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At least 1,117 records · Page 62

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NASA NTRS1981

Distributed photovoltaic systems: Utility interface issues and their present status

Major technical issues involving the integration of distributed photovoltaics (PV) into electric utility systems are defined and their impacts are described quantitatively. An extensive literature search, interviews, and analysis yielded information about the work in progress and highlighted problem areas in which additional work and research are needed. The findings from the literature search were used to determine whether satisfactory solutions to the problems exist or whether satisfactory approaches to a solution are underway. It was discovered that very few standards, specifications, or guidelines currently exist that will aid industry in integrating PV into the utility system. Specific areas of concern identified are: (1) protection, (2) stability, (3) system unbalance, (4) voltage regulation and reactive power requirements, (5) harmonics, (6) utility operations, (7) safety, (8) metering, and (9) distribution system planning and design.

Hassan, M.↗

NASA NTRS1982

Capillary surface discontinuities above reentrant corners

A particular configuration of a vertical capillary tube for which S is the equilibrium interface between two fluids in the presence of a downward pointing gravitational field was investigated. S is the graph a function u whose domain is the (horizontal) cross section gamma of the tube. The mean curvature of S is proportional to its height above a fixed reference plane and lambda is a prescribed constant and may be taken between zero and pi/2. Domains gamma for which us is a bounded function but does not extend continuously to d gamma are sought. Simple domains are found and the behavior of u in those domains is studied. An important comparison principle that has been used in the literature to derive many of the results in capillarity is reviewed. It allows one to deduce the approximate shape of a capillary surface by constructing comparison surfaces with mean curvature and contact angle close to those of the (unknown) solution surface. In the context of nonparametric problems the comparison principle leads to height estimates above and below for the function u. An example from the literature where these height estimates have been used successfully is described. The promised domains for which the bounded u does not extend continuously to the boundary are constructed. The point on the boundary at which u has a jump discontinuity will be the vertext of a re-entrant corner having any interior angle theta pi. Using the comparison principle the behavior of u near this point is studied.

Korevaar, H. J.↗

NASA NTRS1982

Some NTF laser velocimeter installation and operation considerations

Two velocimeter techniques were considered as potential candidates for achieving the flow field angularity measurements. The first was the fringe laser Doppler velocimeter, (LDV). A great deal of experience was obtained with this approach at Langley and the literature is rich with papers describing many experimental applications and system performance details. That is, many velocity flow field measurements were conducted with the LDV but not with high resolution precise angularity measurements. The second candidate considered was the two-spot laser transit anemometer, (LTA). This approach was not as extensively used as the LDV technique, but literature does contain experimental applications and system performance details. Again, a lack of high resolution, high precision angularity measurements is noted for the LTA. The results of the study suggested that the LDV and LTA tests and other efforts did not reveal any fundamental problems that would suggest that laser velocimetry is not a viable diagnostic technique for the National Transonic Facility. However, there are a number of engineering problems that need to be solved.

Hunter, W. W., Jr.↗

NASA NTRS1981

Vibrations of twisted rotating blades

The literature dealing with vibrations of turbomachinery blades is voluminous, but the vast majority of it treats the blades as beams. In a previous paper a two-dimensional analytical procedure was developed and demonstrated on simple models of blades having camber. The procedure utilizes shallow shell theory along with the classical Ritz method for solving the vibration problem. Displacement functions are taken as algebraic polynomials. In the present paper the method is demonstrated on blade models having camber. Comparisons are first made with results in the literature for nonrotating twisted plates and various disagreements between results are pointed out. A method for depicting mode shape information is demonstrated, permitting one to examine all three components of displacement. Finally, the analytical procedure is demonstrated on rotating twisted blade modes, both without and with camber.

Leissa, A. W.↗

NASA NTRS1982

Carbon isotopic ratios in some low-delta N-15 lunar breccias

Lunar soil breccias 10018, 79035 and 79135 were analyzed for carbon and nitrogen contents and isotopic compositions by vacuum pyrolysis, with a 500 C pre-combustion step in some cases. The combustion was used to remove carbon of terrestrial origin. Nitrogen isotopic ratios for the breccias are very low and are in agreement with results in the literature. Nitrogen yields in two cases were lower than literature values, a result attributable to heterogeneous mixing of implanted and implantation-free components in the breccias. Carbon isotopic ratios were found to be low in these breccias, even when reasonable account is taken of terrestrial carbon contamination. The results are consistent with the idea that low-delta N-15 values in lunar soils and breccias are accompanied by low-delta C-13 values, and imply that any secular variation which occurred in the delta N-15 of nitrogen implanted in lunar soils was accompanied by a similar but smaller variation in the delta C-13 of implanted carbon.

