Research Symposium Series: Ning Liu, Kshitij Mall, & Arnau Pons
|Event Date:||March 21, 2018|
|Hosted By:||Aero Assist
|School or Program:||Aeronautics and Astronautics
A new semi-analytical method to study the buckling behavior of sandwich structures
Sandwich structures are important structural members in the modern lightweight engineering. Sandwich structures are usually slender or plat and easily buckle under compressive loads which results in catastrophic failure. Accurate and effective predictions of the buckling behavior are vital to the design and optimization of sandwich structures. While the type I flexural buckling and the local buckling have been well predicted by many approaches, the type II flexural buckling and the torsional buckling were rarely seen and mentioned in literature. This work developed a unified method to study the aforementioned buckling behavior of sandwich structures under compression. The proposed method employed and extended a homogenization theory called the Mechanics of Structural Genome (MSG). The MSG theory was able to well predict the global buckling. To predict the local buckling, MSG was extended by introducing the Saint Venant-Kirchhoff material model and Bloch-wave boundary conditions. Numerical simulation validated the proposed method and showed it provided better solutions (3% error) than one of the existed method (8% error). Parametric studies using this method reveal for the first time that type II flexural mode dominates the buckling behavior of those sandwich columns whose width is smaller than thickness.
Advancing optimal control theory for solving complex aerospace problems
Optimal control theory (OCT) has existed since the 1950s. However, with the advent of modern computers, the task of solving the optimal control problems (OCP) has been delegated largely to computationally intensive direct methods instead of methods that use OCT. Some recent work has shown that solvers using OCT can leverage parallel computing resources for faster execution. The need for near real-time, high quality solutions for OCPs has therefore renewed interest in OCT in the design community. However, certain challenges still exist that prohibits its use for solving complex practical aerospace problems, such as landing human-class payloads safely on Mars. In this study, the usage of trigonometry for incorporating control bounds and mixed state-control constraints into OCPs has been introduced and has been termed as trigonomerization. The method has been validated using results from literature as well as certain benchmark OCPs solved using GPOPS-II. Unlike traditional OCT, trigonomerization converts the constrained OCP into a two-point boundary value problem rather than a multi-point boundary value problem, significantly reducing the computational effort required to formulate and solve it. In this work, trigonomerization has been used to solve some complex aerospace problems including prompt global strike, noise-minimization for general aviation, and shuttle re-entry problem.
Study of the effects of unsteady heat release in combustion instability
Combustion instabilities represent a challenge that hampers the development of low emission gas turbines and high-performance rocket engines. The prediction of combustion instabilities is very complex due to the nonlinear coupling of physical phenomena at different time and spatial scales. The present research seeks to gain insight into the fundamental effects of unsteady heat release and establish the limitations of classical treatments based on the study of combustion instability in rockets. An analytical model based on the linearized acoustic wave equation with an unsteady heat source has been derived and then compared to high-fidelity numerical simulations generated using Purdue's GEMS code. Two different heat addition profiles are used: Gaussian spatial distribution and step temporal profile, and Gaussian spatial and temporal distribution. The heat release rates are sized on the basis of common unsteady heat release events of rocket engines. The analytical models for both profiles match the pressure response of the numerical simulations with a slight overprediction due to the assumption of constant mean flow properties and lack of loss mechanisms. Moreover, the analytical solutions predict two different regimes in the pressure response depending on the ratio of the heat addition duration with respect to the fluid characteristic response time.
What is the Research Symposium Series?
The Research Symposium Series is a department-sponsored forum for graduate students and advanced-level undergraduates to present their research to a general audience.
The Research Symposium Series is designed to:
- Facilitate the exchange of ideas and knowledge among faculty and graduate students.
- Provide opportunities for students to develop their technical presentation skills.
- Promote the research activities of the department to undergraduates and other interested individuals.
- $500, $300, $200 for best three presentations
- $150 for best undergraduate presentation
- $150 for best abstract
Questions about the Research Symposium Series may be directed to:
*Winners in the presentation category cannot compete in that category the following year. The same applies for winners in the abstract category.