Numerical and experimental investigation of hydrodynamic performance of a cylindrical dual pontoon-net floating breakwater

The use of a simple, inexpensive, and effective type of floating breakwater is increasingly becoming a necessity in shoreline and marine structure protection. This study concerns the hydrodynamic behavior of a dual pontoon floating breakwater (DPFB) when attached to one or more rows of plane net by using physical and numerical models. A two-dimensional (2D) fully nonlinear numerical wave tank (NWT) based on a time higher-order boundary element method (HOBEM) and mixed Eulerian-Lagrangian (MEL) approach is applied to obtain numerical solutions. In the model, Darcy's law is used to represent the porous media of the fluid-net interaction, and some auxiliary functions are introduced, instead of an iterative process using the acceleration potential method. Mesh regridding and interpolation combined with a double collocation node technique are implemented to tackle the mismatch between the meshes on the free surface and the wet body surface. In addition, the numerical model is verified with a series of corresponding experimental tests. Numerical solutions and measurement tests are executed to systematically examine the dependence of the reflection coefficient, transmission coefficient and motion responses on the design parameters, such as net number, net porosity, net height, wavelength and wave amplitude. It is found that the new floating breakwater exhibits a better performance with the optimal design parameters as compared with traditional DPFB, especially for long period and large amplitude waves.