Physicists are very familiar with forced and parametric resonance, but usually not with self-oscillation, a property of certain dynamical systems that gives rise to a great variety of vibrations, both useful and destructive In a self-oscillator, the driving force is controlled by the oscillation itself so that it acts in phase with the velocity, causing a negative damping that feeds energy into the vibration: no external rate needs to be adjusted to the resonant frequency The famous collapse of the Tacoma Narrows bridge in 1940, often attributed by introductory physics texts to forced resonance, was actually a self-oscillation, as was the swaying of the London Millennium Footbridge in 2000 Clocks are self-oscillators, as are bowed and wind musical instruments The heart is a "relaxation oscillator," ie, a non-sinusoidal self-oscillator whose period is determined by sudden, nonlinear switching at thresholds We review the general criterion that determines whether a linear system can self-oscillate We then describe the limiting cycles of the simplest nonlinear self-oscillators, as well as the ability of two or more coupled self-oscillators to become spontaneously synchronized ("entrained") We characterize the operation of motors as self-oscillation and prove a theorem about their limit efficiency, of which Carnot's theorem for heat engines appears as a special case We briefly discuss how self-oscillation applies to servomechanisms, Cepheid variable stars, lasers, and the macroeconomic business cycle, among other applications Our emphasis throughout is on the energetics of self-oscillation, often neglected by the literature on nonlinear dynamical systems

Self-oscillation

Optimal weight design of a gear train using particle swarm optimization and simulated annealing algorithms

A new approach for polymer composite gear design

Friction and wear behaviour of acetal and nylon gears

http://digilib.its.ac.id/public/ITS-Undergraduate-13538-Paper-1047672.pdf

Tribological behaviors of several polymer–polymer sliding combinations under dry friction and oil-lubricated conditions

A design of a four square gear test rig that allows the wear of polymer and composite gears to be monitored continuously during operation is described. The wear behavior of three typical gear materials is examined and it is shown that the wear characteristics differ greatly. For Acetal there is a sharp rise in wear as the transmitted torque is increased, effectively limiting the torque that can be transmitted by an Acetal gear pair. This wear transition is shown to be associated with the maximum surface temperature of the gear reaching the melting point of Acetal

D. Walton

Papers

Friction and wear behaviour of acetal and nylon gears

Measurement and Prediction of the Surface Temperature in Polymer Gears and Its Relationship to Gear Wear

Wear behaviour of acetal gear pairs

Acoustic noise from polymer gears – A tribological investigation

The wear of unlubricated metallic spur gears