On the scattering of focused wave by a finite surface-piercing circular cylinder: A numerical investigation

Abstract

For nonlinear wave–structure interactions, the high-frequency scattered waves can be identified within the drag-inertia regime, especially in steep incident waves where viscous effects are not negligible. According to previous studies, this unexpected phenomenon is highly associated with the local flow field, posing challenges to the existing harmonic-based diffraction solutions (mostly up to second-order). To overcome these shortcomings in potential flows, we establish a high-fidelity numerical wave tank to solve this two-phase free surface flow in the open source computational fluid dynamics framework OpenFOAM. We implement the ghost fluid method to eliminate the spurious velocities, mostly reported in two-phase volume of fluid solvers, in the vicinity of the free surface and preserve a sharp air–water interface. A modified generating–absorbing boundary condition is employed to achieve high computational efficiency without passive relaxation zones. Good agreement with experimental data demonstrates the reliability and accuracy of the present numerical wave tank in extreme wave conditions. On this basis, this paper numerically investigates the wave scattering of the focused wave by a finite surface-piercing circular cylinder, with emphasis on the flow mechanism. Three types of high-frequency scattered waves are identified in the near field, namely, Type-1, Type-2, and Type-1* waves. The typical mechanisms of each type are analyzed in depth with detailed flow field data, which confirms and complements the observations from previous experiments. More importantly, the primary vortical structures involved in scattering are extracted by the Liutex vortex identification method. The behaviors of these vortical structures could characterize the evolution of the high-frequency scattered waves and provide new insights into this strongly nonlinear phenomenon. An overall schematic of the wave scattering evolution in this complex condition is summarized for a straightforward understanding.