SEARCH · Engineering Papers

Results for “Smooth approximation”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17

All sources NASA NTRS DOE OSTI

NASA NTRSDate not supplied

High Temperature Emissivity Measurement System (HiTEMS)

The High Temperature Emissivity Measurement System (HiTEMS) is a ground test capability at NASA Marshall Space Flight Center enabling near normal and varied incident angle spectral and total emittance measurements. This data is gathered at vacuum levels as low as approximately 10-7 Torr within a temperature range of 600°C to approximately 2,600°C, providing essential material property data to assist with improved thermal control estimates for spacecraft hardware. Recent work focusing on the measurement of smooth and bead blasted tungsten samples in support of the Propulsion Research and Tech Branch at NASA MSFC provides a thorough examination into HiTEMS capabilities and insight into the variabilities related to sample roughness at extreme temperatures.

Meghan Carrico↗

NASA NTRS2024

‘Trapped Wave’ Resonance Tones Radiated in the Forward Arc of High-Speed Jets

An experimental study is conducted investigating the characteristics of ‘trapped wave’ resonance tones in the forward arc of jet noise radiation fields. While these spectral peaks disappear in the far acoustic field in the aft and sideline directions, which is why they went unnoticed in decades of jet noise measurements, the present study clearly shows that they radiate in the forward arc (shallow upstream polar locations in the approximate range of θ < 45°). Far-field jet noise spectra in the forward arc, data on which had been lacking in the literature, are not smooth but are characterized by these peaks. This is found for high subsonic to supersonic jets up to the highest jet Mach number covered in the experiment (MJ ≈ 1.9), for round, rectangular as well as convergent-divergent nozzles. With heated jets these spectral peaks are weakened especially around transonic conditions, however, they persist in supersonic conditions. Note that digital files containing all spectral data shown in the following are in a supplemental file to this NASA Technical Memorandum (TM-20240009873-SUPPL). These files can be obtained from the NASA Technical Report Server (NTRS) as a separate download from this report.

jets↗

NASA NTRS2014

A Multi-Wavelength Investigation of the Radio-Loud Supernova PTF11qcj and its Circumstellar Environment

We present the discovery, classification, and extensive panchromatic (from radio to X-ray) follow-up observations of PTF11qcj, a supernova (SN) discovered by the Palomar Transient Factory (PTF). Our observations with the Karl G. Jansky Very Large Array show that this event is radio-loud: PTF11qcj reached a radio peak luminosity comparable to that of the famous gamma-ray-burst-associated SN 1998bw (L (sub 5 gigahertz) approximates 10 (sup 29) ergs per second per hertz). PTF11qcj is also detected in X-rays with the Chandra Observatory, and in the infrared band with Spitzer. Our multi-wavelength analysis probes the SN interaction with circumstellar material. The radio observations suggest a progenitor mass-loss rate of approximately 10 (sup -4) the mass of the sun per year times (v (sub omega) divided by 1000 kilometers per second), and a velocity of approximately 0.3-0.5 c (the speed of light in a vacuum) for the fastest moving ejecta (at around 10 days after explosion). However, these estimates are derived assuming the simplest model of SN ejecta interacting with a smooth circumstellar wind, and do not account for possible inhomogeneities in the medium and asphericity of the explosion. The radio data show deviations from such a simple model, as well as a late-time re-brightening. The X-ray flux from PTF11qcj is compatible with the high-frequency extrapolation of the radio synchrotron emission (within the large uncertainties). A light echo from pre-existing dust is in agreement with our infrared data. Our pre-explosion data from the PTF suggest that a precursor eruption of absolute magnitude M (sub r) approximately equal to -13 mag may have occurred approximately 2.5 years prior to the SN explosion. Overall, PTF11qcj fits the expectations from the explosion of a Wolf-Rayet star. Precursor eruptions may be a feature characterizing the final pre-explosion evolution of such stars.

