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1. Power Estimation of an Experimental Ocean Current Turbine Based on the Conformal Mapping and Blade Element Momentum Theory

   https://doi.org/10.1115/IMECE2021-71751  

   Sadeqi, S. ; Xiros, N. ; Aktosun, E. ; VanZwieten, J. ; Sultan, C. ; Ioup, J. ; Rouhi, S. ( November 2021 , ASME International Mechanical Engineering Congress and Exposition (IMECE))

   Conformal mapping techniques have been used in many applications in the two-dimensional environments of engineering and physics, especially in the two-dimensional incompressible flow field that was introduced by Prandtl and Tietjens. These methods show reasonable results in the case of comprehensive analysis of the local coefficients of complex airfoils. The mathematical form of conformal mapping always locally preserves angles of the complex functions but it may change the length of the complex model. This research is based on the design of turbine blades as hydrofoils divided into different individual hydrofoils with decreasing thickness from root to tip. The geometric shapes of these hydrofoils come from the original FX77W121 airfoil shape and from interpolating between the FX77W121, FX77W153, and FX77W258 airfoil shapes. The last three digits of this airfoil family approximate the thickness ratio times 1000 (FX77153 => 15.3 % thickness ratio). Of the different airfoil shapes specified for the optimal rotor, there are 23 unique shapes.[15, 16, 17, 18, 19, 20, 21, 22, 24, 25, 28] This study describes the advantage of using at least one complex variable technique of transformation conformal mapping in two dimensions.

   Conformal mapping techniques are used to form a database for sectional lift and drag coefficients based on turbine blade design to be used in Blade Element Momentum (BEM) theory to predict the performance of a three bladed single rotor horizontal axis ocean current turbine (1.6-meter diameter) by considering the characteristics of the sea-water. In addition, by considering the fact that in the real ocean, the underwater ocean current turbines encounter different velocities, the maximum brake power will be investigated for different incoming current velocities. The conformal mapping technique is used to calculate the local lift coefficients of different hydrofoils with respect to different angles of attack: −180 ≤ AOA ≤ +180. These results will be compared to those from other methods obtained recently by our research group. This method considers the potential flow analysis module that follows a higher-order panel method based on the geometric properties of each hydrofoil cross section. The velocity and pressure fields are obtained directly by the applications of Bernoulli’s principle, then the lift coefficients are calculated from the results of the integration of the pressure field along the hydrofoil surface for any angle of attack. Ultimately, the results of this research will be used for further investigation of the design and construction of a small-scale experimental ocean current turbine to be tested in the towing tank at the University of New Orleans.

    

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2. Applying Artificial Intelligence to Optimize Small-Scale Ocean Current Turbine Performance

   https://doi.org/10.1115/IMECE2022-95804  

   Rouhi, Shahab ; Sadeqi, Setare ; Xiros, Nikolaos ; Birk, Lothar ; Aktosun, Erdem ; Ioup, Juliette ( October 2022 , American Society of Mechanical Engineers)

   A comprehensive artificial intelligence-based motor drive was developed to control the performance of a permanent magnet direct current (PMDC) motor employed as a small-scale three-bladed horizontal axis ocean current turbine. Although the conventional controller performs reasonably in a lab environment where non-linear load is absented; however, for towing tank experiments with noisy and potentially non-linear input, it is crucial to run the small-scale turbine in a robust mode. A mathematical model of a PMDC motor dynamic system is derived incorporating a fuzzy logic controller. In addition, this drive control was validated experimentally. The experimental design is discussed in detail. The system performance was tested experimentally over a wide range of operating condition to validate the fuzzy logic control robustness and effectiveness. Also, it is shown that the speed of the PMDC motor was controlled by using this fuzzy logic controller. The speed tracking shows good agreement with the reference speed regardless of the load condition.

