The Slow-drift Oscillation of Floating Structure

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In the design of mooring systems for a floating ocean structure such as Tension Leg Platform and other type of semi-submersible, the slow drift oscillation is one of the most important problem. In this research project, a fundamental study on the viscous damping forces acting on TLP is carried out by using TLP model and TLP section model. The effects of hydrodynamic forces acting on mooring chains on the motions of floating structure are also researched by comparing the surge of a floating structure moored by chains in irregular waves and that of the structure moored by coil springs.The main conclusions obtained from this research project are as floows:1) Experimental results of two harmonic forced surge tests and the simple harmonic forced surge tests in regular waves shows that the viscous damping forces acting on the TLP model performing the slow drift oscillation in waves are larger than those obtained from the forced or free oscillation tests in a still water except the cases in the small reduced velocity range.2) The drag coefficient obtained on the basis of the relative velocity concept depends on the reduced velocity.