An experimental study of a low-frequency transcritical thermoacoustic device has been conducted at Purdue University's Maurice J. Zucrow Laboratories. The purpose of this study was to characterize the thermoacoustic response of transcritical R-218 and asses it's feasibility for energy extraction and waste heat removal. This rig operated as a standing-wave configuration and achieved pressure amplitudes as high as 690 KPa (100 psi) at a temperature difference of 150 K and a bulk pressure of 1.3 P/P_cr(3.43 MPa). To the author's knowledge, this is the highest ever thermoacoustic pressure amplitude achieved in a non-reacting flow. The thermoacoustic response was characterized by varying temperature difference and bulk pressure parametrically. The effect of resonator length was characterized in a set of tests where resonator length and bulk pressure was varied parametrically at a single temperature difference. Finally, the feasibility for energy extraction was assessed in a set of tests which characterized the ability of the working fluid to pump itself through a recirculation line with check valves. This set of tests showed that the working fluid was able to create self-sustained circulation by inducing a pressure differential across the check valves with the thermoacoustic response. This circulation was induced while still maintaining a significant pressure amplitude, demonstrating promising results as a feasible method for energy extraction and waste heat removal.

Advanced power electronic techniques are crucial to enable high-performance energy conversion systems for the applications of various load and source interfaces, e.g., electric vehicle battery charger, solar power, wind power, motor traction, grid-connection. Also, the improvements on electrification for energy conversion contributes to the Carbon Neutrality with the reduction of fuel combustion. The control and design of the power conversion systems largely determine the efficiency, power density and system cost which typically need specialized design procedures. Since the types of interfaced energy sources may vary, the corresponding control algorithms and hardware configurations will be different. Thus, the power electronics system design is conventionally a specific routine based on the desired source and load requirements. Generally speaking, two main perspectives need to be considered when designing a power conversion system: (1) the power converter circuitry topology with the corresponding hardware components, e.g., low/high power circuits design, passive components design; (2) control algorithms and functions design, e.g., voltage/current control techniques, active/reactive power balancing and adjustment. However, the repetitive and specific power electronics design procedures for different load/source requirements are time-consuming and costly. This thesis proposes a software-defined power electronics concept to develop a generalized auto-converter module (ACM) by leveraging variable-frequency critical-soft-switching, model predictive control techniques and high-performance litz-PCB inductors. The software-defined power electronics techniques can be applied to various types of electrified load/source applications without the need of repetitive hardware components and software algorithms designing procedures. The fundamental unit for the generalized concept, auto-converter module, is a type of MPC-based power module. A hierarchical control architecture is designed to manage the local ACMs and satisfy different load/source energy conversion requirements with high efficiency, high power-density and high-reconfigurability. To achieve high-performance for the software-defined power electronics system, several advanced technologies are developed and integrated including variable-frequency critical-soft-switching, modular model predictive control, litz-PCB inductor design. Firstly, a variable-frequency critical-soft-switching technique is developed to adjust the switching frequency for the zero-voltage soft-switching. Doing so, the switching losses can be largely reduced with high efficiency. Secondly, the critical-soft-switching inductor is designed based on litz-PCB winding structure and neural network model to optimize the inductor losses and reduce the volume for the application of high frequency and large current ripple. Thirdly, a modular model predictive control method is designed for each of the local ACM to improve the dynamic performance and attenuate the oscillation caused by the variable frequency operation. Lastly, a hierarchical control architecture is developed to generalize the software-defined power electronics with multi-layer structure, central control layer, local module control layer and application layer. The hierarchical control architecture can be widely applied to different types of load/source interfaces, e.g., single/three-phase grid-connected inverters, motor traction inverter, battery charger, solar energy and so on. Leveraging the hierarchical control architecture and software-defined power electronics, the repetitive power converter hardware components and software algorithms design procedures can be simplified and standardized. Also, for different power converter applications, the efficiency and power density are both improved with better dynamic performance.

