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At least 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Integrating Characteristic Arctic Vegetation in a Land Surface Model Improves Representation of Carbon Dynamics Across a Tundra Landscape: Modeling Archive

This modeling archive is in support of the Next-Generation Ecosystem Experiments in the Arctic (NGEE Arctic) publication "Integrating Characteristic Arctic Vegetation in a Land Surface Model Improves Representation of Carbon Dynamics Across a Tundra Landscape", by Murphy et al. (2025). This archive contains model input files and outputs from landscape-scale simulations conducted using ELM, the land model component of the Department of Energy’s Energy Exascale Earth System Model (E3SM), at the Council NGEE Arctic field site (Council Road mile marker 71) on Alaska’s Seward Peninsula. Input data and model output from two sets of ELM simulations are provided. The first set of simulations were conducted with the two default ELM Arctic plant functional types (PFTs; broadleaf deciduous boreal shrub and a C3 grass) and the second set of simulations were conducted with a set of nine Arctic-specific PFTs including nonvascular mosses and lichens, graminoids, forbs, evergreen dwarf shrubs, three height classes of deciduous shrubs (dwarf, low, and low to tall), and deciduous alder shrubs (Sulman et al., 2021). Parameter names and major parameter changes in the Arctic-specific PFT configuration are described in Sulman et al. (2021) and archived in the Sulman et al. (2021) dataset (see below). Simulations were spatially explicit, covering an approximately 6.4X3.3 km domain at the Council site with a spatial resolution of 100 m for a total of 2,112 simulated grid cells under each ELM PFT configuration. The modeling archive contains meteorological forcing (seven *.nc files and one *.txt file), a domain definition file (one *.nc files), land surface configuration files (two *.nc files), parameter files (two *.nc files), annual ELM output files spanning 1980-2014 (68 *.nc files), and a User’s Guide (*pdf file). Additional information on the provided files is in the “Modeling Archive Contents” section of the User’s Guide. Model outputs are aggregated to the column scale (i.e. PFT-specific outputs are not provided here).

Murphy, Bailey [ORNL] (ORCID:0000000203995221)↗
DOE OSTI2017

Field Test of Wake Steering at an Offshore Wind Farm

In this paper, a field test of wake steering control is presented. The field test is the result of a collaboration between the National Renewable Energy Laboratory (NREL) and Envision Energy, a smart energy management company and turbine manufacturer. In the campaign, an array of turbines within an operating commercial offshore wind farm in China have the normal yaw controller modified to implement wake steering according to a yaw control strategy. The strategy was designed using NREL wind farm models, including a computational fluid dynamics model, SOWFA, for understanding wake dynamics and an engineering model, FLORIS, for yaw control optimization. Results indicate that, within the certainty afforded by the data, the wake-steering controller was successful in increasing power capture, by amounts similar to those predicted from the models.

17 WIND ENERGY↗
DOE OSTI2019

Model reduction of dynamical systems on nonlinear manifolds using deep convolutional autoencoders

Nearly all model-reduction techniques project the governing equations onto a linear subspace of the original state space. Such subspaces are typically computed using methods such as balanced truncation, rational interpolation, the reduced-basis method, and (balanced) proper orthogonal decomposition (POD). Unfortunately, restricting the state to evolve in a linear subspace imposes a fundamental limitation to the accuracy of the resulting reduced-order model (ROM). In particular, linear-subspace ROMs can be expected to produce low-dimensional models with high accuracy only if the problem admits a fast decaying Kolmogorov n -width (e.g., diffusion-dominated problems). Unfortunately, many problems of interest exhibit a slowly decaying Kolmogorov n-width (e.g., advection-dominated problems). To address this, we propose a novel framework for projecting dynamical systems onto nonlinear manifolds using minimum-residual formulations at the time-continuous and time-discrete levels; the former leads to manifold Galerkin projection, while the latter leads to manifold least-squares Petrov–Galerkin (LSPG) projection. We perform analyses that provide insight into the relationship between these proposed approaches and classical linear-subspace reduced-order models; we also derive a posteriori discrete-time error bounds for the proposed approaches. In addition, we propose a computationally practical approach for computing the nonlinear manifold, which is based on convolutional autoencoders from deep learning. Lastly, we demonstrate the ability of the method to significantly outperform even the optimal linear-subspace ROM on benchmark advection-dominated problems, thereby demonstrating the method's ability to overcome the intrinsic n -width limitations of linear subspaces.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Reactive transport modeling of microbial dynamics

Reactive transport modeling of microbially mediated processes has contributed significantly to an improved understanding of elemental cycling in Earth near-surface environments. We describe key characteristics of microbial reactive transport models (RTMs), recent advances in modeling approaches, and their application to terrestrial and marine environmental problems. We introduce relevant case studies and discuss ways to integrate -omics data that can inform and validate microbial RTMs, improving our ability to address grand challenges in a changing world.

