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arXiv 2019年

作者： Nardone, Marco Patikirige, Yasas Kweon, Kyoung E. Walkons, Curtis Friedlmeier, Theresa Magorian Varley, Joel B. Lordi, Vincenzo Bansal, Shubhra Department of Physics and Astronomy Bowling Green State University Bowling GreenOH43403 United States Lawrence Livermore National Laboratory Materials Science Division LivermoreCA94550 United States Dept. of Mechanical Engineering University of Nevada Las Vegas Las VegasNV89154 United States Zentrum fr Sonnenenergie- und Wasserstoff-Forschung Baden-Wrttemberg Stuttgart Germany

Temporal variations of Cu(In,Ga)Se2 photovoltaic device properties during light exposure at various temperatures and voltage biases for times up to 100 h were analyzed using the kinetic theory of large lattice relaxations. Open-circuit voltage and p-type doping increased with charge injection and decreased with temperature at low injection conditions. Lattice relaxation can account for both trends and activation energies extracted from the data were approximately 0.9 and 1.2 eV for devices with lower and higher sodium content, respectively. In these devices, increased sodium content resulted in higher initial p-type doping with greater stability. First principles calculations providing revised activation energies for the (VSe − VCu) complex suggest that this defect does not account for the metastability observed here. Copyright © 2019, The Authors. All rights reserved.

关键词： Activation energy

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Online measurement of polymer melt viscosity in injection molding 75

Online measurement of polymer melt viscosity in injection mo...

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75th Annual Technical Conference and Exhibition of the Society of Plastics Engineers, SPE ANTEC Anaheim 2017

作者： Huang, Ming-Shyan Nian, Shih-Chih Chen, Jian-Yu Yang, Kai-Jye Tseng, Jian-Chou Dept. of Mechanical and Automation Engineering National Kaohsiung First University of Science and Technology Taiwan Dept. of Power Mechanical Engineering National Taitung College Taiwan Bachelor Program in Precision System Design Feng Chia University Taiwan

ISBN: (纸本)9780692883099

Melt viscosity, determined by the shear rate, barrel temperatures, and pressure during plasticization, greatly affects the flow ability of polymer melts as well as the quality of injection-molded parts. In particular, the consistency of molding qualities is highly relevant to the plasticizing quality at each cycle (i.e., injection molding requiring a high yield rate highly relies on the stability of polymer melts). However, numerous factors affect the plasticizing quality, including the geometry of injection screws, processed polymer materials, processing parameters of plasticization such as the feeding rate, screw rotational speed, barrel temperatures, back pressure, and screw backward speed. The conventional approach of plasticization in injection molding machines uses a single reciprocating screw for conveying, melting, and metering polymer melts. The plasticizing quality is roughly adjusted by indirectly controlling barrel temperatures;thus, the melt viscosity varies. An in-suit approach of assuring melt quality is to measure the melt viscosity variation online, which is a more suitable indicator of the plasticizing quality than temperature. This study thus monitored the melt viscosity variations in polymer melts by using in-mold pressure sensors. Furthermore, the effects of the injection velocity and mold temperature on the melt viscosity variations were examined.

关键词： Polymer melts

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Meta-Learning Related Tasks with Recurrent Networks: Optimization and Generalization

Meta-Learning Related Tasks with Recurrent Networks: Optimiz...

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International Joint Conference on Neural Networks

作者： Thy Nguyen Emmett Redd A. Steven Younger Tayo Obafemi-Ajayi Computer Science Dept. Missouri State University Springfield MO Department of Physics Astronomy and Materials Science Missouri State University Springfield MO Engineering Program Missouri State University Springfield MO

There have been recent interest in meta-learning systems: i.e. networks that are trained to learn across multiple tasks. This paper focuses on optimization and generalization of a meta-learning system based on recurrent networks. The optimization investigates the influence of diverse structures and parameters on its performance. We demonstrate the generalization (robustness) of our meta-learning system to learn across multiple tasks including tasks unseen during the metatraining phase. We introduce a meta-cost function (Mean Squared Fair Error) that enhances the performance of the system by not penalizing it during transitions to learning a new task. Evaluation results are presented for Boolean and quadratic functions datasets. The best performance is obtained using a Long Short-Term Memory (LSTM) topology without a forget gate and with a clipped memory cell. The results demonstrate i) the impact of different LSTM architectures, parameters, and error functions on the meta-learning process;ii) that the mean squared fair error function does improve performance for best learning;and iii) the robustness of our meta-learning framework as it generalizes well when tested on tasks unseen during metatraining. Comparison between No-Forget-Gate LSTM and Gated Recurrent Unit also suggest that absence of a memory cell tends to degrade performance.

