The linearization of drag force and the error estimation of linear force spectrum

Abstract Existing linearization methods for drag force are not perfect in one way or another according to the authors' analysis. In this paper a new double-factor method for a modified vectorial Morison Equation is presented. The coefficients are determined by a least-squares error principle and calculated by a numerical method. According to this method, the correlation matrix and the spectrum matrix of the wave-current force acting on horizontal cylinders are established. The estimate of accuracy of the linearization method is based on the ratio of the zero-order moment of the linearized drag-force spectrum to that of the original drag-force spectrum. It is found that the linear spectra obtained by the proposed method are a better fit to the original spectra.