Heave motion mitigation of semi-submersible platform using inerter-based vibration isolation system (IVIS)

This paper develops an inerter-based vibration isolation system (IVIS) for heave motion mitigation of semi-submersible platforms (SSPs) subjected to sea waves. An analytical model of a classical SSP equipped with IVIS is first established and validated by comparing the heave response amplitude operator (RAO) with the previous experimental and numerical results, and the corresponding equations of motion are derived. Optimization analyses are performed to search for the optimum inertance-to-mass ratio of IVIS by minimizing the heave motion standard deviation of the SSP. A case study is carried out to demonstrate the control performance of IVIS in the frequency and time domains. The results indicate that the proposed IVIS is more effective and has a wider effective frequency range compared to the conventional vibration isolation system (VIS). By introducing a parallel-connected inerter, the reduction ratio of the receiving body can be further improved by more than 23%. More importantly, the IVIS can achieve the best control performance under different wave conditions by adjusting the inertance in the system. The proposed IVIS is an attractive alternative to the conventional vibration isolation systems for offshore platforms.