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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Numerical Modeling of Liquid-Vapor Phase Change

We implemented a two- and three-dimensional finite difference/front tracking technique to solve liquid-vapor phase change problems. The mathematical and the numerical features of the method were explained in great detail in our previous reports, Briefly, we used a single formula representation which incorporated jump conditions into the governing equations. The interfacial terms were distributed as singular terms using delta functions so that the governing equations would be the same as conventional conservation equations away from the interface and in the vicinity of the interface they would provide correct jump conditions. We used a fixed staggered grid to discretize these equations and an unstructured grid to explicitly track the front. While in two dimensions the front was simply a connection of small line segments, in three dimensions it was represented by a connection of small triangular elements. The equations were written in conservative forms and during the course of computations we used regriding to control the size of the elements of the unstructured grid. Moreover, we implemented a coalescence in two dimensions which allowed the merging of different fronts or two segments of the same front when they were sufficiently close. We used our code to study thermocapillary migration of bubbles, burst of bubbles at a free surface, buoyancy-driven interactions of bubbles, evaporation of drops, rapid evaporation of an interface, planar solidification of an undercooled melt, dendritic solidification, and a host of other problems cited in the reference.

Esmaeeli, Asghar↗
NASA NTRS1997

A Simplified Theory of Coupled Oscillator Array Phase Control

Linear and planar arrays of coupled oscillators have been proposed as means of achieving high power rf sources through coherent spatial power combining. In such - applications, a uniform phase distribution over the aperture is desired. However, it has been shown that by detuning some of the oscillators away from the oscillation frequency of the ensemble of oscillators, one may achieve other useful aperture phase distributions. Notable among these are linear phase distributions resulting in steering of the output rf beam away from the broadside direction. The theory describing the operation of such arrays of coupled oscillators is quite complicated since the phenomena involved are inherently nonlinear. This has made it difficult to develop an intuitive understanding of the impact of oscillator tuning on phase control and has thus impeded practical application. In this work a simpl!fied theory is developed which facilitates intuitive understanding by establishing an analog of the phase control problem in terms of electrostatics.

Pogorzelski, R. J.↗
NASA NTRS2006

International Space Station: Transitional Platform for Moon and Mars

Humans on the path to Mars are employing the Space Station to better understand the Life Sciences issues during long duration space flight. In this phase the problems, for example, of bone loss, skeletal muscle atrophy and radiation will be prioritized for countermeasure development. This presentation will feature NASA's critical path to the Moon and Mars as the initial blueprint for addressing these Human Life Sciences challenges necessary to accomplish a successful Mars transit, surface exploration and return to Earth. A Moon base will be the test bed for resolving the engineering obstacles for later establishment of the Mars Crew Habitat. Current engineering concept scenarios for Moon and Mars bases plus Mars transit vehicles will receive the final focus.

Greeniesen, Michael C.↗
NASA NTRS2007

Looking at Hubble Through the Eyes of JWST

The phase retrieval algorithm developed for the James Webb Space Telescope (JWST) is used to process archival image data that was originally used to characterize the Hubble primary mirror edge defect. The Hubble mirror conic constant is inferred from these results and comparisons are made with earlier conic values reported by teams comprising the HARP (Hubble Aberration Recovery Project) study. A number of important lessons learned from the Hubble phase retrieval problem are described and a discussion is given on how these have been incorporated into the JWST Observatory design.

Dean, Bruce H.↗
NASA NTRS2014

On Characterizing Particle Shape

It is well known that particle shape affects flow characteristics of granular materials, as well as a variety of other solids processing issues such as compaction, rheology, filtration and other two-phase flow problems. The impact of shape crosses many diverse and commercially important applications, including pharmaceuticals, civil engineering, metallurgy, health, and food processing. Two applications studied here include the dry solids flow of lunar simulants (e.g. JSC-1, NU-LHT-2M, OB-1), and the flow properties of wet concrete, including final compressive strength. A multi-dimensional generalized, engineering method to quantitatively characterize particle shapes has been developed, applicable to both single particle orientation and multi-particle assemblies. The two-dimension, three dimension inversion problem is also treated, and the application of these methods to DEM model particles will be discussed. In the case of lunar simulants, flow properties of six lunar simulants have been measured, and the impact of particle shape on flowability - as characterized by the shape method developed here -- is discussed, especially in the context of three simulants of similar size range. In the context of concrete processing, concrete construction is a major contributor to greenhouse gas production, of which the major contributor is cement binding loading. Any optimization in concrete rheology and packing that can reduce cement loading and improve strength loading can also reduce currently required construction safety factors. The characterization approach here is also demonstrated for the impact of rock aggregate shape on concrete slump rheology and dry compressive strength.

