shell is about 8.9 years.