Psd Synthesis Example

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   1POWER SPECTRAL DENSITY SYNTHESIS EXAMPLE By Tom Irvine Email: August 12, 2005 0.0010.010.11010010002000FREQUENCY (Hz)    A   C   C   E   L   (   G    2    /   H  z   ) POWER SPECTRAL DENSITY MIL-STD-1540C ACCEPTANCE LEVEL 6.1 GRMS  Figure 1. Table 1. MIL-STD-1540C, PSD, 6.1 GRMS Frequency (Hz) Accel (G^2/Hz) 20 0.0053 150 0.04 600 0.04 2000 0.0036   2Example 1 Synthesize a 10 second time history to satisfy the PSD. Enter the coordinates in Table 1 into an ASCII text file called: The acceleration may be separated from the corresponding frequency by a space or tab. Run psdgen.exe version 3.0. The input file is: Call the output acceleration file: accel_10.dat The names of the output velocity and displacement are unimportant for this exercise. The duration is 10 seconds. The sample rate is 20000 samples per second. The resulting time history is plotted in Figure 1. The histogram is shown in Figure 2. Note that the histogram is a bell-shaped curve.  Next run poweri_lite.exe version 3.1. The input file is: accel_10.dat The output file is: psd_10.dat Select 8192 samples per segment, which yields 48 statistical-degrees-of-freedom. You may also experiment with other values. In each case, there are trade-offs between spectral line bandwidth and statistical accuracy. Select mean removal and the Hanning window, although these parameters are unimportant for this example. The resulting PSD is shown in Figure 3 along with the specification.   3 -150-100-500501001500246810TIME (SEC)    A   C   C   E   L   (   G   ) SYNTHESIZED ACCELERATION TIME HISTORY 10 SECOND DURATION OVERALL LEVEL = 6.1 GRMS  Figure 1.   4 050001000015000-30-25-20-15-10-5051015202530 ACCEL (G)    C   O   U   N   T   S HISTOGRAM SYNTHESIZED ACCELERATION TIME HISTORY 10 SECOND DURATION OVERALL LEVEL = 6.1 GRMS  Figure 2. The amplitude step is 1 G for the histogram.
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