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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Light funnel concentrator panel for solar power

The solar concentrator design concept provides a theoretical concentration efficiency of 96 percent with power-to-weight ratios as high as 50 W/kg. Further, it eliminates the need for fragile reflective coatings and is very tolerant to pointing inaccuracies. The concept differs from conventional reflective mirrors and lens design in that is uses the principle of total internal reflection in order to funnel incident sunlight into a concentrator photovoltaic cell. The feasibility of the light funnel concentrator concept was determined through a balanced approach of analysis, development, and fabrication of prototypes, and testing of components. A three-dimensional optical model of the light funnel concentrator and photovoltaic cell was developed in order to assess the ultimate performance of such systems. In addition, a thermal and structural analysis of a typical unit was made. Techniques of fabricating the light funnel cones, optically coupling them to GaAs concentrator cells, bonding the funnels to GaAs cells, making electrical interconnects, and bonding substrates was explored and a prototype light funnel concentrator unit was fabricated and tested. Testing of the system included measurements of optical concentrating efficiency, optical concentrator to cell coupling efficiency, and electrical efficiency.

Source record↗
NASA NTRS1988

An approach to probabilistic finite element analysis using a mixed-iterative formulation

An efficient algorithm for computing the response sensitivity of finite element problems based on a mixed-iterative formulation is proposed. This method does not involve explicit differentiation of the tangent stiffness array and can be used with formulations for which a consistent tangent stiffness is not readily available. The method has been successfully applied to probabilistic finite element analysis of problems using the proposed mixed formulation, and this exercise has provided valuable insights regarding the extension of the method to a more general class of problems to include material and geometric nonlinearities.

Dias, J. B.↗
NASA NTRS1989

A finite element approach for large motion dynamic analysis of multibody structures in space

A three-dimensional finite element formulation for modeling the transient dynamics of constrained multibody space sructures with truss-like configurations is presented. Convected coordinate systems are used to define rigid-body motion of individual elements in the system. These systems are located at one end of each element and are oriented such that one axis passes through the other end of the element. Deformation of each element, relative to its convected coordinate system, is defined by cubic flexural shape functions as used in finite element methods of structural analysis. The formulation is oriented toward joint dominated structures and places the generalized coordinates at the joint. A transformation matrix is derived to integrate joint degree-of-freedom into the equations of motion of the element. Based on the derivation, a general-purpose code LATDYN (Large Angle Transient DYNamics) was developed. Two examples are presented to illustrate the application of the code. For the spin-up of a flexible beam, results are compared with existing solutions available in the literature. For the deployment of one bay of a deployable space truss (the Minimast), results are verified by the geometric knowledge of the system and converged solution of a successively refined model.

Chang, Che-Wei↗
NASA NTRS1990

A methodology for probabilistic prediction of structural failures of launch vehicle propulsion systems

A quantitative methodology for estimating the probability of occurrence of critical structural failure modes of launch vehicle propulsion systems during mission operation is presented. In this approach, engineering analysis models that characterize specific failure modes based on the physics and mechanics of the failure phenomenon are used in a prescribed probabalistic structure in which quantified uncertainty in the information used in the analysis and quantified uncertainty of the engineering analysis models themselves are both considered in estimating failure risk. The methodology is applicable to high cycle fatigue, low cycle fatigue, flaw propagation stress rupture, and other failure modes of launch vehicle propulsion systems and other space-flight systems. The probabalistic failure assessment presented provides the capability of performing quantitative analyses to rank options to improve reliability, thereby enabling limited financial resources of development and improvement programs to be more effectively allocated.

Moore, N.↗
NASA NTRS1990

An improved approach for flight readiness assessment

An improved methodology for quantitatively evaluating failure risk for a spaceflight system in order to assess flight readiness is presented. This methodology is of particular value when information relevant to failure prediction, including test experience and knowledge of parameters used in engineering analyses of failure phenomena, is limited. In this approach, engineering analysis models that characterize specific failure modes based on the physics and mechanics of the failure phenomena are used in a prescribed probabilistic structure to generate a failure probability distribution that is modified by test and flight experience in a Bayesian statistical procedure. The probabilistic structure and statistical methodology are generally applicable to any failure mode for which quantitative engineering analysis can be employed to characterize the failure phenomenon and are particularly well suited for use under the constraints on information availability that are typical of such spaceflight systems as the Space Shuttle and planetary spacecraft.

Moore, N. R.↗
NASA NTRS1991

Gain in computational efficiency by vectorization in the dynamic simulation of multi-body systems

An improved technique for the identification and extraction of the exact quantities associated with the degrees of freedom at the element as well as the flexible body level is presented. It is implemented in the dynamic equations of motions based on the recursive formulation of Kane et al. (1987) and presented in a matrix form, integrating the concepts of strain energy, the finite-element approach, modal analysis, and reduction of equations. This technique eliminates the CPU intensive matrix multiplication operations in the code's hot spots for the dynamic simulation of the interconnected rigid and flexible bodies. A study of a simple robot with flexible links is presented by comparing the execution times on a scalar machine and a vector-processor with and without vector options. Performance figures demonstrating the substantial gains achieved by the technique are plotted.

