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NASA NTRS1992

First Annual High-Speed Research Workshop, part 2

This workshop provided a national forum for presenting and discussing important technology issues related to the definition of an economically viable and environmentally compatible High Speed Civil Transport. The workshop was organized into 13 sessions. This volume is part 2 of 4 and covers 4 of the 13 sessions: (1) source noise; (2) sonic boom (aerodynamic performance); (3) propulsion systems studies; and (4) emission reduction.

Whitehead, Allen H., Jr.↗

NASA NTRS1992

HSCT high-lift technology requirements

The viewgraphs and discussion of high lift needs and related aerodynamic goals established in system studies are described. The goals are presented for the takeoff, approach, and subsonic climb and cruise modes. The status of the related high lift databases and available design and analysis methods are described. Various high lift research and technology areas for future work including innovative concepts verification, flap design, computational fluid dynamics (CFD) calibration and application, high Reynolds number testing, subsonic/transonic flap optimization, and flight testing are described.

Antani, D. L.↗

NASA NTRS1994

Characterization of Metal Matrix Composites

Experimental methods were developed, adapted, and applied to the characterization of a metal matrix composite system, namely, silicon carbide/aluminim (SCS-2/6061 Al), and its constituents. The silicon carbide fiber was characterized by determining its modulus, strength, and coefficient of thermal expansion. The aluminum matrix was characterized thermomechanically up to 399 C (750 F) at two strain rates. The unidirectional SiC/Al composite was characterized mechanically under longitudinal, transverse, and in-plane shear loading up to 399 C (750 F). Isothermal and non-isothermal creep behavior was also measured. The applicability of a proposed set of multifactor thermoviscoplastic nonlinear constitutive relations and a computer code was investigated. Agreement between predictions and experimental results was shown in a few cases. The elastoplastic thermomechanical behavior of the composite was also described by a number of new analytical models developed or adapted for the material system studied. These models include the rule of mixtures, composite cylinder model with various thermoelastoplastic analyses and a model based on average field theory. In most cases satisfactory agreement was demonstrated between analytical predictions and experimental results for the cases of stress-strain behavior and thermal deformation behavior at different temperatures. In addition, some models yielded detailed three-dimensional stress distributions in the constituents within the composite.

Daniel, I. M.↗

NASA NTRS1994

Heavy ion induced DNA-DSB in yeast and mammalian cells

Molecular changes at the DNA are assumed to be the main cause for radiation effects in a number of organisms. During the course of the last decades techniques have been developed for measuring DNA double-strand breaks (dsb), generally assumed to be the most critical DNA lesions. The outcome of all those different approaches portrays a collection of data useful for a theoretical description of radiation action mechanisms. However, in the case of heavy ion induced DNA dsb the picture is not quite clear yet and further projects and strategies have to be developed. The biological systems studied in our group are yeast and mammalian cells. While in the case of yeast cells technical and methodical reasons highlight these organisms mammalian cells reach greater importance when dsb repair studies are performed. In both types of organisms the technique of pulsed-field gel electrophoresis (PFGE) is applied, although with different modifications and evaluation procedures mainly due to the different genome sizes.

Loebrich, M.↗

NASA NTRS1995

Sensitivity analysis of a model of CO2 exchange in tundra ecosystems by the adjoint method

A model of net primary production (NPP), decomposition, and nitrogen cycling in tundra ecosystems has been developed. The adjoint technique is used to study the sensitivity of the computed annual net CO2 flux to perturbation in initial conditions, climatic inputs, and model's main parameters describing current seasonal CO2 exchange in wet sedge tundra at Barrow, Alaska. The results show that net CO2 flux is most sensitive to parameters characterizing litter chemical composition and more sensitive to decomposition parameters than to NPP parameters. This underlines the fact that in nutrient-limited ecosystems, decomposition drives net CO2 exchange by controlling mineralization of main nutrients. The results also indicate that the short-term (1 year) response of wet sedge tundra to CO2-induced warming is a significant increase in CO2 emission, creating a positive feedback to atmosphreic CO2 accumulation. However, a cloudiness increase during the same year can severely alter this response and lead to either a slight decrease or a strong increase in emitted CO2, depending on its exact timing. These results demonstrate that the adjoint method is well suited to study systems encountering regime changes, as a single run of the adjoint model provides sensitivities of the net CO2 flux to perturbations in all parameters and variables at any time of the year. Moreover, it is shown that large errors due to the presence of thresholds can be avoided by first delimiting the range of applicability of the adjoint results.

