Effects of Passive and Active Heave Compensators on Deepwater Lifting Operation

Abstract

In deepwater installation and lift, amplified vertical motions of equipment can be caused by axial resonance of wire. This can occur even in operational sea state due to the elastic behavior of the wire. In order to reduce the vertical oscillatory motion of the lifted equipment, heave compensation systems have been frequently used in the subsea installation operation. In the present study, a nonlinear time-domain analysis has been applied to investigate the effectiveness of the heave compensator in reducing the vertical amplification near its wire resonance during deepwater lifting operation. Analysis of coupled crane vessel and equipment dynamics connected via crane wire were carried out in time domain. A passive heave compensator was modeled as a combination of nonlinear spring and damper in the axial direction. An active heave compensation system was numerically implemented using classical PD feedback controller. A series of numerical simulations was conducted for a wide range of wave periods and water depths to find effective operational ranges of passive and active heave compensators.