Higher-order diffraction forces on vertical circular cylinders by using a three-dimensional fully-nonlinear potential numerical wave tank

Abstract

The aim of this study is to evaluate higher-order diffraction forces on vertical circular cylinders by using an author-developed three-dimensional fully-nonlinear numerical wave tank (NWT). The nonlinear NWT is based on the potential theory, boundary element method, and mixed Eulerian Lagrangian (MEL) approach. The acceleration-potential method is used to calculate the hydrodynamic pressure accurately. The artificial damping zone is adopted to prevent reflected waves from bodies and side walls. The least square gradient reconstruction method and the thin plate spline method are applied to evaluate the spatial derivatives of physical quantities and updated locations of interpolation points. The third-order stokes monochromatic or bichromatic waves are inputted as incident-wave boundary condition. From the nonlinear NWT simulations with FFT, first-order, second-order, and third-order diffraction forces are simultaneously calculated and the results are systematically compared with published experimental and perturbation-based numerical results. The sensitivity of the nonlinear NWT results with the respective orders of Stokes monochromatic or bichromatic input waves is also investigated. The increase of third-order sum-frequency force in shallow water long wave is noticed.