Molecular engineering of donor-acceptor dyads and multimodular systems to control the yield and lifetime of charge separation is one of the key goals of artificial photosynthesis for harvesting sustainably solar energy. The design of the donor-acceptor systems mimic a part of green plants and bacterial photosynthetic processes. The photochemical events in natural photosynthesis involve the capturing and funneling of solar energy by a group of well-organized chromophores referred to as an ‘antenna' system causing an electron transfer into the ‘reaction center,' where an electron transfer processes occur resulting a long-lived charge separated state. Over the last two to three decades, many efforts have been directed by the scientific community designing of multi-modular systems that are capable of capturing most of the useful sunlight and generating charge separated states of prolonged lifetimes with adequate amounts of energy. In this dissertation, we report on the design and synthesis of donor–acceptor conjugates with the goal of modulating the yield and lifetime of their charge separated states and hence, improving the conversion of light energy into chemical potential. In simple donor-acceptor systems, generally, the energy and electron transfer events originate from the singlet excited state of the donor or acceptor and can store the greatest amount of energy but must be fast to out compete intersystem crossing. To address this limitation, we have designed novel donor –acceptor conjugates that use high-energy triplet sensitizers in which electron transfer is initiated from the long lived triplet state of the donor. The triplet photosensitizers used were palladium(II) porphyrin and platinum(II) porphyrin. Heavy metal effect in these porphyrins promoted intersystem crossing and the energies of their excited state was quite high. For the case of palladium (II) porphyrin the energy stored was found to 1.89 eV and that of platinum(II) porphyrin 1.84 eV. In addition to using triplet photosensitizers as donors, we have used donors that are difficult to oxidize and hence producing long lived charge separated states with adequate amount of stored energy. The system that was used for this study is zinc porphyrin with meso-aryl pentafluorophenyl substituents and fullerene, C60 as the acceptor. The presence of fluorine substituents on zinc porphyrin makes it harder to undergo oxidation. When this high potential donor-acceptor system undergoes a photoinduced charge-separation, the estimated energy stored was found to be 1.70 eV, one of the highest reported in literature so far. To further extend the lifetime of the charge separated states generated in this high-potential zinc porphyrin-fullerene dyad a pyridine functionalized tetrathiafulvalene was axially coordinated to the Zn metal producing a supramolecular triad capable of producing long-lived charge separated state. In a subsequent study, a multi-modular donor-acceptor system composed of a porphyrin, fullerene (C60) and a BF2-chelated dipyrromethene (BODIPY) with a supramolecular arrangement in the form of porphyrin-BODIPY-C60, one of the few reported in literature. By selectively exciting BODIPY and ZnP moieties, efficient singlet-singlet energy transfer from 1BODIPY * to ZnP in toluene was observed in the case of the dyad ZnP-BODIPY. However, when ZnP is excited, electron transfer occurred with the formation ZnP.+-BODIPY-C60.- charge separated state persisting for microseconds.

The increasing global participation of wind power in the overall generation ca- pacity makes it one of the most promising renewable resources. Advances in power electronics have enabled this market growth and penetration. Through a literature review, this work explores the challenges and opportunities presented by offshore wind farms, as well as the different solutions proposed concerning power electron- ics converters, collection and transmission schemes, as well as control and protection techniques. A novel power converter solution for the parallel connection of high power offshore wind turbines, suitable for HVDC collection and transmission, is presented. For the parallel operation of energy sources in an HVDC grid, DC link voltage con- trol is required. The proposed system is based on a full-power rated uncontrolled diode bridge rectifier in series with a partially-rated fully-controlled thyristor bridge rectifier. The thyristor bridge acts as a voltage regulator to ensure the flow of the desired current through each branch, where a reactor is placed in series for filtering of the DC current. AC filters are installed on the machine side to mitigate harmonic content. The mathematical modeling of the system is derived and the control design procedure is discussed. Guidelines for equipment and device specifications are pre- sented. Different setups for an experimental framework are suggested and discussed, including a conceptual application for hardware-in-the-loop real-time simulation and testing.

