Berthing is a common marine operation frequently occuring in harbors and at open sea. It involves a moving vessel closely approaching a moored offshore structure or a pier from a far distance. During the berthing operation, the distance between the stationary structure and berthing vessel decreses continuously, resulting in increasing hydrodynamic interaction. In this study, the berthing problem between a FSRU and a LNGC was investigated by using three different numerical methods including dynamic simulation. At first, frequency-domain diffraction computations were carried out to study hydrodynamic interaction between two floaters in the berthing operation. With various relative positions, the effect of gap resonance and sheltering effect were discussed based on the frequency-domain solution. As the second numerical method, time-domain simulation using convolution integrals was used to simulate the berthing problem. The simulation results were directly compared with the model test data. The third numerical approach is dynamic simulation combined with direct fluid solver. In head sea condition, focus is made on the effect of the gap resonance on the wave forces and related motion responses during berthing operation. As for the quartering sea, the sheltering effect is mainly discussed with different berthing routes based on the dynamic simulation results.