Meile, Christof↗
NASA NTRS1972

Adaption of a corrector module to the IMP dynamics program

The corrector module of the RAEIOS program and the IMP dynamics computer program were combined to achieve a date-fitting capability with the more general spacecraft dynamics models of the IMP program. The IMP dynamics program presents models of spacecraft dynamics for satellites with long, flexible booms. The properties of the corrector are discussed and a description is presented of the performance criteria and search logic for parameter estimation. A description is also given of the modifications made to add the corrector to the IMP program. This includes subroutine descriptions, common definitions, definition of input, and a description of output.

Source record↗
NASA NTRS1999

Modeling the Dynamics of Ensemble-Averaged Linear Disturbances in Homogeneous Shear Flow

In order to expand the predictive capability of single-point turbulence closure models to account for the early-stage transition regime, a methodology for the formulation and calibration of model equations for the ensemble-averaged disturbance kinetic energy and energy dissipation rate is presented. The calibration is based on homogeneous shear flow where disturbances can be described by rapid distortion theory (RDT). The relationship between RDT and linear stability theory is exploited in order to obtain a closed set of modeled equations. The linear disturbance equations are solved directly so that the numerical simulation yields a database from which the closure coefficients in the ensemble-averaged disturbance equations can be determined. Key words: transition/turbulence modeling, homogeneous shear, rapid distortion theory.

Thacker, W. D.↗
DOE OSTI2013

SPIN STATE AND MOMENT OF INERTIA CHARACTERIZATION OF 4179 TOUTATIS

The 4.5 km long near-Earth asteroid 4179 Toutatis has made close Earth flybys approximately every four years between 1992 and 2012, and has been observed with high-resolution radar imaging during each approach. Its most recent Earth flyby in 2012 December was observed extensively at the Goldstone and Very Large Array radar telescopes. In this paper, Toutatis' spin state dynamics are estimated from observations of five flybys between 1992 and 2008. Observations were used to fit Toutatis' spin state dynamics in a least-squares sense, with the solar and terrestrial tidal torques incorporated in the dynamical model. The estimated parameters are Toutatis' Euler angles, angular velocity, moments of inertia, and the center-of-mass-center-of-figure offset. The spin state dynamics as well as the uncertainties of the Euler angles and angular velocity of the converged solution are then propagated to 2012 December in order to compare the dynamical model to the most recent Toutatis observations. The same technique of rotational dynamics estimation can be applied to any other tumbling body, given sufficiently accurate observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Integrated Transmission-and-Distribution System Modeling of Power Systems: State-of-the-Art and Future Research Directions

Integrated transmission-and-distribution (T&D) modeling is a new and developing method for simulating power systems. Interest in integrated T&D modeling is driven by the changes taking place in power systems worldwide that are resulting in more decentralized power systems with increasingly high levels of distributed energy resources. Additionally, the increasing role of the hitherto passive energy consumer in the management and operation of power systems requires more capable and detailed integrated T&D modeling to understand the interactions between T&D systems. Although integrated T&D modeling has not yet found widespread commercial application, its potential for changing the decades-old power system modeling approaches has led to several research efforts in the last few years that tried to (i) develop algorithms and software for steady-state and dynamic modeling of power systems and (ii) demonstrate the advantages of this modeling approach compared with traditional, separated T&D system modeling. In this paper, we provide a review of integrated T&D modeling research efforts and the methods employed for steady-state and dynamic modeling of power systems. We also discuss our current research in integrated T&D modeling and the potential directions for future research. This paper should be useful for power systems researchers and industry members because it will provide them with a critical summary of current research efforts and the potential topics where research efforts are needed to further advance and demonstrate the utility of integrated T&D modeling.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2021

Using Dissipative Particle Dynamics to Model Effects of Chemical Reactions Occurring within Hydrogels

