Prediction approach for wave forces on large-scale offshore structures under linear wave action

Abstract

This paper presents a numerical mothed that is implemented by applying higher-order boundary elements in the hybrid integral equation method for predicting the wave forces on arbitrarily-shaped offshore structures. In this study, the virtual cylindrical boundary (i.e., matching boundary) is set to divide the fluid region into inner and outer subdomains. The velocity potentials in the outer domain are expressed using the eigenfunction expansion method. In the inner domain, the simple Green's function is adopted as the fundamental solution and Green's second theorem is applied to derive the boundary integral equation (BIE). The velocity potentials in the two subdomains are matched on the matching boundary. The higher-order boundary elements are ultimately employed to discretize BIE and the velocity potentials in the inner domain are then solved. The wave forces on the truncated and stepped cylinders are calculated using the presented method, and the results match well with analytical results, which illustrates the validity of the presented method. The effects of element sizes and modal truncation numbers are further explored, and the interaction between waves and square columns is subsequently analyzed. Eventually, the proposed method is extended to the practical engineering application of wave diffractions from quasi-elliptic pile caps for sea-crossing bridges. The results show that the proposed method can deal with boundaries with complex geometries. In addition, satisfactory results can be obtained by setting relatively few elements and control points on boundaries, and this method can also effectively predict wave forces on the multi-column array.