Browsing by Author "Rotea, Mario A."
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Item Aerodynamic Design and Control of Vertical Axis Wind Turbines(2021-12-01T06:00:00.000Z) Sakib, Mohammad Sadman; Griffith, Todd; Iungo, Giacomo Valerio; Rotea, Mario A.; De Tavernier, DelphineThe need to combat climate change and find alternate solutions to fossil fuel is at an all time high. Researchers continue to drive the advancement of wind turbine technology since it is a viable alternate solution towards a sustainable future. With the advancement of wind turbine technology over the last 20 years, horizontal axis wind turbines (HAWTs) particularly have received more attention. But there is an alternate turbine configuration called vertical axis wind turbine (VAWTs). Some of the advantages of VAWTs over HAWTs are namely, it’s independent of wind direction, low sound emissions, easy access to turbine components like generator and gearbox (due to placement at tower base) and lower topside center of gravity compared to HAWTs. This thesis focuses on the aerodynamic design study and development of control strategy of conventional troposkein shaped Darrieus vertical axis wind turbines (VAWTs) using CACTUS (Code for Axial and Crossflow TUrbine Simulation), which is a 3D numerical vortex based lifting line aerodynamic model. The first half of the thesis focuses on the detailed aerodynamic design study of VAWTs and how the selection of various design variables affect this design process. This study systematically analyzes the effect of different design variables including the number of blades (N), aspect ratio (AR) and blade tapering in a comprehensive loads analysis of both the parked and operating aerodynamic loads including turbine power performance analysis. The second half of the thesis focuses on the development of a novel method to control rotor dynamics named intracycle RPM control strategy, for VAWTs. VAWTs perform sub-optimally in regions 2 and 3 due to the absence of a pitch mechanism and low starting torque, which significantly affects their annual energy production. But introducing a pitching mechanism in VAWTs also takes away one of its biggest advantages over its competitors, which is mechanical simplicity. An alternate control strategy named intracycle RPM control or intracycle angular velocity control is presented, where the rotational speed of the turbine is allowed to vary with the azimuthal location of blades, which is able to alter the rotor inflow conditions to maximize power output while having constraining the loads. With the help of an optimizer named GPOPSII, which optimizes the rotational speed over a single revolution at a particular wind speed, coupled with CACTUS, which measures the performance of the rotor, it is shown that the aerodynamic AEP can be increased while restraining loads at prescribed limits.Item Control of Wind Power Systems for Energy Efficiency and Reliability(2018-12) Xiao, Yan; Rotea, Mario A.; Li, Yaoyu; Fahimi, BabakWith decades of development of wind energy technology, the cost of electricity production from wind has decreased significantly. To stimulate higher penetration of wind energy in the electric grid, further research and development are needed to reduce the Levelized Cost of Energy (LCOE) of wind power systems. The LCOE of wind energy may be reduced by: 1) increasing the Annual Energy Production (AEP); 2) reducing the operation and maintenance (O&M) costs; 3) reducing the capital expenditures. On the aeromechanics side, increasing the AEP is achieved by increasing the turbine aeromechanical efficiency (the power coefficient CP of a wind turbine), while reducing the O&M costs could be attained by reducing the aeromechanical forces and moments on the wind turbine rotor and structure. On the electrical side, the AEP is increased by increasing the efficiency of the electricity generation, conversion and transmission, while the capital expenditures may be reduced by lowering the costs of electric components. Conventional wind turbine control schemes are mostly model based, and may rely on wind speed measurements for some cases. However, accurate wind turbine models and wind speed measurements may be difficult and costly to acquire. Extremum Seeking Control (ESC) is a nearly model-free optimization approach suitable for automatically finding the optimal torque gain and blade pitch angle that results in maximized wind turbine aeromechanical efficiency. Previous studies on ESC based wind turbine control are all simulation based. To further evaluate the effectiveness and potential of ESC for wind energy applications, it is necessary to implement the ESC controller on a commercial scale wind turbine, and evaluate the performance through field test. This dissertation presents the results of a field test of an ESC based controller on the NREL’s (National Renewable Energy Laboratory) 600 KW CART3 wind turbine. Also, to reduce the wind turbine aeromechanical loads, while increasing the power coefficient, a multi-objective ESC wind turbine control scheme is proposed. The effectiveness of this multi-objective ESC is evaluated using computer simulations. The second major part of this dissertation is dedicated to investigating two control