The developing of technology has discovered new materials which have been applied to improve the performance of structures. The researchers have recently increased the attention in controllable fluids and its applications. Magnetorheological (MR) dampers are devices that employ rheological fluids to modify their mechanical properties. Their mechanical simplicity, high dynamic range, lower power requirements, large force capacity, robustness and safe manner operation in case of fail have made them attractive devices to passive, semi-active and active control in mechatronic, civil, aerospace and automotive applications. The characteristics of the MR damper change when the rheological fluid is exposed to a magnetic field changing its stiffness and damping coefficients. For this study, a marine structure exposed to different excitations has been considered in which some members have been substituted by the MR dampers. Prevention of serious damage of marine structures like the problems are generated by vibrations might be achieved by monitoring the loading conditions and by inspecting the structural integrity. The concept of smart structures can be applied to marine applications. There are plenty of marine structures in huge dimensions, for example, the overall length of a very large crude carrier exceeds 50 m. This offshore structure has 12 links and 21 nodes in each sides and each node has 2 degrees of freedom in X, Y directions. It is applied 7 MR dampers on critical links and controls the environmental vibrations and loading. Environmental loadings are divided into three general groups; Winds, wave and currents. All of maintained points are considered in analyzing of the offshore structure. Control the vibration of a marine structure in order to prevent the collapse of these structures is final purpose of this research. The controlling and the suppressing of this vibration have been done through Magnetorheological (MR) fluid dampers. The controlling method is used by the linear quadratic Regulator (LQR) as controller of this system and the results shows that it acceptable method in order to the amplitude of these vibrations.

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