Numerical Calculation of Hydroelastic Responses of Pontoon type VLFS

Abstract

Very Large Floating Structures (VLFS) of several thousand meters long are being considered for various applications such as floating airports, offshore cities and so on. The VLFS recently designed have a thin mat-like configuration and very large horizontal size. A typical design, for example, is 5 Km long, 1 Km wide and 5 m high. Therefore this type of structure will be very flexible and the elastic deformation due to wave action will be more crucial than the rigid body motions.For the analysis of the hydroelastic behaviors of VLFS in waves, the conventional numerical techniques can be applied in principle. However, the direct application of such techniques is practically impossible, because the wave length is very small relative to the horizontal size of the structure and it requires enormous computational burden. There are many calculation methods proposed to overcome this difficulty. However, it is still very difficult for the case of the length of structure is more than one hundred times of incident wave length.Then the author propose a new numerical calculation method based on the 3-dimensional eigenfunction expansion method for the diffraction and radiation problems and the modal expansion method for the elastic response representation.This paper describes, at first, a new calculation scheme proposed then the numerical results compared with the model experiments carried out at various institutions which indicate good agreement each others. Finally, based on the calculations, it shows the various features of hydroelastic behaviors of typical VLFS including the effects of water depth, elastic stiffness and so on.