Three-to-one internal resonances in parametrically excited hinged-clamped beams

The nonlinear planar response of a hinged-clamped beam to a principal param etric resonance of either its first or second mode or a combination paramet ric resonance of the additive type of its first two modes is investigated. The analysis accounts for mid-plane stretching, a static axial load, a rest raining spring at one end, and modal damping. The natural frequency of the second mode is approximately three times the natural frequency of the first mode for a range of static axial loads, resulting in a three-to-one intern al resonance. The method of multiple scales is used to attack directly the governing nonlinear integral-partial-differential equation and associated b oundary conditions and derive three sets of four first-order nonlinear ordi nary-differential equations describing the modulation of the amplitudes and phases of the first two modes in the cases of (a) principal parametric res onance of either the first or the second mode, and (b) a combination parame tric resonance of the additive type of these modes. Periodic motions and pe riodically and chaotically modulated motions of the beam are determined by investigating the equilibrium and dynamic solutions of the modulation equat ions. For the case of principal parametric resonance of the first mode or c ombination parametric resonance of the additive type, trivial and two-mode solutions are possible, whereas for the case of parametric resonance of the second mode, trivial, single, and two-mode solutions are possible. The tri vial and two-mode equilibrium solutions of the modulation equations may und ergo either a supercritical or a subcritical Hopf bifurcation, depending on the magnitude of the axial load. For some excitation parameters, we found complex responses including period-doubling bifurcations and blue-sky catas trophes.