An Experimental Study on Rigid-Object Water-Entry Impact and Contact Dynamics

Abstract

The dynamics of a generic rigid water-landing object (WLO) during water impact is presented in this paper. Tests from a range of drop heights were performed in a wave basin using a 1/6th-Froude scale model of a practical prototype using different drop mechanisms to determine the water impact and contact effects. The first experimental case involved dropping the WLO by using a rope and pulley arrangement, while the second case employed an electromagnetic release to drop the object. Hydrodynamic parameters including peak acceleration, touchdown pressure and maximum impact/contact force were measured using the two different drop mechanisms. The WLO was assumed as rigid, so the experimental results could be correlated with von Karman and Wagner closed form solutions and the maximum accelerations predicted are bounded by these classical analytical solutions. The major purpose of this study are to use the experiments to determine trends that occur when the object is dropped from successive heights using different drop mechanisms by varying the entry speed, angle of impact and the weight of the object. The predictions from the experimental results were used for subsequent numerical studies. Results from the drop tests show that the impact acceleration and touchdown pressure increases practically linearly with the increase in the height of the drop and the data provides conditions of drop mechanism that keep impact accelerations under specified limits for the WLO prototype.