Vortex method is a numerical calculation method for a viscous fluid in time domain, which can consider the vorticity creation from body surface and diffusion of the vorticity into the fluid. To apply this method to the actual design of a floating body with fins installed to reduce its motions in waves, extension to 3D problem is required. In this paper, the development and quantitative validation of vortex method by restricting 2D problem are implemented through the calculation of a fluid domain around a 2D cylinder and a forced oscillating plate. The obtained calculation results are compared with experimental results.
It is important to promote the use of ocean renewable energy because there is a possibility of not only creating a new energy source but also leading to power stabilization in regions such as remote island areas. As one of ocean renewable energies, wind energy is given. Offshore wind energy generation facilities have less restriction in location and can supply more stable wind energy than on-land facilities. Offshore wind power generation facilities are classified into a bottom mounted type and a floating type, and adoption of the latter is expected to increase for areas with shallow water in Japan (MLIT, 2014, 2016, 2017).
To promote the adoption and safety of floating offshore wind energy generation facilities, it is required to reduce its motions in mountainous waves. Fins are often installed on the submerged parts of a floating body to reduce its motions in waves. It is expected that its kinetic energy is reduced by the vortex generated from fins because its energy is converted into vortex energy. However, to utilize this method, a numerical calculation method for a viscous fluid is required to optimize the shape and installation positions of these fins.
Currently, in the calculation of hydrodynamic force acting on the floating body considering the effect of vortex generation, Morrison's equation is commonly used. However, it is difficult to apply it to complex shapes because we must obtain mass and drag coefficients by experiments. Therefore, it is required to develop the numerical calculation method for the viscous fluid, which can calculate hydrodynamic force acting on the floating body with fins as shown in Fig. 1.
