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Riley, Zachary BryceInteraction Between Aerothermally Compliant Structures and Boundary-Layer Transition in Hypersonic Flow
Doctor of Philosophy, The Ohio State University, 2016, Aero/Astro Engineering
The use of thin-gauge, light-weight structures in combination with the severe aero-thermodynamic loading makes reusable hypersonic cruise vehicles prone to fluid-thermal-structural interactions. These interactions result in surface perturbations in the form of temperature changes and deformations that alter the stability and eventual transition of the boundary layer. The state of the boundary layer has a significant effect on the aerothermodynamic loads acting on a hypersonic vehicle. The inherent relationship between boundary-layer stability, aerothermodynamic loading, and surface conditions make the interaction between the structural response and boundary-layer transition an important area of study in high-speed flows. The goal of this dissertation is to examine the interaction between boundary layer transition and the response of aerothermally compliant structures. This is carried out by first examining the uncoupled problems of: (1) structural deformation and temperature changes altering boundary-layer stability and (2) the boundary layer state affecting structural response. For the former, the stability of boundary layers developing over geometries that typify the response of surface panels subject to combined aerodynamic and thermal loading is numerically assessed using linear stability theory and the linear parabolized stability equations. Numerous parameters are examined including: deformation direction, deformation location, multiple deformations in series, structural boundary condition, surface temperature, the combined effect of Mach number and altitude, and deformation mode shape. The deformation-induced pressure gradient alters the boundary-layer thickness, which changes the frequency of the most-unstable disturbance. In regions of small boundary-layer growth, the disturbance frequency modulation resulting from a single or multiple panels deformed into the flowfield is found to improve boundary-layer stability and potentially delay transition. For the latter, transitional boundary-layer aerothermodynamic load models are developed and incorporated into a fundamental aerothermoelastic code to examine the impact of transition onset location, transition length and transitional overshoot in heat flux and fluctuating pressure on the response of panels. Results indicate that transitional fluid loading can produce larger thermal gradients, greater peak temperatures, earlier flutter onset, and increased strain energy accumulation as compared to a panel under turbulent loading. Sudden transition, with overshoot in heat flux and fluctuating pressure, occurring near the leading edge of the panel provides the most conservative estimate for determining the life of the structure. Finally, the coupled interaction between boundary-layer transition and structural response is examined by enhancing the aerothermoelastic solver to allow for time-varying transition prediction as a function of the panel deformation and surface temperature. A kriging surrogate is developed to reduce the online computational expense associated with transition prediction within an aerothermoelastic simulation. For the configurations examined in this study, panel deformation has a more dominant effect on boundary-layer stability than surface temperature. Allowing for movement of the transition onset location results in characteristically different panel deformations due to spatial variation in the thermal bending moment. The response of the clamped panel is more sensitive to the transition onset location than the simply-supported panel.

Committee:

Jack McNamara (Advisor); Jeffrey Bons (Committee Member); Datta Gaitonde (Committee Member); Sandip Mazumder (Committee Member); Benjamin Smarslok (Committee Member); S. Michael Spottswood (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

hypersonic; boundary-layer stability; boundary-layer transition; aerothermoelastic; parabolized stability equations; surrogate modeling; kriging

Crowell, Andrew RModel Reduction of Computational Aerothermodynamics for Multi-Discipline Analysis in High Speed Flows
Doctor of Philosophy, The Ohio State University, 2013, Aero/Astro Engineering
This dissertation describes model reduction techniques for the computation of aerodynamic heat flux and pressure loads for multi-disciplinary analysis of hypersonic vehicles. NASA and the Department of Defense have expressed renewed interest in the development of responsive, reusable hypersonic cruise vehicles capable of sustained high-speed flight and access to space. However, an extensive set of technical challenges have obstructed the development of such vehicles. These technical challenges are partially due to both the inability to accurately test scaled vehicles in wind tunnels and to the time intensive nature of high-fidelity computational modeling, particularly for the fluid using Computational Fluid Dynamics (CFD). The aim of this dissertation is to develop efficient and accurate models for the aerodynamic heat flux and pressure loads to replace the need for computationally expensive, high-fidelity CFD during coupled analysis. Furthermore, aerodynamic heating and pressure loads are systematically evaluated for a number of different operating conditions, including: simple two-dimensional flow over flat surfaces up to three-dimensional flows over deformed surfaces with shock-shock interaction and shock-boundary layer interaction. An additional focus of this dissertation is on the implementation and computation of results using the developed aerodynamic heating and pressure models in complex fluid-thermal-structural simulations. Model reduction is achieved using a two-pronged approach. One prong focuses on developing analytical corrections to isothermal, steady-state CFD flow solutions in order to capture flow effects associated with transient spatially-varying surface temperatures and surface pressures (e.g., surface deformation, surface vibration, shock impingements, etc.). The second prong is focused on minimizing the computational expense of computing the steady-state CFD solutions by developing an efficient surrogate CFD model. The developed two-pronged approach is found to exhibit balanced performance in terms of accuracy and computational expense, relative to several existing approaches. This approach enables CFD-based loads to be implemented into long duration fluid-thermal-structural simulations.

