Robust Optimization of Coastal Environmental Impact from Oil Spills, Finding Optimal Position of Barriers.

Abstract

Multidisciplinary Design Optimization (MDO) is achieving more and more agreement in the industry community. For these reasons, many new optimization methodologies have been developed. In particular, the optimization methodologies capable to find stable solutions, is continuously raising importance for the industry. The name of this new optimization method is Robust Design. The need for Robust Design method appears in many contexts. During the preliminary design process, the exact value of some input parameters is not known; consequently the aim is try to look for a solution as less dependent as possible on the unknown input parameters. Another important concern in the optimization problem is to find out a solution that is insensitive to small fluctuations in the operative conditions. In [1] a Multi Objective Robust Design Optimization that looks for solutions which are insensitive to fluctuations of the operative conditions is shown. Starting from the statistical definition of stability, the method finds, at the same time, good solutions for performance and stability. The algorithm used to solve the multi-objective optimisation problem in [1] is MOGA (MultiObjective Genetic Algorithm), that has shown its great efficiency, but has also revealed some limits due to the large number of computation required to obtain a good Pareto front, i.e. the set of not-dominated solutions that represent the best compromise for the two objectives (performance and stability). In [2] a different optimisation approach, based on Game Theory [3, 4], is proposed. The variables and the objectives are divided between two players, and the result is an equilibrium point (Nash equilibrium) that represents the best compromise of the two (contrasting) objectives. Even though the solution may be only a point of the Pareto front obtained by MOGA, that offers more than one solution to the designer’s choice, the Nash approach has the great advantage, particularly important in a Robust Design problem for which the computational cost is heavy, of a higher convergence speed [5, 6]. Oil spills on the open sea and in coastal areas are one of the greatest threats to nature in maritime zones, with damaging effects for tourism, fishing and aquiculture. They are detrimental to the quality and useful properties of water, and can lead to the elimination of trophic chains. In CEANI, software to help spill responders select appropriate response options to minimize coastal environmental impacts when oil spills, has been designed [7]. This software consists on three programs that simulate the oil slick path, weathering and interaction oil slick-coast. In this paper we propose the use of Robust Design Optimization to minimize coastal environmental impact from oil spills and we shown the results obtained from a hypothetical oil spill.