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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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NASA NTRS1985

Direct numerical simulation of equilibrium turbulent boundary layers

This paper describes the simulation of turbulent boundary layers by direct numerical solution of the three-dimensional, time-dependent Navier-Stokes equations, using a spectral method. The flow is incompressible, with Re sub delta = 1000. The equations are written in the self-similar coordinate system and periodic streamwise and spanwise boundary conditions are imposed. A family of nine 'equilibrium' boundary layers, from the strongly accelerated 'sink' flow to Stratford's separating boundary layer is treated. Good general agreement with experiments is observed. The effects of pressure gradients on the structures and statistics, both in the wall and wake regions are discussed.

Spalart, P. R.↗

NASA NTRS1992

Mean free paths of energetic particles at very large heliodistances (Pioneer 11 at 20 AU)

The parallel mean free path and the diffusion coefficient parallel to the magnetic field line are derived from magnetic field data at 20 AU to characterize heliospheric modulation and energetic-particle/magnetic-field interaction. The computational method of Moussas et al. (1975, 1982) is employed, and the values of the parallel mean free path are shown to be significantly larger than the values estimated in studies of up to 6 AU. The distance dependence of the parallel diffusion mean free path is found to follow a power law, and the diffusion coefficient dependence upon energy is determined by a constant mean free path and the velocity of the particle. The contribution of the diffusion coefficient perpendicular to the magnetic field is expected to dominate the radial diffusion coefficient of cosmic rays, although the contribution of the diffusion parallel to the field is important with respect to the small-scale structure of intensity gradients.

Moussas, X.↗

NASA NTRS1992

Thermal design optimization of a segmented GFRP primary reflector for a submillimeter telescope

Results are presented of a thermal design optimization study of the segmented GFRP primary reflector of the earth-orbiting Submillimeter Imager and Line Survey telescope. The paper examines the thermal requirements of the primary reflector and the thermal environment of the telescope and describes the thermal design of the primary reflector. Particular attention is given to the geometric math model and the thermal math model of the telescope. A summary for the steady-state thermal performance of the optimized design is presented, showing that the optimized design has reduced, by an order of magnitude, structural spatial temperature gradients, which were earlier shown to be the most significant obstacle in maintaining the required telescope figure accuracy.

Tsuyuki, Glenn T.↗

NASA NTRS1995

Monthly atmospheric and oceanographic surface fields for the western North Atlantic: December 1986 - April 1989

Monthly atmospheric and oceanographic variables for the western North Atlantic Ocean from various sources are presented as contour or vector maps. These fields were assembled for a study of the upper ocean heat budget. Atmospheric fields include the net surface heat fluxes and wind stress derived from the 1000 mb winds from the European Center for Medium-range Weather Forecasting (ECMWF). Oceanographic fields include the sea surface height from the Geosat radar altimeter and sea surface temperature from the Advanced Very High Resolution Radiometer (AVHRR). An additional estimate of net surface heat flux is shown; this estimate was derived by assimilating winds, currents and ocean temperatures into a mixed layer model. The maps show a complex interplay of fluctuations in the winds and heat fluxes, and in the structure and temperature gradients of the Gulf Stream system. Some comments are offered on a comparison of the two heat flux estimates.

Caruso, Michael J.↗

NASA NTRS2011

A Starshade Petal Error Budget for Exo-Earth Detection and Characterization

We present a starshade error budget with engineering requirements that are well within the current manufacturing and metrology capabilities. The error budget is based on an observational scenario in which the starshade spins about its axis on timescales short relative to the zodi-limited integration time, typically several hours. The scatter from localized petal errors is smoothed into annuli around the center of the image plane, resulting in a large reduction in the background flux variation while reducing thermal gradients caused by structural shadowing. Having identified the performance sensitivity to petal shape errors with spatial periods of 3-4 cycles/petal as the most challenging aspect of the design, we have adopted and modeled a manufacturing approach that mitigates these perturbations with 1-meter-long precision edge segments positioned using commercial metrology that readily meets assembly requirements. We have performed detailed thermal modeling and show that the expected thermal deformations are well within the requirements as well. We compare the requirements for four cases: a 32 meter diameter starshade with a 1.5 meter telescope, analyzed at 75 and 90 milliarcseconds, and a 40 meter diameter starshade with a 4 meter telescope, analyzed at 60 and 75 milliarcseconds.

error budget↗

NASA NTRS2017

Atmospheric Modeling Using Accelerometer Data During Mars Atmosphere and Volatile Evolution (MAVEN) Flight Operations