Waelbroek, C.↗

NASA NTRS1995

Advanced controls for stability assessment of solar dynamics space power generation

In support of the power requirements for the Space Station Alpha (SSA), a joint program by the U.S. and Russia for a permanently manned space station to be launched into orbit by 1998, a robust control scheme is needed to assure the stability of the rotating machines that will be integrated into the power subsystem. A framework design and systems studies for modeling and analysis is presented. It employs classical d-q axes machine model with voltage/frequency dependent loads. To guarantee that design requirements and necessary trade studies are done, a functional analysis tool CORE is used for the study. This provides us with different control options for stability assessment. Initial studies and recommendations using advanced simulation tools are also presented. The benefits of the stability/control scheme for evaluating future designs and power management are discussed.

Momoh, James A.↗

NASA NTRS1995

Design geometry and design/off-design performance computer codes for compressors and turbines

This report summarizes some NASA Lewis (i.e., government owned) computer codes capable of being used for airbreathing propulsion system studies to determine the design geometry and to predict the design/off-design performance of compressors and turbines. These are not CFD codes; velocity-diagram energy and continuity computations are performed fore and aft of the blade rows using meanline, spanline, or streamline analyses. Losses are provided by empirical methods. Both axial-flow and radial-flow configurations are included.

Glassman, Arthur J.↗

NASA NTRS1995

Equivalent plate modeling for conceptual design of aircraft wing structures

This paper describes an analysis method that generates conceptual-level design data for aircraft wing structures. A key requirement is that this data must be produced in a timely manner so that is can be used effectively by multidisciplinary synthesis codes for performing systems studies. Such a capability is being developed by enhancing an equivalent plate structural analysis computer code to provide a more comprehensive, robust and user-friendly analysis tool. The paper focuses on recent enhancements to the Equivalent Laminated Plate Solution (ELAPS) analysis code that significantly expands the modeling capability and improves the accuracy of results. Modeling additions include use of out-of-plane plate segments for representing winglets and advanced wing concepts such as C-wings along with a new capability for modeling the internal rib and spar structure. The accuracy of calculated results is improved by including transverse shear effects in the formulation and by using multiple sets of assumed displacement functions in the analysis. Typical results are presented to demonstrate these new features. Example configurations include a C-wing transport aircraft, a representative fighter wing and a blended-wing-body transport. These applications are intended to demonstrate and quantify the benefits of using equivalent plate modeling of wing structures during conceptual design.

Giles, Gary L.↗

NASA NTRS1996

Review of recent thermophotovoltaic (TPV) research at Lewis Research Center

Thermophotovoltaic (TPV) research at NASA Lewis Research Center that began in the late 1980's is reviewed. This work has been concentrated on low bandgap indium gallium arsenide (InGaAs) PV cells and rare earth yttrium aluminum garnet (YAG) thin film selective emitters, as well as, TPV system studies. An emittance theory has been developed for the thin film emitters. Experimental spectral emittance results for erbium Er-YAG and holmium Ho-YAG show excellent emittance (greater than or equal to .7) within the emission bands. The .75 eV InGaAs PV cells fabricated at Lewis have excellent quantum efficiency. An efficiency of 13% has been measured for this cell coupled to an Er-YAG selective emitter and a short pass IR filter.

