Nonlinear longitudinal vibration of an elastic rod is studied. The motion of a uniform elastic rod is described by a nonlinear partial differential equation, which has a cubic nonlinear term and a Winkler elastic force that acts along the longitudinal axis of the rod. Galerkin method is used to develop the nonlinear differential equation of elastic rod, which resembles similarity with the Duffing equation. Three different types of robust analytical methods are chosen to solve the nonlinear differential equation and obtain the natural frequency of the system. These are the Homotopy analysis method (HAM), Energy balance method (EBM) and Hamiltonian approach (HA). Subsequently, the analytical results are compared with the numerical solution of the exact equation in order to evaluate the correctness of the applied approaches. Moreover, the effects of the constant coefficients of the elastic force on the ratio of the nonlinear to the linear frequencies are studied. The singular points of the nonlinear differential equation of the elastic rod are extracted and the Jacobian matrix is constructed to recognize their types. Finally, phase-plane trajectories of the system are constructed in order to verify the results obtained from the Jacobian matrix.
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