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Multicriterial design methodology with safety as one of the design objectives is presented. The aim of the paper is to analyze the influence of safety based design objectives on generated nondominated designs on the Pareto frontier. Possible improvements in nondominated designs are investigated by comparison to ones obtained with the standard design procedure when safety criteria are used as design constraints only. It is assumed that safety based objectives and targets act as attractors, driving nondominated designs along the constant cost/weight contours in design space towards its safer regions. Global safety objectives (for hogging/sagging modes), are based on the maximization of ultimate longitudinal strength in vertical bending calculated via the extended IACS incremental-iterative method. Applied compound safety measures for gross-panel (stiffened panel with associated girders) are based upon 34 failure modes, belonging to serviceability/collapse subsets. Objectives based on the maximization of safety measures are applied together with standard design objectives such as minimization of initial cost and weight. The following problems were solved with different sets of objectives: (a) minimize cost and weight objectives subject to safety constraints (used for reference), (b) only the maximization of local safety measures is added to (a) as additional objectives, (c) only the maximization of global safety measures is added to (a) as additional objectives, (d) maximization of safety measures ad (b) and (c) are added to (a) as additional objectives. For each of the problems (a–d) the developed design procedure is executed. It contains two basic tasks for structural design of realistic (non-academic) problems: (1) multicriterial optimization with topology / geometry design variables; (2) multicriterial optimization of gross-panels with scantling / material design variables. Design procedure steps are executed using a fast and balanced collection of analysis and synthesis modules/methods of the OCTOPUS design system: • Determination of design load sets; • MOGA / MOPSO based generation of nondominated designs for the selected ship structure; • For each design the following analysis blocks are executed: – calculation of ship’s primary and racking response fields, – calculation of ship’s ultimate longitudinal strength, – calculation of serviceability and collapse safety criteria on the gross-panel level. Comparisons of results, based on generated Pareto hyper-surfaces and on subset of preferred designs, are given for problems (a–d). Insights into the results of optimization process, using 5-D graphics for design and attribute spaces, are also presented. Design problems of modern RoPax and SWATH structures are used in case studies.

The paper presents the principal steps in the definition of a practical design model for multi-criteria synthesis of complex thin-walled ship structures in concept and preliminary design. It elaborates the general requirements on the design procedure, balanced and applicable combinations of design models and a practical example of the basic analysis models/IT modules within the MAESTRO/OCTOPUS design support system. System identification from the multi-stakeholder perspectives of owner and society, and the formulation and solution to the dimensionally large-scale structural designs are presented as a step towards the practical implementation of multi-criteria decision-making in ship design practice since only a joint effort could lead to the satisfaction of all stakeholders in today's challenging ship-building industry. The practical structural design procedure/methodology, capable of embedding multiple design quality criteria, is demonstrated using a benchmark case study on the innovative RoPax ship.

EDITORIAL Methods and concepts for the multi-criteria synthesis of ship structuresThe basic concepts and methods for multi-criteria synthesis of complex thin-walled ship structures in concept and preliminary design are presented. The principal steps in the definition of the design model, the selected general requirements on the design procedure and balanced and applicable combinations of design models are elaborated. The paper also provides an introduction to the basic theory, mappings, non-dominance concepts (Pareto frontier), spaces and sets used for the mathematical definition of design problems (DPs) together with the unified taxonomy applicable in the handling of complex DPs. System identification from the multi-stakeholder perspectives of owner and society and the formulations and solutions of structural DP are discussed.Keywords: design support system (DeSS); Pareto-supported decision making (PSD); thin-walled ship structures; structural design procedure; structural optimisation; Pareto optimality; design synthesis This introductory paper is devoted to my colleague and friend Professor Owen F. Hughes with whom I have had the privilege of sharing the burden and enjoyment of generating methods for the design of efficient and safe ship structures. ForewordIt has been claimed that this century in engineering will be the century of synthesis, after the twentieth century generated fast and reliable analysis methods capable of dealing with complex structural problems. Synthesis introduces the additional level of complexity, encapsulating the analysis models (AMs). For the synthesis problems, there is no universal technique (like finite element method (FEM) in structural analysis) to solve the non-linear, fuzzy, multi-criteria DP of high dimensionality leading to the multiplicity of different solutions/methods.Most of the papers in this SAOS Special Issue come from the structural analysis area. It is an objective of this introductory paper to systematise some of the basic concepts and methods of synthesis, applicable to the realistic ship structural DPs.Available design methods and optimisation techniques also confirm that analysis methods, as presented in this issue, as well as many methods from other authors can be included into the modern design environments and prove that the 'added level of complexity' is within our reach. For these reasons, this editorial is also an attempt to introduce a novel design-oriented point of view to the interested reader, because we all have as an ultimate objective of our respective work a contribution to the design of efficient and safe structures. This special issue is concluded by the autobiographical essay written by Professor Owen Hughes showing the evolution of concepts and methods from his lifetime experience, supported and augmented by recollections from some of his colleagues and friends. In the field of Naval Architecture, it was Owen Hughes who recognised that the utmost simplicity of methods and clarity of ideas are needed in order to apply the 'first principles anal...

This paper presents a design environment capable of embedding multiple quality criteria for structural design and to provide the decision support problem (DSP) rationale for the concept design phase. The general mathematical model contains the analysis and the synthesis modules. The analysis module can be decomposed into six meta-systems of which two basic systems provide physical and environmental definitions of the problem/process and the other four are behavioural systems for modelling of response, adequacy, reliability, and quality. Synthesis modules enable the interactive design problem definition, usage of multiple optimization solvers (Monte Carlo-and fractional factorial experiment-based evolution strategies (ES-MC and ES-FFE), sequential linear programming (SLP), multiobjective genetic algorithms (MOGA), and multiobjective particle swarm optimization (MOPSO)) and fivedimensional graphic views of the Pareto frontier in design and attribute spaces. The methodology combines the fast concept exploration of design variants using generic finite element modelling (FEM) models and a two-step decision support procedure (based on topology and scantling optimization) in the concept design phase. The benefits of using the presented approach are demonstrated on the complex problem of multideck ships with hullsuperstructures interaction. The first example shows the good accuracy of the primary response analysis of the cruise ship generic three-dimensional FEM model. The second example briefly presents the complete structural optimization of the International Ship and Offshore Structures Congress (ISSC'06) passenger ship benchmark.