ABSTRACT

This paper presents a review of recent studies on the prediction of hydroelastic responses of a very large floating structure (VLFS). It is divided into the pontoon type and columnsupported type structures. Studies on the pontoon type are divided further into the frequency-domain and time-domain analyses. A new calculation method for general time-dependent problems is also described, which is one of the future works required. The hierarchical interaction theory, developed recently by the author for analyzing hydrodynamic interactions among a large number of columns, is explained with some equations and numerical results. However, experimental work is not reviewed in detail, because main interest in this paper is placed on analytical calculation methods.

INTRODUCTION

Because of the lack of adequate land space and/or environmental concerns such as the pollution or noise near residential areas, very large floating structures (VLFSs) will become increasingly necessary in the future. Several years ago, "Mega-Float" project has started in Japan, aiming at establishment of technologies for constructing a floating airport. Since then, a large number of studies have been made on hydroelastic problems related to VLFS. The preferred configuration of VLFS in Japan is of pontoon type, and its size is 5 km long, 1 km wide, and a few meters deep. This kind of structure is featured in two points:

  1. the wavelengths of practical interest are very small compared to the horizontal dimensions of the structure;

  2. hydroelastic responses are more important than the rigid-body motions due to the relatively small flexural rigidity of the structure.

Considering realistic waves with wavelengths of 50–100 m, the length ratio to a VLFS under consideration is 1/50–1/100. Conventional calculation methods developed for ordinary offshor structures or ships could not be used for this order of short waves.

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