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NASA NTRS1989

The secondary flow and its stability for natural convection in a tall vertical enclosure

The multicellular flow between two vertical parallel plates is numerically simulated using a time-splitting pseudospectral method. The steady flow of air and the time-periodic flow of oil are investigated, and descriptions of these flows using both physical and spectral approaches are presented. The time dependence of the flow and temperature fields of oil are shown, and the dynamics of the process is discussed. The spectral transfer of energy among the axial modes comprising the flow is explored. The three-dimensional linear stabiltiy of the multicellular air flow is parametrically studied. The domain of stable two-dimensional cellular motion is found to be constrained by the Eckhaus instability and by two types of monotone instability. The two-dimensional multicellular flow is unstable above a Grashof number of about 8550.

Chait, Arnon↗

NASA NTRS1993

NASA/MSFC FY92 Earth Science and Applications Program Research Review

A large amount of attention has recently been given to global issues such as the ozone hole, tropospheric temperature variability, etc. A scientific challenge is to better understand atmospheric processes on a variety of spatial and temporal scales in order to predict environmental changes. Measurement of geophysical parameters such as wind, temperature, and moisture are needed to validate theories, provide analyzed data sets, and initialize or constrain numerical models. One of NASA's initiatives is the Mission to Planet Earth Program comprised of an Earth Observation System (EOS) and the scientific strategy to analyze these data. This work describes these efforts in the context of satellite data analysis and fundamental studies of atmospheric dynamics which examine selected processes important to the global circulation.

Arnold, James E.↗

NASA NTRS2001

Optimizing Orbit-Instrument Configuration for Global Precipitation Mission (GPM) Satellite Fleet

Following the scientific success of the Tropical Rainfall Measuring Mission (TRMM) spearheaded by a group of NASA and NASDA scientists, their external scientific collaborators, and additional investigators within the European Union's TRMM Research Program (EUROTRMM), there has been substantial progress towards the development of a new internationally organized, global scale, and satellite-based precipitation measuring mission. The highlights of this newly developing mission are a greatly expanded scope of measuring capability and a more diversified set of science objectives. The mission is called the Global Precipitation Mission (GPM). Notionally, GPM will be a constellation-type mission involving a fleet of nine satellites. In this fleet, one member is referred to as the "core" spacecraft flown in an approximately 70 degree inclined non-sun-synchronous orbit, somewhat similar to TRMM in that it carries both a multi-channel polarized passive microwave radiometer (PMW) and a radar system, but in this case it will be a dual frequency Ku-Ka band radar system enabling explicit measurements of microphysical DSD properties. The remainder of fleet members are eight orbit-synchronized, sun-synchronous "constellation" spacecraft each carrying some type of multi-channel PMW radiometer, enabling no worse than 3-hour diurnal sampling over the entire globe. In this configuration the "core" spacecraft serves as a high quality reference platform for training and calibrating the PMW rain retrieval algorithms used with the "constellation" radiometers. Within NASA, GPM has advanced to the pre-formulation phase which has enabled the initiation of a set of science and technology studies which will help lead to the final mission design some time in the 2003 period. This presentation first provides an overview of the notional GPM program and mission design, including its organizational and programmatic concepts, scientific agenda, expected instrument package, and basic flight architecture. Following this introduction, we focus specifically on the last topic, that being an analysis which leads to an optimal flight architecture dictated in part by science requirements but constrained by allowable orbital mechanics, instrument scan patterns, and antenna aperture properties. Because the optimal architecture involves an interplay between orbit mechanics and instrument specifications, it is important to recognize that in attempting to serve various scientific themes, the final optimal architecture will represent a compromise concerning dynamic range, spatial resolution, sampling interval, pointing, beam coincidence, and measurement uncertainty. Moreover, cost becomes a major factor in seeking the optimal architecture through the pathways of antenna and instrument scan designs, as well as propulsion requirements associated with the orbit heights of various "constellation" members. Although the results presented at the IGARSS-2001 meeting will likely not be the fully refined flight architecture specifications, they are expected to be nearly complete.

Smith, Eric A.↗

NASA NTRS2011

Star Dust Formation Activities in AzTEC-3: A Starburst Galaxy at z=5.3

Analyses of of high-redshift ultraluminous infrared OR) galaxies traditionally use the observed optical to submillimeter spectral energy distribution (SED) and estimates of the dynamical mass as observational constraints to derive the star formation rate (SFR), the stellar mass, and age of these objects. In this lecture we add this constraint to the analysis of AzTEC-3, a starburst galaxy at z=5.3. We construct different stellar and chemical evolutionary scenarios, constrained to produce the inferred dust mass and observed luminosity before the associated stellar mass exceeds the observational limit. A robust result of our models is that all scenarios require most of the radiating dust mass to have been accreted in molecular clouds. Our new procedure highlights the importance of a multi wavelength approach, and of the use of dust evolution models in constraining the age and the star formation activity and history in galaxies.