Committee:

Jack McNamara (Advisor); Thomas Eason, III (Committee Member); Jeffrey Bons (Committee Member); Mo-How Herman Shen (Committee Member); Mei Zhuang (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Aerodynamic Heating; Pressure; Fluid-Thermal-Structural Analysis; Reduced Order Modeling; Surrogate Modeling; Computational Fluid Dynamics; Hypersonic; Supersonic; High-Speed Flow

Davidson, JamesA Distributed Surrogate Methodology for Inverse Most Probable Point Searches in Reliability Based Design Optimization
Master of Science in Mechanical Engineering (MSME), Wright State University, 2015, Mechanical Engineering
Surrogate models are commonly used in place of prohibitively expensive computational models to drive iterative procedures necessary for engineering design and analysis such as global optimization. Additionally, surrogate modeling has been applied to reliability based design optimization which constrains designs to those which provide a satisfactory reliability against failure considering system parameter uncertainties. Through surrogate modeling the analysis time is significantly reduced when the total number of evaluated samples upon which the final model is built is less than the number which would have otherwise been required using the expensive model directly with the analysis algorithm. Too few samples will provide an inaccurate approximation while too many will add redundant information to an already sufficiently accurate region. With the prediction error having an impact on the overall uncertainty present in the optimal solution, care must be taken to only evaluate samples which decrease solution uncertainty rather than prediction uncertainty over the entire design domain. This work proposes a numerical approach to the surrogate based optimization and reliability assessment problem using solution confidence as the primary algorithm termination criterion. The surrogate uncertainty information provided is used to construct multiple distributed surrogates which represent individual realizations of a lager surrogate population designated by the initial approximation. When globally optimized upon, these distributed surrogates yield a solution distribution quantifying the confidence one can have in the optimal solution based on current surrogate uncertainty. Furthermore, the solution distribution provides insight for the placement of supplemental sample evaluations when solution confidence is insufficient. Numerical case studies are presented for comparison of the proposed methodology with existing methods for surrogate based optimization, such as expected improvement from the Efficient Global Optimization algorithm.

Committee:

Ha-Rok Bae, Ph.D. (Advisor); Ahsan Mian, Ph.D. (Committee Member); Zifeng Yang, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

Surrogate Modeling;Distributed Surrogate;Reliability Assessment;SORA,;Most Probable Point;Surrogate Based Optimization

Clark, Daniel LeeLocally Optimized Covariance Kriging for Non-Stationary System Responses
Master of Science in Engineering (MSEgr), Wright State University, 2016, Mechanical Engineering
In this thesis, the Locally-Optimized Covariance (LOC) Kriging method is developed. This method represents a flexible surrogate modeling approach for approximating a non-stationary Kriging covariance structures for deterministic responses. The non-stationary covariance structure is approximated by aggregating multiple stationary localities. The aforementioned localities are determined to be statistically significant utilizing the Non-Stationary Identification Test. This methodology is applied to various demonstration problems including simple one and two-dimensional analytical cases, a deterministic fatigue and creep life model, and a five-dimensional fluid-structural interaction problem. The practical significance of LOC-Kriging is discussed in detail and is directly compared to stationary Kriging considering computational cost and accuracy.

Committee:

Ha-Rok Bae, Ph.D. (Advisor); Ramana Grandhi, Ph.D. (Committee Member); Joseph Slater, Ph.D., P.E. (Committee Member)

Subjects:

Applied Mathematics; Engineering; Mechanical Engineering

Keywords:

Kriging; surrogate modeling; optimization; fluid-structural interaction; FSI; Fatigue; Creep; Hypersonic; Ti-6242S; Analytical Life Model; Physics metamodeling; Non-stationary; Non-stationary Identification; localities; local surrogates

Thomas, George LBiogeography-Based Optimization of a Variable Camshaft Timing System
Master of Science in Electrical Engineering, Cleveland State University, 2014, Washkewicz College of Engineering
Automotive system optimization problems are difficult to solve with traditional optimization techniques because the optimization problems are complex, and the simulations are computationally expensive. These two characteristics motivate the use of evolutionary algorithms and meta-modeling techniques respectively. In this work, we apply biogeography-based optimization (BBO) to radial basis function (RBF)-based lookup table controls of a variable camshaft timing system for fuel economy optimization. Also, we reduce computational search effort by finding an effective parameterization of the problem, optimizing the parameters of the BBO algorithm for the problem, and estimating the cost of a portion of the candidate solutions in BBO with design and analysis of computer experiments (DACE). We find that we can improve fuel economy by 1.7% compared to the original control parameters, and we find effective, problem-specific values for BBO population size and mutation rate. Finally, we find that we can use a small number of samples to construct DACE models, and we can use these models to estimate a significant portion of the BBO candidate solutions each generation to reduce computation effort and still obtain good BBO solutions.

Committee:

Dan Simon, PhD (Committee Chair); Zhiqiang Gao, PhD (Committee Member); Mehdi Jalalpour, PhD (Committee Member)

Subjects:

Automotive Engineering; Experiments

Keywords:

BBO; Biogeography-Based Optimization; DACE; Design and Analysis of Computer Experiments; EA; Evolutionary Algorithm; VCT; Variable Camshaft Timing; Variable Cam Timing; Surrogate Modeling; Response Surfaces