Damping Characteristics of Heave Plates Attached to Spar Hull

Damping elements are used in ships and offshore structures as response reduction devices for maintaining the hydrodynamic response within acceptable limits. The use of such elements so far has been based on past experience or using empirical based design approach. An investigation of the wave excitation forces acting on these structures with and without damping elements may give an insight into the damping effects of such elements. Also understanding the flow pattern and the magnitude of flow variation around these elements may be useful to improve the design methods. In the present study, measurement of damping forces and response were carried out to establish the relationship between wave frequency amplitude and damping ratio. It was observed that the damping varies with wave period non-linearly and linearly with wave height. Also it was 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 spar with double heave plate at the bottom has higher damping compared to other configurations.