Department of Mechanical and Materials Engineering Graduate Theses

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    Data-Driven Approaches in Gusty Aerodynamics: Insights from Sparse Surface Pressure Measurements
    (2024-04-11) Chen, Dashuai; Mechanical and Materials Engineering; Rival, David
    Gusts are instantaneous and strongly unstable flows that aircraft frequently encounter. It is crucial to predict the sudden changes in gust loads accurately for the stable control of aircraft. However, modeling unsteady aerodynamic loads is a significant challenge in complex, gusty environments due to the associated complexities of flow separation and other nonlinearities. This thesis employs data-driven approaches to accurately estimate gust loads from sparse surface pressure measurements. Additionally, the contribution of the sparse surface pressure taps to gust loads is evaluated, pointing out an optimal layout of the sensors. Furthermore, the low-dimensional dynamics and characteristics of unsteady surface pressure are studied on complex 2D and 3D flows, offering a new paradigm for aerodynamic state estimation and control. Firstly, a nonlinear multilayer perceptron (MLP) is applied to estimate gust loads on a nonslender delta wing, demonstrating the model’s capability to capture the relationship between surface pressure and gust loads with minimum learning samples. The fluctuation of the dynamic response from the surface pressure measurements is then examined by a filtering process. Followed by a sensitivity analysis to evaluate the contribution of surface pressure taps to gust loads. Subsequently, modal analysis is conducted on the unsteady surface pressure by utilizing linear proper orthogonal decomposition (POD) to identify patterns in low-dimensional space. The surface pressures of an SD7003 airfoil with pitching and plunging motions, and then on a more complex delta wing experiencing gusts, are accurately reconstructed by only three principal POD modes, which are found to be intrinsically related to mean flow structure, Reynolds number, and angle of attack. Finally, a hybrid reduced-order deep learning-based model for gust load predictions is introduced for a nonslender delta wing. Drawing on the insights from modal analysis of surface pressure, the three principal POD modes are utilized as inputs of a deep learning model, combining long short-term memory (LSTM) and MLP approaches. The precise predictions of gust-induced lift and drag demonstrate the robustness and effectiveness of hybrid deep learning models in the field of highly unsteady aerodynamic load prediction.
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    Multi-Physics Multi-Material Topology Optimization for Minimum Compliance Problems with Thermal and Structural Considerations
    (2024-03-26) Sinek, Benjamin Dixon; Mechanical and Materials Engineering; Kim, Il Yong
    In response to the growing impact of climate change, the automotive industry has been transitioning towards lightweight designs and electrification to reduce greenhouse gas emissions. Topology optimization (TO) methods, along with modern extensions to this such as multi-material topology optimization (MMTO), have proven to be highly effective tools for reducing mass and improving the structural performance of components. Another key aspect of automotive design is thermal management, where optimizing heat transfer and reducing component temperatures ensures their durability and functionality. Given that many automotive structures are subjected to both structural and thermal loads, combining these engineering disciplines yields innovative multi-physics designs that improve both the thermal and structural performance, while contributing to mass reduction. In recent years, commercial optimization software companies have integrated thermal and thermo-structural optimization features into their solvers. However, these solvers lack the capabilities to properly solve multi-physics problems that encompass both thermal and structural factors in multi-material design. This research addresses these limitations by introducing a multi-physics multi-material TO (MP-MM-TO) methodology, compatible with commercial finite element analysis (FEA) software. The methodology was verified against the finite difference method and through comparison with commercial software. The capabilities of this methodology are demonstrated through the optimization of the thermal and structural characteristics of an automotive alternator bracket using aluminum and magnesium as candidate materials. A multi-objective problem statement was formulated with a thermo-structural compliance minimization objective and mass fraction constraint. Both single and MMTO were then applied to an aluminum baseline design and the optimized solutions were evaluated using a Pareto frontier. The best performing solution was selected for a CAD reinterpretation and features a three-component aluminum and magnesium configuration with considerations for manufacturing, joining and assembly. The final design achieved an 11.8% decrease in thermal compliance and a 23.7% reduction in structural compliance, while maintaining a similar mass to the baseline, demonstrating the developed solver’s capabilities in producing multi-material designs with improved thermo-structural performance.
