Force appropriation of nonlinear structures

• Published in: Proceedings of the Royal Society. A, Mathematical, physical, and engineering sciences Vol. 474; no. 2214; p. 20170880
• Main Authors: Renson, L., Hill, T. L., Ehrhardt, D. A., Barton, D. A. W., Neild, S. A.
• Format: Journal Article
• Language: English
• Published: England The Royal Society Publishing 01.06.2018
• Edition: Royal Society (Great Britain)
• Subjects: Energy Transfer; Excitation; Force Appropriation; Mathematical analysis; Mathematical models; Nonlinear Dynamics; Nonlinear Normal Modes; Phase Quadrature; energy transfer; phase quadrature; force appropriation; nonlinear dynamics; nonlinear normal modes
• ISSN: 1364-5021; 1471-2946
• DOI: 10.1098/rspa.2017.0880

Nonlinear normal modes (NNMs) are widely used as a tool for developing mathematical models of nonlinear structures and understanding their dynamics. NNMs can be identified experimentally through a phase quadrature condition between the system response and the applied excitation. This paper demonstrates that this commonly used quadrature condition can give results that are significantly different from the true NNM, in particular, when the excitation applied to the system is limited to one input force, as is frequently used in practice. The system studied is a clamped–clamped cross-beam with two closely spaced modes. This paper shows that the regions where the quadrature condition is (in)accurate can be qualitatively captured by analysing transfer of energy between the modes of the system, leading to a discussion of the appropriate number of input forces and their locations across the structure.