CONCLUSIONS The RD technique has been introduced and used on simulated modal data in order to compare the bias on the FRF estimates estimated from RD functions with the bias from the traditional Welch based FRF estimates. The RD based technique is buffer oriented like Welch, but is based on the same idea as Blackman-Tukey, i.e. the FRF is estimated by taking a Fourier transform of the bias-free time domain function. Therefore, as expected, the RD based FRF estimation shows a significantly lower bias for the same buffer size (data segment size) than the Welch based FRF estimation. On the other hand, the RD based FRF estimates has larger random errors. These random errors can be reduced by introducing a window on the time domain function; this is to be investigated further in future investigations. Further, RD-based FRF estimates might have a special value in cases where effects of small non-linearities are to be studied. REFERENCES [1] Welch, P.: The Use of Fast Fourier Transform for the Estimation of Power Spectra: A Method Based on Time Averaging Over Short, Modified Periodograms, IEEE Trans. On Audio and Electroacoustics, 1967, AU-15, pp. 70-73. [2] Brandt, A.: Noise and Vibration analysis – Signal Analysis and Measurement Procedures, Wiley, 2011. [3] Bendat, J. & Piersol, A. G.: Random Data: Analysis and Measurement Procedures, 4th Ed., Wiley Interscience, 2010. [4] Brincker, R. and Brandt, A.: Random Decrement Signal Processing of Modal Impact Test Data, Proc 28th International Modal analysis Conference, Jacksonville, Florida, USA, Feb. 1-4, 2010. [5] Antoni, J. & Schoukens, J.: Optimal Settings for Measuring Frequency Response Functions with Weighted Overlapped Segment Averaging, IEEE Transactions On Instrumentation and Measurement, 2009, 58, pp. 3276-3287. [6] Rasmussen, J.C. and Brincker, R.: Estimation of Frequency Response Functions by Random Decrement. Proc 14th International Modal analysis Conference, Dearborn, Michigan, USA, Feb. 12-15, 1996, pp. 246-252. [7] Brincker, R. and Rasmussen, J.C.: Random Decrement Based FRF Estimation. Proc 15th International Modal analysis Conference, Orlando, Florida, USA, Feb. 3-6, 1997, pp. 1571-1576. [8] Rasmussen, J.C. Modal Analysis Based on the Random Decrement Technique. Ph.D. Thesis, Aalborg University, Department of Building Technology and Structural Engineering, 1997. 502
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