Mohammad Reza Tabeshpour - Sharif University of Technology
Rahim Shoghi - MSc Graduate, Faculty of Civil Engineering, Tabriz University, Tabriz, Iran

Solution of the Duffing equation in a non-linear vibration problem is studied in this paper. Clearly, in the case of perturb parameter being a larger value, the traditional perturbation method is no longervalid but also Homotopy perturbation method (HPM) is applicable usually. HPM is used to solveweak and strong nonlinear differential equations for finding perturbed frequency of response. Obtained frequencies via HPM and approximate method have good accordance for weak and strongnonlinear differential equation. Also, calculated responses by approximate method are compared withresponses obtained from Numerical method in time history of response and phase plane, results represent good accordance between those

Duffing; Nonlinear; Perturbation