Lassonde School of Engineering
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Item Open Access A free-standing space elevator structure: a practical alternative to the space tether(Elsevier, 2009-04-19) Quine, Brendan; Seth, R. K.; Zhu, Z. H.Space tethers have been investigated widely as a means to provide easy access to space. However, the design and construction of such a device presents significant unsolved technological challenges. We propose an alternative approach to the construction of a space elevator that utilizes a free-standing core structure to provide access to near space regions and to reduce the cost of space launch. The structure is comprised of pneumatically inflated sections that are actively controlled and stabilized to balance external disturbances and support the structure. Such an approach avoids problems associated with a space tether including material strength constraints, the need for in-space construction, the fabrication of a cable at least 50,000 km in length, and the ageing and meteorite-damage effects associated with a thin tether or cable in Low Earth Orbit. An example structure constructed at 5 km altitude and extending to 20 km above sea level is described. The stability and control of the structure, methods for construction and its utility for space launch and other applications are discussed.Item Open Access Advanced Measurement Techniques for Braided Composite Structures: A Review of Current and Upcoming Trends(Sage, 2020-04-15) Melenka, GarrettBraiding is an advanced textile manufacturing method that is used to produce two dimensional (2D) and three dimensional (3D) components. Unlike a laminated structures braids have interlaced yarns that forms a continuity between layers. This structure allows for improved impact resistance, damage tolerance and improved through-thickness reinforcement. Despite the numerous advantages of braided composites, braids also have shortcomings. Their highly complex fiber architecture presents challenges in the availability and choice of the strain measuring and characterization techniques. Advanced measurement methods such as optical strain measurement, micro-computed tomography, and in-situ strain measurement are required. Optical strain measurement methods such as digital image correlation and high speed imaging are necessary to accurately measure the complex deformation and failure that braided composites exhibit. X-ray based micro-computed tomography measurements can provide detailed geometric and morphologic information for braided structures which is necessary for accurately predicting the mechanical properties of braided structures. Finally, in-situ strain measurement methods will provide detailed information on the internal deformation and strain that exists within braided structures. In-situ sensors will also allow for in-service health monitoring of braided structures. This paper provides a detailed review of the aforementioned sensing technologies and their relation to the measurement of braided composite structures.Item Open Access The bifurcation of periodic orbits and equilibrium points in the linked restricted three-body problem with parameter ω(AIP Publishing, 2019-10-08) Shan, Jinjun; Liang, Yuying; Xu, Ming; Lin, MingpeiThis paper is devoted to the bifurcation of periodic orbits and libration points in the linked restricted three-body problem (LR3BP). Inherited from the classic circular restricted three-body problem (CR3BP), it retains most of the dynamical structure of CR3BP, while its dynamical flow is dominated by angular velocity ω and Jacobi energy C. Thus, for the first time, the influence of the angular velocity in the three-body problem is discussed in this paper based on ω-motivated and C-motivated bifurcation. The existence and collision of equilibrium points in the LR3BP are investigated analytically. The dynamic bifurcation of the LR3BP under angular velocity variation is obtained based on three typical kinds of periodic orbits, i.e., planar and vertical Lyapunov orbits and Halo orbits. More bifurcation points are supplemented to Doedel's results in the CR3BP for a global sketch of bifurcation families. For the first time, a new bifurcation phenomenon is discovered that as ω approaches to 1.4, two period-doubling bifurcation points along the Halo family merge together. It suggests that the number and the topological type of bifurcation points themselves can be altered when the system parameter varies in LR3BP. Thus, it is named as “bifurcation of bifurcation” or “secondary bifurcation” in this paper. At selected values of ω, the phase space structures of equilibrium points L2 and L3 are revealed by Lie series method numerically, presenting the center manifolds on the Poincaré section and detecting three patterns of evolution for center manifolds in LR3BP. Holding the key to the origin of the universe, small bodies, e.g., asteroids are attracting more and more interest from academic