Computational models that reveal the structural response of polymer gels to changing, dissolved reactive chemical species would provide useful information about dynamically evolving environments. However, it remains challenging to devise one computational approach that can capture all the interconnected chemical events and responsive structural changes involved in this multi-stage, multi-component process. Here, we augment the dissipative particle dynamics (DPD) method to simulate the reaction of a gel with diffusing, dissolved chemicals to form kinetically stable complexes, which in turn cause concentration-dependent deformation of the gel. Using this model, we also examine how the addition of new chemical stimuli and subsequent reactions cause the gel to exhibit additional concentration-dependent structural changes. Through these DPD simulations, we show that the gel forms multiple latent states (not just the “on/off”) that indicate changes in the chemical composition of the fluidic environment. Hence, the gel can actuate a range of motion within the system, not just movements corresponding to the equilibrated swollen or collapsed states. Moreover, the system can be used as a sensor, since the structure of the layer effectively indicates the presence of chemical stimuli.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Wind turbulence inputs for horizontal axis wind turbines

Wind turbine response characteristics in the presence of atmospheric turbulence was predicted using two major modeling steps. First, the important atmospheric sources for the force excitations felt by the wind turbine system were identified and characterized. Second, a dynamic model was developed which describes how these excitations are transmitted through the structure and power train. The first modeling step, that of quantifying the important excitations due to the atmospheric turbulence was established. The dynamic modeling of the second step was undertaken separately.

Holley, W. E.↗
NASA NTRS2007

Modeling Tool Advances Rotorcraft Design

Continuum Dynamics Inc. (CDI), founded in 1979, specializes in advanced engineering services, including fluid dynamic modeling and analysis for aeronautics research. The company has completed a number of SBIR research projects with NASA, including early rotorcraft work done through Langley Research Center, but more recently, out of Ames Research Center. NASA Small Business Innovation Research (SBIR) grants on helicopter wake modeling resulted in the Comprehensive Hierarchical Aeromechanics Rotorcraft Model (CHARM), a tool for studying helicopter and tiltrotor unsteady free wake modeling, including distributed and integrated loads, and performance prediction. Application of the software code in a blade redesign program for Carson Helicopters, of Perkasie, Pennsylvania, increased the payload and cruise speeds of its S-61 helicopter. Follow-on development resulted in a $24 million revenue increase for Sikorsky Aircraft Corporation, of Stratford, Connecticut, as part of the company's rotor design efforts. Now under continuous development for more than 25 years, CHARM models the complete aerodynamics and dynamics of rotorcraft in general flight conditions. CHARM has been used to model a broad spectrum of rotorcraft attributes, including performance, blade loading, blade-vortex interaction noise, air flow fields, and hub loads. The highly accurate software is currently in use by all major rotorcraft manufacturers, NASA, the U.S. Army, and the U.S. Navy.

Source record↗
DOE OSTI2022

An effective matrix model for dynamical end of the world branes in Jackiw-Teitelboim gravity

We study Jackiw-Teitelboim gravity with dynamical end of the world branes in asymptotically nearly AdS2 spacetimes. We quantize this theory in Lorentz signature, and compute the Euclidean path integral summing over topologies including dynamical branes. The latter will be seen to exactly match with a modification of the SSS matrix model. The resolution of UV divergences in the gravitational instantons involving the branes will lead us to understand the matrix model interpretation of the Wilsonian effective theory perspective on the gravitational theory. We complete this modified SSS matrix model nonperturbatively by extending the integration contour of eigenvalues into the complex plane. Furthermore, we give a new interpretation of other phases in such matrix models. We derive an effective W(Φ) dilaton gravity, which exhibits similar physics semiclassically. In the limit of a large number of flavors of branes, the effective extremal entropy S0,eff has the form of counting the states of these branes.

2D Gravity↗
NASA NTRS1986

Combining Structural and Substructural Mathematical Models

Automation reduces input length and potential data-entry errors. Matrix Automated Reduction and Coupling (MARC) program used for combining NASTRAN substructural models with primary structural model MARC also constructs job-control language (JCL) stream for NASTRAN batch job that utilizes previously-written user library of dynamic models. Minimizes lengthy input and reduces potential data-entry errors. MARC procedure used in assembling Space Shuttle orbiter dynamic models since 1983 and reduced NASTRAN modeling input time by as much as 50 percent. MARC program written in FORTRAN IV for interactive execution.