Chubb, Donald L.↗

NASA NTRS1997

Evaluation of an Ejector Ramjet Based Propulsion System for Air-Breathing Hypersonic Flight

A Rocket Based Combined Cycle (RBCC) engine system is designed to combine the high thrust to weight ratio of a rocket along with the high specific impulse of a ramjet in a single, integrated propulsion system. This integrated, combined cycle propulsion system is designed to provide higher vehicle performance than that achievable with a separate rocket and ramjet. The RBCC engine system studied in the current program is the Aerojet strutjet engine concept, which is being developed jointly by a government-industry team as part of the Air Force HyTech program pre-PRDA activity. The strutjet is an ejector-ramjet engine in which small rocket chambers are embedded into the trailing edges of the inlet compression struts. The engine operates as an ejector-ramjet from take-off to slightly above Mach 3. Above Mach 3 the engine operates as a ramjet and transitions to a scramjet at high Mach numbers. For space launch applications the rockets would be re-ignited at a Mach number or altitude beyond which air-breathing propulsion alone becomes impractical. The focus of the present study is to develop and demonstrate a strutjet flowpath using hydrocarbon fuel at up to Mach 7 conditions. Freejet tests of a candidate flowpath for this RBCC engine were conducted at the NASA Lewis Research Center's Hypersonic Tunnel Facility between July and September 1996. This paper describes the engine flowpath and installation, outlines the primary objectives of the program, and describes the overall results of this activity. Through this program 15 full duration tests, including 13 fueled tests were made. The first major achievement was the further demonstration of the HTF capability. The facility operated at conditions up to 1950 K and 7.34 MPa, simulating approximately Mach 6.6 flight. The initial tests were unfueled and focused on verifying both facility and engine starting. During these runs additional aerodynamic appliances were incorporated onto the facility diffuser to enhance starting. Both facility and engine starting were achieved. Further, the static pressure distributions compared well with the results previously obtained in a 40% subscale flowpath study conducted in the LERC 1X1 supersonic wind tunnel (SWT), as well as the results of CFD analysis. Fueled performance results were obtained for the engine at both simulated Mach 6 (1670 K) and Mach 6.6 (1950 K) conditions. For all these tests the primary fuel was liquid JP-10 with gaseous silane (a mixture of 20% SiH4 and 80% H2 by volume) as an ignitor/pilot. These tests verified performance of this engine flowpath in a freejet mode. High combustor pressures were reached and significant changes in axial force were achieved due to combustion. Future test plans include redistributing the fuel to improve mixing, and consequently performance, at higher equivalence ratios.

Thomas, Scott R.↗

NASA NTRS1997

Space Transportation Systems Using Tethers

The groundwork has been laid for tether space transportation systems. NASA has developed tether technology for space applications since the 1960's. Important recent milestones include retrieval of a tether in space (TSS-1, 1992), successful deployment of a 20-km-long tether in space (SEDS-1, 1993), and operation of an electrodynamic tether with tether current driven in both directions-power and thrust modes (PMG, 1993). Various types of tethers and systems can be used for space transportation. Short electrodynamic tethers can use solar power to 'push' against a planetary magnetic field to achieve propulsion without the expenditure of propellant. The planned Propulsive Small Expendable Deployer System (ProSEDS) experiment will demonstrate electrodynamic tether thrust during its flight in early 2OOO. Utilizing completely different physical principles, long non-conducting tethers can exchange momentum between two masses in orbit to place one body into a transfer orbit for lunar and planetary missions. Recently completed system studies of this concept indicate that it would be a relatively low-cost in-space asset with long-term multimission capability. Both methods of using tethers for space transportation and propulsion are described in the paper.

