| Summary: | Thesis (MSc)--Stellenbosch University, 2015. === ENGLISH ABSTRACT: Recent studies have shown that considering proof test data in a Reliability
Based Design Optimization (RBDO) environment can result in design improvement.
Proof testing involves the physical testing of each and every component
before it enters into service. Considering the proof test data as part of the
RBDO process allows for improvement of the original design, such as weight
savings, while preserving high reliability levels.
Composite Over-Wrapped Pressure Vessels (COPV) is used as an example
application of achieving weight savings while maintaining high reliability levels.
COPVs are light structures used to store pressurized fluids in space shuttles, the
international space station and other applications where they are maintained at
high pressure for extended periods of time. Given that each and every COPV
used in spacecraft is proof tested before entering service and any weight savings
on a spacecraft results in significant cost savings, this thesis put forward an
application of RBDO that accounts for proof test data in the design of a COPV.
The method developed in this thesis shows that, while maintaining high
levels of reliability, significant weight savings can be achieved by including
proof test data in the design process. Also, the method enables a designer
to have control over the magnitude of the proof test, making it possible to
also design the proof test itself depending on the desired level of reliability for
passing the proof test.
The implementation of the method is discussed in detail. The evaluation
of the reliability was based on the First Order Reliability Method (FORM)
supported by Monte Carlo Simulation. Also, the method is implemented in a
versatile way that allows the use of analytical as well as numerical (in the form
of finite element) models. Results show that additional weight savings can be
achieved by the inclusion of proof test data in the design process. === AFRIKAANSE OPSOMMING: Onlangse studies het getoon dat die gebruik van ontwerp spesifieke proeftoets
data in betroubaarheids gebaseerde optimering (BGO) kan lei tot 'n
verbeterde ontwerp. BGO behels vele aspekte in die ontwerpsgebied. Die
toevoeging van proeftoets data in ontwerpsoptimering bring te weë; die toetsing
van 'n ontwerp en onderdele voor gebruik, die aangepaste en verbeterde
ontwerp en gewig-besparing met handhawing van hoë betroubaarsheidsvlakke.
'n Praktiese toepassing van die BGO tegniek behels die ontwerp van drukvatte
met saamgestelde materiaal bewapening. Die drukvatontwerp is 'n ligte
struktuur wat gebruik word in die berging van hoë druk vloeistowwe in bv.
in ruimtetuie, in die internasionale ruimtestasie en in ander toepassings waar
hoë druk oor 'n tydperk verlang word. Elke drukvat met saamgestelde materiaal
bewapening wat in ruimtevaartstelsels gebruik word, word geproeftoets
voor gebruik. In ruimte stelselontwerp lei massa besparing tot 'n toename in
loonvrag.
Die tesis beskryf 'n optimeringsmetode soos ontwikkel en gebaseer op 'n
BGO tegniek. Die metode word toegepas in die ontwerp van drukvatte met
saamgestelde materiaal bewapening. Die resultate toon dat die gebruik van
proeftoets data in massa besparing optimering onderhewig soos aan hoë betroubaarheidsvlakke
moontlik is. Verdermeer, die metode laat ook ontwerpers
toe om die proeftoetsvlak aan te pas om sodoende by ander betroubaarheidsvlakke
te toets.
In die tesis word die ontwikkeling en gebruik van die optimeringsmetode
uiteengelê. Die evaluering van betroubaarheidsvlakke is gebaseer op 'n eerste
orde betroubaarheids-tegniek wat geverifieer word met talle Monte Carlo
simulasie resultate. Die metode is ook so geskep dat beide analitiese sowel
as eindige element modelle gebruik kan word. Ten slotte, word 'n toepassing getoon waar resultate wys dat die gebruik van die optimeringsmetode met die
insluiting van proeftoets data wel massa besparing kan oplewer.
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