The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft is a NASA orbiter designed to explore the Mars upper atmosphere, typically from 140 to 160 km altitude. In addition to the nominal science mission, MAVEN has performed several Deep Dip campaigns in which the orbit's closest point of approach, also called periapsis, was lowered to an altitude range of 115 to 135 km. MAVEN accelerometer data were used during mission operations to estimate atmospheric parameters such as density, scale height, along-track gradients, and wave structures. Density and scale height estimates were compared against those obtained from the Mars Global Reference Atmospheric Model and used to aid the MAVEN navigation team in planning maneuvers to raise and lower periapsis during Deep Dip operations. This paper describes the processes used to reconstruct atmosphere parameters from accelerometers data and presents the results of their comparison to model and navigation-derived values.

Tolson, Robert H.↗

DOE OSTI2023

Machine learning unifies flexibility and efficiency of spinodal structure generation for stochastic biomaterial design

Abstract Porous biomaterials design for bone repair is still largely limited to regular structures (e.g. rod-based lattices), due to their easy parameterization and high controllability. The capability of designing stochastic structure can redefine the boundary of our explorable structure–property space for synthesizing next-generation biomaterials. We hereby propose a convolutional neural network (CNN) approach for efficient generation and design of spinodal structure—an intriguing structure with stochastic yet interconnected, smooth, and constant pore channel conducive to bio-transport. Our CNN-based approach simultaneously possesses the tremendous flexibility of physics-based model in generating various spinodal structures (e.g. periodic, anisotropic, gradient, and arbitrarily large ones) and comparable computational efficiency to mathematical approximation model. We thus successfully design spinodal bone structures with target anisotropic elasticity via high-throughput screening, and directly generate large spinodal orthopedic implants with desired gradient porosity. This work significantly advances stochastic biomaterials development by offering an optimal solution to spinodal structure generation and design.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2023

Compensating attenuation effects in full-waveform inversion with dissipation-dispersion decoupling

Seismic attenuation poses challenges to velocity model building from acoustic/elastic full-waveform inversion (FWI). In particular, when constructing the FWI gradient for velocity inversion, recent studies have indicated that the high-attenuation structure could distort the gradient by damping the amplitudes and shifting the kinematic phases, resulting in an imbalanced update and thus unreliable velocity model. These Q effects are particularly significant in the reflection acquisition geometry due to the “double-damping” issue. Here, we develop a Q-compensated FWI algorithm for constructing a Q-free FWI gradient. By using a recently developed viscoacoustic wave propagator, this compensation can be done conveniently by keeping the dispersion term and flipping the dissipation term in the wave equation when we simulate the forward and time-reversed adjoint wavefields. The resultant gradient obtained by interacting these two wavefields has correct kinematics and Q-free amplitudes. This Q-compensated FWI can balance the update between Q- and no- Q-areas, which we determine using synthetic examples. In addition, we illustrate how to take advantage of the dissipation-dispersion decoupling to determine the anomalous Q value in the Q model building workflow via Q-compensated reverse time migration.

Geochemistry & Geophysics↗

NASA NTRS2001

Higher-Order Theory for Functionally Graded Materials

Functionally graded materials (FGM's) are a new generation of engineered materials wherein the microstructural details are spatially varied through nonuniform distribution of the reinforcement phase(s). Engineers accomplish this by using reinforcements with different properties, sizes, and shapes, as well as by interchanging the roles of the reinforcement and matrix phases in a continuous manner (ref. 1). The result is a microstructure that produces continuously or discretely changing thermal and mechanical properties at the macroscopic or continuum scale. This new concept of engineering the material's microstructure marks the beginning of a revolution both in the materials science and mechanics of materials areas since it allows one, for the first time, to fully integrate the material and structural considerations into the final design of structural components. Functionally graded materials are ideal candidates for applications involving severe thermal gradients, ranging from thermal structures in advanced aircraft and aerospace engines to computer circuit boards. Owing to the many variables that control the design of functionally graded microstructures, full exploitation of the FGM's potential requires the development of appropriate modeling strategies for their response to combined thermomechanical loads. Previously, most computational strategies for the response of FGM's did not explicitly couple the material's heterogeneous microstructure with the structural global analysis. Rather, local effective or macroscopic properties at a given point within the FGM were first obtained through homogenization based on a chosen micromechanics scheme and then subsequently used in a global thermomechanical analysis.

