Engineering Commons^™

Experimental Investigation Of The Vortex-Induced Vibration Response Of A Flexibly-Mounted Rigid Cylinder In The Shear-Thinning And Inertial-Viscoelastic Flow Regimes, Pieter Boersma

Doctoral Dissertations

Flexible or flexibly-mounted structures with bluff cross-sections in flow can shed vortices at frequencies that increase with increasing flow velocity. When this shedding frequency is equal to the structure's natural frequency, the structure can oscillate. This is called vortex-induced vibrations (VIV). VIV is present in multiple fluid-structure interaction (FSI) systems which can be found in industrial, medical, and engineering applications. These oscillations can be desirable or undesirable, so understanding the physics behind this phenomenon is important. This work seeks to investigate experimentally the VIV response in the inertial-viscoelastic regime where fluid inertia and elasticity influence the system. The subcritical Newtonian …

Thermal Conductivity And Mechanical Properties Of Interlayer-Bonded Graphene Bilayers, Afnan Mostafa

Masters Theses

Graphene, an allotrope of carbon, has demonstrated exceptional mechanical, thermal, electronic, and optical properties. Complementary to such innate properties, structural modification through chemical functionalization or defect engineering can significantly enhance the properties and functionality of graphene and its derivatives. Hence, understanding structure-property relationships in graphene-based metamaterials has garnered much attention in recent years. In this thesis, we present molecular dynamics studies aimed at elucidating structure-property relationships that govern the thermomechanical response of interlayer-bonded graphene bilayers.

First, we present a systematic and thorough analysis of thermal transport in interlayer-bonded twisted bilayer graphene (IB-TBG). We find that the introduction of interlayer C-C …

Micro And Nano R2r Embossing Of Extruded Polymers, Raymond S. Frenkel

Doctoral Dissertations

This dissertation presents a process for directly imprinting or embossing extruded polymers as an advancement in roll-to-roll (R2R) embossing methods that avoids the problems of converting preformed films, increases throughput, and reduces costs. A proof-of-concept R2R apparatus was designed and constructed for directly embossing extruded polymer, and experimental results were evaluated. This laboratory scale R2R apparatus employed a thin metal ribbon belt mold with micro or nano scale features in a calendering setup, with a close coupled induction heating (IH) coil to preheat the ribbon mold above glass transition temperature (T_g) of the polymer, prior to contact with …

Improving Energy Efficiency Of School Buildings With Solar-Assisted Cooling For The Maldives, Ahmed Fathhee

Masters Theses

Anthropogenic activities are responsible for the impact of global climate change because of burning fossil fuels releasing harmful gases into the environment. As a result, the global temperature has risen about 1.18 °C since 1880, causing the global sea level to rise by 178 mm over the past century. This is a threat to countries that are closer to the ocean, especially the low-lying countries such as the Maldives. It is predicted if the sea level keeps rising, most of these islands could be below sea level by 2030.

The Maldives has a tropical climate requiring cooling to achieve thermal …

The Effects Of Hurricane Wind Field Characteristics On Wind Blade Loads, Michael S. Tsai

Masters Theses

Over recent years, offshore wind energy has been growing around the world. This necessitates placing wind turbines directly in or near the oceans where hurricanes can be. Previous research has suggested that hurricane wind veer and direction change can have adverse loading effects on the turbine. Such effects can create damage to the blade or worsen existing ones. Currently, there is no known design standard for addressing wind veer and direction change specifically from hurricanes. Quantifying the loading contribution from these phenomena is not abundant either.

This thesis seeks to demonstrate a proposed procedure for defining design veer profiles and …

Additive Manufacturing Of High-Performance Nanolamellar Eutectic High-Entropy Alloys, Jie Ren

Doctoral Dissertations

Additive manufacturing, also called three-dimensional (3D) printing, is an emerging technology for printing net-shaped components layer by layer for applications in automotive, aerospace, biomedical and other industries. In addition to the vast design freedom offered by this approach, metal 3D printing via laser powder-bed fusion (L-PBF) involves large temperature gradients and rapid cooling and provides exciting opportunities for producing microstructures and mechanical properties beyond those achievable by conventional processing routes. Although these extreme printing conditions enable microstructural refinement to the nanoscale for achieving high strength. However, high-strength nanostructured alloys by laser additive manufacturing often suffer from limited ductility. Eutectic high-entropy …

