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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Innovative design of composite structures: The use of curvilinear fiber format in structural design of composites

The influence is investigated of a curvilinear fiber format on load carrying capacity of a layered fiber reinforced plate with a centrally located hole. A curvilinear fiber format is descriptive of layers in a laminate having fibers which are aligned with the principal stress directions in those layers. Laminates of five curvilinear fiber format designs and four straightline fiber format designs are considered. A quasi-isotropic laminate having a straightline fiber format is used to define a baseline design for comparison with the other laminate designs. Four different plate geometries are considered and differentiated by two values of hole diameter/plate width equal to 1/6 and 1/3, and two values of plate length/plate width equal to 2 and 1. With the plates under uniaxial tensile loading on two opposing edges, alignment of fibers in the curvilinear layers with the principal stress directions is determined analytically by an iteration procedure. In-plane tensile load capacity is computed for all of the laminate designs using a finite element analysis method. A maximum strain failure criterion and the Tsai-Wu failure criterion are applied to determine failure loads and failure modes. Resistance to buckling of the laminate designs to uniaxial compressive loading is analyzed using the commercial code Engineering Analysis Language. Results indicate that the curvilinear fiber format laminates have higher in-plane tensile load capacity and comparable buckling resistance relative to the straightline fiber format laminates.

Charette, R. F.↗
NASA NTRS1990

The free-wake computation of rotor-body flows

In this paper a method is described for predicting the compressible, free-wake, flow about a lifting rotor-body configuration. The method is an extension of a unique vorticity embedded full-potential method used to calculate free-wake rotor hover performance. An unusual feature of this method is that it obviates the requirement for multiple grids to treat the rotor-body problem. The approach used to treat the body is similar to that used to include the rotor wake in the full potential calculation. The body is modeled as a structured circulation sheet and the strength of this sheet is determined in an iterative manner. Initially the method is tested to compute the flow past simple isolated bodies like cylinders and spheres. After a comparison of these simple computations with exact solutions this procedure is included into the HELIX-I, free-wake rotor code, to compute the flow around a rotor mounted on a large whirl tower. The effects of the tower on rotor wake geometry and load distribution are presented.

Ramachandran, K.↗
NASA NTRS1993

Time-variant analysis of rotorcraft systems dynamics - An exploitation of vector processors

In this paper a generalized algorithmic procedure is presented for handling constraints in mechanical transmissions. The latter are treated as multibody systems of interconnected rigid/flexible bodies. The constraint Jacobian matrices are generated automatically and suitably updated in time, depending on the geometrical and kinematical constraint conditions describing the interconnection between shafts or gears. The type of constraints are classified based on the interconnection of the bodies by assuming that one or more points of contact exist between them. The effects due to elastic deformation of the flexible bodies are included by allowing each body element to undergo small deformations. The procedure is based on recursively formulated Kane's dynamical equations of motion and the finite element method, including the concept of geometrical stiffening effects. The method is implemented on an IBM-3090-600j vector processor with pipe-lining capabilities. A significant increase in the speed of execution is achieved by vectorizing the developed code in computationally intensive areas. An example consisting of two meshing disks rotating at high angular velocity is presented. Applications are intended for the study of the dynamic behavior of helicopter transmissions.

Amirouche, F. M. L.↗
NASA NTRS1998

Track Structure Model for Radial Distributions of Electron Spectra and Event Spectra from High-Energy Ions

An analytic method is described for evaluating the average radial electron spectrum and the radial and total frequency-event spectrum for high-energy ions. For high-energy ions, indirect events make important contributions to frequency-event spectra. The method used for evaluating indirect events is to fold the radial electron spectrum with measured frequency-event spectrum for photons or electrons. The contribution from direct events is treated using a spatially restricted linear energy transfer (LET). We find that high-energy heavy ions have a significantly reduced frequency-averaged final energy (yF) compared to LET, while relativistic protons have a significantly increased yF and dose-averaged lineal energy (yD) for typical site sizes used in tissue equivalent proportional counters. Such differences represent important factors in evaluating event spectra with laboratory beams, in space- flight, or in atmospheric radiation studies and in validation of radiation transport codes. The inadequacy of LET as descriptor because of deviations in values of physical quantities, such as track width, secondary electron spectrum, and yD for ions of identical LET is also discussed.

