Page 300 - Practical Design Ships and Floating Structures

Practical Design of Ships and Other Floating Structures 215
You-Sheng Wu, Wei-Cheng Cui and Guo-Jun Zhou (Eds)
0 200 I Glsevier Science Ltd. All rights reserved

RATIONAL DESIGN CRITERIA AND THEIR APPLICATION TO
HULL FORM OPTIMISATION OF FLOATING SYSTEMS
IN RANDOM SEAS

L. Birk and G.F. Clauss
Institute of Land and Sea Transportation
Technical University of Berlin, Germany

ABSTRACT
Efficient design of new floating systems requires more and more numerical tools to develop structures
with excellent motion behaviour in briefer time spans. The paper presents a fully automated numerical
procedure for optimum adjustment of shapes to environmental conditions. Rational design criteria
based on short and long-term wave statistics are introduced and utilized as objective function in the
optimisation process. Nonlinear programming algorithms vary the form parameters of the design and
find a minimum of the objective function within a few iterations. The resulting hull shapes are
characterized by minimized wave loads and motions. Optimization of a semisubmersible illustrates the
efficiency of the proposed procedure.

KEYWORDS

Parametric design. Design criteria, Form optimisation

1 INTRODUCTION

Offshore operation of floating systems must cope with rough and hostile seas. Designs with favourable
motion behaviour yield economic advantages avoiding restrained operation or weather induced
downtime. Therefore, detailed performance analysis and optimization are necessary during initial
design stages, when hull shapes can be adoptcd to sea states of the target location without introducing
unnecessary expense. Currently best seakeeping behavior is obtained by expensive series of model
tests or time consuming interactive design variations. In this paper a fully automated numerical
procedure is described. which achieves an optimum adjustment of the shapes of floating systems to
environmental conditions.

Automated hull design and optimization relies on the availability of a variety of software tools
performing hydrodynamic analysis, assessment of motion behavior, parameter controlled shape
generation and variation as well as nonlinear programming algorithms controlling the optimization
process. Although automated optimization is increasingly perceived as a valuable tool in the design
process. industry does not exercise this option regularly. In the past this may have been justified by