Radio↗

NASA NTRS1980

The applicability of the piecewise linear current profile in the baroclinic instability problem

The applicability of the piecewise linear function in place of a similar smoothly-varying current profile is examined in the baroclinic context. Within the framework of small-perturbation linearization, the behavior of the vertical velocity and the horizontal divergence is analyzed at the discontinuity of the current shear. In the conventional geostrophic-type instability regime, the discontinuity in the horizontal divergence at the shear discontinuity is suppressed, and, therefore, the piecewise linear profile leads to a useful approximation to the true solution. In the symmetric-type instability regime, however, due to the magnified discontinuity in the horizontal divergence at the shear discontinuity, the solution thus obtained will show a major distortion, rendering the piecewise linear profile inadequate for modeling the smoothly-varying current profile. Using exemplary current profiles, numerical results are presented to demonstrate the behavior of the horizontal divergence near the discontinuity of current shear.

Hyun, J. M.↗

NASA NTRS1973

Flight evaluation of two segment approaches for jet transport noise abatement

A 75 flight-hour operational evaluation was conducted with a representative four-engine fan-jet transport in a representative airport environment. The flight instrument systems were modified to automatically provide pilots with smooth and continuous pitch steering command information during two-segment approaches. Considering adverse weather, minimum ceiling and flight crew experience criteria, a transition initiation altitude of approximately 800 feet AFL would have broadest acceptance for initiating two-segment approach procedures in scheduled service. The profile defined by the system gave an upper glidepath of approximately 6 1/2 degrees. This was 1/2 degree greater than inserted into the area navigation system. The glidepath error is apparently due to an erroneous along-track, distance-to-altitude profile.

Rogers, R. A.↗

NASA NTRS1977

Microwave remote sensing and its application to soil moisture detection

The author has identified the following significant results. Experimental measurements were utilized to demonstrate a procedure for estimating soil moisture, using a passive microwave sensor. The investigation showed that 1.4 GHz and 10.6 GHz can be used to estimate the average soil moisture within two depths; however, it appeared that a frequency less than 10.6 GHz would be preferable for the surface measurement. Average soil moisture within two depths would provide information on the slope of the soil moisture gradient near the surface. Measurements showed that a uniform surface roughness similar to flat tilled fields reduced the sensitivity of the microwave emission to soil moisture changes. Assuming that the surface roughness was known, the approximate soil moisture estimation accuracy at 1.4 GHz calculated for a 25% average soil moisture and an 80% degree of confidence, was +3% and -6% for a smooth bare surface, +4% and -5% for a medium rough surface, and +5.5% and -6% for a rough surface.

Newton, R. W.↗

NASA NTRS1984

Effect of boattail geometry on the acoustics of parallel baffles in ducts

Sound attenuation and total pressure drop of parallel duct baffles incorporating certain boattail geometries were measured in the NASA Ames Research Center 7- by 10-Foot Wind Tunnel. The baseline baffles were 1.56 m long and 20 cm thick, on 45-cm center-to-center spacings, and spanned the test section from floor to ceiling. Four different boattails were evaluated: a short, smooth (nonacoustic) boattail; a longer, smooth boattail; and two boattails with perforated surfaces and sound-absorbent filler. Acoustic measurements showed the acoustic boattails improved the sound attenuation of the baffles at approximately half the rate to be expected from constant-thickness sections of the same length; that is, 1.5 dB/n, where n is the ratio of acoustic treatment length to duct passage width between baffles. The aerodynamic total pressure loss was somewhat sensitive to tail geometry. Lengthening the tails to reduce the diffusion half-angle from 11 to 5 degrees reduced the total pressure loss approximately 9%. Perforating the boattails, which increased the surface roughness, did not have a large effect on the total pressure loss. Aerodynamic results are compared with a published empirical method for predicting baffle total pressure drop.

Soderman, P. T.↗

NASA NTRS1984

Nonunique solutions to the transonic potential flow equation

Steinhoff and Jameson (1981) have shown that within a certain range of angle of attack and freestream Mach number, numerical solutions of the full-potential equation for flow past an airfoil are not unique. This study was mainly concerned with showing that the anomaly is inherent to the partial-differential equation governing the flow and not a result of its discrete representation. Steinhoff and Jameson conjectured that the anomaly may have a physical basis. The present investigation has two objectives. Results are to be presented which indicate that the anomaly is due to a breakdown in the potential approximation, rather than a phenomenon associated with the inviscid flowfield. The second objective is to show that the lift coefficient, predicted by the potential equation, is a smooth but multivalued function of the angle of attack.

