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At least 217 records · Page 12

All sources NASA NTRS DOE OSTI

NASA NTRS2012

Improved Displacement Transfer Functions for Structure Deformed Shape Predictions Using Discretely Distributed Surface Strains

In the formulations of earlier Displacement Transfer Functions for structure shape predictions, the surface strain distributions, along a strain-sensing line, were represented with piecewise linear functions. To improve the shape-prediction accuracies, Improved Displacement Transfer Functions were formulated using piecewise nonlinear strain representations. Through discretization of an embedded beam (depth-wise cross section of a structure along a strain-sensing line) into multiple small domains, piecewise nonlinear functions were used to describe the surface strain distributions along the discretized embedded beam. Such piecewise approach enabled the piecewise integrations of the embedded beam curvature equations to yield slope and deflection equations in recursive forms. The resulting Improved Displacement Transfer Functions, written in summation forms, were expressed in terms of beam geometrical parameters and surface strains along the strain-sensing line. By feeding the surface strains into the Improved Displacement Transfer Functions, structural deflections could be calculated at multiple points for mapping out the overall structural deformed shapes for visual display. The shape-prediction accuracies of the Improved Displacement Transfer Functions were then examined in view of finite-element-calculated deflections using different tapered cantilever tubular beams. It was found that by using the piecewise nonlinear strain representations, the shape-prediction accuracies could be greatly improved, especially for highly-tapered cantilever tubular beams.

Ko, William L.↗

NASA NTRS2013

Impact of Radiatively Interactive Dust Aerosols in the NASA GEOS-5 Climate Model: Sensitivity to Dust Particle Shape and Refractive Index

We investigate the radiative effects of dust aerosols in the NASA GEOS-5 atmospheric general circulation model. GEOS-5 is improved with the inclusion of a sectional aerosol and cloud microphysics module, the Community Aerosol and Radiation Model for Atmospheres (CARMA). Into CARMA we introduce treatment of the dust and sea salt aerosol lifecycle, including sources, transport evolution, and sinks. The aerosols are radiatively coupled to GEOS-5, and we perform a series of multi-decade AMIP-style simulations in which dust optical properties (spectral refractive index and particle shape distribution) are varied. Optical properties assuming spherical dust particles are from Mie theory, while those for non-spherical shape distributions are drawn from a recently available database for tri-axial ellipsoids. The climatologies of the various simulations generally compare well to data from the MODIS, MISR, and CALIOP space-based sensors, the ground-based AERONET, and surface measurements of dust deposition and concentration. Focusing on the summertime Saharan dust cycle we show significant variability in our simulations resulting from different choices of dust optical properties. Atmospheric heating due to dust enhances surface winds over important Saharan dust sources, and we find a positive feedback where increased dust absorption leads to increased dust emissions. We further find that increased dust absorption leads to a strengthening of the summertime Hadley cell circulation, increasing dust lofting to higher altitudes and strengthening the African Easterly Jet. This leads to a longer atmospheric residence time, higher altitude, and generally more northward transport of dust in simulations with the most absorbing dust optical properties. We find that particle shape, although important for radiance simulations, is a minor effect compared to choices of refractive index, although total atmospheric forcing is enhanced by greater than 10 percent for simulations incorporating a spheroidal shape distribution versus ellipsoidal or spherical shapes.

radiative forcing↗

NASA NTRS2015

Fast Response, Open-Celled Porous, Shape Memory Effect Actuators with Integrated Attachments

This invention relates to the exploitation of porous foam articles exhibiting the Shape Memory Effect as actuators. Each foam article is composed of a plurality of geometric shapes, such that some geometric shapes can fit snugly into or around rigid mating connectors that attach the Shape Memory foam article intimately into the load path between a static structure and a moveable structure. The foam is open-celled, composed of a plurality of interconnected struts whose mean diameter can vary from approximately 50 to 500 microns. Gases and fluids flowing through the foam transfer heat rapidly with the struts, providing rapid Shape Memory Effect transformations. Embodiments of porous foam articles as torsional actuators and approximately planar structures are disposed. Simple, integral connection systems exploiting the ability to supply large loads to a structure, and that can also supply hot and cold gases and fluids to effect rapid actuation are also disposed.

