Dynamic analysis of fixed platforms equipped with mass dampers under earthquake loading using crow search algorithm

Marine jacket platforms are exposed to environmental loads, such as wind, waves, currents, and earthquakes during their operational lives. Due to their dynamic and periodic nature and the phenomenon of fatigue in the structure, wave and earthquake forces are among the most important loads. There are a variety of methods to investigate the fatigue life of jackets, including deterministic, spectral, and time-domain analysis. Among these methods, the spectral method is a reliable one that considers the random nature of earthquake waves in fatigue analysis. In this paper, the effectiveness of the passive tuned liquid damper (TMD) system in controlling the dynamic responses of fixed platforms equipped with mass dampers under seismic excitation is investigated. Also, the mass, stiffness, and damping matrices of the Nusrat jacket located in the Persian Gulf are examined, which is equipped with a semi-active system of adjustable mass damper (SATMD) system, and its information has been extracted after modeling the structure in the studied articles. Due to the large number of degrees of freedom in the model, the computation of the online SATMD control was time-consuming. For this purpose, the size of the model was reduced to a limited time and frequency interval by programming in the MATLAB software. The SATMD used in this study includes a passive tuned mass damper (TMD) and two magneto-rheological (MR) dampers to demonstrate the control effect of the SATMD. The selected algorithm to control and optimize the performance of the MR damper is PID control optimized with the crow search algorithm. The time-history responses of the platform are compared in cases with and without SATMD under different ground motions. The results show that the jacket equipped with SATMD can significantly reduce the dynamic responses caused by earthquakes. The result of the evaluations to reduce the displacement of the main deck due to the earthquake is estimated to be 46.7%.