| Popis: |
The use of high-speed cameras in the field of structural dynamics for modal identification is a challenging task. High-speed cameras offer several advantages over classical measurement techniques, such as non-contact full-field measurement from a distance. However, it is not easy to obtain as good a measurement as with classical techniques, since various influences play a role, such as: light source, excitation strength, strong noise and the measured displacement, which becomes very small at high frequencies. This makes modal identification from such data very difficult with classical methods, especially when it comes to identifying structural damping. Identifying damping is a challenging task, even with high dynamic range sensors (accelerometers).The main advantage of high-speed camera measurement is the availability of a full-field response, which can be used as an advantage to reduce the uncertainty of the identified results. Due to the high noise, an advanced signal processing method must be used that is able to localise a good portion of the signal and identify damping. Such a method is based on the continuous wavelet transform, which provides very good frequency separation. It is resistant to noise and much faster than the continuous wavelet transform. It is a Morlet-Wave Damping identification method which can be understood as a microscope for the signal we used in this study to identify damping. Damping is a modal parameter that is theoretically not spatially dependent. Therefore, we used spatial overdetermination to increase the accuracy of the damping identification. The full-filed damping identification results were averaged over the identified deflection shapes. The method was tested experimentally on the simple structure up to 2.5 kHz. The results were found to be comparably accurate to the damping identified using the piezoelectric accelerometer with high- dynamic-range and low-noise piezoelectric accelerometer, proving that damping can be accurately identified using high-speed camera measurements, only. |