challenges of the DFIG-DC (DFIG: doubly-fed induction generator; DC: direct current) framework. One of the most critical issues is the torque ripple caused by uncontrollable rectification. In this dissertation, a torque ripple mitigation scheme based on the Multiple Reference Frame (MRF) method is proposed. The effectiveness of the proposed strategy is evaluated through both simulations and experiments. Another control challenge of the DFIG-DC framework is associated with stator frequency control. This dissertation presents computer simulations and experiments indicating that the efficiency of the DFIG-DC system is a unimodal function of the stator frequency. It is also shown that the optimal stator frequency, attaining the highest efficiency, varies with the generator rotor speed. Since it is difficult to obtain an accurate efficiency model of the DFIG-DC system, ESC is implemented to find this optimal frequency in real time. The effectiveness and performance of the proposed ESC based optimal stator frequency control is evaluated with both simulations and experiments.Item Data-Driven RANS for Simulations of Large Wind Farms(Institute of Physics Publishing) Iungo, Giacomo V.; Viola, F.; Ciri, Umberto; Rotea, Mario A.; Leonardi, Stefano; 0000-0002-0990-8133 (Iungo, GV); 0000-0002-9809-7191 (Leonardi, S); Sorensen J.N.; Ivanell S.; Barney A.; Iungo, Giacomo V.; Ciri, Umberto; Rotea, Mario A.; Leonardi, StefanoIn the wind energy industry there is a growing need for real-time predictions of wind turbine wake flows in order to optimize power plant control and inhibit detrimental wake interactions. To this aim, a data-driven RANS approach is proposed in order to achieve very low computational costs and adequate accuracy through the data assimilation procedure. The RANS simulations are implemented with a classical Boussinesq hypothesis and a mixing length turbulence closure model, which is calibrated through the available data. High-fidelity LES simulations of a utility-scale wind turbine operating with different tip speed ratios are used as database. It is shown that the mixing length model for the RANS simulations can be calibrated accurately through the Reynolds stress of the axial and radial velocity components, and the gradient of the axial velocity in the radial direction. It is found that the mixing length is roughly invariant in the very near wake, then it increases linearly with the downstream distance in the diffusive region. The variation rate of the mixing length in the downstream direction is proposed as a criterion to detect the transition between near wake and transition region of a wind turbine wake. Finally, RANS simulations were performed with the calibrated mixing length model, and a good agreement with the LES simulations is observed.Item Data-Driven Reduced Order Model for Prediction of Wind Turbine Wakes(Institute of Physics Publishing) Iungo, Giacomo V.; Santoni-Ortiz, Christian; Abkar, M.; Porté-Agel, F.; Rotea, Mario A.; Leonardi, Stefano; Iungo, Giacomo V.; Santoni-Ortiz, Christian.; Rotea, Mario A.; Leonardi, StefanoIn this paper a new paradigm for prediction of wind turbine wakes is proposed, which is based on a reduced order model (ROM) embedded in a Kalman filter. The ROM is evaluated by means of dynamic mode decomposition performed on high fidelity LES numerical simulations of wind turbines operating under different operational regimes. The ROM enables to capture the main physical processes underpinning the downstream evolution and dynamics of wind turbine wakes. The ROM is then embedded within a Kalman filter in order to produce a time-marching algorithm for prediction of wind turbine wake flows. This data-driven algorithm enables data assimilation of new measurements simultaneously to the wake prediction, which leads to an improved accuracy and a dynamic update of the ROM in presence of emerging coherent wake dynamics observed from new available data. Thanks to its low computational cost, this numerical tool is particularly suitable for real-time applications, control and optimization of large wind farms.Item Data-enhanced Stochastic Dynamical Modeling for Wind Farms(December 2022) Bhatt, Aditya H. 1997-; Zare, Armin; Leonardi, Stefano; Rotea, Mario A.; Zhang, JieLow-fidelity analytical models of turbine wakes have traditionally been used to demonstrate the utility of advanced control algorithms in increasing the annual energy production of wind farms. In practice, however, it remains challenging to achieve significant performance improvements using closed-loop strategies that are based on conventional low-fidelity models. This is due to the over-simplified static nature of wake predictions from models that are agnostic to the complex aerodynamic interactions among turbines. In this thesis, we offer a stochastic dynamical modeling framework to improve the predictive capability of low-fidelity models while remaining amenable to control design. The framework is capable of capturing the effect of atmospheric turbulence on the thrust force and power generation as determined by the actuator disk concept. In this approach, we use stochastically forced linear models of the turbulent velocity field to augment the analytically computed wake velocity and