Offshore structures provide great possibilities for the development and utilization of the resources and energy of the ocean. The environment of offshore structures is usually subjected to more severe load conditions than those on the land. Seismic ground motions and random sea waves are two main design loads for an offshore platform located in a seismically active region. Since these loads have stochastic properties, the random vibration approach provides effective methods of dynamic response evaluations. In order to enhance the reliability of the design of offshore structures, it is important to evaluate the exact dynamic response. If this dynamic response can be reduced using the control methods such as passive control and active control, then the design process of offshore structure can enhance the reliability against the severe load conditions. In this study, the effects on the dynamic response reductions of an offshore platform subjected to seismic loads are examined using the passive and active control methods. It ir shown that the effective reductions of the response can be implemented with the combinations of the passive control method and the active control method.
In a seismically active region, the seismic load is one of the most important excitations for the dynamic response evaluation of an offshore platform. Many researches about the seismic response analyses of offshore structures have been carried out in the past (for example, Penzien et al 1972; Bea 1979). The random vibration approach provides good examples of the dynamic response evaluations because of the stochastic properties of this method and of the seismic motions. In order to enhance the reliability of the design of offshore structures, it is important to carry out not only the exact evaluation but also the reduction of the responses.
