Time domain simulations are used extensively to assess the availability of offshore offloading operations, providing key input for assessing the economical viability and reliability of offshore LNG projects. Traditionally, wave scatter diagrams, RAOs or "look-up tables" have been used for this, comprising assumptions which may be difficult to justify. For free weathervaning structures, the relevant combinations of wind, sea, swell and current conditions are virtually unlimited. The uncertainties related to the approximated methods, together with the increasing computing capabilities, has led to the development of a novel method for direct time domain calculation of the downtime events for several years of environmental data. The new approach provides much better insight in the downtime events, including occurrences of crossed conditions, beam swells and varying vessel headings. The complete operation, including approach, berthing, tug operations, side-by-side offloading and departure, can be studied with properly calibrated numerical models. Persistency and seasonality can be evaluated in a direct and consistent manner. For demonstration purposes the new method was applied for a generic FSRU offshore Rotterdam port (52N/3E). Actual floating LNG terminals will probably be located in more sheltered areas, but the chosen location has the advantage of being far outside the main coastal traffic routes.


Liquefied Natural Gas (LNG) is becoming an increasingly important energy source and the industry is preparing itself by developing the technology for offshore import and export terminals. Due to the cryogenic nature of LNG, the fluid transfer between the offloading LNG carrier and the FSRU (Floating Storage and Regasification Unit) cannot yet be carried out with floating hoses. For LNG carriers on jetties, special cryogenic LNG loading arms are in use, but their allowable motion envelope is limited. Safe LNG transfer from the LNG carrier to the floating terminal with high availability and reliability is crucial for the site selection and economics of the asset.

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