WAVE INDUCED MEAN FORCE ON PLATFORMS IN DIRECTION OPPOSITE TO WAVE PROPAGATION

For certain platforms and sea states, model tests have shown the towing resistance in head seas to be smaller than in calm water. At zero forward speed the phenomenon appears as a mean drift force in the direction opposite to wave propagation. Since potential theory predicts mean wave force only in the direction of wave propagation the phenomenon must be of a viscous nature. The report presents a possible explanation of the phenomenon and some results of model tests. It also presents an approximate method of calculating the force theoretically. According to the magnitude of the numerical and experimental results, this force is not so important in terms of for instance total thruster horse-power. Nevertheless, it should be taken into account for a complete physical understanding of platform behaviour in waves.