Heave Response Control of a Semisubmersible by Passive Dampers

Semisubmersibles, deployed offshore in the deep sea experience undesired motion. Large heave motion is one of the concerns and requires mitigation for operational safety. Passive dampers are used to achieve heave control, but must be tuned over a wider frequency band. In this study, a novel passive damper consisting of stiffeners, mass, and damper elements is attached to the deck and activated by the buoyancy force of the submerged portion of the platform. The optimal parameters of the proposed passive damper were identified through an iterative trial-and-error approach under various sea-state conditions. Dynamic analyses were performed for different mass ratios to achieve the desired heave response, with additional evaluation of mooring interactions. The damper’s performance was compared against second-order wave effects and a conventional heave plate of similar size. Results indicate that the damper with a 2% mass ratio effectively controls heave motion in low and moderate sea states. Second-order analyses show an 8% increase in heave energy content compared to first-order predictions, emphasizing the role of nonlinear wave effects. Overall, the proposed passive damper demonstrates superior heave control and maintains effectiveness even under nonlinear sea conditions, confirming its potential as an efficient motion mitigation system for semisubmersible platforms.