Scale model test of a semi-active heave compensation system for deep-sea tethered ROVs

The deep-sea ROV system is usually equipped with a heave compensation system under harsh sea states, and a semi-active heave compensation system that consists of a passive and an active subsystem is presented, the compensation mechanism of which is derived theoretically and illustrated in detail. A novel scale model for the underwater umbilical cable system is brought forward according to the Froude criterion, and the natural frequency is scaled rigorously to guarantee the dynamics similarity for physical implementation. Then four kinds of model test, including the generation of heave motion, resonance zone, passive and semi-active heave compensation, are investigated in sequence. The test results show that the scale underwater system without compensation will resonate at a critical depth, which corresponds to the resonance zone of its prototype system, and the passive heave compensation is more suitable to compensate tension instead of motion. The semi-active heave compensation has better efficiency than the passive counterpart and is more suitable for compensating the motion instead of the tension. Based on the scale model test results, this paper can provide important references to improve the operation safety of the deep-sea tethered ROVs.