Large-scale free surface measurement for the analysis of ship waves in a towing tank

This paper is presenting an optical method for free surface measurement of a stationary flow suitable for large-scale experiments in a large towing tank. The new measurement device is based on the projection of laser beams on the surface of the fluid and on the use of a stereoscopic system. The principle of the method is to detect the impact of the laser beams on the air/water interface in order to determine the height of the surface by triangulation for a given number of positions. This method is applied to the measurement of the stationary wave field around a ship model at 1/10th scale. The paper also emphasizes that for low Froude numbers, ((F_L = U/√(gL), where U is the ship velocity and L the ship length), the effects of the scale on the flow characteristics are limited. These scale effects are studied by comparison with measurements taken in a smaller towing tank around the same ship model at scale 1/77.5. The free surface and the velocity field near the hull at the two scales are compared.