Zero and root loci of disturbed spring–mass systems

Abstract

Models consisting of chains of particles that are coupled to their neighbours appear in many applications in physics or engineering, such as in the study of dynamics of mono-atomic and multi-atomic lattices, the resonances of crystals with impurities and the response of damaged bladed discs. Analytical properties of the dynamic responses of such disturbed chains of identical springs and masses are presented, including when damping is present. Several remarkable properties in the location of the resonances (poles) and anti-resonances (zeros) of the displacements in the frequency domain are presented and proved. In particular, it is shown that there exists an elliptical region in the frequency–disturbance magnitude plane from which zeros are excluded and the discrete values of the frequency and disturbance at which double poles occur are identified. A particular focus is on a local disturbance, such as when a spring or damper is modified at or between the first and last masses. It is demonstrated how, notably through normalization, the techniques and results of the paper apply to a broad category of more complex systems in physics, chemistry and engineering.

Characterization of forced localization of disordered weakly coupled micromechanical resonators

“…It is strange that the anti-resonance 32 locations of the disordered WCRs, which play an important role in vibration control and dynamic model updating 33 , have seldom been linked to mode localization in the past, although the anti-resonance indicates a valley in the vibrational magnitude of the frequency domain 34 . Several aspects of the linear anti-resonance behavior are very meaningful.…”