Ocean wave energy is currently an untapped resource with tremendous potential. Recent studiesestimate the U.S. technical wave energy resource at 1400 TWhr/year (34% of US electricity consumption in 2019). This is a massive amount of unused renewable energy that could be harnessed along both coasts of the U.S. However, technical challenges and a high levelized cost of energy (LCOE) have led to wave energy not being utilized on a societal scale. In various cost studies and surveys of wave energy converter (WEC) technology developers, structural material costs (usually steel) were identified as the leading cost driver of LCOE. With this challenge in mind, innovative ideas, materials, and designs to cut down the structural material costs for WECs could provide the biggest lever arm to make utility scale wave energy cost competitive. Alongside the potential of large-scale, utility power WECs, there is a need for continuous power at smaller scales (hundreds of watts to a few kilowatts) for applications like powering ocean observing platforms or remote charging of autonomous underwater vehicles (AUV). At these small scales, ongoing technical issues include providing continuous power in small sea states and reducing the complexity of installation procedures.

One design idea that could address the technical challenges at large and small WEC scales is toreplace most or all of a WEC’s structure with inflatables, which use thin, flexible fabrics and pressurized fluid (air or water) to create rigidity and volume. Inflatable WEC absorber structures could enable systems with lower capital and operational costs with reduced and lighter materials, and lower peak forces through active and passive load mitigation. Geometry control with inflatables, or the ability to adjust a WECs surface area and volume, is possible with water pumps or air compressors, and allows for increased energy capture in low sea states with inflation, and lower forces in storm sea states with deflation. Inflatable fabrics would create easy-to-manage devices that are smaller in size and weight when installed or removed for maintenance, because of their capacity to be deflated and folded up. This could allow for entirely new installation and/or maintenance procedures with different marine vessel classes than what is common with expensive offshore operations of conventional marine structures. However, open questions remain about the effect of inflatable flexibility on power generation performance at small and large WEC scales, and on the practicality and effects of an inflation control strategy.

This dissertation will address these open questions on inflatable WEC structure performance relativeto rigid equivalents through the use of numerical modeling of small and large scale WECs with inflatable structures. Structural flexibility is included in the WEC performance analysis through the use of the mid-fidelity generalized modes method. In this method, the structural mode shapes and natural frequencies are added as additional modes on top of the six traditional rigid body modes evaluated in hydrodynamic and multi-body dynamics analyses. In this work, modal analysis is completed in ANSYS, hydrodynamic modeling with the WAMIT boundary element method (BEM) potential flow solver, and time-domain WEC performance analysis using the open source WEC-Sim code in Matlab/Simulink. This process is repeated for both large scale (25 m diameter) and small scale (2 m diameter) heaving WECs simulated in regular and irregular waves with variable passive damping power take-off (PTO) systems. At small scales when the inflatable makes up the full absorber body, the flexibility of an inflatable is found to be small and a rigid body assumption is valid for realistic air pressures. The flexibility effect is small and mostly positive (-1% to +8%) on power production, with the main different from a rigid body at low wave periods ( 5 s). With these small changes, it is assumed the same PTO can be used with a rigid or inflatable absorber. With the effects of inflatable flexibility quantified at small scale, another chapter analyzes a WEC of this same size but with inflation geometry control in the form of inflatables that can expand the WEC diameter from 2 to 3 m. In this case, the inflatables are assumed to be pressurized until rigid. Using this design, an inflation control strategy is formulated where inflation is based on the current sea state (significant wave height and peak period pair). This geometry control ability is found to increase power production by 1.1-2.1 times, depending on deployment location and PTO power limits. Also, less than 1% of the energy increase from using inflation control is needed to power the air compressor for the developed inflation control strategy in a representative year lending merits to the benefit and feasibility of this strategy.

At large scales, where the analyzed WEC is comprised of inflatables in the center of a rigid cylindricalWEC, inflatable flexibility leads to a reduction in power production relative to a fully rigid design. WEC designs with different amounts of rigid reinforcement in the form of steel beams supporting the inflatables are also analyzed. With three steel beams, the structure with inflatables can perform as well as the fully rigid design while still enabling inflation geometry control for load reduction. To make economic comparisons, the material and manufacturing cost estimates from the U.S. DOE Wave Energy prize are implemented. Techno-economic comparisons are completed using the ACE metric also developed for the prize, an early stage technology proxy to LCOE, defined by the ratio of wave power capture efficiency to structural capital costs. On a structural cost and techno-economic basis using the ACE metric, the WEC with inflatables and some rigid reinforcement outperforms the fully-rigid design.

The results from this dissertation are valuable to WEC technology developers and researchers.At small scale, the results from this analysis provide confidence that inflatables can be used in place of a rigid structure with no detrimental effects on power production. Additionally, inflation control’s influence on power production improvements are as effective as reactive PTO control when realistic PTO efficiencies are considered. For large WECs, it can be concluded that some rigid reinforcement may be needed to ensure the same power production as a rigid equivalent. But even with this reinforcement, the economics are better for the inflatable design. Hopefully, these results draw interest in future studies on different WEC architectures using inflatables and motivate both wave tank and open ocean testing and deployments of inflatable structures.

ABSTRACT

Steps Away from (–)-Azaspirene: Synthesis of the Core Spirocycle

Chemical Studies in Copper(I) Iodide Dimethyl Sulfide Catalyzed Asymmetric Conjugate Addition

Wittig Chemistry in the Teaching Laboratory: A Novel Water-Organic Interface Reaction

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Michael John Barker Kelly

Doctor of Philosophy in Chemistry

University of California San Diego 2019

San Diego State University 2019

Doctor Bernt Mikael Bergdahl, Chair

Azaspirene is a fungal metabolite isolated by the Osada1 group in 2002 from the soil fungus Neosartorya sp. that has been shown to have promising inhibition of angiogenesis1,2 in vitro and in vivo, and which may be the key to the synthesis and elucidation of the structurally-similar pseurotin family of compounds. The pseurotin family of compounds is interesting because its members have been shown to have a wide range of interesting therapeutic effects, which will be discussed in detail. Unfortunately, it is impractical to isolate sufficient quantities of azaspirene from its natural source (85 mg were obtained from a 15 liter culture1). In addition, the previous synthetic routes to azaspirene are notoriously difficult and low-yielding. Because of these issues, sufficient material has been difficult to obtain to satisfy the twin goals of thorough biological testing to confirm the anti-angiogenic effects of azaspirene and the synthesis and elucidation of its derivatives. The overarching goal in part I has been to find a simpler, more accessible route to azaspirene, and through it the pseurotin family.

Silyl groups have been used extensively in organic synthesis as valuable protecting groups, bulky directing groups, and masked hydroxyl groups6. In 2002, the Bergdahl lab published new methodology for asymmetric silyl conjugate addition reactions with monosilylcuprates and oxazolidinones7. This methodology was expanded further in 2005 with the introduction of a novel stoichiometric copper iodide-dimethyl sulfide complex8. Combining the two approaches, and with further development that allows the catalytic use of the copper complex, we have probed the scope of the technique and shown its utility in Part II.

The Wittig reaction is a fundamental synthetic organic reaction which has been extensively used for more than fifty years to build organic frameworks through its robust creation of carbon-carbon double bonds3. However, for most of its history relatively harsh conditions have been employed to push the reaction forward. In 2007, the Bergdahl lab was able to conceive an alternative4 which used aqueous sodium bicarbonate and stabilized ylides to effect the same change in high yields. In Part III, this important methodology has been expanded. An efficient lab protocol was developed for use in teaching the reaction to undergraduates in a lab setting5.

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