Ennis, Bryan J.↗
NASA NTRS2014

Upset Recovery Human Factors

Accident and incident analyses as well as industry group concerns and recommendations have justified taking a second look at proficiency standards related to upset recovery training and performance. Quite a number of factors and theories have been suggested-- leading the NASA Aviation Safety Program to reconsider manual handling skills in highly automated aircraft particularly in conditions that can potentially lead to Loss of Control events. Our team of Subject Matter Experts (SMEs) first identified 76 Basic Recovery Skills that were important for effective crew response under five different anomaly conditions. In addition to manual handling skills, the skill set included knowledge and cognitive skills, as well as decision making and management skills. Advanced Recovery Skills were identified by combining skills, integrating with crew resource management skills, and developing heuristics for decision making.Using the Advanced Recovery Skill set, the SMEs then developed a generic process flow starting from the problem discovery phase (e.g., identifying an anomaly) through the decision making and management phase (e.g., assessing response options), through the recovery phase (e.g., controlling the aircraft). The generic process flow was refined by testing it against six additional scenarios. The next part of the project was to develop an approach for assessing and revising a generic training curriculum (we used an operators Advanced Qualification Program (AQP) as a framework). Although many of the Basic and Advanced Recovery Skills could be found in the Job Task Listing, they were not always structured or combined in the most effective way. Recommendations were developed for assessing relevant aspects of the Job Task Listing and Continuing Qualification curriculum so that the more comprehensive set of Upset Recovery skillsincluding Human Factors--could be trained and assessed in the most appropriate and effective context. The existing AQP methodology provides a natural way to insert targeted Upset Recovery skills into its system of proficiency objectives, training devices, training activities, and ultimately, into the event sets of a simulator training scenario.

AQP training↗
NASA NTRS2020

Robotics System Process and Concept for On-orbit Assembly for Potential Mars Sample Return

Proposed Mars Sample Return (MSR) missions would require on-orbit assembly of containment vessels to meet backward Planetary Protection requirements and transfer of the sample container through various stations and positions. Some operations would have to be performed autonomously, and others would require ground-in-loop decision-making stages and verification processes. One concept design for an Earth Return Orbiter (ERO) Capture, Contain, and Return System (CCRS) Transfer Mechanism (TM) is a multi-Degree of Freedom (DOF) manipulator that utilizes a passive End Effector (EE) to assist in containment vessel assembly. To converge on a feasible design, a robotic system process has been instantiated. This process is composed of three main phases: robotic problem definition (operating environment, operations/functions, system goals), robotic solution selection (trade studies on the number of degrees of freedom, number of mechanisms, types of mechanisms), robotic solution design, implementation, and verification and validation (kinematic configuration, robotic and kinematic analysis and topology optimization of components). As a final product of this process, a half-scale functional prototype of the TM was developed to demonstrate the end-to-end operation capability.

Strahle, Jackson W↗
DOE OSTI2022

Method of Distributions for Two‐Phase Flow in Heterogeneous Porous Media

Abstract Multiscale heterogeneity and insufficient characterization data for a specific subsurface formation of interest render predictions of multi‐phase fluid flow in geologic formations highly uncertain. Quantification of the uncertainty propagation from the geomodel to the fluid‐flow response is typically done within a probabilistic framework. This task is computationally demanding due to, for example, the slow convergence of Monte Carlo simulations (MCS), especially when computing the tails of a distribution that are necessary for risk assessment and decision‐making under uncertainty. The frozen streamlines method (FROST) accelerates probabilistic predictions of immiscible two‐phase fluid flow problems; however, FROST relies on MCS to compute the travel‐time distribution, which is then used to perform the transport (phase saturation) computations. To alleviate this computational bottleneck, we replace MCS with a deterministic equation for the cumulative distribution function (CDF) of travel time. The resulting CDF‐FROST approach yields the CDF of the saturation field without resorting to sampling‐based strategies. Our numerical experiments demonstrate the high accuracy of CDF‐FROST in computing the CDFs of both saturation and travel time. For the same accuracy, it is about 5 and 10 times faster than FROST and MCS, respectively.