achieve consistency with higher-fidelity models in capturing power and thrust force measurements. The power-spectral densities of our stochastic models are identified via convex optimization to ensure statistical consistency while preserving model parsimony. We demonstrate the utility of our approach in estimating the thrust force and power signals generated by large- eddy simulations of the flow over a cascade of turbines. We also evaluate the capability of our models in predicting turbulence intensities at the hub height of a multi-turbine wind farm.Item Design of Large Wind Turbine Rotors Through Passive and Active Load Mitigation Strategies(2022-05-01T05:00:00.000Z) Chetan, Mayank; Griffith, D. Todd; Guo, Xiaohu; Rotea, Mario A.; Malik, Arif; Jin, YaqingWind energy over the years has positioned itself to become a primary source of renewable energy and this is attributed to the reduction in the Levelized Cost of Energy (LCOE). Historically, this is accomplished by an increase in tower heights which allow access to higher wind speeds, and also by increasing rotor diameters which allow for more power capture. However, there are significant challenges that come with these large turbines like aeroelastic instabilities of the blades due to their long and slender nature, and the need for more robust turbine components that can withstand the larger loads associated with large turbines. This has motivated the development of design strategies that incorporate different methods of load alleviation to achieve optimized wind turbine designs that can result in lower LCOE. This dissertation presents various methods of designing wind turbine rotors that take advantage of passive and active load reduction strategies. First, classical flutter is addressed for the design of large blades. Flutter is an aeroelastic instability that contributes to fatigue damage, or in the worst case can least to sudden catastrophic turbine failure. A comprehensive evaluation of flutter behavior including classical flutter, edgewise vibration, and flutter mode characteristics for two- and three-bladed wind turbine blade designs is carried out. Further, a study is performed to evaluate mitigation of flutter in the design process via structural redesign by evaluating the effect of leadingvi edge and trailing edge reinforcement on flutter speed and hence demonstrates the ability to increase the flutter speed and satisfy structural design requirements (such as fatigue) while maintaining or even reducing blade mass. This flutter structural mitigation study is conducted for two wind turbine designs, one a two-bladed rotor and the other a three-bladed rotor. Second, a new rotor design methodology is developed to integrate active load control in the form of controllable gurney flaps. A comprehensive sequential iterative design procedure is developed that integrates aerodynamics, structural, and baseline turbine control system design with advanced active load control into a design process. This procedure also takes into account the contribution of loads on all major components of the turbine. To realize the best LCOE reduction solution, new methods to evaluate blade structural properties are developed wherein, the reductions in damage equivalent loads (i.e.; fatigue loads) due to a generic active load control system are mapped to structural design improvements in terms of blade mass reduction, cost reduction in other major turbine components, and LCOE reductions that result from integration and redesign of the turbine with the active load control system. Third, using the design methodologies established, newer rotor designs with a larger rotor radius are explored to examine the impacts of the active load control system. These rotors take advantage of the fatigue load reductions due to the controllable gurney flaps integrated into the design. The effect of the controllable gurney flaps is evaluated for various blade and non-blade component loads on the turbine. This methodology results in larger rotors that have increased energy capture and reduced LCOE’s. For this study, two different turbine operating strategies are followed, one limits the turbine power to that of the baseline while the other allows the turbine to extract more power at higher wind speeds. Finally, a method is introduced to support the realization of new passive and active load mitigation strategies by improving prototype wind turbine development. A novel method of developing a multi-fidelity digital twin structural model of a wind turbine blade is presented. The digital twin model development methodology, presented herein, involves a novel calibration process to integrate a wide range of information including design specifications, manufacturing information, and structural testing data (modal and static) to produce a multi-fidelity digital twin structural model: a detailed high-fidelity model (i.e., 3D FEA) and consistent beam-type models for aeroelastic simulation. Digital twin models are useful to cost-effectively evaluate the performance of new technologies in the field like novel downwind rotors and controllable gurney flaps. Finally, the new methodology is demonstrated for an as-built two-bladed downwind prototype rotor resulting in a multi-fidelity