Page 254 - Practical Design Ships and Floating Structures

Practical Design of Ships and Other Floating Structures 229
You-Sheng Wu, Wei-Cheng Cui and Guo-Jun Zhou (Eds)
8 2001 Elsevier Science Ltd. All rights reservcd

A STUDY ON DECK WETNESS AND SLAMMING OF WRY
LARGE FLOATING STRUCTURES

Hyunkyoung Shin', Ho-Young Lee', Choon-Gyu Lim,' Jeom-Moon Kang', Oi-Hyun Kim2 and
Myung-Cheol Yoon*

' School of Trans rtation Systems Engineering, University of Ulsan, Ulsan, Korea
Qyundai Heavy Industry Co. Ltd., Ulsan, Korea

ABSTRACT
The length and breadth of a very large floating structure(VLFS) are determined by airplane types and
airport facilities in the initial design stage. However, its depth is dependent on hydroelastic behaviors
such as vertical responses as well as buoyancy. Generally speaking, VLFS of the pontoon type has
rather small vertical motions except in both ends, where motions are much larger due to elasticity. In
this paper, numerical predictions of deck wetness and slamming of VLFS with dimensions
LxBxD=l,200mx240mx4.5m in waves are made. The source-dipole distribution method and the finite
element method are employed for the hydroelastic behaviors in the frequency domain and the time
domain.

KEYWORDS
Very large floating structure, VLFS, Time domain, Frequency domain, Memory effect function,
Newmark p method, Hydroelastic responses, Irregular waves, Deck wetness, Slamming

1 INTRODUCTION
The typical configuration of the very large floating structure(VLFS) of the pontoon type is
characterized by large horizontal dimensions compared with the incident wave. VLFS has small
hydroelastic responses in the whole structure due to relatively small wave length, while the responses
at both ends are large due to the elastic characteristics. Therefore, the deck wetness and slamming
phenomena for VLFS must be checked in the initial design stage. A few researches on hydrodelastic
behaviors of VLFS in irregular waves have ben made in the time domain(Ohmatsu(l998), Endo( 1999).
Lee and Shin(2000)).
In this paper, the source and dipole distribution method is employed for predicting hydrodynamic
forces due to radiation and diffraction potentials, which is represented by Green function in finite
depth. The added mass, wave damping coefficients and wave exciting forces calculated in the
frequency domain are used to solve the equation of motion in the time domain. Newmark p method is
applied for time integration considering memory effect function due to wave damping effects.
Numerical prediction of the deck wetness and slamming are mde as a guideline to determine the depth