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Design Automation of Volumetric Enhancement of Additive Manufacturing via Segmentation of Polyhedron Nets
Get PDFAdditive manufacturing (AM) has revolutionized the manufacturing industry by increasing the ease and intricacy of manufacturable structures. With the cost of large-scale additive manufacturing so high, printing segmented structures can be a possible method to overcome these limitations. This work aims to present a framework for the printing of structures larger than a traditional printer envelope. Segments of structures can be printed, folded or otherwise manipulated to construct a larger structure bypassing the limitations of smaller printer envelopes. Printing faces onto a flexible substrate such as a textile can be used as a hinge to hold faces together. A net of a polyhedron can be folded from a 2D plane of finite thickness into a 3D structure. Printing faces of a polyhedron net at the size of the print bed can greatly increase the size of manufacturable objects. A chain net is a net that is unfolded in a linear fashion such that each face is connected to a maximum of two others, preventing interference with printer topology. Finding a chain net of convex polyhedron can be simplified to a Hamiltonian pathfinding problem on the dual graph of the polyhedron. However, some polyhedron nets are not as optimal to print as others, requiring the application of a cost function to be optimized via a depth-first search. Other objectives and constraints for these problems are investigated and discussed.
Volumetric enhancement of 2D objects is also possible, requiring a planar division algorithm. Lloyd’s Algorithm is suitable for the segmentation of 2D shapes. Similar to 3D, constraints for manufacturing 2D objects can be implemented. To further tailor the printing process to the problem, a custom slicing method was implemented. The slicing methodology is discussed, either reducing or eliminating potential errors compounded from using black box functions. The slicer allows for full control over the process of perimeter and infill generation, allowing for variation in the infill density and infill pattern settings to be no infill, rectilinear, aligned rectilinear, line, or spiral. The slicer implements interlayer variation in the printing parameters, allowing the setting for the first layer to differ, maximizing part adhesion to the flexible substrate
Spatial and Temporal Variability of Temperate Snowpack Properties in northern Maine and southeast Alaska with Multi-offset Ground-penetrating Radar
Get PDFGlaciers and surrounding snowpacks in mountainous terrain serve as freshwater reservoirs for nearby communities and ecosystems. Their presence and meltwater runoff support hydroelectricity, irrigation, drinking water, nutrient flux, and navigation. However, the amount of water held within these reservoirs, or the snow water equivalent (SWE), is difficult to quantify, especially in remote, often mountainous regions at mid to high latitudes. Current methods for estimating SWE in mountainous terrain are limited to point sources (e.g., SNOTEL sites), remotely sensed data (e.g. satellite, aircraft, unmanned aerial vehicles (UAVs)), or noninvasive ground-based geophysical techniques (e.g., ground-penetrating radar (GPR)). Notably, Maine and Alaska, USA, exhibit some of the greatest SWE uncertainties and subsequent meltwater runoff predictions.
In the Chapter 2 pilot study, I investigate the spatial variability of snow depth, density and SWE using coupled in-situ snow pit and ~70 km of ultra-high frequency (UHF) 900 MHz common-offset (CO) and 1000 MHz multi-offset (MO) GPR surveys during a temperate northern Maine winter. CO GPR consists of a single transmitter-receiver pair, and relies on assumptions of radio wave velocity, density and liquid water content (LWC). However, the MO GPR system consists of multiple transmitter-receiver pairs, enabling the characterization of radio wave velocity from the raypath geometries and two-way travel times (TWTT) of the electromagnetic energy. I compare depth, density and SWE estimations from each radar system to the in-situ snow pit and find the CO GPR generally underestimates these properties, while MO was more realistic estimation. I also evaluated the influence on terrain variables (e.g., elevation, aspect, northness, and biomass) on GPR-derived snowpack properties to find a weak correlation, likely due to the conditions of the surveyed snowpack.
In Chapter 3, I quantify the sub-seasonal spatiotemporal variability of snowpack properties from two repeat ~32-km-long 500 MHz MO GPR transects across the temperate Juneau Icefield system. The transects span from the low elevation marine-proximal ablation area on the lower T’aakú Kwáan Sít’i to the high elevation continental accumulation zone at the Matthes-Llewellyn-Tulsequah ice divide. With boundary conditions from firn cores, paired with advanced velocity analyses and dielectric mixing methods, I quantify the stacking and interval velocity, permittivity, dry and wet density, and LWC across the transect. Repeat surveys show variable ablation processes across the elevation profile, with meltwater infiltration into the firn below the equilibrium line altitude (ELA) and surface ablation with refreezing and densification processes above the ELA through to the firn. These results emphasize the important role LWC plays in estimating snowpack properties with MO GPR.
These successful research campaigns evaluated the advantages and limitations of CO and MO GPR systems, constrained our understanding of the discrepancies between in-situ snowpack data and CO and MO GPR-derived snowpack properties across two different temperate snowpacks, and laid the foundation for future surveys across Maine and southeast Alaska
Lateral Stability of Earthwork Systems Supported on Unreinforced Rigid Columns
Get PDFAdopting unreinforced rigid columns to support earthwork systems has become a common approach to accelerate construction under challenging subsoil conditions. However, evaluating global stability for these systems using conventional limit equilibrium (LE) methods remains elusive, often violating the complex changes of soil stresses at depth due to the soil and column interaction. Additionally, conventional LE methods typically neglect column failure modes and rely on column strength to provide stability.
