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Description:
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Due to the complexity of body -shape , the investigation of hydrodynamic forces on
mooring lines , especially those comprised of chain segments , has not been conducted to
a sufficient degree to properly characterize the hydrodynamic damping effect of mooring
lines on the global motions of a moored offshore platform . In the present study , an
experimental investigation of the hydrodynamic characteristics of various mooring
elements is implemented through free and forced oscillation tests . Since no direct
measurement capability for distributed hydrodynamic forces acting on mooring line
segments such as chain and wire rope is available yet , an indirect measurement
technique is introduced . The technique is based on the fact that hydrodynamic forces
acting on a body oscillating in still water and on a stationary body in an oscillatory flow
are equivalent except for the additional inertia force , the so -called Froude -Krylov force ,
present in the latter condition . The time -dependent displacement of a slender body
moving in calm water is acquired through optical tracking with a high speed camera . The
distributed hydrodynamic measurements are then used to obtain the force by solving the
equation of motion with the boundary condition provided from tension measurements . Morison’s equation is employed along with Fourier analysis to separate the inertia and
drag components out of the total fluid force . Given the experimentally -derived
information on hydrodynamic behavior , the resistance provided by a mooring line to a
floating structure is briefly studied in terms of damping and restoring force in a coupled
dynamic system . |