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Data Mining-Aided Crystal Engineering for the Design of Transparent Conducting Oxides: Preprint

Description: The purpose of this paper is to accelerate the pace of material discovery processes by systematically visualizing the huge search space that conventionally needs to be explored. To this end, we demonstrate not only the use of empirical- or crystal chemistry-based physical intuition for decision-making, but also to utilize knowledge-based data mining methodologies in the context of finding p-type delafossite transparent conducting oxides (TCOs). We report on examples using high-dimensional visualizations such as radial visualization combined with machine learning algorithms such as k-nearest neighbor algorithm (k-NN) to better define and visualize the search space (i.e. structure maps) of functional materials design. The vital role of search space generated from these approaches is discussed in the context of crystal chemistry of delafossite crystal structure.
Date: December 1, 2010
Creator: Suh, C.; Kim, K.; Berry, J. J.; Lee, J. & Jones, W. B.
Partner: UNT Libraries Government Documents Department

Statistical Modeling of Photovoltaic Reliability Using Accelerated Degradation Techniques (Poster)

Description: We introduce a cutting-edge life-testing technique, accelerated degradation testing (ADT), for PV reliability testing. The ADT technique is a cost-effective and flexible reliability testing method with multiple (MADT) and Step-Stress (SSADT) variants. In an environment with limited resources, including equipment (chambers), test units, and testing time, these techniques can provide statistically rigorous prediction of lifetime and other interesting parameters, such as failure rate, warranty time, mean time to failure, degradation rate, activation energy, acceleration factor, and upper limit level of stress. J-V characterization can be used for degradation data and the generalized Eyring model can be used for the thermal-humidity stress condition. The SSADT model can be constructed based on the cumulative damage model (CEM), which assumes that the remaining test united are failed according to cumulative density function of current stress level regardless of the history on previous stress levels.
Date: February 1, 2011
Creator: Lee, J.; Elmore, R. & Jones, W.
Partner: UNT Libraries Government Documents Department

Numerical Stability and Accuracy of Temporally Coupled Multi-Physics Modules in Wind-Turbine CAE Tools

Description: In this paper we examine the stability and accuracy of numerical algorithms for coupling time-dependent multi-physics modules relevant to computer-aided engineering (CAE) of wind turbines. This work is motivated by an in-progress major revision of FAST, the National Renewable Energy Laboratory's (NREL's) premier aero-elastic CAE simulation tool. We employ two simple examples as test systems, while algorithm descriptions are kept general. Coupled-system governing equations are framed in monolithic and partitioned representations as differential-algebraic equations. Explicit and implicit loose partition coupling is examined. In explicit coupling, partitions are advanced in time from known information. In implicit coupling, there is dependence on other-partition data at the next time step; coupling is accomplished through a predictor-corrector (PC) approach. Numerical time integration of coupled ordinary-differential equations (ODEs) is accomplished with one of three, fourth-order fixed-time-increment methods: Runge-Kutta (RK), Adams-Bashforth (AB), and Adams-Bashforth-Moulton (ABM). Through numerical experiments it is shown that explicit coupling can be dramatically less stable and less accurate than simulations performed with the monolithic system. However, PC implicit coupling restored stability and fourth-order accuracy for ABM; only second-order accuracy was achieved with RK integration. For systems without constraints, explicit time integration with AB and explicit loose coupling exhibited desired accuracy and stability.
Date: February 1, 2013
Creator: Gasmi, A.; Sprague, M. A.; Jonkman, J. M. & Jones, W. B.
Partner: UNT Libraries Government Documents Department

FAST Modular Wind Turbine CAE Tool: Nonmatching Spatial and Temporal Meshes: Preprint

Description: In this paper we propose and examine numerical algorithms for coupling time-dependent multi-physics modules relevant to computer-aided engineering (CAE) of wind turbines. In particular, we examine algorithms for coupling modules where spatial grids are non- matching at interfaces and module solutions are time advanced with different time increments and different time integrators. Sharing of data between modules is accomplished with a predictor-corrector approach, which allows for either implicit or explicit time integration within each module. Algorithms are presented in a general framework, but are applied to simple problems that are representative of the systems found in a whole-turbine analysis. Numerical experiments are used to explore the stability, accuracy, and efficiency of the proposed algorithms. This work is motivated by an in-progress major revision of FAST, the National Renewable Energy Laboratory's (NREL's) premier aero-elastic CAE simulation tool. The algorithms described here will greatly increase the flexibility and efficiency of FAST.
Date: January 1, 2014
Creator: Sprague, M. A.; Jonkman, J. M. & Jonkman, B. J.
Partner: UNT Libraries Government Documents Department

Gearbox Reliability Collaborative: Gearbox Inspection Metadata

Description: NREL has developed a software application called GearFacts that will be distributed to Database Collaborative participants to capture failure information when gearboxes are rebuilt. This publication names and describes each field used in GearFacts and can be used as a reference to the software's design.
Date: September 1, 2010
Creator: Munch, K. & McDade, M.
Partner: UNT Libraries Government Documents Department

IHT: Tools for Computing Insolation Absorption by Particle Laden Flows

Description: This report describes IHT, a toolkit for computing radiative heat exchange between particles. Well suited for insolation absorption computations, it is also has potential applications in combustion (sooting flames), biomass gasification processes and similar processes. The algorithm is based on the 'Photon Monte Carlo' approach and implemented in a library that can be interfaced with a variety of computational fluid dynamics codes to analyze radiative heat transfer in particle-laden flows. The emphasis in this report is on the data structures and organization of IHT for developers seeking to use the IHT toolkit to add Photon Monte Carlo capabilities to their own codes.
Date: October 1, 2013
Creator: Grout, R. W.
Partner: UNT Libraries Government Documents Department

