The reduction of the dynamic responses of offshore towers subjected to wind generated random ocean waves is an important issue in the aspect of serviceability, fatigue life and safety of the structure.
In this thesis, methods of structural control are studied to reduce the responses of a fixed offshore structure subjected to wave forces. Performances of the passive control system with a Tuned Mass Damper(TMD) and the active control system with a active tuned mass damper(ATMD) are examined. For the later system, the instantaneous optimal control scheme is employed. Numerical example studies are carried out to investigate the performance for several sea state conditions. Results show that the active control system is more efficient than the passive control system.
The case of the active control, displacements and velocities of all nodes of structure should be measured to determine the control forces. However, it is not easy to measure responses at all the nodes. In the present study, thus, accelerations and velocities of several nodes near the water surface are assumed to be measured, then velocities and displacements of other nodes are estimated by Kalman Filtering.
