“…Many researchers have applied various approximate methods to analyze different types of nonlinear Duffing oscillator equations. Some of these methods are multiple scales Lindstedt-Poincare method, 7 homotopy analysis method, 8 homotopy Pade technique, 9 stiffness analytical approximation method, 10 homotopy perturbation method, [10][11][12][13][14][15] frequency amplitude formulation, [16][17][18][19][20] energy balance method, 21 straightforward expansion method, 22 global error minimization method, 23 max-min approach, 24 global residue harmonic balance method, [25][26][27][28] variational approach, 29 perturbation method, 30,31 Hamiltonian approach [32][33][34] harmonic balance method, 35 and coupled homotopy-variational approach. 36 The purpose of the current work is to apply a suggested perturbation technique to obtain higher order approximate periodic solutions for strongly nonlinear Duffing oscillators.…”