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At least 469 records · Page 26

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NASA NTRS1988

An Experimental and Analytical Evaluation of a Biaxial Test for Determining Shear Properties of Composite Materials

The results of an experimental and analytical investigation of a biaxial tension/compression test for determining shear properties of composite materials are reported. Using finite element models of isotropic and orthotropic laminates, a specimen geometry was optimized. A kinematic fixture was designed to introduce an equal and opposite pair of forces into a specimen with a one inch square test section. Aluminum and several composite laminates with the optimized geometry and a configuration with large stress gradients were tested in the fixture. The specimens were instrumented with strain gages in the center of the test section for shear stiffness measurements. Pure shear strain was measured. The results from the experiments correlated well with finite element results. Failure of the specimens occurred through the center of the test section and appeared to have initiated at the high stress points. The results lead to the conclusion that the optimized specimen is suitable for determining shear modulus for composite materials. Further revisions to the specimen geometry are necessary if the method is to give shear strength data.

Kennedy, John M.↗

NASA NTRS1979

On truncated expansion self-tuning regulation of a large AMCD

The one-dimensional wave equation models out of plane displacement of a flexible ring and with appropriate boundary conditions the solution is one of uncoupled modes. Identification and control of the behavior of these modes by means of a self-tuning regulator requires precise measurements of the ring shape. Aliasing of modes occurs from a finite number of sensors along the ring causing interference in the modal identification. Nonuniform sensors spacing allows for reduced aliasing effects but introduces spreading of the modes and provides inconsistent measurements. The homogeneous wave equation solution for modal time behavior aids in the separation of the aliasing effects, but difficulty arises when the ring is spinning past the sensors and control forces are being applied.

Hamm, A. L.↗

DOE OSTI2025

Radiation-induced bowing of SiC/SiC composites under neutron flux gradients—integral experimental data for model validation

Here, the radiation-induced swelling of SiC and its composites, including strong dependencies on temperature and dose, can drive significant lateral bowing in the presence of temperature and/or dose gradients. In recent years, simulations have been performed to assess the extent of bowing in SiC composite light-water reactor (LWR) fuel cladding and boiling water reactor (BWR) channel boxes. However, to date, no integral experimental data exist to validate these models. This work provides the first experimental bowing evaluation of three ∼380 mm long SiC composite specimens irradiated under varying neutron dose gradients (∼50°C–60°C, 0.03–0.06 dpa): two tubes (∼9.8 mm diameter) and a miniature BWR channel box (∼30 mm square). The measured radiation-induced length swelling (∼0.3%–0.7% linear) was consistently 10%–21% higher than values obtained from 3D finite element structural analyses with inputs from 3D radiation transport calculations. This discrepancy could be at least partially explained by differences in dose rate (∼10 -8 dpa/s) compared to the literature data (∼10-6 dpa/s) used to establish the dose-to-swelling correlations in the model. Nevertheless, the modeled bowing magnitudes (<2 mm) obtained from finite element analyses and simple analytical equations were within the bounds of the experimental measurements for all specimens. With improved confidence in the ability to predict the structural response and measure the macroscopic deformations, future experiments will target transient bowing under neutron flux gradients at representative LWR temperatures and assess whether grid spacers can mitigate the tens of millimeters of bowing that would otherwise be expected in ∼4 m long LWR components.

bowing↗

NASA NTRS1974

Finite element formulations for problems of large elastic-plastic deformation

An Eulerian finite element formulation is presented for problems of large elastic-plastic flow. The method is based on Hill's variational principle for incremental deformations, and is suited to isotropically hardening Prandtl-Reuss materials. The formulation is given in a manner which allows any conventional finite element program, for "small strain" elasticplastic analysis, to be simply and rigorously adapted to problems involving arbitrary amounts of deformation and arbitrary levels of stress in comparison to plastic deformation moduli. The method is applied to a necking bifurcation analysis of a bar in plane-strain tension. A unified general formulation of finite element equations, both Lagrangian and Eulerian, for large deformations, with arbitrary choice of the conjugate stress and strain measures, and a discussion is given of other proposed formulations for elastic-plastic finite element analysis at large strain.

