A comparison between ship-mounted and cage-mounted passive heave compensation systems

A finite-element lumped-mass model was used to investigate the performance of ship-mounted and cage mounted passive heave compensation systems for the ROPOS deep sea ROV system. Numerical simulations were done for operating depths ranging from 400 to 5000 m and compensator travel ranging from 2 to 5 m. The compensator lowered the natural frequency of the system. The RMS cage motion and the tension in the tether were reduced for all cases except for shallow depth and small compensator displacement. The cage-mounted compensator provided greater attenuation of RMS cage motion and RMS tension than the ship-mounted unit and was easier to design. The best results were achieved at an operating depth of 1730 m where the cage-mounted compensator with 5 m of travel reduced the RMS cage motion and tension by a factor of 1.6 and 3.2, respectively