engleski

Numerical Hydrodynamic Optimization of a Tanker Hull Form

The knowing of the flow around the ship and her resistance components is very important in the hull form de-velopment, as the design of a low resistance ship remains a permanent problem in ship hydrodynamics. At pre-sent the computational tools based on numerical methods can be efficiently used in ship hull form develop-ment, particularly at the early design stages. Numerical optimization is a well-established mathematical field and there are numerous references to the theory and application of numerical optimization tools. These tools require the setting of one or multiple objec- tive functions, which is then minimized. For a various set of constraints imposed on each individual case, it is possible to find the ship hull form which will provide the minimum of the chosen objective function. Tankers are typical ships that sail at two very different conditions: laden and ballast. In the ballast condi-tion there is a major change in the hull form shape and ratios (for example beam-to-draft ratio) from that ap-plying in the laden condition. This results in a substantial change of the hydrodynamic characteristics which strongly affect the ship resistance. It is often given too little consideration to this fact although tankers spend from 40% to 50% of their time sailing in the ballast condition. In the paper, the fact that a tanker spends a large percentage of the time sailing in the ballast condition has been taken as relevant factor. A hydrodynamic optimization problem for a ship bow shape in calm water con-sidering both laden and ballast condition has been treated. A numerical optimization procedure is based on a linear potential flow method as flow solver, and on a genetic algorithm as optimization tool. An automatic mesh generator based on the spline in tension makes an integral part of the procedure. The ship total resistance has been considered as an objective function. The results of the optimization procedure have been presented and compared to the initial hull form in order to demonstrate the effectiveness of the developed procedure.

Numerical optimization

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