digital twin model which has a 1% match in mass properties, 3.2% in blade frequencies, and 6% in deflection to the as-built blade. The rotor examined is the SUMR – Demonstrator (SUMR-D), which was installed on the Controls Advanced Research Testbed (CART-2) wind turbine at the National Wind Technology Center. The digital twin model developed here was utilized to design controllers to safely operate SUMR-D in field tests, which are providing additional data for further evaluation and development of the multi-fidelity digital twin structural model.Item Effect of the Turbine Scale on Yaw Control(John Wiley & Sons Ltd) Ciri, Umberto; Rotea, Mario A.; Leonardi, Stefano; 0000-0002-9809-7191 (Leonardi, S); Ciri, Umberto; Rotea, Mario A.; Leonardi, StefanoYaw misalignment between the incoming wind and the rotor of a turbine causes a lateral displacement of the wake. This effect can be exploited to avoid or mitigate wake interactions in wind farms, so that power losses are minimized. We performed large-eddy simulations to evaluate yaw control for a three-turbine wind farm. We used two different turbine models to assess how the size of the turbine rotor affects the farm efficiency and the effectiveness of the control strategy. A utility-scale wind turbine with rotor diameter of 126 m is compared with a scaled research wind turbine with rotor diameter of 27 m. In both cases, a model-free algorithm is used to determine the turbine yaw set point, which maximizes total power production. The algorithm is the nested extremum-seeking control (NESC), which allows for the coordinated optimization of the wind turbine operating points. The results achieved with NESC are validated by computing a static performance map for different yaw angles. NESC converges to optimal operating conditions, which are in good agreement with the static map benchmark. Numerical results show that a larger rotor diameter induces larger wake deflection, thus achieving higher power improvements. From the analysis of the turbine structural loads, an increase in damage equivalent load is observed for both the yawed turbine and the waked one. Present results suggest that there is a cost-effective trade-off between performance and loads for large turbines. © 2018 John Wiley & Sons, Ltd.Item Evaluation of Log-Of-Power Extremum Seeking Control for Wind Turbines Using Large Eddy Simulations(John Wiley & Sons Ltd) Ciri, Umberto; Leonardi, Stefano; Rotea, Mario A.; 0000-0002-9809-7191 (Leonardi, S); 0000-0002-4239-0591 (Rotea, MA); Ciri, Umberto; Leonardi, Stefano; Rotea, Mario A.The extremum seeking control (ESC) algorithm has been proposed to determine operating parameters that maximize power production below rated wind speeds (region II). This is usually done by measuring the turbine's power signal to determine optimal values for parameters of the control law or actuator settings. This paper shows that the standard ESC with power feedback is quite sensitive to variations in mean wind speed, with long convergence time at low wind speeds and aggressive transient response, possibly unstable, at high wind speeds. The paper also evaluates the performance, as measured by the dynamic and steady state response, of the ESC with feedback of the logarithm of the power signal (LP-ESC). Large eddy simulations (LES) demonstrate that the LP-ESC, calibrated at a given wind speed, exhibits consistent robust performance at all wind speeds in a typical region II. The LP-ESC is able to achieve the optimal set-point within a prescribed settling time, despite variations in the mean wind speed, turbulence, and shear. The LES have been conducted using realistic wind input profiles with shear and turbulence. The ESC and LP-ESC are implemented in the LES without assuming the availability of analytical gradients. ©2019 John Wiley & Sons, Ltd.Item Home-based Lower Limb Immersive Serious Game for Phantom Pain Management(December 2023) Chung, Yu-Yen 1987-; Prabhakaran, Balakrishnan; Rotea, Mario A.; Kim, Jin Ryong; Xiang, Yu; Guo, XiaohuWith recent advances in mixed reality technology, Head Mounted Devices (HMDs) have become a preferred option for immersive gaming at home. Immersive games using HMD have been applied for serious purposes, such as improving motivation for performing rehabilitation activities at home. Mr.MAPP is a virtual mirror therapy system designed for amputees with phantom limb pain. In this work, we first investigate the Mr.MAPP system through a clinical patient study and further improve the system design based on the uncovered insight. In addition, to allow users to experience mixed reality in the first-person perspective using their realistic body reconstruction, we prototype a system to aggregate the body’s texture in realtime. Through simulation using the reconstruction system, we created an optimal camera setup guideline for amputees’ in-home setup. Lastly, a Home-based Lower Limb Immersive Exergame System (HILLES) is developed to address challenges such as system setup, safety, and game engagement for in-home usage. A stomping game using the system is developed for an exploratory user study to evaluate the system and the proposed enhancements. The discovered insight could be helpful for future lower limb exergame design.