Análise de vibrações laterais de linhas de eixo de navios utilizando o método de elementos finitos

Abstract

The present work presents the implementation of a methodology for the numerical analysis of the lateral vibrations of the axis lines of marine propulsion systems. A propeller shaft line is a rocking rotor type with a mass concentrated at the end and this configuration causes in particular some inertia effects and the gyroscopic effect on the propeller, which is generally not taken into account in most designs of rotary machines. The gyroscopic effect is associated with the variation of the sense of the amount of angular momentum, which causes the axis to exhibit precession movement and, therefore, the natural frequencies of transverse flexions are no longer independent and are coupled, generating natural precession frequencies . Then, each point of the axis starts to have elliptical movements forming orbits that vary according to the dynamic characteristics, loads, boundary conditions and especially the speed of rotation. It will be presented the differential equations of motion in the continuous medium, which can be solved analytically but the system will be discretized to be solved numerically. Due to the complexity of the system and the numerous degrees of freedom, the problem will be solved by the finite element method in a commercial program. The main results were obtained the natural frequencies for the operating range of revolutions, their respective modes of direct and retrograde precession and the determination of critical speeds.