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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 307 records · Page 17

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NASA NTRS1983

Spontaneous Raman scattering as a high resolution XUV radiation source

A type of high resolution XUV radiation source is described which is based upon spontaneous anti-Stokes scattering of tunable incident laser radiation from atoms excited to metastable levels. The theory of the source is summarized and two sets of experiments using He (1s2s)(1)S atoms, produced in a cw hollow cathode and in a pulsed high power microwave discharge, are discussed. The radiation source is used to examine transitions originating from the 3p(6) shell of potassium. The observed features include four previously unreported absorption lines and several sharp interferences of closely spaced autoionizing lines. A source linewidth of about 1.9 cm(-1) at 185,000 cm(-1) is demonstrated.

Rothenberg, J. E.↗

NASA NTRS1983

Spontaneous Raman scattering as a high-resolution XUV radiation source

A type of high resolution XUV radiation source is described which is based upon spontaneous anti-Stokes scattering of tunable incident laser radiation from atoms excited to metastable levels. The theory of the source is summarized and two sets of experiments using He (1s2s)(1)S atoms, produced in a CW hollow cathode and in a pulsed high power microwave discharge, are discussed. The radiation source is used to examine transitions originating from the 3p(6) shell of potassium. The observed features include four previously unreported absorption lines and several sharp interferences of closely spaced autoionizing lines. A source linewidth of about 1.9 cm(-1) at 185,000 cm(-1) is demonstrated. Previously announced in STAR as N83-18422

Rothenberg, J. E.↗

NASA NTRS1985

A cracked orthotropic sheet stiffened by a semi-infinite orthotropic sheet

The stress intensity factor is determined for a cracked orthotropic sheet adhesively bonded to an orthotropic stringer. Since the stringer is modeled as a semiinfinite sheet, the solution is most appropriate for a crack tip located near a stringer edge. Both adherends are treated as homogeneous, orthotropic media. It is assumed they are in plane stress and the adhesive is in pure shear. From Green's functions and the complex variable theory of orthotropic elasticity developed by Lekhnitskiy, a set of integral equations is obtained. The integral equations are replaced by an equivalent set of algebraic equations which is solved to obtain the shear stress distribution in the adhesive layer. With these stresses, equations for the stress intensity factors at both crack tips are found. A parametric study is conducted to determine the sensitivity of the system to material properties and specimen configuration. Unless the crack tip is very close to or under the stringer the stress intensity factor is approximately that of an unstiffened sheet. However, as the crack propagates beneath the stringer, the stress intensity factor decreases significantly. Increasing the stiffness of the stringer or the adhesive also results in a decrease in the stress intensity factor.

Bigelow, C. A.↗

NASA NTRS1985

Parametric study of stress-intensity factors in bonded composite stringer panels

Stress-intensity factors are determined for an infinite cracked orthotropic sheet adhesively bonded to an orthotropic stringer. Since the stringer is modeled as a semi-infinite sheet, the solution is most appropriate for a crack tip located near a stringer edge. Both adherends are treated as homogeneous, orthotropic media which are representative of many fiber-reinforced composite materials. The complex variable theory of elasticity was used to obtain a set of integral equations describing the problem. The integral equations are replaced by an equivalent sheet of algebraic equations, which are solved to obtain the shear stress distribution in the adhesive layer. From these adhesive stresses, the stress-intensity factors are found. A parametric study is conducted to determine the sensitivity of the system to material properties and specimen configuration. Unless the crack tip is very close to or under the stringer, the stress-intensity factor is approximately that of the unstiffened sheet. However, as the crack propagates beneath the stringer, the stress-intensity factor decreases significantly. Increasing the stringer stiffness or the adhesive stiffness also decreases the stress-intensity factor.

Bigelow, C. A.↗

NASA NTRS1987

Algebraic multigrid

The state of the art in algebraic multgrid (AMG) methods is discussed. The interaction between the relaxation process and the coarse grid correction necessary for proper behavior of the solution probes is discussed in detail. Sufficient conditions on relaxation and interpolation for the convergence of the V-cycle are given. The relaxation used in AMG, what smoothing means in an algebraic setting, and how it relates to the existing theory are considered. Some properties of the coarse grid operator are discussed, and results on the convergence of two-level and multilevel convergence are given. Details of an algorithm particularly studied for problems obtained by discretizing a single elliptic, second order partial differential equation are given. Results of experiments with such problems using both finite difference and finite element discretizations are presented.

