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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1939

Effect of transition in cross-sectional shape on the development of the velocity and pressure distribution of turbulent flow in pipes

With regard to the change in shape of the cross section while the area remains constant, no investigation results are as yet available. Such an investigation will be the subject of the present paper. For this purpose it is necessary to consider the velocity and pressure relations over each entire cross section so that we are confronted with a three-dimensional problem.

Mayer, Edwin↗
NASA NTRS1988

Characteristics of satellite breakups from radar cross section and plane change angle

A problem of considerable interest in orbital debris research is the determination of the cause of the fragmentation of a satellite from the observed radar cross section and orbital element data. In this paper, analytic representations of the observed distribution functions of the radar cross section and the orbital plane change angle are derived. This then allows for the extraction of a small number of features that describe the observed data. Based on the known cause of fragmentation of a subset of satellites, a linear classifier is trained on these derived features. The discriminant function derived from this training is used to determine the previously unknown cause of the satellite breakup. the technique developed is objective and has been applied to the study of the cause of a number of unknown satellite breakup events.

Badhwar, Gautam D.↗
NASA NTRS1974

Transmission of sound through annular ducts of varying cross sections and sheared mean flow

An asymptotic solution is presented for the transmission and attenuation of acoustic waves in an annular duct of slowly varying cross section which carries a sheared mean flow. The analysis also takes into account the growth of the boundary layer as well as any slow variations in the acoustic liner properties. The problem is reduced to the solution of a first-order ordinary differential equation for the amplitude. The analysis is used to estimate the effects of the variations of the duct cross section and boundary layer growth on the different acoustic modes.

Nayfeh, A. H.↗
NASA NTRS1991

Absolute cascade-free cross-sections for the 2S to 2P transition in Zn(+) using electron-energy-loss and merged-beams methods

Absolute cascade-free excitation cross-sections in an ion have been measured for the resonance 2S to 2P transition in Zn(+) using electron-energy-loss and merged electron-ion beams methods. Measurements were carried out at electron energies of below threshold to 6 times threshold. Comparisons are made with 2-, 5-, and 15-state close-coupling and distorted-wave theories. There is good agreement between experiment and the 15-state close-coupling cross-sections over the energy range of the calculations.

Smith, Steven J.↗
NASA NTRS1997

Correction of Sampling Errors in Ocean Surface Cross-Sectional Estimates from Nadir-Looking Weather Radar

The return from the ocean surface has a number of uses for airborne meteorological radar. The normalized surface cross section has been used for radar system calibration, estimation of surface winds, and in algorithms for estimating the path-integrated attenuation in rain. However, meteorological radars are normally optimized for observation of distributed targets that fill the resolution volume, and so a point target such as the surface can be poorly sampled, particularly at near-nadir look angles. Sampling the nadir surface return at an insufficient rate results in a negative bias of the estimated cross section. This error is found to be as large as 4 dB using observations from a high-altitude airborne radar. An algorithm for mitigating the error is developed that is based upon the shape of the surface echo and uses the returned signal at the three range gates nearest the peak surface echo.

Caylor, I. Jeff↗
NASA NTRS2008

Pion and Kaon Lab Frame Differential Cross Sections for Intermediate Energy Nucleus-Nucleus Collisions

Space radiation transport codes require accurate models for hadron production in intermediate energy nucleus-nucleus collisions. Codes require cross sections to be written in terms of lab frame variables and it is important to be able to verify models against experimental data in the lab frame. Several models are compared to lab frame data. It is found that models based on algebraic parameterizations are unable to describe intermediate energy differential cross section data. However, simple thermal model parameterizations, when appropriately transformed from the center of momentum to the lab frame, are able to account for the data.

Norbury, John W.↗
NASA NTRS2017

Macrosegregation Resulting from Directional Solidification Through an Abrupt Change in Cross-Sections

Simulations of the directional solidification of two hypoeutectic alloys (Al-7Si alloy and Al-19Cu) and resulting macrosegregation patterns are presented. The casting geometries include abrupt changes in cross-section from a larger width of 9.5 mm to a narrower 3.2 mm width then through an expansion back to a width of 9.5 mm. The alloys were chosen as model alloys because they have similar solidification shrinkages, but the effect of Cu on changing the density of the liquid alloy is about an order of magnitude greater than that of Si. The simulations compare well with experimental castings that were directionally solidified in a graphite mold in a Bridgman furnace. In addition to the simulations of the directional solidification in graphite molds, some simulations were effected for solidification in an alumina mold. This study showed that the mold must be included in numerical simulations of directional solidification because of its effect on the temperature field and solidification. For the model alloys used for the study, the simulations clearly show the interaction of the convection field with the solidifying alloys to produce a macrosegregation pattern known as "steepling" in sections with a uniform width. Details of the complex convection- and segregation-patterns at both the contraction and expansion of the cross-sectional area are revealed by the computer simulations. The convection and solidification through the expansions suggest a possible mechanism for the formation of stray grains. The computer simulations and the experimental castings have been part of on-going ground-based research with the goal of providing necessary background for eventual experiments aboard the ISS. For casting practitioners, the results of the simulations demonstrate that computer simulations should be applied to reveal interactions between alloy solidification properties, solidification conditions, and mold geometries on macrosegregation. The simulations also presents the possibility of engineering the mold-material to avoid, or mitigate, the effects of thermosolutal convection and macrosegregation by selecting a mold material with suitable thermal properties, especially its thermal conductivity.