Jardine, Andrew Peter↗

NASA NTRS2014

Constraints on Vesta's Interior Structure Using Gravity and Shape Models from the Dawn Mission

We use the shape and gravity field of Vesta determined from observations of the Dawn spacecraft to place constraints on the asteroid's interior structure. We compute a three-layer interior structure model by minimizing the power of the residual gravity anomaly. The densities of the mantle and crust are based on constraints derived from the Howardite-Eucrite-Diogenite (HED) meteorites. Vesta's present-day shape is not in hydrostatic equilibrium. The Rheasilvia and Veneneia impact basins have a large effect on Vesta's shape and are the main source of deviation from hydrostatic shape. Constraining a pre-giant-impact rotation rate and orientation of the spin axis from an ellipsoidal fit to the parts of Vesta unaffected by the giant impacts, and using the theory of figure, we can constrain the shape of the core. Our solution for Vesta's crust-mantle interface reveals a belt of thick crust around Rheasilvia and Veneneia. The thinnest crust is in the floor of the two basins and in the Vestalia Terra region. Our solution does not reveal an uplift of the crust-mantle boundary to the surface in the largest basins. This, together with the lack of olivine detected by the Visible and Infrared Spectrometer (VIR) data in Rheasilvia and Veneneia, indicates that Vesta's presumed olivine mantle was either not brought to the surface by these large impacts or was covered by ejecta from subsequent impacts.

Interiors↗

NASA NTRS2015

Method to Generate Full-Span Ice Shape on Swept Wing Using Icing Tunnel Data

There is a collaborative research program by NASA, FAA, ONERA, and university partners to improve the fidelity of experimental and computational simulation methods for swept-wing ice accretion formulations and resultant aerodynamic effects on large transport aircraft. This research utilizes a 65 scale Common Research Model as the baseline configuration. In order to generate the ice shapes for the aerodynamic testing, ice-accretion testing will be conducted in the NASA Icing Research Tunnel utilizing hybrid model from the 20, 64, and 83 spanwise locations. The models will have full-scale leading edges with truncated chord in order to fit the IRT test section. The ice shapes from the IRT tests will be digitized using a commercially available articulated-arm 3D laser scanning system. The methodology to acquire 3D ice shapes using a laser scanner was developed and validated in a previous research effort. Each of these models will yield a 1.5ft span of ice than can be used. However, a full-span ice accretion will require 75 ft span of ice. This means there will be large gaps between these spanwise ice sections that must be filled, while maintaining all of the important aerodynamic features. A method was developed to generate a full-span ice shape from the three 1.5 ft span ice shapes from the three models.

swept↗

NASA NTRS2015

Periodic Cellular Structure Technology for Shape Memory Alloys

Shape memory alloys are being considered for a wide variety of adaptive components for engine and airframe applications because they can undergo large amounts of strain and then revert to their original shape upon heating or unloading. Transition45 Technologies, Inc., has developed an innovative periodic cellular structure (PCS) technology for shape memory alloys that enables fabrication of complex bulk configurations, such as lattice block structures. These innovative structures are manufactured using an advanced reactive metal casting technology that offers a relatively low cost and established approach for constructing near-net shape aerospace components. Transition45 is continuing to characterize these structures to determine how best to design a PCS to better exploit the use of shape memory alloys in aerospace applications.

Chen, Edward Y.↗

NASA NTRS2015

Three-Dimensional Piecewise-Continuous Class-Shape Transformation of Wings

Class-Shape Transformation (CST) is a popular method for creating analytical representations of the surface coordinates of various components of aerospace vehicles. A wide variety of two- and three-dimensional shapes can be represented analytically using only a modest number of parameters, and the surface representation is smooth and continuous to as fine a degree as desired. This paper expands upon the original two-dimensional representation of airfoils to develop a generalized three-dimensional CST parametrization scheme that is suitable for a wider range of aircraft wings than previous formulations, including wings with significant non-planar shapes such as blended winglets and box wings. The method uses individual functions for the spanwise variation of airfoil shape, chord, thickness, twist, and reference axis coordinates to build up the complete wing shape. An alternative formulation parameterizes the slopes of the reference axis coordinates in order to relate the spanwise variation to the tangents of the sweep and dihedral angles. Also discussed are methods for fitting existing wing surface coordinates, including the use of piecewise equations to handle discontinuities, and mathematical formulations of geometric continuity constraints. A subsonic transport wing model is used as an example problem to illustrate the application of the methodology and to quantify the effects of piecewise representation and curvature constraints.

