NASA Technical Reports Server (NTRS) 19930017742: Probabilistic structural analysis for nuclear thermal propulsion

6 Pages·0.16 MB·English

by  NASA Technical Reports Server (NTRS)

r 1
Probabilistic Structural Analysis for
Nuclear Thermal Propulsion
Dr. Ashwin Shah
Sverdrup Technology
(presented by J.R. Stone, LeRCINPO)
CERTIFICATION OF SPACE NUCLEAR PROPULSION SYSTEM NOZZLE
WITH ASSURED RELIABILITY
OBJECTIVE: To develop a metliodology to certify Space Nuclear Propulsion System Nozzle
wlth assured relialJility
470 NI' 'ITM 92
SPFICE NUCLERR PRUPULSIUII SYSILPI iiom I . PHI-I IMINWY FE MODEL
Certification of Space Nuclear Propulsion System Nozzle
with Assured Reliability
47 I N'I'I' Technology
ADVANTAGE OF PROBABILISTIC STRUCTURAL ANALYSIS
j - - .
- 1 Case I . Wider scalier in stress and streriglh
I
c 11,f ',,*/ ,
Safety factor .- 6W40 = 1.5
I'IOIO€BNASIBWIL I 1) I / Reliability -= 0.99 II
FUNCTION ~ I' Reliability IS small bccausc
1- -L,.2,. I -.I shaded overlapping area '
< fl 40 IO 110 is large due to wider
Scatter in strcss
w 1 scatter
'-*
I ' - I shaded overlapping area
AI Id; is small due to narrow
c
Scatter in stress scatter
e
Space Nuclear Prol)ulsion System Nozzle
Uncertainties in thc Random Variables
.-.. ... .- . -------L--:- . - - ._-- -.
Randoirr Variable Coetficieiit of Variation Distribution
IStaiidnrtl Devintiriii
~ _L_
NlI'. 'l'ecillllllopy 472
6% 66.7 70
F re q ti e 11c y (ti Iz )
Probability of the natural frequency being less than 66.7 Hz = 0.999
Therefore, to achieve a reliability of 0.999,t he frequency of exciting force
should be larger than 66.7 Hz to avoid resonance.
Sensitivity of prirriitive variable uncertainties
SNPS nozzle natural frequency
Variabes controlling the scatter of natural frequency within 66.7 Hz are
thickness, niodulus of elasticity and mass density. Therefore a tighter tolerance
for the thickness and material properties are essential.
NP 'IZM 92 37 3 N'I'P Technology
SNPS Nozzle
CDF of Effective Stress in the shell
Sensitivity of priniitive variable uncertainties
SNPS nozzle - shell stress=
x -
Geometry Coord
77
'.OO
Geometry Z . Coord
T~v. Inside surface
- Temp. Layer 2
.-A-
t
j; 0 50 Teriip. Layer 3
C
u)
Temp. Layer 4
Temp. Outside surface
0 no Modulus of elasticity
0 01 0 339
PI ob,, 1111 II y
TO control tlie stresses in the stiell airtl ncliieve Iiiylier reliability. the uricertointies in the inside
surface ternr~cratures liould be redtrcetl.
Nil'. I'echnology 474 NP-'IlM-92
Work in pregress:
0 Modelling of NERVA base tnodel with coolant tubes
0 Development of pseudo-super eletiient to reduce the size of the gloabal
model to achieve computatioiial speed and accuracy
475 N'I'P: lichnology