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Experimental Demonstration of Multiport Multifrequency Power Systems
No full textWith considerable improvement on renewable energy and energy storage has been made, the use of renewable power sources and energy storage devices in the power system and the electrification of transportation are becoming a growing trend in recent years. To meet this need, increasing numbers of power electronics converters are included in these systems, which makes these systems become power electronics rich. In these power electronics rich systems, the interaction among the converters is significantly complicated and thus makes the power flow management challenging. The integration of these power electronics converters could be an appropriate solution to simplify the power flow management and enhance the controllability of the system.
In this research, a novel multiport multi-frequency power transfer system is presented. In this system, several independent virtual power flow channels could be established by introducing different switching frequencies in the power electronics converters. Virtual power isolation among the power flow channels could be built up because of orthogonality of the waveform. Hence, the virtual power flow channels in different frequencies will not interfere with each other. Bidirectional Power flow could happen between each port of the system, and they won���t interfere with each other.
In this research, a prototype multiport multi-frequency circuit based on the proposed theory is built up in the lab. Simulations and experiments with several scenarios are conducted. The basic operation of the prototype circuit is analyzed. And the performance of the simulations and experiments will be investigated and discussed. The feasibility of the multiport multi-frequency power transfer is validated by both simulations and experiments
Comprehensive Validation of Semi-Submersible Floater Dynamics: A Coupled CFD-FEM Approach with Iterative Wave Adjustment
No full textThis dissertation presents the development and application of a numerical wave tank based on an in-house Computational Fluid Dynamics (CFD) program, Fintie-Analytic Navier-Stokes (FANS). The CFD solver, featuring overset (Chimera) grid capability and dynamic memory allocation, enables efficient computation of multiple structured grid blocks with a large capacity for data interpolation between overset grids.
An analytic Directional Wave Simulation (DWS) program is coupled with the Navier-Stokes solver at the wave maker location. Numerical wave parameters, including wave elevation and velocity are transmitted from the DWS block to the CFD domain via overlapping grids. To achieve a calibrated numerical wave spectrum at target location, an iterative wave adjustment method is developed, utilizing a 4-wave decomposition scheme based on harmonics separation theory.
The free surface in the CFD domain is captured with the level set method. 5th-order Weighted Essentially Non-Oscillatory (WENO) and 2nd-order Alternative Direction Implicit (ADI) schemes are employed for spatial and time discretization of level set governing equations. To mitigate wave reflection at domain boundaries, a forcing zone method using damping source terms in the governing equations is introduced.
A nonlinear Finite Element Method (FEM) mooring model named MOORING3D is developed to investigate hydrodynamic responses of mooring systems. Coupled with the FANS program, this model explores the global performance of moored floating structures under various environmental conditions. A six-degrees-of-freedom (6-DOF) motion solver is integrated into the FANS program to update the motion of the floater.
A robust verification procedure based on the least-squares Richardson extrapolation method is introduced to estimate the discretization uncertainties of the numerical simulations. The convergence study in this research focuses on spatial and temporal discretization uncertainties.
Data from a comparative study at 2020 ISOPE conference is utilized to assess the wave generation and iterative wave adjustment method. Model tests from this comparative study investigate the nonlinear interactions of steep focused waves with a fixed cylinder. Wave elevations at target locations and wave slamming loads on the cylinder are compared with the experimental measurement and other numerical solutions for validation. The results highlight the positive effect of the iterative adjustment method on highly nonlinear numerical wave generation.
Verification and Validation (V&V) studies are conducted on the coupled CFD-FEM program using a Floating Offshore Wind Turbine (FOWT) platform model. Convergence studies include pitch free decay and regular wave tests, which are parts of the OC5 project (Offshore Code Comparison Collaboration, Continued, with Correlation project). The numerical wave profile and 3-DOF responses of the platform are validated against model test measurement and other numerical solutions. The agreement between the coupled numerical solution and the experiment validates the method.
