Search NASA⌕ Search

SEARCH · Search NASA

Results for “SET THEORY”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Convective response of a wall-mounted hot-film sensor in a shock tube

Shock tube experiments were performed in order to determine the response of a single hot-film element of a sensor array to transiently induced flow behind weak normal shock waves. The experiments attempt to isolate the response due only to the change in convective heat transfer at the hot-film surface mounted on the wall of the shock tube. The experiments are described, the results being correlated with transient boundary layer theory and compared with an independent set of experimental results. One of the findings indicates that the change in the air properties (temperature and pressure) precedes the air mass transport, causing an ambiguity in the sensor response to the development of the velocity boundary layer. Also, a transient, local heat transfer coefficient is formulated to be used as a forcing function in an hot-film instrument model and simulation which remains under investigation.

Roberts, A. Sidney, Jr.↗
NASA NTRS1990

Two-photon transitions in hydrogen - A test of pseudostate summation

A technique in which the intermediate states of conventional second-order perturbation theory are replaced by a finite set of psudostates, while the energy denominators are supplanted by the expectation values of the unperturbed Hamiltonian with respect to those pseudostates, is presently used to investigate the 2S-1S transition rate on the bases of both the E-x and A-p forms of the interaction. The results thus obtained are noted to closely reflect those conventionally derived, even in cases where only a small number of terms are used; these results are also found not to be strongly dependent on the exact form of the basis functions employed.

Drachman, Richard J.↗
NASA NTRS1990

Convective response of a wall-mounted hot-film sensor in a shock tube

Shock tube experiments were performed in order to determine the response of a single hot-film element of a sensor array to transiently induced flow behind weak normal shock waves. The experiments attempt to isolate the response due only to the change in convective heat transfer at the hot-film surface mounted on the wall of the shock tube. The experiments are described, the results being correlated with transient boundary layer theory and compared with an independent set of experimental results. One of the findings indicates that the change in the air properties (temperature and pressure) precedes the air mass transport, causing an ambiguity in the sensor response to the development of the velocity boundary layer. Also, a transient, local heat transfer coefficient is formulated to be used as a forcing function in a hot-film instrument model and simulation which remains under investigation.

Roberts, A. S., Jr.↗
NASA NTRS1993

Isotopic fractionation of hydrogen in planetary exospheres due to ionosphere-exosphere coupling - Implications for Venus

The paper considers isotopic hydrogen fractionation processes in the Venusian exosphere due to ionosphere-exosphere coupling by addressing two deficiencies in the present theory of differential escape. First, a set of D/H isotopic fractionation curves is derived for the ion-neutral interactions of charge and collisional momentum transfer, and these are compared with the results of Gurwell and Yung (1993) for hot O collisional ejection. Then, the question of the relative importance of collisional ejection in atmospheric escape is reexamined using two simple exosphere models. It is shown that O-O collisions suppress the high energy component of the hot O distribution by more than a factor of 10. Moreover, the ballistic trajectories of fast O atoms that reach the nighttime reservoir of exospheric hydrogen favor downward scatter of D and H rather than their escape. It is concluded that, due to severe limits placed on the effectiveness of collisional ejection, the differential escape of D and H from Venus is determined by charge exchange interactions rather than the collisional ejection.

Hodges, R. R., Jr.↗
NASA NTRS1938

Heat-transfer processes in air-cooled engine cylinders

From a consideration of heat-transfer theory, semi-empirical expressions are set up for the transfer of heat from the combustion gases to the cylinder of an air-cooled engine and from the cylinder to the cooling air. Simple equations for the average head and barrel temperatures as functions of the important engine and cooling variables are obtained from these expressions. The expressions involve a few empirical constants, which may be readily determined from engine tests. Numerical values for these constants were obtained from single-cylinder engine tests for cylinders of the Pratt & Whitney 1535 and 1340-h engines. The equations provide a means of calculating the effect of the various engine and cooling variables on the cylinder temperatures and also of correlating the results of engine cooling tests. An example is given of the application of the equations to the correlation of cooling-test data obtained in flight.