and industrial fields. Current simulation on asteroid is implemented based on the regular spinning rate of an asteroid body. However, recently, the observation results on some asteroids show that their spinning velocity varies due to the solar radiation pressure, such as 2000 PH5, whose spinning velocity increases by (2.0 ± 0.2) × 10−4°/day2. The effect of the variable spinning velocity has not been fully understood. To cope with the orbital dynamics near a celestial object with varying angular velocity, a linked restricted three-body problem (LR3BP) is proposed in this paper given that the primary and the secondary are connected by a massless link. The bifurcations motivated by both angular velocity and Jacobi energy are detected to present the influence of the angular velocity. The expected results will provide new insights into orbital dynamics near asteroids, serving for future asteroid exploration mission. The LR3BP and the discovered bifurcation phenomena are important theoretical supplementation to the classic three-body problem theory.Item Open Access Characterization of open-cellular polymeric foams using micro-computed tomography(Elsevier, 2022-08-12) Timpano, Cristofaro; Abdoli, Hossein; Leung, Siu Ning; Melenka, Garrett W.Utilization of Polyvinylidene fluoride (PVDF) open-cellular foam allows for the creation of high-efficiency Triboelectric nanogenerators (TENG). The micro-structure of TENG devices can be problematic to characterize accurately using conventional methods like scanning electron microscope (SEM). This work aims to provide a methodology in which representative 3D measurements can be made on open-cellular PVDF foams. Open-cell PVDF foams were produced through a salt-leeching procedure. Analysis of the PVDF foams was done by imaging the sample through a desktop micro-computed tomography (μ-CT) machine to allow for a full 3D dataset to be obtained. Foams were produced with salt sizes of 250–500 μm, 106–250 μm, 53–106 μm, and <53 μm to explore the capabilities of the segmentation procedure at identifying the microstructure of the foam. Images were segmented and analyzed to calculate the porosity, sample volume, pore volume and surface area. Results from μ-CT analysis were compared to that from a SEM, which is currently the most widely used method for assessing open foam PVDF structures. Results from the μ-CT when quantifying pore dimensions proved to be much more representative than SEM due to its ability to capture the entire volume of the foam rather than a single plane. These techniques can be used as the baseline for further verification and improvement the manufacturing of PVDF foam structures.Item Open Access Comparative study on the detection of early dental caries using thermo-photonic lock-in imaging and optical coherence tomography(The Optical Society of America, OSA, 2018-09-01) Shokouhi, Elnaz B.; Razani, Marjan; Gupta, Ashish; Tabatabaei, NimaEarly detection of dental caries is known to be the key to the effectiveness of therapeutic and preventive approaches in dentistry. However, existing clinical detection techniques, such as radiographs, are not sufficiently sensitive to detect and monitor the progression of caries at early stages. As such, in recent years, several optics-based imaging modalities have been proposed for the early detection of caries. The majority of these techniques rely on the enhancement of light scattering in early carious lesions, while a few of them are based on the enhancement of light absorption at early caries sites. In this paper, we report on a systemic comparative study on the detection performances of optical coherence tomography (OCT) and thermophotonic lock-in imaging (TPLI) as representative early caries detection modalities based on light scattering and absorption, respectively. Through controlled demineralization studies on extracted human teeth and µCT validation experiments, several detection performance parameters of the two modalities such as detection threshold, sensitivity and specificity have been qualitatively analyzed and discussed. Our experiment results suggests that both modalities have sufficient sensitivity for the detection of well-developed early caries on occlusal and smooth surfaces; however, TPLI provides better sensitivity and detection threshold for detecting very early stages of caries formation, which is deemed to be critical for the effectiveness of therapeutic and preventive approaches in dentistry. Moreover, due to the more specific nature of the light absorption contrast mechanism over light scattering, TPLI exhibits better detection specificity, which results in less false positive readings and thus allows for the proper differentiation of early caries regions from the surrounding intact areas. The major shortcoming of TPLI is its inherent depth-integrated nature, prohibiting the production of depth-resolved/B-mode like images. The outcomes of this research justify the need for a light-absorption