Numerical Investigation On The Interaction Of Focused Waves With Uniform Current And Structures

In the complicated ocean environments, there may exist some exceptionally nonlinear water waves devastating ships and offshore structures. Focused waves, often named as extreme wave, freak wave and rogue wave, are exceptionally large and steep waves which may pose potential threats to human activities in ocean.In order to investigate the interaction of focused waves with uniform current and structures, a2D fully nonlinear numerical wave tank was developed based on the potential theory. The higher-order boundary element method (HOBEM) was used in the proposed model and the mixed Eulerian-Lagrangian approach was adopted to update the instantaneous free surface. The focused wave trains were numerically generated through the superposition of different frequency wave components at a specific time and position by the sine motion of a piston wave-maker in the wave flume.At first, the current effect was realized by introducing the current speed to the fully nonlinear free surface boundary conditions. The developed numerical model was verified by comparing with both the published numerical and experimental results. Then the model was utilized to investigate the influence of uniform currents on the focused waves, including the influence on the wave elevation characteristic and the shifts of focal position and focal time. The effects of some important parameters, such as current direction, current speed, focused wave amplitude and wave spectrum bandwidth, were further studied. Apart from this, results of spatial spectral evolutions in the processes of waves focusing and defocusing using the Fast Fourier Transformation (FFT) were studied to find the internal reasons of the effects of uniform currents on the focused waves, and focused on the partial wave blocking due to strong opposing currents. Whereafter the nonlinear focused wave interaction with structures was investigated. The run-up and maximum wave pressure along the vertical wall for different wave spectrum bandwidths, structures positions and wave nonlinearity and the fixed box for different size(immersion depth and width), structures positions and wave nonlinearity were further studied. Then the numerical model was extended to simulation of the focused wave-current inreraction with the submerged bars. The emphasis was focused on the current influence on the wave profile and hydrodynamic characteristics for wave-body interaction. The results will provide certain reference for engineering design.