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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Effects of Imperfections on the Buckling Response of Compression-Loaded Composite Shells

The results of an experimental and analytical study of the effects of initial imperfections on the buckling and postbuckling response of three unstiffened thin-walled compression-loaded graphite-epoxy cylindrical shells with different orthotropic and quasi-isotropic shell-wall laminates are presented. The results identify the effects of traditional and non-traditional initial imperfections on the non-linear response and buckling loads of the shells. The traditional imperfections include the geometric shell-wall mid-surface imperfect ions that are commonly discussed in the literature on thin shell buckling. The non-traditional imperfections include shell-wall thickness variations local shell-wall ply-gaps associated with the fabrication process, sheltered geometric imperfections, non-uniform applied end loads, and variations in the boundary conditions including the effects of elastic boundary conditions. A high-fidelity non-linear shell analysis procedure that accurately accounts for the effects of these traditional and non-traditional imperfections on the nonlinear response, and buckling loads of the shells is described. The analysis procedure includes a non-linear static analysis that predicts stable response characteristics of the shells and a non-linear transient analysis that predicts unstable response characteristics.

Hilburger, Mark W.↗
NASA NTRS1972

Buckling of nearly cylindrical shells under lateral pressure.

The effect of slight meridional curvature on the buckling of shells subjected to an external constant directional lateral pressure is examined. A class of nearly cylindrical shells with constant meridional curvature, a central radius-to-thickness ratio of 500, and central rise-to-shell-length ratios varying from plus 5% to minus 5% is considered. A brief study is presented of the dependence of the critical lateral pressure on the meridional curvature and on the length and meridional edge restraint.

Cooper, P. A.↗
NASA NTRS1989

Penetrative convective flows induced by internal heating and mantle compressibility

Penetrative convective flows induced in a spherical shell by combined effects of internal heating and mantle compressibility are investigated using mathematical and numerical formulations for compressible spherical shell convection. Isothermal stress-free boundary conditions applied at the top and the bottom of the shell are solved using a time-dependent finite difference code in a temperature, vorticity, stream function formulation for Rayleigh numbers ranging from the critical Rc up to 2000 Rc. Results indicate that compressibility, together with internal heating, could be a mechanism capable of generating spontaneously layered convection and local melting in the mantle and that non-Boussinesq effects must be considered in interpretations of geophysical phenomena.

Machetel, Philippe↗
NASA NTRS1994

Evolution of solitary density waves in stellar winds of early-type stars: A simple explanation of discrete absorption component behavior

We model the evolution of a density shell propagating through the stellar wind of an early-type star, in order to investigate the effects of such shells on UV P Cygni line profiles. Unlike previous treatments, we solve the mass, momentum, and energy conservation equations, using an explicit time-differencing scheme, and present a parametric study of the density, velocity, and temperature response. Under the assumed conditions, relatively large spatial scale, large-amplitude density shells propagate as stable waves through the supersonic portion of the wind. Their dynamical behavior appears to mimic propagating 'solitary waves,' and they are found to accelerate at the same rate as the underlying steady state stellar wind (i.e., the shell rides the wind). These hydrodynamically stable structures quantitatively reproduce the anomalous 'discrete absorption component' (DAC) behavior observed in the winds of luminous early-type stars, as illustrated by comparisons of model predictions to an extensive International Ultraviolet Explorer (IUE) time series of spectra of zeta Puppis (O4f). From these comparisons, we find no conclusive evidence indicative of DACs accelerating at a significantly slower rate than the underlying stellar wind, contrary to earlier reports. In addition, these density shells are found to be consistent within the constraints set by the IR observations. We conclude that the concept of propagating density shells should be seriously reconsidered as a possible explanation of the DAC phenomenon in early-type stars.

Waldron, Wayne L.↗
NASA NTRS1986

Ceramic-ceramic shell tile thermal protection system and method thereof

A ceramic reusable, externally applied composite thermal protection system (TPS) is proposed. The system functions by utilizing a ceramic/ceramic upper shell structure which effectively separates its primary functions as a thermal insulator and as a load carrier to transmit loads to the cold structure. The composite tile system also prevents impact damage to the atmospheric entry vehicle thermal protection system. The composite tile comprises a structurally strong upper ceramic/ceramic shell manufactured from ceramic fibers and ceramic matrix meeting the thermal and structural requirements of a tile used on a re-entry aerospace vehicle. In addition, a lightweight high temperature ceramic lower temperature base tile is used. The upper shell and lower tile are attached by means effective to withstand the extreme temperatures (3000 to 3200F) and stress conditions. The composite tile may include one or more layers of variable density rigid or flexible thermal insulation. The assembly of the overall tile is facilitated by two or more locking mechanisms on opposing sides of the overall tile assembly. The assembly may occur subsequent to the installation of the lower shell tile on the spacecraft structural skin.

