Derivation of Morison's Force Coefficients : An Application of Method of Moments

Morison's equation uses two empirical constant coefficients for drag and inertial forces calculation. The values of these empirical coefficients must be determined from laboratory and field experiments. In a typical wave load investigation, the wave force together with corresponding water particle velocity and acceleration are measured. The measured data is then analysed to calculate constant values for Morison's coefficients. One of the methods used in the derivation of Morison's coefficients is the conventional method of moments. However, the coefficients obtained from this method show considerable scatter. The purpose of this investigation is to explain the cause of the scatter and to introduce a more efficient form of the method of moments. Morison's coefficients derived from the conventional method of moments will be compared with corresponding values from the new method of moments to determine the impact of the new method in reducing the observed scatter in Morison's coefficients.