Page 212 - Practical Design Ships and Floating Structures

Practical Design of Ships and Other Floating Structures 187
You-Sheng Wu, Wei-Cheng Cui and Guo-Jun Zhou (Eds)
8 2001 Elsevier Science Ltd. All rights reserved

AN INVESTIGATION INTO WAVE INDUCED DRIFT FORCES AND
MOTIONS OF VERY LARGE FLOATING STRUCTURES

N. Mal, T. Hirayama' and K. Ishikawa'

'National Research Institute of Fisheries Engineering
Ebidai, Hasaki, Kashima, Ibaraki, Japan
*Department of Naval Architecture and Ocean Engineering
Yokohama National University
Tokiwadai 79-5, Hodogaya-ku, Yokohama, Japan
'Sumitomo Heavy Industries, Ltd., Yokosuka, Japan

ABSTRACT

In this paper, the drift forces and motions of very large floating structures (VLFS) in head waves are
investigated through numerical simulations and model experiments. Three dimensional numerical
method based on direct integration of pressure is applied to estimate the steady wave drift forces taking
the elastic modes into account. Numerical simulations and experiments are performed with respect to
two different types of VLFS, pontoon unit type and semi-submersible unit type. Consequently, the
different tendency of motion and wave drift force of these two types had been shown. The numerical
results were verified by the corresponding model experiments using large elastic floating models. Based
on the results, the authors conclude that the near field theory is applicable for predicting both hydro-
elastic response and wave drift force of flexible floating structure with fair accuracy sufficiently, the
elastic deformation of structure can be taken into account satisfactorily by using mode superposition
method. Furthermore, the effects of bending rigidity on both motion and wave drift force are discussed.

KEYWORDS
Very large floating structure, Steady drift force, Hydro-elasticity, Deflection, Numerical simulation.
Near field theory, Mode superposition

1 INTRODUCTION
Very large floating structures (VLFS) are expected to become feasible candidates for purpose of
floating airports, agriculture bases, storage facilities and floating piers and so on, especially in areas
where lack adequate land. Nowadays, the possibility of utilization of VLFS had been enhanced

' Formerly Graduatc School of Yokohama National University