The coupled numerical solution is employed to investigate hydrodynamic responses of the plat-form under highly nonlinear irregular wave conditions, addressing the importance of calibrating the wave to the target spectrum. Short-duration extreme wave cases and a long-duration 3-hour irregular wave case are conducted to comprehensively evaluate the integrated solver���s performanc
Assessing the Potential for Antibiotics to Alter Horizontal Gene Transfer Rates in Aquifers via Artificial Recharge of Treated Wastewater
No full textThe managed artificial recharge (MAR) of groundwater is a topic of growing interest regarding water resource management. MAR utilizes alternative sources of water, including treated wastewater effluent, to augment natural recharge rates and slow water table declines. MAR can be accomplished through constructed infiltration basins with high infiltration rates to the water table, or injection wells screened at the depth of the aquifer bypassing the vadose zone. One emerging contaminant commonly detected in treated wastewater is antibiotics used to treat bacterial infections in humans and agriculture. Sulfamethoxazole and trimethoprim antibiotics are commonly co-detected in treated wastewater. This thesis aims to examine the potential dissemination of antibiotic resistance in groundwater influenced by the artificial recharge of treated wastewater effluent. Recent research suggests that antibiotics can potentially modify the dissemination of antibiotic-resistant bacteria in the environment by inducing horizontal gene transfer (HGT) frequencies. HGT is the exchange of antibiotic resistance, mainly through conjugation, from resistant bacteria to susceptible bacteria. While native subsurface bacteria are often resistant to antibiotics, they pose no direct risk to humans unless pathogens acquire that resistance and an exposure pathway exists. Experimental work includes investigating the background levels of antibiotic resistance in soils and changes in antibiotic resistance after subjecting soil microbiomes to varying antibiotic concentrations. A literature review on artificial recharge, wastewater treatment, bacterial and antibiotic transport in the subsurface influenced by artificial recharge was also conducted. A series of one dimensional, variably saturated flow and solute transport simulations were conducted for an artificial recharge environment using Hydrus 1D and a range of reported concentrations and solute transport parameters in soils from the literature review. Expected results include that artificial recharge of treated wastewater may provide rapid antibiotic solute transport through the soil column and into the water table, highly dependent upon linear sorption coefficients and first-order degradation constants. Significant further research on horizontal gene transfer frequencies in native subsurface microbiomes at sulfamethoxazole and trimethoprim concentrations many times below the minimum inhibitory concentrations is needed to determine the potential risks of enhancing the environmental antibiotic resistance problem in managed artificial recharge
Single-Phase and Two-Phase Flow Visualization Experiments in Molten Salt Natural Circulation Loop
No full textA natural circulation loop facility was designed to mitigate major challenges in flow visualization experiments of molten salt. Single-phase and two-phase flow experiments were conducted for molten salt and compared to experiments with water as a benchmark study. Particle image velocimetry (PIV) measurements and continuous temperature measurements were obtained. In single-phase flow experiments, the full velocity field and near wall velocity field were captured and analyzed as a function of the Prandtl number. The friction factor and Nusselt number were determined and compared with correlations found in literature. System Analysis Module (SAM) code validation was performed using a one-dimensional fluid flow model of the experimental facility. Two model types were developed using the default friction factor in SAM and user input of the experimental friction factor. The accuracy of the model improved in predicting the velocity in the loop with input of the experimental friction factor. Successful validation was found for developed flow cases of water and molten salt. A cooling transient due to heater failure and subsequent salt solidification in the natural circulation loop facility was presented as a scaled-down accident scenario of a salt plug blockage during reactor shutdown. A main heater failure resulted in immediate cooling of temperatures around the loop, and available backup heaters were not able to compensate for the initial loss of power. The transient was analyzed in seven phases to describe the overall behavior in the loop as salt cooled to the freezing point. Two-phase flow visualization experiments were conducted for three argon bubble sizes injected into a co-current stream of molten salt in the natural circulation loop facility. Similar bubble sizes were injected in experiments with water to compare the bubble shape, trajectory, and wake flow behavior of the fluids. The bubble region of interest (ROI) was found to determine the equivalent diameter and terminal velocity as the bubble traveled through the test section. PIV analysis was performed and used with the bubble ROI to determine the slip ratio and slip velocity between the liquid phase and gaseous phase
Thermal Management and Defect Engineering in Reversible Transformations
No full textThis study delves into the nucleation behavior of thermoelastic martensitic transformations in Ni45Co5Mn36.7In13.3 microparticles, examining the influence of mesoscale order-disorder domains and phase boundaries between L21 and B2 phases on nucleation kinetics. The study compares microparticles with varying L21 domain interfacial area densities by employing solution heat treatment and secondary annealing. Characterization of 131 single particles reveals a range of undercooling from 11.3 to 59.4 K, with smaller volumes exhibiting the largest magnitude and variance. Surprisingly, nucleation site potency distributions between different domain sizes are statistically similar, suggesting that anti-site defects do not significantly impact nucleation at the length scales examined.
