The tsunami-height reduction using a very large floating structure, i.e., VLFS, is discussed, with the water waves, interacting with a floating thin-plate, simulated numerically. The final tsunami-height reduction rate increases, as VLFS length, VLFS flexural rigidity, or the wave height of an incident tsunami, is increased. If two VLFSs are utilized, the final tsunami-height reduction rate, also depends on the distance between the VLFSs. In two-dimensional tsunami propagation, another wave propagates to the outside, along the crest line of the main wave, leading to an additional tsunami-height reduction.

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Numerical simulation of nonlinear interaction between floating thin-plates and surface waves has been performed to study the reduction of tsunami height due to propagation of tsunamis through very large floating structures (VLFS). When a solitary wave propagates through a floating thin-plate, wave disintegration occurs, resulting in generation of short floating-body waves, such that the wave height of the main wave is decreased. While the main wave is combined with the short waves after progressing through the thin-plates, the wave height of the main wave is increased. Once the main wave passes the short waves, its wave height decreases, which indicates that a VLFS is applicable to reduce tsunami height. The reduction effect depends on both the length of floating structures and the interval of the structures.