Prediction of propeller induced ship vibration: some structural aspects 1

Abstract

Described are some structural aspects of a finite element model used in the design stage to predict vibration levels of a 150,000 SHP triple screw, high speed trailership. The mode shapes of the model show that at blade frequencies of operating RPM the hull does not vibrate as a beam in bending, shearing and twisting, but rather the decks and double bottom move with different wave lengths, amplitudes and phases. Hull flexibility can significantly affect the transverse vibration frequencies of propulsion shafts. The response of the model shows the importance of detuning of propulsion system resonant frequencies from operating RPM. The proper use of the finite element method in the calculation of propulsion system longitudinal vibration is suggested.