Page 222 - Practical Design Ships and Floating Structures

Practical Design of Ships and Other Floating Structures 197
You-Sheng Wu, Wei-Cheng Cui and Guo-Jun Zhou (Eds)
0 2001 Elsevier Science Ltd. AI1 rights reserved

A STUDY ON THE HORIZONTALLY DYNAMIC BEHAVIOR OF A
VLFS SUPPORTED WITH DOLPHINS

Ha0 Liu
Graduate Student, Osaka Prefecture University, Sakai, Osaka 599-853 1, Japan

Hiroo Okada, Takashi Tsubogo and Koji Masaoka
School of Engineering, Osaka Prefecture University, Sakai, Osaka 599-853 1, Japan

ABSTRACT

This paper deals with the horizontally elastic behavior of a very large floating structure (VLFS)
supported with dolphins under dynamic loads. Eigen frequencies for vertical vibration of VLFS exist
continuously in relatively high frequency zone due to the buoyancy effect. On the other hand, the
lowest eigen frequency for horizontal vibration may appear in the lower frequency zone than the
heave-mode frequency, because of no effect of buoyancy on the horizontal deflection behavior.
Therefore, it is important to investigate the horizontally elastic behavior of VLFS under dynamic loads.
At first, basic studies on the eigen frequency characteristics of a VLFS under trial design are carried
out. The eigen frequency characteristics of a VLFS are investigated by using the combined model
considering the shearing rigidity of the main structure and mooring effects. Effects of mooring
characteristics and structural parameters on dynamic response are also discussed based on results
obtained by using analytical solutions and finite element analyses. Next, a nonlinear finite element
analysis system is developed to simulate the behaviors of the VLFS under dynamic loads. Finally, by
using this analysis system, the response behavior of the VLFS supported with 25 dolphins, which is
modeled as a horizontal elastic plate, supported with springs and dashpots through gap elements were
investigated.

KEY WORDS

Horizontally elastic response. VLFS, Effect of mooring rigidity, Effect of shear rigidity

1 INTRODUCTION

In this paper, the eigen frequency characteristics of a VLFS under trial design are investigated using
the combined model considering the shearing rigidity of the main structure and mooring effects.
Effects of mooring characteristics and structural parameters on dynamic response are also discussed
based on results obtained by using analytical solutions and finite element method analyses firstly. Next.
a three dimensional, nonlinear finite element analysis is used to predict the dynamic response of a