Salas, M. D.↗

NASA NTRS1993

Compton scattering and the gamma-ray power-law spectrum in Markarian 421

The nearest BL Lac object, Mrk 421, has a gamma-ray spectrum which is approximately flat in EF-sub E from E less than about 50 MeV to E greater than about 1 TeV. Inverse Compton scattering can explain this smooth spectrum, despite the structure in the Klein-Nishina cross section, if the injected electron distribution function is proportional to gamma exp -2, where gamma is the electron Lorentz factor. When this is the case, the structure imprinted on the steady state electron distribution function by the structure in the Klein-Nishina cross section is almost exactly compensated in the radiated spectrum. Because particle acceleration in strong shocks injects particles with this distribution function, this shape injection function is in fact quite plausible. Other blazars may be explained by the same model if the cutoff below TeV energies observed in other objects is due to pair production on the cosmological IR background, as suggested by Stecker et al. (1992).

Zdziarski, Andrzej A.↗

NASA NTRS1994

Double-core evolution. 5: Three-dimensional effects in the merger of a red giant with a dwarf companion

The evolution of the common envelope phase of a binary system consisting of a 4.67 solar mass red giant and a 0.94 solar mass dwarf is studied using smoothed particle hydrodynamics. We demonstrate that the three-dimensional effects associated with the gravitational tidal torques lead to a rapid decay of the orbit on timescales approximately less than 1 yr. The relative orbit of the two cores in the common envelope is initally eccentric and tends to circularize as the orbital separation of the two cores decreases. The angular momentum lost from the orbital motion is distributed throughout the common envelope, and the double core does not evolve to a state of co-rotation for the evolutionary time followed. The energy dissipated from the relative orbit and deposited in the common envelope results in the ejection of approximately 13% of the mass of the envelope. The mass is ejected in all directions, but there is a preference for mass ejection in the orbital plane of the binary system. For example, approximately 80% of the ejected mass lies within 30 deg of the binary orbital plane. Because gravitational forces are long range, most of the energy and angular momentum is imparted to a small fraction of the common envelope resulting in an efficiency of the mass ejection process of approximately 15%. The core of the red giant executes significant displacement with respect to the center of mass of the system and contributes nearly equally to the total energy dissipation rate during the latter phases of the evolution. The degree of departure from synchronism of the initial binary system can be an important property of the system which can affect the outcome of the common envelope phase.

Terman, James L.↗

NASA NTRS1990

Electron heating in quasi-perpendicular shocks - A Monte Carlo simulation

To study the problem of electron heating in quasi-perpendicular shocks, under the combined effects of 'reversible' motion, in the shock electric potential and magnetic field, and wave-particle interactions a diffusion equation was derived, in the drift (adiabatic) approximation and it was solved by using a Monte Carlo method. The results show that most of the observations can be explained within this framework. The simulation has also definitively shown that the electron parallel temperature is determined by the dc electromagnetic field and not by any wave particle induced heating. Wave-particle interactions are effective in smoothing out the large gradients in phase space produced by the 'reversible' motion of the electrons, thus producing a 'cooling' of the electrons. Some constraints on the wave-particle interaction process may be obtained from a detailed comparison between the simulation and observations. In particular, it appears that the adiabatic approximation must be violated in order to explain the observed evolution of the perpendicular temperature.

Veltri, Pierluigi↗

NASA NTRS1971

A continued fraction generator for smooth pulse sequences

Digital circuit produces rational output pulse rate at fraction of continuous input pulse rate. Output pulses have average rate with least possible deviation from absolute correct time spacing. Circuit uses include frequency synthesizing, fraction generation, and approximation of irrational sequences.

Cohn, M.↗

NASA NTRS1971

Coordinated auroral-electron observations from a synchronous and a polar satellite.

