Morison Equation in Practice and Hydrodynamic Validity

摘要

This paper presents a practical interpretation of the hydrodynamic force equation developed based on the velocity potential. It expresses the equation in an original version of the Morison equation as well as in its subsequent numerous extended or modified versions in the industry design practice. It is demonstrated that the hydrodynamic force equation derived from a velocity potential for slender structures can be expressed term-by-term in a form of the original as well as modified versions of the Morison equation as used for floating and flexible structures in motion in waves. From this expression, the validity range of Morison equation is presented and discussed from the point of view of the hydrodynamic force equation. Also further discussed are: (a) the drag term empirically added to the hydrodynamic force equation, similar to the term in the Morison equation; (b) the use of the frequency-dependent, added mass and radiation (or wave) damping accounting for free-surface effect; (c) periodic time-dependency in practice; and (d) member diameter relative to incoming wave length.