ABSTRACT

In this paper, a damping adaptable passive heave compensation system for a 600 meters shipwreck salvaging claw and the corresponding control algorithm are proposed. Salvaging claw is a new method for entirely salvaging shipwrecks. Passive heave compensation is added between the vessel and shipwreck to reduce sling tension and payload motion fluctuations. However, the resonance of payload displacement and sling tension may also occur in low wave frequencies due to the lack of system damping. Therefore, a proportional valve is added to the compensation system for flow rate regulation, and the control algorithms using Adam and others are designed. We find that the simulation results show satisfactory load performance.

INTRODUCTION

A rising number of ships and offshore facilities are being constructed, which increases the danger of accidents, as a result of the development of ocean transportation and the exploration of marine resources. Wrecks should be salvaged as soon after emergencies to safeguard the marine environment and navigation. However, due to procedures like deploying salvage buoys, draining oil, and sealing cabins that need to dive, typical salvage methods are mainly for shallow regions. In deep regions, the water pressure limits the diving operation, and the existence of low-frequency swell waves also interferes with the salvaging vessel.

The Russian submarine Kursk, for example, sank in 2000 with 9500 tons of weight. In order to attach slings at a depth of 100 meters and prepare the shipwreck for salvage, divers had to drill 26 holes in it (Chalmers, 2002). The whole salvage project took roughly five months and 130 million USD of earmarked funds. Besides, the collided M.V. Changtong of China, another example, whose 6000 tons stern was sank in shallow water but difficult salvaged by traditional methods. It was finally salvaged through a twin-barge system based on hydraulic synchronizing traction. 28 strand jacks were distributed among the two barges, which were positioned on either side of the shipwreck. But the salvage issue would worsen for a deeper region. Therefore, a mechanical claw, diver-free shipwreck catch and salvage technique will be efficient and convenient. A similar historical example is recovering the Soviet submarine K-129, whose detailed information and description were clearly proposed by Polmar and White (2012). In simple terms, the United States designed a special claw salvage device for secret salvage. The device is made up of an integrated framework that can hold the submarine, numerous hydraulic claws to secure it in place, and hydraulic legs to lift it out of the seabed. However, the fragile hull broke during the lifting process and partly detached from the claws (Dean, 2018). This illustrates that a complex salvage structure may lead to uneven stress on the target shipwreck and lack versatility. Claw salvage system should be designed as separate structures that each claw is a single unit. Shipwrecks can be caught and lifted by combining multiple claws, which is the salvage method of this paper (more details in the next section). But for efficient working, a heave compensation system also should be considered.

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