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.