Performance analysis of the passive heave compensator for hydraulic shipwreck lifting systems in twin-barge salvaging

Passive heave compensation (PHC) is extensively used in marine engineering operations such as offshore hoisting and remote-operated vehicle launching because of its high capacity and no energy requirement. Shanghai Salvage Co. used a new twin-barge hydraulic lifting method with multiple PHC systems to salvage the shipwreck of M.V. Sewol in 2017 and avoid harsh sea conditions. The result opens up a new avenue for rescuing sunken ships with huge tonnage. However, the performance of hydraulic compensators in shipwreck salvaging has rarely been studied. In this paper, we mainly focus on the effect of PHC systems on a twin-barge shipwreck salvaging system. Firstly, the salvage system and the PHC's nonlinear dynamic are mathematically modeled. The frequency characteristics of the salvaging system in five motion states are then analyzed, taking into account compensator stiffness and wave frequencies. Finally, in MATLAB/Simulink, a series of simulations of a salvaging system with multiple PHC systems are carried out. The effects of using PHC systems and changing compensation parameters on load performance, including shipwreck movement and sling tensions, are analyzed. The results suggest that in this salvaging system, PHC systems with proper parameters can compensate for both shipwreck movement and sling tensions with great effectiveness.