Numerical study on wave run-up and forces on a fixed cylinder under linear and nonlinear focused waves

To study the difference between wave run-up and wave forces on a fixed column under the action of focused waves formed with different physical mechanisms, a 3D two-phase numerical wave tank is developed based on the Navier-Stokes equation and the Finite Volume Method. The influences of wave nonlinearity, column radius and water depth on the run-up and force discrepancies are systematically investigated in four sets of numerical experiments. For focused waves with identical crest height and trough-to-trough period, the run-up height and dynamic pressure around the circumference of a cylinder are mostly larger in linear focused waves than in nonlinear focused waves, due to their different hydrodynamic characteristics. With the increased wave nonlinearity either by changing the period or crest height of the focused waves, the discrepancies become greater for run-up height while smaller for dynamic pressure. Moreover, both of them, less affected by water depth, are more sensitive to the variation of column radius in linear focused waves, showing a steeper gradient in space. Therefore, in practical engineering, the physical generation mechanism must be considered in evaluating the safety of columns of wind turbines hit by freak waves.