Yang, Hyung Jun↗
NASA NTRS1984

Twin tilt nacelle V/STOL aircraft

This paper describes the second government-conducted, piloted flight simulation of the Grumman Design 698 V/STOL (vertical and short takeoff and landing) aircraft. Emphasis is on the aircraft's handling qualities as rated by various NASA, Navy, and GAC pilots with flight experience ranging from CTOL (conventional take-off and landing) to V/STOL aircraft. The Design 698 had been modified to resolve the flight problems that were of most concern to the pilots in the first investigation (Phase I). Those problems included an adverse nonminimum phase (NMP) acceleration response in both the longitudinal and lateral axes, a large thrust-response lag, and adverse ground effects. The adverse NMP acceleration is an attribute of the vertical vanes (a Grumman patent) positioned in the fan exhaust flow. The primary modifications included using the vertical-vane deflection as a thrust spoiling method, the addition of the cross-shafted propulsion system, and the implementation of two velocity and attitude control modes (standard and precision) for speeds below 50 knots.

Eskey, M. A.↗
NASA NTRS1968

Phase-lock loop frequency control and the dropout problem

Technique automatically sets the frequency of narrow band phase-lock loops within automatic lock-in-range. It presets a phase-lock loop to a desired center frequency with a closed loop electronic frequency discriminator and holds the phase-lock loop to that center frequency until lock is achieved.

Attwood, S.↗
NASA NTRS1991

Correction of magnetooptic device phase errors in optical correlators through filter design modifications

We address the problem of optical phase errors in an optical correlator introduced by the input and filter plane spatial light modulators. Specifically, we study a laboratory correlator with magnetooptic spatial light modulator (MOSLM) devices. We measure and characterize the phase errors, analyze their effects on the correlation process, and discuss a means of correction through a design modification of the binary phase-only optical filter function. The phase correction technique is found to produce correlation results close to those of an error-free correlator.

Downie, John D.↗
DOE OSTI2021

Machine learning to alleviate Hubbard-model sign problems

Lattice Monte Carlo calculations of interacting systems on nonbipartite lattices exhibit an oscillatory imaginary phase known as the phase or sign problem, even at zero chemical potential. One method to alleviate the sign problem is to analytically continue the integration region of the state variables into the complex plane via holomorphic flow equations. For asymptotically large flow times, the state variables approach manifolds of constant imaginary phase known as Lefschetz thimbles. Furthermore, flowing such variables and calculating the ensuing Jacobian is a computationally demanding procedure. In this paper, we demonstrate that neural networks can be trained to parametrize suitable manifolds for this class of sign problem and drastically reduce the computational cost for different severely afflicted small volume systems. In particular, we apply our method to the Hubbard model on the triangle and tetrahedron, both of which are nonbipartite. At strong interaction strengths and modest temperatures, the tetrahedron suffers from a severe sign problem that cannot be overcome with standard reweighting techniques, while it quickly yields to our method. We benchmark our results with exact calculations and comment on future directions of this work.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Multigrid Algorithms with Projection and Prolongation over Elements of the Phase Space for K-Eigenvalue Transport Problems

This paper describes new multilevel acceleration methods for solving the multigroup neu- tron transport eigenvalue problems. These multilevel algorithms use different projection and prolongation operators in the phase space. The Nonlinear Diffusion Acceleration (NDA) method with multiple grids in energy is formulated with the prolongation oper- ator based on multiplication iterative correction and linear-in-energy mapping. Another multilevel NDA method uses the projection operator with coarsening in energy between the high-order transport and low-order NDA equations. The third algorithm is formu- lated with the partial-current based CMFD low-order equations and applies projection operators in space and energy. The numerical results are presented.

Cornejo, Luke↗
NASA NTRS1998

[Activities of Space Telescope Science Institute with the Hubble Space Telescope]