Choa, V. K.↗
NASA NTRS2002

Dynamical and chemical contributions to variability in microwave limb sounder Arctic stratoshperic column ozone

Analyses of column ozone above 100 hPa (Col100) derived from Upper Atmosphere Research Satellite Microwave Limb Sounder (MLS) data in February/March 1992-1998 show that about half of the interannual variability in Col100 in the Arctic polar vortex in late winter results from interannual variability in chemical loss. A majority of the remainder results from interannual variability in day-to-day dynamical motions including adiabatic warming/cooling and poleward advection of underlying upper tropospheric subtropical air on short timescales, rather than from variations in descent rates and large-scale transport over the winters. The morphology of Col100 from MLS remains very similar to that in the dynamical models even in the years with most chemical ozone loss. The amount and character of day-to-day variability in dynamical models closely follows that in MLS Col100. Although the morphology of and day-to-day variability in Arctic column ozone are controlled by dynamical processes, chemical ozone loss was a major factor in producing both the low values of and the large interannual variability in Arctic column ozone observed during the 1990s.

Arctic ozone loss↗
NASA NTRSDate not supplied

Late Accretion of large Dark Asteroids and Their Implantation into the Outer Main Belt

Dark (geometric albedo < 0.09) asteroidsare genetically linked to carbonaceous chondrites. Most of these asteroids are located in the mid-outer main belt (2.5 < a < 4.0 AU)and thought to be remnants of the primary accretion of the first solar system planetesimals. Here we presentnew near-infrared (NIR: ~0.5-4.0 μm) reflectance spectra of dark and large (diameter > 100 km) asteroidsmeasured atNASA Infrared Telescope Facility (IRTF).We place the astronomical observations of these large dark asteroids in the context of the thermal evolution and dynamical models and provide new interpretations for the origin and evolution of these asteroids. The astronomical observations together with thermal evolution and dynamical modeling show late accretion and implantation to a confined heliocentric region (~3.0 < a < 3.4 AU)for these large dark asteroids, in agreement with the dynamical predictions. Average densities of large and dark asteroids suggest highly porous interiors and, consequently, relatively late accretion ata time of 1.5-3.5 Myr relative to the formation of calcium-aluminum-rich inclusions with maximum interior temperatures of < 900 K. This work demonstrates that thederived accretion times of large dark asteroids do not correlate in any way with their current semimajor axes. Large and dark asteroidswere likely implanted from more distant regions of the solar system during the giant planet’s dynamical instability. The discovery of dark large asteroids that are smaller than Ceres near its orbital vicinity suggests that this dwarf planet is not unique in the main belt and its surface composition is not driven by its very large size.

Driss Takir↗
DOE OSTI2020

Characterization and verification of a two-body wave energy converter with a novel power take-off

The lack of high efficient, predictable and reliable power take-off (PTO) systems limits developments of ocean wave energy technology. In this paper, a two-body self-reacting wave energy converter (WEC) with a novel PTO is designed, modelled and implemented for efficiency enhancement. A novel mechanical motion rectifier (MMR) using a ball screw mechanism and an enclosed gear set is integrated to improve the energy harvesting efficiency and reliability by rectifying the oscillatory wave motion into unidirectional rotation of the generator. Detailed design and dynamic modelling for the proposed WEC are presented. A prototype of the PTO is tested in a dry lab to characterize and refine the dynamic modelling. The characterized PTO model is combined with the WEC model to create an overall system model. A water tank test is conducted to verify the overall system dynamics, which proves the accuracy of the model and shows the advantages of the proposed WEC on efficiency and predictability. Following the method of how the WEC system is characterized, performance prediction of the proposed WEC with MMR PTO can be achieved with high accuracy.

16 TIDAL AND WAVE POWER↗
DOE OSTI2018

A hybrid finite element-spectral boundary integral approach: Applications to dynamic rupture modeling in unbounded domains

The finite element method (FEM) and the spectral boundary integral method (SBI) have both been widely used in the study of dynamic rupture simulations along a weak interface. Here, we present a hybrid method that combines FEM and SBI through the consistent exchange of displacement and traction boundary conditions, thereby benefiting from the flexibility of FEM in handling problems with nonlinearities or small-scale heterogeneities and from the superior performance and accuracy of SBI. We validate the hybrid method using a benchmark problem from the Southern California Earthquake Center's dynamic rupture simulation validation exercises.We further demonstrate the capability and computational efficiency of the hybrid scheme for resolving off-fault heterogeneities by studying a 2D in-plane shear crack in two different settings: one where the crack is embedded in a high-velocity zone and another where it is embedded in a low-velocity zone. Finally, we discuss the potential of the hybrid method for addressing a wide range of problems in geophysics and engineering.

58 GEOSCIENCES↗