Olson, Erik D.↗

NASA NTRS2017

Effect of Ice Shape Fidelity on Swept-Wing Aerodynamic Performance

Low-Reynolds number testing was conducted at the 7 ft. x 10 ft. Walter H. Beech Memorial Wind Tunnel at Wichita State University to study the aerodynamic effects of ice shapes on a swept wing. A total of 17 ice shape configurations of varying geometric detail were tested. Simplified versions of an ice shape may help improve current ice accretion simulation methods and therefore aircraft design, certification, and testing. For each configuration, surface pressure, force balance, and fluorescent mini-tuft data were collected and for a selected subset of configurations oil-flow visualization and wake survey data were collected. A comparison of two ice shape geometries and two configurations with simplified geometric detail for each ice shape geometry is presented in this paper.

Scale models↗

NASA NTRS2018

Further Evaluation of Swept Wing Icing Scaling with Maximum Combined Cross Section Ice Shape Profiles

This study reports results from recent icing scaling tests conducted in the NASA Glenn Icing Research Tunnel (IRT) using recommended scaling methods that were developed for swept wing icing applications. The aluminum test articles used in this study were NACA 0012 Adjustable Sweep Airfoil Models. The reference and scale airfoils have a 36 inch and 15 inch chord measured normal to the leading edge, and a 60 inch and 24 inch span respectively. Reference tests were run with airspeeds of 100, 140.3 and 150 knot and MVD of 41.4, 44.4, 93 and 150 micron. All tests were set at 0⁰ angle of attack (AOA) and 30⁰ sweep angle. Results will be presented for stagnation freezing fractions ranging from 0.3 to 1.0. For non-dimensional reference & scale ice shape comparison, a new post-scanning ice shape digitization procedure was applied to extract 2-D "hand-tracing like" ice shape profiles, i.e. the Maximum Combined Cross Section or MCCS, at selected span-wise locations from the high fidelity 3-D scanned ice shapes obtained in the IRT. Preliminary assessment of ice shape comparison with MCCS showed that good scaling was achieved for the test conditions by using the recommended scaling methods developed for swept wing icing.

MCCS↗

NASA NTRS2019

Shape Sensing for Wings with Spars and Ribs Using Simulated Strain

Active trim shape control can be used to minimize error between target and actual aircraft trim shape during flight. Trim shape sensing for aircraft during flight is not only important for highly flexible aircraft, such as the National Aeronautics and Space Administration (NASA) Helios Prototype remotely piloted flying wing aircraft, but also for a delta-wing type aircraft, such as a supersonic commercial transport aircraft. A two-step theory utilizing distributed strain for a real-time shape sensing of a full three-dimensional structure has been introduced previously. This study focuses on the application of the two-step theory to finite element models of a wing with spars and ribs such as the X-59 QueSST aircraft (Lockheed Martin Corporation, Bethesda, Maryland), a tapered wing, a dihedral/anhedral wing, and a stiffened dihedral/anhedral wing. A finely meshed finite element structural model is desired to capture accurate curvature distributions along the neutral axes of the wing cross sections during pre-test analysis for shape sensing of a wing with ribs and spars. The two-step theory used in this study gives excellent deformation correlation with the MSC/NASTRAN (MSC Software, Newport Beach, California) results along the neutral axis for all test cases used in this study except the X-59 QueSST aircraft.

strain↗

NASA NTRSDate not supplied

Ice Shape Classification for Swept Wings

An important consideration for swept-wing ice shapes is the level of geometric fidelity required to accurately capture the aerodynamics. One way to help make the task of addressing this more manageable is to organize the ice shapes into a small number of classifications. These classifications are done by grouping similar ice shape geometries that also have similar iced wing aerodynamics. Ice shape classifications for airfoils are more mature and are reviewed as an example. Swept wing ice shape classifications are based on the well-established airfoil classifications and here five classifications are proposed: leading-edge roughness, streamwise ice, 3D leading-edge horn, highly 3D leading-edge horn and spanwise ridge. Recent data on swept wing icing aerodynamics is used to develop and support this classification. The development, or suppression, of the leading-edge separation vortex on swept wings without a leading-edge device is seen to be key in the classification of the highly 3D leading-edge horn.

