Aircraft structural safety: Effects of explicit and implicit safety measures and uncertainty reduction mechanisms
Başlık çevirisi mevcut değil.
- Tez No: 400279
- Danışmanlar: DR. RAPHAEL T. HAFTKA
- Tez Türü: Doktora
- Konular: Uçak Mühendisliği, Mühendislik Bilimleri, Aeronautical Engineering, Engineering Sciences
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2006
- Dil: İngilizce
- Üniversite: Unıversıty Of Florıda
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
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Özet (Çeviri)
Aircraft structural safety is achieved by using different safety measures such assafety and knockdown factors, tests and redundancy. Safety factors or knockdown factorscan be either explicit (e.g., load safety factor of 1.5) or implicit (e.g., conservative designdecisions). Safety measures protect against uncertainties in loading, material andgeometry properties along with uncertainties in structural modeling and analysis. The twomain objectives of this dissertation are: (i) Analyzing and comparing the effectiveness ofstructural safety measures and their interaction. (ii) Allocating the resources for reducinguncertainties, instead of living with the uncertainties and allocating the resources forheavier structures for the given uncertainties.Certification tests are found to be most effective when error is large and variabilityis small. Certification testing is more effective for improving safety than increased safetyfactors, but it cannot compete with even a small reduction in errors. Variability reductionis even more effective than error reduction for our examples.The effects of structural element tests on reducing uncertainty and the optimalchoice of additional knockdown factors are explored. We find that instead of usingimplicit knockdown factors based on worst-case scenarios (current practice), using testdependentexplicit knockdown factors may lead weight savings. Surprisingly, we findthat a more conservative knockdown factor should be used if the failure stressesmeasured in tests exceeds predicted failure stresses in order to reduce the variability inknockdown factors generated by variability in material properties.Finally, we perform probabilistic optimization of a wing and tail system underlimited statistical data for the stress distribution and show that the ratio of theprobabilities of failure of the probabilistic design and deterministic design is not sensitiveto errors in statistical data. We find that the deviation of the probabilistic design anddeterministic design is a small perturbation, which can be achieved by a smallredistribution of knockdown factors.
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