Lauer, M.↗
NASA NTRS1943

Torsion of Flanged Members with Cross Sections Restrained Against Warping

The longitudinal stresses and the stiffness of flange members - I-beams, channels, and Z-bars - were investigated when these members were subjected to torque with constraint against cross-sectional warping. Measured angles of rotation agreed with corresponding calculated values in which the torsion bending factor of the cross section was involved; the agreement was better for the I-beam and the Z-bar than for the channel. Longitudinal stresses measured at the mid-span were found to agree with the calculated values that involved unit warping as well as the torsion-bending factors: the channel showed the greatest discrepancy between measured and calculated values. When commonly given expressions for rotations and maximum longitudinal stresses in a twisted I-beam were applied to the channel and to the Z-bar, values were obtained that were in reasonably good agreement with values obtained by the method of torsion-bending constant and unit warping.

Hill, H N↗
NASA NTRS1983

An accelerator test of semi-empirical cross-sections

Experimentally measured yields of isotopes of elements from Mg to K resulting from the fragmentation of Ar-40 are compared with calculated yields based on semiempirical cross-section formulas. Excellent mass resolution is obtained in measurements using a beam of 287 MeV/amu Ar-40 incident on a CH2 target. The resolution is made possible by an Si(Li) detector telescope. Whereas the general agreement between calculation and experiment is good, with an rms difference of approximately 24 percent, attention is called to certain significant differences. It is found that important information for refining the semiempirical calculation of fragmentation cross sections can be obtained from data collected during the calibration of cosmic ray detector systems when such calibrations are performed under suitable conditions.

Lau, K. H.↗
NASA NTRS1958

Stability of Cylindrical and Conical Shells of Circular Cross Section, with Simultaneous Action of Axial Compression and External Normal Pressure

We consider in this report the determination of the upper limit of critical loads in the case of simultaneous action of a compressive force, uniformly distributed over plane cross sections, and of isotropic external normal pressure on cylindrical or conical shells of circular cross section. As a starting point we use the differential equations for neutral equilibrium of conical shells which have been used for the solution of the problem of stability of conical shells under torsion and under axial compression; upon solution of the problem it is possible to satisfy all boundary conditions, in contrast to the report where no attention is paid to the fulfillment of the boundary conditions, and to the report where only part of the boundary conditions are satisfied by solution of the problem according to Galerkin's method. Approximate formulas are used for the determination of the critical external normal pressure with simultaneous action of longituninal compression. Let us note that the formulas suggested in reference 5 are not well founded and may lead, in a number of cases, to a substantial mistake in the magnitude of the critical load.

Mushtari, K. M.↗
NASA NTRS1972

Cross sections for production of the CO(A 1 Pi)-(X 1 Sigma) fourth positive band system and O(3 S) by photodissociation of CO2

The CO(A 1 Pi) cross sections reported here, along with previously determined electron impact results, establish the basis for calculating CO fourth positive system volume emission rates in the Martian dayglow. Calculated volume emission rates in turn determine relative distribution of photon vs. electron impact as mechanisms for producing CO(A 1 Pi) in the Mars atmosphere. The smallness of the O(1304) cross section confirms previous indirect evidence that photodissociative excitation of CO2 is not an important source of O(3 S) in the upper atmosphere of Mars.

Gentieu, E. P.↗
NASA NTRS2007

The Ultimate Monte Carlo: Studying Cross-Sections With Cosmic Rays

The high-energy physics community has been discussing for years the need to bring together the three principal disciplines that study hadron cross-section physics - ground-based accelerators, cosmic-ray experiments in space, and air shower research. Only recently have NASA investigators begun discussing the use of space-borne cosmic-ray payloads to bridge the gap between accelerator physics and air shower work using cosmic-ray measurements. The common tool used in these three realms of high-energy hadron physics is the Monte Carlo (MC). Yet the obvious has not been considered - using a single MC for simulating the entire relativistic energy range (GeV to EeV). The task is daunting due to large uncertainties in accelerator, space, and atmospheric cascade measurements. These include inclusive versus exclusive cross-section measurements, primary composition, interaction dynamics, and possible new physics beyond the standard model. However, the discussion of a common tool or ultimate MC might be the very thing that could begin to unify these independent groups into a common purpose. The Offline ALICE concept of a Virtual MC at CERN s Large Hadron Collider (LHC) will be discussed as a rudimentary beginning of this idea, and as a possible forum for carrying it forward in the future as LHC data emerges.

Wilson, Thomas L.↗