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Turbulence modeling of high speed compressible flows 55

Turbulence modeling of high speed compressible flows

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55th AIAA Aerospace sciences Meeting

作者： Shuai, Shuai Wray, Timothy J. Agarwal, Ramesh K. Dept. of Mechanical Engineering & Materials Science Washington University in St. Louis St. LouisMO63130 United States

ISBN: (数字)9781624104473

ISBN: (纸本)9781624104473

It is well known that the two-equation turbulence models were originally developed and applied to compute flows in subsonic and transonic regimes at relatively low Mach numbers. This paper employs a new temperature gradient correction to the eddy viscosity term in a two-equation k-Ε turbulence model for computing flows at high Mach numbers. The accuracy of the improved k-Ε model is assessed by computing the supersonic/hypersonic boundary layer flow over a flat plate and the jet flows from supersonic nozzles. The results of computations using the modified k-Ε model are in better agreement with the available theoretical and numerical results, and experimental data compared to those obtained with the industry standard two-equation k-Ε and SST k-ω models. © 2017 by Shuai Shuai, Timothy J. Wray and Ramesh K. Agarwal.

关键词： Turbulence Models Incompressible Flow Compressibility Mach Numbers Incompressible Boundary Layer Computing Supersonic Nozzle Reynolds Averaged Navier Stokes Numerical Simulation Turbulence Kinetic Energy

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Prediction, minimization and propagation of sonic boom from supersonic bodies 55

Prediction, minimization and propagation of sonic boom from ...

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55th AIAA Aerospace sciences Meeting

作者： Li, Junhui Krampf, Jeffrey Mitchell, James Agarwal, Ramesh K. Washington University in St. Louis Dept. of Mechanical Engineering & Materials Science St. LouisMO63130 United States

ISBN: (数字)9781624104473

ISBN: (纸本)9781624104473

This paper first describes the numerical simulation and shape optimization of the Lockheed SEEB-ALR and 69 degree Delta wing-body for computing the sonic boom signature in the nearfield and its minimization using a genetic algorithm. Then the propagation of sonic boom in the atmosphere is simulated all the way to the ground for both the original and optimized body shapes. For flow field calculation, the commercial CFD flow solver ANSYS Fluent is employed. The near field pressure disturbance is used to determine the strength of the sonic boom signature. The computational results for the two cases are compared with the experimental data. The body shapes are then optimized using a single-objective genetic algorithm. The results show a significant decrease in strength of the sonic boom. The pressure data from these two models is then scaled and propagated through the atmosphere using the NASA Langley Research Center code sBOOM to predict the far field signature of these bodies at the scale of a commercial supersonic aircraft. © 2017 by The Aerospace Corporation.

关键词： Sonic Booms Delta Wing Multi Objective Genetic Algorithm Commercial Aircraft Shape Optimization NASA Langley Research Center ANSYS Computing Numerical Simulation Wind Tunnel Models

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Computation of flow field of an airfoil with Gurney flap in ground effect 35

Computation of flow field of an airfoil with Gurney flap in ...

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35th AIAA Applied Aerodynamics Conference, 2017

作者： Zhang, Xuan Qu, Qiulin Agarwal, Ramesh K. Dept. of Mechanical Engineering and Materials Science Washington University in St. Louis St. LouisMO63130 United States

ISBN: (数字)9781624105012

ISBN: (纸本)9781624105012

This paper describes the ground effect aerodynamics of an airfoil with Gurney flap. For this purpose, NACA0012 airfoil with different shapes of Gurney flaps is considered. Computational results from ANSYS FLUENT are compared to the wind tunnel test results to verify the simulation model. Computations are then performed to include the ground effect. Computations show that the presence of the ground mainly affects the size of vortices at the trailing edge of the airfoil resulting in larger lift force and smaller drag force compared to the airfoil in unbounded flow. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

关键词： Airfoils

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Numerical simulation of flow past a circular and a square cylinder at high reynolds number 47

Numerical simulation of flow past a circular and a square cy...