A number of studies, especially in recent years with the Hubble Space Telescope's (HST) Goddard High Resolution Spectrograph (GHRS), have been presented on the UV line profiles of late-type stars. Generally, these consist of a few "snapshot" spectra of several different key diagnostic emission lines. From this it has become clear that many active stars possess non-gaussian line profiles. Unlike the case with AR Lac, observed with IUE, no assymetric profile has been clearly identified that results from an inhomogeneous surface temperature or density distribution. In 1993 we attempted to observe the RS CVn binary V711 Tau at several phases with the GHRS in a number of UV bandpasses in order to study profile variations as a function of phase. Unfortunately, scheduling problems, pointing errors, continuous flaring and the sparse and uneven phase sampling prevented us from achieving the primary goal. However, it is clear that a number of UV lines in the system, notably C IV, Si IV and Mg II show very extended emission out to several hundred km/s. The profiles were also clearly variable. Vilhu et al. (1997) and Walter et al. (1995) conducted a campaign on the rapidly rotating, single star AB Dor, where they observed C IV continuously for 14 hours. They found extended, non-gaussian emission in the C IV doublet and that Doppler images derived from these images were remarkably similar to the simultaneous spot-image. In a follow up study of V711 Tau we have observed another RS CVn with complete phase coverage in three key wavelength bandpasses, utilizing the ability of HST to observe some stars at high latitudes in uninterrupted fashion. Generally classified as an RS CVn, V824 Ara (HD 155555) consists of a G5 IV star in a short period orbit (P=ld.68) with a K0 V-IV companion. However, the system does not eclipse and therefore does not rigorously fit the Hall (1976) definition. There is also a visual M star companion (LDS587B) 33 arcsec away. The space velocities of the stars suggests that the binary is part of the young disk population which agrees with the high Li I lambda 6708 abundance. With the M star companion showing very high levels of activity it seems likely that the V824 Ara +LDS587B system is pre-main sequence. With rotational velocities of 37 km/s and 29 km/s for the G and K star components respectively, the system is very similar to V711 Tau. Photometric observations by Cutispoto (1993) show an amplitude, delta V approx. = 0.12 with a period equal to the orbital value derived by Pasquini et at. (1991). Dempsey et al. (1993a) found a PSPC X-ray luminosity of 2.74 x 10(exp 30)erg/s. Two-temperature coronal models were applied to the PSPC X-ray pulse-height spectra by Dempsey et al. (1993b). They found that the lower temperature component was consistent with the full sample of RS CVn binaries studied but that the hot component was slightly lower than the sample as a whole. Moderate Ca II H and K emission, filled in H alpha and radio emission are also consistent with this being a fairly active, short period binary system.

Dempsey, Robert C.↗
DOE OSTI2025

A mixed-integer PDE-constrained optimization formulation for constructing electromagnetic cloaks with multiple materials

We study the design of an electromagnetic cloak from multiple materials with an additional constraint on the mass of the cloak. Our problem is an example of a topology optimization problem, and we formulate this problem as a mixed-integer partial-differential equation constrained optimization (MIPDECO) problem, where Maxwell’s equation models the propagation of the wave through the cloak and surrounding medium. We use binary variables to model the assignment of the different materials, and their relevant properties (permittivity and density). The mass constraint adds a nontrivial constraint to this problem. We propose a two-phase strategy to solve this problem. In the first phase, we solve a continuous relaxation, and then propose a new variant of the feasibility pump that exploits the structure of the PDE to obtain an initial integral solution candidate. In the second phase, we use a trust-region approach to improve this incumbent. We also consider a continuation or mesh-sequencing approach to find better solutions faster on consecutively finer meshes. We present detailed numerical results to illustrate the effectiveness of our approaches for constructing multi-material cloaks with a mass constraint.

Calculus of Variations and Optimization↗
NASA NTRS1997

Numerical Studies of Phase Transition Phenomena in Microgravity

This work was aimed at developing and applying a new methodology for the efficient and accurate computation of problems involving several phases of matter. In particular, solidification processes typically involve melt/solid and sometimes melt//gas interfaces, whose location and shape is unknown a priori. This class of problems is called the free or moving boundary problem, and the numerical approaches for its solution to date are inaccurate, inefficient, and can not be readily extended to multi-dimensions or to time dependent phenomenon. Ongoing research on crystal growth at NASA and other institutions falls into the category of free boundary problems. It is exactly the accurate determination of the process dynamics and the shape and location of the interface between the phases which is responsible for the ultimate chemical segregation and the mechanical properties in the solid. This work developed the Triad Field Formalism approach for the computation of general multi-dimensional and time dependent free boundary problems. The particular subject addressed is solidification phenomena. All the relevant boundary conditions on the developing interface were exactly resolved. Several computer programs were developed during the course of this research, enabling us to determine for the first time the interplay among the various fields operating in tandem to produce the phenomena observed during solidification processes in weld pools and during crystal growth.

Source record↗
DOE OSTI2022

Cluster Analysis of Combined EDS and EBSD Data to Solve Ambiguous Phase Identifications

A common problem in analytical scanning electron microscopy (SEM) using electron backscatter diffraction (EBSD) is the differentiation of phases with distinct chemistry but the same or very similar crystal structure. X-ray energy dispersive spectroscopy (EDS) is useful to help differentiate these phases of similar crystal structures but different elemental makeups. However, open, automated, and unbiased methods of differentiating phases of similar EBSD responses based on their EDS response are lacking. This paper describes a simple data analytics-based method, using a combination of singular value decomposition and cluster analysis, to merge simultaneously acquired EDS + EBSD information and automatically determine phases from both their crystal and elemental data. I use hexagonal TiB 2 ceramic contaminated with multiple crystallographically ambiguous but chemically distinct cubic phases to illustrate the method. Code, in the form of a Python 3 Jupyter Notebook, and the necessary data to replicate the analysis are provided as Supplementary material.

47 OTHER INSTRUMENTATION↗