The homotopy analysis method and the Lienard equation
  In this work, Lienard equations are considered. The limit cycles of these systems are studied by applying the homotopy analysis method. The amplitude and frequency obtained with this methodology are in good agreement with those calculated by computational methods. This puts in evidence that the homotopy analysis method is an useful tool to solve nonlinear differential equations. 
Saied Abbasbandy, Jose-Luis Lopez, and Ricardo Lopez-Ruiz