Cucinotta, F. A.↗
NASA NTRS2001

Design, Generation and Tooth Contact Analysis (TCA) of Asymmetric Face Gear Drive With Modified Geometry

A new type of face gear drive for application in transmissions, particularly in helicopters, has been developed. The new geometry differs from the existing geometry by application of asymmetric profiles and double-crowned pinion of the face gear mesh. The paper describes the computerized design, simulation of meshing and contact, and stress analysis by finite element method. Special purpose computer codes have been developed to conduct the analysis. The analysis of this new type of face gear is illustrated with a numerical example.

Litvin, Faydor L.↗
NASA NTRS2006

Metal Hydride and Alkali Halide Opacities in Extrasolar Giant Planets and Cool Stellar Atmospheres

The lack of accurate and complete molecular line and continuum opacity data has been a serious limitation to developing atmospheric models of cool stars and Extrasolar Giant Planets (EGPs). We report our recent calculations of molecular opacities resulting from the presence of metal hydrides and alkali halides. The resulting data have been included in the PHOENIX stellar atmosphere code (Hauschildt & Baron 1999). The new models, calculated using spherical geometry for all gravities considered, also incorporate our latest database of nearly 670 million molecular lines, and updated equations of state.

Weck, Philippe F.↗
NASA NTRS2010

An Improved Neutron Transport Algorithm for HZETRN

Long term human presence in space requires the inclusion of radiation constraints in mission planning and the design of shielding materials, structures, and vehicles. In this paper, the numerical error associated with energy discretization in HZETRN is addressed. An inadequate numerical integration scheme in the transport algorithm is shown to produce large errors in the low energy portion of the neutron and light ion fluence spectra. It is further shown that the errors result from the narrow energy domain of the neutron elastic cross section spectral distributions, and that an extremely fine energy grid is required to resolve the problem under the current formulation. Two numerical methods are developed to provide adequate resolution in the energy domain and more accurately resolve the neutron elastic interactions. Convergence testing is completed by running the code for various environments and shielding materials with various energy grids to ensure stability of the newly implemented method.

Slaba, Tony C.↗
NASA NTRS2019

Multiple Boundary Layer Instability Modes with Nonequilibrium and Wall Temperature Effects Using LASTRAC

Prediction and control of boundary layer transition from laminar to turbulent is important to many flow regimes and vehicle designs, including vehicles operating at hypersonic conditions where nonequilibrium effects may be encountered. Wall cooling is known to affect the instability characteristics of the boundary layer and subsequently the transition location. Design considerations, including material failure and fuel chemistry, require the use of actively cooled walls in hypersonic vehicles, further motivating the study of wall temperature effects on top of the considerations of reducing heat flux, drag, and uncertainty. In this work, we analyze the stability of a boundary layer with chemical and thermal nonequilibrium on a Mach 20, 6 wedge. We investigate the effects of wall temperature on multiple unstable modes individually and on the integrated growth of disturbances along the surface. We use the LAngley Stability and TRansition Analysis Code (LASTRAC) to evaluate boundary layer stability, using capabilities implemented by the authors. Included are results that address chemical nonequilibrium with both thermal equilibrium and nonequilibrium.

Kline, H. L.↗
NASA NTRS2020

Planning In-Flight Calibration for XRISM

The XRISM X-ray observatory will fly two advanced instruments, the Resolve high-resolution spectrometer and the Xtend wide-field imager. These instruments, particularly Resolve, pose calibration challenges due to the unprecedented combination of spectral resolution, spectral coverage, and effective area, combined with a need to characterize the imaging fidelity of the full instrument system to realize the mission’s ambitious science goals. We present the status of the XRISM in-flight calibration plan, building on lessons from Hitomi and other X-ray missions. We present a discussion of targets and observing strategies to address the needed calibration measurements, with a focus on developing methodologies to plan a thorough and flexible calibration campaign and provide insight on calibration systematic error. We also discuss observations that exploit Resolve’s spectral resolution to calibrate atomic codes, and cross-calibration between the XRISM instruments and with other observatories.

Eric D Miller↗
NASA NTRS1985

PCG: A prototype incremental compilation facility for the SAGA environment, appendix F

A programming environment supports the activity of developing and maintaining software. New environments provide language-oriented tools such as syntax-directed editors, whose usefulness is enhanced because they embody language-specific knowledge. When syntactic and semantic analysis occur early in the cycle of program production, that is, during editing, the use of a standard compiler is inefficient, for it must re-analyze the program before generating code. Likewise, it is inefficient to recompile an entire file, when the editor can determine that only portions of it need updating. The pcg, or Pascal code generation, facility described here generates code directly from the syntax trees produced by the SAGA syntax directed Pascal editor. By preserving the intermediate code used in the previous compilation, it can limit recompilation to the routines actually modified by editing.

