Page 200 - Practical Design Ships and Floating Structures

Practical Design of Ships and Other Floating Structures I75
You-Sheng Wu, Wei-Cheng Cui and Guo-Jun Zhou (Eds)
Q 2001 Elsevicr Scicnce Ltd. All rights reserved

EXTREME RESPONSE AND FATIGUE
DAMAGE OF SHIP-SHAPED FPSO

Chun-Tian Zhao, Yong Bai and Yung Shin

American Bureau of Shipping,
16855 Northchase Drive, Houston, TX 77060

ABSTRACT

In the design of ship-shaped Floating Production Storage Offloading (FPSO) systems, a rational
strength assessment is required to ensure structural safety. This paper presents a systematic method to
predict extreme response and conduct fatigue assessment, in which the site-specific wave conditions
and the service history are accounted for. The extreme response is predicted using both short-term and
long-term approaches, and the fatigue strength is assessed using a closed-form spectral fatigue method.
The proposed approach may be applied to newly built or converted FPSOs.

KEY WORDS
FPSO, FPI, Extreme Response, Strength, Fatigue

1 INTRODUCTION

A FPSO is usually designed for a specific installation site. The site-specific wave environment has to
be taken into account for each design. In addition, if the FPSO is a conversion from an oil tanker, the
evaluation of past fatigue damage is required. This paper aims at developing a reliable and systematic
method with consideration for the long-term wave conditions involved with assessing extreme
structural response and fatigue damages.
To predict the extreme load or extreme structural response, various methods have been proposed (Ochi,
1981). In this paper, approaches based on both long-term and short-term (survival storm) wave data are
recommended, depending on the conditions of application.

In the fatigue-damage, a simplified method is sometimes used, in which a Weibull distribution for the
long-term responses is usually assumed, and Weibull parameters are determined in advance. Due to the
excessive sensitivity of estimated fatigue damage to the Weibull parameters, this kind of method is