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>

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

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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

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

AAE 450 Spring 2008

Backup Slide 1 Thermal Conductivity across tank wall

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Ta(function of

Altitude)

Tf(Foam interface

temp)Tl

(LN2 temp)

Ambient (Air)

Foam Insulation

TankWall

Liquid Nitrogen

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

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