A study on the excitation force induced by the coupling of torsional and axial vibrations in marine propulsion shafting system

摘要

The thrust variation induced by the coupled vibration of torsional and axial propulsionshafting vibrations is one of the major excitations for the longitudinal deck house vibrationof the container carrier. The conventional calculation method of thrust variation has beenperformed using 1D beam crank shaft model with lumped elements of equivalent stiffnessand inertia. The calculation result of thrust variation using conventional method washigher than the measured one. In this study the direct frequency analysis method with the 3dimensional FE model was used to calculate the thrust variation considering the couplingeffects of both the crank throw and the propeller. The thrust variation was measured forthe two(2) container carriers and three(3) crude oil carriers to confirm the proposedcalculation method. The measurement system with the semiconductor sensors was installedat the intermediate shaft of the vessel. From the results of measurement and calculation itwas found out that the calculated thrust variation with the proposed calculation methodagreed well with the measured one. The advanced calculation method proposed in thisstudy will be helpful to predict the accurate value of thrust variation at the design stage.