Transcript No Slide Title

Vibrationdata
Shock and Vibration in
Launch Vehicles
By Tom Irvine
AMERICAN INSTITUTE OF AERONAUTICS AND ASTRONAUTICS
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Vibrationdata
Website
www.vibrationdata.com
Username: vibration
Password: quake
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Shock & Vibration Analysis Areas
Structural
Dynamics
Vibrationdata
Environments
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Structural Dynamics
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Vibrationdata
Analyze natural frequencies and mode shapes of the launch vehicle
and payload system
Coupled-loads analysis to determine payload stresses and deflections
Verify that the control system algorithm accounts for vehicle bodybending frequency
Verify that the launch vehicle and payload can withstand seismic and
wind loading while the vehicle is on the launch pad
Tools: finite element method and modal testing
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Pegasus XL 9.0 Hz Bending Mode
Vibrationdata
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Environments
Vibrationdata
The launch vehicle avionics and the payload must be designed
and tested to withstand shock and vibration environments.
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Transportation and Shipping Shock
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Motor Ignition Shock
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Launch Vibroacoustics
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Pyrotechnic Shock from Stage Separation Events
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Aerodynamic Flow Excitation
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Motor Pressure Oscillation
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Flight Anomalies
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Environment Flow Chart
Vibrationdata
Derive Environments
using Empirical Data
Write Test Plan
Test Components and Payload
Launch the Vehicle
Post-flight Data Analysis
Check for Anomalies
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Environments Analysis Tools
Vibrationdata
Empirical methods are the primary tools for predicting shock
and vibration levels
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Extrapolate levels from test data
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Static fire test of a rocket motor
Stage separation test
Wind tunnel test
•
Extrapolate levels from flight data
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Vibrationdata
Typical Specification Formats
Environment
Format
Sine Vibration
Sine Sweep
Random Vibration
Power Spectral Density
Shock
Shock Response Spectrum
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Environments Analysis References
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Vibrationdata
MIL-STD-1540D - Product Verification Requirements for Launch, Upper-Stage, and
Space Vehicles
MIL-HDBK-340A - Test Requirements for Launch, Upper-Stage, and Space Vehicles
MIL-STD-810F - Test Standard for Environmental Engineering Considerations and
Laboratory Tests
NASA CR 116406 - Aerospace System Pyrotechnic Shock Data
Laganelli, A.L., Wolfe, H.F., "Prediction of Fluctuating Pressure in Attached and
Separated Turbulent Boundary Layer Flow," AIAA Paper AIAA-89-1064, April 1989.
V. Alley and S. Leadbetter, Prediction of Natural Vibrations of Multistage Launch
Vehicles, AIAA Journal.
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Environments Analysis References
(continued)
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Vibrationdata
D. Steinberg, Vibration Analysis for Electronic Equipment, Wiley-Interscience,
New York, 1988.
and many others
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Development Tests
Vibrationdata
Perform development tests to characterize shock and vibration
environments
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Linear Shape Charge Test
Vibrationdata
Derive shock environment from accelerometer measurements.
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Motor Static Fire Test
Vibrationdata
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Flight Vibration Derivation
Vibrationdata
Derive flight vibration environment using empirical techniques.
Vibration depends on vehicle geometry, material, Mach number,
air density and flow regime.
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Aerodynamic Flow Vibration:
Attached Flow
Vibrationdata
Cone-Cylinder Geometry,
Transonic Shockwave
Oscillation with Attached Flow
Cone-Cylinder Geometry,
Supersonic, Attached Flow
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Aerodynamic Flow Vibration:
Compression Corner
Vibrationdata
Cone-Cylinder Geometry with
Separated Flow near
Compression Corner, Transonic
Cone-Cylinder Geometry with
Separated Flow near
Compression Corner and
Shockwaves, Supersonic
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Aerodynamic Flow Vibration:
Boat-tail
Vibrationdata
Shockwave Oscillation with Boattail Induced Separation, Transonic
Attached Flow with Boat-tail
Induced Separation and
Shockwave Oscillation,
Supersonic
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L1011 & Pegasus
Vibrationdata
Aerodynamic flow interaction between L1011 and Pegasus
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Testing
Vibrationdata
Avionics components and payload must be tested to the resulting
shock and vibration environments.
