Analysis of Heave Compensator Effects on Deepwater Lifting Operation

A deepwater lifting operation using crane vessel is investigated by a time-domain analysis program for floating crane vessel systems. In the analysis, a coupled analysis of floating vessel and lifted object dynamics connected via crane wire are simulated with and without heave compensator. For deepwater installation cases, amplified vertical motion of lifted object is anticipated even under mild sea state due to axial resonance of wire because of elastic property of the wire. The vessel motion of 6 degree-of-freedom is solved in time-domain including memory effect, while 3-d.o.f. motion is considered for lifted structures. The wire is modeled as linear spring and heave compensator is modeled as combination of spring and damper in axial direction. A series of numerical simulations conducted for a wide range of wave periods, and discussions are made for making effective operational range of heave compensator and effectiveness of active heave compensator.