Limit cycles in self-excited multi-degree-of-freedom systems

A possibility of generating stable multi-frequency almost-periodic limit cycles in n-degree-of-freedom self-excited systems is investigated. Analytical approximate methods are used. Systems with non-linear forces described by analytical functions are considered. Several examples of two-degree-of-freedom systems with van der Pol terms are analyzed in detail. The effect of non-linear restoring forces is also considered. The possibility of occurrence of multi-frequency limit cycles is proved by means of analytical methods and confirmed by analogue computer results.