Wave force identification for a large-scale quasi-elliptical cylinder from monitored wave elevation

Abstract

Based on the potential theory, the wave force on a large-scale quasi-elliptical cylinder was identified using monitored wave elevation data. Expressions with underdetermined coefficients of quadratic transfer functions for a noncircular cylinder are presented. The linear wave forces, second-order wave forces, and hydrostatic forces on the cylinder are identified using recursive least squares in real time. A comparison between the experimental and identified results of wave forces demonstrates the effectiveness of the identification method for a noncircular cylinder. The identified wave force consisted of several force components that correspond to the Fourier coefficients of the radius function. Generally, at a low wave number, the force components corresponding to the Fourier coefficient of the radius function decrease as the order of the harmonic term increases. With increasing wave number, the force components at the high-order harmonic term may significantly increase and become the dominant components of the wave force. The phase difference between the force components was studied, in which the phase difference of the first two main components was zero in the short-side direction and is π in the long-side direction. Phase jumps occur when the force components are zero.