Additionally, our study explores the effects of helium and localized gallium irradiation on nucleation behavior. Helium irradiation induces Frenkel-pairs at our low doses (��� 0.1 dpa) and penetrates to about 4 ��m at 2 MeV. In comparison, localized gallium irradiation creates high-order defects (��� 140 dpa) and gallium implantation at depths of approximately 10 nm at 5 keV. Interestingly, helium irradiation and associated Frenkel-pairs do not statistically alter nucleation. In contrast, gallium irradiation leads to a notable reduction in the undercooling mean, indicating the potency of localized Ga+ irradiation to create potent nucleation sites.
Furthermore, this dissertation develops a theoretical framework based on thermal impedance to improve the melting efficiency of phase change material composites in transient power systems. The framework highlights the importance of the storage fraction in determining thermal impedance, offering insights into thermal design strategies for pulsed power systems. Finally, the study investigates the thermal impedance of PCM-intercalated copper foams with different pores per inch (40 ��� 90 PPI). Results show that at sufficiently small pores, the time for maximum thermal buffering decreased, peaking near on-times of 7.5 to 8 s, with diminishing returns observed for decreasing pore radii, independent of heat flux. However, the thickness of the foams was found to be a more prominent factor in reducing the observed timescales. This research contributes valuable insights into nucleation phenomena and thermal management strategies in materials science and engineering applications
Structured MXene-Polymer Composites from Pickering Emulsion Templating
No full textStructured polymer composites have gained increasing attention due to their superior property enhancement (e.g., thermal, electrical conductivity) compared to their homogeneous counterparts, by designing the internal filler structures in the polymer matrix. The fabrication and design of structured polymer composites are still challenging and the common methods (e.g., solution casting, melt blending) have limited control over the internal filler structures. Pickering emulsion templating, in contrast, is an attractive approach to creating structured composites due to their well-defined interfaces, manageable structure and dimensions, and ease of scale-up. Among the common Pickering particles, MXenes are of great interest as they have the ability to not only stabilize emulsions but also introduce functional properties into structures, such as high electrical conductivity, high EMI shielding, and rapid radio frequency (RF) heating.
