Petri Varsta

Design of marine structures with improved safety for environment

The paper describes a method for design of marine structures with increased safety for environment, considering also the required investment costs as well as the aspects of risk distribution onto the maritime stakeholders. Practically, the paper seeks to answer what is the optimal amount that should be invested into certain safety measure for any given vessel. Due to the uneven distribution of risk, as well as the differing impact of costs emerging from safety improvements, stakeholders experience conflicting ranking of alternatives. To solve this multi-stakeholder decision-making problem, in which each stakeholder is a decision-maker, the method applies concepts of group decision-making theory, namely the Game Theory. The method fosters axiomatic definition of the optimum solution, arguing that the solution, or the final selected design, should satisfy the non-dominance, efficiency, and fairness. These three are thoroughly discussed in terms of structural design, especially the latter. Considering the coupling of environmental risk and structural design, the method also builds on the preference structure of four maritime stakeholders: yards, owners, oil receivers and the public, who either share the risks or directly influence structural design. Method is presented on a practical study of structural design of a tanker with a crashworthy side structure that is capable of reducing the risk of collision. The outcome of this study outlines a number of possibilities for successful improvement of tanker safety that can benefit, concurrently, all maritime stakeholders.

Multi-stakeholder decision-making in the risk-based design of a RO-PAX double bottom for grounding

Grounding accidents can be fatal for ships. This paper discusses decision-making in risk-based design to avoid such outcomes for a 30 000 GT RO-PAX in a powered hard grounding. Five alternatives of a double-bottom structure are suggested to reduce the risks of loss of life, environmental damage, and material damage. Risk assessment concentrates on the consequences, applying numerical grounding simulations to model the energy absorption of the proposed alternatives. To determine the risks, 1295 Monte Carlo simulations are performed running a quasi-static model of ship motions. Accounting for these risks and the added production costs and operational loss, a new multi-stakeholder approach for selecting alternatives is proposed assuring simultaneous maximal satisfaction to both the shipyard and the ship owner. As an outcome, two alternatives are selected, the first increasing the bottom shell thickness by 50 per cent, and the second increasing the stiffness of longitudinal stiffeners by 90 per cent. If observing their performance, it is possible to recommend the latter as the most effective solution. Such an outcome is in accordance with the established practical opinions in increasing safety for grounding, proving sagacity of the presented approach.