Amirouche, F. M. L.↗
NASA NTRS1991

A sequential approach to multivariable stability robustness analysis

In sequential loop closure, the importance of evaluating the stability and stability robustness at the intermediate loop closures is well known, yet how the stability and stability robustness evaluated at the intermediate steps contribute to the stability and stability robustness of the overall feedback system must be developed. An analysis of the complete feedback system reveals the multivariable Nyquist contributions from the intermediate loop closures. It is also shown that the results greatly simplify if frequency separation exists between the intermediate loops. The analysis is presented with a two-step loop closure procedure using 'inner' and 'outer' loops which can be generalized to multi-step situations. The control of the longitudinal dynamics of an aircraft is addressed to further clarify and demonstrate the results.

Newman, Brett↗
NASA NTRS1992

Analysis of accidents during instrument approaches

General aviation and air taxi approach phase accidents, which occurred during VFR and IFR, respectively over the last 25 years, were analyzed. The data suggest that there is a 204 percent higher risk during the approach and landing phase of VFR flights, than during similar IFR operations (14.82 vs 7.27 accidents/100,000 approaches). Alarmingly, the night single pilot IFR (SPIFR) accident rate is almost 8 times the rate of day IFR, 35.43 vs 4.47 accidents/100,000 approaches, and two and a half times that of day VFR approaches, 35.43 vs 14.82 accidents/100,000 approaches. Surprisingly, the overall SPIFR accident rates are not much higher than dual-pilot IFR (DPIFR), 7.27 vs 6.48 accidents/100,000 approaches. The generally static ratio of the statistics for SPIFR/DPIFR accident rates may be accounted for by little or no change in general aviation cockpit technology during the last 25 years, and because IFR operational flight task management training has not kept pace.

Bennett, C. T.↗
NASA NTRS1993

Statistical Approach To Determination Of Texture In SAR

Paper presents statistical approach to analysis of texture in synthetic-aperture-radar (SAR) images. Objective: to extract intrinsic spatial variability of distributed target from overall spatial variability of SAR image.

Rignot, Eric J.↗
NASA NTRS1992

Computational technology for high-temperature aerospace structures

The status and some recent developments of computational technology for high-temperature aerospace structures are summarized. Discussion focuses on a number of aspects including: goals of computational technology for high-temperature structures; computational material modeling; life prediction methodology; computational modeling of high-temperature composites; error estimation and adaptive improvement strategies; strategies for solution of fluid flow/thermal/structural problems; and probabilistic methods and stochastic modeling approaches, integrated analysis and design. Recent trends in high-performance computing environment are described and the research areas which have high potential for meeting future technological needs are identified.

Noor, A. K.↗
NASA NTRS1993

Impact and volcanism - A momentum scaling law for erosion

The controversy that raged through the 1950s to 1970s over similarities and differences between meteorite impact and volcanic processes is revisited. We propose that there are quantitative similarities in erosion caused by high-speed ejecta produced by either impacts or volcanic processes. Field and petrographic data from the Manicouagan impact crater, Canada, are used to demonstrate that, during the emplacement of the impact melt sheet, erosion occurred at a rate of 2562 kg/sq m per s. Field data for the Mount St. Helens lateral blast of May 18, 1980, suggest an erosion rate of 21 kg/sq m per s, and field data for a small pyroclastic flow on August 7, 1980, suggest an erosion rate of about 14 kg /sq m per s. It is proposed that these three rates were determined dominantly by the momentum of the ejecta, and a quantitative formulation based on lofting theory is given. A new application of the Monte Carlo approach to analysis provides minimum, most likely, and maximum estimates for both the field and the theoretical analyses. The substantial erosion that occurs by fast moving flows results in mixing of stratigraphic components over large distances and to very fine scales.

Simonds, Charles H.↗
NASA NTRS1958

Handbook of structural stability part VI : strength of stiffened curved plates and shells

A comprehensive review of failure of stiffened curved plates and shells is presented. Panel instability in stiffened curved plates and general instability of stiffened cylinders are discussed. The loadings considered for the plates are axial, shear, and the combination of the two. For the cylinders, bending, external pressure, torsion, transverse shear, and combinations of these loads are considered. When possible, test data and theory were correlated. General instability in stiffened cylinders was investigated. For bending and torsion loads, test data and theory were correlated. For external pressure several existing theories were compared. As a result of this investigation a unified theoretical approach to analysis of general instability in stiffened cylinders was developed. (author)

Becker, Herbert↗
NASA NTRS1994

Modeling ozone episodes in the Baltimore-Washington region

Surface ozone (O3) concentrations in excess of the National Ambient Air Quality Standard (NAAQS) continue to occur in metropolitan areas in the United States despite efforts to control emissions of O3 precursors. Future O3 control strategies will be based on results from modeling efforts that have just begun in many areas. Two initial questions that arise are model sensitivity to domain-specific conditions and the selection of episodes for model evaluation and control strategy development. For the Baltimore-Washington region (B-W), the presence of the Chesapeake Bay introduces a number of issues relevant to model sensitivity. In this paper, the specific questions of the determination of model volume (mixing height) for the Urban Airshed Model (UAM) is discussed and various alternative methods compared. For the latter question, several analytic approaches, Cluster Analysis and classification and Regression Tree (CART) analysis are undertaken to determine meteorological conditions associated with severe O3 events in the B-W domain.

