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The work deals with the actual necessity of creating optimal ship designs under uncertainty, also referred as Robust Design Optimization (RDO). The consideration of uncertainties in the optimization process is the future trend of ship design as a more realistic scenario is taken into account leading to the development of more efficient vessels and thus more environmental friendly. 
Several optimization methods were tested for a hull form improvement concerning the total resistance of the vessel at forward speed in calm water condition. The operational profile has been taken into account as a single-objective problem in which several operating conditions are suitably weighted, as a single-objective problem in which one operating point is dominant while others are considered as constraints and as a multi-objective optimization task in which the best design is selected from the Pareto-set. Furthermore, a hybrid method via Gauss-Markov estimation was also tested. The robustness was considered via sensitivity check on slight variation of uncertain operational characteristics. All the processes are compared among them and, in addition, with a single objective optimization process for one specific operational condition. Each approach merits and drawbacks are pointed out in an investigation of which approach is particularly suited for hull form development. The criteria to judge pros and cons are quality of the achieved results (e.g. energy efficiency), computational effort (e.g. number of Computer Fluid Dynamics (CFD) runs needed) and sensitivity to changes (e.g. influence of slight changes on the operational conditions). The study case is an existing vessel that had a change in the operation leading to higher fuel consumption. In addition, the optimization is focus on changes of the forebody form of the vessel (e.g. bulbous bow). 
Finally, the analysis is suitable to assist ship designers regarding the necessity of performing a robust optimization or a typical optimization process plus sensitivity analysis and thus create in short time optimal ship designs even under uncertainties.

Ingénierie, informatique & technologie > Ingénierie civile

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Optimization generally involve picking the optimum solution to a problem considering all the factors or design variables. HOLISHIP (HOLIstic optimisation of SHIP design and operation for life-cycle) is a European Union research project which is a system based approach aimed at developing optimized designs for the future, structure of which is divided into clusters and into several work packages (WP). Structural optimization of RoRo & RoPax vessels pose several challenges due to the unique design features of these type of vessels. This Thesis work concentrates on structural optimization of midship section transverse frame of RoRo & RoPax hulls for minimum weight thus achieving reduction of lightship weight which is one of the major technical requirements during conceptual design phase as part of WP4&WP7 of HOLISHIP project. Rule based tool called ‘STEEL’ by Bureau Veritas is used for the structural & load modeling and further structural analysis of the transverse frame and then optimization loop is established using ‘modeFRONTIER’ and ‘CAESES’ tools to study effect of different design variables. Also the structural optimization loop involving STEEL tool is to couple with a parametric hull in order to enable study of coupled structural analysis for different parametric hull variations. Structural weight is kept as the objective to minimize and design constraints are considered as per applicable Bureau Veritas rules for classification of steel ships. Then surrogate models are generated to replace the optimization loop using Response surface methodology and results obtained with different algorithms like polynomial regression, artificial neural networks etc. are studied further which would reduce complexity associated compared to conventional direct methods

HOLISHIP,Structural optimisation, Rule based analysis,RoRo, RoPax, Response Surface Methodology,Artificial neural Networks, Parametric Hull --- Ingénierie, informatique & technologie > Ingénierie civile

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Optimization is a human trait. Mathematically speaking, it is minimizing (or maximizing) one
or several objectives within a set of constraints. Hull form optimization from a hydrodynamic
performance point of view in calm water and in moderate sea states is an important aspect in
preliminary ship design. The challenge of this work is getting a ship with lowest energy
consumption in calm water and in different sea states by various optimization approaches.
Several optimization approaches were used for a hull form improvement to maximize
seakeeping performance (accelerations based criteria) and minimize the ship resistance at its
given displacement and its service speeds. Different sea-states of operating routes and
different speeds were taken into account for the analysis of seakeeping performance of a
vessel.
An academic container vessel (Duisburg Test Case developed and tested by the University of
Duisburg-Essen) was taken for the study case. The parametric model of the vessel is
developed by modifying the initial geometry with the use of CAESES 4.0. After getting a
parametric model, it was simulated by GL Rankine, potential flow code developed by DNV
GL and validated with experimental results from HSVA. After coupling GL Rankine solver
with CAESES, different optimization approaches were done by using CAESES/Dakota
interface. The optimization was focused on the changes of the forward part of the vessel
(Bulbous bow).
While performing optimization process, not only the main objectives to minimize the energy
consumption of the vessel, also computational effort (how many number of CFD runs needed)
and influence of slightly changes on the operational conditions were taken into account as
major criteria.
As the first approach, the optimal hull form was obtained in calm water condition by different
optimization algorithms and was checked wave added resistance and seakeeping behavior in
moderate sea states. In second approach, optimization process was done by considering calm
water condition and also seakeeping performance in different operation profiles. Finally, the
results of the optimal hull form were compared with original design.

Ingénierie, informatique & technologie > Ingénierie civile