Kimball, Joseph John↗
NASA NTRS1993

MIL-STDS and PTTI: What's available and what needs to be done

The systems developer who needs Precise Time and Time Interval (PTTI) capability has relatively little guidance in the form of military standards, particularly for systems using atomic clocks or other sources of very precise time and frequency. The existing standards, including MIL-STD-188-115, MIL-F-2991(EC), and DOD-STD-1399 are discussed. These documents were written several years ago and do not always reflect current practice or take advantage of more recent technology improvements. User needs have also changed over the years and some of those needs such as more detailed time codes are not being met. We will summarize what's available and what's good and bad about it. The second part will make suggestions about what should be done in the future to promote and facilitate good PTTI design practice. Topics will include clock performance parameters, environmental considerations, time codes, signal isolation, and time dissemination.

Murray, James A.↗
NASA NTRS2011

Atomic Data and Spectral Line Intensities for NI XVII

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for Ni XVII. We include in the calculations the 23 lowest configurations, corresponding to 159 fine-structure levels: 3l3l', 3l4l0'' , and 3s5l0''' , with l,l' = s,p,d, l'' = s,p,d, f, and l''' = s,p,d. Collision strengths are calculated at five incident energies for all transitions at varying energies above the threshold of each transition. One additional energy, very close to the threshold of each transition, has also been included. Calculations have been carried out using the Flexible Atomic Code in the distorted wave approximation. Additional calculations have been performed with the University College London suite of codes for comparison. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates of the present work, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8) - 10(exp 14) / cubic cm and at an electron temperature of logT(sub e)e(K) = 6.5, corresponding to the maximum abundance of Ni XVII. Spectral line intensities are calculated, and their diagnostic relevance is discussed. This dataset will be made available in the next version of the CHIANTI database

Bhatia, A. K.↗
NASA NTRS1977

Differential pulse-code modulation

Systems encoding and decoding method allows data to be transmitted with less bandwidth than required for conventional system codes, and is not affected by data-transition density. In addition it requires no direct-current response of transition link and there is little ambiguity in resolution of digital data.

Herman, C. F.↗
NASA NTRS1980

ASHMET: A computer code for estimating insolation incident on tilted surfaces

A computer code, ASHMET, was developed by MSFC to estimate the amount of solar insolation incident on the surfaces of solar collectors. Both tracking and fixed-position collectors were included. Climatological data for 248 U. S. locations are built into the code. The basic methodology used by ASHMET is the ASHRAE clear-day insolation relationships modified by a clearness index derived from SOLMET-measured solar radiation data to a horizontal surface.

Elkin, R. F.↗
NASA NTRS1983

Wing loading on a 60 degree delta wing with vortex flaps

Wind tunnel tests were conducted on a 60 deg delta wing with three vortex flap designs to determine pressure distributions over the wing and flap. The results showed that an optimum vortex flap design depends on proper definition of the vortex flap deflection angle. They also revealed that flap thickness plays an important role in the behavior of the vortex flow over the flap and wing and can have a substantial effect on wing and flap pressure loading. Design codes which fail to account for thickness may result in a much less than optimum flap and deprive the designer of an important tool in designing an effective flap with optimum loading.

Marchman, J. F., III↗
NASA NTRS1985

A systematic study of magnetic braking in low-mass binaries

A short summary is given of Rappaport et al. (1983) which described results of extending a simplified stellar evolution code covering the evolution of low-mass compact binaries. Magnetic braking is probably an important process in the evolution of such binaries (such as cataclysmic variables and low-mass X-ray sources). The initial simplified code describes the mass-losing star as an n = 3/2 polytrope and was developed to study the evolution of binaries with a secondary of low mass (between 0.01 and 0.4 solar mass) when the angular momentum losses are due to gravitational radiation. In the extended code, a composite polytrope model is used for the secondary, wherein the structure of the radiative core is described by an n = 3 polytrope and the convective envelope by an n = 3/2 polytrope.

Verbunt, F.↗
NASA NTRS1990

Experimental and computational study of the viscoplastic response of high temperature structures

The first nine months of experimental and computational studies of the thermal-structural behavior of thin panels subjected to localized heating are described. Initial experimental studies have focused on developing an experimental set-up with well-defined thermal-structure boundary conditions. Preliminary tests with a Heldenfels panel have demonstrated out of plane bending (thermal buckling) due to panel initial imperfections. Initial computational studies have focused on: (1) validation of a thermoviscoplastic code to predict thermal stresses in the unbuckled panel, and (2) investigating in-plane stresses for test panels under transient thermal loading. Plans for future research are described.

Thornton, Earl A.↗