Dwek, Eliahu↗

NASA NTRS2011

Star and Dust Formation Activities in AzTEC-3: A Starburst Galaxy at z equals 5.3

Analyses of of high-redshift ultraluminous infrared (IR) galaxies traditionally use the observed optical to submillimeter spectral energy distribution (SED) and estimates of the dynamical mass as observational constraints to derive the star formation rate (SFR), the stellar mass, and age of these objects. In this lecture we add this constraint to the analysis of AzTEC-3, a starburst galaxy at z=5.3. We construct different stellar and chemical evolutionary scenarios, constrained to produce the inferred dust mass and observed luminosity before the associated stellar mass exceeds the observational limit. A robust result of our models is that all scenarios require most of the radiating dust mass to have been accreted in molecular clouds. Our new procedure highlights the importance of a multi wavelength approach, and of the use of dust evolution models in constraining the age and the star formation activity and history in galaxies.

Dwek, Eliahu↗

NASA NTRS2011

Star and Dust Formation Activities in AzTEC-3: A Starburst Galaxy at z=5.3

Analyses of of high-redshift ultraluminous infrared (IR) galaxies traditionally use the observed optical to submillimeter spectral energy distribution (SED) and estimates of the dynamical mass as observational constraints to derive the star formation rate (SFR), the stellar mass, and age of these objects. In this lecture we add this constraint to the analysis of AzTEC-3, a starburst galaxy at z=5.3. We construct different stellar and chemical evolutionary scenarios, constrained to produce the inferred dust mass and observed luminosity before the associated stellar mass exceeds the observational limit. A robust result of our models is that all scenarios require most of the radiating dust mass to have been accreted in molecular clouds. Our new procedure highlights the importance of a multiwavelength approach, and of the use of dust evolution models in constraining the age and the star formation activity and history in galaxies.

Dwek, Eliahu↗

NASA NTRSDate not supplied

Temporal Changes in Astronauts’ Muscle and Cardiorespiratory Physiology Before, During, and After Spaceflight

NASA’s planned space exploration missions will require astronauts to safely perform extravehicular activity (EVA) and to safely egress vehicles in a variety of landing scenarios. Prolonged exposure to spaceflight decreases cardiovascular and sensorimotor function, causes loss of bone mineral density, reduces muscle mass and strength, and ultimately diminishes tolerance for physical activity. Although exercise can help mitigate these spaceflight-induced physiological decrements, little is known regarding the time-course of changes in muscle and aerobic performance during spaceflight. Furthermore, these exercise countermeasures are not fully protective. For example, maximal aerobic capacity (VO2pk), lower body muscle cross-sectional area, and strength all decrease by about 10% to 15% after long-duration missions on the International Space Station (ISS). Future long-duration space missions beyond Low Earth Orbit will employ exploration vehicles with less robust exercise hardware and more constrained exercise capabilities (e.g., less operational volume, less active exercise time) than provided on the ISS. Thus, countermeasures will need to be optimized to protect crew health and performance on exploration-class missions lasting up to 3 years. This requires a more detailed understanding of the dynamic effects of spaceflight on human health and performance, the ability of exercise to protect against this deconditioning, and the interaction of exercise with interrelated factors like nutrition, sleep, and environmental conditions.

N.C. Strock↗

NASA NTRSDate not supplied

Temporal Changes in Astronauts’ Muscle and Cardiorespiratory Physiology Before, During, and After Spaceflight

N. Strock↗

DOE OSTI2023

Towards constrained grid-forming control

Grid-forming converters are commonly envisioned to replace conventional synchronous generators as the cornerstone of future power systems. However, compared to synchronous generators, power converters and their power sources (e.g., renewable generation, energy storage) are subject to significant physical constraints (e.g., current limits, modulation limits). Grid-forming controls are commonly designed neglecting these constraints and subsequently augmented with limiters for a subset of constraints. In this work, we propose a systematic approach to constrained grid-forming control of two-level voltage source converters interfacing photovoltaics. We first formulate grid-forming control objectives and constraints of voltage source converters and photovoltaics in a one-step optimal grid-forming control problem. Next, we leverage primal-dual dynamics to obtain a dynamic feedback controller that approximates the solution of the one-step optimal grid-forming control problem. Finally, electromagnetic transient simulations are used to illustrate the results.