Johnson, Les↗

NASA NTRS1997

Effects of FU Orionis Outbursts on Protoplanetary Disks

In the early stages of work under this grant, we developed simulations to match the light curves of the three best studied systems: FU Ori, V1515 Cyg, & V1057 Cyg (Bell et al. 1995). We compared the details of model results to observations to test the validity of the thermal ionization instability model for outburst. In this paper, we were able to answer several of the key objections to the accretion disk outburst model for the FU Orionis phenomenon (eg. Herbig 1989). The declines in line width and reddening observed in V1057 Cyg following peak light had been used as arguments against the disk instability model. We showed these effects to be natural consequences of the slow outward progression and limited radial excursion of the ionization front during outburst. By the end of the grant period, we had begun combining the inner and outer disk models to derive the radiation expected in the planet forming region of the disk. A crucial step in this was the development of a radiative transfer model of the complete inner and outer disk system (Turner, Bodenheimer, & Bell 1997). In this work, wavelength dependent opacities were used to synthesize images and spectral energy distributions of FU Ori objects. New detailed opacities provided by Alexander (1995) allowed the resolution of coarse features such as silicate emission lines. Data for the fits were taken from the time dependent simulations in Bell et al. (1995) to which was added the effect of disk to disk or "self"-reprocessing which accounts for the illumination of the outer disk by the inner disk (Bell 1998). Through the course of work on this grant we have made considerable progress in computing detailed models of both the active outburst region of the disk and the outer quiescent disk. We have begun an investigation into the effects of a cocooning envelope. Direct comparisons with observations lend confidence that the basic underlying assumptions of the outburst model are reasonable. We are now ready to build upon these results to investigate the effects of outbursts on the central star and on the accumulation of small particles in the planet-forming regions.

Bodenheimer, Peter↗

NASA NTRS1997

Evaluation of an Ejector Ramjet Based Propulsion System for Air-Breathing Hypersonic Flight

Thomas, Scott R.↗

NASA NTRS1998

Aircraft Structural Mass Property Prediction Using Conceptual-Level Structural Analysis

This paper describes a methodology that extends the use of the Equivalent LAminated Plate Solution (ELAPS) structural analysis code from conceptual-level aircraft structural analysis to conceptual-level aircraft mass property analysis. Mass property analysis in aircraft structures has historically depended upon parametric weight equations at the conceptual design level and Finite Element Analysis (FEA) at the detailed design level ELAPS allows for the modeling of detailed geometry, metallic and composite materials, and non-structural mass coupled with analytical structural sizing to produce high-fidelity mass property analyses representing fully configured vehicles early in the design process. This capability is especially valuable for unusual configuration and advanced concept development where existing parametric weight equations are inapplicable and FEA is too time consuming for conceptual design. This paper contrasts the use of ELAPS relative to empirical weight equations and FEA. ELAPS modeling techniques are described and the ELAPS-based mass property analysis process is detailed Examples of mass property stochastic calculations produced during a recent systems study are provided This study involved the analysis of three remotely piloted aircraft required to carry scientific payloads to very high altitudes at subsonic speeds. Due to the extreme nature of this high-altitude flight regime,few existing vehicle designs are available for use in performance and weight prediction. ELAPS was employed within a concurrent engineering analysis process that simultaneously produces aerodynamic, structural, and static aeroelastic results for input to aircraft performance analyses. The ELAPS models produced for each concept were also used to provide stochastic analyses of wing structural mass properties. The results of this effort indicate that ELAPS is an efficient means to conduct multidisciplinary trade studies at the conceptual design level.

Sexstone, Matthew G.↗

NASA NTRS1998

Overview of Future NASA Tether Applications

The groundwork has been laid for tether applications in space. NASA has developed tether technology for space applications since the 1960's. Important recent milestones include retrieval of a tether in space (TSS-1, 1992), successful deployment of a 20-km-long tether in space (SEDS-1, 1993), and operation of an electrodynamic tether with tether current driven in both directions-power and thrust modes (PMG, 1993). Various types of tethers and systems can be used for space transportation. Short electrodynamic tethers can use solar power to 'push' against a planetary magnetic field to achieve propulsion without the expenditure of propellant. The planned Propulsive Small Expendable Deployer System (ProSEDS) experiment will demonstrate electrodynamic tether thrust during its flight in early 2000. Utilizing completely different physical principles, long non-conducting tethers can exchange momentum between two masses in orbit to place one body into a higher orbit or a transfer orbit for lunar and planetary missions. Recently completed system studies of this concept indicate that it would be a relatively low-cost in-space asset with long-term multi-mission capability. Tethers can also be used to support space science by providing a mechanism for precision formation flying and for reaching regions of the upper atmosphere that were previously inaccessible.

