Resonance Frequencies of Viscously Damped Structures

MI Friswell & AW Lees (University of Wales Swansea)

Journal of Sound and Vibration, Vol. 217, No. 5, November 1998, pp. 950-959


The analysis of damped structures is becoming increasing important in a variety of fields. Often this damping is non-classical, in the sense that the modes are complex. This paper considers the resonance frequencies of viscously damped structures, defined as the frequency at which the response attains a local maximum. For a single degree of freedom system it is well known that this resonance frequency is neither the undamped nor the damped natural frequency. What is less well known is that for multi degree of freedom systems the resonance frequency can change depending on which degree of freedom is considered. This occurs for well separated complex modes. The phenomena also occurs for systems with real modes, due to the influence of neighbouring modes. This paper explicitly calculates the resonance frequencies for a single complex mode approximation, and incorporates residual terms from neighbouring modes. A discrete mass, spring and damper system, and a rotating machine are used as examples to highlight this phenomena.

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Link to paper using doi:10.1006/jsvi.1998.1795

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