We proposed an application of the ray-theory to hydroelastic behavior of VLFS, since the method is easy to handle and is not time consuming. The theory itself is based on the classical ray theory. The hydro-elastic behavior of VLFS is treated as wave propagation in the platform. The reflection and transmission coefficient of incident waves at the edge of VLFS is estimated by the eigen-function expansion method. The reflection coefficient at the other side is estimated by applying the wide space approximation. This method is applied to the 5000m-class floating airport with the variation of the bottom topology. Some numerical results demonstrate wave propagation from out side of the platform to in the plate as a ray. Results also show the good agreement with the three-dlmensional calculation.
Recently the estimation of elastic motion of a very large floating structure (VLFS) has been carried out for the Mega-Float project in Japan. The latest version of the computer code (Seto and Ochi 1998) is based on the Finite Element Method. This code can deal with arbitrary shape of the structure and the topology of the sea bottom, however the code is very time consuming and is not useful for the conceptual design. Actuary, the committee of the project regards this code as a program for the detail design. It is obvious that we need a method to estimate the effects from all environments, for example the bottom topology, break water, geometry of the structure and so on, in the conceptual design. The method should be easy to handle and should not be time consuming. In this aspect, we propose an application of the ray-theory to hy&''o-elastic behavior of VLFS.