Extraction of damped and undamped natural mode shapes from area-scan ODSs

A. B. Stanbridge; D. J. Ewins

doi:10.1117/12.693159

21 June 2006 Extraction of damped and undamped natural mode shapes from area-scan ODSs

A. B. Stanbridge, D. J. Ewins

Proceedings Volume 6345, Seventh International Conference on Vibration Measurements by Laser Techniques: Advances and Applications; 63450G (2006) https://doi.org/10.1117/12.693159
Event: Seventh International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, 2006, Ancona, Italy

Abstract

Optical techniques are widely used to measure the vibration response patterns (ODSs) of structures over a scanned area, excited at resonance frequencies. The ODSs may be similar to natural mode shapes, but not if there are close modes coupled together by the structural damping. Natural mode shapes are usually extracted by analysis of frequency responses measured at every response point, but this is impracticable with area-scan measurements. The vibration responses at resonance frequencies can be regarded as being a linear combination of just a few natural mode shapes, and these can therefore be separated by combining an equivalent number of area-scan ODSs. For m component modes, measurements of real and imaginary ODS components at m/2 test frequencies and frequency responses at m points on the structure are required. Vibration responses can equally be regarded as being a combination of undamped natural mode shapes and these can be extracted in a similar way, if their amplitudes are known a priori at m points on the structure. Continuous-scan LDV measurements of the ODSs of a damped rectangular plate are used to demonstrate the techniques, and some suggestions are made on the inclusion of split modes and of extraneous resonances.

Citation Download Citation

A. B. Stanbridge and D. J. Ewins "Extraction of damped and undamped natural mode shapes from area-scan ODSs", Proc. SPIE 6345, Seventh International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, 63450G (21 June 2006); https://doi.org/10.1117/12.693159

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