Mitigation of structural responses of a very large floating structure in the presence of vertical porous barrier

Abstract

The effectiveness of partial vertical permeable barriers of three different configurations located at a finite distance from a very large floating structure is analyzed for mitigating the wave-induced response of the structure. The eigenfunction expansion method is employed to obtain solution in case of normal incidence and the study is extended to the case of oblique incident waves. In case of normalized incident waves, a detailed analysis of the results on various physical quantities such as the reflection and transmission coefficients, wave force on the barrier, free surface elevation, plate deflection, shear force and surface strain on the floating structure are presented. For the case of oblique incidence, results on reflection coefficient for various structural parameters are presented. Using Green's identity, energy balance relations are derived in both the cases of normally and obliquely incident surface waves and certain results for normally incident waves are compared for accuracy. The study reveals that wave reflection follows an oscillatory pattern and the minima in the oscillatory pattern increase with an increase in structural porosity. Wave reflection and dissipation attain their optima for the same wave number irrespective of barrier configurations. Occurrences of wave diffraction are observed in case of long waves for barriers of varied configurations with a narrow gap which decreases with the introduction of barrier permeability. Moreover, when the distance between the barrier and the very large floating structure is close to an integer multiple of half of the wavelength, both the wave reflected by the barrier as well as wave forces acting on the barrier attains their optima.