Mcmeeking, R. M.↗

NASA NTRS1975

Finite-element formulations for problems of large elastic-plastic deformation

An Eulerian finite element formulation is presented for problems of large elastic-plastic flow. The method is based on Hill's variational principle for incremental deformations, and is ideally suited to isotropically hardening Prandtl-Reuss materials. Further, the formulation is given in a manner which allows any conventional finite element program, for 'small strain' elastic-plastic analysis, to be simply and rigorously adapted to problems involving arbitrary amounts of deformation and arbitrary levels of stress in comparison to plastic deformation moduli. The method is applied to a necking bifurcation analysis of a bar in plane-strain tension. The paper closes with a unified general formulation of finite element equations, both Lagrangian and Eulerian, for large deformations, with arbitrary choice of the conjugate stress and strain measures. Further, a discussion is given of other proposed formulations for elastic-plastic finite element analysis at large strain, and the inadequacies of some of these are commented upon.

Mcmeeking, R. M.↗

NASA NTRS1996

Finite Element Analysis of a NASA National Transonic Facility Wind Tunnel Balance

This paper presents the results of finite element analyses and correlation studies performed on a NASA National Transonic Facility (NTF) Wind Tunnel balance. In the past NASA has relied primarily on classical hand analyses, coupled with relatively large safety factors, for predicting maximum stresses in wind tunnel balances. Now, with the significant advancements in computer technology and sophistication of general purpose analysis codes, it is more reasonable to pursue finite element analyses of these balances. The correlation studies of the present analyses show very good agreement between the analyses and data measured with strain gages and therefore the studies give higher confidence for using finite element analyses to analyze and optimize balance designs in the future.

Lindell, Michael C.↗

NASA NTRS1999

Finite Element Analysis of a NASA National Transonic Facility Wide Tunnel Balance

Lindell, Michael C.↗

NASA NTRS1999

Preliminary Results from the Confined Helium Experiment

We describe the preliminary results from an experiment to measure the heat capacity of helium confined within a stack of evenly spaced silicon plates at temperatures very close to the superfluid transition. The resolution of the heat capacity measurements was generally about 5x10 (exp -9)K, allowing the finite size peak to be mapped in detail. In addition, wide range data containing information on the behavior of the surface specific heat was collected. The preliminary analysis shows fair agreement with theory, but some discrepancies. The results can also be combined with related ground measurements on smaller length scales to perform additional tests of scaling predictions for cross-over to lower dimensional behavior. Some results in this area are also presented.

Lipa, J. A.↗

NASA NTRS2021

OGLE-2019-BLG-0960 Lb: the Smallest Microlensing Planet

We report the analysis of OGLE-2019-BLG-0960, which contains the smallest mass-ratio microlensing planet found to date (q = 1.2–1.6 × 10^(−5) at 1σ). Although there is substantial uncertainty in the satellite parallax measured by Spitzer, the measurement of the annual parallax effect combined with the finite source effect allows us to determine the mass of the host star (M(L) = 0.3–0.6 Mꙩ), the mass of its planet (m(p) = 1.4–3.1 Mꚛ), the projected separation between the host and planet (a(⊥) = 1.2–2.3 au), and the distance to the lens system (D(L) = 0.6–1.2 kpc). The lens is plausibly the blend, which could be checked with adaptive optics observations. As the smallest planet clearly below the break in the mass-ratio function, it demonstrates that current experiments are powerful enough to robustly measure the slope of the mass-ratio function below that break. We find that the cross-section for detecting small planets is maximized for planets with separations just outside of the boundary for resonant caustics and that sensitivity to such planets can be maximized by intensively monitoring events whenever they are magnified by a factor A > 5. Finally, an empirical investigation demonstrates that most planets showing a degeneracy between (s > 1) and (s < 1) solutions are not in the regime (|log s| ≫ 0) for which the "close"/"wide" degeneracy was derived. This investigation suggests that there is a link between the "close"/"wide" and "inner/outer" degeneracies and also that the symmetry in the lens equation goes much deeper than symmetries uncovered for the limiting cases.

