Design method for safe ship structures

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto. fi Author Alan Klanac Name of the doctoral dissertation Design method for safe ship structures Publisher School of Engineering Unit Department of Applied Mechanics Series Aalto University publication series DOCTORAL DISSERTATIONS 7/2011 Field of research Naval Architecture Manuscript submitted 18.08. 2010. Manuscript revised 01.12. 2010. Date of the defence 11.02. 2011. Language English Monograph Article dissertation (summary + original articles) Abstract At present ships are designed to satisfy the minimum requirements for safety. And history shows that this practice does not suffice, and nor is it sustainable. A new paradigm is needed. This thesis aims to contribute in that respect by proposing a design method that should move ship safety beyond the minimum requirements as much as possible and as long as it is economically sound. The thesis focuses mostly on environmental safety in the event of accidents such as collisions and grounding. A special feature is the consideration of maritime stakeholder preferences regarding safety and profitability. This is an underlying element in all the analysis performed and conclusions reached. This design method features new approaches in multi-objective optimization of ship structures and in advanced decision making for design selection. The multi-objective optimization is based on evolutionary algorithms, more precisely the genetic algorithm (GA) with advanced treatment of design constraints and objectives. Through the approach of vectorization, the GA becomes not only more efficient, but also more flexible in use, bearing in mind the complexity and demands of accident analysis for optimization. The decision making is established on the concepts of Game Theory, resulting in a new criterion for design selection, the Competitive Optimum, based on the maximal concurrent satisfaction of stakeholder preferences. The proposed design method is intended in particular for ship structural design projects, permitting the definition of hull structural scantlings, or even hull topology if desired. The approaches to multi-objective optimization and design selection that are introduced possess a wider basis of application, and are extensible to other fields in maritime safety and naval architecture. The results of the thesis provide several relevant conclusions with an impact on practical naval architecture. For example, i) by increasing ship crashworthiness, significant risk reduction can be attained, ii) raising safety is economically justified if the benefits to the public are considered alongside those of the industry, and iii) the crashworthiness of ships can be controlled effectively with conventional double-bottom and double-sided structures.At present ships are designed to satisfy the minimum requirements for safety. And history shows that this practice does not suffice, and nor is it sustainable. A new paradigm is needed. This thesis aims to contribute in that respect by proposing a design method that should move ship safety beyond the minimum requirements as much as possible and as long as it is economically sound. The thesis focuses mostly on environmental safety in the event of accidents such as collisions and grounding. A special feature is the consideration of maritime stakeholder preferences regarding safety and profitability. This is an underlying element in all the analysis performed and conclusions reached. This design method features new approaches in multi-objective optimization of ship structures and in advanced decision making for design selection. The multi-objective optimization is based on evolutionary algorithms, more precisely the genetic algorithm (GA) with advanced treatment of design constraints and objectives. Through the approach of vectorization, the GA becomes not only more efficient, but also more flexible in use, bearing in mind the complexity and demands of accident analysis for optimization. The decision making is established on the concepts of Game Theory, resulting in a new criterion for design selection, the Competitive Optimum, based on the maximal concurrent satisfaction of stakeholder preferences. The proposed design method is intended in particular for ship structural design projects, permitting the definition of hull structural scantlings, or even hull topology if desired. The approaches to multi-objective optimization and design selection that are introduced possess a wider basis of application, and are extensible to other fields in maritime safety and naval architecture. The results of the thesis provide several relevant conclusions with an impact on practical naval architecture. For example, i) by increasing ship crashworthiness, significant risk reduction can be attained, ii) raising safety is economically justified if the benefits to the public are considered alongside those of the industry, and iii) the crashworthiness of ships can be controlled effectively with conventional double-bottom and double-sided structures.