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Results for “LONGITUDINAL WAVE”

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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

ISEE 3 magnetopause crossings - Evidence for the Kelvin-Helmholtz instability

The role of the Kelvin-Helmholtz instability in driving magnetopause motion is investigated on the basis of correlated ISEE-3 magnetometer measurements and IMP-8 solar-wind/magnetosheath velocities. The data are presented in graphs and briefly characterized, comparing the daily frequency of magnetopause crossings by ISEE-3 with the velocities. It is found that the instability criterion for longitudinal waves is only rarely satisfied in these measurements, while that for waves with an azimuthal component is satisfied in over 50 percent of the cases. It is inferred that the Kelvin-Helmholtz instability is probably the cause of motions with magnetotail-boundary interarrival times of 20 min or less.

Sibeck, D. G.↗
NASA NTRS1989

Magnetohydrodynamic instabilities in coronal arcades

The MHD stability of coronal arcades is studied with and without a detached flux using a two-dimensional linear MHD stability numerical model. Two-dimensional magnetohydrostatic equilibria with and without gravity are computed. A coronal arcade without a detached flux tube is found to be stable for any magnetic shear and for any longitudinal mode. On the other hand, an arcade with a detached flux tube is unstable for perturbations with nonzero longitudinal wave number n and the instability mode structure and growth rate vary depending on the field twist and n. All the equilibria studied are stable to n = 0 perturbations. Gravity has a stabilizing effect on the equilibria. As the ratio lambda of the standard arcade width to the gravitational scale height increases from zero to 0.2, the m = 0 transverse mode growth rate decreases, but high m modes are stabilized. The equilibria studied here are completely stabilized for lambda larger than 0.33.

An, Chang-Hyuk↗
NASA NTRS1990

Enhanced ultrasonic attenuation of Tl-Ca-Ba-Cu-O at the superconducting transition

Temperature-dependent ultrasonic attenuation measurements have been performed on polycrystalline samples of Tl-Ca-Ba-Cu-O at various frequencies. An attenuation anomaly was observed close to the superconducting transition temperature T(c) (103 K) whose temperature position was frequency-independent. The attenuation decreased exponentially with temperature in the superconducting state for both transverse and longitudinal waves. It was also found that the temperature-dependent sound velocity showed a slope change around T(c).

Sun, K. J.↗
NASA NTRS1991

Preliminary investigation of acousto-ultrasonic evaluation of metal-matrix composite specimens

Acoustoultrasonic (AU) measurements were performed on a series of (0)8, (90)8, (+/-30)2s, (+/-60)2s, (0/90)2s, and (90/0)2s tensile specimens composed of eight laminated layers of continuous, SiC-fiber-reinforced Ti-15-3 matrix. The frequency spectrum was dominated by frequencies of longitudinal wave resonance through the thickness of the specimen at the sending transducer; signal propagation from the sender to the receiver was by shear waves. The magnitude of the frequency spectrum of the AU signal was used for calculating a stress-wave factor (SWF) based upon integrating the spectral distribution function. The SWF was sensitive to fiber-matrix debonding caused by mechanical strain and also to unconstrained thermal cycling. Damage in this metal-matrix composite structure due to tensile loading or thermal cycling was detected by this change in the magnitude of the frequency spectrum.

Kautz, Harold E.↗
NASA NTRS1992

Application of neural networks to prediction of advanced composite structures mechanical response and behavior

Two types of neural networks were used to evaluate acousto-ultrasonic (AU) data for material characterization and mechanical reponse prediction. The neural networks included a simple feedforward network (backpropagation) and a radial basis functions network. Comparisons of results in terms of accuracy and training time are given. Acousto-ultrasonic (AU) measurements were performed on a series of tensile specimens composed of eight laminated layers of continuous, SiC fiber reinforced Ti-15-3 matrix. The frequency spectrum was dominated by frequencies of longitudinal wave resonance through the thickness of the specimen at the sending transducer. The magnitude of the frequency spectrum of the AU signal was used for calculating a stress-wave factor based on integrating the spectral distribution function and used for comparison with neural networks results.

Cios, K. J.↗
NASA NTRS1934

Impact buckling of thin bars in the elastic range for any end condition

Following a qualitative discussion of the complicated process involved in a short-period, longitudinal force applied to an originally not quite straight bar, the actual process is substituted by an idealized process for the purpose of analytical treatment. The simplifications are: the assumption of an infinitely high rate of propagation of the elastic longitudinal waves in the bar, limitation to slender bars, disregard of material damping and of rotatory inertia, the assumption of consistently small elastic deformations, the assumption of cross-sectional dimensions constant along the bar axis, the assumption of a shock-load constant in time, and the assumption of eccentricities on one plane. Then follow the mathematical principles for resolving the differential equation of the simplified problem, particularly the developability of arbitrary functions with steady first and second and intermittently steady third and fourth derivatives into one convergent series, according to the natural functions of the homogeneous differential equation.

Taub, Josef↗
NASA NTRS1994

A Method of Poisson's Ration Imaging Within a Material Part

The present invention is directed to a method of displaying the Poisson's ratio image of a material part. In the present invention, longitudinal data is produced using a longitudinal wave transducer and shear wave data is produced using a shear wave transducer. The respective data is then used to calculate the Poisson's ratio for the entire material part. The Poisson's ratio approximations are then used to display the data.