Pinkel, Benjamin↗
NASA NTRS1953

Air-water analogy and the study of hydraulic models

The author first sets forth some observations about the theory of models. Then he established certain general criteria for the construction of dynamically similar models in water and in air, through reference to the perfect fluid equations and to the ones pertaining to viscous flow. It is, in addition, pointed out that there are more cases in which the analogy is possible than is commonly supposed.

SIMILITUDE↗
NASA NTRS1995

Horizontal axis wind turbine post stall airfoil characteristics synthesization

Blade-element/momentum performance prediction codes are routinely used for wind turbine design and analysis. A weakness of these codes is their inability to consistently predict peak power upon which the machine structural design and cost are strongly dependent. The purpose of this study was to compare post-stall airfoil characteristics synthesization theory to a systematically acquired wind tunnel data set in which the effects of aspect ratio, airfoil thickness, and Reynolds number were investigated. The results of this comparison identified discrepancies between current theory and the wind tunnel data which could not be resolved. Other factors not previously investigated may account for these discrepancies and have a significant effect on peak power prediction.

Tangler, James L.↗
NASA NTRS1996

Simplified Micromechanics of Plain Weave Composites

A micromechanics based methodology to simulate the complete hygro-thermomechanical behavior of plain weave composites is developed. This methodology is based on micromechanics and the classical laminate theory. The methodology predicts a complete set of thermal, hygral and mechanical properties of plain woven composites, generates necessary data for use in a finite element structural analysis, and predicts stresses all the way from the laminate to the constituent level. This methodology is used in conjunction with a composite mechanics code to analyze and predict the properties/response of a generic graphite/epoxy woven textile composite and a plain weave ceramic composite. The fiber architecture, including the fiber waviness and fiber end distributions through the thickness, is properly accounted for. Predicted results compare reasonably well with those from detailed three-dimensional finite element analyses as well as available experimental data. However, the main advantage of the proposed methodology is its high computational efficiency as compared with three-dimensional finite element analyses.

Mital, Subodh K.↗
NASA NTRS1995

Partial-Wave Representations of Laser Beams for Use in Light-Scattering Calculations

In the framework of generalized Lorenz-Mie theory, laser beams are described by sets of beam-shape coefficients. The modified localized approximation to evaluate these coefficients for a focused Gaussian beam is presented. A new description of Gaussian beams, called standard beams, is introduced. A comparison is made between the values of the beam-shape coefficients in the framework of the localized approximation and the beam-shape coefficients of standard beams. This comparison leads to new insights concerning the electromagnetic description of laser beams. The relevance of our discussion is enhanced by a demonstration that the localized approximation provides a very satisfactory description of top-hat beams as well.

Gouesbet, Gerard↗
NASA NTRS1997

Numerical Simulation of Rotation-Driven Plasma Transport In the Jovian Magnetosphere

A Jupiter version of the Rice Convection Model (RCM-J) was developed with support of an earlier NASA SR&T grant. The conversion from Earth to Jupiter included adding currents driven by centrifugal force, reversing the planetary magnetic field, and rescaling various parameters. A series of informative runs was carried out, all of them solving initial value problems. The simulations followed an initial plasma torus configuration as it fell apart by interchange instability. Some conclusions from the simulations were the following: 1. We confirmed that, for conventional values of the torus density and ionospheric conductance, the torus disintegrates by interchange instability on a time scale of approx. one day, which is 1-2 orders of magnitude shorter than the best estimates of the average residence time of plasma in the torus. 2. In the model, the instability could be slowed to an arbitrary degree by the addition of sufficient impounding energetic particles, as suggested earlier by Siscoe et al (1981). However, the observed energetic particles do not seem sufficient to guarantee impoundment (e.g., Mauk et al., 1996). 3. Whether inhibited by impoundment or not, the interchange was found to proceed by the formation of long fingers, which get thinner as they get longer. This picture differed dramatically from the conventional radial-diffusion picture (e.g., Siscoe and Summers (1981)), more superficially with the outward-moving-blob picture (Pontius and Hill, 1989). The obvious limitation of the original RCM-J was that it could not represent a plasma source. We could represent the decay of a pre-existing torus, but we could not represent the way ionization of material from Io continually replenishes the plasma. We consequently were precluded from studying a whole set of fundamental issues of torus theory, including whether the system can come to a steady state.