Ruge, J. W.↗

NASA NTRS1989

EAC: A program for the error analysis of STAGS results for plates

A computer code is now available for estimating the error in results from the STAGS finite element code for a shell unit consisting of a rectangular orthotropic plate. This memorandum contains basic information about the computer code EAC (Error Analysis and Correction) and describes the connection between the input data for the STAGS shell units and the input data necessary to run the error analysis code. The STAGS code returns a set of nodal displacements and a discrete set of stress resultants; the EAC code returns a continuous solution for displacements and stress resultants. The continuous solution is defined by a set of generalized coordinates computed in EAC. The theory and the assumptions that determine the continuous solution are also outlined in this memorandum. An example of application of the code is presented and instructions on its usage on the Cyber and the VAX machines have been provided.

Sistla, Rajaram↗

NASA NTRS1990

Bifurcation analysis of axial flow compressor stability

With a one-mode truncation it is possible to reduce the Moore-Greitzer model for compressor instability to a set of three ordinary differential equations. These are approached from the point of view of bifurcation theory. Most of the bifurcations emerge from a degenerate Takens-Bogdanov bifurcation point. The bifurcation sets are completed using the numerical branch tracking scheme AUTO. Despite the severity of the truncation, the agreement with experimental results is excellent.

Mccaughan, F. E.↗

NASA NTRS1995

Shapes and stability of algebraic nuclear models

A generalization of the procedure to study shapes and stability of algebraic nuclear models introduced by Gilmore is presented. One calculates the expectation value of the Hamiltonian with respect to the coherent states of the algebraic structure of the system. Then equilibrium configurations of the resulting energy surface, which depends in general on state variables and a set of parameters, are classified through the Catastrophe theory. For one- and two-body interactions in the Hamiltonian of the interacting Boson model-1, the critical points are organized through the Cusp catastrophe. As an example, we apply this Separatrix to describe the energy surfaces associated to the Rutenium and Samarium isotopes.

Lopez-Moreno, Enrique↗

NASA NTRS1995

Space flight data from the isothermal dendritic growth experiment

The Isothermal Dendritic Growth Experiment (IDGE) is a NASA space flight experiment which flew as part of the United States Microgravity Payload (USMP-2), in early 1994. The IDGE measured dendritic growth rates, tip radii, and crystal morphologies of ultra-pure succinonitrile (CN-(CH2)2-CN) at supercoolings in the range from 0.05 - 2.0 K. Data taken in the form of slow-scan binary digitized images telemetered to the ground from orbit in near-real time, combined with the IDGE terrestrial data set, provide the first quantitative assessment of various theories on dendritic solidification and the effects of convection on dendritic growth.

Glicksman, M. E.↗

NASA NTRS1998

Bounded Error Schemes for the Wave Equation on Complex Domains

This paper considers the application of the method of boundary penalty terms ("SAT") to the numerical solution of the wave equation on complex shapes with Dirichlet boundary conditions. A theory is developed, in a semi-discrete setting, that allows the use of a Cartesian grid on complex geometries, yet maintains the order of accuracy with only a linear temporal error-bound. A numerical example, involving the solution of Maxwell's equations inside a 2-D circular wave-guide demonstrates the efficacy of this method in comparison to others (e.g. the staggered Yee scheme) - we achieve a decrease of two orders of magnitude in the level of the L2-error.

Abarbanel, Saul↗

NASA NTRS2010

Cognitive Modeling of Video Game Player User Experience

This paper argues for the use of cognitive modeling to gain a detailed and dynamic look into user experience during game play. Applying cognitive models to game play data can help researchers understand a player's attentional focus, memory status, learning state, and decision strategies (among other things) as these cognitive processes occurred throughout game play. This is a stark contrast to the common approach of trying to assess the long-term impact of games on cognitive functioning after game play has ended. We describe what cognitive models are, what they can be used for and how game researchers could benefit by adopting these methods. We also provide details of a single model - based on decision field theory - that has been successfUlly applied to data sets from memory, perception, and decision making experiments, and has recently found application in real world scenarios. We examine possibilities for applying this model to game-play data.