    

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3. Performance Characteristics of PMDC Motor of Small-Scale Experimental Ocean Current Turbine

   https://doi.org/10.1115/IMECE2022-95774  

   Rouhi, Shahab ; Xiros, Nikolaos ; Aktosun, Erdem ; VanZwieten, James ; Sultan, Cornel ; Ioup, Juliette ; Sadeqi, Setare ( October 2022 , American Society of Mechanical Engineers)

   A comprehensive numerical model was developed to address the performance of a permanent magnet direct current (PMDC) motor which is employed as a small-scale three-bladed horizontal axis ocean current turbine. This numerical model development is presented along with a comparison to experimental data to quantify the motor performance. The proposed experimental design is discussed in detail. Due to the nature of the ocean current turbine, it is required to run it first by applying input power, subsequently to be governed by hydrokinetic energy. Thus, a detailed performance of the PMDC motor is essential when it runs as a motor and generator. Based on our preliminary work, the angular speed of the small-scale turbine is less than 500 rpm. Thus, a combination of the PMDC motor and a planetary gearhead is used to fulfill this low-speed requirement. The gearhead is driven in reverse when operating as a generator which leads to poor efficiency. This efficiency is experimentally derived to be 47.8% at maximum speed of 479.4 rpm at 12V.

    

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4. Modeling and Numerical Simulation of a Buoyancy Controlled Ocean Current Turbine

   https://doi.org/10.36688/imej.4.47-58  

   Hasankhani, Arezoo ; VanZwieten, James ; Tang, Yufei ; Dunlap, Broc ; De Luera, Alexandra ; Sultan, Cornel ; Xiros, Nikolaos ( July 2021 , International Marine Energy Journal)

   Increased global renewable power demands and the high energy density of ocean currents have motivated the development of ocean current turbines (OCTs). These compliantly mooring systems will maintain desired near-surface operating depths using variable buoyancy, lifting surface, sub-sea winches, and/or surface buoys. This paper presents a complete numerical simulation of a 700 kW variable buoyancy controlled OCT that includes detailed turbine system, inflow, actuator (i.e., generator and variable buoyancy), sensor, and fault models. Simulation predictions of OCT performance are made for normal, hurricane, and fault scenarios. Results suggest this OCT can operate between depths of 38 m to 329 m for all homogeneous flow speeds between 1.0-2.5 m/s. Fault scenarios show that rotor braking results in a rapid vertical OCT system assent and that blade pitch faults create power fluctuations apparent in the frequency domain. Finally, simulated OCT operations in measured ocean currents (i.e., normal and hurricane conditions) quantify power statistics and system behavior typical and extreme conditions. 

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5. Profiling wind LiDAR measurements to quantify blockage for onshore wind turbines

   https://doi.org/10.1002/we.2877  

   Moss, Coleman ; Puccioni, Matteo ; Maulik, Romit ; Jacquet, Clément ; Apgar, Dale ; Valerio Iungo, Giacomo ( October 2023 , Wind Energy)

   Flow modifications induced by wind turbine rotors on the incoming atmospheric boundary layer (ABL), such as blockage and speedups, can be important factors affecting the power performance and annual energy production (AEP) of a wind farm. Further, these rotor‐induced effects on the incoming ABL can vary significantly with the characteristics of the incoming wind, such as wind shear, veer, and turbulence intensity, and turbine operative conditions. To better characterize the complex flow physics underpinning the interaction between turbine rotors and the ABL, a field campaign was performed by deploying profiling wind LiDARs both before and after the construction of an onshore wind turbine array. Considering that the magnitude of these rotor‐induced flow modifications represents a small percentage of the incoming wind speed ( ), high accuracy needs to be achieved for the analysis of the experimental data and generation of flow predictions. Further, flow distortions induced by the site topography and effects of the local climatology need to be quantified and differentiated from those induced by wind turbine rotors. To this aim, a suite of statistical and machine learning models, such as k‐means cluster analysis coupled with random forest predictions, are used to quantify and predict flow modifications for different wind and atmospheric conditions. The experimental results show that wind velocity reductions of up to 3% can be observed at an upstream distance of 1.5 rotor diameter from the leading wind turbine rotor, with more significant effects occurring for larger positive wind shear. For more complex wind conditions, such as negative shear and low‐level jet, the rotor induction becomes highly complex entailing either velocity reductions (down to 9%) below hub height and velocity increases (up to 3%) above hub height. The effects of the rotor induction on the incoming wind velocity field seem to be already roughly negligible at an upstream distance of three rotor diameters. The results from this field experiment will inform models to simulate wind‐turbine and wind‐farm operations with improved accuracy for flow predictions in the proximity of the rotor area, which will be instrumental for more accurate quantification of wind farm blockage and relative effects on AEP.

    

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