Artificially stopping a solid body after surface impact

Many solid bodies decelerate to a stop shortly after impacting the water's surface. These include plunging birds, porpoising pinnipeds, amphibious drones and boat hulls penetrating the surface. However, most solid body entry research involves the body penetrating the surface and continuing at a near constant speed well below the water’s surface. In this work, a motor driven system allows the solid body to be decelerated and stopped at various depths. This results in the formation and collapse of an air cavity that differs from previous results. Specifically, we present the results from a 3D printed sphere that impacts the surface of water at high Reynolds and Froude numbers 130000 and 6.5 respectively, and is abruptly stopped at a range of 1 to 5 diameters below the surface. We observe that stopping the sphere before the full deep seal alters the cavity size and shape. The further down the sphere is stopped before the deep seal would normally occur the more drastic the change will be. Before collapse, the cavity at the same point has been shown to be large in the case where the sphere stops short of the full deep seal. These results can be used to inform design and experimentation of engineered structures with more complex geometries that do not enter as deeply below the surface after impact.