Riccitiello, Salvatore R.↗
DOE OSTI2025

𝐷-shell mixing in light baryons and its effect on the orbital motion

The standard description of the nucleon in the nonrelativistic quark model is an 1S,L = 0 state without orbital motion. Yet, there are several indications from phenomenology that an admixture of states with nonzero orbital motion maybe substantial. In this paper we focus on the “second shell” of the nucleon excitations (D-shell), for which we give a modern description of the wave functions. We follow it by investigating what we call a “maximal mixing” scenario, assuming a hypothetical long-range tensor force. We give the explicit wave functions for all states, before and after mixing, and reassess many predictions such as the magnetic moments, the standard and transitional form-factors from the nucleon to N*. Unexpectedly, in this scenario we can reproduce the long-puzzling features of the Roper resonance N*(1440). But even in this extreme case, the admixture of the 1D,L = 2 state to a nucleon remains significantly smaller than expected from phenomenology.

Baryons↗
NASA NTRS1980

On sound transmission into a stiffened cylindrical shell with rings and stringers treated as discrete elements

In the context of the transmission of airborne noise into an aircraft fuselage, a mathematical model is presented for the transmission of an oblique plane sound wave into a finite cylindrical shell stiffened by stringers and ring frames. The rings and stringers are modeled as discrete structural elements. The numerical case studied was typical of a narrow-bodied jet transport fuselage. The numerical results show that the ring-frequency dip in the transmission loss curve that is present for a monocoque shell is still present in the case of a stiffened shell. The ring frequency effect is a result of the cylindrical geometry of the shell. Below the ring frequency, stiffening does not appear to have any significant effect on transmission loss, but above the ring frequency, stiffeners can enhance the transmission loss of a cylindrical shell.

Koval, L. R.↗
NASA NTRS1992

A methodology to emulate and evaluate a productive virtual workstation

The Advanced Display and Computer Augmented Control (ADCACS) Program at ACT is sponsored by NASA Ames to investigate the broad field of technologies which must be combined to design a 'virtual' workstation for the Space Station Freedom. This program is progressing in several areas and resulted in the definition of requirements for a workstation. A unique combination of technologies at the ACT Laboratory have been networked to effectively create an experimental environment. This experimental environment allows the integration of nonconventional input devices with a high power graphics engine within the framework of an expert system shell which coordinates the heterogeneous inputs with the 'virtual' presentation. The flexibility of the workstation is evolved as experiments are designed and conducted to evaluate the condition descriptions and rule sets of the expert system shell and its effectiveness in driving the graphics engine. Workstation productivity has been defined by the achievable performance in the emulator of the calibrated 'sensitivity' of input devices, the graphics presentation, the possible optical enhancements to achieve a wide field of view color image and the flexibility of conditional descriptions in the expert system shell in adapting to prototype problems.

Krubsack, David↗
NASA NTRS1976

On sound transmission into a stiffened cylindrical shell under flight conditions

In the context of airborne-noise transmission through an aircraft fuselage, a mathematical model is presented for sound transmission into a stiffened cylindrical shell. The stiffening effect of the ring frames and stringers is approximated by a 'smeared'-stiffener theory which includes the eccentricity of the stiffeners. Numerical results are presented for a typical narrow-bodied jet in cruising flight. A comparison is made between noise transmission into a monococque shell and into a stiffened shell. The stiffeners are shown to greatly increase TL for small incidence angles, so that the effective 'window' for noise transmission is restricted to the neighborhood of normal incidence. Flow is shown to increase TL for sound waves propagating 'upstream' against the flow. Stiffeners are also shown to raise the ring frequency at which a dip in cylinder TL occurs. Limitations of the 'smeared'-stiffener theory are also discussed.

