Optimisation of passenger ship structures in concept design stage

Abstract

This paper presents an optimization method for concept design state of passenger ship with focus on utilisation of efficient Finite Element Modelling, evolutionary optimisation algorithm and indirect constraint relaxation. The response is analysed using 3D coarse mesh global finite element (FE) model, where stiffened panels are modelled using equivalent single layer (ESL) elements that follow the first order shear deformation theory. For traditional stiffened panel, the element has three layers, first represents the plate, second the stiffener web and third the stiffener flange. The web frames and girders are modelled with offset beam elements that can model any beam cross-section according to first order beam theory. The simplifications on stiffened panels and beams enable exploration of design space without changing the FE-mesh. As the focus is on conceptual design, the strength is defined based on the analytical formulations from classification society rules. In order to reach lightweight design, local stress peaks are allowed to exceed the rule-based strength limits, i.e. stress constraints are relaxed indirectly. Instead of increasing the allowed stress levels, the amount of material exceeding strength criteria is utilised. This approach results from production requirements where the area of local strengthening is of interest. The influence of this area on the optimization result is investigated and discussed. Optimization is based on Particle Swarm Optimization (PSO) algorithm. The method is applied for a prismatic cruise ship model and objective is to reduce the steel weight. The results show that stress relaxation has significant effect on the obtained total mass.

A multifidelity approach coupling parameter space reduction and nonintrusive POD with application to structural optimization of passenger ship hulls

“… 13 , 14 , 15 , 16 In Reference 17 they compare different surrogate models to improve the design process of complex thin‐walled ship structures, without using any proper orthogonal decomposition (POD)‐based model order reduction. For structural behavior and optimization of passenger ships we cite References 18 and 19 where they used efficient finite element modeling, evolutionary optimization algorithm and indirect constraint relaxation. We used a similar idea for the stability constraints, where local stress peaks are allowed to exceed the rule‐based strength limits.…”

A review on non-classical continuum mechanics with applications in marine engineering

“…A successful design process is a result of the idealizations made in load, response and strength modelling. A numerical design process example is given in Raikunen et al (2019) and Figure 7 where finite elements are coupled with evolutionary optimization algortihm.…”

“…Figure 7. Optimization of a large passenger ship by using beam and shell elements based on classical continuum mechanics (Raikunen et al 2019).…”

A Two-Stage Optimisation of Ship Hull Structure Combining Fractional Factorial Design Technique and NSGA-II Algorithm

“…Through analysing a commercial case study, the study emphasises the importance of combining theoretical models, computer simulations, and experimental approaches for accurate comprehension and decision-making in product development endeavours [8]. Raikunen, J. et al (2019) presented a method to optimise the design of passenger ships during the early concept phase. A 3D finite element model was utilised to evaluate the response, with offset beam elements for the principal stiffeners and equivalent single-layer elements for the stiffened panels.…”