Department of Aerospace Engineering and Mechanics

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Browsing Department of Aerospace Engineering and Mechanics by Author "Aaleti, Sriram"

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    Design and analysis of a carbon composite flap for the Cirrus SF50 jet aircraft
    (University of Alabama Libraries, 2017) Haefner, Andrew; Mulani, Sameer B.; University of Alabama Tuscaloosa
    A new carbon fiber composite flap was designed and analyzed for the Cirrus SF50. This new flap will replace the existing aluminum flap and has the potential to save 5.30 lbs per aircraft. The new flap has the same OML profile as the existing flap and the same hinge locations. This allows the new flap to be either an upgrade option for customers or a supplemental type certificate (STC) option for aircraft in the field. The flap was designed with the same spar location and similar rib locations which allow existing tooling to be used for assembly. The design was analyzed to the static and damage tolerance requirements specified in 14 CFR Part 23. The loads that were utilized for the analysis were calculated using the method in 14 CFR Part 23 Appendix A. The loads are conservative since they consider a load factor of 3.6 instead of 2.2, this was done to make the design and analysis future proof. Since a significant portion of the structure uses minimum gauge layups (2 core 3, 4 ply solid), the weight increase from using the significantly higher load factor is minimal. The flap design and analysis are considered future proof because the loads used will be greater than the required loads if the SF50 were to have either a gross weight increase, a deployment speed increase, a deployment angle increase, or all in combination.
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    Efficient algorithms for uncertainty quantification using polynomial chaos expansion and its applications to composite structures
    (University of Alabama Libraries, 2019) Thapa, Mishal; Mulani, Sameer B.; University of Alabama Tuscaloosa
    Uncertainty Quantification (UQ) deals with the study of variation in the response due to the presence of uncertainties in input parameters and governing models. Among the prevalent probabilistic techniques for UQ, non-intrusive Polynomial Chaos Expansion (PCE) has become more popular recently due to its mean square convergence property and ability to integrate deterministic codes as black-box. However, the number of basis terms in the expansion increases exponentially with the number of random inputs - ‘curse of dimensionality,’ and demands a huge number of function evaluations. Hence, this dissertation has attempted to extensively explore new robust algorithms for PCE while maintaining a proper balance between accuracy and computational efficiency. At first, a new non-intrusive method for PCE called Polynomial Chaos Decomposition with Differentiation (PCDD) is developed. The PCDD utilizes higher-order sensitivities of the responses and requires samples equal to the number of basis terms only. Secondly, the PCDD is utilized to develop a stochastic multi-scale modeling framework for composite structures since the response of composites is hugely influenced by the uncertainties existing at different scales such as micro-scale and macro-scale. Another framework for stochastic progressive failure analysis (PFA) of composites is also developed that allows performing global sensitivity analysis (GSA) to identify the relative importance of random inputs as a post-processing step. To further reduce the number of samples and make the stochastic problem more tractable, an adaptive L2-minimization algorithm that allows basis adaptivity along with sequential adaptive sampling is developed. Finally, an adaptive algorithm to obtain sparse PCE models with L1-minimization and sequential sampling is also proposed for high-dimensional problems. The L1-minimization is capable of solving the under-determined system when the number of samples is minuscule. It is also advantageous in terms of computational storage and memory because of its ability to provide a sparse solution. In general, the overarching goal of obtaining high-fidelity stochastic response models while maintaining a balance between accuracy and computational cost was successfully achieved by the novel algorithms developed in this dissertation. Furthermore, the invaluable information obtained with PCE for composite structures highlighted the benefits of its implementation in engineering problems.
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    Optimization and uncertainty quantification of multi-dimensional functionally graded plates
    (University of Alabama Libraries, 2018) Hussein, Omar Shokry Ahmed; Mulani, Sameer B.; University of Alabama Tuscaloosa
    Functionally graded structures (FGS) are structures that have varying properties in one or more directions that yield better performance over homogenous structures. The grading is usually considered through the thickness of beams, plates, or shells with different grading profiles. In this work, the design and analysis of multi-dimensional functionally graded nanocomposite structures are of interest with a focus on the material grading in the in-plane directions of plates, and the effect of the uncertainties in the elastic properties on the mechanical performance. The dissertation consists of six chapters; chapter one provides a literature review of the recent developments in the area of functionally graded structures, a brief overview of the properties and modeling of nanocomposites, and the uncertainty quantification of nanocomposites. The second chapter proposes a method for the design of multi-dimensional functionally graded structures based on the polynomial expansion of the volume fraction of the reinforcement. The third chapter extends the proposed method to design complex non-rectangular domains via coordinates transformations, and study the effects of the boundary conditions, loading type, and grading direction. The fourth chapter studies the reliability of in-plane FG plates by considering multiple sources of uncertainties (e.g. reinforcement size, volume fraction, and distribution). The fifth chapter studies the nonlinear dynamic and static responses of the FG plates by considering the post-flutter and the post-buckling behaviors. The sixth and last chapter provides a summary of the work done and the proposed future work. Throughout the dissertation work, the in-plane grading is optimized such that the minimum amount of reinforcement is used to satisfy certain mechanical performance constraints. The in-plane FG clamped plates showed a 45% average saving in the reinforcement amount compared to homogenous plates, while for simply supported plates the saving strongly depends on the problem nature and varies from 4% to 45%. For stiffened plates, the in-plane grading of the stiffeners led to a saving that can reach up to 200%. The reliability analysis showed that both homogenous and FG plates have the same level of uncertainty in the global responses. Also, the non-linear analysis indicated that both plates will in general behave similarly