X-ray measurements of plunging breaking solitary waves

Abstract

The aim of this study is to examine and measure the characteristics of air cavities generated by breaking solitary waves by utilizing a novel tomographic X-ray system. Small scale experiments of solitary waves that propagate on a (1:10) beach are conducted. Waves with amplitude normalized with the water depth, on a flat bottom are investigated by two perpendicular X-ray systems. Images are captured at locations from the surf zone to the swash zone and at maximum runup. A large air tube is observed right after the plunger impacts the dry beach. Void velocity and the shape of the large air tube, are measured and reported. The large air tube evolves from a symmetrical shape with two large air pockets located close to the walls of the wave tank, to an asymmetrical shape. Contrast enhanced X-ray images reveal that the swash tongue surface is unstable and that secondary mixing of air and water occurs. X-ray images from the maximum runup reveal that the air is still entrapped by the thin swash tongue at times close to maximum runup.