Components include
• Flight Computer
• Inertial Navigation System (INS)
• Telemetry Transmitter
• C-Band Transponder
• Antennas
• Battery Boxes
• Flight Termination System
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Shaker Table Test
Vibrationdata
Apply base excitation to the test item.
Verify that the item can withstand the
vibration environment.
The test item should be powered and
monitored during the vibration test.
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Vibrationdata
Flight Accelerometer Data
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Vibrationdata
SUBORBITAL ROCKET VEHICLE
FLIGHT ACCELEROMETER DATA
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15
ACCEL (G)
10
5
0
-5
-10
-15
-20
0
5
10
15
20
25
30
35
40
45
50
55
60
65
TIME (SEC)
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Time-Domain Curve-Fitting
Vibrationdata
Demonstrate a time-domain, curve-fitting method for analyzing
accelerometer data.
The method is innovative in that it uses random number generation to
determine the characteristics of the measured data.
These characteristics include the amplitude, frequency, phase angle,
and damping ratio of the signal's components.
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Vibrationdata
Variables
y(t)
Amplitude Function
A
Amplitude constant
wn
Natural frequency
x
Damping ratio
f
Phase angle
t
Time
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Candidate Functions for Data Curve-fit
Vibrationdata
Pure Sine
y(t)  A sin( w n t  f)
Series of Pure Sinusoids
n
y(t)   A sin( w t  f )
i
i
i
i 1
Lightly-damped Sine
y(t)  A exp( xwn t) sin( wn t  f)
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Pegasus
Vibrationdata
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Example 1: Pegasus Drop Transient
Vibrationdata
Consider the Pegasus launch vehicle mounted underneath an L-1011. The most
significant event for the payload is the drop transient from the carrier aircraft.
The Pegasus vehicle is like a free-free beam subjected to an initial displacement
that varies along its length.
During the five-second free-fall interval, the initial strain energy is released, causing
the Pegasus vehicle to experience a damped, transient oscillation.
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Vibrationdata
Example 1: Damped Sine Data
MEASURED DROP TRANSIENT AT PAYLOAD INTERFACE
OF A PEGASUS LAUNCH VEHICLE
NORMALIZED ACCELERATION
1.5
Synthesized Data
Flight Data
1.0
0.5
0
-0.5
-1.0
-1.5
-0.5
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
TIME (SEC)
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Pegasus User’s Guide
Vibrationdata
To minimize coupling of the payload bending modes with
the launch vehicle first bending mode, the first fundamental
lateral frequency must be greater than 20 Hz, cantilevered
from the base of the spacecraft, excluding the spacecraft
separation system.
(octave rule)
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Example 1: Numerical Results
Vibrationdata
y(t)  A exp( xwn t) sin( wn t  f)
Amplitude
A
0.92
Natural
Frequency
fn
9.56 Hz
Damping
x
1.2%
Phase
f
6.108 rad
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Example 2: M57A1 Motor Resonance
Vibrationdata
The M57A1 motor is a solid-fuel motor originally developed as a
third stage for the Minuteman missile program.
This motor has since been used on a variety of suborbital vehicles,
such as target vehicles.
The M57A1 has a distinct pressure oscillation.
The oscillation frequency sweeps downward from 530 Hz to 450
Hz over a 16-second duration.
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Minuteman II Stage III (M57A1)
Vibrationdata
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Vibrationdata
Example 2: Frequency Variation
FREQUENCY vs. TIME SUBORBITAL TARGET VEHICLE
M57A1 MOTOR RESONANCE AVIONICS MODULE SKIN
530
FREQUENCY (Hz)
520
510
500
490
480
470
460
450
440
128
130
132
134
136
138
140
142
144
146
148
TIME (SEC)
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Vibrationdata
Example 2: Time History
SUBORBITAL TARGET VEHICLE
M57A1 MOTOR OSCILLATION AVIONICS MODULE SKIN
4
Synthesized Signal
Measured Data
3
ACCEL (G)
2
1
0
-1
-2
-3
-4
138.00
138.02
138.04
138.06
138.08
138.10
TIME (SEC)
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Vibrationdata
Example 2: Numerical Results
y(t)  A sin( wn t  f)
Amplitude
A
0.82 G
Oscillation
Frequency
fn
488.2 Hz
Phase
f
1.048 rad
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Example 3.
