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Derivation of Morison's force coefficients by three alternative forms of the method of moments

Mohd. Zaki, N. I. and Abu Husain, M. K. and Najafian, G. (2016) Derivation of Morison's force coefficients by three alternative forms of the method of moments. In: ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2016, 19-24 June 2016, Busan, South Korea.

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Morison's equation is the most widely used method of predicting wave forces on slim cylindrical members of offshore structures. The equation assumes that the wave force is composed of two components: a drag force and an inertial force, where the drag component is due to water particle velocity and the inertial component is due to water particle acceleration. Morison's equation has two empirical coefficients, which are usually referred to as the drag and inertia coefficients. The values of these empirical coefficients are determined from laboratory and/or 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 drag and inertia coefficients. One of the methods used in derivation of these coefficients is the (conventional) method of moments. However, the coefficients obtained from this method show considerable scatter due to large sampling variability. The purpose of this paper is to compare the sampling variability of drag and inertia coefficients from the conventional method of moments with those derived from two alternative forms of the method, i.e. methods of linear and low-order moments. Simulated data has been used to compare the efficiency of the three methods of moments. The results indicate that in most cases, the method of linear moments is superior to the other two methods. This is particularly true for drag-dominated forces.

Item Type:Conference or Workshop Item (Paper)
Uncontrolled Keywords:Drag coefficient, Inertia coefficient, Method of moments, Morison's equation, Wave load
Subjects:T Technology > T Technology (General)
Divisions:Razak School of Engineering and Advanced Technology
ID Code:73642
Deposited By: Mohd Zulaihi Zainudin
Deposited On:28 Nov 2017 06:50
Last Modified:28 Nov 2017 06:50

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