Hydrodynamic characteristics of forced oscillation of heave plate with fractal characteristics based on floating wind turbine platform

The heave plate is widely used in the field of marine engineering because of its advantage of increasing damping and added mass. In this paper, the fractal theory is applied to the structure design of the heave plate and a fractal plate has been proposed. With the technology of dynamic mesh and user defined functions (UDF) in Fluent, numerical simulations on forced oscillation of different heave plates have been performed. At different amplitudes of harmonic motion, the hydrodynamic characteristics of solid plate, different fractal order plates (perforation ratios of 5%, 12% and 20%, respectively) and regular ones (different shapes and arrangement of holes with the same perforation ratio of 20%) are compared and analyzed. The time history of vertical force, added mass coefficient (C-m) and damping coefficient (C-d) are obtained for different heave plates. The results show that at the same oscillation period, the C-d value of each heave plate decreases with the amplitude of harmonic motion increases, eventually becoming stable, while the C-m value increases continuously. When comparing different fractal heave plates, the C-m value decreases with the increase of the fractal order, while C-d value increases firstly and then decreases at the same condition. Besides, the C-d value reaches the maximum at the second order. As the hole perimeter becomes higher, the regular ones with the perforation ratio of 20% exhibits a linear increase in damping coefficient with increasing Keulegan-Carpenter Number (KC). The damping coefficient of a fractal plate is obviously larger than that of regular ones, which indicates that the fractal plate has better performance compared to regular ones.