In this work, we focus on the development of MXene Pickering emulsions in diverse fluidfluid systems (e.g., oil-water and oil-oil) and their use as templates for fabrication of functional structured MXene-polymer composites. Pickering emulsions drive nanosheets to the fluid-fluid interfaces and subsequent localized polymerization creates diverse structured polymer composites (e.g., capsules, armored particles, and porous monoliths). The ability to access both aqueous and nonaqueous emulsion systems largely expands the possible polymer compositions. The MXene nanosheets are organized in these composites instead of being randomly distributed throughout. For instance, polymerization of the emulsion interfaces gives polymer shells with nanosheets embedded, polymerization of the dispersed phase gives polymer particles armored with nanosheets, and polymerization of the continuous phase gives porous monoliths with polymer struct and nanosheets coated pores. The incorporation of MXenes imparts functional properties into their structures for additional applications. For example, the MXene armored particles can be used as feedstock to fabricate segregated films for efficient EMI shielding applications at low MXene loadings due to the templated network within the polymers. MXene-polymer capsules and porous monoliths show excellent RF heating performance due to the highly locally conductive regions in these structures. The research work in this dissertation provides a simple platform to produce diverse structured MXene-polymer composites with well-controlled filler distribution, versatile compositions, and functional properties for potential advanced applications
Environmental Impacts on Precipitation-Anvil Relationships
No full textTropical anvil cloud area response to the environmental effects of increased greenhouse gas emission is expected to be a negative cloud feedback for regulating climate sensitivity, although the magnitude of the effect is highly uncertain. This feedback is hypothesized to be caused by tropical deep convection acting as an iris in which anvil cloud coverage and properties are altered allowing more longwave radiation to escape. Recent studies hypothesize that a temperature dependence of convective aggregation could act as a potential mechanism to increase precipitation efficiency at the expense of anvil area. In this study, a precipitating, deep convection cloud object database is created using Tropical Rainfall Measuring Mission satellite observations from 2003-2014 to assess foundational relationships between the environment and precipitation, anvil cloud, and convective aggregation.
Analysis of the largest and strongest storms that contribute the most to tropical anvil cloud area and precipitation shows that precipitation-anvil relationships are more sensitive to changes in moisture rather than temperature, primarily due to greater sensitivity of convective processes to mid-level moisture. Our proxy for convective aggregation, the number of heavy rain cores in the cloud, had the strongest correlation with mid-level moisture increases which was coupled with greater precipitation increases relative to anvil cloud area. As moisture increases, the fractional contribution of different cloud components in the cloud objects shift, with more cold convection area and a reduction in the fraction of thin anvil area. On a system scale, this analysis is consistent with the mechanism that suggests organization and aggregation of convection results in greater precipitation per unit area of anvil cloud
Three-Dimensional Simulations of Ductile Fracture Under Arbitrary Loadings
No full textFracture leads to billions of dollars of losses worldwide every year, leading to material waste in manufacturing or disrupting the safe operation of load bearing components. For structures capable of plastic deformation, the ever-increasing demands on performance under extreme environments, combined with the challenges of an-all-experiments based approach, require the development of reliable and predictive failure models under real-world situations. In addition, new design paradigms and the development of strong, lightweight materials for use in thin-walled structures test the limits of classical methods based on linear elastic fracture mechanics. After half a century of porous material yield function development, there is still no sound basis for predicting pore-mediated ductile failure under general loadings. Tremendous progress has been achieved for modeling failure assuming mesoscopically homogeneous deformation at appropriate length scales. The inherent limitations of available theories due to the neglect of what has recently been termed unhomogeneous yielding at such scales are numerous. For example, no existing theory can predict failure in a simple torsion specimen on a sound physical basis, let alone under more general shear-dominant loadings.
In this work, a data-driven approach is followed to develop a porous material plasticity yield function that accounts for porosity, void shape and orientation. High-throughput computational limit load analysis is used to this end. The same dataset is employed to calibrate evolution equations developed on the basis of Eshelby concentration tensors. A comprehensive constitutive theory, named HUNNY, is then formulated which is applicable under general loading conditions. The theory is akin to crystal plasticity but with dependence on the resolved normal stress. In the isotropic limit, dependence upon all stress invariants is rationalized. The predictive capabilities of the theory are assessed against a large set of micromechanical unit cell calculations under combined tension and shear loading. Several realizations of the theory are implemented as user-defined subroutines to enable three-dimensional structural simulations of crack initiation and growth. Illustrations are given to simulate ductile failure in a round notched bar and a top-hat shear specimen developed at the Sandia National Laboratories. Finally, the formulation is extended to deal with more complex hexagonal materials exhibiting plastic anisotropy, such as magnesium alloys
Pair Production in Strong Fields
No full textThe correction to the Coulomb energy due to virtual production of e+e��� pairs, which is on the order of one percent of the Coulomb energy at nuclear scales, is discussed. The effects of including a pair-production term in the semi-empirical mass formula and the correction to the Coulomb barrier for a handful of nuclear collisions using the Bass and Coulomb potentials are studied. With an eye toward future work using Constrained Molecular Dynamics (CoMD) model, we also calculate the correction to the Coulomb energy and force between protons after folding with a Gaussian spatial distribution.