Bohil, Corey J.↗

NASA NTRS2014

Propulsion System Simulation Using the Toolbox for the Modeling and Analysis of Thermodynamic System T-MATS

A simulation toolbox has been developed for the creation of both steady-state and dynamic thermodynamic software models. This paper describes the Toolbox for the Modeling and Analysis of Thermodynamic Systems (T-MATS), which combines generic thermodynamic and controls modeling libraries with a numerical iterative solver to create a framework for the development of thermodynamic system simulations, such as gas turbine engines. The objective of this paper is to present an overview of T-MATS, the theory used in the creation of the module sets, and a possible propulsion simulation architecture. A model comparison was conducted by matching steady-state performance results from a T-MATS developed gas turbine simulation to a well-documented steady-state simulation. Transient modeling capabilities are then demonstrated when the steady-state T-MATS model is updated to run dynamically.

gas path dynamics↗

NASA NTRS2014

Propulsion System Simulation Using the Toolbox for the Modeling and Analysis of Thermodynamic System (T-MATS)

A simulation toolbox has been developed for the creation of both steady-state and dynamic thermodynamic software models. This presentation describes the Toolbox for the Modeling and Analysis of Thermodynamic Systems (T-MATS), which combines generic thermodynamic and controls modeling libraries with a numerical iterative solver to create a framework for the development of thermodynamic system simulations, such as gas turbine engines. The objective of this presentation is to present an overview of T-MATS, the theory used in the creation of the module sets, and a possible propulsion simulation architecture.

aerothermodynamics↗

NASA NTRS2014

Propulsion System Simulation Using the Toolbox for the Modeling and Analysis of Thermodynamic Systems (T-MATS)

aerothermodynamics↗

NASA NTRS2003

Evidence for Three-Dimensional Radiative Effects in MODIS Cloud Optical Depths Retrieved at Back Scattering View Angles

This study addresses the question whether 1D radiative transfer theory describes well the angular distribution of shortwave cloud reflection. The statistical analysis of a large set of MODIS observations indicates that in oblique backward scattering directions, cloud reflection is stronger than 1D theory would predict. After considering a variety of possible causes, the paper concludes that the most likely reason for the increase lies in 3D radiative interactions. The results' main implication is that cloud optical depths retrieved at back scattering view angles larger than about 50 degrees tend to be overestimated and should be used only with great caution.

Varnai, Tamas↗

NASA NTRS1987

A coupled-mode theory for multiwaveguide systems satisfying the reciprocity theorem and power conservation

Two sets of coupled-mode equations for multiwaveguide systems are derived using a generalized reciprocity relation; one set for a lossless system, and the other for a general lossy or lossless system. The second set of equations also reduces to those of the first set in the lossless case under the condition that the transverse field components are chosen to be real. Analytical relations between the coupling coefficients are shown and applied to the coupling of mode equations. It is shown analytically that these results satisfy exactly both the reciprocity theorem and power conservation. New orthogonal relations between the supermodes are derived in matrix form, with the overlap integrals taken into account.

Chuang, Shun-Lien↗

NASA NTRS1974

Equation solving program for aerodynamic lifting surface theory

A description of and user's manual are presented for one of a group of FORTRAN programs which, together, can be used for the analysis and design of wings in steady, subsonic flow according to a kernel function method lifting surface theory. This particular program is the one which solves the sets of simultaneous, linear, algebraic equations arising from the thin wing analysis. This program has the capability of striking out rows and columns of the aerodynamic influence matrix and rows of the associated boundary condition vectors (right hand sides). This capability significantly enhances the effectiveness of the kernel function method of lifting surface theory because studies of the convergence of solutions with the number of control points can be done with the calculation of only a single influence matrix.

Medan, R. T.↗

NASA NTRS1991

New method for estimating low-earth-orbit collision probabilities

An unconventional but general method is described for estimating the probability of collision between an earth-orbiting spacecraft and orbital debris. This method uses a Monte Caralo simulation of the orbital motion of the target spacecraft and each discrete debris object to generate an empirical set of distances, each distance representing the separation between the spacecraft and the nearest debris object at random times. Using concepts from the asymptotic theory of extreme order statistics, an analytical density function is fitted to this set of minimum distances. From this function, it is possible to generate realistic collision estimates for the spacecraft.

Vedder, John D.↗