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- Uncertainty
Quantification Using Evidence Theory
The mathematical frameworks of quantifying uncertainty in an engineering structural system are studied. And as an alternative to the classical probability theory, evidence theory is proposed for reliability analyses of engineering structural systems. Robust and efficient computational methodologies of using evidence theory are developed for the general informative situation.
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- Stochastic
Modeling And Robust Design Of Structures
One of the important issues in uncertainty analysis is to find an effective way for propagating uncertainty through the system. In this paper, the polynomial chaos expansion (PCE) was selected since this approach can reduce the computational effort in large-scale engineering design applications. An implementation of PCE which includes different probability distributions is the focus of this paper. Two existing techniques, a generalized PCE algorithm and transformation methods, are investigated and verified for their accuracy and efficiency for non-normal random variable cases. A highly nonlinear structural model of an uninhabitated joined-wing aircraft and a three pin-connected rod structure are used for demonstrating the method.
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- Flutter Prediction Of An Aircraft Wing With Multiple Store Configurations
A multidisciplinary optimization procedure is described to delay the occurrence of store-induced flutter of an aircraft wing/tip store configuration. A preliminary design procedure was developed to enhance the performance characteristics of aircraft wing model in the transonic Mach number regime. The research used the Transonic Small Disturbance (TSD) Theory to better understand the dynamic aeroelastic phenomena and factors that effect the onset of flutter and store induced Limit-Cycle Oscillation (LCO) in the transonic regime. A wing/tip store configuration with the store center of gravity (c.g.) located at the 50% aerodynamic tip chord was chosen for structural optimization. The aircraft wing structural weight was chosen as the objective function with constraints on natural frequency, stress and flutter. The addition of the flutter constraints resulted in a negligible increase in flutter speed when compared with the flutter speed obtained from optimization with only frequency and stress constraints.
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- Metal
Forming
Complex forgings are typically forged at high temperatures and then subjected to a cooling process. The final part dimensions are affected by the forging process parameters and process conditions, such as preform design, die velocity, lubrication, initial temperature and cooling parameters. Good diagnostic information for these design parameters in the metal forming process are obtained from finite element based simulations. Optimizing these parameters aids in minimizing the distortions in the final part, thus increasing the efficiency in terms of time, material and man-hours.
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- Thermal
Protection System For Future Spacecraft
Thermal Protection Systems (TPS) design for a spacecraft operating in extreme environments of thermal and acoustic loading is of significant importance for space missions. High re-entry temperatures cause thermal stresses in the TPS material which can be reduced if the TPS is free to expand (loose fitting). However, the acoustic vibrations cause the loosely fitted TPS to get excited and fail due to fatigue, or resonance. Therefore, the design of a TPS is driven by these two opposing criteria, thermal stresses, and acoustic vibrations. This research involves evolving the shape of a TPS configuration using topology optimization that satisfies thermal loads and does not get excited in a certain frequency range.
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- Multi-Disciplinary Designing Of Undersea Weapons
Undersea weapons such as torpedoes need to perform optimally under different operational and loading conditions. CDOC employs simulation based design methodology for the development of robust and reliable undersea weapons. CDOC is currently conducting research on the cavity shape optimization and a variable cavitator design for a supercavitating torpedo, capable of traveling at speeds greater than 200 mph. Various studies such as reliability/uncertainty analysis, acoustic response and explosion response of lightweight torpedoes are done to improve its performance underwater.
