In order to investigate the actual performance of an optimized 2D floating breakwater model which is previously obtained by genetic algorithm (GA), the performance and characteristics in terms of wave reflection of the corresponding 3D model of this shape are computed and analyzed. The hydrodynamic forces, wave-induced body motions, wave elevation on the free surface, and second-order wave drift force are computed at various wavelengths. The accuracy of computed results is confirmed by checking the Haskind-Newman and energy-conservation relations. By extending the longitudinal length of the model in the 3D analysis and comparing the results to corresponding ones in the 2D analysis, 3D effects could be realized and discussed in both cases of fixed and free motions. It is shown that 3D effects on the body motions are not so large in the present case studied but the free-surface wave elevation is spatially three dimensional even near the middle of a longer body.
We have been investigating the performance of floating-type breakwaters based mainly on the 2D analyses. In our previous study (Mahmuddin & Kashiwagi, 2012) on the development of optimal shape of a 2D floating breakwater, a genetic algorithm (GA) was adopted and we could obtain an optimized 2D shape which is efficient in the performance of wave reflection. However, in reality, the floating breakwaters must be finite in longitudinal length and the waves may be incident upon with oblique angle. Thus we should expect some 3D effects (normally reduction) in performance as a floating breakwater. When the body length is long enough like conventional ships, it is known from the results of so-called strip-theory methods that the hydrodynamic forces and resultant wave-induced ship motions computed with 2D analysis are in favorable agreement with 3D results obtained by actual measurements or numerical computations.
