Real-coded genetic algorithm optimization in reduction of wave drift forces on an array of truncated cylinders

Abstract

To reduce wave drift forces acting on an array of truncated cylinders, the optimization of geometrical dimensions of the structure using a genetic algorithm is presented in this paper. Wave drift forces are always the major challenge for offshore floating structures facing to waves. Recently, a cloaking phenomenon has attracted the attention of researchers, which can reduce the scattered wave energy of offshore structures even to zero. In a diffraction problem of water waves, the term cloaking means that there are no scattered waves existing outside the structures. The configuration that a truncated inner cylinder surrounded by four truncated cylinders is considered as an effective way to realize this phenomenon. To accurately calculate the hydrodynamic characteristics of the truncated cylinder array, the Wave Interaction Theory combining with a higher-order boundary element method is adopted. Based on the above numerical methods, three parameters including the radius and the draft of the outer cylinders and the distance between the inner cylinder and outer cylinders are optimized to minimize the scattered wave energy and the wave drift force for a certain wavenumber. It is found that the effect of the draft of outer cylinders on the scattered wave energy is insignificant. Therefore, the optimization with two parameters is carried out additionally without consideration of the draft of outer cylinders. Moreover, the relationship between the wave drift force and the wave distribution around the inner cylinder is discussed.