Aircraft icing↗

NASA NTRS2021

Meta-aerogels: Auxetic Shape-memory Polyurethane Aerogels

Shape-memory poly(isocyanurate-urethane) (PIR-PUR) aerogels are low-density monolithic nanoporous solids that remember and return to their permanent shape through a heating actuation step. Herein, through structural design at the macro scale, the shape-memory response is augmented with an auxetic effect manifested by a negative Poisson’s ratio of approximately -0.8 at 15% compressive strain. Thus, auxetic shape-memory PIR-PUR monoliths experience volume contraction upon compression at a temperature above the glass transition temperature of the base polymer (Tg ~ 30 °C), and they can be stowed indefinitely in that temporary shape by cooling below Tg. By heating back above Tg, the compressed/shrunk form expands back to their original shape/size. This technology is relevant to a broad range of industries spanning the commercial, aeronautical, and aerospace sectors. The materials are referred to as meta-aerogels and their potential applications include minimally invasive medical devices, soft robotics, and in situations where volume is at a premium, as for example for storage of deployable space structures and planetary habitats during transport to the point of service.

Sadeq Malakooti↗

NASA NTRS2022

A Comparative Evaluation of Snowflake Particle Shape Estimation Techniques Used By the Precipitation Imaging Package (PIP), Multi-Angle Snowflake Camera (MASC), and Two-Dimensional Video Disdrometer (2DVD)

Measurements of snowflake particle shape are important for studying snow microphysics. While a number of instruments exist that are capable of measuring particle shape, this study focuses on the measurement techniques of three digital video disdrometers: the Precipitation Imaging Package (PIP), the Multi-Angle Snowflake Camera (MASC), and the Two-Dimensional Video Disdrometer (2DVD). To gain a better understanding of the relative strengths and weaknesses of these instruments and to provide a foundation upon which comparisons can be made between studies using data from different instruments, we perform a comparative analysis of the shape measurement algorithms employed by each of the three instruments by applying the algorithms to snowflake images captured by PIP during the ICE-POP 2018 field campaign. Our analysis primarily focuses on the measurement of the aspect ratio of either the particle itself, in the case of PIP and MASC, or of the particle bounding box, in the case of PIP and 2DVD. Both PIP and MASC use shape-fitting algorithms to measure aspect ratio. While our analysis of the MASC aspect ratio suggests that the measurements are reliable, our findings indicate that both the ellipse and rectangle aspect ratios produced by PIP underperformed considerably due to the shortcomings of the PIP shape-fitting techniques. We also demonstrate that reliable measurements of aspect ratio can be retrieved from PIP by reprocessing the raw PIP images using either the MASC ellipse-fitting algorithm or a tensor-based ellipse-fitting algorithm. Because of differences in instrument design, 2DVD produces measurements of particle horizontal and vertical extent rather than length and width. Furthermore, the 2DVD measurements of particle horizontal extent can be contaminated by horizontal particle motion. Our findings indicate that, although the correction technique used to remove the horizontal motion contamination performs remarkably well with snowflakes despite being designed for use with raindrops, the 2DVD measurements of particle horizontal extent are less reliable than those measured by PIP.

Charles N Helms↗

NASA NTRS2024

3D Scanning System to Assess Gravity-Dependent Body Shape Changes

The human body shows unique physiological and morphological changes when exposed to different gravity conditions, including muscle atrophy, fluid shift, spinal elongation, and body posture adjustments. Such changes need to be incorporated for human-system integration in the vehicle habitat, garment, and spacesuit designs, as inaccurate body measurements can result in suboptimal crew protection that can potentially decrease injury tolerance. However, the traditional linear measurements, such as stature, segment lengths or circumferences measured using a caliper or tape measure, often show limited consistency and are unable to capture the nonlinear characteristics of the human body. While 3D body scanning can provide significant advantages over linear measurements, the technologies have not been fully developed or customized for in-flight scanning. For ground laboratory use, several different scanner types are commercially available. However, in-flight scanning requires additional technical considerations, such as minimal scan time, simplified calibration, and sufficient capture volume. This work aims to develop a prototype 3-D body scanning system that is customized for in-flight use to scan crewmembers, with the configuration and performance optimized for detecting known gravity-dependent body shape and posture changes. A hardware system will be custom built using a network of commercial off-the-shelf 3D sensors. The sensor parameters and settings will be optimized to detect the targeted body shape changes, specifically using body manikins of which the shape and size are iteratively permuted to simulate the known changes by fluid shift and spinal elongation. The capture volume will be also matched for a range of body sizes from a 1st percentile female to 99th percentile male. Unintentional body motions or floating in microgravity will be also simulated and incorporated. A data acquisition software will be developed for efficient in-flight operations with minimal overhead and easy-to-use user interface. A simplified calibration procedure will be designed for robust scanning against frequent vibration or unexpected sensor position shifts. The system will be tested in the ground laboratory for accuracy and reliability against a reference scanning system. New anthropometry measurements will be also identified to sensitively capture the gravity dependent body shape changes, in addition to the traditional anthropometry measurements. A novel landmark-based technique will be tested for consistent anthropometry measurements across posture variations. If successfully developed and deployed, the new system is expected to provide previously unavailable body shape and size data from different gravitational environments, including 0-g, 1/6-g, and 1-g. Such data can improve suit fit, habitat design, exercise efficacy quantification and sizing of orthostatic intolerance garments.