Wolf, Richard A.↗
NASA NTRS2002

Fidelity of the Integrated Force Method Solution

The theory of strain compatibility of the solid mechanics discipline was incomplete since St. Venant's 'strain formulation' in 1876. We have addressed the compatibility condition both in the continuum and the discrete system. This has lead to the formulation of the Integrated Force Method. A dual Integrated Force Method with displacement as the primal variable has also been formulated. A modest finite element code (IFM/Analyzers) based on the IFM theory has been developed. For a set of standard test problems the IFM results were compared with the stiffness method solutions and the MSC/Nastran code. For the problems IFM outperformed the existing methods. Superior IFM performance is attributed to simultaneous compliance of equilibrium equation and compatibility condition. MSC/Nastran organization expressed reluctance to accept the high fidelity IFM solutions. This report discusses the solutions to the examples. No inaccuracy was detected in the IFM solutions. A stiffness method code with a small programming effort can be improved to reap the many IFM benefits when implemented with the IFMD elements. Dr. Halford conducted a peer-review on the Integrated Force Method. Reviewers' response is included.

Hopkins, Dale↗
NASA NTRS2007

Quantum Chemical Evaluation of the Astrochemical Significance of Reactions between S Atom and Acetylene or Ethylene

Addition-elimination reactions of S atom in its P-3 ground state with acetylene (C2H2) and ethylene (C2H4) were characterized with both molecular orbital and density functional theory calculations employing correlation consistent basis sets in order to assess the likelihood either reaction might play a general role in astrochemistry or a specific role in the formation of S2 (X (sup 3 SIGMA (sub g) (sup -)) via a mechanism proposed by Saxena and Misra (Mon. Not. R. Astron. Soc. 1995, 272, 89). The acetylene and ethylene reactions proceed through C2H2S ((sup 3)A")) and C2H4S ((sup 3)A")) intermediates, respectively, to yield HCCS ((sup 2)II)) and C2H3S ((sup 2)A')). Substantial barriers were found in the exit channels for every combination of method and basis set considered in this work, which effectively precludes hydrogen elimination pathways for both S + C2H2 and S + C2H4 in the ultracold interstellar medium where only very modest barriers can be surmounted and processes without barriers tend to predominate. However, if one or both intermediates is formed and stabilized efficiently under cometary or dense interstellar cloud conditions, they could serve as temporary reservoirs for S atom and participate in reactions such as S + C2H2S (right arrow) S2 = C2H2 or S + C2H4S (right arrow) S2 + C2H4. For formation and stabilization to be efficient, the reaction must possess a barrier height small enough to be surmountable at low temperatures yet large enough to prevent redissociation to reactants. Barrier heights computed with B3LYP and large basis sets are very low, but more rigorous QCISD(T) and RCCSD(T) results indicate that the barrier heights are closer to 3-4 kcal/mol. The calculations therefore indicate that S + C2H2 or S + C2H4 could contribute to the formation of S2 in comets and may serve as a means to gauge coma temperature. The energetics of the ethylene reaction are more favorable.

Woon, David E.↗
NASA NTRS2013

Some New Lidar Equations for Laser Pulses Scattered Back from Optically Thick Media Such as Clouds, Dense Aerosol Plumes, Sea Ice, Snow, and Turbid Coastal Waters

I survey the theoretical foundations of the slowly-but-surely emerging field of multiple scattering lidar, which has already found applications in atmospheric and cryospheric optics that I also discuss. In multiple scattering lidar, returned pulses are stretched far beyond recognition, and there is no longer a one-to-one connection between range and return-trip timing. Moreover, one can exploit the radial profile of the diffuse radiance field excited by the laser source that, by its very nature, is highly concentrated in space and collimated in direction. One needs, however, a new class of lidar equations to explore this new phenomenology. A very useful set is derived from radiative diffusion theory, which is found at the opposite asymptotic limit of radiative transfer theory than the conventional (single-scattering) limit used to derive the standard lidar equation. In particular, one can use it to show that, even if the simple time-of-flight-to-range connection is irretrievably lost, multiply-scattered lidar light can be used to restore a unique profiling capability with coarser resolution but much deeper penetration into a wide variety of optical thick media in nature. Several new applications are proposed, including a laser bathymetry technique that should work for highly turbid coastal waters.

