In an exploration of the oil and gas on the sea, floating structures play an important role. The force and motion
prediction of offshore structures may be carried out using time domain or frequency domain on model tests. This paper
proposes a new mathematical model to determine motions of a floating body. The model was developed using 3D
source distribution panel method within the scope of linear potential wave theory. Using the method, the motions of a
semi submersible type GVA 4000 in term of frequency domain were analyzed. The results obtained from the proposed
numerical model are compared with the results obtained from commercial software (HydroSTAR) and experiment
which was carried out at Towing Tank of MTC in UTM. Results of the comparison show good agreement with
experiment and the commercial software.