Abstract
The near-trapping phenomenon, which can lead to high wave elevations and large wave drift forces, is investigated by a floating four-column structure. To solve this wave-structure interaction problem, a numerical model is established by combining the wave interaction theory with a higher-order boundary element method. Based on this numerical model, behaviors of scattered waves at near-trapping conditions are studied; and the superposition principle of free-surface waves is introduced to understand this near-trapping phenomenon. To avoid the near-trapping phenomenon and protect the structure, a way for rotating the structure to change the wave-approach angle is adopted, and improvements of the wave elevations around the structure and the wave drift forces acting on each column are found. Moreover, a genetic-algorithm-based optimization method is adopted in order to minimize the total wave drift force acting on the whole structure at various wavenumbers by controlling the draft of floating bodies, the wave-approach angle and the separation distance between adjacent floating bodies. With the final optimized parameters, the wave drift forces both on each column and on the whole structure can be significantly reduced. The optimized arrangement obtained from a certain wavenumber can work not only at this target wavenumber but also at a range of wavenumbers.
Highlights
The floating column-based structures always face complicated wave-structure interaction problems in ocean engineering [1]
Jiang et al [6] investigated the near-trapping phenomenon of four surface-piercing truncated cylinders to explain the relationship between the large wave drift forces on each cylinder and the high local wave elevations
A real-coded Genetic Algorithm (RGA) proposed in Zhang et al [19] is adopted to minimize the wave drift force acting on the four-column structure by optimizing the dimensions of the structure
Summary
The floating column-based structures always face complicated wave-structure interaction problems in ocean engineering [1]. The occurrence mechanism, wave direction effects on the wave drift force and the optimization method for near-trapping phenomenon are studied using four surface-piercing truncated cylinders. To investigate the mechanism of local oscillation of the water free surface at near-trapping frequencies, the behaviors of scattered waves and the superposition principle of waves are studied based on a combination of the wave interaction theory and the higher-order boundary element method. To reduce the wave drift force on the whole structure, the real-coded genetic algorithm developed by Zhang et al [19] is adopted at near-trapping frequency by controlling the dimension of the structure and the angle of wave approach. It is found that the optimized arrangement obtained from a certain wavenumber can work at this target wavenumber and at a range of wavenumbers
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