Gross, Dominic↗

DOE OSTI2025

Nonlinear Optimal Control of Electron Dynamics Within Hartree-Fock Theory

Consider the problem of determining the optimal applied electric field to drive a molecule from an initial state to a desired target state. For even moderately sized molecules, solving this problem directly using the exact equations of motion—the time-dependent Schrödinger equation (TDSE)—is numerically intractable. Here, we present a solution of this problem within time-dependent Hartree-Fock (TDHF) theory, a mean field approximation of the TDSE. Optimality is defined in terms of minimizing the total control effort while maximizing the overlap between desired and achieved target states. We frame this problem as an optimization problem constrained by the nonlinear TDHF equations; we solve it using trust region optimization with gradients computed via a custom-built adjoint state method. For three molecular systems, we show that with very small neural network parametrizations of the control, our method yields solutions that achieve desired targets within acceptable constraints and tolerances.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2023

Holographic non-Fermi liquids at large d

Motivated by the results of Dynamical Mean Field Theory, we study the two-point function of fermions moving in a charged black brane background in AdS d +1 in the limit of large d . We observe the emergence of a locally critical form of the fermion self-energy, with a strongly constrained range of possible scaling behaviors at large d . Novelties compared to the analysis in d = 3, 4 include an enlarged regime of temperatures where the results apply, and the analytical tractability of the calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Advancing a toolkit of diverse futures approaches for global environmental assessments

Global Environmental Assessments (GEAs) support national and international policy making for sustainable development. They rely on quantitative scenarios produced by Integrated Assessment Models (IAMs) to assess alternative futures. IAM-based scenarios can provide a coherent assessment framework that integrates different subsystems and their interactions. However, these top-down approaches have limited ability to represent key local dynamics, unexpected events, or the role of diverse actors. Other methods, including participatory scenarios, can help co-create narratives that emphasize diverse contents with clear links to existing decision-making. However, these bottom-up approaches provide only limited insight into global processes and are not constrained by measurable parameters. In our review, we identify four key challenges for current GEA scenarios: surprise, scale, diversity and imagination. We illustrate how these challenges can be overcome by combining top-down and bottom-up scenario approaches and conclude with a call to action for future research to take on this trans-disciplinary challenge.

Pereira, Laura M.↗

DOE OSTI2023

Shock-induced metallization of polystyrene along the principal Hugoniot investigated by advanced thermal density functionals

To date, none of the ab-initio molecular dynamics simulations of polystyrene, often used as an ablator material in inertial confinement fusion targets, with the standard ground-state exchange-correlation (XC) functional in density-functional theory can satisfactorily agree with experiments in terms of reflectivity measurements. Here, we use recently developed thermal strongly constrained and appropriately normed Laplacian dependent meta-generalized gradient approximation XC density functional (T-SCAN-L) and thermal hybrid XC density functional (KDT0) to show that the inclusion of thermal and inhomogeneity effects is crucial for accurate prediction of structural evolution and corresponding insulator-metal transition (IMT) during shock compression. Optical reflectivity calculated as an indicator of IMT is in perfect accord with experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2024

Leveraging Optimal Sparse Sensor Placement to Aggregate a Network of Digital Twins for Nuclear Subsystems

Nuclear power plants (NPPs) require continuous monitoring of various systems, structures, and components to ensure safe and efficient operations. The critical safety testing of new fuel compositions and the analysis of the effects of power transients on core temperatures can be achieved through modeling and simulations. They capture the dynamics of the physical phenomenon associated with failure modes and facilitate the creation of digital twins (DTs). Accurate reconstruction of fields of interest (e.g., temperature, pressure, velocity) from sensor measurements is crucial to establish a two-way communication between physical experiments and models. Sensor placement is highly constrained in most nuclear subsystems due to challenging operating conditions and inherent spatial limitations. This study develops optimized data-driven sensor placements for full-field reconstruction within reactor and steam generator subsystems of NPPs. Optimized constrained sensors reconstruct field of interest within a tri-structural isotropic (TRISO) fuel irradiation experiment, a lumped parameter model of a nuclear fuel test rod and a steam generator. The optimization procedure leverages reduced-order models of flow physics to provide a highly accurate full-field reconstruction of responses of interest, noise-induced uncertainty quantification and physically feasible sensor locations. Accurate sensor-based reconstructions establish a foundation for the digital twinning of subsystems, culminating in a comprehensive DT aggregate of an NPP.

