Effects of free surface or floor wall on the hydrodynamic coefficients of the rigid and combined rigid–elastic heave plates in offshore platforms

Instability and vibration of offshore platforms in harsh environmental force can be reduced by installing heave plates underneath of platform columns. Effect of parameters such as excitation Frequency and boundaries are investigated experimentally in this research. On the other hand, regarding to the published papers, both the added mass and damping gradually increase versus vibration amplitude for a rigid heave plate. It is predicted that using a combination of a rigid disk in center and an elastic plate around it can increase the damping.  It is generally observed from forced harmonic vibrations that frequency can decrease and increase hydrodynamic coefficients respectively near free surface and floor wall. Furthermore, frequency has considerable effect on the hydrodynamic coefficients of a rigid heave plate with large elastic part around it. This definitely depends on the excited mode shapes of the elastic edge.