Queen's Graduate Theses and Dissertations

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This is a collection of the Queen's University Masters Degree and PhD Theses and Dissertations. Submissions are limited to officially registered Queen's University graduate students, only.


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Now showing 1 - 5 of 8575
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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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    Three Essays on New Product Introduction and Product Failures
    (2024-04-11) Gong, Yiran; Economics; Clark, Robert
    This thesis presents an empirical study of new product introduction and product failures. First, I investigate reasons for product failures through a case study of the introduction and subsequent exit of Coca-Cola's Vanilla Coke. Using scanner data, we estimate a structural model of the soft drink industry to infer Coca-Cola’s profit gains from the new brand. Results show that they would not cover associated fixed costs. We then analyze the importance of market variables for explaining the failure and find that Vanilla Coke’s profitability is most sensitive to rival reactions. We also find Coca-Cola did anticipate some rival reaction that made survival harder, but the actual changes were even more intense and contributed to Vanilla Coke's exit. I also study the evaluation of new products’ welfare effects. Structural estimation of such effects largely relies on demand models with a logit error. In markets where consumers have both brand and option preferences, nested logit demand models are used. However, the logit errors lead to welfare overestimation and make welfare estimates sensitive to the number of nests. To address these problems, I develop an empirical framework to estimate a pure characteristics demand model that allows for option choices and eliminates logit errors. I provide an application using scanner data to evaluate four new products introduced to the U.S. shampoo market. Compared with models featuring logit errors, my approach reduces the implausibly large estimates by at least 73%. Finally, I explore supply-side optimization problems when the pure characteristics model is employed on the demand side. Pure characteristics models are well-suited for analyzing problems involving a changing number of products. Examples include pricing new products, product assortment, and merger analysis. However, it is challenging to incorporate a supply side because market share functions can be set-valued and discontinuous. To fill the gap, I utilize a regularization method proposed in the mathematical programming literature to obtain a unique and continuous market share function, which can be estimated feasibly. My simulation results suggest that such a method can provide accurate estimates for firms' marginal costs and new equilibrium prices when the number of products changes.
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    (2024-04-09) Poloei, Fereshteh; Electrical and Computer Engineering; Bakhshai, Alireza
    One of the main challenges in power electronic applications is Battery Management System (BMS) that covers battery modeling, charging estimation, and charging control. Lithium Ion (Li-ion) batteries offer uncontested advantages over other types of batteries. They are used in many electronic devices such as cell phones, cameras, laptops, and are an important part of stand-alone wind and solar systems, smart grids applications, and Electric Vehicles (EVs). The goal of a battery management system (BMS) is to optimize the battery’s lifetime while improving the system’s stability, reliability, and cost. Among the factors involved in the battery management system (BMS), State of Charge (SOC) estimation and Charging Equalization (CE) among a set of batteries are of importance greater than the others. An appropriate and accurate modelling of the battery combined with an accurate and fast estimation scheme are required for a good estimation of the battery’s state of charge (SOC). In terms of charging equalization, the efficiency, modularity, algorithm simplicity, CE time, minimum added elements and cost, and maximum possible operation modes involved during CE process should be considered to have a more practical and advantageous CE method and topology. This research focuses on developing a new modelling and SOC estimation technique for Li-ion batteries as well as introducing a novel charging equalization algorithm and topology for all possible operation modes in a battery stack. This research work introduces a comprehensive but simple model for the battery and a novel accurate, fast, and online estimation method for a Li-ion cell and then proposes an innovative advantageous balancing algorithm that includes all modes of operation for a battery stack. Our proposed CE algorithm can not only balance the charge among the modules in the battery stack when it is connected to the grid, either in charging or discharge mode. It is also capable of charge equalizing when the battery stack is disconnected from the grid. This unique feature of our proposed method prolongs the battery life and improves the performance in a modular battery system. The proposed modelling and charging schemes are validated through comprehensive simulations and experimental results.
