چكيده به لاتين
In marine engineering, offshore platforms are used to explore and exploit oil and gas reserves in the depths of the sea. Generally, these structures are affected by different loads. Because the marine environment is quite dynamic, and loads due to waves, winds, and subterranean currents are quite dynamic, it causes fatigue in various structural components. The most important part of the marine structure is its connections, which makes it important to study fatigue phenomena both during the design phase of these structures and during the safety assessment programs of the structure. Due to the fact that underwater inspections of platform joints are costly to ensure their safety and that the implementation schedule of these inspections is determined according to fatigue calculations, the fatigue estimation in these structures should be as accurate as possible. Many offshore platforms are analyzed as rigid joint structures, while the steel tube members are not rigid but flexible. This local flexibility, based on the movement and exit from the central axis of the main member, is created by the force exerted by the bracing members to the main member, which causes the angle along the axial member of the bracing member and the main member to be, which is contrary to the assumptions of rigid connection. During this research, a frame from the SPD19A platform installed in the Persian Gulf has been modeled once with flexible connections, and another time the same frame with rigid connections, in the SACS software. Each of the models is subjected to random waves and then consider the effect of fatigue, then use the Monte Carlo method to analyze the structural reliability in two modes in MATLAB software. Finally, the probability of failure was extracted and analyzed. The results showed that the probability of failure in flexible connections mode is significantly less than that of rigid connections.
