The results of a formal optimization of the internal compartmentation of a typical Ro-Ro passenger ships are presented. The parametric ship model was created using the ship design software NAPA under the following assumptions: (i) The vessel's hull form and drafts are kept constant during the optimization. (ii) The vertical position of the bulkhead deck is a design variable. (iii) The calculation of the structural weight and of the corresponding center of gravity position is based on user-supplied specific weight relations. (iv) Given the hull dimensions and the initial layout of the ship, two lower holds may be generated forward and aft of the Main Engine Room (MER), but only the former can carry vehicles. (v) Both central and side casing main deck configurations are available to the user. The parametric design in both cases generates the appropriate aft casings on each side of the main deck. (vi) The measure for the vessel's transport capacity is the total vehicle's lanes length. It is calculated separately for the main deck and the lower holds. The user defines the typical size of the vehicles carried. A user-supplied equivalence coefficient is used to account for carrying different kinds of vehicles on the main deck and in the lower hold. (vii) Down-flooding openings at constant height provided by the user may be defined to limit the range of positive stability after damage. The optimization environment modeFRONTIER, which uses a multi-objective genetic algorithm (MOGA), has been integrated with NAPA. The objectives were the maximization of the attained subdivision index A (according to SOLAS B-1 Reg. 25), the maximization of the total lanes lengths, and the minimization of the structural weight. Three case studies (comparison of the central and side casing layouts, Comparison of different probabilistic damage stability models, investigation of the impact of the initial population size, and a combination of MOGA with techniques to capture the user's preference) have been carried out. Conclusions from the case studies are: (i) The optimization procedure can be used both at the conceptual design stage and at later design stages. (ii) Improvements in the economic efficiency of the ship, expressed by larger length of the lanes, are achievable with minor changes to the weight of the ship. (iii) The side casings concept considerably increased transport capacity (lanes length) and the attained subdivision index. However, the associated necessary increase in steel weight was not considered in the model. (iv) The selected damage stability model had secondary effect on the ranking of the designs. (v) The size of the initial population is a significant parameter in the optimization procedure, closely linked to the computational cost. Small initial populations permit more generations for the same total computing time. On the other hand, the limited diversity may prevent sufficient exploration of the whole Pareto frontier. (vi) Combining the exploration capabilities of a genetic algorithm with techniques to capture the user's preference and a final optimization using a SIMPLEX algorithm yields an efficient design optimization tool. (vii) Due to the large number of calculations, required within the NAPA shell in order to define the watertight subdivision and especially for the calculation of the attained index, the required time for each run took more than 3.5 min using a PC with Pentium 4 at 2.4 GHz.


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    Title :

    Optimization of arrangements of Ro-Ro passenger ships with genetic algorithms


    Additional title:

    Optimierung der Raumaufteilung von Ro-Ro-Passagierschiffen mit genetischen Algorithmen



    Published in:

    Publication date :

    2004


    Size :

    7 Seiten, 4 Bilder, 2 Tabellen, 13 Quellen



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English




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