This report concerns a numerical calculation procedure for global ship motions of a LNG carrier considering LNG liquid dynamic effect in wave conditions. Both a frequency-domain and a time-domain analysis procedures of the ship motions are developed. The velocity potential of the liquid is obtained in the methods, based on the artificial damping on the free water surface of the liquid. The value of the damping factor is determined by model tests. The response amplitude operators of the hydrodynamic force of the tank are derived and the maximum value of the apparent transverse acceleration of the tank to design is predicted based on the long term distribution of the tank force. The estimated maximum value is almost equal to a conventional design chart method.