Aboudi, J.↗

NASA NTRS2013

The NTF Inlet Guide Vanes Thermal Gradient Problem and Its Mitigation

The National Transonic Facility (NTF) utilizes Inlet Guide Vanes (IGV) to provide precise, quick response Mach number control for the tunnel. During cryogenic operations, the massive IGV structure can experience large thermal gradients, measured as "Delta T or (Delta)T", between the IGV ring and its support structure called the transfer case. If these temperature gradients are too large, the IGV structure can be stressed beyond its safety limit and cease operation. In recent years, (Delta)T readings exceeding the prescribed safety limits were observed frequently during cryogenic operations, particularly during model access. The tactical operation methods of the tunnel to minimize (Delta)T did not always succeed. One obvious option to remedy this condition is to warm up the IGV structure by disabling the main drive operation, but this "natural" warm up method can takes days in some cases, resulting in productivity loss. This paper documents the thermal gradient problem associated with the IGV structure during cryogenic operation and how the facility has recently achieved an acceptable mitigation which has resulted in improved efficiency of operations.

Venkat, Venki S.↗

NASA NTRS2001

Impact of dilution on microbial community structure and functional potential: comparison of numerical simulations and batch culture experiments

A series of microcosm experiments was performed using serial dilutions of a sewage microbial community to inoculate a set of batch cultures in sterile sewage. After inoculation, the dilution-defined communities were allowed to regrow for several days and a number of community attributes were measured in the regrown assemblages. Based upon a set of numerical simulations, community structure was expected to differ along the dilution gradient; the greatest differences in structure were anticipated between the undiluted-low-dilution communities and the communities regrown from the very dilute (more than 10(-4)) inocula. Furthermore, some differences were expected among the lower-dilution treatments (e.g., between undiluted and 10(-1)) depending upon the evenness of the original community. In general, each of the procedures used to examine the experimental community structures separated the communities into at least two, often three, distinct groups. The groupings were consistent with the simulated dilution of a mixture of organisms with a very uneven distribution. Significant differences in community structure were detected with genetic (amplified fragment length polymorphism and terminal restriction fragment length polymorphism), physiological (community level physiological profiling), and culture-based (colony morphology on R2A agar) measurements. Along with differences in community structure, differences in community size (acridine orange direct counting), composition (ratio of sewage medium counts to R2A counts, monitoring of each colony morphology across the treatments), and metabolic redundancy (i.e., generalist versus specialist) were also observed, suggesting that the differences in structure and diversity of communities maintained in the same environment can be manifested as differences in community organization and function.

Non-NASA Center↗

NASA NTRS1987

Nonlinear dynamic analysis of quasi-symmetric anisotropic structures

An efficient computational method for the nonlinear dynamic analysis of quasi-symmetric anisotropic structures is proposed. The application of mixed models simplifies the analytical development and improves the accuracy of the response predictions, and operator splitting allows the reduction of the analysis model of the quasi-symmetric structure to that of the corresponding symmetric structure. The preconditoned conjugate gradient provides a stable and effective technique for generating the unsymmetric response of the structure as the sum of a symmetrized response plus correction modes. The effectiveness of the strategy is demonstrated with the example of a laminated anisotropic shallow shell of quadrilateral planform subjected to uniform normal loading.

Noor, Ahmed K.↗

NASA NTRS2005

Tools for Designing and Analyzing Structures

Structural Design and Analysis Toolset is a collection of approximately 26 Microsoft Excel spreadsheet programs, each of which performs calculations within a different subdiscipline of structural design and analysis. These programs present input and output data in user-friendly, menu-driven formats. Although these programs cannot solve complex cases like those treated by larger finite element codes, these programs do yield quick solutions to numerous common problems more rapidly than the finite element codes, thereby making it possible to quickly perform multiple preliminary analyses - e.g., to establish approximate limits prior to detailed analyses by the larger finite element codes. These programs perform different types of calculations, as follows: 1. determination of geometric properties for a variety of standard structural components; 2. analysis of static, vibrational, and thermal- gradient loads and deflections in certain structures (mostly beams and, in the case of thermal-gradients, mirrors); 3. kinetic energies of fans; 4. detailed analysis of stress and buckling in beams, plates, columns, and a variety of shell structures; and 5. temperature dependent properties of materials, including figures of merit that characterize strength, stiffness, and deformation response to thermal gradients