Koval, L. R.↗
DOE OSTI2025

Impact of Ligands on the Ion–Ion Selectivity of Ligand-Appended-Pillar[ n ]arene Channels

Ligand-appended pillar[5]arene (LAP) channels are emerging as a promising platform for ion-selective membranes. In this study, we investigated the ion selectivities of three LAP channels functionalized with distinct ligands: diglycolamine, carbamoylmethyl phosphine oxide, and propionamide phosphonic acid. These ligands were chosen based on their demonstrated affinities for lanthanides in solvent extraction studies. We examined the selectivity of each channel toward a series of monovalent, divalent, and trivalent ions: Li + , Na + , K + , Mg 2+ , Ca 2+ , La 3+ , Eu 3+ , and Yb 3+ . To quantify ion-channel interactions and the energetics of translocation, we computed the potential of mean force (PMF) profiles for each ion. These PMFs were subsequently recast into permeability coefficients, enabling a direct evaluation of ion permselectivity. Our results reveal distinct selectivity patterns governed by the chemical nature of the appended ligands. The diglycolamine-functionalized channel exhibits strong interactions with monovalent ions, leading to replication of the Li + bulk hydration shell within the channel. This promotes preferential transport Li + ions while effectively excluding divalent and trivalent species. In contrast, the carbamoylmethyl phosphine oxide-functionalized channel displays a reduced selectivity between monovalent ions while similarly exhibiting an effective rejection of divalent and trivalent ions. This arises from steric hindrance around channel-lining oxygens imposed by the ligand's bulky phenyl groups which limits heavy ion coordination and promotes retention of hydration shells effectively increasing effective ion size. The propionamide phosphonic acid-functionalized channel exhibits a different trend, favoring ions with lower hydration free energies, with K + ions showing enhanced permeation. These findings highlight the critical role of ligand-ion interactions in modulating ion selectivity within LAP channels. In particular, the strong coordination exhibited by diglycolamine and propionamide phosphonic acid ligands significantly influences the ion transport energetics and selectivity profiles.

hydration↗
NASA NTRS1982

On the shape and orientation control of an orbiting shallow spherical shell structure

The dynamics of orbiting shallow flexible spherical shell structures under the influence of control actuators was studied. Control laws are developed to provide both attitude and shape control of the structure. The elastic modal frequencies for the fundamental and lower modes are closely grouped due to the effect of the shell curvature. The shell is gravity stabilized by a spring loaded dumbbell type damper attached at its apex. Control laws are developed based on the pole clustering techniques. Savings in fuel consumption can be realized by using the hybrid shell dumbbell system together with point actuators. It is indicated that instability may result by not including the orbital and first order gravity gradient effects in the plant prior to control law design.

Bainum, P. M.↗
NASA NTRS1983

On the shape and orientation control of orbiting shallow spherical shell structure

The dynamics of orbiting shallow flexible spherical shell structures under the influence of control actuators was studied. Control laws are developed to provide both attitude and shape control of the structure. The elastic modal frequencies for the fundamental and lower modes are closely grouped due to the effect of the shell curvature. The shell is gravity stabilized by a spring loaded dumbell type damper attached at its apex. Control laws are developed based on the pole clustering techniques. Savings in fuel consumption can be realized by using the hybrid shell dumbbell system together with point actuators. It is indicated that instability may result by not including the orbital and first order gravity gradient effects in the plant prior to control law design. Previously announced in STAR as N82-17243

Bainum, P. M.↗
NASA NTRS1976

Radiative transfer in circumstellar dust shells

An iterative numerical procedure is developed to calculate the radiation field as a function of position, direction, and wavelength within a spherically symmetric circumstellar dust shell. The dust shell is assumed to consist of gray, isotropically scattering dust particles in thermal equilibrium with the radiation field and to be characterized by seven parameters: radius of the central star, inner radius of the shell, outer radius of the shell, total optical depth of the shell, an index which specifies the density distribution, albedo of the dust particles, and temperature of the central star. When the shell is close to the star, the angular distribution of the stellar component of the radiation field is determined by direct integration along lines of sight to the stellar surface, and the back-warming effect of the shell is included in the calculations to determine the net stellar flux. Using this procedure, the temperature distributions and radiation fields within several model dust shells are determined and used to calculate for each shell the spectral-energy and spatial-energy distributions of the radiation emitted at 11 wavelengths from 0.4 to 20 microns. For shells of moderate optical depth, it is found that the radiation field is quite anisotropic, especially at shorter wavelengths, and that the shape of the spectral-energy distribution is strongly dependent on all seven model parameters. The Eddington factor as a function of wavelength and optical depth is calculated for each model.

Harvel, C. A.↗