Three-dimensional wave diffraction in the vicinity of openings in coastal structures

• Coupled-mode model for wave transmission through openings in coastal structures.
• Accounting for 3D diffraction effects due to sudden changes of water depth and channel width.
• Harmonic incident wave field propagating normally or at an angle to the structure.
• Coupling with mild-slope models describing wave transformation in coastal regions in the presence of structures.
• Numerical simulations compared against experimental measurements in a 3D wave basin.

Wave transformation through openings in coastal structures is dominated by 3D diffraction effects due to sudden changes of water depth, along with the finite width of the channel. In the present work, a novel coupled-mode model, based on eigenfunctions expansions of the Laplace equation, is developed and applied to the numerical solution and the detailed representation of the local 3D wave flow problem in the vicinity of the opening. The harmonic wave field is excited by plane incident wave propagating normally or at an angle with respect to the axis of the opening/channel. The numerical solution converges rapidly, permitting the series truncation at its first terms. The proposed method fully accounts for the 3D diffraction effects and produces necessary information to further couple with mild-slope models describing wave propagation and transformation in coastal regions in the presence of breakwaters and coastal structures containing openings. Calculated results are presented for waves propagating in regions with breakwaters with openings simulating flushing culverts and compared against experimental measurements obtained in a 3D wave basin.