Luz, Paul L.↗

NASA NTRS2012

Deterministic Design Optimization of Structures in OpenMDAO Framework

Nonlinear programming algorithms play an important role in structural design optimization. Several such algorithms have been implemented in OpenMDAO framework developed at NASA Glenn Research Center (GRC). OpenMDAO is an open source engineering analysis framework, written in Python, for analyzing and solving Multi-Disciplinary Analysis and Optimization (MDAO) problems. It provides a number of solvers and optimizers, referred to as components and drivers, which users can leverage to build new tools and processes quickly and efficiently. Users may download, use, modify, and distribute the OpenMDAO software at no cost. This paper summarizes the process involved in analyzing and optimizing structural components by utilizing the framework s structural solvers and several gradient based optimizers along with a multi-objective genetic algorithm. For comparison purposes, the same structural components were analyzed and optimized using CometBoards, a NASA GRC developed code. The reliability and efficiency of the OpenMDAO framework was compared and reported in this report.

Coroneos, Rula M.↗

NASA NTRS2012

Deterministic Design Optimization of Structures in OpenMDAO Framework

Coroneos, Rula M.↗

DOE OSTI2021

Gallidation assisted impurity doping

In one embodiment, a product includes a structure comprising a material of a Group-III-nitride having a dopant, where a concentration of the dopant in the structure has a concentration gradient characteristic of diffusion of the dopant inward from at least a portion of a surface of the structure in a direction substantially normal to the portion of the surface. The structure has less than 1% decomposition of the Group-III-nitride at the surface of the structure.

Voss, Lars↗

NASA NTRS1985

Thermal design of the ACCESS erectable space truss

Thermal design requirements for the erectable truss beam to be assembled in-orbit during extra-vehicular activity as part of the ACCESS experiment to take place in 1985-1986 are formulated and assessed. The coatings, insulation, and materials chosen for the structural elements of the beam are detailed. A combined radiation and conduction thermal model reveals that worst-case thermal gradients within the ACCESS structure over plane-to-sun angles of 0 to 80 deg will be less than 29 F, which is within the allowable limit of 50 F. The individual strut insulation concept using aluminized Kapton is shown to offer significant advantages over white paint or a chromic acid anodized surface for controlling the thermal response.

Bradley, O. H., Jr.↗

NASA NTRS1994

Physical state of the western U.S. upper mantle

Using observed P wave images of the western U.S. upper mantle, which show lateral variations of up to 8%, and existing scaling relations, we infer that the low-velocity mantle is hot and partially molten to depths of 100-200 km, and that the high-velocity upper mantle is subsolidus. Most the high-velocity upper mantle within a few hundred kilometers of the coastline appears to be relatively dense, suggesting that it is relatively cool (i.e., a thermal lithosphere). This is expected for features associated with the subducting Juan de Fuca and Gorda slabs, and the high velocity upper mantle beneath the Transverse Ranges has been attributed to the sinking of negatively buoyant mantle lithosphere. Other high-velocity mantle structures near the continental margin are consistent with this interpretation. In contrast, the generally high elevations of the continental interior imply a buoyant upper mantle there, an inference that holds for both the high- and the low-velocity upper mantle. The only resonable way to produce the high-velocity low-density upper mantle is through basalt depletion, thereby creating mantle of increased solidus temperature and decreased density. We distinguish a marginal domain, within approximately 250 km of the Pacific coast, from an interior domain. This is based on the inferred upper mantle compositional difference and regional associations: beneath the marginal domain, upper mantle structures trend parallel to the surface physiography and young tectonic structures, whereas upper mantle structures beneath the continental interior trend northeasterly. This northeast orientation is discordant with the young tectonic structures, but aligns with young volcanic activity. The high lateral gradients in observed upper mantle seismic structure found throughout the western United States imply high lateral gradients in the associated temperature or partial melt fields. Because these fields diffuse on time scales of less than a few tens of millions of years, the imaged upper mantle structure is young. The following upper mantle processes are hypothesized to account for these findings and inferences. Away from the plate margin, small-scale upper mantle convection driven by partial melt-induced buoyancy of hot upper mantle leads to the production and segregation of melt and the creation of compositional variations. The heterogeneous upper mantle P wave structure of the elevated continental interior is largely a consequence of partial melt variations that are modulated by the compositional variations, and throughout this region we infer high temperatures and low densities. Near the plate margin, relative plate motions force upper mantle flow, although upper mantle flow driven by the positive buoyancy of melt and the negative bouyancy lithosphere is important locally.

Humphreys, Eugene D.↗