based imaging modality with the ability to produce tomographic and depth-resolved images, combining the key advantages of OCT and TPLI.Item Open Access A Comparative Study on the Electromechanical Properties of 3D-Printed Rigid and Flexible Continuous Wire Polymer Composites for Structural Health Monitoring(Elsevier, 2021-09-01) Saleh, M.A.; Kempers, R.; Melenka, GWIn this study, the electromechanical properties of two different three-dimensional (3D) printed continuous wire polymer composites (CWPC) were characterized and compared. The two composite materials were copper wire polylactic acid (PLA) composite (rigid material) and copper wire polyurethane (PU) composite (flexible material). The electromechanical measurements were based on piezoresistive properties of the sensor at which the mechanical strain and the electrical resistance were correlated under a uniaxial loading condition. Both types of materials exhibited a direct linear relationship between the two quantities, indicating the ability of CWPC to be used for strain sensing applications. The gauge factor (GF) sensitivity was compared for the two types of materials. It was found that there is no statistical significance difference between the GF of PLA CWPC (1.36 ± 0.14) and PU CWPC (1.29 ± 0.07)); therefore, the sensing property depends mainly on the wire integrated into the 3D-printed structure rather than the matrix. Thus, different matrices can be used to fit different applications. An analytical model for GF showed agreement with the experimental results for both materials. PU CWPC showed significant improvement in both Young’s modulus (E) and ultimate tensile strength (UTS) (210.5 % and 31.86 %, respectively), compared with pure PU, while the change in Poisson’s ratio (ν) was insignificant. Young’s modulus of PLA CWPC was significantly increased by 80.3 % compared with PLA, while UTS and ν did not significantly change. The experimental mechanical properties showed good agreement with data from the analytical models. The outcome of this study focused on the manufacturing of 3D-printed functionalized structure for strain sensing applications with improved mechanical properties. The wide range of attained strain allowed their use in different applications based on the range of strain needed, such as rigid sports equipment and flexible wearable sensors.Item Open Access Data Driven Models as A Powerful Tool to Simulate Emerging Bioprocesses: An Artificial Neural Network Model to Describe Methanotrophic Microbial Activity(International Society for Environmental Information Sciences, 2021-09) AlSayed, Ahmed; Soliman, Moomen; Shakir, Rahma; Snieder, Everett; ElDyasti, Ahmed; Khan, Usman TThe vision for sewage treatment plants is being revised and they are no longer considered as pollutant removing facilities but rather as water resources recovery facilities (WRRFs). However, the newly adopted bioprocesses in WRRFs are not fully understood from the microbiological and kinetic perspectives. Thus, large variations in the outputs of the kinetics-based numerical models are evident. In this research, data driven models (DDM) are proposed as a robust alternative towards modelling emerging bioprocesses. Methanotrophs are multi-use bacterium that can play key role in revalorizing the biogas in WRRFs, and thus, a Multi-Layer Perceptron Artificial Neural Network (ANN) model was developed and optimized to simulate the cultivation of mixed methanotrophic culture considering multiple environmental conditions. The influence of the input variables on the outputs was assessed through developing and analyzing several different ANN model configurations. The constructed ANN models demonstrate that the indirect and complex relationships between the inputs and outputs can be accurately considered prior to the full understanding of the physical or mathematical processes. Furthermore, it was found that ANN models can be used to better understand and rank the influence of different input variables (i.e., the physical parameters that influence methanotrophs) on the microbial activity. Methanotrophic-based bioprocesses are complex due to the interactions between the gaseous, liquid and solid phases. Yet, for the first time, this study successfully utilized DDM to model methanotrophic- based bioprocesses. The findings of this research suggest that DDM are a powerful, alternative modeling tool that can be used to model emerging bioprocesses towards their implementation in WRRFs.Item Open Access A Data-Driven Approach for Generating Synthetic Load Patterns and Usage Habits(IEEE Transactions on Smart Grid, 2020-07) Pirathayini, Srikantha; S.E. KababjiToday's electricity grid is rapidly evolving to become highly connected and automated. These advancements have been mainly attributed to the ubiquitous communication/computational capabilities in the grid and the Internet of Things paradigm that is steadily permeating modern society. Another trend is