Jennifer C. Yee↗

NASA NTRS1985

Rocket thrust chamber thermal barrier coatings

A research program was conducted to generate data and develop analytical techniques to predict the performance and reliability of ceramic thermal barrier coatings in high heat flux environments. A finite element model was used to analyze the thermomechanical behavior of coating systems in rocket thrust chambers. Candidate coating systems (using a copper substrate, NiCrAlY bond coat and ZrO2.8Y2O3 ceramic overcoat) were selected for detailed study based on photomicrographic evaluations of experimental test specimens. The effects of plasma spray application parameters on the material properties of these coatings were measured and the effects on coating performance evaluated using the finite element model. Coating design curves which define acceptable operating envelopes for seleted coating systems were constructed based on temperature and strain limitations. Spray gun power levels was found to have the most significant effect on coating structure. Three coating systems were selected for study using different power levels. Thermal conductivity, strain tolerance, density, and residual stress were measured for these coatings. Analyses indicated that extremely thin coatings ( 0.02 mm) are required to accommodate the high heat flux of a rocket thrust chamber and ensure structural integrity.

Batakis, A. P.↗

NASA NTRS2011

Dynamic Shape Reconstruction of Three-Dimensional Frame Structures Using the Inverse Finite Element Method

A robust and efficient computational method for reconstructing the three-dimensional displacement field of truss, beam, and frame structures, using measured surface-strain data, is presented. Known as shape sensing , this inverse problem has important implications for real-time actuation and control of smart structures, and for monitoring of structural integrity. The present formulation, based on the inverse Finite Element Method (iFEM), uses a least-squares variational principle involving strain measures of Timoshenko theory for stretching, torsion, bending, and transverse shear. Two inverse-frame finite elements are derived using interdependent interpolations whose interior degrees-of-freedom are condensed out at the element level. In addition, relationships between the order of kinematic-element interpolations and the number of required strain gauges are established. As an example problem, a thin-walled, circular cross-section cantilevered beam subjected to harmonic excitations in the presence of structural damping is modeled using iFEM; where, to simulate strain-gauge values and to provide reference displacements, a high-fidelity MSC/NASTRAN shell finite element model is used. Examples of low and high-frequency dynamic motion are analyzed and the solution accuracy examined with respect to various levels of discretization and the number of strain gauges.

Gherlone, Marco↗

DOE OSTI2023

Absolute electron density fluctuation reconstruction for two-dimensional hydrogen beam emission spectroscopy

Scrape-off layer (SOL) and edge plasma turbulence significantly contribute to the radial particle and heat transport, lowering the plasma confinement and increasing the heat load on the plasma facing components. SOL turbulence is predominantly intermittent, which manifests in the occurrence of isolated density filaments or blobs. Filaments propagate radially outward toward plasma facing components, limiting their lifetime by erosion and sputtering. To characterize this phenomenon in detail, few diagnostic techniques are available. Beam emission spectroscopy is a diagnostic capable of measuring plasma turbulence in both SOL and edge plasmas. Due to the finite lifetime of the excitation states during the beam–plasma interaction and the misalignment between the optics and the magnetic field, spatial smearing is introduced in the measurement. In this paper, a novel method is introduced to overcome this hindering effect by inverting the fluctuation response matrix on an optimally smoothed signal. We show that this method is fast and provides significantly more accurate absolute density fluctuation reconstruction than the direct inversion technique. Here, the presented method is usable for all types of beam emission diagnostics where the spatial resolution is higher than the combined smearing of the atomic physics and the observation.

