A new method for predicting site-specific wave-induced hull girder loads acting on ship-shaped offshore installations in benign conditions

Kim, Hyeong Jin and Mujeeb-Ahmed, M.P. and Cabrera Miranda, José Manuel and Paik, Jeom-Kee (2022) A new method for predicting site-specific wave-induced hull girder loads acting on ship-shaped offshore installations in benign conditions. International Journal of Maritime Engineering, 163 (A4). 706. ISSN 1479-8751 (https://doi.org/10.5750/ijme.v163iA4.14)

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Abstract

The aim of this study is to develop a new method for predicting wave-induced hull girder loads acting on ship-shaped offshore installations in benign conditions. Unlike in trading ships, current classification society rules provide procedures to define the design values of wave-induced hull girder loads for ship-shaped offshore installations in survival conditions with site-specific metocean data considering that the installations always remain on site. However, ship-shaped offshore units with single-point or turret mooring systems can be disconnected to temporally evacuate from the fields during the severe storm. Also, some areas may be fully benign accommodating spread mooring systems. In these cases, their design wave-induced hull girder loads may be defined in a similar way to those of trading ships but associated with site-specific metocean data. This study proposes a probabilistic approach to determine the site-specific design values of wave-induced loads acting on ship-shaped offshore installations in benign conditions that also accounts for the effects of mooring system type. Six target regions – the North Sea, Gulf of Mexico, western coast of Africa, eastern coast of South America, south eastern coast of Asia and north western coast of Australia – were studied to compare the results corresponding to various sea states. A set of wave scenarios representing all possible wave events for each target region were selected using the Latin hypercube sampling technique. To demonstrate this method, the design values of the wave-induced vertical bending moments were determined for a very large crude oil carrier (VLCC)-class structure with a hypothetical floating, production, storage and offloading (FPSO) unit. The effects of the mooring system type (e.g., single-point mooring versus spread mooring) on the wave-induced hull girder loads of the ship-shaped offshore installations were also evaluated. A case study of the developed method was made by comparison with existing results in the literature and design values provided by classification society rules. The novelty of this study is associated with a new approach that can accurately determine wave-induced hull girder loads of ship-shaped offshore installations in benign conditions, taking into account the effects of site-specific ocean environmental conditions and mooring system type, and its main contribution to industry is to provide a practical technology for the safe and economical design of ship-shaped offshore hull structures.

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