Flight Anomaly – TVC System
Vibrationdata
LAUNCH VEHICLE
CONTROL SYSTEM OSCILLATION AT STAGE 1 BURN-OUT
4
3
ACCEL (G)
2
1
0
-1
-2
-3
-4
87.0
87.5
88.0
88.5
89.0
89.5
90.0
90.5
91.0
91.5
92.0
92.5
TIME (SEC)
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Vibrationdata
Example 3: Segment
LAUNCH VEHICLE
CONTROL SYSTEM OSCILLATION AT STAGE 1 BURN-OUT
4
Synthesized Data
Flight Data
3
ACCEL (G)
2
1
0
-1
-2
-3
-4
90.0
90.5
91.0
TIME (SEC)
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Example 3: Numerical Results
Vibrationdata
n
y(t)   A sin( w t  f )
i
i
i
i 1
Parameter
Amplitude
Oscillation Frequency
Phase
Dominant
Signal
Harmonic
1.5 G
0.71 G
12.5 Hz
37.4 Hz
0.854 rad
3.672 rad
The data reveals the dominant forcing frequency and a 3X
harmonic. This data could be used to troubleshoot the anomaly.
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Example 4: Launch Vehicle Transportation
Vibrationdata
A suborbital launch vehicle is being integrated at a missile assembly
building (MAB) at Vandenberg AFB.
The distance from the MAB to the launch pad is 20 miles. The
assembled launch vehicle will be mounted horizontally on a custom
trailer for transportation from the MAB to the pad.
The launch vehicle must withstand the lateral loading that occurs as
the tractor-trailer crosses over potholes, railroad tracks, and joints at
bridges.
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Vibrationdata
Example 4: Time History
VAFB TRANSPORTATION TEST
LAUNCH VEHICLE STAGE 2 VERTICAL
1.0
0.4
0.2
0.8
0
0.6
-0.2
0.4
Synthesized Signal, Right Scale
-0.4
0.2
-0.6
0
-0.8
-0.2
-1.0
0
2
4
6
8
10
12
ACCEL (G)
ACCEL (G)
Measured Data, Left Scale
-0.4
14
TIME (SEC)
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Example 4: Synthesis Equation
Vibrationdata
n
y(t)   Ai exp( xwiˆt) sin( wiˆt  fi )
i 1
Steps:
Synthesize the first damped sinusoid.
Subtract it from the signal.
Synthesize the next damped sinusoid.
Repeat these steps until n sinusoids are synthesized.
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Vibrationdata
Example 4: Numerical Results
Component
Amplitude
(G)
Frequency
(Hz)
Phase
(rad)
Damping
Delay
(sec)
1
0.109
5.22
4.925
0.5%
0.776
2
0.109
5.06
6.311
1.2%
0.881
3
0.040
2.53
5.979
0.6%
0.078
4
0.045
2.64
0.929
1.3%
4.638
5
0.012
1.18
0.517
0.2%
1.438
The synthesis consisted of 30 damped sinusoids. Only the top five are shown for brevity.
The sinusoids near 5 Hz were due to launch vehicle bending modes. The spectral
components near 1 Hz and 2.5 Hz were primarily due to the trailer suspension, with the
launch vehicle acting as a rigid-body.
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Vibrationdata
Example 4: Fourier Transform
FOURIER TRANSFORM MAGNITUDE
TRANSPORATION VIBRATION LAUNCH VEHICLE STAGE 2 VERTICAL
0.04
ACCEL (G)
0.03
0.02
0.01
0
0
1
2
3
4
5
6
7
8
9
10
FREQUENCY (Hz)
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Conclusion
Vibrationdata
Characterization of shock and vibration environments, as
well as structural dynamics, helps ensure mission
success.
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