aae 450 spring 2008 steven (“cj”) hiu 02/20/2008 structural analysis: overpressure safety mat...
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AAE 450 Spring 2008
Steven (“CJ”) Hiu 02/20/2008
Structural Analysis: Overpressure Safety
MAT & FAM Coder – Structures
CAD – Tanks, Intertank Couplers
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AAE 450 Spring 2008
Overpressure Safety Systems Purpose – prevent damage to rocket from
overpressure (tanks, lines, injector) Sensors
– Pressure Transducers, strain gauges
Actuators – Pressure Relief Valves– Burst Disk (single use) – usually rated to high psi
Use – on the ground, in gondola, during firing Feed Lines Oxidizer Tank (not critical, feed line may suffice) Pressurant Tank – vital, cryo LN2 subject to heating LITVC (similar to oxidizer)
Structures<2>
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AAE 450 Spring 2008
Thermal Analysis of Pressurant Tank Assume constant velocity
(terminal rise) Thermal Analysis based on
conduction Conservative (Ignore phase
change, no boundary layer) Findings
– ~30 K rise over 30 km– Pressure rises above critical
tank allowable
Solutions– Relief Valve on pressurant
tank– Umbilical on Gondola
Structures<3>
0 0.5 1 1.5 2 2.5 375
80
85
90
95
100
105
110
time (hours)
Tem
pera
ture
(K
)
Plot of Pressurant Temperature vs Time
200g
1 kg5 kg
0 0.5 1 1.5 2 2.5 36
6.5
7
7.5
8
8.5x 10
6
time (hours)
Pre
ssur
e (P
a)
Plot of Pressurant Pressure vs Time
200g
1 kg5 kg
Max Allowable Stress
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References Hart, G H, Grounding The Space Shuttle, NASA’s Foam
Insulation Problem, www.insulation.org/articles/article.cfm?id=IO51204
http://www.efunda.org – Thermal properties of Aluminum http://www.nist.gov/srd/fluids.htm - Thermal properties of
Liquid Nitrogen
Acknowledgements Many thanks to all FAM team members for their
dedication and perseverance
AAE 450 Spring 2008 <4>Structures
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AAE 450 Spring 2008
Backup Slide 1 Thermal Conductivity across tank wall
Structures<5>
Ta(function of
Altitude)
Tf(Foam interface
temp)Tl
(LN2 temp)
Ambient (Air)
Foam Insulation
TankWall
Liquid Nitrogen
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Backup Slide 2– Thermal Conductivity Values
– Foam – assume constant f
0.161 BTU/hr.ft^2.F (1 in.) 0.023 W/m^2K
– Aluminum – Al function of temperature
AAE 450 Spring 2008Structures
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AAE 450 Spring 2008 <7>
Backup Slide 3 Specific Heat of Liquid Nitrogen, 6 MPa
AAE 450 Spring 2008 <7>
Structures
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Backup Slide 4
AAE 450 Spring 2008 <8>
0 0.5 1 1.5 2 2.5 3270
272
274
276
278
280
282
284
286
288
290
time (hours)
Tem
pera
ture
(K)
Plot of Ambient Temperature vs Time
0 0.5 1 1.5 2 2.5 30
5
10
15
20
25
30
time (hours)
heig
ht (
km)
Plot of Height vs Time