Ryan, William F.↗
NASA NTRS1994

High-spatial-resolution passive microwave sounding systems

The principal contributions of this combined theoretical and experimental effort were to advance and demonstrate new and more accurate techniques for sounding atmospheric temperature, humidity, and precipitation profiles at millimeter wavelengths, and to improve the scientific basis for such soundings. Some of these techniques are being incorporated in both research and operational systems. Specific results include: (1) development of the MIT Microwave Temperature Sounder (MTS), a 118-GHz eight-channel imaging spectrometer plus a switched-frequency spectrometer near 53 GHz, for use on the NASA ER-2 high-altitude aircraft, (2) conduct of ER-2 MTS missions in multiple seasons and locations in combination with other instruments, mapping with unprecedented approximately 2-km lateral resolution atmospheric temperature and precipitation profiles, atmospheric transmittances (at both zenith and nadir), frontal systems, and hurricanes, (3) ground based 118-GHz 3-D spectral images of wavelike structure within clouds passing overhead, (4) development and analysis of approaches to ground- and space-based 5-mm wavelength sounding of the upper stratosphere and mesosphere, which supported the planning of improvements to operational weather satellites, (5) development of improved multidimensional and adaptive retrieval methods for atmospheric temperature and humidity profiles, (6) development of combined nonlinear and statistical retrieval techniques for 183-GHz humidity profile retrievals, (7) development of nonlinear statistical retrieval techniques for precipitation cell-top altitudes, and (8) numerical analyses of the impact of remote sensing data on the accuracy of numerical weather predictions; a 68-km gridded model was used to study the spectral properties of error growth.

Staelin, D. H.↗
NASA NTRS1995

Numerical solution of fluid flow and heat tranfer problems with surface radiation

This paper presents a numerical scheme, based on the finite element method, to solve strongly coupled fluid flow and heat transfer problems. The surface radiation effect for gray, diffuse and isothermal surfaces is considered. A procedure for obtaining the view factors between the radiating surfaces is discussed. The overall solution strategy is verified by comparing the available results with those obtained using this approach. An analysis of a thermosyphon is undertaken and the effect of considering the surface radiation is clearly explained.

Ahuja, S.↗
NASA NTRS1995

Importance of real gas effects in entry technology

Critical issues concerning real gas effects in hypervelocity flows where the thermochemical nonequilibrium effects are pronounced, are described. Emphasis is on the development and validation of benchmark analysis tools. Approaches to develop and/or enhance phenomenological models, including test techniques to acquire databases, and incorporate them into computational flow field simulation codes are described. The performance characteristics of shock tubes, ballistic ranges and arc heated wind tunnels, state of the art diagnostics are included. The following aerothermodynamic phenomena are discussed: aerodynamic parameters, viscous interactions, turbulent transition, forebody heating/heat transfer, radiative heating, Lee-Base flows and low density real gas.

Deiwert, George S.↗
NASA NTRS1997

A Statistical Simulation Approach to Safe Life Fatigue Analysis of Redundant Metallic Components

This paper introduces a dual active load path fail-safe fatigue design concept analyzed by Monte Carlo simulation. The concept utilizes the inherent fatigue life differences between selected pairs of components for an active dual path system, enhanced by a stress level bias in one component. The design is applied to a baseline design; a safe life fatigue problem studied in an American Helicopter Society (AHS) round robin. The dual active path design is compared with a two-element standby fail-safe system and the baseline design for life at specified reliability levels and weight. The sensitivity of life estimates for both the baseline and fail-safe designs was examined by considering normal and Weibull distribution laws and coefficient of variation levels. Results showed that the biased dual path system lifetimes, for both the first element failure and residual life, were much greater than for standby systems. The sensitivity of the residual life-weight relationship was not excessive at reliability levels up to R = 0.9999 and the weight penalty was small. The sensitivity of life estimates increases dramatically at higher reliability levels.

Matthews, William T.↗
NASA NTRS1998

Analysis and Modeling of a Two-Phase Jet Pump of a Thermal Management System for Aerospace Applications

Jet pumps are devices capable of pumping fluids to a higher pressure by inducing the motion of a secondary fluid employing a high speed primary fluid. The main components of a jet pump are a primary nozzle, secondary fluid injectors, a mixing chamber, a throat, and a diffuser. The work described in this paper models the flow of a two-phase primary fluid inducing a secondary liquid (saturated or subcooled) injected into the jet pump mixing chamber. The model is capable of accounting for phase transformations due to compression, expansion, and mixing. The model is also capable of incorporating the effects of the temperature and pressure dependency in the analysis. The approach adopted utilizes an isentropic constant pressure mixing in the mixing chamber and at times employs iterative techniques to determine the flow conditions in the different parts of the jet pump.

Sherif, S.A.↗