Single Buoy Moorings (SBM) Offshore is a pioneer in the offshore and gas industry. Its product line is the supply of facilities and services for the development and production of offshore oil and gas fields as well as the systems relevant to the mooring technology at large. SBM is currently developing various concepts aimed at offloading LNG (Liquefied Natural Gas) carriers offshore. These concepts whether they assume tandem or side-by-side offloading have in common a building block: the LNG carrier. Owing to its unusual shape (shallow draft, non wall sided hull at the waterline with a flared bow and a transom stern and the presence of a bulb just below the sea surface) at least compared to standard VLCCs (Very Large Crude Carrier), difficulties arise when performing diffraction calculations and when comparing model test results in monochromatic, bi-chromatic and irregular waves with numerical time domain simulations. The main objective is to identify whether differences between model tests and standard numerical predictions based on linear potential theory can be bridged in increasingly complex wave fields by resorting to CFD simulations.
The CFD software used is ISIS-CFD, developed by the Numerical Modelling Group of the Fluid Mechanics Laboratory of Ecole Centrale de Nantes and distributed as commercial software by NUMECA International under the name FINE/Marine.
CFD simulations have been performed in monochromatic head wave condition with and without the 4-line mooring system to prevent the LNG carrier from drifting away. The CFD method is described and a comparison between model tests and simulations is presented. CFD shows that it is able to predict the motions measured in model tests. In addition, both the wave frequency and the natural frequency of the mass spring system are correctly linked with the frequencies of the predicted motions.