Damping-Controlled Response of a Truss-Pontoon Semi-Submersible With Heave-Plates

Hydrodynamic added mass and damping are old and popular research topics in the field of offshore structures engineering. The concept of added mass has been used very intelligently in the design of modern deepwater floating vessels. The turning point of the conventional Spar to a Truss-Spar is a typical example in which the added mass created by the heave plates in a Truss Spar efficiently reduced the steel weight and the subsequent cost of the Spar hull. However, the damping is not utilized as efficiently as the added mass in the design of the floating offshore platforms. It should be noted that at resonance damping plays an important role in controlling the response amplitude. This resonance is called damping controlled response. An offshore platform efficiently designed to reduce the wave excitation forces and increase the separated-flow damping could qualify as a platform to operate even near resonance. Such design could make this concept cost effective, as well as operationally more productive with minimum downtime. The principal purpose of this paper is to describe an offshore platform design that could face the resonance efficiently. The paper applies the concept of both hydrodynamic added mass and separated-flow damping intelligently in the design of a large floating vessel on column-stabilized principle. The platform is designed to face resonance due to extreme waves and utilizes the damping to control its motion, thereby qualifying its field application. The design is verified and justified with the help of a scaled-model study in a large wave tank. The results are presented herein.