Dynamic Analysis and Safety Assessment of Ships and Cables during Salvage Operations.

Featured Application: This study is based on the successful salvage of the Korean "Sewol" ferry in 2017. The approach delineated in the manuscript—the arrangement of two lifting barges in symmetrical disposition to retrieve a large-tonnage shipwreck—is increasingly being employed. The manuscript expounds the dynamic response of the salvage system and the technique employed to assess the safety of the system. Moreover, the manuscript articulates technical details, such as selecting the appropriate wave direction interval before initiating the salvage operation, selecting suitable intership connecting cables, and analyzing potential risks arising after the failure of the lifting cables. These elucidations can proffer insights to salvage engineers for optimizing design schemes. The International Maritime Organization (IMO) emphasizes that shipwreck accidents frequently occur at sea and advocates for the safe recovery of shipwrecks. This paper examines the case of the Korean "Sewol" ferry salvage, where two lifting barges were symmetrically utilized to retrieve a substantial shipwreck. The dynamic analysis of the salvage operation is based on the computational fluid dynamics (CFD) approach. The main investigation covers two fundamental physical parameters: the motion response of the lifting barges and shipwreck and the tension response of the lifting cables. Using the parameters of the maximum absolute value (MA), root mean square (RMS), and coefficient of variation (CV), a unified criterion is established to quantitatively evaluate the safety of the salvage operation under different working conditions. The study demonstrates that by carefully considering the enhancement of safety and stability for the three vessels involved in the salvage process and by optimizing the safety performance of the lifting cables, suitable operating windows are determined at wave intervals of (115°, 155°) and (205°, 245°). Under most working conditions, curves illustrating the maximum tensions of lifting cables No. 1–15 and No. 16–30 show a distribution with a "middle part drooping" shape. The placement of connecting cables on the water's surface at 1.1–1.2 times the salvage spacing between the two lifting barges or the arrangement of inclined lifting cables underwater proves advantageous in constraining the motion response of the three vessels. Reinforcing the lifting cables at the bow and stern ends is recommended. This study presents a methodology for salvaging a shipwreck using two lifting barges, which can be used as a reference for designing related salvage approaches. [ABSTRACT FROM AUTHOR]