Inerter-based damping isolation system for vibration control of offshore platforms subjected to ground motions

Offshore structures are critical infrastructure in the field of ocean engineering, which may under the threat of earthquake shaking, especially when they are located in the high-risk seismic zones. This paper proposes using an innovative inerter-based damping isolation system (IDIS) for the seismic protection of offshore platforms. The concept of IDIS is firstly proposed by integrating the conventional bearings with inerter-based dampers (IDs). An analytical model of the system is established, and the corresponding equilibrium equations of motion are derived. Without loss of generality, the deck acceleration, displacement on the jacket cap, and isolating layer deformation are chosen as the performance objectives, and parametric analyses are performed to investigate the influences of the key parameters of IDIS on each performance objective. A performance-based multi-objective optimization framework is then developed for determining the optimal parameters of IDIS. The control effectiveness of IDIS is demonstrated in the frequency domain and compared to that of the traditional damping isolation system (DIS). Finally, case studies are performed to further investigate the performance of IDIS subjected to natural seabed ground motions. The results show that properly optimized IDIS is more effective than the conventional DIS in terms of not only the structural responses but also the deformation of the isolating layer. The proposed IDIS can be an attractive and effective alternative to the conventional DIS in the vibration control of offshore platforms.