A class of solvable coupled nonlinear oscillators with amplitude   independent frequencies
  Existence of amplitude independent frequencies of oscillation is an unusual property for a nonlinear oscillator. We find that a class of N coupled nonlinear Li\'enard type oscillators exhibit this interesting property. We show that a specific subset can be explicitly solved from which we demonstrate the existence of periodic and quasiperiodic solutions. Another set of $N$-coupled nonlinear oscillators, possessing the amplitude independent nature of frequencies, is almost integrable in the sense that the system can be reduced to a single nonautonomous first order scalar differential equation which can be easily integrated numerically. 
V.K.Chandrasekar, Jane H. Sheeba, R. Gladwin Pradeep, R.S. Divyasree   and M. Lakshmanan
nlin.SI