NREL Carbon Metabolism Modeling Intends to Make Biofuels Engineering Routine and Reliable (Fact Sheet)

Description: National Renewable Energy Laboratory (NREL) scientists, supported by the Department of Energy (DOE) Scientific Discovery through Advanced Computing (SciDAC) Program, have assembled and simulated a model of key eukaryotic carbon metabolism that intends to move biochemical simulations into new realms of chemical fidelity.
Date: February 1, 2011
Partner: UNT Libraries Government Documents Department

Design of Shallow P-Type Dopants in ZnO: Preprint

Description: This paper describes approaches to lower the acceptor ionization energy in ZnO by codoping acceptors with donor or isovalent atoms and proposes a universal approach to overcome the doping polarity problem for wide-band-gap semiconductors.
Date: May 1, 2008
Creator: Wei, S.-H.; Li, J. & Yan, Y.
Partner: UNT Libraries Government Documents Department

Step-Stress Accelerated Degradation Testing for Solar Reflectors: Preprint

Description: To meet the challenge to reduce the cost of electricity generated with concentrating solar power (CSP) new low-cost reflector materials are being developed including metalized polymer reflectors and must be tested and validated against appropriate failure mechanisms. We explore the application of testing methods and statistical inference techniques for quantifying estimates and improving lifetimes of concentrating solar power (CSP) reflectors associated with failure mechanisms initiated by exposure to the ultraviolet (UV) part of the solar spectrum. In general, a suite of durability and reliability tests are available for testing a variety of failure mechanisms where the results of a set are required to understand overall lifetime of a CSP reflector. We will focus on the use of the Ultra-Accelerated Weathering System (UAWS) as a testing device for assessing various degradation patterns attributable to accelerated UV exposure. Depending on number of samples, test conditions, degradation and failure patterns, test results may be used to derive insight into failure mechanisms, associated physical parameters, lifetimes and uncertainties. In the most complicated case warranting advanced planning and statistical inference, step-stress accelerated degradation (SSADT) methods may be applied.
Date: September 1, 2011
Creator: Jones, W.; Elmore, R.; Lee, J. & Kennedy, C.
Partner: UNT Libraries Government Documents Department

Lifetime Prediction for Degradation of Solar Mirrors using Step-Stress Accelerated Testing (Presentation)

Description: This research is to illustrate the use of statistical inference techniques in order to quantify the uncertainty surrounding reliability estimates in a step-stress accelerated degradation testing (SSADT) scenario. SSADT can be used when a researcher is faced with a resource-constrained environment, e.g., limits on chamber time or on the number of units to test. We apply the SSADT methodology to a degradation experiment involving concentrated solar power (CSP) mirrors and compare the results to a more traditional multiple accelerated testing paradigm. Specifically, our work includes: (1) designing a durability testing plan for solar mirrors (3M's new improved silvered acrylic "Solar Reflector Film (SFM) 1100") through the ultra-accelerated weathering system (UAWS), (2) defining degradation paths of optical performance based on the SSADT model which is accelerated by high UV-radiant exposure, and (3) developing service lifetime prediction models for solar mirrors using advanced statistical inference. We use the method of least squares to estimate the model parameters and this serves as the basis for the statistical inference in SSADT. Several quantities of interest can be estimated from this procedure, e.g., mean-time-to-failure (MTTF) and warranty time. The methods allow for the estimation of quantities that may be of interest to the domain scientists.
Date: September 1, 2011
Creator: Lee, J.; Elmore, R.; Kennedy, C.; Gray, M. & Jones, W.
Partner: UNT Libraries Government Documents Department

Basic Science Simulations Provide New Insights to Aid Hydrogen Gas Turbine Development (Fact Sheet), NREL Highlights, Science

Description: Massive first-principles simulation provides insight into flame anchoring in a hydrogen-rich jet in cross-flow. When gas turbine designers want to use gasified biomass for stationary power generation, they are faced with a challenge: bio-derived syngas typically contains significant amounts of hydrogen, which is far more reactive than the methane that is the traditional gas turbine fuel. This reactivity leads to a safety design issue, because with hydrogen-rich fuels a flame may anchor in the fuel injection section of the combustor instead of the downstream design point. In collaboration with Jacqueline Chen of Sandia National Laboratories and Andrea Gruber of SINTEF, a Norwegian energy think tank, the National Renewable Energy Laboratory (NREL) is carrying out fundamental simulations to provide new insight into the physics of flame anchoring in canonical 'jet in cross-flow' configurations using hydrogen-rich fuels. To deal with the large amount and complexity of the data, the combustion scientists also teamed up with computer scientists from across the U.S. Department of Energy's laboratories to develop novel ways to analyze the data. These simulations have shown that fine-scale turbulence structures formed at the jet boundary provide particularly intense mixing between the fuel and air, which then enters a quiescent region formed downstream of the jet in a separate, larger turbulent structure. This insight explains the effect that reducing the wall-normal velocity of the fuel jet causes the flame to blow off; with the aid of the simulation, we now understand this counterintuitive result because reducing the wall-normal velocity would reduce the intensity of the mixing as well as move the quiescent region farther downstream. NREL and its research partners are conducting simulations that provide new insight into the physics of flame anchoring in canonical 'jet in cross-flow' configurations using hydrogen-rich fuels. Simulation results explain the mechanism behind flame blow-off occurring when ...
Date: November 1, 2011
Partner: UNT Libraries Government Documents Department