The Effect of Non-Synchronous Sensing in Wireless Sensors on Structural Modal Identification

Abstract eng:
Structural health monitoring (SHM) employing wireless sensor networks (WSN) is becoming increasingly popular in recent years. Accurate synchronized sensing amongst wireless sensors is a key issue enabling the implementation of such smart systems for SHM based on vibration measurements. However, perfect synchronized sensing is unachievable in WSN. The effect of non-synchronous sensing when using wireless sensors on structural modal identification is addressed and a methodology for correcting such errors is proposed herein. This paper first discusses the potential sources causing non-synchronous sensing and estimates their extents based on data samples collected from Imote2 sensors, and then investigates the impact of synchronization errors in the measured output response on modal identification using numerical simulations. The simulation results show that even small synchronization errors in the output response can distort the identified mode shapes. A new methodology is proposed herein for eliminating such errors. This methodology estimates the power spectral densities (PSDs) of output responses using non-synchronous samples directly based on a modified FFT. As long as the corrected PSDs are obtained, the correlation functions can also be easily obtained by IFFT. Then these corrected PSDs or correlation functions can be fed into various output-only modal identification algorithms. The proposed methodology is validated using numerical simulations. It is found that the simulation results closely match the identified parameters based on synchronous data.

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