Ocean wave energy has the potential to play a crucial role in the shift to renewable energy. In order to improve wave energy conversion techniques, a recognition of the sub-optimal nature of traditional sequential design processes due to the interconnectedness of subsystems such as the geometry, power take-off, and controls is necessary. A codesign optimization in this paper seeks to include effects of all subsystems within one optimization loop in order to reach a fully optimal design for an oscillating-surge wave energy converter. A width and height sweep serves as a brute force geometry optimization while optimizing the power take-off components and controls using a pseudo-spectral method for each geometry. An investigation of electrical power and mechanical power maximization also outlines the contrasting nature of the two objectives to illustrate electrical power maximization's importance for identifying optimality. The codesign optimization leads to an optimal design with a width of 12 m and a height of 10 m. The power take-off and controls systems are also examined more in depth to identify important areas for increased focus during detailed design. Ultimately, the codesign optimization leads to a 61.4% increase in the objective function over the optimal design from a sequential design process while also requiring about half the power take-off torque. / Master of Science / Ocean wave energy has the potential to play a crucial role in the shift to renewable energy sources. The Earth's vast oceans have immense energy potentials throughout the world, which often follow the seasonal trends of electricity demand in temperate climates. Wave energy harvesting is a technology which has been studied significantly, but has not yet experienced commercial success, partially due to the lack of convergence on a type of wave energy converter. In order to improve wave energy conversion techniques and support the convergence on a particular type, a recognition of the sub-optimal nature of traditional sequential design processes due to the interconnectedness of subsystems is necessary. A codesign optimization in this paper seeks to include effects of all subsystems within one optimization loop in order to reach a fully optimal design for an oscillating-surge wave energy converter. A width and height sweep serves as a brute force geometry optimization while optimizing the power take-off and control components for each geometry. The codesign optimization leads to an optimal design with a width of 12 m and a height of 10 m. Ultimately, the codesign optimization leads to a 62% increase in performance over the result from a sequential design process.

The core objective of this research is to develop a comprehensive understanding of Floating Offshore Wind Turbines' (FOWTs') dynamic behavior and design robust control strategies to enhance their performance and reliability in offshore environments. This begins with a detailed dynamic model of FOWTs, accounting for complex interactions between the wind field and the turbine, leading to transient motions and structural loadings. The model's novelty lies in its use of an acausal modeling environment, facilitating reconfigurability, reuse, and plug-and-play features for Control Co-Design (CCD), where system design and control development occur in parallel, optimizing performance. A significant contribution of this work is applying the Quantitative Feedback Theory (QFT) framework to FOWT control systems. QFT is a robust control methodology that enables the synthesis of controllers to accommodate uncertainties and disturbances. QFT-based controllers are designed to ensure stable and efficient FOWT operation under varying environmental conditions. Specific goals include reducing vibrational loads from blade root bending moments, tower fore-aft oscillations, and tower side-to-side oscillations, in addition to wind turbine speed control. The main actuations used are generator torque in addition to collective and individual blade pitch actuations. To validate the proposed modeling and control strategies, comprehensive simulations are performed. The dynamic model of FOWTs is rigorously validated against industry-standard tools such as OpenFAST and experimental data from a prototype FOWT. This validation ensures the model's accuracy and reliability, providing confidence in its suitability for control system design and analysis. The validation process includes achieving accurate aerodynamic characteristics, joint force predictions, and blade pitch predictions during operation. The findings of this research significantly advance floating offshore wind turbine technology. By enhancing the understanding of FOWT dynamics and providing robust control solutions, this work contributes to optimizing offshore wind energy generation, reducing the cost of energy production, and improving the sustainability of energy infrastructure.

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This thesis presents an innovative approach to enhance the stability of floating offshore wind turbine (FOWT) platform through mooring actuation. First, an OC3- Hywind spar-buoy floating platform is modeled utilizing the Control-oriented, Reconfigurable, and Acausal Floating Turbine Simulator (CRAFTS) with a specific focus on predicting hydrodynamic and mooring line loads while intentionally excluding consideration of aerodynamic forces. The accuracy of this model is validated against the industry standard OpenFAST simulator through various test cases. The central objective of this study revolves around achieving robust stabilization of the spar buoy platform, primarily focusing on X-Z symmetric planar motions, including surge, pitch, and heave degrees of freedom (DOFs). To accomplish this, two linearization techniques are employed: one transforms the inherently complex nonlinear model from CRAFTS into a linear Mass-Spring-Damper (MSD) system, particularly targeting surge and pitch motions, while the other method involves the conversion of the nonlinear model from CRAFTS into the Functional Mockup Interface (FMI) within MATLAB/Simulink for linearization. The analysis utilizing Bode plots derived from these lin- earized models yields crucial insights into the system's response to mooring actuation. Notably, it emphasizes the inherent challenge in pitch control, characterized by lower gain compared to surge at relevant frequencies, necessitating substantial mooring actuation or cable length modifications for effective pitch stabilization. Then, a Linear Quadratic Regulator (LQR) controller is designed to mitigate surge and pitch motions. Numerical simulations conducted across diverse scenarios reveal the inherent challenge in simultaneously mitigating surge and pitch motions using the original platform configuration. To address this challenge, a control co-design strategy is proposed, leading to the development of an optimized mooring line configuration that effectively stabilizes both motions with minimal adjustments. In summary, this thesis introduces a control-oriented modeling approach and an innovative control strategy to enhance the stability of the floating wind turbine platform through mooring actuation. The results emphasize the potential for broader application of this approach to various floating platforms for FOWTs and the extension of stabilization efforts to address all six DOFs in future research, where aerodynamic loads are also incorporated.

Over the last few decades, many factors, including increased electrification, have led to a critical need for fast and efficient transient cooling. Thermal management systems (TMSs) are typically designed using steady-state assumptions and to accommodate the most extreme operating conditions that could be encountered, such as maximum expected heat loads. Unfortunately, by designing systems in this manner, closed-loop transient performance is neglected and often constrained. If not constrained, conventional design approaches result in oversized systems that are less efficient under nominal operation. Therefore, it is imperative that \emph{transient} component modeling and subsystem interactions be considered at the design stage to avoid costly future redesigns. Simply put, as technological advances create the need for rapid transient cooling, a new design paradigm is needed to realize next generation systems to meet these demands. <br><br>In this thesis, I develop a new design approach for TMSs called hierarchical control co-design (HCCD). More specifically, I develop a HCCD algorithm aimed at optimizing high-fidelity design and control for a TMS across a system hierarchy. This is accomplished in part by integrating system level (SL) CCD with detailed component level (CL) design optimization. The lower-fidelity SL CCD algorithm incorporates feedback control into the design of a TMS to ensure controllability and robust transient response to exogenous disturbances, and the higher-fidelity CL design optimization algorithms provide a way of designing detailed components to achieve the desired performance needed at the SL. Key specifications are passed back and forth between levels of the hierarchy at each iteration to converge on an optimal design that is responsive to desired objectives at each level. The resulting HCCD algorithm permits the design and control of a TMS that is not only optimized for steady-state efficiency, but that can be designed for robustness to transient disturbances while achieving said disturbance rejection with minimal compromise to system efficiency. Several case studies are used to demonstrate the utility of the algorithm in designing systems with different objectives. Additionally, high-fidelity thermal modeling software is used to validate a solution to the proposed model-based design process. <br>