Ning, D.-z.; Li, Q.-x.; Chen, L.-f.; Zhao, M., and Teng, B., 2017. Higher harmonics induced by dual-submerged structures.

Various types of submerged multibody systems are being inserted into and being devised in the real sea. Nonlinear diffraction of regular waves attributable to dual-submerged cylinders and boxes is investigated both experimentally and numerically in this study. The ultimate objective of the study is to provide best practice guidelines for the engineers in the field leading to the better design of the submerged structures with better hydrodynamic performance and higher survival characteristics. A two-dimensional fully nonlinear numerical wave flume based on a time-domain higher order boundary element method is used, and the comparisons between the numerical and experimental results are carried out for cross-checking both the numerical model and physical experiments. The influence of the submergence, gap distance, size, and geometric shape of the two submerged structures on the higher free harmonics is also investigated. It is found that a decrease in the smaller submergence depth of the two submerged structures leads to an increase in the amplitudes of the higher harmonic free waves generated at the lee side of the structures. The amplitude of the higher order free-harmonic waves is found to oscillate with the distance between the two submerged structures periodically, and the oscillating length is about half of the incident wavelength. Furthermore, a phase difference between the two submerged rectangular structures with different widths is observed.