Reducing response of offshore platforms to wave loads using hydrodynamic buoyant mass dampers

In this paper, an innovative concept is introduced for reducing the displacement response of tower type fixed offshore platforms to wave loads. The idea is based on utilizing a Hydrodynamic Buoyant Mass Damper (HBMD), which employs damper's buoyancy and inertia forces, along with hydrodynamic damping effects, to reduce the displacement response of the platform. A four-legged platform is investigated in which the HBMD is added at the appropriate elevation. Because of the high volume of the damper, the associated added mass and consequently the generated inertia force is significant. On the other hand, as a result of the damper's eccentricity with respect to the platform's position in its deformed configuration, the upward buoyancy force causes reversal moment that can potentially counteract those generated by wave loads. Our results indicate that, if positioned and attached appropriately, the damper interacts with the platform in a way that could result in reducing the response of the platform to wave loads. Response reduction factors are proposed to evaluate the performance of the hydrodynamic buoyant mass damper and seek the optimal stiffness in damper's attachment to the platform.