Permanent Means of Access Structural Design Using Multi-Objective Optimization

Permanent means of access (PMA) of oil tankers and bulk carries consists of a wide platform for walk through inspection. Since PMA structures have a tall web plate, they are vulnerable to elastic tripping. A previous paper ^[1] proposed a Rayleigh-Ritz method to analyze elastic tripping behavior of PMA structures. The method is parametric formulated, mesh free, computational efficient, and is able to predict both the flange plate critical tripping stress as well as the web plate local buckling stress; therefore the solution process is suitable for design space exploration. In this paper, multi-objective optimization methods are used to determine the Pareto solutions of a PMA structure based on the proposed tripping algorithm. The objective is to solve a design problem aimed at simultaneously minimizing the weight of a PMA structure and maximizing its critical buckling stress. Three multi-objective methods, Pareto Simulated Annealing (PSA), Ulungu Multi-objective Simulated Annealing (UMOSA) and Multi-objective Genetic Algorithm (MOGA) are presented for a case study. The numerical results show that all three methods can efficiently and effectively solve such optimization problems within a short search time. The critical buckling stress of the final optimal designs is validated by the linear and non-linear buckling analysis of NX-NASTRAN ^[2].