Numerical analysis of stiffness-driven passive heave control in a semisubmersible platform

In recent years, semisubmersibles have increasingly replaced fixed and semi compliant platforms in deep water deployments. Their larger deck area and superior operational stability under severe environmental loads have contributed to their widespread use. However, excessive heave motion remains a critical design concern. Passive and active control strategies have been explored to address this concern. The present study proposes a novel passive damping system suspended beneath the platform deck to suppress excessive heave motion. The results demonstrate the effectiveness of the proposed passive damper in controlling heave motion under low and moderate sea states. At high sea states, however, its performance declines because it does not adequately suppress second-order effects and coupling between degrees of freedom. The controlled response behavior may result from complex inter-degree-of-freedom coupling effects, including second-order interactions. It requires more detailed higher-order analysis, which is beyond the scope of the present study. Additionally, the proposed damper system is uniquely driven by the buoyancy forces generated during submergence, eliminating the need for external power. Thus, the control action is inherently self-induced through the platform’s motion, offering a simple, energy-efficient, and reliable solution for heave mitigation.