Heat Transfer Characteristics Of Latent Heat Thermal Energy Storage, Kedar Prashant Shete

Doctoral Dissertations

Latent heat thermal energy storage (LHTES) systems can be used to reduce electric demand when used in conjunction with Combined Heat and Power Plants or HVAC(Heating, Ventilation, Refrigeration and Air-Conditioning), as they can regulate the demand and supply of thermal energy. They can also be used to integrate renewable energy sources with the grid. A design procedure and performance modeling is required for designing and using thermal energy storage systems effectively. We propose hypotheses about the performance of an LHTES device with different operating conditions and material properties, for devices that are governed by different modes of heat transfer. We …

Controlling Mechanical Properties Of Well-Defined Polymer Networks, Ipek Sacligil

Doctoral Dissertations

Polymer networks are one of the most versatile and highly studied material class that revolutionized many aspects of life. Connecting the final network properties to the molecular parameters of its building blocks remains a major research thrust. Recent advances in network synthesis techniques allowed for accurate predictions of elastic modulus in model networks. Tew Group has developed highly efficient, thiol-norbornene networks with controllable mechanical properties. Chapter 2 focuses on modifying the gel fracture energy predicted by Lake-Thomas theory by accounting for loop defects. This study allowed for a priori estimates of gel fracture energy by combining theory, experiments, and simulations. …

Surface Engineering And Microfabrication Of Pdms-Based Devices For Women’S Health Applications, Jamar Hawkins

Doctoral Dissertations

Poly(dimethylsiloxane) (PDMS) is a widely used polymer in biomedical and microfluidics research due to its optical transparency, castability, gas permeability, and relative biocompatibility. However, while the favorable intrinsic properties of the polymer are typically suitable for preventing experimental artifacts, the true advantage of these devices often comes from their customized patterning and design, which can be tailored to specific applications. Critical parameters in biomedical applications such as chemical concentration profiles, fluid streamlines, substrate topography, and mechanical stiffness can all be fine-tuned simply by selecting the appropriate dimensions and arrangement of PDMS microstructures. To address challenges in expanding the application of …

Thermal Transport Across 2d/3d Van Der Waals Interfaces, Cameron Foss

Doctoral Dissertations

Designing improved field-effect-transistors (FETs) that are mass-producible and meet the fabrication standards set by legacy silicon CMOS manufacturing is required for pushing the microelectronics industry into further enhanced technological generations. Historically, the downscaling of feature sizes in FETs has enabled improved performance, reduced power consumption, and increased packing density in microelectronics for several decades. However, many are claiming Moore's law no longer applies as the era of silicon CMOS scaling potentially nears its end with designs approaching fundamental atomic-scale limits -- that is, the few- to sub-nanometer range. Ultrathin two-dimensional (2D) materials present a new paradigm of materials science and …

Wind-Wave Misalignment Effects On Multiline Anchor Systems For Floating Offshore Wind Turbines, Doron T. Rose

Masters Theses

Multiline anchors are a novel way to reduce the cost of arrays of floating offshore wind turbines (FOWTs), but their behavior is not yet fully understood. Through metocean characterization and dynamic simulations, this thesis investigates the effects of wind-wave misalignment on multiline anchor systems. Four coastal U.S. sites are characterized in order to develop IEC design load cases (DLCs) and analyze real-world misaligned conditions. Stonewall Bank, Oregon showed the highest 500-year extreme wave height, at 16.6 m, while Virginia Beach, Virginia showed the highest 500-year wind speed, at 56.8 m/s. Misalignment probability distributions, at all sites, are found to converge …

Enabling An Equitable Energy Transition Through Inclusive Research, Michael Ash, Erin Baker, Mark Tuominen, Dhandapani Venkataraman, Matthew Burke, S. Castellanos, M. Cha, Gabe Chan, D. Djokic, J.C. Ford, Anna P. Goldstein, David Hsu, Matt Lacker, C. Miller, D. Nock, A.P. Ravikumar, Allison Bates, Anna Stefanopoulou, E Grubert, D.M Kammen, M. Pastor, S.Z, Attari, S. Carley, D.L Clark, D. Dean-Ryan, U. Kosar, Kerry Bowie, Tina Johnson

ETI Publications

Comprehensive and meaningful inclusion of marginalized communities within the research enterprise will be critical to ensuring an equitable, technology-informed, clean energy transition. We provide five key action items for government agencies and philanthropic institutions to operationalize the commitment to an equitable energy transition.