MEASURING DAMPING IN LINEAR AND NONLINEAR SYSTEMS

It is shown how measurements of the decaying response of a vibrating system, following an initial disturbance, can be analysed to extract natural frequency and damping properties. Typically, such data contains a superposition of many vibration modes. By using filtering, it is demonstrated how individual modes can be extracted. The filtering must be done in a special way that involves reversing the data in time and passing it through a narrow band filter and truncating the data. Reversing the data prevents the filter characteristics contaminating the filter output. If the data is from a linear system then the natural frequency and damping are preserved by this process. If the data is nonlinear then the instantaneous frequency and damping are also preserved but are modified in a way that can be reversed. It is shown how all the effects of the filtering can be eliminated so that the decaying response of each mode is obtained. This approach provides a useful extension to experimental modal analysis that is applicable to nonlinear systems.