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47th AIAA Fluid Dynamics Conference, 2017

作者： Zhang, Ling Wray, Timothy J. Agarwal, Ramesh K. Dept. of Mechanical Engineering & Materials Science Washington University in St. Louis St. LouisMO63130 United States

ISBN: (数字)9781624105005

ISBN: (纸本)9781624105005

Increasing the prediction accuracy and computational efficiency of turbulence models at high Reynolds number remains a challenging problem in Computational Fluid Dynamics (CFD). In this paper, several turbulence models are applied for numerical simulation of flow around a circular cylinder and a square cylinder at high Reynolds number. Wray-Agarwal (WA) turbulence model is a recently developed one-equation turbulence model derived from kk-ω closure. Comparisons are made among computational results from WA model, Spalart-Allmaras (SA) model, the shear stress transport (SST) kk-ω model and the standard kk-ω model. For circular cylinder, the computations are performed for Reynolds numbers Ree=6.7×1051×106and 3.6×106;the simulation for a square cylinder is performed at a Reynolds number 2.2×104The computed results are assessed against previous simulations and experimental measurements. Both circular and square geometries produce vortex wakes and oscillating lift and drag. According to the results, the new WA model is competitive in accuracy with the two-equation models and has computational efficiency of a one-equation model. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

关键词： Turbulence models

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A new DES model based on wray-agarwal turbulence model for simulation of wall-bounded flows 55

A new DES model based on wray-agarwal turbulence model for s...

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55th AIAA Aerospace sciences Meeting

作者： Xu, Han Wray, Timothy J. Agarwal, Ramesh K. Dept. of Mechanical Engineering & Materials Science Washington University in St. Louis St. LouisMO63130 United States

ISBN: (数字)9781624104473

ISBN: (纸本)9781624104473

This paper describes a new Detached-Eddy Simulation (DES) model based on the recently developed one-equation Wray-Agarwal eddy viscosity turbulence model. The results from the new model are compared to the experimental data of several standard test cases. Computational results for a flat plate, NASA wall-mounted hump, backward facing step, asymmetric plane diffuser, NACA 4412 airfoil and axisymmetric transonic bump are presented. It is shown that the Wray-Agarwal turbulence model based DES formulation has a good agreement with the experimental results. © 2017 by Xu Han, Timothy J. Wray and Ramesh K. Agarwal.

关键词： Eddy Viscosity Turbulence Models Detached Eddy Simulation NACA 4412 Velocity Profiles Reynolds Averaged Navier Stokes Skin Friction Coefficient Boundary Layer Thickness Separated Flows Freestream Mach Number Isotropic Turbulence

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Application of SST k-ω transition model to flow past smooth and rough airfoils 47

Application of SST k-ω transition model to flow past smooth...

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47th AIAA Fluid Dynamics Conference, 2017

作者： Hou, Yao Wray, Timothy J. Agarwal, Ramesh K. Dept. of Mechanical Engineering & Materials Science Washington University in St. Louis St. LouisMO63130 United States

ISBN: (数字)9781624105005

ISBN: (纸本)9781624105005

This paper employs the four-equation Shear-Stress-Transport k-ω transition model to simulate the transitional flow over smooth and rough airfoils. A surface-roughness modification is incorporated in the model for computing the rough wall flows. Computational results for three benchmark flat plate transitional flow cases T3A, T3B, and T3A- as well as the transitional flow past smooth and rough S809 airfoils are computed. For transitional flow past smooth flat plates and S809 airfoil, good agreement between the computations and the experimental data is obtained. For rough S809 airfoil, it is shown that both surface roughness and transition effects must be accounted to match the computations with the experimental data. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

关键词： Airfoils

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Application of a new DES model based on Wray-Agarwal turbulence model for simulation of wall-bounded flows with separation 47

Application of a new DES model based on Wray-Agarwal turbule...

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47th AIAA Fluid Dynamics Conference, 2017

作者： Xu, Han Wray, Timothy J. Agarwal, Ramesh K. Dept. of Mechanical Engineering & Materials Science Washington University in St. Louis St. LouisMO63130 United States

ISBN: (数字)9781624105005

ISBN: (纸本)9781624105005

This paper describes a new Detached-Eddy Simulation (DES) model based on the recently developed one-equation Wray-Agarwal (WA) eddy viscosity turbulence model. The results from the new model are compared to the experimental data for several standard benchmark test cases. Computational results for a NASA wall-mounted hump, backward facing step, asymmetric plane diffuser, NACA 4412 airfoil, periodic hill, axisymmetric transonic bump and NASA Glenn S-Duct are presented. It is shown that the Wray-Agarwal turbulence model based DES formulation has good agreement with the experimental results. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

关键词： Turbulence models

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