Roth, Don J.↗
NASA NTRS2002

Application of Accelerometer Data to Mars Odyssey Aerobraking and Atmospheric Modeling

Aerobraking was an enabling technology for the Mars Odyssey mission even though it involved risk due primarily to the variability of the Mars upper atmosphere. Consequently, numerous analyses based on various data types were performed during operations to reduce these risk and among these data were measurements from spacecraft accelerometers. This paper reports on the use of accelerometer data for determining atmospheric density during Odyssey aerobraking operations. Acceleration was measured along three orthogonal axes, although only data from the component along the axis nominally into the flow was used during operations. For a one second count time, the RMS noise level varied from 0.07 to 0.5 mm/s2 permitting density recovery to between 0.15 and 1.1 kg per cu km or about 2% of the mean density at periapsis during aerobraking. Accelerometer data were analyzed in near real time to provide estimates of density at periapsis, maximum density, density scale height, latitudinal gradient, longitudinal wave variations and location of the polar vortex. Summaries are given of the aerobraking phase of the mission, the accelerometer data analysis methods and operational procedures, some applications to determining thermospheric properties, and some remaining issues on interpretation of the data. Pre-flight estimates of natural variability based on Mars Global Surveyor accelerometer measurements proved reliable in the mid-latitudes, but overestimated the variability inside the polar vortex.

Tolson, R. H.↗
NASA NTRS1996

Method of Poisson's ratio imaging within a material part

The present invention is directed to a method of displaying the Poisson's ratio image of a material part. In the present invention longitudinal data is produced using a longitudinal wave transducer and shear wave data is produced using a shear wave transducer. The respective data is then used to calculate the Poisson's ratio for the entire material part. The Poisson's ratio approximations are then used to displayed the image.

Roth, Don J.↗
NASA NTRS2010

Analysis of the Effects of Streamwise Lift Distribution on Sonic Boom Signature

The streamwise lift distribution of a wing-canard-stabilator-body configuration was varied to study its effect on the near-field sonic boom signature. The investigation was carried out via solving the three-dimensional Euler equation with the OVERFLOW-2 flow solver. The computational meshes were created using the Chimera overset grid topology. The lift distribution was varied by first deflecting the canard then trimming the aircraft with the wing and the stabilator while maintaining constant lift coefficient of 0.05. A validation study using experimental results was also performed to determine required grid resolution and appropriate numerical scheme. A wide range of streamwise lift distribution was simulated. The result shows that the longitudinal wave propagation speed can be controlled through lift distribution thus controlling the shock coalescence.

Yoo, Seung Yeun (Paul)↗
NASA NTRS1986

Nonlinear upper hybrid drift waves for a longitudinal electric field perpendicular to a uniform magnetic field in the Vlasov-Maxwell approximation

Upper hybrid drift waves are found as a special solution to a Vlasov-Maxwell plasma which has a longitudinal electric field and a perpendicular uniform magnetic field. A single-species plasma with a constant-density mobile neutralizing background supports spatially varying disturbances that oscillate at the upper hybrid frequency. The general functional dependences of the electric field, the plasma number density, and the one-particle distribution function for the special case are found from more general Vlasov-Maxwell equations invariant under a Lie group point transformation. The one-particle distribution function for the plasma is a function of the Liouville invariant, which is the energy in the generalized Bernstein-Greene-Kruskal (BGK) reference frame, and the momentum in the drift direction.

Abraham-Shrauner, B.↗
NASA NTRS1995

Alfven wave resonances and flow induced by non-linear Alfven waves in a stratified atmosphere

A nonlinear, time-dependent, ideal MHD code has been developed and used to compute the flow induced by nonlinear Alfven waves propagating in an isothermal, stratified, plane-parallel atmosphere. The code is based on characteristic equations solved in a Lagrangian frame and is highly accurate. Results show that resonance behavior of Alfven waves exists in the presence of a continuous density gradient and that the waves with periods corresponding to resonant peaks exert considerably more force on the medium than off-resonance periods; this leads to enhanced flow. If only off-peak periods are considered, the relationship between the wave period and induced longitudinal velocity shows that short period WKB waves push more on the background medium than longer period, non-WKB, waves. The results also show the development of the longitudinal waves produced by the finite amplitude of the Alfven waves. The longitudinal wave becomes strong as the Alfven wave relative amplitude grows above 10 percent and will lead to strong damping of the Alfven waves.

Stark, B. A.↗
NASA NTRS1971

Numerical solution for propagation of coupled longitudinal and transverse waves normal to the applied magnetic field in a three-fluid medium.

The solution was obtained without approximating the dispersion relation. This was made possible by the use of a computer method for carrying out the extremely large number of algebraic manipulations involved. The three-fluid model employed accounts for the interaction of the electron, ion, and neutral species. The solution for the e-folding distance describes the damping characteristics of each wave mode. Each of the e-folding solutions corresponds to one of the phase velocity solutions.

Mcclendon, R. W.↗