The ATS 5 satellite in synchronous orbit and the OV1-18 satellite in a low-altitude polar orbit carried similar experiments to measure auroral-particle fluxes in the energy range from 1/2 to 50 keV. Simultaneous electron flux observations are presented from 5 instances when the OV1-18 passed within a few hundred kilometers of the computed conjugate point to ATS 5. The integral flux levels were found to be generally comparable at the two locations with no evidence for angular distributions highly peaked along the field line. The spectrums were significantly harder at ATS 5 with average energies approximately a factor of 2 higher than at OV1-18. Evidence is presented for a dramatic difference in the shapes of the spectrums at the two locations with smoothly falling relatively featureless spectrums observed at ATS 5 and spectrums with a peak in the few keV range observed at OV1-18. Based on the 5 passes described here, there is evidence that the trapped component of the flux increases more rapidly than the precipitating component during more active times.

Sharp, R. D.↗

NASA NTRS1978

Characterization and properties of controlled nucleation thermochemical deposited (CNTD) silicon carbide

The microstructure of controlled nucleation thermochemical deposition (CNTD) - SiC material was studied and the room temperature and high temperature bend strength and oxidation resistance was evaluated. Utilizing the CNTD process, ultrafine grained (0.01-0.1 mm) SiC was deposited on W - wires (0.5 mm diameter by 20 cm long) as substrates. The deposited SiC rods had superior surface smoothness and were without any macrocolumnar growth commonly found in conventional CVD material. At both room and high temperature (1200 - 1380 C), the CNTD - SiC exhibited bend strength approximately 200,000 psi (1380 MPa), several times higher than that of hot pressed, sintered, or CVD SiC. The excellent retention of strength at high temperature was attributed to the high purity and fine grain size of the SiC deposit and the apparent absence of grain growth at elevated temperatures. The rates of weight change for CNTD - SiC during oxidation were lower than for NC-203 (hot pressed SiC), higher than for GE's CVD - SiC, and considerably below those for HS-130 (hot pressed Si3N4). The high purity, fully dense, and stable grain size CNTD - SiC material shows potential for high temperature structural applications; however problem areas might include: scaling the process to make larger parts, deposition on removable substrates, and the possible residual tensile stress.

Dutta, S.↗

NASA NTRS1985

Studies on the interference of wings and propeller slipstreams

The small disturbance potential flow theory is applied to determine the lift of an airfoil in a nonuniform parallel stream. The given stream is replaced by an equivalent stream with a certain number of velocity discontinuities, and the influence of these discontinuities is obtained by the method of images. Next, this method is extended to the problem of an airfoil in a nonuniform stream of smooth velocity profile. This model allows perturbation velocity potential in a rotational undisturbed stream. A comparison of these results with numerical solutions of Euler equations indicates that, although approximate, the present method provides useful information about the interaction problem while avoiding the need to solve the Euler equations.

Prabhu, R. K.↗

NASA NTRS1989

Multigrid solution of the Navier-Stokes equations on triangular meshes

A Navier-Stokes algorithm for use on unstructured triangular meshes is presented. Spatial discretization of the governing equations is achieved using a finite element Galerkin approximation, which can be shown to be equivalent to a finite volume approximation for regular equilateral triangular meshes. Integration steady-state is performed using a multistage time-stepping scheme, and convergence is accelerated by means of implicit residual smoothing and an unstructured multigrid algorithm. Directional scaling of the artificial dissipation and the implicit residual smoothing operator is achieved for unstructured meshes by considering local mesh stretching vectors at each point. The accuracy of the scheme for highly stretched triangular meshes is validated by comparing computed flat-plate laminar boundary layer results with the well known similarity solution, and by comparing laminar airfoil results with those obtained from various well-established structured quadrilateral-mesh codes. The convergence efficiency of the present method is also shown to be competitive with those demonstrated by structured quadrilateral-mesh algorithms.

Mavriplis, Dimitri J.↗

NASA NTRS1990

Multigrid solution of the Navier-Stokes equations on triangular meshes

Mavriplis, D. J.↗

NASA NTRS1993

A finite-volume high-order ENO scheme for two-dimensional hyperbolic systems

The finite-volume approach is presently used to obtain a 2D, high-order accurate and basically nonoscillatory shock-capture method whose high-order spatial accuracy is obtained by means of a piecewise polynomial approximation of the solution from cell averages. Attention is given to a high-order spatial operator that is able to both retain high-order accuracy in smooth regions and avoid the oscillations that are associated with interpolations across steep gradients. The operator is extended to hyperbolic systems of equations and curvilinear meshes.

Casper, Jay↗