Coupled transverse shaft vibrations of modern ships 1

Abstract

The design of main propulsion shafting systems for modern ships, such as VLCC’s, LNG carriers and high-speed containerships, is to a great extent dictated by the requirement of vibration-free performance in service. It is the purpose of this paper to present a method for predicting analytically in the design stage the coupled transverse vibration characteristics of a given propulsion shaft system and to illustrate it with typical examples.

A brief description of the basic problem is first given and this is followed by a review of earlier theoretical work in this field. The transfer matrix approach for the solution of the problem is then introduced and its computational advantages underscored. Special emphasis is given to the modeling process for shaft segments, propeller, bearings, etc. It is then shown how on the basis of this formulation one can predict the shaft natural frequencies and critical speeds.

The SHAFTRAN digital computer program, currently in use by the authors’ firm for routine investigations, is then briefly described. Several examples of this program’s capability are given using actual ship designs. Analytical details are mostly retained in a series of appendices and the paper concludes with a set of recommendations that will increase the accuracy of the calculations.