Becker, R. H.↗

NASA NTRS1982

Effects of fiber/matrix interactions on the properties of graphite/epoxy composites

A state-of-the-art literature review of the interactions between fibers and resin within graphite epoxy composite materials was performed. Emphasis centered on: adhesion theory; wetting characteristics of carbon fiber; load transfer mechanisms; methods to evaluate and measure interfacial bond strengths; environmental influence at the interface; and the effect of the interface/interphase on composite performance, with particular attention to impact toughness. In conjunction with the literature review, efforts were made to design experiments to study the wetting behavior of carbon fibers with various finish variants and their effect on adhesion joint strength. The properties of composites with various fiber finishes were measured and compared to the base-line properties of a control. It was shown that by tailoring the interphase properties, a 30% increase in impact toughness was achieved without loss of mechanical properties at both room and elevated temperatures.

Mcmahon, P. E.↗

NASA NTRS1983

A note on the cracked plates reinforced by a line stiffener

The problem of a cracked plate reinforced by a line stiffener is reconsidered. The original solution of this problem was given in the literature. Also, a variation of the problem with debonding between the plate and the stiffener near the cracked region was reported in the literature. However, the special case of the problem in which the crack tip terminates at the stiffener does not appear to have been studied. In practice, the solution may be necessary in order to assess the crack arrest effectiveness of the stiffener. The problem of a stiffened plate with a crack is reformulated, the asymptotic stress state near the crack tip terminating at the stiffener is examined, and numerical results are given for various stiffness constants.

Yahsi, O. S.↗

NASA NTRS1982

Boundary integral equation method calculations of surface regression effects in flame spreading

A solid-phase conduction problem that is a modified version of one that has been treated previously in the literature and is applicable to flame spreading over a pyrolyzing fuel is solved using a boundary integral equation (BIE) method. Results are compared to surface temperature measurements that can be found in the literature. In addition, the heat conducted through the solid forward of the flame, the heat transfer responsible for sustaining the flame, is also computed in terms of the Peclet number based on a heated layer depth using the BIE method and approximate methods based on asymptotic expansions. Agreement between computed and experimental results is quite good as is agreement between the BIE and the approximate results.

Altenkirch, R. A.↗

NASA NTRS1982

Sulfur-dioxide/water equilibria between 0 and 50 C - An examination of data at low concentrations

In order to resolve the discrepancy noted in values currently used for the first dissociation constant of SO2 in water, the pertinent literature was critically examined and a value of 0.0132 M at 25 C was recommended. An expression correlating this value as a function of temperature for zero-50 C has been developed. Attention is also given to the literature for the Henry's law constant, and a value of 1.242 M/atm at 25 C is recommended. Ionic activity corrections and speciation in more concentrated solutions are discussed, and recommendations are made for estimating the activity coefficients of the various ionic species in solutions of moderate ionic strength.

Maahs, H. G.↗

NASA NTRS1983

Heliospheric magnetic fields and plasmas

A survey of the existing literature on heliospheric physics, covering the period 1972-1982, is presented. Attention is given to observations and theories germane to the examination of the heliosphere as a large-scale astrophysical system that is part of the earth's environment. The literature includes data and models for magnetic sectors and the large-scale magnetic field, the large-scale plasma structure, and models and observed variations in the solar wind. Consideration is also devoted to the transient and corotating streams and shocks, the composition of the solar wind, and to MHD turbulence, waves, and discontinuities. More intensive investigations of the region near 1 AU are recommended, particularly to characterize the coronal source of the solar wind. The solar polar mission will be the first to provide radial measurements for comparisons with previous exclusively ecliptic measurements of solar activities.

Burlaga, L. F.↗

NASA NTRS1983

A note on the cracked plates reinforced by a line stiffener

Yahsi, O. S.↗

NASA NTRS1984

Effect of creep in titanium alloy Ti-6Al-4V at elevated temperature on aircraft design and flight test

Short-term compressive creep tests were conducted on three titanium alloy Ti-6Al-4V coupons at three different stress levels at a temperature of 714 K (825 F). The test data were compared to several creep laws developed from tensile creep tests of available literature. The short-term creep test data did not correlate well with any of the creep laws obtained from available literature. The creep laws themselves did not correlate well with each other. Short-term creep does not appear to be very predictable for titanium alloy Ti-6Al-4V. Aircraft events that result in extreme, but short-term temperature and stress excursions for this alloy should be approached cautiously. Extrapolations of test data and creep laws suggest a convergence toward predictability in the longer-term situation.