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    Ibrahim, Mahmoud Mouhamed Ali; Civil Engineering; Rowe, Kerry; Abdelaal, Fady
    The properties of high-density polyethylene (HDPE) geomembrane (GMB) sheet material and the geometry of the geomembrane surface (i.e., texturing the sheet surface and high irregularity of the weld) play a crucial role in assessing the expected lifespan of a constructed barrier system. In particular, the resistance to stress cracking and the preservation of antioxidants within the GMB are critical factors to both short-term and long-term performance. While the single point notch constant tensile load stress crack resistant (SP-NCTL SCR) test is a conventional method for assessing the stress cracking resistance of the HDPE GMB, the surfactant used to accelerate the test has shown negative effects on human health and the environment, leading to its prohibition in some countries, such as those in the European Union. Therefore, alternative test methods are investigated using the strain hardening modulus of smooth HDPE geomembranes. The proposed methods provide a quick assessment of the SP-NCTL SCR for the resins and conditions examined. The SCR of HDPE GMB extrusion weld for a 1.5 mm HDPE geomembrane is examined. It is shown that the average SCR for a good extrusion weld is 23% of that of the unnotched sheet SCR. The presence of welding-induced geometric irregularities (WIGI) and excessive grinding of the surface adjacent to the weld, caused by the operator, greatly affects the SCR of extrusion welds. High welding geometry irregularity (WIGI) overheated fusion welds and extrusion welds have been found to exhibit SCR failure times that are equivalent to those of notched sheets during 40 months of immersion in a synthetic leachate solution. This study also investigates the impact of texturing on the longevity of a GMB when exposed to MSW leachate over a period of ~8 years. The comparison of the textured/smooth edge portions of the HDPE GMB shows that the antioxidant depletion of the textured part is much faster than that of the smooth edge. However, the time to nominal failure (tNF) assessed based on SCR was similar at 85 and 75C. The degradation in the tensile break properties at 85C is faster for the textured part than for the smooth edge portion and smooth equivalent.
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    The Effects of Diets on Vulnerability to Oscillatory Shear Stress-Induced Endothelial Dysfunction
    (2024-04-09) Etwaroo, Raelisa; Kinesiology and Health Studies; Pyke, Kyra
    Endothelial cells line the walls of the arteries, and the proper function of these cells is essential for maintaining arterial health. Endothelial cells allow the widening of blood vessels (vasodilation) in response to blood flow-associated shear stress (frictional force of blood on artery wall) in a response called flow-mediated dilation (FMD). Oscillatory shear stress (OSS), characterized by low mean shear and retrograde shear stress, occurs in regions of the artery that are curved and branched and results in endothelial dysfunction and increased risk of plaque formation due to increased levels of highly reactive molecules (oxidative stress). No study has explored the impact of chronic dietary antioxidant intake on OSS-induced endothelial dysfunction. The purpose of the study reported in Chapter 3 was to investigate whether high dietary intake of antioxidants confers protection from transient OSS exposure-induced endothelial dysfunction. We hypothesized that diets high in antioxidants indicated by high vitamin C and E intake and a high frequency of fruit and vegetable consumption would be associated with a smaller decline in FMD following transient OSS exposure. Fifteen healthy males (22± 3 years [Mean ± SD]) participated in an experimental visit in which brachial artery FMD was assessed with ultrasound before and after 30 min of OSS exposure induced with mild forearm cuff occlusion. Dietary antioxidant content was estimated from the food tracking app Keenoa (vitamin C and E intake over three days) and frequency of fruit and vegetable intake via a food frequency questionnaire. OSS exposure resulted in a significant decline in FMD (pre 9.9% ± 3.5% vs. post 7.2% ± 3.6% p=<0.001). No relationship was found between the magnitude of post-OSS FMD impairment and either antioxidant vitamin intake (r2= 0.01; p= 0.723) or frequency of fruit and vegetable consumption (r2 = 0.005; p=0.809). These preliminary findings suggest that higher dietary antioxidant intake may not be associated with protection from OSS-induced endothelial dysfunction in healthy young men. However, further research in additional populations with more precise quantification of antioxidant intake and blood levels of antioxidants and estimates of oxidative stress is required to make a more definitive conclusion.

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