Solitary wave diffraction around a concentric porous cylindrical structure in front of a vertical wall

Abstract

This paper investigates solitary wave diffraction around concentric porous cylindrical structure in front of a vertical wall, where the exterior cylinder is permeable and the interior cylinder is impermeable. This problem is transformed into an issue of bi-directional incident waves diffraction around two concentric cylindrical systems based on the image theory. An analytical solution of the problem is obtained by applying the eigenfunction expansion approach and Graf's addition theorem. Unlike previous studies using Airy wave, this paper uses solitary wave as incident wave. The hydrodynamic loads and wave elevations on the concentric cylindrical system are calculated and compared with existing work. An excellent agreement is obtained between the model and data. Parametric studies on porosity, annular spacing, incident wave angle, distance between the concentric structure and wall were also explored. The results indicated that wave loads on the exterior cylinder near a vertical wall could reach twice as large as the force on it in open water, while the magnitudes of wave loads on the interior cylinder are similar for the two cases. In addition, we compared the modelling results of wave surface elevations using solitary wave and Airy waves. It shows that the amplitude of the wave surface elevations caused by the solitary wave is significantly higher than that of the Airy wave, which means the wave effects on offshore structures will be underestimated when using the Airy wave model in the same shallow water conditions.