In the collision of two heavy ions the strong repulsion coming from the Coulomb field is enough to produce real e+e��� pair(s) from vacuum fluctuations. The energy is provided by the kinetic energy of the ions and the Coulomb interaction at the production point. If, for instance the electron is located at the center of mass (C.M.) of the two ions moving along the z-axis, and the positron at a distance x from the electron, the ions can be accelerated towards each other since the Coulomb barrier is lowered by the presence of the electron. This screening results in the increase of the kinetic energy of the colliding ions and may result in an increase of the fusion probability of light ions above the adiabatic limit.
Nuclear scattering is not the only situation where real pairs can be produced by this mechanism. In particular, the fields involved in �� decay and nuclear fission are strong enough to produce pairs. The energy of the e+e��� pair is related to the relative distance and velocity of the daughter nuclei. Thus, the energy distribution of the produced pairs can give information about the dynamics of the fission and �� decay processes. A neck model of nuclear fission is used to illustrate how the pairs can be used as a probe of the dynamics.
This model of pair production is also applied to situations with strong fields involving lasers. In particular, lasers can fully ionize clusters of atoms, which then expand in a ���Coulomb explosion," and when a laser irradiates the surface of a metal, a shower of protons is ejected in a phenomenon known as Target Normal Sheath Acceleration (TNSA). The fields involved in these cases were found to be too weak to produce pairs with this mechanism. Likewise, no pairs are produced by the gravitational field at the event horizon of a black hole, indicating that this mechanism is different from Hawking radiation
Market and Emissions Impact of All-Electric Aircraft
No full textAviation sector greenhouse gas (GHG) emissions are projected to grow nearly 50% by 2050, motivating exploration and future adoption of reduced-emissions aircraft. While all-electric aircraft (AEA) generate effectively zero in-flight GHG emissions, their prospect for commercial implementation faces critical challenges: most notably the comparatively poor specific energy of batteries relative to aviation fuel. Unanswered questions exist regarding the prospective market and emissions impact of future AEA. This dissertation addresses these knowledge gaps, building on detailed AEA designs available in the literature to quantify AEA market impact and emissions reduction potential across thousands of varying model inputs, market bases, emissions scenarios, and timeframes. This work compares the energy consumption and emissions of conventional aircraft and AEA for every domestic commercial flight in the United States ��� nearly 9.2 million flights in total ��� determining feasibility of electrification, energy requirements, and greenhouse gas emissions for each route and providing novel quantitative estimates of potential AEA impact in the United States.
This dissertation demonstrates clear, albeit conditional, pathways for AEA to reduce aviation sector emissions. Modern-day lithium-ion batteries have insufficient energy for use in the aviation sector: AEA potential hinges on development of batteries with a specific energy three to four times greater than modern batteries. Unlike hydrocarbon-powered aircraft, the emissions footprint for AEA varies by point-of-departure based on power sector emissions generated during battery charging. Assuming historic trends in power sector emissions persist, AEA offer regional potential in the Pacific Northwest, California, and the East Coast, but would have limited national impact reducing aviation sector emissions: at maximum market penetration 1.74% to 7.95% depending on emissions timeframe for a 1000 Wh/kg onboard battery. Achieving greater emissions reduction requires transition to reduced-emissions power generation. Assuming net-zero power sector emissions, AEA could reduce total domestic aviation sector emissions by more than 27% at maximum market penetration while capturing the majority of the aviation market in terms of total flights and passenger count but would require roughly 2% of total US electricity generation (96.6 TWh). These results are highly sensitive to inherent uncertainty in the radiative forcing of non-CO��� emissions and vary by emissions model and timeframe