The separation of two combined normal modes

Abstract

The experimental determination of the normal mode properties of a structure is frequently undertaken using the results of small amplitude steady-state vibration excitation. One of the complications which may arise in the interpretation of the results of such dynamic testing arises from interference between the responses in various modes. Specifically the responses of two modes may be superimposed to an extent which prevents the individual normal mode properties from being determined readily. In this paper an iterative technique is presented by which the properties of natural frequency, stiffness and viscous damping for two simple resonators may be derived from an experimentally determined response curve so that the combined responses of the resonators to a sinusoidal excitation is identical to that of the recorded response. The technique does not require the measurement of any phase information, and it can therefore be used in conjunction with simple test instrumentation.