TABLE OF CONTENTS Self-excited systems are those in which the motion of the system itself produces sufficient excitation to sustain an oscillation. There are many such phenomena, and in this chapter we introduce a few of the more important practically. Those discussed are the following:
Vibration induced by friction, which can occur when the rubbing surfaces of items such as tires on runways, brakes and clutches have a coefficient of friction which tends to decrease with increasing velocity.
Aircraft flutter, a branch of aeroelasticity, where the aerodynamic driving forces are derived from the airstream by the elastic motion of the flying surfaces, i.e. the wings, fins, stabilizers, controls, etc.
'Shimmy' of aircraft landing gear, which still tends to occur with cantilevered landing gear units, particularly nose units, when the nose-wheel is free to castor. It is a phenomenon similar to classical flutter, involving two degrees of freedom, which are rotation of the wheel or wheels in a castoring or steering sense, and lateral bending of the leg. The driving force is derived from tire side forces.
The essential mechanism of vibration induced by friction is illustrated by the system shown in Fig. 12.1(a). This shows a spring, mass and damper, where the mass m slides on a surface, which is moving to the right at constant velocity v 1. The argument is unchanged, however, if the surface is fixed and the spring-mass system is moving.
The equation of...
