The purpose of the present article is to set up such equation of motion as can be used to determine the amplitude of the axial vibration of crankshaft, taking into account the excitation due to crank force and propeller thrust, and dampings.
In 1 we make an equation of axial vibration that takes into account radial crank force and variation of propeller thrust only, neglecting tangential crank force.
From this equation we deduce the relation among exciting forces, damping factors and amplitudes. But this relation was found to be unable to explain the measured amplitudes.
Therefore, in 2 we make the equation of coupled torsional and axial vibration, considering also tangential crank force as exciting force.
The comparison of this equation and measured values has not yet been made.
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