LAUSR

ABSTRACT Damping elements are used in ships and offshore structures as response reduction devices for maintaining the motion response within acceptable limits. The design of these elements relies on a combination of empirical approach and past experience. In this paper, an investigation of the wave excitation and hydrodynamic reaction forces acting on floating structures with and without damping elements is presented taking spar platform as the candidate structure. Understanding the flow pattern and vortex structure around these circular heave damping plates helps correlate the energy dissipation and damping. In the present study, measurement of hydrodynamic damping and inertia forces and response were carried out to establish the relationship between wave frequency and damping ratio. Flow pattern around the damping elements has been simulated using computational fluid dynamics (CFD) approach. Furthermore, flow visualisation and velocity measurement using particle image velocimetry (PIV) technique has been carried out in a wave flume for comparison and evaluation of the CFD approach. It was observed that the damping varies with wave period in a nonlinear fashion and it varies linearly with wave height. It was also observed that increase in added mass combined with viscous damping is a key factor for the effectiveness of heave plates in reducing motion response of spar platforms. Of the various configurations tested, the one with spar with double heave plate at the keel has higher damping and superior motion response compared to other configurations. The velocity pattern and vortex formation around the circular plates obtained through PIV study and CFD simulation showed good agreement.