AE Research Publications

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    Wind turbine performance enhancement with minimal structural load penalty: A design philosophy
    (SAGE Publications Inc., 2024-01) Matheswaran, Vijay; Moriarty, Patrick J.
    The performance benefits of using tip devices on wind turbines has been well-documented. However, previous studies show that adding blade tip devices such as winglets leads to a significant increase in blade root bending moment, potentially requiring structural reinforcement with cost and weight drawbacks. A new and unique design philosophy for retrofit blade tip devices for wind turbines is presented. By balancing generated aerodynamic and centrifugal loads, these devices offer an increase in power production without the need for structural reinforcement. Predicted performance and cost benefits of using retrofit blade tip devices on the National Renewable Energy Laboratory 5 MW reference wind turbine are shown. The addition of blade tip devices resulted in significant improvements in the coefficient of power (Cp) and annual energy production (AEP).
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    Effects of Impact Damage on the Energy Absorption Capabilities of Composite Materials
    (DEStech Publications, 2023-09) Bhasin, Akhil; Keshavanarayana, Suresh R.; Maichan, Tanat; Gomez, Luis; Olivares, Gerardo
    In the current investigation, the effects of in-service impact damage on the energy absorption capabilities, and damage evolution of two different geometries, corrugated beams, and c-channel stanchions, have been presented. Both the energy absorber geometries were manufactured using two composite material systems, Hexcel IM7/8552 and Hexcel AS4 PW/8552. Two different stacking sequences evaluated were: [90o/0o]2S and [45o/90o/-45o/0o]s. The pristine specimens were secured in a nonstandard fixture and impacted at the center using a drop tower [1]. The specimens were impacted at different energy levels to introduce varying levels of damage. Post-damage introduction, compression tests were performed at 1 in/s using a high-speed servo-hydraulic test frame. All the tests were supported with high-speed Digital Image Correlation (DIC) to obtain damage evolution and surface strains. A comparison of the energy absorption capabilities and damage modes between the pristine specimens and specimens with impact damage has been reported.
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    Effect of geometrical defects on the acoustical transport properties of periodic porous absorbers manufactured using stereolithography
    (Institute of Noise Control Engineering, 2023-09) Lomte, Amulya; Sharma, Bhisham N.
    Additive manufacturing allows the fabrication of acoustical materials with previously unrealizable micro- and macrostructural complexities. However, the still nascent understanding of various geometrical defects occurring during the additive process remains a barrier to accurately predicting the acoustical behavior of such complex absorbers. In this study, we present the results from our efforts on numerically modeling the absorption behavior of periodic porous absorbers fabricated using the stereolithography (SLA) technique using the hybrid micro-macro multiphysics approach. Specifically, we focus on understanding the role played by the expansion or shrinkage of the solid ligaments during the SLA process on the acoustical properties of the final printed samples. First, the periodic absorbers are modeled using COMSOL multiphysics, where the transport properties are derived using the micro-modeling method and sound absorption behavior using the Johnson-Champoux-Allard-Lafarge-Pride semi-empirical model. Then, results from the expansion study guide the changes in the ligament sizes in the unit cell modeling. Finally, the fabricated samples are tested using an impedance tube, and the measured absorption properties are compared to the a priori numerical predictions. Results indicate that accounting for fabrication defects within the numerical modeling schema can provide reliable sound absorption predictions for additively manufactured porous absorbers.
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    Cascaded deep reinforcement learning-based multi-revolution low-thrust spacecraft orbit-transfer
    (Institute of Electrical and Electronics Engineers Inc., 2023-08-10) Zaidi, Syed Muhammad Talha; Chadalavada, Pardha Sai; Ullah, Hayat; Munir, Arslan; Dutta, Atri
    Transferring an all-electric spacecraft from a launch injection orbit to the geosynchronous equatorial orbit (GEO) using a low thrust propulsion system presents a significant challenge due to the long transfer time typically spanning several months. To address the challenge of determining such long time-scale orbit-raising maneuvers to GEO, this paper presents a novel technique to compute transfers starting from geostationary transfer orbit (GTO) and super-GTO. The transfer is complex, involving multiple eclipses and revolutions. To tackle this challenge, we introduce a cascaded deep reinforcement learning (DRL) model to guide a low-thrust spacecraft towards the desired orbit by determining an appropriate thrust direction at each state. To ensure mission requirements, a gradient-aided reward function incorporating the orbital elements, guides the DRL agent to obtain the optimal flight time. The obtained results demonstrate that our proposed approach yields optimal or near-optimal time-efficient spacecraft orbit-raising. DRL implementation is important for spacecraft autonomy; in this context, we demonstrate that our DRL-based trajectory planning provides significantly better transfer time as compared to state-of-the-art approaches that allow for automated trajectory computation. Author
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    Additively manufactured spinodoid sound absorbers
    (Elsevier B.V., 2023-06-05) Wojciechowski, Brittany; Xue, Yutong; Rabbani, Arash; Bolton, J. Stuart; Sharma, Bhisham N.
    Spinodoid structures, also called spinodoid metamaterials, are non-periodic cellular structures that mimic spinodal topologies that are observed during diffusion-driven phase separation processes. Computationally efficient to model, spinodoid structures can be fabricated using additive techniques and offer an attractive route to the design of multifunctional structures. In this paper, we investigate the normal incidence sound absorption behavior of four distinct spinodoid topologies: isotropic, cubic, columnar, and lamellar. We fabricate the test samples using the fused filament fabrication process and systematically study the effect of the Gaussian Random Field (GRF) parameters on their underlying open pore network and sound absorption behavior. We employ a watershed segmentation-based image processing approach to correlate their pore and throat radii distributions to the GRF parameters. The normal incidence sound absorption properties are experimentally measured using the two-microphone impedance tube test method. Finally, we use a particle-swarm-based inverse characterization approach to extract the bulk properties necessary to model their acoustical behavior by using the Johnson-Champoux-Allard formulation. Our results show that the open pore network and acoustical properties of spinodoid structures are primarily a function of their relative density and wavenumber. Further, while the absorption behavior of the isotropic, cubic, and columnar spinodoids is similar, the lamellar spinodoids display unique low-frequency sound absorption behavior. Overall, all four spinodoid topologies provide favorable sound absorption characteristics, which may be tuned by varying the GRF parameters. The presented work advances the state-of-the art by establishing the feasibility of using additive manufacturing to enable non-periodic porous structures for that can be tuned to simultaneously provide mechanical stiffness and noise dampening capabilities.