Both the supply and demand of Liquefied Natural Gas (LNG) is projected to continue to grow in new markets, requiring novel infrastructure solutions in the shallow water near-shore environment, away from existing ports. LNG transfer operations using ship to ship (STS) transfer can occur in a scenario where a LNG carrier is moored side by side to a floating or fixed LNG receiving terminal in shallow water.
This paper presents a case study of a jetty-moored LNG carrier in the close proximity of a caisson type breakwater structure. The mooring is designed according to the Mooring Equipment Guidelines (MEG) by the Oil Companies International Marine Forum (OCIMF) and checked against Bureau Veritas (BV) Rule Note NR 493. Frequency domain radiation and diffraction analysis is completed using HydroStar, in which a "dissipation zone" is applied to the gap between the LNG carrier and the caisson to deal with unrealistic resonant wave motion. Time domain mooring analysis is performed using ARIANE. In the analysis, the effect of mooring line (fiber rope) change-in-length characteristics is considered. The vessel hydrodynamic performance is examined by taking into account the presence of the caisson structure in close proximity and by using the full Quadratic Transfer Function (QTF) to compute the 2nd order low frequency wave load in shallow water. The fiber rope change-in-length characteristics and the shallow water effect are found to greatly impact the LNG carrier's motion response.