the recent resurgence of machine learning which is especially timely for smart grid applications. However, a major deterrent in effectively utilizing machine learning algorithms is the lack of labelled training data. We overcome this issue in the specific context of smart meter data by proposing a flexible framework for generating synthetic labelled load (e.g., appliance) patterns and usage habits via a non-intrusive novel data-driven approach. We leverage on recent developments in generative adversarial networks (GAN) and kernel density estimators (KDE) to eliminate model-based assumptions that otherwise result in biases. The ensuing synthetic datasets resemble real datasets and lend to rich and diverse training/testing platforms for developing effective machine learning algorithms pertaining to consumer-side energy applications. Theoretical and practical studies presented in this paper highlight the viability and superior performance of the proposed framework.Item Open Access Decentralized Topology Reconfiguration in Multiphase Distribution Networks(IEEE Transactions on Signal and Information Processing over Networks, 2019-02) Srikantha, P.; Liu, J.The cyber-physical nature of the modern power grid allows active power entities to exchange information signals with one another to make intelligent local actuation decisions. Exacting effective coordination amongst these cyber-enabled entities by way of strategic signal exchanges is essential for accommodating highly fluctuating power components (e.g., renewables, electric vehicles, etc.) that are becoming prevalent in today's electric grid. As such, in this paper, we present a novel decentralized topology reconfiguration algorithm for the distribution network (DN) that allows the system to adapt in real time to unexpected perturbations and/or congestions to restore balance in loads across the feeder and improve the DN voltage profile. For this, individual agents residing in DN buses iteratively exchange signals with neighbouring nodes to infer the current state (e.g., power balance and voltage) of the system and utilize this information to make local line switching decisions. Strong convergence properties and optimality conditions of the proposed algorithm are established via theoretical studies evoking potential games and discrete concavity. Comparative simulation studies conducted on realistic DNs showcase the practical properties of the proposed algorithm.Item Open Access Electro‐Thermal Subsurface Gas Generation and Transport: Model Validation and Implications(American Geophysical Union, 2019-06-07) Molnar, Ian; Mumford, Kevin; Krol, MagdalenaGas generation and flow in soil is relevant to applications such as the fate of leaking geologically sequestered carbon dioxide, natural releases of methane from peat and marine sediments, and numerous electro‐thermal remediation technologies for contaminated sites, such as electrical resistance heating. While traditional multiphase flow models generally perform poorly in describing unstable gas flow phenomena in soil, Macroscopic Invasion Percolation (MIP) models can reproduce key features of its behavior. When coupled with continuum heat and mass transport models, MIP has the potential to simulate complex subsurface scenarios. However, coupled MIP‐continuum models have not yet been validated against experimental data and lack key mechanisms required for electro‐thermal scenarios. Therefore, the purpose of this study was to (a) incorporate mechanisms required for steam generation and flow into an existing MIP‐continuum model (ET‐MIP), (b) validate ET‐MIP against an experimental lab‐scale electrical resistance heating study, and (c) investigate the sensitivity of water boiling and gas (steam) transport to key parameters. Water boiling plateaus (i.e., latent heat), heat recirculation within steam clusters, and steam collapse (i.e., condensation) mechanisms were added to ET‐MIP. ET‐MIP closely matched observed transient gas saturation distributions, measurements of electrical current, and temperature distributions. Heat recirculation and cluster collapse were identified as the key mechanisms required to describe gas flow dynamics using a MIP algorithm. Sensitivity analysis revealed that gas generation rates and transport distances, particularly through regions of cold water, are sensitive to the presence of dissolved gases.Item Open Access Experimental evaluation of carbon fibre, fibreglass and aramid tubular braided composites under combined tension-torsion loading(Elsevier, 2021-08-01) Armanfard, Abbas; Melenka, Garrett W.Braided composites are a class of composite materials that feature an inter-woven structure that improves structural stability and damage tolerance. Presently, braided composites under tension and torsion loading have been studied individually. Mechanical behaviour of braided composites under combined tension–torsion loading is common and therefore requires investigation. In this