Vedran Žanić

Design synthesis of complex ship structures

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 todays 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.

Methods and concepts for the multi-criteria synthesis of ship structures

The 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.

Ship structural design support methodology for the reliability based design optimization (RBDO)

The objective of the paper is to present the structural design support system (DeSS) rationale for the reliability based design optimization (RBDO) in the concept design phase. Basic steps are as follows:• Interactive identification of the design problem (design variables, constraints, objectives) as well as design problem variates and their distribution parameters. Safety related design criteria are used as objectives and as constraints in the presented procedure;• Calculation of the cross section ultimate longitudinal strength criteria based on the extended Smith’s method; based on the Report SSC-398;• Selection of non-dominated designs (Pareto-optimal, NDD points) for the given deterministic design criteria;• Calculation of reliability/deterministic safety measures. Novel FASTREL code, based on the Dimension Reduction Method (DRM) is used for the reliability calculations;• Generation of insight into the Multi Attribute Decision Making (MADM) process with 5D graphic presentation of designs in design and attribute spaces in the interactive OCTOPUS Designer (Demak/DeView) IT modules.Practical application of the developed concept design methodology and of the design environment to the structural design of the verifiable test example corresponding to SSC-398 report. DeSS was used in fast generation of optimal designs using MODM (MOSLP) and MADM (MOPSO) techniques. To speed up the RBDO design process deterministic and probabilistic formulations of design problem were run concurrently and supporting each other are presented using the safety related design attributes (deterministic and reliability based) for the NDD supported decision-making technique.Copyright

Reliability and Robustness Based Design Attributes for Multi-Criteria Decision Making

Novel design methodology with inclusion of reliability and robustness-based design criteria is presented. Robustness is defined as the insensitivity of a design attribute to uncontrollable design parameters. The developed design procedure for the concept design phase is divided into two basic, coordinated tasks: (1) multi-criteria topology/geometry optimization of the ship structural model; (2) scantlings / material multi-criteria optimization of structural panels.Reliability criteria and robustness of design attributes are applied as relative measures of quality, besides standard design attributes such as costs and weight. They are used in generation of Pareto-optimal design variants. Reliability attributes used for the panel design are compared with respect to fidelity and computational efficiency. A novel method for fast reliability calculations is presented using dimension reduction method (DRM) as implemented into FASTREL software. The method is verified with respect to accuracy and speed on the box girder design and panel design with CalREL methods (MC, FORM).The design procedure steps are executed in the predefined sequence of design sub-problems, using the fast and balanced collection of analysis and synthesis modules/methods of the MAESTRO/OCTOPUS design system. They are as follows: • Probabilistic determination of design loads; • Calculation of the structural serviceability and ultimate strength criteria on the panel (macro-element) level; • Calculation of the cross section ultimate longitudinal strength criterion; • Calculation of reliability and robustness measures on the panel level (safety) and on the global level. Other design attributes (initial cost, structural weight, etc.) are also determined; • Generation of the Pareto frontier for the selected test structure based upon the cost–safety design paradigm; • Generation of insight into the multilevel optimization process with graphic presentation of designs in design and attribute spaces.Practical application of the developed concept design methodology and of the design environment to the structural design of modern multi-deck ship elements (panels) is presented for verification/validation of accuracy and speed of FASTREL module.Copyright