Jenkins, J. M.↗

NASA NTRS1984

Overview of zirconia with respect to gas turbine applications

Phase relationships and the mechanical properties of zirconia are examined as well as the thermal conductivity, deformation, diffusion, and chemical reactivity of this refractory material. Observations from the literature particular to plasma-sprayed material and implications for gas turbine engine applications are discussed. The literature review indicates that Mg-PSZ (partially stabilized zirconia) and Ca-PSZ are unsuitable for advanced gas turbine applications; a thorough characterization of the microstructure of plasma-sprayed zirconia is needed. Transformation-toughened zirconia may be suitable for use in monolithic components.

Cawley, J. D.↗

NASA NTRS1985

Corrosive Effects of Burning Fuels

Literature synthesized to develop corrosion predictions for unconventional fuels. Report presents studies of probable corrosive effects of such unconventional fuels as liquefied coal. Report prepared by analyzing probable composition of fuels when they come into wide use, identifying important compounds, and searching literature for information about corrosion problems associated with compounds in environments like those in industrial and commercial boilers and furnaces.

Bellan, J.↗

NASA NTRS1985

Microgravity science and applications bibliography, 1985 revision

This edition of the Microgravity Science and Applications (MSA) Bibliography is a compilation of Government reports, contractor reports, conference proceedings, and journal articles dealing with flight experiments utilizing a low-gravity environment to elucidate and control various processes or with ground-based activities that provide supporting research. It encompasses literature published but not cited in the 1984 Revision and that literature which has been published in the past year. Subdivisions of the bibliography include six major categories: Electronic Materials; Metal, Alloys, and Composites; Fluid Dynamics and Transports; Biotechnology; Glass and Ceramics; and Combustion. Also included are publications from the European, Soviet, and Japanese MSA programs. In addition, there is a list of patents and appendices providing a compilation of anonymously authored collection of reports and a cross reference index.

Pentecost, E.↗

NASA NTRS1985

Estimation of finite mixtures using the empirical characteristic function

A problem which occurs in analyzing LANDSAT scenes is the problem of separating the components of a finite mixture of several distinct probability distributions. A review of the literature indicates this is a problem which occurs in many disciplines, such as engineering, biology, physiology and economics. Many approaches to this problem have appeared in the literature; however, most are very restrictive in their assumptions or have met with only a limited degree of success when applied to realistic situations. A proceudre is investigated with combines the k-L procedure of (Feurverger and McDunnough, 1981) with the MAICE procedure of (Akaike, 1974). The feasibility of this approach is being investigated numerically via the development of a computer software package enabling a simulation study and comparison with other procedures.

Anderson, C.↗

NASA NTRS1985

Implications of privacy needs and interpersonal distancing mechanisms for space station design

Privacy needs, or the need of people to regulate their degree of contact with one another, and interpersonal distancing mechanisms, which serve to satisfy these needs, are common in all cultures. Isolation, confinement, and other conditions accociated with space flight may at once accentuate privacy needs and limit the availability of certain common interpersonal contact. Loneliness occurs when people have less contact with one another than they desire. Crowding occurs when people have more contact with one another than they desire. Crowding, which is considered the greater threat to members of isolated and confined groups, can contribute to stress, a low quality of life, and poor performance. Drawing on the general literature on privacy, personal space, and interpersonal distancing, and on specialized literature on life aboard spacecraft and in spacecraft-analogous environments, a quantitative model for understanding privacy, interpersonal distancing, loneliness, and crowding was developed and the practical implications of this model for space station design were traced.

Harrison, A. A.↗

NASA NTRS1985

Quantification of Saint-Venant's principle for a general prismatic member

A method to quantify Saint-Venant's principle for general prismatic members is described. Finite elements are used to model the member cross-section to allow the analysis of arbitrary geometries, material properties, and nonhomogeneities. The variation in the structural response along the member's length, away from the loaded end, is modelled with an exponential decay which has been established in the literature to be the correct form. Many analytic results exist in the literature for special cases. Because of its ability to handle arbitrary cross sectional geometries, this semi-analytic finite element method can provide a firm footing for the utilization of Saint-Venant's principle for whole new classes of problems. Results for several typical problems are given.

Goetschel, D. B.↗