AE301WingVibration17SupplementDataProcessing - These peaks...

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1.7. Supplement for Vibrating Wing Data Processing The calculation of damping involves all aspects of the plucking experiment. From Logarithmic Decrement Theory (see §1.8.) This formula requires the calculation of many parts. A. Calculating the ratios of amplitudes Two important files are obtained from the plucking experiment. For the (t,V) file, the first column is time and the second is accelerometer voltage. A plot of (x,y)= (t,V) should yield a decaying wave form similar to what was observed on the LabVIEW display. This wave should be analyzed by ignoring the first portion of the wave that is dominated by hammer strike effects and a messy looking oscillation ( you will have a clean transient if DAQ is started just after the hammer strike ). Time-window a portion of the wave that follows a classical pattern of a sine wave that is decaying in amplitude. This ‘clean’ portion of the wave should have well defined peaks in successively smaller magnitude.
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Unformatted text preview: These peaks can be sampled (MATLAB code, PeakLocationByMouse.m) and used in the logarithmic decrement theory for calculation of the damping. . In the above equation, the n is the number of cycles separating any two selected maxima. Choosing an initial peak as j=1 , it would have the largest y . Then successive peaks, n=[1,2,3. .] , have lower y as n increases as an integer. We could curve fit the (n, lny) curve and determine the best slope, C 1 . This is then used to calculate the damping ratio by finding the critical damping ratio. B. Calculating critical damping The critical damping is needed for the calculation of the damping coefficient. The natural frequency for a single mass case is obtained by examining the second data file, (f,A) , that has frequency in the first column and amplitude in the second column. The natural frequency is where the amplitude is a maximum. Be sure to convert to [rad/sec] units for frequency....
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This note was uploaded on 02/07/2011 for the course AE/ME 301 taught by Professor Lafleur during the Spring '11 term at Clarkson University .

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AE301WingVibration17SupplementDataProcessing - These peaks...

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