ULTIMATE STRENGTH BASED STIFFENED PANEL DESIGN USING MULTI-OBJECTIVE OPTIMIZATION METHODS AND ITS APPLICATION TO SHIP STRUCTURES

An efficient method of predicting the ultimate strength of stiffened panels under combined loads has been implemented in ALPS/ULSAP. The validity of the method was confirmed by various structural collapse tests and nonlinear FEA. The method is parametric formulated, mesh free, computational efficient, and is able to predict six different failure modes for a stiffened panel; therefore the solution process is suitable for design space exploration. In this paper, multi-objective optimization methods are used to determine the Pareto optimal solutions of a stiffened panel based on the ALPS/ULSAP algorithm. The objective is to solve a design problem aiming at simultaneously minimizing the weight and cost of a stiffened panel, and maximizing its buckling and yielding stress. Two multi-objective methods, Pareto Simulated Annealing (PSA) and Ulungu Multi-Objective Simulated Annealing (UMOSA) are presented for a single panel optimization, where the loads applied to the panel are assumed to be constant. To optimize a system of stiffened panels, e.g., ship structures, where the loads applied to an individual panel are functions of the system structural scantlings, an iterative procedure is presented. The numerical results show that the proposed method is very useful to perform ultimate strength based ship structural optimization with multi-objectives, namely minimization of the structural weight and cost and maximization of structural safety.