EFFECTS OF WIND AND WAVE LOADS ON STRESS INTENSITY FACTORS OF A CRACKED OFFSHORE STRUCTURE

Due to the much higher maintenance and replacement expenses of the offshore wind turbine structures, more attention should be paid for a reliable lifetime analysis of them. Meanwhile, the cyclic nature of wave and wind loads together with the corrosive effects from the sea water are major factors for the creation and growth of flaws and cracks in offshore structures. These cracks can be the cause of instantaneous failure in marine structures. The “Tripod” model is one of the favorite support structures which are used for offshore wind turbines particularly in deeper waters. In this paper, a crack is considered in a support structure that can be typically used in the offshore wind turbine constructions. The finite element code ABAQUS is employed to determine the related stress intensity factors for different types of loads. It is shown that the variations of stress intensity factors with crack length differ significantly for various loading types. Also the mode II stress intensity factor is not negligible compared to the mode I stress intensity factor. Therefore, for analyzing the fatigue life or the fracture load of similar cracked offshore structures, appropriate mixed mode crack growth criteria should be employed together with the curves derived in this research for stress intensity factors.