An Integrated Approach To The Determination Of Propeller Generated Vibratory Forces Acting On A Ship Hull.

A method is developed for predicting propeller-generated hull surface forces which cause a ship to vibrate. The method applies specifically for vertical, athwartship, axial, or torsional steady-state vibration of the hull girder. The exciting forces are made available as generalized forces effective in exciting the normal modes of the hull free vibration. The free vibration characteristics are assumed to be known in advance. The formula by which the generalized forces can be calculated is derived using potential flow theory. The basic ingredient in the derivation is a theorem which permits the problem to be solved without need for the solution of a hull-propeller interaction boundary value problem. To use the method one must have available: data pertaining to the hull and propeller design, the hull normal mode shapes, an estimate of the propeller blade loading distribution, and the fluid velocity-potential function corresponding to free vibration of the bare hull in each normal mode. Very simple, yet accurate, strip formulas for estimating fluid velocity-potential function, the bare hull velocity potential, and associated velocity components, are derived for the case of hull vertical vibration. (Author)