Anna Warminska

Large amplitude vibrations of heated Timoshenko beams with delamination

In this work, the large amplitude vibration of a heated Timoshenko composite beam having delamination is studied. The model of delamination considers the contact interaction between sublaminates including normal forces, shear forces, and additional damping due to the interaction of sublaminates. This work is an extension of the previous analysis based on a model of the dynamic behavior of a beam with delamination considering additionally the nonlinearities due to large displacements and temperature changes. Numerical calculations are performed in order to estimate the influence of the delamination, the geometrically nonlinear terms, and elevated temperature on the response of the beam.

Parametric Resonance of a Self-Excited System Under External Force and Time Delay Influence

Vibrations of a nonlinear self-excited system driven by parametric excitation are presented in the paper. The considered model with one DOF includes a self-excitation term represented by a nonlinear Rayleigh function and also a periodically varied stiffness coefficient which represents parametric excitation. The influence of the external force or/and time delay, treated as a control signal, is demonstrated. Nonlinear parametric resonance is determined numerically and analytically by the multiple time scale method. The influence of time delay on the resonance zones and the frequency locking phenomenon is analysed.Copyright

Hopf Bifurcations, Quasi-Periodic Oscillations and Frequency Locking Zones in a Self-Excited System Driven by Parametric and External Excitations

Vibrations of a nonlinear self-excited system driven by parametric and/or external excitations are studied in the paper. The model is composed of a self-excitation term represented by a nonlinear van der Pol function, periodically varied stiffness which represents parametric excitation and external harmonic force. Interactions between self and parametric or/and external force lead to complex behaviours observed by quasi-periodic or chaotic motions but under specific conditions, near resonance zones the response is harmonic. The transition from quasi-periodicity to periodic oscillations is caused by so called the frequency locking phenomenon which in fact corresponds to the second kind Hopf bifurcation (Neimark-Sacker bifurcation). The periodic resonances can be determined analytically, quasi-periodic oscillations however are investigated mainly numerically. The goal of this paper is to determine quasi-periodic dynamics and Hopf bifurcations analytically by using the multiple time scale method (MSM) in two steps: (1) to determine periodic solutions of the fast flow by the first order MSM and (2) to determine periodic solutions of the slow–flow by the second order MSM. The analytical solutions obtained in both scales allow determining bifurcation points of the system.Copyright

Thermal Effects on Internal and External Resonances of a Nonlinear Timoshenko Beam

Large amplitude vibrations of a Timoshenko beam under an influence of thermal and mechanical loadings are studied in the paper. The structural parameters of the beam are considered enabling internal resonance conditions. Moreover, it is assumed that the beam gets instantly temperature which is distributed along its length and thickness. The mathematical model represented by a set of partial differential equations takes into account coupled mechanical and thermal fields. The problem is transformed to a set of ODEs by the Galerkin method and three modes of a simply supported beam at both ends are studied. The effect of temperature on internal and external resonances is analysed on the basis of the proposed reduced model.Copyright

Dynamics of Beams under Coupled Thermo-Mechanical Loading

An effect of thermal loading on vibrations of beams is investigated in the paper. A beam is considered as an extended Timoshenko beam model with nonlinear terms resulted from large deflections. Dynamics of the structure is analysed under thermal and mechanical loadings considering transient dynamics due to a heat pulse imposed to the beam. The numerical method for solving coupled thermo-mechanical problem is presented. On this basis the importance of the heat pulse intensity around the first resonance condition is demonstrated. The effect of the heat on the the complex transient dynamics of the beam and its qualitatively different response is shown as well.