study, mechanical properties of carbon fibre, fibreglass and aramid 2D tubular braided composites (TBCs) were assessed and compared under coupled tension–torsion loading. The plane stress theory investigated the failure mechanism of braids. A contact-free three-dimensional digital image correlation (3D DIC) technique was used to derive detailed and continuous strain maps and understand the buckling behaviour of TBCs.Item Open Access Exploiting Reward Machines with Deep Reinforcement Learning in Continuous Action Domains(Springer Cham, 2023-09-07) Haolin Sun; Lesperance, YvesIn this paper, we address the challenges of non-Markovian rewards and learning efficiency in deep reinforcement learning (DRL) in continuous action domains by exploiting reward machines (RMs) and counterfactual experiences for reward machines (CRM). RM and CRM were proposed by Toro Icarte et al. A reward machine can decompose a task, convey its high-level structure to an agent, and support certain non-Markovian task specifications. In this paper, we integrate state-of-the-art DRL algorithms with RMs to enhance learning efficiency. Our experimental results demonstrate that Soft Actor-Critic with counterfactual experiences for RMs (SAC-CRM) facilitates faster learning of better policies, while Deep Deterministic Policy Gradient with counterfactual experiences for RMs (DDPG-CRM) is slower, achieves lower rewards, but is more stable. Option-based Hierarchical Reinforcement Learning for reward machines (HRM) and Twin Delayed Deep Deterministic (TD3) with CRM generally underperform compared to SAC-CRM and DDPG-CRM. This work contributes to the ongoing development of more efficient and robust DRL approaches by leveraging the potential of RMs in practical problem-solving scenarios.Item Open Access Fatigue behavior and electromechanical properties of additively manufactured continuous wire polymer composites for structural health monitoring(Wiley, 2022-06-29) Saleh, MA; Kempers, R; Melenka, GWThe fatigue behaviour of continuous wire polymer composite (CWPC) fabricated by fused filament fabrication was investigated. Four compositions were examined: polylactic acid (PLA), PLA with copper wire (Cu), thermoplastic polyurethane (TPU), and TPU with Cu wire. Residual properties were measured after different sets of number of cycles (102, 104, 105). CWPC electromechanical properties under fatigue test demonstrated reverse piezoresistivity behavior. A strain-controlled fatigue life analytical model was compared to the experimental results showing good agreement. This study demonstrates the applicability of FFF technique to print sensors with continuous integrated wire with tunable properties.Item Open Access Feasibility of 20 km free-standing inflatable space tower(British Interplanetary Society, May-10) Seth, R.K.; Quine, Brendan; Zhu, Z.H.This paper describes the theory and analysis for the construction of a thin walled inflatable space tower of 20 km vertical extent in an equatorial location on Earth using gas pressure. The suborbital tower of 20 km height would provide an ideal surface mounting point where the geosynchronous orbital space tether could be attached without experiencing the atmospheric turbulence and weathering in the lower atmosphere. Kevlar is chosen as an example material in most of the computations due to its compatibility in the space environment. The Euler beam theory is employed to the inflatable cylindrical beam structure. The critical wrinkling moment of the inflated beam and the lateral wind load moments are taken into account as the key factors for design guidelines. A comparison between single inflatable cylindrical beam and inflatable multiple-beam structures is also presented in order to consider the problems involving control, repair and stability of the inflated space tower. For enhancing load bearing capacity of the tower and for availability of more surface area at the top, the non-tapered inflatable structure design is chosen for the basic analysis, however further analysis can be performed with tapered structures.Item Open Access Fiber identification of braided composites using micro-computed tomography(Elsevier, 2021-06-02) Melenka, Garrett W.; Gholami, AliBraided composites contain interwoven fibers that are embedded in a matrix material. Advanced measurement methods are required to accurately measure and characterize braided composites due to their interwoven composition. Micro-computed tomography (μCT) is an X-ray based measurement method that allows for the internal structure of objects to be examined. High-resolution μCT of braided composites allows for their internal geometry to be accurately measured. Braid samples were measured with a voxel size of 1.0 μm3, which resulted in a field of view of 4.904 x 4.904 x 3.064 mm3. With this field of view, individual fibers within the braid yarns could be identified and measured. The scientific visualization software package Avizo and the XFiber