This dissertation proposes a rational methodology for evaluating the global stability of reinforced column-supported earthwork systems, integrating the assessment of factor of safety and lateral deformation at the toe. A new limit equilibrium model called LE-RISE (Limit Equilibrium model for Rigid Inclusions Supported Earthwork) is developed, which explicitly capturing the fundamental physical mechanisms governing these systems. LE-RISE is founded on three fundamental assumptions: 1.) columns do not resist lateral load, but modulate vertical stresses imposed on foundation soils; 2.) The slip surface geometry is simplified into three distinct wedges: passive, shear, and active; and 3.) the global stability is evaluated using the strength reduction method, whereby horizontal equilibrium is achieved by reducing the available shear strength of the soil, consistent with conventional global stability analyses.
To address the complex changes of soil stresses, the Load Displacement Compatibility Extension (LDCE) is introduced. LDCE integrates stress-displacement compatibility associated with soil arching and subsurface load transfer by employing t-z and q-z curves to characterize interface column friction and end-bearing resistance, respectively. The resulting changes in vertical stress are subsequently utilized in the LE-RISE model to primarily compute lateral driving stresses.
LE-RISE is verified through comparisons with existing simplified LE models and validated with a comprehensive 3D finite element (FE) parametric study of hypothetical embankments. Complex changes of vertical stresses at depth in the reinforced zone predicted by the LDCE are verified through comparisons with existing analytical models, and validated with field observations of the CBIS field case study, and the FE parametric study. Comparative predictions of the vertical stress changes, factors of safety, lateral deformations at the toe, tensile stress in the geosynthetic reinforcement, and critical slip surface locations demonstrate strong agreement among the proposed models, field observations, and parametric FE results. LE-RISE provides engineers with a tractable approach for making physically meaningful and computationally efficient predictions. These methodologies are expected to enhance communication and decision-making among engineers, clients, and contractors
Ecological and Physiological Characteristics of Island Mass Effect
Get PDFThe Island Mass Effect (IME) describes the localized enhancement of phytoplankton biomass around oceanic islands and atolls, disrupting the nutrient-poor conditions typical of the subtropical oligotrophic Pacific Ocean. Despite its recognized importance, the spatial extent, physiological dynamics, and ecological consequences of IME remain poorly studied.
This dissertation aims to (1) improve the delineation of the spatial extent of IMEs, (2) characterize the physiological dynamics of phytoplankton populations within IMEs, and (3) evaluate the ecological consequences of IMEs on community composition and diversity, using a multidisciplinary approach that integrates satellite remote sensing, in situ bio-optical measurements, and high-resolution taxonomic analyses across the Pacific Ocean.
We developed a novel satellite-based method that merges multi-sensor observations and surface current models to detect and track IME features over time to better delineate the spatial extent of the Island Mass Effect (IME). This approach reveals that IME patches can persist and be advected over distances exceeding 1000 km, substantially extending the known spatial influence of islands on their surrounding oligotrophic ocean.
We characterized the physiological dynamics of IME phytoplankton communities using satellite-derived stress indices and in situ data from the Tara Pacific expedition. Both iron and macronutrient enrichments characterize IMEs across the South Pacific Subtropical Gyre; however, unlike iron, which remains high during offshore advection of coastal IMEs, macronutrients are rapidly consumed.
To evaluate the ecological consequences of IMEs, we analyzed phytoplankton community succession using a combination of metabarcoding, automated imaging, and in situ bio-optical proxies. Phytoplankton community composition differs significantly between coastal IMEs, advected IMEs, and background oligotrophic waters. Distinct shifts in size structure and taxonomic composition emerge between these regions, with evidence suggesting that large, persistent offshore IMEs occur when specific phytoplankton taxa can escape grazing pressure during the advection of coastal water masses into the open ocean.
Together, these studies enhance our understanding of the physiological and ecological consequences of IMEs and the complex interactions between bottom-up and top-down processes involved in IMEs
Using Broccoli Sprout Diets to Understand Gut Bacterial Glucosinolate Metabolism to Resolve Inflammatory Bowel Disease
Get PDFGlobally, millions of people have been diagnosed with a type of inflammatory bowel disease (IBD). These diseases cause dysfunction of the gastrointestinal (GI) tract, resulting in a wide range of symptoms that create disruption in overall health. Research has suggested that diet and the microbial community composition of the gut microbiome play a significant role in regulating gastrointestinal inflammation. Specifically, studies have shown that diets high in cruciferous vegetables, such as broccoli, are associated with a reduction in gastrointestinal inflammation. Glucoraphanin is a compound present in broccoli that can be metabolized by gut bacteria to become an anti-inflammatory compound known as sulforaphane. Our initial research showed that the administration of a broccoli sprout diet to mouse models for Crohn’s disease and ulcerative colitis, two major types of IBD, yields inflammation reduction and symptom resolution. For these trials, fecal samples obtained from different sections of the mouse bowel were tested for presence of glucoraphanin-metabolizing genes present in a common gut bacterium, Bacteroides thetaiotaomicron (B. theta). Glucoraphanin conversion is higher and more reliable in mice than in people, however mouse models are not perfect representatives of humans. Hoping to understand the impacts of broccoli sprouts on the human gut microbiome, fecal samples were obtained from healthy individuals who consumed broccoli sprouts for 28 consecutive days, as long-term diet interventions are needed to meaningfully change gut microbial communities. In a separate trial conducted by the scientists at Brassica Protections Product, fecal samples were collected from people who were administered a single dietary supplement containing a high dose of glucoraphanin with and without plant-sourced myrosinase, as a means of evaluating the effectiveness of glucoraphanin conversation which was or was not reliant on gut microbiota, respectively. These samples were analyzed for glucoraphanin-metabolizing genes from B. theta and other commensal gut bacteria. Data collected from these human trial experiments aided in understanding the impacts of a whole food broccoli sprout diet and supplementation of glucoraphanin on the bacterial community composition of the gut microbiota. Additionally, this work will help grow and strengthen the current knowledge on broccoli as an anti-inflammatory and the variabilities present in the gut microbiomes of humans