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    Improving Usability for Novices in the Design of Mechatronic Devices: A Study Using Arduino Modules
    Huyer, Levi M.; Mechanical and Materials Engineering; Davies, Claire; Pinder, Shane
    Due to the complexity of mechatronic system designs, research was conducted with the objectives of identifying issues encountered by novice users while using and learning to use these systems and providing recommendations on how to improve mechatronic system design. As part of the research, a networked mechatronic system that utilized Arduino Mega microcontrollers and custom printed circuit boards was created. A study was then designed using this mechatronic system with the intention of eliciting feedback relevant to the study objectives. To investigate the research objectives, three research questions were identified. These questions investigated what concepts inherent to mechatronic design were identified by novices, what effect real-time feedback had on mental workload, and whether effort was the highest contributor to mental workload. The study provided participants with a scenario where they were to set up the mechatronic system in an ‘autopilot’ configuration on a model representative of an aircraft. To address the second research question, two instruction sets, or manuals, were created: a control set providing delayed feedback and an experimental set providing instantaneous feedback. The experiment was conducted with 16 student participants identified as novice users, split evenly into a control group and an experimental group based on participant number. Eleven of the participants were from an engineering background and five were from a non-engineering background. Mental workload was measured during the experiment using the raw NASA task load index. Participant information was taken during a pre-experiment questionnaire and responses were recorded during a post-experiment interview and debriefing session. The study found that mental workload was affected by the system designer’s ability to communicate information through their design, and that most issues identified by novices were deficiencies in clarity, simplicity, transparency, consistency, and/or context. Similarly, recommendations on how to improve designs for novice users related to the same five concepts. Additionally, it was identified that designers should use clear and concise universal language in all communication and include accurate pictorial references to enhance user understanding and visualization.
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    Performance Assessment of a Thermoelectric Heat Recovery Ventilator
    Ridings, Erik E.; Mechanical and Materials Engineering; Harrison, Stephen
    Heat recovery ventilators (HRVs) provide significant energy savings for heated buildings in wintertime. By routing warm exiting stale air past incoming cold fresh air, the fresh air is heated without mixing with the stale air. This can save more than half of the heating energy needed to bring the entering cold air to room temperature. Reversing this process can also help to keep buildings cool in the summer. Traditional HRVs use a simple fixed-plate metal heat exchanger to conduct heat between the airstreams. Thermoelectric membranes, otherwise known as Peltier tiles, show promise in increasing the efficiency of HRVs by adding an active heat transfer element to the system. If the cold side of the tile is exposed to a warm airstream it will absorb heat. The warm side will accordingly reject heat into a cold airstream like a heat pump. The focus of this study was the evaluation of a prototype HRV, equipped with a thermoelectric heat pump (TEM-HRV). The concept was conceived by Natural Resources Canada (NRCan) to enhance the performance of HRVs. The protype unit was assembled from components supplied by NRCan and performance tested in accordance with Canadian Standards Association (CSA) guidelines. Four configurations of combined TEM-HRV test units were tested, as well as a standalone TEM heat pump and fixed-plate HRV. Tests were conducted at various flow rates and current inputs to the TEMs. The performance tests were compared to a numerical model of the TEM-HRV, to assess its accuracy. From the results of the physical tests and the computer modelling, recommendations are given for integration of thermoelectrics into residential heat-recovery ventilation systems.
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    Studying the In-situ Irradiation Creep Effects of Zirconium and Its Alloys Using Proton Irradiation
    Moore, Jordan B.; Mechanical and Materials Engineering; Daymond, Mark
    Materials commonly used in nuclear power reactors, such as steel and zirconium alloys, demonstrate significant changes to their material properties over the course of their in-service lifetime. Exposure to the high radiation fields, coupled with the high temperature and stresses inside the core, can lead to several competing and simultaneous phenomena that can drastically affect the in-service performance of materials and components. One of the most notable phenomena is irradiation-induced creep, commonly referred to as “irradiation creep”, in which a material experiences gradual shape change in response to the applied irradiation-induced damage and stress. This shape change can compromise the performance of critical reactor components and have disastrous consequences if not accounted for in reactor maintenance and operation. As such, being able to study and develop a mechanistic understanding of irradiation creep behavior is essential to reactor safety, lifetime extension, and future reactor design. However, studying this behavior in a conventional reactor setting is often met with many challenges such as time constraints, restrictions on experimental control, and large costs. For these reasons, it is becoming common place to use ion irradiations to mimic reactor conditions in a controlled laboratory setting and conduct irradiation damage effect studies. This thesis details the design and implementation of an in-situ testing apparatus capable of simulating the complex environment inside of a reactor using proton irradiations. The primary purpose of this apparatus is to measure the in-situ irradiation creep behavior of material samples while systematically manipulating experimental variables such as temperature, stress, and irradiation damage rate. A detailed summary of the system design and capabilities as well as the results from the apparatus commissioning experiment are provided in manuscript one. A linear fit between the sample creep rate and applied proton flux over the range of 0 – 2.1E17 m-2s-1 was observed and a flux exponent of 1.24 ± 0.21 was determined for pure zirconium. Manuscript two presents an investigation into the viability and limitations of using proton irradiations to mimic the dynamic effects of neutron irradiation seen in a reactor core. It was determined that samples irradiated using proton irradiation must accumulate a minimum ‘saturation damage’ of ~0.1 dpa to reach steady state a-loop density and morphology before their behavior can be considered indicative of the long-term behavior of in-reactor materials. Finally, manuscript three presents an investigation of the in-situ creep behavior of Zircaloy-4 at varying stresses and temperatures and compares the proton irradiation results to values from the literature of other proton irradiation studies as well as neutron irradiation studies. A stress exponent of 4.3 ± 0.8 and an activation temperature of 5000 ± 1700 K was determined for recrystallized Zircaloy-4 at the conditions tested.