Page 76 - Practical Design Ships and Floating Structures

Practical Design of Ships and Other Floating Structures 51
You-Sheng Wu, Wei-Cheng Cui and Guo-Jun Zhou (Eds)
0 2001 Elsevier Science Ltd. AI1 rights reserved

A MODULE-ORIENTED OPTIMIZATION TOOL

Philippe Rigo

Deparment of Naval Architecture (ANAST) and NFSR’, University of Liege.
Chemin des Chevreuils n”1, B52/3, B-4000 Liege, Belgium
(*) National Fund for Scientific Research

ABSTRACT

The development of the LBR-5 “Stiffened Panels Software” is included in the development of a new
design methodology to ease and to improve preliminary studies of naval structures and floating
hydraulic structures. The ultimate target is to link standard design tools (steel structure CAD, hull form,
hydrostatic curves, floating stability, weight estimation, etc.) with a rational optimization design
module and a minimum construction cost objective function. This paper focuses on the “Module-
Oriented Optimization’’ methodology and on the rational constraints. LBRJ allows, as of the first draft,
an optimization of the scantling of the structure’s constituent elements. Relevant limit states of the
structure are taken into account thanks to a 3D rational analysis of the structure. The optimization
module is composed of 3 basic modules (OPTI, CONSTRAINT and COST).

KEYWORDS
Optimization, Preliminary design, Stiffened structure, Construction cost, Design methodology.
Rational constraints, Structural constraints, Limit states.

1 INTRODUCTION
Floating structures are complex structures, generally composed of strongly stiffened plates, deck plates.
bottom plates. and sometimes intermediate decks, fiames, bulkheads, etc. Optimization of these
complex structures is the purpose of this paper.
Structural design is always defined during the earliest phases of a project. It is thus not difficult to
understand why a preliminary design stage optimization tool is attractive. This is precisely the way the
LBR-5 optimization software for stiffened structures was conceptualised (Rigo 2001 .a). “LBR-5“ is
the French acronym of “Stiffened Panels Software”. Our target is to link standard design tools (steel
structure CAD, hull form, hydrostatic curves, floating stability, weight estimation, etc.) with a rational
optimization design module and a minimum construction cost/weight objective function. LBRJ is this
rational optimization module for structures composed of stiffened plates and stiffened cylindrical
shells. It is an integrated model to analyze and optimize naval and hydraulic structures at their earliest
stages: tendering and preliminary design. Initial scantling is not mandatory. Designers can start