Wind Velocity Profile and Representative Wind Velocity for Wind Resistance Measurement of Ship Models

Wind resistances and moment acting on a ship model measured in a wind tunnel are non-dimensionalized using the air density, the projected area of the model and the representative wind velocity. However, there is no common definition of the representative wind velocity in wind tunnel tests for ships, thus wind velocities which are obtained by an anemometer fixed in a certain place in a wind tunnel or measured at a height equivalent to 10 m from the sea surface are often used. In principle, there is no problem as long as the wind velocity profile under the same condition is assumed and the wind velocity at the same position is employed when the wind resistance coefficients are converted into forces of different scales. Nevertheless, if the wind velocity distributions between in the wind tunnel test and the assumed distribution by the user are different, the wind resistance coefficients cannot be used in the first place. And the existence of various definitions of non-dimensionalization makes it difficult to simply compare wind resistance coefficients themselves. Since it is meaningful to clarify the definition of the representative wind velocity which can provide wind resistances in a realistic and reasonable manner using the wind resistance coefficients without being influenced by the assumed wind velocity distribution, it was derived from the results of wind tunnel tests under the conditions of various wind velocity profiles and using various types of ship models. Furthermore, the influence of the wind velocity profile on the wind resistance measurement was evaluated with the results of the wind resistance measurement in different wind velocity profiles. Several findings on the wind velocity profile required for wind resistance measurements are reported in this paper.