Actively Damped Heave Compensation (ADHC) system

In offshore oil and gas exploration and production, high interoperability of underwater components and equipments has become more important in support of Inspection, Maintenance, and Repair (IMR). As drilling goes to deep or ultradeep water, harsh weather leads to an expensive downtime for offshore cranes handling. Active Heave Compensation (AHC) system has been developed to stabilize the crane payload by overcoming the disturbance generated by vessel motion. The conventional AHC technology, however, focuses only on compensating the vessel motion. The cable compliance, which is significant in deep water handling, is usually neglected. As a result, it is difficult to achieve the desired motion control accuracy, in particular as the disturbance is injected other than ship heaving. In this paper, a new type of AHC scheme, Actively Damped Heave Compensation (ADHC) control, is presented. The novelty of this work is, in addition to the vessel motion, the cable dynamics has also been taken into account and compensated. ADHC integrates active damping of cable vibration into the widely adopted vessel heave motion compensation framework. Moreover, a sliding mode control is also presented for actuators to accurately track a displacement demand. The simulation results verify the superior performance of the proposed solution.