abstract: Continuing and increasing reliance on fossil fuels to satisfy our population’s energy demands has encouraged the search for renewable carbon-free and carbon-neutral sources, such as hydrogen gas or CO2 reduction products. Inspired by nature, one of the objectives of this dissertation was to develop protein-based strategies that can be applied in the production of green fuels. The first project of this dissertation aimed at developing a controllable strategy to incorporate domains with different functions (e. g. catalytic sites, electron transfer modules, light absorbing subunits) into a single multicomponent system. This was accomplished through the rational design of 2,2’-bipyridine modified dimeric peptides that allowed their metal-directed oligomerization by forming tris(bipyridine) complexes, thus resulting in the formation of a hexameric assembly. Additionally, two different approaches to incorporate non-natural organometallic catalysts into protein matrix are discussed. First, cobalt protoporphyrin IX was incorporated into cytochrome b562 to produce a water-soluble proton and CO2 reduction catalyst that is active upon irradiation in the presence of a photosensitizer. The effect of the porphyrin axial ligands provided by the protein environment has been investigated by introducing mutations into the native scaffold, indicating that catalytic activity of proton reduction is dependent on axial coordination to the porphyrin. It is also shown that effects of the protein environment are not directly transferred when applied to other reactions, such as CO2 reduction. Inspired by the active site of [FeFe]-hydrogenases, the second approach is based on the stereoselective preparation of a novel amino acid bearing a 1,2-benzenedithiol side chain. This moiety can serve as an anchoring point for the introduction of metal complexes into protein matrices. By doing so, this strategy enables the study of protein interactions with non-natural cofactors and the effects that it may have on catalysis. The work developed herein lays a foundation for furthering the study of the use of proteins as suitable environments for tuning the activity of organometallic catalysts in aqueous conditions, and interfacing these systems with other supporting units into supramolecular assemblies. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2019

A wind turbine array was constructed in the wind tunnel at Portland State University in a standard Cartesian arrangement. Configurations of the turbine array were tested with rotor blades set to rotate in either a clockwise or counter-clockwise sense. Measurements of velocity were made with stereo particle-image velocimetry. Mean statistics of velocities and Reynolds stresses clearly show the effect of direction of rotation of rotor blades for both entrance and exit row turbines. Rotational sense of the turbine blades is visible in the mean spanwise velocity W and the Reynolds shear stress -[macron over vw]. The normalized anisotropy tensor was decomposed yielding invariants [lowercase eta] and [lowercase xi], which are plotted onto the Lumley triangle. Invariants of the normalized Reynolds stress anisotropy tensor indicate that distinct characters of turbulence exist in regions of the wake following the nacelle and the rotor blade tips. Eigendecomposition of the tensor yields principle components and corresponding coordinate system transformations. Characteristic spheroids are composed with the eigenvalues from the decomposition yielding shapes predicted by the Lumley triangle. Rotation of the coordinate system defined by the eigenvectors demonstrates streamwise trends, especially trailing the top rotor tip and below the hub of the rotors. Direction of rotation of rotor blades is evidenced in the orientation of characteristic spheroids according to principle axes. The characteristic spheroids of the anisotropy tensor and their relate alignments varies between cases clearly seen in the inflows to exit row turbines. There the normalized Reynolds stress anisotropy tensor shows cumulative effects of the rotational sense of upstream turbines. Comparison between the invariants of the Reynolds stress anisotropy tensor and terms from the mean mechanical energy equation indicate a correlation between the degree of anisotropy and the regions of the wind turbine wakes where turbulence kinetic energy is produced. The flux of kinetic energy into the momentum-deficit area of the wake from above the canopy is associated with prolate characteristic spheroids. Flux upward into the wake from below the rotor area is associate with oblate characteristic spheroids. Turbulence in the region of the flow directly following the nacelle of the wind turbines demonstrates more isotropy compared to the regions following the rotor blades. The power and power coefficients for wind turbines indicate that flow structures on the order of magnitude of the spanwise turbine spacing that increase turbine efficiency depending on particular array configuration.

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