47 OTHER INSTRUMENTATION↗

NASA NTRS1989

Development of fiber-based laser anemometer for SSME application

A recent study by Rocketdyne for NASA identified laser anemometry, using a compact optical head, as a feasible diagnostic instrument for the Space Shuttle Main Engine (SSME) Model Verification experiments. Physical Research, Inc. (PRI) is presently under contract from NASA Lewis to develop and deliver such a laser anemometer system. For this application, it is desired to place the laser at a remote distance from the engine, and use single mode polarization preserving fiber optics for the transmission of the laser light to and from the measurement head. Other requirements are given. Analytical and experimental tools are being used to develop the technologies required for the laser anemometer. These include finite element analysis of the optical head and vibration tests for various optical and mechanical components. Design of the optical head and the fiber optic connectors are driven by the temperature and vibration requirements for the measurement environment. Results of the finite element analysis and the vibration tests of the components are included. Conceptual design of the fiber optic launcher and the optical probe has also been complete. Detailed design of the probe as well as the fabrication and assembly of the components is in progress.

Modarress, Dariush↗

NASA NTRS1989

Calculation of flight vibration levels of the AH-1G helicopter and correlation with existing flight vibration measurements

Boeing Helicopters, together with other U.S. Helicopter manufacturers, participated in a finite element applications program to give the United States a superior capability to utilize finite element analysis models in support of helicopter airframe design. The program was sponsored by the NASA Langley Research Center. Under this program, an activity was sponsored to evaluate existing analysis methods applicable to calculate coupled rotor-airframe vibrations. The helicopter used in this evaluation was the AH-1G helicopter. The results of the Boeing Helicopters efforts are summarized. The planned analytical procedure is reviewed. Changes to the planned procedure are discussed, and results of the correlation study are presented.

Ditaranto, R. A.↗

NASA NTRS1992

Measured effect of step axial location on labyrinth seal leakage

An advanced, finite volume code has been extensively used in a parametric design study of simple stepped seals, in order to ascertain a leakage-minimizing optimal design and test it, in conjunction with the baseline case of the wear-ring seal of a high pressure pump. It is found that a significant leakage effect arises from this shifting of the rotor and stator sealing surfaces; at extremely low rpm, a significant shaft speed effect occurs for the optimized design in some shaft locations.

Morrison, G. L.↗

NASA NTRS1998

Model Analysis of an Aircraft Fueslage Panel using Experimental and Finite-Element Techniques

The application of Electro-Optic Holography (EOH) for measuring the center bay vibration modes of an aircraft fuselage panel under forced excitation is presented. The requirement of free-free panel boundary conditions made the acquisition of quantitative EOH data challenging since large scale rigid body motions corrupted measurements of the high frequency vibrations of interest. Image processing routines designed to minimize effects of large scale motions were applied to successfully resurrect quantitative EOH vibrational amplitude measurements

Fleming, Gary A.↗

NASA NTRS1976

Scanning laser-velocimeter surveys and analysis of multiple vortex wakes of an aircraft

A laser velocimeter capable of rapidly scanning a flow field while simultaneously sensing two components of the velocity was used to measure the vertical and streamwise velocity structure 1.5 spans downstream in the wake of a model typical of a large subsonic transport (Boeing 747). This flow field was modeled by a superposition of axisymmetric vortices with finite cores. This theoretical model was found to agree with the measured velocities everywhere except where two vortices were in close proximity. Vortex strengths derived from the span loading on the wing as predicted by vortex-lattice theory also agree with the present measurements. The axisymmetric vortex model used herein is a useful tool for analytically investigating the vortex wakes of aircraft.

Corsiglia, V. R.↗

NASA NTRS1972

High-resolution imagery of Uranus obtained by Stratoscope 2

From 17 photographs of Uranus obtained by Stratoscope 2, a composite image has been produced having a Gaussian point spread function with a half maximum intensity diameter of 0.2. No certain surface markings are visible. If there are any faint belts parallel to the rotation equator they have a maximum contrast of 5%. The measured limb darkening does not agree with either a deep Rayleigh atmosphere or with clouds high in the atmosphere; a cloud deck under a finite Rayleigh atmosphere seems to be indicated. The equatorial diameter of Uranus is measured to be 51,800 plus or minus 600 km and the ellipticity is estimated to be 0.01 plus or minus 0.01.

Danielson, R. E.↗