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Vibrationdata 1 Unit 8 Waterfall FFT. Vibrationdata 2 Terrier Black Brant The Terrier-Black Brant is a two-stage, solid propellant, rail launched, guided,

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Presentation on theme: "Vibrationdata 1 Unit 8 Waterfall FFT. Vibrationdata 2 Terrier Black Brant The Terrier-Black Brant is a two-stage, solid propellant, rail launched, guided,"— Presentation transcript:

1 Vibrationdata 1 Unit 8 Waterfall FFT

2 Vibrationdata 2 Terrier Black Brant The Terrier-Black Brant is a two-stage, solid propellant, rail launched, guided, fin-stabilized sounding rocket. This spin-stabilization is clearly visible in the video posted at:

3 Vibrationdata 3 Free-Free Beam, Fundamental Bending Mode Launch vehicles behave somewhat as free-free beams in flight. Excitation sources include high-altitude winds, aerodynamic buffeting, thrust, control systems, etc.

4 Vibrationdata Waterfall FFT Terrier-Black Brant The accelerometer data reveals the fundamental bending mode frequency. The frequency begins at about 8 Hz and then sweeps up to 13.2 Hz as propellant mass is expelled. The spectral peaks at 5 Hz are due to vehicle imbalance at the induced roll rate. This is a 2X of the true roll rate at 2.5 Hz. Frequency (Hz) Time (sec)

5 Vibrationdata 5 Orion Launch Abort System PA-1 Test

6 Vibrationdata 6 Pad Abort 1 Test Configuration Boilerplate Crew Module Abort Motor Jettison Motor Forward Interstage Attitude Control Motor (ACM) Nose Cone Aero Closeout Adapter Cone Raceway Aft Interstage

7 Vibrationdata Waterfall FFT LS051V Fwd LAS (Nose cone) Lo Freq Accelerometer, Tangential axis # 2 The fundamental body-bending frequency begins near 8 Hz and gradually increases over time due to the decrease in propellant mass. Frequency (Hz) Time (sec)

8 Vibrationdata The abort motor had an oscillation which swept downward in frequency from 685 to 670 Hz during the tail-off. This resonance is considered to be a phenomenon of the low pressure end of burn gas dynamics of the reverse flow motor. Frequency (Hz) Time (sec) Waterfall FFT Vibration at S&A Location LS045V

9 Vibrationdata Solid rocket motor with “organ pipe-like” combustion cavities. Standing pressure waves set-up in the cavities, driven by vortex-shedding, etc.

10 Vibrationdata Waterfall FFT Solid Motor Oscillation Suborbital Vehicle “A” Flight Accelerometer Data, Motor Adapter Bulkhead Longitudinal Axis Frequency (Hz) Time (sec) The pressure oscillation sweeps downward from 520 to 450 Hz.

11 Vibrationdata Waterfall FFT Solid Motor Oscillation Suborbital Vehicle “B” Flight Accelerometer Data, Motor Adapter Bulkhead Longitudinal Axis Frequency (Hz) Time (sec)

12 Vibrationdata Frequency (Hz) Time (sec) Waterfall FFT Solid Motor Oscillation Static Test File Data, Forward Motor Dome The pressure oscillation sweeps downward from 700 to 550 Hz, immediately after motor ignition. A different motor…

13 Vibrationdata Shepard Tones Ascending and Descending by Dutch artist M. C. Escher

14 Vibrationdata Waterfall FFT Shepard Tone Frequency (Hz) Time (sec) A Shepard tone, named after Roger Shepard, is a series of sweeping sine tones, with frequencies spaced at one octave intervals.

15 Vibrationdata 15 Exercises Plot a Waterfall FFT for each of the following files: terrier_black_brant_2KHz_lpf_x.txt solid_motor_flight.txt Fwd_Dome_ignition.txt Orion_PA1_LS51v.txt Generate a Shepard Tone using the parameters of your choice. Then plot the Waterfall FFT.


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