Browsing by Subject "Control systems"

Now showing 1 - 3 of 3
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    Dynamics and control of Newtonian and viscoelastic fluids
    (2014-09) Lieu, Binh K.
    Transition to turbulence represents one of the most intriguing natural phenomena. Flows that are smooth and ordered may become complex and disordered as the flow strength increases. This process is known as transition to turbulence. In this dissertation, we develop theoretical and computational tools for analysis and control of transition and turbulence in shear flows of Newtonian, such as air and water, and complex viscoelastic fluids, such as polymers and molten plastics.Part I of the dissertation is devoted to the design and verification of sensor-free and feedback-based strategies for controlling the onset of turbulence in channel flows of Newtonian fluids. We use high fidelity simulations of the nonlinear flow dynamics to demonstrate the effectiveness of our model-based approach to flow control design.In Part II, we utilize systems theoretic tools to study transition and turbulence in channel flows of viscoelastic fluids. For flows with strong elastic forces, we demonstrate that flow fluctuations can experience significant amplification even in the absence of inertia. We use our theoretical developments to uncover the underlying physical mechanism that leads to this high amplification. For turbulent flows with polymer additives, we develop a model-based method for analyzing the influence of polymers on drag reduction. We demonstrate that our approach predicts drag reducing trends observed in full-scale numerical simulations.In Part III, we develop mathematical framework and computational tools for calculating frequency responses of spatially distributed systems. Using state-of-the-art automatic spectral collocation techniques and new integral formulation, we show that our approach yields more reliable and accurate solutions than currently available methods.
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    Reduced-Order Modeling and Data-driven Techniques for Control of Grid-Connected Wind Farms
    (2022-04) Vijayshankar, Sanjana
    This thesis focuses on improving the commercial viability of wind energy systems through modeling, control, and analysis. In the area of modeling, we propose computationally scalable mathematical models that are suitable for real-time control applications. These models are then utilized to systematically analyze the effects of high wind penetration on the grid. Additionally, recognizing the importance of wind energy in providing ancillary services, we propose a control platform that integrates forecasting tools with economic and aerodynamic models to maximize energy value streams. The research presented in this thesis has the potential to enhance the performance and profitability of wind energy systems, contributing to the growth and sustainability of renewable energy sources.
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    Time delay margin analysis for adaptive flight control laws.
    (2010-12) Dorobantu, Andrei
    Adaptive control algorithms have the potential to improve performance and reliability in flight control systems. Implementation of adaptive control on commercial and military aircraft requires validation and verification of the control system's robustness to modeling error and uncertainty. Currently, there is a lack of tools available to rigorously analyze the robustness of adaptive systems due to their inherently nonlinear dynamics. This thesis addresses the use of nonlinear robustness analysis for adaptive flight control systems. First, a model reference adaptive controller is derived for an aircraft short period model. It is noted that the controller is governed by polynomial dynamics. Polynomial optimization tools are then applied to the closed-loop model to assess its robustness to time delays. Time delay margins are computed for various tuning of design parameters in the adaptive law, as well as in the presence of model uncertainty.