Buoyancy-driven vertical piling breakwater-a new type of breakwater formed by upper and lower steel pipes rises above sea level by feeding the air into the upper pipe when high waves or tsunamis are imminent, whereas it normally rests inside the lower pile installed below seabed so that navigation is undisturbed. This paper outlines the results of a series of experiments by a large scale physical model and of the numerical analyses with regard to the rising/sinking behavior of the breakwater. The results clearly demonstrate that: 1) The time required for raising the upper pipe is just a few minutes, being rapid enough to prevent tsunamis from attacking harbors; and 2) The numerical model gives good approximation and is fairly applicable.