Johnson, Les↗

NASA NTRS1997

How Reuse Influences Productivity in Object-Oriented Systems

Although reuse is assumed to be especially valuable in building high quality software as well as in Object Oriented (OO) development, limited empirical evidence connects reuse with productivity and quality gains. The author's eight system study begins to define such benefits in an OO framework, most notably in terms of reduce defect density and rework as well as in increased productivity.

Basili, Victor R.↗

NASA NTRS1999

Kinetics of Nucleation and Crystal Growth in Glass Forming Melts in Microgravity

The following list summarizes the most important results that have been consistently reported for glass forming melts in microgravity: (1) Glass formation is enhanced for melts prepared in space; (2) Glasses prepared in microgravity are more chemically homogeneous and contain fewer and smaller chemically heterogeneous regions than identical glasses prepared on earth; (3) Heterogeneities that are deliberately introduced such as Pt particles are more uniformly distributed in a glass melted in space than in a glass melted on earth; (4) Glasses prepared in microgravity are more resistant to crystallization and have a higher mechanical strength and threshold energy for radiation damage; and (5) Glasses crystallized in space have a different microstructure, finer grains more uniformly distributed, than equivalent samples crystallized on earth. The preceding results are not only scientifically interesting, but they have considerable practical implications. These results suggest that the microgravity environment is advantageous for developing new and improved glasses and glass-ceramics that are difficult to prepare on earth. However, there is no suitable explanation at this time for why a glass melted in microgravity will be more chemically homogeneous and more resistant to crystallization than a glass melted on earth. A fundamental investigation of melt homogenization, nucleation, and crystal growth processes in glass forming melts in microgravity is important to understanding these consistently observed, but yet unexplained results. This is the objective of the present research. A lithium disilicate (Li2O.2SiO2) glass will be used for this investigation, since it is a well studied system, and the relevant thermodynamic and kinetic parameters for nucleation and crystal growth at 1-g are available. The results from this research are expected to improve our present understanding of the fundamental mechanism of nucleation and crystal growth in melts and liquids, and to lead improvements in glass processing technology on earth, with the potential for creating new high performance glasses and glass-ceramics.

Day, Delbert E.↗

NASA NTRS1998

The Problem of Hipparcos Distances to Open Clusters: Constraints from Multicolor a Main-Sequence Fitting - Report 1

Parallax data from the Hipparcos mission allow the direct distance to open clusters to be compared with the distance inferred from main-sequence (MS) fitting. There are surprising differences between the two distance measurements. indicating either the need for changes in the cluster compositions or reddening, underlying problems with the technique of MS fitting, or systematic errors in the Hipparcos parallaxes at the 1 mas level. We examine the different possibilities, focusing on MS fitting in both metallicity-sensitive B-V and metallicity-insensitive V-I for five well-studied systems (the Hyades, Pleiades, alpha Per, Praesepe, and Coma Ber). The Hipparcos distances to the Hyades and alpha Per are within 1 sigma of the MS-fitting distance in B-V and V-I, while the Hipparcos distances to Coma Ber and the Pleiades are in disagreement with the MS-fitting distance at more than the 3 sigma level. There are two Hipparcos measurements of the distance to Praesepe; one is in good agreement with the MS-fitting distance and the other disagrees at the 2 sigma level. The distance estimates from the different colors are in conflict with one another for Coma but in agreement for the Pleiades. Changes in the relative cluster metal abundances, age related effects, helium, and reddening are shown to be unlikely to explain the puzzling behavior of the Pleiades. We present evidence for spatially dependent systematic errors at the 1 mas level in the parallaxes of Pleiades stars. The implications of this result are discussed.

Pinsonneault, Marc H.↗