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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))

   Abstract 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. Sedimentary bed morphology in the wake of flexible aquatic vegetation

   https://doi.org/10.1016/j.wse.2025.03.002  

   Bhamitipadi_Suresh, Dhanush; Wood, Daniel; Jin, Yaqing (September 2025, Water Science and Engineering)

   The sedimentary bed morphology modulated by the wake flow of a wall-mounted flexible aquatic vegetation blade across various structural aspect ratios (AR=l/b, where l and b are the length and width of the blade, respectively) and incoming flow velocities was experimentally investigated in a water channel. A surface scanner was implemented to quantify bed topography, and a tomographic particle image velocimetry system was used to characterize the three-dimensional wake flows. The results showed that due to the deflection of incoming flow, the velocity magnitude increased at the lateral sides of the blade, thereby producing distinctive symmetric scour holes in these regions. The normalized morphology profiles of the sedimentary bed, which were extracted along the streamwise direction at the location of the maximum erosion depth, exhibited a self-similar pattern that closely followed a sinusoidal wave profile. The level of velocity magnitude enhancement was highly correlated to the postures of the flexible blade. At a given flow velocity, the blade with lower aspect ratios exhibited less significant deformation, causing more significant near-bed velocity enhancement in the wake deflection zone and therefore leading to higher erosion volumes. Further investigation indicated that when the blade underwent slight deformation, the larger velocity enhancement close to the bed can be attributed to more significant flow deflection effects at the lateral sides of the blade and stronger flow mixing with high momentum flows away from the bed. Supported with measurements, a basic formula was established to quantify the shear stress acting on the sedimentary bed as a function of incoming flow velocity and blade aspect ratio. 

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3. A double-multiple streamtube model for vertical axis wind turbines of arbitrary rotor loading

   https://doi.org/10.5194/wes-4-653-2019  

   Ayati, Anis A.; Steiros, Konstantinos; Miller, Mark A.; Duvvuri, Subrahmanyam; Hultmark, Marcus (January 2019, Wind Energy Science)

   Abstract. We introduce an improved formulation of the double-multiple streamtube (DMST) model for the prediction of the flow quantities of vertical axis wind turbines (VAWT). The improvement of the new formulation lies in that it renders the DMST valid for any induction factor, i.e., for any combination of rotor solidity and tip speed ratio. This is done by replacing the Rankine–Froude momentum theory of the DMST, which is invalid for moderate and high induction factors, with a new momentum theory recently proposed, which provides sensible results for any induction factor. The predictions of the two DMST formulations are compared with VAWT power measurements obtained at Princeton's High Reynolds number Test Facility, over a range of tip speed ratios, rotor solidities, and Reynolds numbers, including those experienced by full-scale turbines. The results show that the new DMST formulation demonstrates a better overall performance, compared to the conventional one, when the rotor loading is moderate or high. 

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4. Solidity effects on the performance of vertical-axis wind turbines

   https://doi.org/10.1017/flo.2021.9  

   Miller, Mark A.; Duvvuri, Subrahmanyam; Hultmark, Marcus (January 2021, Flow)

   Abstract The variety of configurations for vertical-axis wind turbines (VAWTs) make the development of universal scaling relationships for even basic performance parameters difficult. Rotor geometry changes can be characterized using the concept of solidity, defined as the ratio of solid rotor area to the swept area. However, few studies have explored the effect of this parameter at full-scale conditions due to the challenge of matching both the non-dimensional rotational rate (or tip speed ratio) and scale (or Reynolds number) in conventional wind tunnels. In this study, experiments were conducted on a VAWT model using a specialized compressed-air wind tunnel where the density can be increased to over 200 times atmospheric air. The number of blades on the model was altered to explore how solidity affects performance while keeping other geometric parameters, such as the ratio of blade chord to rotor radius, the same. These data were collected at conditions relevant to the field-scale VAWT but in the controlled environment of the lab. For the three highest solidity rotors (using the most blades), performance was found to depend similarly on the Reynolds number, despite changes in rotational effects. This result has direct implications for the modelling and design of high-solidity field-scale VAWTs. 

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5. Strain predictions at unmeasured locations of a substructure using sparse response-only vibration measurements

   https://doi.org/10.1007/s13349-021-00476-x  

   Tchemodanova, Sofia Puerto; Sanayei, Masoud; Moaveni, Babak; Tatsis, Konstantinos; Chatzi, Eleni (June 2021, Journal of Civil Structural Health Monitoring)

   null (Ed.)

   Structural health monitoring of complex structures is often limited by restricted accessibility to locations of interest within the structure and availability of operational loads. In this work, a novel output-only virtual sensing scheme is proposed. This scheme involves the implementation of the modal expansion in an augmented Kalman filter. Performance of the proposed scheme is compared with two existing methods. Method 1 relies on a finite element model updating, batch data processing, and modal expansion (MUME) procedure. Method 2 employs a recursive sequential estimation algorithm, which feeds a substructure model of the instrumented system into an Augmented Kalman Filter (AKF). The new scheme referred to as Method 3 (ME-AKF), implements strain estimates generated via Modal Expansion into an AKF as virtual measurements. To demonstrate the applicability of the aforementioned methods, a rollercoaster connection was instrumented with accelerometers, strain rosettes, and an optical sensor. A comparison of estimated dynamic strain response at unmeasured locations using three alternative schemes is presented. Although acceleration measurements are used indirectly for model updating, the response-only methods presented in this research use only measurements from strain rosettes for strain history predictions and require no prior knowledge of input forces. Predicted strains using all methods are shown to sufficiently predict the measured strain time histories from a control location and lie within a 95% confidence interval calculated based on modal expansion equations. In addition, the proposed ME-AKF method shows improvement in strain predictions at unmeasured locations without the necessity of batch data processing. The proposed scheme shows high potential for real-time dynamic estimation of the strain and stress state of complex structures at unmeasured locations. 

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