Study on characteristics of propeller exciting force induced by axial vibration of propulsion shafting: Theoretical analysis

Abstract

When the ship propeller works, besides non-uniform flow field can generate exciting force, shaft vibration can also cause the propeller to produce exciting force. This type of force can usually be expressed as a combination of additional mass force and additional damping force. The purpose of this paper is to study this type of force. First, based on boundary element method (BEM) and combined with rotordynamics theories, the new prediction model of the exciting force induced by shaft vibration is established. Second, the model and codes are validated by some numerical and experiment examples. At last, the axial exciting force induced by the axial shafting vibration is investigated. The results show that when the vibration amplitude is small, or the vibration frequency is low, the nonlinear effect of the wake vortex is weak, so that the exciting force is proportional to the vibration amplitude and square to the vibration frequency. This means that the real part and imaginary part of the exciting force can be equivalent to constant added mass and added damping, respectively. By a series calculation of different propellers, the simplified estimation formula of the axial exciting force in linear state is proposed and validated.