Hydrodynamic performance of an array of truncated cylinders in front of a vertical wall

Abstract

In the present paper, the hydrodynamic performance of a linear array of truncated circular cylinders in front of a bottom–mounted vertical wall is analysed in the frequency domain in order to investigate the effect of the wave reflections combined with the disturbances induced by the bodies themselves. Infinite and finite-length wall cases are examined and compared. The former case is formulated and solved using the matched eigenfunction expansion technique and the “direct” solution methodology for the numerical implementation. The existence of a “pure” wave-reflecting wall of infinite length is considered by utilizing the method of images. For the finite-length wall cases the conventional Boundary Integral Equation (BIE) formulation is employed. Emphasis is given on: (a) revealing the limitations of the “infinite wall” concept on the calculation of the exciting forces acting on the cylinders of the array and (b) investigating the effect of the length of the wall on the aforementioned physical quantities. The results demonstrate that the “infinite wall” concept leads to under- or over-estimation of the heave exciting forces at small wave numbers, while this concept seems not to be adequate for the accurate calculation of the horizontal exciting forces in cases of small outer cylinder's center–to–wall's edge distance. The change of the wall's length affects the surge and the heave exciting forces, while, the presence of the wall, contrary to the case of the isolated array, leads to an intense variation pattern of the cylinders' sway exciting forces. This pattern is characterized by successive local minima, which can be related to the existence of a symmetrical wave field in the seaward and leeward sides of the cylinders.