extension was used to identify and measure braid yarn fibers from the collected μCT measurements. Fiber properties such as orientation angles (ϕ and θ), curved fiber length, tortuosity, and fiber diameter were obtained. Additionally, finite element mesh geometries of the braid yarns within a braided structure were created. The presented methodology provides a roadmap for the accurate modeling of braided composite unit cell geometries using high-resolution μCT data.Item Open Access Finite element analysis of 2-D tubular braided composite based on geometrical models to study mechanical performances(Taylor & Francis, 2021-11-21) Gholami, Ali; Melenka, Garrett W.Tubular Braided Composites (TBC) have a higher strength to weight ratio than conventional materials and better mechanical properties compared to laminated composite materials. The optimization of the TBC and the introduction of new applications requires a comprehensive understanding of TBC’s behavior. One efficient way to study the behavior of TBC is using Finite Element Modeling (FEM). This paper will introduce a method for generating geometrical models with different patterns and variables. Micro Computed-Tomography (μCT) is also used for generating an actual 3-D model of a TBC. The geometrical model and the μCT models are visually compared. The geometrical model is inputted into the FEM software package and is studied in different conditions. Finally, the result of FEM is compared against experimental and analytical results.Item Open Access Flexural testing of cellulose fiber braided composites using three dimensional digital image correlation(Elsevier, 2019-10-15) Unlusoy, Can; Melenka, Garrett W.Braided composites consist of woven fibers embedded within a matrix material. Braided structures are commonly produced using conventional materials such as carbon, glass and aramid fibers. However, natural fibers and bio-based resins may also be utilized with this manufacturing process. In this work, the flexural properties of tubular braid structures produced using bio-based materials was investigated. Braid samples were assessed using a contact free three dimensional digital image correlation (3D DIC) technique to assess the strain fields that occur in the samples due to applied flexural loads. Additionally, the bio-based structures were evaluated using micro-computed tomography (µCT) to assess the cross-sectional geometry and void content of the produced samples.Item Open Access Flight Dynamics and Control Strategy of Electric Solar Wind Sails(American Institute of Aeronautics and Astronautics, 2019-11-27) Zhu, Zheng H.; Li, Gangqiang; Du, ChonggangThis paper studies the flight dynamics and control strategy for electric solar wind sails based on the nodal position finite element method, where the coupling effects between tether dynamics and the electrical field are considered. A modified throttling control strategy is proposed to control the attitude of electric sails by modulating individual tether voltage synchronously with the spinning motion of the sails. The effects of four critical physical parameters (tether numbers, tether length, sail spin rate, and mass of remote units) are investigated. The results show that the effect of the relative velocity of the solar wind has a significant effect on the spin rate of the sail in attitude maneuvering, which in turn affects the attitude dynamics and orbit motion of the sail. Numerical results show that the proposed control strategy work successfully stabilizes the spin rate of sail when the new type sail is adopted.Item Open Access Further probing the mechanisms driving projected decreases of extreme precipitation intensity over the subtropical Atlantic(2022) Mpanza, M. A. Thabo; Tandon, Neil F.Item Open Access Hidden Convexities in Decentralized Coordination for the Distribution Networks(IEEE Transactions on Power Systems, 2020-05) Srikantha, Pirathayini; M. MallickThe modern power grid is undergoing unprecedented levels of transformations due to the rising prevalence of diverse power entities, cyber-enablement of grid components and energy deregulations. In this paper, we focus on distribution networks (DNs) to enable the seamless plug-and-play coordination of actuating cyber-enabled power entities for cost-effective and feasible system operations. The proposed distributed algorithm empowers individual cyber-physical agents residing in active power nodes with the ability to iteratively compute local actuation setpoints by exchanging information with neighbouring entities. The main contribution of this work is the identification of hidden convexities in the original non-convex optimal power flow (OPF) formulation for the DN via strategic decomposition and strong duality principles. These eliminate the need for OPF relaxations/approximations. Strong convergence and feasibility results are presented via theoretical analysis and practical simulation studies conducted on realistic systems.