42 ENGINEERING↗

DOE OSTI2021

Phase Modeling of the TRAPPIST-1 Planetary Atmospheres

Transiting compact multiplanet systems provide many unique opportunities to characterize the planets, including studies of size distributions, mean densities, orbital dynamics, and atmospheric compositions. The relatively short orbital periods in these systems ensure that events requiring specific orbital locations of the planets (such as primary transit and secondary eclipse points) occur with high frequency. The orbital motion and associated phase variations of the planets provide a means to constrain the atmospheric compositions through measurement of their albedos. Here we describe the expected phase variations of the TRAPPIST-1 system and times of superior conjunction when the summation of phase effects produce maximum amplitudes. We also describe the infrared flux emitted by the TRAPPIST-1 planets and the influence on the overall phase amplitudes. We further present the results from using the global circulation model ROCKE-3D to model the atmospheres of TRAPPIST-1e and TRAPPIST-1f assuming modern Earth and Archean atmospheric compositions. These simulations are used to calculate predicted phase curves for both reflected light and thermal emission components. We discuss the detectability of these signatures and the future prospects for similar studies of phase variations for relatively faint M stars.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1989

A practical approach for minimum time control of the Spacecraft Control Laboratory Experiment (SCOLE), appendix A

The Space COntrol Laboratory Experiment (SCOLE) is a challenge for control engineering applications. This is a result of the system dynamics, the available measurement information, the actuator capabilities and finally the specified performance requirements set. Results on the use of Model Reference Adaptive Control were reported. In view of the necessity for rapid response, this work deals with an optimal control formulation, with a minimum time requirement and constrained input. A mathematical statement of the problem is presented. The time optimal control formulation is presented and the reasons that make such an approach not promising are discussed. As a result, a pseudo time-optimal control algorithm is discussed. The proposed approach is tested to see if it satisfies the design specifications, and finally a discussion and suggestions for further research are provided.

Kaufman, H.↗

NASA NTRS1997

Sliding Mode Control of a Slewing Flexible Beam

An output feedback sliding mode controller (SMC) is proposed to minimize the effects of vibrations of slewing flexible manipulators. A spline trajectory is used to generate ideal position and velocity commands. Constrained nonlinear optimization techniques are used to both calibrate nonlinear models and determine optimized gains to produce a rest-to-rest, residual vibration-free maneuver. Vibration-free maneuvers are important for current and future NASA space missions. This study required the development of the nonlinear dynamic system equations of motion; robust control law design; numerical implementation; system identification; and verification using the Sandia National Laboratories flexible robot testbed. Results are shown for a slewing flexible beam.

Wilson, David G.↗

NASA NTRS2016

Mineralogy of Mudstone at Gale Crater, Mars: Evidence for Dynamic Lacustrine Environments

The Mars Science Laboratory Curiosity rover landed in Gale crater in August 2012 to assess the habitability of sedimentary deposits that show orbital evidence for diverse ancient aqueous environments. Gale crater contains a 5 km high mound of layered sedimentary rocks in its center, informally named Mount Sharp. The lowermost rocks of Mount Sharp contain minerals that are consistent with a dramatic climate change during Mars' early history. During the rover's traverse across the Gale crater plains to the base of Mount Sharp, Curiosity discovered sedimentary rocks consistent with a fluviolacustrine sequence. Curiosity studied ancient lacustrine deposits at Yellowknife Bay on the plains of Gale crater and continues to study ancient lacustrine deposits in the Murray formation, the lowermost unit of Mount Sharp. These investigations include drilling into the mudstone and delivering the sieved less than 150 micrometers fraction to the CheMin XRD/XRF instrument inside the rover. Rietveld refinement of XRD patterns measured by CheMin generates mineral abundances with a detection limit of 1-2 wt.% and refined unit-cell parameters of minerals present in abundances greater than approximately 5 wt.%. FULLPAT analyses of CheMin XRD patterns provide the abundance of X-ray amorphous materials and constrain the identity of these phases (e.g., opal-A vs. opal-CT). At the time of writing, CheMin has analyzed 14 samples, seven of which were drilled from lacustrine deposits. The mineralogy from CheMin, combined with in-situ geochemical measurements and sedimentological observations, suggest an evolution in the lake waters through time, including changes in pH and salinity and transitions between oxic and anoxic conditions. In addition to a geochemically dynamic lake environment, the igneous minerals discovered in the lake sediments indicate changes in source region through time, with input from mafic and silicic igneous sources. The Murray formation is predominantly comprised of lacustrine mudstone and is 150-200 m thick, suggesting long history of lake environments in Gale crater. Curiosity has traversed through the lowermost approximately 30 m of the Murray formation, and each additional sample provides clues about the climate on early Mars.

Rampe, E. B.↗