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Reliability Assessment, Allocation and Optimization for Launching Systems

Raouf, Naser | 2016

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 48880 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Pourtakdoost, Hossein
  7. Abstract:
  8. The subject of systemic reliability assessment, allocation and optimization as well as structural reliability (SR) of a two stage solid fuel launch vehicle (LV) is investigated. In this regards, first the LV reliability block diagram is broken-down into appropriate subsystems. Subsequently the total LV system reliability is determined assuming the subsystems reliability. In addition, using a hybrid GA-PSO algorithm optimal subsystems redundancy levels, reliabilities as well their type are determined to simultaneously maximize the total reliability while minimizing the LV cost (weight) as a constraint. While the reliability and cost of subsystems are not precisely known, the total LV reliability and cost will be uncertain. In this respect, an uncertainty analysis is performed to study the propagation of subsystem uncertainties in the total LV cost and reliability. Structural reliability analysis (RA) is another focal point of this dissertation that entails looking into static RA of the solid rocket motor case as well as the time varying structural reliability of the total LV. SR of a solid rocket motor (SRM) case with ellipsoidal cap is undertaken in this research, where analytical and finite element results verified the fact that the maximum stress occurs at connection line between the SRM cylindrical casing and its cap. In this sense, an explicit limit state function (LSF) is proposed to determine the SRM structural reliability using various reliability methods such as FOSM, FORM, SORM,… whose results are verified via Monte Carlo simulation (MCS). Moreover, SRM key design variable affecting its SR are identified using a sensitivity analysis. In addition for the motor part, SR of the control jet vanes exposed to the exhaust nozzle gases and erosion/ablation are considered. The last part of the dissertation is concentrated on RA and SR of the LV structure with and without the aeroeleastic effects whose results will be of practical value for reliability based design of the LV structure. As the LV is intrinsically subject to stochastic random loadings in flight, its SR will also be time- varying. Therefore, the process of LV time-varying SR computation is detailed out with elastic and aeroeleastic considerations using FORM reliability method that is verified with MCS as well. In addition, the sensitivity of the LV SR against some design random variables is analyzed to identify the important LV structural design parameters affecting its reliability. The results in general show that LV structural reliability decreases with flight time
  9. Keywords:
  10. Reliability ; Structure ; Optimization ; Allocation Problem ; Launch Vehicle ; Aeroelasticity

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