Page 68 - Practical Design Ships and Floating Structures

Practical Design of Ships and Other Floating Structures 43
You-Sheng Wu, Wei-Cheng Cui and Guo-Jun Zhou (Eds)
0 2001 Elsevier Science Ltd. All rights reserved

OPTIMIZATION OF A WAVE CANCELLATION
MULTIHULL SHIP USING CFD TOOLS

C. Yang, R. Lohner and 0. Soto
School of Computational Sciences, George Mason University
Fairfax VA 22030-4444, USA

ABSTRACT

A simple CFD tool, coupled to a discrete surface representation and a gradient-based optimization
procedure, is applied to the design of optimal hull forms and optimal arrangement of hulls for a wave
cancellation multihull ship. The CFD tool, which is used to estimate the wave drag, is based on the
zeroth-order slender ship approximation. The hull surface is represented by a triangulation, and almost
every grid point on the surface can be used as a design variable. A smooth surface is obtained via a
simplified pseudo-shell problem. The optimal design process consists of two steps. The optimal center
and outer hull forms are determined independently in the fust step, where each hull keeps the same
displacement as the original design while the wave drag is minimized. The optimal outer-hull
arrangement is determined in the second step for the optimal center and outer hull forms obtained in
the first step. Results indicate that the new design can achieve a large wave drag reduction in
comparison to the original design configuration.

KEYWORDS

Hull form design, Hull form optimization, Wave cancellation multihull ship, Trimaran, Wave
resistance, CFD tools, Slender ship approximation, Surface parameterization.

1 INTRODUCTION
A small-water-plane area, tri-hull ship, termed the wave cancellation multihull ship (or trimaran),
offers the possibility of dramatic wave drag reduction due to wave cancellation. Experimental evidence,
e.g. by Wilson et. al. (1993) indicates that indeed these gains are achievable. From a design point of
view, an important question that requires attention is how to deal with these types of multihull ships
inside a general design framework. For example: should one optimize hull position ,and shape at the
same time, or first obtain an optimal placement of hulls, followed by an optimal hull shape? The
answer is not obvious.
As a first attempt to solve such a general design problem, a two-step design process is employed in the
present paper. The optimal center and outer hull forms are determined independently in the first step,
where each hull keeps the same displacement as the original design while the wave drag is minimized.