K H Kim↗

NASA NTRS2024

3D Scanning System to Assess Gravity-Dependent Body Shape Changes

K H Kim↗

DOE OSTI2025

Laser-Modulation-Driven X-Ray Pulse Shaping in Regenerative Amplifier Free-Electron Lasers

In this Letter, we present a robust method for generating custom-shaped, coherent hard x-ray pulses in regenerative amplifier free-electron lasers (RAFELs) using laser-induced energy modulation of the electron beam. A temporally shaped optical modulation imprints an optical-wavelength energy pattern on the beam, which interacts with the recirculated seed in the x-ray cavity to generate spectral sidebands. These sidebands lie outside the Bragg reflection bandwidth and are extracted as out-coupled radiation, while the seed is retained for continued amplification, enabling a novel mechanism for both output coupling and pulse shaping. Furthermore, this approach allows deterministic control over the spectral and temporal properties of the emitted x-rays, including multicolor generation, twin-pulse structures, pulse duration tuning, and complex temporal waveforms. Importantly, it does not require modification of the RAFEL cavity or optics and is fully compatible with high-repetition-rate operation, offering a practical pathway to deliver coherent, shaped, and on-demand x-ray pulses for advanced time-resolved and nonlinear x-ray science.

Free-electron lasers↗

DOE OSTI2026

Picosecond measurements of plastic scintillator pulse shapes from gamma-ray interactions

An understanding of the pulse shape of organic scintillators can provide insight into scintillation mechanisms and inform the selection of the optimal detector material for a given application. Although the timing properties of organic scintillators have been extensively studied, significant discrepancies persist in reported rise and decay times. New plastic scintillating media have also been developed in recent years for which no literature data exist. The goal of this work is to provide high-precision measurements of the pulse shape of a suite of fast plastic organic scintillators from Eljen Technology—EJ-200, EJ-204, EJ-208, EJ-230, EJ-232, and EJ-232Q (with 0.5% benzophenone)—under excitation from $γ$-ray sources. The contributors to the system temporal resolution were quantified, and the dominant source of uncertainty was identified as the determination of the start time of a scintillation event. A pulse shape model was applied to the reconstructed temporal distributions, and rise and decay times were extracted and compared with manufacturer specifications. This work outlines a measurement approach to obtain the pulse shape of organic scintillators in response to $γ$-rays with temporal resolution on the order of tens of picoseconds, yielding data required for modeling plastic scintillator based detection systems for a range of applications.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Crystal structure and shape selection in the growth of 3D metallic crystallites on layered materials: Fe on MoS 2

Nucleation and growth of supported 3D metal clusters or crystallites during deposition on MoS 2 , or on other weakly-adhering layered materials, can potentially produce diverse growth shapes, and even crystal structures differing from the bulk metal. For Fe deposition on MoS 2 , SEM and AFM observations reveal three distinct crystallite shapes. By comparison with atomistic structure models incorporating realistic Fe-MoS 2 interface structures, here we conclude that these are: triangular fcc(111) pyramids with sloped {100} side facets; bcc(110) A-frame tents with sloped {100} side facets; and bcc(110) mesas with vertical {100} and {110} side facets. The following picture is proposed for the competitive formation of clusters and crystallites with different structures: (i) small nanoclusters formed at the onset of deposition exhibit facile fluxional dynamics allowing sampling of different crystal structures and shapes; (ii) sufficient fluxionality implies a Boltzmann distribution of sampled structures, and thus coexistence of different structures follows from the demonstrated similar energies for those structures; (iii) growing clusters reach a threshold size above which the characteristic time scale for restructuring exceeds that for cluster growth. Thereafter, clusters are locked-in to a specific crystal structure and shape as revealed by imaging of larger crystallites. Despite a penalty for fcc(111) over bcc(111) pyramids based on bulk energetics, favorable surface and interface energies makes them preferable for smaller sizes.

36 MATERIALS SCIENCE↗