URANS predictions on the hydrodynamic interaction of a conceptual FLNG-LNG offloading system in regular waves

Abstract

Using an unsteady Reynolds-Averaged Navier-Stokes solver, numerical investigations of hydrodynamic interactions of a conceptual FLNG-LNG offloading system in regular head sea waves are presented. Initially, a verification study is performed on estimating the numerical uncertainties within the URANS model. Based on the validated computational setup, the gap wave responses and wave loads on the FLNG and LNG vessels are studied for different wave frequencies and varying lateral separations. URANS predictions on the gap wave responses are compared with that from the experiments and demonstrate better accuracy over potential flow calculations especially at relatively high wave frequency conditions where gap wave resonance occurs. From the data gathered, it is seen that the gap wave resonance appears when the incident wave frequency approaches the natural frequency of the gap fluid, resulting in significant variation of wave loads in the directions of sway, heave, pitch and yaw. Meanwhile, reduction in the lateral separation shifts the occurrence of gap wave resonance to a higher wave frequency and brings more significant exaggerations on the gap waves and wave loads. Furthermore, when comparing model and full scale wave loads and gap wave responses, the two series of data correlate well implying insignificant influence of scale effects.