Green’s function method with applications to wave-propagation. Regular and singular perturbation techniques with applications, the method of strained co-ordinates,the method of matched asymptotic expansion.
Analytical techniques: Homotopy perturbation method (HPM), Homotopy Analysis method (HAM), Adomian decomposition method (ADM)and its various forms, variation iterative method (VIM), Analytical solutions of various equations such as KDV, MKDV, Navier stokes equations etc.
Perturbation Methods for Engineers and Scientists by 
Introduction to perturbation techniques by 
