Active Magnetic Control of Oscillatory Axial Shaft Vibrations in Ship Shaft Transmission Systems Part 1: System Natural Frequencies and Laboratory Scale Model

Abstract

A ship's main drive shaft axial vibration at propeller blade rate may be transmitted to the hull. A method for reducing these vibrations is investigated in this paper. A proposed design consists of an auxiliary shaft magnetic thrust bearing added in parallel to the shaft fluid film (mechanical) thrust bearing. The blade passing oscillatory load supported by the auxiliary magnetic bearing reduces the overall magnitude of the oscillatory thrust. The magnet current is controlled through an electronic feedback circuit.

The system employs a negative spring stiffness, now realizable with magnetic support systems, for vibration isolation. This approach promises radical changes in the area of machine design for force isolation and noise reduction.

A laboratory scale model of a ship propulsion shaft train was designed and constructed for experimental verification of the theory. Scaling was used so that model dynamic characteristics closely approximated those of the real system.

Classical control theory in the computer simulation was applied to analyze system sensitivity and stability. Analysis revealed the system to be feasible but sensitive to certain critical parameters.

Presented at the 43rd Annual Meeting in Cleveland, Ohio May 9–12, 1988

Notes

Presented at the 43rd Annual Meeting in Cleveland, Ohio May 9–12, 1988