turbid water↗
NASA NTRSDate not supplied

A Study of Preliminary Design Methods for Low Noise Fans

Engineers need theory and computer codes to help them design quiet and efficient fans. A fast method to identify low-noise stator vane counts that might minimize tone noise for axial ducted fans has been developed. The analysis begins with a preliminary aerodynamic fan design. Duct acoustic and rotor-stator interaction theories are combined to predict the set of cut-on circumferential modes that are expected to be generated and propagate through the fan duct. By predicting the number of cut-on circumferential modes for each vane count, a set of low-noise vane counts for a given rotor and duct design can be identified. This method was used to design the stator set for NASA’s spacecraft cabin ventilation fan, in order to minimize tone noise generated by rotor-stator interaction at the first three blade passing frequency harmonics. This method was also applied to three other research fans that NASA uses for aeroacoustics research for comparison. This technique can be used to include acoustic design criteria early in the design of an axial fan and provide valuable information to guide the final design of quiet fans.

Fan↗
NASA NTRSDate not supplied

Structural Sizing of a 50-m-Tall Thermoplastic Composite Solar Array Truss Tower Structure for the Lunar South Pole

At the lunar south pole, solar arrays elevated by truss towers are exposed to near continuous sunlight since the sun remains near the horizon. Recent studies suggest that tower heights on the order of 50 m are needed to meet the power requirements to support a sustained lunar presence. While eventually towers may be constructed using materials sourced in-situ, initially structural elements will likely be brought from the Earth, deployed, and assembled. Thermoplastic composites offer the benefit of high specific stiffness and strength properties along with welding for assembly joints, and therefore represent a promising material system for this application. The focus of this paper is on the structural sizing of such towers. A set of expressions based on beam theory are presented for preliminary sizing of the truss tower structure for strength and buckling. The loading condition that drives sizing is base excitation resulting from moonquakes. A point design, developed through finite element analysis, verifies the analytical sizing routine and shows the importance of joints. The results show a viable point design and highlight the factors most significant in the structural sizing.

Thermoplastic composites↗
NASA NTRSDate not supplied

Structural Sizing of a 50-m-Tall Thermoplastic Composite Solar Array Truss Tower Structure for the Lunar South Pole

At the lunar south pole, solar arrays elevated by truss towers are exposed to near continuous sunlight since the sun remains near the horizon. Recent studies suggest that tower heights on the order of 50 m are needed to meet the power requirements to support a sustained lunar presence. While eventually towers may be constructed using materials sourced in-situ, initially structural elements will likely be brought from the Earth, deployed, and assembled. Thermoplastic composites offer the benefit of high specific stiffness and strength properties along with welding for assembly joints, and therefore represent a promising material system for this application. The focus of this paper is on the structural sizing of such towers. A set of expressions based on beam theory are presented for preliminary sizing of the truss tower structure for strength and buckling. The loading condition that drives sizing is base excitation resulting from moonquakes. A point design, developed through finite element analysis, verifies the analytical sizing routine and shows the importance of joints. The results show a viable point design and highlight the factors most significant in the structural sizing.

Thermoplastic composites↗
NASA NTRS2025

Structural Sizing of a 50-m-Tall Thermoplastic Composite Truss Tower Structure for the Lunar South Pole

At the lunar south pole, solar arrays elevated by truss towers are exposed to near continuous sunlight since the sun remains near the horizon. Recent studies suggest that tower heights on the order of 50 m are needed to meet the power requirements to support a sustained lunar presence. While eventually towers may be constructed using materials sourced in-situ, initially structural elements will likely be brought from the Earth, deployed, and assembled. Thermoplastic composites offer the benefit of high specific stiffness and strength properties along with welding for assembly joints, and therefore represent a promising material system for this application. The focus of this paper is on the structural sizing of such towers. A set of expressions based on beam theory are presented for preliminary sizing of the truss tower structure for strength and buckling. The loading condition that drives sizing is base excitation resulting from moonquakes. A point design, developed through finite element analysis, verifies the analytical sizing routine and shows the importance of joints. The results show a viable point design and highlight the factors most significant in the structural sizing.

Thermoplastic composites↗